Scientific Forecaster Discussion
fxus61 kctp 221129
Area forecast discussion
National Weather Service State College PA
629 am EST Fri Nov 22 2019
a cold front over the lower Great Lakes early this morning
will slide southeast across the commonwealth during the day
today accompanied by just a few showers.
A weak area of high pressure will drift east across the
state with fair weather for tonight and Saturday morning.
A wave of low pressure will lift northeast from the Tennessee
Valley bringing periods of rain, and possibly some mixed
precipitation over the northern mountains of Pennsylvania
Saturday night and early Sunday.
The storm will exit toward the southern New England coast
on Sunday with precipitation diminishing across PA to just a
few flurries or patchy drizzle across the higher terrain.
Near term /until 6 PM this evening/...
surface cold front near the South Shore of Lake Erie at 0930z
and will continue to March steadily southeast across the forecast area
this morning before clearing our far southeast zones in the lower
Susquehanna valley around 17z.
We have high pops for showers with fairly low quantitative precipitation forecast in the region
of weak west-southwesterly warm advection/ascent ahead of the
Rainfall amounts will be mainly between 0.10-0.15 of an inch
across the northwest half of the cwa, and generally less than 0.10 of
an inch across the susq valley and points east.
The northwest wind will kick up in the wake of the front with gusts
into the low to mid 20 kt range through the afternoon hours
today. Some gusts near 30 knots are possible for a few hours
either side of 18z.
We're dealing with a non-diurnal temp curve in the midst of this
fropa and temps should slide slowly throughout the day from
early morning temps in the upper 40s to low 50s. Late day
readings will be near freezing across the northern
mountains...around 40 along the southeast edge of the alleghenies, and
mid 40s in the far southeast.
Short term /6 PM this evening through 6 PM Saturday/...
a compact area of high pressure will slide east from the Ohio
Valley and be over southern PA/nrn Virginia late tonight and Sat
morning with fair weather and diminishing wind.
Sky cover should become scattered for much of the night which
should aid in the amount of radiational cooling. Expect min
temps Sat morning to be mainly in the low-mid 20s, except upper
20s across the southern tier and throughout the lower susq
The timing of thickening cloud cover Saturday will play a role
in precip type. Per Storm Prediction Center hrefv2 hourly ptype, some pockets of
freezing rain will be possible (mainly on the ridge tops) as
the llvls of the atmos wet bulb to near freezing within the
first few hours after the onset of the anticipated light,
00z/06z model consensus however, points toward a mid to late
afternoon onset of the light rain across the SW half of the cwa,
and a strat to the light precip mainly after dusk Saturday
across the NE zones.
Max temps Sat will vary from the upper 30s to low 40s north, to
the mid 40s in the lower susq valley.
Long term /Saturday night through Thursday/...
low pressure causing this mid weekend precip will be moving northwest
from the tenn valley Saturday, then will undergo an energy
Transfer to the Delmarva coast late Sat night/Sunday morning as
an upper level trough moves east across the central
Appalachians. The atmos will be borderline for a transition to
wet snow/sleet pellets across the northern and western mtns
Saturday night and early Sunday.
Maintained light snow accums across the northern and western
mtns where up to a slushy inch of snow is likely on mainly colder
elevated or grassy surfaces.
Precip will taper off to scattered snow showers Sunday, or
perhaps even some light drizzle or freezing drizzle across the
western mtns of PA as low clouds will be quite shallow with
temps of just -4 to -6c supporting supercooled water droplets.
After a chilly day on Sunday, temperatures look like they will
rebound nicely heading into early next week (above normal!)
Before a new cold front moves through the region during midweek.
Though timing/location differences exist between models, we
remain mostly on the warm side of the low which will bring a
shot for primarily rain, with the usual colder air on the
backside of the low bringing a transition over to snow showers
for the northwest half.
Aviation /12z Friday through Tuesday/...
a cold front entering northwest PA at 11z will push southeast
across the region later this morning, accompanied by a few light
rain showers. A plume of low level moisture preceding the front
will result in falling cigs ahead of the fropa, with IFR cigs
very likely over the high terrain of the alleghenies (bfd and
jst) and MVFR likely downwind (east) of the alleghenies.
Expect improving cigs behind the front later this morning and
afternoon, as drier arrives on a northwest flow. Most parts of
central PA should be VFR by the afternoon. However, moisture
flowing off of lk Erie will likely cause MVFR cigs to linger at
bfd until around 00z.
BUFKIT soundings support frequent northwest wind gusts in the
25-30kt range behind the cold front late this morning and
afternoon. Those winds will die down tonight, as high pressure
builds in from the Ohio Valley.
Sat...evening low cigs/rain possible, mainly southern PA.
Sun...am low cigs/rain possible.
Mon-Tue...no sig wx expected.