Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
855 am EDT sun Jul 5 2015
high pressure will ensure a dry and seasonably warm close to the
Holiday weekend for most areas...but rain chances will be on the
increase with the approach of an upper disturbance on Monday...and
continue into Wednesday with passage of a cold front.
Near term /through tonight/...
850 am...no changes needed to going forecast. Still foresee a few
rain showers along the southeast ridges later this afternoon as moisture
creeps up from the south.
Model deviations from previous runs continue today with a split
flow...southern stream shortwave trough now poised to shunt
moisture and weaken the subsidence over the upper Ohio Valley
region. Near term changes thus will include a precipitation probability
expansion for some showers off the ridges for later today...and
into tonight although numbers will remain low.
Seasonably warm conditions can still be expected today...although
increased upper and middle level cloudiness will Mar the sky.
Short term /Monday through Wednesday/...
the aforementioned trough is projected to cutoff over the area on
Monday...then slowly proceed until a northern stream system boots
it eastward on Tuesday. GFS has handled these warm...weak lows and
associated precipitation better this Summer...so will be leaning toward
that solution...albeit with tempered...collaborated probability of precipitation. Monday
numbers have thus been adjusted upward as they have for the
frontal approach and passage on Tuesday and Tuesday night.
Long term /Wednesday night through Saturday/...
model ensemble forecasts continue to show a general zonal flow through
the period...with periodic crossing shortwaves bringing occasional
shower and thunderstorm chances. Opted for wpc ensemble based
guidance to smooth out operational model differences. Main
adjustments to this guidance were for downward pop adjustments and
upward tweaks to the expected seasonally warm temperatures.
Aviation /13z Sunday through Thursday/...
VFR conditions today under surface ridging are expected to be
interrupted by early morning patchy MVFR fog. Better low level
moisture east and S of pit could also lead to some IFR. VFR stratocu
ceilings are expected S of pit this evening with the approach of a
Outlook.../Monday through Thursday/...
periodic restrictions are possible through the period with
several crossing disturbances.