DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 182002
SWODY1
SPC AC 182000

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT THU JUL 18 2013

VALID 182000Z - 191200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF ECNTRL AND NERN
MN AND NRN WI...

...THERE IS A SLGT RISK OF SVR TSTMS PARTS OF THE NRN PLAINS...UPPER
MS VALLEY...GREAT LAKES...NY AND NEW ENGLAND...

THE ONLY CHANGE TO THE OUTLOOK FOR THIS ISSUANCE IS TO EXTEND THE
SLIGHT RISK AREA EWD ACROSS NEW ENGLAND INTO SRN MAINE. THIS IS TO
ACCOUNT FOR STORMS THAT HAVE INTENSIFIED ACROSS SE NH AND SRN MAINE
WHERE MESOANALYSIS SHOWS MODERATE INSTABILITY AND STRONG DEEP LAYER
SHEAR. ALONG WITH THIS CHANGE...ADDED A 2 PERCENT TORNADO
PROBABILITY IN NRN NY AND NEW ENGLAND. FOR THE MODERATE RISK AREA IN
THE UPPER MS VALLEY...WILL LEAVE THE FORECAST OF AN ENHANCED SEVERE
THREAT UNTOUCHED. A VERY UNSTABLE AIRMASS IS STILL IN PLACE ACROSS
THE MODERATE RISK AREA AND POTENTIAL EXISTS FOR A MORE WIDESPREAD
WIND DAMAGE THREAT ASSOCIATED WITH MCS DEVELOPMENT THIS EVENING.

..BROYLES.. 07/18/2013

.PREV DISCUSSION... /ISSUED 1132 AM CDT THU JUL 18 2013/

...SYNOPSIS...
EXPANSIVE FLAT RIDGE OVER THE CNTRL AND ERN U.S. WILL BE SUPPRESSED
SLIGHTLY SWD THIS PERIOD AS STRONG TROUGH ON THE WRN SIDE OF HUDSON
BAY VORTEX ADVANCES S/SE ACROSS NRN MB INTO NW ONT. FALLING HEIGHTS
ON THE SRN FRINGE OF THE VORTEX WILL OVERSPREAD THE FAR NRN
PLNS...THE UPR MS MS...AND THE UPR GRT LKS...INCREASING THE RISK FOR
STRONG TO SVR TSTMS OVER THAT REGION AS WEAK SHORTWAVE IMPULSES
ACCELERATE EWD IN STRENGTHENING WLY MID/UPR-LVL FLOW.

ELSEWHERE...AN EASTERLY WAVE-TYPE DISTURBANCE WILL MOVE WWD ACROSS
THE NRN GULF OF MEXICO IN TANDEM WITH A WEAK COLD-CORE IMPULSE THAT
IN PART WAS RESPONSIBLE FOR YESTERDAYS STORMS IN THE CAROLINAS/GA.
THE COMBINED TROUGH MAY ENHANCE THE POTENTIAL FOR STORMS TODAY OVER
LA AND ADJACENT STATES.

...NRN PLNS/UPR MS VLY/UPR GRT LKS THIS AFTN THROUGH TNGT...
SFC WAVE NOW OVER ERN ND...AND ASSOCIATED WARM/STNRY FRONT EXTENDING
E INTO THE UPR MS VLY/UPR GRT LKS...SHOULD SERVE AS THE MAIN FOCUS
FOR SVR TSTM DEVELOPMENT THIS PERIOD. THE FRONT SHOULD CONTINUE TO
BE REINFORCED...AND ITS NWD ADVANCE SOMEWHAT RETARDED...BY
PERSISTENT ELEVATED CONVECTION/STORMS ALONG THROUGH TNGT. THE
BOUNDARY MAY ALSO SERVE AS THE MAIN FOCUS FOR LARGER-SCALE
CONVECTIVE EVOLUTION/MCS DEVELOPMENT MAY OCCUR TNGT/EARLY FRI.

IN THE MEAN TIME...WDLY SCTD TO SCTD TSTMS SHOULD FORM WITH SFC
HEATING LATER TODAY NEAR ND SFC WAVE...EWD INTO NRN MN. GIVEN
ENVIRONMENT OF STRONG BUOYANCY /MLCAPE AOA 3000 J PER
KG/...FAVORABLE LOW-LVL UPLIFT...45-50 KT WLY DEEP SHEAR...AND
INCREASING HEIGHT FALLS...SUSTAINED STORMS AND SUPERCELLS APPEAR
LIKELY...ESPECIALLY NEAR SFC FRONT WHERE LOW-LVL SRH WILL BE
MAXIMIZED. LARGE HAIL...DMGG WINDS...AND A COUPLE TORNADOES MAY
OCCUR.

BY THIS EVE...DEGREE OF LOW-LVL CONVERGENCE...CONTINUED HEIGHT
FALLS...AND NOCTURNAL STRENGTHENING OF SWLY LLJ FAIRLY STRONGLY
SUGGEST THAT THE STORMS WILL EVOLVE INTO A LARGER-SCALE CLUSTER OR
LINE...WITH AN INCREASING RISK FOR DMGG OVER NRN/ERN MN AND WRN/NRN
WI. WITH RICH BOUNDARY LAYER MOISTURE IN PLACE...THE CONVECTIVE
SYSTEM MAY MOVE/DEVELOP E/SE TOWARD NRN IA...SRN WI...AND LK MI
BEFORE WEAKENING EARLY FRI.

...LWR MI/LWR GRT LKS INTO NEW ENGLAND THIS AFTN/EVE...
STRONG SFC-BASED INSTABILITY...WITH MLCAPE OF 2500-3000
J/KG...SHOULD EXIST WITH SFC HEATING OVER NRN LWR MI...UPSTATE NY
...AND PARTS OF NRN/WRN NEW ENGLAND BY THIS AFTN. WHILE LARGE SCALE
ASCENT LIKELY WILL BE WEAK /OR PERHAPS SLIGHTLY POSITIVE IN
ASSOCIATION WITH PASSING MINOR DISTURBANCES IN SRN ONT-QUE/...30-35
KT WNWLY DEEP SHEAR WILL EXIST AS MODERATE 700-500 MB FLOW PERSISTS
OVER THE REGION.

LOW-LVL CONVERGENCE ALONG LAKE BOUNDARIES...TERRAIN
CIRCULATIONS...AND SFC HEATING SHOULD PROMOTE SCTD STORM DEVELOPMENT
BY MID AFTN. OTHER STORMS MAY MOVE INTO THE REGION LATER IN THE DAY
FROM CANADA. GIVEN DEGREE OF INSTABILITY AND LIKELIHOOD FOR STORM
MERGERS...SETUP COULD YIELD A FEW STORM CLUSTERS WITH A RISK FOR
LOCALLY DMGG WIND AND PERHAPS MARGINALLY SVR HAIL.
FORWARD-PROPAGATING ACTIVITY MAY OCCUR AND EXTEND A CONDITIONAL RISK
FOR STRONG TO SVR STORMS ESE INTO PARTS OF CNTRL/SRN NEW ENGLAND
THIS EVE.

...N CNTRL HIGH PLNS/BLACK HILLS THIS AFTN/EVE...
ISOLD TO WDLY SCTD STORMS ARE EXPECTED THIS AFTN ALONG SRN END OF
SFC TROUGH EXTENDING SW FROM MN SFC LOW. DEVELOPMENT APPEARS MOST
LIKELY OVER THE HIGHER TERRAIN OF ERN WY...NW NEB...AND WRN
SD...WHERE CIN WILL BE WEAKEST. MODEST WNW MID-LVL FLOW ON THE SRN
EDGE OF WLYS MAY BE SUFFICIENT TO SUPPORT A FEW CELLS WITH SVR
WIND/HAIL GIVEN WELL-MIXED SUB-CLOUD LAYER.

...AR/LA/E TX AND VICINITY THIS AFTN/EVE...
WWD MOVING DISTURBANCE SHOULD MOVE ACROSS THE LWR MS VLY/NW GULF
TODAY. WIND PROFILES INVOF THE FEATURE ARE NOT AS STRONG AS
YESTERDAY...BUT REMAIN FAIRLY UNIDIRECTIONAL IN THE LOW TO
MID-TROPOSPHERE. THOSE WINDS ARE...HOWEVER...CARRYING CLOUD DEBRIS
WWD AHEAD OF THE OVERNIGHT CONVECTIVE SYSTEM THAT FORMED IN
ASSOCIATION WITH THE DISTURBANCE. WHILE THIS COMPLICATES THE
FORECAST...IT APPEARS THAT UPLIFT ALONG THE CONVECTIVE SYSTEM GUST
FRONT...AND/OR DIFFERENTIAL HEATING ALONG THE PERIPHERY OF THE
MCS...SHOULD PROMOTE A NEW ROUND OF SCTD STRONG STORMS DOWNSTREAM
ACROSS PARTS OF AR/LA/E TX....AND PERHAPS W TN/SE MO/W KY. ISOLD WET
MICROBURSTS MAY OCCUR GIVEN HI PWS AND STRONGLY HEATED/WEAKLY CAPPED
ENVIRONMENT AWAY FROM EXISTING STORMS.

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