000 FXUS63 KEAX 170802 AFDEAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO 302 AM CDT FRI OCT 17 2008 .DISCUSSION... IN THE UPCOMING 24 HOUR PERIOD...PRECIP CHANCES AND TEMPERATURES REMAIN THE BIGGEST CONCERN. EARLY THIS MORNING...WV IMAGERY INDICATED WEAK UPR-LVL SHORTWAVE RACING ACROSS NORTHERN NEBRASKA. MODEST ISENTROPIC LIFT AND INCREASING VV AHEAD OF THIS SHORTWAVE HAS INDUCED SCT SHRA/TSRA ACTIVITY STRETCHING FROM SIOUX FALLS ALL THE WAY SW TO AURORA NEBRASKA. THIS ACTIVITY WAS MOVING SLIGHTLY FASTER THAN INDICATED BY SHORT RANGE MODEL GUIDANCE FROM 4KM WRF AND RUC DATA...AND WILL REACH NW MO TOWARDS 12Z. ATTM...03Z/17 SREF HAS BEEN HANDLING THINGS WELL...AND WILL FOLLOW ITS GUIDANCE FOR POPS/WX IN THE VERY SHORT TERM. NEVERTHELESS...THE RAPID FORWARD PROPAGATION OF THIS SYSTEM AND MODEST DRY AIR FROM SFC- 700MB WILL LIMIT OVERALL QPF WITH HEAVIEST QPF FOCUSED IN STRONGEST AREA OF LIFT FURTHER NORTH INTO IA. IN ADDITION...WEAK ELEVATED LAYER OF INSTABILITY WILL LEAD TO THE POSSIBILITY OF AN ISOLATED CLAP OR TWO OF THUNDER...MAINLY BEFORE 15Z. BY 18Z...MUCH OF THE AREA WILL FALL ON WESTERN SIDE/SUBSIDENCE SIDE OF THE UPR SHORTWAVE...THUS HAVE ADJUSTED THE TIMING OF THE GRIDS TO REFLECT A SLIGHTLY FASTER DRY OUT THIS AFTN. THEN THE QUESTIONS ARISE IN REGARDS TO TEMPERATURES TONIGHT. BEHIND UPR TROUGH...SFC HIGH PRESSURE IS EXPECTED TO DROP SOUTHWARD INTO THE LOWER MO RIVER VALLEY OVERNIGHT. GIVEN MODEST CAA AND A LIGHT SFC WIND...NORMALLY WOULD EXPECT FROST TO BE A GOOD BET OVERNIGHT ESPECIALLY IN THE NE CORNER OF THE CWFA. HOWEVER...AM CONCERNED ABOUT TWO ITEMS REGARDING THIS POTENTIAL. FIRST AND FOREMOST WILL BE EXTENT OF STRATO-CU WHICH ADVECT SOUTHWARD BEHIND UPR TROUGH THIS AFTN/EVE. 00Z/17 NAM AND 4KM CRAS IR IMAGERY SUGGESTS CLOUD DECK REMAINING UNTIL 06Z THEN GRADUALLY DISSIPATING FROM NW-SE. SECONDLY...NERLY WINDS WILL TRY TO ADVECT SLIGHTLY DRIER AIR INTO THE REGION...BUT DEW POINTS MAY ONLY FALL INTO THE MID 30S IN NE MO. NEVERTHELESS...IF SKIES ARE ABLE TO CLEAR AS ANTICIPATED AFTER 09Z...THE POTENTIAL DOES EXIST FOR PATCHY FROST AND/OR DEW ACROSS AT LEAST THE EASTERN THIRD OF THE CWA. WILL ADD TO GRIDS/ZONES ATTM...AND LET THE DAY SHIFT REEVALUATE THE NEED FOR ANY ADVISORY PRODUCTS. OTHERWISE VERY FEW CHANGES MADE TO THE ONGOING FORECAST PAST TONIGHT...AS LOCAL AREA WILL FALL UNDER THE INFLUENCED OF UPR-LVL RIDGING THROUGH SUNDAY. AS RETURN FLOW SETS UP ON SATURDAY...DRY CONDITIONS WITH STEADILY INCREASING TEMPERATURES INTO THE LOW 70S CAN BE EXPECTED BY SUNDAY. NEXT FRONT WILL SLIP SOUTHWARD THROUGH THE REGION ON MONDAY...AS UPR-LVL TROUGH RACES INTO THE GREAT LAKES. LITTLE IN THE WAY OF MOISTURE AND LIFT WILL LIKELY PRECLUDE PRECIPITATION WITH THIS FRONT. BEYOND MONDAY...BOTH ECMWF/GFS ARE IN GOOD AGREEMENT IN DROPPING STRONGER TROUGH INTO THE WESTERN PLAINS BY TUESDAY. THIS WILL LIKELY LIFT MONDAYS FRONT BACK NORTH AS A WARM FRONT BRINGING WITH IT A BETTER CHC FOR SHRA ACTIVITY TUE NIGHT. HAVE BUMPED UP POPS ON TUE NIGHT AS WELL AS WEDNESDAY. DUX && .AVIATION... FOR THE 06Z TAFS...A FAST MOVING UPPER LEVEL IMPULSE MOVING THROUGH THE CENTRAL PLAINS WILL GENERATE MAINLY MID LEVEL CLOUDINESS AS IT PASSES THROUGH THE TERMINALS DURING THE MORNING HOURS. THUS WILL CONTINUE WITH VFR CONDITIONS FOR THE ENTIRE FORECAST. TOP-DOWN SATURATION MAY RESULT IN SCATTERED VERY LIGHT SHOWERS OR SPRINKLES NEAR KSTJ WITH A MUCH LESSER THREAT AT KMCI/KMKC. AN ASSOCIATED COLD FRONT WILL DROP SOUTHEAST AND PASS THROUGH WESTERN MO DURING THE EARLY AFTERNOON HOURS. SCATTERED/BROKEN STRATOCU CLOUDS WILL SPILL SOUTHWARD ACROSS ALL 3 TERMINALS DURING THE LATE AFTERNOON AND EVENING HOURS. MJ && .EAX WATCHES/WARNINGS/ADVISORIES... MO...NONE. KS...NONE. $$ ----------------------------------------------------------------------
