Scientific Forecaster Discussion
fxus61 kctp 290827
Area forecast discussion
National Weather Service State College PA
427 am EDT Thu Jun 29 2017
High pressure off the eastern Seaboard will set up a warmer and
more humid airflow over the next several days. A cold front on
Saturday will bring a brief break in the humidity.
Near term /through tonight/...
The eastern US is under a broad upper ridge, but close to the
southern edge of the main westerlies. A series of weak
shortwaves rippling through the broad ridge will help advect
more unstable air out of the Midwest into the region.
Deterministic models develop some modest cape and mid level
lapse rates in the 6-7c/km range by afternoon. At least one
upper jet streak is forecast to slide into the lower lakes
which will enhance the wind fields with respectable deep level
shear expected to develop across my northern tier by mid day
into the afternoon. Overall an afternoon or evening shower or
thunderstorm will be possible, with the best chance being north
of I-80. Isolated strong winds and hail will be possible in
some of the stronger updrafts.
Convection will fade with the loss of heating this evening
leading to a warm-muggy overnight and a break in comfortable
sleeping weather we have had for the last several nights.
Short term /Friday/...
A broad west-southwest flow will be well established over the area Friday
making for a hazy-warm and humid day. Highs in the 80s to around
90 over the south will be above normal by about 3-6 deg on
The upper ridge will be giving way to increasingly cyclonic
flow aloft about a large low that will be dropping out of
central Canada toward the upper Midwest and gr lakes. I used a
blend of MOS pops to arrive at a forecast of scattered mainly
afternoon showers and thunderstorms. Near term guidance suggests
mid levels could be a bit on the warm side so the cap might be
tough to break and I might be a tad pessimistic.
Long term /Friday night through Wednesday/...
The extended part of the forecast will be influenced mostly by
a broad upper trough that will swing a series of shortwaves
down into the northestern US. Despite being under the trough into at
least early next week, the upper heights are forecast to remain
seasonably high as the best energy lifts north of PA.
A weak cold front is forecast to pass through the region
Saturday with the best chance for organized showers and
The gefs shows some small chance for precip leftover for
Sunday, but overall it should be a very warm day with a mix of
sun and clouds. Not sure if we will see a noticeable break in
the humidity at this point given how weak the airmass
difference is expected to be.
As we get into next week, differences arise between the GFS/gefs
and the European model (ecmwf) with the ec leaning toward a drier forecast and
the GFS/gefs showing a number of fast moving disturbances
rippling down under the northwest flow aloft creating the potential for
daily diurnal convection.
Despite the dominance of the upper trough, temperatures are
expected to be above normal through the end of the extended.
Aviation /08z Thursday through Monday/...
expect predominately VFR flying through the 29/06z taf period.
Light winds and increasing mid-high clouds should preclude fog
formation early this morning. Light rain showers will drift
across Lake Erie into western New York on the edge of the northwest airspace.
Isolated to scattered thunderstorm activity is possible
Thursday afternoon/evening mainly across the northwest 1/2 of
the airspace. Surface wind gusts 15-20kts from 170-240 degrees
from mid/late morning through the afternoon before diminishing
Fri...isold/sct PM tstm impacts psbl; most likely northwest 1/3.
Sat...tstms likely with MVFR/IFR restrictions.
Sun-Mon...no sig wx expected.