Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 ksew 221634 
afdsew

Area forecast discussion
National Weather Service Seattle Washington
934 am PDT Thu Aug 22 2019

Synopsis...
high pressure is building into western Washington today but high
temperatures will remain a bit below normal. This ridge of high
pressure will be somewhat suppressed by Friday as a low pressure
system pushes across central British Columbia through Saturday. With a few
showers around, the weekend should cloudier but with
temperatures will continue to be near normal. Next week a stronger
ridge of high pressure will attempt to build north into the region
through mid week so temperatures should climb above normal with
more sun and drier weather.

&&

Short term /today through Saturday/...
satellite this morning shows considerable cloudiness across much
of western Washington, with some sunny areas but many cloudy ones.
Temperatures are primarily in the 50s across the area with a few
60s where there is a bit more sun. Some patchy fog also continues
to linger. Expecting a gradual clearing through afternoon as a
ridge of high pressure builds in. Temperatures, however, will
remain below normal for most areas, generally in the upper 60s to
lower 70s. The building ridge will be suppressed and flattened as
a trough of low pressure pushes into central British Columbia by Friday. Heights
will increase from today though, so highs Friday should be a few
degrees warmer than today and close to normal. Aside from a few
showers possible in the far north on Friday, the area is likely to
remain dry, but cloudy. A bit more moisture works its way south
late Friday and into Saturday with falling mid level heights, so
there will be some scattered showers by Saturday but not
significant. The trend will be for cloudy skies to start the day,
with a clearing by late day Saturday. Temperatures will continue
to run from near to slightly below normal.

Key messages and impacts in the short term period:
none

Long term /Sunday through Wednesday/...
by Sunday the general trend is for a rebuilding of the mid level
ridge of high pressure along with rising heights across the area.
Sunday looks drier along with temperatures close to normal. This
trend is set to continue into early next week with The Heights
peaking between 580-586dm. The bulk of the strong ridge will
however be suppressed well south with more troughing pushing into
central British Columbia. Thus the trend continues to be for less height rises
and a diminished threat for a late Summer heat wave. At present,
sunny skies with temperatures in the mid 80s look to be a good
bet, but as of now, the threat of 90 degree temperatures is
diminished.

Key messages and impacts in the long term period:
warming temperatures next week but threat of excessive heat looks
diminished. Several days of above normal temperatures are expected
from Monday through Wednesday, but not hot enough to cause
significant impact.

&&

Aviation...low ceilings abound across the taf sites this morning
with IFR and MVFR the most prevalent categories, tho a few spots are
reporting LIFR amidst some drizzle and fog from leftover weak Puget
Sound convergence zone. Fortunately, ceilings will improve back to
VFR by the afternoon hours as un upper level ridge builds over the
region and sfc high pressure noses into western Washington. Should
see a decent amount of clearing then through the afternoon. Low
clouds do not appear to be an issue Friday morning, except maybe
some patches along the coast. Mid and high level cloud cover,
however, will be on the increase late tonight into Friday morning.

Ksea...IFR cigs (with brief periods of LIFR amidst some fog and
drizzle) will gradually improve to MVFR by late morning and
eventually to VFR this afternoon. After a decent period of clearing
this afternoon, mid and high clouds will then increase tonight. SW
winds this morning will turn more west at 5-10kts through the afternoon
and eventually become more north/NE albeit light at 5kts or less.

Kovacik

&&

Marine...an upper level trough that brought rain to most of the
waters yesterday has departed to the east, along with the associated
surface frontal boundary. Higher pressure can be found in the
front's wake that extends across the offshore waters of the
Washington and Oregon coast. This will keep onshore flow pattern in
place today as the pressure gradient is established towards lower
pressure inland. Current headlines as of 15z include a Small Craft
Advisory for the outer coastal waters for northwest winds 15-25 knots with
accompanying 10-11 foot swell. These conditions should subside by
early afternoon as high pressure builds slightly east. Have opted to
cancel the Small Craft Advisory for the northern inland waters with
this update as current obs appear to be below 21 knots, even across
the Strait of Georgia which appeared to be the original source of
the "stronger" winds.

Small Craft Advisory /although marginal/ will remain in place for
the central and eastern Strait of Juan de Fuca for this
evening/tonight. Onshore flow still appears to prevail thru early
next week.

Kovacik

&&

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

&&

Sew watches/warnings/advisories...
Washington...none.
Pz...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-northern inland waters including the
San Juan Islands.

Small Craft Advisory from 6 PM this evening to 3 am PDT Friday
for central U.S. Waters Strait of Juan de Fuca-East
Entrance U.S. Waters Strait of Juan de Fuca.

National Weather Service Glossary of Abbreviations