Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 032136
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
236 PM PDT Wed Jun 3 2020


.SYNOPSIS...Fairly quiet rinse and repeat weather over the next
several days with a zonal flow pattern. A low pressure system
will move southeast from the Gulf of Alaska on Sat bringing heavy
rain and even a slight chance for thunderstorms this weekend. Active
weather will persist through next week.

&&

.SHORT TERM...Tonight through Friday night...Zonal flow through the
next several days will continue to keep conditions fairly benign.
Expect the area to be dry with seasonable temperatures in the low to
70s through Thur, starting off June with slightly above normal
weather. Satellite imagery depicts the onshore flow pushing some
wispy cirrus over the forecast area, especially along the central
coast and central Willamette Valley. These clouds will slowly
dissipate through the remainder of the afternoon with the daytime
heating. Continued onshore flow on Thu will drop temperatures
slightly, closer to 70 degrees inland and near 60 along the coast.
Overall, a persistence forecast expected through Fri.

The pattern begins to change Fri afternoon as a strengthening low
pressure system, stemming from the Gulf of Alaska, advances towards
the area. A cold front along the leading edge will push inland on Fri
night with temperatures around 5000 ft at 2 degrees Celsius. As
temperatures begin to drop aloft, they will also decrease at the
surface. Expect highs in the mid 60s with increasing chances for
rain. Overall, this approaching system is quite energetic and active
weather is expected beginning late Fri night.  -Muessle

.LONG TERM...Saturday through Tuesday...The deepening Gulf of Alaska
low makes its way towards the coastline Sat morning with cold air
rushing inland behind it. At this time, much of the energy is
elevated with quite a bit of upper level jet support as the low wits
in the left exit region of a 75 kt jet streak at 30,000 ft. The low
is projected to move inland along the southern Oregon coast Sat
afternoon with the associated long wave trough extending north along
the Alaska Peninsula. While cold wrapped, this low and the
strengthening southwesterly flow will bring significant moisture to
the area with the potential to bring moderate rainfall to much of
northwest Oregon and southwest Washington. Accumulations ranging
from 0.25 to 0.50 inches of rain are possible.

With the influx of cold air, snow levels are expected to drop near
pass level. With the increased precipitation, could see some Cascade
snow with possible accumulations around 2 to 3 inches, especially
south of Jefferson. One thing specifically being taken into a
account is the overall pattern and its history of producing
thunderstorms. At this point, the low is dipping down just south
enough that the flow is slightly less favorable for thunderstorms.
However, if the low tracks northward at all, there is an increased
chance for thunder on Sat afternoon into evening. Given some mild
model disagreement, decided to stick with a slight chance over most
of the forecast area on Sat.

Showers will persist through Sun before a ridge builds in early Mon.
While high pressure ridges generally bring drying weather, this ridge
has several shortwave troughs that pass through it. Each trough, one
occurring Mon night and another Tue morning, may bring periods of
rain. The shortwave on Tue is associated with another Gulf of Alaska
low. This low will stay north of the area and rotated within the
Pacific waters before moving north inland over the Alaska
Peninsula. Given the time frame and a some model differences, there
is a chance that each of these shortwaves may move north of the
forecast area. If they do shift northward, the areas that may see
rain will change, and may only be the northern counties of the
forecast area. -Muessle

&&

.AVIATION...Onshore low-level flow will continue over the area
through Thursday. The MVFR cloud cover that existed this morning
has dissipated. Expect MVFR cigs to return to the south Washington
coast and coastal valleys between 02Z and 04Z Thu and then far
north Oregon coast shortly thereafter and KKLS overnight. High
resolution model guidance suggests the MVFR stratus coverage Thu
morning will not be as extensive as today. MVFR conditions may
extend up the Columbia River to near KPDX 12Z to 15Z Thu. All
areas will become VFR by 18Z Thu.

KPDX AND APPROACHES...VFR conditions at the terminal and vicinity
as of 20Z. Sea breeze looks to kick in during the evening hours,
with northwest gusts to 15 kt. MVFR cigs are possible again 13Z
to 16Z Thu, otherwise VFR to prevail. Weishaar

&&

.MARINE...Typical summer pattern continues over the waters through
Thursday. Surface high pressure over the waters will result in
gusty northwest to north wind through 10Z or so Thu and again late
Thu afternoon and evening. Gusts to 25 kt expected this afternoon
through late tonight, especially over PZZ255 and PZZ275. Another
small craft advisory will likely be needed for Thu afternoon and
evening. Northerly surface gradient expected to relax late Thu
night and Fri as surface low pressure develops near 42N 130W. Wind
shifts to a more west direction Fri and Sat with lighter speeds.
High pressure returns across the northeast Pacific late in the
weekend, which will result in strengthening northerly wind.

Seas generally hover in the 5 to 7 ft range for the next few
days. The predominant swell will be west to northwest at 10 to 13
seconds, but model guidance indicates a near-constant 2 ft south
to southwest swell set at 16 to 18 seconds. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 3 AM PDT Thursday for coastal waters
     from Cape Shoalwater WA to Cascade Head OR out 60 NM.

     Small Craft Advisory until 3 AM PDT Thursday 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 nm offshore. This area is commonly
referred to as the forecast area.



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