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Western Washington


287 
FXUS66 KSEW 232247 AAA
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
345 PM PDT Mon Apr 23 2018...Updated

Updated marine headlines.

.SYNOPSIS...A ridge aloft will move into Eastern Washington
tonight and persist into Thursday. Surface high pressure over 
Southeastern British Columbia combined with a developing thermal 
trough of low pressure along the coast will give low-level 
offshore flow. The ridge aloft and offshore flow at lower levels 
will give highs into the 70s across much of the area Tuesday and 
Wednesday, and highs will reach into the lower 80s in some 
locations on Thursday. An upper level low will approach from the 
southwest late in the week bringing a return to seasonably cool 
temperatures and a chance of showers Friday through next weekend. 

&&

.SHORT TERM...Other than a few cirrus, conditions are clear across
the region and temperatures are warming rapidly as offshore flow 
develops. To varying degrees, high pressure aloft and low level 
offshore flow will give very nice weather to the area through 
Thursday! 

After highs near 70 today, we will see highs into the 70s on 
Tuesday (about 5 degrees higher than today) with a possible lower 
80 in the far south interior. Low temperatures tonight will fall
into the 30s in the typically coldest locations (like Arlington
and Olympia Airport), but will generally be about 5 degrees warmer
than this morning. Low temperatures will warm further on Tuesday
night as the air mass continues to warm.

The high temperature forecast for Wednesday is a bit trickier than
the one for Tuesday. A weak shortwave trough will be moving over
the top of the west coast ridge Tuesday night allowing heights to
fall a bit and offshore flow to relax somewhat. Low level 
thickness forecasts from all of the models, however, show a 
slight increase by Wednesday afternoon as ridging and offshore 
flow strengthens. So, temperatures on Wednesday are likely to be 
the same or a degree or two higher than on Tuesday. High 
temperatures Tuesday and Wednesday will threaten the record daily 
maxima at many locations, but will likely fall just short.

Thursday will be the warmest day of this upcoming warm spell and
will be the warmest of the year so far. Current thinking is for in
the mid 70s to lower 80s across the interior and potentially on
the coast as the upper level ridge rebounds over the area and
offshore flow peaks. Daily record highs are a bit warmer on
Thursday, so again records will be threatened - but temperatures
will likely fall just short.

Forecast temperatures are a blend of the previous forecast and a
mean of the various short-term models. Albrecht

.LONG TERM...There continues to be rather large differences 
between the GFS solution and the ECMWF/Canadian solutions today. 
All models agree that a marine push will begin Thursday evening, 
but the ECMWF/Canadian solutions hold most of the precipitation 
just to the south of the forecast area as a weaker shortwave 
trough rotates around a low that will move inland over the 
southern half of Oregon. The GFS is much more robust with the 
strength of the shortwave trough and is farther north with its 
track. The GFS develops a rather heavy rain band with a 
deformation zone over Western Washington Friday through Saturday 
night. The GFS total precipitation amounts are well over an inch 
at SeaTac and some solutions are wetter still. The ECMWF is much, 
much more tame. At this time, a model blend was used to populate 
the forecasts and were weighted more heavily toward the ECMWF. The
models are all showing good continuity with their previous 
solutions; maybe one of them will 'give in' on the next couple of
forecast cycles. 

One sure bet for the upcoming weekend will be much cooler 
temperatures.
Temperatures will fall significantly on Friday. A model blend would 
suggest upper 50s for highs on Friday while the ECMWF would suggest 
highs more into the mid 60s. A weighted blend toward the ECMWF was 
used today. After Friday, temperatures fall to a few degrees below 
for the weekend as deeper cloud cover and precipitation chances 
increase and the air mass aloft continues to cool. Albrecht

&&

.AVIATION...An upper level ridge is over the region with dry 
stable air. At the surface there is high pressure centered over 
southeast British Columbia and thermally induced low pressure 
extending north along the Oregon coast. 

KSEA...Clear skies and a northerly breeze.

&&

.MARINE...High pressure inland and thermally induced low pressure 
along the Oregon and Washington coast will persist until about 
Thursday morning. Northerly flow down Puget Sound should peak around 
20kt this afternoon and evening but overall the flow should become 
become more easterly for some areas. Small craft advisory strength 
easterlies are forecast at the West Entrance of the Strait of Juan 
de Fuca around Cape Flattery. The thermally induced low pressure 
will move inland on Thursday with onshore flow developing Thursday 
night and Friday.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory in effect til noon PDT Tuesday for the 
     Coastal Waters From Cape Flattery To James Island Out 10 Nm
     and the West Entrance U.S. Waters Strait Of Juan De Fuca.
    
     Small Craft Advisory in effect until 900 PM PDT this evening 
     for Puget Sound and Hood Canal.

&&

$$

www.weather.gov/seattle

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

Southwestern Washington and Western Oregon


149 
FXUS66 KPQR 232057
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
200 PM PDT Mon Apr 23 2018

.SYNOPSIS...High pressure over the region will bring lots of 
sun and warm temps to much of the region through mid week. Cooling 
along the coast begins Wed, and spreads inland Thu and Fri. An upper 
level low approaching the north CA coast late in the week will 
spread a chance for showers and maybe even a few thunderstorms to 
the reigon late Thu and Thu night. Low pres will stick around 
through the weekend keeping chances for showers going along with 
seasonably cool temps. 

&&

.SHORT TERM...Tonight through Thursday...An upper level ridge seen 
in water vapor pictures Mon afternoon along 130W, will move inland 
over the Pacific NW tonight, then linger through Wed. With a thermal 
induced trough along the coast, most inland areas will see an 
offshore flow that will help to keep skies mostly clear through Wed. 
Models indicating 850 mb temps continue to warm Tue and Wed, reacing 
close to 15C by Wed, which should be good for highs into the lower 
80s inland valleys, and which may also challenge some of our high 
temp records. Along the coast onshore flow appears likely to develop 
late Tue, then again Wed as the surface trough begins to shift 
onshore. The turn to onshore flow, earliest along the central OR 
coast, will cut off the diurnal temp rise along the coast earlier 
each day. 

By Thu models develop a sse flow over the region as a large upper 
level low approaches the north CA coast. As the upper heights begin 
to come down and the surface trough moves inland, a developing 
onshore flow will begin to bring temps down over the interior as 
early as Thu, although some areas may not see much cooling Thu. The 
se flow and some diffluence aloft may begin to destabilize the 
atmosphere enough Thu afternoon to introduce a slight chance for 
thunderstorms to the Lane County Cascades. 

.LONG TERM...Thursday night through Monday...While models agree on 
the upper low off the north CA and south OR coast eventually moving 
inland, models diverge some on how quickly that happens, and what 
happens afterwards at the end of the weekend. As the low level flow 
likely remains onshore through the extended period, the differing 
models wind up yielding nearly the same forecast; a chance for 
showers each day with temps near seasonal normals. 

&& 

.AVIATION...VFR conditions expected tonight and Tuesday. 
Offshore flow will continue through early Tuesday before easing 
Tuesday afternoon.

KPDX AND APPROACHES...VFR conditions through Tuesday. Fairly
strong easterly wind gusts of 20-30 kt will continue through
18z-20z Tuesday, then ease off.


&&

.MARINE...Surface thermal trough along the coast will drift 
offshore tonight. This will result in winds becoming increasingly
offshore with wind gusts of 15 to 20 kts. Some isolated gusts
near 25 kts possible downwind of the coastal river gaps 
including the mouth of the Columbia River tonight. 

A longer period westerly swell arrives later tonight into
Tuesday, but wave heights remain below 10 ft. During the latter 
half of the week, a southerly wind reversal may develop along the
coast bringing some fog and low clouds. Seas likely will remain 
below 10 ft. Small craft advisory level winds could return 
towards the weekend, as a front moves into the north Oregon and 
south Washington waters. /tw

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$

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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 CWA or forecast area.

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Southeastern Washington and Northeastern Oregon


031 
FXUS66 KPDT 240245
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
745 PM PDT Mon Apr 23 2018

.SHORT TERM...Tonight and Tuesday...Ridge of high pressure will 
continue to build over the region providing clear skies and pleasant 
Spring weather conditions. Minor changes made to temperatures and 
winds for tonight and Tuesday in evening forecast update.


&&

.PREV DISCUSSION... /issued 427 PM PDT Mon Apr 23 2018/ 

SHORT TERM...Tonight through Thursday night...A ridge of high
pressure will continue to shift eastward over the inland northwest
tonight with mostly clear skies and light winds expected. A trough
extending from an upper level low over the Hudson bay will graze
eastern Washington during the day Wednesday weakening the ridge
slightly and allowing scattered mid to upper level cloudiness to
make a brief appearance. The ridge will restrengthen as the trough
departs Wednesday afternoon. Under high pressure and mostly clear
skies high temperatures will be on an increasing trend through
Thursday when highs in the lower elevations will reach the upper
70s to lower 80s - 10 to 15F above normal for this time of year.
Focus then turns to the cut-off low off the coast forecast to be
centered near 40N 135W by Thursday morning. 12Z operational GFS is
significantly slower bringing this feature onshore than the ECMWF,
Canadian, and a few GFS ensemble members keeping the region mostly
dry through Friday. Have opted toward a blend favoring the slower
ECMWF/Canadian solution while retaining an existing slight chance
of showers/thunderstorms for central/north central Oregon Thursday
night/Friday morning to give some weight to the faster GFS
solution as considerable uncertainly remains. Peck

LONG TERM...Friday morning through Monday...The big question for 
Friday through the weekend is just how quickly the mid-upper level 
ridge of high pressure along the Rockies on Friday gives way to a 
large mid-level low pressure system, which will be near 41N/129W 
Friday morning. Over the past three days the extended models have 
predicted that the ridge will eventually break down over the 
forecast area during the time frame of Friday and Saturday. Some of 
the models favor the aforementioned upper level low undercutting the 
ridge by taking a more southerly track across northern California 
and the Great Basin, which would allow wrap around moisture to bring 
showers to the forecast area. As such the forecast for Friday 
through Sunday afternoon is for a chance of showers through the 
weekend. The airmass has marginal instability Friday morning into 
Friday evening for a slight chance of thunderstorms from daybreak 
Friday through Friday evening. Monday looks to be dry due to a drier 
airmass moving into the Pacific Northwest on the heels of a 
northwest flow aloft.  Polan

AVIATION...00Z TAFs...VFR conditions with mainly clear skies for 
next 24 hours. Light winds through tonight at all TAF sites, except
10-12kt overnight at KYKM. Winds 5-12kt during the day on Tuesday.
Polan

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  38  74  44  77 /   0   0   0   0 
ALW  39  76  47  79 /   0   0   0   0 
PSC  38  77  44  81 /   0   0   0   0 
YKM  40  75  45  79 /   0   0   0   0 
HRI  37  77  44  81 /   0   0   0   0 
ELN  37  71  43  76 /   0   0   0   0 
RDM  29  74  37  80 /   0   0   0   0 
LGD  35  68  40  74 /   0   0   0   0 
GCD  37  70  41  76 /   0   0   0   0 
DLS  42  78  47  82 /   0   0   0   0 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

91/91/91

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Northeastern Washington and Northern Idaho


612 
FXUS66 KOTX 232121
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
221 PM PDT Mon Apr 23 2018

.SYNOPSIS...
The Inland Northwest will experience high temperatures in the 70s
for the remainder of the work week. Some of our typically warm
lowland spots will have a shot of 80 degrees or more Thursday and
Friday. Cooler and showery weather will likely arrive over the
weekend and linger into early next week.

&&

.DISCUSSION...

Tonight: Cumulus clouds over the mountains of the Idaho Panhandle
will dissipate early this evening with the setting sun. The Inland
Northwest will experience another mainly clear night. Our
typically chilly, sheltered locations in the valleys of northeast
Washington and north Idaho will dip below freezing for a few hours
late tonight, but the majority of the region will remain in the
mid to upper 30s.

Tuesday and Wednesday: Our warming trend will continue Tue into
Wed. Look for high temperatures to be in the 70s both days as high
pressure expands over the Western US. A weak shortwave trough is
progged by the models to dent the ridge on Wed. The most notable
weather this shortwave will produce will be some increasing high
clouds and north winds of 10 to 15 mph down the Okanogan Valley
Wed afternoon and evening. /GKoch

Thursday through Monday: Models are still showing warm and sunny 
for Thursday across the region. They disagree starting Friday and 
through the weekend with what to do with a cutoff low approaching 
northern California. The GFS continues to be consistent with 
itself, and the ECMWF is consistent with itself as well. The 
Canadian seems to have trended more towards the ECMWF, and have 
therefore trended forecast that way as well. We continue to show 
Friday as the warmest day and for now have a dry forecast for 
Friday and Friday night. Saturday through Monday we bring in a 
chance of precipitation, but have lowered the chances for 
Saturday. Sunday the EC and Canadian show some wrap around energy 
from the closed low digging into California moving up into the 
region. So have our highest chance of precipitation Sunday into 
early Monday and then begin to dry things out again.

Our warm temperatures will cause snow melt across the mountains.
Rises on local rivers and streams are expected. Many rivers are
currently forecasted to approach flood stage with a few exceeding
that. Please continue to monitor the rivers if you are planning
any outdoor activities this week into next. Water temperatures are
still quite cold and hypothermia can quickly set in. /Nisbet

&&

.AVIATION...
18Z TAFS: Mainly clear skies and light winds will be the rule
across central and eastern Washington as well as north Idaho this
afternoon through Tuesday morning. /GKoch

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        37  70  45  73  45  75 /   0   0   0   0   0   0 
Coeur d'Alene  36  71  42  73  43  74 /   0   0   0   0   0   0 
Pullman        33  70  40  72  42  76 /   0   0   0   0   0   0 
Lewiston       40  76  47  78  48  80 /   0   0   0   0   0   0 
Colville       35  74  40  76  40  77 /   0   0   0   0   0   0 
Sandpoint      33  68  37  70  40  73 /   0   0   0   0   0   0 
Kellogg        34  69  40  70  41  72 /   0   0   0   0   0   0 
Moses Lake     39  76  42  78  45  80 /   0   0   0   0   0   0 
Wenatchee      41  73  47  78  49  78 /   0   0   0   0   0   0 
Omak           36  74  44  78  45  77 /   0   0   0   0   0   0 

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.

&&

$$

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