Heavy Snow in Oregon, February 14 to 15, 2019

Area Forecast Discussion...
National Weather Service Portland OR
345 AM PST Thu Feb 14 2019

.SYNOPSIS...An unseasonably cold and moist weather pattern will
continue to produce low snow levels across the region with periods of
winter weather in the Columbia River Gorge Saturday. There may be a
drier period Sunday into Monday, but precipitation returns early next
week.

&&

.SHORT TERM...Today through Sunday...It is a rather complex weather
pattern over the Pac NW for the next couple of days. The upshot is
that there will be a continuation of the cool and wet weather, with
more mountain snow and mainly rain in the lowlands. The exception
will be in the Columbia River Gorge, where there will be more wintry
precipitation today into Fri.

The feature of interest today is an upper level low off the northern
Calif coast. This system is driving surface low pressure development
along the stalled baroclinic zone that was responsible for the
copious amounts of rain over our CWA on Tue into Wed. The surface low
appears to be developing just off the Calif/Oregon border right now,
with a leading warm front now spreading light rain into the southern
portions of the fcst area. Precipitation will spread northward
through the rest of the CWA during the early morning hours.
Meanwhile, with cold air and relatively high pressure remaining
entrenched over the Columbia Basin east of the Cascades, offshore
pressure will continue to increase through the morning as the surface
low lifts northward along the Oregon coast. As of 10Z, the KTTD-KDLS
gradient had reached -8.7 mb, and based on the latest model guidance,
it can be expected to strengthen another couple of millibars by
mid-morning. This will maintain the gusty east winds and keep
temperatures  near or below freezing through most of the day in the
Columbia River Gorge.

The surface low is modeled to move through the CWA this afternoon,
dragging a sharp cold front through. There should be a period of
steadier precipitation accompanying the front. It also appears that
there will be a burst of fairly gusty southerly winds through the
Willamette Valley. As previous shifts have noted, there is a decent
pressure rise/fall couplet that is modeled to track northward
directly over the valley. Based on fcst model soundings, widespread
gusts of 25 to 35 kt can be expected from south of Portland down
through Eugene. This may allow southern portions of the valley to see
temps jump up in the upper 40s later in the afternoon, and it's not
out of the question that some locations reach the low 50s. There
should be plenty of shower activity this evening and overnight behind
the cold front as the upper level shortwave trough moves through. It
is also worth noting that the 4 km NAM Nest model is suggesting that
there could be some convective activity in the valley along or right
behind the cold front. Confidence is not high enough to include
thunder in the fcst, as none of the other high-res models are really
showing this. But it will be worth watching.

Confidence is high that precipitation east of Cascade Locks will
remain mostly snow today, where an additional 3 to 6 inches of
accumulation can be expected on top of the already significant
snowpack out there. The fcst models suggest that a tongue of warm air
from the warm front will reach the western end of the Gorge early
this morning. Will keep the precipitation type a mix of snow and
freezing rain this morning west of Cascade Locks today. Ice
accumulations could total a tenth to a quarter inch. There is also
some concern that the freezing rain threat could potentially reach
into the eastern portions of the Portland/Vancouver metro area this
morning. The latest NAM and WRF-GFS model soundings for KTTD both
suggest a period of potential freezing rain. A chance was added to
the forecast from 12Z-18Z, but at this time it appears that impacts
should be rather limited if this does occur. Temperatures will be
very marginal and should quickly warm above freezing by late morning.
QPF will also be rather light this morning. The cold frontal passage
will significantly weaken the easterly pressure gradient through the
gorge this afternoon. This may allow western portions of the gorge to
change over to all rain by late afternoon or early evening. The
central Gorge and Upper Hood River Valley may not see the cold air
scour out until Fri. The Cascades will see snow levels rapidly rising
to around 4000-5000 this morning. Higher elevations will see several
inches of snow, while there will be potential for some light freezing
rain at some of the passes.

The next system to impact us will be the low pressure that can be
seen west of Haida Gwaii this morning. This feature will be dropping
south along the B.C. coast today, reaching the WA/OR coastal waters
tonight. The upper level trough will approach the coast Fri morning,
then move onshore late Fri into Sat. This will result in more shower
activity across the region. Will need to monitor how much cold air
remains in the Columbia Basin after today's system, as this will
determine whether there will be potential for more wintry weather in
the gorge Fri and Sat.

Yet another upper level trough will dive south out of British
Columbia Sat night into Sun. This system is currently modeled to drop
south right along the Washington and Oregon coast, likely continuing
the shower chances through early Sun. This system looks to bring
another very cold airmass into the region. We may need to watch for
the potential that any wrap-around precipitation on the back side of
the low could fall as snow at lower elevations early Sun as flow
turns offshore. However, at this time, the wrap-around QPF looks to
be pretty light. Expect a trend toward drier weather Sun as the low
drops south into California. Pyle

.LONG TERM...Sun night through Wednesday...It looks like there may be
a short-lived period of dry weather Sun night and much of Mon as an
upper level shortwave ridge moves over the region. However,
additional shortwave troughs are modeled to dive south along the B.C.
coast and into Washington and Oregon late Mon into Tue and again late
Tue into Wed. This will likely result in more cool, wet, and cloudy
weather. Expect more snow in the Cascades, and potentially the Coast
Range and Cascade foothills at times. It appears that precipitation
will be mainly rain for lowlands, with the potential exception of the
Columbia River Gorge again. Pyle

&&

.AVIATION...A surface low pressure will strengthen slightly as it
moves northeastward towards the north Oregon coast today. This
will result in light rain spreading northward this morning and
the current VFR, MVFR and IFR conditions distributed across the
area will likely persist at each taf site through ~18z Thursday.
As moisture spreads northward this morning, snow and freezing
rain will fall in the Columbia River Gorge. There is a small
chance freezing rain could impact KTTD this morning, but at this
point, it appears temperatures will be just warm enough to
prevent it from happening. Thereafter, a surge of strong gusty
southerly winds of 25 to 35 kt should spread northward this
afternoon and result in most locations becoming VFR with only
temporary reductions to MVFR conditions. There is also a nonzero,
but small chance of a thunderstorm impacting the KEUG and KSLE
terminals this afternoon, but it appears this threat is low
enough at this point to keep any mention out of the tafs.

KPDX AND APPROACHES...Gusty east winds should transition to
gusty southerly winds this afternoon as a low pressure moves
northward near the coast. Despite periods of rain over the next
24 hours this should keep the terminal predominantly VFR with
MVFR conditions most likely to occur after ~03z Friday when winds
weaken. /Neuman

&&

.MARINE...An ~985mb low pressure will will move north-
northeastward across the waters today. This will result in a
surge of Small Craft Advisory level westerly wind gusts of 25 to
30 kt to spread northward across the waters today. There will
likely be a brief lull in the winds this evening before winds
back to southerly and once again rise into the 25 to 30 kt range
later tonight. This will be in response to a low pressure system
dropping southeastward out of the Gulf of Alaska. Winds will
likely temporarily drop off Friday evening as the low pressure
moves into the waters, but will likely spike back upward late
Friday night and Saturday as gusty northwesterly winds spread
into the waters. Meanwhile, a large swell accompanying the
aforementioned low pressure system dropping out of the Gulf of
Alaska will arrive and result in seas climbing into the upper
teens off the Columbia River mouth and around 20 ft off the
central Oregon coast on Friday.

The region will remain under an active northwesterly flow
pattern that will occasionally bring Small Craft Advisory level
winds next week, but overall the pattern does not appear
favorable for strong low pressure systems to bring stronger
winds. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning until 10 PM PST this evening for Central
     Columbia River Gorge-Upper Hood River Valley.

     Winter Weather Advisory until 10 PM PST this evening for
     Northern Oregon Cascades-Western Columbia River Gorge.

WA...Winter Storm Warning until 10 PM PST this evening for Central
     Columbia River Gorge.

     Winter Weather Advisory until 10 PM PST this evening for South
     Washington Cascades-Western Columbia River Gorge.

PZ...Small Craft Advisory for winds from 4 PM this afternoon to 7 PM
     PST Friday for Coastal Waters from Cape Shoalwater WA to
     Cascade Head OR out 60 NM.

     Small Craft Advisory for hazardous seas from 7 PM this evening
     to 4 AM PST Saturday for Coastal Waters from Cape
     Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory for winds from 1 PM this afternoon to 7 PM
     PST Friday for Coastal Waters from Cascade Head OR to
     Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar from 10 AM
     this morning to 4 PM PST this afternoon.

     Small Craft Advisory for Rough Columbia River Bar from 8 PM
     this evening to 7 PM PST Friday.

&&

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.