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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 210140
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
940 PM EDT MON MAY 20 2013

.SYNOPSIS...
PERIODIC SHOWER AND THUNDERSTORM CHANCES WILL RETURN TUESDAY...
WITH INCREASING CHANCES WEDNESDAY AND THURSDAY AS A COLD FRONT
APPROACHES AND MOVES THROUGH. HIGH PRESSURE WILL RETURN FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
-- Changed Discussion --
EVE RAOB PLOTS SHOW UPR RIDGING BLDG IN WITH DRY CONDS EXPD
OVRNGT. SKIES HAVE GONE MCLR AND THIS SHOULD CONT TNGT...ALTHOUGH
SHOULD SEE SOME CONVECTIVE DEBRIS CS MOVG IN TWD MRNG. A WARM NGT
IS EXPD WITH LOWS IN THE MID TO UPR 60S.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
ANOTHER DAY MUCH LIKE TODAY LOOKS TO BE IN STORE ON TUESDAY.
ALTHOUGH SOME MODEL SOLUTIONS TRACK A WEAK MID-LEVEL VORT MAXIMUM
THROUGH THE NORTHERN PORTIONS OF THE CWA EARLY IN THE DAY...THE
BEST CHANCES OF SHOWERS SHOULD GENERALLY AGAIN BE RELEGATED TO THE
AFTERNOON. DIURNAL INSTABILITY SHOULD BE A BIT MORE PRONOUNCED ON
TUESDAY AFTERNOON AS THE LOW LEVEL THERMAL RIDGE ARCHES ACROSS THE
AREA DURING THE AFTERNOON HOURS. THIS SHOULD ALLOW FOR CAPE VALUES
TO ECLIPSE 2000 J/KG PER THE NAM. WITH THAT IN MIND...SHEAR IS
ONCE AGAIN RATHER UNIMPRESSIVE...AND GIVEN THE LACK OF LARGE SCALE
FORCING DURING THE MOST UNSTABLE PORTION OF THE DAY...RELATIVELY
DISORGANIZED ISOLATED TO SCATTERED SHOWERS/THUNDERSTORMS SEEM
LIKELY DURING THE AFTERNOON.

WITH THE LOW LEVEL THERMAL RIDGE SWINGING THROUGH AND SOUNDINGS
INDICATING BETTER MIXING DURING THE AFTERNOON TUESDAY...THINGS DO
LOOK LIKELY TO HEAT UP NICELY. TEMPERATURES AT 850 MB RUN UP
TOWARD +16 TO +18C OR SO ON THE CONSENSUS...WHICH SUGGESTS HIGHS
IN THE UPPER 80S WOULD BE LIKELY. THIS IS QUITE WARM FOR THIS TIME
OF YEAR AS RECORDS ARE GENERALLY ONLY IN THE LOWER 90S FOR
TUESDAY.

AS THE SYSTEM CURRENTLY OVER THE UPPER MISSISSIPPI VALLEY FINALLY
WANDERS EASTWARD...THE WEATHER GETS MORE INTERESTING HEADING INTO
WEDNESDAY. FIRST OF ALL...A DECENT CONSENSUS ON THE FORMATION OF A
LOW LEVEL JET OVER WESTERN OHIO COULD DRIVE DISSIPATING NOCTURNAL
CONVECTION INTO SOME OF THE AREA WEDNESDAY MORNING. WHILE THIS
WOULD LIKELY INCREASE LOW LEVEL MOISTURE OVER THE
AREA...CONVECTIVE DEBRIS MAY MAKE WARMING LESS EFFICIENT ON
WEDNESDAY AND LIMIT INSTABILITY. THAT SAID...THE UPPER LEVEL
SYSTEM TRUDGING EASTWARD DOESN`T SEEM TO BRING THE BEST SYNOPTIC
FORCING INTO THE AREA UNTIL AFTER 00Z/8 PM...WHICH IS WELL PAST
THE PRIME DAYTIME INSTABILITY HOURS. HOWEVER...35-40 KTS OF 0-6 KM
SHEAR WITH CAPE VALUES IN THE 1500 J/KG RANGE ALONG WITH AN
INCOMING SHORTWAVE TROUGH AND UPPER JET RIGHT ENTRANCE REGION DO
MEAN WIDESPREAD THUNDERSTORM DEVELOPMENT IS LIKELY BY WEDNESDAY
EVENING. POPS WERE TRANSITIONED A FEW HOURS LATER IN THE FORECAST
TO SUGGEST A LATER ARRIVAL OF THE SYSTEM FOR WEDNESDAY EVENING TO
ACCOUNT FOR A BIT LATER ARRIVAL OF THE MAIN SYSTEM ITSELF.

COLDER AIR FLOODS INTO THE FORECAST AREA STARTING THURSDAY WITH
THE UPPER TROUGH AXIS NEARING. AS THIS OCCURS...WE AGAIN
DESTABILIZE DUE TO MORE RAPID MID-LEVEL COOLING RATHER THAN LOW
LEVEL WARMING. SHOWER AND THUNDERSTORM CHANCES WILL THEREFORE
CONTINUE THROUGH THURSDAY. FRIES

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A COLD FRONT MOVING SLOWLY SOUTH FROM THE GREAT LAKES WILL BRING
SHOWERS AND SCATTERED THUNDERSTORMS FOR THURSDAY NIGHT. BEHIND THE
COLD FRONT FRIDAY THE RISK OF SHOWERS WILL DIMINISH AND TEMPERATURES
WILL DROP BELOW NORMAL. DRY WEATHER CAN BE EXPECTED FOR FRIDAY NIGHT
INTO SUNDAY WITH TEMPERATURES FALLING INTO THE 40S FOR OVERNIGHT
LOWS SATURDAY AND SUNDAY MORNING.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
DIURNAL CU DISSIPATING AS HEAT OF THE DAY HAS PASSED. LIGHT SOUTH
WINDS WILL REMAIN THROUGH THE OVERNIGHT. ANOTHER ROUND OF MVFR FOG
IS A GOOD POSSIBILITY LATE TONIGHT INTO TUESDAY MORNING. MUCH THE
SAME SCENARIO FOR TUESDAY WITH CHANCE POPS FOR SCATTERED AFTERNOON
THUNDERSTORMS AS MODELS DO SHOW A SHORTWAVE APPROACHING AFTER 21Z.
FOR NOW WILL INCLUDE VCTS FROM KPIT NORTH AND WEST IN TERMINALS.

.OUTLOOK.../TUESDAY NIGHT THROUGH SATURDAY/...
SHOWERS AND THUNDERSTORMS WILL INCREASE IN COVERAGE WITH POSSIBLE
RESTRICTIONS FROM WEDNESDAY INTO THURSDAY EVENING AS A COLD FRONT
AND UPPER TROUGH APPROACHES AND PASSES ACROSS THE REGION. BUILDING
HIGH PRESSURE WILL BRING VFR FRIDAY AND SATURDAY.
-- End Changed Discussion --

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

$$

07