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000
FXUS63 KIND 202033
AFDIND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
430 PM EDT MON MAY 20 2013

.UPDATE...
THE AVIATION SECTION HAS BEEN UPDATED BELOW.

&&

.SYNOPSIS...
ISSUED AT 239 PM EDT MON MAY 20 2013

A LARGE UPPER LOW CURRENTLY OVER THE PLAINS IS EXPECTED TO BRING
UNSETTLED WEATHER TO THE AREA THROUGH THURSDAY AS IT SLOWLY MOVES
EAST AND WEAKENS WITH TIME. IN THE WAKE OF THIS SYSTEM...HIGH
PRESSURE IS EXPECTED TO BUILD INTO THE AREA OVER THE WEEKEND AND
INTO EARLY NEXT WEEK.

&&

.NEAR TERM /REST OF THIS AFTERNOON AND TONIGHT/...
ISSUED AT 239 PM EDT MON MAY 20 2013

DEWPOINT DISCONTINUITY LINGERS OVER THE NORTHWEST ZONES...WITH
DEWPOINTS MIXING OUT INTO THE 50S OVER NORTHERN ILLINOIS. THIS MAY
BE EITHER THE REMNANTS OF AN OUTFLOW OR A FRONTAL SYSTEM. IN ANY
EVENT...AIR MASS OVER THE LOCAL AREA CONTINUES TO BE CAPPED...BUT
VERY UNSTABLE. SHORT TERM MODEL DATA SUGGEST THIS CAP MAY WEAKEN
AROUND 202200Z OR SO...LEADING TO THE POTENTIAL FOR THUNDERSTORM
DEVELOPMENT NEAR THIS DISCONTINUITY BY EARLY EVENING.
HOWEVER...THERE IS A QUESTION WHETHER THIS CAP WILL ACTUALLY BREAK.
MODEL DATA ALSO BRING IN AN AREA OF ORGANIZED LIFT DURING THE PRE
DAWN HOURS OF TUESDAY...PROBABLY RELATED TO CONVECTION THAT IS
EXPECTED TO DEVELOP FARTHER WEST LATER THIS AFTERNOON/EVENING.
THIS MAY RESULT IN ANOTHER ENHANCED CHANCE FOR CONVECTION BY EARLY
MORNING TUESDAY. DUE TO QUESTIONS REVOLVING AROUND THE CAP AND ANY
FUTURE STORM DEVELOPMENT...WILL KEEP POPS IN THE CHANCE CATEGORY
TONIGHT...HIGHEST IN THE WEST/NORTHWEST.

LAPSE RATE REMAIN QUITE FAVORABLE FOR SEVERE CONVECTION TONIGHT.
DEEP LAYER SHEAR...INITIALLY RATHER WEAK THIS EVENING...IS EXPECTED
TO STRENGTHEN LATER TONIGHT. AS A RESULT...THINK THE POTENTIAL FOR
ORGANIZED SEVERE CONVECTION SHOULD GRADUALLY INCREASE AS TIME GOES
BY TONIGHT.

GFS MOS LOWS TONIGHT LOOK REASONABLE BASED ON LOW LEVEL THICKNESS
PROGS.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
ISSUED AT 239 PM EDT MON MAY 20 2013

MAIN FEATURE DURING THIS PERIOD WILL BE THE LARGE UPPER LOW OVER THE
PLAINS THAT IS EXPECTED TO GRADUALLY OPEN UP AND MOVE INTO THE
MIDWEST BY THURSDAY...KEEPING THE SHORT TERM UNSETTLED.

DETAILS REVOLVING AROUND THE FRONTAL BOUNDARY OR ANY EFFECTIVE
OUTFLOW BOUNDARIES TO FOCUS CONVECTION ON OVER THE NEXT COUPLE OF
DAYS IS STILL MURKY...WITH SEVERAL ROUNDS OF CONVECTION EXPECTED.
ACTUAL COLD FRONT MAY NOT PASS UNTIL WEDNESDAY NIGHT OR THURSDAY
MORNING. APPEARS FROM THE MODEL DATA...THE BEST PRECIPITATION
SIGNALS ARRIVE TUESDAY NIGHT AND WEDNESDAY...SO WILL GO WITH THE
HIGHEST POPS DURING THOSE TIMES. WILL GO WITH CHANCE POPS IN THE
OTHER PERIODS FOR NOW.

AT THIS POINT...THE COMBINATION OF LAPSE RATES AND DEEP LAYER SHEAR
SUGGEST THAT TUESDAY MAY HAVE THE BEST POTENTIAL FOR SEVERE
CONVECTION OVER THE NEXT COUPLE OF DAYS. BY WEDNESDAY...LAPSE RATES
BECOME POORER...WHICH SHOULD HELP TO DIMINISH THE SEVERE THREAT BY
THAT TIME.

GIVEN PROGGED LOW LEVEL THICKNESSES AND EXPECTED CONVECTION OR CLOUD
COVER...THE GFS MOS HIGHS FOR TUESDAY AND WEDNESDAY LOOK A LITTLE
WARM. WILL NUDGE THE NUMBERS DOWN A FEW DEGREES. GUIDANCE LOWS LOOK
OK.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
ISSUED AT 239 PM EDT MON MAY 20 2013

DRY WEATHER IS ANTICIPATED DURING THIS PERIOD AND THE ECMWF AND
THE GFS BOTH AGREE IN BUILDING A LARGE RIDGE OVER THE CENTRAL
PLAINS ACROSS INDIANA DURING THIS TIME. A SHORT WAVE TROUGH WILL
EXIT THE AREA ON THURSDAY...ALLOWING THE LEE SIDE OF THE RIDGE AND
ASSOCIATED SUBSIDENCE ON NORTHWEST WIND TO ARRIVE ACROSS THE AREA
FOR FRIDAY AND SATURDAY. THIS WILL RESULT IN DRY WEATHER WITH
TEMPS AT OR BELOW SEASONABLE NORMALS AS DUE TO THE COOL CANADIAN
AIR.

TEMPS WILL GRADUALLY WARM ON SUNDAY AND MONDAY AS THE RIDGE
PROGRESSES EASTWARD AND WARMER...MORE HUMID AIR ARRIVES ON
SOUTHERLY WINDS ON THE BACK OF THE RIDGE.

&&

.AVIATION /DISCUSSION FOR THE 202100Z IND TAF UPDATE/...

ISSUED AT 430 PM EDT MON MAY 20 2013

MADE TWEAK TO WINDS. OTHERWISE...BROKEN LINE OF THUNDERSTORMS STILL
LOOKS LIKE IT WILL BE IN THE VICINITY OF IND AROUND 22Z.

PREVIOUS DISCUSSION FOLLOWS...

VFR CONDITIONS ARE EXPECTED FOR MUCH OF THIS TAF PERIOD.

FORECAST SOUNDINGS ACROSS THE AREA INDICATE A DECENT MID LEVEL CAP
IN PLACE ACROSS THE AREA THAT SHOULD INHIBIT CONVECTION FOR
THE FIRST FEW HOURS OF THE TAF PERIOD. HOWEVER...CAPPING APPEARS TO
ERODE LATE IN THE AFTERNOON. THUS HAVE CONTINUED TO KEEP A
MENTION OF VCTS DUE TO DAYTIME HEATING IN THE VERY WARM AND
UNSTABLE AIR MASS THAT REMAINS IN PLACE ACROSS CENTRAL INDIANA.

ANY CONVECTIVE ACTIVITY SHOULD WAVE IN THE EVENING AS HEATING IS
LOST...HOWEVER GFS AND ECMWF SUGGEST CONVECTION WEST OF
INDIANA...OVER MISSOURI AND ILLINOIS MAY DRIFT INTO WESTERN PARTS
OF THE FORECAST AREA OVERNIGHT. AGAIN CONFIDENCE REMAINS LOW WITH
THESE FEATURES...SO FOR NOW JUST A VCTS MENTION.

GOOD MIXING OVERNIGHT SHOULD PREVENT MUCH IN THE WAY OF FOG
FORMATION.

AS THAT WAVE DEPARTS ON TUESDAY MORNING...THE WARM AND UNSTABLE
AIR MASS WILL REMAIN IN PLACE ACROSS CENTRAL INDIANA AS YET
ANOTHER SHORT WAVE APPROACHES FROM THE WEST...PROVIDING MORE
SUPPORT FOR CONVECTION ON TUESDAY AFTERNOON AND TUESDAY NIGHT.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...JAS
NEAR TERM...JAS
SHORT TERM...JAS
LONG TERM....PUMA
AVIATION...JP/MK

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