Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 271949
Area Forecast Discussion
National Weather Service State College PA
349 PM EDT FRI MAY 27 2016
A ridge of high pressure will stay in place over the western
Atlantic...bringing very warm and increasingly humid conditions
to the region through much of the holiday weekend. Cooler and
showery weather may arrive for Memorial Day.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Diurnal heating of the very warm and moist airmass/rising parcels
are starting to penetrate the weak mid-level cap (with 700 mb
temps of plus 4-5C)...leading to isolated-scattered showers/tsra
forming mainly across the ridges of scent and ncent PA at 18z.
This convection will drift east into the more unstable air across
the susq valley where sfc based capes around 2000 j/kg are about
double what we`re seeing in the area of tsra genesis.
The rather slow moving tsra could create locally isold strong
wgusts/hail in best cells. However, wind fields and deep lyr shear
are weak, indicating organized svr wx is unlikely.
Although aftn Pops are generally blw 50 pct, increased pops across
srn penn where convective allowing high res models show some
organized TSRA clusters taking shape across the lower susq valley
(mainly south of I-81 between 20Z and 00Z). What rain does fall
could be locally heavy, due to slow storm motion and high PWATs.
Convection- allowing mdls (HRRR) show this potential with highly
localized amts in excess of around 2 inches possible in just an
hour or so.
18z temps should rise another 1-3F to reach late afternoon highs
of 80-82F across the northern and western mtns...and nr 90F over
the Susq Valley.
Diurnally-driven convection will gradually dissipate with the
loss of heating this evening. Partly cloudy skies and light wind
could yield patchy fog later tonight, especially where the ground
is wet from the pm showers/TSRA.
High dewpoints will lead to another very warm/rather muggy night
with min temps in the mid 60s over much of the area.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Subtropical ridge builds nwwd into Pa on Sat with 500mb height
anomalies reaching 2SD across southeast Pa. The assoc warm temps
aloft should suppress convection across the se counties Sat aftn.
However, sct diurnal tsra again appear likely across the nw half
of the state. Thermodynamic/kinematic profiles appear very similar
to those on Friday, with moderate sfc-based cape of 1500-2500 j/kg
and weak low-mid level shear, suggesting pulse-type convection
and a low risk of organized svr wx.
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Summertime upper level ridge over the Mid Atlantic and Northeast
states is forecast to peak around 29/00z with above normal
heights returning to normal by early next week. Temperatures
should follow a similar trajectory with positive temp departures
trending modestly lower/toward climatology into the first week of
June. The tropical disturbance /Invest AL912016/ approaching the
Southeast U.S. coast will add additional moisture to an already
humid/unstable airmass in place through Memorial day weekend. Some
interaction between the tropical disturbance and mid latitude
trough crossing the Central Appalachians likely favors the
greatest pcpn risk/potential pcpn coverage Sunday night into Memorial
Day (Monday) with a decreasing chance for rain into Tuesday.
Deterministic and ensemble guidance are in broad agreement in a
dry period of weather from Tuesday into Wednesday before pcpn risk
gradually increases into the second half of next week. Heights are
forecast to rise a bit around the end of the period before the
large scale pattern slowly shifts toward a western ridge/eastern
trough configuration by June 5th as depicted by the 27/00z NAEFS
.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Ridge of high pressure remains in control, keeping a genuine
summertime weather pattern in place.
VFR conditions will dominate much of the remainder of the day.
However, there is moderately high low-level moisture/instability
in place to generate sct pulse- type thunderstorms with locally
gusty winds in mid/late afternoon across mainly the southeastern
half of PA. Did mention late-day VCTS in Susq Valley in TAFS. Any
flight restrictions should be mainly 15-30 minutes of mvfr cigs
and vsbys...though very brief ifr conditions are possible.
Vsby reductions to MVFR more likely tonight with humidity
increasing...with a few areas of IFR fog mainly confined to places
that receive rain today.
Sat...Early am low cigs/vsby possible. Isold pm tsra impacts.
Sun...Sct pm tsra impacts possible...mainly nw half.
Mon...Sct pm tsra impacts possible...mainly se half.
Tue and Wed...No sig wx.