821
FXUS61 KPBZ 241155
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
755 AM EDT MON SEP 24 2018
SYNOPSIS
PERIODIC SHOWERS AND THUNDERSTORMS ARE EXPECTED WITH A SERIES
OF CROSSING DISTURBANCES THROUGH MID WEEK.
NEAR TERM /THROUGH TONIGHT/
CLOUDS SHOULD CONTINUE TO INCREASE AHEAD OF A SERIES OF
SHORTWAVE TROUGHS EMBEDDED IN SOUTHWEST FLOW. AT THE SURFACE,
WARM, MOIST AIR CONTINUES TO ADVECT NORTHWARD AND ABOVE A
DIFFUSE WARM FRONTAL BOUNDARY SOMEWHERE NEAR THE VICINITY OF THE
MASON-DIXON LINE.
BY MID-AFTERNOON, RAIN WILL BEGIN TO OVERSPREAD THE REGION
SOUTH-TO-NORTH AS THE FIRST OF SEVERAL SHORTWAVES EMBEDDED IN
SOUTHWEST FLOW MOVE THROUGH. FORCING FROM THE DPVA OF EACH
SHORTWAVE WILL BE MAXIMIZED IN THE VICINITY OF THE OHIO RIVER ON
THE WV/OH BORDER. OPERATIONAL AND ENSEMBLE CONSENSUS DEPICTS,
THROUGH 12Z TUESDAY, A CORRIDOR OF 1-2" ALONG THE WV PORTION OF
THE OHIO TO AROUND 1 INCH IN PITTSBURGH AND LESSER NORTHEAST.
WHILE THAT IS A "DECENT" AMOUNT OF RAINFALL ON TOP OF AN
ALREADY-WET SEPTEMBER, FLOOD GUIDANCE IS IN REASONABLE GOOD
SHAPE FROM THE COUPLE OF RECENT DRY DAYS. FLOODING IS STILL
POSSIBLE, BUT GIVEN THE ISOLATED NATURE OF WHICH IT WOULD
HAPPEN, HAVE NOT ISSUED A FLOOD WATCH.
SHORT TERM /TUESDAY THROUGH WEDNESDAY/
PRECIPITATION WILL LIKELY STILL BE ONGOING OVER THE AREA
TUESDAY MORNING, BUT WILL LIKELY COME TO AN END AS DNVA AND
COMPARATIVELY DRY MID-LEVEL AIR FOLLOWS THE LAST OF THE SERIES
OF SHORTWAVES.
WHILE SOME ISOLATED CONVECTION WILL BE POSSIBLE TUESDAY
AFTERNOON, ESPECIALLY IN AREAS WEST OF PA, THE MAIN SHOW WILL BE
TUESDAY NIGHT AND WEDNESDAY MORNING AS CONVECTION INITIATES AND
ORGANIZES ALONG A COLD FRONT OR JUST AHEAD ALONG A PRE-FRONTAL
TROUGH. LOW-LEVEL WARM AIR ADVECTION AND SOME DIURNAL HEATING
(ESPECIALLY PITTSBURGH SOUTHWESTWARD WHERE BREAKS IN CLOUDS ARE
POSSIBLE) WILL COMBINE THROUGH THE DAY TUESDAY TO DESTABILIZE
THE LOW-LEVELS. MODELS DEPICT A CORRIDOR OF 1500+ J/KG MU CAPE
ALONG OR WEST OF THE OHIO, DECREASING TOWARDS THE EAST.
SUFFICIENT BULK SHEAR AND FAVORABLE LOW- LEVEL HODOGRAPHS
SUPPORT A LIMITED TORNADO THREAT TUESDAY NIGHT FOR REGIONS WEST
OF PA WITH DISCRETE CONVECTIVE CELLS. BY EARLY WEDNESDAY
MORNING, CONVECTION SHOULD CONGEAL AND SEVERE-MODE WILL
TRANSITION TOWARDS A WIND-EVENT. HOWEVER, NEAR-SURFACE
INSTABILITY MAY HINDER FULL POTENTIAL OF DOWNWARD MOMENTUM, THUS
LIMITING THE OVERALL SEVERE THREAT.
PRECIP SHOULD CLEAR MUCH OF THE REGION BY MID-AFTERNOON
WEDNESDAY. A LAGGING UPPER-LEVEL FRONT AND MOIST AIR WILL KEEP
CLOUD COVER AROUND FOR ANOTHER DAY.
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
TEMPERATURES WILL BE NEAR SEASONAL THROUGH MUCH OF THE LONG
TERM PERIOD. WHILE GLOBAL MODEL SOLUTIONS BEGIN TO DIVERGE THIS
WEEKEND, A GENERAL CONSENSUS DEPICTS ANOTHER COLD FRONT, THIS
ONE MOISTURE-LIMITED, MOVING THROUGH THE REGION FRIDAY. HIGH
PRESSURE BUILDING IN BEHIND THIS FRONT SHOULD KEEP TEMPERATURES
NEAR SEASONAL AND LIMIT THE POSSIBILITY OF PRECIPITATION THROUGH
AT LEAST THE WEEKEND.
AVIATION /12Z MONDAY THROUGH FRIDAY/
MVFR TO IFR STRATUS SHOULD CONTINUE IN MOIST E FLOW N OF I 80
THIS MORNING. OTHERWISE, SHOWERS AND CONDITION DETERIORATION TO
MVFR, WITH PATCHY IFR, IS EXPECTED AS A SHORTWAVE TROUGH
CROSSES THE AREA THIS AFTERNOON. ANOTHER SHORTWAVE SHOULD
MAINTAIN THE DEGRADED CONDITIONS OVERNIGHT.
A LOW LEVEL JET IS PROGGED ACROSS THE UPPER OH VALLEY REGION
THIS EVENING/OVERNIGHT, RESULTING IN A LLWS POTENTIAL.
OUTLOOK...
RESTRICTION POTENTIAL WILL CONTINUE UNTIL THE PASSAGE OF A LATE
WEDNESDAY COLD FRONT.
PBZ WATCHES/WARNINGS/ADVISORIES
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.
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