Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 261635
Area Forecast Discussion
National Weather Service Seattle WA
900 AM PDT Wed Oct 26 2016
.SYNOPSIS...A warm front will bring steady rain to Western
Washington today. The trailing cold front will stall over the
interior later this afternoon into this evening before moving east
of the area late tonight. A series of weather systems will move
through Western Washington into the middle of next week keeping at
least a chance of rain in the forecast each day. The best chance for
a short dry spell will be Friday into Friday night.
.SHORT TERM...Radar and obs show steady light to moderate rain
overspreading Western Washington this morning as a warm front lifts
over the area. A few spots over the southwest interior, central
coast, and Olympics have already exceeded a half inch of rain in the
past few hours. The 06z GFS20 run has trended wetter for the
interior lowlands and Cascades compared to the runs from 24 hour
ago. It is possible some interior lowlands could get over an inch,
including greater Puget Sound. Some other models like the Nam-12 are
not as wet as they push the cold front through quicker by early this
evening. QPF was boosted overnight so the forecast looks reasonable
for now but will evaluate all the 12z model data and made QPF
adjustments if necessary.
Rain should transition to showers later tonight as the surface low
offshore lifts into B.C. and the front pushes east of the area. A
trough will still be over the area with another short wave lifting
across the area Thursday and Thursday night with some additional
light rain or showers. This system appears to be much less organized
and significant rain amounts are not expected.
A brief short wave ridge is still advertised by most models for
Friday. Southerly flow aloft may allow for a couple degrees of
warming into the low 60s with partial afternoon sunshine. The dry
weather will be brief as the next system should arrive Saturday with
.LONG TERM...No update from previous discussion...Extended models
are trending wetter with each run. Both the 00z GFS and ECMWF are
more consolidated and organized with at least the first couple of
features versus the previous runs. Have increased the pops into the
likely category for Saturday and again Sunday night. For the first
part of next week the general idea of disorganized systems moving
into the area is still intact but model timing remains inconsistent.
That will keep chance pops in the forecast for Monday and Tuesday.
.AVIATION...An upper level trof will remain offshore through this
evening for strong SW flow aloft. Expect an occluded front to move
across the area this evening. Nly low level flow will become sly
behind the front. LLWS can be expected ahead of the front.
CIGS/VSBYS will continue to deteriorate during the day. Anticipate
wdsprd MVFR CIGs/VSBYS and areas of LIFR CIGs/VSBYs by late this
afternoon. The mtns will be obscd.
KSEA...CIGs should continue to deteriorate and are anticipated to
be in the MVFR category range this afternoon. VSBYs will generally
be in the 4-6SM range, occasionally 2-3SM. Winds will remain E or
nely thru late this afternoon while winds above the sfc remain SE
or S at 25-35 knots, resulting in LLWS at the terminal. Expect
LLWS until winds become sly (late this afternoon or early
A 992 mb low about 220 nm southwest of the WA coast will continue
moving north, eventually moving across northern Vancouver Island
late tonight. Expect weak low pressure systems to move across the
offshore to move across the offshore waters Thursday and Friday.
.HYDROLOGY...System moving up from the south today expected to
produce up to 2 inches of the rain over the south slopes of the
Olympics. Southerly 850 mb winds peak at around 50 knots only for a
six hour period this morning into early afternoon. This amount of
rain should not be enough to drive the Skokomish river above flood
stage. However, sharp rises on the river will occur and will monitor
this closely. Otherwise, flooding is not expected on any rivers over
the next 7 days. Felton
.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 7.67 inches so far this month so it will
take another 1.30 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 once. Felton
PZ...Gale Warning in effect until 3 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 waters.
Small Craft Advisory for rough bar in effect from 2 PM this
afternoon until 3 AM Thursday for the Grays Harbor Bar.
You can see an illustrated version of this discussion at