[ W WA | SW WA and W OR | SE WA and NE OR | NE WA and N ID ]

Western Washington


107 
FXUS66 KSEW 281039
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
300 AM PST Tue Feb 28 2017

.SYNOPSIS...
Weak higher pressure aloft should provide a brief break in the wet 
weather pattern today. The next weather system arrives tonight with 
some rain in the lowlands and snow in the mountains as temperatures 
moderate. Another stronger wetter system is expected by late 
Thursday with more rain and mountain snow into Friday, and 
temperatures close to normal. Lower pressure aloft is forecast to 
develop off the coast this weekend for cooler than early March 
temperatures and wet conditions with snow levels below the passes.  

&&

.SHORT TERM...
The cool upper trough that produced plenty of wintry showers Monday 
has moved inland. Showers tapered off overnight with a few lingering 
showers remaining early this morning. Temperatures will around the 
freezing mark in many areas. Given the wet pavement, icy spots are 
likely. 

The overall pattern looks to finally make some adjustments this 
week. Progs agree on backing the flow from northwest today to more 
westerly through Thursday. The change will permit some temperature 
moderation over the next few days. 

A weak shortwave ridge today before another shortwave in the Gulf of 
Alaska this morning will swing onshore late today and tonight for 
some relatively light precipitation. Snow levels should climb above 
the lowlands but still remain below the passes. Enough QPF with a 
more orographic pattern for a winter weather advisory in the 
Cascades tonight into Wed morning. Low level onshore flow increases 
through the day today for some blustery conditions. 

Wednesday should offer a bit of a break in the weather with some 
lingering showers before the next stronger Pacific system arrives 
Thursday and Thursday night. The moderating trend continues with 
this system with high temperatures rising close to early March 
averages. More rainfall with snow in the mountains expected... 
suggesting March coming in like a lion. Buehner

.LONG TERM...Models are in good agreement that the end of the week 
will be an active period with some generous snowfall in the 
mountains. PoPs and QPF were boosted from previous forecasts for 
Friday through the weekend. Heights will take a tumble on Friday as 
a vigorous front moves through western Washington. A rather deep 
upper level trough will take up residence over the offshore waters 
for the weekend with a series of disturbances rotating into western 
Washington. The UW WRF-GFS shows some rather large swaths of the 
Cascades and Olympics picking up a couple feet of snow in the 48 
hour period ending Saturday afternoon. 

Both the GFS and Euro drop the 1000/850 millibar thickness to sub 
1300m levels with 850 temps of -6 or -7 C by the early hours of 
Sunday. But with a southerly gradient prevailing, this should keep 
snow levels at 500 to 1000 feet. The air mass begins to moderate 
somewhat on Monday, but the pattern remains active with snow levels 
at or below the passes. 27

&&

.AVIATION...An upper trough over the interior Pacific Northwest will 
continue shifting eastward overnight. Light northwest flow aloft 
through Tuesday. Air mass moist and slightly unstable but 
thunderstorms are unlikely. Rain and snow showers will decrease 
Tuesday morning, then a warm front approaching the area will bring 
light rain to the area by Tuesday evening. 

Rain and snow showers tonight will decrease Tuesday morning with 
snow levels near 500 feet. However, heavier showers and any 
convergence zone activity will temporarily drive the snow level down 
to near sea-level at times through early Tuesday morning. 1 to 3 
inches of snow are possible overnight along the Strait and in parts 
of central/north greater Puget Sound, especially above a few hundred 
feet elevation. Terminals that have the best chance of some snow 
accumulation include SEA/PAE and CLM. Temperatures will be near or 
just above freezing through Tuesday morning at most terminals. The 
puget sound convergence zone will also cause short periods of IFR 
cigs/vis with snow and upslope snow along the Strait may produce 
some IFR through around midnight. Elsewhere, mostly MVFR with VFR 
stratus by midday Tuesday. Light rain develops Tuesday evening with 
another slightly warmer system approaching. 

KSEA...The convergence zone remains active and will meander near the 
terminal much of the night. Winds will be fairly light (up to 6 kt) 
and variable or easterly. Precipitation bands may be moderate to 
briefly heavy with mixed rain/snow showers going over to snow. A 
quick inch or two is possible through 12z (4am Tue) before showers 
taper off. Cigs mostly MVFR but IFR will be possible during heavier 
showers or snow. VFR stratus likely by midday Tuesday. Brief drying 
Tuesday afternoon then more rain arrives Tuesday evening. dtm

&&

.MARINE...A weak surface low over Wrn Wa tonight will dissipate by 
Tuesday morning. Small craft northwesterly winds at times across the 
coastal waters with a lull midday Tuesday before picking up again 
late in the afternoon and evening. Seas near 10 feet including Grays 
Harbor where rough bar conditions are expected through Tuesday 
evening, especially around the 530 am and 545 pm ebb currents 
Tuesday. Small craft westerlies could develop Tuesday in the Strait 
by late morning or afternoon. Another front may bring small craft 
winds to some interior waters by Tuesday night and Wednesday. dtm

&&

.HYDROLOGY...No flooding is expected through this weekend.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...

PZ...Small Craft Advisory coastal waters and for Grays Harbor Bar.

&&

$$

www.weather.gov/seattle/

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html

[ W WA | SW WA and W OR | SE WA and NE OR | NE WA and N ID ]

Southwestern Washington and Western Oregon


348 
FXUS66 KPQR 281119
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
318 AM PST Tue Feb 28 2017

.SYNOPSIS...Cool and showery weather continues across western OR/WA
this morning. An upper level trough over the Pac NW will shift
eastward into the Rockies later today, allowing higher pressure to
build into Oregon tonight and Wed. This will probably bring and end
to most of the shower activity south of Salem tonight, but onshore
flow and weak instability will keep some showers around along the
coast and inland north of Salem. Flat upper ridging building north
from California will keep the southern part of the forecast area
mostly dry through Thursday...with milder temperatures. The ridge is
expected to give way to a Pacific frontal system toward the end of
the week, with significant rainfall possible Friday into Saturday.
Cool and unsettled weather is expected to prevail behind the front
for the remainder of the weekend and likely into early next week.

&&

.SHORT TERM...Today through Thursday...Latest radar imagery shows a
gradual decrease in shower activity over the past couple hours, as
our upper trough axis crosses the Cascades and temperatures warm
aloft. The milder temps aloft will limit instability this afternoon,
but probably will not be enough to completely negate the shower
threat due to onshore/cyclonic flow. Snow levels remain rather low in
the Cascades, with ODOT webcams showing showers bringing occasional
dustings of snow to the roads around Zigzag and Detroit...both
roughly near 1500 ft elevation. Temperatures in the Willamette Valley
remain in the mid to upper 30s, so it is unlikely the snow level will
get much below that...especially in regards to accumulating snow.
Accumulation rates have generally decreased to an inch every 2-4
hours in the Cascades based on latest SNOTEL data, so it appears to
have been a good call to allow the the snow advisory to expire last
night.

The emphasis of shower activity will gradually shift north over the
next 24-48 hours as a flat upper ridge slowly builds north from
California. Temperatures will be warming aloft; meanwhile, the 700 mb
flow pattern will be turning increasingly anticyclonic. The resulting
stability and lack of forcing will likely bring an end to shower
activity by late Wed for all but the North Coast and SW WA. The
ridging will also bring milder temperatures...possibly even allowing
highs Wed to approach normal for the 1st of March (mid 50s for most
of the lowlands).

The upper ridge reaches its maximum strength across the CWA Wed
night, possibly allowing some clearing especially for our southern
zones. This brings the threat of some valley fog Wed night/Thu
morning...and it may be dense due to the strengthening inversions and
light surface winds.

Models start to diverge a bit beginning Thu. The 06z GFS and 00z
ECMWF swing a shortwave through the forecast area ahead of an
approaching frontal system, bringing a decent chance for rain with
snow levels near the Cascade passes. The 06z NAM focuses the
shortwave a little further north, with less QPF across the district.
Held PoPs fairly low south of Salem Thu, with likely PoPs or better
PDX metro north. A cold front will be slowly approaching from the
Gulf of Alaska Thu/Thu night, but most models wait until Friday
before an approaching upper trough pushes the front onshore. There
could be a decent burst of precip with this system Thu night or Fri,
as models are hinting at a modest atmospheric river being pulled into
the front. However, the jury is still out on how well any atmospheric
river will hold together as the front moves onshore. At the moment,
it does not appear to be enough QPF to threaten hydrologic issues. 
Weagle

.LONG TERM...Thursday night through Monday...No changes. Previous
discussion follows: Strong westerly flow aloft gives way persists for
much of the second half of the week, until a broad upper trough
pushes deeper into the Pacific Northwest during the by the weekend,
providing for continued precipitation. Snow levels will fall down to
around 2,000 feet on Saturday behind the front, which supports snow
showers down into the higher Cascade foothill elevations. Models
remain in fair agreement that deeper moisture will enhance rainfall
again early Sunday as another shortwave embedded in the flow rotates
around the upper trough and pushes through the region. Model
solutions diverge a bit more significantly by early next week, but
there remains at least some agreement that another round of steady
moisture may again approach.   Cullen

&&

.AVIATION...Mostly VFR conditions early this morning and all
indications are that VFR conditions will continue to prevail.
However, brief high MVFR CIG possible with passing showers. 
Scattered showers will remain through the day.

KPDX AND APPROACHES...Prevailing VFR conditions through the
forecast period, but scattered showers will briefly drop CIG to
high end MVFR occasionally through the day. Bowen

&&

.MARINE...The next disturbance moving through largely to our 
north brings some more SW winds into the waters late Tuesday and 
Tuesday night that will probably exceed Small Craft Advisory 
thresholds, especially in the northern waters. Those winds ease 
up on Wednesday. The next batch of winds increase from the south 
on Thursday and should be high end Small Craft Advisory winds or 
possibly borderline gale force winds. Those winds turn westerly 
and decrease Friday.

Seas look like they've finally generally dropped below
10 ft with even buoy 50 showing 9.8 ft as of 2 AM. Seas continue
to drop through the day today and then may rise up to just above
10 ft again Thursday. Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds from 6 PM this evening to 4 AM 
     PST Wednesday for Coastal Waters from Cape Shoalwater WA 
     to Cascade Head OR out 60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 8 AM 
     PST this morning.

     Small Craft Advisory for Rough Columbia River Bar from 4 PM 
     this afternoon to 9 PM PST this evening.

&&

$$

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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.

[ W WA | SW WA and W OR | SE WA and NE OR | NE WA and N ID ]

Southeastern Washington and Northeastern Oregon


883 
FXUS66 KPDT 281159 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
359 AM PST Tue Feb 28 2017

Updated AVIATION Discussion

.SHORT TERM...Today through Thursday night...A shortwave trough 
will move east of the area today. Westerly upslope flow will keep 
snow showers going over the northeastern mountains especially this 
morning where a couple more inches of snow may fall. Will continue 
the advisory for the Northern Blues into mid morning but drop the 
advisories for Wallowa County and the Grande Ronde Valley at 4 am as 
scheduled. Otherwise expect just a few mountain rain/snow showers to 
continue through the forecast period as flat nw flow aloft 
continues. Temperatures will moderate Wednesday and Thursday with 
highs in the mid 40s to lower 50s lower elevations both days...with 
30s to lower 40s mountains. Snow levels will rise to 3000-4000 feet 
by Thursday. The surface pressure gradient will tighten on Wednesday 
which will cause an increase in sw-w winds across the lower 
elevations of northern Oregon and southern Washington. Right now it 
looks like winds on Wednesday will be mainly 20-25 mph with gusts to 
35 mph or just below advisory criteria. Winds will diminish 
Wednesday evening. 78 

.LONG TERM...Friday through Monday...Friday a warm front with 
associated precipitation moves across the region with snow levels of 
3000-4000 feet. Friday night through Saturday night a large 
mid/upper level trough offshore pushes a cold front slowly through 
the forecast area with the left exit region of an upper level jet 
stream providing good dynamic lift. Sunday and Monday an mid/upper 
level short wave ejects from the base of the longwave trough and 
moves across the interior Pacific Northwest and pushes the cold 
front into Idaho. On Sunday, Another fast moving mid/upper level 
shortwave moves rapidly across the region for another round of 
precipitation with snow levels lowering to around 1000 feet by 
daybreak on Monday.  Polan

&&

.AVIATION...12Z TAFs...The mid/upper level shortwave that triggered 
the snow showers overnight at KPDT has exited the region. As such 
kept VCSH at KALW and KPDT until 13Z. KPDT radar indicates snow 
showers over the Blue Mountains early this morning. A NW flow aloft 
will yield scattered orographic snow showers over the Blue Mountains 
through this morning with snow showers decreasing in areal coverage 
this afternoon into this evening over the Blues. After 20Z only 
isolated lingering mountain snow showers are expected and all TAF 
sites should observe VFR conditions over the next 24 hours. 
Southwest to west winds 10-20 knots gusting to 25 knots can be 
expected through this afternoon with winds diminishing tuesday. 
this evening and overnight to 5-10 knots.  Polan

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  44  31  51  32 /  30  10  10  10 
ALW  44  35  54  36 /  30  10  10  10 
PSC  47  33  54  33 /  10  10  10  10 
YKM  46  26  51  29 /  10  10   0  10 
HRI  47  31  52  33 /  10  10  10  10 
ELN  41  25  47  30 /  10  10   0  20 
RDM  40  24  48  22 /  20  20  10   0 
LGD  39  29  44  28 /  50  20  20  20 
GCD  36  23  45  19 /  50  20  10  10 
DLS  48  33  53  34 /  10  20  10  20 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 AM PST this morning for ORZ502.

     Winter Weather Advisory until 4 AM PST early this morning for 
     ORZ049-050.

WA...Winter Weather Advisory until 10 AM PST this morning for WAZ030.

&&

$$

78/99/99

[ W WA | SW WA and W OR | SE WA and NE OR | NE WA and N ID ]

Northeastern Washington and Northern Idaho


542 
FXUS66 KOTX 281234
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
434 AM PST Tue Feb 28 2017

.SYNOPSIS...
Snow showers will linger over the Idaho Panhandle through the day.
The most significant accumulations will come to an end by mid
morning. The remainder of the week into the weekend will remain
active with the mountains receiving several rounds of snow.
Wednesday and Friday have the potential to be windy with gusts up
to 40 mph over the open country of central and eastern Washington.

&&

.DISCUSSION...

Today: The Idaho Panhandle will continue to receive clusters of
snow showers this morning. As of 230 AM, the axis of our cold
500 mb trough was over the Panhandle. The -36C to -38C
temperatures at 500mb combined with 30-40kts of 850-700mb flow
was a good environment for vigorous orographic snow showers. By
10 AM, mid-level dry advection and warming aloft will begin to 
slowly stabilize the environment over the Panhandle. A surface low
currently over the north Idaho Panhandle will also shear eastward
leading to the demise of a deformation band over the Sandpoint, 
Bonners Ferry, and Metaline Falls areas. The Winter Storm Warnings
for Coeur d'Alene and the Idaho Palouse will be allowed to expire
since most of the snow shower activity will be pushing east 
within the next couple of hours. Same story for the Winter Weather
Advisory for the Washington Palouse. By late morning, what 
showers that remain over the Idaho Panhandle should be losing 
intensity. As pavement temperatures warm, we should be able to 
allow our remaining winter highlights expire at 10 AM. Much of 
central and eastern Washington should enjoy some sunshine today as
dry air overtakes the Inland Northwest.

Tonight and Wednesday: Our next storm system will spread moisture
into the region overnight tonight into Wednesday. The surface low
with this storm will track well north of our region, emerging east
of the Continental Divide Wednesday morning in central Alberta. A
powerful west to northwest jet will produce a pronounced
precipitation shadow over the Columbia Basin late tonight into
Wednesday. The Cascades and mountains of the Idaho Panhandle will
receive more moderate snow accumulations while our lowland areas
experience increasingly gusty west/southwest winds. Sustained
winds of 20 to 25 mph with gusts up to 40 mph are expected over
the Palouse, West Plains, and Upper Columbia Basin. The Waterville
Plateau will have the potential for gusty winds (30-40mph) and 
wind prone ridges in the central Washington Cascades will gust to
50mph or more. /GKoch

Thursday through Sunday....The high index nearly zonal flow pattern 
pushing wet weather systems through The Pacific Northwest allows an 
extremely positively tilted moisture plume to sag through it 
Thursday at the same time the jet stream shows a bit of a retreat to 
the northeast, thus a rather wet/snowy Thursday is the expectation 
with lesser wind compared to Wednesday (and Friday).
On Friday the jet stream is again back in close proximity as the 
longwave pattern shows a deeper longwave trof off the coast with 
very moist disturbances fluxing up along the edge of it and over 
Eastern Washington and North Idaho with the windy conditions. 
Rain/snow shadow development on the lee side of the Cascade Crest to 
result in lower pops in the Columbia Basin. Saturday the moisture 
plume is sagged further south thus allowing a slight decrease in 
pops near the northern edge of the forecast area with pops more 
focused roughly along and south of a line from the Blue Mountains up 
to the North Idaho Central Panhandle Mountains. Later Saturday and 
on through Sunday the highly conditionally unstable air in the cold 
trof to the west approaches closer. Some of the model guidance 
suggests potential for a lowering of the trop and resulting increase 
in winds (windy/gusty conditions) Saturday night. With all the 
mixing brought about by this very progressive weather pattern 
forecast temperatures are expected to remain near normal, and 
perhaps even above normal on Friday with Friday potentially being 
the warmest day of the seven day forecast. /Pelatti

Sunday Night through Wednesday: The warm atmospheric river event
will continue to bring waves of moisture into the Pacific
Northwest. Warm air associated with this event will help the 
precip type transition from snow to rain through the period for
the Columbia Basin and valleys. Small streams and creeks could
rise as snow melt and prolonged rain fall impact the region. Highs
will be around the mid 30s to low 40s and lows will hover around 
freezing. /JDC


&&

.AVIATION...
12z TAFs: Improving conditions are expected for all of our TAF
sites this morning as dry air overspreads the Inland Northwest
behind our departing storm system. Snow showers in the Pullman and
Lewiston areas are expected to dissipate this morning with the
arrival of drier air, but some widely scattered snow showers may
redevelop this afternoon courtesy of low to mid level afternoon
destabilization. Another system will spread moisture into the 
region late tonight. The strong west northwest jet will produce a 
pronounce precipitation shadow over central Washington, but the 
Cascades and Panhandle mountains will receive more precipitation. 
Low level wind shear has been added to the Wenatchee TAF as strong
west winds develop 2000-5000 feet above the surface. /GKoch

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        32  28  44  29  40  32 /  10  30  10  20  60  60 
Coeur d'Alene  33  26  41  28  40  31 /  40  60  50  50  60  80 
Pullman        33  29  44  32  43  35 /  30  30  30  20  40  70 
Lewiston       40  32  52  34  48  36 /  40  10  20  10  20  40 
Colville       35  22  43  27  43  32 /  10  50  20  40  50  70 
Sandpoint      33  24  41  28  40  31 /  60 100  80  60  60  80 
Kellogg        31  24  38  29  39  32 /  90 100 100  80  80  90 
Moses Lake     38  29  51  27  46  33 /  10  10  10  10  20  20 
Wenatchee      35  28  50  28  43  32 /   0  10  10  10  30  30 
Omak           33  23  47  25  42  30 /  10  20  10  10  30  20 

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 7 AM PST this morning for Northern 
     Panhandle. 

     Winter Storm Warning until 10 AM PST this morning for Central 
     Panhandle Mountains. 

     Winter Weather Advisory until 10 AM PST this morning for Lewis 
     and Southern Nez Perce Counties. 

WA...Winter Weather Advisory until 7 AM PST this morning for 
     Northeast Mountains. 

     Winter Weather Advisory until 10 AM PST this morning for 
     Northeast Blue Mountains. 

&&

$$

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