Marine Weather and Tide Forecast for Manson, WA

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
Tonight through Saturday: An upper level trough swinging across the Inland NW will send a fast moving mid level frontal boundary across Eastern WA/North ID this evening. Not much of this stratiform rain band will survive east of the Cascades due to swift mid level downslope westerly flow off the Cascades, some drier air to overcome in the low levels, and the quick movement of this front. Yet mid level instability with the incoming trough combined with increasing lift will lead to an increase in rain showers as mid-level lapse rates steepen across the region tonight into Saturday. This will be especially true along the Cascade crest, Northeast Washington, and the ID Panhandle where low level upslope flow will provided an added boost of lower level lift. Snow levels start off around 4000 feet along the Cascade crest, 5500 feet for the ID Panhandle early this evening, before dropping to 3000-4000 feet Saturday morning. Stevens Pass is expected to be impacted by periods of moderate to heavy snow showers with 4-6 inches, with NBM carrying a 20% chance of amounts exceeding 8 inches. For Lookout Pass there is a 50 percent chance of 1 inch of snow. Lapse rates will steepen further Saturday afternoon when daytime heating kicks in and the upper low moves overhead, with uncapped surfaced based CAPE of 300-600 K/KG. This is expected to lead to isolated thunderstorms across the region with brief downpours, gusty winds, and small hail. A well mixed air mass and a PDX-GEG pressure gradient around 10 mb will also help promote breezy winds across the region, especially in Central Washington with gusts of 25-40 MPH. Temperatures on Saturday will be well below normal with highs in the 50s to low 60s, with even some upper 40s in the ID Panhandle. These values are around 10 to 15 degrees below normal.

Saturday Night and Sunday: The low will shift east into NW Montana Saturday Night. Showers rotating around the back side of the low will track near the ID Panhandle Saturday Night into Sunday morning with snow levels as low as 3000-4000 feet. This could bring more mountain snow to Lookout Pass with a 50 percent chance of an additional inch. Despite the departing low Sunday, lapse rates remain steep as lower levels warm, with a 10-20% chance of thunderstorms over NE WA/ID Panhandle.

Frost potential this weekend: Breezy winds and/or cloud cover tonight is expected to keep the frost threat low so no additional highlights have been issued. Yet localized frost is possible especially around the Methow Valley. Saturday night cloud cover over SE WA/ID Panhandle may limit the potential gain, but clearing over NE Washington and winds decoupling is the most likely area and timing for near freezing temperatures.
More patchy frost is possible for Sunday Night, with broader clearing leading to broader potential over Eastern WA/N Idaho.

Monday through Thursday: Ensembles show a warming and drying trend during this part of the forecast. Some weak waves passing through could produce a few mountain showers at times during the afternoon/evening hours but otherwise dry conditions are expected to prevail. High temperatures by Wednesday and Thursday moderate back towards normal values with readings in the upper 60s and 70s. JW

AVIATION
00Z TAFs: A low pressure system will bring scattered light showers to the Inland Northwest this evening. Showers will then continue across the Idaho Panhandle overnight. Low stratus or stratocumulus clouds are expected to develop over the Idaho Panhandle for Saturday morning with the additional moisture in the boundary layer. This will bring MVFR ceilings to KCOE and KPUW, and potentially as far west as KSFF and KGEG starting around 12Z. MVFR conditions will continue until 16-18Z and then ceilings lifting above 3 kft agl thereafter into the afternoon.
Westerly winds will remain breezy. Gusts will decrease late this evening into the overnight periods, but will see gusts pick up again up to around 25-30 kts by late morning and continuing into the afternoon Saturday. Diurnally forced showers with isolated thunderstorms is also expected for Saturday afternoon.

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.
There is a 40-60% chance for thunderstorms to impact KCOE/KSFF- KGEG/KPUW by 20Z on Saturday. /SVH

----------------------- 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 55 37 61 37 65 / 30 60 20 20 10 0 Coeur d'Alene 39 51 36 58 37 63 / 50 80 30 30 10 10 Pullman 39 51 35 55 34 61 / 20 70 50 20 10 0 Lewiston 44 57 40 59 39 66 / 20 50 40 30 10 10 Colville 36 57 33 66 32 68 / 30 70 50 10 10 20 Sandpoint 39 49 36 58 36 62 / 50 80 40 40 10 20 Kellogg 36 47 34 55 35 62 / 60 100 50 60 20 30 Moses Lake 42 63 39 69 39 72 / 20 10 0 0 0 0 Wenatchee 42 61 42 68 45 71 / 20 0 0 0 0 0 Omak 38 60 39 69 41 71 / 20 50 10 0 0 10

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