Issued by NWS Northern Indiana
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000 FXUS63 KIWX 210907 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 407 AM EST SAT NOV 21 2009 .SHORT TERM... ...TODAY THROUGH SUNDAY NIGHT... HIGH PRESSURE WAS ACROSS MOST OF AREA EARLY THIS MORNING WHILE AN UPPER LEVEL TROUGH WAS MOVING THROUGH. LITTLE SURFACE REFLECTION FROM THE TROUGH BUT CLOUDS WERE HANGING IN ACROSS THE FAR NORTH AND NORTHEAST AHEAD OF THIS FEATURE. MEANWHILE...AREA OF STRATOCUMULUS CLOUDS THAT FORMED LAST NIGHT IN IL AND PERSISTED THROUGH THE DAY HAVE DRIFTED INTO OUR SOUTHWEST COUNTIES. SATELLITE FOG PRODUCT SHOWS THIS AREA SLOWLY EXPANDING AND DRIFTING EAST. FORECAST CHALLENGES CONTINUE TO BE CLOUD COVER...TEMPS AND FOG POSSIBILITY IN THE SHORT TERM PERIOD. WITH WEAK HIGH PRESSURE AND SUBSIDENCE TODAY EXPECT A GRADUAL DECREASE IN OVERALL CLOUDINESS THROUGH THE DAY. CLOUDS ACROSS NORTH AND NORTHEAST SHOULD GRADUALLY DISSIPATE/EXIT OUR AREA BEHIND THE DEPARTING TROUGH THIS AFTERNOON. A LITTLE CONCERNED WITH THE CLOUDS IN THE SOUTHWEST THOUGH AS THEY PERSISTED YESTERDAY AND DID NOT MIX OUT. IT IS POSSIBLE A SIMILAR SITUATION COULD OCCUR AGAIN TODAY. WILL BE OPTIMISTIC WITH A GRADUAL ERODING OF THESE CLOUDS. TEMPERATURES SHOULD BE VERY SIMILAR TO FRIDAY READINGS WITH SIMILAR AIRMASS. DRYING CONTINUES TONIGHT WITH CONTINUED SUBSIDENCE AS MID LEVEL RIDGE NOSES INTO THE AREA. SHOULD SEE MOSTLY CLEAR SKIES AND LIGHT WINDS EARLY WHICH SHOULD SET THE STAGE FOR FOG FORMATION LATE. SETUP LOOKS A LITTLE BETTER THAN THIS MORNING AS RIDGE WILL BE BUILDING IN AND DENSE FOG ALREADY FORMING TO OUR WEST NEAR THIS RIDGING THIS MORNING. FOG MAY TAKE SOME TIME TO BURN OFF SUNDAY MORNING BUT ONCE IT DOES SHOULD BE ANOTHER NICE LATE NOVEMBER DAY WITH HIGHS INTO THE 50S. CONTINUED TO BE A LITTLE CONSERVATIVE WITH POSSIBLE FOG AND STRATUS IN THE MORNING HOURS INHIBITING TEMPERATURE RISE. FEEL FOG COULD FORM YET AGAIN SUNDAY NIGHT AS HIGH SLIDES EAST BUT THERE MAY BE ENOUGH GRADIENT WIND TO PRECLUDE WIDESPREAD FOG. WILL LIKELY HOLD OFF ON ANY MENTION IN THIS PERIOD. && .LONG TERM /MONDAY THROUGH FRIDAY/... MSTR WILL BE WORKING NORTH AT THE START OF THE PERIOD...BUT RH PROFILES SUGGEST SKIES SHOULD STILL GENERALLY BE PARTLY TO MOSTLY SUNNY WITH SOME HIGH CLOUDS. THIS WILL RESULT IN HIGHS LIKELY BEING A FEW DEGREES WARMER THAN PREVIOUSLY THOUGHT SO HAVE BROUGHT UP A BIT BUT HOLDING SHY OF ENSEMBLE AND MET GUIDANCE IN THE MID 50S...WHICH IS STILL ENTIRELY POSSIBLE WITH SLOWER SOLUTIONS FOR THE SYSTEM TO THE WEST. A BIT OF AGREEMENT ON TIMING OF THE INITIAL LOW APPROACHING THE AREA IS ATTEMPTING TO OCCUR. AT THIS POINT...INCREASING CHANCES THAT MONDAY NIGHT AND MAYBE EVEN THE FIRST PART OF TUESDAY MAY END UP DRY. ENOUGH CONFIDENCE IN TRENDS TO REMOVE POPS MON EVE BUT LEAVE UNTOUCHED LATE MON NGT THROUGH MUCH OF THE REMAINDER OF THE PERIOD. MORE THAN LIKELY POPS WILL BE REMOVED ENTIRELY FOR REMAINDER OF MONDAY NIGHT IN FUTURE FORECASTS. WHERE THE CHALLENGES REMAIN IS HOW MUCH COLD AIR ARRIVES AND HOW LONG IT STICKS AROUND. 00Z OPER GFS CONTINUES TO BRING SHOT OF -3 TO -5 C 850 MB TEMPS IN BY WEDS BUT HAS NOW BACKED OFF ON THE MUCH COLDER SCENARIO WITH NEXT PUSH OF COLDEST AIR...STILL ONLY AS LOW AS -6 C...PASSING BY TO THE SW. THIS WOULD RESULT IN THE POTENTIAL FOR RAIN OR SNOW MIXED. 00Z ECMWF PAINTS A DIFFERENT PICTURE WITH THE LOW MOVING TO THE NW SLOWER THAN THE GFS AND THE COLDEST AIR NOT ARRIVING TILL MAINLY THURSDAY. GFS ENSEMBLE SEEMS TO BE MIDDLE OF THE ROAD WITH PROGRESS OF SYSTEM WITH MOST FAVORABLE TIME FRAME STILL IN THE WEDS/WEDS NGT PERIOD FOLLOWED BY A PUSH OF COOLER AIR. WITH SO MANY QUESTIONS IN TERMS OF THERMAL FIELDS AND TIMING...WILL LEAVE TEMPS AND PRECIP TYPES ALONE THROUGH THE REMAINDER OF THE PERIOD WITH ANY CHANGES MADE NOW LIKELY HAVING TO BE MODIFIED ONCE AGAIN...POTENTIAL FLIP FLOPPING. IF MODELS ARE TO BE BELIEVED AFTER THIS SYSTEM MOVES BY...A QUICK MODERATION COULD OCCUR WITH 00Z ECMWF SHOWING SURGE OF WELL ABOVE ZERO 850 MB TEMPS FOR THE HOLIDAY WEEKEND AND GFS NOT TOO FAR OFF. && .AVIATION... CONTINUED CHALLENGES WITH FOG FORECASTS OVERNIGHT AS PATCH OF 3-4KFT CLOUDS ARE DRIFTING ACROSS THE AREA. UPPER SHORT WAVE NEARING KSBN AT ISSUANCE TIME AND WILL TRAVERSE THE AREA OVERNIGHT. LIFT AHEAD OF THIS FEATURE ENOUGH TO GENERATE SMALL AREA OF CLOUDS IN ADDITION TO CLOUDS FROM TODAY ACROSS IL THAT HAVE DRIFTED EAST AND REFUSE TO DISSIPATE. THESE VFR CIGS ABOUT TO MOVE INTO KSBN AND WILL SLOWLY WORK TOWARD KFWA NEXT SEVERAL HOURS. WITH THESE CLOUDS DO NOT EXPECTED IFR VIS DUE TO FOG BUT MVFR STILL POSSIBLE AND STAYED THE COURSE WITH THOSE FOR NOW. IF CLOUDS BEGIN TO DISSIPATE IN WAKE OF SHORT WAVE PASSAGE...COULD SEE VIS DROP LATE. WILL MONITOR FOR THESE TRENDS. OTHERWISE EXPECT WEAK MIXING TO LEAVE BEHIND SCT CLOUDS ON SATURDAY WITH LIGHT WINDS. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SHORT TERM...LASHLEY LONG TERM...FISHER AVIATION...LASHLEY
