Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 181022

Area Forecast Discussion
National Weather Service Portland OR
321 AM PDT Fri Aug 18 2017

.SYNOPSIS...Onshore winds continue 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 or above the seasonal normals. An upper
level ridge is expected early next week for less clouds and slightly
warmer temperatures.


.SHORT TERM...Today through Sunday Night: Another mainly fine day
today with weak short-wave ridging today giving way to a slightly
stronger short-wave trough for Saturday and Sunday. Some morning
radiational low clouds will continue to develop along the coast and
lower Columbia this morning. Inland clouds should give way to a
sunny late morning as high clouds then begin to stream overhead and
somewhat filter the afternoon sun.

The weak trough will bring a slightly cooler air mass Saturday and
Sunday along with much better inland penetration of the low clouds
Saturday. Clouds will likely cover much of the interior below about
3000 feet Saturday, which will be a mixed bag for the ongoing fires.
The higher elevation wildfire activity may see sharp contrast of low
overnight humidity above 4000 feet while elevations below that will
likely be saturated. Temperatures Saturday will be about 3 to 6
degrees cooler than today, but then rebound Sunday close to what we
see today. That said, temperatures will remain near to above normal
through the weekend. Certainly should be great sleeping weather for
those camping outside. A near isothermal lower atmosphere will show
little temperature difference between the Willamette Valley and the
slopes above. Regardless, please follow local burning regulations
for those campfires. /JBonk

.LONG TERM...Monday through Thursday: No Changes...Previous
Discussion Follows. 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...Expect predominately MVFR cigs along the north coast
this morning. The central coast looks to remain VFR this morning,
but could see brief periods of localized IFR fog through around
16Z. Conditions along the north coast may briefly improve to VFR
this afternoon. Expect a mix of IFR/MVFR stratus to return to the
coast this evening and persist into Sat.

The interior will remain predominately VFR today and tonight, but
the northern interior could see a period of MVFR stratus through
around 18Z. Suspect the metro TAF sites will only see patchy MVFR
stratus this morning, with stratus clearing by 18Z. MVFR stratus
likely returns to the interior after 08Z tonight.

KPDX AND APPROACHES...Predominately VFR today and tonight, with a
brief period of MVFR stratus possible between 14-18Z this morning
and again after 08Z tonight. /64


.MARINE...Expect a rather persistent pattern through early next
week with high pres over the coastal waters and thermal low pres
over NW California and SW Oregon. This will maintain northerly
winds, with gustier winds in afternoon/evenings, primarily to
south of Newport. A SCA for winds is now in effect from this
afternoon through Sat for the central waters, and will likely
need to be extended into the northern waters Sat night.

Seas will generally be around 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. /64/Pyle/Rockey


PZ...Small Craft Advisory for winds from 3 PM this afternoon to
     3 PM PDT Saturday 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. This area is
commonly referred to as the forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.