720
FXUS66 KSEW 200928
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
228 AM PDT Mon May 20 2024

.SYNOPSIS...A weak upper level ridge will produce warmer and
drier conditions today. Another trough will drop south into
Western Washington from British Columbia on Tuesday and Wednesday
for a return to cooler and unsettled weather. A brief dry break
is possible on Thursday, before cool and unsettled conditions
return Friday and persist into the start of the weekend.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...Skies are mostly clear
across much of Western Washington early this morning as weak upper
ridging moves into the region. With some sunshine and weaker
onshore flow today, high temperatures will approach seasonal
levels...at least for interior areas. High level clouds will begin
to increase by afternoon as the next in a series of upper level
troughs and associated fronts approaches from the northwest. Rain
will reach coastal areas after midnight tonight then spread into
the interior on Tuesday morning. QPF forecasts remain fairly
impressive for late May with roughly a half inch or more for much
of the lowlands and 1 to 2 inches in the Cascades. The trailing
upper trough will settle over the area on Wednesday for a
continuation of showery, cool conditions with snow levels dropping
to around 4000 feet or so.

.LONG TERM /THURSDAY THROUGH SUNDAY/...The second half of the week
looks to mimic much of what we`ve seen lately. Thursday may end up
being a virtual carbon copy of Monday as weak ridging aloft
briefly noses into the area before yet another trough digs
southward into the area along the British Columbia coast on Friday
with additional shower chances and continued below normal
temperatures. Chance PoPs and below normal temperatures continue
into weekend as the region remains under the influence of
troughing aloft. Global ensembles are hinting at a possible shift
in the pattern early next week with upper ridging rebounding over
the Intermountain West and upper troughing taking up residence
over the Gulf of Alaska. It`s a bit far off to hang one`s hat on,
but it`s something to keep an eye on if you`re looking for more
seasonable conditions. 27

&&

.AVIATION...N/NW flow aloft over western WA today with a trough
over the Intermountain West. The low level air mass remains moist
with onshore flow and there are patchy low clouds (MVFR
conditions) over the coast and south sound. VFR conditions will
prevail in the afternoon. The flow turns westerly late Tuesday
night with rain spreading inland by 12-15z Tue as the next frontal
system moves in. 33

KSEA...Patchy low clouds possible early this morning (20 percent
chance of MVFR conditions). Otherwise, dry today with VFR this
afternoon. Winds S/SW around 5 kt. Moisture increases overnight
with rain spreading inland by 12z Tue. 33

&&

.MARINE...High pressure over the NE Pacific will maintain onshore
flow across western WA this week. Highest wind and waves will be
through the Strait of Juan de Fuca and outer Coastal Waters -
Small Craft Advisories are in effect. A frontal system will cross
the waters on Tuesday with another system on Friday. 33


&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 11 AM PDT this morning 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.

&&

$$