Update: Thu 21 Oct 2010
New map posted Thursday is below. Discussion of the severe risk percentages is new, forecast is essentially the same:
The 30% zone on the map below means a 30% chance of severe weather happening within 25 miles of any one point inside the red area. That's a mouthful, isn't it?
To truly understand what this means, one must know what the "normal" chance for severe storms at any one point would be in late October. Let's say it's 1%; the actual value is somewhere in this range. So the red zone has a 30 times greater than average chance for severe weather tomorrow.
This doesn't mean an apocalyptic weather event; it simply points to ramped up odds which will probably correspond to some severe weather in this zone. In a similar fashion, the 15% and 5% areas are under the gun, but less so than the 30% area.
Here are the primary factors:
>>>> Increasing wind shear
>>>>A stiff southerly wind develops providing deep moisture
>>>>Strong lift provided by mid-level low and dry line (discussion continues below map)
Time of day storms arrive; a late-morning arrival Friday would tend to provide a pocket of rain-cooled air which may not have time to re-heat during the short October afternoon.
Dry line position: If it remains further west than expected, storms could dissipate before reaching Texoma, or at least weaken.
This is essentially a spring-type situation taking place in October.