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Western Washington


243 
FXUS66 KSEW 112237
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
237 PM PST Wed Dec 11 2019

.SYNOPSIS...
An active weather pattern across the Pacific NW the next several
days will continue. A trough of low pressure will bring rain and
mountain snow the next several days with significant snow
accumulation in the highest elevations. There will be drier and 
cool weather by Saturday and Sunday, and early next week, before a
more active pattern develops again in the middle of next week. 

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
Radar shows showers continuing to overspread the forecast area
this afternoon and this trend is set to continue. Snow levels have
started out lower than earlier expectations, with snow falling in
Snoqualmie Pass already. This is due to the local effects of
easterly flow bringing lower snow levels in the pass. This has
been the biggest change to the snow forecast, with heavier
accumulations there. As a result, the winter storm warning was
amended to reflect impacts down to 3000 ft of elevation. Snow
levels will remain in the 3000-3500 foot range for most of the
overnight, and will increase on Thursday morning as westerly flow
pushes in. Thursday will bring showery conditions, with a chance
of heavy mountain snow showers by Thursday evening.

Winds will increase out of the south tonight and into early
Thursday. They will not be overly significant or impactful, but
gusts up to 35 MPH are possible, especially near the water. 

The concern on Thursday will be an increase in intensity of the
showers by later afternoon. 6 hourly model QPF in the .25-.50 inch
range suggests heavy showers in the mountains that will be capable
of local dynamic cooling to cause snow levels to fall and produce
brief periods of heavy snow. This will bring additional travel
concerns, especially for Snoqualmie Pass where the snow levels are
likely to rise Thursday morning, but fall again in the heavier
snow showers Thursday afternoon. 

Additionally, SPC guidance indicates chances of coastal
thunderstorms the next few days, and this seemed reasonable, and
so an isolated mention is present in the coastal areas. 

Friday will bring a decrease in precip and a weak ridge will
attempt to build in aloft. So temperatures will dip to near or
below normal this weekend with somewhat drier weather although
showers will be present in some form across the area through the
weekend, just not overly widespread. 


.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Ridging will actually start off the extended period and it looks
to hold across the area into the start of next week. The breakdown
of this ridging is in question and so the details remain in lower
confidence levels at this time. The overall trend will be however
for temperatures near normal. After this system today through
Friday, there do not appear to be any significant weather impacts
on the horizon. 

&&

.AVIATION...A vigorous frontal system will move through Western 
Washington this evening with strong southwest flow aloft. Tonight 
and Thursday will have periods of rain and typical Western 
Washington rainy day cigs and reduced vsby. The mountains and 
foothills will remain obscured.

KSEA...Periods of rain with breezy southerly winds tonight and 
Thursday. Cigs will average 1500-2500ft and vsby will drop at times 
to 3-5miles in rain. 

&&

.MARINE...A strong frontal system will move through the area
this evening. A trough will move ashore on Thursday. Gale warnings 
are up for the coastal waters, east entrance to the Strait of Juan 
de Fuca, and the northern waters. For the coastal waters, swell 
Thursday and Friday should be 15-18 feet with the main period around 
16 seconds. 

&&

.HYDROLOGY...A wet storm system will impact the region this afternoon
through Friday. Given precipitation amounts and snow levels in 
the 3500-5000 foot range - most rivers are not expected to 
approach flood stage. There is some concern that the Skokomish 
River in Mason County could approach flood stage. We will continue
to monitor this situation.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 10 AM PST Friday for Cascades of 
     Pierce and Lewis Counties-Cascades of Snohomish and King 
     Counties-Cascades of Whatcom and Skagit Counties.

     Winter Weather Advisory until 9 PM PST Thursday for Olympics.

PZ...Gale Warning until 9 PM PST this evening for Coastal Waters From 
     Cape Flattery To James Island 10 To 60 Nm-Coastal Waters 
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters 
     From James Island To Point Grenville 10 To 60 Nm-Coastal 
     Waters From James Island To Point Grenville Out 10 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10 
     To 60 Nm-Coastal Waters From Point Grenville To Cape 
     Shoalwater Out 10 Nm.

     Small Craft Advisory until 2 AM PST Saturday for Grays Harbor 
     Bar.

     Gale Warning until 1 AM PST Thursday for East Entrance U.S. 
     Waters Strait Of Juan De Fuca-Northern Inland Waters 
     Including The San Juan Islands.

     Small Craft Advisory until 4 PM PST Thursday for West Entrance 
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until midnight PST tonight for Central U.S. 
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Thursday for Admiralty Inlet.

     Small Craft Advisory until 5 PM PST Thursday for Puget Sound and 
     Hood Canal.

&&

$$

www.weather.gov/seattle

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Southwestern Washington and Western Oregon


266 
FXUS66 KPQR 112315
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
315 PM PST Wed Dec 11 2019

.SYNOPSIS...Low level rain and high elevation snow will persist
through Thursday, turning to rain and snow showers Friday through
the weekend.

&&

.SHORT TERM...Wednesday afternoon through Saturday...A warm front
lifted north earlier today with some rain remaining in the area
behind it this afternoon. Most areas will see rain briefly become
more showery overnight before the next system arrives. Satellite
imagery this afternoon shows a cloud band associated with a 
strong cold front located around 128W with cold pool convection
behind it. There hasn't been much change in the short term
forecast thinking today, so kept the forecast pretty consistent.
It continues to look like we'll get a significant amount of rain
and high elevation snow over the next 24 hours, but dry antecedent
conditions should mean there's no river flooding threat.
Significant street ponding is likely if any street drains are
clogged, but don't see an overall threat for urban flooding.

In addition to rainy, Thursday also looks windy across the board,
although significant wind impacts aren't expected. Operational
model runs are pretty consistent in showing about a 4 mb gradient
in the Willamette Valley, which should translate to winds well
below Wind Advisory criteria, but people are likely to notice that
it's windy. In the Cascades, wind will combine with snow, but
given the wet nature of the snow, don't think the combo will cause
long lasting significant visibility reductions.

Of note to beachgoers, Thursday's surf is likely to bring 
hazardous beach conditions in the form of consistently higher than 
usual wave run-ups (high surf) and occasional surprising extra 
long run- ups (sneaker waves). See the High Surf Advisory for more
details.

Thursday afternoon, behind the front, kept in a slight chance for
thunderstorms along the north OR and south WA coasts. Lightning
networks have detected some lightning in the cold pool behind the
front (well offshore) this afternoon and models continue to show
favorable instability into Thursday evening as the cold pool moves
towards the local area.

Also with the cold pool, snow levels in the Cascades will fall
late Thursday afternoon through Friday, settling around 3500 to
4000 ft Friday, then dropping further Saturday to around 2500 ft.
Expect showery conditions as the snow level drops, so while
widespread snow accumulations after Friday morning are expected to
be unimpressive, on/off snow will continue through at least
Saturday. Bowen

.LONG TERM...Saturday night through Wednesday...Operational models 
seem to be in agreement that an upper level trough will move through 
the area Saturday night through Monday, increasing chances for 
precipitation for the forecast area. Snow levels during this time 
will settle around 2500 ft bringing snow to the Cascades. Beginning 
Monday night, operational models are in agreement that an upper 
level ridge will develop over the Pacific NW until at least Tuesday. 
This should result in a break from the rainy pattern. However, 
uncertainty remains in the duration of this ridging. Following this 
brief dry period, an active pattern continues for the foreseeable 
future starting Wednesday. -Thaler

&&

.AVIATION...A mix of VFR-MVFR will be the dominant trend with 
southerly, gusty winds through this evening. Rain is expected to
increase later this afternoon and persist through the evening. 
Coastal sites are expected to see gusts around 25 kt through the
night. IFR conditions are expected late this evening around 09Z
as low level stratus pushes onshore from the southwest. LLWS is
expected for KONP and KTTD this evening.

KPDX AND APPROACHES...VFR conditions will deteriorate as the
front passes with accompanying rain. Ceilings will drop to MVFR
this evening with a chance of IFR ceilings but visibility should
stay VFR. Southerly winds will persist through this evening. 
-BPhillips

&&

.MARINE...Winds will ramp up today as a strong front from a Gulf
of Alaska low swings across the waters bringing Gale force winds
between 40 to 45 kt later this afternoon through the evening 
hours. Winds will subside but remain gusty through Thursday 
night which will continue to pose hazards for small crafts. High 
pressure builds over the waters Friday which will weaken the 
winds to 10 kt or lower. There is a possibility of a weaker 
front arriving Saturday but there is too much disagreement on the
strength of the winds to put much confidence in the arrival time

There is a general consensus between models that the primary 
swell will be between 17 to 19 ft and period between 15 and 17s. 
Combined wave heights may reach 20 ft in some areas, mainly 
offshore. Seas will generally stay at or above 10 ft through the 
weekend. Long period swells pose an increased risk for hazardous 
beaches. -BPhillips

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Warning from 4 PM this afternoon to noon PST 
     Friday for Northern Oregon Cascades.

     Winter Storm Warning from midnight tonight to noon PST Friday 
     for Cascades in Lane County.

WA...Winter Storm Warning from 1 PM this afternoon to noon PST 
     Friday for South Washington Cascades.

PZ...Small Craft Advisory until 1 PM PST this afternoon for coastal 
     waters from Cape Shoalwater WA to Florence OR out 60 NM.

     Gale Warning from 1 PM this afternoon to 1 AM PST Thursday for 
     coastal waters from Cape Shoalwater WA to Florence OR out 
     60 NM.

     Small Craft Advisory until 6 AM PST Thursday for Columbia River 
     Bar.

&&

$$

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Southeastern Washington and Northeastern Oregon


681 
FXUS66 KPDT 112226
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
226 PM PST Wed Dec 11 2019

.SHORT TERM...Tonight through Thursday night. The next in a 
series of weather disturbances has started to impact the forecast
area this afternoon. A frontal boundary associated with a low 
pressure system off the coast is moving across Central OR and WA,
with radar showing snow and rain showers impacting Western and 
portions of Central OR and WA at this time. This initial frontal 
boundary will bring periods of rain and high elevation snow 
through tonight into tomorrow, while a follow up of upper level 
disturbances will continue precipitation chances into Friday 
before waning into the weekend. A winter weather advisory was 
issued for areas above 2000 feet along the eastern slopes of the 
WA Cascades, as snow accumulations of 3-6 inches are expected in 
the passes. Snow levels will mostly be between 4000-5000 feet 
through the period, with snow levels in the Kittitas Valley up to 
the East slopes of the WA Cascades between 2500-3000 feet tonight 
and rising by Friday afternoon. Ahead of the frontal boundary 
earlier today, central OR and Grande Ronde valley winds picked up,
and are expected to stay breezy into Friday. Lawhorn

Friday through Saturday...The strong westerly jet will lower south 
and will become positioned just north of 40N on Friday, and the 
moist westerly flow will mainly affect the southern half of Oregon. 
Although colder air will lower snow levels down to around 3000-3500 
feet, most precipitation on Friday will be along the Cascades and 
south of Jefferson and Wheeler Counties. The jet will continue to 
lower southward Friday night, and any showers remaining will be 
isolated to scattered mountain snow showers Friday night and 
Saturday with mostly cloudy skies elsewhere.   Wister

.LONG TERM...Saturday night through Wednesday. A few showers will 
linger over the mountains Saturday night and Sunday in northwest 
flow.  A ridge is expected to build along the coast and then move 
inland Monday and Tuesday with mainly dry conditions. The next 
system to bring a chance of snow showers to the area starting 
Wednesday, with most of the system to move through Wednesday night 
and Thursday.  Temperatures are expected to be near normal through 
the period. 93 

&&

.AVIATION...00z Tafs. Rain will spread west to east with 
snow above 4500 feet overnight. Widespread MVFR and IFR conditions 
are expected for most of the period due to low CIGS and VSBYS in 
-RA and BR. The rain should decrease to showers after 12-15z with
 conditions improving to VFR at most sites. Winds will be 10-15
 kts and gusty at BDN/RDM with light winds at other sites
 overnight and then increasing to 5-10 kts on Thursday. 

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  39  51  38  46 /  60  50  50  20 
ALW  38  50  39  45 /  70  60  60  30 
PSC  37  51  38  47 /  60  40  30  10 
YKM  32  45  29  46 /  70  50  30  10 
HRI  36  52  39  48 /  60  40  30  10 
ELN  30  43  30  41 /  70  50  40  10 
RDM  35  48  30  44 /  70  70  60  30 
LGD  36  47  34  42 /  70  70  60  40 
GCD  36  45  33  41 /  80  70  60  30 
DLS  37  48  37  47 /  80  70  60  20 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Winter Weather Advisory until 4 AM PST Thursday for WAZ520.

&&

$$

82/85/93/93

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Northeastern Washington and Northern Idaho


293 
FXUS66 KOTX 112353
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
353 PM PST Wed Dec 11 2019

.SYNOPSIS...
The next weather system will move in this evening. This next one 
will be a warmer system, however it will carry significantly more 
moisture and will likely lead to a heavy snow in the mountains. 
The threat of the snow will diminish Friday. The weather will 
remain unsettled into the weekend however no significant storms 
are expected at this time. 

&&

.DISCUSSION...

...Mixed Precipitation Valleys and Heavy Mountain Snow Tonight...

Tonight: The next frontal system to impact the Inland Northwest 
is moving into coastal Oregon and Washington this afternoon. The 
thermal profile has warmed a bit since the morning hours and it 
will continue to do so in the warm sector of the incoming 
disturbance, which will include the evening and overnight hours. 
Precipitation type will be much more challenging with this next 
front compared to our last one that brought all snow. A blanket of
stratus and fog cover has kept mixing at a minimum and surface 
temperatures for many valley locations at or below freezing. Where
we have seen temperatures warm above freezing are lower 
elevations southeast of a line from Moses Lake to Coeur d'Alene 
(in general). There are pockets still below freezing around the 
northwest portion of the basin, including along the Columbia 
River. The far northern valley locations are mostly all below 
freezing heading into the late afternoon hours. A warm tongue push
over much of the basin as precipitation begins to fall this 
evening and continue to extend northward through the night.

* Precipitation Type: High confidence for rain along I-90 from
  Moses Lake to Sprague and southeastward across the basin, into
  the Palouse, and into the Lewiston-Clarkston Valley. Precip type
  will be trickier around the northern rim of the Columbia Basin
  where a period of freezing rain will be possible this evening
  from Wenatchee to Quincy, portions of the Waterville Plateau and
  along Highway 2 over to the West Plains. Confidence in freezing
  precipitaiton is too low to include in the official forecast. Snow
  is then expected to be the predominant precip type across the 
  northern mountain valleys.

* Snow Amounts: Looking at around a foot of snow possible in the
  Cascade Mountains (mostly near the Cascade crest) and over the
  Panhandle Mountains. Between 1 to 3 inches of snow is expected
  on the Waterville Plateau, Okanogan Valley/Highlands, Northeast
  Mountains and Northern Panhandle. Local valley accumulations up
  to 4 inches will be possible from the Northeast Mountains to the
  Northern Panhandle.

* Impacts: Heavy snow over Stevens Pass and Lookout Pass is
  expected to impact travel with difficult to impossible winter
  driving conditions. Heaviest snow will occur overnight, although
  will be ramping up over Stevens Pass in the evening. Slippery
  travel conditions are expected in the northern mountain valleys
  through Friday morning. Snow will quickly become slushy in the
  valleys as temperatures warm up Friday morning.

No changes will be made to the current suite of Winter Storm 
Warnings and Advisories. /SVH

Thursday through Friday...One warm front moves through the region
tonight and will be followed quickly by a second warm front 
Thursday afternoon. The cold front will follow Thursday night and 
Friday. Westerly flow behind the front will have several 
additional weak waves with it and that will be more than enough to
keep a chance of rain and snow in the Cascades and the Panhandle 
mountains through Friday night. Westerly flow will likely shadow 
out much of the lower Basin. This is a pretty wet weather system 
with moisture increasing to around 200 percent of normal and 
staying very moist until the cold front passage. Lingering cool 
air in the Cascade valleys, the Okanogan valley and many of the 
northern mountains valleys tonight will keep snow levels bouncing 
between 2500-3000 feet and that means that precipitation will be 
mainly snow Thursday morning. South of about Highway 2 
precipitation will be mainly rain, although there may be some 
rain/snow mix in the northern basin just south of the Columbia 
River. Winter Highlights for snow in the Cascades, Northern 
Mountains, and the Idaho Panhandle are in effect and will last 
into Friday for now. Winds out of the southwest will be on the 
increase through the day on Thursday with gusts 20-30 mph through 
the basin and on some of the ridges. This will likely lead to 
areas of blowing snow in the mountains. With the warm air 
advection and then mixing due to the frontal passage temperatures 
on Thursday will actually be able to climb into the upper 30s to 
lower 40s, then slide back 3-5 degrees on Friday. 

Saturday through Sunday...Model guidance is similar showing 
another upper low dropping south along the Cascades Saturday and 
Sunday. By this time we will lose the deep moisture tap and the 
best forcing will be west of the Cascades, then into Oregon. So 
any lifting in the northwest flow will favor the Cascades, the 
Idaho Panhandle mountains and the Blue mountains. Precipitation 
will not be very much but will fall as all snow with the cooler 
air in place. Shoshone county will likely see a few inches of 
snow. High temperatures will only be able to make it into the mid 
30s.

Monday through Wednesday...High pressure will build into the area
from the west Monday and Tuesday. This will be followed by what 
looks like a split trough that will want to weaken as it gets 
hammered by the ridge. High pressure with generally weak winds 
will once again allow fog and low clouds to spread across the 
region Monday and Tuesday. If the trough splits as the models hint
at this would result in several days of cool cloudy conditions. 
Tobin 


&&

.AVIATION...
00Z TAFS: A couple moisture-laden frontal wave moves in over the
next 24 hours. The first wave moves in this afternoon and tonight,
with increasing precipitation from the southwest. The best threat
will develop after 02-05Z and continue into the overnight. Mixed
precipitation will be possible around EAT/GEG/SFF/COE, which may
include -sn and -ra, with a small risk for -fzra. Temperatures are
expected to climb around GEG/SFF/COE through the night, which
should allow the risk to change to mainly -ra after 08-09Z. Expect
IFR/MVFR conditions, with locally dense fog possible around GEG
before the precipitation moves in. Some breezy conditions are
expected going into mid to later morning Thursday. The threat of
showers will continue into the afternoon, with a better risk
moving in later in the day with the second wave. /Cote'


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        34  43  31  40  28  35 /  90  40  50  10  10  10 
Coeur d'Alene  35  41  33  38  30  35 / 100  70  70  20  20  10 
Pullman        37  45  35  41  30  36 /  90  60  60  20  20  20 
Lewiston       39  50  38  46  33  40 /  80  50  60  30  30  20 
Colville       31  39  28  40  25  37 /  90  30  40  10  10   0 
Sandpoint      33  39  33  37  30  34 / 100  90  80  30  20  10 
Kellogg        34  40  34  37  30  35 / 100  90  90  60  40  30 
Moses Lake     35  47  29  45  25  38 /  80  30  20   0  10  10 
Wenatchee      32  43  30  41  28  36 /  90  60  30  10  10  10 
Omak           30  39  29  38  26  35 /  80  40  20  10   0   0 

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Warning from 7 PM this evening to 10 AM PST Friday 
     for Central Panhandle Mountains-Northern Panhandle. 

WA...Winter Weather Advisory from 7 PM this evening to 7 AM PST 
     Thursday for Northeast Mountains-Okanogan Highlands. 

     Winter Storm Warning until 10 AM PST Friday for East Slopes 
     Northern Cascades. 


&&

$$

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