Area Forecast Discussion
Issued by NWS Portland, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
000
FXUS66 KPQR 231619
AFDPQR

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

.SYNOPSIS...High pressure 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, particularly
Saturday and Sunday. A southwest marine surge occurs along the
central coast Saturday night and Sunday then 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...This afternoon through Sunday...Biggest change this
morning was to drop the Heat Advisory for today (Friday). With low
temperatures this morning just a few degrees above normal and high
temperatures only expected to peak inland around 90 degrees to maybe
the low 90s, which certainly isn`t a rarity for this time of year,
don`t think there will be a big enough impact to warrant an advisory.
In addition, dewpoints will remain in the 40s today, which will
create low humidity and therefore the heat index will actually be
even a couple of degrees cooler than the actual temperature. Other
than dropping the advisory, the forecast looks to be on track with
another day today of lots of sun, a bit of breeze, and a continuing
warming trend. Bowen

The remainder of the short term forecast discussion is unchanged...

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.

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 KPDX 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...No Changes. Previous discussion follows...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...Strengthening high pressure and dry north winds will
continue to bring widespread VFR conditions the next 24 hours.
North winds will become gusty in the afternoon along the coast
and the interior valleys.

KPDX AND APPROACHES...VFR the next 24 hours. North winds will
increase and gust to around 20 kt this afternoon/evening. /64

&&

.MARINE...Expect gusty north winds and steep seas to persist
today, with little change in the overall pressure pattern. Winds
will turn weakly offshore late tonight ending the small craft
winds. However, 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. Seasonal northerly winds return early
next week. /64/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 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 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 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.



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.