Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 040518
SWODY2
SPC AC 040517

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1217 AM CDT MON MAY 04 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 STRONG TO SEVERE THUNDERSTORMS STILL APPEAR POSSIBLE
TUESDAY ACROSS PARTS OF THE CENTRAL AND SOUTHERN HIGH PLAINS.

...SYNOPSIS...
THERE APPEARS LITTLE CHANGE FROM THE PREVIOUS OUTLOOK FOR THIS
PERIOD CONCERNING THE GENERAL LARGE-SCALE UPPER PATTERN EVOLUTION.
THE STRONGER BELT OF MID-LATITUDE WESTERLIES STILL APPEARS LIKELY TO
UNDERGO AMPLIFICATION ACROSS THE NORTH CENTRAL AND NORTHEAST
PACIFIC.  MODELS CONTINUE TO INDICATE THAT A VIGOROUS MID/UPPER
TROUGH ON THE LEADING EDGE OF THIS REGIME WILL BEGIN SPLITTING AFTER
PROGRESSING INLAND ACROSS THE PACIFIC NORTHWEST COAST BY 12Z
TUESDAY.  AS ONE SIGNIFICANT IMPULSE PIVOTS AROUND THE EASTERN
PERIPHERY OF AN EMBEDDED MID-LEVEL LOW...THE CENTER OF CIRCULATION
IS FORECAST TO REDEVELOP EAST NORTHEASTWARD INTO SOUTHERN ALBERTA BY
12Z WEDNESDAY.  AT THE SAME TIME...ANOTHER SIGNIFICANT IMPULSE IS
EXPECTED TO BEGIN TO DIG SOUTH SOUTHEASTWARD ACROSS OREGON/NORTHERN
CALIFORNIA...TOWARD LARGE-SCALE TROUGHING WITHIN A WEAKER SOUTHERN
BRANCH OF MID-LATITUDE WESTERLIES...ACROSS SOUTHERN
CALIFORNIA/NORTHERN BAJA INTO THE SOUTHERN PLAINS.

MEANWHILE...A SHORT WAVE IMPULSE ON THE LEADING EDGE OF THIS LATTER
REGIME...INITIALLY IN PHASE WITH THE SUBTROPICAL STREAM...IS
FORECAST TO PIVOT NORTHEAST OF THE SOUTHERN ROCKIES.  THIS IS
EXPECTED TO OCCUR AS AN UPSTREAM IMPULSE APPROACHES THE SOUTHERN
CALIFORNIA/NORTHERN BAJA COAST...AND BECOMES INCREASINGLY IN PHASE
WITH THE SUBTROPICAL STREAM.

WITHIN THE SUBTROPICAL STREAM...DOWNSTREAM OF THESE
DEVELOPMENTS...HIGH-LEVEL TROUGHING APPEARS LIKELY TO GRADUALLY
SHIFT NORTHEAST OF THE SOUTHEASTERN GULF OF MEXICO/CARIBBEAN REGION.
THIS MAY BE ACCOMPANIED BY THE DEVELOPMENT OF A SURFACE LOW TO THE
EAST OF THE FLORIDA PENINSULA.  THE PRESENCE OF THESE FEATURES MAY
CONTINUE TO IMPACT BOUNDARY LAYER MOISTENING OVER A LARGE PORTION OF
THE NORTHERN GULF OF MEXICO.  RICH TROPICAL MOISTURE MAY REMAIN
CONFINED TO THE VICINITY OF THE MEXICAN GULF COAST...AS WELL AS
PORTIONS OF THE FLORIDA PENINSULA. HOWEVER... FURTHER MOISTENING IS
PROBABLE ON DEEP SOUTHERLY FLOW THROUGH MUCH OF THE PLAINS...WITH
SEASONABLY MODEST MOIST CONTENT PERSISTING WITHIN A PLUME ALONG A
QUASI-STATIONARY FRONTAL ZONE EXTENDING FROM THE NORTHERN MID
ATLANTIC INTO THE UPPER MIDWEST.

...CENTRAL AND SOUTHERN HIGH PLAINS...
ONLY MINOR CHANGES TO THE SEVERE WEATHER PROBABILITIES HAVE BEEN
MADE.  THE LATEST MODEL RUNS ARE NOT SUPPORTIVE OF INCREASING
PROBABILITIES.  IF ANYTHING...CONFIDENCE MAY BE A BIT LOWERED.

IT STILL APPEARS THAT LARGE-SCALE FORCING...DOWNSTREAM OF THE LEAD
IMPULSE EMERGING FROM THE SOUTHERN INTERMOUNTAIN REGION...MAY BE
SUPPORTING CONSIDERABLE CONVECTIVE DEVELOPMENT BY THE BEGINNING OF
THE FORECAST PERIOD ACROSS PARTS OF THE CENTRAL AND SOUTHERN HIGH
PLAINS.  THIS ACTIVITY MAY LINGER...WHILE GRADUALLY SPREADING
EASTWARD DURING THE DAY...AS THE APPROACHING UPPER TROUGH GRADUALLY
PIVOTS NORTHEAST AND NORTH OF THE SOUTHERN ROCKIES.

STRONGEST DESTABILIZATION...ASSOCIATED WITH DAYTIME HEATING BENEATH
RELATIVELY COOL MID-LEVEL AIR ASSOCIATED WITH THE UPPER
TROUGH...PROBABLY WILL BECOME FOCUSED BETWEEN A DEVELOPING
BAROCLINIC ZONE ASSOCIATED WITH DIFFERENTIAL HEATING /ACROSS THE
TEXAS SOUTH PLAINS INTO NORTHEAST NEW MEXICO/ AND THE DRYLINE TO ITS
SOUTHWEST.  MIXED LAYER CAPE MAY BE SOMEWHAT MODEST...ON THE ORDER
OF 1000 J/KG...BUT AN INCREASING WESTERLY COMPONENT TO THE 30-40 KT
CYCLONIC MID-LEVEL FLOW /WITH THE PASSAGE OF THE UPPER TROUGH AXIS/
IS EXPECTED TO CONTRIBUTE TO INCREASINGLY FAVORABLE VERTICAL SHEAR
FOR SUPERCELL STRUCTURES DURING THE LATE AFTERNOON AND EVENING.

..KERR.. 05/04/2015




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