Forecast for March 23, 2009

Forecast Made: March 23, 2009 – 5 Z

Target for Possible Tornadoes: Bassett, NE

Target for Severe Weather in General: Wichita, KS

Initiation Time: Early Afternoon across Nebraska, with initiation in Kansas between 3 and 5pm. Initiation across Oklahoma in the 5 to 7pm timeframe.

Discussion: This appears to be the first major Plains severe weather event of the season. As is typical of March severe weather setups, fantastic dynamics (mainly NE/KS) will be tempered by less than stellar thermodynamics. Usually when this occurs, the best place to chase from a tornado-viewing standpoint is near the upper-level low pressure center. North central Nebraska and possibly southern South Dakota offer the best combination of the cold air aloft and marginal dewpoints in the low to middle 50’s. Low topped supercell development looks possible in this area given the intense wind field associated with the low. A few tornadoes and large hail appear to be the main threat here. Further south, in Kansas, the dynamics still appear to be pretty good. However, the further south you go, the more the winds take on a unidirectional nature. This suggests any discrete supercell development in southern Kansas or northern Oklahoma will probably be short-lived. Better moisture values could allow CAPE’s to reach ~1000-1250 by late afternoon, which would be on the low end of what is needed to sustain an updraft given the amount of shear. Across southwestern Oklahoma and northwest Texas, where the best moisture exists, mid-level capping should hold off storm development until late in the day. However, by 19-23Z, the dryline and cold front are expected to be advancing quickly towards the east. This could maximize surface convergence for storm initiation, while unidirectional flow would suggest any storms that do develop will quickly become linear. Areas across the Rolling Plains and Big Country of Texas will see an isolated shot of a supercell or two along the sharpening dryline, as the forcing from the cold front will not arrive until after sunset. However, the cap in this area will be quite strong, so the likely scenario would only include storms after sunset as the cold front advances.

Conclusion: I suppose the first ‘big-looking’ severe weather event every year is well hyped, but in my opinion this one is being way over-hyped. I have been on many early Spring chases with low moisture / high dynamic events that have not turned out well. Overall, any tornado threat will be rather isolated / short lived because of the lack of low level moisture. Hail appears to be the main threat, with high winds becoming more of an issue across southern Kansas / OK / TX with the possible formation of a squall line.

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