Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS03 KWNS 040732
SWODY3
SPC AC 040730

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 AM CDT SAT JUL 04 2015

VALID 061200Z - 071200Z

...THERE IS A MRGL RISK OF SVR TSTMS MAINLY MONDAY AFTERNOON AND
EVENING ACROSS PARTS OF THE UPPER MIDWEST AND UPPER PORTIONS OF THE
MIDDLE MISSISSIPPI VALLEY INTO THE CENTRAL  PLAINS...

...SUMMARY...
WIDELY SCATTERED STRONG TO SEVERE STORM DEVELOPMENT IS POSSIBLE
MONDAY IN A CORRIDOR FROM THE UPPER MIDWEST SOUTHWESTWARD INTO THE
SOUTH CENTRAL PLAINS.

...SYNOPSIS...
WITHIN A STRONGER BELT OF MID-LATITUDE WESTERLIES EXTENDING ACROSS
SOUTHERN CANADA AND THE NORTHERN TIER OF THE U.S...A SIGNIFICANT
EMBEDDED SHORT WAVE TROUGH IS FORECAST TO GRADUALLY TURN EASTWARD
ALONG THE CENTRAL CANADIAN/U.S. BORDER AREA DURING THIS PERIOD.
THIS FEATURE MAY SUPPORT SIGNIFICANT CYCLOGENESIS ALONG AN
ASSOCIATED SURFACE FRONTAL ZONE...EITHER ACROSS OR NORTHEAST OF THE
UPPER GREAT LAKES REGION.  CONSIDERABLE SPREAD HAS BEEN PRESENT
AMONG THE MODELS AND WITHIN THEIR RESPECTIVE ENSEMBLE OUTPUT
CONCERNING THESE DEVELOPMENTS...AND THIS IS ADDING TO UNCERTAINTY
WITH REGARD TO CONVECTIVE POTENTIAL FOR THIS PERIOD.

...UPPER MIDWEST INTO SOUTH CENTRAL PLAINS...
IN ADVANCE OF THE UPPER IMPULSE...MODELS DO APPEAR IN GENERAL
AGREEMENT THAT A PLUME OF RELATIVELY STEEP MID-LEVEL LAPSE
RATES...ASSOCIATED WITH VERY WARM ELEVATED MIXED LAYER AIR EMANATING
FROM THE ROCKIES/PLATEAU REGION...WILL BEGIN TO STABILIZE BY EARLY
MONDAY.  THIS IS EXPECTED TO RESULT FROM A COMBINATION OF
CONSIDERABLE THUNDERSTORM DEVELOPMENT LATE SUNDAY INTO SUNDAY
NIGHT...ALONG AND AHEAD OF THE FRONT...FROM PORTIONS OF THE NORTH
CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY...AS WELL AS
CONTINUED WARMING AT HIGHER LEVELS ABOVE THIS PLUME /WARMING ABOVE
-6 C AT 500 MB/.  MODELS ALSO APPEAR TO GENERALLY INDICATE THAT THE
SURFACE FRONTAL ZONE WILL CONTINUE TO CONSIDERABLY OUTRUN THE COOLER
AIR ALOFT ASSOCIATED WITH THE UPPER IMPULSE.  STRONGER MID/UPPER
WIND FIELDS MAY ALSO LAG TO THE COOL SIDE OF THE FRONT...EXCEPT
PERHAPS PORTIONS OF WISCONSIN INTO UPPER MICHIGAN...WHERE EARLY
PERIOD CONVECTIVE CLOUDS AND PRECIPITATION MAY LIMIT SURFACE
HEATING.

PERHAPS OFFSETTING THESE POTENTIAL LIMITING FACTORS...MODELS DO
INDICATE CONTINUED MOISTENING WITHIN THE PRE-FRONTAL CORRIDOR FROM
PARTS OF THE SOUTH CENTRAL PLAINS THROUGH THE UPPER MIDWEST...WHERE
LOWER/MID 70S SURFACE DEW POINTS APPEAR POSSIBLE.  DESPITE THE LACK
OF STEEPER MID-LEVEL LAPSE RATES...SEASONABLY HIGH BOUNDARY LAYER
MOISTURE CONTENT MAY CONTRIBUTE TO MODERATELY LARGE CAPE /WITH
LATENT INSTABILITY EXTENDING THROUGH A DEEP TROPOSPHERIC LAYER/.

WHILE THIS ENVIRONMENT IS EXPECTED TO BE CONDUCIVE TO THE
DEVELOPMENT OF CONSIDERABLE THUNDERSTORM ACTIVITY ALONG THE LENGTH
OF THE FRONT MONDAY AFTERNOON AND EVENING...THE EXTENT OF THE SEVERE
WEATHER POTENTIAL REMAINS UNCLEAR.  IT MAY LARGELY HINGE OF THE
STRENGTH OF THE PRE-FRONTAL SOUTHERLY 850 MB WIND FIELDS WHICH
REMAINS UNCERTAIN AT THE PRESENT TIME...WITH HEAVY PRECIPITATION
LOADING AND DOWNWARD MOMENTUM TRANSFER BOTH POSSIBLY CONTRIBUTING TO
THE RISK FOR POTENTIAL DAMAGING WIND GUSTS.

..KERR.. 07/04/2015



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