Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 291623
SWODY1
SPC AC 291621

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1121 AM CDT FRI JUL 29 2016

VALID 291630Z - 301200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF SOUTHEAST WYOMING AND ADJACENT PORTIONS OF THE
NEBRASKA PANHANDLE INTO NORTHEAST COLORADO...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING PORTIONS OF
THE HIGH PLAINS INTO SOUTHERN PLAINS RED RIVER VALLEY...THE OZARK
PLATEAU...MIDDLE MISSISSIPPI AND LOWER OHIO VALLEYS INTO THE
SOUTHERN GREAT LAKES REGION...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF CENTRAL AND
SOUTHEASTERN ARIZONA...

...SUMMARY...
A FEW SEVERE STORMS APPEAR POSSIBLE LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF SOUTHEAST WYOMING INTO NORTHEAST COLORADO.
OTHERWISE...WIDELY SCATTERED STRONG STORMS MAY IMPACT SURROUNDING
PORTIONS OF THE HIGH PLAINS INTO THE SOUTHERN PLAINS RED RIVER
VALLEY...THE OZARK PLATEAU...THE MIDDLE MISSISSIPPI AND LOWER OHIO
VALLEYS...THE SOUTHERN GREAT LAKES REGION...AS WELL AS PARTS OF
CENTRAL AND SOUTHEAST ARIZONA.

...SYNOPSIS...
AT LEAST SOME WEAKENING OF A PROMINENT SUBTROPICAL HIGH CENTERED
OVER THE SOUTHERN GREAT BASIN APPEARS POSSIBLE TODAY...AS A
SIGNIFICANT SHORT WAVE IMPULSE WITHIN THE MID-LATITUDE WESTERLIES
CONTINUES PROGRESSING INLAND ACROSS THE BRITISH COLUMBIA COAST AND
CANADIAN ROCKIES.  DOWNSTREAM FLOW REMAINS SPLIT...WITH A LINGERING
BELT OF WEAK TO MODEST CYCLONIC FLOW ON THE PERIPHERY OF SUBTROPICAL
RIDGING...ACROSS THE NORTHERN U.S. ROCKIES THROUGH THE NORTHERN MID
ATLANTIC COAST.  WITHIN THIS REGIME...ONE SHORT WAVE IMPULSE IS IN
THE PROCESS OF SHIFTING EAST NORTHEAST OF NORTHERN MID
ATLANTIC/SOUTHERN NEW ENGLAND COASTAL AREAS.  A BROADER
PERTURBATION...WITH AT LEAST A COUPLE OF EMBEDDED SMALLER-SCALE
IMPULSES IS FORECAST TO CONTINUE TO TURN EAST OF THE CENTRAL
PLAINS...THROUGH PORTIONS OF THE MIDDLE MISSISSIPPI AND OHIO VALLEYS
TODAY.  AT THE SAME TIME...THE SOUTHERN PORTION OF A SPLITTING
UPSTREAM WAVE WILL CONTINUE TO GRADUALLY DIG ACROSS AND SOUTHEAST OF
THE WYOMING ROCKIES.

...HIGH PLAINS INTO APPALACHIANS...
PROBABILITIES FOR SEVERE STORMS APPEAR LARGELY FOCUSED WITHIN A
LOW-LEVEL UPSLOPE FLOW REGIME ACROSS THE CENTRAL HIGH PLAINS...AND
ALONG AN ASSORTMENT OF SURFACE BOUNDARIES /MAINLY A WEAK SURFACE
FRONT AND CONVECTIVELY GENERATED COLD POOLS/...FROM PARTS OF THE
SOUTHERN HIGH PLAINS/RED RIVER VALLEY REGION INTO THE SOUTHERN GREAT
LAKES REGION.  A CORRIDOR OF STRONGER SURFACE HEATING ALONG AND TO
THE SOUTHEAST OF THIS COMPOSITE BOUNDARY IS EXPECTED TO CONTRIBUTE
TO MODERATE CAPE /ON THE ORDER OF 1500-3000 J PER KG/ BY LATE
AFTERNOON.  THIS WILL BE SUPPORTED BY STEEP MID-LEVEL LAPSE RATES
ASSOCIATED WITH RESIDUAL ELEVATED MIXED LAYER AIR...MOSTLY ACROSS
PARTS OF THE CENTRAL/SOUTHERN HIGH PLAINS...WITH SEASONABLY HIGH
BOUNDARY LAYER MOISTURE CONTENT A MORE PROMINENT CONTRIBUTOR TO THE
EAST.

ASIDE FROM POTENTIAL FOR STRONG SHEAR WHERE CYCLONIC MID-LEVEL FLOW
WILL HAVE A NORTHWESTERLY COMPONENT ACROSS THE CENTRAL HIGH PLAINS
/AND VEERING OF WINDS WITH HEIGHT MOST PRONOUNCED/...20-30+ KT
WESTERLY FLOW /AT AROUND 500 MB AND ABOVE/ MAY ONLY CONTRIBUTE TO
WEAK TO MODEST SHEAR ACROSS MUCH OF THE AXIS OF STRONGER
DESTABILIZATION.  HOWEVER...IT MAY STILL BE ENOUGH TO ALLOW FOR SOME
ENHANCEMENT OF SCATTERED THUNDERSTORM DEVELOPMENT EXPECTED DURING
THE PEAK AFTERNOON INSTABILITY.  EAST OF THE HIGH PLAINS...LOCALIZED
STRONG SURFACE GUSTS SEEM THE PRIMARY SEVERE THREAT.  HOWEVER...A
BRIEF/WEAK TORNADO OR TWO MAY NOT BE OUT OF THE QUESTION NEAR A WEAK
SURFACE LOW TO THE SOUTHEAST OF THE CHICAGO AREA...AND ALONG THE
WEAK SURFACE BOUNDARY EXTENDING TO ITS EAST...ACROSS PARTS OF
NORTHERN INDIANA AND OHIO.

...ARIZONA...
AIDED BY AN INCREASE IN MID-LEVEL MOISTURE...AN INCREASE IN
THUNDERSTORM COVERAGE IS EXPECTED TODAY ACROSS THE MOGOLLON RIM AND
MOUNTAINS OF SOUTHEASTERN ARIZONA.  THIS MAY OCCUR LARGELY IN
RESPONSE TO DIURNAL HEATING AND OROGRAPHIC FORCING.  WIND PROFILES
TO THE SOUTHEAST OF THE SUBTROPICAL HIGH CENTER APPEAR SUPPORTIVE OF
EVENTUAL WESTWARD/SOUTHWESTWARD PROPAGATION OFF THE HIGHER TERRAIN
TOWARD THE LOWER DESERTS.  HOW QUICKLY AND HOW FAR REMAIN IN SOME
QUESTION DUE TO LINGERING UNCERTAINTY CONCERNING THE STRENGTH OF THE
EASTERLY MID-LEVEL FLOW.  HOWEVER...A HOT AND DEEPLY MIXED BOUNDARY
LAYER WILL CERTAINLY BE SUPPORTIVE OF STRONG DOWNBURSTS AND SURFACE
GUSTS.  AND IT IS POSSIBLE THAT CONVECTION MAY IMPACT PORTIONS OF
THE TUCSON AND PHOENIX METRO AREAS BY MID/LATE EVENING.

..KERR/BUNTING.. 07/29/2016

$$


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