Scientific Forecaster Discussion
fxus61 kctp 220338
Area forecast discussion
National Weather Service State College PA
1038 PM EST Thu Nov 21 2019
a cold front will pass through the forecast area Friday and
stall just south of the Mason-Dixon line. A new storm will form
on the front and will move through the region Saturday and
Saturday night, followed by breezy and drier conditions to end
the weekend. Temperatures will be close or slightly warmer than
normal to start the new work week.
Near term /through Friday/...
9 PM update... made a few tweaks to our forecast for the
overnight hours into Friday.
As expected, the incoming cold front is moisture starved, as
evidenced by still fairly large temperature/dew point spreads
across western/central PA. Only sprinkles have been observed so
far over northern parts of the commonwealth, with most of the
actual shower activity not likely to occur until later tonight
and early Friday, closer to surface frontal passage and also
when short-wave energy from the Ohio Valley better influences
Concerning temperatures, good low-level warm advection tonight
ahead of the front should lead to steady or rising temperatures.
Thus, we've adjusted overnight readings upward. Conversely on
Friday, Post frontal-passage, good low-level cold advection
should lead to falling temperatures over the majority of central
PA, with the exception of the lower Susquehanna valley, where
they'll probably hold fairly steady.
We also trended the winds a bit higher tomorrow behind the
front, as steepening low-level lapse rates and decent momentum
Transfer should lead to 20-30 mph gusts for many areas, from
about late morning through mid-afternoon.
Previous discussion... there is good model consensus on a cold
front crossing central PA early Friday. The front doesn't have a
lot of moisture to work with, and rainfall is expected to be
one- tenth inch or less in most places.
The front will move south of the region by late Friday, allowing
a breezy northwest flow to usher cooler and drier air with most of the
showers tapering off during the morning.
Highs will range from around 40 over the northwest to the mid 50s over
Short term /Friday night through Saturday night/...
the frontal boundary will stall south of the PA border and a
new wave of low pressure will develop over the Tennessee Valley
Friday night and push towards Pennsylvania on Saturday. This
system will bring increasing clouds and a chance for rain back
into the area from southwest to northeast as the day progresses
Most locations will see a period of rain Saturday into Saturday
night. However, chillier air will work back into the area
Saturday night, as a secondary area of low pressure develops
over eastern Virginia or the Delmarva Peninsula. This should allow
the precip to taper off as scattered snow showers Saturday night
and Sunday. The main potential for any snow will be Saturday
night, but little or no snow accumulation is expected at this
time. Still something to watch, given model spread this week.
Long term /Sunday through Thursday/...
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 /04z Friday through Tuesday/...
some minor adjustments made to the tafs this evening.
A few showers across the east now, the cold front well to the
west. Showers working on the dry air kicked up some wind from
the northwest at times in spots like ipt. Now ipt back to the NE.
Overall wind fields have increased some since late aft.
Earlier discussion below.
00z tafs sent.
Not a lot of change from the earlier package. I did cut back on
the winds some this evening, given current obs, and that we did
not mix out real good today, given the warm air aloft.
Borderline, but low level wind shear in the western tafs tonight.
Most of the showers on radar to the north of our area, with the
better dynamics. The airmass is not real moist, thus went with
vcsh and did not call for fog.
After lower ceilings later tonight and Friday morning, expect
conditions to improve on Friday afternoon. Gusty winds will
Sat...PM low cigs/rain possible.
Sun...am low cigs/rain possible early. Snow may mix in across
the west and north.
Mon...no sig wx expected.
Tue...mainly dry. Showers possible late across the west.