000 FXUS63 KIWX 061815 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 215 PM EDT MON OCT 6 2008 .SHORT TERM... TONIGHT THROUGH TUESDAY NIGHT RATHER IMPRESSIVE BAROCLINIC ZONE NOW IN PLACE OVER THE REGION...WITH 50S IN SE MI TO THE LOWER 70S IN WEST CENTRAL IN. QUASI-STATIONARY UPPER LEVEL RIDGE OVER THE MIDWEST HAS STALLED AT THE MOMENT DUE TO LL CAA NOW ONGOING ACROSS THE SOUTHERN GREAT LAKES...INDICATED BY CROSS ISOTHERM FLOW HIGHLIGHTED IN SHORT TERM MESO MODELS. RATHER POTENT SW TROUGH NOW PUSHING ACROSS THE NE CONUS SUPPORTED A RATHER STRONG PUSH OF COLD AIR INTO THE NE CONUS...SOME OF WHICH HAS BEEN INCORPORATED INTO THE WIDESPREAD SE FLOW NOW ONGOING ACROSS THE FA PER TRAVERSING LOW PRESSURE OVER THE WESTERN MIDWEST. TWO OTHER IMPORTANT FEATURES WILL AFFECT THE WEATHER DURING THE PERIOD...A NEARLY CLOSED UPPER LOW OVER KS/OK AND AN ADVANCING UPPER TROUGH OVER THE DAKOTAS. BOTH OF THESE UPPER WAVES WILL PUSH EAST AND PARTIALLY PHASE...SUPPORTING INTENSIFICATION OF THE LL VEERED SOUTHERLY FLOW INTO THE REGION AND EVENTUAL RAIN CHANCES...AS AMPLE MOISTURE IS IN PLACE ACROSS THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY...EVIDENCED BY 60S-70S SFC DEWPOINTS THERE. FORECAST MODEL AND ENSEMBLES ARE IN RATHER GOOD AGREEMENT ON FORECAST DETAILS IN THE SHORT TERM. HAVE TAILORED THE MAJORITY OF THE FORECAST TO THE NAM WITH HELP FROM THE GFS/ECMWF/SREF/AND UKMET IN SORTING TIMING OF PRECIP THROUGH DYNAMICAL PROGS ALOFT. TONIGHT...MID LEVEL HEIGHT RISES WILL CONTINUE AS LL WINDS /H925 PROGS/ VEER ALLOWING WAA TO COMMENCE. THIS WILL SUPPORT A DIMINISH IN CLOUD COVER ACROSS THE REGION WITH PERHAPS A FEW MID AND CIRRUS HANGING ON IN THE NE. HAVE ADJUSTED TEMPS TO GUIDANCE PROGS...WHICH RETAIN WARMER 50S IN THE WEST. TURBULENT MIXING DOWNWARD PER STRONGER FLOW JUST OFF THE SFC COMBINED WITH A TIGHTENING SFC PRESSURE GRADIENT SHOULD HOLD SFC WINDS UP SIMILAR TO LAST NIGHT AND ALLOW TEMPS TO REMAIN MILD. EASTERN AREAS WILL SEE BETTER POTENTIAL FOR COOLER TEMPS WITH WEAKER FLOW PROGGED. TUESDAY...UPPER RIDGE AXIS WILL SHIFT EAST ACROSS THE REGION UNDER WELL MIXED FAST LL FLOW. GIVEN CLOUD PROGS BY CRAS AND MID LEVEL RH PROGS BY THE GFS AND NAM...THE MAJORITY OF THE FA WILL SEE MOSTLY SUNNY SKIES FOR A GOOD PART OF THE DAY. HENCE...THE PROSPECT FOR WARM TEMPS LOOKS GOOD. HAVE OPTED FOR A MIX TO H875 BASED ON BUFFER PROGS...COOLING THE NE A COUPLES DEGREES PER ONGOING WAA. THIS SENDS HIGHS SLIGHTLY ABOVE GUIDANCE. THERE WILL BE AN INCREASE IN MID AND CIRRUS CLOUDS BY AFTERNOON WEST TO EAST WITH THE APPROACH OF THE PLAINS UPPER VORTICIES. Q-VECTOR FIELDS CLEARLY DISPLAY WIDESPREAD LARGE SCALE ASCENT WILL BEGIN TO PUSH INTO THE WESTERN FA BY LATE AFTERNOON AND EXPAND EAST AND INCREASE OVERNIGHT. MEANWHILE...LL MOMENTUM PROGS FAVOR THE DEVELOPMENT OF A RATHER POTENT LL JET WITH UP TO 40 KNOTS VEER FLOW INDICATED AT H925. THIS WILL SUPPORT ROBUST MOISTURE ADV INTO THE REGION...A FEATURE THAT IS HIGHLIGHTED ON 305K ISENTROPIC CHARTS...WHERE 40-50 KNOTS OF CROSS ISOBARIC FLOW IS PRESENT ON THE NAM AND GFS DURING THE OVERNIGHT PERIOD...UNDER AFOREMENTIONED LARGE SCALE ASCENT FROM THE APPROACHING NEARLY PHASED UPPER TROUGHS. HAVE RAISED POP FOR THESE CONCERNS WHICH IS IN LINE WITH MOS TRENDS. HAVE NOT ADDED TIMING DETAIL AT THIS TIME TUESDAY NIGHT...DUE TO CONCERNS ON PRECIP ARRIVAL AND FAVORED REGIONS OF LIFT...PREFERRING A 12 HOUR POP. BEST FORCING AND LIFT LOOK TO FAVOR THE WEST AT THIS TIME. ALSO ADDED THUNDER FOR FORECAST NEGATIVE SHOWALTER INDICES AND BUFFER SOUNDING INDICATIONS OF ELEVATED CAPE. && .LONG TERM... WEDNESDAY THROUGH MONDAY MAIN FOCUS FOR THIS PACKAGE ON THE FIRST 24 HOURS OR SO OF THE LONG TERM WITH THE HANDLING OF THE EJECTING UPPER LOW AND FRONTAL BOUNDARY WHICH WILL BE SLIDING THROUGH. SHOWERS AND POSSIBLY A FEW STORMS WILL LIKELY BE SCATTERED AROUND THE AREA WITH THE MAIN FOCUS APPEARING TO BE IN THE EASTERN AREAS. AS A RESULT OF THIS AND ALSO GIVE A BETTER BLEND TO LATE TUES NGT POPS HAVE INCREASES POPS TO LIKELY IN EAST FOR WEDS AM...BUT WILL LEAVE IN CHC CATEGORY FOR THE AFTERNOON AS BEST LIFT AND DYNAMICS WILL BE PULLING AWAY BUT COULD BE SOME LINGERING PRECIP. ANOTHER WEAK WAVE LOOKS TO MOVE THROUGH WEDS NGT SO WILL MAINTAIN CHC POPS BUT BY THURSDAY THINGS SHOULD BE MOVING OUT. WHILE NOT REAL CONFIDENT ON HOW FAST THE SYSTEM LEAVES ON THURSDAY WILL GO AHEAD AND DROP POPS FOR THURS AFTERNOON. IN TERMS OF TEMPS...TREND OF BEING ABOVE NORMAL THROUGH THE PERIOD APPEAR TO BE ON TRACK YET WITH HIGHS GENERALLY IN THE 70S. IN THE WAKE OF THE ABOVE SYSTEM...MEX GUIDANCE IS SHOWING HIGHS INTO THE UPPER 70S OR CLOSE TO 80...WHICH IS NOT OUT OF THE QUESTION...BUT WILL HOLD WITH A MORE CONSERVATIVE APPROACH FOR NOW. && .AVIATION.../18Z TAFS/ VFR CONDITIONS THROUGH THE PD AS THE UPPER LEVEL RIDGE BUILDS ACROSS THE AREA. LGT SHOWERS ACROSS PORTIONS OF MICHIGAN WILL STAY TO THE NNW OF SITES. WINDS REMAIN ESE...STRONGER GUSTS POSSIBLE THROUGH THE PD. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SHORT TERM...CHAMBERLAIN LONG TERM...FISHER AVIATION...WEISSER ----------------------------------------------------------------------
