May 4, 2011

Blizzards and Historic Tornado Outbreak

During my last post on April 14th, a blizzard was in progress in Nebraska and northwest Kansas on the backside of this storm:Up to 16" of snow fell in Nebraska (Paxton) with drifts to 5 feet in the western portion of the state. A 120-mile segment of I-80 was shut down. The band of snow reached Dodge City later that night:
The next morning, the surface low was 992 mb.
Winds in the Dodge City area gusted up to 74 mph, causing significant damage.
This same storm system also produced a tornado outbreak from Oklahoma to North Carolina, killing 17.

On April 22nd, an EF-4 tornado hit St. Louis including Lambert Airport.

On the afternoon of April 26th, tornadic supercells rapidly developed in Texas and Arkansas.This was only the beginning of the historic multi-day tornado outbreak which killed over 300 people. The number of tornadoes is still unknown, but NWS surveys have confirmed 25 from the 25th (12Z 25-12Z 26), 40 on the 26th, and 132 on the 27th. This includes at least 2 EF-5s, 12 EF-4s and 21 EF-3s.

The event was well forecasted by the Storm Prediction Center. I don't remember ever seeing SPC's probabilities for tornado (30%) or wind (60%) as high as they were on April 26th.
Then the next day, the tornado probability was up to 45%.
Here is a water vapor loop of the entire event starting on the 26th:

High resolution visible loop from the 27th:

Here are some RUC analysis charts from 0Z 28 (7PM CDT on the 27th):
Dewpoints were mostly in the low 70s with some mid 70s.
This contributed to both the high cape values and low lifted condensation levels. The sounding from near Birmingham, Al at 0Z 28 put the LCL at only 928 mb despite a surface temperature around 80. Notice also the mid-level dry slot and that the helicity is at 847.
Sounding from Nashville, TN:
And from Peachtree City, GA (about 30 miles southwest of Atlanta)On April 30th, blizzard warnings (in red) were issued for much of North Dakota.
Another 7.9" fell at Williston where they had already had their snowiest season on record. The total is now 107.2", and the old record was 94.7" set in 1895/96.

Last night, freeze warnings (light blue) and frost advisories (blue) were issued down to southeast Missouri:
Frost advisories for tonight include Nashville and part of Alabama:

1 comment:

  1. could you email me at ? I"m trying to find some images weather maps from the Mackinac Race 2011 and i'm not sure where to find historical data. Any help would be appreciated! Thanks