Severe Weather Discussion 2007-3-1

Severe Weather Discussion for February 23 – 24, 2007.
Valid: 02/23/2007.

Highlights:

– Isolated thunderstorms are possible on Friday and then overnight, primarily in western OK/TX. Some severe thunderstorms are possible. Primary threats are hail to nickel size and winds to 60mph.

– Severe thunderstorms are possible on Saturday for the eastern half of Oklahoma.

– Snow is possible in northern Oklahoma late Saturday.

Discussion:

12z NAM/GFS in reasonable agreement in moving the upper system onto the west coast early Friday and then progressing it east into the region Saturday morning. Timing is off for a classic event, but then again this is late February.

Models develop a progressive pattern across the lower 48 with a full latitude trof moving through the region on Saturday. Timing has changed a little from yesterday, but not much and believe it is best to settle with the current progs. This places western and central Oklahoma in the threat region Saturday morning, reducing the severe threat. Eastern Oklahoma into central Texas are a different story as strong surface heating will be underway when the upper system moves into the region. Models rapidly move the system northeast into the Great Lakes by late Sunday.

Before all this happens a weakening upper system will move across the region late today. Moisture is quite limited and the upper system is getting sheared. As such, do not expect much impact from it in this area. SPC has a slight risk up for Arkansas into Tennessee. Current moisture return will be stopped with a southward push on the moisture pool. The incoming ridge will be weak and southerly flow should return by Thursday. Deep layer moisture return will occur ahead of the weekend storm system as the Gulf is wide open.

GFS has backed off on dewpoints for Saturday but this is probably a function of system speed more than anything. Either way, at this point expect 55-60F dewpoints in the state early Saturday morning. Upper system will move into western Oklahoma early Saturday morning with associated 80-100kt jet max. Widespread thunderstorms should initiate along the dryline Saturday morning and progress east during the day. Depending on cloud cover in eastern Oklahoma south-southwest into central Texas, individual storms are possible ahead of the squall line. It is these storms that will posed the highest severe threat. For now the details are still a little muddy and that isn't a great surprise. Suffice it to say that there is the potential for an active severe weather day on Saturday.

Regarding Friday the NAM is showing some decent CAPE and LI values across the region Friday afternoon. There isn't much going on aloft that would trigger activity, but afternoon heating may be enough to cause isolated thunderstorms. Progged surface through 700mb wind speed/direction would be more than sufficient for organized convection. Widespread severe thunderstorms are not expected, but may see a few out west. This activity should decrease after sunset. I'm thinking that SPC might risk part of western OK/TX (north/panhandle) for Day 3, however it may just be a 5% see text. Tough call, but there is potential.

Probabilities:

Risk area for any part of OK/TX (valid: 02/21 Day 3):

Slight: 60%
Moderate: 0%
High: 0%

Chase Status:

Level 1 – Normal

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Common Terms:

AOA = Around or above.
AOB = Around or below.
CAPE = Convective Available Potential Energy.
CDC = Climate Diagnostic Center.
CPC = Climate Prediction Center.
ECMWF = Numerical model run, European Model.
GFS = Numerical model run, Global Forecast System.
LI = Lifted Index
LLJ = Low Level Jet.
NAM-Eta = Numerical model run, about to become the NAM-WRF
NAM-WRF = Numerical model run, the Weather Research Forecast (WRF)
OUN = Norman Forecast Office.
SWODY = Severe Weather Outlook Day 1, 2, 3, and 4-8.
SPC = Storm Prediction Center.
WWA = Warm Air Advection.
00z/06z/12z/18z – Time based on the UTC time scale, z = zulu.

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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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