Wildfire in Washington, July 26, 2022

Area Forecast Discussion
National Weather Service Spokane WA
333 AM PDT Tue Jul 26 2022

.SYNOPSIS...
A long-duration excessive heat event will affect the region
through the end of the week. Unusually hot conditions will lead to
an elevated risk of heat illness, especially for vulnerable
populations, for those outdoors for extended periods of time, and
for those without access to air conditioning. Breezier conditions
and a gradual cooling trend are expected to commence this weekend
into early next week.

&&

.DISCUSSION...
...Long-duration excessive heat event will occur through the end
of the week...

Through Wednesday night: The long-advertised excessive heat is
upon us. A high-amplitude ridge has set up just off the West
Coast, and will only slowly migrate eastward into the Pacific
Northwest the next couple of days. By late Wednesday night, the
ridge axis will be centered near the Cascade crest, allowing for
two days of steadily warming temperatures as large-scale descent
suppresses much if any cloud cover and convection. A thermal low
will persist in the Columbia Basin as a result of the synoptic
setup and the intense diurnal diabatic heating; this will promote
a light but fairly steady north-to-northeast surface wind during
the daytime hours, with potential local enhancement in north-south
oriented valleys in northern Washington/Idaho.

Guidance is generally advertising a 2-3 degree warmup per day the
next two days, which means Lewiston, Moses Lake, and Wenatchee
may reach or even exceed 105 by Wednesday while Spokane flirts
with the century mark. If anything, I suspect consensus is a
little on the low side for highs; they tend to be in "dry"
excessive heat events. However, low temperatures are a trickier
forecast challenge. Guidance has been rather poor the last couple
of nights accounting for substantial nocturnal cooling. This
morning, for example, guidance is roughly 3-6+ degrees too warm on
average across the county warning area. Though lows will trend
upward each night as the excessive heat event worsens, models are
likely a little too warm in most areas (particularly outside more
urbanized areas such as Spokane, Wenatchee, and Lewiston). Have
trended lows just a touch cooler the next couple of nights.
However, overnight lows will remain unusually warm for this area
and will provide limited relief from the sweltering daytime heat,
especially for those without access to air conditioning. Bottom
line: This will be a dangerous heat event for the region.

There is one complication to the forecast worth mentioning. Model
soundings continue to exhibit potential for some instability to
develop via deep inverted-v profiles Wednesday afternoon and night
across north-central and northeast Washington. Coarser models
(e.g., the GFS/CMC) are hinting at potential for isolated
convection to develop in this regime near and just after peak
heating. So far, convection-allowing models do not share this
sentiment (but do tend to bias on the dry side in these setups). As
mentioned above, the proximity of the ridge suggests little
synoptic lift will be in place. However, there are indications a
weak perturbation may approach the Inland Northwest near/after 00z
Thursday. It is not completely out of the question subtle lift
associated with such a perturbation combined with highly-localized
lift via orographic effects may initiate a high-based storm or two.
This potential will need to be watched, as the very dry and very
deep boundary layer suggest the potential for lightning with
little or no measurable rainfall. At this time, this is not
mentioned in the public forecast, but given the hot/dry pattern,
there is at least some concern for fire starts. /CMS

RECORD HOT TEMPERATURES EXPECTED FOR MANY LOCATIONS THURSDAY AND FRIDAY

Thursday and Friday...The model agreement is quite good that
these will be the hottest days of this latest heat wave as the
ensemble members are all showing a strong ridge centered over
central or eastern Washington. The big question isn’t will it be
hot...it will, but rather which day will be the hottest. The
scales are being tipped toward Friday being the hottest day over
the eastern Washington into north Idaho, while Thursday could be
the hottest over central Washington . So how hot will it get on
these days? Let’s take a look.

On Thursday the ensembles are showing the 850 mb temperatures
ranging from 27-29C over most of the area which will easily
support high temperatures in the 100s for most valley locations
with the peak expected over the lower Columbia Basin with some
locations just exceeding 110F. Records will likely be in jeopardy
in a few locations. Here’s a table of a few spots.

Spokane: Forecast: 101F  Record: 102F set in 1939
Pullman: Forecast: 98F  Record: 99F set in 1939
Omak: Forecast: 108F  Record: 110F set in 1928

On Friday the ensembles are either on par with Thursday’s
readings near the Cascades and slightly warmer elsewhere with
850mb readings topping out in the 28-30C range. Once again some
records will likely fall or be threatened. Here’s a table of a
few spots.

Spokane: Forecast: 103F  Record: 100F set in 2014
Pullman: Forecast: 99F  Record: 100F set in 1996
Omak: Forecast: 107F  Record: 110F set in 1928
Lewiston: Forecast 107F  Record: 107 in 1939

Compounding this heat will be the somewhat limited relief
during the overnight hours with lows ranging from the 60s over
most of the northern valleys to the mid 70s expected over the
valleys near the Cascades and lower Columbia Basin. So how does
this compare to last years all-time record heat. We aren’t quite
in the same ballpark yet as 850 mb temperatures peaked in the
28-31C range but we aren’t far off. If we hit 103 in Spokane it
will be the 15th hottest day on record. While that doesn’t sound
that impressive, it really is if we ignore last years extreme
heat. In fact since 1961 we have only seen temperatures of 103 or
warmer in Spokane 4 times. In 2021 we tied or beat that mark 4
times. Needless to say this will pose a high risk to very high
health risk to the people. Mitigation steps are advised including
remaining hydrated if working outdoors, wearing light colored
clothing, avoiding strenuous outdoor activities, keeping your pets
sheltered and out of the extreme heat and seeking air
conditioning if at all possible.

Aside from the heat, we also expect to see a minor shortwave
disturbance traversing locations near the Canadian border from
Thursday afternoon and into the evening. While the trigger won’t
be terribly strong, the capping inversion looks weak and could be
overcome by orographic convergence and the weak forcing from the
shortwave. We have expanded the risk of thunderstorms accordingly,
mainly over the higher terrain.

Saturday through Monday...This is where the forecast become a
little more muddled due to some significant differences between
the various ensembles. Yesterday the GEFS was quite insistent on
shifting the thermal ridge east of our forecast area with a deep
trough gradually moving inland. Meanwhile the Euro ensembles keep
the ridge in place with a much weaker offshore trough. Obviously
this will have a big impact on the high temperatures during this
period. Today’s runs are showing more of the same, however the
GEFS solutions aren’t quite as consistent, with only 60% of them
showing some decent cooling for Saturday. By Sunday the majority
of the GEFS solutions continue to show the trough moving inland
and this has good support from the majority of the Canadian
ensembles. Meanwhile the majority of the ENS show more ridging and
more hot temperatures. This notion is also supported by the latest
operational runs of these models. The more trough-like the
solutions, the greater the cooling trend. Not to mention the
deeper GEFS trough would also support a chance of showers and
thunderstorms for Sunday especially near the Canadian border and
over SE WA into NC ID. For now we will have to hope for better
model agreement for this period. However as things stand, and we
hedge our bets toward the ENS we would have to extend the heat
warnings at least into Saturday with another day of triple digit
heat expected. fx

&&

.AVIATION...
12z TAFs: VFR conditions will continue through the TAF period,
with light and mainly diurnally-driven winds expected. /CMS

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        97  66  99  69 101  68 /   0   0   0   0   0   0
Coeur d'Alene  95  63  97  66  99  65 /   0   0   0   0   0   0
Pullman        94  62  96  65  97  65 /   0   0   0   0   0   0
Lewiston      103  70 104  72 106  71 /   0   0   0   0   0   0
Colville       96  59  99  62 101  62 /   0   0   0   0   0   0
Sandpoint      92  60  95  63  96  61 /   0   0   0   0   0   0
Kellogg        91  67  94  68  96  70 /   0   0   0   0   0   0
Moses Lake    102  69 105  70 106  70 /   0   0   0   0   0   0
Wenatchee     103  76 105  77 107  76 /   0   0   0   0   0   0
Omak          101  69 104  72 108  70 /   0   0   0  10  10   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Excessive Heat Warning from 11 AM this morning to 11 PM PDT
     Friday for Central Panhandle Mountains-Coeur d'Alene Area-
     Idaho Palouse-Lewis and Southern Nez Perce Counties-
     Lewiston Area-Northern Panhandle.

WA...Excessive Heat Warning until 11 PM PDT Friday for Central Chelan
     County-Moses Lake Area-Okanogan Valley-Waterville Plateau-
     Wenatchee Area-Western Chelan County-Western Okanogan
     County.

     Excessive Heat Warning from 11 AM this morning to 11 PM PDT
     Friday for Lower Garfield and Asotin Counties-Northeast
     Blue Mountains-Northeast Mountains-Okanogan Highlands-
     Spokane Area-Upper Columbia Basin-Washington Palouse.

&&