Winter Weather Discussion 2008-4-5

Winter (Severe) Weather Discussion for February 15 – 17, 2008.
Valid: 02/14/2008.

Highlights:

– Active severe weather day is possible on Saturday for much of central/eastern Texas. Tornadoes, large hail, and damaging winds are all possible.

– Light freezing rain is possible tonight across southwest Oklahoma.

– Freezing rain and sleet are possible in western Oklahoma/panhandle Friday night into Saturday morning.

– Snow is possible across northern Oklahoma Sunday.

Discussion:

Absolutely obscene forecast for this weekend. There is little potential of getting any of this correct and I'm about ready to give up. Given the unseasonable warmth and moisture values I have elected to reduce the areal coverage of the winter weather threat for Oklahoma and north Texas. While I'm not sold on the 00z NAM, it is rather consistent and seems to agree with the 12z GFS/ECMWF. I have not spent time reviewing BUFKIT data for western Oklahoma, but a quick look at the mandatory levels certainly points to a winter precipitation setup tonight and especially Fridaynight. Thermodynamic profile would point to freezing rain for SW OK as the incoming Arctic airmass is rather shallow. Amounts should be very low.

By early Saturday the 850mb jet cranks up to 50kts across the region with a direct link to the Gulf. 70F surface dewpoints are available and 850mb dewpoints of 12C. The warm air will definitely win out in Texas, the question is how far north it will get. Models almost always erode Arctic air too fast. However, the upper system and ridge responsible for the incoming Arctic airmass are progged to move rapidly east. This is not a situation with Meridional flow and a surface connection to the Arctic region. Also, there isn't much of a snow pack to our north. Ground temperatures are in the mid 40s in central OK and see little reason why the post-frontal air won't try to modify. No additional Arctic surges are noted through late Saturday. As such, the QPF present over much of Oklahoma on Saturday is expected to be of the liquid variety. Out west in the higher elevation and in an area likely to have a better supply of dry surface air, frozen precip is more likely. The 00z NAM
keeps temps cooler here and this area will also be on the northwest side of the 850mb and surface lows.

The stage appears to be set for a significant severe weather outbreak across much of central/eastern Texas Saturday afternoon. NAM progs of 65F dewpoints and temperatures in the mid 70s should be sufficient for at least a conditionally unstable atmosphere. The big if is how much convection occurs during the day. Although I'm not convinced this setup will follow OK/KS guidelines and Texas coastal supercells tend to act differently even being embedded. 00z NAM helicity values are obscene for Houston and areas north/west Saturday evening at 400 m^2/s^2. NAM QPF fields point towards a strongly forced line of storms in this area late Saturday. The potential for discrete storms cannot be ignored and would certainly indicate a tornado threat. SPC's Day 3 is of interest, especially the 10% hatched and 30% areas.

00z NAM is pointing to a heavy snow event for parts of Oklahoma on Sunday. Since the models are all over the place on the temperature fields, I'm not jumping at this point. I'd like to get past Friday night first.

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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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