textproduct: Spokane

KEY MESSAGES

- Gusty winds into Friday. Gusts up to 50 mph in the morning then 20 to 30 mph throughout the day.

- Snow to impact the Cascades through the end of the week. There is a 90% chance of 2 feet or more of snow at Stevens Pass through Friday afternoon.

- Light to moderate snow possible on higher benches in the valleys near the Cascades, northern valleys and Idaho Panhandle Friday into Saturday.

SYNOPSIS

The Inland Northwest will remain in an active pattern through the end of this week and into next week with several opportunities for impactful mountain snow, light lowland rain and snow, and breezy winds.

DISCUSSION

Today-Saturday: A cold front is pressing through the region this morning delivering gusty winds and last round of moderate rainfall for areas of southeastern WA and the lower Idaho Panhandle. We are seeing the Polar jet finally sagging south of the region and allowing cooler air to infiltrate from the north. 850mb temperatures were near +4C over Spokane Thursday evening and will be cooling near -3C Friday afternoon in response to the transitioning air masses. Pressure gradients will remain elevated leading to blustery conditions through the day with consistent gusts of 20-30 mph bringing a bit of a bite to the day but overall, the enhanced mixing and lack of really cold air will keep afternoon highs in the upper 30s which is still a handful of degrees above Dec 19th 30-year averages. The swift westerly flow across the Cascades will lead to a strong drying and rain shadow across most lowlands. On the windward side of the Cascades and Northern Rockies or Idaho Panhandle, a persistent barrage of orographic snow showers are expected with moderate to heavy snowfall (Cascade Crest has a 90% chance for 1 ft or more and 70% chance for 2 ft or more). Amounts in the Northern Rockies into the Selkirks and at Lookout Pass will be lower with a 40% chance for 8 inches and 20% chance for receiving a foot. Dry conditions for the lowlands on Friday will be interrupted on Saturday as a weak shortwave tracks across central BC and low-level flow backs to more southwest vs west. This will allow precipitation to backfill into Northeastern WA and northern portions of the Palouse. Precip type will be a mix of snow and wet/snow with light accumulations possible outside the warmest time of day. Outside challenging travel conditions over the Cascade passes that are open (Snoqualmie and White), weather impacts will be low for the Inland NW heading into the weekend.

Sunday-Monday: A deeper low begins to carve out of the Gulf of AK and into the Eastern Pacific with a more organized frontal system progged to eject through the Inland NW late Sunday into Monday. This will bring a renewed chance for light precipitation to the Inland NW. Precipitation type will become a bit more complex as the flow buckles a bit more southerly and draws warmer midlevel air in from the south. Model consensus are for 850mb temperatures to warm near 0C or warmer across southeastern WA and the lower Idaho Panhandle and into the Spokane-Cd'A area resulting in a subtle rise of snow levels through the day. Would not rule out light snow impacting the Monday morning commute for many of our communities across northern WA/ID and into Central WA where cooler air is more challenging to scrub out but there is moderate confidence for impacts to become minimal by midday given the projected warming. Snow will continue over the mountains and mountain passes which is welcome news for our local ski resorts.

Tuesday-Wednesday: The weather pattern become a bit more interesting and amplified going into the middle to end portion of the week with an extension of the Gulf of AK low carving southward over the E Pac toward the coast of California. This has strong support from the 100 member ensemble suites with the main uncertainty being exactly how far off the coast or inland this broad upper-low will set up. This will have large ramifications on the amount of warm air that punches northward into the Inland NW....or remains to our east. This will undoubtedly draw moisture northward from a pool of subtropical moisture over California into our region and rising snow levels. The system has potential to bring winter travel conditions to our area for Christmas Eve. Based on the latest probabilistic data, my highest confidence for snow impacts will be across the Cascades and into the northern mountains and lowest over southeastern WA and the lower Idaho Panhandle. A lot of details to sort out between now and then so stay tuned but also continue to monitor the forecast and plan ahead if you are traveling. /sb

AVIATION

06Z TAFs: Moderate impacts to aviation overnight due to a combination of low-level wind shear and/or strong gusty winds surfacing between 40-46kts. The winds are in response to a cold front sagging southward through the region that was near Bonners Ferry to Wenatchee at 06z and expected to reach Pullman-Lewiston 9-10z. Ahead of the front, light to moderate rains will result in 80% chance for MVFR or lower conditions. Behind the front, HREF indicates a 80-90% chance for developing VFR skies with strong midlevel drying. A tight pressure gradient in place through the day Friday will result in persistent winds with gusts 20-27kts.

.FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate confidence for ceiling trends during periods of precipitation. High confidence for LLWS for KPUW-KLWS until the front presses through, especially with prefrontal winds out of the S/SE. High confidence for blustery conditions from the west on Friday. /sb -----------------------

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 39 30 39 28 41 32 / 10 20 40 30 40 70 Coeur d'Alene 41 30 40 29 41 33 / 20 40 70 50 50 90 Pullman 42 30 40 28 40 33 / 60 30 40 20 40 80 Lewiston 47 33 46 33 43 37 / 70 10 10 10 30 70 Colville 39 24 38 26 38 28 / 10 10 60 50 60 80 Sandpoint 39 29 36 30 38 33 / 30 60 90 80 70 100 Kellogg 40 30 35 28 41 34 / 50 80 90 50 60 90 Moses Lake 44 29 44 29 41 28 / 10 0 10 10 20 40 Wenatchee 40 28 40 28 37 28 / 20 20 40 30 40 50 Omak 38 25 36 28 38 28 / 10 10 30 30 50 50

OTX WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory until 4 AM PST early this morning for Lower Garfield and Asotin Counties-Spokane Area-Upper Columbia Basin-Washington Palouse. Winter Storm Warning until 4 PM PST Saturday for Western Chelan County. ID...Wind Advisory until 4 AM PST early this morning for Central Panhandle Mountains-Coeur d'Alene Area-Idaho Palouse- Lewis and Southern Nez Perce Counties-Lewiston Area- Northern Panhandle. Winter Weather Advisory until 10 AM PST this morning for Central Panhandle Mountains.