Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 242127
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
225 PM PDT Sun Jul 24 2016

.SYNOPSIS...A weak upper trough will develop near the coast today
with weak westerly flow aloft over the Pacific Northwest through
Monday and Tuesday. Expect morning low clouds giving way to afternoon
sunshine and warmer but seasonable afternoon temperatures. A stronger
upper level ridge will build for the second half of the week and
bring inland highs well into the 90s Thursday and Friday, before the
next trough arrives to moderate temperatures next weekend.
&&

.SHORT TERM...(Tonight through Wednesday)...As expected, skies have
largely cleared across the region and temperatures well into the
lower 80s as of 2 pm.  Warm and clear this evening but a developing
weak upper trough will develop later today and remain in place over
the region for the next few days.

A weak upper trough will then develop in light westerly flow aloft
later today, and this will persist over the region Monday and into
Tuesday. This may help bring an increased push of marine air the next
few mornings, which will in turn increase the areal extent of low
clouds inland both along the Columbia River and into the interior as
well as thorough the southern gaps into Eugene. This push may be
sufficiently strong to fill the Willamette Valley around daybreak as
the two bands of clouds converge near Salem. However, the clouds will
be relatively quick to clear back to the coast Monday, for plenty of
afternoon sunshine and temperatures right around seasonal norms. The
push Tuesday morning looks to be a little stronger and deeper, so
expect that the clouds will linger a few hours longer and also limit
some of the heating - particularly across the northern half of the
area. This, along with lowering heights as the trough moves across
the area, will leave Tuesday as likely the coolest day in the short
term period.

Upper level high pressure then begins to build over the region late
Tuesday. Expect the surface winds slightly onshore across the
northern half of the forecast area, but with models suggesting the
surface ridge axis aligned southwest to northeast, expect more
northerly to light offshore wind component for the central Oregon
coastal areas. Thus, have tapered back cloud cover for the inland and
southern coastal zones on Wednesday, though some shallow marine
clouds may make it along the Columbia River to around Kelso. 500 mb
heights are modeled to lift to 590 dam by Wednesday afternoon, with
850 mb temperatures increasing to 16-18 degrees C. With only shallow
if any morning stratus, there will be effective warming, allowing
this to translate to afternoon maximum temperatures in the interior
reaching well into the upper 80s on Wednesday. Cullen

.LONG TERM...(Wednesday night through Sunday)...Models continue to
show weak upper level ridging over the Pac NW late next week. This
will bring the typical pattern of morning clouds and afternoon sun,
with temps in the interior rising into the mid 90s on Friday.
Onshore flow looks to increase next weekend as an upper level trough
moves over the region. This will bring more clouds to the interior
and provide for a slight cooling trend on Saturday and Sunday.

The threat of showers through the long term period remains near zero.
However, the GFS continues to show the potential for some monsoonal
moisture streaming north on Saturday. This could produce some
isolated dry thunderstorms in the Cascades, but confidence is low.
/64

&&

.AVIATION...Mostly VFR conditions this afternoon, with the
exception being areas along the coast between KTMK and KONP where
patchy stratus lingers. North winds will gust to around 25 kt along
the coast late this afternoon with gusts 15 to 20 kt in the
Willamette Valley. Marine stratus will return to the coast around
7z with IFR conditions tonight. The stratus will likely push into
the Willamette valley Monday morning from the south and north for
MVFR conditions.

KPDX AND APPROACHES...VFR conditions through this evening. North
to northwest winds will briefly gusts to around 15 to 20 kt late
this afternoon. MVFR cigs return Monday morning around 15z with
clearing around 17 or 18z. TJ

&&

.MARINE...There is a persistent summer-time weather pattern as
high pressure holds over the waters and low pressure remains over
N CA and S OR. The thermal trough over CA will expand north in the
afternoons and evenings for increased gusty winds in the
afternoons and evenings. There has been a delay in the small craft
advisory winds this morning, but still think the gusty winds over
the southern Oregon waters will expand northward to the Central
Oregon waters this afternoon, and to the north Oregon and south
Washington waters this evening. The winds will ease late tonight,
but then increase again to marginal small craft conditions Monday
evening. The seas are primarily wind-driven and steep with little
influence of distant-sourced swells. Areas south of Cascade Head
may have brief square seas this evening with seas around 6 ft at 6
seconds. There will be little change in the weather pattern Tue
and Wed. There is a chance for stronger winds and larger steep
seas Thu and Fri. TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until midnight PDT tonight for
     Coastal Waters from Cape Shoalwater WA to Cascade Head OR
     out 60 nm.

     Small Craft Advisory for winds until 3 AM PDT Monday for
     Coastal Waters from Cascade Head OR to Florence OR out 60
     nm.

&&

$$

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This discussion is for Northwest Oregon and Southwest Washington from
the Cascade crest to 60 nautical miles offshore. The area is commonly
referred to as the forecast area.



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