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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 161515
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1115 AM EDT SUN JUN 16 2013

.SYNOPSIS...
-- Changed Discussion --
A WEAK DISTURBANCE WILL CROSS THE REGION TODAY...BRINGING SHOWERS
AND POSSIBLY AN ISOLATED THUNDERSTORM. A FRONTAL BOUNDARY WILL SAG
SOUTHEASTWARD INTO THE AREA TONIGHT INTO MONDAY...WITH A LOW
CHANCE FOR SHOWERS THROUGH THIS PERIOD. THE FRONT WILL PUSH
SOUTHEAST OF THE AREA LATE ON TUESDAY AND HIGH PRESSURE WILL THEN
BUILD IN FROM THE NORTHWEST AND ALLOW FOR A DRY MID-WEEK.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
15Z ENHANCED SHORT TERM FORECAST HAS BEEN ISSUED TO INCREASE
POP...USING COVERAGE WORDING THROUGH THE EARLY AFTERNOON. IN
ADDITION...WITH EXTENSIVE CLOUD COVERAGE ACROSS THE OHIO
VALLEY...HAVE LOWERED HIGH TEMPS TODAY 1-2 DEGREES.

THE LATEST RAP UPPER LEVEL ANALYSIS INDICATES THE UPPER OHIO VALLEY
IN A ZONAL FLOW WITH A 300MB 100KT JET AXIS CENTERED OVER LAKE
HURON. AT THE MID-LEVELS...A 500MB SHORT WAVE IS WEAKENING AS IT
MOVES EASTWARD ACROSS OHIO. AT THE SURFACE...A 1005MB SURFACE LOW IS
LOCATED NORTH OF LAKE SUPERIOR WITH A ILL-DEFINED FRONTAL BOUNDARY
EXTENDING SOUTH OF THIS FEATURE ACROSS SOUTHERN MICHIGAN. WELL AHEAD
OF THE FRONT...WEAK 700-500MB VORT ENERGY ALONG WITH A MOIST
800-650MB LAYER ARE SUPPORTING SCATTERED SHOWERS MOVING ACROSS THE
AREA. THE 12Z KPIT SOUNDING SHOWS THE AFOREMENTIONED MOIST LAYER
WITH WEAK SBCAPE (APPROX 100 J/KG) WITH A UNIDIRECTIONAL ZONAL
PROFILE THROUGH MUCH OF THE COLUMN.

THIS AFTERNOON...THE SHORT WAVE WILL CONTINUE TO WEAKEN AS IT MOVES
INTO WESTERN PENNSYLVANIA AND THE FRONTAL BOUNDARY WILL SAG FURTHER
SOUTHEASTWARD INTO OHIO. FORCING FROM THE WAVE WILL ALLOW FOR
SCATTERED SHOWERS TO CONTINUE INTO THE EARLY AFTERNOON. SOME
UNCERTAINTY COMES INTO THE FORECAST IN THE 18Z-00Z WINDOW AS HIRES
MODEL SOLUTIONS VARY IN RESOLVING CONVECTION THIS AFTERNOON.
HRRR/WRF-NMM SUPPORT THE DEVELOPMENT OF THUNDERSTORMS ALONG THE
FRONTAL BOUNDARY WHILE THE NAM 4KM INDICATES SHOWERS MORE LIMITED.
WITH EXTENSIVE UPSTREAM CLOUD COVERAGE...BELIEVE THIS WILL INHIBIT
CONVECTIVE TEMPS FROM BEING REACHED. THUS...HAVE GONE WITH
SCATTERED/NUMEROUS SHOWERS AND ISOLATED THUNDERSTORM WORDING TO NOT
COMPLETELY DISCOUNT THE HRRR/WRF-NMM SOLUTIONS. WITH ALL OF THIS
IN MIND...THE STORM PREDICTION CENTER HAS MENTIONED THE AREA IN
ITS SEE TEXT...CONSIDERING THE LOW PROB SCENARIO THAT IF CLOUD COVERAGE
BREAKS THEN THE UNIDIRECTIONAL SHEAR ENVIRONMENT WOULD BE
FAVORABLE FOR A POSSIBLE EWD MOVING STRONG TO SEVERE CONVECTIVE
CLUSTER IN THE 18Z-00Z TIME FRAME. TEMPS HAVE BEEN LOWERED A FEW
DEGREES CLOSER TO LAMP GUIDANCE...WITH HIGHS RANGING FROM THE
LOWER TO MID 70S ACROSS THE AREA.

TONIGHT...THE FRONTAL BOUNDARY WILL CONTINUE TO SAG SOUTHEASTWARD
ACROSS THE AREA...WITH ANY LINGERING COVERAGE OF SHOWERS MOSTLY
DIMINISHING BY 06Z. MOSTLY CLOUDY SKIES WILL BEGIN TO GIVE WAY TO
MORE BREAKS IN CLOUD COVERAGE WITH SHOWERS COMING TO AN END AS A
POCKET OF DRIER AIR ADVECTS IN FROM THE NORTHWEST. CLOUD COVERAGE
FOR MUCH OF THE NIGHT WILL SERVE TO MODERATE LOW TEMPS. FORECAST IS
CLOSEST TO THE WARMER MAV...WITH LOWS RANGING FROM THE LOWER TO MID
60S ACROSS THE AREA.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
HAVE BACKED OFF POPS ON MONDAY DOWN TO SLIGHT CHANCE. FORECAST AREA
SHOULD BE IN THE DRY REGION BETWEEN FRONTS TO THE NORTH AND
SOUTH...AND DO NOT SEE MUCH OF A TRIGGER TO GET PRECIP GOING. MONDAY
NIGHT AND TUESDAY THE NAM/SREF ARE AGGRESSIVE SWEEPING THE NORTHERN
FRONT ACROSS THE REGION AND BRINGING WIDESPREAD PRECIPITATION. WITH
THE ECMWF SHOWING MORE CONSISTENCY...KEEPING THE NORTHERN FRONT DRY
AND FOCUSING PRECIPITATION ALONG THE SOUTHERN FRONT...AND THE GFS
AND GEFS COMING INTO LINE WITH THE ECMWF SOLUTION...HAVE BACKED OFF
POPS ACROSS THE NORTHERN HALF OF THE REGION FOR MON NIGHT/TUES.
ONCE THE FRONT MOVES OFF TO THE EAST...THE ENTIRE AREA SHOULD BE
DRY TUESDAY NIGHT AND WEDNESDAY WITH HIGH PRESSURE MOVING IN FROM
MICHIGAN. LIGHT NORTHERLY FLOW THROUGH THIS TIME PERIOD SHOULD
KEEP TEMPERATURES A FEW DEGREES BELOW NORMAL.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
LATEST GFS AND ECMWF DETERMINISTIC SOLNS AGREED GENLY IN
DEPICTIONS OF THE PROGGED FLOW PTN OVR THE ERN CONUS FOR THE
LATTER HALF OF THE WEEK...WITH ECMWF AMPLIFYING THE PTN CLOSER TO
GFS WITH A RIDGE AXIS EXTENDING FM THE SRN PLNS ACRS THE GREAT
LAKES.

THE LONG TERM FORECAST THUS CONSERVATIVELY FEATURES TEMPS
GRADUALLY WARMING TO SLIGHTLY ABOVE THE SEASONAL AVERAGES BY THE
WEEKEND. PCPN CHCS WERE FORECAST AOB CLIMO NMBRS...BUT WERE GENLY
INCRSD USING A GFS/ECMWF BLEND FOR SHRTWV TIMING INTO THE WEEKEND.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
AN APPROACHING SHORTWAVE AND ASSOCIATED COLD FRONT WILL BRING
SHWRS AND INCRSD EMBEDDED TSTM CHCS TDA. FOR NOW...GIVEN A LACK OF
CONFIDENCE IN INSTABILITY PROGS...WL KP MENTION OF THUNDER OUT OF
ANY SPECIFIC TAF SITE. A GRADUAL DETERIORATION TO MVFR CAN BE
EXPECTED...WITH ISOLD IFR IN HEAVIER SHWRS.

.OUTLOOK.../MONDAY THROUGH THURSDAY/...
PERIODIC RESTRICTIONS ARE ANTICIPATED THROUGH TUESDAY AS ANOTHER
LOW APPRCHS AND CROSSES THE REGION. BLDG HIGH PRES SHOULD RTN VFR
CONDITIONS FOR WEDNESDAY AND THURSDAY.

&&

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

&&

$$

SYNOPSIS...WOODRUM
NEAR TERM...WOODRUM