DISCUSSION
Today through Sunday: There are two features impacting the weather over the next 48 hours. 1) Ridge of high pressure and 2)
Shortwave trof currently off the CA/OR Coast. On Saturday, the ridge will be the dominant feature. High temperatures will climb back into the 90s with a few sites near 100F. Readings should be near or slightly warmer than Friday. The wildcard with temperatures remains haze/smoke which is capable of blocking some solar radiation and keeping temperatures from reaching their full potential. Winds will be light today with a general northeast direction. On Sunday, the aforementioned trof will become the focus as it drifts northeast through the Inland NW. This will result in more clouds and potential for thicker haze or smoke as midlevel flow becomes southerly opening the gates to the Oregon wildfires. This combination will aid in cooling the air mass and knocking high temperatures down a handful of degrees.

The air mass will also moisten leading to modest CAPE along the spine of the Cascades and across far SE Washington and NC Idaho. The Cascades will be lacking a strong lifting mechanism and some CIN will exist but the higher peaks could be effective for cell development and have expanded the threat for thunderstorms. Any cells will be slow moving and capable of isolated lightning, brief downpours, and potential for wind gusts up to 30 mph. Dynamics are a bit stronger passing through SE WA and NC ID which should result in more shower activity and 15% chance for lightning strikes. Thinking the best chance for lightning will be around the Blue Mountains and Camas Prairie with a 5-10% chance northward into Pullman to St Maries. Rainfall amounts from any showers will likely be less than 0.05". For both areas, any strikes will be a concern for new fire starts but coverage and lack of confidence does not warrant any fire weather highlights at this time.

On Sunday, winds will start light from the northeast and swing around to the south/southwest. Breezy conditions are expected near any showers or sprinkles with potential to gusts around 25 mph. Any organized cells around the Blue Mountains could produce local gusts 30 mph or stronger. Winds will increase through the Cascade Gaps in the evening and remain elevated overnight as the ridge begins to break down and cooler air start to arrive in the region.

Monday through Saturday: There remains high confidence of a pattern change going into next week with 100% of the ensembles supporting a trough arriving in the PacNW Tuesday and Wednesday. This will be a slow break-down of the heat with temperatures cooling roughly 5 degrees each consecutive day from Monday through Wednesday.
With the pattern change, winds are likely to become breezy. NBM probabilities for sustained winds of 15 mph have increased for Monday with the latest percentages between 50-80%. With temperatures on Monday still in the 80s to low 90s and RH 17-26%, this will create elevated fire weather conditions. Still some uncertainty if conditions will warrant red flag warnings at this time. Joint probabilities of critical RH/wind thresholds range from 10-30%.

Precipitation chances with the incoming trough will be limited to the areas surrounding the Columbia Basin. Still a tough call on exact rainfall amounts but is looks likely that most areas from the Cascades to the WA/ID border will receive between zero and a tenth of an inch. The Idaho Panhandle stands the best chance for a tenth of rain with probabilities between 30-40%; these percentages are not very convincing. This is due to a lot of uncertainty with the placement of the trof WED into THU and where bands of light to moderate rain setup on its northeastern periphery. There has been quite a bit of wavering with the placement of a north to south axis of rain which varies over 100 miles from one model to another. North Idaho may benefit from this rain or it could set up further east into western Montana.
Needless to say, any light precipitation, cooler temperatures, and higher humidity values will be welcome news in regards to fire weather. This system will drift east on Friday with an 85% chance for another trof to drop into the NW quickly on its heels over the weekend. This scenario will promote near to below normal temperatures, higher humidity, and continued chance for light showers. The remaining 15% of the guidance support weak ridging with a subtle warming and drying trend. The forecast leans toward the trof solution with forecast calling for 10-30% chance of showers and seasonal temperatures. /sb

AVIATION
18Z TAFS: VFR conditions will prevail as high pressure remains over the region. Winds will be light from the east and northeast.
Areas of elevated wildfire smoke coming from Oregon and southern Idaho will continue to produce haze with visibility restrictions of 5-7 SM at times. Greatest risk will continue to be around Pullman, Lewiston, and Ritzville. Mid and high clouds will increase overnight into Sunday as a disturbance tracks northward from Oregon.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Smoke and haze arriving from fires in central Oregon and central Idaho are the main wildcard in the forecast through the weekend. Visibility reductions from smoke are tough to forecast since fire behavior can play a big role in smoke production. Pullman and Lewiston has experienced the most regular visibility reductions in recent days, but all our airports may become susceptible. As the upper high shifts east, increased southerly flow at midlevels will reach Central WA today (SAT) and then all E WA and N ID tomorrow (SUN)
increasing probabilities for Oregon smoke to expand northward.

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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 94 62 92 60 87 57 / 0 0 10 10 0 0 Coeur d'Alene 94 54 90 59 85 55 / 0 0 10 10 0 0 Pullman 95 56 89 57 84 53 / 0 0 10 10 0 0 Lewiston 99 64 93 65 94 61 / 0 0 20 20 0 0 Colville 100 52 93 50 86 48 / 0 0 0 10 0 10 Sandpoint 89 48 91 55 82 52 / 0 0 10 10 0 10 Kellogg 93 54 89 62 82 58 / 0 0 10 20 0 0 Moses Lake 99 60 95 57 90 55 / 0 0 10 0 0 0 Wenatchee 97 67 94 64 87 62 / 0 0 10 0 0 0 Omak 97 58 96 61 90 57 / 0 0 0 0 0 0

OTX WATCHES/WARNINGS/ADVISORIES
ID...Heat Advisory until 9 PM PDT this evening for Central Panhandle Mountains-Coeur d'Alene Area-Idaho Palouse-Lewis and Southern Nez Perce Counties-Lewiston Area-Northern Panhandle.

WA...Heat Advisory until 9 PM PDT this evening 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.