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Area Forecast Discussion
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000
FXUS61 KPBZ 011934
AFDPBZ

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

.SYNOPSIS...
SIGNIFICANT SNOW ACCUMULATIONS ARE EXPECTED ACROSS
THE REGION THIS AFTERNOON INTO THIS EVENING. SNOW WILL MIX WITH
RAIN THIS AFTERNOON FROM PITTSBURGH TO INDIANA SOUTHWARD. 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. TEMPERATURES
WILL GRADUALLY TREND WARMER THROUGH WEDNESDAY...BEFORE COLDER AIR
RETURNS LATER IN THE WEEK.

&&

.NEAR TERM /THROUGH THIS EVENING/...

HIGHLIGHTS: WATER-LADEN SNOW (SNOW/RAIN MIX SOUTH) TO
CONTINUE THROUGH THIS EVENING...AND OVERNIGHT OVER THE EASTERN
RIDGES.

IMPACTS: A VERY HEAVY (WEIGHT) WET SNOW WILL MAKE SNOW REMOVAL
DIFFICULT. SLUSHY NATURE TO SNOW WILL MAKE UNTREATED ROADS VERY
SLICK AND HAZARDOUS.

AMALGAMATION OF SNOW REPORTS FROM VARIOUS SOURCES SHOWS THAT THE
SNOW MEASURING IS AN ART FORM THAT IS NOT WELL UNDERSTOOD NOR
UNIFORMLY MASTERED. FACTORING IN THE MICROPHYSICAL CHALLENGES OF
SURFACE TEMPS ABOVE FREEZING AND SNOW-LIQUID RATIOS AS LOW AS
5:1...AND THE HUMAN ISSUES LIKE MEASUREMENT INTERVALS AND
LOCATIONS...IT'S NO WONDER THAT HALF THE PEOPLE THINK THE FORECAST
IS SPOT ON AND THE OTHER HALF THINKS IT'S WRONG. MELTING...COMPACTION...
COMPRESSION...SETTLING...AND ALL THE OTHER ISSUES WE'VE NOT HAD TO
DEAL WITH DURING THE MANY RECENT BOUTS OF ARCTIC POWDER SNOW MAKE
THIS EVENT A GREAT CHALLENGE IN COMMUNICATION. THUS THE FOCUS
SHOULD REMAIN ON IMPACTS.

IN A NUTSHELL...NO CHANGES TO THE PREVIOUS MID MORNING UPDATE. AS
EXPECTED...IT'S TAKEN EVERY BIT OF 35F 2-METER TEMPERATURES FOR
RAIN TO MIX IN FROM PITTSBURGH SOUTHWARD WITH A DEEP ISOTHERMAL
LAYER ALOFT JUST BELOW 0C. ELSEWHERE...SURFACE TEMPS ARE GENERALLY
AT OR JUST ABOVE FREEZING ACROSS ALL BUT THE FAR NORTHERN
TIER...AND EXPECT SNOW TO CONTINUE IN THESE AREAS FOR THE
DURATION. PRIMARY FOCUS FOR THIS AFTERNOON WILL BE ALONG AND SOUTH
OF ZZV-BVI-DUJ WHERE STRONGER LIFT REMAINS AND TERRAIN ACTS TO
ENHANCE THE SOUTHWEST FLOW. SEVERAL ADDITIONAL INCHES OF "MELT AS
IT FALLS" SNOW ARE LIKELY THROUGH EARLY EVENING BENEATH A RATHER
PRONOUNCED DENDRITIC GROWTH ZONE. A WEST-TO-EAST TEMPORARY LULL IN
THE PRECIP MAY ALSO OVERSPREAD THE AREA AFTER 20Z...WHERE A
TEMPORARY SWITCH TO DRIZZLE MAY OCCUR...BUT THIS SHOULD BE BE
SHORT-LIVED AS ADDITIONAL BANDING DEVELOPS FURTHER WEST.

BOOKBINDER

&&

.SHORT TERM /LATE TONIGHT THROUGH TUESDAY/...

OVERNIGHT:
----------
HIGHLIGHTS: ANY RAIN/MIX CHANGES BACK TO SNOW WITH
FRONTAL PASSAGE. SNOW ENDS EXCEPT LAUREL HIGHLANDS & MD/WV RIDGES
WHERE IT COULD BECOME HEAVY AT TIMES THIS EVENING. GUSTY WINDS
DEVELOPING ACROSS THE RIDGES AS WELL.

FOR MOST OF THE CWA...SNOW SHOULD TAPER OFF WEST-EAST THIS EVENING WITH
THE PASSAGE OF A WEAK COLD FRONT. THE PRIMARY IMPACT OVERNIGHT
WILL BE A RE-FREEZE AS TEMPERATURES SETTLE BACK INTO THE LOW-MID
20S. COULD EVEN SEE SOME AREAS OF FREEZING FOG DEVELOP IF THE WINDS
DECOUPLE SUFFICIENTLY. SOME CLEARING POSSIBLE LATE OVER OHIO AND
POSSIBLY THE NRN WV PANHANDLE TOWARD DAYBREAK.

FOR THE EASTERN RIDGES...SNOW MAY ACTUALLY INCREASE IN INTENSITY
THIS EVENING AS THE COLD FRONT DOES NOT APPEAR TO BE DEEP ENOUGH
TO CLEAR THE HIGH TERRAIN. STRONG WESTERLY MOMENTUM AND UPSLOPE
FLOW WILL LIKELY RESULT...YIELDING A PERIOD OF POTENTIALLY HEAVY
SNOW AND GUSTY WINDS FROM 03-09Z. THIS IS WHERE MOST OF THE 6-8"
TOTAL SNOWFALL FORECAST ALONG THE RIDGES IS ACCOUNTED FOR IN THE
PREVIOUS UPDATE.

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 /18Z SUNDAY THROUGH FRIDAY/...
IFR/OCCASIONAL LIFR CONDITIONS WILL CONTINUE INTO THE EARLY
EVENING IN LOW CIG/VIS FROM SN. RAIN WILL MIX IN AT SEVERAL
TERMINALS...ESPECIALLY SOUTH OF I-70...WHICH COULD ALLOW FOR
TEMPORARY IMPROVEMENT TO MVFR. NORTH OF PIT...PRECIP REMAINS ALL
SNOW WHICH WILL LOCK IN IFR. CIGS AT IFR/MVFR WILL BE MAINTAINED
THROUGH THE NIGHT AS ANY MIXED PRECIP CHANGES BACK OVER TO SNOW.
SLOW IMPROVEMENT BEGINS AFTER MIDNIGHT AS SNOW TAPERS FROM WEST TO
EAST...WITH MVFR CIGS MAINTAINING THROUGH THE REST OF THE TAF
PERIOD. SW WINDS THIS AFTERNOON AROUND 10 KNOTS WILL SETTLE
TOWARDS WEST WITH TIME.  CL

.OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... 
CEILING RESTRICTIONS LIKELY WILL PERSIST THROUGH MUCH OF MONDAY.
LOW PRESSURE CROSSING THE GREAT LAKES IS LIKELY TO SPAWN
WIDESPREAD RESTRICTIONS ONCE AGAIN BY LATE TUESDAY.

&&

.HYDROLOGY...
MANY OF THE AREA RIVERS AND STREAMS ARE ICE COVERED. 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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