Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 270542
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
142 AM EDT Thu Apr 27 2017

.SYNOPSIS...
A strong subtropical ridge over the western Atlantic will
dominate our weather through Monday. A front will weaken as it
moves into the ridge late Thursday triggering thunderstorms.
Then ridge will build westward over the weekend. We will be on
the warm, moist western side of the ridge most of the weekend.
A classic dirty warm up with warm moist air and potential
diurnal thunderstorms. Alas, a strong trough should bring
cooler drier weather to the region for the second part of next
week.

&&

.NEAR TERM /UNTIL 9 AM THIS MORNING/...
GOES-16 3.9-11.2um loop at 05Z showing stratus over eastern
Lancaster and Schuylkill counties making little progress
westward and latest HRRR 925mb RH fields suggest this will
remain the case through dawn, with skies remaining mclear across
the bulk of the CWA. A light southerly breeze should keep fog at
bay over most of the region. However, a lighter gradient across
the Lower Susq Valley will allow patchy fog to remain an issue
over that part of the state early this morning. Temps on track
to bottom out in the mid to upper 50s around dawn.

&&

.SHORT TERM /9 AM THIS MORNING THROUGH FRIDAY NIGHT/...
Other than the morning fog/stratus across eastern Pa, it should
turn out to be a very nice/warm day with many areas topping out
near 80F.

The POP, CAPE, and PWAT fields all suggest a front approaches
from the west in the afternoon. Noted the 12Z GFS is slower and
our superblend is drier than previous runs. No real QPF in our
region until around 2100 UTC and by 0000 UTC it gets to central
PA and dies. The GEFS is not in yet. Clearly any
showers/thunderstorms will most likely be in the late afternoon
or evening hours. Only modest CAPE where the LLJ is the
strongest. In the 600-900JKG-1 range. Better CAPE in some
models/members to southeast where there is less lift and weaker
winds.

The front is moving into a strong ridge and it is a bit moisture
starved.

Overnight Thursday into Friday showers end or die out in central
areas. A bit cooler and drier overnight Friday into Friday AM.
The PW is normal to below normal and the 850 hPa temps are
closer to normal to a tad above normal. There is no CAPE to
speak of. Friday looks potentially like a really nice warm late
April day.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
High amplitude upper pattern to start the period will become more
zonal by Days 2/3 as a vigorous trough and strong cold front swing
through the region on Monday, bringing cooler conditions through
the middle of next week.

The region remains on the western periphery of a strong western
Atlantic upper ridge, which leaves us susceptible to daily mainly
diurnally driven shwr and tstm chances Saturday and Sunday.
Continued to utilize a NBM/ECENS/WPC blend for max/min temps and
POPS which maintained good continuity with previous fcst. While both
weekend days feature a chance of showers and thunderstorms, most of
the time will be dry and warm with highs both days ranging through
the 70s in most places. Saturday may crack 80 over much of the
southeast third of central PA.

Max POPS during the extended period remain centered on Monday/May
1st as the aforementioned cold front crosses the Appalachians and
continues toward the Atlantic seaboard. A severe weather threat may
evolve downstream from the OH Valley into the Mid Atlantic late
Monday before temperatures decline to near normal behind the cold
front for next Tuesday and Wednesday.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 11 PM, starting to see stronger and faster return
flow than I expected. Also some lower clouds at LNS for
a few minutes.

Did adjust 03Z TAF package some for the above factors,
but did not want to back off fog and lower clouds later
too much.

Earlier discussion below.

A nice evening outside. VFR conditions this evening will
prevail.

However, some lower CIGS and visibilities later, given
clear skies, recent wet conditions, and light winds.

Expect poor conditions to burn off by mid to late morning,
as winds pick up and the strong late April sun prevails.

Did not go quite as high as guidance with winds at IPT
Thursday afternoon, this area not quite in the gradient
yet at 00Z. Also strong winds often pick up there just
after 00Z until late evening.

Some showers and perhaps a thunderstorm across western
areas by 00Z Friday, as a cold front moves eastward.

Outlook...

Fri...No significant weather.

Sat-Sun...A few showers possible. Mainly dry with VFR
conditions for much of the time.

Mon...Showers and thunderstorms likely.

&&

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

&&

$$
SYNOPSIS...Grumm
NEAR TERM...Fitzgerald
SHORT TERM...Grumm
LONG TERM...DeVoir
AVIATION...Martin


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