494
FXUS66 KPQR 052209
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
309 PM PDT Sun May 5 2024

.SYNOPSIS...The broad low pressure system has shifted
southeastward over the OR/ID border this afternoon and residual
showers linger in it`s wake. Active showers will persist through
the next 36 hours with snow falling over the Cascades and rain
elsewhere. Accumulations will be more spotty in nature than the
previous days. A strengthening high pressure ridge builds in
starting on Wednesday with increasing chances for some of the
warmest temperatures observed this year so far.

&&

.SHORT TERM...Now through Tuesday...Current radar shows an
intensification of rain showers along the Coast Range and the
valleys, while precipitation has not really taken a break over
the Cascades. While accumulations have been minimal, the
persistent nature of the precipitation will keep conditions
grey and dreary for a few days more. I mention "a few days more"
because the next break is a bit farther off than previously
expected. Starting well aloft at the jet stream, at 250 mb
(~35,000 ft), the jet is beginning to dig southward with the
forecast area sitting in the left exit region of the 150 kt jet
streak. The negatively tilted jet will enhance upper level
support for active weather at the surface. These conditions are
coupled with a weak shortwave showing up at 500 mb (~18,000 ft)
and increased vorticity advection. These features together show
an enhancement of energy which will encourage more active
weather. Combine that with lower level onshore flow, orographic
lifting will tap into these more active conditions aloft and
thus, extend the precipitation.

At 850 mb (~5,000 ft) withs are forecast to be close to 40 kt
early Monday morning during the time of the next round of rain.
Will note though that this system is not necessarily the most
robust but it has stayed fairly consistent over the last few
runs. Hi-resolution models are showing a period of increased
precipitation Monday morning which will increase snowfall over
the Cascades. Given the short time frame between systems, have
decided to just extend the Winter Weather Advisory above 4000 ft
through the "break" as to not over complicate things. Will say
though, snow will lessen between 6 PM Sunday through around 2 AM
Monday.

Conditions will become more showery on Monday. There is some
tropofolding on Monday which can be associated with increased
chances for thunderstorms. This feature combined with the
active jet location, shortwave, and cooler temperatures aloft,
have included slight chances for thunderstorms which encompasses
most of the northwest Oregon and Southwest Washington. Thunder
chances decrease Tuesday morning with chances for precipitation
through the remainder of the day. -Muessle


.LONG TERM...Wednesday through Sunday...If you`re ready for a
break in the rain, the long term forecast is for you. If you`re
looking for temperatures in the 70s, and 80s, then mid and late
this week are definitely for you! A large area of high pressure
builds over the Pacific starting on Wednesday. Clusters are in
very good agreement of this ridging, and how amplified it is
streting from off the coast of California up through southern
Canada. The extent of this high will increase easterly flow as
thermal troughs form along the coast. There will be a slight gap
winds through the Columbia River Gorge and downsloping off of
the Coast Range. There is still a lot of room for conditions to
change, but there are high probabilities of temperatures rising
into the 80s on Friday. The coast will react a bit less. The NBM
is showing around a 10% chance of temperatures in the 90s on
Saturday within the Willamette Valley, but the other long range
models have less than a 5% chance of temperatures greater than
85 degrees inland. This is because the cluster pattern would
favor a transition to onshore flow. At this point, not banking
on temperatures in the 90s as models have started to lower them
a bit, but, it isn`t a bad idea to start preparations for these
warmer temperatures if they do manifest. -Muessle


&&

.AVIATION...Moist westerly flow and scattered light showers
continue across the region this afternoon. Conditions continue to
be a variable mix of IFR to VFR at both inland and coast sites
with this variability likely continuing to fluctuate in
conjunction with shower activity. Still guidance indicates the
possibly for a more pronounced break in shower activity late this
afternoon into the evening for inland sites, roughly 23-05z,
before another frontal system arrives bringing an increase in
rainfall and higher probabilities (60-80%) for widespread MVFR
CIGS. Rain then breaks to post-frontal showers Monday morning,
but confidence in the exact timing of any categorical improvement
back towards VFR is low. It`s worth noting there`ll be slight
chance(15-20%) for weak T-storm activity across the region Monday
afternoon. Wind generally stay breezy out of the south at 10-25
kts - highest coastal sites.

PDX AND APPROACHES...Currently a mix of VFR and MVFR with waves of
light showers progressing through the area - variability in
CIGS/VIS likely continue. HREF is indicating MVFR probabilities
increasing again after a small lull this evening. So will probably
see MVFR prevailing overnight through about 14-16Z Sunday before
a switch to post-frontal shower activity. From there MVFR/VFR
cigs will once again be modulated by showers. It`s worth noting
there`ll be slight chance(15%) for weak T-storm activity locally
Monday after 18-20z . -Schuldt

&&

.MARINE...The active weather pattern continues into Monday before
a gradual transition to to generally calmer/drier conditions and
a much more summer-like pattern by the middle of the week. Our
next and final(at least for awhile) frontal system arrives this
evening into the overnight hours bringing yet another round of
gusts up 25-30 kt as well as steepening seas across most of the
waters through Monday morning. Following this weather disturbance
high pressure begins to build over the northeast Pacific Tuesday
and Wednesday leading to the development of breezy west to
northwest winds (gusting 20-25 kt) across the waters come Tuesday
morning. Also expect the arrival of a fairly pounced WNW 9-10 ft
swell at near 12 seconds in the Monday night time-period. The
broad area of high pressure shifts closer to the waters the second
half of next week followed by a larger offshore component to the
wind in the late Thursday through Saturday timeframe. -Schuldt



&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 11 PM PDT Monday for ORZ126>128.
WA...None.
PZ...Small Craft Advisory until 8 AM PDT Monday for PZZ210.
     Small Craft Advisory until 8 AM PDT Monday for PZZ251>253-
     271>273.

&&

$$

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