Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 270358
Area Forecast Discussion
National Weather Service Seattle WA
900 PM PDT Wed Oct 26 2016
.SYNOPSIS...Rain will taper to showers tonight as a front
gradually pushes east of the Cascades. A weak split upper trough
over the area will maintain a threat of showers across the area
Thursday. High pressure briefly builds on Friday with mostly dry
weather. The large scale trough reloads off the Pacific Northwest
coast by Friday. A series of systems will maintain wet and unsettled
weather through the middle of next week.
.SHORT TERM...Neither the front nor the rain associated with it seem
to be in much of a rush to move on from Western Washington this
evening. Looking at current radar imagery...can see that activity
does look to weaken south of the CWA...which if that trend holds
would indicate activity tapering off to showers later on tonight.
Models look to push the front eastward early Thursday morning
leaving a brief break in the action before a minor shortwave looks
to bring some showers for the afternoon and evening. A weak upper
ridge will provide a dry day Friday...but this is sadly short lived.
Upper level low pressure out over the Pacific waters looks to bring
showers to the area once more starting as early as late Friday night
along the coast...spreading over much of the area by mid-morning
Saturday. These look to be of a generally light and scattered
variety at this time.
Inherited forecast looks good and covers the above well. No evening
update needed at this time. SMR
.LONG TERM...From the 300 PM PDT Discussion...A trough will move
inland with split flow aloft taking the system mainly south of the
area Sunday. There is some threat of light rain but the bulk of
precipitation appears headed for CA/Oregon. There may be a lull in
rain or showers Monday but another system will move into the western
U.S. on Tuesday but dissipate rapidly. Global models are still
hinting at a more consolidated flow pattern possibly developing
around the middle of next week. That could usher in some stronger
fronts with more appreciable rainfall. Mercer
.AVIATION...An upper level trough of low pressure will remain
offshore tonight with southwest flow aloft over Washington. A front
will move slowly across the area tonight. The air mass is moist and
Ceilings will be generally VFR or MVFR with rain. Mountains obscured.
Some improvement is likely Thursday.
KSEA...MVFR or VFR ceilings with rain this evening. Some improvement
late tonight but ceilings will still bounce between VFR and MVFR.
Southerly wind increasing to 10G20 KT. CHB
.MARINE...A 993 mb low about 180 nm west of Cape Shoalwater will
move north and dissipate tonight. The associated front will move
across the area this evening. Expect low pressure systems to impact
mainly the offshore waters Thursday through Saturday.
.HYDROLOGY...From 300 PM PDT discussion...The highest rain amounts
observed along the south facing slopes of the Olympics are around
1.5 to 1.75 inches so far through 3 pm today. Total 12 hour amounts
will likely not pass 2 inches and precipitation already appears to
be lighter on radar. Only slight rises have been observed on the
Skokomish river and flooding is not expected. Up to 2 or locally 3
inches could fall in some Cascade basins but the southerly flow
pattern is not favorable for flooding, just sharp rises tonight.
Flooding is not expected on any area rivers over the next 7 days.
.CLIMATE...Record October rainfall for Seattle is 8.96 inches set
in 2003. That month had the daily record 5.02 inches day on October
20th. Seattle has recorded roughly 8.76 inches so far this month (up
through 8 PM PDT today) so it will take another 0.21 inches to break
the record. Months with 9 inches or more of rain have rarely
happened in Seattle. Even in the wettest month of the year,
November, it has occurred only nine times in 71 years of records (13
percent of the time ). Other months where 9 inches or more has been
recorded, December and January five times, and February and March
PZ...Gale Warning in effect until 6 AM Thursday for the coastal
waters and west entrance to the Strait Of Juan De Fuca.
Small Craft Advisories are in effect for the remaining
Small Craft Advisory for rough bar in effect until 6 AM
Thursday for the Grays Harbor Bar.
An illustrated version of this forecast discussion can be seen at