Area Forecast Discussion
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000 FXUS61 KPBZ 311029 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 629 AM EDT SUN MAY 31 2015 .SYNOPSIS... WARM AND HUMID CONDITIONS WILL CONTINUE UNTIL THE PASSAGE OF A STRONG COLD FRONT LATE TODAY. COOLER WEATHER WILL SETTLE OVER THE REGION TO START THE WORK WEEK. && .NEAR TERM /THROUGH MONDAY/... ...SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY... A COMBINATION OF EARLY MORNING SATELLITE DATA AND INCOMING MODEL DATA...AS WELL AS SPC PROJECTIONS...PAINT A FAIRLY COMPLICATED PICTURE FOR THE DAY TODAY. AS IT SEEMED THIS TIME YESTERDAY...A SURFACE LOW IS SET TO RUN UP THE OHIO VALLEY...AND PASS JUST NORTH OF PITTSBURGH LATE THIS AFTERNOON. MODEL SOLUTIONS HAVE COME MUCH CLOSER TOGETHER ON THE TRACK OF THIS SYSTEM...AND THIS TRACK IS LIKELY TO DICTATE WHERE THE NORTHERN EXTEND OF THE STRONGEST LOW LEVEL LAPSE RATES WILL REACH DURING THE DAYTIME TODAY. REMNANT CONVECTION FROM YESTERDAY DID PROPAGATE THROUGH MUCH OF THE NIGHT ALONG WELL DEFINED OUTFLOW BOUNDARIES THAT HAVE NOW MAINLY PASSED TO THE EAST OF THE AREA. HOWEVER...IT IS LIKELY SEVERAL OF THESE REMAIN AROUND THE AREA EARLY THIS MORNING IN ONE FASHION OR ANOTHER...AND THESE COULD FIRE ADDITIONAL CONVECTION UPON SUNRISE. THAT SAID...DEEP LAYER SOUTHERLY FLOW IS INCREASING THIS MORNING...AND THIS IS PUSHING A FAIRLY EXPANSIVE AREA OF CLEARING TOWARD THE CWA FOR SUNRISE. THIS SHOULD WORK ON INITIALLY DESTABILIZING THINGS AROUND THE AREA IMMEDIATELY UPON SUNRISE...GIVING A HEAD START FOR LATER TODAY WHEN BETTER DYNAMICAL SUPPORT ARRIVES. THE DEEP WAVE OVER THE LOWER OHIO VALLEY EARLY THIS MORNING HAS STRONG MID AND UPPER LEVEL SUPPORT...BEING FIRMLY ENTRENCHED IN THE RIGHT ENTRANCE REGION OF AN UPPER JET STREAK. MODEL SOUNDINGS AHEAD OF THIS SYSTEM SUGGEST A SUPPORTIVE SHEAR ENVIRONMENT FOR THUNDERSTORM DEVELOPMENT THROUGH THE DAY WITH 35-45 KTS OF BULK SHEAR AND AN IMPROVED DIRECTIONAL SHEAR ENVIRONMENT FOR ROTATING UPDRAFT FORMATION GOING INTO THE AFTERNOON. ALONG WITH THAT...EARLY SUNSHINE SHOULD ALLOW FOR A STRONG START AT INCREASED CAPES FOR TODAY...WHICH MODEL GUIDANCES PEGS ANYWHERE FROM 1000-2000 J/KG ALONG AND SOUTH OF THE LOW TRACK...DEPENDING UPON WHEN ANY PARTICULARLY MODEL DECIDES TO BREAKOUT CONVECTION. THE EARLY THAT OCCURS...THE LESS UNSTABLE THINGS BECOME. ALONG WITH THE FAVORABLE UNSTABLE AND HIGHLY SHEARED ENVIRONMENT...PWAT VALUES LOOK TO RUN TOWARD 1.8 INCHES AS THE WAVE MOVES THROUGH...AND GIVEN THE RATHER SLOW FORWARD SPEED OF THE WAVE...IT WOULD SEEM ANY CONVECTION THAT DOES DEVELOP WILL LIKELY BE THE FAIRLY COPIOUS RAIN PRODUCING VARIETY. THAT SAID...SPC HAS OUTLINED MUCH OF THE AREA IN A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH THE DAY...WITH WIND AND LARGE HAIL BEING THE PRIMARY THREATS AS WELL AS A 2 PERCENT TORNADO OUTLINE. ALL OF THESE THINGS SEEM QUITE REASONABLE...AND HAVE BEEN INCLUDED IN THE FORECAST. THE OTHER COMPLICATING FACTOR FOR THE FORECAST WILL BE WHAT HAPPENS NORTH OF THE LOW TRACK. ELEVATED CONVECTION WILL LIKELY STREAM NORTH OF THE BOUNDARY THAT SETTLES OVER THE AREA...AND DEFORMATION ALONG THAT FRONT WILL ACCENTUATE ASCENT AS THE RIGHT ENTRANCE OF THE JET CROSSES THE AREA. GIVEN THE RAPIDLY TIGHTENING THERMAL GRADIENT...FRONTOGENETICAL ASCENT WILL ALSO LIKELY PLAY A ROLE. THE MODELS HAVE CONSISTENTLY BEEN INDICATING FAIRLY HEAVY RAIN IS POSSIBLE NORTH OF THE FRONT...AND GIVEN WHAT IS OCCURRING UPSTREAM NORTH OF THE FRONT AT THE MOMENT...IT CERTAINLY SEEMS THIS THREAT IS REAL. THAT SAID...HEAVY RAIN CHANCES WERE CARRIED ACROSS THE CWA THROUGH THE AFTERNOON. THE SYSTEM AND ATTENDANT FRONT SLOW SLIP EAST OF THE AREA THIS EVENING...HOWEVER THE FRONT SEEMS POISED TO GET HUNG UP IN THE RIDGES INTO MONDAY AS YET ANOTHER WAVE LOOKS TO TRUCK UP IT AND CLIP THE SOUTHEASTERN ZONES. ANOTHER MID-LEVEL WAVE ALSO SEEMS LIKELY TO CROSS THE NORTHERN ZONES AS A DEEPENING UPPER WAVE OVER THE NORTHERN GREAT LAKES TEMPORARILY BACK BUILDS THE UPPER JET STREAK TO THE NORTH. GIVEN THAT LAYER MOISTURE WILL HAVE DECREASED SO SIGNIFICANTLY BY MONDAY AFTERNOON...EVEN WITH DECENT MID AND UPPER SUPPORT FOR ASCENT ACROSS THE NORTHERN HALF OF THE CWA...A LACK OF MOISTURE WILL PRECLUDE ANYTHING MORE THAN A CHANCE OF SHOWERS. THE INCREASE IN UPPER SUPPORT SHOULD FOSTER AN INCREASE IN CLOUD COVER...WHICH ALONG WITH COLD ADVECTION SHOULD HOLD TEMPERATURES BACK QUITE A LOT ON MONDAY RELATIVE TO TODAY. FRIES && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... UPPER-LEVEL TROF AXIS SHIFTS THROUGH THE AREA EARLY TUESDAY MORNING WITH RAIN CHANCES DECREASING IN THE PRE-DAWN HOURS. DRIER AIR WILL BEGIN TO POUR IN FROM THE NORTH DURING THE DAY TUESDAY...EVIDENT BY PRECIPITABLE WATER VALUES DROPPING SIGNIFICANTLY TO BELOW 0.5" NORTH OF PITTSBURGH BY EARLY TUESDAY EVENING. HOWEVER...RESIDUAL MOISTURE ASSOCIATED WITH SOUTHERN CUT- OFF LOW WILL HOLD NEAR THE MASON-DIXON LINE. AN AREA OF MID-LEVEL CONVERGENCE BETWEEN THE DRIER NORTHERN AIR AND THE MOIST SOUTHERN AIR SHOULD AID SHOWER DEVELOPMENT TUESDAY AFTERNOON...RELEGATED PRIMARILY SOUTH OF THE PA BORDER. DRY HIGH PRESSURE WILL STALL ON ITS PUSH SOUTH AS THE SOUTHERN CUT-OFF LOW TRIES TO DISLODGE...TO NO AVAIL. THIS SETUP WILL HOLD THROUGH THE DURATION OF THE SHORT TERM AND INTO THE BEGINNING OF THE EXTENDED PERIOD...RESULTING IN AFTERNOON RAIN CHANCES ACROSS THE SOUTH AND HIGH TERRAIN OF PA/WV/MD AND DRY AND SUNNIER CONDITIONS ACROSS THE NORTH. TEMPERATURES WILL GRADUALLY WARM THROUGH MID-WEEK TO AT OR ABOVE NORMAL BY WEDNESDAY AFTERNOON. TAX && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... HEADING INTO THE LATTER PART OF THE NEW WEEK A SURFACE HIGH PRESSURE LINGERS NORTH...AND AN UPPER-LOW PRESSURE SOUTH...SOMETHING WILL HAVE TO GIVE. BY THURSDAY AFTERNOON THE LOW WILL ADVANCE MOISTURE NORTHWARD ACROSS THE SOUTHERN APPALACHIANS AND BACK TO THE REGION. THE RESULT WILL BE INCREASED SHOWER AND THUNDERSTORM CHANCES EACH AFTERNOON INTO THE EARLY PART OF THE WEEKEND...DESPITE LACK OF SYNOPTIC FORCING. WARMING TREND WILL ALSO CONTINUE THROUGH THE END OF THE WEEK WITH TEMPERATURES ONCE AGAIN WELL ABOVE-AVERAGE. TAX && .AVIATION /10Z SUNDAY THROUGH THURSDAY/... SOME PATCHY FOG WILL CLEAR RELATIVELY QUICKLY AFTER SUNRISE. A STRONG SYSTEM WILL RUN DOWN A FRONT THAT WILL SLOWLY SAG INTO OUR AREA TODAY. THIS WILL BRING AN INCREASING CHANCE FOR SHOWERS AND THUNDERSTORMS THROUGH THE DAY. SOME LOCAL FOG WILL START THE DAY AS LATE EVENING AND OVERNIGHT CONVECTION HAS ALLOWED FOR A VERY MOIST BOUNDARY LAYER TO SATURATE OVERNIGHT. WINDS WILL INCREASE FROM THE SOUTHWEST ALONG AND SOUTH OF THE LOW TRACK FROM KZZV TO KBVI THROUGH THE AFTERNOON...WHILE NORTH OF THERE...WINDS WILL GENERALLY TURN EASTERLY AND INCREASE UNTIL THE SYSTEM SLIDES EAST TONIGHT. WIDESPREAD MVFR AND IFR CIGS WILL FOLLOW IN COLD ADVECTION IN ITS WAKE. FRIES .OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... RESTRICTIONS WILL BE POSSIBLE WITH WITH A SLOW MOVING COLD FRONT AND LOW PRESSURE INTO MONDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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