Severe Storm Outlook Narrative (AC)
Issued by NWS

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948
ACUS01 KWNS 281949
SWODY1
SPC AC 281947

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0247 PM CDT SUN AUG 28 2016

VALID 282000Z - 291200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE UPPER MIDWEST...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE DAKOTAS/UPPER
MIDWEST...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE LOWER GREAT
LAKES/NORTHEAST STATES...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE TN VALLEY/SOUTHERN
APPALACHIANS...

...SUMMARY...
SEVERE STORMS APPEAR MOST PROBABLE ACROSS PARTS OF THE UPPER MIDWEST
LATE THIS AFTERNOON AND EVENING...WHILE OTHER STRONG STORMS MAY
OCCUR ACROSS THE NORTHEAST STATES AND TENNESSEE VALLEY.

NO APPRECIABLE CHANGES WERE MADE TO THE PREVIOUS OUTLOOK.

..SMITH.. 08/28/2016

.PREV DISCUSSION... /ISSUED 1131 AM CDT SUN AUG 28 2016/

...UPPER MIDWEST...
AN UPPER TROUGH MOVING FROM ALBERTA TOWARD SASKATCHEWAN AT MIDDAY
WILL CONTINUE EAST-NORTHEASTWARD...WITH WEAK HEIGHT RISES AND
GENERALLY WEAKENING LARGER-SCALE FORCING EXPECTED DOWNSTREAM ACROSS
THE DAKOTAS/MN INTO THIS EVENING. AN INCREASINGLY MOIST AIR MASS
/60S F SURFACE DEWPOINTS/ WILL DEVELOP NORTHWARD PARTICULARLY ACROSS
THE EASTERN DAKOTAS AND WESTERN/NORTHERN MN...TO THE SOUTH OF A
NORTHWARD-SHIFTING WARM FRONT AND AHEAD OF A COLD FRONT THAT IS
CURRENTLY PROGRESSING EASTWARD ACROSS EASTERN MT.

AFOREMENTIONED WEAK/DETRIMENTAL LARGE-SCALE INFLUENCES AND
INCREASING MID-LEVEL CAPPING SHOULD GENERALLY LIMIT STORM
DEVELOPMENT ACROSS MUCH OF THE REGION THROUGH PEAK HEATING.
HOWEVER...ISOLATED STORMS MAY FORM ALONG THE EASTWARD-MOVING COLD
FRONT IMPINGING ON THE WESTERN PERIPHERY OF RICHER BOUNDARY-LAYER
MOISTURE ACROSS PARTS OF FAR NORTH-CENTRAL ND. A SUPERCELL OR TWO
MAY DEVELOP HERE INTO NORTHEAST ND DURING THE EVENING...WITH ALL
HAZARDS POSSIBLE.

THE MOST PROBABLE SCENARIO MAY BE FOR STORMS TO DEVELOP/INCREASE
AROUND AND AFTER SUNSET ACROSS NORTHWEST MN AND POSSIBLY EXTREME
EASTERN ND NEAR THE WARM FRONT AS WARM-AIR ADVECTION INCREASES ASIDE
FROM A GLANCING INFLUENCE OF A CANADIAN PRAIRIES SHORTWAVE TROUGH.
IN THE PRESENCE OF STEEP LAPSE RATES/AMPLE BUOYANCY...ALL SEVERE
HAZARDS INCLUDING LARGE HAIL AND SOME TORNADO RISK WILL EXIST WITH
THIS INITIAL DEVELOPMENT. SUBSEQUENTLY...AT LEAST A RELATIVELY
SMALL-SCALE DAMAGING WIND RISK MAY ALSO EVOLVE LATER IN THE EVENING
INTO THE OVERNIGHT AS STORMS MERGE/SPREAD EAST-SOUTHEASTWARD ACROSS
NORTHERN MN.

...LOWER GREAT LAKES/NORTHEAST STATES...
A PLUME OF MID TO UPPER 60S SURFACE DEW POINTS EXISTS DOWNSTREAM OF
THE LOWER GREAT LAKES. BOUNDARY-LAYER HEATING OF THIS AIR MASS WILL
SUPPORT MODERATE BUOYANCY BY AFTERNOON. GLANCING MID-LEVEL HEIGHT
FALLS ASSOCIATED WITH THE EASTWARD-MOVING SHORTWAVE TROUGH OVER
NORTHERN ONTARIO SHOULD SUPPORT ISOLATED TO WIDELY SCATTERED STORMS
FORMING ALONG A WEAK COLD FRONT AND PRE-FRONTAL AREAS OF CONFLUENCE.
THE STRONGEST DEEP-LAYER SPEED SHEAR WILL EXIST ACROSS NORTHERN
NY/VT AND THUS HAVE EXPANDED MARGINAL RISK PROBABILITIES FOR LOCALLY
DAMAGING WIND GUSTS.

...TN/KY AND ADJACENT APPALACHIANS...
WATER VAPOR FEATURES A RELATIVELY SUBTLE MID-LEVEL DISTURBANCE OVER
CENTRAL PORTIONS OF KY/TN THIS AFTERNOON...WHILE 12Z OBSERVED
SOUNDINGS FROM NASHVILLE AND WILMINGTON OH SAMPLED RELATIVELY COOL
MID-LEVEL TEMPERATURES AT AROUND -8C AT 500 MB. AS BOUNDARY-LAYER
DESTABILIZATION OCCURS THIS AFTERNOON AS LOW-LEVEL LAPSE RATES
STEEPEN...THUNDERSTORMS SHOULD INCREASE/INTENSIFY ACROSS THE REGION
AND SUBSEQUENTLY DRIFT GENERALLY WESTWARD. DOWNBURSTS CAPABLE OF
LOCALIZED DAMAGING WINDS WILL BE POSSIBLE WITH THE STRONGEST
UPDRAFTS/DOWNDRAFTS THIS AFTERNOON THROUGH EARLY EVENING.

$$



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