112
FXUS66 KPQR 212046
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
144 PM PDT Sat Sep 21 2024

.SYNOPSIS...A weak front will push across the region Sunday/early
Monday, but little if any rain expected.High pressure rebuilds over
inland Pac NW, bringing much warmer temperatures with weak offshore
flow on Tuesday. Then, back to more typical late September
temperatures for the middle through through latter part of next week as
onshore flow returns with the potential for precipitation for the end
of next week.

&&

.DISCUSSION...Tonight through Saturday...Overall a warming and drying
trend will continue through the weekend and into the middle of next
week. A very weak frontal passage will scrape across the northern
portions of our CWA Sunday/Monday morning, but little to no rain is
expected with the frontal passage. After the front, high pressure
will return as the dominant synoptic feature and will result in
temperature peaking on Tuesday with daytime highs in the 70s along
the coast, upper 80s to low 90s for inland locations and upper 70s to
mid 80s for the Cascades. NBM probabilities are showing around a 15%
probability for the Portland/Vancouver Metro area reaching 90 degrees
F, but as you progress further south within the Willamette Valley
that probability increase towards 40% for Eugene, OR. It should be
noted that this warm up will be very short lived as Wednesday highs
are expected to be in the 60s to 70s.

What else that should be noted is that their is the potential
(85%-95% probability) of weak offshore flow on Tuesday. It should be
noted that the overall synoptic pattern is sub-optimal for a stronger
wind event as guidance. The upper level ridge axis is expected to
move quickly inland with a weak thermally induced surface trough
briefly developing. As a result, forecast offshore pressure gradients
remain rather weak around -1mb to -3mb from TTD-DLS and -3mb to -6mb
from OTH-GEG. As such, ensemble members are mostly clustered around
maximum wind gusts in the 20-25 mph range through the Gorge and over
higher Cascade slopes, with the a few of the higher end members
maxing out around 30-40 mph in those locations. There still is some
variability within the models so, we  will continue to monitor and
adjust the forecast as needed. Also, the bulk of model guidance
currently points to a lower end of the wind range as well as
maintaining a short lived offshore flow event.

Beyond Tuesday, GEFS,ENS and other ensembles to include the NBM, are
showing a cooling trend returning. This will bring temperatures more
inline with late September normals. As the end of next week
approaches, models are also showing precipitation coming back into the
forecast, with two slugs of moisture coming into the region Wednesday
and Thursday. While these aren`t looking to be season enders, these
systems could be the vanguard for the fall/autumn season. Only time
will tell if this becomes true or not. /42

&&

.AVIATION...North winds will ease tonight and Sunday as a weak
front approaches. The main aviation impact from the front will be
MVFR ceilings along the coast early Sunday morning. There is a
60% chance for MVFR ceilings along the coast early Sunday morning.
Light onshore winds will help the stratus moving up the coastal
valleys a bit, but do not expect the stratus to move into the
Willamette Valley. MVFR ceilings will move off of the immediate
coast late Sunday morning before returning late Sunday afternoon.
stratus
will retreat much intrusion into the Willamette Valley.

PDX APPROACHES...VFR conditions expected through Sunday. There is
a 5-10% chance for MVFR CIGs 15-17Z Sunday. THere is a better
chance for MVFR cigs early Monday.
~TJ

&&

.MARINE...High pressure across the NE Pacific with low pressure
near the California coast will maintain north winds across the
waters through Tuesday.The northerly surface pressure gradient
will strengthen across the waters, mainly south of Cape Falcon
this afternoon supporting a marginal small craft advisory.

A fetch associated with a low in the west Pacific near 48N 170E
will produce a building NW 7 to 9 ft swell across the waters
Tuesday and Wednesday. A front associated with this low will move
across the waters Wednesday and Thursday for a period of south to
southwest winds.

Another low currently developing near Japan will strengthen as it
moves across the Pacific towards the Pacific NW through the week.
Models are forecasting a larger NW swell with potentially 13 to
15 ft seas in the Oregon waters Friday.
~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM this afternoon to 9 PM PDT this
     evening for PZZ210.

     Small Craft Advisory until 10 PM PDT this evening for PZZ272.

     Small Craft Advisory until 10 PM PDT this evening for PZZ273.
&&


$$

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