Excessive Heat in Washington, June 25 to 30, 2021

Area Forecast Discussion
National Weather Service Pendleton OR
1046 PM PDT Thu Jun 24 2021

Updated Aviation Discussion

SHORT TERM...Strong upper ridge will remain over the Pacific
northwest the next few days with northerly flow aloft and hot
temperatures. Satellite indicates mid and high level clouds
moving over the ridge and across the forecast area tonight into
Friday. Then mainly clear skies Fri night into Saturday. As for
temperatures 850mb and thickness values indicate about 4 degrees
of warming for Friday and another 5 degrees Saturday. This will
put highs at 90-103 Fri and 95-108 Sat. Thermal trough will bring
north-northeast surface winds 10-15 mph each day. 94

PREV DISCUSSION... /issued 453 PM PDT Thu Jun 24 2021/

SHORT TERM...
Tonight through Saturday night...High pressure has begun to build
into the region and will be the dominant weather feature for the
foreseeable future. This subsidence associated with this high
will yield increasingly hot temperatures through the period. Highs
on Friday will be warmer than today, but not unbearable for this
time of year, with most locations in the 90s and the Basin likely
reaching triple digits. The real heat begins on Saturday. The
excessive heat watch was upgraded to an excessive heat warning
earlier for all areas beginning Friday afternoon.

A strong upper-level ridge will continue to build over the PacNW.
This will result in very hot daytime high temperatures around 10
degrees hotter than Friday. Lower-elevation areas of the CWA such
as the Lower Columbia Basin and eastern Columbia River Gorge will
likely fall within the 105-110 range. The heat, combined with a
northeasterly breeze during the afternoon, will exacerbate fire
weather concerns. Central Oregon will be slightly cooler with
highs in the upper 90s.

Remember...stay hydrated...stay inside and in air conditioned
facilities if possible, stay out of the sun and check on relatives
and neighbors. Wear lightweight and loose fitting clothing. If you
must be outside, take frequent breaks and try to find some time in
the shade.

LONG TERM...
Sunday through Thursday...There is good agreement through the
extended period of an upper level ridge of high pressure centered
over the PacNW through at least next Thursday, with uncertainty in
the progression of a weak closed upper low off the coast of
northern CA and OR.

Hot temperatures and dry conditions will continue to headline
through the extended period as an upper level ridge of high
pressure and surface thermal trough sit over the region. Ensemble
and deterministic guidance are currently showing Monday and
Tuesday as the peak days for the heat. Afternoon temperatures are
expected to be 100-115 for most of the lowland areas, with
mountain locations in the 90s and possible breaking 100 degrees
either day. Looking through ensemble spreads, ECWMF, GFS, and even
NBM members are showing high confidence in basin locations
breaking 110 degrees each afternoon starting Sunday through at
least Wednesday. Morning lows will not bring much relief from the
heat either, as ensemble members are consistent in showing morning
lows in the mid 60s to mid 70s. As for heat risk, much of the
guidance puts the region well above the 95th percentile for risk.
This prolonged period of hot and dry conditions with little
overnight relief will greatly raise the potential for heat related
illnesses as well as negatively impact drought conditions across
the region. Otherwise, the extended period will see locally breezy
easterly winds Sunday and Monday as thermal trough axis setups
west of the Cascades.

The other point of interest through the extended period is a
cutoff low off the coast of northern CA and OR Sunday and Monday
that models have been consistent in showing the past several runs.
With it's current track, the low will not have much impact on the
region, however, if it trends closer to the coastline, the
southern OR Cascade region will see a southerly flow develop with
possible increasing instability. Right now, confidence is low that
this cutoff low may make a closer approach, however, any
increasing instability in the Cascades could pose increased risk
for fire behavior. Lawhorn/82

AVIATION...06Z TAFS...A few mid-level clouds are noted at the this
evening around 15000 feet. Broken to scattered periods of these
could be possible as an area of of mid-level moisture moves in
from British Columbia, but broken clouds at high elevations
should return by the day tomorrow, followed by skies clearing
tomorrow by the evening hours. Winds become more northerly across
the region into the day, though remain generally in the 5-10kt
range at ground level. Goatley/87

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  97  65 102 /   0   0   0   0
ALW  68  97  70 106 /   0   0   0   0
PSC  63 101  67 107 /   0   0   0   0
YKM  61  98  66 106 /   0   0   0   0
HRI  67 100  64 107 /   0   0   0   0
ELN  63  96  65 104 /   0   0   0   0
RDM  52  96  58  99 /   0   0   0   0
LGD  57  92  58  96 /   0   0   0   0
GCD  57  92  62  99 /   0   0   0   0
DLS  69 100  69 108 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Excessive Heat Warning from 2 PM Friday to 8 PM PDT Thursday for
     ORZ041-044-049-050-502-503-505>511.

WA...Excessive Heat Warning from 2 PM Friday to 8 PM PDT Thursday for
     WAZ024-026>030-520-521.

&&

SHORT TERM...94
LONG TERM....82
AVIATION...87