Area forecast discussion
National Weather Service Pittsburgh PA
357 am EDT Sat may 18 2013
Synopsis...
seasonably warm weather will continue over the weekend with cooler
than normal temperatures in the mountains. However...a chance of
showers and possibly an afternoon thunderstorm will also be in
the forecast.
&&
Near term /until 6 PM this evening/...
weak frontal system continues to our south. Not a lot of push NE
with 500 mb ridge still to our west and actually sharpens a little with
Midwest low starting to low push east by late Sunday. Heights
actually on the rise. Surface front will try moving NE and fairly
good moisture gradient across County Warning Area at this time with dew point 39 fkl and
58 zzv. Expect moisture to continue to slowly increase but think
probability of precipitation limited to chance. Also sref advertising slowness of
moisture with calibrated probability Thunder Field very slow to progress
NE and tight gradient along PA/Ohio border of thunder probability.
As a result...will keep thunder out most of PA for today and bring
it in along southern portions and east-central Ohio. NAM bias cor
temperatures have been rather good recently...however this guidance advertising
middle 80s many places today. Thought this a little high given
increase in clouds and opted to go with blend NAM bias cor and
MOS. Appalachian plateau to remain rather cool with continued east-
southeast flow.
&&
Short term /6 PM this evening through Monday/...
weak front continues to meander just south of region.
Meanwhile...appalachian plateau continues cool with showers under
east-southeast flow. Remnant moisture will continue to give chance probability of precipitation with
a diurnal minimum overnight and increase with afternoon heating
and subsequent instability increase. Frontal system finally to
push northward later Monday with increase in southerly flow and
rise in temperatures.
&&
Long term /Monday night through Friday/...
upper level ridging continues in part due to Midwest cutoff low
pushing east. Meanwhile...surface front still draped close to or
just north of region. Middle-west upper level low will continue to
push east but lose intensity and in fact opens up as it
approaches our area. As a result...system slows and takes it time
to exit region by end of period. As a consequence...probability of precipitation continue
until late in forecast period.
&&
Aviation /07z Saturday through Wednesday/...
VFR forecast today. Will start with a scattered-broken cirrus deck. As the
early morning progresses and area of middle clouds will move across
northern ports and area of middle clouds will move into southern
ports. This southern deck will decay by late morning...allowing
for sunshine and the development of cumulus. It is possible that a
shower or storm could develop over ports south of pit in the
afternoon...but with low confidence at convection hitting any
particular port... will instead indicate cumulonimbus.
Outlook.../Saturday night through Wednesday/...
there will be an increasing chance for restrictions in diurnally spprted
scattered showers and thunderstorms during the first half of the week.
&&
Pbz watches/warnings/advisories...
Maryland...none.
Ohio...none.
PA...none.
WV...none.
&&
$$
