Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1054 am EDT Monday Sep 22 2014
a large area of high pressure over the Midwest...will build east
across the middle Atlantic region Tuesday before drifting over the
New England states for the latter half of the week. This dominant
weather feature will provide generally fair and cool weather for
the entire week.
Near term /until 6 PM this evening/...
first bout of cold season lake effect clouds and showers in full
swing across the northern and western mountains of Penn...thanks to Delta
Lake-850 mb temperatures around 20c and a deep... well-aligned nwrly
flow across Lake Erie and the long axis of Lake Huron.
The clouds will be tough to break up...and based on several
factors including model forecast of high relative humidity/S in the 925-850 mb
layer...the 850 mb ridge axis well to the west of Penn through 12z
Tuesday...and another /albeit weaker/ 850 mb thermal trough
drifting southeast across Lake Erie in the 06-09z period Tuesday...it
should stay overcast for at least the first half /if not all/ of
the night tonight across the northwest mountains low level trajectories appear
favorable to keep plenty of clouds across the Laurel Highlands as
The thinner...and mainly broken strato cumulus that will be present for
the rest of today across the central and southeast zones should scattered out
early tonight...thanks to the mean surface-850 mb flow veering around
to the north-northwest and decreasing to around 10 kts.
Maximum temperatures today will range from the l-M 50s across the northern and western
mountains...to the middle and upper 60s throughout the lower susq valley.
These readings will give US an early taste of autumn that
officially begins here at 0229z Tuesday. The highs will be a solid
6-10f below normal /with the greatest departures of 12-14f below
normal across the northwest mountains
There will be a few...thin streamers of showers drifting off Lake
Erie and crossing the northwest mountains and Laurel Highlands...so we
maintained the 20-30 probability of precipitation in those areas today. Nothing more than
a few brief sprinkles will occur near...and just to the southeast of the
Short term /6 PM this evening through 6 PM Tuesday/...
high pressure noses in from the Midwest and be right about
overhead by Tuesday evening. 800 mb temperatures will already be rising
tonight. Clearing is expected for much of the area...but some
reinforcement to the clouds may come down from the north late
tonight/Tuesday morning. Refer to the above /near term section/
for additional details on the cloud trends tonight.
The shallow cold air and inversion will let the winds go
calm and temperatures could drop into the M/u30s in the higher
elevations. Employing some of the colder model solutions where skies
do clear out tonight and winds lighten...will mention patchy
frost with min temperatures in the middle 30s. However...a true consensus
all/model blend approach to our temperature grids tonight and early
Tuesday would yield mins in the upper 30s to around 40f with
little or no concern for frost.
A better bet is that some valley fog will form in the
deeper/darker valleys by sunrise Tuesday as the temperatures fall well below
the water temperatures. The colder spots in the eastern valleys will
also drop off near 40f by morning. Tuesday will be a much milder
day with temperatures rising about 25f during the day and reaching about
10f milder than Monday in the northwest - but staying similar to Monday
in the lower susq.
Long term /Tuesday night through Sunday/...
high pressure Will Park itself over New York and New England with
+2 to +3 sigma above normal mslp anomalies by Wednesday-Thursday.
The models seem to be in fair agreement showing a blocking 500 hpa
anticyclone to the northwest as a massive 500 hpa positive height
anomaly of +2 to +3 sigma develops over central Canada by Thursday
and into Friday.
The models and ensemble means do well forecasting anticyclones so
there seems to be more of a consensus on the fair weather forecast
next week. Expect diurnal valley fog and low clouds likely to
affect the region each morning once the big high takes hold....and
continuing daily into next weekend. That massive high should
continue the dry fair weather through next weekend.
Aviation /14z Monday through Friday/...
extensive cloud deck continues to cover western and central areas
late this morning. In the western and northern mountains...
widespread MVFR to IFR ceilings are in place. Over central
airfields...MVFR ceilings prevail. Over eastern areas...VFR conditions
can be found with downsloping leading to a higher...sct-bkn
cloud base. Radar continues to show several narrow...streamers of
light precipitation across western and central areas of the state.
Widespread nature of clouds will mean that they will linger
across the west well into the afternoon...before drier
air...surface ridging...and mixing help to break these up across
the southeast half of the state tonight. The well-alinged and deep nwrly
flow will help to maintain thicker strato cumulus across the northwest
mountains...and to a slightly lesser degree over the Laurel Highlands.
Generally tranquil weather with mainly VFR conditions should
prevail Tuesday through Wednesday...with the exception of some patchy
Tue-Fri...mainly VFR...but with daily restrictions in morning fog