FXUS66 KPQR 271025
Area Forecast Discussion
National Weather Service Portland OR
325 AM PDT Sat May 27 2017
.SYNOPSIS...An upper level ridge of high pressure will maintain it's
presence over the region through the Memorial Day weekend. Afternoon
high temperatures will remain well above normal. The ridge of high
pressure will shift eastward into the northern Rockies early next
week as a weather disturbance approaches the area. Thunderstorm
chances develop Monday over the Cascades but continue Tuesday and
expand westward to the valley as well. Temperatures trend gradually
cooler with rain chances during the second half of the week as a
disturbance tracks across the Pacific Northwest.
.SHORT TERM...Today through Monday Night...Upper ridge well in place
today with probably the warmest temperatures still to come Sunday.
Although, there will be little difference for many areas over the
next 3 days with highs in the very upper 80s to lower 90s. Coastal
temperatures will also be quite pleasant with highs in the 60s to
lower 70s although the forecast there is a little more tricky as
stratus has filled in along the entire south Washington and north
Oregon shoreline. Additionally, have added patchy fog with
occasional drizzle for the morning hours as onshore flow may give
just enough lift against the terrain to squeeze some very light
Sunday looks to be a near repeat of today although do have some
concerns regarding convection over the Cascades and foothills. SPC
has placed most of our area under a general risk for thunderstorms.
0-3km most unstable CAPE and Mixed Layer LI would imply that is
valid for the Cascade foothills, especially east of Eugene. A look
at soundings, however, do show a fairly robust cap around 850 mb
with significantly drier air above it. So, it seems unlikely any
surface based convection will reach sufficiently high to generate
showers or thunderstorms, but do expect we will see cumulus clouds
over the terrain as we have the past couple days. The only exception
could come from temperatures becoming much hotter than forecasted
needing to reach into the upper 90s to overcome the 850 cap.
Monday seems a little better for deeper convection but there is
still the issue of the mid-level cap, although it's a bit higher and
weaker. Stronger onshore flow from a late marine push might be just
enough of a trigger to overcome the cap as the marine front reaches
the foothills. /JBonk
.LONG TERM...Tuesday through Friday...No changes. Previous
discussion follows. Cooler conditions as heights lower by early
Tuesday as the upper ridge shifts east of the Rockies and an upper
trough approaches the Pacific Northwest. With south to southwest
flow aloft over the region, continue to include a small chance of
thunderstorms over the higher Cascade elevations, primarily near the
crest. While some differences in models with the timing of various
shortwave impulses moving through the base of the trough, overall do
see better agreement among the forecast models for the overall
pattern. Better chance for widespread showers, and perhaps even some
thunderstorms, Wednesday as the upper trough axis passes across the
region. Temperatures will trend cooler but still near or slightly
above seasonal norms by the end of the week. Cullen
.AVIATION...VFR conditions inland through Saturday night. IFR
VIS/CIG at the coast with a southerly wind reversal. Coast may
improve to VFR late this morning or early afternoon briefly
before stratus returns Saturday night.
KPDX AND APPROACHES...VFR today and tonight. Bowen
.MARINE...Winds will continue below 20 kt through at least the
middle of next week. Northerly winds continue over most of the
waters through the weekend. However nearshore winds will switch
back to out of the south again tonight, accompanied again by low
stratus and/or fog.
Seas have settled in the 6 to 7 foot range and will settle to
around 5 ft through most of next week. With swell period
increasing, don't even expect particularly steep or choppy seas.
PZ...Small Craft Advisory for Rough Columbia River Bar until 9 AM
PDT this morning.
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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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