723
FXUS66 KOTX 190936
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
236 AM PDT Fri Jul 19 2024

.SYNOPSIS...

Strong high pressure will begin to amplify over the Inland
Northwest during this period continuing our string of hot weather
which began around July 5th. The heat will likely peak this
weekend with widespread triple digit high temperatures and
possible records. There are hints the heat will finally relent by
the middle of next week.

&&

.DISCUSSION...
Today through Sunday Night: Excessive Heat is the main story as
temperatures increase even further across the region. Models are
in good agreement that a strong upper ridge will build over region
into Saturday, and then remain strong with the ridge axis
shifting to over North Idaho on Sunday. Initially with the ridge
overhead, the warming will be due to subsidence associated with
the ridge. On Sunday as the upper flow turn southerly on the back
side of the upper ridge, temperatures increase even further. 850mb
temperatures reach an impressive 30C, with widespread triple digit
heat. The one factor that could knock temperatures down a few
degrees is wildfire smoke coming up from Oregon. Either way, it
will be very hot. Heat Advisories are in effect for most of the
region on Friday, followed by Excessive Heat Warnings Saturday
through Monday. For Sunday Night a mid level wave tracks into
Central Washington on the back side of the ridge. The NAM is
showing elevated CAPE of 100-300 J/KG with some lift as well. At
this time instability parameters and atmospheric lift are not
expected to be strong enough for any precipitation or thunderstorms,
but a potential we will be keeping an eye on since any lightning
would not be good news.

The other potential concern on Sunday is the hot, dry, unstable
atmosphere as the flow turns southerly, especially in the
Cascades. The GFS shows dry adiabatic lapse rates up to near
15000 feet (deep layer of mixing), that could allow fires to get
very active. JW

Monday through Friday: Quite the pattern change is on the horizon as
models are in solid agreement on a deep low moving into British
Columbia and remaining nearly stationary through the work week.

On Monday, as the upper level low strengthens in the Gulf of Alaska,
increasing southwest flow into the PNW will allow an embedded
shortwave to move across the region and initiate the breakdown of
the ridge. Deterministic models are hinting at a pattern for high
based thunderstorms with an increase in elevated moisture and
instability across the region Sunday night into Monday.
Probabilities below 15% in the NBM currently limit confidence in
pinning down a specific area of interest, but this will be something
to monitor. Depending how this shortwave pans out, temperatures may
vary slightly on Monday compared to what is currently forecasted.
Increasing onshore flow will tighten the cross-Cascade pressure
gradient late Monday afternoon into the evening with breezy winds
through the Cascade gaps with a 50-100 percent chance for
sustained wind speeds above 20 mph.

The center of the low will move into northern British Columbia on
Tuesday, with a dry cold front sweeping across the Inland Northwest.
While this will provide much needed relief from the heat, it will
come at a cost as a cool down of this caliber is typically
accompanied by a strong push of winds. With that said, we will need
to monitor this period for critical fire weather conditions as
models show a 60 to 100 percent chance for the lee of the Cascades
to see sustained winds above 20 mph on Tuesday. Continued breeziness
is expected as the center of the low parks itself in northern BC and
additional shortwaves move across the region. Temperatures on
Tuesday look to cool by about 10 degrees with gradual cooling
through Friday. To put this duration of heat into perspective, if
the current forecast for Spokane International (KGEG) pans out, we
would have seen 20 consecutive days with a high temperature above 90
degrees, smashing the current record of 15 consecutive days. The NBM
finally drops below 90 degrees on Thursday, but this could occur as
early as Tuesday or Wednesday with 55 percent chance of a high below
90 both days. /vmt

&&

.AVIATION...
06Z TAFS: The Inland NW expect VFR conditions to continue through
the period. The only exception will be some hazy conditions from
smoke near wildfires that may reduce visibilities along Lake
Chelan, and the Methow Valley.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS:
With the exception of smoke near wildfires confidence is high for
continued VFR conditions.

-----------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70 percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https:/www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        98  64 101  66 106  69 /   0   0   0   0   0   0
Coeur d`Alene  95  60  98  64 103  68 /   0   0   0   0   0   0
Pullman        93  59  98  61 102  63 /   0   0   0   0   0   0
Lewiston      102  70 106  70 111  74 /   0   0   0   0   0   0
Colville       96  56  99  58 104  60 /   0   0   0   0   0   0
Sandpoint      93  54  97  58 101  64 /   0   0   0   0   0   0
Kellogg        93  65  96  67 101  71 /   0   0   0   0   0   0
Moses Lake     99  62 103  61 109  67 /   0   0   0   0   0  10
Wenatchee      98  68 102  73 107  74 /   0   0   0   0   0   0
Omak          102  64 105  67 110  72 /   0   0   0   0   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Heat Advisory until 11 AM PDT Saturday for Central Panhandle
     Mountains-Coeur d`Alene Area-Idaho Palouse-Lewis and
     Southern Nez Perce Counties-Lewiston Area-Northern
     Panhandle.

     Excessive Heat Warning from 11 AM Saturday to 8 PM PDT Monday
     for Central Panhandle Mountains-Coeur d`Alene Area-Idaho
     Palouse-Lewis and Southern Nez Perce Counties-Lewiston Area-
     Northern Panhandle.

WA...Heat Advisory until 11 AM PDT Saturday for Central Chelan County-
     Lower Garfield and Asotin Counties-Moses Lake Area-
     Northeast Blue Mountains-Northeast Mountains-Okanogan
     Highlands-Okanogan Valley-Spokane Area-Upper Columbia Basin-
     Washington Palouse-Waterville Plateau-Wenatchee Area-
     Western Okanogan County.

     Excessive Heat Warning from 11 AM Saturday to 8 PM PDT Monday
     for Central Chelan County-Lower Garfield and Asotin
     Counties-Moses Lake Area-Northeast Blue Mountains-Northeast
     Mountains-Okanogan Highlands-Okanogan Valley-Spokane Area-
     Upper Columbia Basin-Washington Palouse-Waterville Plateau-
     Wenatchee Area-Western Okanogan County.

     Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for Western
     Chelan County.

&&

$$