Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 121700
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
100 PM EDT FRI SEP 12 2014

.SYNOPSIS...
ISSUED AT 1256 PM EDT FRI SEP 12 2014

COOL AND CLOUDY CONDITIONS WILL PREVAIL THROUGH AT LEAST TONIGHT
COURTESY OF A APPROACHING SYSTEM WHICH WILL BRING A REINFORCING
SHOT OF COLD AIR AND HIGHS ONLY IN THE 50S TO LOWER 60S THROUGH
THE WEEKEND. OVERNIGHT LOWS WILL DROP INTO THE 40S WITH A FEW
AREAS THAT SEE CLEARING POTENTIALLY SEEING A FEW UPPER 30S.

&&

.UPDATE...
ISSUED AT 1208 PM EDT FRI SEP 12 2014

FORECAST UPDATED EARLIER TO INCREASE CLOUD COVER...ADD MENTION OF
DRIZZLE AND LOWER HIGHS.

PERSISTENT NE TO N FLOW OFF THE LAKES WAS RESULTING IN WIDESPREAD
LAKE EFFECT CLOUD COVER ACROSS THE REGION. A SMALL AREA OF WHAT IS
LIKELY SUBSIDENCE ALLOWED FOR SOME CLEAR SKIES ALONG WHAT IS
NORMALLY A CLOUDY AREA WITH LAKE EFFECT. THIS WAS QUICKLY FILLING
THOUGH AS COLD AIR ALOFT AND AT LEAST MODERATE LAPSE RATES WAS
ALLOWING FOR CU/SC TO DEVELOP. CLOUD COVER HAS KEPT TEMPS DOWN A
BIT WITH MANY PLACES LIKELY TO STRUGGLE OUT OF THE 50S. HAVE
LOWERED TEMPS A BIT AS A RESULT (PROBABLY NOT LOW ENOUGH).
FINALLY...SOME PATCHES OF DRIZZLE WERE OBSERVED HERE AND THERE
WITH ENOUGH COVERAGE TO WARRANT THROWING THEM INTO THE GRIDS
UNTIL MID AFTERNOON WHEN LAKE EFFECT BAND CURRENTLY INTO N
ILLINOIS TRANSLATES EAST TO INCREASE CHANCES FOR PRECIP IN FAR NW
AREAS AS WELL AS ARRIVAL OF AREA OF LIGHT SHOWERS FROM NE IOWA IN
TO WISCONSIN AHEAD OF THE NEXT WAVE.

&&

.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 TIME FRAME...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
TIME FRAME...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 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1208 PM EDT FRI SEP 12 2014

LOWER END VFR CONDITIONS WILL SLOWLY RETURN THIS AFTERNOON FOR A
BRIEF PERIOD AS LAKE INFLUENCE WANES IN RESPONSE TO APPROACHING
WAVE. ITS ARRIVAL LATER TONIGHT INTO SATURDAY MORNING WILL BRING
BACK MVFR CIGS/VSBYS. IFR CONDITIONS MOST LIKELY NEAR KSBN WITH
INCREASED LAKE RESPONSE ADDING TO PRECIP CHANCES AND LOWER BASES.
ONLY MINOR CHANGES TO TAFS.

&&

.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.

&&

$$

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


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