Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 030853
SWOD48
SPC AC 030851

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0351 AM CDT SUN MAY 03 2015

VALID 061200Z - 111200Z

...DISCUSSION...
MEDIUM RANGE MODEL OUTPUT CONTINUES TO SUGGEST THAT THE SOUTHERN
PORTION OF A SIGNIFICANT SPLITTING UPPER IMPULSE /MIGRATING INLAND
WITHIN THE STRONGER BRANCH OF MID-LATITUDE WESTERLIES ACROSS THE
PACIFIC NORTHWEST/ WILL CONTINUE TO DIG INTO LARGER-SCALE TROUGHING
WITHIN A WEAKER SOUTHERN BRANCH...ACROSS THE SOUTHERN GREAT
BASIN...DURING THE MIDDLE TO LATTER PORTION OF THE COMING WORK WEEK.
POTENTIAL PHASING WITH THE SUBTROPICAL STREAM REMAINS MUCH MORE
UNCLEAR...AS DOES THE TIMING AND STRENGTH OF A NUMBER OF SMALLER
SCALE PERTURBATIONS WHICH MAY PROGRESS OUT OF THE LARGER SCALE
TROUGHING INTO THE PLAINS.  IN GENERAL THOUGH...IT CURRENTLY APPEARS
MOST PROBABLE THAT THE PRIMARY SHORT WAVE IMPULSE WILL NOT BEGIN TO
EMERGE FROM THE INTERMOUNTAIN REGION UNTIL LATE FRIDAY OR EARLY
SATURDAY.

UNTIL THEN...A PERSISTENT SOUTHERLY RETURN FLOW PROBABLY WILL
CONTRIBUTE TO STEADY LOW-LEVEL MOISTENING AND INCREASING POTENTIAL
INSTABILITY ACROSS PARTS OF THE CENTRAL AND SOUTHERN PLAINS INTO THE
MISSISSIPPI VALLEY.  A DEVELOPING LOW/MID-LEVEL CYCLONE ASSOCIATED
WITH LINGERING UPPER TROUGHING ALONG OR EAST OF THE SOUTH ATLANTIC
COAST IS EXPECTED TO INHIBIT SIGNIFICANT MOISTENING AND
DESTABILIZATION ACROSS MUCH OF THE SOUTHEAST.

GUIDANCE HAS BEEN AND REMAINS SUGGESTIVE THAT THIS MOISTENING AND
DESTABILIZATION COULD CONTRIBUTE TO CONSIDERABLE CONVECTIVE
DEVELOPMENT THROUGHOUT THE PERIOD.  THIS MAY AFFORD LITTLE
OPPORTUNITY FOR SUBSTANTIVE STEEPENING OF MID-LEVEL LAPSE
RATES...WITH WARM ELEVATED MIXED LAYER AIR POSSIBLY REMAINING
CONFINED TO THE VICINITY OF THE LOWER RIO GRANDE VALLEY AND ADJACENT
SOUTHERN ROCKIES...AT LEAST UNTIL THE PRIMARY IMPULSE EMERGES FROM
THE INTERMOUNTAIN REGION.  WITH THIS NOT LIKELY UNTIL THE LATTER
PORTION OF THE FORECAST PERIOD...WHEN PATTERN PREDICTABILITY
INHERENTLY DECREASES...UNCERTAINTIES REMAIN TOO LARGE TO ATTEMPT TO
DELINEATE EVEN 15 PERCENT SEVERE PROBABILITIES AT THE PRESENT TIME.

..KERR.. 05/03/2015



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