Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 021729
SWODY2
SPC AC 021728

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT TUE SEP 02 2014

VALID 031200Z - 041200Z

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

...SUMMARY...
ISOLATED TO SCATTERED SEVERE STORMS ARE LIKELY ACROSS PARTS OF THE
UPPER MIDWEST...MAINLY ON WEDNESDAY AFTERNOON AND EVENING.

...SYNOPSIS...
A VIGOROUS SHORTWAVE TROUGH SHOULD TRACK FROM THE NRN ROCKIES ALONG
THE INTERNATIONAL BORDER ACROSS THE NRN PLAINS. ATTENDANT SURFACE
CYCLONE WILL FOLLOW A SIMILAR PATH WITH A COLD FRONT ACCELERATING E
OVER THE NRN PLAINS WED NIGHT. FARTHER E/SE...QUASI-STATIONARY FRONT
CURRENTLY ACROSS THE MIDWEST TO LOWER MO VALLEY WILL ADVANCE N AS A
WARM FRONT AND SHOULD BE ORIENTED FROM SRN MN TO NRN IL BY WED
EVENING.

...UPPER MS VALLEY...
A CLUSTER OF ELEVATED TSTMS SHOULD BE ONGOING AT 12Z/WED ACROSS
PARTS OF THE SIOUXLAND DRIVEN BY LOW-LEVEL WAA WELL N OF THE SURFACE
FRONT. THIS CONVECTION MAY BE SUSTAINED THROUGH THE MORNING ACROSS
PARTS OF CNTRL/SRN MN WITH A MARGINAL HAIL RISK ON THE FRINGE OF
LARGER BUOYANCY. THIS ACTIVITY SHOULD YIELD A PRONOUNCED
DIFFERENTIAL HEATING CORRIDOR AS STRONG POTENTIAL INSTABILITY
DEVELOPS WITHIN THE WARM SECTOR CHARACTERIZED BY UPPER 60S TO LOWER
70S SURFACE DEW POINTS BENEATH AN EXPANDING EML.

NEUTRAL TO WEAK MID-LEVEL HEIGHT RISES ARE ANTICIPATED WELL
DOWNSTREAM OF THE SHORTWAVE TROUGH OVER THE NORTHWEST.
HOWEVER...DIFFLUENT UPPER-LEVEL FLOW IN CONJUNCTION WITH PERSISTENT
LOW-LEVEL WAA SHOULD FOSTER SUFFICIENT ASCENT FOR STORMS DURING THE
AFTERNOON/EVENING ON THE PERIPHERY OF THE EML/CAPPING INVERSION.
DEEP-LAYER SHEAR WILL BE QUITE FAVORABLE FOR ROTATING
UPDRAFTS...WITH ENLARGED LOW-LEVEL HODOGRAPHS TOWARDS THE MS RIVER
VALLEY. SEVERE THREAT WILL BE GREATEST WITH STORMS THAT MANAGE TO
ROOT INTO THE MOIST BOUNDARY LAYER NEAR THE WARM FRONT. LARGE HAIL
/SOME SIGNIFICANT/ AND A FEW TORNADOES ALONG WITH ISOLATED DAMAGING
WINDS APPEAR PROBABLE. HOWEVER...THE SRN EXTENT AND OVERALL
AMPLITUDE OF THE RISK WILL LIKELY BE MODULATED BY STRONGER CAPPING
THAN IS DEPICTED IN MODEL FORECAST SOUNDINGS.

...ND...
LOW-LEVEL MOISTURE WILL BE INCREASING AHEAD OF THE APPROACHING COLD
FRONT...BUT WILL BE COMPARATIVELY SLOWER TO RETURN RELATIVE TO MN.
HOWEVER...FORCING FOR ASCENT WILL BE ROBUST IMMEDIATELY AHEAD OF THE
SHORT-WAVE TROUGH AND STRONGLY CONVERGENT COLD FRONT. INITIAL STORMS
SHOULD FORM WED AFTERNOON NEAR THE MT/ND BORDER WITHIN A MEAGERLY
BUOYANT BUT STEEP LAPSE RATE AND STRONGLY SHEARED ENVIRONMENT. THIS
ACTIVITY SHOULD INTENSIFY DURING THE EVENING AS IT ENCOUNTERS
INCREASINGLY RICH LOW-LEVEL MOISTURE. SEVERE HAIL AND WIND SHOULD BE
THE PRIMARY HAZARDS.

..GRAMS.. 09/02/2014



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