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000
FXUS63 KIWX 150730
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
330 AM EDT SAT JUN 15 2013

.SYNOPSIS...
ISSUED AT 330 AM EDT SAT JUN 15 2013

HIGH PRESSURE WILL SHIFT EASTWARD TODAY AND THE GRADUAL APPROACH
OF A WEAK LOW PRESSURE SYSTEM WILL BRING INCREASING CHANCES FOR
SHOWERS AND THUNDERSTORMS THROUGH SUNDAY MORNING. HIGH
TEMPERATURES TODAY WILL BE IN THE UPPER 70S TO LOW 80S WITH
OVERNIGHT LOWS TONIGHT IN THE MID TO UPPER 60S.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 330 AM EDT SAT JUN 15 2013

LONGWAVE RIDGE RESPONSIBLE FOR RECENT PLEASANT WEATHER WILL DAMPEN
EASTWARD TODAY THANKS TO THE GRADUAL PROGRESSION OF LARGE ALBERTA
CLOSED LOW. THIS WILL FORCE LOW LEVEL ANTICYCLONE TO DRIFT EASTWARD
AND OPEN THE DOOR FOR SOME INCREASING WARM/MOIST AIR ADVECTION.
FIRST SUCH WAVE OF HIGHER THETA-E AIR...ASSOCIATED WITH EXPANSIVE
CONVECTIVE COMPLEX OVER THE UPPER MIDWEST...IS DUE TO REACH OUR CWA
BY LATER THIS MORNING. VERY LITTLE UPPER LEVEL SUPPORT...SAVE FOR A
WEAK CONVECTIVELY ENHANCED WAVE...AND REGIONAL 00Z SOUNDINGS SHOW A
VERY DRY AIRMASS CURRENTLY IN PLACE. INSTABILITY IS ALSO FAIRLY
MEAGER. LATEST SPC/RAP MESOANALYSIS SHOWS BETTER LAPSE RATES AND
MUCAPE VALUES REMAIN CONFINED WEST OF OUR CWA. SOME MODEST
ISENTROPIC ASCENT SEEN IN THE 300-305K SURFACES AND THERE WILL BE A
DECENT 850-700MB THETA-E SURGE BUT DRY/STABLE AMBIENT AIRMASS AND
LACK OF GOOD UPPER LEVEL FORCING WILL LIKELY EAT AWAY AT PRECIP
SHIELD AS IT MOVES EAST...AS SEEN IN MOST OF THE LATEST HI-RES
GUIDANCE. WILL THEREFORE MAINTAIN GENERALLY CHANCE POPS AND LIGHT
QPF AMOUNTS. INCREASING SOUTHWEST FLOW WILL HELP OFFSET BLANKET OF
MID/UPPER LEVEL CLOUDS TODAY AND HIGH TEMPS SHOULD BE A DEGREE OR
TWO WARMER THAN YESTERDAY...AROUND 80F.

MUCH BETTER CHANCE FOR RAIN WILL ARRIVE TONIGHT. MIDLEVEL WAVE
CURRENTLY OVER THE SOUTHERN PLAINS AND ITS ATTENDANT GULF MOISTURE
PLUME WILL CONTINUE TO GET ABSORBED INTO THE WESTERLIES AND ARRIVE
IN OUR REGION DURING THE OVERNIGHT PERIOD. POTENTIAL EXISTS FOR AN
MCS TO FORM UPSTREAM DURING THE LATE AFTERNOON AND PROPAGATE INTO
OUR AREA DURING THE EVENING BUT CONFIDENCE IS LOW. CONTINUED THETA-E
ADVECTION WILL SUPPORT A FAIR AMOUNT OF ELEVATED INSTABILITY BY LATE
EVENING WITH MUCAPE VALUES AROUND 1000 J/KG PER THE LATEST NAM BUFR
SOUNDINGS. WIND PROFILES ALOFT ARE ALSO MARGINALLY SUPPORTIVE OF
ORGANIZED UPDRAFTS. WILL CERTAINLY NEED TO KEEP AN EYE ON UPSTREAM
CONVECTIVE TRENDS LATER TODAY BUT SEVERE WEATHER CHANCES IN OUR AREA
APPEAR LOW GIVEN BETTER INSTABILITY STAYS CONFINED TO OUR WEST...AN
IDEA CONFIRMED BY LATEST SPC SWODY1. PRECIP CHANCES WILL INCREASE BY
LATE OVERNIGHT THOUGH. PASSING MIDLEVEL WAVE WILL SPAWN WEAK SURFACE
CYCLOGENESIS OVER THE GREAT LAKES WITH A DECENT PRESSURE TROUGH
PASSING THROUGH OUR CWA. 30+ KT LLJ WILL CONTINUE TO ADVECT PLENTY
OF MOISTURE INTO THE AREA WITH PWATS APPROACHING 1.75 INCHES.
COMBINATION OF GOOD MOISTURE TRANSPORT AND LARGE SCALE ASCENT SHOULD
FAVOR WIDESPREAD SHOWERS AND A FEW EMBEDDED THUNDERSTORMS BY LATE
TONIGHT. QPF AMOUNTS LOOK TO BE GENERALLY AROUND 0.5 INCHES BUT
HIGHER AMOUNTS ARE POSSIBLE IF ENOUGH ELEVATED INSTABILITY REMAINS
IN PLACE.

&&

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 330 AM EDT SAT JUN 15 2013

THE MAIN FORECAST CHALLENGE FOR THE LONG TERM WILL CENTER ON
RESOLVING PRECIP CHANCES INTO THE EARLY PARTS OF NEXT WEEK.

A SHEARING UPPER LEVEL SHORT WAVE ASSOCIATED WITH REMNANTS OF
SOUTHERN PLAINS UPPER LOW GETTING INGESTED INTO SOUTHWEST UPPER FLOW
SHOULD DEPART OFF TO THE EAST EARLY SUNDAY MORNING. DEEPER MOISTURE
PROFILES WILL ALSO SHIFT SOUTH AND EAST OF THE AREA EARLY SUNDAY AS
LOW/MID LEVEL WINDS VEER IN THE WAKE OF THIS WAVE. INCREASING
SIGNALS NOTED IN LATEST SUITE OF MEDIUM RANGE MODELS OF RATHER
VIGOROUS MID LEVEL DRYING WORKING ACROSS SOUTHERN GREAT LAKES SUNDAY
AFTERNOON VIA EASTWARD ADVECTION OF MID LEVEL DRY SLOT LIKE FEATURE
ASSOCIATED WITH UPPER TROUGH WORKING ACROSS NORTHERN TIER OF US. IN
ADDITION...BY THE AFTERNOON WHATEVER LINGERING LOW LEVEL CONVERGENCE
EXISTS SHOULD BE SHIFTING SOUTHEAST OF THE AREA ASSOCIATED WITH
WEAK SFC REFLECTION OF DEPARTING MID LEVEL FORCING. THUS...HAVE
CONTINUED TREND OF PREVIOUS FORECAST IN LOWERING POPS SUNDAY
AFTERNOON/NIGHT WITH NO CLEAR TRIGGERING MECHANISM AND QUESTIONABLE
INSTABILITY. CANNOT RULE OUT MAINLY DIURNALLY FORCED ISOLD
SHOWER/STORM ACROSS FAR SOUTH/SOUTHEAST SUNDAY AFTERNOON/EARLY
EVENING WHERE SLIGHTLY DEEPER MOISTURE PROFILES RESIDE AND EFFECTS
OF MID LEVEL DRYING MAY NOT BE AS PRONOUNCED. THUS...HAVE HELD WITH
SLIGHT CHANCE TSRA MENTION.

FOR MONDAY...DAMPENING UPPER TROUGH FROM THE NORTHERN PLAINS WILL
DROP INTO THE MID MS VALLEY WITH AT LEAST SOME LIMITED OPPORTUNITY
FOR A BRIEF PERIOD OF WEAK NORTHWARD MOISTURE TRANSPORT. DYNAMICS
QUITE WEAK WITH THIS DAMPENING WAVE...WITH A LACK OF ANY SIGNIFICANT
LOW LEVEL CONVERGENCE SIGNALS. WEAK SFC ANTICYCLONE SHOULD ACTUALLY
BE IN PLACE FOR THE FIRST HALF OF THE DAY. TRACK OF THIS SYSTEM ALSO
SHOULD FOR THE MOST PART REMAIN DIVORCED FROM THE BETTER LOW LEVEL
MOISTURE PROFILES DISPLACED SOUTH OF THE FORECAST AREA. DID MAINTAIN
SOME LOW TO MID RANGE CHANCE POPS MONDAY INTO MONDAY EVENING BUT
PROSPECTS FOR ANY SIGNIFICANT PRECIP LOOK MINIMAL.

REMAINDER OF THE PERIOD SHOULD FEATURE A WEST COAST TROUGH...CENTRAL
CONUS RIDGE LONGWAVE PATTERN THAT WILL KEEP LOCAL AREA IN NORTHWEST
FLOW ALOFT. WEAK PERTURBATIONS IN NORTHWEST FLOW COULD SPARK A STRAY
AFTERNOON SHOWER AT SOME POINT NEXT THROUGH THE LATTER PART OF THIS
FORECAST PERIOD...BUT LIMITED LOW LEVEL MOISTURE AND WEAKLY FORCED
NATURE TO THIS PATTERN PRECLUDES ANY ADDITIONAL PRECIP MENTION POST
MONDAY NIGHT. TEMPERATURES TO COOL BACK TO BELOW SEASONABLE NORMS
FOR TUE-WED WITH SOME MODERATION BACK TO NEAR NORMAL EXPECTED TOWARD
THE END OF THE PERIOD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 134 AM EDT SAT JUN 15 2013

SURFACE HIGH PRESSURE WILL SHIFT EAST TODAY...ALLOWING LOW LEVEL
WARM/MOIST AIR ADVECTION TO INCREASE OVER THE REGION. THE CHANCE
FOR SHOWERS AND THUNDERSTORMS WILL INCREASE THROUGH THE END OF THE
TAF PERIOD AS THIS THETA-E ADVECTION COMBINES WITH WEAK ASCENT
FROM PASSING MIDLEVEL WAVE. MCS CURRENTLY OVER IOWA IS EXPECTED TO
WEAKEN AS IT MOVES INTO INCREASINGLY DRY/STABLE AIRMASS OVER THE
GREAT LAKES BUT A FEW REMNANT SHOWERS ARE POSSIBLE AT KSBN LATER
THIS AFTERNOON BEFORE MORE SUBSTANTIAL FORCED ASCENT SPREADS OVER
THE AREA LATE TONIGHT. CONDITIONS WILL REMAIN LARGELY VFR THOUGH
WITH ONLY BRIEF REDUCTIONS POSSIBLE IN PASSING CONVECTION.

&&

.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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