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March 20-23 Severe Threat


Jim Martin

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I ran some calculations using forecast variables near Atlantic, IA for the 21z time frame this afternoon.

If we can reach 70/60, with about 1500 j/kg CAPE and an LCL around 2,500 ft AGL (which seem reasonable at this point). RUC was aggressive with CAPEs around 2500, so I took a significant percentage off that. It won't take much heating/moisture today with the lapse rates out there.

These values give a straight line wind potential of right around 60 mph and a rotational wind potential of around 110 mph. So winds look marginal to just above severe, with tornadic winds approaching the lower bound of EF2.

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   VALID 221819Z - 222015Z

  SEVERE THUNDERSTORM DEVELOPMENT APPEARS LIKELY TO OCCUR LATE THIS
  AFTERNOON ACROSS ERN NEB AND ECNTRL KS. AS STORMS INITIATE AND
  BECOME INCREASINGLY ORGANIZED...LARGE HAIL...A FEW TORNADOES AND
  ISOLATED WIND DAMAGE WILL BE POSSIBLE. WW ISSUANCE WILL BECOME
  NECESSARY OVER THE NEXT 1 TO 2 HOURS.

post-252-0-93713100-1300818748.gif

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URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 53

NWS STORM PREDICTION CENTER NORMAN OK

205 PM CDT TUE MAR 22 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF

WESTERN AND SOUTHERN IOWA

EASTERN KANSAS

WESTERN MISSOURI

EASTERN NEBRASKA

EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 205 PM UNTIL

900 PM CDT.

SEVERAL TORNADOES

ISOLATED INTENSE TORNADOES POSSIBLE

WIDELY SCATTERED DAMAGING WINDS

ISOLATED WIND GUSTS TO 70 MPH POSSIBLE

SCATTERED LARGE HAIL

ISOLATED HAIL TO 2.5 INCHES IN DIAMETER POSSIBLE

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 90 STATUTE

MILES EAST AND WEST OF A LINE FROM 5 MILES EAST NORTHEAST OF

STORM LAKE IOWA TO 20 MILES SOUTH SOUTHWEST OF CHANUTE KANSAS.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU3).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS.

DISCUSSION...SEVERE TSTMS ARE EXPECTED TO DEVELOP THROUGH MID/LATE

AFTERNOON ACROSS THE REGION. MODERATE INSTABILITY/STEEP LAPSE RATES

COMBINED WITH VERY STRONG VERTICAL SHEAR WILL SUPPORT SUPERCELLS

CAPABLE OF LARGE HAIL AND TORNADOES. WITH INITIAL DEVELOPMENT ACROSS

EASTERN KS AND SOUTHEAST NEB THIS AFTERNOON...THE SEVERE THREAT

SHOULD DEVELOP EASTWARD INTO WESTERN IA/WESTERN MO BY EARLY EVENING.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

450. MEAN STORM MOTION VECTOR 24045.

...GUYER

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The cell near Pilger, NE has a meso through a decent depth now.

Edit: And as I type that...

BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
319 PM CDT TUE MAR 22 2011

THE NATIONAL WEATHER SERVICE IN OMAHA HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
 NORTHEASTERN STANTON COUNTY IN NORTHEAST NEBRASKA...
 EASTERN WAYNE COUNTY IN NORTHEAST NEBRASKA...

* UNTIL 400 PM CDT

* AT 315 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
 SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL.  THIS
 STORM WAS LOCATED NEAR PILGER...OR 18 MILES EAST OF NORFOLK...AND
 MOVING NORTH AT 60 MPH.

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I like the environment that is developing just north of Omaha. Some 0-3km CAPE starting to show up along with good low level lapse rates. This should maximize the updrafts potential to ingest some of this helicity in the low levels.

Yeah, the storms are already looking impressive, and they're still west of the better instability. SPC meso shows a nice bubble of 2000j/kg surface cape bulging northward from southwest Iowa. Effective SRH is much better on the east side of the Missouri as well. Should continue to see these storms blossom and organize over the next few hours. If I were chasing, I'd stay on the Iowa side and let the storms continue to organize and then pick out the best one. Shouldn't have to wait long with these storm speeds. Also, wouldn't want to get landlocked (again) by the damn Missouri River LOL.

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Yeah, the storms are already looking impressive, and they're still west of the better instability. SPC meso shows a nice bubble of 2000j/kg surface cape bulging northward from southwest Iowa. Effective SRH is much better on the east side of the Missouri as well. Should continue to see these storms blossom and organize over the next few hours. If I were chasing, I'd stay on the Iowa side and let the storms continue to organize and then pick out the best one. Shouldn't have to wait long with these storm speeds. Also, wouldn't want to get landlocked (again) by the damn Missouri River LOL.

Tell me about it, awful trying to cross the river around there.

Storm south of Omaha starting to look better too.

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I wonder what kind of a view they have at the WFO in Valley. Rotation just a couple hundred feet off the deck, not especially tight but a couplet nonetheless.

Well they had some moderate sized hail come through at least

0416 PM HAIL VALLEY 41.31N 96.35W 03/22/2011

M1.50 INCH DOUGLAS NE OFFICIAL NWS OBS

GROUND ALMOST COMPLETELY COVERED WITH HAIL CLOSE TO PING PONG BALL SIZE. THE HAIL LASTED FOR AROUND 5 MINUTES.

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Tornado has been confirmed.

441 PM CDT TUE MAR 22 2011

...A TORNADO WARNING REMAINS IN EFFECT FOR SOUTHEASTERN THURSTON AND
CENTRAL BURT COUNTIES UNTIL 500 PM CDT...

AT 441 PM CDT...TRAINED WEATHER SPOTTERS REPORTED A TORNADO.  THIS
TORNADO WAS LOCATED NEAR CRAIG...OR 40 MILES NORTHWEST OF OMAHA...
MOVING NORTHEAST AT 45 MPH.

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