Area Forecast Discussion
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000 FXUS61 KPBZ 291844 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 244 PM EDT SUN MAR 29 2015 .SYNOPSIS... A WEAK SYSTEM WILL BRING RAIN AND SNOW OVERNIGHT INTO MONDAY. && .NEAR TERM /THROUGH MONDAY/... CURRENT SATELLITE IMAGERY SHOWING CLEAR SKIES ACROSS THE REGION AS HIGH PRESSURE BEGINS TO PUSH SOUTHEAST OF THE AREA. SOUTHERLY FLOW IS EXPECTED TO INCREASE THROUGH THE EVENING AS THE CENTER OF THE HIGH MOVES EAST AND THE PRESSURE GRADIENT TIGHTENS. THIS SHOULD HELP ACCELERATE FURTHER WARMING DURING THE LATE AFTERNOON/EARLY EVENING HOURS. TONIGHT...A RELATIVELY DRY AND WEAK SYSTEM WILL MOVE THROUGH THE WESTERN GREAT LAKES AND INTO OUR WEST. AS THE MAIN TROF AXIS ENTERS...A WEAK WARM FRONT WILL LIFT JUST INTO THE SOUTHERN EXTENT OF THE FORECAST AREA...KEEPING TEMPERATURES ACROSS THE SOUTHERN HALF OF OUR COUNTIES ELEVATED. TIMING ACROSS MODEL GUIDANCE HAS BEEN FAIRLY CONSISTENT...BUT THE LATEST RUNS PUSH TIMING BACK AN HOUR OR TWO AS IT FIGHTS THE DRY AIR FIRMLY ENTRENCHED. EXPECTING A SUPPRESSED DIURNAL TEMPERATURE TREND...AS WARM AIR TRIES TO PUSH NORTHWARD THROUGH THE OVERNIGHT INTO THE EARLY HOURS MONDAY. PREDOMINANT PRECIPITATION TYPE NEAR PITTSBURGH AND SOUTH IS EXPECTED TO BE RAIN...BUT AREAS NORTH OF PITTSBURGH WILL COOL ENOUGH TO TRANSITION THE PRECIPITATION FROM RAIN TO A RAIN/SNOW MIX. MODEL SOUNDINGS NORTH OF I-80 INDICATE THIS AREA HAS THE BEST CHANCE TO SEE ALL SNOW. REGARDLESS OF PRECIPITATION TYPE...WITH ONLY MODEST FORCING AND OVERRUNNING OF MID- AND UPPER- LEVEL MOISTURE...PRECIPITATION RATES SHOULD BE LOW. LITTLE...IF ANY...SNOW ACCUMULATION IS EXPECTED THROUGH MONDAY MORNING. STRATIFORM PRECIPITATION WILL QUICKLY DWINDLE QUICKLY WEST TO EAST AFTER SUNRISE MONDAY. THIS IS DUE TO THE DEEPER MOISTURE EVACUATING THE AREA...LEAVING ONLY MODEST RESIDUAL LOW-LEVEL MOISTURE. FORECAST SOUNDINGS INDICATE THE POTENTIAL FOR PATCHY DRIZZLE THROUGH MIDDAY MONDAY...BUT CONFIDENCE NOT HIGH ENOUGH FOR INCLUSION AT THIS TIME. DEEPER MOISTURE WILL LINGER ALONG THE NORTH KEEPING LIGHT RAIN/SNOW POTENTIAL IN THROUGH MUCH OF THE DAY. CHANCES ACROSS THE NORTH WILL INCREASE AGAIN IN THE AFTERNOON AS COLDER MID-LEVEL AIR ASSOCIATED WITH AN UPPER-LEVEL WAVE ARRIVES. THIS WILL SUBSEQUENTLY STEEPEN THE LAPSE RATES AND DEVELOP CONVECTIVELY DRIVEN RAIN/SNOW SHOWERS. ELSEWHERE...CLOUDS COVER SHOULD SCATTER ENOUGH FOR POCKETS OF SUNSHINE AND WARMING. EXPECTING A PRONOUNCED GRADIENT OF HIGH TEMPERATURES MONDAY FROM NEAR 50 ACROSS THE SOUTH TO UPPER 30S NORTH. TAX && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... UNSTABLE NORTHWESTERLY FLOW WILL BRIEFLY TURN WEST-SOUTHWESTERLY BY LATE MONDAY EVENING TO ALLOW FOR THE CWA TO DRY OUT AND AT LEAST PARTIALLY CLEAR OUT. HOWEVER...AN ACTIVE PATTERN LOOKS TO CONTINUE THEREAFTER. RATHER DISTURBING MODEL TRENDS SEEM TO HAVE TAKEN HOLD ON THE 06Z AND 12Z CYCLES TODAY...WITH THE MODELS LARGELY FALLING INTO TWO CAMPS. THE NAM AND CANADIAN FAVOR A MORE NORTHERN TRACK OF A SYSTEM THROUGH THE AREA ON TUESDAY...WHILE THE GFS AND 00Z ECMWF FAVOR A MORE SOUTHERLY TRACK. UNSURPRISINGLY...THE SREF BASICALLY SPLIT THE DIFFERENCE AND ALLOWED FOR A MIDDLE GROUND FORECAST...WHICH WAS LARGELY IN LINE WITH CONTINUITY...SO FORECAST CHANGES REALLY WERE NOT ALL THAT LARGE AS A RESULT. IT DOES SEEM THAT THE GFS WAS SUFFERING FROM SOME GRID SCALE ISSUES...WHILE THE NAM WAS LIKELY SUFFERING FROM ITS HABITUAL OVER DEVELOPMENT ISSUES. THESE PROBLEMS FURTHER LEND CREDENCE TO FAVORING AN ENSEMBLE MEAN APPROACH SUCH AS THE SREF MEAN. A COMPROMISE APPROACH STILL FAVORS RELATIVELY RAPID ENCROACHMENT OF WARM ADVECTION ISENTROPIC ASCENT OVER THE FORECAST AREA LATE MONDAY NIGHT INTO TUESDAY. THIS OCCURS AS A SURFACE LOW CROSSES THE AREA WITH AT LEAST THE SOUTHERN HALF OF THE AREA LIKELY TO ENTER THE WARM SECTOR FOR A PORTION OF THAT TIME AND PROBABLY HALT RAINFALL THERE FOR A TIME. AT THE ONSET...SOME PRECIPITATION TYPE ISSUES MAY BE PRESENT IF THE SOUTHERN SOLUTIONS VERIFY...HOWEVER ANY FROZEN PRECIPITATION SHOULD QUICKLY CHANGE TO RAIN AS WARM ADVECTION QUICKLY LOOKS TO ERODE ANY COLD AIR. THIS IS ESPECIALLY TRUE GIVEN THE LACK OF ANTECEDENT DRY AIR AS THIS SYSTEM ROLLS INTO THE AREA...MINIMIZING THE POTENTIAL FOR WET BULB COOLING AS PRECIPITATION DEVELOPS. A RELATIVELY QUICK DEPARTURE OF THE SYSTEM LOOKS TO OCCUR TUESDAY NIGHT WITH MUCH DRIER AIR FLOODING INTO THE CWA ON WEDNESDAY. SOME TEMPORARY COLD ADVECTION ON WEDNESDAY WILL LIKELY STILL HOLD TEMPERATURES BACK. HOWEVER...DRASTIC PATTERN AMPLIFICATION OF THE PATTERN TO OUR WEST LOOKS TO DEVELOP A STRONG THERMAL RIDGE THAT WILL BE POISED TO PUSH INTO THE AREA LATER IN THE WEEK. FRIES && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... WHILE THE GFS HAS SLOWED THE ARRIVAL OF A FRONT ON THURSDAY FROM PREVIOUS MODEL RUNS...00Z ECMWF IS EVEN SLOWER THAN THAT. GIVEN THAT THE GFS IS THE MOST OPEN WAVE SOLUTION RELATIVE TO THE CANADIAN...GEFS...AND ECMWF...TIMING SLOWER THAN THE GFS IS LIKELY MORE OPTIMAL FOR THE ARRIVAL OF SHOWERS INTO THE CWA. AS A RESULT...WARM ADVECTION WILL RULE THE ROOST ON THURSDAY...LIKELY ALLOWING FOR THE WARMEST DAY OF THE SEASON TO THIS JUNCTURE. HOWEVER ONCE PRECIPITATION ARRIVES...LOW PRESSURE FORMING ALONG THE COLD FRONT WILL KEEP PRECIPITATION IN THE FORECAST FRIDAY UNTIL IT MOVES INTO NEW ENGLAND SATURDAY. TEMPS WILL DROP AFTER THURSDAY...LEADING BACK TO YET ANOTHER PERIOD OF BELOW NORMAL VALUES. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... VFR CONDITIONS WILL PERSIST WITH NEARLY CLEAR CONDITIONS. HIGH CIRRUS BEGINNING TO PUSH IN THROUGH CENTRAL OHIO. A WEAK SYSTEM ENTERING THE REGION LATE THIS EVENING IS EXPECTED TO BRING PRECIPITATION TO ALL SITES. SOUTH AND WEST OF PITTSBURGH SHOULD REMAIN ALL RAIN...WITH SOME SNOW MIXING IN ELSEWHERE. CEILINGS WITH PRECIPITATION SHOULD INITIALLY BEGIN AS VFR...BUT ARE EXPECTED TO QUICKLY DROP TO MVFR. SOME MARGINAL LOW LEVEL WIND SHEAR MAY ALSO DEVELOP OVERNIGHT IF WINDS DECOUPLE...ESPECIALLY WEST OF PITTSBURGH...BUT DID NOT HAVE ENOUGH CONFIDENCE TO INCLUDE IN TAFS AT THIS TIME. SOME IMPROVEMENT WILL OCCUR MONDAY AFTER DAYBREAK WITH MOST LOCATIONS RETURNING BACK TO VFR AS THE FRONT PUSHES EAST. HOWEVER...DEEPER MOISTURE WILL LINGER ALONG OUR NORTH AND CONTINUE TO IMPACT FKL/DUJ. LINGERING RAIN/SNOW SHOWERS WILL BE REINVIGORATED BY THE UPPER-LEVEL LOW A IT SWINGS THROUGH MONDAY AFTERNOON NEAR THE END OF THE TAF PERIOD. TAX .OUTLOOK.../MONDAY THROUGH THURSDAY/... RESTRICTIONS ARE POSSIBLE ONCE AGAIN WITH CROSSING LOW PRESSURE TUESDAY AND THURSDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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