Severe Thunderstorm Warning 256, NWS Topeka, KS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1147 PM CST FRI DEC 26 2008

.UPDATE...
UPDATED DISCUSSION FOR CONVECTIVE TRENDS.

&&

.DISCUSSION...
LATEST RADAR TRENDS SHOW THE SFC COLD FRONT IS ACTUALLY UNDERCUTTING
THE CONVECTION...WHICH INITIALLY DEVELOPED AHEAD OF THE FRONT. WITH
THIS ACTIVITY REMAINING ELEVATED AND THE FRONT PUSHING
SOUTHEAST...THE TREAT FOR DAMAGING WINDS AND HAIL WILL LIKELY
DECREASE. THOUGH LARGE HAIL MAY STILL BE POSSIBLE. THE GREATER
TORNADO THROUGH WOULD BE WITH ANY DISCRETE THUNDERSTORMS THAT FORM
AHEAD OF THE FRONT OVER EAST CENTRAL KS.

WOLTERS

&&

.AVIATION...
OUTSIDE OF THE THUNDERSTORMS...AM BECOMING A LITTLE MORE PESSIMISTIC
FOR LOW CIGS AND PRECIP. 00Z NAM HAS BACKED OFF ON THE LOW LEVEL
SATURATION BEHIND THE FRONT AND THIS IS SUPPORTED BY OBS UPSTREAM.
WILL MONITOR TS COVERAGE ALONG THE FRONT. OTHERWISE WILL OPT TO GO
VFR THROUGH THE PERIOD. CONFIDENCE IN PRECIP THROUGH THE DAY
SATURDAY IS NOT HIGH ENOUGH TO INCLUDE ATTM MAINLY DUE TO THE MID
LEVEL DRY AIR SEEN ON 00Z TOP RAOB AND 05Z WATER VAPOR NOT SHOWING
MUCH OF A FETCH OF MID LEVEL MOISTURE. THOUGH IF THERE IS SOME LIGHT
PRECIP...IT MAY END UP BEING FZDZ OR FZRA WITH THE SNOW GROWTH
REGION TO DRY FOR ICE CRYSTALS.

WOLTERS

&&

.DISCUSSION.../314 PM CST FRI DEC 26 2008/
THE 19Z WATER VAPOR SATELLITE IMAGERY ALONG WITH THE 12Z UPPER AIR
MAPS SHOWED AN INTENSE UPPER LEVEL TROUGH MOVING ACROSS SOUTHEAST CA
SOUTHERN NV INTO UT AND AZ. A LEAD UPPER LEVEL TROUGH WAS LIFTING
NORTHEAST ACROSS THE NORTHERN PLAINS. 850MB ANALYSIS SHOWED DEEP
GULF MOISTURE EXTENDING NORTHWARD FROM THE GULF INTO CENTRAL OK AND
EASTWARD ACROSS THE AR AND MO BORDER. THE DEEPER MOISTURE MAY HAVE
MOVED NORTHEAST ACROSS SOUTHEAST KS THIS AFTERNOON.

THE 20Z SURFACE MAP SHOWED A DEEP 992 MB LEE CYCLONE ACROSS
SOUTHEAST CO WITH AN INVERTED SFC TROUGH EXTENDING NORTHEAST INTO
SOUTHEAST SD. STRONG SOUTHERLY WINDS WERE ADVECTING MOISTURE
NORTHWARD ACROSS OK AND INTO EASTERN KS. HIGHS HAVE WARMED INTO THE
MID AND UPPER 60 ACROSS MOST OF THE CWA. TOPEKA BROKE THE RECORD
HIGH OF 64 DEGREES FOR THIS DATE.

TONIGHT...THE 5H TROUGH ACROSS THE 5H CONUS WILL LIFT NORTHEAST INTO
THE CENTRAL AND SOUTHERN HIGH PLAINS. DEEP MOISTURE WILL CONTINUE TO
BE ADVECTED NORTHEAST ACROSS CENTRAL TX...EASTERN OK AND ACROSS
SOUTHEAST AND EASTERN KS. BY 00Z THE WESTERN EDGE OF THE DEEPER
MOISTURE WILL BE ALONG AND SOUTHEAST OF THE KS TURNPIKE BY 00Z. THE
18Z RUN OF THE NAM SHOWS CONVECTION BREAKING OUT SOUTHEAST OF THE
TURNPIKE AFTER 00Z. IF THUNDERSTORMS DO DEVELOP ACROSS THE SOUTHEAST
COUNTIES THIS EVENING THE ENVIRONMENT MAY BE FAVORABLE FOR SOME OF
THE SFC BASED STORMS TO BECOME SEVERE GIVEN MLCAPE VALUES IN THE
500-1000 J/KG RANGE...ALONG WITH 60 KTS OF 0-6KM SHEAR AND 0-3KM SRH
OF 200-250 J/KG. THE PRIMARY THREAT FROM ANY SEVERE THUNDERSTORM
WOULD BE LARGE HAIL AND DAMAGING WINDS.

ANOTHER CONCERN WOULD BE IF A LINE OF STRONGER CONVECTION DEVELOPS
ACROSS THE SOUTHEAST COUNTIES OF THE CWA EARLY THIS EVENING... IT
COULD LIMIT THE THE DEEPER MOISTURE AHEAD OF THE SFC COLD FRONT
MOVING ACROSS THE CWA LATER TONIGHT. HOWEVER...IF STORMS REMAIN
ISOLATED TO SCATTERED...THE DEEPER MOISTURE WILL BE IN PLACE ACROSS
MOST OF EAST CENTRAL AND NORTHEAST KS FOR SCATTERED THUNDERSTORMS TO
DEVELOP AHEAD OF THE SURFACE COLD FRONT LATE THIS EVENING AND
THROUGH THE EARLY MORNING HOURS. ONCE AGAIN THE ENVIRONMENT WILL BE
FAVORABLE FOR SOME OF THESE THUNDERSTORMS TO BE SEVERE WITH QUARTER
SIZE HAIL AND DAMAGING OUTFLOW WINDS. THE SCATTERED THUNDERSTORMS
MAY CONGEAL INTO A SQUALL LINE FROM I-35 SOUTH.

SATURDAY...THE UPPER TROUGH ACROSS THE HIGH PLAINS WILL MOVE EAST
ACROSS THE CENTRAL AND SOUTHERN PLAINS. THE COLD FRONT WILL MOVE
SOUTHEAST OF THE CWA. HIGHS WILL ONLY REACH THE LOWER TO MID 30S
ACROSS MOST OF THE AREA. HIGHS ACROSS THE SOUTHEAST COUNTIES MAY
FALL THROUGH THE DAY DUE TO THE LOW-LEVEL CAA BEHIND THE FRONT.

LIFT AHEAD OF THE 5H TROUGH WILL CAUSE SOME LIGHT SNOW OR RAIN MIXED
WITH SNOW TO DEVELOP DURING THE LATE MORNING AND AFTERNOON HOURS.
TEMPERATURES SHOULD COOL ENOUGH WITHIN THE VERTICAL COLUMN FOR LIGHT
SNOW DURING THE AFTERNOON HOURS. NO ACCUMULATIONS ARE EXPECTED.

GARGAN

UPPR LVL TROF AXIS WILL BE SWINGING THRU THE FA ON SAT NIGHT.
DESPITE STG Q-G FORCING FOR ASCENT IN THE H5 TO H3 LAYER...IT
APPEARS OVERALL VERTICAL MOTION WL BE LIMITED DUE TO A FAIRLY STABLE
ATMOSPHERE AND LIMITED MOISTURE. THUS WL MAINTAIN PREVIOUS DRY
FORECAST...BUT NAM/EC CONT TO WANT TO PAINT LIGHT QPF IN THIS Q-G
BULLSEYE ON SAT EVNG. OTHERWISE...AIR BEHIND SYSTEM CONTS TO LOOK TO
BE OF PACIFIC ORIGIN AND WAA WL ALREADY GET STARTED BY SUN AFTN.
THIS WL LEAD TO ABOVE NORMAL TEMPERATURES GENERALLY THROUGH OUT THE
EXTENDED FORECAST. THE WARMEST DAY ATTM APPEARS TO BE ON MON WHERE
HIGHS WERE INCREASE INTO THE 50S. ZONAL FLOW OVERHEAD COMBINED WITH
DECENT MIXING AND H85 TMPS ARND +10 C SHLD YIELD A WARM DAY UNDER
MOSTLY SUNNY SKIES.

NEXT CLIPPER IN THE ZONAL FLOW WL RACE ACRS THE NRN PLAINS ON TUES
SENDING A WK AND DRY CDFNT THRU THE AREA AREA. TMPS WL BE KNOCKED
DOWN BACK INTO THE 40S FOR HIGHS FOR TUES/WED. NEXT CLIPPER IN
THIS FORECAST PERIOD WL START TO DROP INTO THE NRN PLAINS ON THUR.
00Z/26 DEC EC REALLY AMPLIFIED THIS SHRTWV AS IT CROSSED THE
CENTER OF THE CONUS...BUT THIS SEEMED TO BE AN OUTLIER AND WAS
DISCOUNTED WITH A MORE FLAT ZONAL FLOW PREFERRED. DID GO A LITTLE
COOLER FOR TMPS ON THURS AND FRI /CLOSER TO CLIMO/ GIVEN THE
UNCERTAINLY OF THE UPPR LVL PATTERN AT THIS RANGE...BUT CONT WITH
A DRY A DRY FORECAST GIVEN LITTLE MOISTURE RETURN EXPECTED AND
GENERALLY WEAK SYSTEMS.

BOUSTEAD

&&

.TOP WATCHES/WARNINGS/ADVISORIES...NONE.

&&

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