Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 261056
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
356 AM PDT Tue Mar 26 2024

.SYNOPSIS...Scattered showers this morning will diminish in
coverage through this afternoon as weak high pressure crosses
the region. A strong low pressure system will approach tonight
and bring moderate to locally heavy rain, gusty south winds,
and hazardous marine conditions Wednesday into Thursday. Warmer
and drier conditions return Friday and persist into early next
week.

&&

.SHORT TERM...Through Thursday Night...Radar shows scattered
shower activity continuing across the area this morning as broad
onshore flow remains in place over the Pacific Northwest.
Showers will diminish in coverage through the day as transient
shortwave ridging builds overhead this afternoon, helping to
limit rainfall totals to a tenth of an inch or less across most
of the area through this evening. Minor snow accumulations will
continue across the High Casacdes today as snow levels remain
above 3000 feet. Expect high temperatures this afternoon to run
a few degrees ahead of Monday`s highs, generally close to
seasonal normals in the upper 50s across the lowlands.

More active weather is still on track to return tonight as a
980 mb surface low rapidly develops approximately 700 miles off
the Washington Coast beneath the left exit region of an intense
140 kt jet streak helping to dig a deep trough over the NE
Pacific. This will drive a strong Gale Force front through the
coastal waters early Wednesday morning, bringing moderate to
locally heavy rain and breezy conditions to the area as it
sweeps inland on Wednesday. Expect wind gusts as high as 50 mph
along the beaches and coastal headlands, with south winds
gusting 25-35 mph across the Willamette Valley as the front
pushes inland during the afternoon. Expected precipitation
amounts have not changed appreciably from previous forecast
packages as guidance continues to depict QPF amounts ranging
from 0.50-0.75 inches in the inland valleys and closer to
1.00-1.50" along the coast and into the Coast Range through
Wednesday evening. Winter weather concerns across the High
Cascades will remain limited as snow levels initially rise to
4000-5000 feet with the arrival of the system, keeping modest
snow accumulations limited to the passes and above.

Precipitation becomes more showery in nature later Wednesday
into Thursday behind the front as the upper trough gradually moves
closer to shore. This will in introduce a slight chance of
thunderstorms for most areas west of the Cascades Wednesday
evening through the day on Thursday as mid level lapse rates
begin to steepen with the approach of the trough. Deep layer
southwest flow will keep the bulk of the precipitation focused
along the coast and Coast Range through Thursday, bringing an
additional inch of rain with locally as much as 2 inches in
orographically favored terrain. Meanwhile, most areas east of
the Coast Range with the exception of the South Washington
Cascades can generally expect a quarter inch or less of rain
through the day on Thursday. Do not anticipate any significant
hydro issues as guidance continues to show less than a 5
percent chance for any area rivers to reach action stage.
Thursday also looks to be the breezier of the two days for the
inland areas as the surface low moves closer to the coast and
tightens the gradient across the valley, with probabilistic
guidance showing a 20-30 percent chance for gusts as high as 40
mph through Thursday afternoon. Shower activity will begin to
diminish across the area Thursday night as the vertically
stacked low offshore continues to weaken and begins to shift
south of the region. /CB

.LONG TERM...Friday through Monday...Friday will feature
improving conditions across the region as the deep trough
offshore pivots south towards the California coastal waters,
leaving the Pacific Northwest in weaker flow aloft with a few
lingering showers across the area, with guidance in good
agreement on temperatures rebounding into the low 60s. The
warming trend continues into the weekend as WPC ensemble
clusters show strong agreement on a positively tilted ridge
building over the region from the Pacific as the upper trough
continues to sink south towards southern California. This will
bring drier weather, with NBM guidance depicting temperatures
well into the 60s from Saturday through the early part of next
week. /CB

&&

.AVIATION...Early this morning conditions are largely a mix of
MVFR and VFR with temporarily lowered cigs below 3kft mainly
found around and under shower activity. As the day progresses, a
transitory ridge of high pressure moving overhead will trend
conditions back towards prevailing VFR cigs/vis however the until
lingering shower activity finally comes to an end around mid to
late afternoon(21-00z inland sites) periods of MVFR cigs remain
possible at times. High confidence in VFR conditions this evening
and overnight as we await the arrival of another weather
disturbance approaching from the west. Winds generally stay below
5 to 10 knots through today and this evening.

* Note: The observations out of KONP are generally limited to wind
  and pressure at this time. Periodically cloud cover, vis, and
  present wx are reported but are unreliable.

PDX AND APPROACHES...Conditions will continue to fluctuate
between between VFR and MVFR this morning but will trend
predominately towards VFR as the day goes on - lower cigs are
most likely near scattered shower activity. Dry conditions return
this evening with a very high likelihood (>80-90%) of VFR
conditions continuing overnight. /Schuldt

&&

.MARINE...Active conditions are expected to develop this evening
before persisting into the end of the week as a broad low pressure
system pushes into the northeastern Pacific. At least through the
daytime hours today however, conditions remain rather benign as a
transient ridge of high pressure quickly passes overhead. Headed
into the evening and overnight hours a strengthening area of low
pressure and accompanying frontal boundary will lead to increasing
southerly winds. Confidence remains high(>75-85% chance) for Gale
Force wind gusts in the 35-45 knot range to spread across the
waters overnight through Wednesday morning leading to seas to
building into the low to mid teens. Behind the frontal boundary
winds abruptly decrease midday followed by seas temporarily
subsiding the latter half of Wednesday. That said, any reprieve is
short lived. The aforementioned surface low meanders closer to
the coastal waters Wednesday night bringing another decent
chance(>60-80%) of Gale Force wind gusts on Thursday. Coinciding
with the secondary increase in winds will also be the arrival of a
larger westerly swell, helping to push combined seas into the
15-20 ft range. Fortunately, high pressure then builds across the
northeast Pacific this weekend into early next week resulting in
lighter northerly winds. This will allow seas to drop below 10 ft
by Friday afternoon and/or early Saturday. /Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Warning from 4 AM to noon PDT Wednesday for PZZ210.
     Gale Warning from 1 AM to noon PDT Wednesday for PZZ251>253.
     Gale Warning from 10 PM this evening to noon PDT Wednesday for
     PZZ271>273.
&&

$$

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