Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 012231
Area Forecast Discussion
National Weather Service Seattle WA
300 AM PDT Sat Oct 1 2016
.SYNOPSIS...An upper level low off the Washington coast will shift
south tonight with showers decreasing from the north. The low moves
into southern Oregon Sunday with just a few showers lingering from
around Puget Sound southward, mainly early. A weak ridge will bring
dry weather Monday. A couple of splitting fronts will move across
the area Tuesday through Thursday with a chance of showers. A
stronger front may bring rain on Friday, then taper to showers
.SHORT TERM...Latest radar loop showers fairly widespread showers,
even reaching northern parts of the interior this afternoon. Some
showers have produced brief heavy rain, especially near the coast
and southwest interior where instability is greatest. Lightning
detection indicates a couple strikes at the coast but most the
activity is offshore closer to the upper low center. The best chance
for thunder remains at the coast and southwest interior early this
evening where models show LI`s reaching 0 or -1C, marginal at best.
Showers will begin decreasing overnight across the north as the
upper low offshore moves southeast into southern Oregon. The
diffluent region of the upper low over Washington will shift south
and there will be little in the way of forcing by Sunday. Kept some
low chance pops in the forecast from around Puget Sound southward as
some models suggest a few diurnally driven showers could linger into
the afternoon. Most the area will stay dry with partial afternoon
Sunday night and Monday look mostly dry between weather systems.
There could be some areas of morning fog, especially in prone
valleys. Mostly sunny skies in the afternoon but remaining cool in
the upper 50s to lower 60s.
A split in the upper flow pattern will weaken the next couple fronts
to approach the area. Most models take the bulk of moisture south of
the area on Tuesday, bypassing our area for the most part. There is
still enough uncertainty to keep some low chance pops in the
.LONG TERM...The large scale upper trough shifts further eastward on
Wednesday. There could be a few showers as a weak short wave on the
back side of the low weakens and moves through. Any precipitation
with this feature looks light.
Models now show a brief ridge over the area Thursday. Kept much of
the interior from Puget Sound northward dry but left some pops in
the mountains and coastal areas. Timing remains uncertain but if
models continue to shower ridging, all pops might need to be removed.
The next system poised to arrive Friday appears to be much more
consolidated but also progressive in nature. After a good shot of
rain Friday, the air mass turns showery Friday night into Saturday.
Highs will be mostly in the low 60s over the entire extended period.
.AVIATION...Low pressure at the surface and aloft is sitting in
the offshore waters off the central Washington coast. The low will
move onto the southwest coast of Oregon midday Sunday. The air mass
is moist and unstable. Moisture will slowly decrease from the north
late tonight through Sunday.
Radars and satellite imagery show scattered showers across the
interior of Western Washington while a more consolidated band of
showers and thunderstorms sits from the northern coast and coastal
waters southward into the Oregon coastal waters. While there have
been a few isolated lightning strikes over the northern coastal
waters, most of the lightning strikes have been seen from off the
coast of Hoquiam southward. Some of the thunderstorm activity off
the central Washington coast may pivot inland into the south
interior from Olympia or so southward, but it appears that the
threat of tstm activity north of Olympia in the interior will remain
quite low this evening. Conditions are generally VFR in the interior
(except isolated MVFR conditions in heavier showers) and MVFR on the
coast. Conditions will generally improve from north to south
overnight as the upper low drops southeastward toward southern
The air mass is moist enough that some sheltered locations in the
south interior will see low stratus and some fog late tonight into
Sunday morning. Elsewhere conditions are expected to remain VFR
tonight into Sunday morning with cigs generally 4000 ft or above.
KSEA...Occasional showers this evening will gradually taper off
overnight. A small chance of showers will continue into Sunday but
ceilings should stay 4000 feet or higher. South winds 8 to 12 KT
with gusts to 22 KT early this evening will become light
southeasterly after 03. Albrecht
.MARINE...A weakening 1010 MB low over the offshore waters off the
central Washington coast (PIC13) will slide southeastward into the
southwest Oregon coast on Sunday (PIC14). Small craft advisory
conditions on the coastal waters are now limited to the near shore
waters from Point Grenville southward and will come to an end there
by 9 PM. Small craft advisory conditions in Admiralty Inlet, the
East Entrance to the Strait of Juan De Fuca, and the Northern Inland
Waters are expected to diminish to 20 KT or less after 6 PM this
South to southeast winds will become light late tonight then will
become light northerly later Sunday and Sunday night as the low
moves inland well to the south of the area.
The next frontal system will be weakening as it moves through the
waters later Monday. Small craft advisory southeast winds conditions
are likely over portions of the coastal waters ahead of the front.
Winds are expected to remain below 21 knots elsewhere.
A stronger frontal system will approach the coastal waters from the
west on Thursday. Expect small craft advisory conditions to develop
over the coastal waters during the day on Thursday. Albrecht
.CLIMATE...Seattle ended the water year ( Oct 1 - Sept 30 ) with
49.17 inches. This is the 6th highest total since records started
at Sea-Tac in 1945. The vast majority of the precipitation ( 88
percent ) fell in the first six months with the October 1 - March
30 total a record breaking 43.33 inches ( 154 percent of normal
value of 28.19 ). The second half of the water year ( April 1 -
Sept 30 ) was very dry with only 5.84 inches ( 63 percent of the
normal value of 9.30 inches ). This was the 5th driest April
through September on record at the airport. Felton
PZ...Small Craft Advisory until 5 PM PDT this afternoon for Admiralty
Inlet-East Entrance U.S. Waters Strait Of Juan De Fuca-
Northern Inland Waters Including The San Juan Islands.
Small Craft Advisory until 9 PM PDT this evening for Coastal
Waters From Point Grenville To Cape Shoalwater Out 10 Nm.
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