Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 220459
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
956 PM PDT Thu Mar 21 2024

.UPDATED AVIATION...

.SYNOPSIS...
Temperatures will remain relatively warm through Friday, then
cooling throughout the weekend into next week. Expect mostly
dry conditions, with a few stray showers along the SW Washington
coast through the afternoon. Light showers through the region
tonight, then returning to widespread rain as the next upper
low pressure system arrives Friday morning. This low will bring
cooler and showery weather this weekend. Snow levels fall
to 3500 to 4000 feet this weekend, bringing a few inches of
snow to the Cascades passes with little to no winter weather
impacts expected. Rain will persist through early next week,
with a shortwave trough Monday and a low pressure system
Tuesday.

&&

.DISCUSSION...THROUGH WEDNESDAY...A transient ridge begins to
bring mostly dry conditions through the region, except for a
few lingering showers or sprinkles along the SW Washington
Coast. Temperatures will remain seasonably high today and
Friday, with highs forecasted in the upper 50s to low 60s for
inland valleys and mid 50s along the coast. With lingering mid
to high level clouds expected through most of Friday, inland
temps are not expected to warm up well beyond 60 degrees (40-60%
chance to exceed 60 F).

Friday, a broad low pressure system over the NE Pacific will
approach the Pacific Northwest. The occluded front will push
inland Friday morning, returning widespread rain across the
area. QPF 24 hour amounts ending 5 AM Saturday are forecast
around 0.25-0.50 inch for the coast and inland valleys, and
0.50-0.75 inch for the Coast Range and Cascades. Chances around
20-30% for QPF to exceed these forecasted values. Snow levels
will remain between 5000-6000 feet through Friday, therefore no
snow impacts are expected. This system will bring cool and
showery conditions through the weekend.

On another note, thunderstorms are possible for Friday and
Saturday afternoon. With the colder air aloft (850 mb temps
around 0 degree C), thunderstorms will be possible (10-20%
chance) along with potential of small graupel. With limited
instability/CAPE, potential of small graupel would be limited to
only strong showers.

This weekend, accumulating snow is expected in the Cascades and
Cascade passes, as the snow level drops to around 3500-4000
feet. Travel impacts should remain minimal as only a few inches
of snow is expected at pass level (20-40% chance to exceed 4
inches). Otherwise, expect non-impactful showers through the
weekend.

Monday through Tuesday, the majority of ensemble members from
the WPC cluster analyses suggest cool, northwesterly flow
aloft, maintaining showery conditions. Showers will briefly change
to widespread rain as a shortwave moves through the region
Monday afternoon. Rain will be light, with NBM guidance
suggesting chances of 24-hr QPF exceeding 0.5 inch around 40-50% for
the Coast Range and Cascades and 10% chance for the Coast and
Willamette Valley for both Monday and Tuesday.

Tuesday night into Wednesday morning, a low pressure system
west of Vancouver Island will bringing a sweeping front into the
region. Winds along the coast expected to gust up to 30 mph and
inland up to 25 mph, with around a 50% chance to exceed these
values. As for snow amounts within the Cascades, 12 hour snow
amounts on Wednesday near 1 foot for Cascades of Lane and
Marion/Linn County. While this is far out, current NBM
probabilistic guidance suggests a 10-20% chance to exceed 1
foot. Otherwise, 24 hour QPF is currently forecast to be 1-2
inches for the Cascade foothills and Coast Range, and 0.25-0.50
inch inland. -JH


&&

.AVIATION...VFR conditions are in place throughout region, with
ceilings above 10,000 feet at all terminals as of 05z. The next
front arrives from the south, reaching southern terminals (KEUG,
KONP) around 16-17z Friday. This brings widespread rain, with a 40%
chance of MVFR ceilings at coastal terminals. Inland terminals only
see a 10% chance of MVFR conditions. Models continue to push back
the start time of this front, and conditions Friday morning are
trending dryer/more clear skies. If sufficient clearing/daytime
heating occurs Friday morning, ie. temperatures reaching into the
low 60s, we could see enough instability to generate some
thunderstorms throughout the area once the front moves in. Current
models show around a 10-30% chance of this occurring.

* 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...VFR conditions expected throughout the TAF
period. The next front arrives at PDX around 20z Friday, allowing
for light to moderate rain, but low-end VFR ceilings are expected
during the frontal passage. Around a 10-30% chance of thunderstorms
during the frontal passage if enough clearing and heating occurs
Friday morning. /JLiu

&&

.MARINE...A more active weather pattern is expected through the
remainder of the week and into the the start of next week as a
broad area of low pressure moves eastward. This low pressure
system will send a series of fronts across the waters and maintain
elevated winds and seas. The multiple fronts which will impact all
waters will bring southerly small craft wind gusts to all
waters. Therefore have issued and adjusted Small Craft
Advisories for all waters. General seas will build through the
weekend around 5-8 ft through the start of next week. A far more
robust system sliding in from the northeastern Pacific towards
the middle of next week, will likely bring Gale force gusts and
seas into the low teens. However, timing and strength are still
in flux as this system is towards the end of the forecast
period. /42


&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 8 PM this evening to 3 AM PDT Friday
     for PZZ251.

     Small Craft Advisory until 5 PM PDT Friday for PZZ252-253.

     Small Craft Advisory from 8 PM this evening to 3 AM PDT Saturday

     for PZZ271.

     Small Craft Advisory until 5 AM PDT Saturday for PZZ272-273.
&&

$$

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