Heavy Snow in Washington, March 3 to 4, 2024

Area Forecast Discussion
National Weather Service Portland OR
327 AM PST Sun Mar 3 2024

.SYNOPSIS...A long wave trough remains nearly stationary over
the region which is producing a series of showers. Showers have
been observed as both snow and rain with the precipitation type
mainly due to the precipitation rates and the cold air present.
Will see minimal change in the forecast over the next few days
as there will be little altering of the pattern itself. Cooler
airmass arrives Tuesday morning.

&&

.SHORT TERM...MONDAY THROUGH TUESDAY NIGHT...As of 3:30am Monday, a
more prominent wave of showery moisture is breaking up over the Coast
Range, with another one rapidly approaching from offshore. The
long-wave trough continues to remain off the coast, spinning a few
progressively weaker  rounds of precipitation through Tuesday
morning. Snow levels are currently around 300-500 feet throughout the
region, with light snow accumulations in the Coast Range above 500
feet. The Winter Weather Advisory for the Coast Range has been
extended to 10am due to precipitation continuing longer than
previously forecast, now including areas down to 500 feet due to
lowered snow levels. Most of this moisture is expected to break up as
it heads further east, and the Willamette Valley could see
potentially some minor impacts early Monday morning at slightly
higher elevation areas. Snow levels rise to around 1200-1500 feet by
Monday afternoon, ending concerns for areas below that. The Cascades
foothills continue to see some more significant higher elevation
accumulations above 1500 feet, caused by showers fueled by orographic
lift. Ensemble guidance suggests a 50-70% chance of accumulations
over 4 inches from 4am Mon to 4am Tue in the foothills.

With NW winds bringing cold air aloft and S winds bringing warmer
temperatures at the surface, instability remains relatively high at
the coast, spreading to the Willamette Valley by Monday afternoon.
CAPE values are around 150-250 J/kg throughout the area, and a
widespread 20-30% of thunderstorms is expected west of the Cascades
throughout Monday, but particularly in the afternoon. Threat
decreases Monday evening, though the coast and Coast Range could see
some weak isolated thunderstorms as late as Tuesday afternoon.

Model guidance is beginning to trend towards the trough passing
further to our south in northern California, and it looks like
Tuesday should see precipitation tapering off. While snow levels will
lower back down to 500 feet or so Tuesday night, precipitation should
be very weak, and minimal impacts are currently expected.

.LONG TERM...WEDNESDAY THROUGH SUNDAY...00Z WPC cluster analysis
shows troughlike conditions continuing, with a brief shortwave ridge
arriving near the end of the week. There is currently a 70% chance of
the ridge arriving by Friday, though uncertainty exists regarding how
long its expected to stick around. Until then, a few more weak waves
of moisture will continue being spun at us, with possiblY some light
snow at elevation on Wednesday morning. Temperatures will warm enough
that the predominant precipitation type will be rain from Thursday
onwards throughout the region. /JLiu

&&

.AVIATION...A broad upper level trough remains over the region wit
moist, westerly flow aloft. Continued onshore flow will maintain
showers and a chance of thunderstorms (mainly for the coast)
through tonight. As such, expect a mix of MVFR and VFR conditions
through the period, with IFR conditions possible with heavier
showers. This morning, observations show predominately MVFR
inland, with CIGS around 1000-1500 ft. Radar and satellite imagery
(as of 10Z) show shower activity picking up, with a mix of rain
and snow likely through this morning. Southerly winds up to 10-12
kt expected at the surface.

PDX AND APPROACHES...Predominately MVFR conditions expected
through 20Z, with IFR possible (20-30% chance) through 16Z this
morning. VFR becomes more likely this afternoon (60-70% chance),
although heavier showers will likely bring periods of MVFR. Will
continue to monitor chances for snow this morning, although
temperatures are again expected to remain above freezing.
Southeast winds this morning expected to become southerly around
8-10 kt this afternoon. /DH

&&

.MARINE...Low pressure off the Washington coast will maintain
breezy southwest to westerly winds across the coastal waters
today, with gusts up to 25 kt. An unstable atmosphere will also
maintain a chance for thunderstorms across the waters through
tonight. Locally strong and erratic wind gusts are likely with any
thunderstorm that does develop. A westerly swell around 10 to 12
ft at 11-12 seconds will gradually subside with seas expected to
fall below 10 ft by Monday morning. High pressure begins to build
across the waters late Monday, which should push a low pressure
system south of the area toward northern California. Winds turn
northerly and seas continue to fall to around 5 to 7 ft through
the middle of next week as transition toward more tranquil
conditions. /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory until 10 AM PST this morning for Central

     Coast Range of Western Oregon-Coast Range of Northwest
     Oregon.

     Winter Weather Advisory until 4 PM PST this afternoon for
     Cascade Foothills in Lane County-Northern Oregon Cascade
     Foothills.

WA...Winter Weather Advisory until 10 AM PST this morning for Willapa

     Hills.

     Winter Weather Advisory until 4 PM PST this afternoon for South
     Washington Cascade Foothills.

PZ...Small Craft Advisory until 4 AM PST early this morning for
     Columbia River Bar.

     Small Craft Advisory until 4 PM PST this afternoon for Coastal
     waters from Cape Shoalwater WA to Cape Falcon OR out 60 NM.

     Small Craft Advisory until 10 PM PST this evening for Coastal
     waters from Cape Falcon OR to Cape Foulweather OR out 60 NM.

     Small Craft Advisory until 1 AM PST Monday for Coastal waters
     from Cape Foulweather to Florence OR out 10 NM-Waters from
     Cape Foulweather to Florence OR from 10 to 60 NM.

&&

www.weather.gov/portland

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