The above map is based off the latest NAM/SREF blend. We feel it may be necessary to clarify an issue in regards to the maps that are made.
1. If an area is expected to be mainly garden variety type storms with just isolated severe (less then a handful of reports) then we are not going to include that area in our maps.
2. If an area has excellent severe parameters but is in a CAP situation we are going to include that area in case the CAP is broken. Because if that CAP breaks and with the parameters in place then severe storms would rapidly develop. We feel that it is better for people to be aware that in case that happens then think there is not a slight chance at all.
3. The severe zone is the region where the severe weather should occur. If you think of SPC they issue a “see text” area which is generally for 5%. We do not place percentage zones because if you have a 5 % chance of a tornado for example, that means there is a 95% chance you are not going to see any! So we feel its better to place a zone that should capture ALL the severe reports. Sometimes this works out excellent and other times it misses reports because the area that guidance is suggesting should be “isolated” ends up over achieving.
So..with that said and out of the way lets look at the severe parameters for tomorrow.
1. CAPE is from 500-6000 depending on where you are located
2. Lift Index is anywhere from 0 to –12 depending on where you are located
3. SWEAT index is above 400 from Eastern Ok to western Arkansas and stretching into eastern Ks and western Missouri and then into southern Nebraska and extreme SW Iowa.
4. EHI is also above 1 in those same general locations above.
5. Lapse rates across the area are at about 7.5 so they are sufficient for severe weather.
6. Shear is roughly about 25-35 knots which is marginal. Generally we like to see anywhere from 40 or above .
Weather Synopsis
A deep trough is going to be moving from the western region into the plain states on Monday.
Currently low pressure is over Virginia and there is a cold front working its way across the state of PA and the NE. This cold front is responsible for the isolated severe in the NE and the scattered showers and thundershowers in the region. We talked about this yesterday. This cold front will push thru the region in the overnight period and the low pressure over VA will move ENE to a position off the delmarva by afternoon tomorrow.
Several pieces of energy are going to be advancing from the west towards the east and keep the chances for heavy rain and severe weather from the plains states into the southeast as well as the south central part of the US. The first now is over E KS and will lift ENE and be over IOWA by 18 Z tomorrow. This should cause the warm front to lift up towards Upper MI region and send some showers and thunderstorms into that region. Parameters are not strong across the area so we think that it would be more an isolated situation with more in the way of rain and garden variety storms.
This low pressure then is expected to start to move off to the east south east so by tomorrow evening it is over western Indiana. This should keep the progression of the warm front from lifting North into the great lakes and more or less spare the Great Lakes region any severe weather.
This low pressure will then continue to advance ENE and should be located over NW ohio overnight tomorrow night causing a warm front to begin lifting into Western PA and could have some showers break out across that part of the state.
Overall its going to be one piece of energy after another ..kind of like a wave train that will be progressing from the west to the east which is going to keep things quite active and potentially wet for the severe weather zones.
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