FXUS63 KIWX 050025
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
724 PM EST THU DEC 4 2008

.AVIATION...
00 UTC TAFS. SHORTWAVE MOVG ACRS SRN GRTLKS THIS EVE WITH CLOUD
BEARING WINDS TO VEER/INVERSION HGHTS LIFT AROUND MIDNIGHT BRINGING
GRTR CHC FOR MVFR CIGS AND VSBYS TO DIP SOUTH INVOF KSBN. BREVITY OF
FAVORED LES CONDS WITH INVERSION HGHTS AGAIN FALLING EARLY AM...TO
KEEP PD OF VSBY RESTRICTION LIMITED...THOUGH MVFR CIGS LIKELY INTO
EARLY AM IN MOIST CYCLONIC LLVL FLOW. AS WINDS BACK FRI ANTICIPATE
LOSS OF HIGH END MVFR CIGS.

&&

.SHORT TERM...
CAA/LAKE EFFECT CLOUDINESS CONTS OVER THE GRTLKS REGION...INCLUDING
NE 1/2 OF OUR CWA THIS AFTN. SOME LAKE EFFECT SNOW HAS OCCURRED MUCH
OF THE DAY ACROSS MUCH OF SRN MI AND ADJACENT NRN INDIANA
COUNTIES...HWVR INVERSION WHICH TAMDAR SOUNDINGS INDICATE IS BASED
AROUND 3-5KFT...ALONG WITH SHORT WNW FETCH HAS LIMITED INTENSITY
OF SNOW SHOWERS IN OUR AREA. COLDER AIR WILL CONTINUE TO ADVECT
INTO THE REGION TONIGHT. SHRTWV SEEN ON WATER VAPOR OVER THE UPR
MS VALLEY WITH A SFC REFLECTION SEEN IN SFC OBS MOVG INTO NW IL
ACCOMPANIED BY A FEW FLURRIES IS EXPECTED TO MOVE EAST ACROSS OUR
CWA TONIGHT PSBLY CAUSING SOME FLURRIES OUTSIDE OF LAKE EFFECT
AREAS. ALSO INVERSION WILL RISE OVERNIGHT AS THE TROF MOVES
THROUGH WHICH SHOULD INCREASE INTENSITY OF LAKE EFFECT SNOW
SHOWERS... THOUGH CONTD SHORT FETCH WILL STILL BE LIMITING FACTOR
TO SGFNT ACCUMS...WENT WITH 1-2" OVER SRN MI WITH <1" IN ADJACENT
IN/OH COUNTIES. H85 TEMPS EXPECTED TO FALL TO AROUND -15C IN OUR
CWA OVERNIGHT. UPSTREAM TEMPS THIS MORNING IN THIS AIRMASS IN
SINGLE DIGITS/TEENS. WITH LESS SNOW COVER IN OUR AREA THAN IA/NRN
IL AND PARTLY TO MOSTLY CLOUDY SKIES EXPECTED OVERNIGHT...KEPT LOWS
IN THE TEENS.

WITH THERMAL TROF MOVG ACROSS THE AREA ON FRIDAY...TEMPS ONLY
EXPECTED TO RISE INTO THE L-M20S. SFC RIDGE WILL MOVE ACROSS THE
AREA DURING THE DAY CAUSING WINDS TO BACK TO SW BRINGING LAKE EFFECT
TO AN END ACROSS OUR CWA BY EVE WITH THE PSBL EXCEPTION OF NRN
BERRIEN COUNTY. AMOUNT OF CLOUDS QUESTIONABLE. BOTH NAM AND GFS
INDICATE H925 WILL BE SATURATED...BUT THIS LAYER WAS TOO MOIST IN
MODELS TODAY...SO OPTIMISTICALLY WENT WITH PARTLY SUNNY SKIES
AGAIN ACROSS SRN PORTION OF THE CWA.

ANOTHER STRONG CDFNT WILL DROP SE INTO THE WRN GRTLKS FRI NIGHT. ANY
REMAINING LOW CLOUDS EXPECTED TO ADVECT NE OUT OF THE AREA IN THE
EVE AS SWLY LOW LEVEL FLOW INCREASES. HIGH CLOUDS WILL BE SPREADING
INTO THE AREA AHD OF THE UPR TROF SO EXPECTING MOSTLY CLOUDY SKIES
WITH LITTLE TEMP DROP. CONTD WITH SMALL CHC OF SNOW FOR LATE FRI
NIGHT AS FRONT APPROACHES...BUT STILL APPEARS BEST CHC OF SNOW
WITH THE FRONT WILL BE SATURDAY.

&&

.LONG TERM...(SATURDAY THROUGH THURSDAY)...

CONTINUED COLD AND ACTIVE PATTERN THROUGH THE EXTENDED PERIOD WITH
QUICK CLIPPER AND LAKE EFFECT SAT NITE/SUN FOLLOWED BY ANOTHER
POTENTIAL STRONG SYSTEM MOVING THROUGH THE EASTERN US MIDWEEK.

EXTENDED BEGINS WITH CLIPPER SYSTEM IMPACTING NW CWA AS SFC
LOW MOVES THROUGH THE UPPER GREAT LAKES. SIGNIFICANT TIMING
DIFFERENCES BETWEEN SLOWER NAM/FASTER GFS BRINGING PRECIP INTO THE
CWA ON SATURDAY AND HAVE SIDED WITH THE TIMING OF 09Z SREF AS A
COMPROMISE. HWVR AS AN ADDNL NOD TO MODEL PERFORMANCE WITH THE PREV
SYSTEM HAVE MAINTAINED EARLIER POPS INDICATED BY THE GFS AND
UNDERCUT THE MODEL CONSENSUS QPF BY A MARGINAL AMOUNT AS THE 12Z GFS
DECREASED QPF FROM 00Z/06Z RUNS POSSIBLY FORESHADOWING SIMILAR
OUTCOME OF REALIZING LESSER AMOUNTS. NET RESULT IS LIGHT/MOD SNOW
SETTLING IN SATURDAY MORNING AND EXPANDING ACROSS THE CWA WITH
RELATIVELY MINOR SYNOPTIC QPF AMOUNTS. ZONE-OMEGA TECHNIQUE
INDICATES SNOW RATIOS ON THE ORDER OF 15:1 TRANSLATING TO 2-3 INCH
SNOW TOTALS TAPERING OFF FROM NW TOWARDS THE SE. AS SYNOPTIC FORCING
WANES IN WAKE OF SFC LOW WINDS TURNING NW PRODUCE LAKE EFFECT SETUP
BEGINNING AROUND 00Z SAT AND CONTINUING INTO SUNDAY. BUFR SOUNDINGS
SHOW DELTA-T'S PEAKING AT 20 DEG WITH INVERSION LOCATED IN LOW END
OF GROWTH ZONE AND UNIDIRECTIONAL 20KT WINDS THROUGH THE LAYER. HAVE
REMAINED CONSERVATIVE WITH SNOW AMOUNTS GIVEN LOCATION OF EQL LEVELS
HWVR POTENTIAL EXITS FOR MORE SIGNIFICANT SNOW WITH SMALL CHANGE IN
THERMAL PROFILE FAVORING BETTER SNOW GROWTH.

UPR TROF SHIFTS EASTWARD WITH FLOW RETURNING TO SOUTHERLY BY MONDAY
SHUTTING DOWN ANY LEFTOVER LAKE EFFECT MECHANISM AND WARMING TEMPS
BACK TO UPPER 20S AND INTO LOW 30S FOR TUESDAY. RELIEF IS
POTENTIALLY SHORT LIVED HOWEVER AS MODELS CONTINUE TO SHOW STRONG
MID WEEK STORM TAKING SHAPE AS SFC LOW EJECTS NE THROUGH THE EASTERN
US WHILE SECOND DEEPER LOW WRAPS UP NEAR BASE OF MID LEVEL TROF
ALONG GOMEX WHILE A PUSH OF ARCTIC AIR INTO THE US FOLLOWS.
CONSIDERABLE SPREAD AMONG OPERATIONAL MODELS AND ENSEMBLES AS ONE
WOULD EXPECT THIS FAR OUT SO HAVE NOT ATTEMPTED TO GO BEYOND THE BIG
PICTURE WHICH PAINTS POPS MON-WED AND COLDER TEMPS BEHIND FRONT ON
WEDNESDAY. HAVE KEPT LATE WEEK TEMPS ABOVE GUIDANCE AS GFS TENDS TO
CONSISTENTLY OVERDO COLD AIR INTRUSIONS SEVERAL DAYS OUT AND ECMWF
IS NOT AS AGGRESSIVE WITH ADVANCEMENT OF COLD AIR INTO THE UPPER
MISSISSIPPI VALLEY. STAY TUNED.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 PM EST SATURDAY FOR LMZ043-046.

&&

$$

SHORT TERM...TAYLOR
LONG TERM...LUDINGTON
AVIATION...MURPHY


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