Scientific Forecaster Discussion
fxus61 kctp 091145
Area forecast discussion
National Weather Service State College PA
645 am EST Mon Dec 9 2019
after a fair weather weekend, a more active and occasionally
stormy pattern is expected during the second week of December.
Temperatures are forecast to surge well-above normal today and
Tuesday, followed by a sharply colder trend Wednesday into
Thursday. The brief warm-up will be accompanied by periods of
rain which may end as light snow late Tuesday night. A mid to
late week drying trend will likely reverse by next weekend with
another complex storm system on the horizon.
Near term /until 6 PM this evening/...
low clouds now into the portions of the middle and lower
Susquehanna valley as of 4 am. Been watching the temperatures
across the southeast, as radar returns are now just brushing
southeastern Lancaster co. So far, temperatures been holding up
and dewpoints are coming up.
Not much on radar to the west, until one gets into southern Ohio.
Patchy rain will overspread the region this morning and continue
during the afternoon as strong warm advection continues. Overall,
the heaviest quantitative precipitation forecast is still expected to the west and east, given
two pressure systems.
Short term /6 PM this evening through Tuesday night/...
after some discussion with wpc, did up amounts a small amount,
mainly along the higher terrain across the southeast and east.
Earlier discussion below.
Evening shift has a band of snow of 1 to 2 inches in the fcst.
While there could be a little more, temperatures are warm to
start, then drier air could limit precipitation later on. Will
continue to look over the situation.
More information below.
Highest quantitative precipitation forecast shifts to mainly the western half where 36hr rain
totals will be around an inch.
As the aforementioned low level wind Max feature departs toward the
New England states Monday night, rainfall intensity will
decrease and lingering low clouds and some patchy light
rain/drizzle will occur. Breezy and unseasonably mild temps
are expected within the warm sector and min temps will be
4-6 deg f above normal high temps for the date (between 40 and
50f from northwest to se).
Sfc cold front pushes east across PA Tuesday morning, before
slowing as it reaches the Delmarva/Virginia coast.
A secondary and moderately tight 850-700 mb thermal gradient and
fgen forcing will occur across the southeast 1/3 to 1/2 of the cwa, as
the thermally direct r.E. Region of a strong upper level jet
approaches from the mid Ohio Valley and accentuates upward
Boundary layer temps slip to critical changeover levels for wet
snow beginning in the early evening Tuesday across the central
mtns and mid susq valley, then across our southeast zones around 03-05z
Wednesday. A second, Post-frontal period of rain Tuesday
afternoon/evening will likely change to a several to 6-8 hour
period of light to moderate wet snow with 1-3 inches of
accumulation looking increasingly likely southeast of a kaoo to kseg
and kmpo line with the highest amounts occurring across the
ridges. Could see a few higher amounts on the ridges. Depending
on the temperature and snowfall rates, some travel impacts are
possible for the morning commute to work and school Wednesday.
Long term /Wednesday through Sunday/...
main change so far was to adjust lake effect snow showers
a little further south. Overall, rising height fields will
limit response in our area. Thus I did not want to go much
further south the snow showers.
Other issue the weather for next weekend. In some regards,
models show a similar pattern to what we have today.
Models show a lot of spread from model to model and day to day.
Earlier discussion below.
It will turn sharply colder midweek as Arctic air blasts into
the region. Temperatures will be on the decline over the northwest
Tuesday afternoon (non diurnal over the northwest half) and drop
quickly Tuesday night areawide. There will be some potential for
residual water or slush to freeze up quickly by Wednesday.
Highs are forecast to drop by 20-30 degrees between Tuesday and
Thursday, with minimum wind chills in the single digits and
teens Thursday morning.
Strong 1040+mb high pressure moves NE across the region
Thu/Fri followed by another system which could bring rain or
mixed precipitation Friday into Saturday.
Aviation /12z Monday through Friday/...
low pressure heading for lm this am is drawing deep moisture
into PA from the S. Lowering cigs and rain are expected into
Tuesday. Weak low moving up the coast is currently causing LIFR
cigs in the southeast. That might be brief, but could last all day as
the conditions around them deteriorate. Most locations should
drop to IFR and stay there. Strong south/southwest winds aloft,
combined with lighter surface winds, is leading to llws, and
this may not go away until cfropa on tues. After midnight is the
next possibility of some lifting of the low clouds and perhaps
a dry break for the southeast. But, the northwest looks wet/IFR most of the
next 24 hours. Cold front moves through northwest to southeast on Tuesday. As
it does so, the temps get cold enough to cause snow instead of
rain. The greatest threat for reductions to l/IFR in snow is to
the southeast of unv and ipt Tuesday night and early Wed am.
Tue...am low cigs/shra, mainly north mtns. Evening and overnight light
snow possible southeast PA.
Wed...am light snow possible southeast PA. MVFR west with sct
Thu...no sig wx expected.
Fri...low cigs possible, especially late.