Tuesday, July 31, 2007
CHANTAL
Earlier this morning, winds of tropical depression three were estimated to be around 30 kts. or approximately 35 mph. A Storm gets named once winds reach 39 mph or better. This happened in the case of TD3 and now it has become the third named storm of the Atlantic tropical season, Chantal. Naming of storms is predetermined and rotates every six years. In the case of a particularly bad storm, such as Katrina, the name gets retired.
Chantal presently has winds of 40 mph and is moving to the northeast at 23 mph. It is mainly a threat for the shipping industry and poses no threat to the States.
Posted by Ted Zarras at 7:18 AM
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Monday, July 30, 2007
Fayetteville tops 90 F
It took almost all of July to finally hit 90F in Fayetteville. Yesterday Drake Field hit 91F. At this point last year 90F or above had been reached some 28 times. It's quite likely that we'll be flirting with the somewhat elusive mark this week as well. On the positive side, we're almost into August and by the 15th of the month, average highs begin to lower.
In Fort Smith, 90F or better has been reached some 24 times. This compared to last years 54 times at this point is low. Yesterday's high of 95F is the highest of the summer thus far. Last year by this time Fort Smith had seen 100F or better several times. What we'll be contending with this week is a high heat index. By the time moisture is factored in it can feel much hotter than it actually is. Be especially careful this week to; drink plenty of fluids, take frequent breaks, and keep an eye on pets and the elderly.
Posted by Ted Zarras at 11:55 AM
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Sunday, July 29, 2007
Sunday's Outflow Boundary
The heat and humidity of Sunday gave way to more storms along a washed out frontal boundary; moreover, what started out as isolated convection near Franklin county, quickly developed into scattered showers and storms throughout the River Valley. Take a look at the radar image above. You are looking at 2 separate outflow boundaries from a complex of storms that originally developed near Ozark.
An outflow boundary is the rain cooled air that flows away from a thunderstorm. You can think of outflow like exhaust from an engine. These boundaries are typically picked up on radar, and they look like a fuzzy curved line moving away from storms. These outflow boundaries act like mini cold fronts that help lift the warm and humid air.
This particular outflow boundary created a line of strong storms from Marble City all the way to Poteau around 5:45 p.m.
Posted by Drew Michaels at 3:50 PM
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Sunday Afternoon Storm Update
The washed out frontal boundary is now starting to fire across our area. Look for scattered afternoon showers and storms to persist as we go throughout the afternoon and evening hours. Very isolated strong to possibly severe storms can't be ruled out.
CAPE values are running close to 3,000 this afternoon, so small dime size hail will be a possibility within the stronger storms. Dry air aloft is still present from Oklahoma City to Springfield. This may contribute to strong gusty thunderstorm winds around 50 mph.
This front will give us chances for storms throughout the upcoming work week. Remember you can always check our super doppler radar loop to find out where the storms are going.....4029tv.com is the only television weather website to have that feature for your convenience!
CAPE values are running close to 3,000 this afternoon, so small dime size hail will be a possibility within the stronger storms. Dry air aloft is still present from Oklahoma City to Springfield. This may contribute to strong gusty thunderstorm winds around 50 mph.
This front will give us chances for storms throughout the upcoming work week. Remember you can always check our super doppler radar loop to find out where the storms are going.....4029tv.com is the only television weather website to have that feature for your convenience!
Posted by Drew Michaels at 11:30 AM
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Saturday, July 28, 2007
Saturday Evening Storm Update
It's turned out to be one of the hottest days of the summer! The frontal boundary we've been watching has blown up across Kansas and Missouri this afternoon; however, the boundary's slowly moving south, so we're still expecting a chance for showers and storms this evening across NE OK and NW AR.
CAPE values this afternoon have climbed around 2,000 J/KG, which still suggests that the storms could produce small hail. Dry air aloft may also contribute to strong gusty winds around 50 mph.
Posted by Drew Michaels at 3:08 PM
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Saturday Storm Potential
A slow moving frontal boundary could provide the focus for showers and storms this afternoon. The best coverage area for storms will remain north of I-40 across NE OK and NW AR in association with the front.
Morning sunshine combined with low level moisture will contribute to CAPE values approaching 3,000 J/KG this afternoon. The Little Rock upper air sounding above indicates a substantial pool of dry air aloft, and that favors strong gusty winds due to evaporational cooling aloft.
Widespread strong to severe storm activity is not expected; however, a few storms may need to be watched, so we'll monitor the afternoon closely.
Posted by Drew Michaels at 7:24 AM
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Friday, July 27, 2007
Dog Days of Summer....
We're in the thick of it now, and there's no turning back! Typically, from the 21st of July through the 12th of August, we see the hottest temperatures throughout our area. During this period our average high in Fort Smith is 94 degrees while Fayetteville typically climbs to 90.
Record highs during this stretch are impressive. On August 10th, 1936, Fort Smith climbed to a sweltering 113 degrees. Fayeteville's mercury reached 106 back on August 4th 1964.
The forecast is for a below average August, so we'll see which way the mercury goes!
Posted by Drew Michaels at 3:21 PM
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DALILA
That swirl in the clouds off the Baja coast is "Dalila", A weakening tropical storm. As of this blog entry, Dalila has 30 mph winds and continues to move to the WNW at 9 mph. The storm is encountering cool waters not conducive to intensification and it will likely become a remnant Low.
The picture comes from a favorite website of mine to grab satellite info worldwide. Check it out. http://www.ghcc.msfc.nasa.gov/GOES/
Posted by Ted Zarras at 10:50 AM
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Thursday, July 26, 2007
THIS DAY IN WEATHER
July 26, 1943: Tishomingo, OK, which is southwest of McAlester, baked in the heat as the mercury soared to 121 degrees! This is the Sooner State record high temperature.
Posted by Ted Zarras at 4:45 PM
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BLIND SPOT... this is neat!
Look around. Do you see a blind spot anywhere? Maybe the blind spot for one eye is at a different place than the blind spot for the other (this is actually true), so you don't notice it because each eye sees what the other doesn't. Close one eye and look around again. Now do you see a blind spot? Hmm. Maybe its just a little TINY blind spot, so small that you (and your brain) just ignore it. Nope, its actually a pretty BIG blind spot, as you'll see if you look at the diagram below and follow the instructions.
Close your left eye and stare at the cross mark in the diagram with your right eye. Off to the right you should be able to see the spot. Don't LOOK at it; just notice that it is there off to the right (if its not, move farther away from the computer screen; you should be able to see the dot if you're a couple of feet away). Now slowly move toward the computer screen. Keep looking at the cross mark while you move. At a particular distance (probably a foot or so), the spot will disappear (it will reappear again if you move even closer). The spot disappears because it falls on the optic nerve head, the hole in the photoreceptor sheet.
So, as you can see, you have a pretty big blind spot, at least as big as the spot in the diagram. What's particularly interesting though is that you don't SEE it. When the spot disappears you still don't SEE a hole. What you see instead is a continuous white field (remember not to LOOK at it; if you do you'll see the spot instead). What you see is something the brain is making up, since the eye isn't actually telling the brain anything at all about that particular part of the picture.
Forget the: "the models didn't have a good handle on the system", "the initialization scheme was off", "bad data in yields bad data out" excuses! If I should happen to botch a forecast, and we all know this hardly ever happens... ;) but, IF I SHOULD...
I'll blame it on my blind spot!
Posted by Ted Zarras at 2:00 PM
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Wednesday, July 25, 2007
Interesting Summer Averages...
What a difference a day makes! Southerly winds have allowed dewpoints to creep back into the low to mid 60's this afternoon. Yesterday, the dewpoints hovered in the 50's, with a relative humidity between 30%-40%. The moisture does look to slowly increase into the weekend, providing a chance for afternoon showers and storms.
I think most people will agree that the summer of 2007 has seemed far from normal, so here are some numbers to back up that claim.
Fort Smith:
Average High 88
Rainfall 5.83"
Fayetteville:
Average High: 84
Rainfall 4.87"
Fort Smith should have a high around 92 for the first month of summer, with Fayetteville usually around 88. We've seen temperatures about 4 degrees cooler than average!
As you can see from the graphic above, the Climate Prediction Center has a forecast for cooler than average temperatures for the month of August. Will we break the current pattern? My guess is no, but we'll have to wait and see.
Posted by Drew Michaels at 4:17 PM
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Another foggy / misty start
This morning along with yesterday morning our atmosphere became very stable and winds became light to calm. At night, under such conditions, heat that’s radiated back to space does not mix well and rises, settling above cooler and denser air. This forms a temperature inversion. If sufficient moisture is available and depending on the depth of the inversion fog and mist can develop.
The sounding of KRKR, which is the identifier from Poteau, OK highlights such an inversion up to about 950 mb. This is roughly 1900 feet. At the top of most of our weather updates on the sunrise show we’ll start off with views from around the area. Yesterday there was a layer of clouds roughly around 1000 ft. and today in the Poteau area, moderate mist was spread across the area up to at least 1900 feet. The sounding above is from the RUC model and variations of 500 feet are entirely possible. In all likely hood the inversion was up to some 2500 feet, which is just about at camera level, making for some "spooky" above or slightly in the cloud images.
The sounding of KRKR, which is the identifier from Poteau, OK highlights such an inversion up to about 950 mb. This is roughly 1900 feet. At the top of most of our weather updates on the sunrise show we’ll start off with views from around the area. Yesterday there was a layer of clouds roughly around 1000 ft. and today in the Poteau area, moderate mist was spread across the area up to at least 1900 feet. The sounding above is from the RUC model and variations of 500 feet are entirely possible. In all likely hood the inversion was up to some 2500 feet, which is just about at camera level, making for some "spooky" above or slightly in the cloud images.
We shall see what tomorrow brings. Actual tower cam height on Cavanal Mtn. is some 2,635 feet up, making it higher than Mt. Magazine!
Posted by Ted Zarras at 10:15 AM
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Monday, July 23, 2007
So What is Ground Clutter?
A viewer recently e-mailed me this question, and I thought the blog would be a fun place to answer it. The picture above looks like an explosion, however, instead of bombs, all you need is a change of temperature to create this ground clutter. Every now and then you'll hear Ted and I mention it, but what is happening within the atmosphere to paint this picture?
Ground clutter is created when the beam of the radar is bent more toward the earth's surface, allowing objects near the ground to scatter the radar beam's energy. This typically happens when we have a temperature inversion.
An inversion occurs when you have warm air on top of a shallow cold air mass; moreover, an inversion is a very stable environment, and it refracts the radar toward the ground. In fact, we have ideal inversion conditions over the next couple of nights as the surface cools faster than the warm air aloft, so take a look at the radar late at night.
Posted by Drew Michaels at 4:25 PM
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Showers / Storms Remain West
We’ve got a frontal boundary still poised just to our west and this again will be the focal point for showers and storms. Overnight, a complex of storms raced from north east Iowa to the southwest. This has now pushed into north central OK. The feature was very reminiscent of phenomena that are called “ridge-runners”. These complexes circle an area of high pressure, feeding off of a moisture channel.Moisture convergence to our west that stretches well north of the map above provided the necessary fuel to sustain a batch of showers and storms overnight. This is on the edge of a High to our north west under a ridge. Of particular interest though was the path of motion of the complex. With the Low parked to our north east and the high to our north west, as Drew depicted in the previous blog entry, our winds aloft are predominantly out of the north. Complexes will follow the moisture and the mean motion of the mid to upper level wind field, which in the case of our present set-up is north northeasterly, making the complex move to the south southwest. Typically we see movement more to the south southeast.
Posted by Ted Zarras at 10:15 AM
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Sunday, July 22, 2007
Is This Summer?
We should be experiencing temperatures in the 90's during this part of July; however, we're about 5 to 10 degrees below average, and we'll have a few more days of this to enjoy! The dewpoints have also been lowered, creating less of a heat index. So what's behind these unseasonably cool conditions?
A significant trough has developed over the east coast, which in turn, has created an area of high pressure at the surface over the Great Lakes. Look at the picture above. Winds aloft that converge represent an increased density within the atmosphere. A higher density translates to higher pressure at the surface. Imagine somebody pushing their weight down upon your head, in essence, that's what's happening where air converges high above. Our weather at the surface is directly controlled by the winds aloft!
Winds around the surface high travel clockwise, shutting off the Gulf of Mexico, and allowing temperatures to stay slightly below average. We're tapping into cooler air from the NE, and that's helping to take the edge off of the summer.
Posted by Drew Michaels at 3:28 PM
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Friday, July 20, 2007
Friday Afternoon Update......
Scattered showers and storms have developed along a frontal boundary stretched across central Arkansas this afternoon. The best chance for storms will remain near the front across western Arkansas. The upper air sounding indicates a substantial amount of dry air aloft, so storms that do fire could become severe with strong gusty winds. We'll watch the storms closely!
Posted by Drew Michaels at 11:58 AM
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FRIDAY FEATURE!
Amazing video captured by the cameras on the side of the Solid Rocket Boosters (SRBs) as they're blown clear of the space shuttle Atlantis during the launch of STS-115.
Posted by Ted Zarras at 10:00 AM
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TEMPERATURE INVERSION!
Air moves in all directions. The horizontal transport of air is called "advection". When an air masses source region is warmer than the region in which it's blowing into, we simply refer to the processes as warm air advection. If winds are light and not a whole lot of mixing is happening in the vertical, then a temperature inversion can result, in essence trapping a cooler layer of air at the surface. Clouds will be unable to rise above the warmer layer, making the inversion visible if you have a high enough vantage point.
This shot, looking down at the inversion, was captured from Mt. Washington, NH. The tracks are those of the Cog Mountain Railway. I've never been on the train that goes up the mountain, but from what I hear, it's quite a thrilling ride! For more information check out here, http://www.thecog.com
Posted by Ted Zarras at 9:30 AM
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Thursday, July 19, 2007
Mature / Dissipating Stage
Check out this great shot that was sent in from a weather tracker in the Springdale area. It was captured this past Saturday. This is what we often refer to as a "garden variety" thunderstorm. They build up with the heat of the day, drop plenty of rain (often accompanied by lots of lightning and thunder), and then dissipate in the course of some forty five minutes to an hour. This cell is just about at it's mature stage or just in the dissipating stage. Once rain begins to fall within the storm, evaporational cooling shuts off the inflow and the storm rains itself out. Sometimes the characteristic anvil top will hang in upper levels of the atmosphere and just drift around a bit before dissipating.
Thanks for the picture!
Posted by Ted Zarras at 11:35 AM
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Wednesday, July 18, 2007
Friday's Cold Front...Lower Humidity
It's very rare this time of the year to see a cold front clear the entire viewing area. I still have some doubt that the front will make it into Texas; however, the weekend looks mostly dry, with high temperatures in the 80's to near 90 degrees with lower dewpoints.
One of the obvious changes will be an overall reduction of the humidity. The drop in moisture is directly related to changes in the upper level wind flow. The pictures above represent the wind field around 5,000 ft. On Thursday the flow will remain out of the south as you can see in the top picture above. A southerly flow off the gulf keeps the moisture flowing north, but our expected frontal passage will reduce the flow off the Gulf of Mexico, and by Saturday, the upper level winds will blow from the northeast, helping to drop the humidity.
It's looking to be a wonderful weekend to enjoy the outdoors!
Posted by Drew Michaels at 3:45 PM
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WEIGHT OF A THUNDERSTORM
We were recently asked how much water was contained in a thunderstorm. I remembered doing such a problem back in school, but had to brush up on the approximation; it’s really quite staggering.
A typical t-storm is roughly 15 km X 15 km X 15km. The density of water is 1g / m3.
3375 cubic kilometers is equal to 3.375 E12 m3.
3.375 E12 m3 X (1g/m3) = 3.375 E12g = 7 440 601 348.739 617 lbs. !
A fully loaded 18 wheeler weighs 80,000 lbs.
So, your typical thunderstorm weighs approximately as much as 93 thousand fully loaded 18 wheelers. (93007.51686 lbs.)
OR
An adult elephant weighs roughly 12000 lbs.
So, your typical thunderstorm weighs approximately as much as 620 thousand elephants! (620050.1124 lbs.)
Posted by Ted Zarras at 2:00 PM
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Tuesday, July 17, 2007
Storms May Contain Strong Gusty Winds...
Ahhhh yes, it's finally feeling like summer around the area, and that means typical afternoon and early evening pop-up showers and storms. Tonight on 40/29 news at 5 we'll show you the typical life cycle of summer storms. Ted Zarras will explain that in our double team report during weather.
In the blog post below, I talked about how the mountainous terrain helps to produce thunderstorms, and that scenario looks to be the same for today; however, looking at an upper air sounding, I also noticed that we have some dry air aloft, and that could mean strong gusty winds within the storms.
Take a look at this morning's sounding from Little Rock (LZK). Notice how the dewpoint temperature rapidly decreases from about 600 mb to 450 mb. This dry air has a tendency to create evaporational cooling within the thunderstorms. The rapidly cooled air drops quickly and falls toward the surface as a microburst type of wind. The hotter the temperatures at the surface, the faster the air will fall.
It's also interesting to note that the dry air also can help with hail production. The freezing level today is around 579 mb. When you take in account the dry air, your wet bulb temperature drops to 683 mb. In essence, the dry air drops the freezing level, making it easier for hail to grow.
Posted by Drew Michaels at 11:14 AM
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Monday, July 16, 2007
Terrain Induced Storms....
Today was dominated by a hot and humid atmosphere! Dewpoints were in the upper 60s and lower 70s, creating a heat index close to 100 degrees across eastern Oklahoma. This time of the year it can be very difficult to get a cold front to provide widespread showers and storms; however, locally, we have mountain ranges that tend to help in the development of thunderstorms if you can get convergence. Take a look at the picture above by 40/29 storm chaser Brian Emfinger.
Convergence takes place when two opposite winds come together to lift air parcels; moreover, mountainous terrain can act like a ramp in order to lift the air high into the upper levels of the troposphere.
The dominant surface wind flow today was out of the south. This morning, a complex of showers and storms died out to our west, leaving a cool outflow boundary that moved over eastern Oklahoma and western Arkansas. This outflow boundary met up with a southerly surface wind creating showers and storms, and interestingly enough, the storms formed over the terrain of the area, but why?
Warm air aloft was running around 10 degree Celsius, creating a bit of cap across the River Valley, so weak convergence and convection wasn't enough to develop storms; however, there was enough forcing along the mountains to beat the cap, and form showers and storms. We'll continue to see this pattern over the next couple of days before a cold front moves in for the weekend!
Posted by Drew Michaels at 3:58 PM
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AMPLIFICATION
Jet flow around the Northern Hemisphere is comprised of a series of amplified troughs and ridges, though due to the positioning, flow coming over the pacific sort of hits a road block. The trough, ridge, trough pattern over the states is near alike to the pattern over the Atlantic. These two “omega blocks” look to keep our long wave pattern somewhat stagnant. We’ll look for and anticipate change through systems moving through the Jet.
There has been some consistency of a short wave dropping into the northern plains around the Wednesday / Thursday time-frame and then getting pinched off in the Ohio valley. This would be very interesting for us, seeing that we would end up with a northerly breeze with the Low setting up just to our northeast. This is the set-up for cooler than average highs and a few comfortable nights! It’s not quite like we’ve been basking in the upper 90s or triple digit land, though a mid-summer “cool period” might just feel pretty good!
We shall see.
Posted by Ted Zarras at 11:00 AM
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Sunday, July 15, 2007
Possible MCC early Monday AM
Check out these clusters of convection (thunderstorms) that have formed in northern Nebraska and southern South Dakota. Upper air flow is from the NW to the SE. As we've seen recently, these clusters have led to organized complexes of showers and storms or otherwise named, Mesoscale Convective Complexes (MCC). Along the leading edge winds can race at better than 60 mph and embedded cells often contain hail. So will we be dealing with such a complex tomorrow morning?
This map highlights an average wind field aloft, coupled with precipitable water; the amount of moisture that is contained in a vertical column of the atmosphere if you were able to squeeze it out. By this alone, if the complex hangs together, it's quite likely that some of it will impact our area early tomorrow. Usually throughout the course of the evening it becomes apparent, by mostly monitoring radar and satellite data, how developed these systems will become.
Drew Michaels will have the latest tonight at ten. Stay tuned!
Posted by Ted Zarras at 6:30 PM
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Saturday, July 14, 2007
WAVY YET STAGNANT
Despite there being some 6 to 7 long waves around the northern hemisphere, our pattern is somewhat blocked. A deep trough off the west coast, coupled with the high over western Canada and the trough in the east sets up an omega block; but, about the same type of pattern is situated across the Atlantic!
The ridge out west looks to slowly drift eastward, though we're still getting a hefty fetch of moisture off the Gulf from a broad Bermuda high circulation. This will keep the chances of afternoon showers and t-storms in the forecast over the week ahead and by the same token, help keep temps from really sky-rocketing.
Triple digit heat still is eluding us! Perhaps we'll have a repeat performance of 2004 where the mercury only hit 97 in Fort Smith and 93 in Fayetteville.
Posted by Ted Zarras at 10:45 PM
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Friday, July 13, 2007
FRIDAY FUN!
Insane Ski Gliding down Mount Eiger in the Swiss Alps!
Nutty, absolutly crazy, but...
just imagine.
WOW!
Posted by Ted Zarras at 6:45 PM
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Thursday, July 12, 2007
Impressive Pictures....Same Pattern
What an awesome picture taken over the Bentonville area. This is what we call a shelf cloud, and it's a great indicator of the thunderstorm's gust front. Sometimes these clouds can be mistaken for wall clouds; however, this cloud occurs at the front of the storm, and when you see this type of cloud, you'll quickly experience the cold outflow winds produced by the storm.
Today's MCS (mesoscale convective system) was pretty impressive. We'll expect another round of showers and storms in a similar fashion for early Friday morning. Another wave will drop out of the northwest and head over Oklahoma and Arkansas. The disturbance will interact with a moist boundary layer, and showers and storms will move through. MCS complexes are usually nocturnal, feeding off a strengthening 850 mb low level jet. They typically can produce heavy flooding rainfall, and strong damaging wind gusts.
Posted by Drew Michaels at 4:34 PM
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Wednesday, July 11, 2007
Friday Morning MCC
Due to the positioning of the jetstreak rounding the base of the trough in the east, the area within the red ellipse is a favored region for upper level divergence or a spreading out of winds aloft. This infers surface convergence and lift. As we've discussed before, there are two meteorological "sweet spots" with all jetstreaks; one in the right entrance region and the other in the left exit region of the jet. Forces become out of balance when wind enters a jetstreak and counterclockwise circulation develops in the vertical at the entrance region. Air converges at the surface on the right hand side which a causes lift. In the map above, an upper air forecast chart for midnight tomorrow, this area is over Kansas.
This mid-level chart highlights a disturbance some six hours later than the above chart, situated over eastern Oklahoma. This trough will help in sustaining convection and thunderstorm development. Once initial activity develops, sometime in the late evening tomorrow, outflow from individual cells will help form new thunderstorms,until a large area of heavy rain and thunderstorm activity is joined together in a complex. These nocturnal self-sustaining features are often referred to as MCC's or Mesoscale Convective Complexes. They are also kept going by a low level jet.
Lastly, check out the bulls-eye of precipitation over OK! This is the NAM forecast models interpretation of where the heaviest rain will fall. This could easily be off by 100 miles to the east or the west. These type of features usually develop a squall line along the leading edge and as we've seen this year already just as they push through, winds can reach damaging speeds, sometimes well in excess of 60 mph! We're monitoring developments closely over the next 24 hours and should have a good handle on our imminent threat by this time tomorrow. For now, it is something that definitely bears watching.Keep the blog bookmarked, we'll keep you advised!
Posted by Ted Zarras at 9:47 AM
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Tuesday, July 10, 2007
Late Week Severe Weather??????
Take a look at this forecast chart for late Thursday evening at 18,000ft! A monster ridge across the west will trigger northwesterly flow aloft across the plains, and this type of pattern can spell nocturnal thunderstorm complexes capable of severe weather.
In the meantime, Wednesday looks like a wonderful summer day! Highs will climb into the 80s with a slightly drier air mass overhead; however, Thursday night could be rather stormy as another wave of low pressure comes into play. I have marked that wave out on the picture above.
Right now the computer models are holding off precipitation until Thursday night into Friday morning. We'll look to destabilize during the afternoon on Thursday, providing a rich environment for showers and storms to survive after sundown. A low level jet will likely develop and fuel strong to severe showers and storms to our north after dark. These storms may produce large hail and damaging winds. We'll keep you posted!
Posted by Drew Michaels at 4:25 PM
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THIS DAY IN WEATHER
1913: The mercury hit 134 degrees at Greenland Ranch in Death Valley, CA, the highest temperature reading of record for the North American continent. Sandstorm conditions accompanied the heat. The high the previous day was 129 degrees, following a morning low of 93 degrees.
Posted by Ted Zarras at 8:35 AM
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A DRY AFTERNOON TOMORROW
It’s looking like we may be in the clear prior to tomorrow morning. A pre-frontal trough is now kicking off showers and storms just to the south and west of the Tulsa area, though dryer air is still several hundred miles back to the northwest. This afternoon may still bring some isolated heavy downpours with a few of the stronger thunderstorms, though enlarge, our atmosphere is more stable today than it was yesterday and cloud cover will help us from really heating up and destabilizing.
By the time the actual front meanders through, rainfall may be somewhat scattered in nature. With a little luck, tomorrow afternoon will pleasant with a much drier air mass in place. We should see some good breaks of sun too.
With an impressive Low to our north and east we’ll be a northwest flow pattern heading into the weekend. Thursday afternoon along with Friday morning could bring bouts of precipitation to our area in the form of showers and t-storms. We’re entering a period where we can see overnight complexes race through our area with impressive straight line winds along the leading edge. We’ll be monitoring developments closely.
By the time the actual front meanders through, rainfall may be somewhat scattered in nature. With a little luck, tomorrow afternoon will pleasant with a much drier air mass in place. We should see some good breaks of sun too.
With an impressive Low to our north and east we’ll be a northwest flow pattern heading into the weekend. Thursday afternoon along with Friday morning could bring bouts of precipitation to our area in the form of showers and t-storms. We’re entering a period where we can see overnight complexes race through our area with impressive straight line winds along the leading edge. We’ll be monitoring developments closely.
Posted by Ted Zarras at 8:18 AM
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Monday, July 09, 2007
Early Evening Update SEVERE T-STORM WATCH through 10:00 PM
A series of waves of low pressure are impacting our area. The first slid through this morning, only to be followed by a more substantial wave this afternoon. This feature is passing through an environment that is extremely unstable. Check out the mass of clouds in the above satellite image just to the west of the Fort Smith area. This flattened appearance that you see is the tops of many strong and severe thunderstorms hitting the top of the tropopause, some 55,000 to 60,000 feet up. CAPE values are better than 3000 J/Kg with a bulls eye of 5500 J/Kg off to our southwest. Most of the heavy activity this morning was to our south and east so eastern OK is still very "ripe" and with the heat of the day we are seeing explosive growth of thunderstorms.
The threat of damaging wind gusts in excess of 60mph along with quarter sized hail and an isolated tornado looks to carry into the evening hours as this wave passes through our area. The third wave is visible in the Satellite shot that encompasses Kansas. This feature will likely ramp up tonight as it encounters a developing low level jet. This wave looks to bring the threat of gusty winds and hail to our area but more of concern will be the amount of rain associated with the event. Rain, heavy at times will continue to fall on areas that are already beyond saturated through tomorrow night. All of this water will flow eastward through various creeks, streams and rivers, emptying in the Arkansas River which is already high.
Flash Flood issues are likely and of a major concern. Flooding is the number one killer among weather related phenomena. Please do not try to cross flooded roadways or swiftly moving water. Just a foot and a half will float your car, truck or van. Please do not allow your children to play in or around flooded creeks or streams. Just a half foot of swiftly moving water can knock a grown man over. Above all remember to TURN AROUND, DON'T DROWN. The majority of flooding deaths occur in automobiles.
Posted by Ted Zarras at 5:30 PM
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REX BLOCK
The yellow fuzzy line with the arrows is loosely aligned with the Jet stream. Take note of the general arced shape of the jet as it moves in from the pacific and enters North America. This is a ridge of high pressure. With the pattern that we’re in now, air moving across the pacific is splitting as it nears the west coast; some is moving north and some is heading south. With this “split-flow”, a blocking form usually develops and we’re seeing that now with a closed isobar below the high, under the ridge. This upper air pattern of a High over a Low is a called a rex block and can stay fixed in position for days.
As the ridge out west begins to further build we’ll get into a northwesterly flow regime here. Look at how wavy the flow is just below the ridge, heading into the central part of the country. Each wave, coupled with daytime heating could kick off heavy bouts of rain in the form of showers and t-storms.
By the time we reach the middle to end part of the week we’ll be watching closely for the possibility of a nocturnal complex of showers and storms developing. Right now early Friday morning is looking interesting. We’ll be monitoring developments closely.
As the ridge out west begins to further build we’ll get into a northwesterly flow regime here. Look at how wavy the flow is just below the ridge, heading into the central part of the country. Each wave, coupled with daytime heating could kick off heavy bouts of rain in the form of showers and t-storms.
By the time we reach the middle to end part of the week we’ll be watching closely for the possibility of a nocturnal complex of showers and storms developing. Right now early Friday morning is looking interesting. We’ll be monitoring developments closely.
Posted by Ted Zarras at 9:30 AM
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Sunday, July 08, 2007
More Rain & Storms.....Severe Potential?
Were you able to dry out over the weekend? The rainfall quickly went down, but the heat index rose quickly thanks to dewpoints in the 70s! I don't expect the semi-dry weather to stick around though. A developing trough to our north will send us more rain chances starting on Tuesday, and will likely last through Friday.
I do think we need to watch for potentially strong to severe storms for Tuesday afternoon and evening. Here's the situation. A pre-frontal trough is forecast to move in by Tuesday, and this will likely act as our "lift" mechanism to initiate scattered showers and storms by the afternoon and evening. A trough is unique because the air aloft is generally cooler, so the atmosphere should become unstable toward the afternoon as the surface heats up.
We'll see a mix of clouds and sun with dewpoints back in the upper 60s and lower 70s. I think CAPE values will quickly climb between 2000 and 3000 J/KG, providing chances for hail and strong gusty winds. Some wind shear will be present within the atmosphere, so storms could support larger hail, especially with strong rotating updrafts across eastern Oklahoma.
Posted by Drew Michaels at 3:33 PM
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Saturday, July 07, 2007
FIREWORKS FROM SPACE
Twenty years ago, astronomers witnessed one of the brightest stellar explosions in more than 400 years. The titanic supernova, called SN 1987A, blazed with the power of 100 million suns for several months following its discovery on Feb. 23, 1987. Observations of SN 1987A, made over the past 20 years by NASA’s Hubble Space Telescope and many other major ground- and space-based telescopes, have significantly changed astronomers' views of how massive stars end their lives. Astronomers credit Hubble's sharp vision with yielding important clues about the massive star's demise.
Posted by Ted Zarras at 8:29 PM
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Friday, July 06, 2007
Amazing Flash Flooding Video......
Look at this impressive video! This was taken by 40/29 Storm Chaser Brian Emfinger on the Little Mulberry River in the Ozark Mountains. This started as a quiet stream and ended up as a raging flash flooded river. This is why it's so important to stay away from flooded areas. Water is very deceiving, so always turn around and don't drown.
Posted by Drew Michaels at 8:42 PM
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FOCUS ON STORM POTENTIAL
We’re capped over right now by a steady advection of warm moist air aloft that has pushed in throughout the night. The sun is strong this time of year though and with enough sunshine, by the early afternoon we’re likely to see convection develop across a stalled boundary, draped horizontally just north of the River Valley, loosely paralleling I-40. 
The map above is of downdraft cape. This highlights regions where gusty downdrafts may occur. As thunderstorms begin to drop precipitation at the end of the mature stage of development, evaporation takes place. This is a cooling process. This air, cooler and denser than the surrounding environment, can fall like a rock. A dry layer in the atmosphere further adds to cooling and ultimately wind speed as thunderstorms die-out or collapse.There are some high values horizontally situated across NE OK and NW AR. Like yesterday we'll look for afternoon heating to initiate activity and we'll be monitoring developments closely for the potential of some gusty winds.
Posted by Ted Zarras at 9:50 AM
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Thursday, July 05, 2007
Almost Identical Days.....Some Forecasting Tips
This is what Ted and I call a persistence forecast. We're hardly changing at all, and that's a huge key when you're forecasting the weather. Everyday you need to ask yourself, is the atmosphere going through a change? If there is no major change in air mass or overall pattern, then you'll likely see a repeat performance.
Heading into Friday, our dewpoints will remain in the upper 60s and lower 70s, creating heavy rainfall potential yet again. The upper level feature to our south isn't forecast to move a whole lot, so more high level clouds from 700 to 500 mb will exist south of I-40, limiting high temperatures in the mid to upper 80s; however, more widespread showers and storms will be possible across SE OK and SW AR due to their proximity to the upper level feature. Look at the comparison above from Thursday to Friday....the low isn't really moving!
The stalled out frontal boundary will hang around for Friday afternoon, so expect more afternoon showers and storms capable of small hail and gusty winds near the vicinity of the front. The warmest part of the area will remain across NE OK with more available sunshine.
Posted by Drew Michaels at 8:19 PM
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A WET WEEK AHEAD
OH Funsville...The big red letters spelling out NEXT WEEK are sitting in a trough that is slated to transition our way sometime next week. Troughiness as it sometimes called or "being in a period of troughiness" conjures up images of gray skies, precipitation and stagnation. How grand! We’re likely not to see it quite that bleak, but the rain machine looks to continue.
There has been consistency with long-range models that after a series of short waves, moving through the jet, which is far to our north, a trough as pronounced in the present chart above, will dig into the central plains. This may be icing on the cake, in the form of additional rain to our area, sometime around the middle to late part of next week. The cake itself looks to be yet another cut-off feature that develops just to our west as early as this Sunday. Just as we’ve seen over the past two months little disturbances will spiral around this Low, kicking off round after round of predominantly afternoon showers and storms.
Cool (relatively speaking) and Showery… will these words continue to have validity? Quite possibly so!
Posted by Ted Zarras at 1:45 PM
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Wednesday, July 04, 2007
Thursday's Hail & Wind Potential
Happy 4th of July everybody! If you read Ted's blog below, we're finally saying goodbye to a pesky cut off low, but now we look to the north for more chances for showers and storms. The picture above depicts a cold front that's sparking off strong to severe showers and storms across Kansas and Missouri this 4th of July. Overnight, we'll watch this boundary move south, and eventually set up across eastern Oklahoma and western Arkansas by Thursday afternoon.
This front will be our new focus for afternoon shower and storm activity. I have included a CAPE forecast above for Thursday afternoon. Sunshine and moisture will combine to produce CAPE values from 2,000-3,000 J/KG. This leads me to believe that large hail could be an issue with the strongest storms. Large CAPE values represent the ability for an air parcel to rise rapidly within the atmosphere; moreover, strong rising air currents have the potential to support large hail stone growth!
The computer models also hint at some dry air aloft, which could lead to strong gusty downdrafts. The Skew-T plot shows this dry layer from roughly 10,000ft to 18,000ft. We'll watch the storms closely on Thursday afternoon.
Posted by Drew Michaels at 3:57 PM
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