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Severe thread August 14-17


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Things are starting to look a bit interesting for the above time frame. A warm front looks to move north from say Monday evening the 13th through Wednesday the 15th, followed by a strong cold front by Friday in the Uppper Mississippi Valley. At this time (like usual this far out) timing is a big question, but this set up has had my attention since yesterday. I debated about starting this thread but decided to go ahead after tonight's run of the GFS. Thoughts anyone?

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Could be active today/night

http://www.spc.noaa.gov/products/md/md1766.html

Mesoscale Discussion 1766

mcd1766.gif

MESOSCALE DISCUSSION 1766

NWS STORM PREDICTION CENTER NORMAN OK

0256 PM CDT WED AUG 15 2012

AREAS AFFECTED...EXTREME SE ND...FAR ERN SD...NW IA...MUCH OF

MN...FAR WRN WI

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 151956Z - 152100Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...ADDITIONAL THUNDERSTORM DEVELOPMENT IS EXPECTED BY 21Z.

SEMI-DISCRETE CELLS ARE EXPECTED TO TRANSITION INTO LINEAR SEGMENTS

ALONG COLD FRONT. LARGE HAIL MAY INITIALLY BE POSSIBLE IN ADDITION

TO DAMAGING WIND THREAT. WW WILL LIKELY BE NEEDED IN THE NEXT HOUR

OR SO.

DISCUSSION...AN EASTWARD ADVANCING COLD FRONT WAS LOCATED FROM FAR

NW MN INTO ERN SD AS OF 1930Z. TEMPERATURES HAVE WARMED INTO THE MID

70S TO LOW 80S AHEAD OF THE FRONT WITH DEWPOINTS INCREASING INTO THE

LOW TO MID 60S. AS SUCH...ENVIRONMENT HAS BECOME MODERATELY UNSTABLE

AND UNCAPPED. CONVECTION HAS BEEN SLOW TO DEVELOP IN THE VICINITY OF

THE FRONT AND THIS IS LIKELY DUE TO LOW TO MIDLEVEL CLOUD COVER THAT

DEVELOPED ACROSS CENTRAL MN THIS MORNING. HI-RES WRF-NMM...NSSL WRF

AND HRRR ALL INDICATE CONVECTIVE DEVELOPMENT BY AROUND 20-21Z

HOWEVER. LATEST RADAR DATA ALSO SEEMS TO BE INDICATING A SLOW UPWARD

TREND WITH STRONGER CORES DEVELOPING FROM NEAR BELTRAMI TO MAHNOMEN

COUNTY IN NW MN. SO...WHILE CONVECTIVE INITIATION HAS LIKELY BEEN

DELAYED DUE TO THE AFOREMENTIONED CLOUD COVER...STORMS ARE STILL

EXPECTED BY 21Z. STRONG DEEP LAYER SHEAR OF AROUND 30-50 KT WILL AID

IN ORGANIZATION OF CELLS...WHICH MAY REMAIN SEMI-DISCRETE

INITIALLY...INTO LINEAR SEGMENTS ALONG THE FRONT. STEEPENING LAPSE

RATES AND STRONG MIDLEVEL FLOW WILL RESULT IN DAMAGING WIND

THREAT...ESPECIALLY ONCE LINEAR ORGANIZATION OCCURS.

OTHERWISE...STRONGER CELLS MAY INITIALLY ALSO POSE A LARGE HAIL

THREAT.

A WW WILL LIKELY BE NEEDED IN THE NEXT HOUR OR SO. THERE MAY BE THE

NEED FOR TWO SEPARATE WATCHES WHERE CONVECTION FURTHER SOUTH ACROSS

FAR ERN SD INTO NW IA/SW MN MAY BE SLOWER TO DEVELOP THAN THAT

ACROSS NORTHERN AND CENTRAL MN.

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This sealed our fate further east: Notice the dry layer. The only rain I have really had in the north TC metro is the .20 I got today, but the southern metro got some good rains.

MPX.gif

The dry layer didn't do you in. You have plenty of moisture in the low-levels. The -142J/kg of MLCINH did, though.

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