Area Forecast Discussion
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000 FXUS61 KPBZ 210447 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1247 AM EDT TUE APR 21 2015 .SYNOPSIS... SHOWERS WILL DIMINISH OVERNIGHT AS A COLD FRONT SWINGS EAST OF THE RIDGES. UNSEASONABLY COOL TEMPERATURES CAN BE EXPECTED THE REMAINDER OF THE WEEK. && .NEAR TERM /THROUGH TODAY/... QUICK UPDATE TO LOWER PRECIPITATION CHANCES BEHIND THE FRONT BASED ON LATEST OBSERVATIONS AND GUIDANCE. PREVIOUS DISCUSSION FOLLOWS. WIND SHIFT HAS REACHED THE RIDGES AND TEMPERATURES HAVE DROPPED OFF NICELY THIS EVENING. COLD FRONT WILL CONTINUE TO PUSH EAST WITH MUCH COOLER AIR WORKING IN OVERNIGHT. POPS MAY STILL BE OVERDONE FOR LATER TONIGHT BUT SCT SHOWERS STILL LINGERING BACK ACROSS SOUTHEAST OHIO AND NRN WEST VIRGINIA...AND MAY BE ABLE TO HOLD TOGETHER AS UPPER LEVEL SHORTWAVE PASSES. TEMPERATURES AND WINDS APPEAR ON TRACK WITH NO CHANGES. AN UPPER-LEVEL LOW WILL PIN-WHEEL INTO THE NORTHERN GREAT LAKES TUESDAY...SETTING UP A BROAD TROF OVER THE AREA THAT WILL INCLUDE SEVERAL WEAK DISTURBANCES CYCLING THROUGH. THE FIRST SUCH DISTURBANCE WILL BRING THE CHANCE OF RAIN SHOWERS BACK TO THE AREA TUESDAY EVENING. WITH THE BROAD TROF OVERHEAD...WINDY CLOUDY AND COOL CONDITIONS WILL EXIST TUESDAY. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... THE LONG WAVE PATTERN LOOKS TO FULL TRANSITION INTO TROUGHING OVER OUR REGION ON TUESDAY NIGHT. MODEL GUIDANCE HAS BEEN HINTING AT THIS FOR ABOUT A WEEK IN THIS INTERLUDE...AND IT LOOKS TO COME TO FULL FRUITION BY THIS TIME. AS OUR REGION SITS IN THE BASE OF THE LONG WAVE TROUGH...WITH THE MAIN JET AXIS TO OUR SOUTH...THIS WILL RESULT IN TEMPERATURES DROPPING SIGNIFICANTLY FROM OUR RECENT WARM PERIOD...AS WELL AS WITH A FEW VERY FAST MOVING SYSTEMS AFFECTING THE AREA THROUGH THE SHORT TERM. AS THESE SYSTEMS WILL BE EMBEDDED IN HIGH SPEED UPPER FLOW...THEIR TIMELINESS IS A BIT MORE DIFFICULT TO PIN DOWN. ADDITIONALLY...AS LAYER TEMPERATURES FALL PROGRESSIVELY AS TROUGHING BECOMES MORE DEEPLY ENTRENCHED...BOTH LOW LEVEL STABILITY AND THE FREEZING LEVEL START TO FALL. THIS MEANS PREDICTING DRY WEATHER BECOMES MORE TENUOUS...AS DO SUNNY SKIES...AND EVEN PRECIPITATION TYPES START TO BECOME QUESTIONABLE AT TIMES. ALL THAT SAID...THE MODEL CONSENSUS FAVORS THE STRONGEST SHORT WAVE PASSAGE FOR WEDNESDAY AFTERNOON. POPS WERE ADJUSTED TO LIKELY FOR THE BULK OF THE AREA FOR THIS TIME FRAME. HOWEVER...GIVEN THE SPEED OF THE MID-LEVEL FLOW...IT WILL LIKELY EXIT BY WEDNESDAY NIGHT...WITH JUST INSTABILITY DRIVEN SHOWERS REMAINING UNDER THE MID-LEVEL COLD POOL ACROSS THE NORTH...AS WELL AS A FEW UPSLOPE SHOWERS. BUFKIT SOUNDINGS SUGGEST THAT BY WEDNESDAY NIGHT...A FEW OF THESE COULD TRANSITION TO SNOW SHOWERS WITH BOUNDARY LAYER COOLING AND A VASTLY DECREASED MELTING DEPTH IN THE LOWEST LAYERS. THIS WINDOW FOR THIS WILL BE SHORT AS MOISTURE PEELS EASTWARD RATHER RAPIDLY AND THE JET CORE SHIFTS TOWARD THE ATLANTIC SEABOARD BY THE END OF THE SHORT TERM. THIS PLACES US IN THE LEFT ENTRANCE REGION OF THE UPPER JET STREAK...WHICH WOULD BECOME DECREASINGLY FAVORABLE FOR ANY ORGANIZED PRECIPITATION DEVELOPMENT. THE FORECAST WAS THUS MAINTAINED DRY INTO THE LATTER HALF OF THE WORK WEEK. WHILE THE WET WEATHER WILL LIKELY BE CURTAIL BY THE LATTER HALF OF THE WEEK...CYCLONIC FLOW THROUGH THE ATMOSPHERE WILL REINFCORCE COLDER TEMPERATURES AT THE SURFACE. MODEL CONSENSUS 850 HPA TEMPERATURES FAIL TO RISE ABOVE 0C AFTER WEDNESDAY MORNING THROUGH THE REMAINDER OF THE SHORT TERM. BECAUSE OF THIS...HIGHS WILL LIKELY STRUGGLE MIGHTILY TO REACH 50F THE REST OF THE WEEK. ADDITIONALLY...OVERNIGHT LOWS WILL FLIRT WITH OR DROP BELOW FREEZING SEVERAL TIMES. THIS WILL SEEM COLD...BUT IT IS IN NO WAY ABNORMAL AS THE GROWING SEASON CLIMATOLOGICALLY DOES NOT START UNTIL MAY FOR ANY OF OUR FORECAST AREA. THUS...WE ARE STILL QUITE A BIT FROM THE START OF THE FROST/FREEZE PROGRAM FOR THE YEAR. FRIES && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... SOME ISOLATED SHOWERS WILL REMAIN THURSDAY MORNING...BUT WILL DIMINISH THROUGH THE DAY. GFS/ECMWF GENERALLY SHOW ONE SYSTEM IN THE REGION THROUGH THE EXTENDED FORECAST...BUT THE ECMWF IS SLOWER WITH THE SYSTEM AND ALSO MUCH FARTHER TO THE SOUTH. CONSIDERING ENSEMBLES SHOW GOOD SUPPORT FOR THE EUROPEAN SOLUTION...HAVE REMOVED THE LOW POPS THAT WERE IN THE FORECAST OVER THE WEEKEND. HOWEVER...MODELS DO SHOW AGREEMENT ON BROAD UPPER LEVEL LOW ACROSS NORTHEASTERN NORTH AMERICA...AND THIS WILL KEEP TEMPERATURES 5-10 DEGREES BELOW NORMAL THROUGH THE PERIOD. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... A COLD FRONT WAS EXITING THE AREA INTO CENTRAL PA...THOUGH SOME POST FRONTAL SHOWERS WILL REMAIN POSSIBLE THROUGH THIS EVENING. OTHERWISE...VFR STRATOCU IS EXPECTED THROUGH TUESDAY. A BROAD UPPER TROUGH IS EXPECTED TO SET UP ACROSS THE GREAT LAKES TUESDAY...AND COULD BRING SCATTERED SHOWERS FOR AREAS FROM PIT NORTH. INCLUDED A VCSH MENTION IN THE TAFS FOR THIS. IN ADDITION...WEST WINDS COULD GUSTS TO AROUND 30 KT TUESDAY WITH A TIGHT PRESSURE GRADIENT REMAINING. .OUTLOOK.../TUESDAY NIGHT THROUGH SATURDAY/... PERIODIC RESTRICTIONS A ARE POSSIBLE MUCH OF THE PERIOD MAINLY NORTH OF PIT AS THE UPPER TROUGH PERSISTS OVER THE GREAT LAKES. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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