NWS Portland, OR wrote its last area forecast discussion before the first event at Jan 7, 5:52 AM PST, 4 hours 8 minutes earlier.
Area forecast discussion, Jan 7, 5:52 AM PST, 4 hours 8 minutes before
Area Forecast Discussion...updated
National Weather Service Portland Oregon
552 AM PST Sat Jan 7 2017
.SYNOPSIS...A complex low combined with a moist warm front will
result in a mix of snow, sleet, and freezing rain today. THe
precipitation will gradually turn to rain from south to north Sunday
and Sunday night. Rain showers will decrease Monday night and Tuesday
as the low departs the area. Another low approaches Tuesday for a
chance of low elevation snow, mainly north of Salem mid week.
&&
.UPDATE...The temperatures along the Central Oregon Coast have
remained above freezing as the precipitation is nearing. THe wet
bulb lowered a little bit, but not enough to support much if any
winter weather. Have therefore canceled the winter weather advisory
of the Central Oregon coast. Forecast confidence for the North
coast is low as well since those temperatures are also above
freezing.
.Previous SHORT TERM...Today through Monday night...A complex weather
pattern will produce a mix of winter precipitation types for NW
Oregon and SW Washington today, Sunday, and in some areas Monday
morning. The main weather players today are a large low moving south
offshore from the Gulf of Alaska, and a moist warm front approaching
from the south.
Radar imagery shows precipitation moving into southern Oregon early
this morning, with the leading edge rapidly approaching Lane County.
The northern low continues east winds across NW Oregon and SW
Washington this morning supporting widespread sub freezing
temperatures east of the coast. Coastal temperatures are currently
above freezing, but low dew point temperatures show potential for
evaporative cooling to lower the temperatures a couple of degrees
when the precipitation arrives.
The two lows will merge into a broad complex low later this morning
and remain offshore through Monday. A series of waves rotating around
the low will support precipitation over the area today through Monday
with surges of moderate to heavy precipitation at times. The main
forecast challenge with this weather scenario is precipitation type
as south winds and warmer air aloft with the warm front will compete
with the east winds and cold surface temperatures associated with the
offshore low. The most likely scenario is that the precipitation will
first be snow, then quickly turn to sleet, then freezing rain.
Another forecast challenge is the timing of when the warmer air will
dominate, and the frozen precipitation will end and become all rain.
This should happen fairly quickly for coastal areas, with low-level
frozen precipitation remaining the longest for the Columbia River
Gorge and Upper Hood River Valley. These areas could have freezing
rain into Monday morning. THe precipitation should turn to rain in
all areas Monday evening. TJ
.LONG TERM...Tuesday through Friday...Concern is increasing for
another impactful winter storm by the middle of next week. Exact
details still remain unclear, but most models show a reinforcing
shot of cold air into the Columbia basin. In addition, 00Z GFS
ensembles, GEM, and ECMWF are in pretty good agreement about a
surface low along the Oregon coast. The uncertainty is related to
the intensity and exact track with strengths between 975 and 1000 mb
and some surface lows tracking inland and others staying offshore.
This leaves a wide range of potential impacts with wind storm, low
elevation snow and ice, and another extended freezing rain/snow
event for the gorge all possibilities. Expect models to get a better
handle on this situation by later in the weekend and into early next
week once we get this weekend storm system through the area.
Beyond mid week, things become a bit more unclear, but some models
(GEM and ECMWF) hold on to the Columbia basin high pressure and
continue to feed cold air into the region, so we may not be done
with winter yet. This pattern has been pretty persistent, and even
when models try to break us out of it (as they were earlier this
week for next week), it seems that once the time gets closer, we
remain stuck in the cold pattern. /Bentley
&&
.AVIATION...Definitely a No-Go day, as conditions will deteriorate
rapidly this am. Low pres off the n Calif coast will push
increasing clouds and precipitation north this am. Expect period
of light snow for a few hours with the precipitation onset, but
will see widespread freezing rain over most areas by 21z except
for rain along the coast. But snow/sleet continue at PDX/VUO area
TAFs through 00Z, then turn to freezing rain. Expect snow through
tonight in the Columbia Gorge and higher Cascades. Generally,
flight conditions start as VFR this am, but drop quickly to MVFR
and occasionally IFR with the snow. Even after transition to
freezing rain, low MVFR will dominate. /Rockey.
&&
.MARINE...As expected, winds have turned more east to southeast
this am. Will maintain Small Craft Advisory for the coastal
waters through Sun, with 15 to 25 kt winds and gusts to around 30
kt, though could see a few gusts near 35 kt on the outer waters.
Seas now at 4 to 6 ft. Will see overall seas build a bit more,
running at 8 to 11 ft over the outer waters this afternoon, and
bit less closer to shore due to easterly winds. Small Craft
Advisory for Seas just for the waters beyond 10 nm looks good as
easterly winds will likely limit swell nearer to shore.
No big change in the overall forecasts for next week as remains
quite active, with gale force southerlies possibly from time to
time. But confidence remains low in the models having good output
in any timing. In any case, mariners should plan for active
weather next week. /Rockey
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning Today through Sun night for...
Western and Central Columbia River Gorge
Upper Hood River Valley.
Winter Storm Warning Today through Sunday evening for...
North Willamette Valley, including Portland Metro Area
Coast Range of Northwest Oregon.
Winter Storm Warning Today through Sunday morning for...
Northern Oregon Cascade Foothills.
Winter Storm Warning Today through Sunday afternoon for...
Central Willamette Valley, including Salem Area.
Winter Storm Warning Today through tonight for...
Cascade Foothills in Lane County
Central Coast Range of Western Oregon
South Willamette Valley, including Eugene Area.
Winter Weather Advisory Today through Sunday afternoon for...
Northern Oregon Cascades
North Oregon Coast.
Winter Weather Advisory Today through Sunday morning for...
Cascades in Lane County
Lower Columbia.
WA...Winter Storm Warning Today through Sunday night for...
Western Columbia River Gorge
Central Columbia River Gorge
South Washington Cascades.
Winter Storm Warning Today through Sunday evening for...
Clark County, including Greater Vancouver Area
South Washington Cascade Foothills.
Winter Weather Advisory Today through Sunday morning for...
I-5 Corridor in Cowlitz County
Willapa Hills.
Winter Weather Advisory Today for...
South Washington Coast.
PZ...Small Craft Advisory for winds on all waters through Sunday.
Small Craft Advisory for hazardous seas Today through Sunday
on coastal waters from Cape Shoalwater to Florence, and 10 to 60 nm
offshore.
&&
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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.