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Area Forecast Discussion
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000
FXUS61 KPBZ 281459
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
959 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/...
MINOR UPDATES TO TEMPERATURES AND SKY GRIDS FOR THE AFTERNOON.
TEMPERATURES RECOVERING FROM WIDESPREAD BELOW ZERO MINIMUMS AS
BOUNDARY LAYER INVERSION BREAKS...AND HIGHS IN THE 20S STILL
EXPECTED. AS SURFACE HIGH DEPARTS TO THE EAST...CLOUDS WILL BE
INCREASING THIS AFTERNOON IN WSW FLOW ALOFT AHEAD OF THE NEXT
WEATHER SYSTEM.  CL

&&

.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 /15Z 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 THRU
THURSDAY MAR 3 THRU 5...

MANY OF THE AREA RIVERS...THEIR TRIBUTARIES AS WELL AS SMALLER 
STREAMS AND CREEKS ARE ICE COVERED. 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 CRITICAL FACTORS 
...INCLUDING CHANGE OVER TO RAIN...RAINFALL AMOUNT...TEMPERATURE AND 
SNOW MELT. ICE MOVEMENT WILL INITIALLY BEGIN IN SMALL STREAMS AND 
TRIBUTARIES TUESDAY MAR 3 WITH A CASCADING EFFECT WHEN COUPLED WITH 
RAINFALL AND SNOWMELT RUNOFF STARTING TUESDAY NIGHT. RISES ON THE 
MAJOR RIVERS ARE PROJECTED TO BEGIN OCCURRING LATE TUESDAY NIGHT 
OVER THE SOUTHERNMOST RIVER BASINS. THESE RISES AND POSSIBLE ICE 
MOVEMENT WILL EXTEND FURTHER DOWNSTREAM THROUGH THURSDAY MAR 5.

&&

.CLIMATE...
RECORD LOW TEMPERATURES WERE SET THIS MORNING.  PIT TIED ITS
PREVIOUS RECORD LOW OF -1 SET IN 1934. ZZV SET A NEW RECORD LOW OF
-1...BREAKING THE OLD RECORD OF ZERO FROM 1947.

&&

.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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