Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 151320
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
920 AM EDT MON SEP 15 2014

.SYNOPSIS...
ISSUED AT 445 AM EDT MON SEP 15 2014

CLOUDS WILL BE ON THE INCREASE TODAY AS AN UPPER LEVEL DISTURBANCE
ACROSS THE NORTHERN PLAINS APPROACHES. THIS DISTURBANCE WILL BRING
THE LIKELIHOOD OF RAIN SHOWERS LATER TODAY INTO THIS EVENING. DRY
CONDITIONS WILL RETURN LATER THIS EVENING BEHIND THIS SYSTEM...WITH
A REINFORCING PUSH OF COOL AIR RESULTING IN CONTINUED BELOW NORMAL
TEMPERATURES THROUGH MID WEEK. HIGH TEMPERATURES THIS AFTERNOON WILL
REACH INTO THE 60S...EXCEPT LOWER 70S ACROSS CENTRAL INDIANA INTO
CENTRAL OHIO. LOW TEMPERATURES TONIGHT WILL RANGE FROM THE MID 40S
TO AROUND 50.

&&

.UPDATE...
ISSUED AT 920 AM EDT MON SEP 15 2014

VERY STEEP MIDLEVEL LAPSE RATES...OVER 8 C/KM ON LATEST SPC/RAP
MESOANALYSIS...HAVE SUPPORTED A FEW ELEVATED THUNDERSTORMS AS
INITIAL SATURATION OCCURS. RAP FORECAST SOUNDINGS AND MUCAPE
FIELDS INDICATE THIS INSTABILITY WILL DECREASE THROUGH THE DAY BUT
SUGGEST LAPSE RATES WILL REMAIN JUST STEEP ENOUGH IN OUR SOUTHERN
COUNTIES TO ALLOW FOR A FEW ISOLATED THUNDERSTORMS ALONG ELEVATED
FRONTAL ZONE THROUGH THE EARLY AFTERNOON. CURRENTLY NUMEROUS
THUNDERSTORMS IN SOUTHERN IOWA AND WESTERN ILLINOIS. THIS ACTIVITY
IS ENTRENCHED IN THE BETTER THETA-E PLUME BUT SUSPECT A FEW
THUNDERSTORMS WILL CONTINUE TO CLIP OUR SOUTHWEST COUNTIES AT
LEAST. HAVE UPDATED THE FORECAST ACCORDINGLY. OTHERWISE FORECAST
REMAINS IN GOOD SHAPE WITH JUST A FEW CHANGES TO INHERITED POPS TO
REFLECT LATEST RADAR TRENDS AND INCREASING CONFIDENCE THAT MOST
AREAS WILL SEE AT LEAST A HUNDREDTH TODAY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 445 AM EDT MON SEP 15 2014

THE NEXT UPPER LEVEL SHORT WAVE OF INTEREST IS WELL PRONOUNCED ON
WATER VAPOR IMAGERY THIS MORNING ACROSS THE DAKOTAS. ALREADY HAVE
NOTED SOME VERY WEAK ELEVATED ECHOES UPSTREAM ACROSS
CENTRAL/NORTHERN ILLINOIS WHERE BACKING OF LOW LEVEL WINDS HAS
ALLOWED FOR AN INCREASE AN ISENTROPIC LIFT. AT LEAST OVER THE NEXT
SEVERAL HOURS...SHOWER POTENTIAL SEEMS SOMEWHAT MINIMAL DUE TO
HIGHLY ELEVATED NATURE OF THIS FORCING AND INITIALLY QUITE DRY LOW
LEVELS. SOUTHWESTERLY LOW LEVEL FLOW WILL RAMP UP SOMEWHAT IN
ADVANCE OF THIS WAVE ALLOWING BROAD WEAK LOW LEVEL THETAE RIDGING
ACROSS THE MID MISSISSIPPI RIVER VALLEY TO SHIFT INTO THE OHIO
VALLEY/SOUTHERN GREAT LAKES. LOW/MID LEVEL FRONTOGENESIS WILL ALSO
BE ON THE UPSWING IN ADVANCE OF THIS WAVE...ESPECIALLY DURING THE
MID TO LATE AFTERNOON HOURS. LOCAL AREA WILL ALSO BECOME
INCREASINGLY FAVORED IN RIGHT ENTRANCE REGION OF GREAT LAKES UPPER
JET STREAK. GIVEN FAIRLY STRENGTH OF UPPER WAVE...MID/UPPER LEVEL
FRONTOGENESIS...AND STRENGTHENING ISENTROPIC UPGLIDE...HAVE STAYED
THE COURSE WITH HIGH END LIKELY POPS. MAY EVENTUALLY NEED TO
CONSIDER NUDGING INTO CATEGORICAL POP RANGE FOR PORTIONS OF THE AREA
HOWEVER AS STRONGER ISENTROPIC UPGLIDE/FRONTAL FORCING BECOME
ESTABLISHED LATER THIS AFTERNOON/EARLY EVENING. MAIN TWEAK TO
FORECAST WAS TO PUSH TIMING OF HIGHER POPS BACK JUST A FEW HOURS
INTO THE LATE AFTERNOON HOURS AS APPROACHING FRONTAL FORCING SHOULD
ALLOW PRECIP TO CONTINUE.

A FEW THUNDERSTORMS HAVE DEVELOPED ACROSS SOUTHERN IOWA THIS MORNING
IN ZONE OF STRONGER ISENTROPIC LIFT/LOW LEVEL MASS CONVERGENCE.
CURRENT FORECAST THINKING IS THAT BETTER THUNDER POTENTIAL WILL
REMAIN SOUTHWEST OF LOCAL AREA IN RICHER LOW LEVEL THETAE AIRMASS.
WHILE CANNOT COMPLETELY RULE OUT AN ISOLATED THUNDERSTORM
PARTICULARLY ACROSS THE SOUTHWEST...FEEL PROSPECTS ARE BELOW
MENTIONABLE LEVELS AT THIS TIME.

AXIS OF MORE PRONOUNCED MID LEVEL FRONTO FORCING TO LINGER ACROSS
THE CENTRAL/EASTERN AREAS EARLY THIS EVENING WHERE HAVE CARRIED
LIKELY POPS...WITH CONDITIONS DRYING OUT FROM WEST TO EAST. SKIES
SHOULD CLEAR OR PARTIALLY CLEAR TONIGHT AS LOW LEVEL TROUGH AXIS
CLEARS AREA...ALTHOUGH AS HAS BEEN THE CASE OVER THE PAST SEVERAL
DAYS...PERSISTENT LOW LEVEL INVERSION GIVES SOME HESITATION FOR MORE
LONGEVITY OF STRATOCU THAN CURRENTLY FORECASTED. LOWS SHOULD DROP
INTO THE MID 40S TONIGHT...BUT PROBABLY MORE INTO THE UPPER 40S TO
AROUND 50 RANGE WHERE STRATUS PERSISTS LONGER. SOME LAKE EFFECT LOW
CLOUDINESS MAY ALSO PROVIDE WARMER CONDITIONS NEAR THE NW INDIANA
LAKESHORE AREAS...BUT LAKE INDUCED INSTABILITY DEPTHS APPEAR TO BE
TOO SHALLOW FOR ANY PRECIP INCLUSION AT THIS TIME.

&&

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 445 AM EDT MON SEP 15 2014

TRANQUIL WEATHER IS EXPECTED FOR TUESDAY INTO SATURDAY WITH
GRADUALLY MODERATING TEMPERATURES AS THE FLOW BECOMES MORE HIGH
ZONAL AND AS THE AIRMASS OVER THE AREA MODIFIES. AT THE START OF THE
PERIOD...THE SHORT WAVE WILL HAVE MOVED EAST OF THE AREA BY TUESDAY
MORNING...WITH DECREASING CLOUDS EXPECTED DURING THE DAY AS
SUBSIDENCE BEHIND THE TROF INCREASES. FAVORABLE NOCTURNAL
RADIATIONAL COOLING CONDITIONS ARE EXPECTED TUESDAY NIGHT WITH LOWS
DROPPING WELL BELOW 50 DEGREES. COULD BE SOME PATCHY FROST IN
LOCALLY COLD SPOTS...BUT OTHERWISE...FROST IS NOT EXPECTED AND HAVE
NOT MENTIONED ANY FROST IN THE GRIDS/FORECAST. THE GFS HAS BEEN
REASONABLY CONSISTENT WITH THE WARM UP THIS WEEK...AND THE GFS/MEX
MEAN ENSEMBLE MOS TEMPERATURES APPEAR ON TRACK. FOR THIS COMING
WEEKEND...THE GFS AND ECMWF HAVE COME INTO A LITTLE BETTER AGREEMENT
ON TIMING OF THE NEXT SYSTEM...WITH AN UPPER LEVEL SYSTEM AND
ASSOCIATED COLD FRONT MOVING ACROSS THE AREA BY LATE IN THE WEEKEND.
FOR NOW...KEPT A CHANCE FOR SHOWERS SATURDAY THROUGH SUNDAY. THUNDER
MAY NEED TO BE ADDED AT SOME POINT...BUT FOR NOW KEPT THUNDER OUT
GIVEN CAPE VALUES VERY SMALL PER GFS/BUFKIT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 653 AM EDT MON SEP 15 2014

LOW LEVEL WARM ADVECTION WILL CONTINUE TO INCREASE THROUGH THE
MORNING IN ADVANCE OF NEXT NORTHERN PLAINS UPPER TROUGH
APPROACHING THE REGION. ENOUGH ELEVATED INSTABILITY MAY EXIST FOR
AN ISOLATED THUNDERSTORM AT KSBN THROUGH 14Z...BUT OTHERWISE
POTENTIAL OF THUNDER APPEARS TO BE QUITE LOW FOR TERMINALS...WITH
BETTER INSTABILITY SETTING UP SOUTH/SOUTHWEST. COVERAGE OF RAIN
SHOWERS WILL INCREASE LATE MORNING INTO THIS AFTERNOON AS WARM
ADVECTION FORCING INCREASES. LIKELIHOOD OF RAIN WILL CONTINUE
THROUGH MOST OF AFTERNOON AS UPPER TROUGH/MID LEVEL FRONTOGENESIS
APPROACH FROM THE WEST...WITH CONDITIONS DRYING FROM WEST TO EAST
THIS EVENING. HAVE MAINTAINED TREND OF PREVIOUS TAF TO LOWER END
MVFR CIGS LATE THIS AFTERNOON/EARLY EVENING WITH THE POSSIBILITY
OF SOME SHORT LIVED IFR CONDITIONS. SOME STRATUS OR PATCHY FOG MAY
DEVELOP BEHIND SFC TROUGH TONIGHT GIVEN LINGERING LOW LEVEL
MOISTURE AND LOW LEVEL INVERSION...BUT WILL MAINTAIN VFR
CONDITIONS AT THIS TIME FOR THE LATTER PORTIONS OF THE FORECAST PERIOD.


&&

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

$$

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


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