Marine Weather and Tide Forecast for Winthrop, WA

SYNOPSIS
A cold front passage this afternoon into Wednesday will bring lowland rain, mountain snow, and breezy to windy conditions. Some snow will make it down to the lowlands Wednesday night into Thursday morning on the tail end of the mid-week system.

DISCUSSION
Tonight through Thursday: A Gulf of Alaska Low continues pushing a decent amount of moisture and cooler air into the Inland Northwest. Precipitable water amounts are around half an inch (120-140 percent above normal). The colder air will drop the snow levels from 4000ft to 2000ft through Wednesday.
Mountain snow will continue with valleys along the Cascades and northern valleys changing from rain to rain/snow mix or snow by early Wednesday morning. Snow accumulation will be confined to above 3500ft as ground surface temperatures will be too warm for snow accumulation. Winter weather advisories and a warning have been issued for many of the regions mountain passes through Thursday. Stevens Pass has a 25-75 percent probability snow range of 11-13 inches. Sherman has a 4-5 inches range. Lookout has a 9-14 inch range. Snoqualmie Pass has a 12-14 inch range.
Models are indicating weak convection over the higher terrains of the region. The strongest chance for thunder is over Northeast Washington and North Idaho. There is not enough confidence to include thunder for the Cascades.

The Low is also tightening the pressure gradient as it swings through the region. It will lead to breezy conditions through the period. Strongest winds will be tonight with gusts into the 30-40 mph range across the Basin. Winds will remain breezy with gusts 15-25 mph. Sustained winds will be in the teens.

Overnight temperatures are also expected to dip. While the highs will mainly be in the 40s to low 50s. The lows will drop into the upper 20s and 30s Wednesday night into Thursday morning. Portions of the Columbia Basin have reached early growing season. Cold sensitive vegetation could be impacted. If winds remain breezy, it will lower the potential for frost/freeze impacts.

Friday through Tuesday: High pressure fills in behind the exiting Low. A dry warning trend is expected through the weekend and into the start of next week. Something to keep an eye is a Low moving near coast of Southern Oregon on Monday. Depending on the strength and placement, it could lead to light showers returning to the region for the start of the week. /JDC

AVIATION
18Z TAFS: The next system moves in today into tonight with rain and a return to MVFR at GEG/SFF/COE/PUW. Downslope flow off the Cascades will keep conditions VFR at KEAT/KMWH, while similar effects off the Blue Mountains keep LWS VFR until after the cold front passage Wednesday morning. CIGS are expected to degrade further as well for KPUW, becoming IFR around 15z Wed. The system will also usher in gusty west-southwest winds through the TAF period, shifting to west-northwest behind the cold front in Central WA Wednesday morning.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Moderate confidence in CIGS dropping to MVFR for KGEG/KSFF/KCOE/KPUW tonight. Moderate confidence in KPUW dropping to IFR 15-18z Wed. High confidence that VFR conditions persist through the TAF period at KEAT/KMWH. JW

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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

Preliminary Point Temps/PoPs
Spokane 38 49 29 50 29 54 / 80 70 30 30 0 0 Coeur d'Alene 37 47 30 48 29 51 / 100 90 50 50 10 10 Pullman 37 44 29 45 29 50 / 90 90 60 50 10 10 Lewiston 43 51 34 50 34 55 / 80 90 50 40 10 0 Colville 34 52 27 54 26 59 / 90 60 30 30 0 0 Sandpoint 37 45 30 46 29 51 / 100 90 60 70 20 20 Kellogg 36 42 28 42 29 46 / 100 90 70 80 30 40 Moses Lake 39 56 30 58 30 60 / 30 20 10 0 0 0 Wenatchee 37 51 33 55 34 59 / 50 20 10 0 0 0 Omak 35 53 31 58 32 61 / 50 20 10 0 0 0

OTX WATCHES/WARNINGS/ADVISORIES
WA...Freeze Watch from late Wednesday night through Thursday morning for Moses Lake Area-Upper Columbia Basin- Wenatchee Area.
Winter Weather Advisory until 5 PM PDT Wednesday for Okanogan Highlands.
Winter Storm Warning until 5 AM PDT Wednesday for Western Chelan County.
Winter Weather Advisory until 5 AM PDT Wednesday for Western Okanogan County.
ID...Winter Weather Advisory from 8 PM this evening to 5 AM PDT Thursday for Central Panhandle Mountains.