Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 030600
SWODY1
SPC AC 030558

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT SUN MAY 03 2015

VALID 031200Z - 041200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM A WRN PORTION OF UPPER
MI...WI...SOUTHEAST MN AND NORTHEAST IA...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK
AREA AND EXTENDING SOUTHWEST THROUGH PORTIONS OF THE MID MO VALLEY
TO WRN NEB...

...SUMMARY...
SCATTERED STRONG TO SEVERE STORMS WITH HAIL AND DAMAGING WINDS ARE
EXPECTED THIS AFTERNOON AND EVENING FROM WESTERN UPPER MICHIGAN
THROUGH WISCONSIN...SOUTHEAST MINNESOTA TO NORTHEASTERN IOWA.  A
MARGINAL RISK OF SEVERE STORMS SURROUNDS THE SLIGHT RISK AREA AND
EXTENDS SOUTHWEST THROUGH WESTERN IOWA...EASTERN NEBRASKA TO WESTERN
KANSAS.

...SYNOPSIS...
A PROGRESSIVE BROAD UPPER TROUGH WITH AN EMBEDDED SHORTWAVE TROUGH
WILL SKIRT THE U.S./CANADIAN BORDER FROM THE NRN PLAINS TO THE UPPER
GREAT LAKES WITH WLY 700-500-MB WINDS STRENGTHENING ACROSS MN/WI AND
UPPER MI.

IN THE LOWER LEVELS...RIDGING EXTENDING W/SWWD FROM A SURFACE HIGH
SHIFTING EAST OF THE SRN MID-ATLANTIC COAST IS EXPECTED TO REMAIN
PROMINENT INLAND OF THE WRN AND CENTRAL GULF COAST TODAY.  THIS
LIKELY WILL PRECLUDE A SUBSTANTIVE RETURN FLOW OF GULF MOISTURE TO
THE VICINITY OF A COLD FRONT ADVANCING SOUTHEAST OF THE NORTHERN
PLAINS.  BY MID-LATE AFTERNOON...THIS FRONT SHOULD EXTEND FROM
WESTERN UPPER MI THROUGH SOUTHEAST MN...NORTHWEST IA...AND NORTHEAST
TO SOUTH-CENTRAL NEB...WHERE IT WILL INTERSECT THE NORTHERN EXTENT
OF A DRY LINE /EXTENDING SWD THROUGH WRN KS TO WRN TX/.
MEANWHILE...A STRENGTHENING S/SWLY LLJ THROUGH THE AFTERNOON AND
EVENING FROM OK/W TX INTO KS AND ARCING NEWD THROUGH IA TO WI/UPPER
GREAT LAKES REGION WILL AID IN A RELATIVELY NARROW CORRIDOR OF
MOISTURE RETURN ALONG AND AHEAD OF THE COLD FRONT.

...UPPER MI/WI/SOUTHEAST MN/NORTHEAST IA...
SURFACE DEW POINTS IN THE 50S F EXPECTED INTO THIS REGION DURING THE
AFTERNOON COMBINED WITH STRONG SURFACE HEATING AHEAD OF THE COLD
FRONT BENEATH STEEPENING MIDLEVEL LAPSE RATES /7.5-8 C PER KM/
SHOULD RESULT IN MLCAPE OF 1000-1500 J/KG.  DESPITE THE LACK OF
STRONGER FORCING ALOFT...ASCENT ALONG THE COLD FRONT AND SURFACE
HEATING SHOULD SUFFICIENTLY WEAKEN INHIBITION FOR TSTM DEVELOPMENT
BY MID-LATE AFTERNOON.  EFFECTIVE BULK SHEAR UP TO 35 KT /ATTENDANT
TO STRENGTHENING WIND PROFILES/ SUGGESTS THE LIKELIHOOD FOR
ORGANIZED STORMS...WITH LARGE HAIL AND DAMAGING WINDS BEING THE
PRIMARY THREATS.  MIXED STORM MODES ARE EXPECTED WITH HIGH-RES
MODELS INDICATING INITIAL STORMS SHOULD BE DISCRETE...WHILE LINEAR
FORCING FOR ASCENT WITH THE FRONT FAVORS UPSCALE GROWTH INTO A
QUASI-LINEAR CONVECTIVE SYSTEM ADVANCING EWD THROUGH UPPER
MI...WI...SERN MN AND NRN IA THROUGH THE EVENING.  SINCE LINEAR
FORCING MAY BE GREATER FOR THIS OUTLOOK...THE TORNADO THREAT IS LOW
/2 PERCENT/.

...ERN NEB TO WRN KS...
STRONG HEATING BENEATH A PLUME OF STEEP MIDLEVEL LAPSE RATES /8-8.5
C PER KM/ SHOULD WEAKEN SURFACE-BASED INHIBITION BY AFTERNOON WITH
STORMS DEVELOPING ALONG THE WRN EXTENT OF THE COLD FRONT AS IT
ADVANCES SE/SWD.  ALTHOUGH INSTABILITY SHOULD BE COMPARABLE TO
LOCATIONS FARTHER NORTHEAST ACROSS THE SLIGHT RISK AREA...WEAKER
EFFECTIVE BULK SHEAR /20-30 KT/ IS EXPECTED TO LIMIT THE OVERALL
SEVERE RISK.  A DEEP MIXED BOUNDARY LAYER WILL SUPPORT ISOLATED
STRONG TO SEVERE WIND GUSTS...WHILE STEEP LAPSE RATES ALSO AID IN A
MARGINALLY SEVERE HAIL THREAT.  MODELS CONTINUE TO SUGGEST UPSCALE
GROWTH OF STORM CLUSTERS WILL BE POSSIBLE ACROSS NRN KS INTO NEB
RESULTING IN A CONTINUED MARGINAL SEVERE RISK WITHIN THE NOSE OF A
STRENGTHENING SLY LLJ.

..PETERS/CARBIN.. 05/03/2015




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