Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 130211
Area Forecast Discussion
National Weather Service State College PA
911 PM EST Thu Jan 12 2017
-- Changed Discussion --A cold front is exiting the southern tier of PA. High pressure
will build into the region on Friday. An anomalous upper level
ridge will build over the southeast United States this weekend
into early next week. At the surface, a quasi-stationary frontal
boundary will oscillate in the vicinity of PA through early next
week. Milder conditions will work back into the area for mid week.
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.NEAR TERM /UNTIL 8 AM FRIDAY MORNING/...
-- Changed Discussion --Wind has switched to the NW at most sites. However, the light wind
in the eastern valleys is allowing fog to form. As of yet, no
M1/4SM obs. But, if the wind does not pick up a few knots, it may
get dense. Rain band breaking up and getting lighter. Rain has
ended in the NW, but some flooding is still on-going. Latest
reports indicate few if any new areas of flooding have developed
in the last couple of hours. Have therefore canceled the flood
watch. What is on-going should start to recede soon - but the
larger waterways, esp the Conewango Creek in Russell, will rise a
Front is through 85% of the area at 7pm/00z. Precip is holding
together slightly better than expected, but is on the wane. Wind
is still light in the ern valleys and some fog has started to
form. while winds will not be all that strong overnight, the fog
should not get dense as there will be some gradient wind. Temps
will be getting cool enough by midnight in the NW that if
something were to fall, it could be flurries or sprinkles or some
fzdz. Will have to watch for that possibility.
Radar continues to show moderate to heavy rain moving across my
NWRN counties. Flood advisories continue for reported minor
flooding as snow melt, rainfall and frozen ground conspire to
cause rapid runoff.
The latest HRRR shows the heaviest rain beginning to move
southeast out of the northern mountains by mid afternoon so
conditions should begin to improve over the next 3-6 hours.
Will maintain POPs at or around 100% across the northwest
counties, while the southern half of the state should see no more
than a passing shower at times through 3PM. With the showers
expected to diminish as they enter the central counties and lower
Susq, I tapered the POPS to cover this. Guidance further suggests
the rain that makes it into my southern counties will taper off
rapidly between about 6 and 9 pm tonight, leading to a mainly dry
overnight. As of right now I expect enough post frontal
cloudiness to keep fog from becoming a widespread problem. But if
we scatter out, that will change.
Another threat will be for an isolated severe storm. Meso anal
shows a nose of meager Cape but with intense windshear nosing
into western Pa along and just ahead of the surface front.
Lightning data shows an occasional cluster of strikes indicating
thunder is occurring. SPC has a marginal risk up into western Pa
so the potential for a strong wind gust cannot be ruled out with
any potentially well organized convection.
Lows will range from the mid 20s over the NW to around 40 over the
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.SHORT TERM /8 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Friday looks basically dry with brightening skies as cooler and
drier air works in from the north and west. Highs will be 20 to
30 deg cooler than today.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Did not change much for the weekend.
Colder air at low levels this weekend will keep the risk of mixed
precipitation across the area on Saturday, and again by the later
part of Monday. Main area of concern will be the southern part of
central PA. Not looking at much QPF with either system, but type
of precipitation being the concern.
More detail below.
This weekend, central PA will be in between an anomalous upper
ridge over the southeast conus and shortwave traversing southeast
Canada. At the sfc, a weak wave of low pressure is progged to pass
south of PA along a quasi-stationary front. A period of light
snow or wintry mix will likely accompany this feature Sat/Sat
evening, mainly across the southern counties. Fairly good
agreement among med range guidance for a dry/seasonable Sunday, as
high pressure builds southeast into the region. Main change was to
edge a little precipitation a few miles further north.
Next week looking mild and showery, as bulk of med range guidance
shows a building ridge along the east coast with a surface low
track west of PA. It looks like there will be enough low lvl cold
air to support some ice ahead of first low on Monday.
For Tue-Thu, med range guidance placing PA in deep southerly flow
ahead of a trough over the midwest. Plume of anomalous PWATS over
the region supports the idea of warm and showery weather. GEFS
temp plumes showing no below freezing temps (even at BFD) Tuesday-
Some variation with potential waves on the front by late next
week, thus did not want to take mention of showers out for late
Thursday at this point.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
A cold front will exit the southern tier of PA this evening. High
pressure will build into the region on Friday.
Rain band in association with the cold front was earlier much more
notable with a period of heavier rain and gusty winds, but at 02z
it is quickly diminishing as it pushes across the southern
mountains and Lower Susquehanna Valley. LLWS also coming to an end
as parent low tracks further into New England and low level flow
weakens a bit as it turns to the west.
Winds at the surface will pickup as the night wears on - they
already have across portions of the west. But until they do, the
light winds and plentiful ground moisture will bring areas of
fog - some dense - to the valleys of the east (including KIPT).
This should mix out overnight as winds increase with drier air
moving in. Over the west, upslope flow should keep IFR/MVFR in
place through much of the overnight before gradual improvement Fri
morning - as KBFD looks to be the last to improve to VFR.
Developing downslope flow will bring improvement to VFR early
overnight to the central mtns.
Fri...Mainly VFR with decreasing winds.
Sat...Sub-VFR likely with wintry mix southern 1/2 airspace.
Mon-Tue...Sub-VFR likely with another period of mixed pcpn psbl.
Daily max temperature records for today...
Harrisburg 60/1890 == 65 today
Williamsport 57/1986 (55 today)
Altoona57/2006 == 66 today
Bradford 53/2013 == 56 today
Johnstown 66/1898 (63 today)
NEAR TERM...Dangelo/La Corte
SHORT TERM...La Corte