Wednesday, April 6, 2011

Severe Weather Threat Indicator (April 9-10 Forecast)

This number is suggestive of a few strong, long-lived tornadoes, very large hail, and damaging winds.

April 9-10 2011: Severe Weather Risk- Midwest (April 6)

This is subject to major changes.

April 7-10 Severe Weather Outbreak: Overview (April 6)

There is a very concerning risk over the West IL and North MO areas this weekend for a severe weather event. At this time, long lived tornadoes, violent tornadoes and extreme severe weather are still on the table.
I am here to asses this situation.

In the hours leading up to the outbreak, a disorganized cap will set-up, providing some instability. Contributing more so to the instability will be the advection of warm air into the Midwest Region.
There will also be diverging jet stream winds. When that happens, this means air rising is forcing the jet stream to separate, which is hard to do.
12z GFS data indicates the jet stream will be splitting up, mainly around the areas to the east of the outbreak.
The lower level jet stream will also be present in the area forecasted for the tornado outbreak.
Temperatures will be very high proceeding this event. Below is the forecasted maximum temperatures.

The images about to be posted are from the 12z GFS.

These images are from the Significant Tornado Parameter. It does appear there will be a sudden and intense risk area over the Midwest and Lower Great Lakes.
By analyzing these images, it appears that the jet stream may be the controlling factor in this risk.
However, this far out, it is too unsure to be sure.

Another piece to bring up is CAPE values of instability. Below is an image from the 12z GFS of CAPE values.
CAPE values of 4000 are extremely unstable. Anyone within the region of 3000 j/kg and above are in an intense risk of severe storms due to these high values.

The Severe Weather Center page will be under renovations today, April 6, 2011.

April 7-10 Severe Weather Outbreak Series: 4-8 Day SPC Map (April 6)

There have been some timing differences through the GFS and ECMWF models. However, the 0z runs proved they were working towards a compromise. The difference is now 6 hours, with a good meeting point and overall fairly well understanding of the storms track.
NOGAPS model has the squall line into Chicago IL in the early morning.
GEM model is potentially the slowest.
All the models have a good understanding of where the low will go, but timing is in all different directions.