Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 251952
SWODY1
SPC AC 251950

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0250 PM CDT MON JUL 25 2016

VALID 252000Z - 261200Z

...THERE IS AN ENH RISK OF SVR TSTMS ACROSS PORTIONS OF CNTRL/ERN
PA...SERN NY...NJ...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE ENH ACROSS
PORTIONS OF THE NORTHEAST AND MID-ATLANTIC...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLGT FROM
PORTIONS OF THE NORTHEAST AND MID-ATLANTIC TO THE LOWER OHIO
VALLEY...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PORTIONS OF THE
CNTRL/NRN GREAT PLAINS AND VICINITY...

...SUMMARY...
SCATTERED SEVERE THUNDERSTORMS PRODUCING DAMAGING WIND GUSTS ARE
ANTICIPATED THROUGH MID-EVENING ACROSS PARTS OF THE NORTHEAST AND
MIDDLE ATLANTIC STATES.  ISOLATED STRONG TO SEVERE STORMS MAY ALSO
BE POSSIBLE LATE THIS AFTERNOON INTO TONIGHT OVER PARTS OF THE
NORTHERN AND CENTRAL HIGH PLAINS AND VICINITY.

...PRIMARY CHANGES TO THE DAY-1 CONVECTIVE OUTLOOK...

/1/ A CATEGORICAL UPGRADE TO ENH HAS BEEN INCLUDED ACROSS PORTIONS
OF CNTRL/ERN PA...SERN NY...AND NJ FOR SEVERE WINDS. MODERATE TO
STRONG INSTABILITY COUPLED WITH 30-50 KT OF MID-LEVEL FLOW WILL
CONTINUE TO SUPPORT THE RISK FOR LONGER-LIVED CONVECTIVE CLUSTERS
WITH DMGG WIND GUSTS SPREADING ACROSS THE ENH AREA THROUGH EARLY/MID
EVENING. AMPLE SFC HEATING AMIDST A VERY MOIST BOUNDARY LAYER -- SFC
DEWPOINTS IN THE LOWER/MIDDLE 70S -- S OF AN OUTFLOW BOUNDARY ACROSS
FAR NRN PA/SERN NY IS SUPPORTING MLCAPE AROUND 1500-3000 J/KG. WITH
NOTABLE INCREASES IN CONVECTION ACROSS N-CNTRL/CNTRL/WRN PA AIDED BY
DCVA CROSSING THE AREA...CONFIDENCE HAS INCREASED IN A GREATER
DMGG-WIND POTENTIAL DOWNSHEAR OF THIS ACTIVITY EWD TOWARD THE
ATLANTIC COAST THROUGH EARLY/MID EVENING.

/2/ THE SLGT AREA HAS BEEN EXTENDED EWD ACROSS PARTS OF SRN NEW
ENGLAND TO ACCOUNT FOR A LEAD CLUSTER OF TSTMS. THIS ACTIVITY IS
FORECAST TO DEVELOP EWD INTO A MODERATELY UNSTABLE ENVIRONMENT
ACROSS PARTS OF CT AND VICINITY. WIDELY SCATTERED DMGG WIND GUSTS
MAY ACCOMPANY THIS ACTIVITY.

/3/ THE SLGT AREA HAS BEEN EXTENDED SWD ACROSS PARTS OF NRN VA...SRN
MD...AND ERN WV/VICINITY WHERE TSTMS WILL POSE THE POTENTIAL TO
PRODUCE WIDELY SCATTERED DMGG WIND GUSTS...AS THE BOUNDARY LAYER HAS
STRONGLY DESTABILIZED AMIDST MODERATE DEEP SHEAR.

/4/  THE 2-PERCENT TORNADO AREA HAS BEEN FOCUSED ALONG THE
AFOREMENTIONED OUTFLOW BOUNDARY ACROSS PARTS OF NERN PA...SERN
NY...AND NRN NJ. LOCALLY BACKED SFC WINDS/ENHANCED VERTICAL
VORTICITY IN PROXIMITY TO THE OUTFLOW BOUNDARY MAY SUPPORT A
BRIEF-TORNADO RISK WITH CONVECTION EVOLVING IN ITS VICINITY.

/5/ THE GREAT PLAINS MRGL AREA HAS BEEN EXTENDED NEWD ACROSS
ADDITIONAL PORTIONS OF ERN ND AND NWRN MN. CONVECTION MAY FORM
ACROSS THESE AREAS IN RESPONSE TO MODEST INCREASES IN LOW-LEVEL WARM
ADVECTION ACCOMPANYING A STRENGTHENING LLJ THIS EVENING. SUFFICIENT
BUOYANCY WILL EXIST AMIDST MODERATE DEEP SHEAR FOR A FEW SUSTAINED
TSTMS CAPABLE OF ISOLATED SVR HAIL/WIND.

..COHEN.. 07/25/2016

.PREV DISCUSSION... /ISSUED 1105 AM CDT MON JUL 25 2016/

...LOWER GREAT LAKES INTO SRN NEW ENGLAND AND THE MIDDLE ATLANTIC
REGION...
SEVERAL BANDS OF STRONG STORMS ARE OCCURRING ACROSS THE WRN PARTS OF
THIS AREA EARLY THIS AFTERNOON.  THE INITIAL ACTIVITY MOVING TOWARD
SERN NY AND EXTREME NERN PA IS MOVING INTO AN AREA OF INCREASING
SURFACE MOISTURE /DEW POINTS RISING INTO THE MID-UPPER 60S/ WHERE
STRONG DIABATIC HEATING IS OCCURRING.  WARM MID-LEVEL TEMPERATURES
AND ASSOCIATED MODEST LAPSE RATES ARE TEMPERING THE MAGNITUDE OF
INSTABILITY BUT SOME DESTABILIZATION IS LIKELY TO OCCUR AS LOW-LEVEL
THETA-E INCREASES...WITH MLCAPE OF 1000-1500 J/KG EXPECTED THIS
AFTERNOON.  THESE STORMS MAY BEGIN INTENSIFYING DURING THE EARLY-MID
AFTERNOON AND WILL NEED TO BE MONITORED FOR  POTENTIAL TO PRODUCE
DAMAGING WIND GUSTS ALONG THE LEADING EDGE.

UPSTREAM QUASI-LINEAR STORMS ACROSS ERN LAKE ERIE ARE IN CLOSER
PROXIMITY TO THE PROGRESSIVE UPPER SHORT WAVE TROUGH AND ASSOCIATED
DYNAMIC FORCING FOR LARGE SCALE ASCENT THAT IS CROSSING THE GREAT
LAKES.  THEY ARE ALSO EMBEDDED WITHIN STRONGER DEEP LAYER WESTERLY
FLOW /VAD PROFILES SHOW 30-40 KT WINDS ABOVE 1-2 KM AGL/ THAT WILL
ADVANCE EWD ACROSS THE REGION TODAY.  THESE STORMS ARE EXPECTED TO
MOVE EWD/ESEWD THIS AFTERNOON INTO A MORE UNSTABLE AIR MASS /MLCAPE
OF 2000-2500 J PER KG/ OVER PA WHERE DEW POINTS ARE IN THE LOWER 70S
AND TEMPERATURES ARE EXPECTED TO WARM INTO THE LOW-MID 90S.
STRONGER STORMS WILL HAVE POTENTIAL TO PRODUCE DAMAGING DOWNBURST
WINDS AS THEY SPREAD EWD/ESEWD ACROSS PARTS OF THE MIDDLE ATLANTIC
REGION.

ADDITIONAL STRONG/SEVERE CONVECTION IS EXPECTED TO DEVELOP FARTHER
SOUTH ACROSS PA TOWARD NRN WV AND MD/NRN VA AS THE CAP WEAKENS THIS
AFTERNOON...WITH DAMAGING WIND POTENTIAL ASSOCIATED WITH STRONGER
STORMS.  THE OVERALL SEVERE THREAT WILL PERSIST THROUGH THE EVENING
HOURS BEFORE SLOWLY DIMINISHING AFTER SUNSET.

...NRN AND CENTRAL HIGH PLAINS AREA...
RESIDUAL MOISTURE IS EVIDENT OVER THE PLAINS WITH SURFACE DEW POINTS
NEAR 60F OVER THE HIGH PLAINS IN THE WAKE OF THE AFOREMENTIONED
GREAT LAKES SYSTEM.  STEEP LAPSE RATES OVER THE AREA AND STRONG
DIABATIC HEATING THIS AFTERNOON WILL CONTRIBUTE TO AN AXIS OF
STRONGER INSTABILITY NEAR THE N/S LEE TROUGH WHERE MLCAPE OF
1000-2000 J/KG IS EXPECTED.  WIND PROFILES WILL EXHIBIT VEERING WITH
HEIGHT...AND DESPITE MODEST WESTERLY FLOW IN THE MIDDLE LEVELS
/20-25 KT AT 500 MB/...SUFFICIENT VERTICAL SHEAR WILL PROMOTE
ORGANIZED PRIMARILY MULTI-CELL CONVECTIVE STRUCTURES FOR ANY STORMS
THAT CAN DEVELOP.  GENERALLY WEAK FORCING FOR LARGE SCALE ASCENT IS
EXPECTED TO LIMIT OVERALL STORM COVERAGE BUT STEEP LAPSE RATES/DRY
SUB-CLOUD LAYER WILL PROMOTE STRONG WIND GUSTS AND POSSIBLE HAIL
WITH ANY PERSISTENT STORMS THAT DEVELOP.

OTHER STRONG NOCTURNAL STORMS MAY DEVELOP TONIGHT ACROSS PARTS OF ND
WHERE LOW-LEVEL WARM ADVECTION IS EXPECTED TO INCREASE IN
ASSOCIATION WITH A STRENGTHENING LOW-LEVEL JET OVER THE NRN PLAINS.

$$



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