Scientific Forecaster Discussion
fxus61 kctp 281052
Area forecast discussion
National Weather Service State College PA
652 am EDT sun may 28 2017
a warm front will approach from the south today as a cold front
approaches from the west. The cold front will pass through later
tonight and early Monday. Low pressure will become stalled over
northern Ontario during mid-week and will create a slightly
cooler than normal and unsettled stretch of weather.
Near term /until 6 PM this evening/...
sunrise special fog obs with fog getting worse at many ob sites.
Will issue dense fog advy for the south for the next few hours.
Otherwise, the showers to the south have not made it north of WV
and may dissipate totally before reaching the County Warning Area.
fog and some low stratus make it murky this morning, especially
in the southern tier. Some fog has also crept into the rest of
the area. This was expected, but the more interesting aspect of
the weather this morning is the development of a cluster of
showers and thunderstorms over northern WV that are headed this
way steadily. The instability there is more likely aloft and
right over or NE of the warm front. The dewpoints are much
higher there than central PA, and it is all moving this way. We
do expect that the convection will wane some as it works NE and
farther from the good sfc dewpoints. But, scattered showers are
in the forecast for The Laurels this morning. The upper level
feature associated with this cluster will doubtlessly linger and
will likely be a force in popping additional showers later this
morning on the high terrain of central PA.
Destabilization is most likely to the west of the County Warning Area first. The
fog and stratus around locally will keep heating slow this
morning. But, when we break out and in those spots which do not
have lower clouds this morning, we'll see showers spread out and
cover much of the area by sunset. The guidance trend recently
is for more showers more quickly/earlier in the day. Almost all
models and members of the various ensembles make storms over the
alleghenies before noon. A likely scenario is that the mountain
tops will destabilize first and convection will drift NE. Wind
profile is not terrifying, wbz about medium or perhaps a little
lower, and heating will be questionable. This does not Bode well
for severe storms, but the storms moving into the County Warning Area from the
west out of the warm-er sector will have some punch. Marginal risk
includes Warren to Chambersburg and all areas SW, and there is a
slight risk for Somerset co. While this delineation is rather
specific, in reality, it may be an even sharper drop off
(perhaps only 20 or 30 miles) from a location where storms will
almost- certainly be severe to a place where storms will not be
severe at all. Will mention the isold severe threat in the west
and SC mtns in the severe weather potential statement.
Short term /6 PM this evening through 6 PM Monday/...
precipitable water GOES up to about 35mm before noon in the west, and this
maximum slides to the east during the late aftn and evening.
Storm motion to the NE is fairly certain but slow. The low level
flow is very light and out of the southeast at first, so the cells may
not move far and mbe vectors will be short during the evening.
So, expect a few heavy rainers. Widespread showers and storms
will occur this evening and through the night. The NAM had
trended faster with the cfropa, but has reversed with the 06z
run. Now, this puts it more in line with the other guidance, but
it may be a temporary thing. If the slower models come to
fruition, the front will be Half Way through the County Warning Area at 12z and
little if any showers are expected after noon in the east. The
front does not hurry along on Monday, though. It should turn
out to be a really nice day with just a westerly breeze in the
west, but the slowing front may keep it muggier in the east and
isold storms would then be possible in the east early in the
aftn. Temps may be a bit higher than currently advertised due
to some earlier clearing and the downslope effect.
Long term /Monday night through Saturday/...
a secondary surge of cooler air moves across Monday night. This
will ring showers in from the W/NW. However, timing is against
these surviving too far to the east.
Pops during this midweek period will be painted as chc -
translating to scattered showers with preference for the
majority of the quantitative precipitation forecast (albeit quite light at that)to be across the
typical west-nwrly flow upslope prone areas of the Laurel
Highlands and northwest mtns. The chance for any thunder will be very
minimal Tuesday through Thursday.
Generally dry northwest flow occurs late in the week into next weekend as
a 1020 sfc high over the upper Midwest Friday evening builds southeast twd
the region. Pops thur night through Fri night will be 30 percent or
After our bout of coolish weather with temps several deg f below
normal Sunday and Monday, gefs mean temps rebound back to near or
slightly above normal (even under slightly cooling 850 mb temps)
for Tuesday through at least Thursday. Ecens mean temps are several
deg warmer than the gefs and nat'l blend of models temps. Leaned
closer to the cooler solutions based on the few-svrl deg c of
cooling aloft with near to slightly below 850 mb temps.
Aviation /12z Sunday through Thursday/...
fog of varying density continues across central Pennsylvania
this morning. Conditions vary from VFR across the kipt area, to
vlifr in the lower Susquehanna valley.
Early morning fog and stratus will lift this morning, followed
by VFR conditions at most airfields for the afternoon. Showers
and scattered thunderstorms will move in from the west during
the afternoon. These have the potential to produce isolated to
scattered restrictions, but at this point, coverage appears to
warrant only vcsh mention in the tafs.
More widespread showers, and possible thunder, overnight, with
widespread restrictions expected.
A cold front will move through on Monday, ushering out
precipitation from west to east during the day.
Mon...showers ending west to east. Restrictions possible.
Tue...scattered showers possible mainly northwest. Otherwise no sig wx
Wed...slight chance of showers with reduced ceilings.
Thu...no sig wx expected.
dense fog advisory until 9 am EDT this morning for paz017>019-