Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 232238 CCA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
338 PM 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 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 and
Wednesday, potentially followed by a gradual warming trend late in
the week.

&&

.SHORT TERM...This afternoon through Monday...An upper level ridge
remains offshore this afternoon, but continues to approach the local
area. With rising heights today, temperatures are a number of degrees
warmer than yesterday across the board. A trough of low pressure at
the surface has developed over the western side of the Cascades,
inducing the beginning of offshore flow with relatively higher
pressure on the east side of the Cascades. The KTTD-KDLS pressure
gradient is only -1.7 mb at the moment, but the gradient will
strengthen into Saturday as the surface trough builds. With offshore
flow, expect low temperatures tonight to be a few degrees warmer than
last night, particularly in and near the Columbia River Gorge.

The upper ridge moves almost directly over the local area Saturday
with surface thermal troughing along the coast, which will strengthen
offshore flow and enhance daytime heating. Didn`t do much to the
temperature forecast with 90s expected across the board with the
exception of some coastal spots and the elevation of the Cascades.
However, did change the heat products in effect. See the NPW product
for specific changes, but overall cancelled the Heat Advisory for the
coast because recent heat risk guidance indicates that temperatures
of around 90 degrees do not actually pose widespread threat to the
general population. Elsewhere, where temperatures will be in the mid
90s Saturday, there is increased heat risk, so upgraded the
Excessive Heat Watch to a Heat Advisory. The only Excessive Heat
Warning is for the Western Columbia River Gorge, or the area around
Multnomah Falls on the Oregon side and Cape Horn on the Washington
side, where lots of people will no doubt be out and about,
temperatures are likely be in the 95 to 100 degree range both
Saturday and Sunday, and offshore flow will prevent temperatures
from falling below around 70 degrees Saturday night, providing
little in the way of relief between the two hot days. These
conditions will also apply to the far eastern Portland Metro area
from about Gresham and Camas east, but those areas are such a small
part of the forecast zone that we decided to just stick with the
western gorge for the warning.

Things get a little bit more interesting on Sunday. The 12Z NAM
continues its trend of showing a southwest marine surge beginning
early Saturday evening along the southern Oregon coast. By 12Z
Sunday, the NAM has the south wind reversal to around Newport.
Meanwhile, an upper level trough is forecast to track across British
Columbia Sunday, which begins to flatten the upper ridge. Models show
the thermal trough hanging tough over the northern third of the
forecast area Sunday morning then jumping to the eastern side of the
Cascades in the early evening, returning the west side to cooler
onshore flow. 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 Sunday afternoon, which will likely
prevent those areas from warming as much as on Saturday. For this
reason, the Heat Advisory for the Coast Range and Southern Willamette
Valley zones is only in effect through the day Saturday. Elsewhere,
temperatures will likely be a couple of degrees warmer on Sunday than
Saturday with offshore flow continuing most of the day.

Models continue to be in good agreement showing a significant cooling
trend starting Monday with a shortwave approaching the N California
coast 12Z Mon, while another shortwave drags across SW British
Columbia during the day Monday. With developing upper level S-SW flow
locally Monday, left the slight chance mention of thunderstorms for
the higher Lane County Cascades and near the Cascade crest late
Sunday night through Monday. Model soundings are still not all that
impressive and the mid-level flow becomes more westerly Monday, but
cannot rule out some elevated convection 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. For most people, the bigger story will be the significant
cooling Monday as maximum temperatures fall to around 80 degrees
inland, which is near climatological normals for this time of year.
Bowen

.LONG TERM...Onshore flow continues through at least Wednesday with
seasonable temperatures and morning marine stratus both Tuesday and
Wednesday. Starting Thursday, there are some differences between the
GFS and ECMWF with the GFS moving an upper ridge over the local area
starting Thursday and into Friday, while the ECMWF delays it until
Friday or even Saturday. The differences would be apparent in
temperatures, where the GFS would indicate a significant warming
trend Thursday and Friday. The ECMWF shows a similar trend, but
manifesting more Saturday and Sunday again. Bowen

&&


.AVIATION...Strengthening high pressure will continue to bring
widespread VFR conditions and diurnally driven winds the next 24
hours, with gusty northerly winds in the afternoon and evening.

KPDX AND APPROACHES...VFR and diurnally driven winds the next 24
hours, with gusts to around 20 kt in the afternoon/evening. /64

&&

.MARINE...High pressure over the northeast Pacific and a thermal
trough along the northern California and southern Oregon coast
will continue to bring gusty northerly winds and locally steep
seas through late tonight. Winds will turn weakly offshore by
early Saturday morning which will bring an end to our current
small craft advisories. Winds on Saturday look to remain below
advisory criteria, but occasional gusts to 20 kt remain possible
beyond 20 nm. A southerly wind reversal will move northward
across the waters Saturday night and Sunday. Seasonal northerly
winds return early next week. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from noon Saturday to 9 PM PDT Sunday
     for Western Columbia River Gorge.

     Heat Advisory from noon Saturday to 9 PM PDT Sunday for Cascade
     Foothills in Lane County-Central Columbia River Gorge-
     Central Willamette Valley-Greater Portland Metro Area-
     Lower Columbia-Northern Oregon Cascade Foothills.

     Heat Advisory from noon to 9 PM PDT Saturday for Central Coast
     Range of Western Oregon-Coast Range of Northwest Oregon-
     South Willamette Valley.

WA...Excessive Heat Warning from noon Saturday to 9 PM PDT Sunday
     for Western Columbia River Gorge.

     Heat Advisory from noon Saturday to 9 PM PDT Sunday for Central
     Columbia River Gorge-Greater Vancouver Area-I-5 Corridor
     in Cowlitz County-South Washington Cascade Foothills.

     Heat Advisory from noon to 9 PM PDT Saturday for Willapa Hills.

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 6 PM
     PDT this evening.

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

&&

$$

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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.


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