FXUS63 KIWX 230517
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1217 AM EST WED DEC 23 2009

.AVIATION /06Z TAFS/...

SOME VFR CONDITIONS HAVE BEEN OBSERVED AT BOTH TERMINALS RECENTLY
AS LIGHT SNOW GRADUALLY COMES TO AN END AND DRY LLEVEL EASTERLY
FLOW KEEPS THE LLEVEL CLOUDINESS AT BAY FOR NOW.

AT FWA...EXPECT THE DRY LLEVEL EASTERLIES TO WIN OUT THROUGH THE
TAF PERIOD. SOME CIGS NEAR 1KFT ARE IN THE VICINITY ATTM...SO
COULD SEE A PERIOD OF RESTRICTION OVER THE NEXT 2-3 HOURS.
OTHERWISE...EXPECT 5KFT CIGS AND A STIFF 15KT EASTERLY WIND
THROUGH THE PERIOD. CAN/T RULE OUT A STRAY SHSN OVERNIGHT...BUT
ANY IMPACT ON FLIGHT CONDITIONS LOOKS TO BE MINIMAL/SHORT-LIVED.  

AT SBN...LLEVEL MOISTURE TO THE WEST WILL GRADUALLY ENCROACH ON
THIS TERMINAL THROUGH THE PERIOD AND WHILE VFR CONDITIONS HAVE
DEVELOPED HERE...EXPECT A TREND BACK TOWARD MVFR BY DAYBREAK WITH
1.5KFT CIGS LIKELY TO PREVAIL THROUGH WEDNESDAY AND INTO WEDNESDAY
NIGHT. IN ADDITION TO A POSSIBLE EARLY MORNING SHSN...THERE IS ALSO
THE POTENTIAL FOR SOME LIGHT MIXED PRECIP BY MID/LATE AFTERNOON.
BEST GUESS IS FOR ANY PRECIP TO FALL AS SN/IP BUT ANY SLIGHT
AMOUNT OF INCREASED WARMING ALOFT COULD LEAD TO A PERIOD OF ZR.
WILL KEEP AN EYE ON THIS FOR LATER ISSUANCES. WINDS HERE WILL ALSO
BE EASTERLY 10-15KTS THROUGH THE PERIOD.

&&

.PREV DISCUSSION... /ISSUED 1116 PM EST TUE DEC 22 2009/ 

UPDATE...

UPDATE TO GOING FORECAST TO PROLONG SNOW MENTION AND INCREASE POPS
TO CAT OVER NORTHEASTERN AREAS AS SLOWLY WEAKENING AREA OF H85-H7
FGEN CONTINUES TO BE EFFICIENT AT SQUEEZING OUT SOME LIGHT SNOW.
FURTHER SOUTH AND WEST...SOME MORE SHOWERY RETURNS HAVE BEEN NOTED
WITH RUC ANALYSIS AND EVENING RAOBS/TAMDARS SUGGESTING A BAND OF
GOOD MID LEVEL LAPSE RATES SUSTAINING THIS PRECIP GIVEN THE LLEVEL
ISENTROPIC LIFT OF A PRETTY MOIST AIRMASS. EXPECT LESS THAN AN
INCH OF ADDITIONAL SNOW OVER THE NORTHEAST BEFORE PRECIP TAPERS
OFF. FINALLY...WILL WATCH FOR PATCHY ZL OVER SOUTHWESTERN AREAS
GIVEN SOME BREAKS IN THE DEEPER MOISTURE...BUT CURRENT TRENDS
INDICATE NO HEADLINES NEEDED FOR THIS AREA OVERNIGHT.  

HAVE ALSO TRENDED TOWARDS WARMER LAV NUMBERS AS LLEVEL CLOUD COVER
SHOWS NO SIGNS OF GIVING WAY.

UPDATED GRIDS/PRODUCTS OUT.  

PREV DISCUSSION... /ISSUED 736 PM EST TUE DEC 22 2009/ 

UPDATE...
UPDATE ISSUED TO UP POPS THIS EVENING GENERALLY ALONG AND NORTH OF
US 30 IN PERSISTENT AREA OF SNOW. RADAR RETURNS ON THE SOUTHERN
FRINGE OF THE AREA HAVE INCREASED SOMEWHAT WITH VSBYS DROPPING TO
CLOSE TO ONE MILE...INCLUDING HERE AT THE OFFICE. QUICK FEW TENTHS
OF SNOW ACCUMULATED. DRY AIR IS TRYING TO WORK SOUTH BUT STRENGTH
OF LIFT AND AMOUNT OF MSTR SEEMS TO BE WINNING AT THE MOMENT SO
INCREASE WARRANTED. WILL MONITOR TRENDS OVER THE NEXT COUPLE OF
HOURS FOR ADDITIONAL CHANGES.

RADARS TO THE WEST AND SOUTH SHOWING LIGHT RETURNS TRYING TO WORK
TOWARDS SW AREAS BUT NOTHING SHOWING UP ON OBS. SO FOR NOW HAVE
LEFT CHC POPS INTACT IN THESE AREAS. 

PREV DISCUSSION... /ISSUED 401 PM EST TUE DEC 22 2009/

SHORT TERM...

TONIGHT THROUGH WEDNESDAY NIGHT

WEAK SLOW MOVING UPPER LEVEL TROUGH CONTINUES TO SUPPORT LIGHT SNOW 
ACROSS THE FA IN A WAA REGIME ALOFT. WEAK CROSS ISOBARIC ASCENT ON 
ON 290-300K SFC CONTINUES TO OFFER LL LIFT...SUPPORTING THE LIGHT 
SNOW...BEING ENHANCED BY THE DEPARTING WAVE. SUBSIDENCE WILL TAKE 
OVER WITH MID LEVEL DRYING EXPECTED THIS EVENING...AS EVIDENT IN 
UPSTREAM SAT OBS. AMPLE LL SATURATED PROFILES IN THE PRESENCE OF A 
GROWING INVERSION WILL TEND TO HOLD THE LL CLOUD DECK IN PLACE 
ACROSS MOST OF THE SOUTHERN/WESTERN FA...WITH BACKING LL WINDS 
SUPPORTING DRYING ACROSS THE NORTH AS CP SFC HIGH PRESSURE ADVECTS 
ACROSS THE NORTHERN GREAT LAKES. FURTHER UPSTREAM...A POTENT UPPER 
LEVEL TROUGH ENTERING THE HIGH DESERT CONTINUES TO DIG INTO THE THAT 
REGION...AND WILL BEGIN TO EJECT INTO THE SOUTHERN PLAINS ON WED. A 
MORE IMPORTANT AND KEY INGREDIENT TO THE DEVELOPING WINTER STORM IS 
THE ADVANCING UPPER SHORTWAVE OVER THE PAC NW. THIS NEGATIVE HEIGHT 
ANOMALY AND ITS ASSOCIATED LL CAA FIELDS WILL HELP SUPPORT PHASING 
OF THE SOUTHERN STREAM WAVE...ACTING TO SLOW DOWN EASTERN 
PROGRESSION OF THE ENTIRE SYSTEM INCLUDING LL REFLECTED FIELDS...AS 
UPPER LEVEL BACKSIDE MOMENTUM TRANSPORT CONTINUES TO SUPPORT FLOW 
CUTTING TO HIGHER HEIGHTS ALOFT. THIS PROCESS WILL BE CRITICAL TO 
THE WX FORECAST IN THE LATER PERIODS AND BEYOND...EFFECTIVELY 
SHUNTING THE BEST LL MOISTURE TRANSPORT AND LARGE SCALE ASCENT WEST 
OF THE FA THROUGH MUCH OF THE PERIOD. HAVE UTILIZED VARIOUS FORECAST 
MODELS...INCLUDING THE NAM/GFS/AND ECWMF WITH NO PARTICULAR FAVORED 
WEIGHT TO ONE MODEL GIVEN OVERALL GENERAL HEIGHT AND FLOW AGREEMENT. 

TONIGHT...MID LEVEL SUBSIDENT FLOW WILL DOMINANT WITH LINGERING LL 
LIFT/UPGLIDE EXPECTED THROUGH OVER MUCH OF THE WESTERN FA PER A WAA 
REGIME IN THE H8-H7 LAYER...SUPPORTING LIGHT SNOW AND A PATCHY ZL 
THREAT...GIVEN PROGS OF GENERAL SATURATION REMAINING ABOVE -10C. NE 
AREAS MAY SEE PARTIAL CLEARING GIVEN BACKED LOCAL FLOW SUPPORTING 
NEGATIVE THETA-ADV WITH LL NE FLOW EMANATING FROM ADVECTING SFC HIGH 
PRESSURE OVER THE NORTHERN GREAT LAKES. HAVE ADJUSTED LOWS DOWN SOME 
IN THE NE WHERE THE OVERLAP OF DRIER PROFILES/CAA/AND PARTIAL 
CLEARING WILL RESIDE.

WEDNESDAY...LEAD SURGE OF THETA-E ADVECTION PER THE EJECTING 
SOUTHERN STREAM WAVE WILL SUPPORT THE DEVELOPMENT OF A LIGHT PRECIP 
BAND PER REFLECTED ACCENT IN THE H85-H7 LAYER. UTILIZING NAM/GFS 
290K PROGS...A BAND WOULD BE POSSIBLE NEAR THE WESTERN FA TOMORROW 
AFTERNOON INTO WED NIGHT...COINCIDENT WITH A WEAK SHORTWAVE LEAD 
DISTURBANCE. STRONG BAROCLINIC ZONE IN PLACE WILL LIKELY ENHANCE 
HYDROMETER PRODUCTION LENDING TO LIGHT TO MODERATE RETURNS CLOSER 
THE BEST LARGE SCALE ASCENT...WHICH WILL BE WEST OF THE FA. HAVE 
OPTED TO FOR A FLURRY AND ZL MENTION IN THE SW FA THROUGH ALL WED 
GIVEN INCREASING LL MOISTURE COINCIDENT WITH INCREASING LL LIFT. 
LINGERING DRY SUBSIDENT FLOW WILL CONTINUE TO DOMINATE OVER THE 
EASTERN HALF OF THE FA INTO THUR UNTIL MID LEVEL RIDGING SHIFTS EAST 
OF THE REGION. HENCE...HAVE RETAINED HIGHER POP MENTION IN THE 
WESTERN FA...WITH SHARP SW-NE DEGRADATION. PRECIP TYPE BECOMES AN 
ISSUE GIVEN SFC-2KFT EASTERLY FLOW SUPPORTING CONTINUE REINFORCEMENT 
OF LL COLD DRY AIR. GIVEN FORECAST THERMAL FIELDS ALOFT SUPPORTING 
ROBUST WARM NOSE AROUND H925 OF 5 C IN THE WESTERN FA WED 
EVENING...EXPECTING ANY PRECIP TO START AS A SLEET MIX...RAPIDLY 
CHANGING TO A ZR/IP MIX WITH A PERIOD OF ZR POSSIBLE IN THE WEST. 
FEEL AFOREMENTIONED THERMAL NUMBERS ARE REPRESENTATIVE GIVEN WEAK A 
ADIABATIC COOLING REPONSE IN THE PRESENCE OF MINIMAL LL WET BULB 
EFFECTS. QPF PROGS/EXPECTED WEAK LSA NUMBERS/AND CONCERNS ON 
DURATION PRECLUDE ANY HEADLINES/HIGHLIGHTS ATTM...ESPECIALLY GIVEN 
THE POSSIBILITY OF A WESTWARD HEIGHT PATTERN SHIFT GIVEN PRONOUNCED 
WAVE PHASING...AND WILL DEFER ANY TO THE NEXT SHIFT GIVEN THE PERIOD 
AND THE NEED FOR ADDITIONAL OBSERVATIONAL DATA. REGARDLESS...A SHORT 
DURATION OF ZR WOULD CAUSE MAJOR TRAVEL CONCERNS AND THIS THREAT 
SHOULD BE MONITORED.

LONG TERM...
THURSDAY THROUGH TUESDAY...THE MAIN CONCERN THIS PERIOD IS THE 
POTENTIAL FOR A WINTRY MIX LATE THURSDAY THROUGH THURSDAY NIGHT. 
HAVE BLENDED THE NAM 12 KM WRF...GFS AND SREF ENSEMBLE FOR THIS 
PACKAGE. GIVEN THERMAL PROFILES...EXPECT TO SEE A MIX OF MAINLY 
SLEET AND FREEZING RAIN NORTH THURSDAY AFTERNOON...WITH JUST RAIN 
SOUTH. GIVEN RECENT MODEL HANDLING OF THIS TYPE OF SHALLOW COLD AIR 
EVENT WITH OVERRUNNING PRECIPITATION...CONCERN THAT TEMPS WILL STILL 
BE BELOW FREEZING THROUGH THURSDAY AFTERNOON OVER FAR NORTHERN 
INDIANA INTO LOWER MICHIGAN AND FAR NW OHIO. BUFKIT SFC TEMPS OVER 
NORTHERN AREAS 0C TO 1C. ALTHOUGH NOT OVERWHELMING SUPPORT FROM 
THESE MODELS FOR A WIDESPREAD FREEZING RAIN/ICE EVENT...BELIEVE THE 
POTENTIAL FOR ROADS TO BECOME EXTREMELY SLIPPERY BY THURSDAY EVENING 
ESPECIALLY NORTH OF ROUTE 6 WITH SFC TEMPS JUST BELOW FREEZING. 
GIVEN THE POTENTIAL FOR A HUGE HOLIDAY TRAVEL IMPACT...HAVE DECIDED 
AFTER COORDINATING WITH NEIGHBORING OFFICES TO ISSUE A WINTER STORM 
WATCH FOR THIS WINTRY FREEZING RAIN AND SLEET MIX OVER FAR NORTHERN 
INDIANA INTO LOWER MICHIGAN. A LARGE SFC ANTICYCLONE WILL INITIALLY 
KEEP A COOL AND DRY EASTERLY FEED INTO THE REGION BEFORE MOISTURE 
FLUX INCREASES RAPIDLY THURSDAY NIGHT. TEMPERATURES OVER THE ENTIRE 
AREA SHOULD RISE ABOVE FREEZING AS THE DRY SLOT SURGES NORTH. MUCH 
COLDER AIR WILL THEN MOVE INTO THE AREA DURING THE AFTERNOON AND 
EVENING WITH A FLASH FREEZE LIKELY. TEMPS SHOULD BE BELOW NORMAL 
THIS WEEKEND INTO EARLY NEXT WEEK. AS FOR LAKE EFFECT SNOW...GIVEN 
THE CUT OFF POSITION OF THE LOW...THE WIND DIRECTION SHOULD NOT BE 
FAVORABLE FOR LAKE EFFECT SNOW...SO MAINLY LIGHTER SYNOPTIC SNOW IS 
EXPECTED.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY 
     MORNING FOR INZ003>007.

MI...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY 
     MORNING FOR MIZ077>081.

OH...NONE.
LM...GALE WATCH FROM THURSDAY MORNING THROUGH FRIDAY AFTERNOON FOR 
     LMZ043-046.

&&

$$

SHORT TERM...JC
LONG TERM...SKIPPER
AVIATION...ARNOTT