Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
814 am EDT Thursday Jul 10 2014
a persistent upper level trough over the Great Lakes will dampen
as it crosses the New England states into the weekend...with a
weakening quasi-stationary front trailing southward along the middle
Atlantic coast. Despite the influence of high pressure at the
surface...the area will remain vulnerable to isolated showers and
thunderstorms into the first part of the weekend. A series of
reinforcing cold fronts will provide several opportunities for
rainfall through early next week...while helping to carve out a
highly anomalous upper trough and bonafide polar vortex across
southeastern Canada and the upper Great Lakes.
Near term /through tonight/...
isolated pockets of fog and low clouds will burn off completely in
the next hour or two. Elsewhere mosunny skies should be the rule
for most of the day. An upper level trough moving eastward across the
lower Great Lakes...combined with weak instability...should be enough
to generate scattered rain showers/thunderstorms and rain during the afternoon...mainly across the scntrl
mountains 800 mb temperatures between 12-14c should translate to highs from the m70s
over the highest terrain of the alleghenies...to the m80s across
the lower susq valley.
A shower or two may linger over the southeastern zones late this
evening...but high pressure will dominate for the most part with clearing
and patchy valley fog developing overnight and into early Friday
morning. GFS MOS appears too cool tonight based on blend of all
model surface dewpoints. Bcconsall appears much more reasonable...with lows
ranging from the l50s over the northwest mountains to the m60s over the lower
Short term /Friday through Friday night/...
very little change in the overall pattern expected into day 2
with even weaker forcing aloft due to dampening of upper trough.
Expect bulk of precipitation to remain confined to eastern NC/Virginia to the
Delaware-Maryland-Virginia near q-stationary front and hi moisture precipitable waters axis. Still cant rule
out an isolated rain showers/thunderstorm during the afternoon over eastern prtns of the County Warning Area
but probability of precipitation will be barely mentionable/at or below 20 percent. Temperatures should edge
a little warmer than Thursday. Strong warm air advection upstream over the Great
Lakes/Ohio Valley will likely bring some middle-high clouds into western sections by
Long term /Saturday through Wednesday/...
the area should be in more of a return flow regime by Sat as the
surface high slips off the East Coast. Similar to days 1 and 2..still
cant rule out an isolated rain showers/thunderstorm in spots while most areas stay
dry. Stalled front along the southeast coast should pivot back
northward as warm front Sat night into early Sunday with S-southwesterly low level jet increase
low level moisture flux through the upper Ohio Valley into western PA in advance of
lead shortwave energy and associated surface cold front moving southeastward across the
Amplification of the upper pattern begins early next week with a
model consensus generally indicating a frontal precipitation axis shifting
southeastward through the Great Lakes/Ohio Valley regions into central PA sun-Mon.
Although predictability is too low at this time...a severe weather threat
should spread southeastward in time from the upper Midwest/Great Lakes/Ohio Valley
into the middle Atlantic and northeast states...along southern periphery of
stronger winds/cyclonic flow aloft and several reinforcing cold
frontal surges associated with the amplifying synoptic upper
trough. Each cold frontal surge will provide an opportunity for
showers/thunderstorms through at least Tuesday.
The highly anomalous amplification of the large scale pattern is
a virtual lock by the end of the period as indicated by all medium
range global numerical models and ensemble systems. This well-
advertised high meridional event will feature a full-latitude
ridge and searing heat out west...not be be outdone by the return
of the polar vortex in the east over Quebec/ont and the upper Great
Lakes. Considering the magnitude of the upper level trough with
500mb standardized anomalies on the order of -3 to -4sd in both
the deterministic global models and their respective ensemble
means...confidence in a period of below average temperatures /during what is
climatologically the hottest time of the year/ is very high from
Tuesday-Thursday of next week.
Aviation /12z Thursday through Monday/...
11-3.9um satellite imagery showing extensive valley fog across the
northern mountains early this morning. However...any low ceilings/fog
should rapidly mix out around 12z...with predominately VFR conds
expected for the rest of the day. However...a trough of low pressure
approaching from the west will likely trigger scattered rain showers/thunderstorms and rain during
the afternoon and evening hours. The best chance of a brief visible reduction
will be across the SC mountains...including kjst and kaoo.
Clearing skies and a light wind will promote patchy fog
tonight...especially where rain falls later today.
Fri-Sat...patchy am fog possible.
Sun-Mon...brief...mainly PM...thunderstorm impacts possible.