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000 FXUS63 KEAX 242043 AFDEAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO 243 PM CST TUE NOV 24 2009 .DISCUSSION... CONCERNS IN THE SHORT TERM PORTIONS OF THE FCST REMAIN ON TEMPS THROUGH THE THANKSGIVING HOLIDAY. THIS AFTN...WV IMAGERY INDICATES A MATURE UPR LOW NOW BEGINNING TO ACCELERATE NE ACROSS IA/IL...WITH ASSOCIATED SFC LOW NOW CENTERED OVER NEWTON IA. LOW-LVL MOISTURE CONTINUES TO ROTATE AROUND THIS UPR LOW...HOWEVER MID-LVL AND UPR LEVEL MOISTURE IS BEING WRAPPED INTO THIS SYSTEM LIMITING ADDITIONAL PRECIP DEVELOPMENT TO DRIZZLE ACROSS THE NORTHERN ZONES. AS EXPECTED...TEMPS HAVE REMAIN SITUATED IN THE LOWER TO MIDDLE 40S IN MUCH OF THE AREA...WITH A SLIGHT WESTERN DOWNSLOPING EFFECT ALONG WITH CLEAR SKIES BUMPING TEMPS IN THE SW CWA INTO THE LOW 50S. FOR TONIGHT...THIS UPR LVL SYSTEM WILL CONTINUE TO RAPIDLY SURGE NE AS NEXT CLIPPER SYSTEM IN ALBERTA RACES SE. CPD PLOTS SUGGEST THAT CLOUDS WILL CONTINUE TO LINGER ACROSS THE EASTERN HALF OF THE CWA FOR MUCH OF THE NIGHT...AND THUS HAVE SLOWED THE DIURNAL CURVE DOWN IN THOSE AREAS. FURTHER WEST...WEAK ADVECTION OF DRIER BOUNDARY LAYER AIR FROM THE WESTERN PLAINS ALONG WITH CLEARING SKIES MAY ALLOW TEMPS TO FALL TO NEAR FREEZING BY DAYBREAK WEDNESDAY. FOR WEDNESDAY...ALBERTA TROUGH WILL CONTINUE TO SURGE SE PUSHING A WEAK SURFACE FRONT AND ASSOCIATED BAND OF MOISTURE RAPIDLY THROUGH THE AREA DURING THE MORNING. NW-SE CROSS SECTIONS OF THIS BAND DO SUPPORT MODEST LOW-LVL MOISTURE...ALONG WITH A VERY NARROW AND INTENSE FRONTOGENESIS AXIS BETWEEN 800:650 MB. HOWEVER VV ARE NOT THAT INTENSE AND MOISTURE DOES REMAIN FAIRLY LOW IN THE COLUMN. SO WHILE AN INTENSE PRECIP BAND WOULD NOT BE FAVORED...A QUICK BURST OF SPRINKLES OR FLURRIES MAY BE POSSIBLE. THIS COLD FRONT AND LOW-LVL LIFT WILL FLY THROUGH THE CWA...BRINGING MODEST CAA ALOFT THROUGH THE CWA. I`M EXPECTING TEMPS TO WARM FAIRLY RAPIDLY IN THE MORNING...BUT QUICKLY LEVEL OFF BY THE AFTN ESPECIALLY IN NORTHERN MO. WEDNESDAY NIGHT...THIS UNUSUALLY STRONG AND AMPLIFIED CLIPPER WILL DIVE INTO THE MID MS RIVER VALLEY WEDNESDAY EVE BEFORE PIVOTING THROUGH THE OHIO RIVER VALLEY ON FRIDAY. A FAIRLY WIDESPREAD AREA OF MOISTURE WILL WRAP AROUND THIS UPR LOW INTO THE NORTHEASTERN PORTIONS OF THE CWA WED EVE. NAM AND GFS BUFR SOUNDINGS SUPPORT A 2-4 HOUR PERIOD OF MODEST COLUMN SATURATION...WHICH WOULD SUPPORT AT LEAST SOME TYPE OF CONVECTIVE SNOW/RAIN SHOWER GIVEN H500 TEMPS -32C TO -33C. WILL BUMP UP TO LOW CHC POPS IN THE NE CORNER. SOME OF THE COLDEST READINGS OF THE FALL SO FAR WILL ADVECT SOUTHWARD INTO THE CWA WED NIGHT. CLOUD COVER OVER THE EASTERN CWA WILL KEEP READINGS NEAR 32. HOWEVER WITH A SHARP CLOUD COVER DELINEATION LINE EXPECTED...READINGS IN AREAS OF EASTERN KS AND WESTERN MO SHOULD FALL INTO THE UPR 20S FOR A BRIEF TIME THU MORNING. THANKSGIVING DAY...SOME INDICATIONS ARE APPEARING THAT THE SFC RIDGE AXIS WILL BEGIN TO SLIDE EAST LATE ON THU AS UPR RIDGING WILL BE A LITTLE FASTER TO SET IN. EXPECTING MUCH OF THE DAY TO BE RATHER CHILLY...BUT WITH AMPLE SUNSHINE AND A LIGHT WIND. HAVE NUDGED TEMPS IN THE WESTERN CWA UP A HAIR GIVEN SOME SIGNALS OF WEAK LOWER TROPOSPHERIC WAA ARRIVING LATE IN THE AFTN. HOWEVER...THIS WARMING MAY ARRIVE TOO LATE IN THE DAY TO JUSTIFY A MORE PRONOUNCED UPWARDS BOUNCE IN TEMPS. SOUNDINGS SUPPORT STEADY MIXING TO AROUND 900 MB...WHICH WAS THE PRIMARY METHOD USED FOR THE TEMP FCST. DUX MEDIUM RANGE (FRIDAY THROUGH TUESDAY)... HEMISPHERIC WATER VAPOR IMAGERY SHOWS A MASSIVE STORM IN THE GULF OF ALASKA WITH A HIGHLY AMPLIFIED RIDGE ALONG THE WEST COAST. THE ULTIMATE BREAKDOWN OF THESE HEIGHT ANOMALIES BY A SERIES OF SHORTWAVE TROUGHS TRAVERSING THE NORTHERN PACIFIC WILL BE THE KEY TO UNLOCKING THE MEDIUM RANGE FORECAST. UNFORTUNATELY...WHILE THIS SOUNDS GREAT ON PAPER...EVEN NOTICEABLE SHORT-TERM ERRORS IN PLACEMENT AND INTENSITY OF THE CRITICAL UPSTREAM WAVES HAVE LED TO MAJOR INTER AND INTRAMODEL DIFFERENCES OF SIZABLE SIGNIFICANCE IN THE DAY 4 THRU 7 PERIOD. IN ESSENCE...THE OVERALL LONGWAVE PATTERN UNDERGOES A SLIGHT RETROGRESSION AND MORE AMPLIFICATION OF THE CURRENT 12Z 500MB PATTERN...BUT SUBTLE VARIATIONS IN THE CENTRAL CONUS TROUGH WILL YIELD LARGE DIFFERENCES IN THE SENSIBLE WEATHER FOR OUR REGION. THE PRIMARY DIFFERENCES STEM FROM THE PRIMARY SHORTWAVE WHICH WILL MOVE ONTO THE PAC NW COAST FRIDAY MORNING. SOME SOLUTIONS BREAK THIS WAVE INTO NRN AND SOUTHERN STREAM COMPONENTS...LEADING TO A SLOWER EASTWARD PROGRESSION OF THE MEAN TROUGH AND A DEEPER SOUTHERN STREAM SYSTEM. OTHERS FEATURE A SINGLE PROGRESSIVE NORTHERN STREAM INFLUENCED PHASED SYSTEM WHICH BYPASSES THE AREA BEFORE GULF MOISTURE CAN RETURN. WHILE THERE IS FAIRLY HIGH CONFIDENCE THAT PRECIPITATION WILL FALL ACROSS THE REGION DURING THE SUNDAY TO TUESDAY TIME FRAME...BUT LOW PREDICTIVE SKILL IN TIMING AND DURATION. THE OVERALL FLOW REGIME SHOULD MITIGATE ANY SIGNIFICANT COLD INTRUSIONS AND KEEP PRECIPITATION MAINLY LIQUID...BUT HAVE OPTED TO KEEP THE RAIN/SNOW MIX MENTIONED ALONG WITH BROAD BRUSHED 25-30 PERCENT CHANCES GIVEN THE MARGINAL TEMPERATURES. I DO EXPECT THAT PREDICTIVE SKILL WILL INCREASE DRAMATICALLY AFTER THE 12Z FRIDAY RUNS ONCE DATA SAMPLING CAN IMPROVE AND THE SATELLITE PRESENTATION OF THE SHORTWAVE INTERACTIONS OFFSHORE HAVE BEEN MOSTLY RESOLVED. BOTTOM LINE...THE MEDIUM RANGE FORECAST DOES NOT SHOW STRONG DEVIATION FROM CLIMATOLOGY. BOOKBINDER && .AVIATION... FOR THE 18Z TAFS...UPR LVL SYSTEM NOW BEGINNING TO PICK UP STEAM AS IT LIFTS NORTHEAST. PRECIP CONTINUES TO DIMINISH LATE THIS MORNING AS DRIER AIR IS BEING WRAPPED INTO THE SYSTEM FROM THE SW. FOR THE REMAINDER OF THE AFTN...GRADUAL CIG INCREASING FROM LOW MVFR TO HIGH MVFR CAN BE EXPECTED...WITH VFR CONDITIONS LIKELY BY 00Z. WNW WINDS ARE EXPECTED TO REMAIN RATHER GUSTY THROUGH THE AFTN AND EVE HOURS RELINQUISHING BY THIS EVE AS UPR LOW AND DEVELOPING SFC LOW LIFT AWAY FROM THE AREA. FOR WED...VFR CONDITIONS WILL ONCE AGAIN PREVAIL AHEAD OF THE NEXT FAST MOVING CLIPPER SYSTEM ARRIVING FROM THE NW. THIS SYSTEM WILL PUSH A COLD FRONT THROUGH THE AREA BY MID-MORNING WITH A VERY NARROW BAND OF VFR CIGS LIKELY. WHILE A SPRINKLE OR FLURRY CAN`T BE RULED OUT...MORE LIKELY IMPACT WILL BE A RETURN TO GUSTY NWLY WINDS. DUX && .EAX WATCHES/WARNINGS/ADVISORIES... MO...NONE. KS...NONE. && $$
