High Wind in Washington, September 27, 2023

Area Forecast Discussion
National Weather Service Portland OR
302 AM PDT Wed Sep 27 2023

.SYNOPSIS...Low pressure moving into the south Washington Coast early
this morning for windy conditions at the coast and inland areas as
well Showers with a chance of thunderstorm today. Less active
weather sets up for the latter part of the week as an upper trough
forms over the Pacific Northwest, bringing a chance of showers and
near seasonal temperatures.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Occluding front associated with a 1000 mb low pressure system moving
east of the Coast Range into the Willamette Valley as of 2 am. Gusty
winds hit parts of the coast as the front moved through. Newport
airport had a 55 mph gust around midnight. The low center is about 65
miles west of Astoria. Satellite shows a bent back occlusion around
the low moving through the coastal waters, so will probably have
gusts 40 to 50 mph for the north Oregon/south Washington coast
between 2 and 4 am per the HREF guidance. Winds then gradually
subside as the low tracks to the south Washington Coast.
Thunderstorm activity has been quite active around the low overnight
and we'll continue to have a chance for thunderstorms over the
coastal waters and inland west of the Cascades through the afternoon
in the unstable post-frontal air mass.

As the surface low pressure dissipates over western WA later today
and tonight, surface high pressure will build in from the west. This
will be shortlive as the next system will approach Oregon from the
west on Thursday. This system will be weaker as the jet energy is
much weaker and more meridional, taking the system towards northern
CA.

.LONG TERM /FRIDAY THROUGH TUESDAY/...Friday and through the weekend
the aforementioned jet stream become increasingly meridional with a
north to south flow along the West Coast, elongating the upper
trough. This will result low chances (20-30%) for showers Friday. But
by later Saturday showers should be about done as upper level ridging
builds in. WPC Cluster analysis in good agreement with a ridge
building over the region by Sunday. This will bring less cloud cover
for chillier nights with lows in the 40s (compared to lows in the 50s
recently) but high temperatures near seasonal with highs in the 60s
to low 70s over the weekend. Cluster analysis in decent agreement
with zonal flow returning to the northeast Pacific early next week.
The main differences in the clusters is how fast and how much the
ridge will weaken - and how fast we'll see a return to wet weather.
/mh

&&

.AVIATION...As of 10z, a band of widespread rain along a cold
front was pushing into the Cascades. Behind this front, wind
gusts up to 25-35 kts from the southwest are expected across the
lowlands, up to 35-45 kts from the west to southwest along the
coast and mountains, through 18-21z Wednesday. Winds are forecast
to calm below 10 kts after 00z Thursday. Showers expected to
continue through at least 03z Thursday, becoming more scattered in
nature after ~15z Wednesday. Isolated thunderstorms are possible
through the forecast period, though the probability at any given
terminal is low enough as to not warrant inclusion in the TAFs.
Coastal terminals have dropped to MVFR conditions with a 40-60%
probability of these conditions continuing through at least 21z
Wednesday. Localized MVFR conditions expected with heavier showers
for inland locations, otherwise VFR conditions expected inland.

KPDX AND APPROACHES...Showers continue through at least 03z
Thursday with 15-20% probability of isolated thunderstorms.
Southwest wind gusts up to 25-30 kts possible through 21z
Wednesday, then diminishing to below 10 kts by 00z Thursday. -HEC

&&

.MARINE...A compact surface low developed rapidly Tuesday night
and is moving through the waters offshore of N Oregon and SW
Washington early Wednesday morning. Latest model guidance along
with latest observations suggest the low will track toward the far
S Washington Coast by mid-morning Wednesday. This low is producing
a quick burst of gales through early Wednesday morning, with
strongest winds north of Cape Foulweather and especially in zones
PZZ271 AND PZZ251. A few localized storm force gusts have been
observed, but they are not expected to be widespread enough for a
Storm Force Warning. Winds will diminish below gales fairly
quickly from the south to the north early Wednesday morning,
with gusts up to 25-40 kts through Wednesday. The uptick in short
period wind- driven seas coupled with the existing large westerly
swell has push combined seas back into the upper teens, which
will also decrease to below 10 feet by late Wednesday afternoon.
Gale Warning remains in effect until 8 AM Wednesday for central
and northern zones. Gale Warning transitioned to a Hazardous Seas
Warning for southern zones at 3 AM Wednesday, extending through 5
PM Wednesday. Additionally have issued a Hazardous Seas Warning
for central and northern zones 8 AM to 5 PM Wednesday.

Expect quieter marine conditions by Wednesday night as upper level
troughing settles over the Pacific Northwest and British Colombia
for the end of the week. -HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Gale Warning until 8 AM PDT this morning for Coastal waters from

     Cape Shoalwater WA to Cape Foulweather OR out 10
     NM-Columbia River Bar-Coastal waters from Cape Shoalwater
     WA to Cape Foulweather OR from 10 to 60 NM.

     Hazardous Seas Warning from 8 AM this morning to 5 PM PDT this
     afternoon for Coastal waters from Cape Shoalwater WA to
     Cape Foulweather OR out 10 NM-Columbia River Bar-Coastal
     waters from Cape Shoalwater WA to Cape Foulweather OR from
     10 to 60 NM.

     Gale Warning until 3 AM PDT early this morning for Coastal
     waters from Cape Foulweather to Florence OR out 10 NM-
     Waters from Cape Foulweather to Florence OR from 10 to 60
     NM.

     Hazardous Seas Warning until 5 PM PDT this afternoon for Coastal

     waters from Cape Foulweather to Florence OR out 10 NM-
     Waters from Cape Foulweather to Florence OR from 10 to 60
     NM.
&&

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Gale Warning until 8 AM PDT Wednesday for Coastal waters from
     Cape Shoalwater WA to Cape Foulweather OR out 10
     NM-Columbia River Bar-Coastal waters from Cape Shoalwater
     WA to Cape Foulweather OR from 10 to 60 NM.

     Gale Warning until 3 AM PDT Wednesday for Coastal waters from
     Cape Foulweather to Florence OR out 10 NM-Waters from Cape
     Foulweather to Florence OR from 10 to 60 NM.
&&

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