Area Forecast Discussion
Issued by NWS Sterling, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KLWX 170057
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
857 PM EDT Sat Jul 16 2016
A weakening cold front will remain in the area through tonight.
The front will dissipate Sunday. Another cold front will cross the
area Monday night and Tuesday with high pressure building in for
Wednesday through Friday.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Earlier convection has diminished to showers SE of I-95. These
will continue to exit the area over the next few hours. Additional
thunderstorms have formed closer to the actual surface boundary in
PA as shortwave energy approaches. Currently, the only shower
targeting our forecast area is pushing east from Garrett County
MD. Will leave low end POPs across the northern tier to account
for this through midnight. Would think diurnal stabilization (in
addition to that provided by earlier storms) would take care of
these small showers, although some models try to produce
convection overnight. Will keep forecast dry after 2 AM for now,
but will monitor trends. There should be enough breaks in the
clouds for radiational cooling to occur, and temperatures aren`t
too far from the dewpoints due to the rain. Therefore some fog is
expected, although extent is uncertain. Minimal changes needed for
low temperature forecast...ranging from near 60 in the western
areas to mid 70s in the urban centers.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
High pressure just barely nudges in from the north on Sunday as
the frontal boundary dissipates. Heights will also rise.
However...given lack of true cleansing of the atmosphere and
expected continuation of hot weather...an isolated thunderstorm
mainly south and east of I-95 can`t be completely ruled
out...though put the odds at 10 percent. Thus...its not in the
forecast right now.
Winds shift southerly again Sunday night into Monday as next front
approaches. There is considerable difference among the guidance
about just when this front crosses the area...with the Canadian
suite showing significant convection Monday afternoon/evening with
frontal passage overnight...the EC with less convection and a
early Tuesday frontal passage (these likely are related)...and the
GFS also not showing much convection but showing a later Tuesday
passage. Given that...it was hard to concentrate PoPs or go very
high with them during this period...but certainly potential of
showers and t-storms exists. Highs on Monday should spike a few
degrees ahead of the front with mid-90s expected...though heat
indices should stay below advisory levels. Cooler Tuesday.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
High pressure builds into the area Wednesday and lasts through at
least Thursday. Wednesday likely the most pleasant day, with
relatively low humidity and seasonable temperatures. While
temperatures rise each day through the end of the work week,
humidity stays relatively low...so not too uncomfortable.
Return of southerly flow late in the week would help to gradually
increase humidity by early next weekend.
.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
Convection has pushed east of the terminals. Some forecast models
indicate isolated overnight showers, but I do not think this is a
likely outcome. The bigger concern overnight will likely be fog
due to moisture from rain and clearing skies...potentially
affecting all terminals except DCA. Have kept MVFR vsby for now
due to uncertainty. Dry conditions and VFR expected Sunday.
Patchy fog possible in climatological locations Monday morning.
Next chance of storms starts Monday afternoon through Tuesday with
next front. Wednesday-Friday look VFR with high pressure.
Weakening showers continue to push across the Bay and lower tidal
Potomac through mid-evening. Although lightning has waned, still
seeing some scattered gusts from the outflow up to 30 kt. Have
covered this with an MWS as upstream obs show winds quickly
diminish as showers exit.
Should be better conditions Sunday with weak high pressure.
Northwest flow becomes southerly late. Southerly channeling with
SCA conditions possible Sunday night into Monday night with
t-storms also possible late Monday into Tuesday, all associated
with next cold front. SCA with northwest flow behind front also
possible later Tuesday. Likely to drop below SCA Wednesday thru