Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 291748
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
148 PM EDT SAT AUG 29 2015

.SYNOPSIS...
ISSUED AT 146 PM EDT SAT AUG 29 2015

A WEAKENING TROUGH WILL CROSS OVER THE REGION TODAY AND SUNDAY.
SCATTERED TO NUMEROUS RAIN SHOWERS ARE EXPECTED...AND AN ISOLATED
THUNDERSTORM IS POSSIBLE. HIGHS TODAY WILL BE IN THE 70S AND LOW
80S. LOWS TONIGHT WILL BE IN THE 60S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 330 AM EDT SAT AUG 29 2015

MAIN FOCUS TODAY INTO TONIGHT WILL BE ON SHOWER/ISO THUNDER CHANCES
AS A DISJOINTED MID-UPPER LEVEL TROUGH AXIS AND ASSOCIATED WEAK LOW
LEVEL TROUGH WEAKEN ESE INTO THE LOWER LAKES.

CORRIDOR OF DEEPER MOISTURE (PWATS EXCEEDING 1.50 INCHES) WITHIN LOW
LEVEL JET IMMEDIATELY DOWNSTREAM OF THIS FEATURE WILL SLOWLY EDGE
INTO NORTHWESTERN ZONES MID MORNING-EARLY AFTERNOON AND POINTS ESE
THEREAFTER. SUPPORT ALOFT INITIALLY WILL COME FROM WEAK UPPER JET
SUPPORT (RRQ OF A 80 KT NORTHERN LAKES 300-200 MB JET) AND MID
LEVEL UVM/MOISTURE ADVECTION SURGE TIED TO AN EMBEDDED VORT MAX
OUTRUNNING TROUGH AXIS THROUGH CENTRAL LOWER MI. THIS
FORCING/DEEPER MOISTURE WILL CLIP OUR FAR NORTHERN ZONES MID-
MORNING THROUGH AT LEAST EARLY AFTERNOON WHERE POPS WERE
RAISED...ALTHOUGH DID OPT TO DROP THE THUNDER MENTION GIVEN
LIMITED INSTABILITY/MID LEVEL LAPSE RATES. SHOWER COVERAGE WILL BE
MORE ISOLATED IN NATURE FARTHER SOUTHEAST THROUGH EARLY
AFTERNOON...WITH AREAS SOUTHEAST OF THE HWY 24 CORRIDOR LIKELY
REMAINING COMPLETELY DRY.

STEADY IMPROVEMENT IN MOISTURE QUALITY AND WEAK MID LEVEL
DCVA/DEFORMATION TIED TO SHEARED OUT UPPER PV FILAMENT SHOULD KEEP
SCATTERED SHOWERS AROUND INTO THE MID AFTERNOON/EVENING (BEST
CHANCES NW OF HWY 24). ANY THUNDERSTORM ACTIVITY WITH SFC
HEATING/MOISTENING SHOULD REMAIN ISOLATED AT BEST GIVEN THICKER
MID/HIGH CLOUD CANOPY AND WARM COLUMN...WITH CONVECTION HAPPY HI-
RES GUIDANCE LIKELY OVERLY AGGRESSIVE REGARDING SFC HEATING/DEWPOINTS.


&&

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 330 AM EDT SAT AUG 29 2015

ON SUNDAY...THE UPPER LEVEL PV ANOMALY TRACKING ACROSS THE REGION
WILL CONTINUE TO LOSE POTENCY AND BECOME HIGHLY ATTENUATED.
PERSISTENCE OF THIS WEAKENING FORCING COMBINED WITH DIURNAL HEATING
SHOULD YIELD ISOLATED TO SCATTERED AFTERNOON SHOWERS AND
THUNDERSTORMS HOWEVER. WHILE APPRECIABLE MOISTURE SHOULD BE IN PLACE
ON SUNDAY...UNCERTAINTY IN PRECISE MAGNITUDES OF LOW LEVEL MOISTURE
LEND SOME LOWER CONFIDENCE INTO EXTENT OF THUNDER POTENTIAL GIVEN
SENSITIVITY OF SBCAPES TO NEAR SFC MOISTURE WITH CONTINUED MARGINAL
MID LEVEL LAPSE RATES. WEAK FORCING WITH SHEARED VORTICITY MAX MAY
TEND TO MAXIMIZE ACROSS SOUTHEAST PORTIONS OF THE FORECAST
AREA...ALTHOUGH WEAK LAKE ENHANCED LOW LEVEL CONVERGENCE ZONE MAY
ALSO BE A SECONDARY FOCUSING AREA ACROSS NORTHWEST PORTIONS OF THE
CWA DOWNWIND OF LAKE MICHIGAN. WITH DECAYING NATURE OF UPPER PV
ANOMALY HAVE MAINTAINED LOW TO MID CHANCE POPS SUNDAY...PEAKING IN
THE AFTERNOON. SLIGHT CHANCE/LOW CHANCE POPS WERE ALSO MAINTAINED
INTO SUNDAY NIGHT FOLLOWING SOUTHEAST PROGRESSION OF WEAKENING
MID/UPPER LEVEL FORCING.

VORT FILAMENT ASSOCIATED WITH WEAKENING WAVE WILL LIKELY RESIDE
ACROSS THE REGION THROUGH TUESDAY AFTERNOON WITH THE POSSIBILITY OF
WEAK HIGHLY SHEARED WAVES LIFTING NORTHWARD OUT OF THE LOWER/MID MS
RIVER VALLEY TOWARD MID WEEK. THE DOMINANT FEATURE WILL BE
AMPLIFYING BACKGROUND UPPER RIDGING TO AFFECT MUCH OF CENTRAL CONUS
THROUGH THE REMAINDER OF THIS FORECAST PERIOD. MEDIUM RANGE MODELS
DO POINT TOWARD POSSIBILITY OF THE SOUTHERN EXTENT OF PACIFIC WAVE
PROGRESSING THROUGH MEAN RIDGING PROVIDING SOME WEAK FORCING IN THE
WED-THU TIMEFRAME...BUT CONFIDENCE WITH ANY OF THESE EMBEDDED WAVES
IS LOW. THE GENERAL IDEA OF PREVIOUS FORECAST WITH ISOLD DIURNAL
POPS FOR THE TUE-THU PERIOD WAS LEFT AS IS GIVEN THIS PATTERN.

BUILDING HEAT FOR NEXT WEEK COULD BE SOMEWHAT TEMPERED BY OCCASIONAL
WEAK BACKDOOR COOL FRONT TYPE FEATURES IMPACTING THE EASTERN GREAT
LAKES...WITH UPPER RIDGE AXIS LIKELY REMAINING JUST WEST OF THE
LOCAL AREA THROUGH MOST OF THE UPCOMING WEEK WHICH SHOULD CONFINE
HIGHS TO THE MID-UPPER 80S THROUGH MUCH OF THE TUE-FRI PERIOD. THIS
IDEA IS INLINE WITH PREVIOUS GRIDDED FORECAST AND NO SIGNIFICANT
CHANGES WERE MADE TO MAX/MINS AT THIS TIME FOR MUCH OF THE EXTENDED
PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 146 PM EDT SAT AUG 29 2015

RAIN SHOWERS OVER MUCH OF THE NORTHWESTERN PORTIONS OF THE FORECAST
AREA WILL GRADUALLY SHIFT EASTWARD OVERNIGHT AS SEVERAL UPPER LEVEL
DISTURBANCES MOVE THROUGH ALOFT. MOST OF THE CEILINGS WITHIN SHOWERS
TODAY AND UPSTREAM HAVE REMAINED VFR-MVFR AT VARIOUS SITES...SO HAVE
KEPT CEILINGS RANGING FROM 4000-7000FT THROUGH THE PERIOD. SHOWERS
ARE FAIRLY SCATTERED IN NATURE...MAKING IT DIFFICULT TO PINPOINT
EXACT TIMES OF PRECIPITATION FOR THE TAF SITES. KSBN MAY SEE A BRIEF
BREAK BEFORE SHOWER ACTIVITY RESTARTS LATER THIS AFTERNOON AS THE
NEXT UPPER LEVEL TROUGH MOVES IN. SHOWERS ARE MORE ISOLATED THIS
AFTERNOON NEAR KFWA BUT EXPECT ACTIVITY TO INCREASE TOWARDS THE LATE
AFTERNOON EARLY EVENING. WITH ABUNDANT MOISTURE THINKING THAT BOTH
SITES MAY HAVE A SHOT AT SEEING SOME LOWERED VISIBILITIES DUE TO BR
LATE TONIGHT/EARLY SUNDAY...BUT CONFIDENCE WAS PRETTY LOW SO KEPT IT
MVFR AT WORST FOR NOW.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SYNOPSIS...MCD
SHORT TERM...STEINWEDEL
LONG TERM...MARSILI
AVIATION...MCD


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