Scientific Forecaster Discussion
fxus66 ksew 231636
Area forecast discussion
National Weather Service Seattle Washington
936 am PDT Fri Aug 23 2019
a ridge of high pressure will be forced south today as a trough
pushes through central British Columbia. This will bring some showers, cloudier
skies, and temperatures ranging from near to below normal. By
Sunday, high pressure will build back into the area through the
middle of next week. This will bring dry weather and temperatures
climbing well above normal by the middle of the week.
Short term /today through Sunday/...
radar showing showers sliding across the northern tier this
morning. A quick update to bump chances up and include mention of
showers to the north. Satellite depicts mid level cloudiness
steadily pushing across the southern half of the area but with a
fair amount of breaks. Temperatures look on track to top out from
the 60s to mid 70s today. Additional chances of showers tonight
and Saturday, with the greatest likelihood on the coast and
olympic peninsula. Will update to increase pops there as well to
reflect ensemble output and Euro trend to continue shower chances
tomorrow in those areas. Highs tomorrow will be very similar to
today. The trough will exit east on Sunday but with a few
lingering showers along the far northern tier of the forecast
area. Heights will be slow to rise on Sunday and expect that the
warming trend will be somewhat slower Sunday with temperatures
rising only a couple degrees from the previous days to top out in
the upper 60s to mid 70s again. More appreciable increases in
500mb heights are expected overnight Sunday as the strong ridge
anchored through northern California extends north as the trough
exits well east.
Long term /Monday through Thursday/...
the trend for this coming week continues to be one of drying and
warming conditions. This ridge of high pressure to the south will
continue to build north. While heights get into the mid 580s, it
is noted that 850mb temps should exceed +20c by Tuesday and
Wednesday, along with a low level offshore flow. Thus Tuesday and
Wednesday should range from very warm to hot across the area.
Widespread low to mid 80s with some upper 80s south by Tuesday,
and a notch warmer for Wednesday with low 90s likely from Seattle
southward. The combination of 850mb temps in excess of 21 to 24c
on Wednesday and the presence of a thermal trough along the coast
suggest Wednesday to be the hottest. At least a weak push and cool
down on Thursday with the strength a bit uncertain at this time.
European model solutions are fairly aggressive in cooling things
off on Thursday with a weak mid level trough pushing in more rapidly.
Extended looks dry. Will fine tune heat forecasts over the next
couple of days.
Aviation...the upper level flow has become more zonal this morning
with a weak system passing through the northern section of
Washington, while at the surface, the flow continues to remain
onshore as higher pressure remains located across the ocean.
Associated with the upper level weather system is a rain shield
extending from the Canadian border into the northern olympic
peninsula. This morning have added a tempo group for showers from
clm to bli. Will keep a watch on pae. Elsewhere the best chance for
showers will remain displaced to the north.
Some ground fog /LIFR conditions/ has affected olm this morning and
expect these conditions to improve over the next hour or so. Some
patchy stratus exists along the coast but appears to be sparing hqm.
Elsewhere VFR conditions with mid and high clouds. The trend will be
for VFR conditions to continue thru the day with broken 10k-20k ft
likely the rule. Onshore flow will likely allow stratus to push
further inland tomorrow and affect ceilings. Winds today generally
Ksea...will continue to monitor rain showers west and north of the
area today but think activity will largely remain north. Ceilings
will be VFR at scattered-broken 10k-20k ft. Some stratus may push inland
close to the terminal Saturday morning. Winds north at 10kts or less.
Marine...mid and upper flow becoming more zonal today with a weak
shortwave passing through the northern section of the area and
southern British Columbia. This shortwave is carrying with it some shower activity
thru the Strait into the northern inland waters and Admiralty Inlet.
This will likely continue into the afternoon before the system pulls
to the north and east. Winds and waves are rather tranquil this
morning, with no headlines currently in effect.
Later this afternoon and evening, typical westerly push down the
central and eastern Strait of Juan de Fuca will lead to the next
round of Small Craft Advisory winds. Will monitor data coming in
later this morning/afternoon to determine whether this advisory will
need to be expanded into Admiralty Inlet and northern inland waters.
Onshore flow will then continue into the weekend with the potential
for near-gale force winds on Saturday evening. The flow is then
expected to turn offshore around Tuesday and continue thru late next
Hydrology...the daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
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.