FXUS63 KIWX 260543
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1243 AM EST SAT DEC 26 2009

.AVIATION...
PERIODIC SNOW SHOWERS AND PERSISTENT MVFR CIGS WILL CONTINUE
OVERNIGHT AS MOISTURE BEGINS TO WORK BACK INTO MID LEVEL DRY SLOT
OVER THE REGION. AN ENHANCED BAND OF SNOW ADVANCING NE THROUGH
CENTRAL INDIANA WILL FOR THE MOST PART PASS BETWEEN TERMINALS HWVR
EXPECTING KFWA TO BE IMPACTED BETWEEN 07Z-10Z. UPSTREAM THIS BAND
BROUGHT LOCALIZED LIFR CONDS TO KHUF AND WHILE THIS IS NOT
ANTICIPATED A SHORT PD OF OPTIMISTIC VSBY/CIG RESTRICTION IS INCLUDED IN
KFWA TAF. INTO SATURDAY...INCREASING MOISTURE AS SFC LOW ADVANCES
INTO NORTHERN ILLINOIS IS EXPECTED TO BRING A PERIOD OF SNOWFALL
DURING THE AFTERNOON HOURS...WHILE SHSN AND GUSTY SSE WINDS
CONTINUE THROUGHOUT THE PERIOD AS MOIST SYSTEM CONTINUES TO LINGER
IN THE AREA.

&&

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...

DEEP LOW WAS CENTERED OVER IA THIS AFTN WITH ASSOCIATED STRONG CDFNT
LIFTING NE AHEAD OF IT INTO SWRN PORTION OF CWA. FRONT WILL CONT
TO MOVE NE ACROSS THE CWA LATE THIS AFTN/EARLY THIS EVE WITH BAND
OF RAIN IN ADVANCE OF THE FRONT LIKELY HOLDING TOGETHER AND MOVG
ACROSS THE AREA. STRONG CAA BEHIND THE FRONT WILL RESULT IN CHANGE
OVER OF RAIN SHOWERS TO SCT SNOW SHOWERS LATE THIS AFTN AND THIS
EVE. MID LEVEL DRY SLOT FCST BY MODELS TO MOVE ACROSS THE CWA
OVERNIGHT WITH DEEPER MOISTURE WRAPPING AROUND THE LOW FROM THE
WSW TOWARD MORNING. IN SPITE OF THE DRY SLOT, CONTD MENTION OF CHC
SW- THROUGH THE ENTIRE CWA OVERNIGHT AS -12C H85 TEMPS MOVG INTO
THE AREA WITH MOIST LOW LEVELS SHOULD RESULT IN SOME -SHSN CONTG
WITH HIGHEST POPS NW WHERE DEEPER MOISTURE WILL BE PRESENT THE
LONGEST.

WITH COLD AIR WRAPPING AROUND IA LOW, SYSTEM WILL WEAKEN SAT/SAT NGT 
AND SHOULD DRIFT SLOWLY EAST TOWARD THE GRTLKS. CYCLONIC CIRCULATION 
EXPECTED TO REMAIN STRONG ENOUGH TO MAINTAIN SOME LIGHT SNOW OR
PERSISTENT SNOW SHOWERS NEAR THE LOW CENTER AS WK SHRTWV'S ROTATE
AROUND IT. TRENDED POPS UP WITH 1-2" OF ACCUM EXPECTED NW AND <1"
SE DURING THIS 24HR PD.

STRONG CAA TONIGHT SHOULD ALLOW TEMPS TO FALL INTO THE L-M20S.
COLD AIR ALOFT AND WELL MIXED/MOIST LOW LEVELS EARLY SATURDAY 
SUGGEST TEMPS WILL CLIMB LITTLE FROM OVERNIGHT LOWS WITH HIGHS 
RANGING FROM THE U20S NW TO L30S SE. LOW CLOUDS REMAINING TRAPPED 
BENEATH INVERSION BASED AROUND 5KFT ALONG WITH CONTD MODERATE MIXING 
SHOULD LIMIT TEMP FALL SAT NIGHT... TRENDED MINS UP A BIT TOWARD 
LATEST MOS GUIDANCE. 

LONG TERM...

SUNDAY THROUGH FRIDAY

MASSIVE NEGATIVE HEIGHT ANOMALY WILL DOMINATE THE WEATHER THROUGH THE 
FIRST PART OF THE LONG TERM PERIOD...WITH SEVERAL FLOW EMBEDDED WEAK 
VORT LOBES ACTING TO ENHANCE MESOSCALE SNOW SHOWER PRODUCTION. 
GENERAL BLOCKING PATTERN WILL BEGIN TO BREAK DOWN BY MONDAY WITH 
EVENTUAL EJECTION OF THE EASTERN CONUS UPPER TROUGH AND A RETURN TO 
THE FAVORABLE SPLIT FLOW PATTERN PREVALENT OVER NOAM THIS PAST FALL 
SEASON. DOMINATE SIBERIAN NEGATIVE HEIGHT ANOMALY BEARS WATCHING AS 
A WESTERN NOAM RIDGE LOOKS TO POSSIBLY SUPPORT CROSS POLAR FLOW BY 
MID TO LATE NEXT WEEK...ALLOWING THE POSSIBLE SETUP FOR AN ARCTIC 
INTRUSION NEXT WEEKEND BEHIND A DEEP PHASED TROUGH. LIKELY EL NINO 
INFLUENCE OBSERVED IN THE PAC CONTINUES TO SUPPORT A POWERFUL MID 
LATITUDE UPPER JET...WHICH CONTINUES TO SUPPORT SW CONUS TROUGH 
RELOADING AND A PERIODIC WESTERN NOAM RIDGING...WITH AN ATYPICAL 
EASTERN BIAS /POSSIBLY ATTRIBUTED TO DOMINATE WESTERN ATLANTIC 
BLOCKING. HENCE...FEEL THE ECMWF /AND TO A LESSER EXTENT/ THE GFS 
PORTRAY THE GENERAL PATTERN WELL...WITH HINTS TO THIS SOLUTION. HAVE 
TRIED TO TAYLOR THE LATER PORTIONS OF THE EXTENDED TO AN EXPECTED 
LONG WAVE PHASED TROUGH ADVECTING THROUGH THE REGION BY 6-7...WITH 
ANOTHER ROUND OF CP TO POSSIBLY ARCTIC AIRMASS CAA. HAVE FOLLOWED 
CLOSEST TO THE ECMWF.

SUN-MON...BROAD UPPER TROUGH WILL SUPPORT CONTINUED CHANCES FOR SNOW 
SHOWERS WITH A SFC TROUGH /POSSIBLY A GREAT LAKES MOBILE TROUGH 
HYBRID/ EXPECTED TO ADVECT SOUTHWARD INTO THE FA BY LATE SUN. CAA 
AND VEERING LL WINDS WILL SUPPORT LAKE ENHANCEMENT WITH A PURE LAKE 
MI RESPONSE SUNDAY NIGHT. NAM AND GFS H925-H85 THERMAL/MOMENTUM/AND 
FORCING PROGS CONTINUE TO SUPPORT A DECENT LAKE REPONSE WITH A 
PERIOD OF DEEP UVM SUNDAY NIGHT INTO MONDAY...IN THE PRESENCE OF 
NEARLY 400 J/KG OF LAKE INDUCED CAPE. THIS MAKES SENS GIVEN RAISED 
INVERSION HEIGHTS AND LONGER TRAJECTORY FLOW COMBINED WITH AN 
ADVANCING UPPER LEVEL IMPULSE. FEEL THAT A 1-2 INCH SNOW MENTION 
IS WARRANTED WITH POSSIBLE HIGHER ACCUMS. HAVE RAISED POPS TO LIKELY 
IN THE NW ZONES WHERE FLOW/FORCING/AND DURATION BEST OVERLAP. LOOK 
FOR HIGHS GENERALLY IN THE MID TO UPPER 20S WITH LOWS IN THE LOWER 
20S TO UPPER TEENS. RATHER STRONG SFC PRESSURE GRADIENT COMBINED 
WITH STRONG LL FLOW IN THE LOWEST 1-3 KM WILL CONTINUE TO SUPPORT A 
WELL MIXED BL.

TUE-FRI...SFC HIGH PRESSURE WILL BUILD INTO THE REGION TUE 
SUPPORTING A LIGHT FLOW REGION WITH COLD THERMAL FIELDS IN PLACE. 
EXPECTING COOLER HIGHS GIVEN LACK OF APPRECIABLE MIXING. POSSIBLE 
INSOLATION MAY ADD A FEW DEGREES. DEVELOPING DISTURBED NW FLOW WILL 
SUPPORT SEVERAL SMALL SCALE WAVES WITH LIKELY MID AND HIGH CLOUD 
ASSOCIATION. DIGGING SW CONUS WAVE WILL EJECT COINCIDENT WITH A 
NORTHERN STREAM WAVE. TIMING AND PHASE POTENTIAL IS STILL 
UNCERTAIN...BUT CURRENT ENSEMBLE AND MODEL TRENDS STILL SUPPORT A 
LONG WAVE PHASED TROUGH ACROSS THE CONUS WITH SNOW CHANCES 
INCREASING WED NIGHT THROUGH FRI. DID ADD POPS ON FRIDAY PER COLLAB 
AND GIVEN A TYPICAL AND EXPECTED SECONDARY CP-ARCTIC AIRMASS PUSH 
INTO THE REGION...WHICH ALSO HAS THE SUPPORT OF AO INDEX PROGS FROM 
THE MEAN GEFS ENSEMBLE.

AVIATION...
DEEP LOW OVER IOWA WILL REMAIN NEARLY STNRY THROUGH THIS TAF PD.
A STRONG CDFNT WAS LIFTING NE AHEAD OF THE LOW ACROSS SWRN
INDIANA. THIS SHOULD MOVE THROUGH SBN AND FWA TERMINALS AROUND 00Z
SHIFTING WINDS FROM SE TO SSW. BAND OF RAIN SHOWERS OUT AHEAD OF
THE CDFNT WILL ROTATE THROUGH THE AREA THIS AFTN CAUSING VSBYS TO
LOWER TO 3SM OR LESS. SNOW SHOWERS SHOULD DEVELOP SHORTLY AFTER
FROPA AND CONT IN MOIST CAA REGIME THROUGH THE NIGHT AND INTO
SAT... THOUGH ATTM EXPECT THE SNOW TO BE LIGHT WITH MVFR
CONDITIONS PREVAILING.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SHORT TERM...JT
LONG TERM...JC
AVIATION...LUD