Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 172142
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
242 PM PDT Thu Aug 17 2017

.SYNOPSIS...Persistent surface high pressure over the NE Pacific
combined with low pressure east of the Cascades will maintain onshore
winds the next several days. Slight variations of the upper level
pressure pattern will result in slight variations in how expansive
nighttime/morning clouds will be through early next week. The clouds
should clear in the afternoons with temperatures remaining near the
seasonal normals. An upper level ridge is expected early next week
for less clouds and slightly warmer temperatures.

&&

.SHORT TERM...This afternoon through Sunday...Morning clouds have
cleared from all but the most northern Oregon coast and southern
Washington coast. Even there, though, skies should become sunny by
late afternoon. Expect a quick return of marine stratus to the coast
late this evening with a little bit less inland penetration,
particularly south of about Salem where skies may remain clear
tonight.

There will be little change in the weather Friday as another upper
level trough passes by to the north and low-level onshore winds
persist. The marine layer should deepen late Friday night and early
Saturday morning as an upper level trough develops over NW Oregon for
a better chance for more widespread clouds Saturday morning.
Therefore the temperatures Saturday afternoon will be slightly
cooler. The pattern remains much the same Sunday, but 850 mb
temperatures warm a couple of degrees, so expect seasonable but
slightly warmer afternoon temperatures Sunday after morning clouds
dissipate. Bowen

.LONG TERM...Sunday night through Thursday...First up, for your
ECLIPSE FORECAST: Thermal trough that develops along the northern
California coast may be the saving grace for eclipse viewers on
Oregon`s Central Coast. The ECMWF brings that trough north into
southwest Oregon, which may turn flow offshore enough to keep clouds
out of the path of totality along the coast. We know eclipse viewers
are rooting for that solution. However, the evil GFS is keeping the
thermal trough farther south and flow more northerly which would
allow marine clouds to come onshore along Oregon`s Central Coast.
Really and truly we have two scenarios: One where the sky along the
coast remains overcast and another where the sky is clear and it`s
about 50-50 right now which scenario will occur. Locations farther
north up near Astoria have a higher chance of marine clouds sticking
around through the eclipse. For those inland, under northerly or
northeasterly flow we typically don`t see marine clouds make it very
far inland, so locations from the Coast Range eastward have a very
good chance of clear skies for the eclipse Monday morning.

The approaching trough will make it to our area on Wednesday,
bringing a chance for drizzle or light rain to the north coast on
Wednesday and cloud cover for the rest of the area. As the trough
moves inland, there will be a slight chance for thunderstorms up in
the Cascades Wednesday afternoon and evening. As the trough
continues to pass over the area, expect another slight chance of
thunderstorms in the Cascades on Thursday. -McCoy

&&

.AVIATION...Dry and stable northwesterly flow aloft. Marine
stratus around Astoria and northward into early this evening,
as well as pockets of stratus to north of Kalama until around
23Z. Generally VFR overnight with light flow aloft. But will see
coastal stratus return later tonight to the coast and inland
areas north of Salem. But, like today, clouds will break up over
most areas between 18Z and 20Z.

KPDX AND APPROACHES...VFR tonight with light northwesterly winds
through this evening. Will see MVFR stratus creep back into
region from the north after 11Z, linger Fri am, then burn out
between 18Z and 20Z Fri.      Rockey.


&&

.MARINE...Rather persistent pattern through Sunday, with high
pres over the Pac, and thermal low pres over nw Calif and sw
Oregon. This will maintain northerly winds, with gustier winds
in afternoon/evenings, primarily to south of Newport.

Seas will generally 5 to 7 ft through the period, but may build
to around 8 ft at times to south of Newport with the stronger
north winds.      Rockey

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds through late tonight on
       coastal waters from Cascade Head to Florence.

&&

$$

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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.


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