FXUS63 KIWX 050921
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
421 AM EST SAT DEC 5 2009
.SHORT TERM...
TODAY THROUGH SUNDAY NIGHT
DIRTY HIGH PRESSURE CONTINUES TO OFFER COLD DRY AIR AND LINGERING LOW
CEILINGS ACROSS THE FA. SCT FLURRIES CONTINUE ACROSS PORTIONS OF THE
FA...WITH LIGHT SNOW BEING REPORTED AT SBN AND BEH. LAKE EFFECT SNOW
SHOWERS HAVE HEAVILY WANED IN THE PRESENCE OF CRASHING INVERSION
HEIGHTS AND BACKED LL FLOW. TEMPS HAVE HELD STEADY AT MOST PLACES
WHERE CLOUD COVER IS PERSISTENT. DO EXPECT MANY PLACES TO REACH
MINIMUMS SHORTLY BEFORE SUNRISE AS CLOUD COVER CONTINUES TO SCT
OUT. THIS IS ESPECIALLY TRUE FOR THE SW FA. GENERAL SYNOPTIC PATTERN
FEATURES A DEEP H5 HEIGHT ANOMALY OVER JAMES BAY EXTENDING SOUTH
INTO THE GREAT LAKES/MASSIVE RIDGING OVER THE WESTERN ATLANTIC AND
EASTERN PAC/AND A POTENT DIGGING UPPER LEVEL TROUGH OVER THE THE NW
CONUS. SFC HIGH PRESSURE CONTINUES TO SLIDE EAST ACROSS THE OH RIVER
VALLEY AS A WEAK SFC TROUGH PUSHES EAST ACROSS THE UPPER MIDWEST
ASSOCIATED WITH THE EAST ADVECTING CENTRAL NOAM NEGATIVE HEIGHT
ANOMALY. OVERALL SYNOPTIC PATTERN WILL FEATURE CONTINUED SFC RIDGING
THROUGH TODAY...WITH WEAK MID LEVEL RIDGING AND WAA COMMENCING LATE
TONIGHT INTO SUNDAY...AHEAD OF A FRACTURED MID LEVEL IMPULSE
STEMMING FROM THE CURRENT NW CONUS SYSTEM.
TODAY...NOT MUCH TO SPEAK PER WX DETAILS IN THIS PERIOD. SFC RIDGING
COINCIDENT WITH A LL TEMP TROUGH WILL SUPPORT COLD/DRY CONDITIONS
WITH MOSTLY SUNNY SKIES EXPECTED...SAVE THE FAR NW WHERE LAKE CLOUDS
AND LIGHT SNOW WILL HANG ON THROUGH MORNING...WITH CLEARING NOT
EXPECTED UNTIL LATE TONIGHT. H85 T/S HOVERING AROUND -12C WILL ONLY
OFFER HIGHS IN THE LOWER 30S AT BEST...WITH INSOLATION POSSIBLY
ADDING A DEGREE OR TWO.
TONIGHT...COLD CONDITIONS ARE EXPECTED FOR MUCH OF THE FA AS CLEAR
SKIES/LIGHT WINDS/AND VERY DRY AIR IN PLACE SUPPORTS SHARP T FALLS.
ONE CAVEAT TO THE FORECAST IS HOW WELL SFC WINDS RESPOND TO A
TIGHTENING PRESSURE GRADIENT PER PRESSURE FALLS OVER THE UPPER
MIDWEST. MOS CERTAINLY SUPPORTS INCREASING LL WIND IN THE WESTERN
HALF OF THE FA...WHICH IS QUITE PLAUSIBLE. HOWEVER...GIVEN AN
EXPECTED STRONG INVERSION IN PLACE...SFC WINDS MAY BE VERY SLOW TO
RESPOND UNTIL AFTER SUN RISE.
SUN...STRENGTHENING LL FLOW/WEAK RIDGING AND WAA WILL BE ONGOING
THROUGH THE PERIOD. EXPECT AND INCREASE IN MID AND HIGH
CLOUDINESS...ESPECIALLY IN THE LATE AFTERNOON. PAC NW SYSTEM WILL
ADVECT TOWARD THE REGION IN FAST WESTERLY FLOW...WITH CLIPPER LIKE
CHARACTERISTICS. STRONG MOMENTUM FIELDS ASSOCIATED WITH RAPID
PRESSER FALLS WILL OFFER STAUNCH THETA-ADV NORTH WITH AN EXPECTED
WELL ORGANIZED WAA WING TO THE SYSTEM...SUPPORTING DEVELOPING SNOW
OVER THE FA BY LATE SUN NIGHT. MODEL QPF PROGS ARE ALL ON THE SAME
PAGE OFFERING 0.05 TO 0.10 OF LIQUID IN THE WEST BY 12Z MON. TEMP
PROFILES WOULD SUPPORT AN AVERAGE LIQUID TO SNOW RATIO OF AROUND
15:1 TO 20:1 SUPPORTING AROUND AN INCH OF SNOW ACROSS THE WESTERN
THIRD OF THE FA. HAVE ADJUSTED POPS UP IN THE NW GIVEN CONTINUED
MODEL CONSISTENCY AND PREFERRED FASTER ADVECTION/PROPAGATION
SPEEDS.
&&
.LONG TERM...
CRUX OF FCST CNTRS ON WINTER STORM POTENTIAL MID WEEK AS A POTENT
JET STREAK AND EMBEDDED SW TROUGH OVR NW CANADA DIGS SHARPLY SWD
INTO THE FOUR CORNERS AND THEN EJECTS OUT ACRS THE SRN PLAINS.
LEAD LOW AMPLITUDE SW WITHIN EVOLVING WRN TROUGHING WILL KICK OUT
RAPIDLY EWD SUN AFTN WITHIN FLAT DOWNSTREAM FLW. HWVR MODEST HGT
FALL COUPLET ASSOC/W MID LVL WAVE AGAIN PROGGED TO TRACK OVERHEAD
WHICH SUGGESTS GREATEST SNOWFALL WILL LIE N/NW OF HERE ON MON. BUT
00Z GUIDANCE AS IN PREV CYCLES CONTS TO INDICATE A PRONOUNCED LL WAW
HAD OF APCHG MID LVL TROUGH AND XPC THAT WILL LEAD TO A BURST OF
SNOW MON AM TIMED W/ENTRAINING THETA-E BULGE ADVTG OUT OF THE MID
MS VALLEY. HIGHER END OF CHC POPS STILL FITTING AS MORE PRECISE
ACCUMULATION DETAILS FALL OUTSIDE HIGHRES GUIDANCE WINDOW.
12-00Z TRENDS W/PRIMARY WAVE EJECTION OUT OF THE ROCKIES TUE AFTN
RIGHT OF TRACK COMPARED TO LAST NIGHT W/A SHARPER MID LVL TROUGH AND
SLWR DVLPG SFC CYCLONE AND NOTED IN YDAS DISC. OVERALL PRIOR GRIDDED
DETAIL NOT TOO BAD YET WILL INCORPORATE LATEST IDEAS WHICH KEEP
EVENT MAINLY SNOW NW...MIX CNTRL AND ICE S/SE. DETAILS WILL WAVER
FURTHER IN SUCCESSIVE MODEL CYCLES ESP GIVEN XPCD INITIALIZATION
ERRORS W/JET STREAK...SW INTENSITY AND DEPTH OF PV ANOMALY DROPPING
OUT OF CANADA AND COULD TAKE UNTIL MONDAY TO GET FULLY RESOLVED.
HWVR MED RANGE CONSISTENCY LENDS CONSIDERABLE CERTAINTY AND WILL
BUMP POPS EVEN HIGHER TUE AFTN-THU. RAPIDLY DEEPENING SFC CYCLONE
TAKING A MORE SRN ROUTE ALSO POINTS TO CONSIDERABLE GRADIENT WIND
POTENTIAL WED AFTN-THU AS COLDEST AIR OF SEASON WRAPS IN BEHIND THIS
DEEP SYS. THIS WILL AGAIN FOSTER TEMPS WELL BLO NORMAL UNTIL LT IN
THE PD.
CONTD HIGH MOMENTUM/PERTURBED FLW ACRS THE CNTRL/ERN PACIFIC
UNDERCUTTING EPAC RIDGE LOOKS TO BRING ANOTHER BOUT OF SNOW TO THE
AREA CNTRD ON DY7 (FRIDAY).
&&
.AVIATION.../06Z TAFS/
MVFR CIGS WITH SCT FLURRY ACTIVITY WILL CONTINUE TO SHIFT NE
THROUGH THE PERIOD WITH A TREND TO VFR CONDITIONS OVER MUCH OF
THE FA BY MID TO LATE MORNING. SCT MVFR CIGS WILL PERSIST OVER
PORTIONS OF BERRIEN AND CASS COUNTIES PER A CONTINUED LAKE
RESPONSE...WHICH WILL BEGIN TO WANE BY LATE MORNING...WITH A TREND
TO VFR FLIGHT CONDITIONS.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...JC
LONG TERM...HOLSTEN
AVIATION...JC
