233
FXUS66 KPQR 070440
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
840 PM PST Wed Nov 6 2024

.SYNOPSIS...High pressure will maintain dry weather and clear
skies through tomorrow (Thursday). Clear skies will also lead to
enhanced cooling at night, bringing frost potential to interior
lowland valleys. More active weather returns late Friday into
Saturday, with several rounds of rain leading to some potential
for river flooding along the coast early to mid next week.

&&

.SHORT TERM...Now through Friday Night...Dry weather and clear
skies dominate the region through tomorrow (Thursday) as upper
level ridging settles over the Pacific Northwest. Satellite
imagery as of 130 PST also show low clouds finally beginning to
dissipate in the southern Willamette Valley. High temps in the
south Valley could be a few degrees cooler than forecast this
afternoon due to these lingering low clouds.

Clear skies with calm winds will enhance radiational cooling
tonight, leading to chilly temps and areas of frost and/or
patchy fog. Locations with frost potential include the
Willamette Valley, parts of the north Oregon Coast Range,
southwest Washington lowlands, and Upper Hood River Valley.
Early Thursday morning lows are forecast in the mid 30s in these
locations, but will note NBM suggests a 30-40% chance that the
southern Willamette Valley drops below freezing tonight. Frost
and fog may be more difficult to form in the Portland/Vancouver
Metro Area as winds through the Gorge may keep air well-mixed
and prevent the best cooling.

Any fog or frost that develops early Thursday morning should
dissipate by mid to late morning (around 1000 PST). Otherwise,
benign weather continues tomorrow with sunny skies. Pressure
gradients are pretty loose tomorrow, so expect mostly light and
variable winds except through the Columbia River Gorge. Model
pressure gradients from KTTD-KDLS are around -2 to -4 mb, so
could see some easterly winds with gusts up to 20-25 mph through
the Gorge and into the far eastern Portland/Vancouver Metro
Area tomorrow.

Thursday night into Friday, high clouds will begin filtering
into the region as the ridge shifts eastward with an approaching
trough. The system remains well-offshore on Friday so most
places will remain mostly dry, however, the coast will see a
return of rainfall chances. PoPs begin to increase and spread
inland by Friday night as the system moves closer.     -Alviz

&&

.LONG TERM...Saturday through Tuesday night...Cooler and wetter
weather will return to the area by this weekend as the next
upper trough accompanied by the aforementioned front moves
across the area late Friday into Saturday. Forecast amounts from
late Friday evening through late Saturday evening are around
0.50-0.75 inch along the coast and Coast Range, and 0.10-0.40
inch. With this system, NBM suggests a 10-20% chance for 1 inch
or greater for inland locations, and a 50-60% chance along the
coast and Coast Range.

Not expecting any significant hydro impacts through the weekend,
but this will set the stage for potentially greater responses
on area rivers next week as additional systems follow Sunday
through Wednesday. Following the Saturday system, models suggest
the next front arriving some time on Sunday-Monday. While there
remains uncertainty with the exact timing of this front, this
system is looking more robust in terms of QPF. The ECMWF Extreme
Forecast Index (EFI) is highlighting a signal for heavier QPF
amounts across northwest Oregon and southwest Washington between
Sunday afternoon to Monday afternoon. NBM suggests a 30-50%
chance for 48 hour QPF amounts exceeding 2 inches for interior
valleys ending Tuesday morning, with an 80-90% chance for the
coast, Coast Range, and Cascades.

Models still depict a large spread on potential precipitation
amounts during this time, but HEFS guidance continues to
indicate a 10-25% chance for flooding on some areas rivers next
week, particularly those draining the Coast Range. Will
therefore need to keep a close eye on rainfall amounts and
potential hydro impacts going forward. Additionally, snow levels
dropping back down to around 4000 feet will bring potential for
accumulating snow back to the Cascade passes during the first
half of next week.       -Alviz/CB

&&

.AVIATION...Currently widespread VFR conditions throughout the
airspace. Light north/northeast flow will continue through the TAF
period. Conditions begin to dry a bit, offering the possibility of
frost rather than fog, beginning around 12Z Thursday. While frost
is more probable, there is a 20-30% chance for fog/LIFR conditions
to form throughout the region between 10-17Z Thursday, highest at
KHIO and KEUG. Otherwise, expect VFR to prevail through the
period. Additionally, expect gusty east winds up to 25 kt near
KTTD and the mouth of the Columbia River Gorge through the TAF
period, with highest magnitudes in the early morning (10-19Z
Thursday).

PDX APPROACHES..VFR expected to persist through the TAF period,
with a 15-20% chance of fog/LIFR conditions between 12-17Z
Thursday. However, cooler lows will bring a higher probability of
frost (65% probability) rather than fog overnight. With increased
winds in the Columbia River Gorge, could see gusts up to 20 kt at
times through the TAF period. ~Hall

&&

.MARINE...Light offshore flow across all waters to persist
through at least Thursday morning as high pressure inland and a
thermally induced trough along the south Oregon coast. This
pattern begins to break down Thursday afternoon as the next
system is expected Friday night/Saturday morning. This system will
bring a series of fronts across the waters through early next
week, which will result in increasing wind and seas.

Seas currently around 5 to 7 ft with a 12 to 13 second period.
Seas will build back towards the mid to upper teens towards the
end of this week/weekend. Current guidance is showing a 25%-45%
probability of seas 18-20 ft next Monday into Tuesday along with
westerly winds with gusts up to 30 kt. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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