Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 200541
SWODY1
SPC AC 200539

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT SUN APR 20 2014

VALID 201200Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF THE TEXAS SOUTH PLAINS...

...SUMMARY...
SCATTERED THUNDERSTORMS CAPABLE OF PRODUCING SEVERE HAIL AND A FEW
STRONG WIND GUSTS ARE POSSIBLE ACROSS THE TEXAS SOUTH PLAINS
TODAY...MAINLY LATE THIS AFTERNOON INTO EARLY EVENING.

...SYNOPSIS...
MODELS INDICATE THAT LARGE-SCALE UPPER TROUGHING WITHIN THE
MID-LATITUDE WESTERLIES ACROSS THE EASTERN PACIFIC MAY UNDERGO
SIGNIFICANT AMPLIFICATION DURING THIS PERIOD AS IT APPROACHES THE
PACIFIC COAST.  BUT THE WESTERLIES WILL REMAIN SPLIT ACROSS MUCH OF
THE DOWNSTREAM U.S...WITH ONE ZONAL BRANCH...ACROSS THE NORTHERN
TIER STATES...REMAINING A BIT STRONGER AND MORE PROGRESSIVE THAN A
SLIGHTLY MORE AMPLIFIED BUT WEAKER BRANCH ACROSS THE SOUTHERN TIER.

WITHIN THE SOUTHERN BRANCH...ONE PROMINENT WAVE AND EMBEDDED CLOSED
LOW APPEARS LIKELY TO CONTINUE SLOWLY EAST OF SOUTH ATLANTIC COASTAL
AREAS...WHILE ANOTHER WAVE...COMPRISED OF A NUMBER OF SMALLER SCALE
IMPULSES...GRADUALLY DEVELOPS EAST OF THE SOUTHERN ROCKIES INTO AND
THROUGH THE SOUTHERN PLAINS.  ALTHOUGH SUBSTANTIAL DRYING HAS
OCCURRED ACROSS MUCH OF THE GULF OF MEXICO IN THE WAKE OF THE LEAD
SYSTEM...A NARROW PLUME OF AT LEAST MODEST MOISTURE RETURN IS
EXPECTED TO CONTINUE...FROM THE SOUTHWESTERN GULF OF MEXICO AND
MEXICAN GULF COAST AREA THROUGH THE RIO GRANDE VALLEY.
MEANWHILE...SEASONABLY WEAK TO MODEST MOISTENING WILL CONTINUE ON
SOUTHERLY FLOW...AHEAD OF THE LEE SURFACE TROUGH ACROSS THE SOUTHERN
INTO CENTRAL PLAINS...AND ALONG A STALLING FRONTAL ZONE ASSOCIATED
WITH A SIGNIFICANT NORTHERN-BRANCH IMPULSE NOW CROSSING ONTARIO.

THIS MOISTENING...IN THE PRESENCE OF SEASONABLY STEEP LOWER/MID
TROPOSPHERIC LAPSE RATES...PROBABLY WILL CONTRIBUTE TO SUFFICIENT
INSTABILITY TO SUPPORT CONSIDERABLE THUNDERSTORM ACTIVITY TODAY AND
TONIGHT ACROSS THE MIDDLE OF THE COUNTRY.  HOWEVER...THE RISK FOR
SEVERE STORMS IS EXPECTED TO REMAIN RELATIVELY LOW FOR THE TIME OF
YEAR.

...SOUTHERN PLAINS...
CONSIDERABLE UNCERTAINTY EXISTS CONCERNING THE EXTENT OF THE
CONVECTIVE POTENTIAL AS UPPER TROUGHING CONTINUES EAST OF THE
SOUTHERN ROCKIES TODAY.  A BROAD EMBEDDED CYCLONIC MID-LEVEL
CIRCULATION...WITH SMALLER SCALE IMPULSES PIVOTING AROUND IT...
APPEARS LIKELY TO MIGRATE ACROSS THE TEXAS PANHANDLE REGION DURING
THE AFTERNOON HOURS.  SOME VARIABILITY EXISTS AMONG THE MODELS
CONCERNING JUST HOW QUICKLY THIS OCCURS.  FURTHERMORE...THE IMPACT
OF EARLY DAY CONVECTIVE CLOUD COVER AND PRECIPITATION /EXPECTED
ACROSS PARTS OF THE TEXAS SOUTH PLAINS AND NORTHWEST TEXAS INTO THE
CENTRAL HIGH PLAINS...AS WELL AS ACROSS PARTS OF CENTRAL AND EASTERN
NEW MEXICO/ ON DESTABILIZATION ACROSS THE REGION REMAINS UNCLEAR.
HOWEVER...AT LEAST A NARROW CORRIDOR OF SUBSTANTIVE BOUNDARY LAYER
HEATING APPEARS POSSIBLE BETWEEN THESE TWO AREAS BY LATE AFTERNOON.
BENEATH THE -14 TO -16C 500 MB COLD CORE OVERSPREADING THE
REGION...THIS MAY CONTRIBUTE TO MIXED LAYER CAPE UP TO AROUND 1000
J/KG.

MID/UPPER FLOW IS FORECAST TO BE RATHER MODEST IN STRENGTH AND
SOUTHWESTERLY THROUGH MUCH OF THE DAY...RESULTING IN MARGINAL
VERTICAL SHEAR FOR ORGANIZED CONVECTIVE DEVELOPMENT...AT BEST.
HOWEVER...AROUND/SHORTLY AFTER PEAK HEATING...IT APPEARS POSSIBLE
THAT THE PROGRESSION OF THE CYCLONIC MID-LEVEL CIRCULATION ACROSS
THE PANHANDLE REGION COULD BE TIMED FAVORABLY TO ALLOW FOR VEERING
MID/UPPER FLOW TO INCREASE SHEAR SUFFICIENTLY TO ENHANCE STORM
DEVELOPMENT.  SUPERCELL STRUCTURES MAY NOT BE OUT OF THE
QUESTION...CONTRIBUTING THE RISK FOR SEVERE HAIL AND WIND GUSTS
THROUGH EARLY EVENING...PARTICULARLY ACROSS AND EAST/SOUTHEAST OF
THE PLAINVIEW/LUBBOCK AREA.

..KERR/MOSIER.. 04/20/2014



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