Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 211727
SWODY2
SPC AC 211727

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 AM CST SUN DEC 21 2014

VALID 221200Z - 231200Z

...THERE IS A MRGL RISK OF SVR TSTMS OVER PARTS OF THE LOWER MS
VALLEY AND GULF COAST STATES...

...SUMMARY...
ISOLATED SEVERE STORMS WILL BE POSSIBLE MONDAY NIGHT INTO EARLY
TUESDAY ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY AND GULF COAST
STATES.

...SYNOPSIS...
ON THE LARGE-SCALE...MODEL CONSENSUS SUGGESTS THAT A BROAD
UPPER-LEVEL TROUGH WILL AMPLIFY OVER THE CNTRL CONUS AS AN INTENSE
MID-LEVEL JET /AOA 100 KT AT 500 MB/ DIGS SEWD TOWARDS THE BASAL
PORTION OF THE TROUGH. AT THE SURFACE...PRIMARY CYCLONE SHOULD
GRADUALLY SHIFT FROM ERN SD TO ERN IA DURING THE PERIOD. ATTENDANT
COLD FRONT SHOULD ARC FROM IL TO S TX BY 12Z/TUE. WARM FRONT WILL
ADVANCE N ACROSS PARTS OF THE CNTRL/ERN GULF COAST STATES AND DEEP
SOUTH.

...GULF COAST AND LOWER MS VALLEY...
SUBSTANTIAL SPREAD EXISTS IN GUIDANCE WITH THE EVOLUTION OF
SHORTWAVE IMPULSES EMBEDDED WITHIN THE BROADER CNTRL CONUS TROUGH.
THIS YIELDS BELOW-AVERAGE CONFIDENCE IN THE AMPLITUDE AND
SPATIOTEMPORAL DETAILS OF THE KINEMATIC AND THERMODYNAMIC
ENVIRONMENT...MITIGATING A SLIGHT RISK ISSUANCE THIS OUTLOOK.
PRIMARY CHANGE THIS OUTLOOK IS TO EXPAND COVERAGE OF LOW SEVERE
PROBABILITIES.

SLY LOW-LEVEL MOISTURE TRANSPORT WILL SUPPORT A BROADENING WARM
SECTOR WITH SURFACE DEW POINTS AOA 60 DEG F BECOMING ESTABLISHED MON
NIGHT FROM LA TO SRN AL. CONSISTENT WITH WPC PREFERRED NON-NCEP
GUIDANCE...ONLY MINOR MID-LEVEL HEIGHT FALLS ARE EXPECTED LATE IN
THE PERIOD AS A LEAD IMPULSE PIVOTS FROM THE LOWER MO TO THE UPPER
MS VALLEY WHILE UPSTREAM VORTICITY MAXIMA REMAIN OVER NM/W TX.
PRIMARY CONVECTIVE DEVELOPMENT SHOULD CONSIST OF ELEVATED PARCELS
DRIVEN BY ISENTROPIC ASCENT N OF THE SURFACE WARM FRONT...BUT NEAR
SURFACE-BASED TSTMS MAY DEVELOP INVOF THE TRIPLE POINT OVER THE
LOWER MS VALLEY. STRONG EFFECTIVE SHEAR AMIDST WEAK BUOYANCY MAY
SUPPORT A RISK FOR MARGINALLY SEVERE HAIL/LOCALLY DAMAGING WIND.

OF GREATER CONCERN IS THE POTENTIAL FOR A TORNADO/WIND RISK
DEVELOPING TOWARDS 12Z/TUE ALONG THE WARM FRONT AND ADJACENT WARM
SECTOR. STRENGTHENING LOW-LEVEL MASS RESPONSE TO THE SRN HIGH PLAINS
PORTION OF THE MID-LEVEL TROUGH APPEARS TO HOLD OFF UNTIL AFTER
12Z/TUE IN NON-NAM GUIDANCE. THE BULK OF SURFACE-BASED TSTM
DEVELOPMENT ALIGNED WITH FAVORABLE LOW-LEVEL HODOGRAPHS FOR ROTATING
UPDRAFTS WILL PROBABLY BE DELAYED UNTIL THE D3 TIME FRAME.

..GRAMS.. 12/21/2014




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