000
FXUS61 KCTP 210749
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
349 AM EDT Sat May 21 2022

.SYNOPSIS...
A surge of summerlike heat and humidity (the hottest weather
since last summer) will bring record challenging/breaking
temperatures and scattered strong to severe thunderstorms to
central PA this weekend. Conditions will dry out into early
next week with noticeably cooler temperatures and more
comfortable humidity.

&&

.NEAR TERM /THROUGH TONIGHT/...
Very warm and muggy start to the weekend with locally dense fog
in the central and eastern valleys. We are monitoring ASOS/RWIS
observations and may issue a dense fog advisory soon as visby
trends continue to deteriorate as high clouds peel off to the
northeast.

An anomalous upper level ridge building along the east coast
will bring a surge of summerlike heat and humidity with record
challenging/breaking high temperatures (see climate section of
the AFD). Model 850mb temps around 18C should support max temps
ranging form the upper 80s over the Alleghenies to the low and
mid 90s in the Lower Susquehanna Valley (+10-20F above climo and
warmer than yesterday).

An examination of latest model soundings suggests deep mixing
will result in afternoon dewpoints a few degrees below NBM
guidance, especially over the central mountains. However, max
heat indices peaking in the mid-upper 90s are still likely over
parts of the Lower Susquehanna Valley. While max HX values peak
just below 100F or advisory criteria, heat stress impacts are
still expected given limited exposure/acclimation to the heat
this early in the season. Poor air quality will also be a
factor with a code orange air quality alert in effect for a
portion of the lower Susquehanna Valley.

Fog dissipates to mostly sunny skies before scattered cumulus
develop during late morning and afternoon. Warm temps aloft
associated with building ridge should largely suppress
convection over the majority of CPA later this afternoon and
evening. Hires models indicate a SW-NE oriented corridor of
t-storms should fire within a seasonally moist 1-1.5" pwat
plume extending from TX through the lower Great Lakes. Pre-
frontal or lake-breeze convergence may also act as a triggering
mechanism for convection which should approach/reach the far NW
zones by 00Z/8PM.

Heating of high-pwat air mass will yield significant CAPE by
late in the day. However, deep layer shear looks fairly weak at