Excessive Heat in Oregon, July 15 to 16, 2023

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1030 PM PDT Fri Jul 14 2023

Updated aviation discussion

.EVENING UPDATE...A ridge of high pressure remains centered over
our area tonight and there is little in the way of sensible
weather aside from above normal temperatures. Temperatures
tonight will be a few degrees warmer than last night with
overnight lows in the upper 50s to mid 60s in the lower elevations
and in the 50s in the mountains. Winds continue at 10 to 15 mph in
the Kittitas Valley and Columbia Gorge and should slowly decrease
overnight. Did make a couple of small adjustments to low
temperatures overnight and winds this evening. Satellite imagery
shows only a very few cumulus clouds over the mountains, so
adjusted cloud cover to show clear skies rather than mostly clear.
Otherwise, the forecast was in good shape and no other changes
were made. Forecast update already out.

Temperature guidance continue to show high temperatures tomorrow
and Sunday of 97-105 in the lower elevations, so the heat advisory
for those days will remain unchanged. Models also continue to show
breezy winds Sunday afternoon and windy conditions on Sunday so
fire weather concerns will continue be a large concern on those
days. Perry/83

&&

.AVIATION...06Z TAFs...VFR conditions with clear skies will
continue through the next 24 hours. Winds will remain light and
terrain-driven through 20Z tomorrow. After 20z, KDLS, KRDM and KBDN
will have northwest winds at 10-15 kts with gusts to 20-25 kts.
Other TAF sites will remain below 12 kts. Perry/83

&&

.PREV DISCUSSION... /issued 232 PM PDT Fri Jul 14 2023/

SHORT TERM...Tonight through Sunday...Weather concerns become
active again as we see what will likely be one of the hottest
weekends of the year while fire weather concerns ramp up prior to
a cool down in the long term.

High pressure remains over the region, and will continue to be the
primary weather influence at least through Saturday. With this,
temperatures continue to warm, with widespread areas of 90's for
highs today, and areas of 90's to 100's Saturday and Sunday. With
overnight lows still cool but definitely warmer (in the 60's), a
heat advisory remains in effect for much of the region for
Saturday and Sunday. These temperatures aren't unusual for this
time of year climatologically, and with the lows still cool enough
an excessive heat warning isn't necessary. The NBM indicates
around a 20-60% chance of widespread highs peaking just above 100
degrees on Saturday, with portions of the Columbia Basin as high
as 60-80% chance. By Sunday, a deep upper low will swing across
southern Canada and bring a cold front that should transition
across our region through Monday. The approach of this feature
should begin to tighten the pressure gradient and cause breezy
winds that will peak into Monday. Winds could start to become
breezy across the Cascade gaps as early as Saturday, and with RH's
expected to be low already we continue to monitor the potential
for some fire concerns for tomorrow. On Sunday winds continue to
strengthen, and more widespread fire weather concerns look likely
for the Columbia Gorge/Basin, Foothills of the Blue Mountains, and
Yakima/Kittitas Valleys. The NBM shows the 50th percentile of
sustained winds on Sunday between 15-25 mph, with gusts 25-40 mph.
The strongest winds may be a bit more localized to the Cascade
Gaps regions on Sunday, but by Monday expect this to become more
widespread. Finally, although this boundary should remain mostly
dry on our side, showers are likely on the west side of the
Cascades with a few potentially reaching western Kittitas and
Yakima counties across the high terrain before falling apart.
Goatley/87

LONG TERM...Monday through Friday...Monday looks to be awfully
blustery given the time of year as the center of an upper-level low
crosses over BC and swings a potent shortwave through the forecast
area. This system will bring an end to the weekend heat, but EPS
ensemble guidance is suggesting widespread wind gusts eclipsing 30
mph for the Columbia Basin, especially for the Oregon end. And when
looking at our Cascade Gaps, wind gusts start to flirt with the 40+
mph range. EFI from the EPS thus suggests values in the 0.8-0.9
range, which makes sense as such wind events are not unusual for the
cold season, but certainly gustier than we'd expect for mid-July.
Fire Weather Watch remains in effect through Monday across areas
where we expect the strongest winds. RHs will definitely be lower on
Sunday, and may even increase above critical levels on Monday as the
cooler air mass behind this system filters in, but given the
climatologically unusual winds, fire spread risks will remain
elevated, so will encompass both Sunday and Monday into the Watch
even as RHs increase well into the 20s by Monday afternoon.

Rain showers could impact the central WA Cascades Monday afternoon
as the combination of upslope flow and moisture transport from the
SW triggers some orographic showers, but guidance looks to be in
good agreement that any showers that do form will be of minimal
impact. CAPE and overall instability is also low, so not
anticipating anything in the way of thunderstorms at this time as
well.

For the rest of the week, guidance depicts a relatively benign
pattern, with the GEFS favoring more weak and dry SW flow aloft
while the EPS favors more of a zonal pattern. Either way temps look
to gradually increase under these dry and clear conditions, up to
around 10 degrees above average across much of the forecast area.
Ensembles then bring in another system of similar structure next
weekend, but details are to be ironed out with the system's arrival
looking to be beyond the period. Given the early consensus across
models, however, another round of windy conditions and potential
fire weather concerns does look possible next weekend. Evans/74

&&

FIRE WEATHER...High pressure will bring hot temperatures through
the weekend while a deep upper low approaches and moves across
southern Canada, dragging a cold front across the region that is
expected to move through by early next week. These two features
will tighten the pressure gradient and promote enhanced winds to
go along with our low RH's, with critical fire conditions likely.
For Saturday, there is a risk winds could become strong enough
across the Kittitas Valley and also near the Columbia Gorge
(though less compared to Kittitas), and we continue to monitor
expected conditions for perhaps a red flag warning for tomorrow in
these regions. Then on Sunday as winds continue to ramp up across
the region, a fire weather watch remains in effect that is
expected to be upgraded either overnight or on Saturday during the
day. Winds become strongest on Monday, but RH's are expected to
come up. Still, with how strong conditions will be, even increased
RH's from the marine push may not be enough to mitigate critical
fire concerns, and therefore the fire weather watch extends
through Monday. By Tuesday winds calm and temperatures cool, with
calmer conditions then expected moving into the middle of next
week. Goatley/87

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  59  98  63  96 /   0   0   0   0
ALW  64 101  66 101 /   0   0   0   0
PSC  66 101  68 102 /   0   0   0   0
YKM  62  99  63  97 /   0   0   0   0
HRI  63 103  67 101 /   0   0   0   0
ELN  61  98  64  93 /   0   0   0   0
RDM  54  98  56  94 /   0   0   0   0
LGD  58  96  62  96 /   0   0   0   0
GCD  58  98  60  98 /   0   0   0   0
DLS  64 101  67  95 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from 11 AM Saturday to 11 PM PDT Sunday for ORZ041-
     044-505-507.

     Fire Weather Watch from Sunday afternoon through Monday evening
     for ORZ641.

     Heat Advisory from 11 AM Saturday to 8 PM PDT Sunday for ORZ049-
     506-509-511.

WA...Heat Advisory from 11 AM Saturday to 11 PM PDT Sunday for WAZ024-
     026>029-521.

     Fire Weather Watch from Sunday afternoon through Monday evening
     for WAZ690-691.

&&

EVENING UPDATE...83
SHORT TERM...74
LONG TERM....74
AVIATION...83
FIRE WEATHER...87