Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
923 am EDT Monday Jul 28 2014
a broad area of low pressure will keep showers in the forecast
this afternoon. Below average temperatures will be felt through
the end of the week.
Near term /through tonight/...
previous forecast on track with surface low now into New York
state and upper level trough/shortwave to cross region this
afternoon. Minor adjsutments to grids. Previous discussion
Surface low pulling away east of the area this morning...but its
influence will still remain today. Along the back edge of the surface
low another middle-level vorticity lobe is swinging down from near Lake
Erie. Convective showers are on the increase currently and will
begin to stream in across the north through midday. Expecting to
see showers and isolated thunder chances increase in spatial
coverage southward through the early afternoon and evening. Strength
will remain limited...however...as instability will be marginal at
best due in large part to the homogeneous cloud cover. Expecting
gusty winds as the low level pressure gradient remains tight and
cold air advects in behind the low. Near term models are a little
more aggressive with the erosion of the low level moisture this evening
and thus have sped up the drying and clearing trend tonight. Much
cooler temperatures expected today as increased cloud cover and cold air
advection will keep highs about 10 degrees below average. We could
even see some record low highs challenged.
Short term /Tuesday through Thursday/...
upper trough will be entrenched over the Great Lakes/northeast
during midweek...as upper low center sinks southward from the
southern end of Hudson Bay. Although weak vorticity maxes will be
rotating through and keeping the trough in place...h500 heights
will be on a slow increase. This will allow for a moderating trend
in temperatures...from readings around 70 on Tuesday to the upper
70s on Thursday.
There will be the potential for at least a few diurnally-forced isolated
rain showers each afternoon. This will be mainly confined to northwest PA on
Tuesday as moisture remains relatively low. On
Wednesday...moisture is better...and chance probability of precipitation are indicated in
most areas. Upper cold pool also passes overhead...which will
enhance instability enough to allow for an isolated thunderstorm
or two. Thursday will see less activity...and little thunder
chance...as cold pool slides away and h500 heights continue their
Long term /Thursday night through Sunday/...
the upper trough remains in place through the extended period.
H500 heights rise a bit more Friday..allowing a few locations to
touch the lower 80s for high temperatures. Isolated diurnal showers once
again...particularly in the northwest. Models then hint that the trough
gets reinforced slightly over the weekend...knocking temperatures
back a couple of degrees. Better shower chances return as
well...with chance probability of precipitation each day through Monday as minor waves rotate
through the trough. Left thunder out for now but cannot rule out
over the weekend. All in all...no major systems or Summer heat
Aviation /14z Monday through Friday/...
advancing Great Lakes low pressure will bring MVFR SC and a scattered-numerous showers to the
region through this afternoon. Some IFR ceilings are also expd this morning north of I
80. Lingering VFR SC is expd after the passage of the low tonight.
Outlook.../Tuesday through Thursday/...
brief rstrns are possible Wednesday with an upper level disturbance.