Area Forecast Discussion
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000 FXUS61 KPBZ 280917 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 417 AM EST SAT FEB 28 2015 .SYNOPSIS... CLOUD COVERAGE WILL INCREASE TODAY BEFORE RAIN AND SNOW IMPACT THE REGION SUNDAY THROUGH MONDAY MORNING. A SIGNIFICANT WARM-UP IS POSSIBLE TUESDAY INTO WEDNESDAY BEFORE COLD AIR RETURNS. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... LATEST OBSERVATIONS SHOW TEMPERATURES FALLING RAPIDLY OVER THE PAST SEVERAL HOURS AS WINDS HAVE GONE CALM AND CLOUD COVERAGE IS LIMITED. ANOTHER COUPLE DEGREE DROP IS EXPECTED BEFORE DAYBREAK...RESULTING IN MIN TEMPERATURES CLOSE TO RECORD VALUES. DRY CONDITIONS ARE EXPECTED TODAY WITH TEMPERATURES RECOVERING INTO THE TWENTIES AS SURFACE HIGH PRESSURE SLOWLY TRANSITIONS OVER THE AREA. MID AND UPPER LEVEL CLOUD COVERAGE WILL INCREASE THIS AFTERNOON AHEAD OF THE NEXT AREA OF LOW PRESSURE TO IMPACT THE REGION. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... MINIMAL CHANGES WERE MADE TO THE INHERITED SHORT TERM FORECAST AS MODELS HELD GOOD CONTINUITY WITH PREVIOUS RUNS. PRECIPITATION WILL SPREAD ACROSS THE REGION EARLY SUNDAY MORNING IN THE FORM OF SNOW BUT WILL BEGIN CHANGING OVER TO MIXED PRECIPITATION AND RAIN OVER THE COURSE OF THE MORNING. THIS CHANGEOVER STILL LOOKS TO BE LIMITED TO LOCATIONS SOUTH OF INTERSTATE 80. SNOW RATIOS SHOULD BE NOTHING TOO IMPRESSIVE WITH THE STRONG WARM AIR ADVECTION IN THE LOWEST LEVELS AND FORECAST SOUNDINGS ACROSS NORTHERN COUNTIES WHICH SHOW NEAR ISOTHERMAL AND SATURATED PROFILES UP TO OVER 10KFT WARMER THAN -8C...WHICH SHOULD GIVE RATIOS NO MORE THAN 10:1 AND LIKELY LESS AS MOST CRYSTAL GROWTH SHOULD BE VIA DEPOSITION RATHER THAN AGGREGATION GIVEN THE SATURATED AND RELATIVELY WARM PROFILE. DESPITE THIS...QPF AMOUNTS ARE STILL PROGGED TO BE RATHER HIGH AND FOR THE NORTHERN LOCATIONS WHERE PRECIPITATION TYPE SHOULD BE MAINLY SNOW...AND SNOW AMOUNTS GREATER THAN 6 INCHES STILL LOOK POSSIBLE IN THE END. THEREFORE...THEN WINTER STORM WAS LEFT UNCHANGED OVERNIGHT...OPTING TO WAIT ANOTHER MODEL RUN AS THERE IS STILL SOME UNCERTAINTY ON THE NORTHWARD REACH OF SIGNIFICANT WARM AIR ADVECTION. LOCATIONS SOUTH OF INTERSTATE 80 WILL SEE A CHANGEOVER TO RAIN OR MIXED PRECIPITATION SUNDAY AFTERNOON...WHICH WILL SIGNIFICANTLY IMPACT ACCUMULATIONS. 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 /TUESDAY THROUGH FRIDAY/... LOW PRESSURE WILL DEEPEN AS IT MOVES INTO THE MIDWEST MONDAY NIGHT AND TUESDAY MORNING. PRECIP WILL BEGIN TO OVERSPREAD THE AREA TUESDAY MORNING. TIMING OF THE ONSET WILL NEED TO BE ADJUSTED AS THE SYSTEM IS LIKELY TO SLOW AS THE LOW DEEPENS. COULD SEE A WINTRY MIX AT THE ONSET UNTIL THE COLDER AIR ALOFT AND AT THE SURFACE IS FORCED NORTHWARD. THE ASPECT OF THE SYSTEM THAT WILL NEED TO BE CLOSELY WATCHED IS THE HIGH AMOUNTS OF RAINFALL THAT ARE POSSIBLE AS IT MOVES THROUGH. COLDER AIR WILL MOVE BACK INTO THE AREA WEDNESDAY WITH THE PASSAGE OF THE COLD FRONT. A SECONDARY WAVE WILL DEVELOP WEDNESDAY AFTERNOON OVER THE SOUTHEASTERN US ALONG THE FRONT. THIS COULD PUSH SOME PRECIP NORTHWARD LATE WEDNESDAY INTO THURSDAY. COLD AND DRY TO END THE LONG TERM. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... VFR CONDITIONS WILL PERSIST THROUGH SATURDAY. WINDS WILL BE LIGHT. .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... 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. && .CLIMATE... RECORD LOW TEMPERATURES ARE FORECASTED THIS MORNING AT MANY SITES. THE TABLE BELOW ILLUSTRATES THE FORECASTED TEMPERATURE AND THE RECORD LOW TEMPERATURE FOR 28 FEB. SITE RECORD FCST LOW TEMP LOW ---- -------- ---- PIT -1F /1934/ -1F MGW 6F /1986/ 1F ZZV 0F /1947/ -2F && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...WINTER STORM WATCH FROM LATE TONIGHT THROUGH MONDAY MORNING FOR PAZ007>009-013>016. WV...NONE. && $$

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