FXUS63 KIWX 042107
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
407 PM EST FRI DEC 4 2009
.SHORT TERM...
FORECAST CONCERNS LIE WITH LINGERING LAKE EFFECT IN EXTREME
NORTHWEST AREA AND CLOUD COVER AND TEMPS REMAINDER OF AREA. SHORT
WAVE TROUGH UPSTREAM FROM WI TO EASTERN MO THIS AFTERNOON WILL
GRADUALLY MOVE EAST TONIGHT. AREA OF PERSISTENT CLOUDS AHEAD OF THIS
TROUGH IN CENTRAL IL HAS BEEN EXPANDING EAST AND NORTHEAST TODAY.
MODELS NOT HANDLING THIS AREA WELL WITH RUC HAVING BEST HANDLE IN
ITS LOW LEVEL RH PROGS. MODELS SHOW DEVELOPING INVERSION OVERNIGHT
AND THIS GIVES ME CONCERN AS LOW LEVEL MOISTURE WOULD BECOME TRAPPED
AND WOULD HAVE TO RELY ON SUBSIDENCE FOR DISSIPATION. HAVE INCREASED
SKY COVER GRIDS LATE THIS AFTERNOON AND EVENING BASED ON SAT TRENDS
WITH A SLOW DISSIPATION OVERNIGHT. HAVE KEPT PARTLY CLOUDY SKY COVER
PERCENTAGES AS A PRUDENT HEDGE. IF SKIES CAN CLEAR AS MODELS
SUGGEST...LOWS WILL BOTTOM OUT TOWARD DAYBREAK IN MID TO UPPER TEENS
FOR COLDEST LOWS OF THE SEASON.
SOUTHWEST FLOW WILL CONTINUE INTO BERRIEN AND EXTREME NORTHWEST CASS
COUNTY TONIGHT. AS WE HAVE BEEN MENTIONING THE SOUTHWEST FLOW IS
LEAST FAVORABLE FOR LAKE EFFECT SNOW ACCUMULATIONS WITH SHORT FETCH.
HOWEVER...DELTA T VALUES INTO THE LOWER 20S WITH WINDS ONLY IN 10 TO
20 KNOT RANGE SHOULD STILL YIELD SOME GOOD SNOW SHOWERS. QUESTION
REMAINS WHETHER TRAJECTORIES WILL KEEP IT JUST NORTH OF BERRIEN OR
INTO THE NORTHERN TIP. KBEH HAS SEEN VIS DOWN TO 1/2SM MILE THIS
AFTERNOON WITH THIS SHORTER FETCH. EXPECT UP TO A COUPLE INCHES
STILL POSSIBLE ACROSS NORTHERN TIP OF BERRIEN COUNTY OVERNIGHT WITH
SOME LOCALLY HEAVIER AMOUNTS POSSIBLE THOUGH AREA IS QUITE SMALL
WITHIN OUR CWA. STILL A CHANCE FOR LINGERING SNOW SHOWERS SATURDAY
BUT MOISTURE BEGINS TO WANE AND FOCUS SHIFTS NORTH LATER IN THE DAY
AND ESPECIALLY SAT NIGHT.
WEAK HIGH PRESSURE RIDGE TO SLIDE ACROSS THE AREA SATURDAY AND
SATURDAY NIGHT. TEMPS MIXED FROM 925MB ON SATURDAY ONLY YIELDS UPPER
20S TO LOWER 30S. WILL NUDGE UP JUST A BIT AS NAM MAY BE A BIT TOO
COOL BUT WILL STAY BELOW MOS THROUGH THE PERIOD.
&&
.LONG TERM...
SUNDAY THROUGH FRIDAY...THE MAIN CHALLENGES THIS PERIOD INCLUDE THE
CONCERNS FOR WINTRY WEATHER DEVELOPING TUESDAY AND PERSISTING INTO
THURSDAY AS A POTENT UPPER LEVEL SYSTEM AND SFC LOW MOVE INTO THE
AREA. FOR THIS PACKAGE...PREFER A SFC LOW TRACK NORTHEAST THROUGH
ABOUT FORT WAYNE WEDNESDAY MORNING. THIS TRACK HAS SUPPORT FROM THE
CANADIAN OPERATIONAL RUN...AND THE GFS ENSEMBLES. IT IS ALSO A BLEND
OF THE ECMWF AND THE GFS OPERATIONAL RUNS AND IS REASONABLY
CONSISTENT WITH THESE PREVIOUS RUNS. KEPT THE CHANCE FOR FREEZING
RAIN TUESDAY INTO EARLY WEDNESDAY AS WARM AND MOIST AIR RIDES OVER A
WEDGE OF COLD AIR. STILL HARD TO TELL HOW MUCH ICE ACCUMULATION
POTENTIAL GIVEN TEMPS CLOSE TO FREEZING AND THE POTENTIAL ALSO FOR
SLEET AND SNOW BESIDES RAIN. IT APPEARS THE BEST CHANCES FOR SNOW
ACCUMULATION IS OVER NW AREAS INCLUDING SOUTH BEND AND SW LOWER
MICH. WINDS WILL INCREASE RAPIDLY AFTER THE SFC LOW RACES NORTHEAST
WEDNESDAY AFTERNOON WITH RAIN CHANGING TO ALL SNOW. LAKE ENHANCED
PRECIPITATION WILL CHANGE TO ALL SNOW BY LATE WEDNESDAY WITH AT
LEAST SOME ACCUMULATIONS LIKELY DOWNWIND OF LAKE MICHIGAN. WINDY
CONDITIONS ARE ALSO EXPECTED...SO WITH THE POTENTIAL FOR
ACCUMULATING SNOW AND STRONG WINDS...WINTER WEATHER HEADLINES WILL
LIKELY BE NEEDED AT SOME POINT. LAKE EFFECT SNOW SHOULD PERSIST INTO
THURSDAY AS DELTA T VALUES APPROACH -20C. HAVE CONTINUED TO TREND
HIGH TEMPS THURSDAY DOWN GIVEN VERY COLD AIR AND PRECIPITATION.
&&
.PREV DISCUSSION... /ISSUED 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.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 AM EST SATURDAY FOR LMZ043-046.
&&
$$
SHORT TERM...LASHLEY
LONG TERM...SKIPPER
AVIATION...LASHLEY
