Winter Weather Discussion 2008-4-1

Winter Weather Discussion for February 14 – 16, 2008.
Valid: 02/09/2008.

Highlights:

– Light freezing rain/drizzle is expected late Sunday into early Monday.

– Severe Thunderstorms are likely on Monday across much of Oklahoma, primary threat is large hail. However, given nature of directional shear and elevated moisture isolated tornadoes are possible primarily in southern Oklahoma.

– Winter precipitation is expected late Thursday into Saturday across much of Oklahoma.

Discussion:

12z models are in general agreement with the expected pattern over the next six days. For the initial 48 hour period, two primary weather episodes are expected.

First, an Arctic airmass will invade the state and potentially move into north Texas on Sunday. Given density of the cold air, the models are likely not handling the southern extent of this airmass. Arctic airmasses tend to ooze in this type of pattern and can move much farther south than model progs. At this time I agree with the NWS regarding the southward push of the incoming Arctic air. This should make Sunday on the cool side and much colder overnight. During the night an upper system will approach the region and result in isentropic lift across the state. This may result in light freezing drizzle. The front should not penetrate much farther south than north Texas so the threat of freezing drizzle is expected to remain confined to Oklahoma.

Second, Monday afternoon the Arctic ridge should be retreating allowing for more near surface moisture return. The effective warm front will be in central Oklahoma as the upper system moves across the region. Combination of strong moisture return and directional shear should provide a favorable environment for severe thunderstorms. SPC has a slight risk posted for Monday and this looks good. Isolated tornadoes are possible in southern Oklahoma with discrete activity.

Another Arctic airmass is expected late Thursday, dropping temperatures below freezing. This as an upper system digs into the southwest U.S. What this system ultimately does is in dispute by the models. The GFS has a southern stream closed low while the ECMWF is more phased with the northern jet stream and hence more progressive. The ECMWF would tend to limit precip totals while the GFS is very robust. Tough call at this point, but the ECMWF would fit the most recent pattern. The main issue here is precip type and amouints. The GFS would argue for freezing rain and early Saturday transitioning to snow as the upper system moves east along the Red River. The ECMWF would argue for a freezing rain event and that is it. The concern, as always, is that a little freezing rain goes a long ways. Friday and Saturday will be closely monitored and discussions are initiated due to the potential for a significant winter weather event.


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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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