Area Forecast Discussion
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000 FXUS61 KPBZ 271658 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1158 AM EST FRI FEB 27 2015 .SYNOPSIS... DRY CONDITIONS AND A WARMING TREND IN TEMPERATURES CAN BE EXPECTED AS WE HEAD INTO THE WEEKEND BEFORE THE NEXT AREA OF LOW PRESSURE RESULTS IN RAIN AND SNOW SUNDAY THROUGH MONDAY MORNING. && .NEAR TERM /THROUGH SATURDAY/... CUT BACK ON CLOUD COVER THIS MORNING THROUGH MIDDAY WHERE AT LEAST MOSTLY SUNNY CONDITIONS ARE EXPECTED. DESPITE THE MORE POTENT LATE FEBRUARY SUNSHINE...TEMPERATURES WILL REMAIN COLD THROUGH THE DAY AS COLD AIR CONTINUES TO ADVECT IN. COLDEST 850MB TEMPERATURES NEAR -22C WILL BE DIRECTLY OVERHEAD THIS AFTERNOON AS HIGH PRESSURE BUILDS. AS THE SUN SETS TONIGHT...TEMPERATURES WILL FALL QUICKLY UNDER CALM...DRY AND MOSTLY CLEAR CONDITIONS. THIS SHOULD OPTIMIZE RADIATIONAL COOLING FOR MOST LOCATIONS...ESPECIALLY THOSE LOCATIONS THAT RECEIVED A FRESH COATING OF SNOW. SFC HIGH PRESSURE WILL BE DIRECTLY OVER THE FORECAST AREA PRE-DAWN SATURDAY. MODELS CONTINUE TO SHOW WARMING OF THE MID-LEVELS TO THE TUNE OF 6 TO 8 DEGREES C ABOVE THE 00Z MINIMUMS. WITH A LACK OF FLOW BETWEEN THE SFC AND 750MB...A NEAR SFC INVERSION WILL DECOUPLE THE ATMOSPHERE AND DROP TEMPERATURES BELOW ZERO FOR MOST LOCATIONS...WELL BELOW ZERO ACROSS THE NORTHERN ZONES. AT THIS POINT...THE ONLY FLY IN THE OINTMENT FOR TEMPERATURES AS LOW AS FORECAST IS POSSIBILITY OF HIGH CLOUDS SHIELDING THE OUTGOING LONGWAVE RADIATION. THE 00Z NAM IS A LITTLE BIT FASTER IN INTRODUCING HIGH CLOUDS IN RESPONSE TO A WEAK UPPER LEVEL WAVE. ULTIMATELY TWEAKED SAT MORNING LOWS...WHICH INCLUDES BUMPING UP TEMPERATURES ACROSS THE SRN 1/2 OF THE CWA BY A DEGREE OR TWO. AFTER DAYBREAK SATURDAY...THE NEAR SFC TEMPERATURE INVERSION SHOULD MIX OUT AND ALLOW FOR A QUICK WARM-UP UNDER MOSTLY SUNNY CONDITIONS. TAX && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... LATEST MODEL RUNS SHOW RELATIVELY GOOD AGREEMENT FOR THE NEXT LOW PRESSURE SYSTEM TO IMPACT THE REGION...AND OVERNIGHT CHANGES TO THE FORECAST WERE BASED MAINLY ON A BLEND OF EC...GFS...AND ENSEMBLE GUIDANCE AS THE HPC PREFERRED SOLUTIONS...WITH LESS WEIGHT PUT ON THE SREF AND NAM. THIS TRENDS TOWARDS A MORE AMPLIFIED AND COLDER SOLUTION. PRECIPITATION WILL START OUT AS ALL SNOW...BUT BEGIN CHANGING OVER TO RAIN OVER THE COURSE OF THE MORNING AND NOW ANTICIPATE SNOW SLIGHTLY FARTHER TO THE SOUTH...AND A RAIN AND/OR RAIN/SNOW MIX MAINLY LIMITED TO LOCATIONS SOUTH OF INTERSTATE 80. LOOKING AT CRITICAL THICKNESSES THERE IS STILL SOME UNCERTAINTY...LARGELY SOUTH OF INTERSTATE 80 AS LOW LEVEL WARM AIR ADVECTION WILL BE STRONG ON SUNDAY WHICH IS REFLECTED IN THE 850-700MB VALUES. THEREFORE...HAVE HELD BACK FORECAST SNOW AMOUNTS SOUTH OF INTERSTATE 80 FOR NOW AS A CHANGEOVER TO RAIN ON SUNDAY AFTERNOON OR MIXED PRECIPITATION WILL IMPACT ACCUMULATIONS. NORTH OF I-80 SNOW AMOUNTS WERE INTRODUCED OR INCREASED AS FORECAST CONFIDENCE IN ALL SNOW IS HIGHER HERE...AND BASED ON THE LATEST HEADLINES MAY BE INTRODUCED SOON...AT LEAST FOR NORTHERN LOCATIONS. BY MONDAY MORNING...ANY ONGOING PRECIPITATION WILL HAVE CHANGED BACK OVER TO SNOW WITH COLD AIR ADVECTION ON THE BACKSIDE OF THE SYSTEM. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... 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 WILL 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 MORE RIPE SNOWPACK TO THE SOUTH RAISES FLOODING CONCERNS AND WILL BE FOLLOWING THIS CLOSELY IN UPCOMING MODEL RUNS. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... SNOW AND ASSOCIATED MVFR CLOUD COVER IS CONTINUING TO WANE THIS MORNING. THE LATEST SATELLITE IMAGERY REVEALS CLEARING SKIES WEST TO EAST. MVFR CEILINGS MAY HOLD IN MGW AND LBE THIS MORNING FOR A FEW MORE HOURS...BUT ALL SITES ARE EXPECTED TO BE VFR WITH MOSTLY CLEAR SKIES SHORTLY AFTER DAYBREAK. HIGH PRESSURE WILL ENSURE VFR CONDITIONS WITH WEAK SURFACE FLOW THROUGH THE BALANCE OF THE TAF PERIOD. TAX OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/... RESTRICTIONS ARE LIKELY WITH CROSSING LOW PRESSURE SUNDAY INTO MONDAY. && .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. CURRENTLY FORECAST HAS A HIGH LEVEL OF UNCERTAINTY ABOUT MANY FACTORS INCLUDING RAIN AMOUNT...TEMPERATURE...SNOWMELT...ICE MOVEMENT. SMALL STREAMS AND TRIBUTARIES WILL BE FIRST AFFECTED TUESDAY MAR 3. RISES ON THE MAJOR RIVERS IS PROJECTED TO OCCUR STARTING TUESDAY NIGHT AND CONTINE THROUGH WEDNESDAY MAR 4.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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