781
FXUS66 KSEW 151613
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
913 AM PDT Mon Jul 15 2024

.SYNOPSIS...An upper level ridge will remain in control over
Western Washington through the week for continued dry conditions
and above normal temperatures. Minor day to day variations in
onshore flow will bring the marine layer locally inland each night
and morning. A subtle shortwave entering the area on Wednesday
may bring an increased risk of convection over the Cascades.

&&

.UPDATE...No major changes to the forecast. Cloud cover remains
parked over much of the inland this morning from the marine push
overnight. Still expecting the cover to erode late this
morning/early afternoon, which will reveal mostly sunny skies.
High temperatures will be noticeably cooler than yesterday (mid
70s to 80). Additional details are available below in the
discussion (along with an updated aviation section).

HPR

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...A stronger marine push
underway will bring stratus inland across much of the interior
lowlands near and west of Puget Sound this morning. As of 08Z, the
marine layer had already reached Bremerton. The low clouds will
be relatively quick to burn back to near the coast later this
morning, but the increased marine influence will knock several
degrees off of high temperatures today. Opted to discard the
inferior NBM numbers and go closer to old fashioned MOS...which
puts Seattle in the upper 70s today. The cooling trend will be
short-lived as thermally induced low pressure expands northward
from the Willamette Valley on Tuesday. This will result in less
of a marine layer across the interior on Tuesday morning and high
temperatures will respond accordingly with 5 to 10 degrees of
warming for most of the interior. Even coastal areas will see some
sunshine Tuesday afternoon with high temperatures warmer than
recent days.

Models remain relatively consistent with the idea of a negatively
tilted weak short shortwave lifting northward across the area on
Wednesday. This will introduce the possibility of some elevated
instability and possible thunderstorms for the Cascades. Given the
elevated nature of the instability, I wouldn`t be too surprised if
the thunderstorm threat also includes some of the lowlands, but
we`ll have a better handle on this as the time period in question
draws closer. This shortwave will also likely induce another
marine push Wednesday evening...for another inland intrusion of
stratus and a temporary cooling trend to begin the extended
forecast period.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Strong upper ridging
centered over the Four Corners region will continue to provide dry
conditions and above normal temperatures heading into the end of
the week. Models have the ridge retrograding westward slightly and
gaining some amplitude toward the weekend with 500 millibar
heights approaching 590 decameters over Western Washington. Some
degree of low level onshore flow should keep temperatures from
getting out of hand, but it wouldn`t be too surprising to see some
interior locations from Seattle southward approaching the 90
degree mark once again. 27

&&

.AVIATION...Westerly zonal flow aloft becoming southwesterly ahead
of an incoming shortwave trough. IFR to MVFR cigs this morning
with low level marine status. Low clouds will burn back toward
the coast by 18-21Z. Light S/SW winds will continue through this
morning, becoming more W/NW this afternoon and evening.

KSEA...MVFR to IFR ceilings through 18-21Z. Stratus will
evaporate, leaving clear skies through the remainder of the TAF
period. S/SW winds up to 10 kt will slowly veer this afternoon
becoming NW by 00Z Tuesday.

33/LH

&&

.MARINE...High pressure situated offshore will continue into the
early week, allowing for diurnally driven pushes through the Strait
of Juan de Fuca and marine stratus along the coast. Northwesterly
winds continue through early Wednesday across the coastal waters,
becoming southerly ahead as a weak low pressure system moves
eastward towards the region late week. Several additional pushes
of westerlies down the Strait of Juan de Fuca are expected on
Wednesday and Thursday evening, which may require additional
headlines.

Seas remain around 3 to 6 ft through the week.

33/LH

&&

.FIRE WEATHER...High pressure will persist over the Pacific
Northwest for continued warm and dry conditions, with low level onshore
flow providing good relative humidity recoveries each night. Flow
aloft will start to turn southerly Tuesday night into Wednesday,
with an increased potential for convection in the Cascades, with
RH values remaining in the mid to upper 30s during this time.

It is worth noting that especially with a pattern like this, with
our fuels already being so receptive, all it takes is a rogue
lightning strike from a thunderstorm to light these fuels.
Will continue to monitor this threat as latest model guidance is
not latching on to any specifics. For now, will monitor for the
potential of thunderstorms and elevated instability.

Mazurkiewicz/27

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.
&&

$$