Scientific Forecaster Discussion
fxus61 kctp 290318
Area forecast discussion
National Weather Service State College PA
1118 PM EDT sun may 28 2017
a warm front over western Pennsylvania will drift slowly
northeast across the state tonight and early Monday. A cold
front will push east from the Ohio Valley and cross the state
during the day Monday. Low pressure will become stalled over
northern Ontario during mid-week and will lead to a period of
slightly cooler than normal temperatures and occasionally
unsettled weather during the upcoming week.
Near term /until 6 am Monday morning/...
meso anal shows a Stark contrast between the warm-humid air
streaming into western PA and the cold dome of cool-air damming
stuck over central PA. The warm front has not moved from its
north-south position pretty much stalled along and parallel to
the Laurel Highlands.
Radar shows an MCS, the result of an earlier southward sagging
outflow boundary over northwestern PA, now approaching my central zones
from the west. The hrrr keeps the convection active well into
the wee hours of Monday morning in the warm advection ahead of
the approaching front. The airmass is marginally unstable
judging by the rap cape, and guidance suggests a continued slow
erosion of the low level instability as the cold front works
into the area later tonight and early Monday. There are also
indications of inertial instability looking aloft along the
strong jet streak sliding into the lower gr lakes.
So the radar should remain active with the threat for the next
several hours being for additional locally heavy rains. We had
some significant flooding in and around Somerset but the rain
has finally tapered off to light showers over my southwestern zones. The
Flash Flood Watch has been canceled and any additional flooding
if it occurs is expected to be minor.
Average rainfall is expected to total from around .50" over the
far southeast to between 1.00 and 1.50" over much of my central and
western zones. Locally higher amounts have already been
observed in the earlier heavier thunderstorms.
Short term /6 am Monday morning through 6 PM Monday/...
cold front will be slicing through central PA during the mid to
late morning hours, crossing the susq valley during the early-
mid afternoon hours.
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 (especially near the I-99/Route 220 corridor.
Long term /Monday night through Sunday/...
the long term period will be dominated by a large upper level
low the will slowly moving through the upper Great Lakes and
southern Canada. As that quasi stationary low slowly moves to
the northeast, it will bring surges of cool moist air across the
The first surge of cooler air moves across Monday night. This
will bring showers in from the W/NW. However, any precipitation
will cease as the night continues due to lack of diurnal
A reinvigorated boundary should bring a chance of precipitation
through the northern half of PA. Several successive shortwave
will move through mid to late week which will bring the
possibility of 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
Late in the week the models begin to diverge on the location
and timing of the upper level low so there is less confidence on
precipitation late in the week. However depending where the
boundary sets up there could be periods of showers Friday
through Saturday, though currently should be mainly along the
Aviation /03z Monday through Friday/...
adjusted thunder for 03z taf package.
Poor night for aviation, given low ceilings in spots, showers
and still some thunderstorms.
Conditions should improve from west to east on Monday, as
weak cold front moves across the area.
Tue...chance of showers and thunderstorms.
Wed...chance of showers.
Thu...no sig wx expected.
Fri...chance of showers and thunderstorms.