FXUS63 KIWX 290541
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1241 AM EST SUN NOV 29 2009
.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.
&&
.PREV DISCUSSION... /ISSUED 739 PM EST SAT NOV 28 2009/
UPDATE...
OBS SUGGEST A FEW AREAS HAVE DECOUPLED SUFFICIENTLY THIS EVE TO
ALLOW FOR STRONG RADIATIONAL COOLING. THIS MAINLY COVERED IN GOING
GRIDS BUT DID UPDATE TO LOWER MINS IN SW MICHIGAN WHERE A COUPLE
OF SITES WERE ALREADY NEAR OR BLO EARLIER FCST MINS.
PREV DISCUSSION... /ISSUED 421 PM EST SAT NOV 28 2009/
SHORT TERM...
TONIGHT THROUGH SUNDAY NIGHT
SHORTWAVE RIDGING CONTINUES TO BRING CLEAR SKIES AND WARMER
CONDITIONS TO THE REGION AHEAD OF THE NEXT UPPER IMPULSE AND
ASSOCIATED SFC REFLECTION. TEMPS HAVE RESPONDED WELL DUE TO
INSOLATION/MIXING/AND WAA WITH 50S COMMON ACROSS THE FA...ESPECIALLY
THE SW. UPPER TROUGH OVER THE NORTHERN PLAINS AS WELL AS A
DISTURBANCE OVER THE EASTERN TX/WESTERN MISSISSIPPI VALLEY WILL
SUPPORT INCREASED RAIN CHANCES BY SUNDAY AS AN ASSOCIATED SFC COLD
FRONT ENTERS THE FA. MAIN PLAYER WILL BE THE NORTHERN STREAM
TROUGH...SUPPORTING INCREASED THETA-E ADV TONIGHT AHEAD OF THE
ADVANCING LL TROUGH FEATURE. LL MOISTURE AXIS NOW OVER OK/KS/NE WILL
CONTINUE TO PUSH EAST TONIGHT...WITH SUSTAINED 1-5 KFT FLOW OF 20
TO 40 KNOTS. HAVE REMAINED CLOSE TO A NAM/LOCAL WRF/GFS SOLUTION
GIVEN FAVORED INITIATION AND GOOD AGREEMENT WITH MOMENTUM AND
THERMAL FIELDS AT 12Z SAT...AS WELL PREFERRED WAVE HANDLING.
TONIGHT...SFC TROUGH WILL CONTINUE TO PUSH SE TOWARD THE REGION WITH
INCREASING LL FLOW. POSITIVE THETA-E ADV AHEAD OF THIS FEATURE WILL
SUPPORT AN INCREASE IN LL MOISTURE. EXPECTED MOSTLY CLEAR SKIES
SUPPORTING DECENT RADIATIONAL COOLING WILL OFFER INCREASED BR
CHANCES TOWARD DAWN. HOWEVER...INCREASED LL WINDS SHOULD KEEP FOG
PRODUCTION AT BAY. OTHERWISE...TEMPS ARE EXPECTED TO BE WARMER
COMPARED TO LAST NIGHT WITH LOWS IN THE 30S.
SUN...UPPER IMPULSE OVER THE NORTHERN PLAINS WILL DIG SE INTO THE
MIDWEST...AND PHASE WITH THE EASTERN TX WEAK SYSTEM. INCREASED
LARGE SCALE ASCENT AHEAD OF THIS SYSTEM IN THE PRESENCE OF WEAK
UPGLIDE WILL OFFER INCREASED POPS FOR RAIN. RAIN CHANCES ARE
EXPECTED TO START IN THE NW CLOSER TO THE LL TROUGH AND SPREAD EAST
THROUGH THE DAY AS UVM INCREASES OVER THE FA. WITH THE BULK OF
ASCENT REMAINING NORTH OF THE FA AND GIVEN THE DIGGING NATURE OF THE
UPPER WAVE OVER THE FA...BETTER ASCENT IS EXPECTED SE OF THE FA. ONE
CONCERN SUN IS HIGHS. SFC TROUGH WILL BE SLOW TO PUSH THROUGH THE FA
AND GIVEN STRONG MIXED FLOW ON THE SE PERIPHERY OF THE FRONT...SE
AREAS LOOK TO WARM QUITE WELL AS RAIN AND CLOUDS ARE EXPECTED TO
HOLD OFF UNTIL THE AFTERNOON. OPTED FOR WARMER NUMBERS THERE WITH
COOLER READINGS IN THE NW WHERE CLOUDS AND RAIN ARE
EXPECTED/POSSIBLE.
SUN NIGHT...COLD FRONT WILL PUSH SE OF THE FA WITH INCREASING NW
FLOW AND CAA ENSUING. FORECAST MODELS PROG H85 TS DOWN TO -7 C
SIMILAR TO THU. THIS AGAIN SUPPORTS A WEAK LAKE RESPONSE WITH LIGHT
RAIN AND SNOW POSSIBLE IN A WELL MIXED LAKE MODIFIED BL. MODEL PROGS
INDICATE A LITTLE HIGHER UPSTREAM RH THAN AVAILABLE WITH THE LAST
COLD FRONT ON THU. HOWEVER...RELATIVELY MODEST DELTA T/S OF ONLY
12-13 C /H85/ WILL ONLY SUPPORT A WEAK LAKE RESPONSE GIVEN FLOW
TRAJECTORY. NAM BUFR DATA SUPPORTS ONLY 150 J/KG OF LAKE INDUCED
CAPE...WHICH LIKELY WILL ONLY OFFER FLURRIES/LIGHT RAIN. HAVE
RETAINED PREVIOUS LOW POPS UNTIL A BETTER GRASP OF THERMAL FIELDS
ARE OBTAINED. LOOK FOR COOLER TEMPS WITH LOWS GENERALLY IN THE LOWER
30S.
LONG TERM...
MONDAY THROUGH FRIDAY. FEW CHNGS WRT LONG TERM PD. CONTD RA/SN MIX
POTNL ON MONDAY WITH SLIGHT SFC LYR BASED COOLING WITH SFC-1.5 KFT
LYR TW RMNG AOA 0C...AS MIDLVL S/WV ACRS SASK/ERN MT SHARPENS ERN
GRTLKS TROF AND FORCES NEW ENGLAND CYCLOGENESIS BY MONDAY AFTN. REAL
CRUX OF FCST ISSUES HOWEVER ARE RELEGATED TO DYS5-7 TIMEFRAME AS KEY
PLAYERS ARE NRN STREAM GULF OF AK AND CURRENT SOCAL CUTOFF EMERGE
EWD INTO NRN PLAINS AND ERN TX RESPECTIVELY BY 12 UTC WED.
INTRODUCED LOW CHC RASN EARLIER/WED AFTN AS RAPID NNEWD ADVANCE OF
SRN STREAM SFC REFLECTION MOVES INTO KY/TN WITH GOOD LLVL MOISTURE
TAP AHEAD AND NORTH OF FEATURE AND INTO INVERTED SFC TROFING ACRS
MID/SRN GRTLKS. PREFERENCE STILL LIES WITH A MORE SLOWER/WRN
EVOLUTION...AS PER 28/00 UTC GEM AND 12 UTC OP GFS AND MANY ENSEMBLE
MEMBERS...OF DEEP GREAT LAKE VORTEX AS 140-160M/12HR 7-5H HGHT FALLS
CONGEAL ACRS OH VLY/SRN GRTLKS BY 00 UTC THU. 12 UTC ECMWF WHILE
STILL MORE PROGRESSIVE HAS TRENDED OVER LAST RUNS WITH DEEPER AND
MORE WEST/NORTHWEST SOLN WHICH BEARS TO REASON GIVEN STRENGTH OF NRN
STREAM 150W STRENGTH WITH 170E KICKER PER WV IMAGERY AND THE INITIAL
TRAILING OF SRN STREAM SYSTEM AT LEAST INTO MIDWEEK. RAPID DEEPENING
HAS LED TO A SQUELCHED DIURNAL RISE ON THU AND EXTENSION OF LES
EVENT INTO FRI NIGHT BEFORE INVERSION LOWERS/WINDS BACK ON DY7 TO
END WHAT COULD BE FIRST ACCUM SNOW EVENT/ALBEIT PRIMARILY FOR LES
FAVORED NRN/NWRN CWA.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...JC
LONG TERM...MURPHY
AVIATION...ARNOTT
UPDATE...JT
