SWODY3
SPC AC 170641
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0141 AM CDT SUN OCT 17 2010
VALID 191200Z - 201200Z
...SYNOPSIS...
BASIC UPPER AIR PATTERN THIS PERIOD WILL BE CHARACTERIZED BY BROAD
CYCLONIC FLOW COVERING AREAS FROM HUDSON BAY CYCLONE SWD TO NEAR
GULF COAST...AND UPSTREAM REX PATTERN OVER WRN NORTH AMERICA
ANCHORED BY CUT-OFF CYCLONE INVOF SRN CA/NRN BAJA OFFSHORE WATERS.
MOST GUIDANCE PACKAGES...INCLUDING OPERATIONAL WRF/SPECTRAL AND
GREAT MAJORITY OF SREF MEMBERS...FCST ASSOCIATED 500 MB LOW TO TURN
EWD AND INLAND OVER NRN BAJA BY LATTER HALF OF PERIOD...AS HEIGHTS
FALL TO ITS NW IN ADVANCE OF HIGH-AMPLITUDE NERN PAC TROUGHING.
DESPITE SUCH STG NUMERICAL CONSENSUS...CONCERNS REMAIN REGARDING
PROGS OF THIS PROCESS...GIVEN
1. LARGE DISTANCE FROM CYCLONE TO APPRECIABLE PAC HEIGHT FALLS AND
2. POOR HISTORY OF PROGS VALID AT OR BEYOND DAY-3 FOR TIMING OF
EJECTING CUT-OFF/BAJA LOWS.
MEANWHILE...HEIGHTS ALOFT SHOULD FALL ACROSS MUCH OF OH VALLEY AND
SE AS SERIES OF SHORTWAVES MOVES THROUGH BELT OF CYCLONIC FLOW FROM
UPPER MS VALLEY TO CENTRAL/SRN APPALACHIANS. SFC COLD FRONT SHOULD
MOVE SWD ACROSS SRN APPALACHIANS/TN VALLEY REGIONS...WHILE
DECELERATING AND PERHAPS BECOMING QUASISTATIONARY AMIDST WEAK SFC
FLOW OVER N-CENTRAL/W-CENTRAL TX.
...CENTRAL TX TO MS/AL...
ANTECEDENT RIDGING OVER GULF COAST REGION WILL LEAD TO
WEAK...PARTIALLY MODIFIED RETURN FLOW REGIME THIS
PERIOD...CHARACTERIZED BY SFC DEW POINTS MAINLY IN 50S F...WITH
ISOLATED LOW 60S. EVEN WITH RATHER MODEST LAPSE RATES ALOFT...THIS
MOISTURE COMBINED WITH DIURNAL HEATING SHOULD BE SUFFICIENT FOR
TSTMS FROM CENTRAL TX EWD ACROSS LOWER MS VALLEY...NEAR FRONT. WEAK
LOW-LEVEL SPEEDS WILL LIMIT HODOGRAPH SIZE. LACK OF STRONGER WINDS
IN MIDLEVELS AND AT SFC ALSO WILL LIMIT SHEAR THROUGH THAT
LAYER...DESPITE STG VEERING WITH HEIGHT. BY CONTRAST...STRONG
VENTING FLOW NEAR ANVIL LEVEL -- I.E. 80-90 KT 250 MB SUBTROPICAL
JET CORE PROGGED OVER MUCH OF CENTRAL TX AND LA AT
20/00Z...INDICATES POTENTIAL FOR A FEW ORGANIZED MULTICELLS. ATTM
SVR POTENTIAL APPEARS TOO CONDITIONAL/ISOLATED TO ASSIGN
PROBABILITIES.
...SWRN CONUS...
WIDELY SCATTERED TSTMS FCST AGAIN DAY-3 FROM SRN CA TO CENTRAL/SRN
NV AND PORTIONS NM. MOST AREAS WILL EXPERIENCE WEAKNESSES IN SHEAR
AND/OR LOW-LEVEL THETAE UNSUITABLE FOR ORGANIZED SVR. SMALL BELT OF
FAVORABLE DEEP-LAYER SHEAR MAY DEVELOP OVER PORTIONS S-CENTRAL/SERN
AZ NEAR TIME OF PEAK DIURNAL HEATING...IN PRESENCE OF AT LEAST MRGL
BOUNDARY-LAYER MOISTURE FOR TSTMS. SVR THREAT APPEARS TOO UNCERTAIN
TO ASSIGN UNCONDITIONAL PROBABILITIES...GIVEN CONCERNS ABOUT
EJECTION OF MID-UPPER CYCLONE AND MRGL NATURE OF EXPECTED BUOYANCY.
..EDWARDS.. 10/17/2010
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