Funnel Cloud in Oregon, November 14, 2024

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
950 AM PST Thu Nov 14 2024

Updated Aviation Discussion

.SYNOPSIS...Post-frontal showers will continue through Thursday
before decreasing in coverage Thursday night into Friday. Some
clearing Friday night will favor chilly overnight lows with near
freezing to below freezing temperatures likely, especially in
rural areas. Areas of frost Saturday morning, then back to wet
and breezy conditions late Saturday through Sunday as a Pacific
frontal system moves inland. Post-frontal showers Sunday night
into Monday will end by Tuesday as offshore flow develops,
bringing several days of dry weather with breezy east winds
Tuesday through next Friday.

&&

.SHORT TERM...Now through Friday Night...The short term
forecast is highlighted by a cool and showery post- frontal
weather pattern. Radar and surface weather observations from
early Thursday morning depicted widespread light rain showers
moving northeastward across western WA/OR ahead of a surface
trough located over the coastal waters, around 30 miles
offshore. This trough is associated with a weakening surface low
that is moving towards the Olympic Mountains. As this low
pushes inland, showers will continue through the day. A few
heavier showers or thunderstorms are possible, especially near
the coast where thunder chances range between 15-30%. That said,
most of the showery activity should remain light with minimal
impacts. Different story for elevations above 4000-4500 feet in
the Cascades where snow showers continue to bring travel
impacts. Expect another inch or two of snow at pass level today.

Hi-res model guidance continues to show decreasing showers over the
area Thursday night into Friday. In fact, most of the day looks dry
on Friday. Showers look to end altogether Friday night as high
pressure builds into the area, aside from a few stray light showers
lingering in the Cascades. With high pressure and northerly flow
aloft, expect cloud cover to clear out a bit Friday night, allowing
for radiational cooling and chilly overnight low temps. The
deterministic NBM still suggests widespread lows in the 30s across
the lowlands, including the coast. While urban area will likely stay
a few degrees above freezing, rural areas will likely dip to around
32F or colder (60-80% chance). Many locations will likely see frost
late Friday night into Saturday morning. There could be a few slick
spots on surfaces that remain wet heading into the overnight hours.
-TK

.LONG TERM...Saturday through next Friday...While conditions will
likely start off dry on Saturday with areas of morning frost,
conditions will change fairly quickly as cloud cover increases ahead
of an incoming swath of stratiform rain associated with a Pacific
frontal system. Rain associated with a warm front will begin first,
impacting the coast by late Saturday morning and inland areas by the
late afternoon. Snow levels look to rapidly rise to 6000-7000 feet
Saturday evening into Saturday night as the warm sector behind the
warm front spreads farther inland. Shortly after the warm frontal
passage, a cold front will follow. Models seem to agree well on the
timing of this cold front, pushing eastward over western WA/OR on
Sunday. This will bring yet another round of stratiform rain on
Sunday, albeit heavier than the first round. Post-frontal showers
will then continue Sunday night into Monday along with a 15-20%
chance of thunderstorms at the coast. WPC and NBM QPF do not suggest
enough rain will fall for river flooding to occur, however there is
some uncertainty. The wettest ensemble members from the GEFS/EPS
suggest minor river flooding may be possible for a few coastal
rivers, albeit the probability for river flooding is low (5-15% for
minor flooding along the Willapa River near Willapa, the Naselle
River near Naselle, the Nehalem River near Foss, and the Wilson River
near Tillamook). All other rivers have less than a 5% chance to reach
minor flood stage, aside from the Grays River near Rosburg which will
also need to be monitored closely as this river responds quickly to
heavy rain. This system will also bring breezy south winds, albeit
not strong enough for significant impacts to occur. Will also need to
watch for potential minor urban flooding in low-lying areas that have
poor drainage and clogged storm drains.

The weather pattern quickly changes Monday night into Tuesday as
offshore flow develops. As of right now, it looks like there will be
a solid four days in a row or more with dry offshore flow
and breezy east winds, from Tuesday through next Friday. Winds will
be strongest in the Columbia River Gorge, eastern Portland metro and
high Cascades, however exact wind speeds are uncertain at the moment.
-TK

&&

.AVIATION...Post cold frontal air mass continues to swing through
the airspace, bringing post-frontal showers and a mix of VFR/MVFR
conditions. Chance of thunderstorms will continue through most of
today, primarily along coast but still possible over the Coast
Range and just east of it. Along the Coast Range, expect a 15-20%
chance of thunderstorms until 00-03Z. Expect brief moments of
deteriorated conditions at times with passing heavy showers or
thunderstorms.

Expect showers along the coast to taper off around 00Z Friday and
inland around 06Z Friday. With skies forecasted to thin out and
clear around then, could see some patchy fog and lowered
visibility inland given cool temperatures and wet ground.

PDX APPROACHES...Showers and a mix of VFR and MVFR through
the TAF period. Will see brief MVFR conditions as heavier showers
pass through, with only a 5-10% chance of IFR during the afternoon.
There is about a 10-15% chance for thunderstorms through today,
ending by 06Z Friday. -Batz/Hall

&&

.MARINE...
Gusty south to southwest winds begin to decrease as the
post cold frontal air mass moves past the Coast Range. Showers
with a chance of thunderstorms and possibility of a waterspout
continue this morning, with chances of a waterspout decreasing by
sunrise. Wind gusts should remain below gale force, but
thunderstorms can produce brief gales as they move through. Winds
will ease through today as high pressure builds offshore. Seas
will remain steep and hazardous through today, then decrease to
Small Craft seas overnight into early Friday morning.

Steep westerly swell at 14 to 17 feet around 13 to 15 seconds
this morning will begin to gradually decrease this evening. Once
this swell passes the wave state finally calms for the second half
of Friday into Saturday with significant wave heights dipping
below 10 feet. However we'll need to watch another weather
disturbance expected to arrive late Sunday into Monday bringing
another round of active weather. /mh/Hall

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Hazardous Seas Warning until 7 PM PST this evening for PZZ210-
     251>253-271>273.
     Small Craft Advisory from 7 PM this evening to 10 AM PST
     Friday for PZZ210-251>253-271>273.
&&

www.weather.gov/portland

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