Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 242158
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
245 PM PDT Mon Jul 24 2017

.SYNOPSIS...Expect a mix of morning clouds along the coast and lower
Columbia River valley, plenty of afternoon sunshine and high
temperatures near to slightly above average for much of the next
week.


&&


.SHORT TERM...Today through Thursday...Overall expect few noticeable
changes to our weather over the next few days. Southwesterly to
westerly flow aloft and low level northwesterly flow will continue to
produce some morning clouds along the coast and lower Columbia River
valley with plenty of sunshine elsewhere. High temperatures will cool
closer to seasonal averages towards Thursday.

The primary issue in the short term is a small thunderstorm threat
across primarily the Lane and Linn County Cascades through Tuesday.
This is in response to moisture and instability sneaking its way
northward into the region due to an upper level low pressure
currently spinning off the California coast. This low pressure is
forecast to slowly shift eastward over northern California over the
next couple of days, which should produce few changes between today
and Tuesday across Lane and Linn Counties. Even though the GFS model
produces QPF bullseyes over eastern Lane County both afternoons,
model soundings do not appear conducive for surface based convection
given a sizeable cap. The HRRR and NCAR ensemble do suggest that
storms over eastern Douglas and northern Lake and Klamath Counties
could sneak their way towards Willamette Pass later this evening and
overnight as outflows intersect so kept a slight chance mention for
this period near the immediate Cascade crest.

As the aforementioned upper level low pressure shifts inland,
southwesterly to westerly flow aloft should increase just enough
Wednesday and Thursday that any thunderstorm development should
remain east of the Cascade crest. This will also help to produce
more marine clouds along the coast and lower Columbia River valley
Wednesday and Thursday, which should help to cool temperatures
closer to seasonal averages. Both the GFS and EC suggest some light
showers could impact the northern coastal zones Wednesday morning.
Given the instability appears quite shallow in model soundings, kept
PoPs below mentionable criteria for now. /Neuman


.LONG TERM...Thursday night through Monday...Onshore flow from a
series of weak shortwave troughs will continue through next week.
This will maintain near normal temperatures with low clouds at the
coast most mornings. No chance of precipitation or thunder during
this time. -Bishop


&&


.AVIATION...VFR across the area as of 20Z, except for a narrow
ribbon of IFR stratus/fog from near Tillamook Bay south to
Florence. Expect the current IFR stratus/fog area to extend
inland to the coastal valleys by around 04Z and possibly reach
the west slopes of the Central Oregon Coast Range by 07Z. IFR
returns to the North Oregon coastal strip around 04Z and up the
Columbia River to near KKLS overnight. Elsewhere, VFR to prevail
through Tue afternoon.

Cannot rule out some TCU or CB developing in the Cascades E-SE of
KEUG this late this afternoon into the evening. Thunder is not
expected for any of our terminals, but is a possibility in the
Lane County Cascades, although the likelihood appears less
probable based on latest model guidance.

KPDX AND APPROACHES...VFR through Tue afternoon. Surface wind
gusts to around 20 kt late this afternoon through the evening.
Weishaar


&&


.MARINE...Strong north wind continues over the waters today.
Several models indicating 20-25 kt boundary layer wind speeds
with gusts to 30 kt through late evening. A few gusts to 35 kt
can be expected over PZZ255 and PZZ275. Latest model runs suggest
wind speeds ease just a bit Tue, but will extend the Small Craft
Advisory for all waters through late Tue night. The pressure
gradient and associated surface and boundary layer wind speeds
ease even more Wed through late week.

Very steep and choppy sea conditions to persist for the next
couple of days. This is nearly a uni-wave pattern with spectral
guidance showing a wind wave component up to 8 ft at buoy 050
this afternoon through Tue, with a minimal background swell.
Combined seas could briefly reach 10 ft at times this afternoon
through the evening. However, the combination of at least 7 ft
seas with 6-8 seconds periods constitutes hazardous sea
conditions. Slightly less fetch and gradually decreasing wind
over the next couple of days will result in less wind wave
component. However, expect choppy conditions to continue through
at least mid-week. Overall, seas subside to 4 ft or less Wed
and hold through late week. Weishaar


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until midnight PDT Tuesday night for
     Coastal Waters from Cape Shoalwater WA to Cascade Head OR
     out 60 nm.

     Small Craft Advisory until 2 AM PDT Wednesday for Coastal
     Waters from Cascade Head OR to Florence OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar from 4 PM
     this afternoon to 8 PM PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM to
     7 AM PDT Tuesday.


&&


$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.



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