Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 121052
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
652 AM EDT FRI SEP 12 2014

.SYNOPSIS...
ISSUED AT 426 AM EDT FRI SEP 12 2014

ANOTHER COOL DAY WILL BE IN STORE FOR THE REGION TODAY...WITH DRY
CONDITIONS EXPECTED TO PERSIST THROUGH EARLY THIS EVENING. THE NEXT
UPPER LEVEL SYSTEM ACROSS THE ROCKIES WILL REACH THE WESTERN GREAT
LAKES TONIGHT PROVIDING A GOOD CHANCE OF RAIN. THIS SYSTEM WILL PULL
OFF TO THE EAST EARLY SATURDAY WITH PERHAPS SOME LINGERING LIGHT
RAIN SHOWERS OR PATCHY DRIZZLE IN THE MORNING. DRY...BUT COOL
CONDITIONS CAN THEN BE EXPECTED FOR THE REMAINDER OF THE WEEKEND.
HIGH TEMPERATURES THIS AFTERNOON WILL RANGE FROM THE UPPER 50S
ACROSS NORTHEAST ILLINOIS INTO CENTRAL LOWER MICHIGAN...TO THE MID
AND UPPER 60S ACROSS CENTRAL INDIANA. LOW TEMPERATURES TONIGHT WILL
GENERALLY BE IN THE UPPER 40S TO LOWER 50S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 426 AM EDT FRI SEP 12 2014

MAIN FORECAST ITEMS FOR THE SHORT TERM WILL CONTINUE TO BE THE MUCH
BELOW NORMAL TEMPERATURES...AND LIKELIHOOD OF RAIN TONIGHT.

IN THE VERY NEAR TERM...SKY COVER TRENDS WILL POSE THE BIGGEST
CHALLENGE. LOW LEVEL FLOW HAS VEERED MORE NORTHEASTERLY THIS MORNING
AS LOW LEVEL ANTICYCLONE ACROSS THE GREAT LAKES MIGRATES EASTWARD.
SEE LITTLE OPPORTUNITY FOR STRATUS TO CLEAR ACROSS THE EAST OVER THE
NEXT SEVERAL HOURS. VEERED FLOW HAS PROMOTED SOME BREAKS IN STRATUS
ACROSS PORTIONS OF NORTHWEST/NORTH CENTRAL INDIANA AND SOUTHWEST
LOWER MICHIGAN HOWEVER. WITH LOW LEVEL TRAJECTORIES PROVIDING SOME
MARINE INFLUENCE FROM LAKE ERIE/HURON THIS MORNING AND PERSISTENCE
OF FRONTAL INVERSION TODAY...WILL MAINTAIN MOSTLY CLOUDY CONDITIONS
ACROSS APPROXIMATELY EASTERN TWO THIRDS...WITH PARTLY TO MOSTLY
CLOUDY CONDITIONS ACROSS THE FAR WEST GIVEN MORE PRONOUNCED LAKE
MICHIGAN INFLUENCE SHIFTING WEST OF THE AREA THIS MORNING. SLIGHTLY
HIGHER INVERSION HEIGHTS TODAY COMBINED WITH HIGHER BASED
STRATUS...AND POSSIBILITY OF SOME INSOLATION ESPECIALLY WESTERN
AREAS...SHOULD PROVIDE SOME SLIGHT MODERATION TO MAX TEMPS TODAY
GENERALLY IN THE LOWER 60S.

FOR TONIGHT...A STRONG UPPER LEVEL PV ANOMALY ACROSS THE NORTHERN
ROCKIES WILL TRACK INTO THE WESTERN GREAT LAKES. STRONG MID/UPPER
LEVEL FRONTOGENESIS WILL DEVELOP DOWNSTREAM OF THIS PV ANOMALY
ACROSS THE WESTERN GREAT LAKES THIS EVENING...ALLOWING FOR EASTWARD
EXPANSION OF CENTRAL PLAINS PRECIP SHIELD ACROSS LOCAL AREA. A
STRONG 500-300 HPA Q-VECTOR CONVERGENCE SIGNAL NOTED WITH THIS
FEATURE ESPECIALLY IN THE 03Z-09Z TIMEFRAME...WITH 00Z NAM
REPRESENTING SLIGHTLY SLOWER TIMING COMPARED TO GFS/EC/SREF
CONSENSUS. HAVE TRIED TO INCORPORATE BLENDED APPROACH FOR THIS
FORECAST IN REGARDS TO THE INCREASE IN POPS FROM WEST TO EAST THIS
EVENING. STRENGTHENING UPPER LEVEL DIVERGENCE IN LEFT EXIT REGION OF
UPPER JET STREAK SHOULD ALSO AID IN DEVELOPMENT OF INVERTED LOW
LEVEL TROUGH WHICH WILL LIKELY BE ENHANCED THERMALLY ACROSS EASTERN
LAKE MICHIGAN. WILL CONTINUE UPWARD TREND IN POPS TO CATEGORICAL
ACROSS NORTH GIVEN MORE FAVORABLE PROXIMITY TO PV ANOMALY TRACK AND
LOW LEVEL CONVG SIGNALS.

PRECIP SHOULD BEGIN TO LESSEN IN COVERAGE IN THE 09Z-12Z
TIMEFRAME...ALTHOUGH LAKE EFFECT RAIN SHOWERS WILL LIKELY PERSIST
GIVEN MID/UPPER LEVEL COLD CORE PASSING ACROSS WESTERN GREAT LAKES.
DEPTH OF LAKE INDUCED INSTABILITY SHOULD RAMP UP SIGNIFICANTLY AFTER
06Z AND HAVE ADDED SLIGHT CHANCE OF THUNDER FOR SOUTHERN LAKE
MICHIGAN AND IMMEDIATE LAKESHORE AREAS...AS MODIFIED BUFFER
SOUNDINGS SUGGEST EQUILIBRIUM LEVELS AROUND 20K FT AND LAKE INDUCED
CAPES AROUND 1000 J/KG. DESPITE STRONG FORCING...RAINFALL AMOUNTS
ACROSS THE NORTH SHOULD BE LIMITED TO THE QUARTER OF AN INCH TO HALF
INCH RAIN GIVEN OVERALL LIMITED MOISTURE...AND LESSER AMOUNTS ACROSS
THE SOUTH.

&&

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 426 AM EDT FRI SEP 12 2014

A SHORT WAVE TROF WILL BE LIFTING NORTHEAST OVER THE AREA EARLY
SATURDAY. ADDED A CHANCE FOR SOME SHOWERS SATURDAY MORNING GIVEN A
BRIEF WINDOW FOR LAKE EFFECT SHOWERS WITH DELTA T VALUES NEAR
20C. ALSO...FAVORABLE ISENTROPIC LIFT ON THE 295K SURFACE FOR A
SHORT TIME MAY ALLOW SOME SHOWERS OVER NORTHEAST AREAS EARLY
SATURDAY.  OTHERWISE...A CHILLY AIRMASS WILL GRADUALLY MODIFY INTO
NEXT WEEK...ALTHOUGH TEMPERATURES WILL STILL REMAIN BELOW NORMAL AS
A NEGATIVE HEIGHT ANOMALY REMAINS OVER THE REGION. THIS ANOMALY IS
SUPPORTED BY UPSTREAM TELECONNECTIONS WITH A LARGE UPPER LEVEL RIDGE
AXIS OVER WESTERN NORTH AMERICA. GFS 500 MB ANALOGS SUPPORT A COOL
PERIOD FOR MOST OF NEXT WEEK...WITH SOME MODERATION POSSIBLE BY THE
END OF THE WEEK. THE GFS/MEX MOS HAS SHOWN CONSISTENCY FROM THE 12Z
RUN AND APPEARS ON TRACK. THE LATEST ECMWF SUGGESTS TEMPERATURES MAY
BE A LITTLE COOLER THAN THE ONGOING FORECAST INDICATES DURING THE
MIDDLE OF NEXT WEEK. KEPT A SMALL CHANCE FOR SHOWERS MONDAY/MONDAY
NIGHT WITH THE PASSAGE OF AN UPPER LEVEL TROF.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 636 AM EDT FRI SEP 12 2014

SFC WINDS VEERING TO THE NORTHEAST HAS ALLOWED FOR SOME BREAKS IN
STRATUS ACROSS NORTH CENTRAL INDIANA. STRATUS DECK MAY TRY TO
CREEP BACK WESTWARD LATER THIS MORNING...ALTHOUGH TREND TO HIGHER
END MVFR OR VFR CIGS SHOULD BECOME ESTABLISHED AFTER 16Z. MORE
SOLID MVFR DECK PERSISTS AT KFWA EARLY THIS MORNING...BUT
CURRENTLY EXPECTING SIMILAR TRENDS TO HIGHER END MVFR OR VFR CIGS
TOWARD MIDDAY. NEXT UPPER LEVEL SYSTEM ACROSS THE ROCKIES WILL AFFECT
NORTHERN INDIANA TONIGHT BRINGING A LIKELIHOOD OF RAIN SHOWERS.
PRECIP IS EXPECTED TO BE MORE WIDESPREAD AT KSBN...BUT GIVEN
STRENGTH OF UPPER WAVE WILL ALSO INCLUDE TEMPO RAIN LATE IN THE
PERIOD AT KFWA. DURATION OF PRECIP IS EXPECTED TO BE GREATER FOR
KSBN AS A BRIEF PERIOD OF LAKE EFFECT RAIN SHOWERS IS EXPECTED
TOWARD THE END OF THE FORECAST VALID PERIOD ON THE BACKSIDE OF
THIS SYSTEM. HAVE TRENDED CIGS BACK TO LOWER END MVFR AT KSBN LATE
TONIGHT...ALTHOUGH BRIEF IFR CONDITIONS ARE A POSSIBILITY.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...BEACH HAZARDS STATEMENT THROUGH SATURDAY EVENING FOR INZ003.

MI...BEACH HAZARDS STATEMENT THROUGH SATURDAY EVENING FOR MIZ077.

OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 11 PM EDT SATURDAY FOR LMZ043-046.

&&

$$

SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...SKIPPER
AVIATION...MARSILI


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