Area Forecast Discussion
Issued by NWS Portland, OR

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424
FXUS66 KPQR 282210
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
307 PM PDT Fri Apr 28 2017

.SYNOPSIS...Warmer and drier weather will build across the region
this afternoon through early Saturday. A front dropping southeastward
Saturday evening will spread rain across the area. Weak high pressure
should bring a return to drier weather overall early next week, but
there is still a chance that a day or two could end up wet.


&&


.SHORT TERM...Today through Monday...Water vapor satellite imagery
shows a large trough digging southward into the Great Basin and Great
Plain states. Shortwave ridging building into the northeast Pacific
has placed the Pacific Northwest under large scale north to
northwesterly flow aloft. High clouds rounding the top of a
shortwave ridge are pushing into the northeast Pacific and will
arrive later tonight. Doppler radar and surface observations
continue to indicate a few light showers over the higher terrain of
the Coast Range and Cascades. Expect these showers to decrease
rapidly this evening as shortwave ridging builds overhead and
surface heating wanes.

Expect a mostly clear and cool night tonight before clouds thicken
from northwest to southeast across the area on Saturday. Valley
high temperatures should climb into the 60s Saturday despite the
increasing cloud cover. A front dropping southeastward across the
area late Saturday should spread rain onto the south Washington coast
as early as mid-late afternoon and into the Willamette Valley,
especially the northern half, during the mid to late evening hours on
Saturday. Some lingering low level instability may allow for a few
showers to persist into Sunday afternoon, but overall Sunday looks
considerably more dry than wet as shortwave ridging slowly
redevelops. Another shortwave trough riding up and over the ridge
could bring rain back on Monday, but the operational EC and many GEFS
members shunt most of the moisture north of the CWA. Did raise PoPs,
but still kept them generally below climo since it appears Monday
stands a better chance of staying dry than turning wet. /Neuman


.LONG TERM...Monday night through Friday...A weak disturbance will
continue to bring a few showers to the forecast area late Monday.
Models continue to keep the bulk of the moisture to our north so
expect minimal accumulations. Conditions will then become warmer and
drier for a few days starting Tuesday as an upper level ridge builds
across the Pac NW. Today`s 12Z runs show a slightly dirtier ridge
over the region next week, but given the forecasted 500 mb heights
and 850 mb temps, Wednesday is expected to be the warmest day of the
year thus far, with afternoon highs climbing into the low to mid 70s
across the Willamette Valley. The ridge starts to breakdown Thursday
as a weak frontal system approaches the region. Expect mostly cloudy
conditions to return by Thursday, with a slight chance of showers,
mainly over the Cascades. Could also see a few thunderstorms over
the Cascades on Thursday, but confidence is not high enough to add
it to the forecast. Conditions become a lot more uncertain late next
week due to model difference so will stick close to climo and keep
partly cloudy skies and a slight chance of showers in the forecast.
/64


&&


.AVIATION...Weak daytime instability has brought a fairly dense
cumulus field across the area this afternoon.Light shower
activity generated across SW Washington will drift SE toward the
northern terminals and decided to extend the vcsh threat into
the early evening for most sites. Brief ridging will drift across
the region tonight and tomorrow for VFR conditions with
increasing high clouds. Low pressure will approach the coast
tomorrow afternoon and could bring light rain and cigs 030-050 to
KAST by 29/22z.

KPDX AND APPROACHES...Vicinity showers with variable cigs mainly
040-050 through 29/02z. Skies will clear this evening before
increasing cirrus moves overhead tonight. VFR and light winds
through 30/00z. /JBonk


&&


.MARINE...A front will pass across the region late Sat and Sat
evening with south to southwesterly winds of 15 to 25 kt across
the north and slightly weaker winds for the central coastal
waters. Seas will get a minor bump, but stay under 10 ft. Once
the front passes, winds will ease back and turn more
northwesterly.

High pressure aloft returns early next week with northerly winds
for the bulk of the time. However, the strength of the upper
ridge looks to be considerably weaker than 24 hours ago. This may
open the door for a brief southerly wind reversal monday night
and early Tuesday. Seas appear to remain 7 ft or less through
that time. /JBonk


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds from 11 AM to 9 PM PDT Saturday
     for Coastal Waters from Cape Shoalwater WA to Cascade Head
     OR out 60 nm.

     Small Craft Advisory for winds from 2 PM Saturday to 1 AM PDT
     Sunday 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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