Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
250 am EDT Tuesday Jul 7 2015
a weakening upper low will track east across the region tonight.
A weak ridge will bring very warm and humid conditions to the
region today. A cold front will approach tonight...then stall
out along...or just south of the Mason Dixon line for midweek. A
few waves of low pressure will ripple east along this boundary
bringing the likelihood for showers and thunderstorms Wednesday
afternoon and evening...and again on Thursday. High pressure will
build in for Friday and bring slightly cooler and notably less
humid weather with little chance for rain.
Near term /through today/...
last vestiges of the greatly weakened upper trough are seen as
just a few highly isolated /but briefly heavy/ rain showers
drifting north across the region early this morning.
Plenty of clouds and patchy fog will be around early today as
this features departs to our east. For the late morning and
afternoon hours. Deep southwesterly flow...slightly decreasing surface
dewpoints...and middle- level warming will combine to bring US a very
warm day with temperatures a few- several degree f above normal...and
little chance for rain in most places.
A weak Lee trough over and to the east of the susq valley...and a
cold front well off to the northwest will bring low chances for pulse
showers/thunderstorms and rain to our eastern zones during the middle to late
afternoon hours...and perhaps some more organized/stronger
multi-cell thunderstorms and rain clusters across the far northwest late in the day into
High today will likely be the warmest this week...and about 3-4
degree above normal. 800 mb temperatures temperatures near 17c should translate to maximum
temperatures well into the 80s over most of central PA.
Short term /tonight through 6 PM Wednesday/...
surface cold front slides slowly to the southeast across the
commonwealth tonight through Wednesday morning...before stalling out
near...or just to the south of the Mason-Dixon line.
Main forecast problem/challenge for the upcoming shifts will be to
try to pin down /via some semblance of model consensus/ the
location and timing of convective features/areas of low pressure
that will form and ride east along this boundary Wednesday into
Currently...a gefs/NAM/sref blend point toward the best chance for rain
with embedded thunderstorms and rain focused across the southern third to half of
Penn Wednesday...where precipitable water will stay at or above 2.0 inches. The sharp
gradient to much lower precipitable water /aob 0.75 of an inch/ will stay near
or just to the north of the Penn/New York border where chances for
rain will be quite low Wednesday and most of Wednesday night.
Maximum temperatures Wednesday could easily turn out to be several degree f or
more below current forecast values depending on the timing and extent
of convection across the central and south. Current temperature forecast
busting on the low side for wednesday's high is a very low
probability. Will be adjusting these temperatures with 03z sref and 06z
op guidance where needed.
Long term /Wednesday night through Monday/...
the 07/00z model and ensemble guidance is providing a fairly
consistent signal that the area will remain in a low amplitude
quasi-zonal middle/upper flow pattern within the northern stream
westerlies. As might be expected in this pattern...there is low
predictability/confidence given degree of spread and meaningful
differences associated with shortwave details. This largely
unsettled and recently persistent weather pattern for the local
area will be modulated to some extent by retrogression of
unseasonably strong upper trough/ridge couplet off the West Coast
and over the southeast and scentrl U.S. There is broad support for
another mean trough to develop over the northeast/Middle Atlantic
States by next week/July 13th as energy ejecting from California upper low
evolves downstream in the westerlies and teams with vortex over
In terms of sensible weather...a well-defined cold front enters
central PA early Wednesday accompanied by showers/tstms...then
becomes wavy as it stalls out from near the Ohio River/Mason Dixon
line. Expect one or more episodes of precipitation through late week most likely
due to mesoscale convective system remnants or convectively induced lows tracking eastward from
the middle MS/Ohio Valley...but too difficult to Pin Point timing/location
at this point. Fwiw the model bias is usually too far north with
mesoscale convective system activity. Precipitation risk should eventually be enhanced toward the
end of the period into early next week as California low energy and
associated surface system reaches the Great Lakes.
What we can say with relative certainty is that we do not expect
any heat waves or extended periods of dry weather over the next 7+
Aviation /06z Tuesday through Saturday/...
sent 03z taf package.
Still some showers and storms across the east.
Earlier discussion below.
Conditions over the still mainly rain free lower susq
valley...with reduced conditions continuing over the Laurel
Highlands where showers are more numerous.
Expect shower activity to increase in coverage and spread from
south to north through the afternoon. Showers will tend to be
slow-moving and could produce heavy downpours and local IFR
conditions. The upper low will weaken as it enters central PA
overnight...but we should maintain a risk for scattered showers.
Expect ceilings/visibilities to trend gradually lower overnight given
diurnal cooling...very humid airmass and light winds...with at
least marginal restrictions likely at many sites into Tuesday
Lower conditions Tuesday morning will improve by middle morning to
middle day. A cold front will approach the airspace from the lower
lakes/Ohio Valley by late in the day and shift slowly southeastward into the
airspace Tuesday night/Wednesday before stalling out near PA/Maryland border
Thursday into Friday.
Wed-Sat...VFR/MVFR with periods of rain showers/afternoon thunderstorms.
short term...la corte/Lambert