Winter Weather Discussion 2008-4-2

Winter Weather Discussion for February 14 – 16, 2008.
Valid: 02/10/2008.

Highlights:

– Isolated freezing drizzle/rain is possible tonight across Oklahoma and maybe the Red River counties of north Texas. Tulsa has a few counties highlighted with advisories.

– Isolated severe thunderstorms are expected in south-central and southeast Oklahoma Monday afternoon and evening. Primary threat is large hail, although an isolated tornado is possible.

– Winter precipitation is possible late Thursday through Saturday morning.

Discussion:

Arctic cold front moved through Oklahoma as expected earlier today. This resulted in temperatures from the low 30s north to mid 50s south. Said front has oozed into north Texas, where it should stall tonight as an upper system moves towards the region. System will be approaching in northwest flow, which is usually not that favorable for precipitation this time of year. However, prior 850mb/surface ridge will be departing, allowing moisture to return north. This will setup isentropic lift across areas north of the front. As such, light freezing drizzle/rain are possible across parts of Oklahoma tonight. There seem to be two focus areas 1) in southern OK where thunder may occur and second, in northeastern Oklahoma where deep layer lift will be better focused. Since thunder is possible, rapid accumulations of ice would occur. Tulsa has a winter storm watch up for a few counties in northeast Oklahoma and a winter weather advisory just south of that location. Tulsa is also
monitoring the potential for more freezing rain Monday night, but this is highly dependent on surface temperatures. Models prog the system to swing east through Kansas/Nebraska with the 500mb jet max moving across Oklahoma.

On Monday, return flow continues and increases across the region as the upper system digs southeast through Colorado. 850mb flow is focused from Oklahoma City south and east with 30-35kts around 6pm. This should be the best area for thunderstorm development per Day 2. The front will likely struggle to move north, if at all on Monday. I think the cold air is very shallow across much of Oklahoma, except northern areas where the low temperatures today indicated deeper cold air and frontogenesis due to cloud cover. NAM shows the expected gradient pretty well for Monday and this will be used. The best focus for surface based convection will be Waco northward to Durant and then east to Latimer County. In this area the primary threats will be large hail to quarter size and isolated tornadoes. Farther north, on the north side of the front, large hail will be the primary threat. Convection should end early Tuesday morning as mid-level lift decreases.

Another Arctic cold front is expected late Thursday and may set the stage for a significant winter weather event. Models have changed quite a lot the past few days, with the GFS making the majority of the changes. The ECMWF is consistent, although seemingly a little cooler on the 12z run. The 12z/18z GFS runs do agree with the ECMWF on taking the southern stream system along the Red River, somewhat phased with the northern stream system. This would place Oklahoma in a favorable environment for winter precipitation. I think it is too far out to call this an ice storm or snow. The ECMWF would certainly point to more of a snow event for northern Oklahoma. Time will tell and of course the models are all over the place on QPF. I'm not convinced of a major ice storm at this point, lots of cold air around at all levels.


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About Putnam Reiter

Putnam has been storm chasing since 1990 and is a co-founder of Hook-Echo.com. For his day job, Putnam works in emergency management for information technology.
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