Special Weather Statement, NWS Indianapolis, IN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
1210 AM EDT TUE APR 26 2011

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

&&

.SYNOPSIS...
A FRONTAL SYSTEM CURRENTLY HUNG UP ACROSS THE LOCAL AREA IS EXPECTED
TO OSCILLATE BACK AND FORTH THROUGH THE MIDDLE OF THE WEEK AS
DISTURBANCES OF INCREASING INTENSITY MOVE THROUGH THE OHIO VALLEY.
THE STRONGEST DISTURBANCE APPEARS TO MOVE THROUGH THE AREA AROUND
WEDNESDAY. AFTER THE PASSAGE OF THIS LAST SYSTEM...HIGH PRESSURE
EXPECTED TO BRIEFLY MOVE INTO THE AREA LATE THIS WEEK. ANOTHER
FRONTAL SYSTEM MAY MOVE INTO THE AREA FROM THE PLAINS BY NEXT
WEEKEND. IN THE WAKE OF THIS FRONT...HIGH PRESSURE IS EXPECTED TO
BUILD INTO THE AREA EARLY NEXT WEEK.

&&

.NEAR TERM /REST OF TONIGHT/...

WAVE SEEN IN WATER VAPOR IMAGE CONTINUES TO GENERATE A LARGE AREA OF
CONVECTION...NOW LOCATED ACROSS ILLINOIS AND MISSOURI. THIS LINE
WILL CONTINUE TO MARCH SLOWLY EAST INTO THE FORECAST AREA TONIGHT.
MESOANALYSIS SHOWS 850MB MOISTURE TRANSPORT INCREASING ACROSS THE
AREA...AND PRECIPITABLE WATER VALUES REMAIN AROUND 1.5 INCHES.
THUS...HEAVY RAIN REMAINS A THREAT ACROSS THE AREA...ESPECIALLY
GIVEN THE RELATIVELY SLOW MOVEMENT OF THE STORMS.

ONGOING FORECAST HAD THIS HANDLED WELL. ONLY CHANGED THE WORDING SO
THAT IT INDICATES PERIODS OF STORMS SINCE ITS DRY ACROSS MANY AREAS
AT THE MOMENT. THAT WILL CHANGE THOUGH AS THE CONVECTION MOVES
IN...SO THE NEAR 100 POPS LOOK GOOD.

DID HAVE TO DECREASE LOW TEMPERATURES SOME THOUGH. NORTHEAST WINDS
ACROSS THE NORTHEAST FORECAST AREA HAVE ALLOWED READINGS TO DIP INTO
THE MID 50S...AND THE RAIN EARLIER THIS EVENING HAS ALLOWED READINGS
ACROSS THE SOUTH TO GET TO NEAR 60 IN SOME AREAS. TEMPERATURES
SHOULD REMAIN STEADY OR SLOWLY RISE LATER TONIGHT THOUGH AS WARM
ADVECTION INCREASES.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
LONG WAVE TROUGH EXPECTED TO GRADUALLY SHIFT EAST TOWARDS THE LOCAL
AREA DURING THIS PERIOD. INDIVIDUAL DISTURBANCES ROTATING AROUND THE
APPROACHING TROUGH WILL KEEP THINGS UNSETTLED THROUGH THE MIDDLE OF
THE WEEK.

DISTURBANCE ARRIVING LATER TONIGHT EXPECTED TO BE IN THE PROCESS OF
EXITING THE FORECAST AREA DURING THE MORNING HOURS ON TUESDAY. WILL
GO WITH HIGH POPS IN THE MORNING ON TUESDAY...TAPERING OFF TO
CHANCE DURING THE AFTERNOON. COULD BE SOME CONVECTION DEVELOP
ALONG TRAILING COLD FRONT DURING THE AFTERNOON AS AIR MASS WILL BE
RATHER UNSTABLE...BUT THE EXITING UPPER WAVE AND WEAK LOW LEVEL
CONVERGENCE IN THE VICINITY OF FRONT MAY SERVE TO KEEP CONVECTIVE
DEVELOPMENT DOWN. SEVERE WEATHER PARAMETERS IMPRESSIVE TUESDAY
AFTERNOON WITH STRONG DEEP LAYER SHEAR COUPLED WITH STEEP LAPSE
RATES...ALTHOUGH AS STATED ABOVE...OTHER FACTORS ARE WORKING
AGAINST CONVECTION ON TUESDAY.

STRONG LIFT AHEAD OF NEXT WAVE SHOULD ALLOW FOR WIDESPREAD
PRECIPITATION TO DEVELOP LATER ON TUESDAY NIGHT...WHICH WILL CONTINUE
INTO WEDNESDAY NIGHT. STILL SOME VARIANCE IN THE SURFACE TRACK OF
FINAL WAVE ON WEDNESDAY...BUT THE TREND IS FOR A SHIFT TO THE
WEST. DEEP LAYER SHEAR OVER THE WARM SECTOR ON WEDNESDAY LOOKS
STRONG WITH GOOD ALIGNMENT OF THE LOWER AND MID LEVEL JETS...SO
TRACK OF THIS FINAL WAVE WILL HAVE TO BE WATCHED.

LOW LEVEL THICKNESSES SUGGEST THE GFS MOS HIGHS FOR TUESDAY MAY BE A
LITTLE ON THE COOL SIDE. WILL NUDGE THE GUIDANCE DOWN A COUPLE OF
DEGREES. THE THICKNESSES ALSO DO NOT SUPPORT HIGHS AS WARM AS THE
GFS MOS ON WEDNESDAY...BUT THESE TEMPERATURES MAY BE WITHIN REACH IF
THE AREA CAN REMAIN IN THE WARM SECTOR UNTIL WEDNESDAY. FOR
NOW...WILL SPLIT THE DIFFERENCE BETWEEN THE GFS AND NAM GUIDANCE.
GFS MOS LOWS LOOK REASONABLE.

&&

.LONG TERM /THURSDAY THROUGH NEXT MONDAY/...
ENSEMBLE DATA SUGGEST A PROGRESSIVE UPPER PATTERN DURING THIS
PERIOD. LONG WAVE TROUGH THAT WILL BE AFFECTING THE AREA DURING THE
SHORT TERM IS EXPECTED TO BE IN THE PROCESS OF PASSING EAST OF THE
LOCAL AREA. NEXT TROUGH LOOKS TO MOVE INTO THE GREAT LAKES AND OHIO
VALLEY OVER THE WEEKEND...PUSHING EAST TOWARDS THE EAST COAST BY
EARLY NEXT WEEK. WILL KEEP SOME CHANCE POPS FOR SHOWERS ON THURSDAY
TO COVER ANY LINGERING ACTIVITY THAT MAY BE AROUND FROM DEPARTING
SYSTEM. ENSEMBLES STILL SUGGEST LITTLE THREAT FOR PRECIPITATION FROM
THURSDAY NIGHT THROUGH FRIDAY NIGHT WITH SOME UPPER RIDGING MOVING
THROUGH BEFORE THE NEXT CHANCE OF PRECIPITATION ARRIVING OVER THE
WEEKEND. UPCOMING WEEKEND SYSTEM LOOKS PROGRESSIVE IN NATURE...SO
DRIER CONDITIONS EXPECTED BY NEXT MONDAY.

&&

.AVIATION.../DISCUSSION FOR THE 26/06Z TAFS/...
BECOMING MVFR WITH SOME AREAS OF IFR OVERNIGHT AND THEN VFR AFTER
15Z UNTIL LATE TUESDAY NIGHT.  SHOWERS AND THUNDERSTORMS ALONG THE
INDIANA ILLINOIS BORDER WILL SPREAD EAST ACROSS CENTRAL INDIANA NEXT
SEVERAL HOURS.  WILL MENTION A PERIOD OF TEMPO THUNDERSTORMS KHUF
AND KIND SOUTHWARD.  MODELS INDICATE THUNDERSTORMS MAY WEAKEN
TOWARDS MORNING AND THEN MVFR CEILINGS IMPROVING TO VFR AFTER 15Z.
WIDELY SCATTERED THUNDERSTORMS WILL POSSIBLE SO WILL KEEP CB IN
TAFS.

MODELS SOUNDINGS INDICATE STRONG LOW LEVEL WIND SHEAR OCCURRING
OVERNIGHT AS STRONG LOW PRESSURE OVER NORTHEAST MISSOURI LIFTS TO
THE NORTHEAST.  WINDS WILL BECOME SOUTHERLY AND INCREASE TO 15 KNOTS
WITH GUSTS TO 25 KNOTS LATE TONIGHT. BETTER MIXING WILL OCCUR AFTER
15Z AND WIND GUSTS IN EXCESS OF 30 KNOTS POSSIBLE. FINALLY WINDS
SHOULD DIMINISH TUESDAY EVENING AS SURFACE LOW MOVES FARTHER NORTH
AND GRADIENT DECREASES. ANOTHER AREA OF LOW PRESSURE WILL MOVE INTO
THE OHIO VALLEY LATE TUESDAY NIGHT CAUSING CONDITIONS TO WORSEN
RAPIDLY AFTER 270600Z.

&&

.HYDROLOGY...
THREAT FOR ROUNDS OF HEAVY RAINFALL/FLOODING APPEARS TO CONTINUE
THROUGH WEDNESDAY AS PRECIPITABLE WATERS REMAIN 150-200% OF NORMAL.
CONVECTIVE BOUNDARIES THAT HAVE BEEN FOCUSING THE HEAVY RAINFALL
FARTHER SOUTH OVER THE PAST FEW DAYS SHOULD BEGIN TO MIX OUT WITH
TIME AS A STRONGER SOUTHERLY GRADIENT DEVELOPS ACROSS THE
OHIO/TENNESSEE VALLEYS...WHICH SHOULD HELP TO FOCUS THE HEAVIER RAIN
FARTHER NORTH STARTING TONIGHT. THE FLASH FLOOD WATCH HAS BEEN
EXTENDED IN TIME THROUGH 00Z THURSDAY TO COVER THE CONTINUING THREAT.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR INZ021-028>031-
035>049-051>057-060>065-067>072.

&&

SYNOPSIS...JAS
NEAR TERM...50
SHORT TERM...JAS
LONG TERM....JAS
AVIATION...JH
HYDROLOGY...JAS

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