FXUS63 KIWX 021745
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1245 PM EST WED DEC 2 2009
.AVIATION...
MODELS CONTINUE TO GRADUALLY BACK OFF ON PCPN WITH DEEP SYSTEM
MOVING BY TO OUR SOUTH TONIGHT. MODELS HAVE ALSO SLOWED COLD AIR
INTRUSION IN LOWER LEVELS DELAYING CHANGEOVER TO ALL SNOW. CIGS WILL
GRADUALLY LOWER THIS AFTERNOON AND EVENING. RAIN WITH VIS
RESTRICTIONS WILL LIKELY HOLD OFF AT TAF SITES UNTIL EARLY EVENING.
RADAR SHOWING RETURNS JUST SOUTH OF KFWA BUT MOST REPORTING SITES
NOT INDICATING ANY RAIN REACHING SURFACE WITH DRY NORTHEAST LOW
LEVEL FLOW. HAVE BACKED UP ONSET OF PCPN A FEW HOURS ALONG WITH
SLOWED TIMING FOR MVFR CIGS. EXPECT WITH NIGHTTIME COOLING AND
SATURATION THAT CIGS AND EVENTUALLY VIS WILL REACH MVFR LEVELS
OVERNIGHT. HEAVIEST PCPN WILL BE FROM KFWA SOUTH AND EAST. LOW LEVEL
THICKNESS AND WET BULB TEMPS FROM 12Z MODEL SUITE SUGGEST ANY
CHANGEOVER TO SNOW WILL BE CLOSER TO 12Z AT KSBN AND POSSIBLY AS
LATE AS 16 TO 18Z AT KFWA. LEFT A MIX IN AT KSBN AND KEPT KFWA ALL
RAIN. COULD SEE PERIODS OF ALL SNOW LATE MORNING ON AT KSBN
DEPENDING ON LAKE EFFECT MOISTURE PLUME AND STRONGER LIFT.
&&
.PREV DISCUSSION... /ISSUED 356 AM EST WED DEC 2 2009/
SHORT TERM...
WV LOOPS CLEARLY SHOWS THE STAGE IS SET FOR THE LONG ADVERTISED
MID WEEK SYSTEM TO COME TOGETHER OVER THE EASTERN HALF OF THE
COUNTRY. UPPER LOW THAT WAS STUCK OVER THE SOUTHWEST HAS BEEN
KICKED OUT BY SOUTHERN STREAM AND IS MOVING NORTHEAST TROUGH TEXAS
WHILE THE ASSOC SFC LOW IS CENTERED ALONG THE GULF COAST OF
LOUISIANA. NARROW RIDGING BECOMING MORE AMPLIFIED OFF THE PAC NW
COAST AS BROAD COLD TROUGH DIGS SOUTH THROUGH THE CENTRAL PLAINS
WORKING TO FUNNEL COLD AIR MASS SOUTH. AFOREMENTIONED UPPER LOW
WILL BE ABSORBED INTO NE FLOW ON THE SOUTHERN FLANK OF DEEPENING
TROUGH BRINGING ITS ASSOCIATED LLEVEL CIRCULATION AND ITS DEEP
MOISTURE FEED THROUGH THE OHIO VALLEY. RAIN WILL MOVE INTO THE CWA
FROM THE SOUTH DURING THE AFTERNOON AND OVERSPREAD THE CWA DURING
BY EVENING WITH THE QUESTION OF WHEN/WHERE ANY PTYPE TRANSITION
WILL OCCUR OVERNIGHT.
THE MODELS ARE NOW LESS SPREAD REGARDING THE SFC LOW TRACK BUT STILL
SHOW THE SAME VARIATIONS TO LESSER DEGREE... /THE 00Z GFS FURTHEST
EAST AND THE NAM AND SREF TO THE WEST/... WHILE H850 LOW POSITIONS
ARE MORE TIGHTLY CLUSTERED NEAR CLEVELAND BY 06Z THU. STILL PREFER
THE MORE WESTERLY TRACK AS DEEPENING SFC LOW LIFTS UNDER A NEGATIVELY
TILTED MID LEVEL WAVE. THIS FAVORS THE WARMER SIDE OF GUIDANCE WITH
1310M 1000-850 THICKNESSES AND 35C SFC WET BULBS IN PLACE THROUGH
06Z OVER ALL BUT THE EXTREME NW CWA. NAM BUFR SOUNDINGS ARE
SIMILARLY PESSIMISTIC TOWARDS A CHANGEOVER WITH THE BULK OF MOISTURE
AND DEFORMATION LIFTING TO THE NE WELL AHEAD OF SUBSTANTIAL CAA. AS
SUCH...RAIN AND RASN MIX IS EXTENDED WITH TRANSITION TO ALL SNOW
PUSHED BACK BOTH GEOGRAPHICALLY AND TEMPORALLY TO 06Z IN THE NW AND
12Z IN THE SE. BY THIS TIME PRECIPITATION RATES SHOULD BE MILD...AND
ANY AREAS THAT MANAGE ACCUMULATION ARE EXPECTED ONLY TO SEE UP TO AN
INCH OR LESS MOSTLY ON GRASSY SURFACES. IF THE MODELS ARE STILL
HOLDING AN EASTWARD BIAS EVEN THIS MAY YET PROVE TO BE TOO
OPTIMISTIC. AS COLDER AIR OVERSPREADS THE CWA THURSDAY MORNING
FLURRIES WILL BE POSSIBLE THROUGH THE DAY UNDER COLD AND DREARY
SKIES.
BY 18Z AS WINDS BACK NW AND SUFFICIENTLY COLD H85 TEMPS ARRIVE LAKE
EFFECT BEGINS TO KICK IN QUICKLY ON THE HEELS OF DEPARTING SYSTEM
AND OVERALL REASONING HAS NOT CHANGED MUCH FOR SEVERAL RUNS. A
PERIOD OF LAKE ENHANCEMENT INTO NORTHERN INDIANA COUNTIES IS
POSSIBLE AS H95 TEMPS COOL TO -8C BY 18Z THU BUT WINDS BACK STEADILY
WEST WHILE LAKE INDUCED INSTABILITY INCREASES THURSDAY NIGHT AS
TEMPS FALL FURTHER GENERATING DELTA TS ON THE ORDER OF 20C BY FRIDAY
MORNING...BUT WITH SW FETCH TAKING THE BULK OF THE ACTION
FURTHER NORTH INTO CENTRAL MICHIGAN.
LONG TERM...
STG SW TROUGH OVR CNTRL TX THIS AM WILL LIFT RAPIDLY NEWD THROUGH
THE OH RVR VALLEY AHD OF DIGGING NRN STREAM TROUGH OVR WY SHRT TERM
AND OFF THE NEW ENGLAND COAST TO START THE LONG TERM. COLD POCKET
UNDERNEATH NRN STREAM TROUGH WILL ADV EWD W/CORE OF COLDEST AIR XPCD
FRI/FRI NIGHT. HWVR LL FLW ALIGNMENT IN WAKE OF LEAD SRN STREAM SW
BACKS RAPIDLY TO THE SW AND W/LOSS OF APPRECIABLE SYNOPTIC SCALE
MSTR LES POTENTIAL LIMITED. IN FACT DOUBT ANY APPRECIABLE
ACCUMULATION IS ON TAP EVEN OVR NRN BERRIEN WHERE BTR MSTR/LL
FORCING COINCIDES LT THU NIGHT/FRI. EVEN THOUGH WILL LEAVE POPS
GENERALLY AS IS OTHER THEN A SLIGHT NWD BUMP IN PREV N/S GRADIENT.
OTHERWISE AMPLIFIED PATTN BREAKS DOWN INTO PROGRESSIVE/UNSETTLED
WESTERLY FLW BY LT WEEKEND AND ULTIMATELY LIKELY TO REAMPLIFY INTO
NXT WEEK ALTHOUGH MED RANGE MODEL GUIDANCE ALL OVR THE PLACE IN THAT
REGARD. GGEM HAS PROVEN SUPERIOR LATELY AND ITS SUGGESTION ON DEEP
PLAINS CYCLOGENESIS MID NXT WEEK ALIGNS WELL W/OP GFS/ENSEMBLE MEAN.
HWVR TYPHOON NADI OVR THE WPAC WILL UNDERGO A QUICK YET WEAK
EXTRATROPICAL TRANSITION AHD OF A MID LAT TROUGH COMING OUT OF
CHINA. HWVR GIVEN THE HIGH MOMENTUM FLW EXISTING DOWNSTREAM THROUGH
THE NPAC...XPC THIS SYS WILL REGENERATE FURTHER DOWNSTREAM INTO A
MORE INTENSE BAROCLINIC WAVE AS SEEN IN GFS/GGEM SOLUTIONS AND WHICH
FVRS THEIR DEEP PLAINS CYCLONE IDEA TWD DY8 GIVEN XPCD CONCURRENT
HIGH AMPLITUDE WRN RIDGE/PLAINS TROUGH DVLPMNT AT THAT TIME.
TEMPS THROUGH THE PD BLO NORMAL.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...LUD
LONG TERM...T
AVIATION...LASHLEY
