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000 FXUS63 KIWX 250535 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 1235 AM EST WED NOV 25 2009 .AVIATION /06Z TAFS/... BAND OF SHRAS PASSING EAST OF THE TERMINALS ATTM WITH SURFACE COLD FRONT ABOUT TO PROVIDE A WIND SHIFT FROM SOUTHEAST TO SOUTHWEST. BEHIND THE COLD FRONT A VERTICALLY STACKED LOW PRESSURE SYSTEM WILL MOVE INTO THE AREA TODAY...LIKELY MAINTAINING MVFR RESTRICTIONS /DUE MAINLY TO CIGS/ THROUGH THE DAY. AS THIS WAVE DEPARTS THIS EVENING...ANOTHER WILL QUICKLY TAKE IT/S PLACE WITH A RENEWED CHANCE OF SHOWERS. COULD SEE A FEW BREAKS TO VFR DURING THE 7-10Z TIMEFRAME BEFORE DEEPER MOISTURE ASSOCIATED WITH THE LOW ROTATES IN. OTHERWISE... MVFR RESTRICTIONS WILL PREVAIL THROUGH THE PERIOD. CAN/T RULE OUT IFR CIGS WEDNESDAY EVENING /ESP AT SBN/ AS THE SECOND WAVE APPROACHES ALREADY SATURATED LLEVEL AIRMASS...BUT CONFIDENCE NOT YET HIGH ENOUGH TO INCLUDE IN THIS TAF PACKAGE. SOUTHEAST WINDS 10-15KTS WILL SHIFT SOUTHWESTERLY BY 7Z AND THEN INCREASE TO 14G20KTS FOR THE DAYTIME ON WEDNESDAY...SUBSIDING BACK TO 10-15KTS WEDNESDAY EVENING. && .PREV DISCUSSION... /ISSUED 1050 PM EST TUE NOV 24 2009/ UPDATE... HAVE UPDATED GRIDS/PRODUCTS LATE THIS EVENING FOR A QUICKER END TO PRECIP GIVEN EVENING RADAR TRENDS WHICH SHOW BACK EDGE OF MEANINGFUL RAINFALL ALREADY INTO MY WESTERN ZONES...WITH EXTRAPOLATION BRINGING THIS BACK EDGE THROUGH THE REMAINDER OF THE CWA IN BY 9Z. DEEPER MOISTURE ASSOCIATED WITH STACKED LOW WILL ARRIVE AT THE SAME TIME...LIKELY CONTINUING AT LEAST SCT SHRAS...PARTICULARLY OVER NORTHWESTERN AREAS SO WILL NOT COMPLETELY DRY ANYONE OUT OVERNIGHT. OTHER GRIDS IN GOOD SHAPE WITH NO CHANGES MADE. PREV DISCUSSION... /ISSUED 406 PM EST TUE NOV 24 2009/ SHORT TERM... TONIGHT THROUGH WED DEEPENING CYCLONE OVER THE MID MISSISSIPPI VALLEY REGION WILL CONTINUE TO PROGRESS EAST INTO THE FA DURING THE PERIOD...OFFERING RAIN AND POSSIBLY MIXED PRECIPITATION. OCCLUDED TROUGH CONTINUES TO SUPPORT A BAND OF LIGHT TO MODERATE RAINFALL ACROSS PORTIONS OF IA/IL/AND MO...IN A ZONE OF INCREASING LARGE SCALE ASCENT. SFC TEMPS HAVE RESPONDED SOME TO WAA ALOFT WITH MID 50S PUSHING INTO THE FAR SOUTHWEST. EXPECT WEAK WAA TO CONTINUE OVER THE FA INTO THE EVENING ASSOCIATED WITH THE PROGRESSING OCCLUDED FRONT. TONIGHT...FRONTAL RAIN BAND WILL CONTINUE TO PUSH EAST ACROSS THE REGION TONIGHT WITH RAIN EXPECTED OVER THE MAJORITY OF THE FA...ESPECIALLY IN THE NW. HAVE RAISED POPS TO REFLECT WHERE THE BEST COLLOCATION OF LL CONVERGENCE AND UVM FROM LARGE SCALE ASCENT IS EXPECTED. GIVEN GOOD CORRELATION WITH OBSERVATIONS...HAVE USED NAM 12 290K ISENTROPIC PROGS TO ADJUST POP GRIDS THROUGH THE NIGHT PERIOD. GIVEN NEGATIVE SHOWALTER INDICES EXPECTED TONIGHT/12Z SGF SOUNDING HIGHLIGHTING RATHER STEEP MID LEVEL LAPSE RATES AND THE ADVECTION OF THIS ZONE OVER THE FA TONIGHT/AND A STRENGTHENING H9-H8 WIND FIELD...HAVE ADDED SLIGHT CHANCE T MENTION IN THE NW. WED...PRIMARY COLD FRONT WILL PUSH THROUGH THE REGION WITH A PERIOD OF MID LEVEL DRY SLOTTING EXPECTED. HAVE CONTINUED WITH PREVIOUS POP GRIDS...OPTING TO HOLD HIGHEST POPS TO THE NW ZONES...GIVEN PROXIMITY TO MOST INTENSE HEIGHT FALLS. OTHERWISE...EXPECT TEMPS TO HOLD IN THE 40S...TO AROUND 50 IN THE FAR EAST. MAINLY CLOUDY CONDITIONS ARE EXPECTED...WITH A BRIEF PERIOD OF SUN POSSIBLE WITH THE ADV OF THE MID LEVEL DRY SLOT OVER THE AREA. WED NIGHT...SECONDARY VORT MAX NOW PUSHING INTO THE NORTHERN PLAINS WILL DIVE SE INTO THE FA SUPPORTING THE REFLECTION OF ANOTHER SFC WAVE AND SECONDARY COLD FRONT. PRECIP CHANCES WILL BE ASSOCIATED WITH WEAK LIFT ALONG/AHEAD OF THE UPPER WAVE AND LL THERMAL TROUGH IN THIS PERIOD. CONCERNS ON TIMING/LL MOISTURE AND STRENGTH OF FORCING PRECLUDE POP ADJUSTMENT ATTM. BEST PRECIP CHANCES ARE EXPECTED TO RESIDE WITHIN THE CAA COMMA HEAD OF THE UPPER WAVE. DID RETAIN MIX MENTION ALTHOUGH LACK OF DEEP MOISTURE PER BUFR PROGS...WOULD CERTAINLY FAVOR A RAIN/DRIZZLE ENVIRONMENT. LONG TERM... SW TROF DROPPING RAPIDLY SEWD THROUGH THE SK PRAIRIES WILL AMPLIFY CONSIDERABLY AS IT SETTLES INTO THE SRN LAKES THU. CONSENSUS TRACK OF MID LVL CLOSED LOW HAS CHGD LTL W/A TRACK ACRS NRN IN DURING THE DAY AND RATHER POTENT LOOKING DEFORMATION RAINBAND WRAPPING ARND WRN PERIPHERY OF SYS. TEMPTED TO BUMP POPS TO LIKELY BUT ALSO CAUTIOUS OF SLIGHTLY SLWR/DEEPER TREND OF GFS/NAM AND MORE IN LINE W/PREV ECMWF RUNS WHICH WOULD POINT TO THU AFTN/THU EVENING TIMING. THUS W/XPCD PCPN/CLDS DOUBT MUCH OF A DIURNAL PSBL AND WILL KEEP W/UNDERCUT GUIDANCE MAX TEMPS/PREV GRIDS. NAM 2M TEMPS LOOK IDEAL W/UPR 30S NOTED AND WILL LIKELY SWING THIS WAY ONCE TIMING OF DEFORMATION BAND PRECIP SOLIDIFIES FURTHER. FLW ALOFT REMAINS PROGRESSIVE AS NXT POTENT SW COMES ONSHORE OVR THE PAC NW FRI AND WILL DISLODGE LAKES TROUGH EWD INTO NEW ENGLAND. WILL SCALE BACK PRECIP MENTION ON FRI TO MORNING PD AND NE HALF. OTHERWISE SHRT AMPLITUDE RIDGING STILL XPCD SAT AHD OF NXT SYS ALTHOUGH THERMAL RIDGE/MIXING LOOKS STGR THEN IN PRIOR RUNS AND BUMPED MAX TEMPS SLIGHTLY. LOT OF DETAIL DIFFS BEYOND W/ARRIVAL OF NXT SYS SUN/MON AND WILL KEEP W/PRIOR GRIDS IN ORDER TO MAINTAIN CONTINUITY AS MODEL SPREAD REMAINS QUITE LARGE AND NO CONFIDENCE IN CHOOSING ANY PARTICULAR SOLUTION FOR DETAILS. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SHORT TERM...JC LONG TERM...HOLSTEN AVIATION...ARNOTT
