FXUS63 KIWX 051816
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
116 PM EST SAT DEC 5 2009
.UPDATE...
PAIR OF UPDATES SENT IN PAST FEW HRS AS CLOUD COVER PROVING VERY
TRICKY AS HIGH PRESSURE ATTEMPTS TO NUDGE IN FROM THE SOUTH WHILE
AT THE SAME TIME A PROGRESSIVE WEAK UPR WAVE BREEZES THROUGH. UPR
WAVE HAS PROVIDED JUST ENOUGH SUPPORT TO EKE OUT SCATTERED FLURRIES
OVER MUCH OF ERN 2/3 OF THE CWA THIS MORNING AND GRIDS HAVE BEEN
UPDATED TO MAINTAIN FLURRY CHANCES THROUGH EARLY AFTERNOON IN ERN
1/3 OF CWA BEFORE WAVE CLEARS CWA LATE AFTERNOON. OTHER MAJOR
HEADACHE OF THE DAY PERSISTENT LAKE EFFECT OVER BERRIEN COUNTY
THAT LOOKS TO BE ACCUMULATING SLIGHTLY PER MORNING METARS AT KBEH
REPORTING BLO 2SM VISBYS AND WEBCAMS. HAVE TRENDED ALL THE WAY TO
CATEGORICAL POPS THROUGHOUT BERRIEN AND IN NW CASS COUNTIES WITH A
EXTREMELY SHARP CUTOFF TO PRECIP EDGE. EXPECT UP TO A HALF INCH OR
INCH OF SNOW WILL BE POSSIBLE IN THESE AREAS THROUGH THE REST OF
THE AFTERNOON. INCREASED CLOUD COVER ALSO RESULTING IN LOWER
AFTERNOON HIGH TEMPERATURES /MAINLY ERN CWA/ AND GRIDS HAVE BEEN
ADJUSTED ACCORDINGLY. UPDATED ZONES/GRIDS OUT...AGAIN.
&&
.PREV DISCUSSION... /ISSUED 1240 PM EST SAT DEC 5 2009/
AVIATION...
PERSISTENT CLOUD DECK THAT WE WERE CONCERNED WITH ON FRIDAY DID
INDEED GET TRAPPED UNDER INVERSION AND IS FINALLY SHOWING SIGNS OF
BECOMING MORE CELLULAR. HOWEVER...CU RULES INDICATE SCT-BKN CU
POSSIBLE THIS AFTERNOON AND SATELLITE SHOWS THIS DEVELOPMENT. CIGS
ARE RIGHT AROUND 3KFT SO MVFR A POSSIBILITY FOR A FEW MORE HOURS
BEFORE RISING INTO VFR RANGE...MAINLY AT KFWA WHERE MVFR CURRENTLY
BEING REPORTED. GIVEN MOSTLY CLEAR SKIES UPSTREAM AND CELLULAR LOOK
TO CLOUD FIELD OVER TAF SITES WILL CONTINUE TO CLEAR SKIES AROUND
00Z WITH VFR CONDITIONS REMAINDER OF PERIOD.
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).
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...JC
LONG TERM...HOLSTEN
AVIATION...LASHLEY
UPDATE...SIMPSON
