Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 291255
SWODY1
SPC AC 291253

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0753 AM CDT THU SEP 29 2016

VALID 291300Z - 301200Z

...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS UPPER OH VALLEY TO
CAROLINAS...

...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS SERN AZ/SWRN NM...

...SUMMARY...
AT LEAST ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE IN A SWATH FROM
THE CENTRAL CAROLINAS TO SOUTHEASTERN OHIO...AS WELL AS OVER PARTS
OF SOUTHEASTERN ARIZONA AND EXTREME SOUTHWESTERN NEW MEXICO.

...SYNOPSIS...
HIGHLY AMPLIFIED UPPER-AIR PATTERN WILL PERSIST OVER CONUS THROUGH
PERIOD...FEATURING MEAN TROUGH JUST OFFSHORE PAC COAST...WEAKENING
SYNOPTIC RIDGE OVER GREAT PLAINS STATES...AND PERSISTENT/CLOSED
CYCLONE OVER OH VALLEY AND VICINITY.  ASSOCIATED MID/UPPER-LEVEL LOW
-- CENTERED NEAR SDF ATTM -- IS FCST TO WOBBLE ERRATICALLY OVER
CENTRAL KY THROUGH 12Z BEFORE RETROGRADING NWWD DAY-2.  SEVERAL
SUBTLE VORTICITY LOBES WILL ORBIT THIS CYCLONE...MOSTLY WITHIN 300
NM OF ITS CENTER AND BEHIND SFC FRONT DESCRIBED BELOW.  HOWEVER...
ASSOCIATED CYCLONIC FLOW WILL REMAIN EXTENSIVE...COVERING CONUS FROM
HUDSON VALLEY TO ERN GREAT PLAINS AND GREAT LAKES TO FL.

MEANWHILE...REMNANT UPPER LOW -- NOW MANIFEST AS WEAKENING OPEN-WAVE
TROUGH OVER PORTIONS UT/NV -- WILL EJECT NEWD TO NRN WY AND SRN MT
THROUGH 12Z.  SEPARATE/SRN-STREAM SHORTWAVE TROUGH  OVER CENTRAL/WRN
SONORA APPEARS TO BE A MID/UPPER-LEVEL VORTICITY LOBE ADVECTED AWAY
FROM LOW-LEVEL REMNANTS OF ERN PAC TS ROSLYN.  THIS FEATURE --
POORLY RESOLVED BY SYNOPTIC MODELS -- IS QUITE APPARENT IN MOISTURE-
CHANNEL IMAGERY...AND SHOULD EJECT NNEWD OVER ERN AZ TODAY.

AT SFC...11Z ANALYSIS SHOWED PRIMARY LOW OVER SERN INDIANA/SWRN
OH/NRN KY AREA NEAR CVG...CLOSELY ASSOCIATED WITH MIDDLE/UPPER-LEVEL
CYCLONE.  TROUGH/OCCLUDED FRONT EXTENDED SEWD ACROSS WRN VA...WITH
SECONDARY COLD FRONT OVER FAR WRN NC...NRN GA...CENTRAL/SRN MS...
N-CENTRAL TX..AND NERN NM.  THIS BOUNDARY WILL CATCH UP TODAY TO
ORIGINAL/SYNOPTIC FRONTAL ZONE ANALYZED FROM WEAK LOW OVER CENTRAL
SC...SWWD ACROSS SWRN GA...COASTAL MS/AL...NEAR GLS...TO BIG BEND
REGION OF TX.  QUASISTATIONARY FRONTAL ZONE WAS ANALYZED FROM LOWER
CHESAPEAKE BAY REGION EWD ACROSS ATLC...BUT WAS POORLY DEFINED
FARTHER W TOWARD DEEP-LAYER LOW DUE TO ANTECEDENT CONVECTIVE
STABILIZATION OF BOUNDARY LAYER.

...UPPER OH VALLEY TO CAROLINAS...
WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP THROUGHOUT PERIOD
OVER OUTLOOK AREA...GENERALLY IN ARC-SHAPED BANDS OR CLUSTERS OF
VARIABLE MODE.  SPECIFIC FOCI FOR CONVECTION APPEAR RATHER NEBULOUS
ATTM EXCEPT FOR QUASI-MERIDIONAL SEGMENT OF FRONTAL ZONE ACTING AS
FAIRLY SHARP WRN BOUND TO POTENTIAL.  A FEW SUPERCELLS ARE
POSSIBLE...ALONG WITH MULTICELLS...OFFERING ISOLATED SVR HAIL/WIND
POTENTIAL.  A TORNADO OR TWO CANNOT BE RULED OUT...BUT THIS RISK IS
CONDITIONAL ON FAVORABLE MESOSCALE AND SMALLER PROCESSES THAT ARE
POSSIBLE...YET NOT WELL-RESOLVED IN PROGS.

AIR MASS E AND S OF COMBINED FRONTAL ZONES ACROSS
VA/CAROLINAS...THEN NWWD OVER WV/OH TOWARD DEEP-LAYER
CYCLONE...SHOULD DESTABILIZE IN AT LEAST PATCHY FASHION TODAY AS
COMBINATION OF WAA AND DIABATIC HEATING TAKES PLACE BEHIND EARLIER
CONVECTION.  RESULT SHOULD BE AREAS OF MLCAPE NEAR 2000 J/KG ACROSS
CENTRAL/ERN CAROLINAS WHERE HEATING WILL BE STRONGEST AND PRIOR
CONVECTIVE INFLUENCE LEAST IMPACTFUL.  MAGNITUDE OF BUOYANCY...AS
WELL AS CONTINUITY AND WIDTH OF UNSTABLE SECTOR...WILL DECREASE WITH
NWWD EXTENT TOWARD DEEP-TROPOSPHERIC LOW...WITH POCKETS OF MLCAPE
NEAR 500 J/KG OVER PORTIONS WV/OH.  DEEP SHEAR AND LOW-LEVEL
HODOGRAPH SIZE EACH SHOULD BE MOST SUPPORTIVE OF SUPERCELL POTENTIAL
BENEATH ZONE OF ENH MID/UPPER WINDS ROUGHLY CORRESPONDING TO 2%
TORNADO PROBABILITIES IN THIS OUTLOOK EDITION.  CONVECTIVE MODE AND
LONGEVITY OF ANY DISCRETE SUPERCELL POTENTIAL REMAIN UNCERTAIN ATTM.

...SERN AZ/SWRN NM...
WIDELY SCATTERED TSTMS ARE EXPECTED TO DEVELOP PRIMARILY THIS
AFTN...BOTH ALONG WELL-HEATED HIGHER TERRAIN AND AREAS OF UPSLOPE
FLOW.  ISOLATED DAMAGING GUSTS MAY OCCUR.

RELATIVELY RICH LOW/MIDDLE-LEVEL MOISTURE SHOULD REMAIN IN PLACE
WITH PW IN 1.2-1.5-INCH RANGE.  THIS WILL BE JUXTAPOSED WITH
GRADIENT-FLOW ENHANCEMENT ALOFT RELATED TO SYNOPTIC AND SHORTWAVE
TROUGHS...CONTRIBUTING TO SUFFICIENT CLOUD-LAYER SHEAR FOR SOME
STORM ORGANIZATION.  DEPTH/STRENGTH OF BUOYANCY WILL DEPEND STRONGLY
ON AMOUNT OF SFC HEATING/DESTABILIZATION AVBL BEHIND AFOREMENTIONED
SONORAN PERTURBATION...BEFORE TOO MUCH POST-TROUGH/LARGE-SCALE
DCVA/DRYING IN MID/UPPER LEVELS SETS IN.  FORECAST SOUNDINGS SUGGEST
AROUND 500-1000 J/KG MLCAPE MAY DEVELOP ATOP WELL-MIXED BOUNDARY
LAYER...SUGGESTING STG/ISOLATED SVR GUSTS CANNOT BE RULED OUT.

..EDWARDS/PICCA.. 09/29/2016

$$


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