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Area Forecast Discussion
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000
FXUS61 KPBZ 201912
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
212 PM EST SAT DEC 20 2014

.SYNOPSIS...
HIGH PRESSURE IN CONTROL INTO MONDAY. INCREASING PRECIPITATION
CHANCES TUESDAY. STORM SYSTEM BRINGS RAIN AND WIND CHRISTMAS
EVE...AND SNOW SHOWERS CHRISTMAS DAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
WEAKER INVERSION ACROSS PORTIONS OF SOUTHERN PA HAS ALLOWED LOWER 
CLOUDS TO BREAK UP SOMEWHAT...ALTHOUGH THEY ARE HANGING TOUGH SO FAR 
ACROSS THE NORTHERN COUNTIES NEAR FKL/DUJ AS WELL AS IN SOUTHEAST 
OHIO.  EXPECT THESE TO REFORM TONIGHT AS INVERSION SHARPENS UP AGAIN 
IN VERY WEAK FLOW...THUS GOING MOSTLY CLOUDY MOST AREAS.  GOING TO HANG 
ON TO SLIGHT CHANCE POPS IN THE SOUTHEAST WITH SHORTWAVE TROUGH 
MOVING ACROSS AND SLIGHTLY BETTER MOISTURE PROFILE...BUT SNOW 
ACCUMULATION IS NOT EXPECTED.  THIS POSSIBILITY ENDS BY 09Z. ONLY 
MINOR MODIFICATION TO GENERALLY SEASONABLE TEMPERATURES.

INVERSION IS MAINTAINED SUNDAY MORNING...BUT BY AFTERNOON EXPECT 
STRATUS TO MIX OUT INTO A CU FIELD AND THEN SCATTER OUT BY EVENING.  
A BIT MORE SUN SHOULD ALLOW FOR AFTERNOON HIGH TEMPS AROUND 5 
DEGREES WARMER THAN TODAY. CL

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
BENIGN WEATHER INITIALLY WITH HIGH PRESSURE TO OUR EAST AND IN 
CONTROL.  SOUTHEAST WINDS IN RESPONSE TO SURFACE ANTICYCLONE 
POSITION WILL FACILITATE DEVELOPMENT OF STRATUS OVER EASTERN 
PORTIONS OF TUCKER AND GARRETT COUNTIES MONDAY INTO MONDAY NIGHT. 
PCPN ONSET HAS SLOWED DOWN FROM PREVIOUS CYCLES...BUT THERE REMAINS 
A VERY LOW PROBABILITY OF FREEZING RAIN AND/OR SLEET OVER 
AFOREMENTIONED AREAS MONDAY.  FOR NOW...TRENDED FORECAST WITH PCPN 
COMMENCING DURING THE AFTERNOON WHICH REFLECT LATEST NUMERICAL 
MODELS.  WITH THIS SCENARIO...LOW LEVEL SUB-FREEZING AIR SHOULD 
SCOUR OUT YIELDING AN ALL RAIN PTYPE.

RAIN SHADOW EFFECT TAKES PLACES TUESDAY WITH SOUTHEAST WINDS 
WIDESPREAD OVER THE REGION. AN ISOLATED SHOWER REACHING EASTERN OHIO 
AND FAR NWRN PA IS NOT OUT OF THE QUESTION...SO KEPT A SLIGHT 
CHANCE.  WOULD NOT BE SURPRISED TO SEE BREAKS IN THE CLOUDS WHICH 
COULD ALLOW FOR A FEW LOCATIONS TO EXCEED 60 DEGREES.  RECORD HIGHS 
FOR PITTSBURGH...MORGANTOWN...AND ZANESVILLE ALL RESIDE WELL INTO 
THE UPPER 60S...SO AT THIS JUNCTURE RECORD WARMTH IS NOT FORESEEN.  
PRECIP ASSOCIATED WITH THE SURFACE LOW PRESSURE SYSTEM EJECTING FROM 
THE GULF COAST REGION REACHES SERN AREAS OF THE FORECAST AREA THAT 
EVENING.

A BLEND OF THE ONGOING FORECAST AND BIAS CORRECTED ECMWF WERE USED 
FOR TEMPERATURES.  

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
HIGHLIGHTS:
- A WET CHRISTMAS EVE 
- TEMPERATURES RETURN BACK TO NORMAL VALUES CHRISTMAS DAY
- SLIGHTLY ABOVE NORMAL TEMPERATURES RETURN BY FRIDAY

STRONG LOW PRESSURE SYSTEM THAT HAS BEEN MUCH ADVERTISED GIVEN THE 
TIME PERIOD WHICH IT AFFECTS OUR AREA IS STILL ON TRACK.  LONG RANGE 
ENSEMBLE PREDICTION SYSTEMS AND OPERATIONAL MODELS ARE CONVERGING ON 
A TRACK THROUGH IND / ILL THEN NORTH INTO CANADA.  THIS WILL MAKE 
FOR ALL LIQUID PRECIPITATION ON THE FRONT END.  TEMPERATURES WILL 
SOAR TO NEARLY 20 DEGREES ABOVE NORMAL WEDNESDAY WITH 50S COMMON.  
COUPLED WITH INFLUX OF MOISTURE FROM THE GULF OF MEXICO...SOUNDINGS 
ILLUSTRATE ELEVATED INSTABILITY WHICH PUSHES TEMP DIFFERENTIAL 
BETWEEN H8 AND H5 TO NEARLY 0C.  THIS COULD LEAD TO ISOLATED 
THUNDERSTORMS AHEAD OF THE BAROCLINIC ZONE.  FOR THE TIME 
BEING...OPTED TO LEAVE THUNDER OUT OF THE FORECAST AND WAIT FOR 
BETTER CONTINUITY GIVEN THIS STILL IS FIVE DAYS OUT.  DESPITE PWATS 
NEARLY TWO STANDARD DEVIATIONS ABOVE NORMAL...COMBINATION OF 
KATABATIC WINDS AND DRY CONVEYOR BELT WILL LIMIT QPF POTENTIAL TO 
NEGATE ANY FLOOD THREAT.  LONG RANGE HYDROLOGIC MODELS SHOW VERY 
LITTLE RISE IN AREA RIVERS...WHICH CORRELATES WELL TO THE PROJECTED 
QPF OF 0.50 TO 1.00".

WITH THE TRACK OF THE CYCLONE DUE N...COLD AIR INJECTED INTO THE 
AREA WILL BE OF MIDWEST ORIGIN...SO TEMPS WILL RETREAT BACK TO 
SEASONAL BENCHMARKS CHRISTMAS DAY.  FOR THOSE WHO ARE LOOKING FOR 
SNOW ON CHRISTMAS...A CHANCE OF SNOW SHOWERS EXIST...BUT GIVEN 
TRAJECTORY FROM THE SOUTHWEST ANY ACCUMULATION ASSOCIATED WITH THE 
UPPER LEVEL SYSTEM WILL BE LIGHT AT BEST.  HISTORICALLY...THERE IS 
ONLY A 17 PERCENT CHANCE OF AT LEAST ONE INCH OF SNOW ON THE GROUND 
AT PITTSBURGH CHRISTMAS MORNING. 

H8 WINDS PUSH 50KTS WEDNESDAY NIGHT INTO THURSDAY AND HIGHEST 
ANOMALIES RESIDE ALONG THE LAKE SHORE...SO EXPECT HIGHEST GUSTS 
WOULD DO SO AS WELL.  NONETHELESS...PERIOD FROM WEDNESDAY NIGHT INTO 
THURSDAY STRONG ISALLOBARIC FLOW COULD YIELD GUSTS IN EXCESS OF 40 
MPH ESPECIALLY IN THE MOUNTAINS OF WRN MD AND NRN WV.  

BALANCE OF THE EXTENDED IS CHARACTERIZED BY UNCERTAINTY AS ONE WOULD 
EXPECT IN THE DAY 6 -7 TIME FRAME.  ECMWF HAS A STRONGER SYSTEM 
CROSSING FRIDAY NIGHT VERSUS GFS WHICH IS MUCH WEAKER.  EITHER CASE 
PTYPE SHOULD BE RAIN WITH SNOW SHOWERS ON THE BACKSIDE.  NO PLUNGES 
OF ARCTIC AIR ARE FORECAST IN THE NEXT 10 DAYS.  MAX/MIN 
TEMPERATURES WERE A BLEND OF THE FORECAST AND ECMWF BIAS CORRECTED 
DATA SET.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
CLOUDS HAVE MANAGED TO THIN SOMEWHAT ACROSS SOUTHERN PA/NORTHERN
WV AND EXPECT THIS TO PERSIST FOR A FEW HOURS. HOWEVER...SW FLOW
WILL BRING A BIT MORE MOISTURE ALOFT...AS WELL AS WARM
ADVECTION...WHICH WILL HELP TO SHARPEN UP THE INVERSION ALOFT.
THUS...EXPECTING MOST AREAS TO SEE MVFR CIGS BECOME REESTABLISHED
BY THE LATE EVENING HOURS...AND PERSIST THROUGH THE REST OF THE
TAF PERIOD. CANNOT RULE OUT A FEW SNOWFLAKES TONIGHT IN LOCATIONS
LIKE MGW AND LBE...BUT THIS IS NOT EXPECTED TO CREATE ANY
RESTRICTIONS. ZZV COULD SEE SOME BREAKUP PAST 15Z THOUGH. WINDS
WILL REMAIN CALM OR VERY LIGHT.


OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/... 
NEXT STORM SYSTEM WILL BEGIN TO IMPACT THE REGION ON TUESDAY AND
RESULT IN WIDESPREAD RAIN...CIG/VIS RESTRICTIONS...AND PERIODS OF
LLWS INTO THURSDAY.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

$$






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