Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 251617
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1217 PM EDT SAT APR 25 2015

.SYNOPSIS...
ISSUED AT 232 AM EDT SAT APR 25 2015

WIDESPREAD RAIN WILL CONTINUE THIS AFTERNOON AS A STORM SYSTEM
TRACKS ACROSS THE SOUTHERN GREAT LAKES AND OHIO VALLEY. A LOW
PRESSURE AREA ASSOCIATED WITH THIS SYSTEM WILL MOVE EAST TONIGHT
AS RAIN ENDS ACROSS THE REGION. TEMPERATURES THROUGH THIS
AFTERNOON WILL GENERALLY BE IN THE MID TO UPPER 40S...AND LOWS
TONIGHT WILL DROP BACK INTO THE LOWER TO MID 30S.

&&

.UPDATE...
ISSUED AT 1158 AM EDT SAT APR 25 2015

ONLY MINOR TWEAKS WERE MADE TO GOING FORECAST THIS MORNING. LOW
LEVEL SOUTH-SOUTHEAST FLOW HAS ALLOWED FOR AXIS OF BETTER LOW
LEVEL MOISTURE TO OVERSPREAD THE LOCAL AREA THIS MORNING.
ISENTROPIC UPGLIDE AND LOW/MID LEVEL FGEN FORCING DOWNSTREAM OF
APPROACHING UPPER TROUGH HAS ALLOWED FOR EXTENSIVE RAIN. SOME
THUNDER HAS ALSO DEVELOPED OVER PAST FEW HOURS ACROSS WEST CENTRAL
INDIANA/EAST CENTRAL ILLINOIS AT THE LEADING EDGE OF DRY SLOT.
CONFIDENCE REMAINS LOW ON NORTHWARD EXTENT OF THUNDER GIVEN MORE
LIMITED ELEVATED INSTABILITY ACROSS NORTHERN INDIANA. UPPER
FORCING SHOULD BE ON THE INCREASE OVER THE NEXT FEW HOURS IN A
BRIEF WINDOW BEFORE BLOCKING NORTHERN STREAM BEGINS TO SUPPRESS
FORCING SOUTH OF THE LOCAL AREA. THUS...STILL EXPECTING SOME
NORTHWARD EXPANSION OF RAIN SHOWERS ACROSS SOUTHERN LOWER MICHIGAN
OVER NEXT FEW HOURS BEFORE BACKING LOW LEVEL WINDS BEGIN TO
TRANSPORT DRIER AIR BACK SOUTHWARD LATE THIS AFTERNOON. OVERALL
TEMPERATURE FORECAST APPEARS TO BE ON TRACK...MAYBE JUST A BIT
WARM IN SPOTS WHICH RECEIVE STEADIER RAINFALL THROUGH THE
AFTERNOON. PRECIP SHOULD RAPIDLY DIMINISH THIS EVENING AS LOW
LEVEL DRY AIR ADVECTION ADVANCES SOUTHWARD.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 505 AM EDT SAT APR 25 2015

AN UPPER LEVEL DISTURBANCE OVER NORTHEAST KANSAS EARLY THIS MORNING
WILL EJECT NORTHEAST TODAY AND WILL BRING ANOTHER ROUND OF
PRECIPITATION TO THE FORECAST AREA. AN AREA OF RAIN HAS BEEN
TRANSLATING SOUTH AND WAS BEING SUPPORTED AND ENHANCED BY THE
COMBINATION OF THE LEFT EXIT REGION OF AN UPPER JET ALONG WITH
SURFACE CONVERGENCE ALONG A WEAK BOUNDARY. FOR LATER TODAY...THE
GFS...ECMWF AND NAM HAVE INITIALIZED THIS SYSTEM VERY WELL AND ARE
SIMILAR IN HANDLING THE MASS FIELDS OF THIS EJECTING SYSTEM.
HOWEVER...THE GFS WAS FARTHER NORTH AND AN OUTLIER AMONG THESE
MODELS WITH THE DEVELOPMENT OF PRECIPITATION. FAVOR A MORE
INTERMEDIATE ECMWF/NEW 06Z NAM SOLUTION WHICH BRINGS 0.75 TO 1.25
INCHES OF RAIN OVER THE SOUTHERN THIRD OF THE FORECAST AREA....BUT
MUCH LOWER AMOUNTS FARTHER NORTH. A TROWAL SHOULD TRANSLATE OVER THE
AREA WITH ABOUT A 9 HOUR DURATION AND WITH A TIGHT NORTHERN GRADIENT
IN THE RAINFALL...AS BEST DEPICTED ON THE NEW 06Z NAM. THE LATEST
COMPOSITE RADAR WAS ALREADY SHOWING THIS NEXT ROUND OF PRECIPITATION
DEVELOPING OVER ILLINOIS. HOWEVER...DRY AIR ENTRAINMENT AND THE LOSS
OF UPPER LEVEL JET SUPPORT WAS VAPORIZING THE NORTHERN RETURNS. AS A
RESULT...HAVE CUT BACK RAINFALL AMOUNTS SIGNIFICANTLY OVER FAR NORTH
AREAS...WITH LESS THAN A TENTH OVER FAR SOUTHERN LOWER MICHIGAN TO
0.75 OVER SOUTHERN AREAS. THE SYSTEM WILL MOVE EAST TONIGHT WITH RAIN
ENDING AND SOME CLEARING POSSIBLE LATE. FROST IS POSSIBLE LATE...BUT
FOR NOW HAS LEFT FROST OUT DUE TO UNCERTAINTY OF CLEARING TIMES.

&&

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 505 AM EDT SAT APR 25 2015

COUPLE OF SHRTWVS EXPECTED TO ROTATE AROUND CLOSED LOW OFF THE NEW
ENGLAND COAST AND MOVE S-SE ACROSS THE GRTLKS AND OH VALLEY
SUNDAY-MONDAY. MOISTURE LACKING FOR PRECIP WITH MAIN IMPACT JUST TO
SUSTAIN COOL AIRMASS OVER THE REGION. UPR LEVEL RIDGE EXPECTED TO
BUILD EAST INTO THE AREA TUE PROVIDING CONTD FAIR WX AND WARMER
TEMPS... HWVR WK N-NE LOW LEVEL FLOW SHOULD LIMIT THE WARMUP. RATHER
DEEP TROF EXPECTED TO DVLP OVER THE ERN CONUS MID/LATE WEEK AS A
CLOSED LOW MOVG EAST FROM THE SRN PLAINS PHASES WITH AN UPR LEVEL
LOW/TROF DIGGING S-SE FROM CENTRAL CANADA.  00Z MEDIUM RANGE
MODELS CONT TO HAVE SGFNT DIFFERENCES ON TIMING/EVOLUTION OF THIS
DEVELOPMENT WITH ECMWF MOVG UPR LOW ACROSS OUR AREA WED WHILE GEM
MOVES ONE LOW SOUTH THROUGH THE MS VALLEY WED WITH A SECOND LOW
DROPPING THROUGH THE GRTLKS/OH VALLEY THU... AND GFS INDICATES AN
OPEN WAVE MOVG SE THROUGH THE LWR GRTLKS THU. GIVEN THE LARGE
DIFFERENCES AMONG THE MODELS... FOLLOWED A HIGHLY SMOOTHED MODEL
BLEND WHICH YIELDED A SLIGHT CHC OF SHOWERS WED... WITH DRY
CONDITIONS AND A WARMING TREND TO ABOVE NORMAL TEMPS LATE WEEK AS
THE DEEP TROF MOVES OFF THE EAST COAST AND A STRONG RIDGE BUILDS
EAST FROM THE PLAINS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 640 AM EDT SAT APR 25 2015

BAND OF RAIN MOVG EAST ACROSS NWRN EXPECTED TO REACH THE TERMINALS
SHORTLY AFTER 12Z WITH RAIN LIKELY LINGERING MUCH OF THE DAY AS LOW
PRESSURE CURRENTLY CENTERED OVER NE KS MOVES ESE INTO THE LWR OH
VALLEY. AS LOW PASSES BY TO THE SOUTH THIS EVENING... WINDS WILL
BACK FROM EAST TO NE ALLOWING DRIER AIR TO ADVECT INTO NRN
INDIANA BRINGING THE RAIN TO AN END AND IMPROVING FLIGHT
CONDITIONS BACK TO VFR AFTER LOWERING TO MVFR DURING THE RAIN
TODAY. TIGHT PRESSURE GRADIENT WILL CONTINUE TO SUPPORT GUSTS OF
20-25KT TODAY... WITH WINDS DIMINISHING TONIGHT AS GRADIENT
WEAKENS.


&&

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

$$

UPDATE...MARSILI
SYNOPSIS...LOTHAMER/SKIPPER
SHORT TERM...SKIPPER
LONG TERM...JT
AVIATION...JT


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