Weather Service Report


865 
FXUS66 KPQR 230917
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
216 AM PDT Fri Jun 23 2017

.SYNOPSIS...High pressure aloft over the forecast area will
strengthen through the weekend. A thermally-induced surface trough
and resultant offshore low-level flow will result in hot temperatures
Friday through Sunday. A southwest marine surge occurs along the
central coast Saturday night and Sunday. A deeper marine push occurs
Monday for cooler temperatures inland. Strong onshore flow continues
Tuesday through mid-week, potentially followed by a gradual warming
trend late in the week. 

&&

.SHORT TERM...Friday through Sunday...The big picture remains
virtually unchanged. Still looking at a couple hot days followed by a
significant cooling trend. However, there are several subtle details
to think about, which makes the short term forecast not as
straight-forward as one might think. Water vapor imagery early this
morning shows a strong 500 mb high pres cell centered near 41N 132W.
Very dry air aloft, as evidenced by the dark water vapor colors,
covers much of Oregon. The 00Z KSLE sounding shows the classic
subsidence inversion with an RH around 3 percent near 800 mb. 

Today starts the main warming trend. The 23/00Z KSLE sounding came in
with an 850 mb temp of 15.8C, about as forecast 24 hours ago. The 00Z
NAM, GFS, and ECMWF all show 850 temps warming to 18C today in the
far north to 22C in the far south, or another 4-5 deg C from Thu. The
18Z GEFS plumes for KPDX suggest upper 80s today. The low-level flow
remains more north this morning, then should shift to northeast by
the afternoon. The NAM shows offshore flow developing  in the Gorge
this morning, but it may not impact KTTD until early afternoon.
Overall, nudged todays max temps down a couple degrees. 

Will also make some adjustments to the heat advisory that is valid
for today. The most recent heat impact tools, which were run early
this morning, show the primary area of concern to be the north and
central Willamette Valley, Clark County in SW Washington and the west
Gorge. Another issue to consider is the afternoon humidity. The
offshore flow will maintain fairly low dew points, with minimum
humidity in many areas below 20 percent. Today is a borderline case
for a heat advisory, but will maintain it for the aforementioned
areas. 

Friday night the thermally-induced surface trough is expected to the
cover the coast, Oregon Coast Range and SW Washington Willapa Hills.
The offshore flow should peak late Friday night and Sat morning. The
NAM indicates a KTTD-KDLS gradient around -3 to -4 mb 12Z Sat. Expect
pronounced subsidence inversions in the higher terrain as well. The
operational run of the GFS and ECMWF boost 850 mb temps to around
22-25C 00Z Sun. The 18Z GEFS plumes for KDPX show many ensemble
members in the mid 90s Sat. As has been the case the past few days,
believe the latest MET and MAV guidance are too warm for Sat. In any
event, heat advisory conditions are highly likely across much of the
forecast area Sat, including the coast. 

Things get a little interesting Sun. The 00Z NAM continues its trend
of showing the southwest marine surge beginning early Sun evening
along the south coast. By 12Z the NAM has the south wind reversal to
near KONP. Meanwhile, an upper level trough is forecast to track
across Central and South British Columbia Sun, which flattens the 500
mb ridge. Models show the thermal trough hanging tough over the
northern third of the forecast area Sun morning. The NAM wants to
shift it east of the Cascades by Sun afternoon. This trend is a
well-known bias for the NAM. Typically, the thermal trough does not
jump the Cascades until early evening. However, some marine air
seepage is expected to leak into the Central Oregon Coast Range
valleys and get into the south end of the Willamette Valley Sun
afternoon. The Central Columbia Gorge and Mt. Adams area will have
their warmest day Sun. Another expected subtle change Sun will be
higher dew points. South to southwest mid-level flow will allow some
moisture to creep north from the Sierras. In addition, there will be
less wind, except near the west end of the Gorge, to make things feel
a little more sticky. Weishaar
    
.LONG TERM...Sunday night through Friday...Models in good agreement
showing a significant cooling trend early next week. The GFS and
ECMWF generally agree showing a one-two punch Sun night through Mon.
Both models show a short-wave approaching the N California coast 12Z
Mon, while another short-wave drags across SW British Columbia. Have
left the slight chance mention of thunderstorms for the higher Lane
County Cascades late Sun night through Mon. Model soundings are not
all that impressive and the mid-level flow becomes SW-W by late Sun
night, but cannot rule out some elevated convection over the higher
Lane County Cascades at the leading edge of the deepening marine
layer. A few storms could initiate just before the marine air
arrives, but any that do develop will be quickly pushed east. 

The bigger story will be the significant cooling Mon as max temps
fall to near normal values. Models maintain a deep marine layer Tue
and Wed, which lowers max temps to a few degrees below normal. The
onshore flow should bring plenty of marine stratus into the
region Tue morning, with clouds clearing back to the coast in the
afternoon. The same general pattern holds through the rest of the
week, but inland marine intrusion may be less widespread each
morning. The GFS and ECMWF show much more variance late next week,
with the ECMWF moving a 500 mb ridge axis to the near the coastline
12Z Fri. The GFS keeps it much more offshore, with cyclonic NW flow
aloft over the area, which would result in stronger onshore flow
compared to the ECMWF. Weishaar

&&


.AVIATION...Widespread VFR conditions under strengthening high 
pressure and dry north winds. North winds will become gusty in
the afternoon along the coast and the interior valleys. 

KPDX AND APPROACHES...VFR conditions. North winds will increase
and gust to around 20 kt in the afternoon.  Strengthening high 
pressure and dry northerly flow will bring VFR conditions through
06z Saturday. ~TJ 

&&

.MARINE...There will be little change in the pressure pattern 
today, and gusty north winds and steep seas will persist. Winds 
will turn weakly offshore late tonight ending the small craft
winds. THe winds beyond 20 nm will still be gusty, and close to
small craft advisory criteria through Saturday night. A 
southerly wind reversal will move northward across the waters 
Saturday night and Sunday. These have a tendency to end up 
stronger and earlier than forecast so will need to monitor this.
A seasonal north wind pattern return early next week. ~TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Watch from Saturday afternoon through Sunday 
     evening for Cascade Foothills in Lane County-Cascades in 
     Lane County-Central Coast Range of Western Oregon-Central 
     Columbia River Gorge-Central Willamette Valley-Coast Range 
     of Northwest Oregon-Greater Portland Metro Area-Lower 
     Columbia-Northern Oregon Cascade Foothills-Northern Oregon 
     Cascades-South Willamette Valley-Upper Hood River Valley-
     Western Columbia River Gorge.

     Heat Advisory from noon today to noon PDT Saturday for Central 
     Willamette Valley-Greater Portland Metro Area-Northern 
     Oregon Cascade Foothills-Western Columbia River Gorge.

     Heat Advisory from noon to 9 PM PDT Saturday for Central Oregon 
     Coast-North Oregon Coast.

WA...Excessive Heat Watch from Saturday afternoon through Sunday 
     evening for Central Columbia River Gorge-Greater Vancouver 
     Area-I-5 Corridor in Cowlitz County-South Washington 
     Cascade Foothills-South Washington Cascades-Western 
     Columbia River Gorge-Willapa Hills.

     Heat Advisory from noon today to noon PDT Saturday for Greater 
     Vancouver Area-South Washington Cascade Foothills-Western 
     Columbia River Gorge.

     Heat Advisory from noon to 9 PM PDT Saturday for South 
     Washington Coast.

PZ...Small Craft Advisory for winds until 5 AM PDT Saturday for 
     Coastal Waters from Cape Shoalwater WA to Florence OR out 
     60 nm.

     Small Craft Advisory for hazardous seas until 3 AM PDT Saturday 
     for Coastal Waters from Cascade Head OR to Florence OR out 
     60 nm.

     Small Craft Advisory for Rough Columbia River Bar until 7 AM 
     PDT this morning.

     Small Craft Advisory for Rough Columbia River Bar from 3 PM 
     this afternoon to 6 PM PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM to 
     7 AM PDT Saturday.

&&


$$

Interact with us via social media:   
www.facebook.com/NWSPortland 
www.twitter.com/NWSPortland    

This discussion is for Northwest Oregon and Southwest Washington 
from the Cascade crest to 60 nautical miles offshore. This area is 
commonly referred to as the forecast area.

Return to Home page


Western Regional Climate Center, wrcc@dri.edu