FXUS63 KIWX 271129
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
629 AM EST FRI NOV 27 2009
.AVIATION /12Z TAFS/...
CONDITIONS AT BOTH SBN AT FWA HAVE IMPROVED MORE QUICKLY THAN
EXPECTED WITH CIGS RETURNING TO VFR IN THE PAST FEW HOURS. WITH
SOME MVFR CIGS STILL FLOATING AROUND...CAN/T RULE OUT SOME
OCCASIONAL RESTRICTIONS OVER THE NEXT FEW HOURS...BUT AFTER THIS
POINT...EXPECT CIGS TO REMAIN VFR. CLOUDS SHOULD SCATTER OUT
THIS AFTERNOON WITH JUST A FEW HIGH CLOUDS LEFTOVER TONIGHT.
A FEW FLURRIES ARE POSSIBLE DURING THE FIRST FEW HOURS OF THE TAF
PERIOD...BUT THESE ARE NOT EXPECTED TO CAUSE ANY RESTRICTIONS TO
VSBYS.
WEST-NORTHWEST WINDS 12G18KTS ARE EXPECTED TODAY BEFORE BACKING
SOUTHWESTERLY AND DIMINISHING TO 5KTS OR LESS FOR THE OVERNIGHT
TONIGHT.
&&
.PREV DISCUSSION... /ISSUED 303 AM EST FRI NOV 27 2009/
SHORT TERM /TODAY THROUGH SATURDAY NIGHT/...
SHORT TERM WEATHER QUIETING DOWN SOME THIS MORNING AS OUR MOST
RECENT SHORTWAVE PRESSES EAST WITH RIDGING NOW OVER THE CENTRAL AND
WESTERN PORTIONS OF THE COUNTRY POISED TO MOVE EASTWARD UNDER
CONTINUED SUPPORT FROM AMPLE EASTERN PACIFIC JET ENERGY.
PRECIP DOWNWIND OF LAKE MICHIGAN IS BEGINNING TO FALL APART AS
UPSTREAM DEWPOINTS NEAR KMKE HAVE DROPPED TO NEAR 20F. EXPECT ANY
REMAINING RAIN AND SNOW SHOWERS TO COME TO AN END BEFORE DAYBREAK
BUT THE LAKE INDUCED CLOUD COVER IS ANOTHER MATTER. WILL INCLUDE A
PRE-FIRST PERIOD WITH ECHOES STILL ON THE SCOPE AND MORE LOCATIONS
SWITCHING TO ALL SNOW GIVEN THE COOLING COLUMN.
CLOUD COVER AND IT/S IMPACT ON TEMPS ARE THE BIGGEST CHALLENGES
TODAY. MODELS HOPELESSLY TOO DRY IN THE LOWER LEVELS EARLY THIS
MORNING. SHORTWAVE ROTATING INTO SOUTHERN MICHIGAN EARLY THIS
MORNING ON THE WESTERN FLANK OF THE NEGATIVELY TILTED TROUGH AXIS
CENTERED FROM OH TO GA HAS BRIEFLY BACKED THE LLEVEL FLOW SOME...BUT
THIS FLOW WILL REGAIN A MORE NORTHERLY COMPONENT UPON IT/S PASSAGE
WITH NO SIGNIFICANT CHANGE IN THE FLOW TRAJECTORY EXPECTED UNTIL
TONIGHT. GIVEN THIS AT TEMPS ALOFT SUPPORTIVE FOR A LAKE RESPONSE
AT LEAST THROUGH 18Z...SEE NO REASON FOR AT LEAST THE NORTHEASTERN
2/3RDS OF THE CWA TO REMAIN IN THE CLOUDS THROUGH MID/LATE AFTERNOON
WITH CLOUDS POTENTIALLY SCATTERING LATE. GIVEN THE CLOUD
COVER...HAVE KEPT TEMPS BELOW GUIDANCE OVER NORTHEASTERN
AREAS...CLOSER TO 3 HOURLY MOS TEMPS.
CLEARING SHOULD TAKE OVER TONIGHT AS H85 RIDGE AXIS PASSES BY WITH
CONTINUED WARMING AND BACKING FLOW ALOFT. WITH DEPRESSED DAYTIME
HIGHS AND CONTINUED LLEVEL DRY ADVECTION EXPECT THAT WE/LL BE SET UP
FOR PRETTY CHILLY LOWS OVERNIGHT. WILL CONTINUE LOWS ALONG THE
LOWER END OF GUIDANCE. COULD SEE TEMPS DROP ANOTHER 1-2F COOLER
THAN THIS FORECAST IF WE COMPLETELY CLEAR IN THE EAST QUICKLY
ENOUGH...AND WILL LET LATER SHIFTS REASSESS.
NICER DAY ON TAP FOR SATURDAY AS SHORTWAVE RIDGING MOVES OVERHEAD
AND TEMPS ALOFT RAPIDLY WARM. WITH MODELS IN GOOD AGREEMENT ON
POTENT LOW DEVELOPMENT OFF THE NORTHEASTERN US COAST...EXPECT THE
WARMUP TO LIKELY BE LITTLE SLOWER THAN THE NAM/ECMWF ARE
SHOWING...CLOSER TO THE GFS. ALSO IN THESE SCENARIOS WITH SUBSIDENCE
IN THE LOWER TO MIDDLE TROPOSPHERE AND RAPID WARMING ALOFT...WE TEND
TO HAVE TROUBLE MIXING VERY HIGH WITH THE NAM SUGGESTING THAT WE MAY
TO FULLY MIX TO EVEN H92. WITH THESE IDEAS IN MIND...WILL KEEP HIGHS
NEAR THE LOWER END OF GUIDANCE BUT THIS WILL STILL BRING HIGHS INTO
THE UPPER 40S OVER NORTHEASTERN AREAS INCREASING TO THE LOWER 50S IN
THE SOUTHWEST.
MODEL TRENDS HEADING INTO SATURDAY NIGHT SUGGEST A SLIGHTLY FASTER
APPROACH OF SHORTWAVE SEEN IN WATER VAPOR IMAGERY EARLY THIS MORNING
COMING ASHORE OVER WESTERN BRITISH COLUMBIA. THIS FASTER MOVEMENT
APPEARS DUE BOTH TO LESS RETARDING INFLUENCE FORM THE DEVELOPING
SOUTHWESTERN US CUTOFF...AS WELL AS A RIBBON OF PRETTY FAST MID
LEVEL FLOW DEVELOPING ALONG THE SOUTHWESTERN FLANK OF THE POTENT
EASTERN CANADA LOW HEIGHT CENTER. EVEN AT THEIR INITIALIZATION TIME
THE GFS/NAM ARE OVERDOING ANY MOISTURE RETURN OVER THE CENTRAL
PLAINS...WHICH IS NONEXISTENT AT THIS TIME. COMBINE THIS WITH A
PRETTY QUICK WINDOW OF POTENTIAL MOISTENING SOUTHWEST LLEVEL FLOW IN
OUR VICINITY AND IT APPEARS THAT EVEN WITH A WEAK FRONT SETTLING
INTO THE REGION MORE QUICKLY...IT WILL COME IN DRY. MAIN IMPACT
FROM THE FRONT AND UPSTREAM INCREASING FORCING WILL BE TO INCREASE
THE MID/UPPER LEVEL CLOUDINESS SOMEWHAT AND KEEP THE WINDS UP
OVERNIGHT...WHICH SHOULD SPELL LOWS ALMOST 10F WARMER THAN THE NIGHT
BEFORE...CLOSER TO THE WARMER SIDE OF THE GUIDANCE ENVELOPE.
LONG TERM...
ONLY MINOR ADJUSTMENTS TO THE EXTENDED AS MODELS IN DECENT AGREEMENT
THROUGH EARLY PART OF WORK WEEK CONCERNING LEAD WAVE MOVING THROUGH
ON MONDAY BEFORE INCREASING DISAGREEMENT ON NORTHERN STREAM
EVOLUTION IN LATE PERIOD CONTINUES TO YIELD LOW CONFIDENCE BY LATE
WEEK.
UPPER TROF DROPS THROUGH THE NORTHERN PLAINS SUNDAY AND INTO THE
GREAT LAKES WHILE LEAVING BEHIND UPPER LOW NEAR THE NORTHERN GULF OF
CALIFORNIA. ASSOC LLEVEL BOUNDARY PASSES ON SUNDAY BUT DESPITE
SUPPORTING MID/UPPER LEVEL DYNAMICS RESULT IS UNIMPRESSIVE AS
MOISTURE RETURN IS QUITE LIMITED UNTIL BNDRY IS JUST OVER THE CWA.
LEFT INHERITED POPS ALONE FOR SUNDAY AFT INTO MONDAY MORNING.
AFTER A BRIEF PERIOD OF CALM MID WEEK WITH THE CWA LYING BETWEEN
SPLIT FLOW THE SW CONUS LOW WILL LIFT NE AND PHASE WITH ANOTHER
TROUGH DIGGING SOUTH THROUGH THE GREAT PLAINS. IMPACT ON THE CWA WILL
DEPEND ON HOW THIS EVOLVES/WHERE PHASING OCCURS AND THERE IS
CONSIDERABLE SPREAD AMONG THE MODELS AND THEIR ENSEMBLES.
GFS/ENSEMBLE MEAN IS FURTHEST EAST WITH A DRY LATE WEEK PERIOD...
AND THOUGH THE ECMWF BRUSHES THE CWA WITH PRECIP IT HAS TRENDED EAST
WITH THE 00Z RUN. WILL LEAVE GRIDS DRY GIVEN THE EASTERLY SHIFT IN
PHASING THOUGH IT HAS SHOWN THE INVADING TROUGH CLOSING OFF OVER THE
GREAT LAKES AND CONTINUED CONSISTENCY WITH THIS FEATURE IN FUTURE
RUNS COULD NECESSITATE A CHC POP ADDITION. ONE THING IN COMMON
ACROSS THE SPECTRUM OF SOLNS...COLDER TEMPS FALLING TO CLIMO OR
COOLER AT THE TAIL END OF THE EXTENDED.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LMZ043-
046.
&&
$$
SHORT TERM...ARNOTT
LONG TERM...LUDINGTON
AVIATION...ARNOTT
