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

Western Washington


182 
FXUS66 KSEW 211012
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
313 AM PDT Sat Sep 21 2019

.SYNOPSIS...High pressure will keep conditions dry and warm today 
although some clouds will be present. A cold front will spread rain 
through the area on Sunday. Wet and showery weather will continue 
through early next week with temperatures trending below normal. 

&&

.SHORT TERM /TODAY THROUGH MONDAY/...Current IR satellite shows 
fairly clear in the mid and upper levels while switching to lower 
levels the beginnings of some fog development can be seen...mainly 
within the more prone areas of the CWA.

As one would expect from such conditions...an upper level ridge is 
in place over W WA this morning and will weaken as well as move 
eastward throughout the day today. This will bring about the warmest 
temperatures of the forecast period with most lowland locations 
reaching highs in the mid to upper 60s...with maybe an isolated 70 
here or there. 

An approaching cold front tonight will kick off a 
period of active weather...both in the short and long term. This 
feature will make it to the coast late tonight but will not begin 
its inland push until early Sunday morning. Rain will be the order 
of the day for the most part with a transition to showers expected 
in the afternoon as the front slowly moves away. A brief break in 
the action is expected during the overnight hours Sunday night into 
early Monday morning...but a system passing just to the north will 
have enough moisture sag down over the Canadian border to keep PoPs 
in the forecast for north of Seattle most of the day before a 
southward push will spread the chance of rain over the entire CWA 
Monday night. Temps in the lowlands during this period will cool 
with afternoon highs Sunday in the lower to mid 60s and ranging in 
the upper 50s to mid 60s Monday.  SMR

.LONG TERM /TUESDAY THROUGH FRIDAY/...There are hints at a break in 
the action Tuesday as a large scale trough shifts more toward the 
center of the US...the ECMWF showing this a bit better than the 
current GFS...but models come back in agreement that another large 
scale trough will begin to set up shop over the area starting 
Wednesday night with a series of upper level lows dipping down into 
the area and making for a generally wet remainder of the week. 
Models do disagree on timings and paths of these lows however...so a 
break or two in the action is certainly possible. For example...the 
GFS tries to push an upper level low south of the area to the CA/OR 
border Friday which would make for a potentially dry day...but the 
ECMWF keeps the system further north close to the WA/OR border which 
would keep the potential for rain going. Opting to split the 
difference and thus advertise a generally wet pattern until a more 
concrete consensus emerges.  Temps will continue their cooling trend 
through this period. Lowland highs will start off Tuesday in the 
lower to mid 60s but fall into the mid to upper 50s Thursday which 
is cooler than what would normally be seen this time of year.  SMR

&&

.AVIATION...Northerly flow aloft will transition more westerly to 
southwesterly today as an upper level ridge slides over the area. 
Patchy stratus over W WA at this hour with areas of LIFR over the 
Sound and MVFR/IFR across portions of the interior. Some VFR will 
become MVFR/IFR this morning as stratus is expected to become more 
widespread. Fog at KPWT into the morning with fog possible at KOLM. 
Cigs will transition to VFR by early afternoon as stratus clears. 

The next frontal system will approach the area later today through 
tonight with the next chance for rain and lower ceilings. Winds 
generally southerly through today 4 to 8 knots. JD

KSEA...IFR cigs at this hour with MVFR/IFR through the morning. 
Stratus will clear by midday and improve to VFR for the afternoon. 
Winds southerly 4 to 8 knots. JD

&&

.MARINE...Lighter onshore flow through today. A frontal system will 
move through the area late tonight through Sunday. Small Craft 
Advisory issued for the coastal waters with increased southerlies 
ahead of the front tonight into early Sunday. Small Craft westerlies 
following the frontal for the coastal waters through Sunday night 
with SCA level winds possible in the central and eastern portions of 
the Strait of Juan de Fuca Sunday night. Another front will slide 
through Monday into Monday night across the area. JD

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 2 AM Sunday to 2 AM PDT Monday 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.

     Small Craft Advisory from 2 AM to 8 AM PDT Sunday for Coastal 
     Waters From Cape Flattery To James Island Out 10 Nm-Coastal 
     Waters From James Island To Point Grenville Out 10 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out 
     10 Nm.

&&

$$

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


826 
FXUS66 KPQR 211041
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
341 AM PDT Sat Sep 21 2019

.SYNOPSIS...High pressure will result in less clouds and slightly
warmer temps today, especially in the afternoon. However clouds will
be on the increase again tonight ahead of a cold front that will
spread more rain across the forecast area Sunday. After what may be
the coolest night so far this season Sunday night, dry and mild
weather is likely Monday. Additional frontal systems may bring more
wet weather Tuesday and again later in the week, with temperatures
remaining a little cooler than typical for late September.

&&

.SHORT TERM...Today through Monday...Low clouds and patchy fog are
expanding across portions of the forecast area, though dry weather
generally prevails early this morning. Very shallow instability was
just enough to produce a shower at Astoria at 2 AM, but any lingering
shower activity this morning will be isolated, light, and mostly
confined to coastal areas. Otherwise, areas of morning low clouds and
fog will give way to increasing sunshine throughout the day, allowing
temperatures to climb close to late-September normals with lower to
mid 70s for the inland valleys and mid 60s to lower 70s along the
coast.

Model time-heights and 00z HREF suggest high clouds will increase and
thicken this evening as a frontal system now crossing 135W-140W
approaches the region. Rain will likely move onshore by dawn Sunday,
then spread inland and south across the forecast area during the day
Sunday. Jet forcing continues to look weak ahead of this system, with
winds generally 50 kt or less above at 500 mb and above. This will
keep winds modest ahead of the front, and should limit the potential
for orographic enhancement rainfall as the front moves through.
Therefore we are expecting QPF to be more uniform across the area
than the past couple fronts, at least based on terrain. Most
locations in our forecast area should receive around 0.25" from this
system, plus or minus 0.10" or so. Model soundings suggest some weak
instability/thin CAPE along and just behind the front, which may
introduce convective elements which could locally push rainfall into
the 0.50 to 1.00" range. There will be a brief window for isolated
thunder Sunday afternoon and evening as the associated cold pool
aloft swings through. The 06z NAM continues to suggest a capping
inversion will quickly develop around 700 mb Sunday evening, which
should cause showers to taper off quickly overnight.

High pressure builds into the region Sunday night and early Monday,
which may lead to rapid clearing for the valleys. Given the cool air
mass left behind (with 850 mb temps around +5 deg C) and improving
conditions for radiational cooling, the stage may be set for the
coolest night so far this season for many locations within the
forecast area. Most locations will likely dip well into the 40s
Sunday night, with some higher elevation valleys possibly getting
into the upper 30s. Is this enough for records Monday? Not even
close. The record low for Monday is a frosty 31 degrees at Hillsboro
and Eugene, while the record is 40 for PDX. Our forecast lows for
Monday are a good 10 or more degrees warmer than these temperatures.
Still, it will be a noticeable touch of autumn after a summer where
mild to warm nights have been the norm.

After a cool start with areas of valley fog Monday morning, high
pressure should result in increasing sunshine Monday afternoon with
temperatures rebounding to the mid to upper 60s for the lowlands. One
tricky aspect about Monday may be how slow morning fog/low clouds are
to clear; with little low-level flow to speak of west of the
Cascades, mixing may be slower than usual to occur. With Monday being
the first day of astronomical autumn, the sun isn't as strong as it
was a few weeks ago but should still be enough to poke some decent
sunbreaks into the stratus deck Monday afternoon.  Weagle

.LONG TERM...Monday night through Friday...Strong but flat upper
level ridging develops across the NE Pacific Monday and Tuesday,
resulting in fairly strong zonal flow into the BC/WA through midweek.
This may clip our primarily our northern zones with some light rain
at times, mainly late Monday night/early Tue and again Wed night.
Areas Portland-Tillamook northward will likely remain cloudier
through midweek than areas to the south, due to their proximity to
the above-mentioned zonal jet. Therefore areas Salem southward have a
better chance of reaching the 70s Tuesday and potentially Wednesday,
though our forecast for Wed is a little cooler due to the potential
for increasing high clouds. Zonal flow begins to buckle Wednesday
night as a deep upper trough begins to develop over western Canada,
pushing into the Pac NW Thursday and Friday. The 00z ECMWF remains
more amplified/less progressive with the late-week upper trough,
keeping the trough axis offshore through Saturday while the 00z GFS
pushes the trough axis onshore by Friday. Either solution would be
chilly for our forecast area, but the placement is important in
determining whether the bulk of associated shower activity remains
over our forecast area or east of the Cascades, and whether or not
snow levels will dip low enough to bring the first snow of the season
to many of our ski resorts and Cascade passes.	Weagle 

&&

.AVIATION...VFR conditions prevailing but spots of MVFR and IFR
have developed at the coast and inland with low stratus or fog.
There is also a layer around 3500-5000 feet likely extending off
the Cascades into parts of the Willamette Valley. GOES-W flight 
category probability product trending towards higher probability 
of low MVFR to IFR conditions over the past few hours. Guidance 
and overall synoptic pattern indicate that low MVFR to IFR 
conditions will become more widespread this morning. Visibility 
also likely to be reduced at times below 1 SM in fog. It may be a
battle between low MVFR stratus and IFR fog for this morning. 
Model BUFR soundings (and current cloud trends) show low MVFR 
cigs developing in some locations and may hinder or prevent fog 
from developing. Whatever develops, should generally see 
improving conditions by 18Z, with VFR conditions likely around 
20Z. The north coastal areas may hang on to MVFR conditions 
through 00Z.

Next front moving to the coast late tonight and inland Sunday
bringing rain with MVFR conditions as it moves through.

KPDX AND APPROACHES...VFR conditions should give way to low MVFR
cigs around 1000-1500 ft. May also see brief IFR cigs 12-17Z. VFR
conditions expected to return by 18-20Z with cigs around
3500-4500 feet. Cloud should slowly decrease through the
afternoon. /mh

&&

.MARINE...A transient surface ridge over the waters will shift
inland this evening. A front will move across the waters tonight
and ashore Sunday morning with high pressure building over the
waters Sunday afternoon. Expect Small Craft Advisory conditions
over the northern marine zones ahead of the front. The northern
outer zones should have northwest wind gusting 25 kt into Sunday
evening as high pressure build behind the front. Right now, not
expecting Small Craft Advisory conditions for the central Oregon
marine zones but future model runs may increase winds into the
advisory category. The next front for later Monday looks to be a
little weaker than the Sunday front. 

Seas will remain in the range of 4 to 6 ft through Saturday evening. 
The cold front Sunday will boost seas into the 8 to 10 ft range 
through Sunday night. A west to northwest fetch developing in the 
northeast Pacific will bring building seas to above 10 ft around mid 
week. 

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 3 AM to 11 PM PDT Sunday for Waters 
     from Cape Shoalwater WA to Cascade Head OR from 10 to 60 
     NM.

     Small Craft Advisory from 3 AM to 1 PM PDT Sunday for Coastal 
     waters from Cape Shoalwater WA to Cascade Head OR out 10 
     NM.

&&

$$

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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


413 
FXUS66 KPDT 210906
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
205 AM PDT Sat Sep 21 2019

.SHORT TERM...Today through Monday...An upper ridge with warmer and 
dry conditions will move across the region and forecast area today. 
Winds will be light and temperatures will be pleasant in the mid to 
upper 70s in the lower elevations and mostly 60s in the mountains. 
Then a change is in store for tonight and Sunday as another upper 
trough drops down from the northwest into the region. This will 
bring a period of rain by morning and through the morning on Sunday, 
followed by instability showers Sunday afternoon and evening as the 
upper trough axis passes over the forecast area with colder air 
aloft. This instability will be too marginal to mention any 
thunderstorms, but would not rule a stray lightning strike somewhere 
in the forecast area Sunday afternoon or early evening. Temperatures 
on Sunday will only be a degree or two cooler than today due to 
mainly the southwest flow ahead of the trough axis. On Monday a 
transitory ridge will move across the region with mostly dry 
conditions. It will be a several degrees cooler behind Sunday's 
upper trough. There will be some slight increase in wind with the 
passing trough on Sunday, and then again on Monday afternoon due to 
mixing, but winds will be mostly light through the short term 
forecast period. Despite the few degrees differences in temperatures 
from day to day, temperatures will be not be too far from normal for 
late mid-late September on any of the days in the short term. 88

.LONG TERM...Monday night through Saturday...A dry northwest flow 
will be over the region Monday night through Wednesday. It will be 
warm on Tuesday with highs in the 70s and 60s in the mountains. A 
dry cold front will cross the area Tuesday with gusty west winds. By 
Wednesday night a few showers will be possible as an upper low 
starts to develop over the Northwest. The low will settle over 
Oregon by Friday with cold temperatures, continued showers and some 
snow showers above 5000 feet especially at night. Snow levels lower 
even further on Saturday with the upper low lingering. Snow showers 
will be possible down to 3500-4000 feet Saturday morning before snow 
levels rise and temperatures warm during the afternoon. Friday and 
Saturday's high temperatures could be 10 to 15 degrees below normal 
for this time of year. 78  

&&

.AVIATION...12Z TAFS...VFR conditions through the period. Just a few 
high clouds. Winds less than 10 kt except 10-15 kt at KDLS this 
afternoon. 

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  74  48  72  48 /   0   0  40  40 
ALW  76  52  77  52 /   0   0  40  50 
PSC  78  54  75  53 /   0   0  40  20 
YKM  76  49  69  45 /   0   0  60  20 
HRI  79  51  76  50 /   0   0  40  30 
ELN  74  49  67  46 /   0   0  60  30 
RDM  73  46  67  40 /   0   0  60  40 
LGD  71  47  71  48 /   0   0  40  60 
GCD  73  46  73  46 /   0   0  40  60 
DLS  78  55  70  52 /   0   0  60  30 

&&

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

&&

$$

88/78/78

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

Northeastern Washington and Northern Idaho


924 
FXUS66 KOTX 211151
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
451 AM PDT Sat Sep 21 2019

.SYNOPSIS...
Warm and dry weather is expected today, then a quick moving
weather system will bring showers Sunday. Dry weather returns
early next week, with gusty winds expected on Tuesday. Much cooler
and unsettled weather is likely late next week. 


&&

.DISCUSSION...
Today: A positively-tilted upper level ridge has begun to build 
into the region from the eastern Pacific. Mainly dry weather is 
expected across the forecast area today, with the exception of a 
few showers possible over the higher terrain of the Idaho 
Panhandle. The main forecast challenge for today will be the 
extent of low clouds and fog this morning. Early morning infrared 
satellite imagery shows patchy coverage across portions of the 
Idaho Panhandle and the NE Washington river valleys. Expect this 
coverage to slowly expand through sunrise, with the potential for 
patchy fog across the Palouse and into the Spokane area. Look for 
high temperatures this afternoon in the upper 60s to mid 70s 
across the region. 
Dang

Sunday through Monday...This period will witness the arrival and 
passage of an upper level trough with an appreciable feed of 
precipitable water. The trough will be splitting as it arrives
with the dynamic base transiting Oregon leaving the Washington 
segment a bit less energetic but still with a fairly strong mid
level frontal surface. This should be sufficient for showers in 
the cascades during the morning hours with scattered showers 
slowly advancing into the basin during the afternoon and into the
Idaho panhandle Sunday evening with some residual showers
lingering into Monday morning. Precipitation amounts don't look
very significant...perhaps a quarter of an inch in the mountains
ringing the basin with only a few hundredths of an inch and
spottier in the basin itself. 

On Monday a flat ridge in the wake of the trough will
prevail...but a strong fetch of Pacific moisture will begin to 
feed into the region. Most of this moisture will be in the form of
thick mid and high clouds with only the higher terrain especially
in the Cascades under threat for further precipitation on Monday.

Tuesday through Wednesday...A fast and flat westerly to
northwesterly flow will set up over the region during this period.
In general a rain shadow will form in the basin under this flow
with showers expected over the higher terrain ringing the basin.
The main weather issue for this period...especially on
Tuesday...will be breezy and gusty conditions in response to a 
tightening pressure gradient and momentum mixing from swift winds 
aloft down to the surface during the afternoons and early evening 
hours. This set up may result in wind gusts of 35 mph over much of
the exposed terrain of the Columbia Basin and also on ridge tops 
of the higher terrain surrounding the basin. /Fugazzi

Thursday through Saturday: A upper level trough will be digging 
into the region for this period bringing a wet and cold pattern. 
Models are in good agreement with pattern shift but differ 
slightly on timing and moisture amounts. The first push of 
moisture will be Thursday morning as the zonal flow pattern begins
to be influenced by the trough and a low along the Canadian 
border. This will bring mostly mountain showers with snow expected
above 5000ft through Thursday evening. Another low will be right 
behind the first one and is expected to dig further south through 
Oregon and bring the better chance of widespread showers across 
the entire Inland Northwest from Friday morning through Saturday. 
Winds will be slightly breezy during the afternoon mixing with 
gusts near 20mph for the South. This Low is also bringing a push 
of colder air. 

Overnight lows are expected to be in the mid 30s to low 40s. SNow
levels will be above 4000ft for Friday morning and expected to
drop to 3000ft for Saturday morning. These cold overnight temps
could bring the first freeze of the season for many locations in
the Northern Portion of Columbia Basin. Daytime highs are expected
to be in the 50s to low 60s. /JDC 

&&

.AVIATION...
12Z TAFs: An isolated shower will pass near KLWS around 12z.
Otherwise, patchy dense fog has developed near KCOE and is slowly
moving westward. This fog may bring brief MVFR-IFR conditions to 
KSFF-KGEG-KPUW, but forecast confidence remains low. Any fog that
develops should erode and become VFR after 18z.
Dang

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        69  46  71  48  65  47 /   0   0  20  40  10  10 
Coeur d'Alene  68  46  71  49  65  46 /   0   0  20  40  10  10 
Pullman        69  44  72  45  65  45 /   0   0  20  60   0  10 
Lewiston       75  52  79  55  73  54 /   0   0  20  60   0   0 
Colville       74  39  72  41  70  40 /   0   0  40  50  10  10 
Sandpoint      67  45  70  49  63  45 /   0   0  20  50  20  10 
Kellogg        64  48  70  52  63  48 /  10   0  20  60  30  10 
Moses Lake     76  47  72  45  73  47 /   0   0  40  20   0  10 
Wenatchee      74  54  67  51  69  53 /   0   0  60  20  10  10 
Omak           74  49  68  47  68  49 /   0   0  60  20  10  10 

&&

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

&&

$$

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