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Severe Weather Thread (April 26 - May 3)


David Reimer

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A little too close to home for comfort... Did go after the smaller storm in Sherburne county before I had to break off and go pick up the daughter at the bus stop... Very nice structure with wall cloud that looked like it could do it ... Crazy night here...

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This was an un-tornado warned (Severe T-storm warned) spin-up EF-2 tornado that happened last night in NE OK with the bow echo.

.WELCH TORNADO /CRAIG COUNTY/...

START DATE: MAY 1 2012

START TIME: 130 AM CDT

START LOCATION: 1 MILE NORTH OF WELCH

START LAT/LON: 36.8872 N / -95.0940 W

END TIME: 132 AM CDT

END LOCATION: 1.8 MILES NORTHEAST OF WELCH

END LAT/LON: 3 36.8961 N / -95.0796 W

RATING: EF-2

ESTIMATED PEAK WIND: 110 TO 120 MPH

PATH LENGTH /STATUTE/: 1 MILE

MAXIMUM PATH WIDTH: 150 YARDS

FATALITIES: 0

INJURIES: 1

SURVEY SUMMARY:

THIS TORNADO TORE THE ROOF OFF OF A PERMANENT HOME...SHIFTED

ANOTHER HOME OFF ITS FOUNDATION AND BLEW OUT AN EXTERIOR

WALL...TURNED OVER AN OUTBUILDING...ROLLED TWO HORSE

TRAILERS...DESTROYED A 40 FOOT BY 60 FOOT STEEL FRAMED BARN...AND

SNAPPED OR UPROOTED TREES. A PERSON WAS INJURED IN ONE OF THE

PERMANENT HOMES WHEN THE WINDOW IN HER BEDROOM SHATTERED.

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Grading the SPC performance in Mn for today. The outlooks were just about right on with the TC metro being on the far east side of the 30% hatched hail. The 2 and 5% tornado risk was right on. Outlook forecast from the 1st day one graphic through today would warrant a A grade. My issue was with the extension of the Tornado Watch to include the TC metro, I thought it was somewhat questionable at the time of issuance, but I can certainly understand the idea of being cautious. Overall grade for the SPC is a B- .

As far as the American Models 24 hours out based on the STP effective layer, the GFS was the much better model. The more and more I look at this, the Nam is not the trusted model 24hrs out. It seems like the GFS is much better at both winter and summer events.

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As far as the American Models 24 hours out based on the STP effective layer, the GFS was the much better model. The more and more I look at this, the Nam is not the trusted model 24hrs out. It seems like the GFS is much better at both winter and summer events.

The NAM has outperformed the GFS with multiple events this year within the 48 hour period.

Also, WRT the MDT risk, I have a feeling there may be some OFBs to interact with later on to locally enhance tornado potential.

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The NAM has outperformed the GFS with multiple events this year within the 48 hour period.

Also, WRT the MDT risk, I have a feeling there may be some OFBs to interact with later on to locally enhance tornado potential.

There is certainly a southwestward moving OFB from about KFNB through KLNK and arcing back north towards NOFK. Should see that start to retreat northward as southerly boundary layer flow picks up today.

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Grading the SPC performance in Mn for today. The outlooks were just about right on with the TC metro being on the far east side of the 30% hatched hail. The 2 and 5% tornado risk was right on. Outlook forecast from the 1st day one graphic through today would warrant a A grade. My issue was with the extension of the Tornado Watch to include the TC metro, I thought it was somewhat questionable at the time of issuance, but I can certainly understand the idea of being cautious. Overall grade for the SPC is a B- .

As far as the American Models 24 hours out based on the STP effective layer, the GFS was the much better model. The more and more I look at this, the Nam is not the trusted model 24hrs out. It seems like the GFS is much better at both winter and summer events.

The NAM has outperformed the GFS with multiple events this year within the 48 hour period.

Also, WRT the MDT risk, I have a feeling there may be some OFBs to interact with later on to locally enhance tornado potential.

Yes, agreed with the NAM comment. From a pure forecasting standpoint, the NAM has a ton of utility in the shorter range with convective weather....especially in modeling mesoscale boundaries/features which can have major impacts on storm environments. It is never a good idea to simply "ride" one numerical model for all situations...especially with convective weather where it is often a better idea to employ a multi-model approach in the forecast.

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MD for the plains.

MESOSCALE DISCUSSION 0663

NWS STORM PREDICTION CENTER NORMAN OK

0334 PM CDT WED MAY 02 2012

AREAS AFFECTED...NE...SD...MN...IA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 022034Z - 022200Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...TSTM DEVELOPMENT APPEARS POSSIBLE OVER THE NEXT FEW HOURS

FROM PORTIONS OF NERN NEB ACROSS SERN SD TO SRN MN AND NWRN IA. IF

THIS POTENTIAL BECOMES INCREASINGLY LIKELY...A WATCH IS POSSIBLE.

DISCUSSION...VERY UNSTABLE CONDITIONS HAVE DEVELOPED IN THE VICINITY

OF NUMEROUS AND SUBTLE SMALL SCALE BOUNDARIES FROM THE MIDDLE

MISSOURI RIVER VALLEY INTO THE UPPER MS VALLEY THIS AFTERNOON.

RESIDUAL OUTFLOW BOUNDARY APPEARS TO HAVE MERGED WITH WEAK SURFACE

INVERTED TROUGH AXIS OVER NERN NEB WHERE RECENT SATL IMAGERY WAS

SHOWING CU CONGESTUS INCREASING. THE CU ALSO CONTINUE TO BUILD ALONG

NERN SEGMENT OF THIS TROUGH AXIS INTO PORTIONS OF SCNTRL MN. IT ALSO

APPEARS THAT A WARM FRONT IS BEGINNING TO TAKE FORM ACROSS SRN MN

WHERE AIRMASS CONTINUES TO DESTABILIZE AND CONVECTIVE INHIBITION HAS

LIKELY WEAKENED. THE ENTIRE REGION LIES BENEATH A BELT OF

ANTICYCLONICALLY CURVED SWLY MID LEVEL FLOW AROUND 50KT THAT IS

SUPPORTING EFFECTIVE VERTICAL SHEAR ON THE ORDER OF 45-55KT.

WHILE LATEST CALIBRATED ENSEMBLE GUIDANCE INDICATES A HIGH

PROBABILITY OF SEVERE STORMS TO FORM OVER THE NEXT FEW HOURS IN THIS

GENERAL AREA...DETAILS OF INITIATION AND SUBSEQUENT STORM EVOLUTION

REMAIN COMPLEX AND UNCERTAIN. LATEST 18Z NAM-WRF SHOWS LIMITED QPF

SIGNAL ON THE MISSOURI RIVER WITH MORE ROBUST POTENTIAL EAST ALONG

THE WARM FRONT INTO MN/WI THIS EVENING. MOST LIKELY REASON FOR THESE

VARIOUS SCENARIOS IS THE LACK OF MORE PRONOUNCED LARGE SCALE FORCING

FOR ASCENT ACROSS THE AREA UNTIL LATER THIS EVENING WHEN A SHORT

WAVE TROUGH NOW ACROSS MT BEGINS TO INFLUENCE THE REGION.

IF PERSISTENT MESOSCALE FORCING IN THE ABSENCE OF STRONGER FORCING

ALONG THE BOUNDARIES CAN PROMOTE STORM DEVELOPMENT IN THE NEXT

COUPLE OF HOURS...MAGNITUDE OF CAPE AND SHEAR IN PLACE WOULD

CONTRIBUTE TO POSSIBLE SUPERCELLS WITH THE THREAT OF VERY LARGE HAIL

AND LOCALLY DAMAGING WINDS. WHILE WEAK LOW LEVEL WINDS OVER MOST OF

THE AREA SHOULD NEGATE GREATER TORNADO THREAT...ENHANCED SHEAR NEAR

BOUNDARY/FRONT/TROUGH INTERSECTIONS...COINCIDENT WITH STORM

DEVELOPMENT IN SUCH AN UNSTABLE REGIME...MIGHT RESULT IN A HIGHER

CHANCE FOR A TORNADO OR TWO.

THE REGION WILL CONTINUE TO BE MONITORED AND A WATCH IS POSSIBLE IF

THIS DEVELOPMENT BEGINS TO OCCUR.

..CARBIN.. 05/02/2012

ATTN...WFO...ARX...MPX...DMX...FSD...OAX...GID...LBF...

LAT...LON 42349639 40879786 40729851 41079867 42649801 43519752

43969702 44309643 44609527 44749466 44759388 44629319

44529301 44119245 43749272 43339395 42789580 42349639

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Going to be an interesting convective day with all sorts of potential modes...quite a bit of uncertainty with how this will all play out.

I for one am not buying the NAM depiction of a large bowing segment tracking through all of NE. Dews are mixing out here across central NE...and I think any activity that develops across the high terrain of WY/Panahndle will likely fall apart before interacting with the rich boundary layer moisture farther E.

Northern IA seems the place to be, at least IMHO for early discrete activity. Low level backing is not really pronounced anywhere...but long hodographs will still support some nice early splitters.

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Going to be an interesting convective day with all sorts of potential modes...quite a bit of uncertainty with how this will all play out.

I for one am not buying the NAM depiction of a large bowing segment tracking through all of NE. Dews are mixing out here across central NE...and I think any activity that develops across the high terrain of WY/Panahndle will likely fall apart before interacting with the rich boundary layer moisture farther E.

Northern IA seems the place to be, at least IMHO for early discrete activity. Low level backing is not really pronounced anywhere...but long hodographs will still support some nice early splitters.

I'm not quite sure why SPC has the tornado probs as high as they do west of the current MD. Low-level moisture is really lacking west of Norfolk/Grand Island. Seems to me it would be more of a hail threat, but maybe they're seeing something I'm not.

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Some pretty frisky looking towers building now between Norfolk and Grand Island. Nice surface moisture convergence in that area.

That area looks primed to go soon. Latest RAP mesoanalysis has that entire area CINH free.

Also just glanced at the new NAM...finally backed off that long tracking bowig segment/mini derecho it was trying to track across NE. Rapid Refresh performed very nicely since late last night w.r.t. dewpoints across central NE.

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