FXUS66 KSEW 192128
Area Forecast Discussion
National Weather Service Seattle WA
230 PM PDT Thu Jul 19 2018
.SYNOPSIS...An upper low will move through British Columbia tonight
and Friday. Onshore flow will keep Western Washington cool with
clouds. A weak residual upper trough will shift inland through the
region Saturday. Rather warm weather and sunny skies will return
Sunday through next week.
.SHORT TERM...Mostly cloudy weather will continue through Friday--
generally overcast in the morning, with the clouds breaking
up for the afternoon and evening hours. At 230 pm the clouds seem
to be thinning in some areas, but I wouldn't count on much more
than some sunbreaks this evening. There were a couple sunny webcams
today--Sunrise Mount Rainier and Hurricane Ridge cams--elsewhere
it stayed cloudy most of the time. We might squeeze out a little
drizzle or shower activity here and there through Friday morning--
the UW mm5nam had a little shower activity developing over the North
Cascades tonight and Friday morning--but the wrfgfs was dry. The
regional Canadian model showed some PSCZ activity by daybreak Friday
but most models are dry south of the border. Temps will be cool, but
then warming a little Saturday with more sunshine, and then another
round of really warm weather kicks in again Sunday and next week.
.LONG TERM...Sunny and rather warm weather is likely next week as
the air warms rapidly Sunday. Monday and Tuesday look rather warm
and then the 12z GFS showed a weak trough moving through the ridge
Wednesday--knocking down temps a notch for a day (500mb heights only
come down to about 585dm over Seattle next Wed). The ECMWF shows
warm weather for the first half of the week--but not exceptionally
warm--500mb heights average around 587dm for the first half of the
week, but then the ECMWF builds the ridge a bit more and puts the
ridge axis right over the area Thursday and Friday--but the 500mb
height never gets higher than about 588--but the 850mb temp warms
from around +17 early in the week to around +22c late in the week.
Well, let us not get ahead of ourselves--comparing the UW wrfgfs
temps for next Monday afternoon looks very similar to where temps
peaked during this last round of warmth, so the forecast for Sea-Tac
shows a high of 91 next Monday and Tuesday.
.AVIATION...An upper trough will move slowly through the area
tonight and Friday with westerly flow aloft. At the surface,
onshore flow will continue with high pressure offshore and lower
pressure inland. The air mass is stable.
Low clouds have been slowly lifting this afternoon but ceilings
are stubbornly persisting for many locations. The slow trend of
lifting and scattering should continue into the evening but some
areas probably won't scatter at all. Areas that do scatter should
fill in again later tonight with widespread MVFR Friday morning.
KSEA...It is looking iffy for the low clouds to scatter but there
is still a chance late this afternoon or this evening. Either
way, MVFR ceilings are expected again after midnight tonight.
Southerly wind 5-10 knots is still expected to become northerly
for a few hours this evening but this is also looking more iffy.
.MARINE...Onshore flow will continue for the next few days with
high pressure offshore and lower pressure inland. Gale force west
winds are likely in the central and eastern Strait this evening
with small craft advisory strength westerly winds for the adjacent
inland waters. Another round of small craft advisory strength
westerly winds is likely for the Strait and adjacent waters Friday
night but gales are less likely as onshore flow eases a bit.
Small craft advisory strength northwest winds are also expected
for the Coastal Waters at times the next couple of days.
Onshore flow will ease and turn more northerly Sunday. Weak
offshore flow is possible early next week as a thermal trough
builds north along the coast. Schneider
PZ...Small Craft Advisory until 6 AM PDT Saturday 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 11 PM PDT this
evening 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.
Gale Warning from 5 PM this afternoon to 1 AM PDT Friday for
Central U.S. Waters Strait Of Juan De Fuca-East Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 6 PM this evening to 3 AM PDT Friday
for Admiralty Inlet-Northern Inland Waters Including The
San Juan Islands.
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