Scientific Forecaster Discussion
fxus61 kctp 181253
Area forecast discussion
National Weather Service State College PA
753 am EST Mon Nov 18 2019
low pressure about 200 miles east of Cape Hatteras North
Carolina will drift gradually to the northeast today. An upper
level trough and weak surface low will move out of the Ohio
Valley and bring a few periods of light rain, and the chance of
some light freezing rain then snow across the higher terrain
east of the Susquehanna mainstem.
The middle of the week will hold a Few Lake effect snow
showers across the northwest part of the state. Elsewhere,
for much of the time it will be mainly dry and seasonable. A
fast-moving cold front will arrive Friday morning.
Near term /until 6 PM this evening/...
widespread low clouds, mainly under 1500 ft mean sea level across the
east, and under 1000 ft across the central and western portions
of the state, will result in areas of light drizzle throughout
much of the central valleys and Susquehanna region
Temperatures were just cool enough across the higher terrain
early today to produce some patchy light ice from freezing
drizzle over favorable upslope areas on the southeast facing slopes.
Atlantic low will move northward as an upper trough approaches
from the southwest thru the period. The European model (ecmwf) has trended a bit
weaker and further east with the precip areas from the upper
trough tonight. Similarly, U.S. High res models have shifted
slightly to the east over the past several runs.
Href shows little or no measurable rainfall through the early
afternoon hours, prior to the region of strengthening upper
level diffluence and deep uvvel overspreading the County Warning Area (late
morning across the Laurel Highlands and in the late afternoon or
evening in the far northeast).
Light rain will develop across the eastern half of PA later
this afternoon through this evening. Href indicates the
potential for icing across Sullivan County this evening before
the precip ends as a 1 to few hour period of wet snow.
Small accums of up to several tenths of an inch are expected
very late tonight
High temps this afternoon will vary from the upper 30s over the
higher terrain north and east of kipt to the mid 40s in the
Short term /6 PM this evening through 6 PM Tuesday/...
the aforementioned western Atlantic low will drift NE to become
located over Nova Scotia late this evening. Marginally colder
air will move in on west to northwest llvl flow tonight through
midweek. Subsidence inversion base will lift up to 4-6 kft agl
later tonight and Tuesday. Favorable thermal ribbon for
dendritic snow growth will be several kft or more above the
relatively warm cloud tops, so will go with scattered light snow
showers or evening some patchy freezing drizzle (mainly later
tonight) on the west slopes of the ridges.
Long term /Tuesday night through Sunday/...
*not as cold but below-average temperature bias continues
*potential for light wintry precip off and on this coming week
Looking to the week ahead, expect temperatures to gradually
trend milder but with a below-normal bias. Thursday looks like
the only day that most locales slip just above average, with the
southeast potentially ending up a bit above normal on Fri as well. The
latest long term temperature outlooks favor below average
readings through the end of the month.
There remains some variability in the model guidance (low
confidence forecast) concerning the precipitation type and
occurrence this week.
Another northern stream disturbance/upper level low or clipper
moves across PA Tuesday night into Wednesday bringing chance for
rain and snow showers over the northwest. A brief period of
lake effect/upslope precipitation on the back end of this is
possible hence low pops continue.
Next wave deepens as it crosses the Great Lakes Thu and Fri.
Looks like the precip should hold off late enough Thu to miss
shot at a light wintry mix at onset, with precip type being
primarily rain as we remain on east side of this system.
On Thursday night some snow may work in over the higher terrain
of the NW, and across the northwest half on Fri as precip shield
retreats back toward the northwest before ending. Another brief period
of lake effect is possible on the back side of this system by
Sat looks pretty quiet, but yet another weak system sneaks in by
Sat night/Sunday with potential for a wintry mix.
Aviation /13z Monday through Friday/...
As the bands of stratocu continue to overspread the region the
stable airmass is bringing IFR and lower to all but MDT and lns
taf sites. Along with low cigs is patchy drizzle which is
helping to reduce visibilities.
Latest model soundings show improving conditions as the bands
move to the northeast. This should allow for LIFR and IFR cigs
to improve to MVFR between 15z to 18z.
The improving conditions will continue through Monday
afternoon across central and western PA, where low level
moisture should mix out. Ensemble output suggests VFR conditions
will become likely over this part of the state by late in the
day, while MVFR cigs linger over eastern PA.
Another round of IFR is possible Monday evening into Tuesday
Tue...am fog possible. Evening low cigs possible northwest mtns.
Wed...am low cigs possible west mtns.
Thu...patchy am fog possible.
Fri...early am low cigs/showers possible west mtns.