Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 261730
SWODY2
SPC AC 261729

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT TUE JUL 26 2016

VALID 271200Z - 281200Z

...THERE IS A MRGL RISK OF SVR TSTMS WEDNESDAY AFTERNOON AND EVENING
ACROSS PARTS OF THE CENTRAL PLAINS INTO THE NORTHERN HIGH PLAINS...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF THE MID
ATLANTIC COAST REGION...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF NORTHERN
MAINE...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF SOUTHEASTERN
ARIZONA...

...SUMMARY...
STRONG THUNDERSTORMS MAY IMPACT PARTS OF THE CENTRAL PLAINS...THE
HIGH PLAINS...THE MID ATLANTIC COAST REGION...SOUTHEASTERN ARIZONA
AND NORTHERN MAINE ON WEDNESDAY...WITH SOME RISK FOR SEVERE WEATHER.

...SYNOPSIS...
SUBTROPICAL RIDGING APPEARS LIKELY TO REMAIN PROMINENT ACROSS MUCH
OF THE WESTERN AND SOUTHEASTERN U.S. DURING THIS PERIOD.  MODELS
INDICATE SOME WEAKENING OF THE HIGH CENTER NEAR THE SOUTH ATLANTIC
SEABOARD MAY OCCUR...TO THE SOUTH OF A PROGRESSIVE LOW-AMPLITUDE
WAVE WITHIN THE MID-LATITUDE WESTERLIES ACROSS EASTERN CANADA.  AT
THE SAME TIME SOME STRENGTHENING AND/OR A SLIGHT WESTWARD SHIFT OF
THE HIGH CENTER OVER THE SOUTHERN GREAT BASIN MAY OCCUR.

IN ASSOCIATION WITH THIS REGIME...STRONGEST MID-LEVEL WIND FIELDS
SOUTH OF THE CANADIAN/U.S. BORDER MAY BE CONFINED TO PORTIONS OF
NORTHERN NEW ENGLAND.  HOWEVER...AT LEAST MODEST WESTERLY OR
NORTHWESTERLY MID-LEVEL FLOW APPEARS POSSIBLE ACROSS THE CENTRAL
APPALACHIANS THROUGH THE MID ATLANTIC COAST...AND ACROSS PARTS OF
THE NORTHERN ROCKIES INTO THE MID MISSOURI VALLEY...ALONG THE
PERIPHERY OF THE SUBTROPICAL RIDGING.

IN LOWER LEVELS...AN INITIAL WEAK SURFACE FRONT IS EXPECTED TO
CONTINUE TO STALL ACROSS PARTS OF THE MID ATLANTIC COAST...WHILE
BECOMING INCREASINGLY DIFFUSE ACROSS PARTS OF THE OHIO INTO MIDDLE
MISSISSIPPI VALLEYS.  ANOTHER FRONT MAY SLOWLY ADVANCE
SOUTHEASTWARD/SOUTHWARD INTO PARTS OF NORTHERN NEW ENGLAND...THE
GREAT LAKES REGION...AND THE UPPER MIDWEST INTO THE CENTRAL PLAINS.

STEEP MID-LEVEL LAPSE RATES WILL REMAIN GENERALLY CONFINED TO
PORTIONS OF THE CENTRAL  PLAINS INTO THE MID/LOWER MISSOURI
VALLEY...ASSOCIATED WITH A PLUME OF VERY WARM ELEVATED MIXED LAYER
AIR EMERGING FROM THE INTERMOUNTAIN WEST.  SEASONABLY MOIST AIR MAY
LARGELY BE CONFINED TO A PLUME NEAR THE FRONT ACROSS THE MID
ATLANTIC COAST...AND NEAR A WEAK MID/UPPER WAVE MIGRATING INLAND OFF
THE GULF OF MEXICO THROUGH THE LOWER MISSISSIPPI/TENNESSEE
VALLEYS...AROUND THE PERIPHERY OF THE WEAKENING SUBTROPICAL HIGH.

...CNTRL/NRN HIGH PLAINS INTO MID MISSOURI VALLEY AND UPPER
MIDWEST...
A MID-LEVEL CYCLONIC VORTICITY CENTER...OR AREA OF ENHANCED
MID-LEVEL FORCING FOR ASCENT...COULD PERHAPS FOCUS STRONG
THUNDERSTORM DEVELOPMENT NEAR THE FRONT ACROSS PORTIONS OF THE UPPER
MIDWEST WEDNESDAY AFTERNOON AND EVENING.  UNCERTAINTY ACROSS THIS
REGION LINGERS...HOWEVER...CONCERNING THE STRENGTH OF FLOW/SHEAR AND
INSTABILITY...WHICH PRECLUDES INTRODUCING EVEN 5 PERCENT SEVERE
PROBABILITIES AT THIS TIME.  IN THE WAKE OF THIS
PERTURBATION...POTENTIAL FOR AT LEAST ISOLATED TO WIDELY SCATTERED
STRONG THUNDERSTORM DEVELOPMENT APPEARS SOMEWHAT BETTER IN A
DEVELOPING LOW-LEVEL UPSLOPE FLOW REGIME...GENERALLY TO THE
IMMEDIATE EAST OF THE NORTHERN AND CENTRAL ROCKIES.
HOWEVER...VIGOROUS THUNDERSTORM DEVELOPMENT CURRENTLY SEEMS MOST
CERTAIN WITHIN THE CORRIDOR OF STRONGEST PRE-FRONTAL SURFACE HEATING
ACROSS PARTS OF SOUTHERN NEBRASKA INTO NORTHERN KANSAS...WHERE
BOUNDARY LAYER MOISTURE IS EXPECTED TO BE SUPPORTIVE OF LARGE CAPE.
AT THIS TIME...THOUGH...THE LACK OF A MORE SUBSTANTIVE LOW-LEVEL JET
APPEARS ONE FACTOR LIMITING THE RISK FOR THE EVOLUTION OF A
SUSTAINED ORGANIZED MESOSCALE CONVECTIVE SYSTEM...AND HIGHER SEVERE
PROBABILITIES THAN THE 5 PERCENT CURRENTLY DEPICTED.

...MID ATLANTIC COAST REGION...
MODEST WESTERLY 500 MB FLOW /PERHAPS 30+ KT AT 500 MB/...COULD
CONTRIBUTE TO SOME ENHANCEMENT OF THUNDERSTORM DEVELOPMENT IN THE
PRESENCE OF SEASONABLY HIGH MOISTURE CONTENT WEDNESDAY AFTERNOON AND
EVENING.  DOWNBURSTS WITH LOCALIZED STRONG SURFACE GUSTS APPEARS THE
PRIMARY SEVERE THREAT AT THE PRESENT TIME.

...NORTHERN MAINE...
MOISTURE MAY BE SUFFICIENT FOR ONLY MODEST DESTABILIZATION /CAPE UP
TO AROUND 1000 J PER KG/ OF THE PRE-FRONTAL BOUNDARY LAYER WEDNESDAY
AFTERNOON AND EVENING.  HOWEVER...THIS MAY BE SUFFICIENT...COUPLED
WITH THE ANTICIPATED SHEAR...TO SUPPORT ORGANIZED CONVECTIVE
DEVELOPMENT...INCLUDING SUPERCELLS...ACROSS PARTS OF SOUTHEASTERN
QUEBEC INTO NORTHERN MAINE.

...SOUTHEASTERN ARIZONA...
LOW-LEVEL MOISTURE CONTENT MAY NOT BE PARTICULARLY HIGH...BUT A HOT
AND DEEPLY MIXED BOUNDARY LAYER MAY BECOME AT LEAST WEAKLY UNSTABLE
BY LATE WEDNESDAY AFTERNOON.  WITH MODELS INDICATING THE DEVELOPMENT
OF AT LEAST WEAK TO MODEST NORTHEASTERLY/EASTERLY MID-LEVEL FLOW
ACROSS THE REGION...THUNDERSTORM PROPAGATION OFF THE HIGHER TERRAIN
WITH POTENTIAL FOR LOCALIZED STRONG SURFACE GUSTS APPEARS POSSIBLE
THROUGH WEDNESDAY EVENING.

..KERR.. 07/26/2016

$$


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