Marine Weather and Tide Forecast for Spokane Valley, 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
00Z TAFS: The next system has moved in, ushering in rain and lowering ceilings at GEG, SFF, COE, and PUW. As these rounds of precipitation move through, ceilings will drop to MVFR. Ceilings may improve to VFR briefly in between rounds of precip. There is little confidence for all sites but PUW to drop further to IFR. Ceilings are expected to drop down to IFR at PUW around 14-15Z. Gusty west- southwest winds are being observed at each TAF site, with maximum wind gusts expected to hit 25-30kts.
Behind the front, colder air will move in, with HRRR showing a 20-40% chance of a rain snow mix at GEG, SFF, COE, and PUW starting around 18Z. However, whether thermal profiles will cool enough for mixed rain/snow is one of the more uncertain parts of this forecast, since GFS/ECMWF wet bulb temps remain above freezing and indicate only rain. This will be something to closely monitor. Winds are expected to stay elevated even after the cold front passes, and through the forecast period. MWH/EAT will remain at VFR through the forecast period, and is expected to see chances of rain through around 12Z.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence in precipitation type through 18Z for all TAF sites. Moderate confidence in ceilings dropping to MVFR with precipitation at GEG, SFF, COE, and PUW. Moderate confidence in PUW dropping to IFR starting around 14-15Z. Low to moderate confidence in a rain/snow mix at GEG, SFF, COE, and PUW starting around 18Z. Most impactful alternate scenario would be either precipitation remaining rain or staying as a rain mix later than expected, which would require amendments. /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

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.