FXUS63 KIWX 041745
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1245 PM EST FRI DEC 4 2009
...AVIATION...
CIGS ARE MAIN CONCERN AT TAF SITES WITH THIS PACKAGE. AREA OF
DIURNAL MVFR CU CURRENTLY AT KFWA WHILE MORE SOLID CLOUD DECK JUST
TO THE WEST OF THERE EXTENDING SOUTHWEST INTO IL. SATELLITE LOOP
INDICATING THIS AREA OF CLOUDS BEGINNING TO EXPAND NORTHEAST WITH
SOUTHWEST FLOW AHEAD OF MID LEVEL TROUGH. EXPECT MVFR CIGS TO
PREVAIL AT BOTH SITES MOST OF AFTERNOON THOUGH OCCASIONAL BREAKS TO
VFR POSSIBLE. STILL UNCERTAIN WHETHER THESE CLOUDS WILL BE ABLE TO
BREAK APART AND DISSIPATE AS MODELS SUGGESTING FOR TONIGHT. HAVE
KEPT MVFR CIGS GOING AT KSBN AND TRANSITION TO VFR AT KFWA PER
RECENT SATELLITE TRENDS BUT WILL HAVE TO MONITOR EVOLUTION OVER NEXT
SEVERAL HOURS FOR MORE CERTAINTY. OTHERWISE NO SIGNIFICANT PROBLEMS
AS LAKE EFFECT SNOW SHOWERS SHOULD REMAIN NORTH OF KSBN WITH
SOUTHWEST FLOW AND WINDS BECOME LESS THAN 10 KNOTS TONIGHT.
&&
.SHORT TERM...
TODAY THROUGH SATURDAY NIGHT
MID LEVEL IMPULSE CONTINUES TO PUSH EAST ACROSS THE GREAT
LAKES...WITH SHARP CAA ON THE BACKSIDE OF THE SYSTEM. SYSTEM
GENERATED AND LAKE ENHANCED SNOW/RAIN CONTINUES TO FALL OVER
PORTIONS OF CENTRAL MI...WITH SOME VIGOR EVIDENCED BY LIGHTNING
RETURNS NEAR HOLLAND. CAA CONTINUES TO INCREASE LAKE INDUCED
INSTABILITY AS H85 T/S CONTINUE FALL...SUPPORTING DELTA T/S
APPROACHING -12 C APPROX. A NOTED INCREASED IN LAKE EFFECT SNOW
SHOWERS IS ONGOING AS INSTABILITY CONTINUES TO GROW...WITH ACTIVITY
NOW BEGINNING OVER FAR SOUTHERN LAKE MI. ELSEWHERE...PARTLY TO
MOSTLY CLOUDY CONDITIONS CAN BE FOUND UPSTREAM OVER IL/IA/MO...WITH
AREAS OF LIGHT SNOW AND FLURRIES. TEMPERATURES WERE GENERALLY IN THE
LOW TO MID 20S WITH MOSTLY CLEAR SKIES OVER THE MAJORITY OF THE FA.
TODAY...LAKE EFFECT SNOWS OVER SW MI WILL BE THE FOCUS OF THE PERIOD
AS LAKE INDUCED CAPES OVER GROW TO 700-800 J/KG GIVEN LAKE TEMPS IN
THE MID 40S SUPPORTING DELTA T/S OF 15 TO 20C. MODERATE INSTABILITY
IS EXPECTED UNDER RELATIVELY MOIST FLOW AND EQUILIBRIUM LEVELS OF
8-12 KFT. HOWEVER...GENERAL WSW FLOW WITH A SOME BACKING
POSSIBLE...WILL HIGHLY LIMIT LAKE SNOW OVER THE FA...WITH THE
HEAVIEST SNOW RESIDING OVER WEST CENTRAL MI...WHERE UP TO 9
INCHES HAVE FALLEN ALREADY. QPF VALUES FROM THE LOCAL WRF AND RUC 13
SEEM VERY REASONABLE...WITH 0.10-0.15 INCHES PROGGED IN THE FAR NW
BY THE LOCAL WRF...AND FELT THIS WAS A GOOD PLACE TO START. SNOW
RATIO PROBS SUPPORT A HIGHER END VALUE OF 15:1 WITH ANY SNOW
FALL...AND GIVEN EXPECTED DURATION OF 24-36 HOURS...FEEL GENERAL 1-3
INCH AMOUNTS OVER FAR NORTHERN BERRIEN AND NW CASS ARE LIKELY WITH
HIGHER AMOUNTS POSSIBLE. MOST UNSTABLE PERIOD WILL BE FROM 12Z-21Z
TODAY...WHEN INVERSION HEIGHTS AND DELTA T/S WILL BE AT THEIR
RESPECTIVE PEAKS. LOOK FOR PARTLY SUNNY SKIES AWAY FROM THE LAKE
WITH A FEW FLURRIES POSSIBLE. A WELL MIXED...BUT COLD BL WILL ONLY
OFFER HIGHS INTO THE LOW 30S.
TONIGHT...MOSTLY CLEAR SKIES ARE EXPECTED SAVE THE NW ZONES.
NEGATIVE THETA-E ADV WITH DEWPOINTS FALLING INTO THE TEENS WILL
ALLOW AN EXCELLENT RADIATIONAL COOLING SETUP AS WINDS GO LIGHT. LOOK
FOR LOWS IN THE UPPER TEENS WIDESPREAD. LAKE EFFECT SNOW SHOWERS
WILL CONTINUE OVER THE PORTIONS OF BERRIEN AND CASS COUNTIES.
HOWEVER...BACKED LL SW FLOW WILL AGAIN SUPPORT MARGINAL TRAJECTORIES
IN THE PRESENCE OF DRYING UPWIND FLOW. BEST CHANCES FOR SNOW WILL BE
ACROSS NORTHERN BERRIEN AND CASS COUNTIES WHERE AND ADDITIONAL 1-2
INCHES WILL BE POSSIBLE AT BEST.
SAT...SFC HIGH PRESSURE WILL DOMINATE THE WEATHER WITH LOWERING
INVERSION HEIGHTS AND MUCH DRIER AIR WORKING INTO THE AREA. HAVE
CONTINUED LAKE SNOW CHANCES GIVEN PROGGED DELTA T/S OF 15C. BUT ONCE
AGAIN...POOR TRAJECTORY ORIENTATION WILL ONLY OFFER A LOW CHANCE
POP. COLD CONDITIONS CAN BE EXPECTED ONCE AGAIN WITH HIGHS GENERALLY
IN THE MID 30S. LOOK FOR MOSTLY SUNNY SKIES SAVE FOR EXTREME SW
LOWER MI.
&&
.LONG TERM...
00Z MODEL SUITE IN PRONOUNCED AGREEMENT W/FLW EVOLUTION OVR THE
CONUS THIS PD. GFS/EC HAVE BOTH TRENDED SHARPLY TWD 12/02 00Z GGEM
SOLUTION WHICH IS FITTING GIVEN UPSTREAM FLW AMPLIFICATION ONGOING
ACRS THE CNTRL/ERN PACIFIC THIS MORNING. THUS GIVEN THE RARE
EXCELLENT CONSENSUS AGREEMENT WILL MAKE SOME RATHER SIG MID PD CHGS
WRT TO DEEP MID LAT CYCLONE DVLPMNT ACRS THE PLAINS.
LEAD SW TROUGH OVR BC THIS MORNING WILL DIG SHARPLY SWD TWD THE FOUR
CORNERS BFR ITS KICKED OUT AHD OF MORE POTENT UPSTREAM DVLPMNT TIED
TO COMMENSURATE VRY DEEP TROUGH/RIDGE DVLPMNT ACRS THE CNTRL PACIFIC
INTO SIBERIA. HWVR FLAT DOWNSTREAM FLW W/LTL SFC DVLPMNT SUGGEST
KEEPING W/LOW CHC SNOW POPS EVEN THOUGH 00Z GUIDANCE AS A WHOLE A
BIT STGR/LONGER DURATION OF FOCUSED SATURATED ASCENT OVR COLD DOME.
TRACK OF 5H HGT FALL CNTR OF 100M WITHIN FVRBL LL BAROCLINIC ZONE
MONDAY WOULD PUT REGION OF BEST SNOWFALL PRODUCTION N/NW OF CWA AND
WILL KEEP W/LOW CHC POPS FOR NOW.
OTHERWISE BLENDED MEANS POINT TO DEEP SFC CYCLONE EJECTING OUT OF
SRN PLAINS TUE AND INTO LWR MI WED AND GIVEN THAT TRACK LTL THREAT
NOW FOR ANY SIG SNOWFALL ACCUMULATION HERE AS INTENSE DOWNSTREAM LLJ
PUSHES ELEVATED WARM SECTOR WELL NORTH INTO MI. HWVR CAA BEHIND WK
LEAD WAVE EJECTING OUT OF THE SRN ROCKIES SUNDAY AND ARRIVING HERE
MONDAY COULD YIELD A PD OF FREEZING PCPN TUE AFTN/TUE EVENING BFR
WARM BULGE OVERWHELMS SHALLOWING COLD WEDGE W/THE MORE FAVORED
PTYPE BECOMING RAIN LT TUE NIGHT/WED. POTENTIAL ICE STORM SHLD SFC
CYCLONE TRACK E/S OF 00Z CONSENSUS OR SYS IS SLWR DVLPG EWD THUS
SLOWING ERODING SHALLOW COLD DOME. THUS HAVE TO PUT IN AN ICE
MENTION TUE/TUE NIGHT TO ACCOUNT FOR THE PROMINENT GUIDANCE TREND
THAT WAY. COLDEST AIR OF SEASON WILL FOLLOW IN BEHIND THIS SYS AND
POSES ADDNL PROBS BEYOND DY 7 AS HIGH MOMENTUM/PERTURBED FLW THROUGH
THE CNTRL PACIFIC TYPICAL OF EL NINO WILL UNDERCUT EPAC RIDGE LT
WEEK/NXT WEEKEND.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM EST SATURDAY FOR LMZ043-046.
&&
$$
SHORT TERM...JC
LONG TERM...TJB
AVIATION...LASHLEY
