Area Forecast Discussion
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000
FXUS61 KPBZ 282322
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
622 PM EST SAT FEB 28 2015

.SYNOPSIS...
LOW PRESSURE WILL SPREAD SNOW AND RAIN OVER THE UPPER OHIO REGION
ON SUNDAY. WARMER...MORE SEASONABLE...WEATHER CAN BE EXPECTED FOR
THE COMING WEEK.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
NO CHANGES WERE NEEDED FOR THE EARLY EVE UPDATE.

PREVIOUS...
BROAD WARM ADVECTION WILL BE THE MAIN DRIVER OF PRECIPITATION
THROUGH THE PERIOD...UNTIL FROPA SUNDAY NIGHT. A FRONTAL BOUNDARY
WILL START TO ORGANIZE TO THE NORTHWEST OF THE CWA ON SUNDAY...
WITH MOIST SW FLOW OVER OUR AREA. THIS WILL ALSO PUSH WARMER AIR
NORTHWARD. SHORTWAVE CROSSES THE GREAT LAKES SUNDAY NIGHT AND ACTS
AS THE IMPETUS TO GET THE FRONT MOVING...AND EXPECT IT TO CROSS BY
06Z MONDAY. COLDER AIR THEN SPILLS BACK IN BEHIND. MODELS ARE IN
GENERAL AGREEMENT WITH THIS PATTERN.

EXPECT FIRST FLAKES TO ARRIVE NEAR ZZV AROUND MIDNIGHT...AND
SPREAD EAST FROM THERE. EXPECT MOST POINTS TO SEE SNOW BY 12Z AS
LIFT FED BY WARM ADVECTION AND A MODEST ISENTROPIC CONTRIBUTION
BECOMES MORE WIDESPREAD. EXPECTING RAIN TO MIX IN LATER IN THE
MORNING AS THE TRUE LOW-LEVEL WARM PUNCH ARRIVES. ICING THREAT IS
FAIRLY LOW OVERALL WITH NOT MUCH OF A WARM LAYER ALOFT...BUT COULD
SEE A TRACE OF ICING FROM FZRA/IP ACROSS SOME OF THE SOUTHERN
COUNTIES AT THE BEGINNING OF THE CHANGEOVER. EXPECT THE RAIN/SNOW
MIX TO REACH AS FAR NORTH AS BVI/IDI...WITH A PERIOD OF ALL RAIN
AT SOUTHERN SITES LIKE MGW...AND MOSTLY SNOW TO THE NORTH.
CHANGEOVER BACK TO SNOW WILL OCCUR AFTER 00Z AS COLD ADVECTION
RETURNS BEHIND FRONT.

REGARDING SNOW AMOUNTS...AM STILL NOT IMPRESSED BY SNOW RATIOS
GIVEN THE WARM INTRUSION. DESPITE EXPECTING MOSTLY SNOW ACROSS THE
NORTH...THE EXPECTED LOW RATIOS...DROPPING TO AROUND 12 TO 1
SUNDAY ACROSS THE NORTH AND LOWER TO THE SOUTH... PLUS THE
24-30 HOUR DURATION OF THE STORM... POINT TO THE NEED FOR A HIGH-END
ADVISORY RATHER THAN A WARNING. SURROUNDING OFFICES AGREED TO
THIS...AND WE ENDED UP WITH A BROAD WINTER WEATHER ADVISORY.
TOTALS RANGE FROM 6-8 INCHES IN 24-30 HOURS ACROSS THE FAR
NORTH...TO 3-6 IN A RIBBON FROM ZZV THROUGH PIT TO LBE...AND 3 OR
LESS TO THE SOUTHEAST. KEEP IN MIND THAT A MIX WITH OR CHANGE TO
RAIN WILL OCCUR FOR MUCH OF THE AREA...SO SOME OF THE INITIAL
SNOWFALL WILL MELT ON THE GROUND IN RAIN. KEPT SEVERAL SOUTHERN
COUNTIES OUT OF THE ADVISORY GIVEN LESSER SNOW TOTALS AND NO
SIGNIFICANT ICING.

EXPECT PRECIPITATION TO START TO WIND DOWN LATER SUNDAY NIGHT AS
DEEPER MOISTURE PULLS OFF TO THE EAST AND SUBSIDENCE TAKES OVER.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
SNOW WILL BE WINDING DOWN ACROSS THE AREA ON MONDAY MORNING AS
HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST. SNOW SHOWERS
ALONG THE RIDGES WILL PERSIST UNTIL INVERSION HEIGHT LOWERS
SUFFICIENTLY...LIKELY BY LATE MONDAY AFTERNOON.

AGGRESSIVE SOUTH-SOUTHWESTERLY 850MB JET WILL STRENGTHEN MONDAY
NIGHT...PROMOTING ADVECTION OF ANOMALOUSLY POTENT WARM AND MOIST
AIR FROM THE GULF OF MEXICO. LIGHT PRECIPITATION IN THIS WARM AIR
ADVECTION REGIME WILL BEGIN TO ENCROACH ON THE FORECAST AREA LATE
MONDAY NIGHT AND RAPIDLY ACROSS THE REGION TUESDAY MORNING.
PRECIPITATION LIKELY WILL BEGIN AS LIGHT SNOW AS OVERNIGHT
TEMPERATURES WILL DROP INTO THE MID-UPPER TEENS.

IN RESPONSE TO DEEPENING LOW PRESSURE IN ILLINOIS...WIND WILL
SHIFT TO THE EAST-SOUTHEAST LATE MONDAY NIGHT...WHICH WILL DO
LITTLE TO VACATE THE VERY COLD LOW-LEVEL AIRMASS DESPITE THE
STRONG WARM AIR ADVECTION ALOFT. HISTORICALLY...SOUTHERLY WIND
DIRECTION IS NEEDED TO ERADICATE LOW-LEVEL COLD AIR...WHICH WILL
NOT OCCUR UNTIL LATER IN THE DAY TUESDAY WHEN SURFACE LOW
PRESSURE NEARS. AS A RESULT...THE ATMOSPHERE WILL BE PRIMED FOR
THE EARLY LIGHT SNOW TO TRANSITION TO A PERIOD OF FREEZING RAIN/SLEET
ON TUESDAY MORNING. WEATHER AND ICE GRIDS WERE ADJUSTED TO REFLECT
THIS EXPECTATION.

SURFACE TROUGH AND COLD FRONT WILL ENCROACH UPON THE AREA TUESDAY
LATE AFTERNOON AND EVE...WITH SURFACE LOW PRESSURE PASSING TO THE
NORTHWEST OF THE FORECAST AREA. THE OHIO VALLEY WILL BE SOLIDLY IN
THE WARM SECTOR AS WIND VEERS TO SOUTHWESTERLY...HELPING TO ERODE
THE LOW-LEVEL COLD AIR AND CHANGE ALL PRECIPITATION TO RAIN.

ALL MODELS AND MOS GUIDANCE OFFER STRONG EVIDENCE OF MEASURABLE
PRECIPITATION OCCURRING TUESDAY NIGHT...FOCUSED IN PART BY THE
APPROACHING BOUNDARY. POPS WERE INCREASED TO 100 PERCENT DURING
THIS TIME PERIOD TO REFLECT THIS EXPECTATION...TIMED WITH THE
PASSAGE OF THE BOUNDARY.

THERE IS A GOOD SYNOPTIC SIGNAL FOR AN ANOMALOUS RAINFALL EVENT
WITH THIS SYSTEM...AMID STRONG MOISTURE FLUX /PWATS APPROACHING
MAXIMUM CLIMATOLOGICAL VALUES/ AND PERSISTENT SOUTHWESTERLY LOW-
LEVEL FLOW. THAT SAID...MODELS ALSO TEND TO OVERDO QPF IN WARM AIR
ADVECTION PATTERNS. GIVEN THAT THIS SYSTEM IS AN OPEN WAVE AND
PRECIPITATION IS DRIVEN IN PART BY WARM ADVECTION...QPF ON TUESDAY
WAS TONED DOWN SLIGHTLY FROM THE MORE ASSERTIVE GFS VALUES.

TEMPERATURES TUESDAY NIGHT LIKELY WILL CLIMB OR REMAIN STEADY IN
THE 40S...PERHAPS WARMER THAN THEIR TUESDAY DAYTIME VALUES.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
COLD AIR ADVECTION IN THE WAKE OF THE TUESDAY NIGHT COLD FRONTAL
PASSAGE WILL RETURN THE REGION TO NEAR- OR SUB-FREEZING
TEMPERATURES FOR THE REMAINDER OF THE WEEK. UPSLOPE SNOW SHOWERS
LIKELY WILL PERSIST THROUGH WEDNESDAY EVENING...BUT SHOULD SEE A
MARKED DECREASE IN COVERAGE BY LATE WEDNESDAY NIGHT.

A QUICK-MOVING SHORTWAVE TROUGH COULD AFFECT THE REGION LATE IN
THE WEEK WITH LITTLE FANFARE ANTICIPATED. THE DRY AIRMASS AT THE
SURFACE PRECLUDES SIGNIFICANT IMPACTS AT THE MOMENT SAVE MODEST
LAKE-ENHANCED SNOW.

&&

.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
SNOW IS EXPECTED TO DEVELOP LATE TONIGHT...AROUND 6Z NEAR ZZV TO
AROUND 9Z NEAR LBE/DUJ. ONCE SNOW COMMENCES...CONDITIONS WILL
DETERIORATE TO IFR BY MORNING.

SNOW WILL MIX WITH AND CHANGE TO RAIN AT MOST TERMINALS /EXCEPT
FKL AND DUJ/ MID-DAY...WITH MGW SEEING MOSTLY RAIN THRU THE DAY. A
WIND SHIFT IS EXPECTED SUNDAY EVE ASSOCIATED WITH A COLD FRONTAL
PASSAGE. PRECIPITATION WILL CHANGE BACK TO SNOW IN THE WAKE OF
THE COLD FRONT.

.OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/...
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 FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR MDZ001.
OH...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR OHZ039>041-048>050-057>059.
PA...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR PAZ007>009-013>016-020>023-029-073>076.
WV...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 7 AM EST MONDAY
     FOR WVZ001>003-023-041.

&&

$$

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