Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 270407 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
907 PM PDT Mon Jul 26 2021

Updated aviation and marine discussions.

.SYNOPSIS...Above normal temperatures continue through this
week as high pressure strengthens across the Intermountain West,
with the hottest conditions expected Thursday and Friday, with hot
temperatures continuing through Sunday. A slight chance of showers
and thunderstorms along the central Oregon Cascades tonight and
continuing through at least the middle of the week.

&&

.SHORT TERM...Tonight through Friday...A broad upper level high
pressure anchored across The Great Basin will slowly meander
northward through the middle of the week. This will result in a
gradual warming trend over the next few days, as reflected in the 850
mb temperatures, with the hottest days expected Thursday and Friday.
850 mb temperatures will slowly increase from the low to mid teens
Tuesday and Wednesday, peaking around 20C to 22C Thursday and Friday.
This will mean that temperatures for the week will remain above
normal in the upper 80s to low 90s for Tuesday and Wednesday, and
likely reaching into the mid to upper 90s Thursday and Friday. At
this time models including the NBM, which did an outstanding job at
predicting the record breaking heat in June, are not showing triple
digit temperatures except, in the 90th to 95th percentile runs, which
means that there is a ~10% chance that temperatures of 100 to 105
could happen within the Willamette Valley during this event.
Therefore, while temperatures will be very hot, am not expecting
record breaking temperatures through the weekend. Even though
temperatures will likely not be record breaking, precautions should
be taken during this period of time.

As the high pressure moves northward, expect the southwest upper
level flow to persist, with surface winds remaining primarily onshore
at least through Wednesday. Within this upper level southwest flow
small perturbations within the flow are present. At this time, these
perturbations are currently causing precipitation in central and
northern California. High-resolution models such as the HRRR and the
HRW ARW models are showing these perturbations following the
southwesterly flow. As these perturbations move across the area, they
will bring a slight chance of showers and thunderstorms to the Lane
and Linn County Cascades Tuesday, Wednesday and Thursday. Thursday,
the onshore surface winds will slowly weaken for inland locations
becoming more north/northeast during the daytime Thursday and Friday.
While an easterly wind event is not expected, the slacking winds will
enable the warm 850 mb temperatures to mix down towards the surface.
In addition expect night time cloud cover, which has been aiding in
moderating temperatures, to diminish through Friday. The hottest days
at this time are expected to be Thursday and Friday, the reason that
it could be ether day is due to the very little chances currently
seen in the models. Some locations could see the peak heat on
Thursday while others could see it on Friday and vice versa. While
daytime temperatures will be hot, overnight temperatures will drop
into the lower to mid 60s, which will provide some respite from the
daytime heat. There remains no precipitation chances across the
majority of the CWA through this time period. /42

.LONG TERM...Friday night through Monday...Saturday is expected to be
the last day in this string of hot temperatures as the high pressure
ridge axis anchored across The Great Basin starts to shift eastward
and breakdown into the start of next week. As this breakdown occurs
an upper level low from the Gulf of Alaska looks to push
southeastward along the western Canadian coast line. This will bring
a resurgence of onshore flow to the area and enable a cooling trend
for the area. Given that the NBM, GFS, ECMWF and Canadian models and
their ensembles all show this slight cooling trend, there is little
reason to deviate from the NBM. Unfortunately, there continues to be
no precipitation expected across the CWA through the start of next
week. However, there could be a slight chance of showers and
thunderstorms across the Lane and Linn County Cascades through the
weekend but, overall confidence on the exact timing and coverage
remains low. /42

&&

.AVIATION...High pressure over the area keeps much of the area
dry and under southwesterly flow aloft. Northwesterly winds at
the surface will continue through the forecast period with these
evening gusts dissipating overnight. Mid-level moisture is
beginning to filter into inland areas bringing some clouds around
4500-6000 ft. Will likely see these VFR clouds stretch north
through the evening, reaching the Columbia River Gorge around 14Z
Tuesday. There is a chance of broken MVFR cigs near KPDX/KTTD
early Tue morning around 14Z to 16Z. Elsewhere inland, expecting
VFR broken skies.

Upwelling has brought IFR to LIFR CIGs along the coast...especially
the central Oregon coast near KONP. Those CIGs are expected to
develop to the north where they should persist through the
evening. With little mixing expected tomorrow, most likely will
see IFR conditions around KONP through the next 24 hours, with
some slight improvement to the north after 17Z Tuesday. Patchy
fog also likely along the coast mainly south of KTMK.

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

KPDX AND APPROACHES...Mainly VFR conditions expected. Chance for
shallow MVFR stratus to return early Tue morning for a couple
hours around 14Z to 17Z. Breezy northwest diurnal winds will
return after 20Z Tuesday. -Muessle/DDH

&&

.MARINE...Have expired the small craft advisory as wind speeds
have fallen below criteria. May see some isolated gusts up to 25
kt in the central waters near the shore, but not expected to be
widespread.  -Muessle

Previous discussion follows: High pressure remains offshore with
low pressure over SW Oregon and NW California. This will bring
the typical northerly wind pattern over the next several days.
Strongest winds likely through Monday evening. The pressure
gradient is expected to weaken Tuesday and Wednesday with wind
gusts generally up to around 20 kt. Northerly winds likely to
increase again Thursday with winds gusting up to 25 kt through
the end of the week. Seas will be wind wave dominated and choppy
at 4-6 ft on top of a minimal south to southwest swell of 1. /DDH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&

$$

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