Area Forecast Discussion
Issued by NWS Portland, OR

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000
FXUS66 KPQR 280500
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1000 PM PDT Wed Mar 27 2024

.SYNOPSIS...
Post-frontal showers with a slight chance of thunderstorms
continuing through Thursday evening as a low pressure system spins
offshore. Conditions begin to improve on Friday, with high
pressure bringing another period of warm and dry weather this
weekend into early next week.

&&

.SHORT TERM...Now through Friday Night...Satellite imagery
shows a well defined 980mb low over the NE Pacific and frontal
clouds beginning to clear from west to east as of 1PM Wednesday.
Precipitation has begun to become more showery through the
region as the front continues to move east over the Cascades.
Thereafter, widespread showery conditions will continue through
late Thursday night as the low makes slow progress towards the
coast. With southwest flow, the bulk of the precipitation is
expected to fall over the coast and Coast Range. QPF guidance
indicates an additional 1.00-1.50 inch of rain in these areas
through Thursday evening. Rainfall amounts will remain more
modest over the valley through Thursday, but could still see
another quarter to half inch with higher amounts in heavier
showers and thunderstorms. Hydro concerns remain minimal as
guidance continue to depict probabilities of 5 percent or less
to reach action stage on area rivers.

A chance of thunderstorms for most locations west of the
Cascades through Wednesday evening as the advancing low pressure
system steepens lapse rates. With good shear conditions through
Wednesday evening, small hail within stronger showers is
possible. Thursday morning through Thursday night, thunderstorm
chances will decrease but will still remain possible as lapse
rates will remain increased.

Snow levels of 4000 to 4500 feet will gradually decrease to
2500 feet by early Thursday morning, keeping light snow limited
to Cascade passes and above. Through Thursday evening, passes
are expected to receive at most 4 inches of snow within 12
hours (20-30% chance to exceed 4"). As for snow totals through
Thursday evening, a total of 6 to 12 inches of snow is
expected.

Breezy conditions also persist through Thursday evening as the
low center nears the coast and maintains a tight pressure
gradient. As a result, southerly winds gusting to 40 mph along
the coast (50-60% chance to exceed 40 mph) and 35 mph inland
(60-70% chance to exceed 35 mph) through Thursday afternoon.

Otherwise, conditions will show an improving trend Thursday
night into Friday as the low offshore begins to drop south and
weaken. This low will then be absorbed into a new dominant low
that rides the trough towards California coastal waters. As a
result, benign conditions with a few lingering showers for
Friday, with high temperatures warming into the high 50s to low
60s during the afternoon.
-JH

.LONG TERM...Saturday through Tuesday...Guidance continues to
indicate warm and dry conditions returning this weekend into
early next week as the upper low moves south into southern
California and is replaced by a strong ridge building over the
Pacific Northwest. This is reflected by NBM forecast
temperatures which show high confidence in highs in the mid
60s Saturday through Monday (60-80% chance to exceed 65 F). WPC
cluster analysis depicts about 85 percent of individual ensemble
members keeping the ridge over the region through Tuesday
before temperatures drop back down towards seasonal normals
later in the week.
-JH/CB

&&

.AVIATION...Threat of thunderstorms has passed, and VFR conditions
dominate until at least 11z Thu. Less than 10% chance for any
passing showers to drop any terminals into MVFR until then. High
resolution model guidance does suggest the probability of MVFR
conditions increases between 11-16z Thursday across the region, with
likely 40-70% chance of MVFR afterwards through the TAF period.
Winds will also become gustier around that time, with gusts up to 26-
28 kts possible at all terminals at that time. Given the pattern,
would still expect many sites to bounce up and down between MVFR and
VFR during that time, though.

* 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 continue through 13z, and any
passing showers are not expected to drop ceilings to MVFR criteria.
Currently around a 50-70% chance of MVFR conditions from 13z
onwards. /JL

&&

.MARINE...A cold front is now pushing inland across the Pacific
Northwest. Expect wind gusts of 20 to 25 kt across the waters
tonight with seas temporarily subsiding through this evening.
However, the surface low pressure responsible for the cold front
pushing across the region this morning will gradually shift
eastward towards western Washington tonight into Thursday and
weaken substantially. Nonetheless, it will bring a return to
stronger southwest winds and showers that will occasionally mix
stronger winds from aloft down to the surface of the ocean. There
is an ~80% chance for at least a few wind gusts of 35 to 40 kt to
mix down to the surface of the ocean from time to time on
Thursday across the waters. A large westerly swell will push into
the waters during this time as well with seas climbing into the
16-20 ft range. Seas will most likely peak sometime during the
late afternoon and early evening hours on Thursday before falling
back down into the mid teens by midnight and below 10 ft sometime
during the second half of Friday.

Weather models are in general agreement high pressure will shift
across the waters and Pacific Northwest this weekend. This will
produce a more summer-like northerly wind pattern. The waters off
the central coast of Oregon will generally experience stronger winds
and steeper seas than waters off the south Washington coast.
There is an 50% chance that wind gusts climb back up into the
30-35 kt range towards next Wednesday as a front may slide
southeastward across the region. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Thursday for PZZ210.

     Hazardous Seas Warning from 2 AM to 8 PM PDT Thursday for
PZZ210.

     Hazardous Seas Warning until 5 AM PDT Thursday for PZZ251>253-
     271>273.

     Gale Warning from 5 AM to 8 PM PDT Thursday for PZZ251>253-
 271>273.

&&

$$

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