NWS Portland, OR wrote its last area forecast discussion before the first event at Dec 22, 5:30 AM PST, 2 hours 40 minutes earlier.
Area forecast discussion, Dec 22, 5:30 AM PST, 2 hours 40 minutes before
Area Forecast Discussion
National Weather Service Portland OR
530 AM PST Thu Dec 22 2022
.SYNOPSIS...An arctic air mass will remain over the region through at
least Thursday night, bringing the coldest temperatures the region
has experienced since February 2014. A wintry mix of snow, sleet, and
freezing rain will occur late Thursday into Friday, resulting in
significant travel impacts. While most locations should warm above
freezing Friday night into Saturday morning, the Gorge will remain
below freezing with freezing rain lingering through at least Saturday
night. Becoming warmer and wetter next week.
&&
.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT...
KEY POINTS...
* Very cold temperatures and dangerous wind chills will continue
through Thursday night.
* A mix of wintry precipitation will spread across the area late
Thursday into Friday. Light snow will transition to sleet and
freezing rain, with accumulating freezing rain expected across
much of the area.
* Another weather system will move through on Saturday, with mainly
rain expected and snow levels around 7000 to 8000 feet. The
exception will be in the central Columbia River Gorge, as
persistent below freezing surface temperatures will likely result
in another round of freezing rain and accumulating ice.
Our message remains the same for the upcoming winter storm. Be
prepared for an impactful mix of wintry precipitation and very cold
temperatures, including accumulating freezing rain, through at least
Friday. At 4 AM PST Thursday, a 1040-1050 mb surface high was located
over central and eastern WA/OR. Observed temperatures were around -10
to +10 degrees east of the Cascade crest with wind chills even colder
than that. Temperatures west of the crest in northwest OR and
southwest WA were in the 20s with wind chills in the single digits
and teens, coldest near the Gorge. Wind chills as low as 20 below
zero are occurring in the Cascades. Very little to no warming is
expected Thursday into Thursday night as very strong low-level
offshore flow continually advects a fresh supply of arctic air from
east of the Cascade crest and strong winds maintain dangerously cold
wind chills. Therefore, Wind Chill Warnings and Advisories remain in
effect for the Cascades, the Gorge, the Cascade foothills, the
Portland/Vancouver metro, and the north OR Coast Range. Make sure to
keep your pets warm and take any precautions you may need to take to
prevent pipes from bursting. Anyone who is exposed to the outdoors
and is not dressed properly will be at risk of developing frostbite
and/or hypothermia.
East winds are already gusting to 30-45 mph across the Portland
metro, however winds were only gusting 15-25 mph in Vancouver. Winds
around 50-60 mph are occurring in the western Gorge. Expecting winds
to increase in strength even more later this morning as the pressure
gradient between TTD-DLS increases to around -13 mb. This is when
winds are going to be gusting to around 60-80 mph through the western
Gorge (possibly as high as 100 mph at Crown Point), and 40-55 mph in
the Portland metro (except 20-30 mph from Vancouver northward).
Therefore, a High Wind Warning remains in effect for the western
Gorge and a Wind Advisory remains in effect for the Portland metro.
Now onto the most challenging part of the short-term forecast. A warm
front is still expected to lift across the region late Thursday into
Friday, with a pronounced warm layer aloft moving in behind the warm
front. Given the below freezing surface temperatures, this warm front
will spell trouble and result in a messy mix of sleet and freezing
rain across southwest WA and northwest Oregon. Forecast NAM BUFR
soundings at Portland and Troutdale are now suggesting the duration
of sleet may wind up being longer than initially expected, thus
delaying the transition over to freezing rain. The latest iteration
of the HREF backs this up well and suggests the dominant
precipitation type will be sleet across the greater
Portland/Vancouver metro and east slopes of the Coast Range Thursday
evening through most of Thursday night, before finally switching over
to freezing rain between 2-4 AM PST Friday morning. Freezing rain is
then expected to continue through the day on Friday before
temperatures slowly warm above freezing Friday night, except in the
Columbia River Gorge (this zone is discussed below). Precipitation
should mainly be in the form of freezing rain at the coast, southern
Willamette Valley, and central OR Coast Range where forecast ice
accumulations have increased in these areas as a result. In fact,
decided to upgrade to an Ice Storm Warning for these zones as ice
accumulations as high as half an inch are now expected with minimal
snow/sleet accumulation.
Unlike the rest of southwest WA and northwest OR, the main
precipitation type in the Gorge should be snow and sleet initially,
especially in the central Gorge near Hood River. Still expecting at
least 3-6 inches of snow and sleet in the central Gorge and Upper
Hood River Valley before precipitation finally switched over to
freezing rain Friday night. Below freezing surface temperatures
will most likely persist through Saturday across the Gorge as east
wind continue. This will result in yet another round of freezing rain
and significant ice accumulations as a secondary weather system moves
into the region. Total ice accumulations will likely exceed one inch
over a 48 hour period through much of the Gorge.
When will temperatures warm elsewhere? That will depend on if and
when winds are able to switch directions, from east/north to
southerly. And often, models bring that warmer air in too soon. If
colder temperatures are able to hang on (longer than what the NBM
suggests), could make for some more interesting winter weather later
in the week, including the Portland metro. There is a chance that
temps warm above freezing Friday night, but confidence in that is low
and the actual timing may wind up being around 12 hours later than
that. Although some uncertainty remains with exact timing and exact
snow/sleet/ice amounts, confidence remains high that significant
impacts to travel will occur with this winter storm. Anyone with
travel plans Thursday night and/or Friday should either reconsider
their plans or ensure they are well prepared for a messy mix of
snow/sleet/ice on roads. Still expecting warmer temperatures and
widespread rain on Christmas Eve with rain amounts around half an
inch or more across the interior lowlands and around 1 inch or more
at the coast. Main concern on Christmas Eve will be for the Gorge and
Upper Hood River Valley where freezing rain will likely continue and
bring additional ice accumulations. -TK
.LONG TERM...SUNDAY THROUGH WEDNESDAY NIGHT...The long term forecast
is highlighted by much milder temperatures and plenty of rain. Models
and their ensembles are showing very impressive agreement regarding
temperatures in the long term, and the NBM 1D Viewer backs this up by
showing a very low degree of model spread. In fact, the NBM 25th to
75th percentile for high temperatures generally ranges from the low
to mid 50s Sunday through Tuesday. This is no surprise after
analyzing the WPC's 500 mb heights and anomalies on Sunday into
Monday, which depicts a very strong signal for upper level ridging
across the western United States.
It is unclear how wet or dry we will be during that time, but most
ensemble members from the GEFS/ECM do bring in at least some
precipitation. However, there is a stronger signal for heavy rain
Tuesday into Wednesday as an upper level trough pushes into the
region and brings an impressive surface low with it. Still plenty of
details to be worked out, but it appears we may have some hydro
concerns next week as chances for heavy rain increase. -TK
&&
.AVIATION...12z TAFs: Dry offshore flow is resulting in VFR
conditions across most of the forecast area north of KSLE, with
mainly MVFR cigs to the south of KSLE. East winds increased
substantially overnight, with gusts as high as 41 kt already
reported at KPDX. East winds will gust 30-35 kt across much of the
PDX metro all the way through Fri morning, with winds up to 50-60
kt just above the surface. South of the PDX metro, sfc winds will
be more northeasterly and a bit lighter.
The east winds are ushering in very cold air which will
eventually lead to wintry precipitation moving in from the
southwest later today. Precipitation will likely start off as a
brief period of snow or sleet for most of the forecast area this
afternoon, transitioning quickly to freezing rain for areas KUAO-
KMMV southward. Precip should remain snow or sleet longer north
of KUAO-KMMV, and longest in the Columbia Gorge. Thus KHIO/KUAO
will likely be the first to transition to FZRA this evening, with
KPDX and KTTD eventually making this transition later on in the
night. As usual, confidence in the timing of precip type
transitions is low. Perhaps the more important thing to note is
that confidence is high that there will be widespread impacts due
to lowland snow, ice, and blustery E-NE winds in the lowlands
tonight into Fri morning. It may be well into the day Friday that
even KEUG warms above freezing.
As far as cigs, MVFR may linger south of KSLE as precipitation
chances increase. Areas KUAO northward should remain mostly VFR
due to the dry offshore flow. Although precip should start this
afternoon or evening, most areas north of KSLE should see VFR
through about 23/08z before MVFR becomes more widespread. Snow or
sleet should be light, but MVFR or IFR will be possible in any
snow.
For detailed Pac NW aviation weather information, go online to:
http://weather.gov/zse
KPDX AND APPROACHES...VFR with cold east winds and increasing high
clouds this morning. Precip will likely start off as flurries this
afternoon, with only minimal accumulations. Snow and sleet will
increase this evening, eventually transitioning to FZRA by around
12z. Occasional -FZRA will persist all the way through Fri, along
with MVFR and perhaps IFR cigs/vsbys. East winds will continue to
gust 30-40 kt through Fri morning, with wind chills as low as zero
degrees Fahrenheit at times. Weagle
&&
.MARINE...Very strong and cold high pressure over the Columbia
Basin continues to drive strong offshore flow across the Pac NW
and adjacent waters. Solid Small Craft Advisory level winds are
occurring through most of our waters, along with localized gusts
to Gale Force abeam gaps in the coastal terrain. This will persist
through Friday morning, with winds slowly veering and decreasing
thereafter. S-SW winds likely increase again Fri night/Sat as low
pressure moves into Vancouver Island from the Pacific and its
associated front move across the Pac NW waters. The National
Blend of Models (NBM) v4.0 indicates a greater than 90 percent
chance of gale force gusts Saturday morning. Yet another
possibility of gale force conditions looks possible Sunday.
Seas remain well below 10 ft through Thursday night, then are
forecast to exceed 10 ft by 12Z Friday. Seas hover close to 10 ft
Friday through Friday night, then ease to around 8 ft Saturday
morning. Longer range guidance shows seas building into the mid
to upper teens Sunday night and possibly exceeding 20 ft early
Monday.
Several forecast models show an even stronger system Tue or Wed,
with many showing winds to Storm Force and seas well above 20 ft.
We held our seas fairly close to the output from the NBM wave
guidance, if not just a little below it. The rationale behind
this is mostly uncertainty due to strength and timing of any
strong low approaching the Pac NW - however it should be noted
that the 06z run of the GFS global wave model shows a large slug
of seas 30 ft and higher reaching the Pac NW coast during the
middle of next week. Weagle
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 2 PM this afternoon to 7 AM PST Friday
for North Oregon Coast.
Wind Chill Advisory until 6 AM PST Friday for Central Columbia
River Gorge-Coast Range of Northwest Oregon-Greater
Portland Metro Area-Northern Oregon Cascade Foothills-Upper
Hood River Valley-Western Columbia River Gorge.
Winter Storm Warning from 2 PM this afternoon to 10 PM PST
Friday for Coast Range of Northwest Oregon.
Ice Storm Warning from noon today to 7 AM PST Friday for Central
Coast Range of Western Oregon-South Willamette Valley.
Winter Storm Warning from 4 PM this afternoon to 1 PM PST Friday
for Central Willamette Valley-Lower Columbia-Northern
Oregon Cascade Foothills.
Wind Advisory until 7 AM PST Friday for Greater Portland Metro
Area.
Winter Storm Warning from 4 PM this afternoon to 10 PM PST
Friday for Greater Portland Metro Area.
Wind Chill Warning until 6 AM PST Friday for Northern Oregon
Cascades.
Winter Storm Warning from 4 PM this afternoon to 6 PM PST Friday
for Northern Oregon Cascades.
Winter Storm Warning from 4 PM this afternoon to 10 PM PST
Saturday for Central Columbia River Gorge-Upper Hood River
Valley-Western Columbia River Gorge.
High Wind Warning until 1 PM PST Friday for Western Columbia
River Gorge.
WA...Winter Storm Warning from 2 PM this afternoon to 7 AM PST Friday
for South Washington Coast.
Wind Chill Advisory until 6 AM PST Friday for Central Columbia
River Gorge-Greater Vancouver Area-South Washington Cascade
Foothills-Western Columbia River Gorge.
Winter Storm Warning from 4 PM this afternoon to 1 PM PST Friday
for I-5 Corridor in Cowlitz County-South Washington Cascade
Foothills-Willapa Hills.
Wind Advisory until 7 AM PST Friday for Greater Vancouver Area.
Winter Storm Warning from 4 PM this afternoon to 10 PM PST
Friday for Greater Vancouver Area.
Wind Chill Warning until 6 AM PST Friday for South Washington
Cascades.
Winter Storm Warning from 4 PM this afternoon to 6 PM PST Friday
for South Washington Cascades.
Winter Storm Warning from 4 PM this afternoon to 10 PM PST
Saturday for Central Columbia River Gorge-Western Columbia
River Gorge.
High Wind Warning until 1 PM PST Friday for Western Columbia
River Gorge.
PZ...Gale Warning until 8 AM PST Friday for Columbia River Bar.
Small Craft Advisory until 6 PM PST Friday for coastal waters
from Cape Shoalwater WA to Florence OR out 60 nm.
&&
www.weather.gov/portland
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