Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS02 KWNS 180601
SWODY2
SPC AC 180600

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1200 AM CST THU DEC 18 2014

VALID 191200Z - 201200Z

...THERE IS A MRGL RISK OF SVR TSTMS FRIDAY ACROSS PARTS OF THE
MIDDLE AND UPPER TEXAS COAST THROUGH THE CENTRAL GULF COAST...

...SUMMARY...
STRONG THUNDERSTORMS ARE POSSIBLE FRIDAY ACROSS PARTS OF MID AND
UPPER TEXAS COASTAL AREAS INTO THE VICINITY OF THE LOUISIANA COAST.

...SYNOPSIS...
SOME AMPLIFICATION OF INITIALLY STRONG ZONAL FLOW ACROSS THE
MID-LATITUDE PACIFIC APPEARS POSSIBLE AS EARLY AS THIS FORECAST
PERIOD.  BUT THIS IS NOT YET EXPECTED TO IMPACT THE PATTERN MUCH
ACROSS NORTH AMERICA...WITH LITTLE CHANGE FROM THURSDAY THROUGH
FRIDAY.  SHORT WAVES WITHIN SPLIT WESTERLIES EMERGING FROM THE
PACIFIC SHOULD REMAIN PROGRESSIVE...INCLUDING ONE FORECAST TO
ACCELERATE EAST NORTHEAST OF THE TEXAS BIG BEND...THROUGH PORTIONS
OF THE LOWER MISSISSIPPI VALLEY BY 12Z SATURDAY.

FORCING ASSOCIATED WITH THIS IMPULSE PROBABLY WILL SUPPORT A
DEVELOPING WAVE ALONG A REMNANT FRONTAL ZONE...EXTENDING ACROSS THE
NORTHERN GULF OF MEXICO AND MIDDLE TEXAS COAST INTO THE LOWER RIO
GRANDE VALLEY.  HOWEVER...DRY/POTENTIALLY COLD BOUNDARY LAYER AIR
INITIALLY PRESENT ACROSS MUCH OF THE GULF COAST STATES...TO THE
NORTH OF THE FRONT...AS WELL AS ACROSS THE NORTHEASTERN GULF OF
MEXICO...MAY BE SLOW TO MODIFY.  AND IT APPEARS INCREASINGLY
PROBABLE THAT STRONGER FORCING FOR LARGE-SCALE ASCENT WILL SHIFT
NORTHEASTWARD...AWAY FROM THE SURFACE FRONT...EARLY IN THE PERIOD.
MODELS SEEM TO BE TRENDING TOWARD AN EVEN MORE SUPPRESSED/WEAKER
FRONTAL WAVE...TRACKING NEAR OR JUST SOUTH OF COASTAL AREAS...AFTER
MIGRATING EAST OF THE TEXAS COAST.

...MID/UPPER TEXAS COAST THROUGH CENTRAL GULF COASTAL AREAS...
GIVEN THE STILL FAIRLY MODEST NATURE OF THE BOUNDARY LAYER RECOVERY
OVER THE WESTERN GULF...ANY BOUNDARY LAYER DESTABILIZATION LIKELY
WILL REMAIN RATHER WEAK...WITH LITTLE APPRECIABLE STEEPENING OF
MID-LEVEL LAPSE RATES FORECAST ACROSS MUCH OF THE REGION.  WHILE 5
PERCENT SEVERE PROBABILITIES ARE BEING MAINTAINED...THEY ARE NOW
CONFINED TO MORE IMMEDIATE COASTAL AREAS TO ACCOUNT FOR THE LATEST
MODEL TRENDS CONCERNING THE SURFACE LOW...AND POTENTIAL FOR THE WARM
SECTOR TO ADVANCE INLAND.  WITH CURRENT TRENDS ALSO SUGGESTING
CORRESPONDING WEAKER LOW-LEVEL WIND FIELDS AND SHEAR WITHIN THE WARM
SECTOR...IT IS BECOMING MORE UNCLEAR JUST HOW CONDUCIVE THE
ENVIRONMENT WILL BE TO SEVERE WEATHER POTENTIAL.  IF CURRENT TRENDS
PERSIST...SEVERE PROBABILITIES COULD BE REMOVED IN LATER OUTLOOKS
FOR THIS PERIOD.

...PACIFIC NORTHWEST...
AS THE MID-LEVEL COLD POOL /WITH 500 MB TEMPS AS COLD AS -30C/
ASSOCIATED WITH A SIGNIFICANT SHORT WAVE IMPULSE CONTINUES TO
PROGRESS INLAND...AND A MOIST ONSHORE FLOW PERSISTS...SCATTERED WEAK
THUNDERSTORM ACTIVITY MAY REMAIN POSSIBLE WEST OF THE
WASHINGTON/NORTHERN OREGON CASCADES THROUGH MUCH OF THE DAY FRIDAY.

..KERR.. 12/18/2014



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