-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 271830 AAC
AFDPBZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
130 PM EST FRI FEB 27 2015

.SYNOPSIS...
DRY CONDITIONS AND A SLIGHT WARMING TREND IN TEMPERATURES CAN BE
EXPECTED AS WE HEAD INTO THE WEEKEND BEFORE LOW PRESSURE PROVIDES
RAIN AND SNOW SUNDAY THROUGH MONDAY MORNING. A SIGNIFICANT WARMUP
IS POSSIBLE TUESDAY INTO WEDNESDAY BEFORE COLD AIR RETURNS.

&&

.NEAR TERM /THROUGH SATURDAY/...
ANY LINGERING SNOW SHOWERS WILL DISSIPATE QUICKLY THIS AFTERNOON
AS HIGH PRESSURE BUILDS INTO THE REGION. SKY WILL CLEAR
CONSIDERABLY AMID SUBSIDENCE...SNOW COVER AND LIGHT WIND...
PROMOTING CONDITIONS THAT WILL BE FAVORABLE FOR EFFECTIVE
RADIATIONAL COOLING TONIGHT.

THE ONLY FLY IN THE PROVERBIAL OINTMENT WILL BE INCREASING CIRRUS
DEPICTED IN THE MODELS ASSOCIATED WITH A MID-LEVEL JET STREAK. THE
CIRRUS SHOULD NOT BE THICK ENOUGH TO INHIBIT COOLING BY ANY
RADICAL MARGIN...SO SHARP COOLING CONTINUES TO BE EXPECTED. MINIMA
TONIGHT MAY REACH NEAR-RECORD LOW FOR 28 FEB. SEE CLIMATE SECTION
BELOW.

THE DAY WILL START EXCEPTIONALLY COLD ON SATURDAY. HIGH PRESSURE
WILL DOMINATE THE WEATHER ON SATURDAY. SKY WILL BE MOSTLY CLEAR
THROUGH EARLY AFTERNOON AS VERY DRY AIR INVADES...OFFERING FULL
SUN AND A SHARP TEMP INCREASE INTO THE 20S BY AFTERNOON. CIRRUS
AHEAD OF AN APPROACHING TROUGH WILL BEGIN TO INFILTRATE LATE IN
THE DAY ON SATURDAY.

MODEL TRENDS HAVE BEEN TOWARD A FASTER ONSET OF PRECIPITATION WITH
A SYSTEM ON SUNDAY...WITH LIGHT SNOW EXPECTED TO DEVELOP LATE
SATURDAY NIGHT AS A WARM FRONT SHARPENS FROM WESTERN PA THRU OH TO
AN ORGANIZING LOW PRESSURE SYSTEM IN EASTERN INDIANA. POPS WERE
INCREASED SLIGHTLY FROM PREV SHIFT...WHICH ALREADY HAD A WELL-
TIMED RAPID ONSET OF SNOW.

&&

.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. 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. 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 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 RIPER SNOWPACK TO THE SOUTH RAISES FLOODING
CONCERNS. WE WILL BE FOLLOWING THIS CLOSELY IN UPCOMING MODEL
RUNS.  SEE HYDROLOGY SECTION BELOW.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
SCATTERED SNOW SHOWERS VCTY KLBE AND KMGW WILL DISSIPATE QUICKLY
AS SFC HIGH PRESSURE BUILDS INTO THE REGION. VFR CONDITIONS WILL
PERSIST OVERNIGHT AMID LIGHT WIND...AND THROUGH SATURDAY AS THE
CENTER OF HIGH PRESSURE MOVES ACROSS THE AREA.

CIRRUS WILL INCREASE SATURDAY EVENING AHEAD OF AN APPROACHING
SYSTEM. LIGHT SOUTHERLY WIND AND A RAPID ONSET OF LIGHT SNOW ARE
EXPECTED LATE SATURDAY NIGHT...WITH LIGHT SNOW DEVELOPING AT ALL
TERMINALS BY MID-MORNING SUNDAY.

RESTRICTIONS IN SNOW/RAIN CAN BE EXPECTED AT ALL TERMINALS ON
SUNDAY. A SHARP WIND SHIFT TO THE NORTHWEST IS EXPECTED IN THE
WAKE OF THE SYSTEM AS A COLD FRONT TRAVERSES THE OHIO VALLEY.


OUTLOOK.../MONDAY THROUGH WEDNESDAY/...
RESTRICTIONS ARE LIKELY AS LOW PRESSURE YIELDS WIDESPREAD RAIN
TUESDAY NIGHT AND WEDNESDAY.

&&

.CLIMATE...
RECORD LOW TEMPERATURES ARE FORECASTED TONIGHT AT MANY SITES. THE
TABLE BELOW ILLUSTRATES THE FORECASTED TEMPERATURE AND THE RECORD
LOW TEMPERATURE FOR 28 FEB.

SITE  RECORD       FCST
      LOW TEMP     LOW
----  --------     ----

PIT   -1F /1934/   -2F
MGW    6F /1986/    1F
ZZV    0F /1947/   -4F

&&

.HYDROLOGY...

...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. CURRENT FORECAST HAS A HIGH LEVEL OF UNCERTAINTY
ABOUT MANY FACTORS...INCLUDING RAIN AMOUNT...TEMPERATURE...SNOW
MELT AND ICE MOVEMENT. SMALL STREAMS AND TRIBUTARIES WILL BE FIRST
AFFECTED TUESDAY MAR 3. RISES ON THE MAJOR RIVERS ARE PROJECTED TO
OCCUR STARTING TUESDAY NIGHT AND CONTINUE THROUGH WEDNESDAY MAR 4.

&&

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

&&

$$