WAVE # 1 tapering off...

Snow is still coming down across NW AR and into the River Valley though we’re seeing a clearing line off to the west. We’ve received many reports of 1 to 2” on the ground with a higher totals coming in from the Pea Ridge area of Benton County where three inches plus have been reported and it is still snowing.

This first batch of snow will slowly transition to flurries and freezing rain which will be off and on through the overnight period. WAVE # 2 will likely move into our area by tomorrow morning. Interestingly, model initialization has been slow with the precipitation. In fact, there was a good lag of some four hours with the on set of today’s snow, so with that being said, we’re looking for an earlier start than the noontime which the latest model data supports.

WAVE # 2 looks to be light, but the inch to two additional inches of snow that we are expecting will still likely plague traveling and cause road issues once again. We’re still looking to have plenty of cold air in place so what does fall will stick and last for awhile. Another shot of brutally cold air is still slated to move through the area late Friday and into Saturday. It is likely that during the day on Friday we will have some light Flurries as we’re still situated within the mean trough of Low pressure to our west. Temperatures at 850mb by Sunday night are near -18C. If that air gets mixed out under calm conditions and clear skies, we could be looking at surface temps by Sunday morning in the low single digits… OUCH!

We’ve been receiving reports of some freezing drizzle in the Roland, OK area and into Fort Smith and the River Valley. It’s likely that in-between waves tonight, as precipitation is light and predominantly in lower layers of the atmosphere, from the ground up to about 10,000 feet or so (700mb), we will experience periods of troublesome freezing drizzle.

Snow flake formation and growth typically occurs between 18,000 feet and 10,000 feet (500mb to 700mb). Within this layer that has a typical temperature range of -5 to -15C air, the largest concentrations of CCN’s (Cloud Condensation Nuclei) exist. This region also is where dendritic growth and snowflake formation occur. Right now our wave is drying up in this region and there is a lack of moisture that is being transported in, but at the surface to the aforementioned 700mb level, we still have a feed from the south south west of moisture laden air. This moisture is basically shut off from snowflake formation processes and the water droplets remain in liquid state. Formally stated, they are “supercooled”. Upon reaching the ground they freeze as glaze or freezing rain even though the whole column above the surface is frozen.

Summed up… The roads will continue to be hazardous!



Thanks for all of the reports!

Snow continues to fall across all of NE OK and NW AR. Many locations have already picked up over an inch of snow. The snow will continue to fall through 7 p.m. An additional .25" to 1.00" will be possible this evening. We'll see a lot of the moderate snow taper off to flurries after midnight, with more light snow developing by Thursday morning across the entire area.

South throughout the River Valley, we're seeing some snow mixing in with sleet. The snow/sleet mixture is still accumulating on the roads. Accumulations between a dusting to an inch have been reported across the River Valley, with an additional .10" to .25" possible this evening.

More updates to come!

The River Valley into SE OK is reporting roads that are becoming slick and hazardous, especially along the bridges and overpasses. Over the next couple of hours look for light to moderate snow to continue, likely covering the roads and creating issues. 1 to 2 inches is still a good bet by Thursday afternoon.

NE OK and NW AR will see more of a moderate steady snow through 5 p.m. This will only cause more road issues. Expect between 1 and 2 inches of snow toward the evening, with additional snow possible overnight. I'll update my snowfall map coming up soon...more snow accumulation will be possible across sections of NE OK and NW AR.

Roads all across NW AR and NE OK are becoming slick and hazardous. Snow has been accumulating on roads, creating numerous accidents. The State Police discourage travel in Benton county at this time due to the amount of car accidents. Between 1/4" to 1/2" of snow has already accumulated north of I-40, and we're expecting additional snows into the evening and overnight. 2 to 4 inches is still a good bet.

The River Valley is also seeing snow starting to accumulate; however, it is very fine and dry, but that will change over the next several hours. Be very careful driving. 1 to 2 inches is not out of the question by Thursday across the River Valley.

Keep checking the blog for more updates!

Forecast models have a tough time handling closed Lows. Put that Low over the Pacific, like we presently have and the lack of real data available over water makes modeling solutions that much weaker. That being said, confidence in the long range forecast remains less than grand. The one certain thing is that there is a lot of cold air just to our north that will be continually funneled into the central part of the country by a succession of waves over the upcoming week. Throw some moisture into the mix and we’ve got snow, though timing when, where as well as how much is proving to be quite the challenge.

Cold air strengthens and aids in Cyclogenesis or Low pressure formation. We recently received an email, questioning how a shot of arctic air effects development and it’s a simple as that. A more formal definition from a case study entitled Useful Relationships Between 500 mb Features and Major Freeze Events in the Lower Rio Grande Valley of Texas is posted below.

“The differential horizontal advection of temperature produces the major amplitude changes in a traveling wave. The 500 mb height will fall at a point where cold air advection exists with increasing strength downward; a common situation with a cold front. The strong low-level cold air advection of an Arctic outbreak will produce a rapid deepening of the 500 mb trough; similarly, a pronounced deepening of a 500 mb trough on a prog chart indicates strong surface cold air advection. The 1000-500 thickness and the inferred thickness advection may be used, with caution, to forecast the Arctic outbreak with the related 500 mb features.”

Here’s the link to the paper:

http://www.srh.noaa.gov/ssd/techmemo/tm88.htm


The above takes me back to my senior year at Plymouth State University and every forecaster’s most favorite class...(possible pun intention), Calculus based Dynamics I and II ;) I can still hear my professor say in layman’s words… “A blast of arctic air is like a shot in the arm to a developing low”. OK ...enough about Dynamics, but this is the crux of what cold air can do, in some cases sending ordinary events into the record books. For snow, we want this!

The ingredients are available for measurable snow this week; it will just take the right proportions at the right time. There has been better consistency for a late week into the early weekend snow event versus a mid week one at this point.

We’ll be updating this tricky situation frequently.

Bottom line, temperatures will really drop late Saturday night into Sunday. On Saturday, a wave of low pressure will provide the lift for some light rain across SE OK and SW AR, with a wintry mix likely throughout NE OK and NW AR. Precipitation amounts look to be fairly light, mainly a few tenths of an inch areawide. We're not expecting major accumulations north of I-40, possibly a dusting at the most. The River Valley will see rain, and then slowly transition by the late afternoon to a mix of rain and snow. A cold rain is anticipated south of the River Valley.

Right now, a blocking pattern is taking hold of the West Coast, allowing polar air to spill south. Until the block is removed, we'll continue to see reinforcing shots of cold air come our way. The GFS continues to be active next week with another storm system coming into focus for Tuesday or Wednesday. The cold air won't be in question, so snowfall would be likely, but right now the time of the event is not clear. Keep up with the 40/29 Super Doppler Storm Team this weekend for the latest.

It’s always wise to jump off of something solid and real versus a computer model. So what does that mean exactly might you ask? Well, in the world of weather forecasting there’s both real and simulated data, the later which is often referred to as “the models”, in weather office lingo. The above map is a real sampling of the atmosphere at a pressure level of 500 millibars (mb). This correlates to about 18,000 feet. We’ll start here with the real.

Near the Gulf of California there are two closed isobars or lines of equal pressure that make a circle. This feature is the “cut-off closed low” that Drew highlighted on both the five and six o’ clock shows, and also our chance of a little rain and snow late on Saturday. The numbers on the isobars on the whole map correlate with the height at which the pressure is 500mb. The two around the Gulf of California Low happen to be 558 and 570. These numbers are listed in decameters, so for the 570 height contour we would give this a height of 5700 meters (m). After a little quick math, this correlates to a height of 18701 feet (ft).

Looking upstream or to the West, the next feature of interest is a Low that just about has a closed contour around it off the coast of Northern California. It is this storm system that is prognosticated to move through our area by the second half of next week. The dip in the isobars just above this Low, to the east of Alaska, represents a shot of cold air that will spill in here early on Sunday. This is a precursor for any hopeful snow event. The more cold air we have the better and the way things are looking a few successive shots will be moving in.

Back to the Low off the coast of California. Long range models have this system (music please) spinning and spinning and not moving much and then spinning some more and then finally breaking up somewhat in a few pieces that look to scoot through the central plains next week. There is a reason for this. Back to the 500mb map. The east coast is presently within a deep trough of Low pressure. The central Atlantic is dominated by a strong ridge of high pressure and lastly the Mediterranean has a strong Low pushing in. This pattern of Low, High, and Low is a blocking pattern known as an Omega block. An Omega block thwarts westward movement and with this present set-up a building of cold air over much of the country can be expected.

So with assumed cold air place, finally things can get interesting! The map in color above is a simulated state of the atmosphere for Friday February 2nd at noon. It’s cold, snowy and very much a picture of winter across much of the country. This latest run of the GFS (18Z) at this time, already had a system that passed through our area late Wednesday into Thursday but this image highlights a Low forming south of Colorado with yet another push of cold air. This one will have jet stream energy to work with and just may be the one to watch out for!

Will things change? You bet! Will the models continue to hint at a legitimate winter scenario? Say your prayers!

But, will it be turning COLD? Bank on it!

THINK SNOW!

After reading our blog posts from the weekend, I realize we have a lot of winter weather fans across our area. As I looked over our long range GFS model, more winter weather potential exists for the middle of next week. Let me say that this is still a very long way off, and it will be fun to see how the models handle this system; however, I have seen some consistency from the last 3 model runs, and that could mean the possibility for winter weather by next Wednesday.

A trough is forecast to swing across the Central United States by early next week, allowing cold air to dive across the plains. Low level moisture is also forecast to increase as the cold air moves south. We'll be keeping our eyes on this system over the next couple of days. Let it snow!

From the very get go of this winter event we’ve been dealing with a limited amount of cold air. The last blast of cold that moved in with the ice storm last weekend had been lingering over us and with the onset of the precipitation earlier today; there was enough, it was dry, and thanks to a little help in the evaporational cooling department, we saw a little sleet and snow. Ultimately though, along with the continually feed of moisture from the south which saturated the atmosphere, came warm air aloft, otherwise known as warm air advection. This is the horizontal transport of warm air to a region and more often than not the guilty culprit that’s robbed more than one potential big snowstorm. It can also be your best friend for a huge snow if and only if sufficient cold air is in place. It wasn’t the case for us and truth be told, never really appeared as if it would be.



It seems as if the NWS was getting some exercise this morning on the ol’ bicycle…

.DISCUSSION...MAJOR WINTER WEATHER BACK PEDAL UNDERWAY...SNOW - SLEET / RAIN LINE CLOSELY FOLLOWINGI-44 THIS MORNING. 750-800 MB TEMP FORECASTYESTERDAY LOOKS TO PAN OUT. DELETED WINTERADVISORY SOUTH WITH RAIN PRIMARY PRECIP THERE.SOUTH PORTION OF PREVIOUS WARNING CONVERTED/DOWNGRADED TO ADVISORY STATUS. DROPPED SNOWAMOUNTS ABOUT IN HALF AREAS NORTHWEST I-44.

Regardless, this event still has the possibility of going over to a little sleet with some lingering flurries and or sprinkles when it comes to an end early tomorrow morning. For the most part we’ll continue to see the rain and remain above freezing. Check out the updated totals map and thanks for all of the forecast contest entries on the prior post. Keep em’ coming and we’ll tally everything up when this is through.

So after an updated discussion it might be fun to collect a table of forecasts, wishcasts, and just plain ol’ hunches from you as to what we get when all is said and done for both the River Valley and Fayetteville. To make these legitimate, try to throw out your take on things prior to the start of the event and use the format of:

River valley: xx inches of _____

Fayetteville: xx inches of _____

Make up a name and put it under the prediction and we’ll see…



After checking the latest data, a warm up, be it ever so slight, is still showing up around 800mb in the column of air over the River Valley. This is that southerly feed kicking in and it will be a battle to see how long it looses to the colder air. Check out the soundings from both the NAM and the GFS. They both have this feature showing up by tomorrow evening.

Fayetteville is so ridiculously close to be isothermal that it may be the case that they start off as snow and then just go to sleet and end that way. Still, it is a frugal forecast that points to the north and west of Fayetteville will just have that much more of the necessary cold to work with that will bring in the higher numbers.

Points south of I40 will still likely see some sleet and possibly some snow at the onset of this event tomorrow, though given the warming trend of the atmosphere’s profile as made evident by a sampling of points southward; rain still looks like the end result.

Just an FYI… Grid interpolations are kicking out just around a half inch for this event. Factor in a standard 10 to 1 ratio with a frozen column and you’ve got 5”. We’ll be so very close to freezing that ratios will likely chime in a little lower.

Our map hasn’t changed a whole bunch as to amounts though we’ll be fine tuning throughout.

Our entire team remains in steady communication and we’ll be conducting special on-air updates as need be and Drew says hello!

Our thinking remains the same. The best snow accumulations look to be toward I-44, with most of the area seeing a mix of rain/sleet/snow with only minor accumulations across northwest Arkansas.

I have attached two posts from the National Weather Service from today. The first was from this morning...and the second was during the late evening. It's funny how the weather service is now starting to change their tune. I think they jumped on this way too early...I'll let you post your comments, and you can tell us what you think. Read and enjoy!


AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TULSA OK
242 AM CST THU JAN 18 2007.

DISCUSSION......WINTER WEATHER AGAIN EXPECTED INTO THE WEEKEND...HIGH CLOUDS CONTINUE TO SPREAD ACROSS THE AREA THIS MORNING AS STRONG SUBTROPICAL JET MOVES INTO THE CENTRAL PLAINS. IT APPEARS THAT INGREDIENTS ARE COMING TOGETHER FOR ANOTHER WINTER WEATHER EVENT SATURDAY INTO SATURDAY NIGHT ACROSS MUCH OF FA AS UPPER LOW...CURRENTLY OFF OF THE SOUTHWEST CALIFORNIA COAST...LIFTS NORTHEAST INTO SOUTHERN KANSAS BY SATURDAY NIGHT. MODELS IN GENERAL AGREEMENT WITH MOVEMENT/STRENGTH OF UPPER FEATURES HOWEVER THE NAM/WRF SLIGHTLY MORE NORTH WITH UPPER LOW TRACK AND DEVELOPS LESS PRECIPITATION DUE TO DRIER LOW LEVELS. ITAPPEARS THE GFS HAS A BETTER HANDLE WITH OVERALL PRECIPITATION AMOUNTS AND WILL GENERALLY FOLLOW THIS TIMING THROUGH THE WEEKEND.FORECAST POINT SOUNDING INDICATE THAT PRECIPITATION WILL REMAIN MAINLY SNOW NORTH OF A MLC/FSM LINE...WITH A SNOW/SLEET MIXTURE FURTHER SOUTH TO THE RED RIVER. WARM LAYER ACROSS AFOREMENTIONED AREA EXPECTED TO BE ONLY AROUND 1 TO 2 DEG C AT MOST AND THEREFORE ONLY EXPECT PARTIAL MELTING WITH LESS OF A THREAT OF FREEZING RAIN COMPARED TO THIS WEEKENDS ICE STORM (WARM LAYER WAS AROUND 10 DEGC). AREAS OF SNOW/SLEET ARE EXPECTED TO DEVELOP ACROSS SOUTHEAST OKLAHOMA FRIDAY NIGHT INTO SATURDAY WITH SNOW SPREADING ACROSS NORTHEAST OKLAHOMA AND NORTHWEST ARKANSAS DURING THE DAY. WITH PRECIPITATION EXPECTED TO REMAIN MAINLY SNOW NORTH OF INTERSTATE 40 EXPECT TOTAL SNOWFALL ACCUMULATIONS OF 5 TO 7 INCHES. SOUTH OFA MLC/FSM LINE DUE TO THE SNOW/SLEET MIX EXPECT 2 TO 3 INCHES...HOWEVER THIS COULD FALL MAINLY AS SLEET AND WILL THEREFORE ISSUE AWINTER STORM WATCH FOR THE ENTIRE FA FRIDAY NIGHT THROUGH SATURDAY NIGHT.MAIN CONCERNS REMAIN THE EXACT STRENGTH/TRACK OF UPPER LOW AND DEPTH/STRENGTH OF THE WARM LAYER PRIMARILY ACROSS SOUTHERN ZONES. HEAVY SNOW EVENT WOULD BECOME EVEN MORE LIKELY IF UPPER LOW TRACK IS ANY FURTHER SOUTH THAN CURRENTLY FORECAST BY THE GFS.





AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TULSA OK
906 PM CST THU JAN 18 2007.

UPDATE...LOTS OF HIGH CLOUDS TONIGHT. WIND IS ALSO LIGHT AND MAINLYFROM THE NORTHWEST. UPDATED THE ZONES TO FRESHEN THE SKYCOVER WORDING. PARTLY CLOUDY WILL DUE AS THERE WILL LIKELYBE THIN SPOTS. GOING LOWS LOOKED GOOD AND DID NOT CHANGE THEM.STILL WATCHING THE STORM FOR THE WEEKEND. A SIGNIFICANTPRECIPITATION EVENT WILL OCCUR. THERE IS SOME UNCERTAINTYABOUT PRECIP TYPE. THE WRF IS WARMER AND DRIER AND THE GFSIS COOLER AND MORE MOIST. IF THE WRF IS RIGHT...ALONG ANDSOUTH OF A MLC-FSM LINE WILL HAVE TO BE CONSIDERED FORA COLD RAIN AND SLEET. THE GFS WOULD SAY SNOW. TULSAWILL LIKELY SEE SNOW NO MATTER WHICH MODEL IS RIGHT.THE WINTER STORM WATCH IS O.K. GIVEN THE UNCERTAINTY ANDTHE POTENTAIL FOR WINTER WEATHER. HAVE NOT CHANGED THEFORECAST FOR THE WEEKEND AT THIS TIME BUT THE MID SHIFT WILL HAVE TO TAKE A HARD LOOK AT IT.

I don't know about you, but all I heard today was the amount of snow that's supposed to fall throughout the area this weekend. Yes it's true, the Weather Service in Tulsa has issued a Winter Storm Watch, but I have some reservations to the amount of snow that's being forecasted and what will actually accumulate. Sounds like the hype is getting out of control.

I talked about the model differences on our blog entry last night, and most of those still exist today. The GFS continues to be faster with the storm compared to the NAM; however, both the NAM and the GFS continue to warm temperatures aloft in each model run. This tells me that the area has a greater chance to see a mix of rain/sleet/snow throughout the event. Greater chance for a mix, less of a chance for total accumulation.

The National Weather Service and other media outlets in the area are buying into higher totals, and quite frankly, hyping this event. We're not. I have included a preliminary totals map that we'll be updating over the next couple of days. At this point the best spot in our area for accumulating snow will occur across western Benton county and across northeastern Oklahoma. Locations North and west of I-44 will see a good swath possibly over half a foot. Please check back for the latest!

Plenty of uncertainty still exists with our upcoming winter storm. I'm sure that's not a shocker to you. The NAM's timing at this point seems to be more for Saturday night into Sunday afternoon. The GFS supports a faster solution that moves the winter weather in by Saturday afternoon and ending by Sunday morning. Our upper level storm is currently over southern California, and this will create the lift for the forecasted winter weather.

Looking at the 0Z NAM data, temperatures look cold enough Saturday night for snow to fall; however, warm air advection around 5,000 feet looks to take place toward Sunday morning. This warming may change the snow to more of a rain/sleet mix for Sunday morning.

The GFS supports a colder solution. The 850 mb -5C isotherm cuts north of I-40, which would create the possibility for heavy snow to fall Saturday night across northwest Arkansas. The GFS also paints snow for the River Valley.

There is still too much of a difference between models to confidently say what will happen. I'm feel good to say that everybody will see some sort of winter precipitation, but we're not ready to forecast snowfall totals.

Here's a couple of interesting winter weather rules of thumb:

1. It takes about 1200ft of warm air to melt snow.

2. Sleet is the result of a warm layer greater than 1200ft melting the frozen precipitation as it falls. The precip them falls through a freezing layer at least 4,000 feet thick.

We're just starting to recover from the ice and cold, and now we're looking at another system to potentially drop snow across eastern Oklahoma and western Arkansas for Sunday. Right now we're expecting the jetstream to drop along the west coast and intensify a wave of low pressure for us to deal with by the weekend. High pressure over the gulf of Mexico will act as a pump feeding moisture into the developing system. In addition to the 850 flow off the gulf, the subtropical jetstream will transport moisture from the Pacific Ocean. Needless to say, this system will have plenty of moisture to work with.

The 0Z GFS paints the 850 mb 0 degree isotherm as far south as the Red River. If this holds true, we would likely deal with a snow event across the entire area. We're still about a day out until our short range models get a handle on the storm system, so we'll wait for more guidance before going with any snowfall totals. Stay tuned!

Talk about a wild weekend. Over the last three days, the area was blanketed with clouds, rain, and ice, and finally we're going to dry out this week. Many locations received between 2 and 6 inches of rainfall. In Garland county Arkansas, 9.07" was recorded near the Blakely Mountain Dam. Unfortunately, the cold air is coming to replace the wet weather, and we're talking unseasonably cold.

Temperatures will likely stay below freezing across NE OK and NW AR throughout Tuesday afternoon, especially if you have ice on the ground. Single digit lows are expected by Wednesday morning. To put this cold in perspective, average lows for this time of the year should be in the low to mid 20s with afternoon highs in the upper 40s and lower 50s. Even though we'll be running 10 to 15 degrees below normal, I don't feel that we'll set any records. The record low for Fayetteville on Wednesday is "1" set back in 1982.

As we look ahead, a storm system will drop across the West Coast; however, we're not looking for anything major to develop at this point. A few showers are possible by the weekend.

A band of moderate freezing rain, sleet and snow is just off to the west our area. This will be the last concentrated bout of precipitation that will move through, in association with this system since it began over 48hours ago. We also will the have largest area of cold air in place as it moves in. Right now temps across NW AR in large have slipped below freezing. The River valley is precariously close, at 36 in Fort Smith, but points westward are at freezing and below.

McAlester, Talihina, Wilburton, Eufaula, Tahlequah, Jay and Grove are all getting freezing rain right now. This last hoorah could put as much as an additional half inch of ice on top of areas that have already seen damaging accumulation. We’ll transition into a steadier cooling throughout the day on Monday as we dry out, though a few flakes of snow could be flying as more and more cold air works in.

Monday morning will be tough, travel and road wise. Roads have already been collecting ice in many locations north and westward. As we head into tomorrow, many of us will not get above freezing. Undoubtedly, this will make for a difficult clean up and some slick roads.

We can’t thank you enough for all of the reports.

The freezing line throughout this entire event has remained just west of the AR / OK border, stretching from NW Benton County through central Sequoyah County and point’s southward. We’ve had many calls and emails with reports of ice just now starting to form on trees and power lines just 10 miles west of the Fort Smith area. Remember, the first sign that precipitation has shifted to freezing rain will be icicles forming on tree branches.

Regardless of type, we would love to have your reports and help us “see” exactly what’s happening in the in-between areas. Also, thanks big time to everyone that has been emailing us and calling with the reports… keep em’ coming!

We’re still anticipating a falling of temperatures, as we're starting to see now, throughout the rest of the evening. This will give almost our entire area icy conditions. A feed of moisture back behind this present fetch continues to blossom and it’s likely that throughout the overnight we’ll continue to see light freezing drizzle which may mix in with some sleet in areas to the north and west. A few flurries can’t be ruled out by the time this system departs tomorrow and then it’s going to get COLD!

Taking a peak at the extended… we may be in for a bit more wintry weather by next weekend!

No doubt about it, temperatures are slowly starting to fall, especially across NW AR. Today we have watched a surface low allow for some warmer surface temperatures; however, as that low departs to the northeast, our winds will back, and colder air will spill south.

Trees and powerlines have already taken a beating across western Benton county along with a good majority of northeastern Oklahoma. Temperatures will remain below freezing tonight, with light freezing drizzle possible. Travel is not advised!

In the short term, expect temperatures to drop close to freezing across NW AR this evening, allowing for spotty freezing rain. Light precipitation may fall overnight, but we're only expecting more of a light freezing drizzle. Freezing rain will be a big problem for Sunday afternoon, creating travel issues across northwest Arkansas. A quarter of an inch to an inch of ice is still forecast for Sunday.

Throughout the River Valley expect temperatures by morning to hover close to freezing. Mainly light drizzle will fall overnight, but some spots could see some patchy freezing drizzle. Heavy rain will develop again for Sunday afternoon, and if temperatures are around freezing, the River Valley may experience periods of freezing rain toward Sunday evening. A tenth of an inch to a half inch of ice is forecast by Sunday night.

I just looked over the current model data, and Sunday is really looking like the worst day of the weekend. Benton, Cherokee, Adair, and Delaware counties will likely deal with ice all weekend; however, both NW AR and the River Valley will be blasted on Sunday with temperatures in the 20's and lower 30's along with a surge of heavy rainfall as a wave of low pressure moves overhead. Many spots could pick up over an inch of rain throughout Sunday afternoon, creating icing throughout the area. Roads, powerlines, and trees could be heavily impacted when it's all said and done by Sunday evening.

A dusting of light snow could occur on the back edge of the storm early Monday morning before we dry out for early next week.

I want to update you on our current thoughts regarding the ice storm. I'm going to break this down into 3 regions to make it easier.......

Northeastern Oklahoma

Ice accumulation will be possible tonight through Sunday. Ice accumulations from 1" to 2" will be possible throughout the weekend. Travel is not recommended. Widespread power outages and tree damage is expected, so please prepare for the ice.

Northwest Arkansas
Freezing rain will occur tonight through Saturday morning. During the day on Saturday, a surface low to the south will nudge temperatures at or just above freezing, so a mix of freezing rain and rain will be possible. The exception will likely be Benton county, where freezing rain may occur all throughout your Saturday. More freezing rain is anticipated Saturday night into Sunday, where the majority of heavy ice accumulation will occur. Travel on Sunday may be very dangerous. Total ice accumulations across western Benton county may approach 2 inches. The majority of northwest Arkansas will see between .50" to 1.50" of total ice.

River Valley
Computer model guidance continues to support a freezing rain situation for Sunday across the River Valley. If those temperature projections are verified, many spots could receive between a 0.25" to an 1.00" of ice by Sunday night. Travel may become an issue, we'll continue to watch the new data.

I have looked over the latest OZ run of the NAM, and just as we have been thinking, the computer model has developed a colder solution. The model is handling the cold air very well, so confidence is running pretty high. This could mean significant ice accumulations throughout parts of our viewing area. The cold air will move in throughout the day tomorrow, dropping temperatures into the upper 30s and low to mid 40s toward sunset. Here are the counties that have the greatest chance for ice accumulation from 1/4" of an inch to 1 inch through the weekend......

Benton, Delaware, Adair, Cherokee, Muskogee, McIntosh, Pittsburg Counties

If you live in these counties, please prepare for a major ice storm this weekend. Significant tree and power line damage will be possible.

The above topographical maps highlight the interesting terrain that encompasses our area. Take note of the absence of precipitous variances in Northeastern Oklahoma versus North West Arkansas. Elevations throughout Benton County are right around 1200 feet plus / minus a few hundred and most of the area is rather plateau like, where as the Ozarks rise to some 2000’ plus / minus a few hundred in central Washington county and areas just south and eastward. Much of Northeastern Oklahoma is a continuation of the plateau with various rises in elevation throughout Cherokee and Adair County which are an extension of the Ozarks.

The latest runs of the NAM show an interesting correlation between these topographical variances and the shallow nature of the arctic air. Below are two model Thermodynamic soundings, the first of which is from Grove, OK.

This is off the 18Z run of the NAM and is the "proposed" thermal profile of the atmosphere directly over Grove.The red line on the right is the temperature profile and the black dashed is the dew point. In this particular sounding the atmosphere is nearly saturated through 700mb or roughly 10,000 feet. Of particular interest though is the slope of the sounding from the surface upwards to about 940mb. This layer, from the surface up to roughly 480 meters or 1575 feet, is below freezing temperature wise. This is what the dreaded “freezing rain” looks like on a Skew-T chart.

Fayetteville’s sounding looks like this off of the same model run. Note how temperatures from the surface to nearly 700mb are entirely above freezing. This is the profile of rain, but interestingly the temperature does fall from the surface through the first 10-20mb (250-500 feet) or so before beginning to rise.

After perusing many of these soundings today throughout the entire region, there is definitely a deeper layer of cold air prognosticated to move in over the relatively flat areas of NE OK and westward, stretching into the flatter areas of NW AR.

The mountains may indeed hold up the colder air until late in the weekend when the layer of arctic air becomes deeper. Higher terrain typically known for wintry precipitation will be above the cooler denser air and it's likely that a rain event will initially unfold, going over to a mix sometime on Sunday. Another day of assessing the leading edge of the cold air through real data and making the comparisons with hopeful model consistency should continue to fine tune the forecast.

This map highlights where we expect freezing rain to cause problems Saturday night into Sunday!

The latest oZ run of the NAM has come out, and it backs what our forecast has advertised over the last 2 days. The storm system in general is slowing down and deepening, allowing for more warm and moist air to move north from the Gulf of Mexico. This warm air will override a shallow cold air mass at the surface. The cold air at the surface will move across NE OK and NW AR on Saturday, creating a freezing rain potential by the afternoon and evening.

Freezing rain is the result of liquid precipitation falling through a surface based cold layer that's less than 4,000 feet. The height of our forecasted arctic air mass is relatively small. We're freezing from the surface to roughly 1,500-2,000 feet or around 950 mb. This will present ideal conditions for freezing rain. Travel may become slick and hazardous for Sunday.

Early indications point to freezing rain to continue on Sunday. As more data comes out, we'll continue to update our forecast.

Comet McNaught will be visible to the naked eye this evening. Shortly after sunset focus your attention to the western horizon to view the comet. Some clouds may hinder the viewing, but McNaught is considered to be the brightest comet in 30 years!

The latest 0Z run of the GFS continues to hold the cold air north of our area until Sunday. We're still holding to the idea that the shallow nature of the arctic air will undercut the warm air aloft, creating a freezing rain scenario for Saturday night. If this scenario plays out, substantial ice accumulation will occur. We'll have plenty of moisture in place, so the cold air continues to be the major question. 1 to 3 inches of rain is still expected.

Temperatures in central Canada are hovering around 0! Regardless of the winter weather potential, this air will be a shock to all of us. We'll go from highs in the 50s and 60s on Thursday, down into the 20s and 30s for Sunday and Monday.

Here's the latest on our weekend winter weather situation. Precipitation will start out as rain on Friday with many locations receiving 1 to 3 inches throughout the weekend. Rain will persist through Saturday; however, the big question remains, when will the rain change to freezing rain?

The computer models continue to zone in on the cold air moving in by Sunday. Unfortunately, the models have trouble when it comes to forecasting the depth and the timing of a shallow cold air mass, so we are banking on a faster solution at this point. Looking at previous storms, we feel the timing of the cold air is most likely toward Saturday afternoon. Temperatures will fall throughout the day on Saturday!

Ice accumulations could be a factor, and this would likely create travel issues for Saturday night, mostly across northwest Arkansas and northeastern Oklahoma. Cold air aloft will change any freezing rain over to sleet and eventually snow for Sunday.

Our polar plunge is still on track to make it through the area by this weekend. Right now our computer models are tracking the shallow cold air to move into northeastern Oklahoma by Friday night. The shallow nature of the cold air is causing issues for our computer models to handle; however, we think that temperatures will fall close to freezing north of I-40 by Saturday evening, and that may cause freezing rain issues for Saturday night.

Air aloft around 5,000 ft will remain above freezing, so any rain that does fall may be subject to freezing temperatures at the surface. That's where the freezing rain issue comes into play. It's likely that Oklahoma City will be impacted the most by freezing rain on Friday and Saturday due to their proximity to the cold air. Travel west of our area may become dangerous!

This is a developing winter situation that we'll be watching closely. Most of the precipitation will move out by Sunday.

Air circulations just above the earth to about 5000 feet are influenced greatly by the friction of the Earth’s surface. Eddies of air continually bring air down to the surface and also transport it upwards in the vertical. By looking at air temperatures at the top of this column, which correlates closely to an atmospheric pressure of 850 millibars (mb), we can get a ball park idea of probable highs and lows by bringing the air down to the surface and accounting for compressional heating as well as other factors including: winds, cloud cover and ground cover (snow, dry soil, wet soil, etc. etc.)

With this understanding, air temps at 850mb late into the upcoming weekend look to be around -12 to -15 degrees Celsius. Converted to degrees Fahrenheit this is 10 to 5 degree air! Now brought down to the surface it will warm, but we could still be looking at overnight lows Monday and Tuesday of next week in the upper single digits and low teens across the area. Sunday is still looking like the day that a mix of cold air and moisture will take place. To what capacity and where the freezing line will set up is still uncertain, though any frozen precipitation that falls is likely to remain on the ground at least for the start of next week.

This is tricky forecasting at its finest and we will be constantly adjusting the extended outlook as new information becomes available.

Meteorologist Ted Zarras

Even though severe storm season is still a few months away, the National Weather Service is already preparing to train community volunteers. If you're interested in becoming a certified storm spotter, please visit this link....

http://www.srh.noaa.gov/tsa/spotter2007.htm


You will find a calendar containing many different certification dates. There is no cost to become certified, and you will be doing a great service to the community.

Temperatures for the upcoming week will remain above average, especially as we head toward the Thursday/Friday time frame; however, a trough of low pressure diving across the Pacific Northwest will create colder changes for us by next weekend.

That trough will deepen to allow moisture to increase, creating rain chances from Thursday through Saturday. Temperatures aloft will be too warm to support any wintry precipitation, but that could change.

As the trough deepens, a polar plunge of air will head south across the northern plains. We're expecting a modified cold air mass to reach us by Saturday night. If the moisture lingers into Sunday, we could see a light wintry mix of precipitation. The latest information from our computer models has most of the moisture moving east by the time the cold air moves in.

This will remain a timing issue, and we'll continue to update you throughout the week.

Impending Winter Weather!?

Some of the long range forecasting models have been progressively hinting at an arctic outbreak around the 12th-13th of the present month. This could bring in overnight lows in the low teens and single digits. On a more interesting note, successive short wave disturbances look to be moving through the mean trough of low pressure that will be carved out by this cold air, should it hit. If that's the case and it's a big "if", then we could luck out or be stuck with some winter precipitation, depending on your take on snow, sleet and the dreaded freezing rain.

Certainly, we've been mild. In fact the average high for Fort Smith so far this year has been 57 degrees which is about 11 degrees above average. Fayetteville has averaged a high of 51 degrees, which is 7 degrees above average. With our weather pattern being dominated by northwesterly flow for the next several days those average highs look to drop down and only time will tell what late next weekend has in store for us. But, if you're a snow fan, at least there's a glimpse of hope.

THINK SNOW!

Meteorologist Ted Zarras

It's hard to believe that we're in the first week of January. Temperatures on Friday afternoon were above average by some 5 to 15 degrees; however, the unseasonably warm air is coming to an end. We should be in the 40's for this time of the year. We're watching two cold fronts that will come through over the next 48 hours. The first boundary will move through Friday night into Saturday morning, providing for a cooler Saturday afternoon.

Another quick moving wave of low pressure across the Northern Plains will drop our second shot of cooler air just in time for Sunday afternoon. Moisture will be limited, so just look for an increase in clouds over the weekend.

I want to take this opportunity to welcome you to the 40/29 Weather Blog. We realize that the viewers across eastern Oklahoma and western Arkansas have a lot of questions and interest when it comes to the weather, and now you have the ability to learn more from the 40/29 meteorologists.

This blog was created with you the viewer in mind. We now have the opportunity to expand upon our forecasts in order to provide you with more weather information. We'll be updating this site daily, so please check back often.

Thanks for your continued support!
Chief Meteorologist Drew Michaels