Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 152123
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
523 PM EDT Sun Apr 15 2018

.SYNOPSIS...
A markedly cooler airmass is in place today courtesy of a
backdoor cold front that pushed south and west through the
forecast area last night and early today. A strong storm system
will sweep through the region tonight and early Monday. Much
cooler weather will follow through the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
The strong back door cold front has made for a chilly damp day
with areas of drizzle and fog shrouding the ridges.

Guidance agrees in timing our strong low and cold front through
the region overnight and early Monday. The front should be
entering my western zones around midnight, finally clearing the
east between about 6-9AM.

Biggest issue remains the potential for heavy rain/flooding as
the wavy surface front sweeps through overnight into mid morning
Monday. The cool air damming assures a chilly soaking rain for
most of the region, and the chance for a thunderstorm cannot be
ruled out just in advance of the front. The HRRR develops a few
hundred joules of CAPE over my far SERN zones and even tosses in
some modest helicity right along the warm front and near a
surface wave that the models want to track over the lower Susq
Valley. With the mean wind between 800-500mb averaging some
50-80kt, any convection that develops will be capable of
transferring strong wind gusts down to the surface.

At this stage I have downplayed the already small chance mention
of pockets of freezing rain overnight. I think the SPC HREF is
being too aggressive with their icy precip type given their own
forecast skin temps. While it will likely be in the 30s and
raining, I removed the freezing rain from the forecast.

Overall ensemble model QPF has been lowering. The GEFS now
centers our best chance for rain exceeding 2 inches over my SWRN
zones and has dropped the chances for 3 inches or more of rain
down to negligible chances. The ECENS also centers the best
chance for the heaviest rain over my SW counties. HPC was more
broad and covers much of my southern forecast area with 1.5 -
2.5" of QPF. FFG is highest over the area of expected heaviest
rains complicating the decision making for a possible flood
watch. Will consult with the swing shift before deciding on
potential flood headlines.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
Monday will see us transitioning into a gusty and colder NW flow
behind the departing surface wave and cold front. Snowflakes
will likely mix with the rain drops in the showers that will
develop in the cyclonic flow behind the system, especially over
the higher terrain. The incoming airmass will more resemble one
common in early March than mid April.

Highs in the 40s over most of the area will be some 10-15 deg
colder than normal.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
On the back side of the strong front crossing the state Sunday
night and early Monday, we will see yet another return to colder
than normal weather and even a couple of opportunities for snow
showers. The first chance for snow showers will be Monday night
and early Tuesday as the upper low swings through to our north.
Another system may bring more snow showers Wednesday night into
Thursday. We don`t expect any significant accumulations, but as
we enter mid April, the prospects for snow are less than
welcome.

Past Thursday we foresee a break of dry weather into early next
weekend as energy reloads over the southwestern U.S. allowing
weak upper ridging to build over the eastern part of the
country. Yet another upper low in this busy pattern looks to
drop into the deep south toward the end of the period...possibly
spreading some precipitation toward our region for the
beginning of next week.

&&

.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
Low CIGS across the area at 5 PM.

21Z TAFS updated.

Earlier discussion below.

Widespread, persistent IFR conditions are expected through
tonight. The main period of rain will be roughly 03Z-14Z (west
to east), and it could be heavy at times. Included LLWS this
evening into tonight with very intense 60-70kt LLJ in advance
of strong cold front.

Conditions will slowly begin to improve Monday morning east of
the Allegheny Front, as winds shift to the west and begin to
downslope behind the cold front.

Outlook...

Mon...Rain will taper to showers W to E. MVFR/IFR early trending
VFR PM central/eastern 2/3. Rain/snow showers and sub-VFR cigs
continue western 1/3 into Mon night.

Tue...MVFR ceilings western 1/3 with lingering rain/snow
showers. VFR elsewhere.

Wed-Fri...Chance of rain/snow showers with sub VFR most likely
NW 1/2.

&&

.HYDROLOGY...
1 to 2 inches of rain is expected Sunday night into Monday
morning and will result in significant rises on area rivers and
streams. Latest guidance has trended a bit lower on total
rain/QPF and shifted the axis of heaviest rain slightly eastward
toward the Lower Mainstem Susq basin, where FFG values are the
highest. High res models still show the potential for localized
max amounts of 3+ inches which would cause some runoff
problems.

Small streams will see the greatest runoff-response with
rapid/sharp rises expected. Small streams will be the most
susceptible to flooding. Several river points are forecast to
reach action/caution stage and minor flooding is possible. There
is also the potential for localized short duration ponding/flooding
especially in urban corridors and poor drainage areas.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...La Corte
NEAR TERM...La Corte
SHORT TERM...La Corte
LONG TERM...La Corte/Gartner
AVIATION...La Corte/Martin
HYDROLOGY...Steinbugl



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