West Clarkston-Highland, WA Weather

Key Messages

- Light rain chances through Tuesday morning with the first of two weather systems moving through. Lingering showers in mountains through Tuesday afternoon.

- On Tuesday night, another colder system moves in, with snow levels lowering to 2500 to 4000 feet. Mountain snow will start Tuesday night and continue through Thursday, bringing winter travel over mountain passes in the Cascades.

Synopsis

The first of two weather systems moved across the area today and brought light precipitation, especially across southeast WA and the ID Panhandle. A second, colder weather system moves in on Tuesday night through Thursday night. This will drop snow levels to 2500 to 3000 over the Cascades and north- central WA and down to around 4500 feet in the ID Panhandle. Valley rain and mountain snow is expected, with winter travel conditions over mountain passes.

Discussion

Today through tomorrow afternoon: An upper-level low off the Washington coast is moving southeastward, and will bring a few rain bands through the forecast area as the day goes on. Snow levels are 5000 to 6000 feet, and little to no snow accumulations are expected. Precipitation totals will overall be low across the Inland Northwest, with 0.05-0.10 inches expected. Higher rainfall totals will be confined to far SE Washington and the central ID Panhandle, where rainfall totals could reach 0.3-0.35 inches. Though the low will move out of the area by late tonight, residual moisture will keep showers across the mountains, WA/ID Palouse, and ID Panhandle. For the Spokane to Wenatchee area and southward, there will be a break in precipitation Tuesday morning through afternoon.

Tuesday evening through Thursday: On Tuesday evening, another stronger low pressure system will move southward down into the forecast area. This will be a colder system, with snow levels lowering to 2000 to 3000 feet. Snow will start late Tuesday night in the Cascades, then will start in the northern mountains and ID Panhandle early Wednesday morning. Stevens and Washington Passes have the highest probabilities of receiving 6 inches or more of snow over 48 hours, with a 35-40% chance. Other passes, including Sherman, Lookout, and Blewett Passes, have a 15% chance or less of 4 inches. This will create winter driving conditions at Stevens and Washington Pass, and a Winter Weather Advisory has been issued for these passes from Tuesday afternoon through Wednesday afternoon. Elsewhere, expect light precipitation. Temperatures will be cooler after the low moves through, with highs in the 40s and low 50s and lows in the 30s.

Friday through Monday: The low will remain just off the Washington coast for Friday and Saturday, weakening each day. As it weakens, chances for precipitation decrease. Main chances for showers are in the mountains due to orographic lift. Long-range models show snow levels dropping to 2000 feet over north central Washington, but given the decrease in precipitation chances, snow accumulations are not expected at this elevation. Any lingering showers will be light. Sunday into monday, the low will shift southward and a ridge will build into the area, prompting warm-up into Monday. Ensemble clusters show 80% support for this pattern, favoring a warming trend into Monday. /AS

Aviation

18Z TAFS: Current radar depicts band of precipitation associated with a low pressure system just off the Washington coast. Terminals that are seeing rain or will see rain within the hour include EAT, PUW, and LWS. Showers look to develop a little later, around 19Z, are GEG and SFF. COE will see rain just a bit later at 20Z. MWH looks to be mostly rain shadowed and chances for precipitation are too low (10-15%) to be included in the TAFs. The first band of rain will end around 02Z for EAT and LWS. LWS will see a short break in rainfall through 06Z. GEG, SFF, COE, and PUW look to see prevailing rain through 12Z, then chances lower to PROB30. With this rainfall moving in, GEG, SFF, COE, and PUW all have a moderate chance at seeing ceilings drop to MVFR once the rain starts, and ceilings look to remain at MVFR into the next TAF period.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: As rain spreads across the forecast area, there is a moderate chance of MVFR conditions at GEG, SFF, COE, and PUW between 19Z and the end of the forecast period. There is moderate confidence in timing of rainfall. The primary alternate scenario involves ceiling restrictions, and amendments may be needed if ceilings are lower than anticipated. /AS

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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