NWS Portland, OR wrote its last area forecast discussion before the first event at Feb 11, 6:10 AM PST, 50 minutes earlier.
Area forecast discussion, Feb 11, 6:10 AM PST, 50 minutes before
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
610 AM PST Thu Feb 11 2021
Updated short term discussion.
.SYNOPSIS...A very cold arctic airmass is pushing south from
Canada over the Rocky Mountains bringing significantly cooler air
into the area over the next few days. Challenging forecast comprised
of two incoming systems. The first, a warm front followed by a cold
front, will move over the area today bringing wintery precipitation
to much of the forecast area. A chance for widespread snow, some
areas of freezing rain, and rain are all possible throughout the
forecast area. Breezy winds likely through the Columbia River Gorge.
The next system arrives on Friday night through Saturday, again
bringing even more winter weather with snow and a chance for
freezing rain throughout the area. Will see gradual warming with a
return to likely rain next week.
&&
.SHORT TERM...Today through Saturday...What feels like the first
taste of winter is finally approaching today. Continental arctic air
is pushing southward from Canada into the Columbia Basin this
afternoon which will be the main driver of the freezing temperatures
expected through the weekend. The next few days can be summarized as
a tale of two storms. The first system, a warm front followed by a
cold front, and associated low pressure system, will move over the
area later today. The combination of low pressure over the Pacific
and the colder air over the basin will cause easterly winds to
increase and bring that cold air westward. With the warm front
advecting inland though, expecting quite a bit of moisture ahead of
the cold front. The cold air and moisture combined will bring
significant winter weather to much of the forecast area today
through Friday morning.
The timing of the system is still a challenge as models are still
struggling on the track of this system even less than 12 hours out.
A as temperatures are just starting to drop near freezing around the
Hood River area, the snow is beginning to fall slightly later than
previously expected. Temperatures through the Gorge are beginning to
follow suit with temperatures near Corbett nearing 30 degrees F.
Likely, the system will just move a few hours slower than previously
thought, but shouldn't have an impact on precipitation type. As the
day progresses, the east-west pressure gradient will increase with
the gradient from Troutdale to the Dalles peaking around 9 mb this
afternoon. The north-south pressure gradient is quite a bit less so
not expecting much of the cold air to trickle south. Likely cold air
will remain north of Albany but should make it to the north coast
today. While warmer than inland locations, still the chance for
wintery precipitation along the coast, more as freezing rain than
snow though. This also rings true for the Coast Range at elevations
above 800 ft where freezing rain is more likely and could see up to
a quarter inch of ice accumulation. Snow and ice build-up on
roadways is also a strong possibility.
The cold front will quickly trail the warm front enhancing
precipitation and reinforcing the cool air. This much stronger
system will be the main weather maker for the area this afternoon.
Models are finally beginning to hone in on the track for the main
surface low, looking to make landfall along central Oregon. This
location is often associated with more precipitation and the cold
air making it over the Cascades inland. With the low position, will
likely see warmer air through the southern portions of the forecast
area so have kept those areas as rain for the most part. Cannot rule
out some snow though at higher elevations, especially as you move
north towards Salem and McMinnville. North of Newberg though, snow
will be the name of the game. Early on in the transition from a
rain/snow mix to all snow, there may be a period of freezing rain
extending northwest from Newberg to the Willipa Hills. Could see
some light freezing rain along the coast, Coast Range valleys, and
even some in the Portland-Vancouver Metro area. This freezing rain
inland though is not expected to accumulate significantly as it
turns over the snow in the evening. One of the main factors to
consider when determining if the precipitation will be freezing rain
or snow is the precipitation rates;the higher the rate, the more
likely to be snow as there will not be enough time to melt. If it is
slower and enough cold air pools at the surface, freezing rain has a
fighting chance.
Snowfall and ice accumulation are the most challenging parts of the
forecast. Likely will see drastic differences moving east to west
and at elevations. In general though, expect more snow above 500 ft,
with the highest amounts through the Cascades and Columbia River
Gorge. Snow accumulations of 5 to 9 inches seems on tap for Thursday
through Friday morning in the Gorge and Hood River Valley, with
similar snowfall for the Cascades foothills. From Portland/Vancouver
area north through the Cowlitz Valley, expect 2 to 6 inches, with
light ice accumulations (mainly west and south of Portland). More
ice will fall in the valleys of the Willapa Hills and north Oregon
Coast Range, with 0.10 to 0.30 inch likely with 2 to 6 inches of
snow. No snow or ice is expected along the coast south of Lincoln
City, and little if any ice to south of Albany. Because of the
chance for some freezing rain along the coast, have kept the Winter
Weather Advisory going for the South Washington and North Oregon
Coast, Cascades and Oregon foothills, as well as the Central
Willamette Valley. Winter Storm Warnings issued for the Hood River
Valley, Central Columbia River Gorge, Willapa Hills, North Oregon
Coast Range, as well as the Cowlitz Valley southward through the
Portland/Vancouver metro area.
Worst conditions will be in the Columbia River Gorge, where robust
east winds will be gusting 50 to 70 mph. That, along with increasing
precipitation rates, will see blizzard conditions through the day.
Will go with Blizzard Warning for the western Columbia River Gorge
due to significantly reduced visibilities in snow and blowing snow.
Be sure to dial 5-1-1 for current road conditions before traveling.
After a brief break in the heaviest precipitation on Friday
afternoon, another system is quickly approaching for late Friday
night into Saturday. This next storm is very similar to the first in
that it is composed of a warm front briskly followed by a cold
front...but this time it is stronger. Expecting another round of
precipitation, and an even deeper cold air pool from the Columbia
Basin. There is still quite a bit of variability with the low
position of this storm, however it is trending more north than the
current system. This likely will bring a bit more of a warm nose of
air along the coast which should keep that area as mostly rain.
However, the challenge will be when the rain meets the higher
terrain and colder portions of the coast and Coast Range. Here,
there is a strong chance for some freezing rain, especially in areas
where roads have cooled and snow has accumulated.
Precipitation is likely going to be heavier with this system so
accumulations of snow is a concern. Could see an additional few
inches along the northern Coast Range and through the Portland-
Vancouver Metro. Some models are suggesting up to 10 inches of snow
north of Aurora, but those are trending as the outliers so decided
to tone it down a bit. Could see an additional 3 inches or so for
the northern Willamette Valley. The highest precipitation rates will
occur Friday night into Saturday morning; so for those not working
the midnight shift, expect to wake up to a few inches of new snow.
Even more snow expected for the Gorge and Cascades Friday night into
Saturday as the cold air funnel and moisture continue. Overall, a
very active few days with quite a bit of winter weather expected.
-Muessle/Rockey
.LONG TERM...Sunday through Wednesday...Conditions will begin to warm
as easterly winds die off and the fronts all progress inland. Will
see gradual warming through early next week. Another system
approaches sunday night, bringing even more precipitation with it.
However, with a lack of cold air and increased snow levels, it likely
will be more of a rain event. Precipitation will slow through the day
on Monday, becoming showery through the middle of the week. A nice
break after a very active few days. -Muessle
&&
.AVIATION...12Z TAF: A weak warm front with light pcpn along a
line from Tillamook to Santiam Pass is slowly lifting northward.
This front will intensify north of Salem during the day today. MVFR
cigs will likely develop by or shortly after 12Z KSLE northward.
MVFR becomes more widespread as a low pressure area approaches the
coast from the southwest. The combination of moisture from the west
coupled with cold air from the east will make for a mixed
precipitation across the region, primarily after 18Z Thu. Precip
type favors snow for the KPDX, KTTD, and KHIO terminals while
freezing rain/snow mix is favored in the northern Coast Range
Valleys and Willamette Valley between Oregon City and Salem. Areas
south of Salem will likely only see rain.
The offshore pressure gradient through the Columbia Gorge
strengthens rapidly Thu. The latest model guidance indicates a KTTD-
KDLS gradient close to -9 mb by 00Z Fri. Typically models tend to be
1 to 2 mb too low. Thus, a -10 mb gradient equates to at least 55-65
kt wind gusts at the most exposed locations at the west end of the
Gorge.
For detailed regional Pac NW aviation weather information, go online
to: https://weather.gov/zse
KPDX AND APPROACHES...MVFR with light rain likely by 12Z or shortly
after, the transition to snow expected to occur around 21Z but there
may be mix rain/snow/sleet up to then. Flight conditions likely to
lower to IFR this evening as pcpn intensifies. Accumulating snow on
runways highly likely, especially late afternoon through tonight
with a rough estimate of 1 to 3" snow fall by 12Z Fri. East wind
gusts 25-40 kt at the terminal and vicinity this afternoon through
tonight. /mh Weishaar
&&
.MARINE...Increasing offshore flow today as a low approaches the
central Oregon coast then tracks slowly northward through
Friday. Easterly winds are expected to reach gale gusts for the
northern waters this afternoon through tonight. The strongest
east winds nearshore are usually through the gaps in the coastal
terrain near the Columbia River, Tillamook. The east winds will
generate choppy seas with east wind wave along with westerly
swell.
Another low approaches the waters early Saturday morning and
moves to or near the coast Saturday afternoon somewhere near the
Columbia River entrance, depending on the forecast model. This
low may bring gale force winds especially to the outer zones,
PZZ270/275 Friday night early Saturday. By Saturday evening
winds ease, but a warm front moves to the waters by Sunday
afternoon. This too may bring gale force winds. The following low
pressure tracks to the south WA coast Monday afternoon. The
pressure gradient on the backside of the low may bring gale force
west to northwest winds. Seas will build Saturday morning as a
northwesterly swell moves across the waters. Seas will likely
stay in the mid teens through the weekend. Depending on the track
and strength of the low for Sunday and Monday, seas could
approach 20 ft Monday per the ENP. The ECMWF is lower so for now
have split the difference. /mh
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 7 AM this morning to noon PST Friday
for Central Columbia River Gorge-Upper Hood River Valley.
Blizzard Warning from 10 AM this morning to noon PST Friday for
Western Columbia River Gorge.
Winter Weather Advisory from 10 AM this morning to noon PST
Friday for Northern Oregon Cascade Foothills.
Winter Weather Advisory from 7 AM this morning to noon PST
Friday for Cascades in Lane County-Northern Oregon
Cascades.
Winter Storm Warning from noon today to noon PST Friday for
Coast Range of Northwest Oregon-Greater Portland Metro
Area-Lower Columbia.
Winter Weather Advisory from 2 PM this afternoon to noon PST
Friday for North Oregon Coast.
Winter Weather Advisory from 4 PM this afternoon to noon PST
Friday for Central Willamette Valley.
WA...Winter Storm Warning from 7 AM this morning to noon PST Friday
for Central Columbia River Gorge.
Blizzard Warning from 10 AM this morning to noon PST Friday for
Western Columbia River Gorge.
Winter Weather Advisory from 7 AM this morning to noon PST
Friday for South Washington Cascades.
Winter Storm Warning from noon today to noon PST Friday for
Greater Vancouver Area-I-5 Corridor in Cowlitz County-
Willapa Hills.
Winter Weather Advisory from 2 PM this afternoon to noon PST
Friday for South Washington Coast.
Winter Storm Warning from 10 AM this morning to noon PST Friday
for South Washington Cascade Foothills.
PZ...Small Craft Advisory from 5 AM early this morning to 1 PM PST
this afternoon for coastal waters from Cape Shoalwater WA
to Cascade Head OR out 60 NM.
Gale Warning from 1 PM this afternoon to 4 AM PST Friday for
coastal waters from Cape Shoalwater WA to Cascade Head OR
out 60 NM.
Small Craft Advisory from 7 AM this morning to 8 AM PST Friday
for coastal waters from Cascade Head OR to Florence OR out
60 NM.
&&
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