High Wind Warning 1, NWS Portland, OR

Area Forecast Discussion
National Weather Service Portland OR
209 PM PST Fri Jan 3 2020

.SYNOPSIS...A series of fronts will result in Cascades snow and low
elevation rain tonight through most of next week. Temperatures will
be much cooler behind the first cold front tonight, and snow levels
will settle around 2500 to 3000 feet for the weekend and into early
next week. A warm front will lift the snow levels closer to the
Cascade passes briefly on Tuesday.

&&

.SHORT TERM...Tonight through Monday...The Portland forecast area is
in the warm sector of a frotnal system in the wake of a warm front
that is now well north, and ahead of a cold front that is approaching
the coast. Temperatures have been warmest on the Oregon coast with
observations in the lower 60s. South winds will increase this
afternoon and evening as the front nears and could see gusts up to 35
mph in the interior low lands and the I5 corridor and gusts up to 45
mph along the beaches and headlands, and higher terrain of the coast
range and Cascades.

The rain with the front may be delayed a couple of hours from the
forecast 24 hours ago with rain increasing along the coast around 7
PM and in the Willamette Valley around 10 PM. The front will move
through fairly quickly, but still with a punch as rain totals are
expected to be around 0.75 to 1.5 inch for the coast and higher
terrain within a 12 hour period. The Willamette valley will be
rainshadowed a bit once the west winds kick in, around midnight
resulting in lighter rain totals (0.25 to 0.5 inch) there. Snow
levels start out above the Cascade Passes this evening, but will
lower dramatically behind the front. The snow amounts and timing in
the current Snow Advisory looks good, and no changes were made to it.

Thunderstorms are not out of the question as the cold air behind the
front first interacts with the preceding warmer air. THe best chance
for this is right along the front as it reaches the coast, and have
maintained the slight chance for thundersotrms along the coast from
late tonight through early Saturday morning.

The showers will lighten on Saturday, but not fully stop in areas
north of Lane County as another front quickly follows. This front is
weaker, but may stall across the central Oregon coast to the south
Washington Cascades through Saturday night for additional rain and
snow showers. Colder air remains with snow levels remaining near 2500
feet, and the day time temepratures will likely be greater than 10
degrees cooler than the previous 24 hours. The Oregon Cascades could
see another 2 to 5 inches of snow  with possibly an additional 4 to
10 inches for the south Washington Cascades Saturday through Saturday
night. The coast range could see an inch or two of snow at the
highest elevations as well. Expect less than 0.2 inch of rain for the
Willamette Valley on Saturday and between 0.25 and 0.5 inch of rain
for the coast and lower elevations of the Cascades and coastal
mountains.

Another front will bring additional rain and Cascade snow on Sunday.
The snow levels will remain around 2500 feet with the bulk of the
rain, and expect an additional 4 to 8 inches of snow for the
Cascades. Another 0.25 inch of rain is likely for the Willamette
Valley on Sunday, with 0.5 to 0.75 inch for the coast and the lower
elevations of the coast range and Cascades.

And then, another front looks likely for Monday, a warm front.
Timing the warming with the precipitation provides a challenge to the
location and amount of the snow, but have notices that the models
ususally warm up Cascade temperatures after snow events quicker than
what is observed, and additional snow accumulations are very likely
for the Cascades, at least at pass level and possibly below the
passes on Monday. ~TJ

.LONG TERM...Tuesday through Thursday...Snow levels will rise
on Tuesday in the wake of a warm front to around 4000 feet as a cold
front approaches the coast. Most of TUesday may be dry, with the cold
front likely holding off on its arrival until Tuesday night. THen the
snow levels will lower again as another round of fronts brings
precipitation to the region.  This means that there will overall be
little change to the weather pattern through Thursday with rain
likely most days than not for the lower elevations, and snow for the
Cascades at and just below the pass level. ~TJ

&&

.AVIATION...Current VFR conditions will persist before a strong
cold front reaches the coast between 00Z and 03Z Sat and then
reach the Cascades between 06Z and 09Z. Flight conditions will
quickly lower to MVFR and could see marginal IFR conditions just
ahead and with the front. South wind gusts up to 50 kt can be
expected along the coast late this afternoon through the evening.
Gusts 30-35 kt possible for the inland valleys. The front is
fast moving and conditions are likely to improve to VFR with
southwesterly winds by 09Z.

KPDX AND APPROACHES...VFR conditions are expected to continue
until 05Z Sat when a strong cold front moves across the terminal
and vicinity. Ceilings will drop into MVFR criteria. Conditions
are expected to improve to VFR by 09Z Sat in the post-frontal
air mass. BPhillips

&&

.MARINE...Recent ASCAT pass at 18Z confirms sustained winds of
30 kt in PZZ270 and 25 kt in PZZ275. Gale force gust will
continue through this evening and into Sat morning as boundary
layer wind speeds reach 35-45 kt associated with a fast
approaching cold front. This front is expected to develop a
coastal jet, particularly in PZZ255 in the 00Z to 03Z Sat time
frame. Localized storm force wind gusts are possible at this
time.

Another frontal system is expected to pass through the waters
late Sat night through Sun morning, which may produce low-end
gale force gusts across the north zones. Wind speeds lower to
small craft advisory criteria Sat afternoon and remain in the
20-25 kt range into early next week.

Seas will build to near 20 ft by late Fri afternoon. There is
high confidence that wave heights will exceed 18 ft by this
afternoon in the northern outer waters according to the GWES
probabilistic wave heights. Seas should progressively subside by
tomorrow night down to 12 to 15 ft. -BPhillips/Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from midnight tonight to 8 AM PST
     Saturday for Cascades in Lane County-Northern Oregon
     Cascades.

WA...Winter Weather Advisory from midnight tonight to 8 AM PST
     Saturday for South Washington Cascades.

PZ...Gale Warning until 7 AM PST Saturday for coastal waters from
     Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory until 4 PM PST Saturday for Columbia River
     Bar.

&&

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This discussion is for Northwest oregon and Southwest Washington
from the Cascade crest to 60 nm offshore. This area is commonly
referred to as the forecast area.