Scientific Forecaster Discussion
fxus66 kpqr 282123
Area forecast discussion
National Weather Service Portland or
221 PM PDT sun may 28 2017
Synopsis...the upper level ridge of high pressure is beginning
to shift east and will allow coastal clouds to penetrate further
inland tonight. Clouds will retreat mostly out of the valley today by
the afternoon temperatures will be a few degrees cooler than Sunday.
Thunderstorms are possible near Willamette Pass this evening with
chances expanding northward Memorial Day. Cascade thunderstorm
chances continue Tuesday and expand westward to the valley as well.
Temperatures trend gradually cooler with rain chances during the
second half of the week as a disturbance tracks across the Pacific
Short term...(today through wednesday) stratus has cleared most
areas except for the coast, but even the coast may go clear in spots
for an hour or two late this afternoon based on current satellite
trends. Kept a slight chance for thunderstorms down near Willamette
Pass, but couldn't go any higher than slight chance based on the lack
of moisture and flat nature of the current cumulus clouds.
Thunderstorm chances will increase in the Cascades the next 2 days as
moisture increases and temperatures cool aloft. Will have to watch
for any drift of these thunderstorms into the valley based on backed
flow through the mid levels.
Continued overnight shift trend of decreasing temperatures tomorrow.
Given how far east the thermal trough is already, along and slightly
east of the Cascades, it will likely be well east of The Gorge by
tomorrow afternoon, so brought these temperatures down significantly.
Elsewhere temperatures were decreased, but not as drastically.
Long term...(wednesday night through saturday) the Tuesday trough
will bring a cool down to the area starting Tuesday with more
seasonable weather through the remainder of the week. Additional
shortwaves will move through the area Thursday and Friday which will
increase shower chances. The forecast becomes a lot more uncertain
towards next weekend as the European model (ecmwf) trys to cut off an upper low
overhead while the GFS strengthens a ridge into the area. Went with a
consensus blend today and will work to add more details this week as
things become more clear. /Bentley
Aviation...clouds are breaking up a bit along the coast, while
clear skies reign inland. Looking likely that AST will clear to
VFR for a few hours this afternoon, and possibly onp as well.
Expect clouds to reform along the coast this evening, so VFR
conditions will only last for a few hours. Will see another
marine surge this evening, with marine stratus making it into at
least the southern half of the Willamette Valley Monday morning,
similar to this morning. This will reduce cigs at eug and sle to
IFR for most of the morning hours, but clouds should break up
again by late morning, noon at the latest, for VFR conditions
Monday afternoon. Stratus will probably hang on to the coast
again Monday, with maybe only a few hours of VFR conditions late
in the afternoon.
Kpdx and approaches...likely VFR through the next 24 hours,
however, a slight chance of cigs coming down the Columbia River
impacting the terminal around 15z-18z Monday. -McCoy
Marine...quiet conditions continue with northerly winds below
20 kt through at least the middle of this week and likely
longer. Seas are down around 4 ft and will remain around 4 ft
through at least the middle of the week. Weak system appears
likely later this week, with winds shifting to southerly on
Wednesday, but winds right now appear to remain below 20 kt with
this system as well. Seas may come up a foot or two with this
system, but should be little impact.
Next chance for Small Craft Advisory conditions will be next weekend as a broad
upper-level ridge builds over the NE Pacific, setting up a
Summer-like gusty northerly wind pattern over our waters. -McCoy
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