Area Forecast Discussion
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000 FXUS61 KPBZ 201828 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 228 PM EDT MON APR 20 2015 .SYNOPSIS... A PASSING FRONTAL SYSTEM WILL RESULT IN SCATTERED SHOWERS AND THUNDERSTORMS THROUGH THE LATE EVENING. UNSEASONABLY COOL TEMPERATURES CAN THEN BE EXPECTED THE REMAINDER OF THE WEEK AS AN AREA OF LOW PRESSURE PERSISTS OVER THE NORTHEAST. && .NEAR TERM /THROUGH TUESDAY/... CURRENT VISIBLE SATELLITE IMAGERY SHOWING AN AGITATED CU FIELD OVER THE BULK OF THE FORECAST AREA. CONTINUED POCKETS OF SUNSHINE SHOULD CONTINUE TO DRIVE SURFACE TEMPERATUES UP THROUGH THE AFTERNOON. THIS WILL CONTINUE TO FEED INSTABILITY AS THE FRONT APPROACHES THE AREA. SCATTERED SHOWERS HAVE BEGUN TO DEVELOP AHEAD OF A SHORTWAVE TROF EVIDENT ON WATER VAPOR IMAGERY. LATEST RADAR IMAGERY SHOWING MORE VERTICAL DEPTH TO THE SHOWERS/THUNDERSTORMS THAN EARLIER...INDICATING THE RADAR SHOULD BEGIN TO BLOSSOM WITH STRONGER ECHOES. AS THE TROF AXIS MOVES OVERHEAD THROUGH EARLY AFTERNOON...COLDER MID- AND UPPER- LEVEL AIR WILL ADVANCE WEST TO EAST ACROSS THE AREA...GENERATING ROUGHLY 1000-1500 J/KG OF SURFACE-BASED CAPE. THE CO-LOCATION OF INSTABILITY AND AROUND 40KTS OF MOSTLY UNIDIRECTIONAL SHEAR...SHOULD BE ENOUGH TO SUPPORT SEVERAL STRONG TO SEVERE THUNDERSTORMS...WITH ISOLATED DAMAGING WIND AND LARGE HAIL THE PRIMARY THREATS. COLD FRONT PUSHES THROUGH LATER THIS EVENING...USHERING IN A CHANGE IN AIRMASS. STRONG COLD AIR ADVECTION WILL BRING 850MB TEMPERATURES BACK DOWN TOWARDS THE ZERO DEGREE MARK. THIS WILL TRANSLATE TO OVERNIGHT LOWS NEARING SEASONAL AVERAGES AFTER SPENDING SOME TIME ABOVE AVERAGE. BRIEF RIDGING IN THE LOW- LEVELS AND EROSION OF MOISTURE DEPTH WILL EFFECTIVELY END RAIN CHANCES EARLY TUESDAY MORNING. THE 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. TAX && .SHORT TERM /TUESDAY NIGHT 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 /18Z MONDAY THROUGH SATURDAY/... SHOWERS AND THUNDERSTORMS BEGINNING TO DEVELOP ACROSS THE FORECAST AREA CURRENTLY. THROUGH FURTHER DE-STABILIZATION OF THE ATMOSPHERE THIS EVENING...THIS ACTIVITY SHOULD ONLY INCREASE. HAVE INCLUDED VICINITY THUNDERSTORMS FOR ALL TERMINALS AND HAVE INCLUDED TS TEMPO GROUPS FOR MOST TERMINALS EAST OF THE OHIO. OUTSIDE OF THUNDERSTORMS...BKN VFR CONDITIONS ARE EXPECTED WITH FREQUENT WIND GUSTS UP TO 30 KTS. SOUTHERLY WINDS WILL VEER TO THE WEST DURING THE EVENING BEHIND THE FRONT. SHOWERS AND THUNDERSTORMS WILL DECREASE LATE THIS EVENING AS THE FRONT PUSHES EAST OF THE AREA. BKN CIGS MAY DROP TO MVFR THROUGH THE NIGHT...BEFORE MIXING BACK UP TO VFR TUESDAY. SURFACE FLOW WILL STAY STRONG TUESDAY FROM THE WEST WITH GUSTS 20-25KTS. TAX .OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... PERIODIC RESTRICTIONS WILL BE POSSIBLE AS COLD UPPER LOW PRESSURE SETTLES JUST NORTH OF THE GREAT LAKES. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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