STORM2K

Severe weather threat is expected to increase very rapidly this afternoon and evening across Nebraska and into west central Iowa. Supercells with very large hail of softball sized or greater and strong to violent tornadoes are expected. The area of greatest risk will be from Des Moines through Omaha and Grand Island where a high risk is being considered in later outlooks. This could be the most violent tornado outbreak date of the year so far. Statement from SPC is below.

PRESENT INDICATIONS ARE THAT SCATTERED THUNDERSTORMS WILL FIRST
INITIATE OVER THE HIGH PLAINS OF WESTERN NEB BY MID AFTERNOON AS
SHORTWAVE TROUGH APPROACHES REGION. STORMS WILL DEVELOP EASTWARD
ACROSS CENTRAL NEB THROUGH THE AFTERNOON...WITH MORE THAN SUFFICIENT
SHEAR FOR SUPERCELLS WITH VERY LARGE HAIL. OTHER ISOLATED SUPERCELL
STORMS WILL LIKELY DEVELOP RAPIDLY OVER EASTERN NEB AND
WESTERN/CENTRAL IA BY LATE AFTERNOON OR EARLY EVENING...IN REGION OF
WEAK LOW LEVEL WARM ADVECTION NORTH OF WEAKENING OUTFLOW BOUNDARY.
THESE STORMS APPEAR TO HAVE THE GREATEST RISK OF TORNADOES DUE TO
VERY FAVORABLE LOW LEVEL SHEAR PROFILES AND MOIST BOUNDARY LAYER
/1KM SHEAR OVER 20 KNOTS AND DEWPOINTS NEAR 70F/. ALONG WITH STRONG
TORNADOES...VERY LARGE HAIL ALSO APPEARS LIKELY. CONSIDERED
UPGRADING SMALL AREA FROM GRI/HSI - DSM TO HIGH RISK...BUT CONCERN
OF CAP AND TIMING OF CONVECTIVE INITIATION LED TO MAINTENANCE OF
MODERATE RISK. WILL RE-EVALUATE AT 20Z FOR CONFIDENCE IN INITIATION
IN THIS REGION AND POSSIBLE UPGRADE.

After 508 reports of severe weather countrywide yesterday, 26 of those tornadoes, we could be equaling that number again today with even more tornadoes. 50 tornadoes or more could be possible by days end, some of them strong to violent in intensity.

Jim

Thanks for the heads up! I'll have my digital camera with me this afternoon and evening!

WXBUFFJIM wrote:
After 508 reports of severe weather countrywide yesterday, 26 of those tornadoes, we could be equaling that number again today with even more tornadoes. 50 tornadoes or more could be possible by days end, some of them strong to violent in intensity.
Jim

You do realize that that's not 26 tornadoes, that's 26 POSSIBLE reports of tornadoes, including multiple reports for the SAME tornado?

More than likely there will end up having been something like five or six actual tornadoes yesterday.

Interestingly tornado activity has been very, very, very low this year through May 21st....


http://www.spc.noaa.gov/climo/torn/mont ... stats.html

April was below average, and 2/3rds of the way through May, only 99 prelim tornadoes, compared to an average for a (full) May of 328.

16z mesoanalysis showed mixed layer CAPE already 1500-2000 J/kg over eastern KS. What's the real kicker however is the very impressive deep layer shear evident over most of the SPC moderate risk area. boundary layer to 6 KM shear of >50 KT, with a generally 35-40 KT minimum needed for suprecells. 4-6 KM S-R winds of 30-35 KT would similarly favor suprecells over multicells and other convective modes.

As far as large hail goes, some impressive CAPE in the -20 to -40 DEG C layer combining with the aforementioned BL-6 KM shear values in excess of 50 KT and increasing instability should support sustained/vigorous convective updrafts capible of producing very large hail.

Derecho wrote:

WXBUFFJIM wrote:
After 508 reports of severe weather countrywide yesterday, 26 of those tornadoes, we could be equaling that number again today with even more tornadoes. 50 tornadoes or more could be possible by days end, some of them strong to violent in intensity.
Jim

You do realize that that's not 26 tornadoes, that's 26 POSSIBLE reports of tornadoes, including multiple reports for the SAME tornado?

More than likely there will end up having been something like five or six actual tornadoes yesterday.

Interestingly tornado activity has been very, very, very low this year through May 21st....


http://www.spc.noaa.gov/climo/torn/mont ... stats.html

April was below average, and 2/3rds of the way through May, only 99 prelim tornadoes, compared to an average for a (full) May of 328.

I realize that fact alright. Most of those tornadoes could have come from the same supercell. In the case of the April 20th outbreak, there was over 51 reports. But in reality it was much less than that because multiple tornadoes were reported from the same storm system including in Utica, Illinois.

Jim

WXBUFFJIM wrote:I realize that fact alright. Most of those tornadoes could have come from the same supercell. In the case of the April 20th outbreak, there was over 51 reports. But in reality it was much less than that because multiple tornadoes were reported from the same storm system including in Utica, Illinois.

Jim

Thats the reason why the data is considered PRELIMINARY