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000
FXUS63 KIWX 100100
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
800 PM EST TUE FEB 9 2010

.UPDATE...

GOING FCST IN GOOD SHAPE AND ONLY MINOR TWEAKS MADE IN AN ATTEMPT
TO HANDLE LOW LVL COLD POCKET OF AIR THAT IS JUST BEGINNING TO
SKIRT SW CWA AS WE SPEAK. TEMPS HAVE DROPPED INTO THE SINGLE
DIGITS OVER CENTRAL ILLINOIS AND HAVE TAKEN THIS INTO ACCOUNT AS
LOWS WERE TRENDED DOWNWARD BY SEVERAL DEGREES IN SOUTHERN CWA. STG
GRADIENT EVIDENT IN OBS AND MODEL PROGS WITH RUC APPEARING TO HAVE
VERY GOOD HANDLE SO ATTEMPTED TO FCST GRADIENT IN CWA WITH LOWS IN
LOWER TEENS SOUTH SHARPLY TRANSITIONING TO LOWER 20S CENTRAL AND
NORTH. SNOWFALL FCST STILL ON TRACK WITH ANOTHER 3 TO 5 EXPECTED
TONIGHT OVER MOST AREAS WITH NUMBERS PROBABLY ON THE HIGHER END OF
THAT RANGE IN LAKE EFFECT AREAS WHERE BAND WILL DEVELOP TOWARD
DAYBREAK.

&&

.PREV DISCUSSION... /ISSUED 632 PM EST TUE FEB 9 2010/

AVIATION...
UPR LOW EVIDENT IN STLT/RADAR DATA MOVG ESE ACROSS SRN IL THIS
EVE. LARGE AREA OF SNOW IN TROWAL/DEFORMATION ZONE TO THE NORTH OF THIS
CIRCULATION EXTENDED ACROSS NRN IL/IN/OH AND SRN MI. THIS PCPN
SHIELD SHOULD CONT TO AFFECT THE TERMINALS OVERNIGHT, THEN TAPER
OFF TO SHSN WED MORNING AS DEEP MOISTURE AND FORCING MOVE EAST OF
THE AREA. BROAD SFC LOW OVER NE IN/NW OH ATTM WILL MOVE EAST OF
THE AREA OVERNIGHT RESULTING IN INCREASING NW WINDS AT THE
TERMINALS CAUSING CONSIDERABLE BLOWING/DRIFTING SNOW WHICH SHOULD
REDUCE VSBYS TO LIFR LATE TONIGHT AND EARLY WED. CONDITIONS
EXPECTED TO IMPROVE TO MVFR WED AFTN AT FWA AS BULK OF NEWLY
FALLEN SNOW SETTLES INTO DRIFTS BY THAT TIME, WHILE CONTD LAKE
ENHANCEMENT SHOULD KEEP IFR CONDITIONS IN SHSN/BLSN GOING AT SBN
THROUGH EVE.

PREV DISCUSSION... /ISSUED 412 PM EST TUE FEB 9 2010/

SHORT TERM...

.TONIGHT THROUGH WEDNESDAY NIGHT...

A VERY INTERESTING AND DIFFICULT FORECAST CONTINUES INTO WEDNESDAY
AS SNOW CONTINUES ACROSS AREA AND MORE SNOW STILL EXPECTED TONIGHT
INTO WEDNESDAY. NUMEROUS FORECAST CONCERNS TO ADDRESS.

SATELLITE SHOWED UPPER LOW EXITING EASTERN MO THIS AFTERNOON AND
STILL EXPECT THIS TO MOVE EAST ACROSS SOUTHERN INDIANA TONIGHT.
MEANWHILE SURFACE LOW WILL MOVE NORTHEAST THROUGH THROUGH CENTRAL
OHIO AND DEEPEN SLIGHTLY WHILE MAIN ENERGY TRANSFERS TO EAST COAST
LOW DEVELOPMENT LATE TONIGHT. MID LEVEL LOW EXPECTED TO MOVE ACROSS
CENTRAL AND SOUTHERN FORECAST AREA WHICH WOULD KEEP CENTRAL AND
NORTHERN AREA IN BEST LOCATION FOR HEAVIEST SNOW OVERNIGHT WITH
DEFORMATION AREA AND STRONG TROWAL. NAM12 650MB THETA E ANALYSIS
SUGGEST TROWAL FEATURE TO WRAP INTO NORTHERN AREAS LATE EVENING AND
OVERNIGHT WITH INDICATIONS OF THIS FEATURE MOVING OVER TOP EXPECTED
LAKE BAND. MORE ON THIS SHORTLY.

DENDRITIC GROWTH ZONE...DGZ...HAS STRUGGLED TODAY WITH SMALL FLAKES
IN MANY AREAS DUE TO LACK OF STRONG FORCING. HOWEVER...EMBEDDED
MESOSCALE BANDING HAS LED TO POCKETS OF HEAVIER SNOWFALL AND VARIED
SNOWFALL ACCUMULATIONS UP THROUGH THIS AFTERNOON. THESE AMOUNTS HAVE
RANGED FROM JUST A FEW INCHES TO SIX INCHES AS OF THIS WRITING.
THIS PROVES DIFFICULT IN DETERMINING OVERALL STORM TOTAL AMOUNTS
GIVEN THIS DISPARITY ACROSS RATHER SMALL AREAS.

AFOREMENTIONED TROWAL COUPLED WITH A DEEPER DGZ AND STRONGER LIFT
OVERNIGHT SHOULD LEAD TO LARGER DENDRITES AND BETTER ACCUMULATIONS
OVERNIGHT. STILL FEEL MOST OF PREVIOUS SNOWFALL GRIDS ON TRACK BUT
FEEL THE HIGHER AMOUNTS WILL BE MORE LOCALIZED GIVEN THE DISPARITY
FROM TODAY. WILL CONTINUE WITH GENERALLY 5 TO 10 INCHES WITH HIGHER
AMOUNTS NORTH AND LOWER AMOUNTS SOUTH. LOCALIZED AMOUNTS OF 12 TO 15
INCHES POSSIBLE ESPECIALLY NEAR LAKE MICHIGAN. THIS IS WHERE
IMPRESSIVE BUT RELATIVELY SHORT LIVED SINGLE LAKE BAND IS EXPECTED
TONIGHT PER NAM12 LAKE PARAMETERS AND 925MB PLUME ANALYSIS. THIS
WOULD BRING STRONG BAND INTO LAPORTE AND SOUTHWEST BERRIEN COUNTIES
TOWARD 09Z AND INTO WESTERN ST JOSEPH COUNTY TOWARD 12Z. SOME
INDICATIONS BY NAM12 THAT TROWAL FEATURE COULD BECOME STACKED OVER
LAKE BAND EARLY WEDNESDAY MORNING. THIS WOULD SIMPLY ACT TO ENHANCE
THE SNOWFALL RATES WITH DEEP SYNOPTIC MOISTURE AND GOOD SEEDER
FEEDER TYPE MECHANISM. HAVE CONTINUED WITH HIGHER AMOUNTS THESE
AREAS.

INCREASING GRADIENT AND MIXING OVERNIGHT INTO WEDNESDAY STILL
EXPECTED TO YIELD WINDS OF 20 TO 30 MPH WITH GUSTS TO 40 MPH STILL
POSSIBLE. THIS WILL LEAD TO BLOWING AND DRIFTING WITH 2 TO 4 FOOT
DRIFTS LIKELY WHERE THE HEAVIER SNOW OCCURS. NEAR BLIZZARD
CONDITIONS EXPECTED LATE TONIGHT INTO WEDNESDAY BUT DURATION AND
VISIBILITIES MAY NOT QUITE MEET CRITERIA. FOR NOW WILL CONTINUE WITH
NEAR BLIZZARD WORDING IN THE WINTER STORM WARNING AND WILL MONITOR
CONDITIONS AS THEY DEVELOP FOR POSSIBLE UPGRADES IF NEEDED.

FINALLY WE HAVE TO DEAL WITH TEMPERATURES AND A UNIQUE AND
INTERESTING TREND TONIGHT. UPPER LOW HAS AN IMPRESSIVE COLD CORE
CENTER WITH 850MB TEMPS ON THE RUC40 DOWN TO -20C OVER EAST CENTRAL
MISSOURI THIS AFTERNOON. THIS HAS LED TO SURFACE TEMPERATURES
DROPPING INTO SINGLE DIGITS UNDER AND SURROUNDING THE CORE OF THIS
LOW. MEANWHILE AS LOW DEPARTS TEMPERATURES HAVE BEEN RISING BACK
INTO 20S. NAM12 HAS THIS HANDLED FAIRLY WELL AND WITH COLLABORATION
HAVE USED NAM12 WITH SLIGHT ADJUSTMENTS. THIS AFFECTS MAINLY SOUTH
WHERE TEMPS WILL FALL INTO LOWER TEENS BEFORE REBOUNDING LATE. WIND
CHILLS EXPECTED TO DIP AS WELL INTO LOWER SINGLE DIGITS BELOW ZERO
DURING THIS TIME.



LONG TERM...

THUR THROUGH TUESDAY

COLD NORTHWEST FLOW WILL PREVAIL THROUGH THE PERIOD AS WESTERN NOAM
RIDGING AND GREENLAND BLOCKING CONTINUE. GEFS STANDARDIZED ANOMALIES
INDICATE 2-3 STANDARD DEVIATIONS ABOVE NORMAL PER GREENLAND H5
HEIGHTS...BY THIS WEEKEND INDICATING THE STRENGTH OF EXPECTED
RIDGING. HOWEVER...THE BULK OF COLD AIR WILL REMAINED LOCKED OVER
PORTIONS OF SIBERIA AND FAR NW PORTIONS OF CANADA GIVEN THE DEGREE
OF WESTERN NOAM RIDGING...LIMITING THE INTENSITY OF CAA INTO THE
REGION. WITH NW FLOW COMES INCREASED CHANCES FOR CLIPPER TYPE
SYSTEMS GIVEN THE POSITION OF A NE PAC TROUGH. EXACT TIMING OF THESE
SYSTEMS STILL REMAINS UNCERTAIN GIVEN GFS/ECMWF/GEFS/AND NAEFS
PROGS...BUT A PREFERRED WINDOW IS BECOMING MORE FAVORED FOR AT
LEAST ONE OF THESE SYSTEMS AND THAT IS IN THE SAT-SUN PERIOD.
NAEFS/GEFS PROGS DO INDICATED MEMBER SUPPORT FOR SNOW WITH SAT-SAT
NIGHT BEING THE HIGHLIGHTED PERIOD PER CLUSTER ANALYSIS. HAVE
FOLLOWED A NAEFS/GEFS BLEND WITH SOME AID FROM THE LATEST GFS/ECMWF.
GIVEN THE OVERALL PATTERN...BELOW NORMAL TEMPS ARE EXPECTED THROUGH
THE PERIOD WITH HIGHS GENERALLY IN THE 20S AND LOWS IN THE TEENS TO
SINGLE DIGITS...WITH SUB ZERO READING POSSIBLE THU NIGHT WHERE
CLEARING OCCURS.

THUR-FRIDAY...NOT MUCH CHANGE IN THIS PERIOD. DID TWEAK SKY GRIDS
SOME TO REFLECT A CONTINUED LAKE MI INFLUENCE GIVEN LL FLOW
TRAJECTORIES AND THERMAL FIELDS. CONTINUED WITH TEMPS SLIGHTLY BELOW
GUIDANCE GIVEN W/WNW FLOW WITH AN EXPANSIVE FRESH SNOWPACK IN PLACE.
HAVE CONTINUED TEMPS BELOW GUIDANCE THUR NIGHT AND FRIDAY NIGHT
GIVEN SNOW PACK/LIGHT WINDS/SKY COVER/AND SFC RIDGING. SUBZERO TEMPS
WILL BE POSSIBLE ESPECIALLY THUR NIGHT GIVEN THE POSITION OF SFC
RIDGING AND EXPECTED CLEAR SKIES OVER THE SOUTHERN CWA.

SAT-SUN...CLIPPER WAVE IS EXPECTED IN THIS TIME FRAME AND HAS BEEN
HIGHLIGHTED FOR SEVERAL MODEL RUNS...ALTHOUGH THE EXACT PERIOD HAS
WAVERED. GIVEN THE ACTIVE NW PATTERN COMBINED WITH ENSEMBLE
TRENDS...FEEL THE ADDITION OF LOW POPS IS WARRANTED AT THIS TIME
WITH FURTHER FINE TUNING EXPECTED. HAVE CONTINUED WITH AN INCREASED
SKY GRID AND BELOW NORMAL TEMPS GIVEN PATTERN SIGNALS AND PROGGED
ANOMALIES.

MON-TUE...HAVE TRENDED TOWARD CLIMO...REMAINING BELOW CLIMO
AVERAGES GIVEN PATTERN CONCERNS. RETAINED DRY FORECAST AT THIS POINT
UNTIL A BETTER HANDEL ON CONUS FLOW IS ASCERTAINED.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...WINTER STORM WARNING UNTIL 7 PM EST /6 PM CST/ WEDNESDAY FOR
     INZ003>009-012>018-020-022>027-032>034.

MI...WINTER STORM WARNING UNTIL 7 PM EST WEDNESDAY FOR MIZ077>081.

OH...WINTER STORM WARNING UNTIL 7 PM EST WEDNESDAY FOR OHZ001-002-004-
     005-015-016-024-025.

LM...GALE WARNING UNTIL 11 PM EST WEDNESDAY FOR LMZ043-046.

&&

$$

SHORT TERM...LASHLEY
LONG TERM...JC
AVIATION...JT
UPDATE...SIMPSON