Area Forecast Discussion
Issued by NWS

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000 FXUS61 KPBZ 280139 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 839 PM EST FRI FEB 27 2015 .SYNOPSIS... AFTER A COLD NIGHT CLOUDS WILL INCREASE SATURDAY FOLLOWED BY RAIN AND SNOW SUNDAY THROUGH MONDAY MORNING. A SIGNIFICANT WARM-UP IS POSSIBLE TUESDAY INTO WEDNESDAY BEFORE COLD AIR RETURNS. && .NEAR TERM /THROUGH SATURDAY/...
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MINOR ADJUSTMENTS TO DEW POINTS AND SKY GRIDS. NO OTHER CHANGES AND PREVIOUS DISCUSSION FOLLOWS. ADJUSTED TEMPERATURES AND SKY GRIDS BASED ON CURRENT READINGS...SAT PIX...AND 18Z GUIDANCE. CLEAR SKIES FOLLOWED BY SOME CIRRUS AS SURFACE RIDGE SITS ON TOP OF REGION OVERNIGHT. SNOW COVER AND LIGHT WINDS WILL ALLOW FOR GOOD RADIATIONAL COOLING AND LOWS NEAR OR WELL BELOW ZERO. SURFACE RIDGE WILL MOVE EAST DURING THE DAY SATURDAY WITH CIRRUS AND MID DECK INCREASING TOWARD EVENING. HIGHS WILL RECOVER INTO THE 20S.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... MODEL GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT IN THE LOW PRESSURE SYSTEM THAT IS FORECAST TO MAKE ITS APPROACH LATE SATURDAY NIGHT/SUNDAY MORNING. THIS LOW WILL MOVE NORTHEASTWARD THROUGH THE UPPER OHIO VALLEY WITH THE SUPPORT OF A DIGGING UPPER LEVEL TROUGH DURING THE DAY ON SUNDAY. WITH THE LOWS PLACEMENT JUST A BIT TO THE NORTH...WARM ADVECTION LOOKS TO SUPPORT A MIX OF RAIN AND SNOW FOR PART OF THE REGION. ALTHOUGH CONFIDENCE ON THE EXACT PLACEMENT OF THE RAIN-SNOW LINE AND IT`S MOVEMENT ON SUNDAY STILL REMAINS IN QUESTION...THE LAST SEVERAL MODEL RUNS HAVE TRENDED WARMER WITH NEAR/ABOVE FREEZING SURFACE TEMPERATURES AND HAVE PUSHED CRITICAL THICKNESS VALUES FURTHER NORTH. THUS...WHILE ALL OF THE DETERMINISTIC RUNS SUGGEST 0.75 INCHES OF QPF AREA- WIDE...WARM AIR ALOFT AND AT THE SURFACE SHOULD CUT DOWN ON SNOWFALL ACCUMULATIONS FOR THE LOCATIONS THAT REMAIN IN THE AREA WITH GREATEST UNCERTAINTY. AT THIS POINT...THE HIGHEST CONFIDENCE IN ACCUMULATING SNOW REMAINS FOR POINTS NORTH OF I-80 AND A WINTER STORM WATCH HAS BEEN ISSUED FOR THOSE COUNTIES. WITH THESE LOCATIONS REMAINING COLDEST THROUGH THE ENTIRE DAY ON FRIDAY...EVEN MODEST SNOW RATIOS SHOULD BRING VALUES CLOSE TO 6 OR MORE INCHES. FURTHER SOUTH...THE CHANGEOVER TO RAIN SHOULD CUT DOWN ON ACCUMULATION AND POINTS SOUTH OF I-70 ARE MOST LIKELY TO SEE THE LONGEST PERIOD OF RAIN AT THIS POINT. A CHANGEOVER BACK TO SNOW IS EXPECTED EVERYWHERE OVERNIGHT SUNDAY AS COLD ADVECTION RETURNS WITH THE DEPARTURE OF THE LOW. SUBSIDENCE WILL QUICKLY END SNOWFALL FOR MOST OF THE AREA BY MONDAY MORNING...WITH LINGERING SNOW POSSIBLE IN THE RIDGES. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... A WARM UP IN TEMPERATURES EXPECTED EARLY ON IN THE EXTENDED AS TROUGHING DEEPENS OVER THE WESTERN US AND SOUTHWESTERLY FLOW SETS UP ACROSS THE EASTERN STATES. A CLOSED-OFF AREA OF LOW PRESSURE EJECTING OUT OF THE DESERT SOUTHWEST EARLY IN THE WEEK WILL START TO TRANSITION EAST MONDAY AND HELP DRAG IN MOISTURE OFF THE SOCAL COAST INTO THE STRONG SOUTHWESTERLY FLOW...WITH ADDITIONAL MOISTURE POOLING IN FROM THE GULF. ENSEMBLE MEMBERS ARE SHOWING MINIMAL SPREAD IN THIS SETUP...WHICH MAY RESULT IN A SIGNIFICANT AMOUNT OF PRECIPITATION THROUGH THE MIDDLE OF THE WEEK ACROSS THE REGION. FORECAST PWAT VALUES ARE AROUND THE 99TH PERCENTILE BY WEDNESDAY OVER THE AREA AND IVT VALUES ARE SHOWING A BULLS EYE OVER THE REGION. THIS...COMBINED WITH THE ADDITIONAL SNOW ACROSS THE NORTH AND A RIPER SNOWPACK TO THE SOUTH RAISES FLOODING CONCERNS. WE WILL BE FOLLOWING THIS CLOSELY IN UPCOMING MODEL RUNS. SEE HYDROLOGY SECTION BELOW. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... VFR CONDITIONS WILL PERSIST OVERNIGHT AMID LIGHT WIND...AND THROUGH SATURDAY AS THE CENTER OF HIGH PRESSURE MOVES EAST OF THE AREA. OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/... RESTRICTIONS ARE LIKELY SUNDAY INTO EARLY MONDAY...AND AGAIN TUESDAY NIGHT AND WEDNESDAY AS LOW PRESSURE SYSTEMS CROSS THE REGION. && .HYDROLOGY...
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FIRST SIGNIFICANT RIVER RISE OF THE SEASON EXPECTED TUESDAY AND WEDNESDAY MAR 3 AND 4... GIVEN THE FACT THAT MANY OF THE AREA RIVERS... TRIBUTARIES AND SMALLER STREAMS AND CREEKS ARE COVERED OVER WITH ICE... A DRAMATIC INCREASE IN FLOW AND STAGE LEVELS WILL CAUSE ICE MOVEMENT STARTING TUESDAY MAR 3. CURRENT FORECAST HAS A HIGH LEVEL OF UNCERTAINTY ABOUT MANY FACTORS...INCLUDING RAIN AMOUNT...TEMPERATURE...SNOW MELT AND ICE MOVEMENT. SMALL STREAMS AND TRIBUTARIES WILL BE FIRST AFFECTED TUESDAY MAR 3. RISES ON THE MAJOR RIVERS ARE PROJECTED TO OCCUR STARTING TUESDAY NIGHT AND CONTINUE THROUGH WEDNESDAY MAR 4.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY MORNING FOR PAZ007>009-013>016. WV...NONE. && $$

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