Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 221256
SWODY1
SPC AC 221254

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0754 AM CDT MON SEP 22 2014

VALID 221300Z - 231200Z

...NO SVR TSTM AREAS FORECAST...

...SUMMARY...
THUNDERSTORMS MAY APPROACH OR BRIEFLY REACH SEVERE LEVELS TODAY OVER
PARTS OF THE CENTRAL ROCKIES AND ADJACENT HIGH PLAINS...AS WELL AS
THE GEORGIA AND SOUTH CAROLINA COASTAL PLAIN.

...SYNOPSIS...
SEASONALLY HIGH-AMPLITUDE SYNOPTIC PATTERN CHARACTERIZES
MIDDLE-UPPER LEVELS TODAY.  EMBEDDED WITHIN LARGER-SCALE CYCLONIC
FLOW THAT COVERS MUCH OF ERN NORTH AMERICA...THREE PRIMARY
SHORTWAVE TROUGHS WILL BE EVIDENT TODAY...
1. PERTURBATION OVER SRN QUE AND NORTHERN NEW ENGLAND WILL EJECT
NEWD ACROSS LABRADOR OVERNIGHT AS...
2. UPSTREAM FEATURE NOW OVER FAR NRN ONT AMPLIFIES AND PIVOTS
SEWD/EWD ACROSS NEW ENGLAND.
3. TRAILING VORTICITY/SPEED MAX NOW OVER MID SOUTH MOVES SEWD THEN
DECELERATES OVER GA...BECOMING CLOSED 500-MB LOW BY 12Z.

FARTHER W...MEAN RIDGING OVER HIGH PLAINS AND NWWD ACROSS WRN CANADA
WILL BE PENETRATED BY PERTURBATION NOW DEVOLVING FROM CLOSED CYCLONE
TO OPEN-WAVE TROUGH OVER UT/SRN ID.  TROUGH SHOULD CROSS WY TODAY
AND REACH WRN PARTS OF SD/NEB OVERNIGHT.

AT SFC...11Z ANALYSIS SHOWED COLD FRONT FROM OFFSHORE MID-ATLC
REGION TO ERN NC...NRN GA...CENTRAL LA...AND W-CENTRAL TX.  FRONT IS
FCST TO MOVE SEWD ACROSS SERN STATES THROUGH PERIOD...HANGING UP
SOMEWHAT INVOF WEAK FRONTAL-WAVE LOW THAT WILL DEVELOP TODAY OVER
SERN GA IN ADVANCE OF APCHG MID-UPPER-LEVEL SHORTWAVE TROUGH.  LEE
TROUGHING WILL DEEPEN OVER HIGH PLAINS.

...SRN ATLC COASTAL PLAIN...
WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP THIS AFTN IN
MULTICELLULAR CLUSTERS ALONG AND AHEAD OF SFC COLD FRONT...LIKELY TO
BE MOST CONCENTRATED BETWEEN FRONTAL-WAVE LOW-PRESSURE AREA AND
SC/GA SEA-BREEZE BOUNDARIES.  LATEST SFC ANALYSIS SHOWS POCKET OF
RELATIVELY MINIMIZED SFC DEW POINTS OVER SRN GA AND COASTAL SC THAT
MAY LINGER THROUGH MUCH OF TODAY GIVEN
1. LACK OF STG SFC WINDS TO ADVECT GREATER MOISTURE FROM ELSEWHERE
AND
2. DIABATICALLY DRIVEN VERTICAL MIXING OF BOUNDARY LAYER.

THIS FACTOR WILL LIMIT MLCAPE TO AROUND 1000 J/KG -- LOCALLY HIGHER.
STILL...BUOYANCY/HEATING AND LIFT NEAR AFOREMENTIONED BOUNDARIES
SHOULD BE SUFFICIENT TO SUPPORT TSTM DEVELOPMENT...AMIDST
STRENGTHENING LARGE-SCALE ASCENT THAT PRECEDES APCHG TROUGH.
MEANWHILE...WELL-MIXED SUBCLOUD LAYER SHOULD SUPPORT MAINTENANCE OF
ANY HAIL AND STG GUSTS TO SFC.  LACK OF MORE SUBSTANTIAL LOW-LEVEL
FLOW AND SHEAR SHOULD PRECLUDE WELL-ORGANIZED SVR RISK...ALTHOUGH
STRONG UPPER WINDS WILL AID IN VENTILATING DEEP/PERSISTENT
CONVECTION.

...FRONT RANGE AND ADJACENT HIGH PLAINS...
WIDELY SCATTERED TSTM DEVELOPMENT IS EXPECTED MID-LATE AFTN OVER
FRONT RANGE AND ADJACENT HIGHER PLAINS TERRAIN NEAR LEE TROUGH.
CONVECTION WILL MOVE EWD TO SEWD...OFFERING GUSTS AND HAIL NEAR SVR
LIMITS AND CONDITIONAL/MRGL TORNADO RISK.  THREAT SHOULD WANE SOON
AFTER SUNSET WITH LOSS OF SFC-BASED INSTABILITY.

PATCHY CLOUD COVER WILL SLOW PACE OF DIURNAL/DIABATIC
DESTABILIZATION TODAY.  NONETHELESS...ENOUGH HEATING IS EXPECTED TO
REMOVE MLCINH AND OVERCOME MODEST LAPSE RATES ALOFT...FOR
ESSENTIALLY UNINHIBITED MLCAPE IN 500-1000 J/KG RANGE.  LOW-LEVEL
SHEAR SHOULD INCREASE DURING LATE AFTN INTO 00-02Z TIME
FRAME...ALONG WITH 35-40 KT EFFECTIVE-SHEAR MAGNITUDES...BEFORE
STRENGTHENING/DEEPENING LAYER OF NEAR-SFC STATIC STABILITY TAKES
OVER.  THIS MAY SUPPORT A SUPERCELL OR TWO FOR A SHORT PERIOD.  MAIN
LIMITING FACTORS APPEAR TO BE SPARSE COVERAGE AND LACK OF MORE
ROBUST BUOYANCY.

..EDWARDS/MARSH.. 09/22/2014



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