FXUS63 KIWX 292116
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
416 PM EST SUN NOV 29 2009

.SHORT TERM...

TONIGHT THROUGH MONDAY NIGHT

SFC TROUGH AND ASSOCIATED MID LEVEL IMPULSE CONTINUES TO PROGRESS 
EAST THIS AFTERNOON...SUPPORTING WIDESPREAD SHOWER ACTIVITY OVER THE 
FA. RAINFALL AMOUNTS HAVE GENERALLY BEEN LIGHT...WITH MAINLY LESS 
THAN A TENTH SO FAR. THIS IS EXPECTED GIVEN A RATHER LIMITED SUPPLY 
OF DEEP MOISTURE. TEMPS HAVE WARMED QUITE NICELY IN THE SE HALF OF 
THE FA WITH MID AND UPPER 50S COMMON. NORTH OF THE SFC TROUGH THAT 
BIFURCATES THE FA...TEMPS HAVE FALLEN OR HAVE HELD INTO THE 40S. SFC 
TROUGH AND ASSOCIATED UPPER LEVEL WAVE WILL CONTINUE TO PUSH EAST 
TONIGHT...WITH RAIN CHANCES ENDING AND CAA ENSUING. WEAK SFC RIDGING 
CAN BE EXPECTED THROUGH THE REMAINDER OF THE PERIOD WITH ANOTHER 
WEAK LAKE RESPONSE EXPECTED. SECONDARY MID LEVEL IMPULSE NOW 
TOPPING A WESTERN ROCKIES RIDGE OVER NORTHERN SK...WILL DIVE SE ON 
THE BACKSIDE OF THE DEPARTING EASTERN CONUS TROUGH. THIS FEATURE 
WILL RESIDE IN A ZONE OF PREVAILING WAA ON THE EDGE OF HEIGHT RISES 
AND WILL SUPPORT INCREASED CHANCES FOR LIGHT SNOW OF FLURRIES MONDAY 
NIGHT...NE 2/3 OF THE FA.

TONIGHT THROUGH MONDAY...FORCED ASCENT THE SFC TO H7 LAYER WILL 
CONTINUE TO SUPPORT RAIN SHOWERS THROUGH THE EVENING...TRENDING 
EAST. HAVE MADE MINOR TWEAKS TO THE END TIME OF RAIN...REFLECTING 
LATEST OB CONCERNS. WATER VAPOR IMAGERY AND RAOB DATA SUPPORT A 
PERIOD OF DIGGING WITH THE ADVANCING TROUGH...AND THIS HAS AND WILL 
CONTINUE TO OFFER SLOWER PROPAGATION SPEEDS. NAM AND LOCAL WRF 
TIMING ARE VERY REASONABLE. NOT EXPECTING A WASH OUT BY ANY MEANS 
GIVEN SOMEWHAT LIMITED MOISTURE...SUPPORTING A HIGH POP LOW QPF 
EVENT. SFC TROUGH WILL CONTINUE TO PUSH SE THROUGH THE PERIOD WITH 
CAA SUPPORTING A WEAK LAKE RESPONSE BY LATE TONIGHT. MARGINAL DELTA 
T/S OF AROUND 13 BY DAYBREAK WILL ONLY OFFER A LIGHT RAIN/SNOW OR 
FLURRY EVENT...GIVEN ONLY 150-175 J/KG OF LAKE INDUCED CAPE. 
HENCE...HAVE TRIMMED BACK POPS AND LIMITED MAIN PRECIP MENTION TO 
THE NW ZONES...WITH FLURRIES POSSIBLE DOWNWIND LK MI THROUGH LATE 
MORNING MON. LAKE CLOUDS ARE EXPECTED TO HOLD STRONG ACROSS MOST OF 
THE FA/ SAVE THE SW/ THROUGH MONDAY MORNING...WITH A NORTHWARD TREND 
IN RESPONSE TO BACKED FLOW AHEAD OF THE SK UPPER WAVE. EXPECTING 
COOL T/S WITH HIGHS GENERALLY IN THE LOWER 40S...UPPER 30S WHERE 
CLOUDS HANG ON LONGEST.

MONDAY NIGHT...ANOTHER MID LEVEL DISTURBANCE...AKIN TO A CLIPPER 
SYSTEM WILL PUSH INTO THE REGION AND SUPPORT INCREASED ASCENT IN THE 
H8-H7 LAYER. COLD PROFILES WITH ASCENT MAXIMIZED NEAR THE DGZ WILL 
FAVOR LIGHT SNOW OR FLURRY CHANCES...GIVEN LIMITED MOISTURE AND 
FORCING. HAVE ADDED A LOW POP FOR THIS IN THE NE WHERE FORCING WILL 
BE MAXIMIZED AND A HUNDREDTH IS NOT OUT OF THE QUESTION. 
HOWEVER...MOST AREAS ARE EXPECTED TO SEE AT MOST VERY LIGHT SNOW OR 
FLURRIES...IF ANYTHING AT THIS POINT. LOOK FOR MOSTLY CLOUDY SKIES 
WITH LOWS IN THE LOW TO MID 30S.

&&

.LONG TERM...
TUESDAY THROUGH SATURDAY. MODEL TRENDS CONT TO CONCUR WITH FCST WITH 
INCRSD LAKE EFFECT POTNL LATER IN WEEK. CURRENTLY A FULL LATITUDINAL 
TROF EXITS NR 150W WITH STRONGER PV ANOMALY IN GULF OF AK AND A BAJA 
H5 CUTOFF. BY MIDWEEK THE NORTHERN STREAM EJECTION INTO NRN MN/WRN 
LAKE SUPR WITH SOUTHERN WAVE TRAVERSING EWD INTO ARKLATEX BY 12 UTC 
WED. SOUTHERN SYSTEM THEN BEGINS NWD TREK WITH DECENT LLVL GOMEX 
TAP. QUESTION REMAINS ON SYSTEMS ABILITY TO DRAW SUFFICIENT MSTR NWD 
INTO CWA BY LATE WED AFTN...HOWEVER AS SYSTEM BEGINS TO PHASE WITH 
NRN STREAM ENERGY...ANTICIPATE A FAIRLY RAPID MOISTURE PUSH WITH NRN 
IN COL DEEPENING INTO TN VLY WED AFTN TO UPR OH VLY WED NIGHT. LARGE 
SCALE ASCENT WITH BROAD AREA OF H7-H5 WITH 100-140DAM/12 HR FALLS BY 
ERLY THU ACRS OH VLY INTO SOUTHERN GREAT LAKES CONT TO SUPPORT CHC 
POPS WED NIGHT WITH A SLIGHT UPWARD NUDGE FOR RASN MIX GIVEN COOLER 
SUB-CLOUD T/TW PROFILES. GOOD CHC FOR RAIN CHANGING TO SNOW SOMETIME 
WED EVE/NIGHT...HOWEVER ATTM UNCERTAINTIES IN TRACK AND STRENGTH AS 
SRN SYSTEM BECOMES IGNITED BY PHASED NRN STREAM ENERGY TO HAVE 
IMPACT ON DEGREE OF COLD AIR INTRUSION AND TIMING...SO WL CONT WITH 
MIX MENTION FOR NOW. SUFFICIENTLY DEEP COLD AIR ACRS REGION INTO THU 
WITH FAVORABLE THU AFTN/NIGHT LES EVENT. MOST FCST CHANGES WERE 
CENTERED ON THE PENDING LES EVENT WITH PRELIMINARY LAKE EFFECT SNOW 
PARAMETERS RISING INTO 2.0-2.3 RANGE THURSDAY NIGHT. FAVOR A MORE 
WESTERN/NORTHWEST DRAW INTO NRN STREAM S/W PER LATEST GEM/ECMWF AND 
SEVERAL OF GFS ENSEMBLE MEMBERS...AS 12 UTC GFS HAS NOW BECOME THE 
PROGRESSIVE OUTLIER WITH THIS EVENT IN SPITE OF PREV GFS ITERATIONS. 
BUMP TO LIKELY SHSN WITH ANTICIPATED ACCUMULATIONS IN FAVORED 
BERRIEN/NERN LAPORTE INITIALLY THU AFTN TO MORE BERRIEN/CASS COUNTY 
MI THU NIGHT AS CBL WINDS BACK. SHIED AWAY FROM OPER GFS WARM AIR 
ADVECTION PRECIP BREAKOUT ON DY7 AS SATURDAY NRN STREAM S/WV INTO 
WRN GRTLKS SUSPECT GIVEN EARLIER MODEL BREAKDOWN.   

&&

.AVIATION.../18Z TAFS/
UPPER LEVEL IMPULSE AND ASSOCIATED SFC COLD FRONT WILL CONTINUE TO
SLOWLY PUSH EAST ACROSS THE FA TODAY. EXPECT SCT-NUMEROUS SHOWERS
ACROSS THE FA...WITH VEERING LL WINDS BEHIND THE SFC TROUGH. A
PERIOD OF IFR CIGS IS EXPECTED WITH THE FROPA AS CAA ENSUES AND
THE LL/S BEGIN TO COOL TOWARD SATURATION. LOW END MVFR VIS IS ALSO
POSSIBLE UNTIL DRIER AIR MOVES INTO THE AREA LATE THIS EVENING.
EXPECT BKN-OVC CIGS THROUGH MUCH OF MON GIVEN LK MI MODIFIED BL FLOW
IN A CAA REGIME...WITH MVFR CIGS ARE EXPECTED. A PERIOD OF LIGHT
LAKE EFFECT RAIN OR SNOW IS ALSO POSSIBLE IN THE NW MON MORNING.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 1 PM EST TUESDAY FOR LMZ043-046.

&&

$$

SHORT TERM...JC
LONG TERM...MURPHY
AVIATION...JC