Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 240540
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
140 AM EDT SUN AUG 24 2014

.SYNOPSIS...
ISSUED AT 344 PM EDT SAT AUG 23 2014

AN UPPER LEVEL DISTURBANCE TRACKING ACROSS THE WESTERN GREAT LAKES
WILL BRING SHOWERS AND THUNDERSTORMS TO PORTIONS OF SOUTHWEST LOWER
MICHIGAN AND NORTH CENTRAL INDIANA THROUGH EARLY THIS EVENING.
THE COVERAGE OF SHOWERS AND THUNDERSTORMS WILL DIMINISH THIS
EVENING AS AN UPPER LEVEL RIDGE CONTINUES TO BUILD ACROSS THE
REGION. WARM CONDITIONS WILL CONTINUE INTO SUNDAY WITH MOST AREAS
REMAINING DRY. THERE IS A SLIGHT CHANCE OF AN AFTERNOON
THUNDERSTORM ACROSS NORTHWEST AND WEST CENTRAL INDIANA. LOW
TEMPERATURES TONIGHT WILL RANGE FROM THE LOWER 60S ACROSS
SOUTHEAST LOWER MICHIGAN...TO AROUND 70 ACROSS NORTHEAST ILLINOIS.
HIGH TEMPERATURES ON SUNDAY WILL REACH BACK INTO THE MID 80S.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 344 PM EDT SAT AUG 23 2014

MAIN FORECAST ITEMS TO ADDRESS FOR THE SHORT TERM WILL BE CONVECTIVE
POTENTIAL THROUGH SUNDAY.

MCS ACROSS ILLINOIS HAS BECOME MORE DIFFUSE OVER PAST FEW HOURS WITH
AN OVERALL WEAK BACKGROUND SHEAR ENVIRONMENT. OUTFLOW HAS ALLOWED
FOR REGENERATION OF SHOWERS AND THUNDERSTORMS ACROSS NORTHEAST
ILLINOIS IN MODERATELY UNSTABLE ENVIRONMENT. WEAKENING COLD POOL
WITH THIS MCS AND EASTWARD PROGRESSION INTO A MORE WEAKLY FORCED
ENVIRONMENT ACROSS LOCAL AREA LENDS SOME QUESTIONS AS TO HOW FAR
EAST TO BRING HIGHER POPS THIS EVENING. WILL CONFINE CATEGORICAL
POPS TO FAR WESTERN PORTIONS OF FORECAST AREA WITH EXPECTATION
CONVECTION MAY BE MORE SCATTERED IN NATURE ACROSS SOUTHERN LOWER
MICHIGAN AND NORTH CENTRAL INDIANA. SEVERE THREAT APPEARS TO BE LOW
GIVEN MEAGER DOWNSTREAM SHEAR...BUT SLOW MOVEMENT OF STORMS AND
REGENERATION ALONG COMPOSITE OUTFLOW COULD YIELD SOME LOCALIZED
HEAVIER RAINFALL AMOUNTS ACROSS THE FAR WEST. OUTSIDE OF HEAVY
RAINFALL POTENTIAL...SECONDARY CONCERN COULD BE SOME POCKETS OF
SLIGHTLY STRONGER WIND WITH GREATER PRECIP LOADING ASSOCIATED WITH
STRONGER STORMS...BUT GENERALLY OF SUB-SEVERE NATURE. ISOLATED
CELLS SHOULD CONTINUE TO DEVELOP IN ADVANCE OF MAIN AREA OF
SHOWERS AND THUNDERSTORMS WITH MODERATE INSTABILITY AND SEVERAL
POCKETS OF WEAK SYNOPTIC CONVERGENCE/LAKE BREEZE CONVERGENCE.

WILL MAINTAIN SOME SLIGHT CHANCE POPS THROUGH THE EVENING ACROSS
MAINLY SOUTHWEST HALF OF THE AREA AS RESIDUAL CONVECTIVELY ENHANCED
VORT SLOWLY DROPS SOUTHEAST ACROSS THE AREA. WILL KEEP NORTHEAST
LOCATIONS DRY WITH WEAKER ELEVATED INSTABILITY EXPECTED AND A LESS
FAVORABLY PROXIMITY TO MID/UPPER FORCING WITH AFOREMENTIONED VORT
MAX.

FOR SUNDAY...DRIER LOW LEVEL AIR WILL CONTINUE TO ADVECT WESTWARD IN
RESPONSE TO SOUTHWARD SHIFTING ANTICYCLONE ACROSS THE EASTERN GREAT
LAKES. THIS SHOULD CONTRACT AXIS OF APPRECIABLE LOW LEVEL MOISTURE
ACROSS THE MID MS RIVER VALLEY/WESTERN GREAT LAKES. DIFFICULT TO
LATCH ONTO ANY SUBSTANTIAL FORCING MECHANISM FOR TOMORROW...AND
GIVEN BEST INSTABILITY ACROSS THE FAR SOUTHWEST HAVE INCLUDED SLIGHT
CHANCE POPS DURING PEAK HEATING. HAVE MADE JUST SOME SLIGHT DOWNWARD
ADJUSTMENTS TO MAX TEMPS FOR SUNDAY WITH PERSISTENT LOW LEVEL
EASTERLY COMPONENT KEEPING BRUNT OF LOW LEVEL THERMAL RIDGE JUST
WEST OF THE AREA.

&&

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 344 PM EDT SAT AUG 23 2014

HOT/HUMID/MAINLY DRY WX WILL PERSIST INTO MONDAY AND TUESDAY AS THE
LOCAL AREA REMAINS ON THE NORTHERN PERIPHERY OF A HIGH AMPLITUDE
SUBTROPICAL RIDGE...WITH AFTERNOON HEAT INDICES LIKELY REACHING THE
MID-UPPER 90S EACH DAY. A FRONTAL BOUNDARY WILL GRADUALLY SHIFT
SOUTHEAST ON THE SOUTHERN FRINGE OF SHORTWAVE JET ENERGY/WEAK HEIGHT
FALLS WORKING NORTHEAST INTO THE UPPER MIDWEST/NORTHERN LAKES BY THE
MIDDLE OF THE WEEK. THIS FEATURE WORKING INTO A VERY MOIST/UNSTABLE
AIRMASS WILL BRING INCREASING CHANCES FOR SHOWERS/STORMS AND HEAVY
RAINFALL BY WEDNESDAY-THURSDAY...WITH MID LEVEL CAP, WEAK
FORCING/FLOW, AND RELIANCE ON CONVECTIVE OUTFLOW OR UPSTREAM
CONVECTION TO SINK INTO THE AREA SUGGESTS MUCH LOWER CHANCES FOR
CONVECTIVE INITIATION MONDAY NIGHT-TUESDAY. ONLY ADJUSTMENT BEYOND
THURSDAY WAS TO ADD LOW CHANCE POPS...MAINLY FOR COLLABORATION
PURPOSES...WITH LARGE MODEL DIFFERENCES REGARDING TIMING/SPEED OF A
LONGER WAVELENGTH TROUGH MODELED TO PROPAGATE EAST THROUGH THE
MIDWEST/GREAT LAKES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 135 AM EDT SUN AUG 24 2014

NO SIGNIFICANT CHANGES TO THE TAFS WITH FOCUS STILL ON FOG/STRATUS
POTENTIAL OVER THE NEXT 6 TO 9 HOURS. LOW LEVEL FLOW HAS REMAINED
UP SOMEWHAT IN THE 8 TO 12 KT RANGE KEEPING ANY STRATUS AND FOG
AT BAY THUS FAR. STILL EXPECTED WINDS TO DROP TO AROUND 5 KTS AND
ENOUGH COOLING TO TAKE PLACE TO ALLOW FOR AT LEAST SOME
STRATUS/FOG DEVELOPMENT. SOME CONCERNS THAT WE MAY NOT REACH IFR
CIGS BUT WILL HOLD ONTO FOR NOW AND WATCH TRENDS NEXT COUPLE OF HOURS.

ANY STRATUS/FOG SHOULD BURN OFF QUICKLY WITH JUST SOME FAIR
WEATHER CU AND HIGH CLOUDS AS DRIER EASTERLY FLOW KEEPS ANY PRECIP
WELL WEST OF TAF SITES THROUGH THE REMAINDER OF THE PERIOD.

&&

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

$$

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


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