Sunday, 22 March 2009

USA Storm chances - Mon 23rd March

After a fair while without severe weather, the central Plains of the USA look set to receive some on Monday. An approaching upper trough should promote lee cyclogenesis and set the stage for thunderstorms, some severe, on Monday afternoon and evening.

Whilst moisture is not going to be plentiful, there looks like there will be enough for some severe weather. Dewpoints in the 50s F are already across much of Texas and Oklahoma, with 60s dews arriving on the southern Gulf coast. Another 24 hours of return flow should deepen the moist sector. The upper system will serve to steepen lapse rates as it moves in through the day.
The best compromise of ingredients and shear appears to be, to me, over central and northern Oklahoma on Monday afternoon. The dry line looks like stalling through the area, although will be overtaken by the cold front overnight. Supercells seem likely to develop along the dry line and the propogate into the moist sector - WRF seems to indicate the chance of long-lived supercells/supercell clusters through the evening, moving from west-central OK north-eastwards to the OK/KS border around I-35. If chasing, you would want to get ahead of these cells as the cells will be moving quite fast.

High shear-limited moisture set-ups often lead to storms leaning towards the LP end of the spectrum, bringing the risk of large hail and high winds. However, moisture pooling could locally enhance tornado potential. Analysis through the day on Monday will help pin down the regions most at risk.

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