FXUS63 KTOP 061733
AFDTOP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1233 PM CDT MON OCT 6 2008
.UPDATE...
UPDATED FOR 18Z AVIATION DISCUSSION...
&&
AVIATION...
ANTICIPATE RAIN AT TAF SITES AT THE BEGINNING OF THE 18Z FORECAST
PERIOD. ACTIVITY APPROACHING TOP/FOE HAS UNDERGONE A SLOW
STRENGTHENING TREND AND MAY BE ACCOMPANIED BY LIGHTING.
THEREAFTER...MAJORITY OF PRECIPITATION SHOULD BE THUNDERSTORM-FREE
DURING THE EVENING/OVERNIGHT. HAVE RETAINED LOW-END VFR
VISIBILITIES THROUGH THE PERIOD ALTHOUGH HEAVIER ACTIVITY WILL
UNDOUBTEDLY BRING SHORT PERIODS OF IFR-MVFR VIS. MVFR CEILINGS
WILL BECOME MORE COMMON AS THE AFTERNOON/EVENING PROGRESSES.
FRONTAL BOUNDARY WILL PASS THROUGH TAF SITES AROUND SUNRISE
TOMORROW MORNING WITH A NORTHERLY WIND SHIFT AND IMPROVING WEATHER
CONDITIONS. BLAIR
PREV DISCUSSION... /ISSUED 432 AM CDT MON OCT 6 2008/
DISCUSSION...
PRIMARY FORECAST CONCERNS ARE PRECIPITATION CHANCES AND AMOUNTS
THROUGH THE FIRST 24 HRS OF THE FORECAST PACKAGE.
00Z UPPER AIR ANALYSIS INDICATED NEGATIVELY TILTED TROUGH AXIS
EXTENDING FROM THE TX HIGH PLAINS NORTHWEST INTO WESTERN CANADA.
60 DM HEIGHT FALLS WERE ANALYZED NEAR THE TX AND OK PANHANDLES
JUST AHEAD OF THE TROUGH AXIS. AT THE H850 LEVEL A TONGUE OF
DEEPER MOISTURE WAS ANALYZED EXTENDING FROM THE GULF COAST
NORTHWEST INTO THE UPPER MO RIVER BASIN. AT KTOP THE H850 DEW
POINT HAD INCREASED FROM 2 DEG C ON 05/12Z TO 10 DEG C ON 06/00Z
INDICATING THAT PERSISTENT STRONG SOUTHERLY FLOW OVER THE LAST
12-24 HRS HAS BROUGHT A RETURN OF LOW LEVEL MOISTURE TO THE
REGION.
TODAY...AT FORECAST TIME RAIN SHOWER ACTIVITY WAS WIDESPREAD
THROUGH WESTERN OK AND CENTRAL KS AS DEFORMATION ZONE ASSOCIATED
WITH LARGE UPPER TROUGH TO THE WEST WAS AIDING IN THE DEVELOPMENT
OF PRECIPITATION OVER THIS REGION. ALSO AIDING DEVELOPMENT OF
PRECIPITATION WAS LOW LEVEL JET OF APPROXIMATELY 45-50 KTS BASED
ON H850 VWP AT 08Z PROVIDING AN AXIS OF MOISTURE CONVERGENCE OVER
CENTRAL NE AND KS. BASED ON HEIGHT FALLS OVER THE OK AND TX
PANHANDLES NORTHEAST OF THE TROUGH AXIS AT 06/00Z...EXPECT THAT
THE TROUGH WILL MOVE NORTHEAST TODAY AS MODELS ADVERTISE BRINGING
WIDESPREAD PRECIPITATION INTO THE CWA FROM WEST TO EAST. PLACED
CATEGORICAL POPS IN THE FORECAST IN LINE WITH POSITIVE PRESSURE
ADVECTION ON THE GFS AND NAM 06/00Z DYNAMIC TROPOPAUSE
SURFACE...WHICH SHOULD BE A GOOD INDICATION OF WHEN THE BEST LARGE
SCALE ASCENT WILL ENHANCE PRECIPITATION OVER EASTERN KS TODAY.
AS NEGATIVELY TILTED TROUGH MOVES NORTHEAST TODAY HEIGHT FALLS AND
COOLER AIR ALOFT LOOK TO BRING SUFFICIENT INSTABILITY INTO THE CWA
TO ALLOW FOR SOME EMBEDDED CONVECTIVE ELEMENTS WITHIN THE
WIDESPREAD RAIN SHOWER ACTIVITY TODAY. ANY BREAKS IN THE CLOUD
COVER WOULD ENHANCE THIS INSTABILITY...AND AT FORECAST TIME THIS
LOOKS MOST LIKELY OVER THE EASTERN PORTIONS OF THE CWA WHERE THIN
HIGH CLOUDS AND SCATTERED LOW CLOUDS MAY ALLOW FOR SOME PEEKS OF
AM SUNSHINE. CANNOT COMPLETELY RULE OUT POTENTIAL FOR SOME
THUNDERSTORMS TO BECOME ORGANIZED ENOUGH TO PRODUCE SOME LARGE
HAIL...HOWEVER THERMODYNAMIC PROFILES INDICATE A TALL AND SKINNY
CAPE TYPE PROFILE WHICH IS TYPICALLY MORE SUITED TO PRODUCE HEAVY
RAINFALL RATHER THAN LARGE HAIL OR DAMAGING WINDS. GFS AND NAM
BOTH INDICATE INCREASINGLY FAVORABLE SHEAR PROFILES THIS
AFTERNOON...SO IF A LOW TOPPED SUPERCELL THUNDERSTORM WERE ABLE TO
ORGANIZE...AN ISOLATED LARGE HAILER COULD NOT BE RULED OUT.
OVERALL WOULD EXPECT THAT CONVECTIVE ELEMENTS EMBEDDED WITHIN
WIDESPREAD PRECIPITATION TODAY WOULD PRODUCE HEAVY RAINFALL WHICH
WOULD HAVE TO BE MONITORED FOR LOCALIZED FLOODING. WIDESPREAD
FLOODING CONCERNS ARE NOT ANTICIPATED AS FLASH FLOOD GUIDANCE
VALUES ARE HIGH...AND CWA CREEKS AND STREAMS HAVE AVERAGE OR BELOW
LEVELS INDICATING THE GENERAL AREA CAN TAKE A GOOD SOAKING OVER
THE NEXT 24 HRS WITHOUT NEGATIVE CONSEQUENCES.
TONIGHT...CATEGORICAL POPS CONTINUE AS COLD CORE OF THE UPPER
TROUGH MOVES OVER EASTERN KS AS SYNOPTIC COLD FRONT SWINGS
SOUTHEAST THROUGH THE AREA. CHANCES FOR EMBEDDED THUNDERSTORM
ACTIVITY LOOK TO ONLY RESIDE OVER THE EASTERN PORTIONS OF THE CWA
TONIGHT AS COOL AIR IN THE LOW LEVELS CATCHES UP WITH THE COLD
CORE LOW ALOFT FROM WEST TO EAST. THOUGHTS REGARDING THUNDERSTORM
HAZARDS REMAIN THE SAME AS THIS AFTERNOON...BUT EXPECT
THUNDERSTORM ACTIVITY...IF PRESENT...TO REMAIN EAST OF AN EMPORIA
TO SENECA LINE OVERNIGHT.
TUESDAY...RAIN SHOWER ACTIVITY WILL GRADUALLY DIMINISH FROM WEST
TO EAST DURING THE DAYTIME HOURS AS LARGE SCALE ASCENT HAS LARGELY
MOVED OFF TO THE NORTHEAST AFTER SUNRISE. THE BEST PRECIPITATION
CHANCES TUESDAY SEEM TO BE ASSOCIATED WITH A TROWAL TYPE FEATURE
OF MID LEVEL FRONTOGENETIC FORCING AND MOISTURE WRAPPED UP BEHIND
THE SHORTWAVE TROUGH AND SFC LOW. AS THIS FEATURE IS MESOSCALE IN
NATURE...NOT VERY CONFIDENT IN THE TIMING OF REDEVELOPMENT AND
EVENTUAL EXIT OF RAIN SHOWER ACTIVITY OVER THE CWA...DID CUT BACK
ON POPS OVER NORTH CENTRAL KS QUITE A BIT...BUT OTHERWISE LEFT
PREVIOUS FORECAST THOUGHTS ALONE FOR CONSISTENCY AND UNCERTAINTY.
BY 00Z ON WEDNESDAY...GFS AND NAM HAVE SUBSIDENCE THROUGH ALL
LEVELS OF THE TROPOSPHERE...SO ENDED PRECIPITATION CHANCES AFTER
SUNSET TUESDAY.
WEDNESDAY AND THURSDAY...A RETURN SUNNY SKIES LOOKS IN STORE AS
SUBSIDENCE CONTINUES THROUGH THE CWA ON WEDNESDAY...AND THEN UPPER
LEVEL RIDGING AND LEE TROUGHING BUILD BACK INTO THE PLAINS ON
THURSDAY. HAVE A GRADUAL WARM UP IN THE FORECAST FOR THE 48 HR
PERIOD...BUT OTHERWISE NO CHANGES MADE FROM PREVIOUS FORECAST.
EXTENDED...NO CHANGES MADE AT THIS TIME.
CAVANAUGH
&&
.TOP WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
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