Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 311251
SWODY1
SPC AC 311249

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT TUE MAY 31 2016

VALID 311300Z - 011200Z

...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS UPPER MS VALLEY TO WRN
NM...RIO GRANDE VALLEY OF TX...AND CENTRAL/ERN GULF COAST...

...SUMMARY...
ISOLATED STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED THIS AFTERNOON
INTO EARLY EVENING FROM THE UPPER MISSISSIPPI VALLEY SOUTHWESTWARD
INTO THE SOUTHERN GREAT PLAINS.  A FEW STRONG THUNDERSTORMS ARE
POSSIBLE FROM THE LOWER MISSISSIPPI VALLEY INTO THE GULF COAST
REGION.  DAMAGING WIND GUSTS AND HAIL ARE THE PRIMARY THREATS.

...SYNOPSIS...
UPPER-AIR PATTERN OVER CONUS WILL FEATURE TWO SLOWLY PROGRESSIVE
CYCLONES...
1.  NRN-STREAM VORTEX CURRENTLY CENTERED OVER SWRN ND...AND FCST TO
SHIFT ENEWD TO NWRN MN BY END OF PERIOD...
2.  SRN-STREAM GYRE THAT IS WEAKER BUT WITH COMPARABLE AREA OF
ACCOMPANYING CYCLONIC FLOW AS CYCLONE OVER NRN PLAINS...FCST TO MOVE
SEWD FROM SWRN AZ ACROSS SONORA THROUGH 12Z.
SECONDARY/LOW-AMPLITUDE PERTURBATIONS -- SOME CONVECTIVELY ENHANCED
OR GENERATED...WILL TRAVERSE BELT OF MODEST AND GENTLY CONFLUENT
MID/UPPER-LEVEL FLOW OVER CENTRAL/SRN PLAINS S OF NRN-STREAM
SYSTEM...AND NE OF SRN-STREAM LOW.  LOW/MIDDLE-LEVEL VORTEX
SIGNIFYING REMAINS OF TC BONNIE SHOULD CONTINUE DRIFTING ERRATICALLY
OVER COASTAL CAROLINAS AND ADJACENT WATERS...WITH SLOW...NET NEWD
SHIFT.

AT SFC...OCCLUDED LOW WAS ANALYZED OVER EXTREME N-CENTRAL ND NEAR
TURTLE MOUNTAINS...WITH OCCLUDED FRONT SEWD TO W-CENTRAL/SWRN
MN...AND COLD FRONT ARCHING FROM THERE ACROSS SERN NEB...CENTRAL
KS...AND SERN CO.  THAT FRONT WAS PRECEDED BY AGGREGATE OUTFLOW
BOUNDARY FROM S-CENTRAL MN ACROSS WRN IA TO CENTRAL/SW OK...AND SRN
TX PANHANDLE.  WARM FRONT EXTENDED FROM TRIPLE POINT ESEWD ACROSS
WRN/SERN WI.  COLD FRONT SHOULD MOVE SEWD ACROSS LOWER MO VALLEY
REGION...PORTIONS OK...AND SRN HIGH PLAINS TODAY...PRECEDED BY
OUTFLOW BOUNDARY OVER OK FROM ONGOING CONVECTION.  SFC TROUGH
EXTENDING WSWWD TO WWD FROM REMNANTS OF BONNIE WILL REMAIN
QUASISTATIONARY ACROSS PORTIONS SRN GA...AL...MS AND AR.

...SRN PLAINS...
TSTMS OF HIGHLY VARIABLE COVERAGE ARE EXPECTED TO DEVELOP TODAY AND
OFFER ISOLATED DAMAGING GUSTS AND LARGE HAIL.  ALTHOUGH MODULATED ON
SMALLER SCALES DUE TO EFFECTS OF OUTFLOW AND ANTECEDENT
CONVECTION...GENERALLY SUPPORTIVE MOISTURE WILL PREVAIL IN
PRECONVECTIVE ENVIRONMENT TODAY.  SFC DEW POINTS WILL RANGE FROM
LOW/MID 50S E OF DRYLINE IN ERN NM TO MID/UPPER 60S S OF OK OUTFLOW
BOUNDARY AND 70S OVER MUCH OF S TX.  SATELLITE IMAGERY SHOWS
PATCHWORK DISTRIBUTION OF CLOUD COVER...MOSTLY RELATED TO EARLIER
CONVECTION...WHICH WILL MODULATE SFC HEATING IN SOME AREAS WHILE
GENERATING BOUNDARY-LAYER/DIFFERENTIAL-HEATING SOLENOIDS ALONGSIDE
RELATIVELY SLOW-MOVING OR QUASISTATIONARY CLOUD EDGES.

THESE VARIOUS BOUNDARIES WILL SUPPORT AFTN AND EARLY EVENING TSTM
DEVELOPMENT REGIONALLY...BUT VERY NONUNIFORM IN
DISTRIBUTION...ACROSS THIS BROAD-BRUSHED MRGL OUTLOOK AREA.  EARLY
CONVECTION...IN TURN...WILL SPAWN MORE BOUNDARIES UPON WHICH
ADDITIONAL STORMS SHOULD FORM.  ATTM MESOSCALE UNCERTAINTIES REMAIN
TOO GREAT TO ASSIGN AOA-15% PROBABILITIES WITHIN BROADER MRGL
OUTLOOK...BUT CONCENTRATIONS OF MULTICELL TO MRGL SUPERCELL
STRUCTURES MAY YIELD LOCALLY DENSE CLUSTERING OF SVR REPORTS.

...UPPER MS VALLEY REGION...
AGGREGATE OUTFLOW BOUNDARY SHOULD DRIFT EWD THROUGH EARLY AFTN...
SUPPORTING DEVELOPMENT OF TSTMS AS PROXIMAL MLCINH WEAKENS AMIDST
BOTH WEAK CONVERGENCE AND INSOLATION.  SOME OF THIS CONVECTION MAY
PRODUCE MRGLLY DAMAGING GUSTS...THOUGH WEAK MIDLEVEL LAPSE RATES AND
LACK OF SUBSTANTIAL LOW-LEVEL FLOW/SHEAR SHOULD LIMIT OVERALL
ORGANIZATION.  THREAT WILL DECLINE PRECIPITOUSLY AFTER SUNSET AS
BOUNDARY LAYER STABILIZES DIABATICALLY IN BOTTOM-UP FASHION.

...LOWER MS VALLEY THROUGH GULF COAST...
WIDELY SCATTERED TO SCATTERED TSTMS IN CLUSTERS ARE EXPECTED TO
DEVELOP PRIMARILY FROM MIDDAY THROUGH AFTN...NEAR AND S OF SFC
TROUGH AND INVOF ASSORTED OUTFLOW/SEA-BREEZE BOUNDARIES.  THIS MAY
INCLUDE OUTFLOW/DIFFERENTIAL-HEATING ZONE ULTIMATELY PRODUCED BY
AREA OF PRECIP NOW OVER SRN/ERN AR AND NRN MS.  SFC DEW POINTS
COMMONLY MID 60S TO NEAR 70 F...AND STG DIURNAL HEATING...SHOULD
CONTRIBUTE TO POCKETS OF MLCAPE UP TO ABOUT 1500 J/KG...ATOP
INCREASINGLY WELL-MIXED PRE-DOWNDRAFT BOUNDARY LAYERS WITH TIME THIS
AFTN.  DEEP-LAYER HODOGRAPHS WILL BE QUITE MINUSCULE...AND SUCH WEAK
SHEAR WILL LIMIT OVERALL STORM ORGANIZATION.  LOCALIZED
CONCENTRATIONS OF DAMAGING...NEAR-SVR...WATER-LOADING-AIDED GUSTS
MAY OCCUR FROM PULSE/MULTICELLULAR TSTMS.  SUCH RESULTS WILL BE
QUITE DEPENDENT ON MESOBETA- TO STORM-SCALE PROCESSES YET TO
EVOLVE...OUTSIDE OF AFOREMENTIONED MS/AR BOUNDARY.

..EDWARDS/ROGERS.. 05/31/2016

$$



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