Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 301300
SWODY1
SPC AC 301258

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0758 AM CDT TUE JUN 30 2015

VALID 301300Z - 011200Z

...THERE IS A SLGT RISK OF SVR TSTMS MUCH OF ERN CONUS...

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NRN HIGH PLAINS AND
BLACK HILLS...

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL/SRN AZ...

...THERE IS A MRGL RISK OF SVR TSTMS ELSEWHERE FROM ERN CONUS ACROSS
LOWER MO VALLEY TO NRN PLAINS...

...THERE IS A MRGL RISK OF SVR TSTMS ELSEWHERE OVER CENTRAL/SRN
AZ...

...SUMMARY...
SCATTERED SEVERE STORMS WITH DAMAGING WINDS AND SOME HAIL ARE MOST
PROBABLE ACROSS THE OHIO VALLEY TO THE DEEP SOUTH AND THE
MID-ATLANTIC STATES THIS AFTERNOON INTO EARLY EVENING.  AFTERNOON
THUNDERSTORMS WILL OFFER A DAMAGING-GUST THREAT OVER PARTS OF
CENTRAL AND SOUTHERN ARIZONA.  LARGE HAIL AND SEVERE WINDS ARE
EXPECTED WITH A FEW SEVERE STORMS OVER THE NORTHERN GREAT PLAINS AND
BLACK HILLS IN THE LATE AFTERNOON AND EVENING.

...SYNOPSIS...
POSITIVE PNA PATTERN PERSISTS IN MID/UPPER LEVELS OVER CONUS...AS
CHARACTERIZED BY MEAN ERN TROUGH AND WRN RIDGE.  EMBEDDED WITHIN
THIS BASIC REGIME...TWO PAIRS OF SHORTWAVE FEATURES SHOULD BE MOST
PERTINENT TO DAY-1 SVR POTENTIAL.
1. CLOSELY SPACED PERTURBATIONS ARE EVIDENT IN MOISTURE-CHANNEL
IMAGERY OVER OH AND OVER LM.  LEADING FEATURE WILL EJECT NEWD ACROSS
WRN/NRN NY ROUGHLY ALONG CANADIAN BORDER AND WEAKEN...WHILE LM
TROUGH PIVOTS SEWD THEN EWD TO WRN NY BY 12Z.
2. TROUGH NOW PENETRATING LARGE-SCALE RIDGE POSITION OVER SERN
AB/NWRN MT/SWRN SK AREA WILL TURN SEWD OVER NRN/ERN MT THROUGH AFTN
THEN ACROSS DAKOTAS OVERNIGHT.  SMALLER/WEAKER PERTURBATION
IMMEDIATELY PRECEDING THIS ONE OVER SRN SK LIKEWISE SHOULD TURN
SEWD...REACHING SRN MN AROUND 00Z AND SRN INDIANA BY END OF PERIOD.
THIS PAIR OF FEATURES IS RATHER MESSY IN STRUCTURE...AND
SMALLER-SCALE VORTICITY LOBES MAY BE PRESENT BETWEEN THEM THAT WOULD
REACH THE LOWER-MID MO VALLEY OVERNIGHT BASED ON EXTRAPOLATION.

SEPARATE SHORTWAVE TROUGH -- LIKELY INCLUDING CONVECTIVELY
GENERATED/ENHANCED VORTICITY LOBE -- IS SUPPORTING CONVECTION OVER
PERMIAN BASIN REGION OF W TX ATTM.  HOWEVER...THIS FEATURE SHOULD
PASS SWWD OVER NWRN MEX AND REMAIN TOO FAR S TO EXERT SUBSTANTIAL
INFLUENCE ON AZ AREA.

AT SFC...OLD/FRONTOLYTIC BAROCLINIC ZONE FROM CAROLINAS TO MID SOUTH
HAS BEEN OBSCURED FURTHER IN MANY AREAS BY SUCCEEDING CONVECTIVE
OUTFLOWS.  FARTHER N...WEAK LOWS OVER LM AND LE SHOULD CONSOLIDATE
TODAY AHEAD OF NRN-STREAM SHORTWAVE TROUGHS...RESULTING IN SOMEWHAT
BETTER-DEFINED LOW MOVING NEWD OVER SRN ONT MID-LATE PERIOD.
TRAILING/WEAK COLD FRONT SHOULD REACH SRN INDIANA AND SRN IL BY
12Z...BECOMING STATIONARY/WARM FRONT WWD TO ANOTHER WEAK LOW THAT
SHOULD DEVELOP INVOF SERN WY/NEB PANHANDLE AND MOVE ESEWD ACROSS NRN
KS.  SFC TROUGHING WILL EXTEND FROM CENTRAL PLAINS LOW NNWWD ACROSS
WRN SD AND ERN MT.

EXTENSIVE SWATH OF CENTRAL-ERN CONUS WILL EXPERIENCE AT LEAST
ISOLATED TO WIDELY SCATTERED TSTMS AND MRGL-SLGT CATEGORICAL SVR
POTENTIAL TODAY.  THOUGH THESE AREAS HAVE SOME SPATIAL OVERLAP...WE
WILL TREAT CAUSATIVE REGIMES INDEPENDENTLY BELOW.

...SERN CONUS...
SEVERAL MULTICELLULAR CLUSTERS OF TSTMS ARE ONGOING OVER SRN
APPALACHIANS AND PORTIONS MS/AL/AR.  ISOLATED STG-SVR GUSTS WILL
REMAIN POSSIBLE WITH THIS ACTIVITY FOR ANOTHER FEW HOURS DUE TO
SPORADIC PRODUCTION OF LOCALLY INTENSE/WATER-LOADED DOWNDRAFTS.  REF
SPC MESOSCALE DISCUSSION 1237 FOR ADDITIONAL/NEAR-TERM GUIDANCE.

THESE TSTMS...AND/OR ADDITIONAL DEVELOPMENT ALONG THEIR ASSOCIATED
OUTFLOW/DIFFERENTIAL-HEATING BOUNDARIES...ALONG WITH
SUBSEQUENT/SEPARATE CONVECTION OVER THIS GENERAL REGION...SHOULD
INCREASE IN SVR POTENTIAL FROM MIDDAY THROUGH AFTN. AMBIENT BOUNDARY
LAYER DIABATICALLY DESTABILIZES AMIDST SFC DEW POINTS COMMONLY MID
60S TO LOW 70S F...AMIDST FAVORABLY STEEP DEEP-TROPOSPHERIC LAPSE
RATES.  PRECONVECTIVE AIR MASS BY MID-AFTN ACCORDINGLY SHOULD BE
CHARACTERIZED BY MLCAPE AROUND 3000 J/KG...LOCALLY HIGHER...ATOP
WELL-MIXED SUBCLOUD LAYER.

MULTIPLE CLUSTERS OF SCATTERED TO LOCALLY NUMEROUS TSTMS ARE
EXPECTED IN AGGREGATE OVER THIS REGION BETWEEN NOW AND LATE
EVENING...CONTRIBUTING TO BROAD AREA OF 15% SVR-WIND RISK...WITH
LOCALIZED/DENSER CONCENTRATIONS OF SVR REPORTS POSSIBLE.
HOWEVER...MESO- AND SMALLER-SCALE PROCESSES DRIVING THOSE
CONCENTRATIONS REMAIN TOO UNCERTAINLY PLACED TO ASSIGN CORRIDORS OF
HIGHER UNCONDITIONAL PROBABILITIES ATTM.  ISOLATED LARGE HAIL ALSO
MAY OCCUR.  SVR THREAT SHOULD BECOME MORE DISPERSED AND MRGL THROUGH
TONIGHT.

...OH VALLEY...
COMBINATION OF SFC HEATING AND WEAK LARGE-SCALE ASCENT AHEAD OF
NRN-STREAM PERTURBATIONS WILL DESTABILIZE SUFFICIENTLY MOIST AIR
MASS ACROSS THIS REGION TODAY...AHEAD OF AFOREMENTIONED SFC COLD
FRONT.  THIS SHOULD SUPPORT DEVELOPMENT OF SCATTERED TSTMS FROM ERN
INDIANA TO CENTRAL/SERN IL TODAY...PERHAPS AS EARLY AS LATE MORNING
BUT EXPANDING/INTENSIFYING EWD ACROSS OUTLOOK AREA THROUGH MUCH OF
THIS AFTN.  LARGE HAIL AND DAMAGING GUSTS WILL BE MAIN
CONCERN...FROM MULTICELLULAR CLUSTERS.  TRANSIENT SUPERCELLULAR
CHARACTERISTICS ALSO MAY BE NOTED AMIDST SMALL AREAS OF 30-35-KT
EFFECTIVE-SHEAR MAGNITUDES...THOUGH NEARLY UNIDIRECTIONAL DEEP-LAYER
WIND PROFILES IN MOST AREAS WILL LIMIT TOTAL SHEAR.

...MID-ATLANTIC STATES...
SCATTERED TSTMS IN CLUSTERS AND SMALL BANDS SHOULD DEVELOP TODAY
WITH OCNL DAMAGING GUSTS POSSIBLE...ALONG WITH ISOLATED/MRGL SVR
HAIL.  GRADUALLY TIGHTENING HEIGHT GRADIENT ALOFT WILL SUPPORT 30-40
KT EFFECTIVE-SHEAR MAGNITUDES OVER MUCH OF THIS REGION THIS AFTN IN
SUPPORT OF STORM ORGANIZATION.  HIGHER LOW-LEVEL MOISTURE CONTENT
SHOULD REMAIN S OF WEAK/QUASISTATIONARY FRONT EVIDENT OVER
DELMARVA/ERN VA/CAROLINAS.  RELATIVE MIN IN CONVECTIVE COVERAGE HAS
BEEN INCONSISTENTLY PROGGED BY SEVERAL OPERATIONAL MODELS AND
CONVECTION-ALLOWING GUIDANCE SOMEWHERE BETWEEN ERN PA AND CAROLINAS.
 THIS MAY BE REASONABLE CONSIDERING MRGL LAPSE RATES FCST BETWEEN
NRN AREAS OF COLDER TEMPS ALOFT AND SRN AREAS OF STRONGER
HEATING/CAPE.  HOWEVER...MESOSCALE UNCERTAINTIES REMAIN TOO GREAT TO
CARVE RELATIVE MIN OUT OF EXISTING PROBABILITIES ATTM.

...NRN GREAT PLAINS/BLACK HILLS...
WIDELY SCATTERED TSTMS SHOULD FOR THIS AFTN ACROSS WRN/NRN PARTS OF
THIS REGION...AND PERHAPS HIGHER TERRAIN OF BLACK HILLS AS
WELL...OFFERING SVR HAIL AND SPORADIC DAMAGING GUSTS.  INCREASING
LARGE-SCALE LIFT/DESTABILIZATION ALOFT IS EXPECTED FROM NW-SE ACROSS
THIS REGION TODAY AHEAD OF SHORTWAVE TROUGH...ALONG WITH
STRENGTHENING MID-UPPER WINDS DUE TO APCH OF RELATED SPEED MAX.
HIGH CLOUDS NOW EVIDENT IN IR IMAGERY WILL DELAY/RESTRICT SFC
DIABATIC HEATING W OF ONGOING PRECIP PLUMES OVER NERN MT/DAKOTAS.
HOWEVER...SUFFICIENT INSOLATION SHOULD OCCUR THROUGH CLOUD
BREAKS/THINNESS...IN CONJUNCTION WITH SFC DEW POINTS 50S TO LOW 60S
F...TO PRODUCE NARROW SWATH OF 500-1500 J/KG MLCAPE ATOP WEAK CINH
AND INVERTED-V THERMODYNAMIC PROFILES.

ALTHOUGH HODOGRAPH CURVATURE IS NOT EXPECTED TO BE VERY LARGE GIVEN
GEOMETRY OF LOW-LEVEL FLOW...STG SPEED SHEAR WILL CONTRIBUTE TO
LONG...RATHER STRAIGHT HODOGRAPHS AND AT LEAST SOME SUPERCELL
POTENTIAL WITH ASSOCIATED ENHANCEMENT TO HAIL RISK.  GIVEN
WELL-MIXED SUBCLOUD LAYERS...STG-SVR GUSTS MAY OCCUR AS WELL.

...CNTRL/SRN AZ...
WIDELY SCATTERED TSTMS ARE FCST TO DEVELOP ALONG/NE OF MOGOLLON RIM
THIS AFTN AND GROW IN COVERAGE WHILE SHIFTING WWD TO WSWWD
TOWARD/OVER LOWER DESERTS.  DAMAGING GUSTS WILL BE PRIMARY CONCERN.
MORNING TUS SOUNDING WAS AFFECTED BY EARLIER CONVECTION BUT PHX RAOB
SHOWED DAILY RECORD PW ABOVE 1.5 INCHES...WITH UPPER 60S/LOW 70S SFC
DEW POINTS OVER SOME OF THIS AREA.  WHILE MIXING IS EXPECTED
TODAY...THIS WILL SUPPORT ROBUST INSTABILITY.  CONCERNS ABOUT
SUFFICIENT COVERAGE STILL LINGER...HOWEVER... PRESENCE OF RICH
LOW-LEVEL MOISTURE BENEATH 30-40 KT MID-UPPER-LEVEL ELYS IS UNCOMMON
FOR END OF JUNE AND HEATING SHOULD BE STRONG OVER MUCH OF THIS AREA
BASED ON IR CLOUD TRENDS.  AS SUCH...PROBABILITIES ARE BEING RAISED
OVER PORTIONS/CENTRAL AZ.

...LOWER MO VALLEY...
ELEVATED/LOW-LEVEL WAA WILL STRENGTHEN OVERNIGHT AHEAD OF
SEWD-MOVING/NRN-STREAM PERTURBATIONS.  WITH STEEP MIDLEVEL LAPSE
RATES AND FAVORABLE DEEP SHEAR PROGGED...ISOLATED LARGE HAIL IS
POSSIBLE FROM OVERNIGHT TSTMS STREAKING SEWD ACROSS THIS REGION.

..EDWARDS/ROGERS.. 06/30/2015




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