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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KIND 212300
AFDIND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
700 PM EDT TUE MAY 21 2013

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

&&

.SYNOPSIS...
ISSUED AT 227 PM EDT TUE MAY 21 2013

A LARGE UPPER LOW CURRENTLY OVER THE NORTHERN 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 IN FOR FRIDAY AND
SATURDAY. A FRONTAL SYSTEM MAY MOVE INTO THE AREA BY SUNDAY AND ON
INTO EARLY NEXT WEEK.

&&

.NEAR TERM /REST OF THIS AFTERNOON AND TONIGHT/...
ISSUED AT 227 PM EDT TUE MAY 21 2013

AIR MASS HAS BECOME MODERATELY UNSTABLE ACROSS THE AREA...ALTHOUGH
THE MAIN INSTABILITY AXIS HAS BEEN PUSHED WELL TO THE SOUTH OVER THE
TENNESSEE VALLEY. NOT REALLY SEEING MUCH OF A TRIGGER FOR CONVECTION
UNTIL EARLY WEDNESDAY MORNING...WHEN ANOTHER PIECE OF UPPER ENERGY
ROTATING AROUND LARGE UPPER LOW MOVES INTO THE AREA FROM THE
SOUTHERN PLAINS. MODEL DATA SUGGEST BEST LIFT PROBABLY WON/T ARRIVE
UNTIL AFTER ABOUT 220800Z. WILL KEEP SOME CHANCE POPS GOING INTO THE
PRE DAWN HOURS...THEN HIGH POPS TOWARDS DAYBREAK ON WEDNESDAY.

UNLIKE LAST NIGHT...MODEL DATA SUGGEST SEVERE PARAMETERS WILL BE
WANING WITH TIME TONIGHT...AS LAPSE RATES BECOME PROGRESSIVELY
POORER AND DEEP LAYER SHEAR WEAKENS. AS A RESULT...NOT SURE THERE
WILL MUCH OF A SEVERE THREAT WHEN THE MAIN LIFT ARRIVES.

PROGGED LOW LEVEL THICKNESSES SUGGEST THE GFS MOS LOWS TONIGHT LOOK
ON TARGET FOR THE MOST PART.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
ISSUED AT 227 PM EDT TUE MAY 21 2013

COMBINATION OF UPPER ENERGY MOVING THROUGH DURING THE MORNING AND
PASSAGE OF COLD FRONT DURING THE DAY SUGGEST HIGH POPS ARE IN ORDER
AT THAT TIME. WILL ALSO KEEP SOME LINGERING CHANCE POPS FOR SHOWERS
WEDNESDAY NIGHT AND THURSDAY AS THE REMNANTS OF THE PLAINS UPPER LOW
IS PROGGED TO MOVE THROUGH.

BY THURSDAY NIGHT AND FRIDAY...HIGH PRESSURE BEGINS TO BUILD OVER
THE AREA FROM THE NORTH IN THE WAKE OF THE UPPER SYSTEM. WILL GO DRY
AT THOSE TIMES.

GIVEN THE CONSIDERABLE CLOUD COVER/PRECIPITATION EXPECTED TO BE
AROUND ON WEDNESDAY...THE GFS MOS HIGHS LOOK TOO WARM. WILL CUT
ABOUT 5 DEGREES OFF OF THE GUIDANCE. THE REMAINDER OF THE
TEMPERATURE GUIDANCE IN THE LATER PERIODS LOOK REASONABLE AT THIS
TIME BASED ON PROGGED LOW LEVEL THICKNESSES.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
ISSUED AT 227 PM EDT TUE MAY 21 2013

ECMWF AND GFS BOTH BUILD A LARGE AREA OF HIGH PRESSURE ACROSS THE
OHIO VALLEY ON FRIDAY INTO SATURDAY. THIS SHOULD LEAD TO DRY AND
COOL WEATHER AS THE WEEKEND BEGINS.

ECMWF AND GFS ALSO BOTH INDICATE SOME LOWER LEVEL CONVERGENCE
ACROSS THE SOUTHWEST PARTS OF THE FORECAST AREA ON SUNDAY INTO
MONDAY. GULF REMAINS PRIMARILY SHUT OFF AND RIDGING APPEARS IN
PLACE ALOFT WHILE THE MODELS DO EJECT A RIDGE RIDING SHORT WAVE
OVER THE LOWER LEVEL CONVERGENCE AREA. THUS WITH LIMITED MOISTURE
CONFIDENCE REMAINS LOW. HAVE DECIDED TO INCLUDE SOME LOW CHC POPS
GIVEN THIS FOR SUNDAY AND MONDAY FOR NOW.

DRY WEATHER RETURNS ON TUESDAY AS STRONG RIDGING BUILDS ACROSS THE
OHIO VALLEY AND THE WEAK UPPER SHORT WAVE DRIFTS EAST OF INDIANA.

&&

.AVIATION /DISCUSSION FOR THE 220000Z TAF ISSUANCE/...
-- Changed Discussion --
ISSUED AT 700 PM EDT TUE MAY 21 2013

NUMEROUS SHOWERS AND THUNDERSTORMS POSSIBLE LATE TONIGHT THROUGH
MIDDAY WEDNESDAY. GENERALLY VFR REST OF THE TIME.

LOW PRESSURE IN THE UPPER ATMOSPHERE WAS OVER THE UPPER MIDWEST. AN
UPPER DISTURBANCE ROTATING AROUND THE SOUTH SIDE OF THE UPPER LOW
WAS PRODUCING NUMEROUS SHOWERS AND THUNDERSTORMS OVER MIDDLE AND
LOWER MISSISSIPPI VALLEY FROM THE SOUTHERN TIP OF ILLINOIS AND
SOUTHWARD.  RAPID REFRESH MODEL INDICATES ONLY WIDELY SCATTERED
THUNDERSTORMS UNTIL LATE TONIGHT ACROSS CENTRAL INDIANA AND WILL
KEEP TAFS MOSTLY VFR UNTIL AROUND 08Z. AFTER THAT WILL MENTION VCTS
AND CEILINGS AND VISIBILITIES MAY BECOME MOSTLY MVFR BY SUNRISE
WEDNESDAY.  RAPID REFRESH MODEL INDICATES NUMEROUS SHOWERS AND
THUNDERSTORMS FIRST HALF OF THE DAY WEDNESDAY WITH ACTIVITY BECOMING
A LITTLE LESS NUMEROUS LATER ON.  MODEL SOUNDINGS INDICATE
PREVAILING CEILINGS AND VISIBILITIES SHOULD BECOME MOSTLY VFR
BY WEDNESDAY AFTERNOON.

WINDS TONIGHT WILL BE SOUTH TO SOUTHWEST DECREASING TO 8 TO 10 KNOTS
BY 01Z AND WITH DAYTIME MIXING SOUTH TO SOUTHWEST WINDS OF 15 KNOTS
AND GUSTS UP TO 25 KNOTS WILL BE THE RULE.
-- End Changed Discussion --

&&

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

$$

SYNOPSIS...JAS
NEAR TERM...JAS
SHORT TERM...JAS
LONG TERM....PUMA
AVIATION...JH

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