Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS03 KWNS 030730
SWODY3
SPC AC 030729

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0229 AM CDT SUN MAY 03 2015

VALID 051200Z - 061200Z

...THERE IS A SLGT RISK OF SVR TSTMS TUESDAY AFTERNOON AND EVENING
ACROSS PARTS OF EASTERN NEW MEXICO AND THE TEXAS SOUTH PLAINS INTO
THE PECOS VALLEY...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS SURROUNDING PORTIONS OF
THE CENTRAL AND SOUTHERN HIGH PLAINS...

...SUMMARY...
SCATTERED SEVERE STORMS ARE POSSIBLE TUESDAY ACROSS PARTS OF THE
SOUTHERN HIGH PLAINS.

...SYNOPSIS...
CONSIDERABLE SPREAD PERSISTS WITHIN THE ENSEMBLE OUTPUT OF THE
VARIOUS MODELS CONCERNING THE EVOLUTION OF THE UPPER FLOW NEAR THE
PACIFIC COAST DURING THIS PERIOD.  IN GENERAL...THOUGH...IT DOES
APPEAR THAT UPPER TROUGHING MIGRATING INTO THE PACIFIC
NORTHWEST...WITHIN THE STRONGER BELT OF MID-LATITUDE
WESTERLIES...WILL ELONGATE ALONG A NORTH-SOUTH AXIS.  GUIDANCE
SUGGESTS THAT THIS WILL OCCUR AS ONE SIGNIFICANT IMPULSE PIVOTS
AROUND THE EASTERN PERIPHERY OF THE EMBEDDED CLOSED LOW...SUPPORTING
REDEVELOPMENT OF THE CENTER OF CIRCULATION EAST NORTHEASTWARD INTO
ALBERTA.  AT THE SAME TIME ANOTHER SIGNIFICANT IMPULSE IS FORECAST
TO BEGIN DIGGING SOUTHWARD...ACROSS OREGON/NORTHERN
CALIFORNIA...INTO LARGER SCALE TROUGHING WITHIN A WEAKER SOUTHERN
BRANCH OF MID-LATITUDE WESTERLIES.  AS THIS OCCURS...AN IMPULSE
WITHIN THE LATTER STREAM IS FORECAST TO GRADUALLY APPROACH THE
SOUTHERN CALIFORNIA AND BAJA COAST...COMING INCREASINGLY IN PHASE
WITH THE SUBTROPICAL JET...WHILE A MORE PROMINENT DOWNSTREAM IMPULSE
PIVOTS NORTHEAST OF THE SOUTHERN ROCKIES.

IN RESPONSE TO THESE DEVELOPMENTS...SURFACE TROUGHING IS EXPECTED TO
DEEPEN THROUGH MUCH OF THE HIGH PLAINS.  ASSOCIATED STRENGTHENING OF
SOUTHERLY LOW-LEVEL FLOW TO THE EAST WILL CONTRIBUTE TO FURTHER
MOISTENING...ACROSS AND NORTH OF THE LOWER RIO GRANDE VALLEY.
HOWEVER...IN THE WAKE OF DOWNSTREAM UPPER TROUGHING...CONTINUING TO
EVOLVE ACROSS THE FLORIDA PENINSULA AND CARIBBEAN...RICHER TROPICAL
BOUNDARY LAYER MOISTURE IS EXPECTED TO REMAIN CONFINED TO MEXICAN
GULF COASTAL AREAS...AND PERHAPS ADJACENT DEEP SOUTH TEXAS PORTIONS
OF THE RIO GRANDE VALLEY.

...CENTRAL/SOUTHERN HIGH PLAINS...
CONSIDERABLE CONVECTIVE DEVELOPMENT MAY BE ONGOING ACROSS PARTS OF
THE TEXAS SOUTH PLAINS EARLY TUESDAY...IN RESPONSE TO FORCING FOR
UPWARD VERTICAL MOTION DOWNSTREAM OF THE LEAD SOUTHERN STREAM
IMPULSE.  A LOW-LEVEL BAROCLINIC ZONE GENERATED BY CONVECTIVE
OUTFLOW/DIFFERENTIAL SURFACE HEATING MAY THEN PROVIDE A FOCUS FOR
RENEWED AFTERNOON AND EVENING THUNDERSTORM ACTIVITY...WHILE THE
DRYLINE PROVIDES ANOTHER FOCUS FOR STORM INITIATION ACROSS THE
CENTRAL AND SOUTHERN HIGH PLAINS.

ALTHOUGH SUBSTANTIVE STABILIZATION OF MID-LEVEL LAPSE RATES MAY HAVE
OCCURRED ACROSS MUCH OF THIS REGION BY EARLY TUESDAY...IT DOES
APPEAR THAT DAYTIME HEATING ACROSS THE HIGHER TERRAIN...IN
CONJUNCTION WITH MID-LEVEL COOLING ASSOCIATED WITH THE UPPER TROUGH
/AND CONTINUED LOW-LEVEL MOISTENING/...WILL CONTRIBUTE TO WEAK TO
MODEST DESTABILIZATION BY LATE AFTERNOON.  STRONGEST INSTABILITY IS
EXPECTED TO DEVELOP SOUTH AND WEST OF THE OUTFLOW BOUNDARY INTO THE
DRYLINE ACROSS SOUTHWEST TEXAS AND EASTERN NEW MEXICO...WHERE
VEERING OF 30-40+ KT FLOW TO AN INCREASINGLY WESTERLY COMPONENT IS
EXPECTED TO YIELD THE STRONGEST VERTICAL SHEAR.  A FEW SUPERCELLS
APPEAR POSSIBLE...ACCOMPANIED BY THE RISK FOR SEVERE HAIL AND
LOCALLY STRONG WIND GUSTS.  STORMS CROSSING...OR FORMING ALONG...THE
OUTFLOW BOUNDARY MAY BE ACCOMPANIED BY THE RISK FOR TORNADOES.

..KERR.. 05/03/2015



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