Area Forecast Discussion
Issued by NWS State College, PA

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551
FXUS61 KCTP 221004
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
504 AM EST Thu Feb 22 2018

.SYNOPSIS...
A nearly stationary frontal boundary will remain just south of
out Pennsylvania today through Saturday, before lifting north
across the commonwealth as a warm front Saturday night. Several
weak waves of low pressure will ride northeast up the Ohio River
Valley and move over this boundary, leading to periods of rain
over most of Central and Southern Pennsylvania.

The air will be cold enough across Northern Pennsylvania to
support periods of wintry precipitation in the form of a few
to several inches of snow today, along with a light glazing
from freezing rain or freezing drizzle, and more light
icing possible tonight and Friday morning. The Laurel Highlands
and portions of the Central Mountains will also become cold
enough to support periods of freezing rain or freezing drizzle
today through Friday morning.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A well defined mid-upper level shortwave and strengthening jet
entrance region will move northeast from the Ohio River Valley
cross PA duirng the late morning through early afternoon hours.

Slowly cooling and deepening low-mid levels of the Atmos will
combine with pulses of mdtly strong UVVEL from areas of
enhanced FGEN to paint a narrow band of accumulating snow (to
the tune of a few to several inches) near and to the north of
Route 6 in the northern Tier of PA, while a 30-50 mile wide band
of light to moderate icing from FZRA occurs between RT 6 and
Interstate 80. HREFV2 suggests a period of heavy snow is possible
between 9am and noon along the NY border, as influx of
anomalous PWATS combines with strong fgen forcing within jet
streak right entrance region.

Pops were raised slightly today to reflect the nearly 100
percent certainty of precip across all of Central and Northern
PA. Precipitable Water values of 1-1.25 inches suggests that
there could be atleast some brief periods of decent rainfall
rates of 0.25 inch or so per hour today - with totals raching
near 1 inch by late tonight across parts of the Laurel
Highlands. Given that 6-12 hourly Flash Flood Guidance is
1.6-1.8 inches across Cambria and Somerset counties (where the
heaviest rain is expected today), don`t see the need for a Flood
Watch at this point. Any trend toward heavier amts in the form
of guidance trends or peristent FGEN banding would prompt us to
consider issuing one. For now, will highlight the chc for some
minor small stream and basement flooding in our Hazardous
Weather Outlook.

Based on regional model soundings and the latest HRRR/RAP and
HREFV2, it looks like mixed precip to turn to snow around 12Z
across the northern tier of counties. Further south, precip may
initially begin as rain, but expect a transition to freezing
rain over the high terrain along I-80 during the mid to late
morning hours as temps sink slowly from the low to mid 30s.

Based on model blended qpf, most likely snow accums range from
around 3 inches along the NY border, to nothing from I-80
southward. Ice accums over most of northern Pa should average
around a tenth of an inch. However, the higher terrain along
I-80, where ptype should be primarily fzra, could see close to a
quarter inch.

The Central Ridge and Valley Region should stay primarily in the
form of rain today with the precip intensity varying between
light and moderate. Temps near 40F at 09Z will slip about 3-5
deg F this morning before levelling off this afternoon in the
mid 30s in the valleys and lower 30s with some glazing from FZRA
on the ridges (elevations AOA 1800 feet MSL).

The SE zones will see rain overspreading the region from the
west during the mid morning with temps in the mid to upper 40s
to start the day, before sliding slowly top the upper 30s for
the afternoon.

Expect precipitation to taper off from west to east between
19Z-21Z, as low level jet and associated plume of deep moisture
shifts east of the state.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Residual low level moisture, combined with an upsloping
easterly flow, is likely to yield lingering drizzle over much of
the region into this evening with occasional light rain, -FZRA
or FZDZ possible over the higher terrain of northern Pa tonight
through Friday morning. Throughout the central valleys, patchy
light drizzle and freezing drizzle will be found.

Temps tonight will be in a rather tight range tonight in the
30-35 deg F range.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The weekend still looks similar to the last few days with a few
periods of rain, drizzle and ridge shrouding fog Friday night
throgh Saturday night, before the frontal boundary to our south,
lifts north as a warm front. Temps will slowly moderate through
the weekend.

The best chance for a warm up is Sunday...as system lifts to
the north and west of central PA. This track is a little further
west now...which would keep the heavy rain threat further away
from our area. Depending on the mixing...more record highs could
occur.

Looks dry after Sunday evening.

More information below.

Forecast for Thursday into Friday looks cloudy and damp with
periods of light rain/drizzle and areas of fog. The fog will be
locally dense at times, especially on East-Facing slopes and
ridgetops during the overnight and early to mid morning hours.

Stalled out sfc front across the Virginias and Ohio River
Valley and SW flow aloft will be the conduit for a few waves of
low pressure to ripple NE along, and bring us this rather dismal
weather.

There is the potential for a significant change in practical
weather...if frontal position changes north or south very much.

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
VFR is dominating the pattern as a brisk northerly wind is
transfering the region. Light rain continues to bring MVFR to
JST and they remain the best chance for IFR cigs and vsbys. IFR
cigs remain probable overnight tonight and through Thursday.
Some drier air and improved conditions will move in this evening
as the front settles south, but will be replaced by lowering
ceilings once again between about 06-12Z as a new area of rain
overspreads the region. Across the far north a wintry mix of
freezing rain, sleet and snow is likely by sunrise. This could
last into the early afternoon hours.

An active second half of the week follows, as several weak
waves of low pressure bringing bouts of rain, and even some
light freezing precipitation to the north Thu into early Fri.

Outlook...

Fri...Widespread restrictions in periods of rain. Some
improvement poss SW late.

Sat...Rain remains likely. Widespread restrictions north,
gradual improvement south.

Sun...Widespread restrictions likely in periods of rain.

Mon...No sig wx.

&&

.HYDROLOGY...
Recent rainfall and snowmelt has resulted in wet soil and well
above normal streamflows across much of the area especially
south-central PA. Rainfall of 0.50 to 1.00 inch is forecast
today and tonight, with additional rainfall likely from Friday
into/over the weekend. River flood potential (including small
streams, creeks and tributaries) is above normal and we will
continue to monitor the risk in the coming days.

&&

.CLIMATE...
Record high temp of 69 tied at KIPT for Wednesday while an all-
time Feb high was reached at KMDT with 79 degrees, and breaking
the old record for the day pf 71F in 1997.


&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 4 PM EST this afternoon for
PAZ004>006-010>012-017-018-037-041-042.

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert/Fitzgerald
LONG TERM...Lambert/Martin
AVIATION...La Corte/Lambert/Gartner
HYDROLOGY...Lambert
CLIMATE...Lambert



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