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000
FXUS63 KIWX 170810
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
410 AM EDT MON JUN 17 2013

.SYNOPSIS...
ISSUED AT 410 AM EDT MON JUN 17 2013

A WEAK COLD FRONT WILL APPROACH THE REGION LATER TODAY AND BRING A
CHANCE FOR SHOWERS AND THUNDERSTORMS OVERNIGHT AND AGAIN TUESDAY
AFTERNOON. HIGH PRESSURE WILL THEN BUILD OVER THE GREAT LAKES BY
MIDWEEK WITH A RETURN TO DRY AND COOLER CONDITIONS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 410 AM EDT MON JUN 17 2013

CHALLENGING FORECAST WITH RESPECT TO CONVECTION TIMING/COVERAGE
CONTINUES INTO THIS SHORT TERM PERIOD. VERY WEAK FORCING AND ONLY
MODEST INSTABILITY WILL LIKELY LEAD TO ANOTHER ROUND OF SPORADIC
SHOWERS AND PERHAPS A FEW THUNDERSTORMS LATE THIS EVENING AND INTO
THE OVERNIGHT. LATEST WATER VAPOR LOOP SHOWS CENTRAL CANADA PV
ANOMALY CONTINUES TO GET SHEARED AND STRETCHED OUT AS IT IS ABSORBED
INTO A STRONG WESTERLY JET AXIS ASSOCIATED WITH LARGE EASTERN CANADA
NEGATIVE HEIGHT ANOMALY. THE GRADUAL SOUTHEASTWARD PROGRESSION OF
THIS VORTICITY FILAMENT WILL ALLOW A WEAK COLD FRONT TO SAG SOUTH
ACROSS THE GREAT LAKES AND MAY PROVIDE A FOCUS FOR CONVECTION BY
TONIGHT. MANY QUESTIONS REMAIN THOUGH...ESPECIALLY REGARDING
UNFAVORABLE DIURNAL TIMING. PRONOUNCED POCKET OF LOWER THETA-E
AIR...WELL SAMPLED BY UPSTREAM 00Z SOUNDINGS...WILL CONTINUE TO
SPILL INTO OUR AREA WITH LINGERING ANTICYCLONIC FLOW. THIS WILL
LIKELY KEEP OUR CWA DRY AND LARGELY CLOUD FREE THROUGH AT LEAST MID
AFTERNOON. THIS WILL ALSO ALLOW FOR SOME IMPRESSIVE MIXING DEPTHS.
UPSTREAM AREAS OF IOWA AND SOUTHERN WISCONSIN CLIMBED WELL INTO THE
MID 80S UNDER SIMILAR PROFILES YESTERDAY AND EXPECT THE SAME FOR OUR
AREA TODAY. MOISTURE POOLING ALONG THE FRONTAL BOUNDARY AND
RELATIVELY COOL MIDLEVEL TEMPS WILL ALLOW DECENT INSTABILITY TO
BUILD WELL NORTH OF OUR AREA BUT VERY DRY PROFILES WILL SEVERELY
LIMIT LOCAL DESTABILIZATION. AND BY THE TIME MOISTURE DOES BEGIN TO
INCREASE AROUND 00Z...THE DIURNAL HEATING COMPONENT IS LOST.
MID/UPPER LEVEL FORCING AND THE ASSOCIATED LOW LEVEL COLD FRONT ALSO
BECOME INCREASINGLY DIFFUSE BY TONIGHT AS THE LEAD VORTICITY
FILAMENT BECOMES INCREASINGLY SHEARED. BETTER SUPPORT MAY ARRIVE ON
TUESDAY WHEN THE MAIN VORT MAX CROSSES THE REGION BUT BECOMES VERY
DIFFICULT TO PINPOINT A SUBSTANTIAL LIFTING MECHANISM FOR THE
OVERNIGHT PERIOD. HAVE THEREFORE MAINTAINED JUST LOW CHANCE POPS.
COULD BE SOME DECAYING PRECIP ARRIVING FROM THE NORTH BY THE EVENING
HOURS...AND SOME HIGH-RES MODELS SHOW SOME CONVECTION CLIPPING OUR
SOUTHERN CWA THANKS TO BETTER INSTABILITY WELL SOUTH OF HERE...BUT
THIS ACTIVITY WILL LIKELY BE FAIRLY ISOLATED. OVERNIGHT LOWS WILL BE
SIMILAR TO THE PAST FEW NIGHTS WITH POTENTIAL CLOUD COVER AND DECENT
BOUNDARY LAYER MOISTURE KEEPING MIN TEMPS AROUND 60F.

&&

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 410 AM EDT MON JUN 17 2013

SURFACE TROUGH WILL BE POSITIONED SOUTH OF LOCAL AREA TUESDAY BUT
LINGERING LOW LEVEL TROUGH AXIS WILL BE DRIFTING SOUTH ACROSS THE
SOUTHERN GREAT LAKES TUESDAY AFTERNOON. UPPER PV ANOMALY
POSITIONED ACROSS SOUTHERN BC CANADA THIS MORNING WILL TRACK INTO
THE MID MS RIVER VALLEY EARLY TUESDAY MORNING. PREVIOUS FORECAST
UNCERTAINTY ON WHETHER TO ADD POPS FOR THIS PERIOD HAS CENTERED
MAINLY ON LOW LEVEL MOISTURE CONSIDERATIONS. HOWEVER...IT
INCREASINGLY APPEARS AS THOUGH LOW LEVEL MOISTURE WILL NOT BE MORE
AGGRESSIVELY SCOURED OUT UNTIL PASSAGE OF THIS PV ANOMALY TUESDAY
NIGHT WHEN SFC HIGH DROPS SOUTHWARD INTO THE REGION. GIVEN
FAVORABLE TIMING OF THIS SHORT WAVE AND WEAK AFTERNOON INSTABILITY
ON THE ORDER OF 500-1000 J/KG EXPECTED...HAVE GONE AHEAD AND
INCLUDED SOME ISOLD TSRA POPS ESPECIALLY ACROSS SOUTHEAST HALF OF
THE AREA MAINLY BASED ON TIMING PV ANOMALY WITH PEAK INSTABILITY
AND EXPECTED WEAKER INSTABILITY LAKE SHADOW. LINGERING SHOWER
POSSIBLE ACROSS THE FAR SOUTHEAST EARLY TUESDAY EVENING WITH A
PERIOD OF DRY WEATHER EXPECTED THROUGH FRIDAY. ONLY OTHER
ADJUSTMENT TO TEMPERATURES WAS TO NUDGE HIGHS A BIT WARMER FOR THE
TUES-THURS TIMEFRAME BASED ON RECENT GUIDANCE BIASES AND LOCAL
AREA POSITIONED MORE ON SOUTHERN PERIPHERY OF NORTHEAST CONUS
THERMAL TROUGHING.

WEDNESDAY THROUGH FRIDAY SHOULD FEATURE BENIGN WEATHER WITH LARGE
SCALE AMPLIFICATION TO UPPER PATTERN EXPECTED. A STRONG EASTERN
PACIFIC JET IS STILL EXPECTED TO CARVE OUT A LARGE NEGATIVE UPPER
HEIGHT ANOMALY ACROSS THE PACIFIC NORTHWEST INDUCING CENTRAL CONUS
RIDGE AMPLIFICATION. MEDIUM RANGE MODELS HAVE BEEN FAIRLY CONSISTENT
IN ADVERTISING SMALLER SCALE COMPACT VORT PROGRESSING THROUGH THIS
RIDGE INTO THE MID MS VALLEY/OH VALLEY WED NIGHT/THU BUT THIS
POTENTIAL SHORT WAVE WILL BE MOISTURE STARVED AND DRY CONDITIONS
WERE MAINTAINED THROUGH FRIDAY.

LOW/MID LEVEL THERMAL RIDGE TO ADVECT INTO WESTERN GREAT LAKES
REGION FRIDAY NIGHT INTO SATURDAY. 00Z GFS/EC 850 HPA TEMPS INCREASE
INTO THE 18-22 DEG CELSIUS RANGE DURING THIS PERIOD...AND DPROG/DT
OF EC OVER PAST FEW RUNS INDICATES A TREND TO SLIGHTLY MORE
AGGRESSION IN BUILDING MID/UPPER LEVEL RIDGING INTO SOUTHERN GREAT
LAKES. LATEST MEX GUIDANCE SEEMS TO BE ON THE HIGH END OF MOS
ENSEMBLE VALUES WHICH HAVE GENERALLY BOUGHT INTO FOR THIS FORECAST
AND HAVE NUDGED UP CRALLBLEND VALUES MORE INLINE WITH THIS SCENARIO
WITH HIGHS FROM MID 80S TO AROUND 90. THIS PATTERN WOULD BE
CONDUCIVE FOR MCS DEVELOPMENT UPSTREAM ACROSS THE UPPER MIDWEST
POSSIBLY DROPPING INTO THE SOUTHERN GREAT LAKES...BUT IF CAPPING
ISSUES DO PERSIST THROUGH THE WEEKEND...WILL LIKELY NEED FURTHER
UPWARD ADJUSTMENTS TO MAX TEMPS SAT/SUN. WITH LOW CONFIDENCE IN
CAPPING ISSUES AND RESOLVING SMALLER SCALE WAVES TOPPING RIDGE...
WILL KEEP LOW CHANCE TSRA POPS SAT-SUN UNTIL THIS CAN BE BETTER
RESOLVED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 120 AM EDT MON JUN 17 2013

A FEW ISOLATED SHOWERS REMAIN AROUND KFWA...SUPPORTED BY SOME WEAK
LOW LEVEL CONVERGENCE...DESPITE DRY AIR ADVECTION AND NOCTURNAL
STABILIZATION. THESE SHOWERS WILL DISSIPATE IN THE NEXT FEW HOURS
WITH NO AVIATION IMPACT EXPECTED. A BRIEF PERIOD OF MVFR BR AND/OR
STRATUS REMAINS POSSIBLE AT KFWA JUST BEFORE SUNRISE GIVEN VERY
LIGHT WINDS AND RELATIVELY HIGH BOUNDARY LAYER MOISTURE. FORECAST
SOUNDINGS NOT VERY SUPPORTIVE BUT A FEW AREA SITES ARE BEGINNING
TO REPORT SLIGHT VIS REDUCTION SO WILL CONTINUE WITH LOW END MVFR
TEMPO MENTION. BEYOND THAT...VFR CONDITIONS EXPECTED FOR THE REST
OF THE TAF PERIOD. A WEAK FRONT WILL APPROACH BY LATE THIS EVENING
BUT MOISTURE AND INSTABILITY CONCERNS REMAIN AND WILL FORGO ANY
MENTION OF PRECIP IN THE TAFS AT THIS TIME.

&&

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

$$

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


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