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000
FXUS63 KIWX 220043
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
843 PM EDT TUE MAY 21 2013

.SYNOPSIS...
ISSUED AT 550 PM EDT TUE MAY 21 2013

LOW PRESSURE OVER THE UPPER MIDWEST WILL TRACK EAST INTO THE GREAT
LAKES REGION TOMORROW. THIS SYSTEM WILL BRING INCREASING CHANCES
FOR SHOWERS AND THUNDERSTORMS TO THE AREA...MAINLY LATER TONIGHT
INTO WEDNESDAY. A FEW THUNDERSTORMS MAY BECOME STRONG TO SEVERE. A
FEW SHOWERS MAY LINGER INTO THURSDAY...WITH COOLER AND DRIER AIR
FORECAST TO SETTLE INTO THE REGION LATE THIS WEEK INTO THE
HOLIDAY WEEKEND.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 314 PM EDT TUE MAY 21 2013

DEEP MIXING TO NEAR 800 MB...SAMPLED BY DTX 18Z SOUNDING...HAS
MIXED DOWN GUSTY WINDS TODAY BETWEEN 15-20 KTS WITH GUSTS AS HIGH
AS 30 KTS. THESE WINDS WILL DIMINISH INTO THE EVENING AS BOUNDARY
LEVEL DECOUPLING COMMENCES. EASTERN AREAS ARE NEARLY CLOUD FREE AS
DEWPOINTS HAVE MIXED INTO THE UPPER 50S TO NEAR 60 WHICH HAS
LIMITED INSTABILITY AND CONSEQUENT CU DEVELOPMENT. EVEN IN WESTERN
AREAS WHERE DEWPOINTS HAVE REMAINED IN THE LOW TO MID 60S...CU
DEVELOPMENT HAS LACKED VERTICAL DEVELOPMENT AS MEAGER MID LEVEL
LAPSE RATES LEFT IN THE WAKE OF MORNING CONVECTION HAVE YET TO
STEEPEN. GIVEN THE LACK OF FORCING AND NEARLY MOIST ADIABATIC
LAPSE RATES FROM THE LCL TO THE TROPOPAUSE...HAVE VERY LITTLE
CONFIDENCE IN ANY DIURNAL SHOWER OR THUNDERSTORM DEVELOPMENT.

CHANCES FOR RAINFALL DURING THE EARLY MORNING HOURS ON WEDNESDAY
LOOK QUITE FAVORABLE AS A STRONG VORT MAX PIVOTS OUT OF OKLAHOMA AND
EJECTS TOWARDS OUR AREA OVERNIGHT. THE BEST CHANCE FOR SHOWERS AND
THUNDERSTORMS SHOULD ARRIVE BETWEEN 06 AND 12Z AS MID-LEVEL HEIGHT
FALLS OVERSPREAD THE AREA. MID-LEVEL HEIGHT PERTURBATION WILL BE
DAMPENING AS IT MOVES ACROSS THE AREA...BUT WITH 500-1000 J/KG OF
CAPE ACROSS THE AREA...INSTABILITY SHOULD BE SUFFICIENT FOR STORMS
TO SUSTAIN THEMSELVES. SHEAR PROFILE WILL ONCE AGAIN REMAIN
FAVORABLE...BUT AFOREMENTIONED WEAKENING FORCING AND INSTABILITY
SHOULD KEEP THE SEVERE THREAT MINIMAL.

BUMPED UP HIGH TEMPERATURES SLIGHTLY ON WEDNESDAY AS BREAKS IN THE
CLOUDS DURING THE MORNING HOURS SHOULD ALLOW TEMPERATURES TO WARM
SLIGHTLY MORE THAN PREVIOUSLY FORECAST...ESPECIALLY IN EASTERN
AREAS.  THERE SHOULD BE A LULL IN THE PRECIPITATION DURING THE
MORNING HOURS AS THE OVERNIGHT WAVE LIFTS NORTH...BUT ADDITIONAL
AFTERNOON DEVELOPMENT IS LIKELY AS BREAKS IN THE CLOUDS ALLOW ENOUGH
SURFACE HEATING FOR INSTABILITY BETWEEN 500 AND 1000 J/KG. SEVERE
WEATHER THREAT DOES EXIST IN EASTERN AREAS IF GREATER
DESTABILIZATION CAN OCCUR...BUT CURRENT THINKING IS THAT THE
GREATEST THREAT WILL BE EAST OF OUR FORECAST AREA.

&&

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 314 PM EDT TUE MAY 21 2013

CLOSED UPPER LOW OPENING UP AND SHIFTING EASTWARD INTO THE MID MS
VALLEY TO BEGIN THE FORECAST PERIOD. SFC LOW PRESSURE WILL BE IN
EASTERN GREAT LAKES AND ASSOCIATED COLD FRONT EXPECTED TO ALREADY BE
EAST OF THE CWA. UPPER TROF AXIS THEN MOVES THROUGH THE AREA ON
THURSDAY BRINGING LINGERING CHANCES FOR SHOWERS BEFORE SYSTEM
FINALLY EXITS AND MAKES WAY FOR MUCH COOLER CANADIAN HIGH PRESSURE.
SFC HIGH PRESSURE TO DOMINATE THE PATTERN FOR FRI AND SAT WITH MUCH
COOLER BUT NOT TOO UNSEASONABLE WITH M60S AND M40S EXPECTED. SFC
RIDGE AXIS SLIDES EAST OF THE REGION AND NW FLOW PATTERN ALOFT
OFFERS A LOT OF UNCERTAINTY AMONG THE MEDIUM RANGE MODELS BY DAYS
6 AND 7. AGREEMENT EXISTS IN ATTEMPTING TO BRING SHORT WAVE
DISTURBANCE FROM THE PLAINS EASTWARD...BUT VARY IN TIMING AND
RANGE IN LOCATION FROM TN VALLEY TO THE GREAT LAKES REGION. GULF
SUFFICIENTLY CUT OFF BY SFC RIDGE BRINGING AVAILABLE MOISTURE INTO
QUESTION AS WELL. MEAN ENSEMBLE AND EVEN MOST OF THE HIGHER END
MEMBERS STILL RUNNING BELOW CLIMATOLOGY FOR POPS SO STILL LEANING
TOWARD STAYING WITH DRY FORECAST UNTIL BETTER CONSENSUS AND
STRONGER MODEL SIGNAL PRESENTS ITSELF.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 840 PM EDT TUE MAY 21 2013

ATTEMPT TO TARGET CONDITIONAL CONVECTIVE CHANCES THIS FORECAST
PERIOD. MARGINAL SURFACE BASED INSTABILITY ACROSS NORTHERN INDIANA
WITH ONLY A FEW CELLS BETWEEN KSBN/KFWA THIS EVENING...FAILING TO
SUSTAIN AS WELL SOUTH OF BETTER SBCAPE/EFFECTIVE SHEAR OVERLAP THAT
RESIDES FARTHER NORTH...FROM THE MI THUMB SOUTHWEST TO NEAR KGRR
VCNTY. ISOLATED NOW INTO SOUTHERN LOWER MICHIGAN BARELY MUSTERING
DEPTH FOR GLACIATION/LIGHTNING PRODUCTION AMID WEAK MID LEVEL LAPSE
RATES AROUND 5 C/KM. ONLY SUBSTANTIVE CHANCE WILL BE NEAR DAYBREAK
AS BACKED/RAMPING NOCTURNAL LOW LEVEL JET ASSERTS FROM 40-50KT
SSWRLY FLOW FROM WESTERN TN INTO SOUTHERN INDIANA AROUND 09-12 UTC.
MIDLEVEL SHORTWAVE/SPEEDMAX SUPPORTS UPTICK IN OVERALL UPSTREAM DEEP
LAYER BULK SHEAR PROFILE NECESSARY FOR SUSTENANCE GIVEN GENERALLY
ANEMIC AND DECLINING THERMODYNAMIC PROFILE ACROSS NORTHERN INDIANA
LATE TONIGHT. ATTEMPT TO TARGET 3 HOUR WINDOWS FOR TEMPO TSRA WITH
OVERALL CONDITIONS AOA FUEL ALTERNATE...WITH MUCH LOWER CHANCES THAT
CELL CENTROIDS AND ASSOCD IFR MET CONDITIONS WOULD AFFECT AIRFIELD
DIRECTLY. ANOTHER TIMED CHANCE FOR CONVECTION LATE IN FORECAST
PERIOD AT KFWA IMMEDIATELY AHEAD OF FRONTAL BOUNDARY AND
DIFFERENTIAL CYCLONIC VORTICITY ADVECTION EARLY WED AFTERNOON.

&&

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

$$

SYNOPSIS...STEINWEDEL/KG
SHORT TERM...BENTLEY
LONG TERM...JAL
AVIATION...MURPHY


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