Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 060544
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
144 AM EDT WED MAY 6 2015

.SYNOPSIS...
ISSUED AT 820 PM EDT TUE MAY 5 2015

A STALLED FRONTAL BOUNDARY ACROSS THE AREA WILL RESULT IN ISOLATED
TO SCATTERED SHOWERS THIS EVENING ACROSS PORTIONS OF NORTHEAST AND
NORTH CENTRAL INDIANA...SOUTHERN LOWER MICHIGAN...AND EXTREME
NORTHWEST OHIO. THIS FRONTAL BOUNDARY WILL MOVE SLIGHTLY NORTHWARD
FOR WEDNESDAY...BUT MOST AREAS WILL BE DRY AS AN UPPER LEVEL RIDGE
BUILDS INTO THE REGION. LOW TEMPERATURES TONIGHT WILL RANGE FROM
THE UPPER 50S TO AROUND 60 ACROSS NORTHWEST INDIANA...TO THE LOWER
50S ACROSS SOUTH CENTRAL LOWER MICHIGAN. HIGH TEMPERATURES ON
WEDNESDAY WILL RANGE FROM THE MID 70S TO LOWER 80S.

&&

.UPDATE...
ISSUED AT 928 PM EDT TUE MAY 5 2015

SCATTERED SHOWERS/THUNDERSTORMS HAVE DIMINISHED IN COVERAGE OVER
THE PAST HOUR...AND THIS TREND SHOULD CONTINUE OVER THE NEXT FEW
HOURS DUE TO THE COMBINATION OF WANING INSTABILITY AND LACK OF
STRONG MID/UPPER LEVEL FORCING. HAVE MAINTAINED SLIGHT CHANCE POPS
INTO THE OVERNIGHT HOURS ACROSS THE NORTH DUE TO SOME SLIGHT
NORTHWARD PROGRESSION OF LOW LEVEL WARM FRONT AND ISENTROPIC
UPGLIDE. SOME LIGHT FOG HAS FORMED ACROSS MOST OF THE AREA THIS
EVENING...AND WOULD EXPECT ESPECIALLY NORTHERN HALF OF THE
AREA...JUST NORTH OF SFC FRONTAL BOUNDARY TO EXPERIENCE THE MORE
SUBSTANTIAL FOG ISSUES OVERNIGHT. NO MAJOR CHANGES ANTICIPATED TO
PREVIOUS FORECAST WITH EVENING UPDATE SENT JUST TO FRESHEN UP
CURRENT POP TRENDS AND FOR A SLIGHTLY EARLIER ONSET TO FOG MENTION.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 400 PM EDT TUE MAY 5 2015

LATEST SURFACE ANALYSIS SHOWS QUASI-STATIONARY FRONTAL BOUNDARY
CURRENTLY DRAPED ALONG THE TOLL ROAD. COMBINATION OF RIGHT ENTRANCE
JET DYNAMICS...PASSAGE OF AN OLD (CONVECTIVELY-ENHANCED)
SHORTWAVE...AND GOOD LOW LEVEL MOISTURE CONVERGENCE DOWNSTREAM OF
DEEP LONGWAVE TROUGH ALLOWED FOR SOAKING RAIN EARLIER TODAY.
RAINFALL AMOUNTS HAVE GENERALLY WEAKENED AND SHIFTED NORTH THIS
AFTERNOON AS THE MAIN SYNOPTIC FORCING LIFTS NORTHEAST. STILL...A
FEW SHOWERS AND THUNDERSTORMS HAVE MANAGED TO DEVELOP ALONG AND
SOUTH OF THE SURFACE FRONT AS OF PRESS TIME. THIS WILL LIKELY
CONTINUE THROUGH THE EVENING GIVEN SOME MARGINAL SURFACE BASED
INSTABILITY IN THE PRESENCE OF DECENT LOW LEVEL CONVERGENCE. SEVERE
WEATHER IS NOT EXPECTED GIVEN MARGINAL DEEP LAYER SHEAR AND MLCAPE
BUT A FEW STRONG STORMS ARE POSSIBLE.

SURFACE AND MIDLEVEL EXTENSION OF THIS FRONT WILL SLOWLY LIFT
NORTHWARD OVERNIGHT IN RESPONSE TO LIFTING UPPER JET AND BUILDING
LONGWAVE RIDGE. KEPT LOW CHANCES IN OUR FAR NORTH THROUGH THE EARLY
MORNING BUT SUSPECT A LARGE PART OF PRECIP IN OUR CWA IS DIURNALLY
DRIVEN AND WILL DISSIPATE/SHIFT NORTH AROUND 03Z. OVERNIGHT TEMPS
MAY BE A TOUCH COOLER THAN LAST NIGHT GIVEN LESS RAIN/CLOUDS BUT
SHOULD STILL GENERALLY HOLD IN THE MID TO UPPER 50S. THERE IS SOME
THREAT FOR FOG DEVELOPMENT EARLY TOMORROW MORNING GIVEN SATURATED
GROUND AND VERY LIGHT S/SE SURFACE WINDS. CROSS OVER TEMPS ARE
AROUND 60F AND SHOULD DROP BELOW THAT THRESHOLD TONIGHT. MOS
GUIDANCE AND FORECAST SOUNDINGS DO NOT SUPPORT A WIDESPREAD/DENSE
FOG THREAT AT THIS STAGE BUT WILL BE SOMETHING TO MONITOR OVERNIGHT.

FRONT WILL LIFT FURTHER NORTH TOMORROW...LEAVING OUR AREA MAINLY
CAPPED WITH LITTLE TO NO FORCING FOR ASCENT. LATEST NAM12 SUGGESTS
SURFACE BASED INSTABILITY WILL CLIMB TO AROUND 2000 J/KG IN A
LARGELY UNCAPPED ENVIRONMENT BUT THIS SEEMS WILDLY OVERDONE AND
PREFER MORE SUBDUED GFS SOUNDINGS/CAPE FIELDS...WHICH HAVE SUPPORT
FROM SEVERAL OF THE LATEST HI-RES RUNS. NEVERTHELESS...NEARLY ALL OF
THESE HI-RES MODELS INDICATE THAT AFTERNOON HEATING WILL BE ENOUGH
TO WEAKEN THE CAP AND GENERATE SCT SHOWERS AND THUNDERSTORMS WITH
AROUND 500 J/KG OF CAPE. DO HAVE SERIOUS DOUBTS GIVEN LACK OF GOOD
SYNOPTIC TRIGGER AND LACKLUSTER THERMODYNAMIC PROFILES BUT AT THE
SAME TIME DO NOT FEEL COMFORTABLE WITH AN ENTIRELY DRY FORECAST
GIVEN PLETHORA OF MODELS GENERATING CONVECTION. WILL THEREFORE
INTRODUCE SOME LOW CHANCE POPS...MAINLY FOR OUR NORTHERN HALF...WITH
TEMPERATURES IN THE UPPER 70S TO LOWER 80S. NO SEVERE WEATHER IS
EXPECTED.


&&

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 400 PM EDT TUE MAY 5 2015

LEAD SHRTWV LIFTING NE ACROSS THE NRN PLAINS WILL PRODUCE INCRSG
SOUTHERLY FLOW ACROSS OUR AREA WED NGT/THU ENSURING WK REMNANT E-W
ORIENTED STNRY FRONT LIFTS NORTH OR WASHES OUT. THIS SHOULD RESULT
IN DRY/WARMER CONDITIONS ACROSS OUR AREA. GFS CONTS TO SUGGEST A FEW
SHOWERS/TSTMS WILL DEVELOP OVER ERN PORTION OF CWA IN AREA OF WK
BOUNDARY LAYER CONVERGENCE AND WK-MOD INSTABILITY... BUT WITH LITTLE
SUPPORT FROM OTHER MODELS KEPT POPS IN THE UNMENTIONABLE RANGE.
TEMPS SHOULD BE MUCH ABOVE NORMAL WITH LOWS IN U50S/L60S AND HIGHS
IN THE L-M80S.

FRONT WILL SAG SE TOWARD OUR AREA FRI AS SFC LOW LIFTS NE ACROSS
JAMES BAY BRINGING INCREASING CHANCES OF SHOWERS/TSTMS FROM NW-SE
ACROSS THE CWA. CDFNT EXPECTED TO MOVE INTO THE AREA BY SATURDAY...
RESULTING IN A LITTLE COOLER TEMPS AT LEAST ACROSS NW PORTION OF THE
CWA.

MEDIUM RANGE MODELS DIFFER ON HOW FAR S-SE FRONT WILL MAKE IT BEFORE
STALLING OUT WITH GFS MORE PROGRESSIVE SUGGESTING A DRIER WEEKEND
THAN THE ECMWF/GEM. GIVEN THE RATHER SGFNT DIFFERENCES WILL CONT TO
FOLLOW MODEL CONSENSUS BLEND YIELDING A LITTLE COOLER TEMPS BUT
STILL ABOVE NORMAL AND A CHC OF SHOWERS/TSTMS THROUGH THE WEEKEND.
WRN UPR TROF EXPECTED TO MOVE INTO THE PLAINS MONDAY WITH ASSOCIATED
SFC LOW MOVG INTO THE MIDWEST LIKELY BRINGING SHOWERS/TSTMS TO MUCH
OF OUR AREA BY MONDAY AFTN WITH TEMPS REMAINING WELL ABOVE NORMAL.
COOLER TEMPS EXPECTED FOR TUE AS SFC LOW MOVES EAST TO THE LWR
GRTLKS WITH CAA AND PSBLY SOME LINGERING SHOWERS IN ITS WAKE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 138 AM EDT WED MAY 6 2015

WEAK FRONTAL BOUNDARY HAS SAGGED SOUTHWARD TO CENTRAL INDIANA AND
BECOME DIFFUSE. LARGE AREA OF IFRLIFR CIGS AND VIS HAVE EXPANDED
ACROSS NORTHERN INDIANA. KSBN ALREADY IFR AND KFWA IS SURROUNDED
BY IFR AT 0530Z. PER LATEST HIRES GUIDANCE SOUNDINGS...STRONG LOW
LEVEL INVERSION TO PERSIST OVERNIGHT WITH LIGHT FLOW SO EXPECT
THESE CONDITIONS TO PREVAIL AND CONTINUE EXPANDING. EARLIER
RAINFALL HAS COOLED AND STABILIZED AIR NORTH OF FRONT AND WILL
MAKE IT DIFFICULT FOR THIS BOUNDARY TO MOVE NORTH OVERNIGHT. LATEST MODEL
SOLUTIONS HAVE SLOWED THIS NORTHWARD PROGRESSION AND INDICATE WEAK
BOUNDARY WILL BEGIN TO MIX NORTH MID TO LATE MORNING. HELD ONTO
LOWER END CONDITIONS THROUGH THE MORNING HOURS BEFORE RAPID
IMPROVEMENT EARLY AFTERNOON. ISOLATED TSRA POSSIBLE LATE WED AFTN
BUT TOO LOW OF A PROBABILITY FOR TAF INCLUSION AT THIS TIME.

&&

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

$$

UPDATE...MARSILI
SYNOPSIS...MARSILI
SHORT TERM...AGD
LONG TERM...JT
AVIATION...LASHLEY


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