FXUS66 KSEW 241608

Area Forecast Discussion
National Weather Service Seattle WA
905 AM PDT Mon Sep 24 2018

.SYNOPSIS...An offshore upper level ridge will produce sunny, warm
days and cool, clear nights through Saturday. Northerly low level
flow will become offshore Thursday into Friday. The offshore ridge
will slowly weaken late in the week with a weather system moving
into the area Sunday.


.SHORT TERM...The areas of stratus and fog that formed
overnight will clear this morning to sunny skies. The offshore upper
level ridge will slowly shift inside of 140W this afternoon and
evening which will help boost heights over Western Washington. At
low levels, pressure gradients will become more northerly later
today and linger into Tuesday which will help keep high temperatures
in the mid to near 70 today despite the rising upper level heights
and sunny skies. Skies will remain mostly clear tonight, with light
winds so that areas of valley fog will once again form Tuesday
morning, especially in the Southwest Interior. Lows Tuesday morning
will be chilly again, in the upper 30s to near 50. Morning fog will
once again burn off quickly Tuesday morning, to sunny skies with
highs on Tuesday warming a bit over Monday`s highs into the mid 70s
at some locations. Tuesday night and Wednesday will much the same -
light northerly winds, chilly overnight temperatures, morning fog
giving way to sunny skies and normal to above normal high

.LONG TERM...from previous discussion...Extended models continue to
be inconsistent in their solutions. There is some general agreement
with the upper level ridge gaining amplitude Thursday and Friday
with the ridge drifting west. Both the GFS and ECMWF on the 00z run
turn the surface gradients offshore Thursday and Friday. This
solution has come and gone in the models for the last few days but
with some consensus this morning have increased the high
temperatures a little for Thursday and Friday even with the 500 mb
heights falling in response to the westward movement of the ridge.
Highs Thursday and Friday remaining in the mid 60s to mid 70s. If
the offshore flow gets strong enough the warmest locations will be
along the coast.

Ridge continuing to drift west and north over the weekend with an
upper level trough digging south along the British Columbia
coastline arriving in Western Washington Saturday night or Sunday.
Some timing and intensity differences this far out in the model
run. At this point have added pops to Saturday night and increased
the pops on Sunday but still kept them in the chance category.
Temperatures will be cooler over the weekend with highs back down
into 60s. Felton


.AVIATION...Northwest flow aloft continues today as high pressure
offshore builds into the region. At the surface, flow will turn more
northerly. Patchy stratus will dissipate this morning with VFR
conditions expected across the area today. Less cloud coverage
expected Tuesday morning but may see a brief period of IFR/LIFR
again at KOLM and across portions of the southwest interior.

KSEA...VFR conditions expected through the period. Light and
variable winds this morning will turn northerly after 18Z,
increasing to 7 to 10kts this afternoon. CEO


.MARINE...Northerly flow will prevail this week with high pressure
in control. Winds will be breezy over the coastal waters but will
likely remain below small craft advisory. Onshore flow may return by
the weekend. CEO





NWS SEW Office Area Forecast Discussion

Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather