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

Western Washington


233 
FXUS66 KSEW 201530
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
830 AM PDT Wed Sep 20 2017

.SYNOPSIS...A large upper level low will maintain a chance of 
showers and cooler temperatures over Western Washington through 
Thursday. Drier north flow aloft from an upper level ridge will 
bring more sunshine and a little warming Friday through Tuesday. 

&&

.SHORT TERM...A large upper level low remains over the PacNW with 
the main low center over Alberta. An upper level shortwave trough 
rotating around the main low was over the S WA coast this morning, 
and was dousing the central/south WA coast, the SW interior, and the 
S Cascades with rain. Models slide the shortwave trough over the S 
Cascades by 21Z, allowing the area of rain to break up. Otherwise 
the rest of W WA will have scattered showers. NAM bufr soundings 
show the lower air mass unstable up to a little above 700 MB.

As the shortwave trough slides E tonight, somewhat drier N flow 
aloft from an approaching offshore upper level ridge will develop 
over W WA. The lower air mass will still remain fairly moist on 
Thursday, so not a lot of clearing is expected. The air mass should 
be stabilizing for just a slight chance of showers. 

Dry N flow aloft ahead of the approaching offshore upper level ridge 
will strengthen on Friday for a dry day with more sunshine. High 
temperatures will warm a bit but should still be a couple of degrees 
below normal. Kam

.LONG TERM...Previous discussion from the 326 AM AFd...The medium 
range solutions were suggesting that the tail end of frontal systems 
passing to our north might bring a threat of light rain to the 
northwest part of the CWA this weekend into Monday. The GFS was 
starting to come more in line with the wetter ECMWF solution. For 
now, decided to keep the inherited dry forecast but will need to 
introduce rain if the 1200 UTC cycle continues with the idea of 
wetter conditions. At any rate, expect the ridge to be a bit dirty 
(mid and/or high clouds streaming across the area) through Monday. 

Anticipate the upper ridge to rebound the end of the period for
dry weather with near normal temps.

&&

.AVIATION...There are areas of rain or showers from about 
Hoquiam south and south of Seattle this morning--and there were some 
showers up over the San Juans. An upper level trough is over the 
region with light flow over Western Washington. Drier northerly flow 
will develop slowly and northerly flow aloft will develop so that 
will help drive the system over Oregon slowly away. There is some 
clearing north of Seattle this morning and overall more clearing 
from the north is likely through this evening before low clouds 
redevelop overnight due to the light flow, stabilizing air, and low 
level moisture.

KSEA...Winds should come around to light nw today and most of the 
showers should stay south of the area now.

&&

.MARINE...A weather system is over the region but the blustery 
pressure gradients are south of the WA/Oregon border--Western WA 
has rather light gradients. Weak low pressure will remain over the 
WA coastal waters through Thursday and then high pressure will build 
Friday and Saturday.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 6 PM this evening to 2 AM PDT Thursday 
     for Coastal Waters From Cape Flattery To James Island 10 To 
     60 Nm-Coastal Waters From James Island To Point Grenville 
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape 
     Shoalwater 10 To 60 Nm.

&&

$$

www.weather.gov/seattle

An illustrated version of this forecast discussion can be seen at
www.wrh.noaa.gov/sew/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


060 
FXUS66 KPQR 201726 CCA
AFDPQR

Area Forecast Discussion...Correction
National Weather Service Portland OR 
955 AM PDT Wed Sep 20 2017

.SYNOPSIS...Showers across northwest Oregon and southwest Washington
as an upper low moves over the area today. Cold air aloft will
continue to keep snow levels low and allow a few thunderstorms to
develop over the area today. Brief heavy showers are possible today
but will become lighter after sunset. The primary upper
trough/low will linger over Washington and Oregon Thursday then
slowly move east by the weekend, with showers slowly decreasing. High
pressure builds in over the weekend and continues into early next
week for some great late September weather in store for the region,
with cool nights with patchy fog but mild sunny days.
&&

.SHORT TERM...Today through Friday...Deformation band precipitation
associated with upper low and surface trough is near, and north of
the Columbia river this morning with some moderate showers to the
south over the remainder of northwest Oregon. Snow levels will be 
near their lowest levels today, between 5000 and 5500 feet in the 
north with some snow down to as low as 4500 feet as the cold air 
associated with the upper tough moves over. Don't expect much 
accumulation below 5000 feet but I have extended the Winter weather 
advisory through early evening for the higher elevations. Snow will 
taper off this evening. Model soundings agree that there should 
still be enough instability this afternoon for a continued threat of 
thunderstorms. There is not as much shear today as yesterday as the 
upper jet shifts south but surface heating from sunbreaks should 
allow for some isolated stronger storms. 

A threat of flash flooding will still exist this afternoon in
possible heavy showers but that threat will decrease after sunset as
heavier shower decrease. Will extend the flash flood watch through
early evening and then the threat will end for the next week as
ridging and dry fall weather returns. Schneider


.LONG TERM...Friday night through Tuesday...No updates, Previous 
discussion follows. An upper ridge builds over the NE Pacific this 
weekend and slowly expands into the Pacific Northwest early next 
week as the inland upper low finally but slowly moves eastward. This 
will bring drying and warming to the area, though the warming will 
be more of the fall variety than of the summer variety as the ground 
is wetter and we will probably see areas of radiational morning low 
clouds and fog as nights are lengthening and cooling. The models 
show some energy riding over the upper ridge to our north that may 
keep some low clouds along the south Washington and far north Oregon 
coasts at times, especially in the nights and mornings. Tolleson &&

.AVIATION...Mainly VFR conditions today with showers. Brief MVFR
vis and/or cig possible with heavier showers. Small chance of a
thunderstorm through the evening hours. 

KPDX AND APPROACHES...VFR with showers and small chance of TS.
Possible brief MVFR with any heavier showers. Bowen

&&

.MARINE...Dropped Small Craft Advisory for the waters within 10
nm of the coast this morning as buoys have been reporting
winds below 20 kt. Seas dropping as well, but still 10 ft at buoy
89, so kept SCA in place for offshore waters. Seas may still come
up a little bit to as high as 11 ft before finally dropping below
10 ft tonight or early Thursday morning.

Quieter marine weather is expected by late this week and into 
the weekend as typical summertime northerlies return to the area.
Bowen 

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 8 PM PDT this evening for 
     Northern Oregon Cascades.

     Flash Flood Watch until 8 pm this evening for Cascades in Lane 
     County-Central Columbia River Gorge-Northern Oregon 
     Cascades-Western Columbia River Gorge.

WA...Winter Weather Advisory until 8 PM PDT this afternoon for South 
     Washington Cascades.

PZ...Small Craft Advisory for winds until 2 PM PDT this afternoon 
     for Waters from Cape Shoalwater WA to Cascade Head OR from 
     10 to 60 NM-Waters from Cascade Head to Florence OR from 
     10 to 60 NM.

     Small Craft Advisory for hazardous seas until 5 AM PDT Thursday 
     for Waters from Cape Shoalwater WA to Cascade Head OR from 
     10 to 60 NM-Waters from Cascade Head to Florence OR from 
     10 to 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 1 PM 
     PDT this afternoon.

&&

$$

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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.

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

Southeastern Washington and Northeastern Oregon


748 
FXUS66 KPDT 201735 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1035 AM PDT Wed Sep 20 2017

Updated aviation discussion

.UPDATE...A band of moderate showers is moving through Walla 
Walla and Meacham this morning. Additional showers are expected
with an upper level low moving over southeastern WA today. A vort
max associated with a jet max will move over WA/OR this 
afternoon. The colder air aloft from the low and dynamic lift from
the jet max may trigger a few thunderstorms this afternoon. 
Coonfield

&&

.AVIATION...18Z TAFs...An upper level trough will continue to send 
mostly cloudy skies and unsettled weather across the area for the 
next 24 hours. Conditions will be mainly VFR, though MVFR CIGs and 
visibilities may occur with some moderate rain showers and or 
thunderstorms at times through around 02Z this evening. Thunderstorm 
activity will be too limited to mention at any TAF site. After 02Z 
cloud cover will be more scattered to broken and there will be a 
break in the rain showers until they begin returning around 15Z. 
Winds will increase today to 10-20 kts sustained with gusts to 25-30 
kts mainly from 18z-03z at KRDM, KBDN, KDLS, and KPDT. KYKM, KPSC 
and KALW will generally remain below 15 kts for the next 24 hours. 
Perry

&&

.PREV DISCUSSION... /issued 300 AM PDT Wed Sep 20 2017/ 

SHORT TERM...Today through Thursday night...KPDT radar and surface 
observations indicate rain showers south of a line from White Swan 
to Kennewick to Dayton early this morning. The showers are being 
triggered by dynamic lift associated with the left exit region of an 
upper level 125 mph jet stream around 30000 feet. Upstream a 
mid/upper level shortwave offshore of the Washington coast will move 
inland and east of the Cascades today and deliver categorical rain 
accumulations in the Blue Mountain Foothills and the Blue Mountains.
The shortwave will remain over the region through tonight and 
the sweep into Idaho by day break Thursday  for unsettled conditions.
Polan

LONG TERM...Friday through Wednesday...Models in good agreement 
that the persistent cold upper level trough will finally exit the 
region towards the end of the week and be replaced by an upper level 
ridge of high pressure for the first of next week. What the models 
do not agree on is the amplitude and location of the highs ridge 
axis during this time. So, will see a few lingering showers mainly 
in the eastern mountains Friday and possibly into Saturday before 
the ridge begins to build into the region from the west. With the 
ridge intensity and position uncertain but known to be in general 
over the region there will be a warming trend heading into the 
weekend and then remain warm into the first of the week. Overall the 
forecast looks dry after the trough exits but the uncertain position 
of the ridge will lead to some uncertainty in the temperature 
forecast for the first of the week.  

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  43  58  42 / 100  40  20  20 
ALW  57  44  59  44 / 100  40  20  20 
PSC  59  43  63  43 /  90  20  10  10 
YKM  58  40  61  42 /  60  20  10  10 
HRI  60  44  62  43 / 100  20  10  10 
ELN  57  40  59  41 /  40  20  10  20 
RDM  55  31  53  33 /  70  40  20  20 
LGD  53  39  52  35 /  90  60  30  30 
GCD  52  38  51  37 /  80  60  30  30 
DLS  60  46  62  48 / 100  30  10  10 

&&

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

$$

76/83/83

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

Northeastern Washington and Northern Idaho


915 
FXUS66 KOTX 201800
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1100 AM PDT Wed Sep 20 2017

.SYNOPSIS...
Cool, showery and breezy weather will continue today along with
the potential for high mountain snow and isolated thunderstorms.
A swath of moderate rain should span over northern Oregon into 
southeast Washington and the southern Panhandle today. Hit and 
miss showers are expected Thursday and Friday before a drier and 
warmer pattern returns for the weekend and early next week.

&&

.DISCUSSION...
Today through Thursday: The cold upper level trough will keep the
Inland NW cool and showery with disturbances in the flow enhancing
the shower development. Currently there's a wave moving onto the
coast, which is expected to track along the WA/OR border through
the day. A fragmented low level boundary lies there and is getting
enhanced by the approaching feature. Radar returns are increasing
from the Gorge to the foothills of the Blue mountains, and looks
to spread toward the LC valley into the Camas Prairie. 00z runs
were keeping the bulk of the precipitation south of region,
although the 06z nam is now inching northward. Could see the rain
band increase across the southern Basin into the Palouse this
morning. Northcentral WA will remain on the drier side today,
although surface based instability should increase convection in
all areas by afternoon. Temperatures will remain on the cool side
similar to yesterday, while breezy west to southwest develop
especially this afternoon. Light amounts of high mountain snow is
possible again with heavier showers. Will keep a mention of 
thunder across the southeast and northeast corners where the 
instability is the strongest and the upper trough axis will 
reside. By tonight into Thursday, the upper trough pivots into 
north Idaho, while a moist northeast flow spills down from BC. 
Anticipate more cloud cover and spotty showers increasing from 
northwest to southeast through Thursday. Winds will also increase 
out of the north by Thursday afternoon as cool temperatures 
persist. /rfox. 

Thursday night through Saturday...The upper level low will slowly
move through the region through Friday, meanwhile high pressure 
will begin to nose into the region from the west. Scattered 
showers will remain in the forecast through Friday for the 
mountains ringing the Columbia basin. By Saturday the ridge will 
have pushed far enough into the region for the flow to become 
northerly. This will put the focus of the showers along the 
Idaho/Montana. Any precipitation will be light. Temperatures will 
remain chilly Friday and Saturday but will begin to warm a few 
degrees each day. 

Saturday night through Wednesday...Saturday through Tuesday...The
ridge of high pressure will slowly move into the region through
this period. Some moisture moving over the building ridge may
result in a few showers for the north Cascades and the Idaho
Panhandle on Sunday and Monday, but a this time the chances are
small enough to leave any showers wording out of the forecast.
Otherwise this will be a warming and drying period. Temperatures
will increase 2 to 4 degrees each day and will approach seasonal
normals by Tuesday and Wednesday. Tobin 

&&

.AVIATION...
18Z TAFS:A disturbance is tracking along the WA/OR border today. 
This will focus the best chance of rain and rain showers across
southern WA. Showers could extend as far north as KGEG-KSFF-KCOE
taf sites aft 21Z. Showers are expected to decrease after 03z, 
and could see cigs drop to MVFR to local IFR for a few hours. 
Partial clearing possible early this evening, before mid and high
clouds increase from the north overnight and spotty mountain 
showers. Showers are expected to develop around 14Z around 
Spokane/COE area. 
 

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        53  38  54  40  57  41 /  30  20  30  10  10  10 
Coeur d'Alene  52  39  54  36  57  36 /  30  20  40  20  10  10 
Pullman        52  37  55  36  56  37 /  80  60  20  20  10  10 
Lewiston       56  43  60  43  63  43 /  90  60  20  20  10  10 
Colville       58  40  60  34  62  36 /  40  20  30  10  10  10 
Sandpoint      52  39  53  33  57  32 /  60  20  50  20  10  20 
Kellogg        48  37  50  34  52  33 /  80  60  60  30  20  20 
Moses Lake     61  40  63  41  66  41 /  20  10  10  10  10  10 
Wenatchee      63  45  62  44  67  47 /  20  10  20  10  10  10 
Omak           64  43  64  39  66  40 /  20  20  20  10  10  10 

&&

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

&&

$$

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