Scientific Forecaster Discussion
fxus61 kctp 231654
Area forecast discussion
National Weather Service State College PA
1154 am EST Tue Jan 23 2018
expect a mild start today with periods of drenching rain this
morning. The weather will turn windy and colder later this
afternoon with scattered rain and snow showers over the
alleghenies. The colder temperatures will continue through
midweek before another mild trend develops into the weekend.
Near term /through tonight/...
most of the rain is out of the area. But, the wrap around
showers/clouds are already into Warren co and covers most of the
western part of the state. Fast movement to the showers in the
fast westerly flow will keep amounts down to just a few
hundreths for the rest of the day. The turn over to snow should
still occur on the current schedule. The wind gusts are already
kicking in with a 33kt gust at kagc. Could see a gust or two
appch 40kts, but the threat is not high enough for an advy.
radar trends have evolved pretty much as expected with the
heaviest rain along the I-81 corridor. Max 3-hr mrms rainfall
estimates generally agree with gauge amounts in the 0.75-1.00"
range. Considering a flood advisory for poor drainage areas into
A strong closed low moving over Illinois/in at 08z will take on a
negative tilt as it crosses the lower Great Lakes into upstate
New York by 24/00z. The trailing cold front will plow eastward across
the Keystone state early today with above average moisture/precipitable water
available along and ahead of the boundary. Hires model blends are
showing a pretty strong signal for an organized but fast-moving
area of moderate to locally heavy rainfall to quickly drench
the southeast 1/2 to 1/3 of the County Warning Area between 06 and 15z Tuesday.
This area appears to be blossoming now over northern Virginia. Quantitative precipitation forecast
amounts are solidly in the 0.50 to 1.00 inch range with local
point amounts over 1 inch possible. The fast-moving cold front
will limit duration but brief/heavy rain rates may lead to
isolated runoff issues with gridded marfc 1hr ffg as low as
0.50-1" in spots.
The afternoon period through tonight will turn windy and
progressively colder across central Pennsylvania. Wind gusts of 25
to 35 mph from the west are expected with 40+ mph gusts in the
Laurel Highlands. Scattered rain showers will turn to snow
showers over the alleghenies with a coating to 1" of snow likely
by Wednesday morning. 24hr temperature change of around 20f by
12z Wed. Will be quite noticeable with brisk winds making it
feel even colder.
Short term /Wednesday through Thursday night/...
brisk and colder weather will last through midweek with snow
showers continuing over parts of the western alleghenies. A
reinforcing shortwave may enhance snow showers Wednesday night
over The Laurels but overall additional accumulations should be
less than 1 inch through 12z Thursday. Dry weather is expected
on Thursday as high pressure slides over PA. Daytime/high temps
will reach a weekly bottom during this period, averaging a few
to several degrees below normal for late January.
Long term /Friday through Monday/...
uncertainty surrounding the timing and amplitude of the upper
trough moving from The Rockies through the central and eastern
U.S. Continues to plague the long term forecast with
significant sensible weather implications by later in the
weekend. Followed wpc preference favoring blends toward a
slower, non-GFS solution. This would result in a stronger wave
of low pressure to develop over the Appalachians and bring the
potential for significant rain or mixed precipitation Sunday
into Monday. The greatest confidence is for the period to start
dry (friday) with temps moderating to above average levels.
Aviation /18z Tuesday through Sunday/...
low clouds in MDT look very temporary, with the west wind
expected to kick in in just an hour or two. Elsehwere, it is
slowly turning to the very normal Post-frontal/wrap-around
pattern. Expect the major gusts over the west (esp at kjst) to
continue into the first half of the night, but decrease to less
than 25 kts before 06z.
showers are moving through central PA brining IFR and lower
conditions at MDT, lns, ipt and bfd. The bfd and ipt reductions
are mainly due to low stratocu and vsbys due to the moisture and
fog. MDT and lns are related due to the convection moving
through. Once these showers move through expect conditions to
improve. Expect improvements between 14z to 16z. There has been
some isolated thunder so continue to mention thunderstorms in the vicinity at MDT however
they are not expected to be on station at the airports. The
strongest convection currently is southeast of ipt and moving to
the northeast. Any low level wind shear will fade after frontal passage and then
mechanical mixing will make it very gusty today. The highest
gusts will be at jst.
Cold air will turn the lingering rain showers over the west in the aftn to
shsn. Scattered shsn will then continue over the high terrain of the
west into Wednesday.
Wed...am shsn possible W mtns.
Thu-Sat...no sig wx expected.
some convection/heavier rain made a stripe of 1-2 inches from
South Mountain through nrn York co and into
Dauphin/Lebanon/Schuylkill cos. This has made a very sharp rise
on the Swatara and a Flood Warning was issued for Harper Tavern.
Hershey is being watched closely as well. However, the burst of
rain was brief and the flow should peak this afternoon before
falling almost as quickly. Any other minor flooding outside of
the Swatara should also come to an end this afternoon.
Flood Watch remains in effect into the afternoon with lingering
concerns surrounding minor flood/ice jam potential along and
near the Susquehanna River between York Haven and safe Harbor.
This will be extended for another two days per coordination with
local ems and the srbc.
Much drier weather over the next 4 days and a gradual warm up
back well above normal later this week should greatly reduce
the threat for ice jam flooding.
Flood Watch until 1 PM EST this afternoon for paz065-066.