Area Forecast Discussion
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520 FXUS61 KPBZ 120926 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 426 AM EST FRI FEB 12 2016 .SYNOPSIS...
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A COLD FRONT WILL BRING MORE SNOW SNOW TO THE AREA LATER TODAY THROUGH SATURDAY. MUCH COLDER TEMPERATURES AND DANGEROUS WIND CHILLS WILL CONTINUE INTO THE WEEKEND BEHIND IT.
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&& .NEAR TERM /THROUGH SATURDAY/...
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CLEAR SKIES CONTINUE TO DOMINATE THE AREA EARLY THIS MORNING WITH OVERNIGHT DECOUPLING KEEPING WARM ADVECTION TO OUR WEST FROM GENERALLY IMPACTING SURFACE TEMPERATURES. HIGH CLOUDS HAVE GENERALLY BEEN RELEGATED TO OUR SOUTH THROUGH THE NIGHT...WHICH MEANS A VERY COLD START TO THE DAY TODAY. THAT SAID...280-290K LAYER ASCENT WILL INCREASE SLOWLY GOING INTO THE AFTERNOON WITH GFS AND NAM CONDENSATION PRESSURE DEFICITS IN THE LAYER DROPPING BELOW 10 MB SHORTLY AROUND 18Z OR SHORTLY THEREAFTER. AS SUCH...WHILE A DRY BOUNDARY LAYER WILL LIKELY KEEP MUCH MORE THAN VERY LIGHT SNOW FROM FALLING OUT...GENERALLY CHANCE POPS FOR LIGHT SNOW WERE MAINTAINED IN THE AFTERNOON. A COLD FRONT WILL FOLLOW THE WARM ADVECTION WITH GOOD HI-RES AND NAM/GFS MODEL AGREEMENT ON TIMING IT INTO THE NORTHERN REACHES OF THE CWA TOWARD 00Z...DOWN TOWARD PITTSBURGH AROUND 03Z OR SO. THE SNOW SQUALL PARAMETER IS STILL KEYING ON THIS BOUNDARY...AND HI- RES REFLECTIVITIES ARE RATHER IMPRESSIVE AS IT SLICES THROUGH THE NORTHERN PORTIONS OF THE AREA. HOWEVER...AS IT STRAY FARTHER SOUTH AND AWAY FROM A BOUNDARY LAYER MOISTURE SOURCE..AKA LAKE ERIE...IT GETS FAR LESS IMPRESSIVE. THUS...ACCUMULATIONS ABOVE AN INCH OR SO WERE GENERALLY RELEGATED NORTH OF METRO PITTSBURGH. BEHIND THE FRONT...VERY STEEP LAPSE RATES AND RISING INVERSION HEIGHTS DUE TO RAPID COOLING AT 700 MB SHOULD ALLOW FOR LAKE EFFECT BANDS TO PROPAGATE INLAND FAIRLY EFFICIENTLY. HI-RES ARW/HRRR/NAM/GFS CONSENSUS DOES FAVOR A MULTI-LAKE FETCH DEVELOPING ONE DOMINANT BAND DOWN THE LENGTH OF LAKE HURON AND ACROSS LAKE ERIE INTO NORTHWESTERN PENNSYLVANIA OVERNIGHT TONIGHT INTO SATURDAY MORNING. THE CONSENSUS OF THE POSITIONS FAVORS VENANGO COUNTY IN OUR AREA...THUS A LAKE EFFECT SNOW WATCH WAS ISSUED. THIS IS JUST A WATCH AND LATER MODEL RUNS MAY MEANDER THIS BAND ONE WAY OR ANOTHER...SO FUTURE FORECASTS SHOULD BE MONITORED. IN ADDITION TO PURE LAKE EFFECT...FAIRLY EFFICIENT UPSLOPE WILL LIKELY COME INTO THE RIDGES TONIGHT INTO SATURDAY MORNING AS WELL. SHALLOW MOISTURE WILL LIKELY BE OVERCOME BY EFFICIENT MICROPHYSICS...HOWEVER EVEN WITH EFFICIENT RATIOS...A LACK OF QPF SEEMS TO FAIL TO ALLOW MOST AREAS TO SURPASS ADVISORY CRITERIA ON A WIDESPREAD BASIS. THUS...WHILE ACCUMULATING SNOW IS ALMOST GUARANTEED...SIGNIFICANT SNOW SEEMS RATHER UNLIKELY. ONE ADDITIONAL EVENTUALITY WITH THE COLD FRONTAL PASSAGE SEEMS TO BE A FAIRLY DEEP MIXING PROFILE. JUST OFF THE SURFACE...ROUGHLY 25-35 KTS OF MOMENTUM LOOKS TO BE PRESENT. THIS COMBINED WITH BOUNDARY LAYER TEMPERATURES PLUMMETING TOWARD 0F OVERNIGHT SHOULD ALLOW FOR ALL AREAS TO SEE WIND CHILL TEMPERATURES DROP BELOW -10F...WHICH NECESSITATED A WIND CHILL ADVISORY FOR MOST OF THE AREA. IN THE HIGHEST TERRAIN...ADDITIONAL MOMENTUM AND COLDER TEMPERATURES MAY ALLOW FOR SOME AREAS TO DROP BELOW -25F. BECAUSE OF ONLY MODEST CONFIDENCE IN WIDESPREAD -25F NUMBERS IN THE HIGHER TERRAIN...A WIND CHILL WATCH WAS ISSUED. FURTHER SHIFTS CAN REFINE WHETHER THIS SHOULD BE UPGRADED TO A WARNING OR ADVISORY. EITHER WAY...VERY COLD WIND CHILLS WILL LIKELY PERSIST IN THE RIDGES WELL BEYOND THE NEAR TERM. FRIES
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
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LAKE-EFFECT SNOW SHOWERS ACROSS THE NORTH WILL BE WANING LATE SATURDAY NIGHT AS THE UPPER-LEVEL LOW MOVES EAST AND A SURFACE HIGH APPROACHES FROM THE WEST. NORTHWEST FLOW BEHIND THE EXITING FRONT WILL BRING TEMPERATURES NEAR THE ZERO DEGREE MARK FOR SUNDAY MORNING LOWS. WITH HIGH PRESSURE STARTING TO BUILD IN...WINDS WILL BE DECREASING ACROSS EASTERN OHIO. TO THE EAST AND NORTH HOWEVER...SEVERAL MORE HOURS OF STRONG AND GUSTY WINDS WILL MEAN WIND CHILL VALUES BELOW -10F. THE HIGHEST ELEVATIONS COULD SEE WIND CHILLS AT OR BELOW -25F. WITH THIS IN MIND...THE WIND CHILL ADVISORY WILL CONTINUE FOR MUCH OF THE CWA INTO SUNDAY MORNING...WITH A WIND CHILL WATCH ACROSS GARRETT AND EASTERN TUCKER COUNTIES. BRIEF RIDGING SUNDAY AFTERNOON WILL FINALLY DISRUPT THE MEAN NORTHWEST FLOW PATTERN ALOFT. WARM AIR ADVECTION WILL GRADUALLY KICK INTO GEAR...BUT WITH SUCH A LOW STARTING POINT...HIGHS WILL STAY WELL BELOW AVERAGE SUNDAY. THE NEXT WEAK WAVE ARRIVES MONDAY MORNING SPREADING CLOUDS AND LIGHT SNOW BACK ACROSS THE FORECAST AREA. AN INCREASE OF CLOUD COVER AND RELATIVELY WARMER AIR SURGING NORTHWARD WILL KEEP LOWS FROM BOTTOMING OUT MONDAY MORNING. TAX
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&& .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
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A DIGGING TROUGH WILL DEEPEN A SURFACE LOW NEAR THE LOWER MISSISSIPPI VALLEY MONDAY. STRONG SUPPORT FROM THE UPPER-LEVEL JET WILL DEEPEN THE LOW FURTHER AS IT ADVANCES THROUGH THE SOUTHEASTERN CONUS MONDAY AFTERNOON. INCREASED SOUTHERLY FLOW WILL TAP INTO GULF AND ATLANTIC MOISTURE...SPREADING IT NORTHWARD INTO OUR REGION AND EAST. STRONG ISENTROPIC ASCENT WILL BRING PRECIPITATION THROUGH AT LEAST OUR EASTERN ZONES BY LATE MONDAY INTO TUESDAY MORNING. STILL QUESTIONS SURROUNDING THE EXACT TRACK OF THE LOW AND THE RESULTANT WESTWARD EDGE OF PRECIPITATION...PRECIPITATION TYPE...AND INTENSITY. AS OF THE 00Z RUNS...GUIDANCE IS FAIRLY CONSISTENT ACROSS THE MODEL SUITE...BUT ALL HAVE NUDGED THE SURFACE LOW WEST OF THEIR POSITION 24HRS AGO. CURRENT FORECAST CALLS FOR LIKELY SNOW TUESDAY MORNING REACHING WEST TO THE OHIO RIVER INCLUDING PITTSBURGH. SIGNIFICANT MODEL SPREAD DOES EXIST FOR HIGH TEMPERATURE VALUES TUESDAY...AND WITH THE WESTWARD TREND...HAVE BUMPED UP HIGHS A FEW DEGREES. THIS WOULD FAVOR AT LEAST SOME MIX OF RAIN/SNOW TUESDAY AFTERNOON THAT COULD ULTIMATELY CUT INTO THE POTENTIAL FOR ACCUMULATING SNOW. BEHIND THIS SYSTEM...THE BROAD UPPER TROUGH WILL BRIEFLY RE-ESTABLISH OVER THE NORTHEAST. TEMPERATURES WILL INITIALLY DROP BELOW AVERAGE THURSDAY...BEFORE REBOUNDING WITH WARM AIR ADVECTION BY THE WEEKEND. TAX
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&& .AVIATION /09Z FRIDAY THROUGH TUESDAY/... VFR CONDITIONS EXPECTED OVERNIGHT AND INTO FRIDAY MORNING BEFORE THE NEXT SYSTEM BRINGS ANOTHER ROUND OF SNOW AND FLIGHT RESTRICTIONS FRIDAY AFTERNOON/EVENING. GUSTY NORTHWEST WINDS WILL COMMENCE BY FRIDAY EVENING AS A COLD FRONT MOVES THROUGH THE AREA WITH A BURST OF SNOW SHOWERS ALONG IT. .OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/... RESTRICTIONS WILL BE POSSIBLE IN SNOW SHOWERS LATER FRIDAY INTO SATURDAY. THE NEXT CHANCE FOR WIDESPREAD IFR WILL BE WITH LOW PRESSURE MONDAY AND TUESDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...WIND CHILL WATCH FROM LATE TONIGHT THROUGH SUNDAY MORNING FOR MDZ001. OH...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST SATURDAY FOR OHZ039-048-049-057>059-068-069. WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SUNDAY FOR OHZ040-041-050. PA...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SUNDAY FOR PAZ007>009-013>016-020>023-029-031-073>076. LAKE EFFECT SNOW WATCH FROM THIS EVENING THROUGH SATURDAY AFTERNOON FOR PAZ008. WV...WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM EST SATURDAY FOR WVZ003-004-012. WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EST SUNDAY FOR WVZ001-002-021-509>513. WIND CHILL WATCH FROM LATE TONIGHT THROUGH SUNDAY MORNING FOR WVZ514.
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