Area Forecast Discussion
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FXUS61 KPBZ 201830
Area Forecast Discussion
National Weather Service Pittsburgh PA
230 PM EDT FRI MAY 20 2016
Low pressure will bring rain tonight and Saturday, with a few
lingering showers into Sunday. Dry conditions and a warming trend
in temperatures are expected during the first half of next week.
.NEAR TERM /THROUGH SATURDAY/...
A veil of cirrus currently covers the CWA as the 500 mb ridge axis
crosses. Rain has progressed to a point just southwest of
Recent hi-res model runs have slowed down the arrival of
precipitation to mainly past 00Z. This makes sense given the dry
airmass in place and the more NNE trajectory of the better
moisture and lift. Will be backing off on PoPs for a few hours as
a result. Still, there is still enough model support to justify
categorical PoPs across most of the CWA tonight. We expect a
surface low tracking across the Ohio Valley to open into an
inverted trough across West Virginia on Saturday, with a new
coastal low taking over. While the best push of moisture still
remains off to the southeast, a secondary precipitable water
maximum crosses our area with the surface low and ahead of the 500
mb trough. This will lead to a soaking rain for much of the
southeastern CWA with rain totals of 1 inch or more. Amounts will
taper off to the north and west. Think rainfall rates and the
overall lack of convection will preclude a large-scale flooding
threat, but can`t rule out isolated issues in the southern CWA
where FFG values are a bit lower.
The steadier synoptic rainfall will degenerate into showers as
time goes on Saturday with the arrival of the upper trough. PoPs
and rainfall rates fall off a bit as a result, but dry weather
can`t be guaranteed at any point during the day.
A small diurnal range in temperature is forecast for the period
given the wet conditions. Used a blend of guidance for the values.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
-- Changed Discussion --Although the primary focus of the precipitation will shift well
to our east with a deepening coastal low, the upper-level trough
axis directly overhead will keep rain showers in the area through
early Sunday morning. Have increased PoPs before daybreak
accordingly. Expecting a break in rain during the mid-morning hours
as moisture erodes west to east.
Weak forcing and modest instability behind the upper-level trough
should be enough to develop afternoon showers and with isolated
thunder. Most of the activity should be confined to the higher
terrain of the east where elevated heating sources may initiate
convection. High pressure building in from the west will quickly
dissipate clouds and rain showers after sunset Sunday. High pressure
will then lead to a dry period at the beginning of next week.
-- End Changed Discussion --
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Overall models show average agreement and continuity with previous
runs with regards to the central conus ridge shifting to the east
and bringing a warming trend in temperatures to the region. Have
maintained a dry forecast through the first half of the week until
flow shifts to the southwest and moisture advection increases.
.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
VFR conditions will continue through the evening, although clouds
will be lowering and thickening with time ahead of approaching low
pressure. Rain will overspread the region tonight, with an
areawide drop through MVFR towards IFR conditions by Saturday
morning. Rainfall will taper off to showers as time progresses on
Saturday, but IFR to possibly even LIFR ceilings will persist
through most of the day as an upper level trough crosses.
.OUTLOOK /FRIDAY NIGHT THROUGH TUESDAY/...
Restrictions are likely to continue into Saturday night, with
improvement on Sunday.