Area Forecast Discussion
Issued by NWS Portland, OR

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Area Forecast Discussion...UPDATED
National Weather Service Portland OR
929 AM PDT Sat Mar 24 2018

...Updated for aviation and marine sections.

.SYNOPSIS...A disturbance moving through northwest Oregon and
southwest Washington overnight will move east of the forecast area by
sunrise with decreasing rain and snow. The next low is along 130W
early this morning and will move onshore into southern Oregon and
northern California tonight, but not before spreading more showers
into the forecast area this afternoon and tonight, with possibly a
thunderstorm this afternoon and evening. Snow levels will be 500 to
1000 feet this morning and again tonight and early Sunday, rising a
bit in the afternoons. Showers will continue Sunday into Sunday night
in the wake of the departing low. Another modest front will move
through the forecast area Sunday night into early Monday. An upper
ridge will strengthen in the Gulf of Alaska, but some moisture and
energy will ride over the upper ridge and spread some light
precipitation at times into the Pacific Northwest during the first
part of next week before finally drying out for the second part of
the week. The next system may reach the forecast area next weekend.

.SHORT TERM...Today through Monday...A disturbance that rotated
onshore overnight and brought rain and snow to southwest Washington
and northwest Oregon will move east by sunrise with decreasing
precipitation. Snow levels this morning are again around 500 to 1000
feet with the main sticking snow more likely to be near or above 1000

The next disturbance is a low out near 130W that will move into
southern Oregon and northern California tonight. As it does, it will
spread more showers of rain and snow into northwest Oregon and
southwest Washington this afternoon and tonight. Snow levels will
rise a touch this afternoon, but then fall back to near 500 to 1000
feet tonight and Sunday morning. Amounts should be lighter tonight
and Sunday, including in the mountains, than what has occurred in the
last 24-48 hours.

With the cooler air aloft, there will again be a chance of thunder
today as well as small hail.

Showers will continue on Sunday, especially in the afternoon, in the
residual onshore flow in the wake of the departing low.

Another modest front is forecast to drop down Sunday night into
Monday for more rain and snow. Snow levels will still be low, perhaps
not as low as the last couple of days. Additional moisture and energy
will spread into the Pacific Northwest through the day Monday in the
wake of the modest front, riding over the building offshore upper
ridge, what we call a "dirty" ridge. This pattern will last into the
middle of the coming week. Tolleson

.LONG TERM...No Changes. Previous discussion follows...
Monday night through Friday...No changes. Previous discussion
follows. An upper ridge will dominate much of the long term period,
however, our area will remain on the southern edge of the "ridge
runner" weak disturbances which will be traversing the ridge. This
will keep at least a slight chance for precipitation most days, and
the upper clouds will limit the warming that may be seen otherwise.
However, temperatures are still expected to warm into the upper 50s
to lower 60s. The best chance for a completely dry day next week
still appears to be Thursday. Beyond this ridge, models are in
agreement with a longwave trough re-establishing across the Pacific
NW. This would keep the cool pattern well into April with additional
chances for late season foothill snow, and below normal temperatures.

.AVIATION...Low pressure is passing offshore this morning and
will drop south of the region later today. A band of light rain
will lift north through the region this morning, which will
likely result in MVFR conditions developing at the coast, and
perhaps some patchy MVFR inland as well. The trend will be
towards mainly VFR conditions this afternoon and evening, with
scattered showers across the region. There will be a chance of
thunderstorms at the coast through tonight. The models are
suggesting clouds may settle toward MVFR late tonight into Sun

PDX AND APPROACHES...Expect mainly VFR conditions this evening
with continued showers. There may be brief periods of MVFR in
showers, particularly through the morning hours. Cigs will likely
settle overnight, reaching near MVFR by early Sun morning. Pyle


.MARINE...Satellite imagery shows a 1005 mb surface low above
225 nm west of Florence OR as of 9 AM. This low is bringing some
gusty winds to the Oregon coast waters. Winds south of Newport
have been gusting around 30 kt for the last several hours. Will
stick with a small craft advisory, but expect isolated gusts to
35 kt through the morning hours. North of around Tillamook Head,
winds will be much lighter, generally SE at 10 to 15 kt. The
surface low will weaken and move inland later today, allowing
winds to weaken considerably. Wind speeds should be around 10 kt
or less by tonight. Models show a surface trough moving through
the waters Sun evening, which could boost wind speeds up to 20-25
kt. Higher pressure builds over the NE Pac for most of next
week, which will lead to a period of much more benign conditions.
A thermal trough is expected to build into northern CA towards
the middle of next week, which will bring northerly winds to the

Seas will remain a mix of NW swell and fresh S-SW swell through
Sun. Will also maintain the current small craft advisory for
hazardous seas through 00Z Sun, although the highest seas will be
in PZZ255/275. Areas north of Cape Falcon will likely remain
under 10 ft today. However, periods are such that square sea
conditions could be met. Seas will be well below 10 ft Sat night
through much of next week. Pyle/Weishaar


PZ...Small Craft Advisory for winds until 5 PM PDT this afternoon
     for Coastal Waters from Cape Shoalwater WA to Florence OR
     out 60 NM.

     Small Craft Advisory for hazardous seas until 5 PM PDT this
     afternoon for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until noon
     PDT today.



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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. is the U.S. government's official web portal to all federal, state and local government web resources and services.