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fxus61 kpbz 270941 
afdpbz

Area forecast discussion
National Weather Service Pittsburgh PA
541 am EDT Thu Apr 27 2017

Synopsis...
a very warm day on tap. Showers and storms return this
afternoon ahead of a cold front. Unsettled but warm weather
through the weekend,

&&

Near term /until 6 PM this evening/...
a cold front associated with an occluding system will cross the
County Warning Area during the late afternoon/early evening. Latest models runs
are increasing the eastward speed of the system, so have sped
up the onset of pops today. This appears to be mostly related to
a faster and stronger shortwave trough, which will more
efficiently break down the eastern ridge. Energy aloft splits
this afternoon with the best dynamics spinning northward toward
the Great Lakes surface low. As this large scale ascent rushes
northward, models are showing a decrease in intensity and
coverage of the convection ahead of the front. Atmosphere does
destabilize ahead of the boundary, but the best instability
remains aloft. Additionally, convection that does develop will
be sustained by the well sheared environment. The greatest
threat today remains damaging winds and large hail. A couple of
elements will be working against the development of strong
storms. First, pre-frontal upper and mid-level clouds, and
second, the very warm air aloft. Any cooling aloft is closely
linked to the surface front, so this leads ME to believe that
any strong convection will also be tied to frontal passage.

&&

Short term /6 PM this evening through Saturday/...
cold front and associated convection will quickly exit to the
east this evening.

Dry weather returns Friday with high pressure. Any cooler air
behind today's front will be quickly ejected to the north as
strong warm air advection takes over.

Eastern ridge will try to build late Friday, but will be shunted
by a series of upper level waves which will ride over the top of
the rising heights. These wave will bring showers and storms
back to the area late Friday night and Saturday. Seeing
discrepancies in models solutions on Saturday with the position
and timing of the shortwaves. Have leaned toward a more
northern track, which complies with slowly rising 500mb heights
on Saturday.

&&

Long term /Saturday night through Wednesday/...
an active pattern is figured for the remainder of the weekend
into early next week. A few shortwaves will cross in continued
moist southwest flow along the front of a broad trough, leading
to rain chances again on Sunday. Timing remains tricky, but
Saturday night currently looks to be the period with the lowest
coverage in the warm sector. Temperatures remain above normal.

The trough lifts out as a closed upper low into the Great Lakes
by Monday, pushing a fairly strong boundary across US. Given
system strength, the amount of moisture, and a possibly negative
tilt to the upper trough, strong storms appear possible. Behind
this system, quieter weather and seasonable temperatures are
expected into the middle of next week.

&&

Aviation /10z Thursday through Monday/...
VFR conditions are forecast for the morning hours, although
clouds will be thickening with time ahead of an approaching cold
front. Winds will pick up out of the south and gust to 20 to 25
knots once mixing gets going. Timing for the frontal passage
will be between roughly 18z and 02z, with showers and
thunderstorms along and ahead. Coded up a period of MVFR showers
with vcts, with exact timing still a bit uncertain, but brief
IFR conditions will be possible in any downpours. Stronger wind
gusts are also possible in the strongest storms. Behind the
front, winds will diminish and MVFR ceilings will linger.
Considered adding fog, but think it will be patchy at best as
boundary layer should remain fairly mixed overall.

Outlook...
occasional restrictions are possible this weekend along a
stalled frontal boundary. Better restriction chances arrive with
a strong cold front Sunday night into Monday.

&&

Pbz watches/warnings/advisories...
Maryland...none.
Ohio...none.
PA...none.

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