Area Forecast Discussion
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000
FXUS61 KPBZ 012346
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
646 PM EST SUN MAR 1 2015

.SYNOPSIS...
SNOW WILL WIND DOWN OVERNIGHT. A SECOND STORM...ACCOMPANIED BY
MILDER TEMPERATURES...WILL BRING POTENTIALLY HEAVY RAINFALL TO
THE REGION TUESDAY AND TUESDAY NIGHT...LIKELY BEGINNING AS A
PERIOD OF SLEET AND FREEZING RAIN EARLIER IN THE DAY. ICE
ACCUMULATIONS ARE POSSIBLE.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
BACK EDGE OF SNOW IS MOVING INTO OHIO. WITH THE SPEED THAT
PRECIPITATION IS MOVING TO THE EAST...HAVE SPED UP THE TIMING THAT
PRECIPITATION WILL DIMINISH...AND MAY STILL NOT HAVE BEEN
AGGRESSIVE ENOUGH. AS FOR PRECIPITATION TYPE ITSELF...RAIN/SNOW
LINE HAS MADE IT AS FAR NORTH AS PITTSBURGH AND LATROBE.
HOWEVER...THE NWS OFFICE NEAR PITTSBURGH INTERNATIONAL AIRPORT HAS
ONLY REPORTED SNOW...WHILE ALLEGHENY COUNTY AIRPORT NEAR DOWNTOWN
HAS MANAGED TO SWITCH OVER TO SNOW. EVEN THE HIGHER ELEVATIONS IN
GARRETT AND TUCKER COUNTIES HAVE SWITCHED OVER TO RAIN...WITH
MORGANTOWN REPORTING 40 DEGREES. ALL PRECIPITATION WILL CHANGE
BACK OVER TO SNOW BY MIDNIGHT...BUT WITH PRECIPITATION DECREASING
BY THAT TIME...THAT SHOULD HELP LIMIT ANY LARGE ACCUMULATIONS OF
SNOW AFTER MIDNIGHT. IN ADDITION...SNOW RATIOS HAVE BEEN VERY LOW
CONSIDERING TEMPERATURES ARE SO CLOSE TO FREEZING...WITH A 6:1
RATIO BEING OBSERVED LOCALLY. THE VERY WET SNOW CONTINUES TO MELT
ON CONTACT IN MANY LOCATIONS. WITH PRECIPITATION CONTINUING AT
ALL LOCATIONS AT THIS TIME...NO CHANGES TO HEADLINES WILL BE MADE
AT THIS TIME. WITH THE EXTENSIVE CLOUD COVER
OVERNIGHT...TEMPERATURES WILL ONLY DROP INTO THE MID 20S. THESE
VALUES WILL BE THE FIRST TIME MUCH OF THE REGION HAS SEEN NEAR
NORMAL LOW TEMPERATURES IN AT LEAST A WEEK.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...

MONDAY AND MONDAY NIGHT:
------------------------

A BRIEF LULL IN THE ACTIVE PERIOD AS HIGH PRESSURE SLIDES ACROSS
THE REGION. WITH A FRESH SNOW PACK...HIGHS WILL STRUGGLE TO REACH
THE MELTING POINT TOMORROW EVEN WITH SOME SUNNY INTERVALS
EXPECTED.

AT FIRST GLANCE...WOULD EXPECT TEMPERATURES TO FREE FALL TOMORROW
NIGHT UNDER THE INFLUENCE OF HIGH PRESSURE AND FRESH SNOW. HOWEVER...
MODEL CROSS SECTIONS SHOW RAPID ADVANCEMENT OF MID-HIGH LEVEL
OVERCAST DURING THE EVENING AHEAD OF THE NEXT SYSTEM. THUS THIS
BECOMES A HUGE TIMING ISSUE OF HOW FAST READINGS PLUMMET DURING
THE EVENING BEFORE THE LONGWAVE RADIATION OUTBURST CEASES. HAVE
DROPPED LOW TEMPS CONSIDERABLY OVER THE NORTHEAST CWA WHERE
CONDITIONS ARE OPTIMAL THE LONGEST. VERY LOW CONFIDENCE
TEMPERATURE FORECAST...ESPECIALLY IN THE NORTHERN MOUNTAINS WHERE
THERE IS AN EQUAL POTENTIAL OF SEEING LOWS -5 TO -10...OR +5 TO
+10 DEPENDING ON THE TIMING OF CLOUD COVER. WILL GO LOW SINGLE
DIGITS FOR NOW ON A HEDGE...AND TEENS TO LOWER 20S ELSEWHERE.

TUESDAY AND TUESDAY NIGHT:
--------------------------

HIGHLIGHTS: A MAJOR STORM SYSTEM AND WARMER AIR WILL BRING
RAINFALL (POTENTIALLY HEAVY) TO THE REGION.
IMPACTS: INCREASING CONCERNS FOR BOTH RUNOFF AND ICE JAM INDUCED
FLOODING. ADDITIONAL CONCERNS ABOUT SIGNIFICANT FREEZING
RAIN/SLEET POTENTIAL EARLY IN THE EVENT.

NUMEROUS FORECAST CHALLENGES THIS PERIOD AS MODELS CONTINUE TO
DEPICT A TWO PART STORM PHASING AND DEEPENING AS IT CROSSES THE
GREAT LAKES BENCHMARK. THIS PUTS THE CWA WELL INTO THE WARM SECTOR
ALOFT...WITH ANOMALOUSLY HIGH MOISTURE CONTENT ROOTED IN BOTH THE
PACIFIC AND GULF. INFLUX OF DEEP MOISTURE...COUPLED WITH STRONG
AND PROLONGED WARM ADVECTION...AND A FAVORABLE JET STRUCTURE WILL
COLLECTIVELY BRING PERIODS OF MODERATE TO HEAVY RAIN TO THE REGION
TUESDAY AND TUESDAY NIGHT.

KEY ISSUE NUMBER 1 IS AT THE ONSET. HAVING STARTED THE DAY
OVERCAST WITH TEMPERATURES IN THE TEENS (IF NOT SINGLE
DIGITS)...IT SEEMS TO REASON THAT A SIGNIFICANT ICING EVENT IS
LIKELY TO OCCUR BETWEEN MID MORNING AND THE EARLY AFTERNOON
BEFORE PRECIPITATION DRAG/WARM ADVECTION WARM THE BOUNDARY LAYER
ABOVE FREEZING...PARTICULARLY OF CONCERN WOULD BE THOSE SAME
NORTHEAST COUNTIES. SLEET/FREEZING RAIN ARE ACCOUNTED FOR IN THIS
FORECAST UPDATE.

KEY ISSUE NUMBER 2 IS WITH THE QPF. SEVERAL ENSEMBLE MEMBERS
CONTINUE TO SHOW WIDESPREAD LIQUID QPF AMOUNTS ON THE ORDER
1-1.50" THROUGH TUESDAY NIGHT. THESE AMOUNTS ARE CERTAINLY
JUSTIFIED...ALBEIT HIGHLY UNUSUAL FOR EARLY MARCH. A RAIN EVENT OF
THIS MAGNITUDE...COUPLED WITH AN EXISTING HIGH-WATER CONTENT SNOW
PACK...FROZEN GROUND AND ICED-OVER RIVERS/CREEKS...CERTAINLY HAS
ME CONCERNED ABOUT FLOOD POTENTIAL -- BOTH FROM RUNOFF AND
POTENTIAL ICE JAMS AS TEMPERATURES WARM INTO THE 40S TO THE SOUTH.

KEY ISSUE NUMBER 3 IS WITH SURFACE TEMPERATURES. AS EXPECTED...A
HUGE MODEL SPREAD EXISTS WITH RESPECT TO HIGH TEMPERATURES ON
TUESDAY...NEVER MIND THE HOURLY TRANSITION. EXISTING SNOW
PACK...PREVIOUS MORNING LOWS...PRECIPITATION INTENSITY AND THERMAL
ADVECTION WILL ALL COMPETE TO WHAT LEADS TO A HIGH BUST POTENTIAL
FORECAST ON TEMPERATURES -- THEREBY PLAYING INTO BOTH
PRECIPITATION TYPE AND FLOODING POTENTIAL.

THIS IS A HIGH CONFIDENCE...POTENTIALLY HIGH IMPACT EVENT WITH
LOW CONFIDENCE DETAILS. HEADLINES FOR FREEZING RAIN AND/OR
FLOODING MAY BE NECESSARY OVER THE NEXT 24 HOURS. PERSONS ARE
URGED TO CLOSELY MONITOR FORECASTS OVER THE 24-36 HOURS.

BOOKBINDER

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
COLD FRONT CROSSES THE REGION TUESDAY NIGHT...REACHING THE MID-
ATLANTIC REGION AROUND DAWN WEDNESDAY. RAIN WILL CONTINUE TO FALL
AS THE FRONT PASSES THROUGH. WILL DECREASE POPS FROM NORTHWEST TO
SOUTHEAST WEDNESDAY WITH COLDER AND DRIER AIR ADVECTING IN. ANY
LINGERING PRECIPITATION WEDNESDAY AFTERNOON...WILL CHANGE TO SNOW
SHOWERS AS COLDER AIR RUSHES IN FROM THE NORTHWEST.

SURFACE HIGH MOVES IN THURSDAY...KEEPING THE REMAINDER OF THE LONG
TERM DRY AND COLD.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
IFR/OCCASIONAL LIFR CONDITIONS WILL CONTINUE THIS EVENING AS A
PASSING SHORTWAVE TROUGH CONTINUES TO SPREAD SNOW AND RAIN OVER
THE REGION. GENERAL IFR CEILINGS ARE EXPECTED TO CONTINUE THROUGH
THE NIGHT AS COLD ADVECTION ENSUES IN THE WAKE OF THE PASSING
SYSTEM...BUT IMPROVEMENTS TO MVFR...AND FINALLY VFR CAN BE
EXPECTED LATER ON MONDAY AS STRATOCU FINALLY GIVES WAY TO
BUILDING HIGH PRESSURE.

.OUTLOOK.../MONDAY NIGHT THROUGH FRIDAY/...
LOW PRESSURE CROSSING THE GREAT LAKES IS LIKELY TO SPAWN WIDESPREAD
RESTRICTIONS ONCE AGAIN BY TUESDAY AFTERNOON.

&&

.HYDROLOGY...
AN INCREASE IN FLOW AND STAGE IS EXPECTED TO CAUSE ICE MOVEMENT
STARTING TUESDAY...BEGINNING ON THE SOUTHERNMOST RIVER BASINS. THE
CURRENT FORECAST CONTINUES TO HAVE A HIGH LEVEL OF UNCERTAINTY ABOUT
PRECIPITATION PHASE AND AMOUNTS AS WELL AS THE DEGREE OF SNOW MELT.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR MDZ001.
OH...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR OHZ039>041-
     048>050-057>059.
PA...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR PAZ007>009-
     013>016-020>023-029-073>076.
WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR WVZ001>003-
     023-041.

&&

$$





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