Area Forecast Discussion
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000 FXUS61 KPBZ 050834 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 434 AM EDT TUE MAY 5 2015 .SYNOPSIS... A SLOW MOVING FRONTAL BOUNDARY WILL KEEP RAIN CHANCES IN THE FORECAST THROUGH WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... CURRENT RADAR IMAGERY SHOWS ISOLATED TO SCATTERED SHOWERS STRETCHING FROM WEAK ECHOES OVER FAYETTE COUNTY PA WEST TO STRONGER RETURNS NEAR DAYTON OH. THIS ACTIVITY IS LOCATED ALONG AND JUST SOUTH OF THE CURRENT WEAK SURFACE FRONT...ORIENTED WITH HIGHER MOISTURE CONTENT. EXPECTING CURRENT TRENDS OF DECAYING CONVECTION TO FURTHER WEAKEN AS IT MOVES INTO THE FORECAST AREA DURING THE PRE-DAWN HOURS. BROAD FRONTAL ZONE AND DEEPER MOISTURE WILL SHIFT NORTH SOME THROUGH MIDDAY AS A WAVE CURRENTLY PRODUCING STRONG CONVECTION OVER EASTERN IOWA TRACKS ACROSS THE SOUTHERN GREAT LAKES. THIS WILL SHIFT THE FOCUS OF ANY AFTERNOON SHOWER OR THUNDERSTORM ACTIVITY NORTH AS WELL. HI-RES MODELS THAT ARE HANDLING THE CURRENT TRENDS WITH SOME SUCCESS...ARE BEARISH WHEN IT COMES TO CONVECTIVE DEVELOPMENT THIS AFTERNOON...TO THE POINT OF VERY LITTLE PRECIPITATION ACROSS THE FORECAST AREA. DONT THINK THIS IS NECESSARILY PRUDENT...GIVEN THE AVAILABILITY OF MOISTURE AND THE AT LEAST MARGINAL INSTABILITY NOTED IN THE AFTERNOON SOUNDINGS. WILL MAINTAIN CHANCE TO LIKELY POPS NORTH OF PITTSBURGH. MODEL GUIDANCE HAS TRENDED FURTHER NORTH WITH THE TRACK OF THE UPPER-LEVEL WAVE TONIGHT...AS THE RIDGE OF HIGH PRESSURE RE-BUILDS IN THE MID-WEST. MODIFICATIONS WERE MADE TO PUSH TONIGHTS RAIN CHANCES WELL NORTH OF PREVIOUS FORECAST. SOME OF OUR SOUTHERN AND WESTERN ZONES SHOULD EVEN GET SOME CLEARING HEADING INTO TONIGHT WITH THE FOCUS OF DEEPER MOISTURE SHIFTING NORTH. TAX && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... RIDGING STARTS TO BUILD OVER THE OHIO VALLEY DURING THE DAY ON WEDNESDAY. THIS WILL DROP H500 HEIGHTS ACROSS THE CWA IN RESPONSE AND HELP TO SAG THE FRONTAL BOUNDARY A BIT FURTHER SOUTH DURING THE DAY. FOCUSED HIGHER POPS IN SOUTHERN PORTIONS OF CWA DURING THE AFTERNOON. ENOUGH INSTABILITY IS PRESENT FOR THE CONTINUED CHANCE OF THUNDER AS WELL. KEPT POPS IN CHANCE CATEGORY WITH CONTINUED UNCERTAINTY AS TO FRONTAL EVOLUTION. AS RIDGE STARTS TO BUILD EASTWARD...FRONTAL BOUNDARY WILL BECOME MORE DIFFUSE WITH TIME. ALLOW POPS TO FALL OFF DURING THE EVENING HOURS WITH LOSS OF HEATING. H500 RIDGE IS IN CONTROL FOR THE REMAINDER OF THIS PERIOD...WITH THE RIDGE AXIS PASSING BY AROUND 00Z FRIDAY. GFS/ECMWF BOTH PAINT SOME DIURNAL QPF ACROSS THE AREA THURSDAY AND FRIDAY AFTERNOONS. THINK THAT THIS IS OVERDONE FOR THE MOST PART AS AT LEAST MODEST CAPPING SHOULD BE PRESENT UNDER THE RIDGE. EXCEPTION COULD BE ALONG THE EASTERN RIDGES WITH MODEST UPSLOPE FLOW...AND KEPT AN AFTERNOON/EVENING SLIGHT CHANCE BOTH AFTERNOONS IN THIS AREA. OTHERWISE...DRY AND WARM CONDITIONS WILL PERSIST. A SLOW WARMING TREND WILL SEE TEMPERATURES RISE BACK INTO THE LOWER AND MID 80S FOR MOST AREAS BY FRIDAY. CL && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... UPPER RIDGE GETS SLOWLY DISLODGED WITH TIME AS ENERGY EJECTS FROM WESTERN U.S. TROUGH AND TOWARDS THE UPPER MISSISSIPPI VALLEY BY 00Z MONDAY. RESULTING SURFACE LOW AND FRONTAL SYSTEM WILL ADVANCE EASTWARD WITH TIME...PERHAPS ARRIVING MONDAY NIGHT OR TUESDAY. AHEAD OF THIS...MAINLY DIURNAL POPS GET A BIT HIGHER EACH DAY WITH THE DEPARTURE OF THE RIDGE. RIPPLES ALONG THE BACK SIDE OF THE RIDGE MAY PROVIDE LOCALIZED ENHANCEMENT...WHICH OF COURSE ARE TOUGH TO TIME AT THIS DISTANCE. THE FRONT BRINGS MORE GENERALIZED PRECIPITATION CHANCES MONDAY INTO TUESDAY. FAIRLY STATIC ABOVE NORMAL TEMPERATURES ARE FORECAST FRIDAY NIGHT THROUGH MONDAY NIGHT...WITH HIGHS IN THE 80S AND LOWS ON EITHER SIDE OF 60. COOLER TEMPERATURES MAY ARRIVE TUESDAY WITH THE FRONT. CL && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... A COMPLICATED NEAR-TERM FORECAST EARLY THIS MORNING AS A BROAD FRONTAL ZONE IS HOLDING HIGHER MOISTURE CONTENT ACROSS THE FORECAST AREA. THIS HAS RESULTED IN VERY SELECT REGIONAL TERMINALS DROPPING DOWN TO VERY LOW VISIBILITIES...ALTHOUGH MOST OF OUR MAJOR TERMINALS HAVE BEEN IMMUNE THUS FAR. HAVE CURRENT VFR CONDITIONS GIVING WAY TO MVFR IN THE PRE-DAWN HOURS WITH VISIBILITY REDUCTIONS. THIS IS BY FAR THE AREA OF LEAST CONFIDENCE. ADDITIONALLY A LINE OF RESIDUAL SCATTERED SHOWERS STRETCHES FROM ZZV TO JUST SOUTH OF HLG. NOT EXPECTING MUCH FURTHER EXPANSION OR STRENGTHENING OF THESE SHOWERS...BUT IF ONE DRIFTS OVER ZZV/HLG...IT COULD LEAD TO TEMPORARY RESTRICTIONS. LATER TODAY...HAVE THIS LINE OF SHOWERS LIFTING NORTH WITH THE BROAD FRONTAL ZONE WHERE INSTABILITY THIS AFTERNOON COULD DRIVE ADDITIONAL SHOWERS/THUNDERSTORMS. HAVE INCLUDED VCTS FOR MOST TAF SITES...BUT SPATIAL EXTENT OF THUNDERSTORM ACTIVITY SHOULD BE FAIRLY LIMITED. TAX .OUTLOOK.../TUESDAY NIGHT THROUGH SATURDAY/... SCATTERED RESTRICTIONS IS A POSSIBILITY EARLY WEDNESDAY AS FRONTAL BOUNDARY SLOWLY DECAYS. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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