Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS02 KWNS 050502
SWODY2
SPC AC 050501

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1201 AM CDT SUN JUL 05 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...
MODELS SUGGEST THAT WEAK SUBTROPICAL RIDGING MAY BECOME EVEN A BIT
MORE SUPPRESSED DURING THIS FORECAST PERIOD...AS THE MID-LATITUDE
WESTERLIES GRADUALLY SHIFT SOUTH OF THE CANADIAN/ U.S. BORDER...AND
BECOME BROADLY CYCLONIC ACROSS MUCH OF THE NORTHERN TIER STATES.
THIS PATTERN TRANSITION APPEARS UNDERWAY AS A SIGNIFICANT UPPER
TROUGH WITHIN THE WESTERLIES BEGINS TO TURN EAST SOUTHEAST OF THE
CANADIAN ROCKIES.  DURING THE NEXT 24-36 HOURS...MODELS SUGGEST THAT
THIS TROUGH WILL GRADUALLY SPLIT...WITH ONE IMPULSE ACCELERATING
EAST NORTHEASTWARD TOWARD HUDSON BAY...WHILE A TRAILING IMPULSE DIGS
ACROSS THE MONTANA/NORTH DAKOTA BORDER AREA.  BY MONDAY
MORNING...THIS LATTER FEATURE IS EXPECTED TO TURN EASTWARD NEAR/JUST
SOUTH OF THE INTERNATIONAL BORDER...BEFORE PROGRESSING ACROSS THE
UPPER GREAT LAKES REGION BY 12Z TUESDAY.  MODELS CONTINUE TO SUGGEST
THAT FORCING FOR UPWARD VERTICAL MOTION COULD SUPPORT SIGNIFICANT
CYCLOGENESIS ALONG AN ASSOCIATED SURFACE FRONT...ACROSS OR NORTHEAST
OF THE UPPER GREAT LAKES REGION.  OTHERWISE...THE FRONT IS FORECAST
TO CONTINUE ADVANCING STEADILY SOUTHEASTWARD THROUGH THE UPPER GREAT
LAKES REGION...UPPER PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY AND
THE CENTRAL PLAINS...CONSIDERABLY TO THE SOUTHEAST AND SOUTH OF THE
TRAILING SOUTHERN IMPULSE THROUGH MUCH OF THE PERIOD...BEFORE IT
BEGINS ASSUMING A MORE NEUTRAL TO NEGATIVE TILT.

...UPPER MIDWEST INTO SOUTH CENTRAL PLAINS...
BY MONDAY MORNING...IT STILL APPEARS THAT RELATIVELY STEEP MID-LEVEL
LAPSE RATES ABOVE THE SOUTHWARD ADVANCING FRONT...ASSOCIATED WITH A
REMNANT PLUME OF ELEVATED MIXED LAYER AIR EMANATING FROM THE
ROCKIES/PLATEAU REGION...WILL BEGIN TO STABILIZE.  MODELS INDICATE
THAT THIS WILL OCCUR IN PART DUE TO THE INFLUENCE OF CONSIDERABLE
THUNDERSTORM DEVELOPMENT...BUT ALSO DUE TO CONTINUED WARMING IN A
PLUME AT MID/UPPER LEVELS...AHEAD OF THE LAGGING IMPULSE NEAR THE
INTERNATIONAL BORDER AREA.  AT THE SAME TIME THOUGH...BOUNDARY LAYER
MOISTENING MAY CONTINUE WITHIN A PRE-FRONTAL CORRIDOR FROM THE SOUTH
CENTRAL PLAINS THROUGH THE UPPER MIDWEST.  SURFACE DEW POINTS
CLIMBING INTO THE LOWER/MID 70S MAY STILL CONTRIBUTE TO SIZABLE
MIXED LAYER CAPE WITH DAYTIME HEATING...BUT THIS LIKELY WILL BE
DISTRIBUTED THROUGH A RATHER DEEP TROPOSPHERIC LAYER...WITH HIGH
EQUILIBRIUM LEVELS.

WHILE THERMODYNAMIC PROFILES ARE NOT EXPECTED TO BECOME PARTICULARLY
CONDUCIVE TO SEVERE WEATHER POTENTIAL...INSTABILITY AND FORCING FOR
ASCENT ALONG THE SOUTHWARD ADVANCING FRONT MAY SUPPORT CONSIDERABLE
THUNDERSTORM ACTIVITY MONDAY AFTERNOON AND EVENING.  IT IS POSSIBLE
THAT A COMBINATION OF HEAVY PRECIPITATION LOADING AND THE DOWNWARD
TRANSFER OF MOMENTUM ASSOCIATED WITH 20-30+ KT PRE-FRONTAL SOUTHERLY
850 MB FLOW MAY CONTRIBUTE TO POTENTIALLY DAMAGING SURFACE GUSTS IN
STRONGER CONVECTION.

SOME RISK FOR AN ISOLATED SUPERCELL OR TWO CAPABLE OF PRODUCING
TORNADOES DOES SEEM EVIDENT ACROSS PARTS OF NORTH CENTRAL WISCONSIN
INTO THE UPPER PENINSULA OF MICHIGAN...WHERE DEEP LAYER SHEAR MAY
BECOME SUFFICIENTLY STRONG IN THE WARM SECTOR OF THE DEEPENING
SURFACE LOW.  HOWEVER...CONSIDERABLE SPREAD PERSISTS AMONG THE MODEL
OUTPUT CONCERNING THIS DEVELOPMENT...AND WARM DESTABILIZATION.

..KERR.. 07/05/2015



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