Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 242208
Area Forecast Discussion
National Weather Service Seattle WA
300 PM PDT FRI JUN 24 2016
.SYNOPSIS...Residual clouds and a few showers tonight will end
on Saturday as high pressure offshore moves over the region. The
upper ridge will shift slightly inland over the interior Pacific
Northwest and Great Basin by Tuesday. This pattern will favor mostly
dry weather and above average temperatures through next week.
.SHORT TERM...A weakly unstable air mass and residual low level
moisture are producing scattered showers across Western Washington
this afternoon. Shower coverage will decrease with loss of daytime
heating, but lift provided by the mountains and a possible weak
Puget Sound convergence zone will maintain some threat of showers
overnight. High pressure offshore will shift east over the Pacific
Northwest on Saturday. low stratus across the area during the
morning will give way to partly sunny skies in the afternoon.
Northwesterly onshore flow will weaken while rising upper heights
and less cloud cover allow much of the interior to reach the low or
even mid 70s. Any remaining clouds should mostly clear out during
Models show a weak short wave passing north of the area Saturday
evening not having much impact on our weather. 500 mb heights still
rebound over 5800m Sunday with light northerly flow at the surface.
Temperatures will warm further, with many locations around greater
Puget Sound and the southwest interior reaching the low 80s.
Both the GFS/ECMWF shift the upper ridge axis a bit eastward Sunday
night which becomes centered over the Great Basin and interior
Pacific Northwest. A short wave will flatten the ridge and cause
thermally induced low pressure to mainly stay east of the Cascades.
A warm air mass will already be in place over interior Western
Washington with only weak onshore flow will result in another dry
and warm day. Highs are expected to reach the low to mid 80s except
upper 60s coast and 70s north interior. There is an outside chance
of a few cumulus developing over the north cascades late in the day
but will hold off on adding pops or any mention of thunder.
.LONG TERM...Global models show little change in the general pattern
through next week. High pressure aloft will remain anchored over the
Great Basin and Rockies with a series of weak upper lows brushing by
just north of Washington. This will cause some variation in the
strength of onshore flow which will affect temperatures a bit. Went
with a model blend in the extended which generally indicates
slightly above average temperatures and dry weather. Morning low
clouds could develop at the coast at times and may seep into the
western Strait or lower Chehalis gap, but nothing significant. Mercer
.AVIATION...An upper low moved inland and a weak upper ridge
will move over Western Washington tonight. Westerly flow. High
pressure offshore and lower pressure inland. The air mass is moist
and slightly unstable but the scattered showers will end later this
evening as the air stabilizes.
KSEA...Partly to mostly cloudy with the chance of showers ending
later this evening, the wind should be light and variable this
evening in weak convergence.
.MARINE...Onshore flow will prevail for the next several days with
high pressure offshore and lower pressure inland. Small craft
advisory west winds are likely in the Central and East Strait most
evenings with this pattern. There will also probably be some small
craft advisory northwest winds for the coastal waters most evenings
starting Saturday as northerly gradients tighten a bit.
PZ...Small Craft Advisory Strait of Juan de Fuca.
You can see an illustrated version of this discussion at