Area Forecast Discussion
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000 FXUS61 KPBZ 270237 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 937 PM EST FRI DEC 26 2014 .SYNOPSIS... HIGH PRESSURE THROUGH SATURDAY WITH DRY AND MILD CONDITIONS. A COLD FRONT WILL BRING THE NEXT CHANCE OF RAIN SATURDAY NIGHT AND SUNDAY. && .NEAR TERM /THROUGH SATURDAY/... HIGH CLOUDS HAVE LARGELY ENVELOPED THE CWA THIS EVENING AS MID AND UPPER LEVEL RH VALUES HAVE SURGED UPWARD. HOWEVER...UNDER THOSE LAYERS...FAIRLY DRY AIR REMAINS FIRMLY ENTRENCHED. ADDITIONALLY...WITH THE INVERTED TEMPERATURE PROFILES...RH VALUES ALONG THE RIDGETOPS CONTINUE TO BE WELL BELOW THOSE IN THE LOWER ELEVATIONS OF THE CWA. THAT SAID...MID AND HIGH CLOUDS ADVANCING NORTHWARD SHOULD PUT A LID ON HUGE TEMPERATURE FALLS TONIGHT. WHILE STATISTICAL GUIDANCE SUGGESTS MUCH OF THE CWA SHOULD CHALLENGE FREEZING WITH LOWER 20S IN THE RIDGES...THIS MAKES NO METEOROLOGICAL SENSE. INVERTED PROFILES SHOULD ALLOW FOR MID- SLOPES AND RIDGES TO BE WARMER THAN THE VALLEYS THROUGH THE NIGHT...PARTICULARLY AS 850 MB TEMPERATURES REMAIN AROUND +4 TO +5C. WITH THAT SAID...LOW TEMPERATURES WERE ADJUSTED UPWARD MOST EVERYWHERE...PARTICULARLY OVER OHIO AND IN THE HIGHER ELEVATIONS. CLOUD EXPECTATIONS WERE LIKEWISE INCREASED SUBSTANTIALLY THROUGH THE EVENING. DRIER AIR IN THE LOWER LEVELS LOOKS TO START TO GET ERODED OVERNIGHT AS MODEL SOUNDING PROFILES SUGGEST DEWPOINT DEPRESSIONS SAG SUBSTANTIALLY AFTER 06Z. GFS AND NAM SOLUTIONS BOTH INDICATE A WEAK CONVECTIVE VORT SEEMS TO PUSH THROUGH THE AREA IN THE 06Z TO 15Z TIME FRAME. WHILE LIFT IS RATHER LIMITED AND SATURATION QUESTIONABLE...IT WOULDN`T BE PARTICULARLY SHOCKING TO SEE A SPRINKLE FALL OUT AS THE VORT PUSHES THROUGH. HOWEVER...OUTSIDE OF THE WINDOW WITH WEAK LIFT AHEAD OF THE VORT...CONDITION SEEM LIKELY TO REMAIN RELATIVELY DRY INTO MUCH OF THE DAY SATURDAY. FRIES && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... HIGH PRESSURE BECOMES DISLODGED AND PUSHED OFFSHORE FROM THE MID-ATLANTIC SAT NIGHT AS A LOW PRESSURE SYSTEM MOVES THROUGH THE WRN GREAT LAKES. BY LATE SAT NIGHT...MOISTURE FROM ANOTHER LOW PRESSURE SYSTEM NEAR THE LOWER MS VALLEY WILL MOVE NORTHWARD ALONG A SHARED BOUNDARY. THIS RELATIVELY WEAK BOUNDARY WILL APPROACH OUR WRN PERIPHERY AS A COLD FRONT LATE SAT NIGHT INTO EARLY SUN MORNING. RAIN SHOWERS WILL OVERSPREAD THE FORECAST AREA INTO THE DAY SUN...ALTHOUGH WITH LIMITED MOISTURE ALONG THE WEAK FRONT...PRECIPITATION IS EXPECTED TO BE LIGHT. FRONTAL PROGRESS SLOWS AS IT GETS STRETCHED OUT AND BECOMES PARALLEL TO THE MIDLEVEL FLOW. HOWEVER...A FRESH WAVE WILL RIDE NORTHEASTWARD ALONG THE BOUNDARY DURING THE DAY ON SUNDAY...KEEPING PRECIPITATION IN THE FORECAST. BEST SUPPORT/MOISTURE CLIPS THE SOUTHEASTERN CORNER OF THE CWA..AND KEPT CATEGORICAL POPS HERE. BEHIND THE FRONT SUNDAY NIGHT...COLDER AIR SAGS IN SLOWLY ON INITIAL WESTERLY FLOW. EXPECT MOST AREAS WILL SEE PRECIPITATION END BEFORE ANY MEANINGFUL CHANGEOVER TO SNOW. A FEW SHOWERS WILL LINGER ON MONDAY IN THE SOUTHEAST CWA AS THE BOUNDARY FINALLY PULLS AWAY...WHILE DRY WEATHER AND SOME CLOUDS LINGER FOR THE BULK OF THE AREA. WHILE PRECIP ENDS IN THE SOUTHEAST MONDAY NIGHT...ANOTHER VERY WEAK BOUNDARY MAY TRY TO SAG INTO THE NORTHERN COUNTIES THROUGH TUESDAY. AGAIN...MOISTURE AND SUPPORT WILL BE VERY LIMITED AND ELECTED TO MAINTAIN SLIGHT CHANCE POPS HERE. AFTER ABOVE NORMAL TEMPERATURES CONTINUE SUNDAY AND SUNDAY NIGHT...MORE SEASONABLE VALUES RETURN MONDAY AND CONTINUE THEREAFTER. && .LONG TERM /TUESDAY THROUGH FRIDAY/... THE EXTENDED WILL LARGELY BE DRY WITH A DECREASING TREND IN TEMPERATURES AS A BROAD TROUGH IN THE LONGWAVE PATTERN SLOWLY SAGS SOUTH ACROSS THE EASTERN CONUS. THERE IS A SLIGHT CHANCE OF LIGHT SNOW SHOWERS ASSOCIATED WITH A SHORTWAVE TRANSITIONING THROUGH THE FLOW DEVELOP MAINLY ALONG AND NORTH OF INTERSTATE 80 DURING THE MIDDLE OF THE WEEK...BUT MOISTURE APPEARS TO BE QUITE LIMITED. FURTHER OUT...AN AREA OF LOW PRESSURE PREVIOUSLY CLOSED OFF OVER THE SOUTHWEST WILL EVENTUALLY IMPACT THE REGION...BUT MODELS VARY WIDELY IN TIMING OF THIS FEATURE...BY A MARGIN OF SEVERAL DAYS. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... RETURN FLOW QUICKLY BECOMING RE-ESTABLISHED ACROSS THE AREA EARLY THIS EVENING WITH AMPLE HIGH CLOUD EXPECTED TO OVERSPREAD THE REGION OVER THE NEXT SEVERAL HOURS. WITHIN BROADER SOUTHWESTERLIES...MODELS DEPICT A SHORTWAVE IMPULSE MOVING THROUGH THE AREA BETWEEN ROUGHLY 09 AND 15Z LATE TONIGHT/SATURDAY MORNING. CONVECTIVE MID CLOUD HAS BEEN DEVELOPING ACROSS SRN OHIO THROUGH WV OVER THE PAST SEVERAL HOURS...SUGGESTING THIS IMPULSE MAY BE A BIT STRONGER THAN ADVERTISED. NONETHELESS...MODELS SHOW MODEST ISENTROPIC LIFT OVERSPREAD THE AREA ALONG WITH ABUNDANT RELATIVE HUMIDITY AND CROSS-TERRAIN FLOW TO SUPPORT THE NOTION OF LOW END VFR IF NOT LOCALLY MFVR CEILINGS ROUGHLY IN THE 09-15Z WINDOW ACROSS THE TERMINALS OVERNIGHT. NOT A HUGE WEATHER IMPACT...BUT ONE WORTH NOTHING. ADDITIONALLY...GIVEN THE MID LEVEL SUPPORT AND LOW STABILITY WITHIN THE STRENGTHENING WARM ADVECTION REGIME...WOULD NOT BE SURPRISED TO SEE A FEW SCATTERED SHOWERS IN THIS TIME FRAME AS WELL. WINDS WILL BE LIGHT FROM THE SOUTH TO SSW OVERNIGHT...INCREASING BACK TO AROUND 7-8 KNOTS AFTER 16Z ONCE THE SHORTWAVE CLEARS AND WE BREAK OUT INTO THE TRUE WARM SECTOR. EXPECT THE COLD FRONT/ATTENDANT PRECIPITATION TO HOLD OFF UNTIL SHORTLY AFTER 00Z TOMORROW EVE. OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/... RESTICTIONS POSSIBLE WITH THE COLD FRONT SATURDAY NIGHT AND THEN AGAIN WITH A PASSING WAVE ACROSS OUR SOUTH SUNDAY NIGHT. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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