FXUS66 KPQR 081043

Area Forecast Discussion
National Weather Service Portland OR
240 AM PST Fri Dec 8 2023

.SYNOPSIS...Decreasing showers today, but cooler. Dry weather later
today through tonight. But, next front will bring rain to the region
on Saturday, with heaviest rain later in the day into Sunday morning.
Showers to start next week. But, building high pressure over the Pac
NW look to bring cooler dry weather for Tue, perhaps longer.

.SHORT TERM...Cool westerly flow aloft maintaining scattered showers
across the region, along with some patchy fog. But, overall, rainfall
has not been all that great. This good news, as allows for rivers and
streams to recede. In the Cascades, snow continues to fall at times
above 3000 feet. But, accumulations not all the impressive this am.
Generally, will see another 2 to 5 inches of snow before showers
decrease later this morning. So, will allow Winter Weather Advisory
early, as impacts have been minimal.

Otherwise, scattered showers will decrease, gradually coming to an
end over most areas this afternoon as air mass stabilizes. Will have
increasing thin high clouds later today, thanks to next system well
offshore approaching. Will be cooler today, despite mix of sunshine
and clouds. Will follow guidance, keeping maximum temperatures into
upper 40s, and 30s in the high mountains.

Chilly tonight, with temperatures dropping back to the 30s for most
area valleys, and 20s in the higher terrain. Though most roadways
will likely be dry, may have areas where moisture may not fully
evaporate today. As such, could be few slick spots in the Coast Range
and Cascade foothills tonight, as that lingering moisture on roads
may freeze in spots.

Models have been rather consistent in showing next system slowing as
it arrives to the Pac NW later tonight and early Sat. In coordination
with neighboring forecast offices, will follow said model trends.
First, a warm front will buckle northeast across the offshore waters,
then lift up the far northwest corner of Oregon on its way into
Washington Sat am. This will This will bring rain to the coast
sometime around or just after daybreak Saturday, with that rain
spreading inland through the early afternoon. With this, bulk of the
rain will be north of a Tillamook to Portland line. Much drier to the
south, and now appears that areas to south and east of Salem may not
see much in way of precipitation until mid afternoon, or possibly the
early evening. With snow levels on the rise, will get rather heavy
shot of snow (8 to 15 inches) for the south WA and north Oregon
Cascades before snow levels rise too high. Likely will issue Winter
Weather Advisory or Winter Storm Watch for higher terrain for Sat
into Sat night, but will defer to day shift to make final decision.
Rain will spread south and southeastward Saturday night, as the cold
front slowly approaches from the west. Looks to be rather wet Sat
night into Sun am.

Now, while this system will have rather potent moisture potential,
its sub-tropical moisture feed has been waning as it has been
disconnected from its source. Integrated water vapor transport
suggests this is a moderate atmospheric river connection, but it is
weakening. Even so, it will bring decent rainfall across the region
Sat afternoon into Sat night, with locally heavy rain along the south
Washington coast and Willapa Hills, extending as far south as
Tillamook and nearby Coast Range. All in all, total rainfall
(Sat-Sun) looks to be quite varied across the region, with 3 to 5
inches of rain for south WA Coast/Willapa Hills southward to
Tillamook area/Coast Range, with 2 to 3 inches for south Washington
Cascades. But, as move south and east, much less rainfall, with 1 to
2 inches along the central coast/Coast Range, with 0.50 to 1.00 inch
on to the east across the Willamette Valley.

While most rivers draining the Coast Range and Willapa Hills will see
rises again this weekend, does not appear will see repeat of early
last week, with lots of flooding. But, a few rivers (such as the
Grays, Naselle and Wilson) could get close to flood stage Saturday
night into Sunday.

In addition, landslides are possible with this next round of rain,
considering that soils are already saturated. We do not put out
alerts or warnings for landslides, and we do not know exactly where
they will occur. The biggest threat will be along the coast, through
the Coast Range and Willapa Hills, as well as the Columbia River
Valley, Cowlitz River Valley, and Portland/Vancouver Metro area.

.LONG TERM...Monday through Thursday...majority of WPC clusters are
in agreement of upper level ridging building over the Pacific NW. As
such, showers coming to an end on Monday. Then, as high pressure
builds over the inland Pac NW, will see dry but cool weather for
Tuesday. Models differ a bit for middle of next week, with some
favoring longer duration of the high pressure and subsequent dry
weather (GFS model), while others (ECMWF) favor a fast moving front
with clouds and rain for Wed. Suspect the GFS will win out, but with
uncertainty in the models trends, will keep some chance of
precipitation for Wed and Thu. Again, could just as easily be dry
with some offshore flow for Wed and Thu. Lets hope for the latter.


.AVIATION...Lingering showers this morning will give way to high
pressure. VFR through the next 24 hours with westerly winds. No
real concerns at this point aside from breezy winds over the
mountains and the Columbia River Gorge. Localized reduced VIS/CIGs
during periods of showers. Will note that there is saturation
occurring in some locations which, when combined with the cooling
temperatures, could bring periods of patchy ground fog. Around a
20% chance of MIFG forming around KHIO and other terminals in the

PDX AND APPROACHES...VFR through the next 24 hours with light
showers through 21Z Friday. Around a 30-60% chance of MVFR CIGs
during periods of showers. High clouds through the day.


.MARINE...High pressure will build across the waters Friday
bringing weaker northwesterly winds with a westerly swell between
8-10 ft remaining. Based on area observations, still seeing seas
hovering right around the 10 ft mark with periods of lower and
higher heights. Have maintained the Small Craft Advisory. An
upper level trough will send its attendant surface low towards the
coast Friday night into Saturday bringing southerly winds back
across the waters. Gale Force wind gusts likely ahead of the cold
front starting around 9-11 AM Saturday and continuing through much
of the day. Seas will likely build into the mid to upper teens
within the persistent southwesterly flow. Have decided to extend
the small craft advisory through 8 AM Saturday when it transitions
into possible gales. However, there will be around a 9 hour break
or so in conditions mid-Friday morning through the evening. Then
there will be a slow incline as the trough approaches.

High pressure will build across the waters early next week
bringing more quiet weather into the forecast. Seas are expected
to drop below 10 ft Sunday afternoon and remain below Advisory
threshold through midweek.



PZ...Small Craft Advisory today through 8 am SAT on all coastal
       waters from Cape Shoalwater to Florence.

     Gale Watch from Saturday afternoon through late Saturday night
     for Columbia River Bar.

     Gale Watch for SAT and SAT night for all coastal waters from
      Cape Shoalwater to Florence.



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