Monday, March 21, 2011

Notice 3/21

-Forecast Discussion images will be edited to be more user friendly.
-Only ONE Forecast Discussion will be issued at the beginning or evening of the day. This is in order to better manage the many forecast discussions that would otherwise be posted everyday.

March 21 Forecast Discussion

This is an image of the 18z GFS 24 hours out from now.
Strong low pressure will be carrying warm front into the Upper Midwest and a cold front behind it. The warm front will carry warm air into the area of Central Illinois southward and westward.
However, the real concern will be the cold front behind it. That cold front will create a squall line. At this time, we can expect the squall line to be, at best, moderately strong. The 'fire' inside the storm just won't be there. However, the severe weather risk is still there. A write up will be issued tomorrow.
In the Southeast, high pressure will reign supreme and keep the atmosphere nice and sunny. I cannot rule out sprinkles due to all the humidity and warm air.
Low pressure out east will stretch the warm air along the Eastern Seaboard.
Curving arctic air flow from above will keep some areas of the East Great Lakes cool.
Cold air in the Northwest will keep the atmosphere likely cloudy.
This has been a forecast discussion. Another one will be issued at 7:30pm CDT tomorrow.

March 21 Severe Weather Outbreak Forecast Discussion

This is a forecast discussion concerning the severe weather outbreak predicted tomorrow.

According to basic look-overs on forecasts, a squall line should develop tomorrow and push into the Midwest as it weakens.

Here we have the Storm Prediction Center's outlook for tomorrow. Immediately, based on the way the slight risk area is organized, a squall line will be the method this time for severe weather.
A warm front will lift into Wisconsin and Michigan, dragging in nice, warm air. At the same time, a strong low pressure system with a cold front behind it will be the ignition for this squall line.
Based on latest forecasts, this should not be a terribly intense storm system and the storms will weaken as they move into Illinois.
However, the percentage risk for severe storms is somewhat concerning.
The 15% is the base starting point for a slight risk situation. This morning, where was even a 45% risk area in Iowa. However, as we see above, that area has been cancelled. At the same time, the 30% area has been expanded east.
Based on outlooks, it appears the primary risk of severe weather will be hail. Since hail is created by strong lifting up and down in the clouds, it can be assumed that these storms that do produce hail will be accompanied by strong lifting in the clouds.

In summary, the main risk of severe weather is Iowa into Illinois. The main threat type of severe weather is hail. A squall line is expected to develop.

Storm Prediction SREF ensembles indicate the Craven/Brooks significant severe weather parameter is still about double the threshold for what is considered the potential for significant severe weather. Image below.
This shows that the strongest part of the squall line should be in Iowa extending through Kansas and Oklahoma. Will keep an eye on this parameter.

Other concerns...
Lapse Rates looking fairly unstable.

Another update may be issued tonight, with another full write-up tomorrow.

March 21 Severe Weather Event- Happening Now

This is a statement concerning today's severe weather event.

SPC Outlooks indicate there will be some portions of slight risk areas in the US today, especially in the middle of the plains.
Below is an image of that risk.
We definitely see a severe weather risk over the Ohio Valley and a portion of the Plains. We do not expect these storms to be in a squall line, likely either a bunch of pop up storms or a multi-cell storm complex in the Plains area, and likely weakening storms out east in the Ohio Valley.
Below are specific risks of severe weather. The images go in order: Hail, Tornado, High Winds.
Based on those risks, it would appear that the Ohio Valley does have a more significant threat for wind based severe thunderstorms, such as tornadic storms or damaging winds.
The Plains are in their own slight risk due to a risk of hail. That would imply strong lifting is occurring in the atmosphere, which can make the atmosphere very unstable.