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Office: SEW

FXUS66 KSEW 190944
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
244 AM PDT Thu Jul 19 2018

.SYNOPSIS...An upper level low over southeastern Alaska will drop
southeastward into Southern British Columbia on Friday. The
combination of the upper low and a deep marine layer will result
in clouds and cool conditions over the area. The upper low will
move away from the area later Friday into Saturday resulting in a
clearing and a warming trend. Offshore flow and building high
pressure aloft will result in a strong warming trend starting
Sunday. Hot weather appears likely Monday through Wednesday of
next week.


&&

.SHORT TERM...Areas of cloudiness have formed over Western
Washington overnight, and lower stratus appears to be rapidly
developing across the interior. A 5000 foot deep marine layer with
a couple of cloud decks within it will result in clouds
persisting into the mid afternoon today, and high temperatures
around the area will range from the mid 60s on the coast to the
lower to mid 70s in the interior. These temperatures are about 4-5
degrees below normal for this time of year.

An upper level low that is presently centered over the Alaskan
Panhandle will drop southeastward into southern portions of
British Columbia later Friday. This upper level low will keep the
marine layer deep (but perhaps with a few less clouds on Friday).
Temperatures on Friday will be similar to what is observed today.
Low temperatures both days will generally be in the 50s.

Changes will begin to take shape on Saturday as the upper low
ejects northeastward into central Alberta and surface high
pressure starts building in its wake over southern BC. The
resulting development of offshore flow over the region will result
in the dissipation of marine clouds and gradual warming by
adiabatic compression from the easterly flow off the mountains.
Highs on Saturday will be 2-5 degrees higher than Friday across
much of the area.

The weather through the short term will be really nice across the
area with pleasant temperatures and a mix of clouds and sun.
Enjoy the cool weather, as a change to a hot weather pattern will
begin late in the weekend. Albrecht

.LONG TERM...Models are showing rather good consistency and
continuity. They all show offshore flow giving strong warming
starting on Sunday with highs getting well into the 80s across the
area, including on the coast. The Monday through Wednesday
period is looking hot across the Pacific Northwest! It also looks
like there will be no precipitation for the next 7-10 days.

Offshore flow will result in the development of a thermal trough
over the interior of Western Washington on Monday with highs in
the lower 90s in the Seattle area, and mid to upper 90s from
Tacoma, Bremerton and Shelton southward through the southwest
interior. The coast may see slight cooling as afternoon
northwesterly seabreezes kick in. Tuesday looks about the same as
Monday. Wednesday may see a slight increase in onshore flow for
minor cooling in some areas, but the heat will still be on and
dewpoint temperatures will gradually increase making for more
muggy conditions. The ECMWF shows cooler low level temperatures
than the GFS during the Monday-Wednesday period, but with 850 mb
temperatures 20-21C as seen in the GFS, the GFS temperatures
appear more reasonable. If 850 mb temperatures do reach the
20-21C range, Seattle may see mid 90s. Low temperatures Monday
through Wednesday over the urban heat island areas will likely
stay in the lower to more likely middle 60s -and the nighttime
lows will only occur for a brief time resulting in a good deal of
discomfort for those without access to air conditioning. Albrecht

&&

.AVIATION...Westerly flow aloft with upper level trough to the north
moving into the area on Friday. Low level onshore flow
continuing into Friday.

Multiple cloud layers over Western Washington early this
morning. In general along the coast ceilings 1000-2000 feet
while in the interior ceilings are mostly in the 3500-5000 foot
range with an area of ceilings near 1000 feet around KSHN.
Ceilings lowering all areas except in Whatcom county down to
1000-2000 feet in the 12z-15z time window. Tops in the 4000-5000
foot range. Ceilings rising to 2000-3000 feet late morning with the
stratus dissipating over the interior 20z-22z and along the coast a
short time later. Ceilings near 2000 feet reforming along the coast
in the evening hours with the stratus spreading inland early Friday
morning.

KSEA...Ceilings near 3500 feet lowering to 1000-1500 feet 12z-
14z. Ceilings slowly lifting late morning/early afternoon to 2000
feet with the stratus deck scattering out 20z-22z. Southwest
winds 4 to 8 knots becoming northwesterly 00z-03z. Felton

&&

.MARINE...Winds in the Central Strait continue to hit gale speeds
via gusts while obs in the Eastern Strait have had a hard time
getting out of small craft range. Will allow for those gale warnings
to continue until 5 AM PDT based on the continued obs from Race
Rocks. Winds at Point Wilson in Admiralty Inlet continues to show
SCA winds at the time of this writing...so will leave headline alone
there as well. Obs over the Northern Inland waters show no sites
meeting any criteria...as such will end that headline with morning
forecast package. Winds will continue to ease this morning before
increasing again later this afternoon. High pressure over the NE
Pacific will maintain onshore flow through the remainder of the
week. Highest wind and waves will be over the outer Coastal Waters
and central and eastern Strait of Juan de Fuca. As such...have
extended inherited SCA for the outer coastal waters into Friday.
Strongest winds in the strait will occur during the late afternoon
and evening hours each day. The flow may turn offshore early next
week. SMR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 PM PDT Friday 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 5 PM this afternoon to 5 AM PDT Friday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 5 AM PDT early this morning for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 5 AM PDT early this morning for
     Admiralty Inlet-Northern Inland Waters Including The San
     Juan Islands.

&&

$$

www.weather.gov/seattle



Office: OTX FXUS66 KOTX 191122 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 422 AM PDT Thu Jul 19 2018 .SYNOPSIS... Temperatures will cool slightly each day going into the weekend, with readings expected to be near normal by Saturday. Conditions will remain dry with locally breezy winds expected near the Cascades through Friday then northern mountain valleys over the weekend. The dry weather looks to persist into next week, with the potential for another strong warming trend. && .DISCUSSION... Today through Friday: Dry, locally breezy conditions continue, with some fire weather concerns, but with more seasonal temperatures. The region will remain in a west/southwest flow with low pressure over northern BC tracking toward the WA border through the period. A very dry atmosphere will keep only limited thunderstorm chances near the Canadian border as impulses slip by. The cross-Cascade gradient and afternoon mixing will produce some breezy conditions, especially over central WA. Though guidance is not in solid agreement that wind speeds will achieve strict criteria, they will be close enough. So combined with low afternoon RH's comparable or slightly lower than recent days, red flag warnings continue. We will have to contend with some smoke and haze from regional wildfires, the most robust which are in southern BC and Oregon with more localized smoke from the fires in WA and ID. /Cote' Friday night through Monday...An upper level low will slowly track through central British Columbia Friday night, through Alberta on Saturday, with the low heading east across the Canadian Plains Sunday and Monday. Model guidance is also similar showing a secondary low dropping south down the B.C./Alberta border Sunday night and Monday. No major changes in the model guidance that shows the moisture and dynamics remaining well north of the Canadian border. So the big impacts will be temperatures cooling back to seasonal normals with highs mainly in the 80s. The surface pressure gradient will shift to northerly and tighten some Saturday afternoon through Sunday with winds down the Okanogan valley in the 10-15 mph range and gusts as high as 25 mph. The atmosphere will remain very dry with relative humidity in that 15-25 percent range. On Monday a short wave disturbance will wraparound the parent low. The ECMWF does show some limited moisture brushing the north Idaho Panhandle Monday afternoon. At the time the forecast will be kept dry, but this will be monitored as there could easily be some isolated lighting up near the border. High pressure will begin to the strengthen over the 4 corners region as well which will allow temperatures to 4-7 degrees over Sunday. Tuesday through Friday...The 4 corners high shifts a bit to the west and strengthens through this period allowing the the ridge to move north. Temperatures will be on the rise with highs well into the 90s and a few of the warmer locations breaking the century mark. No relief from the dry conditions in sight and over night recoveries will be poor at best. Model guidance is showing a couple of weak waves trying to move through the ridge. This time of the year these waves typically get sheared apart as they move into the ridge. But this will have to be monitored closely, because if a wave does manage to get through the ridge or undercut the ridge it would likely kick off convection, and that would increase fire concern across the region. Tobin && .AVIATION... 12Z TAFS: A dry westerly flow continues, even as low pressure in BC drops toward the WA border late. The dry atmosphere will mean primarily VFR conditions with no precipitation. A few flat afternoon cu are possible, along a few elevated smoke layers from regional wildfires. There is a limited threat of FU/HZ near KSFF to reduce vis, but confidence remains low. Winds will be breezy near EAT, esp early this morning and again toward late afternoon. Some afternoon gustiness is expected elsewhere. /Cote' && .PRELIMINARY POINT TEMPS/POPS... Spokane 85 56 83 54 82 55 / 0 0 0 0 0 0 Coeur d'Alene 85 54 83 51 82 51 / 0 0 0 0 0 0 Pullman 83 52 81 50 80 51 / 0 0 0 0 0 0 Lewiston 93 59 90 58 88 59 / 0 0 0 0 0 0 Colville 87 54 84 48 82 50 / 0 0 0 0 0 0 Sandpoint 84 53 80 48 79 48 / 0 0 0 0 0 0 Kellogg 82 54 79 50 79 50 / 0 0 0 0 0 0 Moses Lake 90 54 88 54 87 56 / 0 0 0 0 0 0 Wenatchee 87 57 85 57 85 61 / 0 0 0 0 0 0 Omak 90 55 87 53 86 57 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Red Flag Warning from 10 AM this morning to 9 PM PDT this evening for East Washington Central Cascade Valleys (Zone 677)-East Washington Northern Columbia Basin (Zone 673)- East Washington South Central Cascade Valleys (Zone 676). Red Flag Warning from 11 AM to 9 PM PDT Friday for East Washington Central Cascade Valleys (Zone 677)-East Washington Northern Columbia Basin (Zone 673)-East Washington South Central Cascade Valleys (Zone 676). && $$