Scientific Forecaster Discussion
fxus66 kpqr 192119
Area forecast discussion
National Weather Service Portland or
220 PM PDT Mon Mar 19 2018
Synopsis...rather quiet weather with morning clouds and fog I nthe
valleys continues through Tue under weak high pres. Wed and Wed
night low pres off the California coast will spread moisture north over the
region as a cold front from the NW pushes through bringing rain, and
then a cool showery air mass for the end of the week.
Short term...tonight through Thursday...the weak upper low off the
Oregon coast near 43n 129w is expected to swing inland across
central and southern Oregon late tonight into Tue. This returns a
chance for some showers to the far southern part of the forecast
area, mainly the Lane County Cascades tonight and Tue. To the north,
the area will remain under a weak surface high pres, with light
winds favorable for radiational fog to develop again in the valleys
late tonight and continuing through Tue morning.
Tue night and Wed models indicate some moisture creeps up again from
the south as the closed low well off the California coast begins to open up.
This spread chances for rain northward, and by late Wed deeper
moisture arrives bringing the prospects for more substantial rain.
As the deeper moisture spreads up from the south, warmer air
associated with it likely raises snow levels above the passes Wed
night. The warmer air will be short-lived though, as a cold front
ahead of a deep trough of low pres from the Gulf of Alaska pushes in
Wed night, adding additional lift for a wet night.
Showers will decrease behind the cold front Thu as low level onshore
flow temporarily weakens as a surface ridge of high pres moves in.
Cooler air arrives Thu as the upper trough moves closer. Thickness
values indicate snow levels to drop well below Cascade Pass levels
by Thu afternoon.
Long term...Thursday night through Sunday...models in good
agreement moving an upper low, with origins in the Gulf of Alaska,
down the British Columbia coast Thu night and Fri, then inland across the region
Sat. This brings a showery and quite cool air mass across the
region. Thickness values down into the range of 522 to 525 dm Fri
and Sat morning suggest snow levels well down into the Coast Range
and Cascade foothills, with maybe some flakes seen in the higher
hills of the low elevation valley zones. Sun the upper trough is
expected to move east with weak ridging following. A weak short wave
is hinted at Mon in both the GFS and ec, so will need to hang on to
some low pops sun and Mon, with temps warming a bit, but still
likely cooler than seasonal normals.
Aviation...almost exclusively VFR this afternoon should last
into the early overnight hours. The small area of IFR left over
this afternoon will clear within the next hour. However, IFR and
LIFR flight restrictions should return to at least inland taf
sites towards 12z Tuesday. If LIFR conditions do develop, they will
likely not clear until early afternoon again Tuesday. Light
offshore flow may keep the coast VFR but any calm winds would
allow development of IFR or LIFR conditions.
Kpdx and approaches...VFR through this evening and into tonight.
Then clear skies and light winds will likely to IFR or LIFR flight
restrictions developing after about 12z Tuesday, similar to this
Marine...expect winds to generally remain less than 20 kt
through midweek, but could see some gusts to around 20 kt
tomorrow evening as high pressure to the northwest and low pressure to
the SW squeeze the local pressure gradient just a bit. Models
continue to show a more active weather pattern returning Thursday
and continuing through the weekend. Small Craft Advisory level
wind gusts of 25 to 30 kt and seas climbing above 10 ft appear
most likely during this time. Bowen
Interact with US via social media: