NWS Portland, OR wrote its last area forecast discussion before the first event at Jun 10, 8:23 PM PST, 3 hours 37 minutes earlier.
Area forecast discussion, Jun 10, 8:23 PM PST, 3 hours 37 minutes before
Area Forecast Discussion
National Weather Service Portland OR
923 PM PDT Fri Jun 10 2022
Updated Aviation and Marine discussions
.SYNOPSIS...Another batch of moderate to locally heavy rain is
expected for much of the forecast area tonight as another disturbance
interacts with a late season atmospheric river. The heaviest rain is
expected to slowly sag southward and decrease, affecting mostly areas
south and east of Salem Saturday morning. Scattered showers will
persist elsewhere until the next organized batch of rain arrives
Sunday afternoon, also affecting mainly the southern half of our
forecast area. Cool, less humid, and showery weather is expected
Monday, then the region should start drying out Tuesday or Wednesday.
&&
.SHORT TERM...Tonight through Monday...After a break in the precip
between weather disturbances this morning, KRTX doppler radar shows
rain spreading back into the region early this afternoon. Water vapor
and Blended Total Precipitable Water (TPW) imagery show a long
atmospheric river of moisture aimed toward Oregon, extending all the
way back to the tropical latitudes near the International Dateline.
TPW values on the order of 1.25 to 1.50 inches are in play over
northwest and west-central Oregon...perhaps even higher than that
given the 1.58 inches of TPW in this morning's 12z KSLE sounding.
These TPW values are unusually high for our CWA, but they aren't
all-time records. But this is why it feels a bit humid to some this
afternoon, with dewpoints in the upper 50s to mid 60s for most of the
forecast area. This moisture is expected to be available as the next
wave of low pressure, just now getting its act together in the
vicinity of 40N and 135-140W, moves across northwest and west-central
Oregon later tonight and early Saturday morning.
While the last batch of heavier rain impacted mainly the northwestern
half of our forecast area, tonight's batch is shown by the HREF to
focus a little further south. Rainfall rates will probably reach
their maximum as the above-mentioned wave of weak low pressure moves
onshore around midnight. At that time, most models show the
baroclinic zone sagging slowly southward, with the axis of heaviest
rainfall being near a line from Florence to eastern Clackamas County.
Given the moisture transport involved, rainfall rates should become
heavy with some orographically-favored areas possibly seeing 0.3 to
0.5 inch per hour between 10 PM this evening and around 8 AM Saturday
morning. Overall, a few locations may exceed 2 inches of rain in a
12-hour period, which could come close to overwhelming some creeks
and small streams. This would be most likely in our Oregon Cascade
foothills, where the high moisture content is likely very efficient
at melting off snow in the headwaters up higher in the Cascades.
Overall, most of the lowlands can expect another 0.50-1.00 inch of
rain by midday Saturday, with some coastal locations getting into the
1-2 inch range and, as mentioned above, some Cascade foothill
locations may exceed 2 inches.
Models show good agreement that the precip turns more showery
Saturday afternoon, though a few keep steadier precipitation over
portions of Lane County throughout the day. Models appear to have
latched on to another disturbance presently near 40N/155W that should
arrive late Sat night or Sunday morning. By then, the core of the
atmospheric river should be well to our south, but this wave will
still have plenty of moisture to work with over our CWA. Details are
uncertain in regards to the track this system will take, or where the
heaviest rain will fall. Cooler air on the back side of this system
will cause snow levels to dip to near Cascade pass level by Monday
morning. Monday looks to be a cool and showery day under the upper
trough. With 850 mb temps progged to be around 0 deg C, it'll be
tough for anyone to get much above 60 degrees Monday afternoon. But
with the sun nearly as strong as it gets, most of the lowlands should
be able to at least touch 60 degrees. Also, the combination of strong
June sunshine and cool temps aloft could touch off a couple of
thunderstorms Monday afternoon, especially east of the I-5 corridor.
Weagle
.LONG TERM...Tuesday through Friday...Ensemble systems indicate that
the Sunday shortwave trough will shift east of the region Monday
into Tuesday. Nonetheless, there should be enough moisture and cool
air aloft to keep showers going on Monday and perhaps even into
Tuesday. Shortwave ridging should at least briefly shift across the
Pacific Northwest Tuesday and/or Wednesday. This will likely bring at
least a 24-48 hour period of drier weather and allow temperatures to
moderate. However, most members in the EPS and a sizable number of
the GEFS and CMCE members suggest another shortwave trough will push
towards the Pacific Northwest Thursday...bringing with it another
round of rain to the region late next week. For what it's worth, the
12z WPC cluster analyses strongly suggest a troughy pattern returning
to the Pacific Northwest by next weekend. Weagle/Neuman
&&
.AVIATION...06Z TAFs: As this atmospheric river continues to push
across the region bringing near record high amounts of moisture,
expecting a mix of MVFR and IFR conditions due to both vis and
ceilings, with some periods of LIFR due to low ceilings
overnight. The atmospheric river will be advecting southward
through the morning before weakening by 18Z Saturday. Stratiform
rain will then likely transition to showers with weak post-
frontal showers persisting through the day. Ceilings and vis will
improve to MVFR, further improving after 00z to VFR.
For detailed Pac NW aviation weather information, go online to:
https://weather.gov/zse
KPDX AND APPROACHES...MVFR with rain through the next 6-12 hours
as the atmospheric river intensifies. Slow improvement with
lingering showers expected through 18Z, before the weather system
really drops further south to bring VFR back to the area.
-Muessle/Kriederman
&&
.MARINE...An atmospheric river continues in southwesterly flow
over the waters and inland. Unseasonably high
moisture content with the atmospheric river impacting the waters
through early Saturday will result in areas of fog over the
waters, with visibilities below 1 statute miles at times.
Seas continue to subside as with winds. Seas around 4 to 6 ft at
10 seconds is expected through at least Monday. Southwesterly
winds may impact the waters closest to the shore increasing wind
waves there, however most of the waters will experience minimal
wind wave impacts. Expect light southwesterly winds, 5 to 10 kts
to transition to northwest by Saturday night.
On Sunday, another disturbance will pass over the waters from the
southwest which will likely bring another period of more active
weather. Will see winds intensify from the northwest where we
could see speeds around 10 to 15 kt with gusts up to 20 kt. Seas
likely will not respond in the same way as this is a fairly fast
moving system. Will likely see the combined swell become
northwesterly which, when combined with the northwesterly winds,
may increase wave heights slightly higher than currently forecast.
More settled weather is possible early next week if the high
pressure ridge that some models are attempting to build over the
waters actually develops. -Muessle/Kriederman
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
www.weather.gov/portland
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