Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
314 PM EDT Sat Apr 18 2015
dry and warm conditions will give way to increasing rain chances
on Sunday and Monday. Unseasonably cool temperatures are expected
for the remainder of the week.
Near term /through Sunday night/...
skies are mostly clear under high pressure. Abundant sunshine
this afternoon will give way to a pleasant evening and the
addition of a few more high clouds. Temperatures tonight will
remain above average as low- to middle-level flow begins to veer to
Sunday will begin dry with clouds increasing quickly from the
south. Cloud cover will help keep temperatures in check compared
to saturdays Marks...but are expected to be average. A low
pressure system currently coming together over the lower
Mississippi Valley will move north through the day on Sunday...
spreading clouds and then rain showers south to north through the
Rain is expected to begin in the early afternoon along our
southern zones...reaching Pittsburgh by late afternoon. At this
time...the heaviest precipitation is expected to fall along the
eastern slopes of the high terrain within the upslope flow...and
through Ohio...closer to the track of the low and the stronger
low-level jet. A relative minimum in precipitation is expected
just west of the ridges as downsloping east-southeasterly flow
will work to counteract some of the ascent along the warm front.
Still...enough moisture and lift exists with the warm front that
everyone is expected to get precipitation through Sunday night. A
large upper-level dry slot will move in with the warmer air
Sunday night...reducing shower chances and coverage. Tax
Short term /Monday through Tuesday night/...
subsidence is expected on Monday morning in the wake of a
departing shortwave trough...which will aid in eroding any
lingering precipitation from late Sunday night. This subsidence
will promote the modest heating of a relatively-moist airmass on
Monday beneath 45-50kt of 500mb southwesterly flow.
A second shortwave trough will move quickly northeastward through the flow
and will cross the region by late Monday afternoon. Lift in
association with this wave will aid in convective development by
middle-afternoon Monday. Showers and thunderstorms are expected to
develop on the higher terrain first and along the surface trough
associated with the upper wave later in the afternoon.
Although temperatures will reach the lower 70s...low-level lapse
rates will be quite steep...supporting a threat of gusty winds
from any vigorous and deep convection. Widespread severe
thunderstorms are not expected owing to weaker middle-level lapse
Unusually strong upper low pressure will build southeastward into the Great
Lakes region by Tuesday...with its associated cold front expected
to cross the forecast area during Tuesday morning. This low will
persist through much of the week.
Cold advection behind the frontal passage will provide increased
coverage of stratocu and possible lake enhancement to light
precipitation...but any precipitation likely will be limited only
to the northern zones owing to westerly fetch and advection of
very dry air in the Post-frontal airmass. Maxima on Tuesday will
reach only the middle-50s at best. Kramar
Long term /Wednesday through Saturday/...
unsettled weather is expected to continue through next week with
a broad upper trough influencing much of the eastern US.
Confidence is low with differing model solutions later in the
week...and probability of precipitation were kept low. Temperatures were forecast using
wpc guidance...which were at...or slightly below the seasonal
Aviation /19z Saturday through Thursday/...
VFR conditions expected the remainder of the day under high
pressure. A system approaching from near the Gulf of Mexico will
spread clouds and stronger suface flow through the forecast area
Sunday. Clouds will gradually transition from an upper- to middle-
level deck before the low ceilings and rain come in right at the
end of the current taf period. Tax
Outlook.../Saturday night through Wednesday/...
restrictions are likely later Sunday and Monday as low pressure
develops toward the Great Lakes and pulls a cold front across the