FXUS66 KOTX 230616 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 1016 PM PST Fri Nov 22 2024 .SYNOPSIS... The weekend into early next week will feature seasonably cool temperatures and chances for valley rain and brief snow and periods of mountain snow. Moderate rain amounts for portions of eastern Washington and the Idaho Panhandle will lead to the threat of rock and mud slides near steep terrain. && .DISCUSSION... Far north Idaho around Bonners Ferry has been on the rain/snow line the last 24 hours. Early evening spotter reports north of Bonners Ferry observed a couple inches of wet accumulation through the day with a temperature near 32 degrees. The airport has reported a change over to rain this evening with a consistent 32 degrees suggesting that the air aloft has warmed a bit, snow is probably not far away since low level winds on the NAM and GFS remain out of the east through the night. The forecast has been updated to place the snow level between 2000-2500 feet in that area until morning with up to 2 inches in the valley and 4 to 6 inches above 3000 feet. Another problem area through Saturday morning will be the Gwen burn scar south of Julietta, ID. An early morning report of boulders on Highway 12 in the burn scar indicate how susceptible this area is to soaking rain. A Flood Advisory highlighting the potential for rock/mud slides is in effect through the morning with an additional half inch to inch of rain expected. /GKoch .PREVIOUS DISCUSSION... Tonight through Sunday Night: Strong low pressure system will continue to spin off the Washington and southern BC coast. The first band of rain that brought moderate amounts of rain to the region this morning is exiting to the north. The next area of rain is already moving across central WA and will keep rain going across the eastern third of WA and the ID Panhandle this evening through Saturday morning. Most of the aforementioned locations will see another quarter to half an inch of rain...with parts of the ID Panhandle seeing up to three quarters of an inch. Probabilities of three quarters of an inch of rain through Saturday afternoon are over 90% for Sandpoint and Kellogg, and 60-75% for Bonners Ferry, St Maries, Pullman and Deer Park. The Spokane area has about a 30-45% chance. Snow levels this evening will be generally be 4k ft or higher. Towards Saturday morning they will lower down to 3-4k ft. There is some stubborn cold air in the Methow and Bonners Ferry northward. They will transition to rain in the next hour or two, if they have not done so already. Fortunately the Methow valley will not see much more precip this evening or Saturday. Bonners Ferry will need to be watched, as their temps will dip just below freezing Saturday morning and they could see light accumulations as the precipitation begins to wind down. Saturday precipitation will be mostly confined to the WA/ID border eastward. By Sunday morning, a shortwave ridge builds into the area with a weather disturbance moving through. Upslope flow into the Cascades will bring a 40-60% chance of snow. Snow chances across northern WA and the ID Panhandle are about 30-50%. Valley temps will be warm enough by mid to late morning that snow is not expected to accumulate in the valleys. /Nisbet Monday and Tuesday: An upper-level low will remain planted offshore through Monday, slinging weak disturbances into the Inland Northwest and keeping chances for light precip in the forecast. Snow levels fluctuating between 1.5k and 3k ft will bring intermittent snow for the mountains and mountain passes and a mix of rain and snow for valley locations. Valleys north of US-2 have the best chance of receiving lowland snow Monday, though confidence in amounts is low due to the potential for abundant boundary layer moisture and fog formation to keep lower elevations on the warmer side. Chances for at least 1 inch of lowland snow on Monday range from 10 to 30 percent north of a line from Waterville to St. Maries. Heading into Tuesday, the offshore upper-level low will track to the southeast and move inland over the Oregon/California border. Precip chances on Tuesday for our area will recede to the Cascades, Idaho panhandle, and eastern third of Washington. Wednesday through Friday: We'll transition into a cool northwesterly flow regime as a ridge of high pressure amplifies off of the coast over the second half of next week. Temperatures will gradually decrease with highs in the 30s and lows in the teens to 20s. The greatest uncertainty for this period is in regard to precip chances. Models have yet to come to a consensus on where exactly the ridge axis will set up offshore. If the axis is close enough to the coastline, any shortwave disturbances that drop down the east side of the ridge will be deflected into Montana and will bring little to no precip to eastern Washington and Idaho. If the ridge is further west of the coastline, shortwave disturbances may drop right into Washington and Idaho resulting in more precipitation. Currently the forecast has a 20 to 50 percent chance for precip for the Cascades, Idaho panhandle, and the eastern third of Washington, though these chances are subject to change over the next few days as model solutions converge. /Fewkes && .AVIATION... 06Z TAFS: A persistent band of light to moderate rain won't move much until 18-21z when the models finally push it out of eastern Washington and the Coeur d'Alene area. Soaking rain has been common region-wide over the last 24 hours. The combination of wet ground, decreasing winds in the boundary layer, the continued influx of rain, should lead to decreasing visibility and lower ceilings region-wide through mid morning. Drier and cooler air aloft and a modest increase in post-frontal winds should lead to improvements between 18-00z Saturday as the Inland Northwest finally dries out. /GKoch FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moisture laden environments like this are tough as they produce variable low cloud and visibility conditions. Amendments will be necessary as rain intensity varies. /GKoch ----------------------- 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 38 42 32 44 29 40 / 100 80 10 20 10 30 Coeur d'Alene 37 41 32 42 28 40 / 100 100 20 30 20 50 Pullman 38 41 30 42 30 40 / 100 100 20 10 20 30 Lewiston 42 47 35 47 33 47 / 100 100 10 0 10 20 Colville 34 42 27 39 24 38 / 50 50 10 30 30 40 Sandpoint 35 38 28 37 26 36 / 100 90 30 50 20 60 Kellogg 36 38 31 39 25 41 / 100 100 70 40 20 60 Moses Lake 39 45 32 44 32 42 / 30 20 10 20 20 20 Wenatchee 34 43 31 39 33 41 / 10 10 10 20 40 30 Omak 34 42 29 41 32 40 / 20 10 10 20 30 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$