Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1115 am EDT Tuesday may 5 2015
a slow moving frontal boundary will keep rain chances in the
forecast through Wednesday.
Near term /through tonight/...
mesoscale shortwave moving across Michigan at 15z with front
draped from Northern Ohio into western PA and beginning to
transition back north. Likely probability of precipitation for the afternoon with
redevelopment of showers and isolated thunderstorms expected as
front shifts northeast. Lower probability of precipitation I-70 south farther from
Model guidance has trended further north with the track of the
upper-level wave tonight...as the ridge of high pressure re-builds
in the mid-west. Best rain chances look to be across the far
north. Remainder of region will be in the warm sector behind front
with building ridge aloft. Relatively mild temperatures will
Short term /Wednesday through Thursday/...
ridging starts to build over the Ohio Valley during the day on
Wednesday. This will drop h500 heights across the County Warning Area in response
and help to sag the frontal boundary a bit further south during
the day. Focused higher probability of precipitation in southern portions of County Warning Area during
the afternoon. Enough instability is present for the continued
chance of thunder as well. Kept probability of precipitation in chance category with
continued uncertainty as to frontal evolution. As ridge starts to
build eastward...frontal boundary will become more diffuse with
time. Allow probability of precipitation to fall off during the evening hours with loss of
H500 ridge is in control for the remainder of this period...with
the ridge axis passing by around 00z Friday. GFS/European model (ecmwf) both paint
some diurnal quantitative precipitation forecast across the area Thursday and Friday afternoons.
Think that this is overdone for the most part as at least modest
capping should be present under the ridge. Exception could be
along the eastern ridges with modest upslope flow...and kept an
afternoon/evening slight chance both afternoons in this area.
Otherwise...dry and warm conditions will persist. A slow warming
trend will see temperatures rise back into the lower and middle 80s
for most areas by Friday.
Long term /Thursday night through Monday/...
upper ridge gets slowly dislodged with time as energy ejects from
western U.S. Trough and towards the upper Mississippi Valley by
00z Monday. Resulting surface low and frontal system will advance
eastward with time...perhaps arriving Monday night or Tuesday.
Ahead of this...mainly diurnal probability of precipitation get a bit higher each day
with the departure of the ridge. Ripples along the back side of
the ridge may provide localized enhancement...which of course are
tough to time at this distance. The front brings more generalized
precipitation chances Monday into Tuesday.
Fairly static above normal temperatures are forecast Friday night
through Monday night...with highs in the 80s and lows on either
side of 60. Cooler temperatures may arrive Tuesday with the front.
Aviation /15z Tuesday through Saturday/...
visibility restrictions this morning have been confined to a
select few terminals where at least some clearing had taken
place...and fog was able to form. Any remaining restrictions
due to fog should end quickly after sunrise with mixing and as a
broader cloud shield moves in.
Additionally...an area of showers is moving along the broad
frontal zone...and are currently through eastern Ohio. Not
expecting much further expansion or strengthening of these
showers through mid-morning...but they could bring temporary
visibility restrictions as they slowly move east across
Later today...have this line of showers lifting north with the
broad frontal zone where instability this afternoon could drive
additional showers/thunderstorms. Have included thunderstorms in the vicinity for northern
and eastern taf sites...but spatial extent of thunderstorm
activity should be fairly limited.
Outlook.../Tuesday night through Saturday/...
scattered restrictions is a possibility early Wednesday as
frontal boundary slowly decays.