Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
FXUS66 KSEW 241030
Area Forecast Discussion
National Weather Service Seattle WA
330 AM PDT SUN JUL 24 2016
.SYNOPSIS...High pressure will bring dry and mild weather today
and Monday. A weak system will move by Monday night bringing some
marine air into the interior for Tuesday. The ridge will
strengthen Wednesday into the end of the work week with the
warmest temperatures of the month expected Thursday and Friday.
.SHORT TERM...Satellite imagery shows not much in the way of low
clouds over Western Washington this morning. An area along the
north coast and a ribbon of stratus down the Strait is about it.
There is some cloud cover hanging on along the Cascade crest early
this morning. Temperatures at 3 am/10z were in the lower 50s to
Sunny and warmer is the weather message for today. The shallow low
clouds will burn off this morning. Flat upper level ridge over
Western Washington with 500 mb heights in the lower to mid 580
dms. Temperatures aloft have warmed up significantly overnight
with 850 mb temperatures rising from near plus 7c Saturday
afternoon to plus 12-13c. The warming aloft will continue with
model 850 mb temperatures around plus 15c at 00z Monday. Surface
gradients are already light northerly over the interior. By this
afternoon the KOLM-KBLI gradient will be near -1 mb. This could
knock a couple of degrees off the highs for locations near the
Sound but locations away from the water in the interior should see
up to 10 degrees of warming versus Saturday high temperatures.
Today looks to be the warmest day in the short term with highs
near 70 along the coast and 70s to mid 80s inland.
Little change in the weather pattern tonight with a shallow marine
layer only along the coast. Lows will be in the 50s and lower
Some small changes in the pattern start to develop on Monday. Model
850 mb temps drop a couple of degrees C. At the surface...onshore
gradients increase in the afternoon. Conditions will still be
sunny but with the increasing onshore flow will drop highs
slightly on Monday with the warmer locations getting into the
Weak shortwave ripples by Monday night. This will deepen the
marine layer over Western Washington into Tuesday morning.
Onshore gradients peaking Monday evening with model KOTH-KSEA
gradients near plus 4 mb and KHQM-KSEA near plus 3 mb. This is
strong enough to push the stratus along the coast into the
interior overnight Monday night into early Tuesday morning. The
marine push will be short lived with onshore gradients weakening
later Monday night into Tuesday. 500 mb heights also rebound a
little Tuesday afternoon. Will go with the weak marine push
scenario...about 5 degrees of cooling for the highs Tuesday...mid
60s coast and upper 60s and 70s for the interior...with sunshine
in the afternoon for the interior.
.LONG TERM...Extended models in good agreement with the upper
level ridge strengthening over Western Washington Wednesday and
Thursday. 500 mb heights near 590 dms by late Thursday afternoon
with the 500 mb heights remaining in the mid to upper 580 dms on
Friday. Temperatures aloft warming with model 850 mb temperatures
peaking out on Friday near plus 20c. Surface gradients never turn
offshore and remain northwesterly. This will put a cap on the high
temperatures. Highs on Wednesday in the 70s to mid 80s will warm
to the mid 70s to near 90 for Thursday and Friday. Thursday and
Friday will be the warmest days in July. Extended models also in
good agreement with a weak upper level trough approaching the
coast on Saturday. This will increase the low level onshore flow
resulting in some cooling of the high temperatures on Saturday by
a few degrees with the warmest locations dropping back into the
mid 80s. Felton
.AVIATION...A flat upper ridge will peak in strength over western
Washington today. Light NW flow aloft this morning, becoming west
this afternoon. Low marine stratus this morning confined mainly to
the North Coast, with more inland penetration on Monday morning.
The air mass will be stable and dry for the next 24 hours, except
for shallow low-level marine moisture.
KSEA...Clear skies at the terminal through Monday morning.
Northerly component winds persisting as well. Haner
.MARINE...Onshore flow of varying strength will continue through
the week ahead, with northwest winds prevailing over the Pacific
coastal waters. Westerlies through the Strait are forecast to
reach gale-force on Monday night. Small craft westerlies will
prevail most other afternoons and evenings this week. Haner
PZ...Small Craft Advisory until 3 AM PDT early this morning for
Central U.S. Waters Strait Of Juan De Fuca-East Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Monday
for Central U.S. Waters Strait Of Juan De Fuca-East
Entrance U.S. Waters Strait Of Juan De Fuca.
You can see an illustrated version of this discussion at