NWS Portland, OR wrote its last area forecast discussion before the first event at Sep 6, 1:48 AM PST, 4 hours 32 minutes earlier.
Area forecast discussion, Sep 6, 1:48 AM PST, 4 hours 32 minutes before
Area Forecast Discussion
National Weather Service Portland OR
248 AM PDT Fri Sep 6 2019
.SYNOPSIS...Cooler today, with clouds giving way to sunshine. Still a
few showers and thunderstorms around, mainly over the Cascades this
morning. Plenty of clouds tonight into Saturday morning, along with
some drizzle. Appears will enter a period of unsettled weather for
later Saturday, as low pressure arrives from the west. This will
bring increasing showers, and even a few thunderstorms in the
afternoon. Cool west to northwesterly flow off the Pac into the Pac
NW will maintain unsettled weather for Sunday into next week, with
lots of cloud, showers, and cooler weather.
&&
.SHORT TERM...Today through Sunday...Upper low now pushing inland
over southwestern Oregon, maintaining somewhat unstable south to
southeasterly flow over the region. Still have scattered showers and
even a few isolated thunderstorms over Lane and Douglas counties, At
230 am, most of the lightning was just to south and east of Cottage
Grove. Now, as the upper low continues to push northeast across
western Oregon early this am, and then into central Oregon by noon,
will see the area of showers and thunderstorms shift a bit more to
the north, but mainly on the the east. Will keep a slight chance of
showers for this morning to south of a Newport to Portland line, with
thunderstorms potential staying over the Cascades, extending back to
the southwest along and south of a Corvallis to Sandy line. So, will
adjust morning forecasts to reflect this movement. Do think that
thunderstorm potential ends between 10 and 11 am. This about the time
the upper low will be shifting into north central Oregon, with flow
aloft becoming more westerly.
Other interesting note this am is the moderate onshore flow that is
spreading into the Willamette Valley. Observations at 2 am showing
south to southwest wind 10 to 15 mph over much of the Willamette
Valley. This is deepening the marine layer inland, as apparent from
low clouds reported at Eugene and Creswell. With this flow continuing
this morning, and with gradients leaning towards Portland, seems
reasonable to expect low clouds to spread north throughout the
Willamette Valley and into Clark County this am.
But, will low off the east this afternoon, and drier air aloft,
marine clouds will break up by afternoon, with plenty of sunshine.
Temperatures will be cooler today, generally in the upper 70s to
lower 80s.
Onshore flow tonight, with low clouds spreading inland again
overnight. This time, marine layer will be rather deep, with
persistent clouds later tonight through Sat am. Upper trough will be
slowly approaching the region on Sat. Weak lifting with the
approaching trough, combined with deep moist marine layer, should be
enough for occasional drizzle along the coast, and patchy drizzle
inland late tonight into Sat am.
Now, this new trough will turn upper flow more southerly again on
Sat. With increasing instability, will see showers increasing in the
afternoon, and even some thunderstorms, especially over the Cascades.
Relatively cool and unsettled weather appears likely to persist into
Sunday as troughing continues. But, do not think will have the enough
instability aloft to support thunderstorms. Rather, looks to be more
showery and cloudy for Sunday. Rockey.
.LONG TERM...Sunday night through Thursday...Model/ensemble
consensus is to bring a weakening front and shortwave trough
onshore Sunday night and Monday. This system brings a chance of
precipitation to the entire forecast area Sunday night, and
cooler, showery post-frontal conditions Monday. After that, slow
moving upper troughiness becomes established along the PacNW coast.
This will maintain onshore flow, seasonably cool temperatures, and
a chance of showers particularly over the higher coastal and Cascade
terrain into Wednesday. By Thursday, the ensemble consensus is to
move this trough eastward, and bring a shortwave Pacific ridge
inland for drying and milder temperatures the second half of the
week. Bright
&&
.AVIATION...With an upper level trough moving onshore, a
southerly wind reversal occurred along the coast late yesterday.
This resulted in the arrival of IFR fog and low stratus at the
coastal TAF sites, which has gradually been lifting over the
past couple of hours. Expect predominantly low MVFR cigs to
continue at the coast through much of, if not through the entire
day. Stratus is also pushing through the gaps in the central
Oregon Coast Range and is now impacting KEUG. With southerly
winds developing through the valley at this time, think that MVFR
cigs may push through much of the Willamette Valley by mid-
morning. Any interior stratus should dissipate by midday, with
VFR conditions then prevailing through the afternoon and tonight.
If any clearing occurs at the coast later this afternoon, MVFR
stratus should quickly return early this evening.
Mid-level moisture and instability spreading in from the south
will result in continued thunder chances for the southern
portions of the fcst area through around 12Z. KEUG may be
impacted during this time.
KPDX AND APPROACHES...Stratus currently moving into the southern
Willamette Valley may push up the valley into the vicinity of
the terminal by 15Z. This could result in a few hours of MVFR
cigs in the mid to late morning. Otherwise, expect VFR
conditions to prevail through tonight. Pyle
&&
.MARINE...Southerly winds have spread through the nearshore
waters this morning. Expect W-SW winds to remain 10 kt or less
today and tonight. Winds remain rather benign over the weekend
and into early next week as upper level low pressure settles over
the coastal waters. A couple of weak fronts are expected to
arrive, on Sat and Mon, which will temporarily turn winds
southerly. The front on Mon may bring some breezy conditions,
potentially resulting in some low end small craft advisory wind
speeds.
Seas generally 5 ft or less through early next week. Pyle
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 2 AM PDT early this morning for Central
Oregon Cascade Foothills-Mt. Hood National Forest West of
Cascade Crest-Willamette National Forest.
WA...None.
PZ...None.
&&
Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland
This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.