DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 201933
SWODY1
SPC AC 201931

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0131 PM CST WED NOV 20 2013

VALID 202000Z - 211200Z

...NO SVR TSTM AREAS FORECAST...

...20Z OUTLOOK UPDATE...
THE LATEST MODEL AND OBSERVATIONAL DATA SUGGEST LITTLE NEED FOR
OUTLOOK AMENDMENT...AND NO CHANGES HAVE BEEN MADE TO THE 1630Z
CATEGORICAL AND PROBABILISTIC OUTLOOK LINES. SEVERAL WATERSPOUTS
HAVE BEEN REPORTED WITH CONVECTION NEAR FLORIDA ATLANTIC COASTAL
AREAS. THIS MAY CONTINUE INTO EARLY EVENING...BUT THE ENVIRONMENT
OVER INLAND AREAS STILL DOES NOT APPEAR LIKELY TO BECOME SUPPORTIVE
OF AN APPRECIABLE RISK FOR TORNADOES.

..KERR.. 11/20/2013

.PREV DISCUSSION... /ISSUED 1011 AM CST WED NOV 20 2013/

...SYNOPSIS...

THE LARGE-SCALE PATTERN WILL UNDERGO AMPLIFICATION DURING THE D1
PERIOD OWING TO THE INTENSIFICATION OF A POSITIVELY TILTED
MULTI-STREAM TROUGH FROM CNTRL CANADA TO OFF THE CA COAST. MORE
SPECIFICALLY...A POLAR BRANCH SHORT-WAVE TROUGH OVER SERN BC/SRN
AB/NWRN MT WILL PROGRESS ENEWD INTO MB WHILE AN INTERMEDIATE-STREAM
SHORT-WAVE TROUGH TRANSLATES FROM THE CNTRL PLAINS THROUGH UPPER
GREAT LAKES. MEANWHILE...A SHORT-WAVE TROUGH WITHIN A
LOWER-LATITUDE BRANCH OF WESTERLIES WILL BECOME INCREASING CUT-OFF
OVER THE GREAT BASIN TO OFF THE CA COAST...WHILE A WEAKER DOWNSTREAM
PERTURBATION MOVES FROM THE SRN ROCKIES INTO THE CNTRL/SRN PLAINS.

IN THE LOW LEVELS...A POLAR FRONT FROM THE UPPER MS VALLEY TO NRN
HIGH PLAINS WILL ADVANCE SWD AND GRADUALLY OVERTAKE A PRE-FRONTAL
TROUGH CURRENTLY LYING ACROSS CNTRL PARTS OF NEB/KS. ANOTHER COLD
FRONT --WEST OF THE CONTINENTAL DIVIDE-- FROM CNTRL ID TO NRN
CA...WILL PROGRESS SWD THROUGH THE GREAT BASIN.

...NWRN TX/OK TONIGHT...

MID-MORNING SURFACE OBSERVATIONS AND 12Z SOUNDINGS SHOW THE PRESENCE
OF A PARTIALLY MODIFIED CP AIR MASS RETURNING NWD THROUGH THE LOWER
RIO GRANDE VALLEY INTO NWRN TX WITH BOUNDARY LAYER DEWPOINTS
COMMONLY IN THE 50S. THIS PROCESS WILL CONTINUE TODAY EAST OF THE
PRE-FRONTAL TROUGH/WEAK FRONT...ALLOWING DEWPOINTS TO CLIMB INTO THE
MID/UPPER 50S INTO WRN/CNTRL PARTS OF OK BY TONIGHT.

INCREASING WAA/ISENTROPIC ASCENT ALONG A NOCTURNALLY STRENGTHENING
LLJ WILL BE AUGMENTED BY DCVA ATTENDANT TO A LOW-AMPLITUDE
PERTURBATION MOVING OUT OF THE SRN ROCKIES TO FOSTER ISOLATED TO
WIDELY SCATTERED ELEVATED TSTMS...MAINLY AFTER 21/03Z.
MODEL-DERIVED FORECAST SOUNDINGS INDICATE THAT THESE STORMS WILL
FORM IN AN ENVIRONMENT CHARACTERIZED BY MUCAPE APPROACHING 1000 J/KG
AND EFFECTIVE BULK SHEAR VALUES OF 40-50 KT WHICH MAY PROMOTE SOME
UPDRAFT ROTATION AND A RISK FOR MARGINALLY SEVERE HAIL.

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