Weather Service Report

FXUS66 KPQR 200413

Area Forecast Discussion...Update
National Weather Service Portland OR 
911 PM PDT Mon Mar 19 2018

Updated short term, aviation, and marine discussions

.SYNOPSIS...Rather quiet weather with morning clouds and fog in the 
valleys continues through Tue under weak high pres. Wed and Wed 
night low pres off the CA coast will spread moisture north over the 
region as a cold front from the nw pushes through bringing rain, and 
then a cool showery air mass for the end of the week.


.SHORT TERM...Tonight through Thursday...Dropped overnight low
temperatures a couple degrees, so now temperatures in the north and
central Willamette Valley will be flirting with freezing. No
additional changes. Previous discussion follows. -McCoy

The weak upper low off the Oregon coast near 43N 129W is expected to
swing inland across central and southern Oregon late tonight into
Tue. This returns a chance for some showers to the far southern part
of the forecast area, mainly the Lane County Cascades tonight and
Tue. To the north, the area will remain under a weak surface high
pres, with light winds favorable for radiational fog to develop again
in the valleys late tonight and continuing through Tue morning. 

Tue night and Wed models indicate some moisture creeps up again from 
the south as the closed low well off the CA coast begins to open up. 
This spread chances for rain northward, and by late Wed deeper 
moisture arrives bringing the prospects for more substantial rain. 
As the deeper moisture spreads up from the south, warmer air 
associated with it likely raises snow levels above the passes Wed 
night.The warmer air will be short-lived though, as a cold front 
ahead of a deep trough of low pres from the Gulf of Alaska pushes in 
Wed night, adding additional lift for a wet night. 

Showers will decrease behind the cold front Thu as low level onshore 
flow temporarily weakens as a surface ridge of high pres moves in. 
Cooler air arrives Thu as the upper trough moves closer. Thickness 
values indicate snow levels to drop well below Cascade pass levels 
by Thu afternoon.  

.LONG TERM...Thursday night through Sunday...Models in good 
agreement moving an upper low, with origins in the Gulf of Alaska, 
down the BC coast Thu night and Fri, then inland across the region 
Sat. This brings a showery and quite cool air mass across the 
region. Thickness values down into the range of 522 to 525 dm Fri 
and Sat morning suggest snow levels well down into the Coast Range 
and Cascade Foothills, with maybe some flakes seen in the higher 
hills of the low elevation valley zones. Sun the upper trough is 
expected to move east with weak ridging following. A weak short wave 
is hinted at Mon in both the GFS and EC, so will need to hang on to 
some low pops Sun and Mon, with temps warming a bit, but still 
likely cooler than seasonal normals.


.AVIATION...VFR conditions prevail this evening. Skies are clear
aside from some high clouds KEUG southward. High pressure and 
clear skies will result in excellent radiational cooling 
conditions overnight, making IFR/LIFR fog likely for most 
terminals by sunrise Tuesday. The exception may be along the 
coast, where light offshore flow may keep fog from forming. Fog
is expected to lift/clear between 16z-18z Tue morning, though
light northerly flow may jam low clouds against the south end of
the Willamette Valley until about 20z...similar to today. VFR is
expected Tuesday after the fog burns off.

KPDX AND APPROACHES...VFR conditions will likely give way to IFR
or LIFR fog/stratus by 13z Tue morning. Fog is expected to slowly
lift during the mid to late morning hours Tuesday, then scatter 
out to VFR conditions with onshore flow by 19z. Weagle


.MARINE...Expect winds to generally remain less than 20 kt
through midweek, but could see some gusts 20-25 kt Tue afternoon
and evening as high pressure to the NW and low pressure to the 
SW squeeze the local pressure gradient just a bit. Strongest 
winds will be in the southern waters. Models continue to show a 
more active weather pattern returning Thursday and continuing 
through the weekend. Small Craft Advisory level wind gusts of 25 
to 30 kt and seas climbing above 10 ft appear most likely during 
this time.  Bowen/Weagle




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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 CWA or forecast area.

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