Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 192035
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
435 PM EDT TUE AUG 19 2014

.SYNOPSIS...
ISSUED AT 430 PM EDT TUE AUG 19 2014

A WEAK COOL FRONT WILL TRACK ACROSS THE OHIO VALLEY TONIGHT. THIS
WILL RESULT IN DIMINISHING COVERAGE TO SHOWERS AND THUNDERSTORMS
THIS EVENING. A WEAK RIDGE OF HIGH PRESSURE WILL SETTLE INTO THE
AREA...WITH JUST A LOW CHANCE OF AFTERNOON SHOWER OR THUNDERSTORM
ACROSS SOUTHEAST LOWER MICHIGAN...FAR NORTHEAST INDIANA...AND
NORTHWEST OHIO. LOW TEMPERATURES TONIGHT WILL DROP INTO MID 60S.
HIGH TEMPERATURES ON WEDNESDAY WILL RANGE FROM THE UPPER 70S
ACROSS CENTRAL LOWER MICHIGAN...TO THE LOWER TO MID 80S ACROSS
CENTRAL INDIANA.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 430 PM EDT TUE AUG 19 2014

SHOWERS AND THUNDERSTORMS HAVE INCREASED IN COVERAGE ALONG WEAK COOL
FRONTAL BOUNDARY. LARGE SCALE FORCING HAS ALSO BEEN AIDED BY A PAIR
OF UPPER LEVEL DISTURBANCES...ONE MOVING INTO THE WESTERN GREAT
LAKES...AND ANOTHER CONVECTIVELY ENHANCED VORT MAX WORKING EASTWARD
OUT OF CENTRAL ILLINOIS. AN AXIS OF 1500-2500 SBCAPES EXISTS
DOWNSTREAM OF STORMS...ALTHOUGH DEEP LAYER SHEAR PROFILES REMAIN
SOMEWHAT ON THE MARGINAL SIDE IN THE 20 TO 30 KNOT RANGE SUGGESTING
COLD POOL BALANCE MAY BE INCREASINGLY DIFFICULT TO ATTAIN. SOME LOW
END SEVERE THREAT WILL EXIST OVER AT LEAST THE NEXT FEW HOURS INTO
NORTHEAST INDIANA/NORTHWEST OHIO...MAINLY IN THE FORM OF ISOLATED
DAMAGING WIND GUSTS. WITH MID/UPPER LEVEL FORCING LINGERING UPSTREAM
ACROSS THE WESTERN GREAT LAKES...ADDITIONAL ISOLATED OR SCATTERED
SHOWERS AND THUNDERSTORMS MAY STILL DEVELOP IN THE WAKE OF PRIMARY
CONVECTION...BUT CURRENTLY NO SEVERE RISK IS ANTICIPATED WITH ANY
POTENTIAL REDEVELOPMENT LATER THIS EVENING. WEAK GRADIENT AND
LINGERING LOW LEVEL MOISTURE COULD PROMOTE SOME PATCHY FOG
REDEVELOPMENT LATE TONIGHT...OR PERHAPS SOME PATCHY STRATUS. WILL
OMIT FOG MENTION FROM THE FORECAST FOR NOW BUT LATE EVENING/EARLY
OVERNIGHT TRENDS WILL NEED TO BE MONITORED.

ON WEDNESDAY UPPER LOW WILL SLOWLY MEANDER EASTWARD ACROSS THE GREAT
LAKES REGION...WITH A FEW WEAK VORT LOBES LIKELY ROTATING AROUND
PARENT UPPER LOW INTO ESPECIALLY NORTHEAST PORTIONS OF THE AREA.
WILL MAINTAIN SOME LOW POPS ACROSS THE NORTHEAST...AND SHOULD BE
TIED TO PEAK HEATING HOURS. NO SIGNIFICANT CHANGE MADE TO TEMPS FOR
TONIGHT/WEDNESDAY WITH LOWS IN THE LOWER TO MID 60S AND HIGHS IN THE
LOWER TO MID 80S.

&&

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 430 PM EDT TUE AUG 19 2014

WARM AND MUGGY CONDITIONS STILL ON SCHEDULE FOR THE GREAT LAKES
LATER THIS WEEK AS UPPER LOW EXITS EASTWARD AND RIDGE BUILDS
DOWNSTREAM OF DIGGING NORTHERN ROCKIES TROUGH. PRECIP CHANCES AND
TIMING REMAIN THE BIGGEST SOURCES OF UNCERTAINTY. WARM FRONT WILL
BEGIN TO LIFT NORTH AS EARLY AS WEDNESDAY NIGHT AND THURSDAY MORNING
WILL PROBABLY BE THE BEST CHANCE FOR WIDESPREAD PRECIP IN OUR CWA.
305K ISENTROPIC FIELDS SHOW GOOD SYSTEM RELATIVE CROSS-ISOBAR FLOW
WITH A MODEST DEGREE OF MOISTURE ADVECTION AS WELL. THE PROBLEM IS
THERE IS VERY LITTLE SUPPORT ALOFT GIVEN BUILDING LONGWAVE RIDGE.
MIDLEVEL VORTICITY FIELDS SHOW JUST A WEAK AND HIGHLY SHEARED WAVE
CASCADING OVER THE RIDGE. EXPECT SCT SHOWERS AND THUNDERSTORMS TO
SPREAD FROM SOUTHWEST TO NORTHEAST EARLY THURSDAY MORNING BUT
CONFIDENCE IN COVERAGE IS TOO LOW FOR LIKELY POPS AT THIS POINT. THE
BIG QUESTION WILL BE HOW MUCH...IF ANY...CONVECTION DO WE SEE
THURSDAY AFTERNOON. FORECAST SOUNDINGS INDICATE A HEALTHY CAPPING
INVERSION MAY DEVELOP IMMEDIATELY BEHIND THE WARM FRONT. WHERE
EXACTLY THE FRONT SETS UP...AND THE TIMING/COVERAGE OF MORNING
PRECIP...WILL LIKELY DETERMINE THE LOCATION AND DEGREE OF AFTERNOON
CONVECTION. FOR NOW...EXPECT THE BEST CHANCES IN OUR NORTHEAST
ZONES. DECENT MIDLEVEL LAPSE RATES AND VERY MOIST ENVIRONMENT NEAR
THE SURFACE GENERATES AROUND 2000 J/KG OF MLCAPE BY THURSDAY
AFTERNOON ACCORDING TO THE LATEST GFS AND NAM. WITH 0-6KM SHEAR
VALUES AT OR ABOVE 30 KTS...THERE WILL BE POTENTIAL FOR SEVERE
WEATHER. IT IS A HIGHLY CONDITIONAL THREAT THOUGH...DEPENDENT ON
EVOLUTION OF MORNING CLOUDS/PRECIP AND DEGREE OF FORCING LEFT IN OUR
CWA.

LOWER CHANCES FOR PRECIP EXPECTED FRIDAY AND SATURDAY AS THERMAL
RIDGE PUSHES NORTHEAST AND CAP STRENGTHENS. GFS IS VERY AGGRESSIVE
WITH CONVECTIVE QPF BUT ALSO HAS SURFACE DEWPOINTS NEAR 80F. SUSPECT
A MORE REALISTIC SURFACE DEWPOINT IN THE LOW TO MID 70S WILL BE
INSUFFICIENT TO BREAK THROUGH THE CAPPING INVERSION GIVEN LITTLE TO
NO TRIGGER MECHANISM. KEPT JUST A SLIGHT CHANCE WITH DRY CONDITIONS
EXPECTED SUNDAY AND MONDAY. AS PREVIOUSLY MENTIONED IT WILL BE VERY
WARM THOUGH. COULD SEE THE HOTTEST CONDITIONS OF THE YEAR THIS
WEEKEND. 850MB TEMPS CLIMB TO AROUND 20C...SUPPORTING HIGHS AROUND
90F. AND DEWPOINTS IN THE LOW TO MID 70S WOULD PUSH HEAT INDEX
VALUES TO NEARLY 100F.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1253 PM EDT TUE AUG 19 2014

INCREASING LARGE SCALE SUPPORT IN TERMS OF A PAIR OF UPPER LEVEL
DISTURBANCES TRACKING ACROSS THE REGION COMBINED WITH WEAK LOW
LEVEL FRONT WILL ALLOW FOR INCREASING SHOWER/THUNDERSTORM COVERAGE
ACROSS NORTHERN INDIANA EARLY THIS AFTERNOON. BEST CHANCES OF TSRA AT
ONSET OF TAF VALID PERIOD WILL BE AT KSBN...WITH CHANCES INCREASING
TO KFWA CLOSER TO THE 20-21Z TIMEFRAME. SOME OF THE STORMS MAY
PRODUCE SOME GUSTY WINDS IN EXCESS OF 35 KNOTS. GREATEST
THUNDERSTORM COVERAGE IS ANTICIPATED FOR THE 19Z-22Z TIMEFRAME AT
KSBN AND FROM ROUGHLY 21Z-00Z AT KFWA. WEAKENING FRONTAL
BOUNDARY...RESIDUAL LOW LEVEL MOISTURE...AND LIGHT GRADIENT WILL
LIKELY PROMOTE PATCHY FOG/STRATUS DEVELOPMENT AGAIN OVERNIGHT AND
HAVE TRENDED FORECAST TO MVFR CONDITIONS AFTER 06Z. DETAILS IN
THIS REGARD WILL HAVE TO BE FINE TUNED IN UPCOMING FORECASTS.

&&

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

$$

SYNOPSIS...MARSILI
SHORT TERM...MARSILI
LONG TERM...AGD
AVIATION...MARSILI


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