Marine Weather and Tide Forecast for Lewiston, ID

SYNOPSIS
A cool and showery weather pattern will continue through at least early next week. In addition, breezy winds are expected at times.

DISCUSSION
Tonight through Friday Night: A weakening and stretching frontal boundary moving into western Washington this afternoon will cross the Cascades into Central WA this evening, and then into Eastern WA/N Idaho overnight into Friday morning. Despite the weakening nature, models are in good agreement that as the front encounters the rising terrain of Eastern WA/N Idaho light rain will develop.
Also boosting confidence in the high moisture content with this wave as precipitable water values increase to 125-140 percent of normal. For Central WA weak downslope flow off the Cascades combined with dry air in the lower levels to initially overcome is expected to result in little to no rain for places like Omak, Wenatchee, and Moses Lake. Friday afternoon as this wave exits showers will become focused over the orographically favored terrain of NE Washington and the ID Panhandle. For Friday Night the next system approaches with a chance of showers mainly in the Cascades and NE Washington. JW

Friday night through Sunday morning: A low pressure system off the coast of the Pacific Northwest will begin spinning up Friday evening into Saturday. By Sunday, the system will be moving southeast and stretching, centered over Idaho and Utah. This system will bring a rainy weekend to most of the forecast area.
Ensembles and clusters are still struggling with the track of the low, with half the WPC clusters favoring the low swinging further south and the other half showing it staying a bit north of Utah. There is also the chance for a deformation band to move through the Lewiston/Pullman/southern Panhandle area, which could lead to higher rain amounts. Currently, in far eastern Washington (Spokane/Pullman/Northeast Blue Mountains) and the Idaho Panhandle have a 30 percent chance or higher of seeing at least a quarter inch of rain between Saturday and Sunday afternoon. Other parts of the forecast area, including the Cascades and areas east of Omak, have a 20 percent chance or higher of seeing a wetting (0.1 inches) amount of rain, with those percentages increasing as you move eastward. On Saturday afternoon, as the trough axis is sitting right above us, there will be enough lift for a chance of thunderstorms. While SBCAPE is relatively low (100 to 200 J/kg), there could be a few isolated thunderstorms throughout the day across the forecast area. As such, the SPC has us in general thunderstorms Saturday afternoon and evening. The heaviest rain will occur late Saturday night through Sunday afternoon, with the highest rainfall totals anticipated in the southern Panhandle and the Northern Mountains. Due to the aforementioned ensemble model disagreement, we will keep a close eye on this system in the next few days, as any major changes in the low pressure track have the potential to change rainfall totals.

After the low pressure system moves out of the area, weather will remain slightly unsettled with light bouts of precipitation as small waves move through. This precipitation will be mainly confined to the mountains due to orographic lift.
As mostly dry conditions prevail, temperatures will rise back into the mid to high 60s for much of the area. Right now, due to much of the area outside of the mountains being dry after the weekend storm, the CPC's 6-10 and 8-14 Day Outlooks have the forecast area either at near normal or leaning below normal precipitation through the end of May. /AS

AVIATION
06Z TAFS: VFR conditions will continue through 12z tonight. A system comes in overnight, with a chance for -ra over TAF sites.
Around 12-14z, light rain will increase over the eastern TAF sites, with widespread MVFR conditions expected to develop.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: MVFR conditions will develop overnight.

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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 44 57 44 64 45 57 / 40 70 20 60 60 60 Coeur d'Alene 43 54 41 65 45 55 / 30 70 20 60 60 70 Pullman 42 55 41 61 42 55 / 40 70 10 60 70 60 Lewiston 48 62 46 69 49 61 / 50 70 10 60 70 60 Colville 43 56 39 63 39 60 / 20 60 40 70 60 60 Sandpoint 43 54 42 64 44 54 / 20 70 40 60 60 80 Kellogg 42 52 43 62 47 50 / 30 70 20 50 70 80 Moses Lake 46 69 49 68 45 67 / 20 20 10 60 40 10 Wenatchee 47 68 49 66 48 63 / 20 10 10 60 30 10 Omak 47 65 46 65 44 65 / 20 40 20 70 60 20

OTX WATCHES/WARNINGS/ADVISORIES
WA...None.
ID...None.