Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 010548
SWODY1
SPC AC 010546

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1246 AM CDT SUN MAY 01 2016

VALID 011200Z - 021200Z

...THERE IS A MRGL RISK OF SVR TSTMS THIS AFTERNOON AND EVENING
ACROSS PARTS OF THE OHIO VALLEY AND CENTRAL APPALACHIANS REGION...

...THERE IS A MRGL RISK OF SVR TSTMS TODAY INTO TONIGHT ACROSS MUCH
OF CENTRAL/SOUTHERN TEXAS AND THE CENTRAL GULF COAST REGION...

...SUMMARY...
SCATTERED STRONG TO SEVERE STORMS ARE POSSIBLE TODAY ACROSS PARTS OF
THE OHIO VALLEY INTO THE CENTRAL APPALACHIANS...AS WELL AS ACROSS
SOUTHERN INTO CENTRAL TEXAS AND THE CENTRAL GULF COAST REGION.

...SYNOPSIS...
BROAD POSITIVELY TILTED UPPER TROUGHING CURRENTLY ENCOMPASSES MUCH
OF THE U.S...WITH A COUPLE OF EMBEDDED MID-LEVEL CLOSED LOWS...ONE
NOW CENTERED OVER THE CENTRAL PLAINS...ANOTHER OVER ARIZONA.
HOWEVER...WITHIN A BUILDING UPPER RIDGE...NOW EVIDENT IN SATELLITE
IMAGERY ACROSS THE NORTHEASTERN PACIFIC INTO BRITISH
COLUMBIA...MODELS CONTINUE TO INDICATE THAT A SIGNIFICANT UPPER HIGH
WILL EVOLVE AND BECOME CENTERED EAST OF THE CANADIAN ROCKIES DURING
THIS PERIOD.  BY 12Z MONDAY...THIS LATTER FEATURE MAY ENCOMPASS MUCH
OF WESTERN CANADA...AND THE U.S. PACIFIC NORTHWEST/NORTHERN
INTERMOUNTAIN REGION AND NORTHERN ROCKIES.

LOW AMPLITUDE TROUGHING MAY LINGER WITHIN THE SOUTHERN BRANCH OF
SPLIT WESTERLIES ACROSS THE SOUTHWEST AND SOUTHERN ROCKIES...BUT THE
INCREASINGLY SHEARED/DEFORMED REMNANTS OF THE AFOREMENTIONED
MID-LEVEL CLOSED LOWS ARE EXPECTED TO ACCELERATE EAST NORTHEASTWARD.
AROUND THE NORTHERN PERIPHERY OF BROAD SUBTROPICAL RIDGING...THE
LEAD IMPULSE IS GENERALLY FORECAST TO REACH THE UPPER OHIO
VALLEY/LOWER GREAT LAKES REGION BY THE END OF THE PERIOD.  THE
TRAILING IMPULSE MAY CROSS THE SOUTHERN ROCKIES INTO CENTRAL PLAINS.


IN THE WAKE OF THE LEAD IMPULSE...THE LEADING EDGE OF DEEPENING
LOW-LEVEL COOLING IS EXPECTED THROUGH MUCH OF THE MIDDLE MISSISSIPPI
VALLEY AND SOUTHERN PLAINS BY 12Z TODAY.  IT APPEARS THAT THIS MAY
PROGRESS ACROSS THE TEXAS BIG BEND REGION AND MUCH OF THE LOWER RIO
GRANDE VALLEY BY EARLY MONDAY...WHILE ADVANCING MORE SLOWLY THROUGH
PORTIONS OF THE LOWER OHIO AND MISSISSIPPI VALLEYS.  AHEAD OF THE
IMPULSE...A WEAK LOW MAY TRACK ALONG THE STALLED PORTION OF THE
FRONTAL ZONE ACROSS THE OHIO VALLEY INTO LOWER GREAT LAKES REGION.
AT THE SAME TIME...A BAROCLINIC ZONE ...ASSOCIATED WITH THE REMNANTS
OF COLD AIR DAMMING TO THE LEE OF APPALACHIANS...IS EXPECTED TO
RETREAT NORTHWARD INTO THE NORTHERN MID ATLANTIC COAST REGION.

TO THE SOUTH OF THESE FRONTS...IT GENERALLY APPEARS THAT MODERATE TO
STRONG POTENTIAL INSTABILITY /2000+ J PER KG/ WILL BECOME CONFINED
TO PORTIONS OF THE LOWER GRANDE VALLEY INTO UPPER TEXAS AND
LOUISIANA COASTAL AREAS.  BUT...WEAK TO MODERATE BOUNDARY LAYER
DESTABILIZATION /CAPE OF 1000+ J PER KG/ ALSO APPEARS POSSIBLE
ACROSS THE OHIO VALLEY AND CENTRAL APPALACHIANS BY THIS AFTERNOON.

...OHIO VALLEY INTO CENTRAL APPALACHIANS...
DETAILS OF POTENTIAL CONVECTIVE EVOLUTION ARE RATHER UNCERTAIN.
HOWEVER...GIVEN AFOREMENTIONED DESTABILIZATION...COINCIDING WITH
STRENGTHENING OF MID/UPPER WIND FIELDS WITH THE APPROACHING
IMPULSE...THE ENVIRONMENT IS EXPECTED TO BECOME AT LEAST MARGINALLY
CONDUCIVE TO SEVERE STORM DEVELOPMENT.  WHILE THE DEEP LAYER SHEAR
WILL PROBABLY BE STRONG...AND POTENTIALLY SUPPORTIVE OF
SUPERCELLS...LOW-LEVEL HODOGRAPHS ARE FORECAST TO BE RELATIVELY
MODEST IN SIZE.  THIS IS EXPECTED TO TEND TO MINIMIZE THE TORNADIC
POTENTIAL.  BUT SEVERE HAIL AND LOCALIZED STRONG SURFACE GUSTS WILL
BE POSSIBLE IN STRONGEST STORMS...WHICH MAY NOT BECOME MUCH MORE
THAN WIDELY SCATTERED IN COVERAGE THIS AFTERNOON AND EVENING.

...CENTRAL AND SOUTHERN TEXAS INTO CENTRAL GULF COAST...
DETAILS OF POTENTIAL CONVECTIVE EVOLUTION ARE UNCERTAIN.  MUCH OF
THE REGION MAY REMAIN SOUTH OF THE STRONGER MID-LEVEL FLOW
ASSOCIATED WITH THE POLAR JET.  BUT HIGH-LEVEL FLOW WILL BE
GENERALLY STRONG...BENEATH AND BETWEEN THE DIFLUENT POLAR AND
SUBTROPICAL JETS.  GIVEN THE POTENTIAL INSTABILITY...BOTH AHEAD OF
THE SOUTHWARD ADVANCING FRONT...AND TO THE COOL SIDE/ABOVE THE
FRONT...THE ENVIRONMENT IS EXPECTED TO BE AT LEAST SUPPORTIVE OF
SEVERE STORM POTENTIAL.

GUIDANCE IS SUGGESTIVE THAT ONE AREA OF CONVECTION MAY DEVELOP EARLY
NEAR UPPER TEXAS AND LOUISIANA COASTAL AREAS.  OTHERWISE... STORM
INITIATION IS MOST CERTAIN NEAR THE HIGHER TERRAIN WEST OF THE RIO
GRANDE RIVER LATE THIS AFTERNOON AND EVENING.  AS THE UPPER IMPULSE
PROGRESSES ACROSS THE SOUTHERN ROCKIES INTO THE SOUTHERN AND CENTRAL
PLAINS TONIGHT...IT IS POSSIBLE THAT AN ORGANIZING CLUSTER OF STORMS
COULD CROSS THE RIVER...THROUGH DEEP SOUTH TEXAS AND TEXAS COASTAL
AREAS BY 12Z MONDAY.

ADDITIONAL STORMS...WITH AT LEAST SOME RISK FOR SEVERE HAIL...MAY
NOT BE OUT OF THE QUESTION ACROSS PARTS OF THE EDWARDS PLATEAU AND
HILL COUNTRY THROUGH MUCH OF CENTRAL TEXAS.

..KERR/PICCA.. 05/01/2016

$$



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