Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 011537 AAA

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
836 AM PDT Fri Jul 1 2022

Updated aviation section.

.SYNOPSIS...Mild and seasonable weather expected today and Saturday,
with cooler conditions likely towards the end of the holiday
weekend. An upper low pressure system will bring chances for showers
and thunderstorms, mainly over the Cascades. Mild conditions
continue through next week as broad upper level troughing persists
over the NE Pacific.


.SHORT TERM /TODAY THROUGH SUNDAY/...Another seasonable mid-summer
day on tap for today, the first day of July. Low clouds at the coast
are spreading into the southern Willamette Valley as well as through
the lower Columbia this morning. May see a scattering of low clouds
through the remainder of the interior valleys this morning, but
skies expected to clear again by the afternoon. Should allow
temperatures to once again warm into the upper 70s to lower 80s
inland today, while the onshore breeze keeps the coast moderated in
the 60s. Breezy northwest expected later today as onshore begins to
strengthen again.

Will see the current weather pattern shift somewhat this weekend as
an upper level low stalls off shore. Broad area of low pressure near
Vancouver Island today will become more organized and drift south
through Saturday. Mid level moisture increases across the region as
southwesterly flow aloft becomes more southerly, setting up a
pattern that is conducive to convection and possible thunderstorm
development over the Cascades. 00Z HREF guidance suggests a 20-40%
chance for thunderstorms occurring along the crest of the central
Oregon Cascades on Saturday afternoon, before moving east.
Northwest, onshore flow will be maintained in the lower levels, with
mostly cloudy skies likely. This may cool temperatures a few
degrees, but still quite seasonable conditions on Saturday.

One of the big challenges will how the upper level system evolves
through Saturday night into Sunday. Models have come into better
agreement with the upper level synoptic pattern, as the upper low
drifts closer to the coast later in the weekend. But model forecast
precipitation details differ substantially. Therefore will maintain
a 20-30% chance for showers on Saturday night for areas near the
Portland metro and into southwest Washington, with PoPs of 20-40%
becoming more widespread by Sunday morning. Ensemble guidance has
backed off somewhat on interior lowland precip potential, but still
shows good chances for light rain along the north coast on Sunday.

Another round of convection will be possible Sunday afternoon near
the Lane County Cascades, but most model guidance keeps chances for
thunderstorms east of the Cascades. The upper low begins to swing
onshore by Sunday evening. Along with height falls, cooler
temperatures aloft will move in over the region. Temperatures at 850
mb cool to around 6-8 degrees C, while skies remain mostly cloudy.
High temperatures on Sunday may struggle to reach 70 and onshore
flow persists. /DH


deterministic models show the upper level low positioned over the
Pacific NW on Monday with varying details that will impact sensible
weather during the Independence Day holiday. The general pattern
appears to bring 25-50% chances for precipitation to occur across
the northern half of the forecast area, including Salem, with
highest PoPs over southwest Washington. A handful of ensemble
members (~20%) show the possibility of a few modest showers producing

0.1-0.2 inches of rainfall in the Portland metro through Monday
afternoon, but the majority indicate little to no impactful
rainfall. By Monday evening, rain chances decrease to below 20%
while model guidance suggest clouds decrease from south to north by
Monday night. Temperatures will likely remain below normal on the
Fourth of July, expected to warm into the lower 70s inland, and
lower 60s at the coast.

After the upper low lifts north toward Canada, expect to see
conditions return to more seasonable as heights rise and mid level
temperatures warm. But long term forecasts do not show any
significant warm-up. In fact, could see more shower activity along
the Cascades into the middle of next week. Cluster analysis shows
broad upper level troughing persisting offshore across the NE
Pacific. Both the GFS and ECMWF show the potential for convective
showers developing in the Cascades Tuesday, Wednesday and Thursday
as southwest flow aloft continues across the region. Lowland
temperatures are expected to return to the upper 70s to lower 80s
through the remainder of the long term period./DH


.AVIATION...18z TAFs: Inland MVFR ceilings and coastal low
MVFR/high IFR are ongoing at 1530z amidst weak onshore low level
flow. Both inland and coastal TAF sites should go VFR between 18z
and 20z as surface heating burns off inland stratus and surface
flow along the coast turns offshore to push marine stratus back
over the water.

VFR should continue inland through around 09-10z when low MVFR
(and possibly IFR in places) stratus redevelops (1) along the
north Oregon Cascades/Foothills amidst another night of weak
onshore flow and (2) in the southern Willamette Valley where flow
turned northerly by terrain will experience gentle uplift.
However, along the coast low stratus will be faster to return,
with HREF guidance forecasting the return of MVFR ceilings by
02-03z Saturday and giving a 60-80% for IFR ceilings by 05z.

For detailed Pac NW aviation weather information, go online to:

KPDX AND APPROACHES...MVFR ceilings should come to an end over the
next couple ours as surface heating gradually burns off the low
stratus through around 19z. VFR should then prevail until around
12-13z Saturday, when backbuilding stratus forming along the
Cascades/Foothills in onshore flow moves over the terminal from
the east. There is around a 30% chance that this will be IFR, but
most likely MVFR ceilings will result. -Bumgardner


.MARINE...Persistent high pressure will maintain fair weather
through Saturday. Northerly wind gusts peaking near 20 kts will
occur through Saturday as thermally induced lower pressure
strengthens each afternoon and evening across northern California
and southern Oregon. A weak upper level low pressure will then
settle across the region and weaken pressure gradients even
further. Expect seas to generally remain in the 3-5 ft range
for much of the next week, but will be a bit choppy at times due
to wind waves and fresh swell dominating the sea state. /Neuman

For more information about upcoming marine zone changes, go online





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