Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/26/22

Area Forecast Discussion ...UPDATED

National Weather Service Portland OR

 503 PM PDT Tue Oct 25 2022

Updated aviation

.SYNOPSIS...A weather system will push through tonight to bring
accumulating snow over 4000 feet and rain elsewhere, along with the
potential of thunderstorms. Showers will linger in through Wednesday
and Thursday before another stronger system in the active weather
pattern will bring a wet weekend.

&&

.SHORT TERM...Tonight through Friday...As a vigorous upper trough
dives south near Vancouver Island this afternoon, satellite and radar
show the frontal band pushing into our northern waters this
afternoon. Stratiform precipitation is filling in ahead of this
front, spreading east and south, with snow levels currently around
4500-5000 feet MSL. While we`ve already had some lightning along and
ahead of the front, good cloudtop cooling evident on satellite shows
the continued potential for lightning especially over the waters this
evening. This cloudtop cooling is also reflecting the good dynamics
of this system, which is expected to bring most of the rain/snow
expected over the area more in a relatively short amount of time.
This will include the snowfall expected over the high mountains
tonight, which are under a Winter Weather Advisory.  Southwesterly
winds ahead of the front, gusting to 35 mph at Buoy 29, will spread
inland late this afternoon into the evening. This will align well
into the Willamette Valley to bring similar gusts along with
increasing rain for around rush hour time as well.  While HREF shows
the thunder chances decreasing into the evening, especially into
inland areas, enough mixed layer CAPE and shear will exist to keep
the chance to slight chance of thunder into the evening and early
morning. Snow accumulations around 6 to 10 inches of snow are
expected around pass level tonight, along with gusty winds along the
front to potentially impact visibilities.

Weather will turn to showers behind the frontal passage and continue
into Wednesday. With northwesterly flow, look for temperatures to be
cooler than average. An upper ridge will then push up over the area
Wednesday night into Thursday. Skies clearing Wednesday night will
lead to colder readings as well. Flow aloft will turn southwesterly
to bring warmer temperatures for Thursday, before a decaying weather
system drops down into WA and potentially into OR and stalls into
Friday. Will have to watch the evolution of this system and how much
precipitation would be involved if it did just sit over one area as
both the GFS and EC deterministic models show. NBM currently has
0.5-1.25 inches across southwestern WA and northwestern OR for the 48
hour period.

.LONG TERM...Friday night through Saturday...WPC Cluster analysis
show a larger upper trough started to drop down the Canadian coast
during the weekend while still having a good connection to an
atmospheric river of moisture.This looks to end up potentially
bringing a more significant and wetter system for Sunday along with
some stronger winds. The wet pattern looks to continue into early
next week for a normal active fall pattern to last. /Kriederman

&&

.AVIATION...00Z TAFs: The upper trough digging over the PacNW is
pushing a rather aggressive front across the north Oregon coast as
of 2345Z. There are isolated thunderstorms embedded within the
front and have started out the KAST and KONP TAFs with VCTS and
notable IFR conds to start. Note: KONP is still very sporadically
reporting so will continue AMD NOT SKED until consistent obs
return. Gusts to around 35 kt have been observed coming off the
open water. Saw a fairly abrupt wind shift at KAST and expect this
will occur shortly at KONP. The front will continue pushing
inland over the next couple hours. Cannot rule out isolated Tstms
this evening east of the Coast Range for the remaining terminals
but will add those in as needed since the terrain forcing will be
much weaker within the immediate vcty of those terminals. After a
couple hours behind the front, conds should improve with showers
and MVFR cigs eventually giving way to VFR closer to sunrise near
1430Z. Will likely then see a several hour break in shower
activity under brief passing high pressure.

KPDX AND APPROACHES...Conditions will continue to deteriorate as
the cold front continues pushing inland from the coast. Current
expected arrival somewhere between 0130 and 0215Z. Do expect a
brief period of southerly wind gusts of 25-30 kt will approach
crosswind thresholds for some aircraft between now and then, but
primarily for a short period just ahead of the frontal passage.
Then expect winds to east and conds to remain MVFR for several
hours overnight. /JBonk


&&

.MARINE...Winds are hovering around 33 kt at the buoys as of 3 PM
Tuesday. Will not upgrade to a Gale Warning as conditions will be
intermittent and not widespread. However, gusty winds with
isolated thunderstorms are likely across the waters through this
evening. Buoy 46005 which is currently in the path of the
strongest winds is observing wave heights of 17 ft at 11 seconds.
GFS Wave is resolving these conditions well which increases
confidence for seas to build into the 13-15 ft range with a
dominant period of 11 seconds during the overnight hours producing
steep and hazardous conditions. Have issued a Hazardous Seas
Warning during this time.

Winds and seas will gradually ease Wednesday morning as transient
high pressure moves over the area. This will bring quieter weather
Wednesday into Thursday. Will see more fronts arriving to close
the week. Likely to have gale force winds at times on Friday.
Seas will also be on the rise, with seas 15 to 18 ft late Thursday
night and Friday. Active weather continues through the coming
weekend.

The new moon on Tuesday will continue to produce strong tidal
currents during the evening ebb cycle. Those moving in and out of
harbors and crossing coastal bars should use caution and be aware
of any bar restrictions in place. -BMuhlestein

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory until 6 AM PDT Wednesday for Cascades in
     Lane County-Northern Oregon Cascades.

WA...Winter Weather Advisory until 5 AM PDT Wednesday for South
     Washington Cascades.

PZ...Small Craft Advisory until 6 PM PDT Wednesday for coastal waters
     from Cape Shoalwater WA to Florence OR out 10 nm.Columbia
     River Bar.

     Small Craft Advisory until 8 PM PDT this evening for coastal
     waters from Cape Shoalwater WA to Florence OR from 10 to 60
     nm.

     Small Craft Advisory from 8 AM to 6 PM PDT Wednesday for coastal
     waters from Cape Shoalwater WA to Florence OR from 10 to 60
     nm.

     Hazardous Seas Warning from 8 PM this evening to 8 AM PDT
     Wednesday for coastal waters from Cape Shoalwater WA to
     Florence OR from 10 to 60 nm.
&&


$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland