Marine Weather and Tide Forecast for Troy, MT

UPDATE
A Winter Weather Advisory has been issued for the Stevens Pass area from 8 PM tonight through 11 AM Saturday morning. An incoming weather system will result in increasing precipitation along the Cascade crest through the day. But the warm road temperatures of mid-May will make it difficult to stick other than grassy surfaces. This is expected to change tonight with the setting sun, as well as increasing lapse rates as the cold pool associated with the upper low moves overhead combined with low level upslope westerly flow. This will result in moderate to locally heavy snow showers, with 4 to 6 inches forecast to call through Saturday morning. JW

SYNOPSIS
Breezy winds and chances for mostly mountain showers and thunderstorms linger Thursday through Saturday. Some frost is possible toward Friday into the weekend.

DISCUSSION
Friday through Sunday: The weekend will remain active as another shortwave moves through the forecast area. This will result in colder than normal temperatures, continued gusty winds, rain showers, and mountain snow. The low that moves through tomorrow will be the strongest of the multiple shortwaves that tracked through the area. This continued westerly flow will cross the Cascade gaps and spill into the rest of the basin, keeping winds elevated through Saturday.
Expect wind gusts 20-25 mph each afternoon through Saturday, with stronger gusts 30-40 mph along the Cascade gaps. Though wind headlines are looking unlikely, impacts such as blowing unsecured objects and small tree limbs alongside difficult driving conditions for high profile vehicles could be seen.

This low will bring precipitation to the area, but it will not be widespread due to rain shadowing in the deeper basin.
Precipitation will be mostly confined to the mountains and fall Saturday morning through evening. Only mountain areas will see more than 0.10 inches of rain, with Spokane, Lewiston, Pullman, and Omak seeing a couple hundredths of an inch. This will be a colder system, with 850mb temperatures 5-10 degrees lower than normal. This will result in mountain passes seeing a return of snow and associated travel impacts. Through Sunday, Stevens Pass has a 50% chance of seeing 6 or more inches of snow. Lookout Pass will receive less, with a 60% chance of 2 inches or more of snow. Much of this snow will fall Saturday. Travelers should prepare for wintry travel conditions across mountain passes over the weekend.

Overnight temperatures through Monday will be 5-10 degrees cooler than normal, falling into the mid-30s. Given that growing season has started, frost impacts look likely. Tonight, there is a Frost Advisory out for the Northeast Mountains, Okanogan Highlands, and Western Okanogan County, which have a 60% chance of seeing overnight temperatures 36 degrees or lower. Coverage of 60%+ probabilities increases tonight into Saturday and expands down into the Spokane and Palouse area Saturday evening into Sunday. Frost Advisories are likely, and these temperatures could harm sensitive outdoor vegetation.

There is a chance for thunderstorms each afternoon and evening through Sunday as well as the low passes through. Tonight, thunderstorms will largely be confined to the Cascades and northern mountains. Through the weekend, lowering temperatures will increase lapse rates. CAPE values of 100-200 J/kg will be seen over northeast Washington and the Idaho Panhandle, resulting in a 20-30% chance of thunderstorms Saturday and Sunday evening.

Monday through Wednesday: Clusters and long term models are in decent agreement of a strengthening upper level ridge moving in as the low pressure system tracks eastward. This will usher in temperatures warming to near or slightly above normal and drying conditions. Uncertainty in the long term pattern comes from 15% of clusters showing the low over the Central US retrograding back west, bringing cooler temperatures and more chances for precip. /AS

AVIATION
18Z TAFs: Another incoming weather system will bring increasing showers across the region starting in the Cascades and northern mountains today before expanding tonight into Saturday morning.
Most of these showers in the lowlands will be isolated to scattered in coverage with the highest focus in the Cascades, NE Washington, and ID Panhandle due to swift mid level westerly flow resulting in some rain shadowing across Central Washington.
Look for increasing clouds, with predominantly VFR conditions this afternoon into the evening. Then a moistening boundary layer from showers will lead to increasing areas of MVFR conditions over NE WA/N Idaho overnight into Saturday morning.
There is also a slight for thunderstorms this afternoon mainly near the Canadian border. Breezy conditions will continue with west- southwest winds over the region.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Latest HRRR guidance starting around 08z-11z tonight through 18z Saturday has a 60-90% chance of MVFR conditions developing at KPUW/KCOE, near 50% for KGEG/KSFF, 10% KLWS, AND 0% KEAT/KMWH.
JW

----------------------- 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 58 39 55 35 61 37 / 0 30 60 20 20 10 Coeur d'Alene 56 39 51 35 58 37 / 0 50 80 30 30 10 Pullman 56 39 51 34 55 34 / 0 20 70 50 20 10 Lewiston 64 44 57 40 59 39 / 0 20 50 40 30 10 Colville 60 36 57 29 66 32 / 10 30 70 50 10 10 Sandpoint 55 39 49 35 58 36 / 10 50 80 40 40 10 Kellogg 55 36 47 35 55 35 / 10 60 100 50 60 20 Moses Lake 63 42 63 36 69 39 / 0 20 10 0 0 0 Wenatchee 60 42 61 42 68 45 / 10 20 0 0 0 0 Omak 61 38 60 37 69 41 / 30 20 50 10 0 0

OTX WATCHES/WARNINGS/ADVISORIES
WA...Winter Weather Advisory from 8 PM this evening to 11 AM PDT Saturday for Western Chelan County.
ID...None.