Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 010750
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
350 AM EDT TUE SEP 1 2015

.SYNOPSIS...
ISSUED AT 157 AM EDT TUE SEP 1 2015

PATCHY FOG WILL CONTINUE TO DEVELOP ACROSS THE AREA THIS
MORNING...BUT WILL BURN OFF SHORTLY AFTER SUNRISE. ISOLATED
SHOWERS AND THUNDERSTORMS ARE POSSIBLE FROM LATE MORNING INTO
TONIGHT AS AN UPPER LEVEL DISTURBANCE IS SLOW TO EXIT TO THE EAST.
WARM AND HUMID CONDITIONS ARE IN STORE TODAY...WITH HIGHS REACHING
INTO THE MID TO UPPER 80S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 345 AM EDT TUE SEP 1 2015

ANOTHER HOT AND HUMID DAY IN STORE WITH MAIN FORECAST CHALLENGE
TODAY AND TONIGHT ATTEMPTING TO RESOLVE ANY CONVECTIVE POTENTIAL.

IN THE VERY NEAR TERM...AREAS OF FOG HAVE DEVELOPED AGAIN THIS
MORNING...MAINLY NORTH OF ROUTE 6. DENSE FOG IS NOT EXPECTED TO BE
AS EXPANSIVE AS YESTERDAY...ALTHOUGH PATCHY DENSE IS A POSSIBILITY
UNTIL SHORTLY AFTER DAYBREAK.

WATER VAPOR IMAGERY THIS MORNING CONTINUES TO DEPICT A RATHER
IMPRESSIVE COMPACT UPPER LEVEL CIRCULATION CENTERED ACROSS CENTRAL
INDIANA. A VORT LOBE ROTATING THROUGH THIS CIRCULATION APPEARS TO BE
SHIFTING CIRCULATION SLOWLY BACK TO THE WEST...BUT A SLOW EASTWARD
MIGRATION OF THIS FEATURE ACROSS CENTRAL INDIANA AND EVENTUALLY
NORTHWEST/WEST CENTRAL OHIO IS EXPECTED LATER TONIGHT. A FEW SHOWERS
HAVE DEVELOPED DURING THE OVERNIGHT HOURS NORTH OF THIS CIRCULATION
IN WEAK DPVA ZONE...BUT CONTINUED DIURNAL COOLING APPEARS TO BE
LIMITING ELEVATED INSTABILITY. AS THIS VORT MAX BEGINS TO SHIFT BACK
EASTWARD LATER THIS MORNING...ISOLATED/SCATTERED SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS THE AREA...WITH
GREATEST COVERAGE ACROSS THE SOUTHERN TWO THIRDS OF THE AREA IN
CLOSER PROXIMITY TO STRONGER UPPER FORCING. A CONSISTENT SIGNAL ALSO
APPEARS IN GUIDANCE IN BETTER CONVECTIVE POTENTIAL IMMEDIATELY
BEHIND THIS VORT MAX...MORE TIED INTO A NARROW CORRIDOR OF STRONGEST
ISENTROPIC UPGLIDE IN ASSOCIATION WITH RETREATING THICKNESS MINIMUM.
PERHAPS BEST COVERAGE WITH THIS FORCING WILL RESIDE ACROSS WEST
CENTRAL INDIANA JUST SOUTH OF THE FORECAST AREA...BUT DID MAINTAIN
CHANCE POPS ACROSS THE SOUTHWEST INTO THIS AFTERNOON. FURTHER TO THE
NORTH DID MAINTAIN SOME ISOLATED POPS ACROSS MOST OF THE FORECAST
AREA FOR LATER THIS AFTERNOON.

A LARGE SPREAD AMONG DETERMINISTIC SOLUTIONS REGARDING MAGNITUDE OF
INSTABILITY NOTED FOR THIS AFTERNOON...AND WOULD SUSPECT A
COMPROMISE BETWEEN MORE ROBUST INSTABILITY OF NAM AND THE MORE
TEMPERED GFS IS REASONABLE...WITH SBCAPES GENERALLY IN THE 1000-2000
J/KG RANGE ANTICIPATED. MID/UPPER LEVEL FLOW FIELDS WILL BE WEAKER
TODAY...AND THUS CONVECTION SHOULD BE PULSEY IN NATURE WITH OVERALL
WEAK STORM MOTION VECTORS POSSIBLY FAVORING SOME ISOLATED HEAVY
DOWNPOURS. TEMPS WILL BE DEPENDENT ON CONVECTIVE COVERAGE/HIGH CLOUD
DEBRIS...BUT HAVE NOT STRAYED FAR FROM PREVIOUS FORECAST WITH MID-
UPPER 80S MAX TEMPS.

BY TONIGHT...UPPER VORT MAX SHOULD BE DEPARTING THE AREA INTO
SOUTHERN OHIO...BUT PREVIOUSLY MENTIONED 850-700 HPA WAA INDUCED
FORCING WITH RAMPING UP LOW LEVEL WAA VIA 15-20 KNOT WESTERLY
LLJ/FAIRLY GOOD THERMAL PACKING ARGUES FOR A SLIGHT CHANCE TSRA
MENTION. SOME PATCHY FOG POSSIBLE ONCE AGAIN...BUT CURRENTLY NOT
IMPACTING SIGNIFICANT IMPACTS.

&&

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 345 AM EDT TUE SEP 1 2015

A STRONG MID-UPPER LEVEL RIDGE WITH 588 DAM PLUS AT 500 MB WILL
CONTINUE TO PROVIDE THE REGION WITH UNSEASONABLE WARMTH/HUMIDITY AND
MAINLY DRY WX THROUGH THE PERIOD.

SIMILAR TO WHAT IS GOING ON IN THE SHORT TERM LOW-ISOLATED CHANCES
FOR SHOWERS/STORMS WILL BE TIED TO WEAKNESSES IN THE HEIGHT FIELD
AND POSSIBLE SMALL SCALE CIRCULATIONS THAT EMERGE. ONE SUCH FEATURE
OVER WEST-CENTRAL INDIANA AS OF THIS WRITING WILL LIKELY DRIFT
SOUTHEAST OF THE LOCAL AREA BY WEDNESDAY...HOWEVER MAY STILL SEE A
FEW SHOWERS ON THE BACKSIDE OF THIS CIRCULATION ALONG/EAST OF THE
INTERSTATE 69 CORRIDOR WHERE SLIGHT CHANCE POPS WERE RETAINED.
DRY OTHERWISE INTO WEDNESDAY EVENING AS SHORTWAVE RIDGING
OVERSPREADS IN ADVANCE OF A SMALLER SCALE/LEAD SHORTWAVE (NOW
ENTERING THE HIGH PLAINS) MODELED TO LIFT INTO THE UPPER
MIDWEST/WESTERN LAKES BY WEDNESDAY NIGHT-THURSDAY. RE-AMPLIFICATION
OF THE LONGWAVE RIDGE AXIS INTO ONTARIO WILL AID IN
STALLING/DRIFTING THIS WEAK SHORTWAVE AND POSSIBLE CIRCULATION INTO
THE GREAT LAKES REGION BY THURSDAY AND FRIDAY. AN ASSOCIATED
WEAK/ILL-DEFINED SFC TROUGH ON THE SOUTHERN FLANK MAY BE ENOUGH TO
SPARK SPOTTY SHOWERS/STORMS EACH DAY...BEST CHANCES (10-30%) IN THE
AFTERNOON GIVEN EXPECTATIONS FOR LOW-MODERATE SURFACE BASED
INSTABILITY. AS FOR THE HOLIDAY WEEKEND...RETAINED A DRY/HOT
FORECAST WITH RIDGING ANTICIPATED BOTH ALOFT AND AT THE SFC.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 157 AM EDT TUE SEP 1 2015

NEAR TERM CONCERN WILL CONTINUE TO BE POTENTIAL FOG DEVELOPMENT
IMPACTING TERMINALS THROUGH EARLY THIS MORNING. ANOTHER NIGHT OF
IDEAL RADIATIONAL COOLING CONDITIONS HAS ALLOWED FOR A FEW
LOCATIONS ACROSS NORTHERN INDIANA/SOUTHERN LOWER MICHIGAN TO DROP
TO IFR/LIFR VSBYS AS OF 0530Z. STILL SOME LOW CONFIDENCE IN TERMS
OF IFR/LIFR CONDITIONS AT TERMINALS...WITH LATEST AMDAR DATA STILL
SUGGESTING SOME MODEST LOW LEVEL FLOW RAISING SIMILAR QUESTIONS
AS LAST NIGHT IN TERMS OF FOG VS STRATUS. GROUND CONDITIONS DID
DRY OUT SOMEWHAT YESTERDAY WITH BETTER INSOLATION/SFC HEATING
WHICH MAY ALSO PLAY SOME ROLE IN LIMITING EXTENT OF FOG AS
COMPARISON TO YESTERDAY. AT THIS TIME WILL MAINTAIN TEMPO IFR
VSBYS AT BOTH TERMINALS IN THE 09Z-12Z TIMEFRAME...BUT CERTAINLY
NOT OUT OF THE REALM OF POSSIBILITY FOR SOME LIFR VSBYS DURING
THIS TIMEFRAME PARTICULARLY AT KSBN.

OTHERWISE...DEPARTING UPPER VORT MAX ACROSS NORTHEAST INDIANA MAY
TRIGGER ISOLATED SHOWERS/STORMS LATE MORNING/AFTERNOON WITH SOME
INDICATIONS THAT EVEN KSBN COULD BE SUSCEPTIBLE TO ISOLATED
SHOWERS AS A CORRIDOR OF WARM ADVECTION SETS UP IN THE WAKE OF
THIS VORT MAX. POINT PROBABILITIES ARE TOO LOW FOR PRECIP MENTION
AT THIS TIME HOWEVER AND WILL CARRY DRY/VFR FORECAST AFTER THIS
MORNINGS FOG ERODES AFTER 12Z.

&&

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

$$

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


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