Weather Service Report


921 
FXUS66 KPQR 230328 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR 
827 PM PDT Wed Sep 22 2021

Updated Aviation Discussion

.SYNOPSIS...High pressure will build Thursday and Friday bringing 
warm and dry weather through the remainder of the week and into the 
weekend. After another day of temperatures in the 80s Friday, a 
slight cooling trend is expected into early next week. A weak front 
may move through late Saturday into Sunday. Cooler, wetter and more 
unsettled weather is likely for early next week. 

&&

.SHORT TERM /THROUGH SATURDAY/...Water vapor satellite imagery this 
afternoon shows the upper level shortwave that enhanced showers 
along a cold front this morning sliding east into central Oregon. 
High pressure will build in behind the front tonight with skies 
clearing this evening, although some lingering clouds will be 
possible late tonight into Thursday morning. An upper level ridge 
offshore will slide inland on Thursday while subsidence will allow 
temperatures to warm to a few degrees above normal. Northerly winds 
expected to increase late Thu afternoon with gusts of 15 to 20 mph 
likely, especially through the central and southern Willamette 
Valley.  

Northerly low level flow is expected to become more offshore by 
Friday morning as the west coast thermal trough builds along the 
Oregon coast into western Washington. This will cause temperatures 
to warm again into the mid to upper 80s inland, while many coastal 
locations will also warm at least into the 70s. The WCCT is expected 
to shift inland over the Cascades by Friday evening with light 
northwest flow setting in. Expect the dry and sunny weather to 
continue into Saturday. Stronger onshore flow on Saturday will 
likely moderate temperatures, but many inland areas will still warm 
to around 5 degrees above normal. Overall, a fairly mild, albeit 
warm, end of the work week/start of the weekend. /DDH 

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...More active weather is 
expected in the long term starting on Sunday and into early next 
week. Deterministic models are in good synoptic agreement that a 
broad upper level trough over the NE Pacific will deepen offshore 
Sunday and Monday. Models also show a strong low pressure system 
currently forecast to be west of Haida Gwaii Sunday to slowly move 
east through Monday. A series of multiple fronts associated with 
this low will likely impact western Oregon and southwest Washington, 
but timing of the fronts and precipitation amounts is still somewhat 
uncertain. There is a very high likelihood that a decent amount of 
rain will fall across the CWA sometime beginning late Sunday or 
Monday and continue through Tuesday. At this time, rainfall amounts 
do not look to be as high as last week's front, but ensemble means 
and NBM guidance suggest 1.0 to 1.5 inches of rainfall may be 
possible. Temperatures are expected to fall below normal by Monday 
and continue to remain cool through the middle of next week. Models 
show the mid to lower levels cooling from around 12C Sunday at 850 
mb to around 3C Tuesday. Snow levels will also drop to around 5500-
6000 ft beginning Monday night and continuing into Wednesday. /DDH

&&

.AVIATION...Satellite observations show cloud cover increasing 
across southwest WA and northwest OR as a secondary low pressure
over the coastal waters continues to slowly push inland through
tonight. Current observations across the area showed cigs were 
generally between 3000-5000 feet. Expecting cigs to fall towards
high-end MVFR/low-end VFR for inland locations starting around 
06Z-08Z Tuesday. 

Overall, the current MVFR/IFR conditions along the coast will 
become more IFR/LIFR around 04Z-06Z Tuesday. The exception at 
this time is KONP, which has been bouncing between VFR/MVFR/IFR 
over the past few hours. The reason is the low mentioned 
previously, that is causing a challenging forecast. However, am 
expecting conditions to stabilize around 06Z Thursday as IFR/LIFR
conditions are expected to manifest through the overnight hours.

Expect conditions to improve across the entire area starting around
16Z-18Z Thursday, which will result in widespread VFR conditions
with FEW/SCT high level clouds through the daytime.

For detailed regional Pac NW aviation weather information, go 
online to: https://weather.gov/zse

KPDX AND APPROACHES...Expect VFR conditions to continue through
the next few hours. High-end MVFR/Low-end VFR cigs expected to
develop
between 06Z-08Z Thursday and continue through 16Z-18Z Thursday 
then becoming VFR. /42

&&

.MARINE...Buoy observations from Wednesday afternoon showed
relatively light winds with seas running a foot or two higher 
than expected, hovering around 9 to 10 feet with a dominant wave
period of 15 seconds. Model guidance continues to suggest seas 
will fall a foot or two this evening, so would expect seas in the
7 to 9 foot range through tonight and into tomorrow.

High pressure will build over the coastal waters tonight while a
thermal trough hugs the northern CA/southern OR coastline. This 
will bring a transition to northerly winds over the coastal 
waters for tonight through Friday night, which look to become 
rather gusty on Thursday, especially during the afternoon and 
evening hours. At this time, it looks like winds will gust as 
high as 25 kt during that time, except for the central outer 
waters where gusts as high as 30 kt are expected. Winds should 
gradually ease Friday night into Saturday as the pressure 
gradient relaxes.

A frontal system will push across the waters Saturday evening 
through Sunday, bringing a transition to southerly winds. There
is still some uncertainty in regards to the timing of this
frontal system, which could arrive as late as Sunday afternoon.
This system should bring slightly higher seas, but not by much. 
Combined seas may rise into the 10 to 15 foot range early next 
week due to increasing westerly swell and breezy southwest to 
west winds. -TK 

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 11 AM Thursday to 5 AM PDT Friday for 
     Waters from Cape Shoalwater WA to Cascade Head OR from 10 
     to 60 nm.

     Small Craft Advisory from 2 PM Thursday to 2 AM PDT Friday for 
     coastal waters from Cape Shoalwater WA to Florence OR out 10 nm.

     Small Craft Advisory from 5 AM Thursday to 5 AM PDT Friday for 
     Waters from Cascade Head to Florence OR from 10 to 60 nm.

&&


$$

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Western Regional Climate Center, wrcc@dri.edu