Severe Weather Discussion for February 25 – March 2, 2008.
– Temperatures in the upper 50s/60s for Oklahoma this week, except for Tuesday which will be in the 40s. Farther south in Texas, temperatures will be in the 60s and 70s. Tuesday will also be a somewhat cooler day for Texas.
– Isolated severe thunderstorms are possible in southeast Oklahoma/NE Texas this evening, see SWOMCD for details. The window for severe in Oklahoma is limited to the next few hours.
– Severe thunderstorms are possible on Sunday for eastern Oklahoma/Texas.
– Fire danger will be high all week with Thursday and Saturday particularly bad days. Sunday may also be a bad fire weather day, but tough call this far out.
– Severe Thunderstorms in Oklahoma: 15%
– Storm Chase: 5%
– Winter Precip: 5%
Four different runs of the GFS and four different solutions. I will note that the 18z GFS tends to mirror the 06z run, but I'm not hanging my hat on any of it. And, to help matters I've prepped the chase vehicle for Storm Season 2008, that should jinx things.
Sensible weather will be at a minimum this week and in many respects a very pleasant late February week. The main impacts will be a strong cold front today/tonight and then a weak passage later in the week. Fire danger will be high all week given dormant vegetation and seasonably dry conditions across the state. Thursday will be very high, with Saturday and Sunday approaching critical levels.
The part of the GFS I trust runs for a few days. The general 500mb pattern indicates that a southern stream shortwave trof will traverse the region tonight as it phases with a northern stream shortwave trof and develops a full latitude eastern U.S. longwave trof. The resulting Pacific surface high and base of the longwave trof will push Gulf moisture to Cuba. This will keep precipitation chances low through Saturday. The pattern should remain progressive with the eastern U.S. longwave trof moving out of the lower 48 by Thursday. A weak northern stream shortwave trof will move through the Great Lakes region and should push a weak front into the region. This front isn't expected to have much of a cold air push on it, as the surface ridge will be 1028 and Pacific origin. It will be enough to knock daytime highs down some, but the high moves rapidly east and we warm back up on Saturday.
The higher impact weather is at D7 for this forecast, my least favorite time period, given only the weekly issuance of this product. The 15% severe probability is up for chances tonight, maybe until 9:00pm and then again Sunday. The astute readers will notice the 5% chase probability. All the probabilities are a little higher than I'd normally go given the high variance in the models and potential for sensible weather impacts.
The general issue at hand here is a southern stream shortwave trof currently located near Japan per Edward's Day 4-8 SPC product. The 12z ECMWF and variants of the GFS all handle this feature differently. The GFS, in general, wants to keep some phasing with the northern jet stream as this system moves into the central U.S. The GFS solutions tend to vary from this system digging into New Mexico to moving across KS/OK as a weak wave. The ECMWF is much more robust with this wave and would fit the general atmospheric trend this winter, reference Lezack and company 30 day cycle. Even the weaker version of the GFS may provide an opportunity for modified moisture return and resultant low-end severe weather threat. The ECMWF trends place a slower and deeper system in New Mexico on Sunday, with some potential for this feature to close off. This solution would provide a better opportunity for moisture return and resultant threat for more robust severe weather chances.
Time of year yields low chances of special discussion for Sunday, but will have to monitor when the models converge on a solution. There really isn't a reason to pick the GFS or ECMWF, other than I've seen the ECMWF solution verify a little more this year with a closed low out west. The ECMWF may be overdoing the low, as it did with the weak southern stream low over South Texas on the 00z 12z/24 run. I do think the GFS's cold front on Sunday is overdone, but we'll see. Also, the ECMWF's solution would provide a frozen precip threat, but that is probably D8 and luckily out of range for this forecast.
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