Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service State College PA
356 PM EDT Friday Apr 18 2014

Synopsis...
sprawling high aloft and at the surface over the western Atlantic
will slowly weaken over the next several days as another ridge
over the U.S. Rockies reaches the northeast late Saturday and
Sunday. The result is mainly fair weather with surface ridging and
cold air damming east of the alleghenies into early next week. A
trough in the northern stream should weaken the ridge and could
trigger showers Tuesday- Wednesday but yet another ridge moves in
quickly behind this system by next Thursday. Near normal
temperatures are expected most of the period.

&&

Near term /until 6 PM this evening/...
surface ridge axis extends from Gulf of Maine southwestward through
central New Jersey to east central Virginia this afternoon. Earlier
easterly flow and shallow maritime air mass over my southeast
counties has mixed out with the slight southeast adjustment of the
surface ridge axis...alleviating the easterly component. Much of PA is
now enjoying a good amount of sunshine through thin broken-overcast high
clouds. Temperatures are responding with return flow west of the ridge
axis with widespread 50s across central and western areas...and
even kbfd approaching 60f over the interior northwest...while
eastern areas are slower to recover from the morning maritime
influence and remain in the upper 40s to around 50 at middle
afternoon.

A shearing surface front is now pushing across Lake Erie and will
approach my northwest counties late this afternoon and this
evening...bringing a slight chance of -shra with it. Broadbrushed
a slight chance -shra across the entire northern tier in
collaboration with kbgm...but any rain that does fall will be
brief and very light. Any chance of showers comes before 06z...with
high pressure rebuilding southward from a 1036 mb ridge centered
over eastern Ontario by 12z Sat. Mins Sat morning will reach the
lower 30s north...while the southern half of central PA sees mins
in the lower 40s.

&&

Short term /6 PM this evening through 6 PM Saturday/...
aforementioned Canadian surface high will keep fair and dry conditions
over PA this weekend. Northerly gradient and dry air mass will
provide mostly sunny Saturday across central PA...with 850 mb temperatures
in the +3 to 0c range...yielding highs ranging from middle 50s north
to low to middle 60s central and south and light northerly breezes.

&&

Long term /Saturday night through Friday/...
an active split flow pattern over North America is forecast to
evolve into a fairly well phased upper ridge over the eastern
U.S. Toward the end of the period. This will result in limited
chances for precipitation through much of the period.

At this time the ensembles suggest the best chance of rain in the
next week will be in the Tuesday-Wednesday timeframe. Gefs favors
rain ahead of the deepening trough and frontal system mainly
Tuesday. But timing could change and some chance lingering into
early Wednesday.

The coming 7 days in general...
Saturday night into Sunday the region will be dominated by a
strong anticyclone. Should be generally fair dry weather. The
anticyclone weakens Monday but still in a ridge. Very weak flow
ahead of the approaching frontal boundary. There is no pressure
gradient over most of the eastern United States Monday in the gefs
or naefs.

A shortwave and front should trigger showers and rain Tuesday into
early Wednesday. Trough over a ridge and no big precipitable water surge...not a
big rain event. Heights should drop slightly below normal
Wednesday and 850 hpa temperatures drop to just below normal.

Heights and temperatures rebound back toward normal Thursday and
Friday could be a relatively warm day. Uncertainty grows in
forecast and some ensemble members show surge of moisture in warm
air ahead of yet another potential trough. The chance of rain
should gradually increase in the Friday or Saturday time frame.

&&

Aviation /20z Friday through Wednesday/...
thin middle/high clouds will stream overhead as VFR conditions
prevail tonight. A dissipating frontal system may spread a
shower into the far northwest late this afternoon or evening with low probability of
restrictions. VFR will continue elsewhere through the overnight.

Outlook...
tonight-Sat...areas MVFR this evening northwest...VFR elsewhere.

Sun-Mon...no sig weather.

Tuesday...several-hour period of MVFR ceilings poss with brief MVFR visibilities
in showers accompanying a cold frontal passage.

Wednesday...MVFR north/west with chance -shra...VFR elsewhere.

&&

Ctp watches/warnings/advisories...
none.

&&

$$
Synopsis...grumm/devoir
near term...grumm/devoir
short term...dangelo/Lambert
long term...grumm/gartner
aviation...rxr