FXUS63 KIWX 290908
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
408 AM EST SUN NOV 29 2009
.SHORT TERM /TODAY THROUGH MONDAY NIGHT/...
TRICKY FORECAST TODAY WITH APPROACHING UPPER SHORTWAVE NEARING A
SURFACE COLD FRONT THAT WAS DRAPED FROM SOUTHEASTERN IOWA
NORTHEAST THROUGH NORTHERN ILLINOIS AND INTO NORTHERN LOWER
MICHIGAN. THE SUBSTANTIAL UPPER FORCING OVERSPREADING THE SURFACE
BOUNDARY AND WEAK ISENTROPIC LIFT AHEAD OF IT SOUNDS LIKE A GOOD
RECIPE FOR PRECIP. THE CAVEAT IS A DRY ANTECEDENT AIRMASS IN THE
H85 THROUGH H5 LAYER. THE QUESTION IS...HOW LONG WILL IT TAKE THIS
AIRMASS TO SATURATE. UPSTREAM REGIONAL RADAR SHOWS ALMOST NO
PRECIP ASSOCIATED WITH THE SURFACE COLD FRONT...AND THE ONLY
PRECIP AROUND BEING THAT IMMEDIATELY AHEAD OF THE APPROACHING UPPER
TROUGH. WHILE 00Z OPERATIONAL GUIDANCE REASONABLY INITIALIZED THIS
DRY AIRMASS...THE GFS/NAM LOOK A LITTLE TOO MOIST...PARTICULARLY AT
MID LEVELS. ALSO...GIVEN THE ONLY MODEST STRENGTH OF THE
SOUTHWESTERLY H92-H85 FLOW ADVECTING MOISTURE INTO THE
REGION...BELIEVE THE MOISTENING WILL BE A LITTLE SLOWER THAN THE
MODELS /PARTICULARLY THE GFS/ INDICATE. THEREFORE EXPECT PRECIP
TO PRETTY MUCH BLOSSOM OVERHEAD LATE THIS MORNING...WHICH MAKES
POPS TIMING/PLACEMENT A CHALLENGE. WILL UP POPS TO LIKELY OVER THE
SOUTHEASTERN 2/3RDS OF THE CWA WITH THESE LOCATIONS MOST LIKELY TO
HAVE SUFFICIENT TIME TO MOISTEN AHEAD OF THE UPPER WAVE. WILL
CONTINUE CHC POPS IN THE FAR WEST. TEMPS WILL ALSO BE PROBLEMATIC
AS NEARING SURFACE FRONT AND THE POSITIVE LLEVEL THETAE ADVECTION
MAY CAUSE SOME STRATUS TO DEVELOP OVER NORTHWESTERN
AREAS...WHEREAS THE SOUTHEAST HAS REMAINED COUPLED ALL NIGHT WITH
TEMPS ALREADY IN THE MID 40S. EXPECT NEARLY FULL MIXING TO 925
GIVEN STRONG LLEVEL WIND FIELD OVER THE SOUTHEAST AND MORNING SUN
WHILE EARLIER CLOUD ARRIVAL AND LOWER MORNING TEMPS WILL KEEP
HIGHS MUCH LOWER IN THE NORTHWEST. UPPED HIGHS TO THE UPPER 50S
NEAR LIMA WITH 60 NOT OUT OF THE QUESTION...AND KEPT HIGHS IN THE
MID 40S NEAR LAKE MICHIGAN.
SHRAS ALONG THE FRONT MAY LINGER THROUGH MID EVENING OVER
SOUTHEASTERN AREAS. FOR THE REMAINDER OF THE CWA...THE UPPER
TROUGH WILL STILL BE UPSTREAM OF THE AREA EARLY IN THE EVENING AND
ALTHOUGH T85S WILL NOT BE COLD ENOUGH FOR THE LAKE ALONE TO
GENERATE PRECIP...EXPECT THAT SOME LAKE ENHANCED SHRAS WILL LINGER
BEHIND THE FRONT. AFTER MIDNIGHT...T85 DROPS TOWARDS -6C WHICH
WILL LIKELY SUPPORT A MODEST LAKE RESPONSE. LIKE THE PREVIOUS
SHIFT/S USE OF /LIGHT/ WORDING AND WILL CONTINUE THAT THROUGH
MORNING. BL TEMPS LOOK SIMILAR TO OUR LAST LAKE EFFECT EVENT...SO
EXPECT A RASN MIX WITH ANY PRECIP THAT FALLS AFTER MIDNIGHT EXCEPT
NEAR THE LAKE SHORE WHERE THE LAKE-MODIFIED BL SHOULD KEEP PRECIP
LIQUID. DON/T FORSEE ANY SNOW ACCUMS AT THIS POINT. LOWS IN THE
LOWER TO MIDDLE 30S LOOK REASONABLE.
ON MONDAY UPPER TROUGH AXIS PASSES EAST WITH BACKING LLEVEL FLOW
AND LLEVEL WARM ADVECTION. EXPECT ANY LAKE SHRASN TO SLOWLY
MIGRATE NORTH AND EAST...DWINDLING THROUGH THE DAY AND REALLY NOT
HAVING MUCH OF AN IMPACT. THE CLOUD COVER...ON THE OTHER
HAND...WILL HAVE AN IMPACT ESP OVER THE NORTHERN HALF OF THE CWA
WHERE THE LACK OF INSOLATION WILL KEEP TEMPS DEPRESSED. FULLY
MIXED TO H92 WOULD ONLY SUPPORT LOWER 40S...AND HAVE GONE WITH
THESE VALUES IN THE SOUTH...BUT UNDERCUT THESE BY A FEW DEGREES
OVER NORTHERN AREAS...WITH HIGHS HERE STRUGGLING TO REACH 40. THIS
IS CLOSER TO THE COOLER MET NUMBERS.
NEXT CHALLENGE COMES MONDAY NIGHT AS A FAST MOVING VORT MAX DIVES
DOWN THE WESTERN EDGE OF TROUGH NOW DIGGING INTO NEW ENGLAND. THIS
FEATURE IS STILL CURRENTLY OVER THE GULF OF ALASKA SO DETAILS ON
IT/S EVOLUTION ARE LIKELY SUSPECT GIVEN DATA SPARSITY IN IT/S
INITIALIZATION. HOWEVER...GIVEN IT/S SOURCE REGION AND
TRAJECTORY...IT WILL CERTAINLY BE MOISTURE STARVED. ALSO...IT
APPEARS THAT THE REINFORCING SHOT OF COLD AIR WITH THE FEATURE
WILL PRETTY MUCH MISS US TO THE NORTH AND EAST...WITH ANY LAKE-
INDUCED PRECIP BEHIND IT PERHAPS BRUSHING MY NORTHEASTERN
ZONES...BUT NOT HAVING MUCH OF AN IMPACT. WILL ADD FLURRIES OVER
MY NORTHEASTERN ZONES...BUT GO NO HIGHER WITH POPS IN THIS
PACKAGE. EXPECT LOWS TO FALL TO NEAR 30...PERHAPS A DEGREE OR TWO
WARMER OVER THE NORTH WHERE THERE WILL BE MORE CLOUDINESS.
&&
.LONG TERM...
FOCUS OF ATTENTION IN EXTENDED CONTINUES TO BE WED-THU TIME FRAME AS
CUTOFF LOW OVER EXTREME SOCAL MOVES EAST AND PHASES WITH INCOMING
TROUGH DROPPING OUT OF CANADA. OP GFS HAS SWAYED BACK TO AN
EASTERLY PHASE/DRY SOLN WHILE THE 12Z/00Z ECMWF ARE QUITE SIMILAR TO
ONE ANOTHER AND CONTINUE A CLOSE CALL TAKING H85 LOW THROUGH CENTRAL
TN. STILL UNCERTAIN WRT TO MEASURABLE PRECIP OUT OF THIS SYSTEM
BUT STILL WORTHY OF CHC POPS WEDNESDAY NIGHT INTO THURSDAY AS
ROUGHLY HALF OF THE 00Z GFS ENSEMBLE MEMBERS INCL THE ENSEMBLE MEAN
STILL SUPPORT POPS ESP OVER THE SE HALF.
LESS IN DOUBT IS ARRIVAL OF COLDER TEMPS BY LATE WEEK AS SOLNS
ACROSS THE MODEL SUITE CONTINUE TO SHOW COLD AIR INTRUDING AND
DROPPING H85 TEMPS BELOW -10C BY FRI AFT. TEMPS/WIND DIR ALSO APPEAR
FAVORABLE FOR LAKE RESPONSE BEGINNING LATE THURSDAY. KEEPING POPS
FAVORING NE HALF AS ALTHOUGH THERE IS OBVIOUSLY CONSIDERABLE
UNCERTAINTY IN EVENTUAL LLEVEL FLOW DIR THIS FAR AHEAD...A GENERAL
PICTURE OF NW WIND BACKING W TO SW WITH TIME HAS BEEN SEEN FOR
MULTIPLE RUNS. TEMPS APPEAR SET TO FALL BACK TO NEAR/BELOW
CLIMO WITH MEX GUIDANCE LIKELY INFLUENCED BY CLIMO LATE BECOMING TOO
WARM. AS IT STANDS...GRIDDED HIGHS IN THE MID 30S BY SATURDAY UNDER
CLOUDY CYCLONIC FLOW ALOFT MAY BE OPTIMISTIC IF CURRENT TRENDS
CONTINUE.
&&
.AVIATION /06Z TAFS/...
FOG IS DEVELOPING NORTH AND WEST OF THE TERMINALS EARLY THIS
MORNING IN MOISTENING LLEVEL AIRMASS AHEAD OF SURFACE COLD FRONT.
EXPECT FOG TO EXPAND INTO THE TERMINALS BETWEEN 8-9Z...BUT GIVEN
SOME RESIDUAL LLEVEL FLOW...EXPECT ONLY MVFR RESTRICTIONS. FURTHER
MOISTENING SHOULD YIELD A STRATUS DECK BY MID MORNING AT
SBN...BEFORE THE COLD FRONT BEGINS TO MARCH EAST AND BRING A
CHANCE OF SHRAS TO THE TERMINALS THIS AFTERNOON. EXPECT A 4-6 HOUR
PERIOD OF POTENTIAL RAINFALL WITH CONDITIONS LIKELY DROPPING TO
IFR AT SBN...AND LOW MVFR AT FWA WITH IFR NOT OUT OF THE QUESTION
HERE IN THE 20-00Z TIMEFRAME. CONFIDENCE NOT YET TO THE POINT FOR
A TEMPO. FRONT CLEARS THE REGION THIS EVENING WITH RESIDUAL LAKE
INDUCED CLOUDINESS A GOOD BET. HAVE MAINTAINED MVFR CIGS THROUGH
THE END OF THE TAF PERIOD AS A RESULT. TOWARDS 6Z...COULD SEE
SOME LAKE EFFECT SHRASN APPROACH THE SBN TERMINAL.
LIGHT SOUTHWEST WINDS AROUND 5KTS WILL CONTINUE FOR THE OVERNIGHT.
BY MID MORNING...WINDS WILL FRESHEN TO 12G20KTS FROM THE
SOUTHWEST. THE WINDS WILL VEER THROUGH THE AFTERNOON AND BY
EVENING BE FROM THE NORTHWEST 12G18KTS.
CONDITIONS STILL LOOK A LITTLE TOO MARGINAL TO INCLUDE LLWS WITH
2KFT WINDS ABOUT 25KTS ABOVE LLEVEL INVERSION.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 1 PM EST
TUESDAY FOR LMZ043-046.
&&
$$
SHORT TERM...ARNOTT
LONG TERM...LUDINGTON
AVIATION...ARNOTT
