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

.SYNOPSIS...Mild and dry weather will continue into Saturday, though
there will be a chill to the air tonight and Saturday morning. A
front dropping southeastward Saturday evening will spread rain across
the area, followed by decreasing showers Sunday. Another system
ejecting northeast from Hawaii brings a small chance for rain late
Monday into Monday night, then high pressure is expected to dominate
for dry and warm weather midweek.

&&


.SHORT TERM...Today through Monday...No changes were made to the
forecast this evening other than a couple minor tweaks to the wind
grids. Inherited forecast appears to be in very good shape, and
showers have ended across the forecast area as expected. Low temps
Sat morning will be similar to this morning, so there could be some
patches of frost in the outlying valleys. Decided to leave it out of
the forecast though, since there is a fair chance that high clouds
over the NE Pacific will spread into the forecast area by daybreak.
Forecast discussion from earlier this afternoon (below) remains
valid.Weagle

Previous discussion issued 307 PM Fri Apr 28 2017 below:

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...VFR conditions overnight. Expect high clouds moving
in to preclude any chances for fog or low stratus. Brief ridging
will drift across the region 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.

PORTLAND AND APPROACHES...VFR conditions and light winds through the
period. /Bentley

&&

.MARINE...No Changes. Previous Discussion Follows. 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.

&&

$$



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.