Sunday, January 28, 2007
Closed Lows, Dynamics & A Chilly Week!
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.
Posted by Ted Zarras at 4:43 PM
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