Twin States Weather Blog

New Model Output

* The evening run of the NAM (North American Mesoscale model) is in, and continues the idea of a low CAPE, high shear severe weather event. Here are the raw numbers, valid midnight Saturday night:

CAPE (measure of instability): 296.6
0-1KM SRH (wind shear in lowest 1km of atmosphere): 551.1
850mb winds: 58 kts (almost 67 mph)

To clarify, the CAPE (instability) above is fairly low for severe weather. However, the wind shear in the lowest levels of the atmosphere is extremely high, and wind speeds aloft are quite impressive.

Here is a scale, courtesy of Ohio State, that shows some APPROXIMATE benchmarks for CAPE measurements. Please note that these are just guidelines and are not firm rules:

CAPE value	Convective potential
0	Stable
0-1000	Marginally Unstable
1000-2500	Moderately Unstable
2500-3500	Very Unstable
3500 +	Extremely Unstable

* We have seen many tornado events over the years that have had CAPE values below 1000 and high wind shear. Will this be another? Impossible to tell at this point. What we do know is that we will see a round of thunderstorms, some severe, push through on Saturday night. At this point, it's my opinion that the primary threat is damaging wind gusts within those thunderstorms. But, tornadoes are also a possibility.

* The weather office will be fully staffed over the weekend for the possibility of severe weather.

posted by WTOK Weather Staff @ 9:01 PM