Marine Weather and Tide Forecast for Lewiston, ID

SYNOPSIS
Temperatures will gradually warm through Sunday as high temperatures warm into the 70s and 80s for the weekend. There is growing potential for showers and thunderstorms from Sunday night into Memorial Day.

DISCUSSION
Friday through Sunday: Weather will trend warmer and drier for this weekend as an upper level ridge builds over the Pacific Northwest in response to a closed low over the Gulf of Alaska digging off the west coast. For Friday, residual moisture from yesterday's showers combined with weak ascent from a passing weak vort lobe will support scattered afternoon showers primarily across the northern mountains and the Idaho Panhandle.

Models are in good agreement for the upper level ridge to strengthen over the Inland Northwest Saturday and Sunday as a slow moving cold front and upper level trough near the west coast. There is high confidence for temperatures to warm into the mid 70s to low 70s on Saturday, then for widespread highs in the 80s on Sunday. These temperatures will be 12 to 17 degrees above average for this time of year and result in a minor risk for heat related illnesses for individuals extremely sensitive to heat. Those planning to spend the holiday weekend out on the lake or river should prepare for very cold water temperatures.
Please wear a life jacket if heading out on the water.

Sunday night into Monday: A breakdown of the upper level ridge looks to take place Sunday night into Monday. Deep southerly flow ahead of the cold front will bring anomalous moisture into the Inland Northwest with PWATs 150-200 percent of normal.
Following the very warm day on Sunday, we will need to monitor this period for thunderstorms late Sunday into Monday morning across central Washington and then into eastern Washington and north Idaho by the late morning and afternoon. High temperatures on Monday are currently forecasted to cool by about 10 degrees compared to Sunday. In addition to the thunderstorm potential, breezy west to southwest winds will accompany the cool down.
Sustained winds of 15 to 25 mph with wind gusts 25 to 35 mph are not strong enough to result in widespread impacts, but are enough to result in choppy conditions over area lakes. Those heading out on the water for the holiday should be prepared for these conditions.

Tuesday through Thursday: Models are in general agreement for the upper level ridge to rebuild over the Inland Northwest with temperatures trending into the 80s and low 90s by Wednesday.
Confidence in the forecast wanes for Thursday as 50 percent of the global ensembles show an upper level trough breaking down the ridge. This scenario would bring cooler temperatures along with the potential for showers and thunderstorms. The other 50 percent of global ensembles keep the ridge in place with a warmer and drier forecast. /vmt



AVIATION
12Z TAFS: A weak upper system pushes by today, with isolated showers around the mountains but the TAF sites are forecast to remain dry. Recent rain and lower level moisture may produce some patchy fog in the vicinity of GEG/SFF/COE/PUW this morning, but confidence is too low to include in a TAF.
Otherwise look for partly to mostly cloudy skies.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: This carries a very low confidence, but residual boundary layer moisture combined with clearing may allow for patchy fog to develop over the ID Panhandle valleys and near SFF/GEG/COE/PUW.

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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 68 44 75 49 83 54 / 0 0 0 0 0 20 Coeur d'Alene 68 44 76 48 83 52 / 10 0 0 0 0 10 Pullman 66 43 73 47 81 51 / 0 0 0 0 0 20 Lewiston 74 49 80 53 88 57 / 0 0 0 0 0 10 Colville 70 40 76 42 83 49 / 10 0 0 0 0 30 Sandpoint 67 44 75 47 83 51 / 20 0 0 0 0 10 Kellogg 64 47 73 51 82 54 / 10 0 0 0 0 10 Moses Lake 76 47 81 50 89 57 / 0 0 0 0 0 50 Wenatchee 75 51 80 56 87 58 / 10 0 0 0 0 50 Omak 75 47 80 49 86 55 / 0 0 0 0 0 50

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