FXUS63 KIWX 291617
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1117 AM EST SUN NOV 29 2009
.UPDATE...
UPPER LEVEL IMPULSE AND ASSOCIATED LL TROUGH FEATURE WILL CONTINUE
TO PUSH EAST ACROSS THE REGION TODAY. PROFILER WINDS HAVE
RESPONDED QUITE WELL AS EVIDENCED AT WOLCOTT...WITH 35 KNOTS AT H85
PRESENT THERE. INCREASED LL MOMENTUM FIELDS CONTINUE TO SUPPORT
THETA-E ADVECTION AHEAD OF THE LL TROUGH AXIS. STRONG FORCING
ALONG THIS STACKED LL TROUGH FEATURE IN THE PRESENCE OF INCREASED
LARGE SCALE ASCENT CONTINUES TO SUPPORT INCREASING COVERAGE SHRA
AND EVEN TS. INCREASED INSTABILITY WITH SHARP COOLING ALOFT CAN BE
SEEN IN THE 12Z DVN SOUNDING WHERE NEARLY 300 J/KG OF ELEVATED
PARCEL LIFT CAPE AROUND THE H75 LEVEL IS PRESENT. LARGE SCALE
ASCENT WILL CONTINUE TO INCREASE ACROSS THE REGION TODAY WITH
INCREASING SHOWER CHANCES THIS AFTERNOON. HAVE ADDED A SLIGHT
CHANCE THUNDER MENTION ACROSS THE NORTH WHERE FORCING FOR ASCENT
AND LL CONVERGENCE WILL BE MAXIMIZED.
ALL ELSE IN GOOD SHAPE.
&&
.PREV DISCUSSION... /ISSUED 625 AM EST SUN NOV 29 2009/
AVIATION /12Z TAFS/...
CONDITIONS LOOKING A LITTLE BETTER THAN PREVIOUSLY THOUGHT AS
THICKER FOG HAS REMAINED JUST NORTH OF SBN WITH STRATUS DECK STILL
WELL NORTH OVER CENTRAL AND NORTHERN LOWER MICHIGAN. SO...DO
EXPECT A PERIOD OF VFR CONDITIONS TO START THE DAY BEFORE
DETERIORATION OCCURS BY EARLY AFTERNOON.
EXPECT VFR CONDITIONS TO RAPIDLY DETERIORATE IN THE 16-18Z
TIMEFRAME AT SBN WITH IFR CIGS AND MVFR VSBYS DEVELOPING ALONG WITH
SOME SHRA. WILL CONTINUE TO BE A LITTLE MORE OPTIMISTIC AT FWA
WITH LOW MVFR CONDITIONS EXPECTED AFTER 20Z. A 4-5 HOUR PERIOD OF
SHRAS IS EXPECTED BEFORE THESE END WITH RESIDUAL MVFR CIGS THROUGH
THE REMAINDER OF THE TAF PERIOD. SOME WEAK LAKE EFFECT SPRINKLES/SHRAS
POSSIBLE AT SBN THROUGH THE EVENING HOURS AND HAVE INDICATED THIS
POTENTIAL WITH A TEMPO.
SOUTHWEST WINDS WILL STRENGTHEN TO 12G20KTS FOR THE DAY
TODAY...GRADUALLY VEERING MORE WESTERLY DURING THE AFTERNOON.
WINDS WILL CONTINUE TO VEER NORTHWESTERLY 12G18KTS FOR THE
OVERNIGHT TONIGHT.
PREV DISCUSSION... /ISSUED 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.
&&
.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
UPDATE...JC
