Friday, July 20, 2018, 12:35 PM EDT
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Area Forecast Discussion
||Wed, Dec 31, 7:00pm EST
FXUS61 KCTP 201504
Area Forecast Discussion
National Weather Service State College PA
1104 AM EDT Fri Jul 20 2018
The recent stretch of pleasant and conformable weather across
central PA will come to an end this weekend, as the pattern
turns decidedly unsettled, muggy and rather wet through next
.NEAR TERM /THROUGH TONIGHT/...
One more nice day across central PA with plenty of sunshine and
afternoon temperatures in upper 70s to mid 80s. Dewpoints into
the low 60s in the southern tier will make the humidity a bit
more noticeable. Enjoy and take advantage of the dry weather
while you still can - as there are changes afoot.
Latest hires models show a north-south line of convection
developing this afternoon/evening along the I-79 corridor. This
line may clip the border counties adjacent to WFO PBZ and will
continue slight chance POPs. The majority of central PA stays
dry, basking in what could the last sunny day for a while.
For tonight, I trended the POP/Wx/QPF forecast strongly toward
the 00/06Z HREF mean and WPC/NBM blend. The HREF mean spreads
showers northward from the Delmarva/Chesapeake Bay region into
south central/southeast PA by 12Z Saturday. An increasing southeast
low level flow will help to bring low clouds into much of the
area by Saturday morning.
.SHORT TERM /SATURDAY/...
A moistening south-southeast flow should result in low clouds
expanding to cover a good portion of the CWA by Saturday
morning. The model RH progs put the thickest clouds over the
central mountains. This seems like a good start, but the ridges
perpendicular to the SE flow over the east will also have a high
chance of getting very cloudy. The clouds will likely keep the
heating down to only a meager rise for the day. Maxes may
struggle to get to 70F in lots of places. There is even a chc
of a shra - or perhaps drizzle - over the central mtns.
The bigger trouble in the forecast is the complicated sfc
pattern and resulting rainfall from the coastal low and the
broad low over the Midwest. Models still differ on timing and
location of the coastal low. The dynamics around this storm will
have a direct influence on the area, keeping it either fair or
making it miserable this weekend. This is all still too muddy to
make more than an increase in PoPs for the east through all the
weekend. It may actually warrant a decrease in PoPs for the
west, where it could influence the weather by providing
subsidence and suppressing convection.
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
By the weekend, inverted low centered over Lake Michigan will be
channeling tropical-like moisture northward into PA as our
weather becomes unsettled. A compact wave of low pressure forms
near the Carolinas and slides northward toward NJ by Sat night,
enhancing rain/convection chances further. EC and GFS differ
slightly on the intensity of the coastal low. Will need to keep
an eye on this feature as could focus heavier rains over eastern
portions of the state. Sat and Sat PM could be dry over most of
the CWA with us in-between this system and the upper low off to
Upper low begins to fill in Sun into Mon but high PWATs will
keep mention of daily convection in the forecast through much
of the week - peaking in the afternoons - as a tropical feel
persists. An approaching cold front for mid/late week will
enhance precip chances further before weather becomes more
settled for first part of next weekend. Have peaked the bell
curve of PoPs in mid-week.
Temperatures will be a bit below normal Sat/Sun with thicker
cloud cover, then highs return close to normal for next week
while lows look to remain on the muggy side.
.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
VFR conditions will trend lower late tonight into Saturday as
low clouds develop across the airspace. This trend was reflected
in the 09z intermediate TAF update and continued in the 12Z
scheduled issuance. Low VFR to MVFR ceilings are probable
Saturday into Saturday night, with some pockets of IFR Saturday
night into early Sunday. Showers are expected to spread
northward from the Delmarva/Chesapeake Bay region into the south
central/southeast airspace early Saturday morning. Plan to
extend the aforementioned ceiling and precip trends with 18Z
Sun-Tue...Frequent showers/isolated T'storms with associated