Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 250343
Area Forecast Discussion
National Weather Service Portland OR
843 PM PDT Wed Aug 24 2016
.SYNOPSIS...A warming trend will continue across the region as a
strengthening high pressure aloft builds over the region. A thermal
trough over the Willamette Valley Thursday and Friday will support
offshore flow and afternoon inland temperatures reaching the upper
90s to around 100. Onshore winds will return Friday night and
Saturday. A persistent upper level trough will maintain onshore flow
and inland morning clouds, along with more seasonably normal
temperatures, for at least the first half of next week.
.SHORT TERM...(Tonight through Saturday)...Forecast remains on track
this evening with no changes necessary to the grids. Expect clear
skies to continue overnight the lower atmosphere continues to dry
out in northerly flow. Heights continue to rise as an upper level
ridge builds over the Pacific Northwest. Meanwhile, a thermal trough
will continue to build north along the Oregon Coast overnight
through Thursday, likely centered squarely over the Willamette
Valley or Coast Range. This will maintain offshore flow across NW
Oregon and SW Washington, resulting in temperatures warming into the
mid to upper 90s across the interior on Thursday. The offshore flow
should be strong enough on Thursday to allow coastal temps to warm
into the 80s. Not much change is expected for Friday as the general
pattern remains similar to Thursday, but the thermal trough will
begin to push eastward. This should usher in a return to cooling
onshore flow by late Friday afternoon for the coastal areas.
Therefore, the current heat advisory for Thursday afternoon through
Friday evening remains unchanged - in effect for all of the forecast
area except for the coastal and Cascade zones. Daily record maximum
temperatures are likely to fall for a handful of stations across the
Willamette Valley on Thursday and Friday.
Heights begin to fall Friday night as the upper ridge weakens and the
thermal trough moves east of the Cascades. Models continue to support
a southerly surge Friday night, bringing a return of marine stratus
and fog to the coast, with possibly some local areas of stratus to
make it into the interior early Saturday morning. Temperatures will
be notably cooler - in the mid 80s - inland on Saturday. Cullen
.LONG TERM...(Saturday night through Wednesday)...General period of
troughiness settles in to the PacNW by the latter part of the weekend
and into early next week. This will bring cooler temperatures,
cloudiness, and chances for showers to the area. The best chance of
showers will be for far NW Oregon and SW Washington as well as marine
areas Sunday evening through Monday as a weak low forms off the coast
on Sunday night and moves into Vancouver Island on Monday night.
There are still timing and strength differences between the ECMWF and
GFS, but either way, confidence in precipitation is high enough to
introduce PoPs during the period with highest chance during the day
on Monday. /Bentley
.AVIATION...With light offshore flow, generally VFR conditions
continuing tonight through Thu, though some patchy IFR is possible
near the coast briefly early Thu.
KPDX AND APPROACHES...VFR tonight and Thu. pt
.MARINE...High pressure will continue over the northeast Pacific
through end of the week. Surface thermal low pressure will
develop near the coast tonight, move just onshore late Thursday,
move back to the coast Friday morning, before moving onshore late
Friday and continuing onshore through the weekend and into next
week. Net result will be borderline Small Craft Advisory winds in
the central coastal waters for a while tonight and possibly
Thursday night. The surface gradient turns more westerly on Friday
and believe the winds will be more oriented onshore and be below
Small Craft Advisory thresholds. Winds over the weekend look to
stay below 20 kt as well.
Seas are around 4 or 5 ft this evening and will be at most 5 or 6
ft through this weekend into next week. pt
OR...Red Flag Warning from noon to 9 PM PDT Thursday for Central
Oregon Cascade Foothills-Central Oregon Coastal Strip-East
Slopes of the Central Oregon Coast Range-Mt. Hood National
Forest -West of Cascade Crest-North Oregon Cascade
Foothills-North Oregon Coast-North Oregon Coast Range-
Willamette National Forest-Willamette Valley.
Heat Advisory from 2 PM Thursday to 8 PM PDT Friday for Cascade
Foothills 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-South Willamette Valley-Upper Hood River Valley-
Western Columbia River Gorge.
WA...Red Flag Warning from noon to 9 PM PDT Thursday for Clark
County Lowlands-East Willapa Hills-Extreme South
Washington Cascades-South Washington Coast Including The
West Willapa Hills.
Heat Advisory from 2 PM Thursday to 8 PM PDT Friday for Central
Columbia River Gorge-Greater Vancouver Area-I-5 Corridor
in Cowlitz County-South Washington Cascade Foothills-
Western Columbia River Gorge-Willapa Hills.
PZ...Small Craft Advisory for winds until 3 AM PDT Thursday for
Waters from Cascade Head to Florence OR from 10 to 60 nm.
Interact with us via social media:
This discussion is for Northwest Oregon and Southwest Washington from
the Cascade crest to 60 nautical miles offshore. The area is commonly
referred to as the forecast area.