Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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339 FXUS66 KOTX 160457 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 957 PM PDT Sat Jun 15 2024 .SYNOPSIS... Gusty winds along with thunderstorm outflow winds and rain showers into this evening. Snow will be possible down to 4000 feet by Sunday morning. Temperatures will trend cooler into the start of early next week with the potential for frost in colder pockets Sunday and Monday morning. Showers and thunderstorms, mainly in the mountains will be possible each afternoon through midweek with gradual warming by late week. && .DISCUSSION... Tonight through Sunday night: Showers and thunderstorms will develop into the early evening. Thunderstorms will be more isolated in nature over northeast Washington into the Northern Panhandle. A convergence zone extending from around Yakima to the Central Panhandle Mountains will be a source of more substantial convection that forms with thunderstorms more scattered in nature on the Palouse. This convection will wane through the evening with the loss of daytime heating. One area of concern will be for travel over Stevens Pass as the Puget Sound Convergence Zone (PSCZ) will result in more intense precipitation over the pass. Snow levels will be right around pass level and more intense precipitation under the convergence zone may result in heavy wet snow with slippery travel. Total snow accumulation over Stevens Pass is expected to be between 1 to 3 inches, but there is a lot of uncertainty. Warm road temperatures should limit the amount of snow that accumulates, but heavier intensity snow could over come the warm road temperatures. The National Blend of Models indicates a 10% chance for over 4 inches of snow. Winds will also remain breezy into the early evening hours. A wind advisory will remain in effect until 8 PM, but its likely that winds will be just shy of advisory criteria at 20-25 mph sustained and gusts up to 35-40 mph over much of the area. Clouds look to clear out over much of the region aside from over the Cascades and right near the Canadian border. Dry air mixing down with winds weakening will result in good radiational cooling. Low temperature over much of the upper basin into the Spokane Area, Palouse, and northern mountain and Panhandle valleys are expected to drop down into the lower to mid 30s. A frost advisory remains in effect. People with sensitive vegetation should cover their plants to protect from frost damage. An area of deformation over southern British Columbia will move south into the northern mountain zones by Sunday morning. Snow levels will be down around 4000 feet with light snow expected over Washington Pass and Sherman Pass. Snow looks to get going late enough in the day at Sherman Pass that it may have a hard time accumulating. Sunday will be a cool and showery day over the northern mountains and into the Cascades. Precipitation amounts will be light, but it will be welcomed precipitation for an area that is seeing moderate drought conditions. There will also be a 15-20% Chance for thunderstorms on over the mountains as the deformation band breaks up and weakens with sun breaks warming up the surface and destabilizing lower levels of the atmosphere. /SVH Monday through Saturday: The broad upper level trough will dip through the Northern Rockies Monday and head southeast. The Inland Northwest will be left in a deformation zone, prime for unsettled cloudy conditions especially in the higher terrain areas. Monday and Tuesday temperatures will remain below normal under the cold air aloft, and then Wednesday into next weekend the warming trend will settle in as daytime temps climb back into the 80s. Speaking of Monday and Tuesday, the cold air aloft and cooler profile (850mb temps 2-4C), there is some ensemble guidance suggesting up to 3-4" of snow in the far north Cascade mountains along the crest. These values are at the 90th percentile, with only up to 1-2" for the forecast mean. Needless to say, it will be difficult to accumulate anything on roads this time of year. Midweek through late week, the flow aloft will shift more zonal versus northwest as we maintain a broad yet weak trough pattern across the Northwest. A rather weak ridge will begin to build by late week, which will aid our daytime heating to settle into a warming trend through the week ahead. Little to no weather hazards are expected during the workweek at this time, outside of some terrain driven showers early in the week. /Dewey && .AVIATION... 06Z TAFS: Snow showers will continue in the Cascades through the night. Rain showers will go for another couple hours along the US/Canadian border. Showers will regenerate again Sunday especially across northern WA/ID and central WA with some embedded thunderstorms across NE WA and north ID. Have mention of some -shra for MWH/EAT, but confidence was not high enough to put mention elsewhere. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence in continued VFR conditions through Sunday morning. One potential caveat is there is a 10% chance of MVFR ceilings to develop at KPUW between 15-18Z. ----------------------- 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 40 64 40 67 43 71 / 20 10 10 30 10 20 Coeur d`Alene 38 61 39 64 43 66 / 20 10 10 30 30 30 Pullman 36 60 39 61 40 68 / 20 10 10 30 20 10 Lewiston 44 68 48 69 48 76 / 0 10 20 40 20 10 Colville 32 59 32 66 36 68 / 40 50 40 50 30 50 Sandpoint 37 58 38 63 42 62 / 40 30 20 50 50 60 Kellogg 40 58 42 58 45 63 / 30 10 20 50 40 40 Moses Lake 40 69 43 73 44 77 / 0 20 30 10 0 0 Wenatchee 45 66 47 71 48 76 / 10 30 30 10 0 0 Omak 41 64 44 73 45 76 / 10 30 30 20 10 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Frost Advisory from 1 AM to 8 AM PDT Sunday for Central Panhandle Mountains-Idaho Palouse-Northern Panhandle. WA...Frost Advisory from 1 AM to 8 AM PDT Sunday for Northeast Mountains-Okanogan Highlands-Spokane Area-Upper Columbia Basin-Washington Palouse-Western Okanogan County. Wind Advisory until 8 PM PDT this evening for Lower Garfield and Asotin Counties-Moses Lake Area-Spokane Area-Upper Columbia Basin-Washington Palouse. && $$