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000
FXUS63 KIWX 041753
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1253 PM EST WED DEC 4 2013

.SYNOPSIS...
ISSUED AT 1245 PM EST WED DEC 4 2013

RAIN SHOWER CHANCES WILL INCREASE THROUGH THE AFTERNOON AND INTO
THE OVERNIGHT AS A COLD FRONT CROSSES THE AREA. THIS COLD FRONT
WILL BRING A RETURN TO MUCH COLDER TEMPERATURES FOR THE END OF THE
WEEK WITH A CHANCE OF SNOW THURSDAY NIGHT AND FRIDAY. BELOW NORMAL
TEMPERATURES ARE EXPECTED THIS WEEKEND AND INTO EARLY NEXT WEEK AS
AS COLD CANADIAN AIR FILTERS INTO THE GREAT LAKES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 350 AM EST WED DEC 4 2013

LEE CYCLONE CURRENTLY OVER THE SOUTHERN PLAINS WILL BEGIN TO LIFT
NORTHEAST TODAY AND TAKE THE CLIMATOLOGICALLY FAVORED PATH THROUGH
THE NORTH CENTRAL GREAT LAKES BY TONIGHT AS POSITIVELY TILTED
LONGWAVE TROUGH LIFTS OUT OF THE ROCKY MOUNTAIN STATES. FURTHER
DEEPENING OF THIS SURFACE LOW WILL BE SUPPORTED BY UPPER DIVERGENCE
IN LEFT EXIT REGION OF A 150+ KT JET STREAK...DEEP/FOCUSED PV
ADVECTION ASSOCIATED WITH MID/UPPER LEVEL WAVE ON CYCLONICALLY
SHEARED SIDE OF AFOREMENTIONED JET STREAK...AND OF COURSE LAKE
AGGREGATE INSTABILITY CONTRIBUTIONS. THE VAST MAJORITY OF THIS
FORCING FOR ASCENT WILL BE FOCUSED WELL NORTH AND NORTHWEST OF HERE
BUT THE DYNAMIC NATURE OF THIS SYSTEM IS STILL IMPORTANT TO NOTE FOR
LOCAL PRECIP CHANCES LATE THIS AFTERNOON AND INTO TONIGHT...EVEN IF
QPF AMOUNTS WILL BE LIGHT. LULL IN STEADIER RAIN WILL CONTINUE
THROUGH THE MORNING HOURS AS THE MAIN WARM FRONT SLOWLY LIFTS NORTH.
SOME VERY LIGHT DRIZZLE MAY BE POSSIBLE BUT ANYTHING MORE THAN A
TRACE WILL BE DIFFICULT. LATEST OBS/RADAR DATA ACTUALLY SUPPORT JUST
WIDESPREAD BR FOR OUR AREA AND WILL THEREFORE GO WITH JUST FOG
MENTION AND NO PRECIP. THIS WILL CHANGE BY LATE AFTERNOON AS
STRENGTHENING SURFACE LOW APPROACHES THE UPPER MIDWEST. TIGHTENING
PRESSURE/HEIGHT GRADIENT WILL LEAD TO A STRENGTHENING LLJ...TO OVER
40 KTS BY 00Z THIS EVENING. CORRESPONDINGLY...A MARKED UPTICK IN
295K ISENTROPIC OMEGA FIELDS IS SEEN BY LATE THIS AFTERNOON. ALL OF
THE 00Z DETERMINISTIC MODELS...SAVE FOR THE SLIGHTLY DRIER
NAM...DEPICT SOME LIGHT QPF FOR THE AREA BY 00Z AND THIS MAKES SENSE
GIVEN STRENGTH OF LOW LEVEL THETA-E SURGE/ISENTROPIC ASCENT.
LIMITING FACTOR WILL BE MIDLEVEL DRY AIR ENTRAINMENT SEEN ON WATER
VAPOR LOOP AND MODEL RH FIELDS. LACK OF MORE EFFICIENT BERGERON
PRECIPITATION PROCESSES WILL CERTAINLY LIMIT QPF TOTALS BUT MOST
PLACES SHOULD BE ABLE TO SQUEEZE OUT AT LEAST A FEW HUNDREDTHS GIVEN
STRENGTH OF ISENTROPIC ASCENT AND AT LEAST A BRIEF PERIOD OF
SUFFICIENTLY DEEP MOISTURE SEEN ON FORECAST SOUNDINGS. MAY
TRANSITION TO MORE OF A DRIZZLE EVENT AFTER THE INITIAL WARM/MOIST
AIR SURGE BUT AT LEAST LOW END LIKELY POPS SEEM WARRANTED IN THE
21Z-03Z TIMEFRAME. SURFACE COLD FRONT WILL THEN PASS THROUGH THE
AREA BY LATE TONIGHT WITH LITTLE FANFARE. AS PREVIOUSLY MENTIONED
THE BEST HEIGHT FALLS AND UPPER JET DYNAMICS WILL PASS WELL TO OUR
NORTHWEST. LOW LEVEL FRONTAL RESPONSE IS THEREFORE FAIRLY MUTED FOR
OUR AREA AND EXPECT JUST A BROKEN LINE OF LIGHT SHOWERS. WORTHY OF A
HIGH CHANCE POP BUT ONLY A HUNDREDTH OR TWO OF QPF. COLDER AIR WILL
BEGIN TO FILTER INTO THE AREA BY 12Z THURSDAY BUT APPEARS TO BE A
SUFFICIENT LAG IN ADVECTION OF SUBFREEZING TEMPS TO KEEP ALL PRECIP
LIQUID.

HIGH TEMP FORECAST CONTINUES TO BE A STRUGGLE...SPECIFICALLY WHAT
AREAS...IF ANY...ARE ABLE TO MIX OUT AND TAP INTO VERY WARM 925MB
TEMPS. BRUTE FORCE SLUG OF WARM/MOIST AIR AT THE SURFACE SHOULD GET
US INTO AT LEAST THE LOW TO MID 50S BUT WHETHER WE CLIMB MUCH HIGHER
IS QUESTIONABLE GIVEN STUBBORN NEAR SURFACE INVERSION. TOOK A
CONSENSUS APPROACH FOR NOW GIVEN LOW CONFIDENCE AND WENT WITH MID
50S NORTH/UPPER 50S SOUTH. ADJUSTMENTS IN EITHER DIRECTION ARE
POSSIBLE LATER TODAY. MIN TEMPS WILL DEPEND ENTIRELY ON TIMING OF
COLD FRONT OVERNIGHT AS WE WILL PROBABLY HIT OUR MINIMUMS RIGHT AT
12Z AS CAA RAMPS UP. BEST GUESS AT TIMING GIVES MID 30S FOR OUR
EXTREME NORTHWEST AND ONLY AROUND 50F FOR OUR SOUTHEAST BUT FURTHER
ADJUSTMENTS MAY BE NECESSARY.

&&

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 350 AM EST WED DEC 4 2013

THE PRIMARY FORECAST CONCERNS FOR THIS PERIOD WILL BE TRANSITION TO
COLDER TEMPS WITH FRONTAL PASSAGE THURSDAY...FOLLOWED BY INCREASING
CHANCES OF MEASURABLE SNOW ACROSS SOUTHEAST HALF/THIRD THURSDAY
NIGHT/FRIDAY...WITH ANOTHER CHANCE OF SYNOPTIC SNOW LATE WEEKEND
LEADING INTO MUCH COLDER CONDITIONS.

UPPER PV ANOMALY WILL CONTINUE TO LIFT NORTHWARD ACROSS SOUTHERN
ONTARIO EARLY THURSDAY AS SFC FRONT CLEARS FAR EASTERN LOCATIONS
AROUND 12Z. BROAD SOUTHWESTERLY MID/UPPER FLOW IN THE WAKE OF THIS
PV ANOMALY WILL RESULT IN MID LEVEL FRONT HANGING UP ACROSS THE
REGION WITH TIGHT BAROCLINIC ZONE RESIDING ACROSS THE SOUTHERN GREAT
LAKES/OHIO RIVER VALLEY THROUGH MUCH OF THIS PERIOD. COLD ADVECTION
WILL BE STRONG ENOUGH ON THURSDAY FOR NON-DIURNAL TRENDS WITH HIGHS
LIKELY REACHED EARLY MORNING. DID HOLD ONTO SOME MORNING SLIGHT
CHANCE -RA POPS ACROSS THE FAR EAST WITH FRONTAL PROGRESSION...BUT
DEEPER MOISTURE PROFILES PRECEDING THE FRONT WILL QUICKLY SHIFT EAST
OF THE AREA DURING THE MORNING. OTHERWISE...DRY CONDITIONS EXPECTED
FOR THE REMAINDER OF THE DAY THURSDAY WITH BREEZY CONDITIONS UNDER
STRONG CAA AND WELL MIXED LOW LEVELS.

THE FOCUS FOR THURSDAY NIGHT THROUGH FRIDAY WILL BE NEXT UPPER LEVEL
SHORT WAVE KICKING OUT OF THE FOUR CORNERS REGION THAT WILL BEGIN TO
INTERACT WITH PREEXISTING BAROCLINIC ZONE ACROSS THE AREA THURSDAY
NIGHT. INCREASING MID LEVEL FRONTOGENESIS SHOULD SPREAD FROM
SOUTHWEST TO NORTHEAST ACROSS THE AREA THURSDAY NIGHT WITH SOME
QUESTIONS AS TO PRECIP TYPES AT ONSET...ESPECIALLY ACROSS FAR
SOUTHEAST. THERMAL PROFILES SUGGEST THAT ANY POTENTIAL MIXED PRECIP
SHOULD BE SHORT LIVED AND RELATIVELY LIGHT IN NATURE...AS LOW LEVEL
EVAPORATIVE COOLING PROCESSES SHOULD TAKE PRECIP TO THE FORM OF SNOW
IN THE EVENING. MID LEVEL FRONTOGENESIS WILL ACT TO STRENGTHEN UPPER
LEVEL JET STREAK (170 KNOTS) ACROSS THE GREAT LAKES REGION...FURTHER
ENHANCING SYNOPTIC FORCING IN RIGHT ENTRANCE REGION ACROSS SOUTHERN
GREAT LAKES/OHIO VALLEY. CONFIDENCE STILL SOMEWHAT LOW IN REGARDS TO
PLACEMENT OF HIGHEST QPF...GIVEN ANTICIPATED SHARP CUTOFF TO
MID/UPPER LEVEL FGEN FORCING ACROSS THE AREA...BUT HAVE NOT STRAYED
MUCH FROM PREVIOUS FORECAST WITH 1-3/2-4 INCH TYPE SNOW
ACCUMULATIONS POSSIBLE ACROSS THE FAR SOUTH/SOUTHEAST THURSDAY NIGHT
INTO FRIDAY.

AFOREMENTIONED UPPER WAVE KICKING OUT OF SOUTHWEST CONUS WILL RACE
EASTWARD ACROSS THE REGION FRIDAY NIGHT IN A DAMPENING STATE...BUT
SOME LIGHT SNOW MAY LINGER ACROSS THE SOUTHEAST IN THE EVENING UNTIL
THIS TROUGH AXIS CLEARS TO THE EAST. SOME LAKE EFFECT SNOW SHOWERS
ARE POSSIBLE FRIDAY NIGHT INTO EARLY SATURDAY ALTHOUGH RELATIVELY
SHALLOW LAKE INDUCED EQUILIBRIUM HEIGHTS AND DRY MID LEVEL PROFILES
SHOULD BE LIMITING FACTORS. A BROAD 1035 MB HIGH WILL THEN BUILD
ACROSS THE REGION SATURDAY/SUNDAY PROVIDING DRY CONDITIONS FOR
MOST OF THE WEEKEND.

MEDIUM RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT IN A MORE
SIGNIFICANT UPPER TROUGH TAKING SHAPE ACROSS SOUTHWEST CONUS
SATURDAY NIGHT INTO SUNDAY...EVENTUALLY ALLOWING STRONGER BAROCLINIC
ZONE TO SHIFT BACK NORTHWARD INTO THE AREA SUNDAY NIGHT. WAA/THETAE
SURGE DOWNSTREAM OF THIS WAVE SHOULD PRODUCE ANOTHER ROUND OF PRECIP
SOMETIME IN THE LATE SUNDAY/MONDAY TIME PERIOD. SOME POTENTIAL MAY
EXIST FOR BRIEF PERIOD OF MIXED PRECIP AS ELEVATED WARM LAYER LIFTS
NORTHWARD. 00Z EC APPEARS TO HAVE COME MORE INLINE WITH GFS/GEFS
MEANS IN FURTHER EAST SFC DEVELOPMENT...SO AT THIS TIME WILL KEEP
MENTION ALL -SN BUT MAY NEED TO ADJUST THIS IN FUTURE FORECASTS.
MAIN LIMITING FACTOR TO PRECIP AMOUNTS WITH THIS SYSTEM MAY END UP
BEING A RELATIVELY BRIEF RESIDENCE TIME OF DEEPER MOISTURE PROFILES.
ALL SIGNALS STILL POINT TO ARCTIC AIRMASS OVERSPREADING THE AREA
BEHIND THIS SYSTEM TOWARD THE END OF THE PERIOD WITH HIGHS LIKELY
STRUGGLING TO REACH 20 BY TUESDAY. ALONG WITH THE ARCTIC AIR MASS
WILL COME INCREASED LAKE EFFECT SNOW SHOWER CHANCES FOR THE
EARLY/MID PORTIONS OF NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON) ISSUED
AT 1258 PM EST WED DEC 4 2013

MORE FERVENT MIXING WITHIN SATURATED BLYR FINALLY BRINGING VSBYS UP
SUBSTANTIALLY. PRESENCE OF ELEVATED INVERSION AND RAMPING SSWRLY
FLOW ALOFT NECESSITATES WS MENTION INTO AT LEAST LATE AFTN-LATE
EVENING HOURS. OTHERWISE FOCUS ON RISING CIGS AND TIMING OF
SIGNIFICANT WINDSHIFT/FROPA TOWARD DAYBREAK WHEN CIGS SHOULD FINALLY
RISE ABOVE ALT FUEL REQUIREMENTS.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...DENSE FOG ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LMZ043-046.

&&

$$

SYNOPSIS...BENTLEY
SHORT TERM...AGD
LONG TERM...MARSILI
AVIATION...MURPHY


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