Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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512 FXUS66 KOTX 151135 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 435 AM PDT Sat Jun 15 2024 .SYNOPSIS... Breezy to gusty winds along with isolated thunderstorms and rain showers are expected Saturday afternoon and evening. Snow will be possible down to 5000 feet. Temperatures will trend cooler into 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. && .DISCUSSION... Today through Sunday Night: Closed low over Vancouver Island will track east across northern Washington and southern British Columbia today. Cooling aloft associated with the low (500mb temps dropping to near -28C), combined with afternoon heating will destablize the atmosphere. Surface based CAPE increases to 200-400 J/KG over the region, except 400-700 J/KG over NE Washington into the Idaho Panhandle where the best chances for thunderstorms will be found. Another story for today will be the wind. A well mixed atmosphere and cold air advection will promote breezy to windy conditions regionwide, with the strongest gusts (30-40 MPH) found across the Columbia Basin into the West Plains and Palouse. Localized gusts to 45 MPH will be found in the windiest prone areas include the Waterville Plateau and Alpowa Summit. Added boost to the gusts will also be found near thunderstorms. Finally, 850mb temperatures drop to near 0C along the Cascade crest this morning and near 2C in the Okanogan Highlands. This will support snow levels near 4500 feet along the crest and 5500-6000 feet in the Okanogan Highlands. This will support light snow over Washington Pass, with a rain/snow mix at Stevens and Sherman Passes. A persistent Puget Sound Convergence Zone will be aimed at near Stevens Pass this afternoon and evening producing moderate rain, with snow possibly mixing in at times. For tonight models continue to advertise clearing skies and decreasing winds for cooler temperatures. Areas of frost are expected for the northern mountain valleys, and across the Upper Columbia Basin, West Plains, and Palouse. There are a couple wildcards though. Cloud cover associated with a deformation zone could hold lows up near the Canadian border. And southwest winds around the Upper Columbia Basin into the West Plains may not completely decouple making it more difficult for temperatures to drop into the mid 30s for frost formation. Frost advisories are in place though given at least patchy frost is likely where winds decouple and skies clear. On Sunday another closed low develops over the region for hit and miss showers. The cold advection comes to an end and pressure gradients are much lighter equating to much less wind. High temperatures will make into the 60s for most areas, although cloud cover over the northern valleys and mountains from a deformation area may mean temperatures don`t even get out of the 50s in some spots such as Colville and Republic. JW Monday through Friday: The Low from Sunday will continue to exit the region through Monday. Ongoing shower activity is expected over Northeast Washington and the Idaho Panhandle. Amounts are not forecast to be more than an additional few hundredths. Weak convection could bring an isolated lightning strike from these showers. High for the day will be in the 60s to low 70s. For the rest of the week, a broad trough will set up over Western Conus. Weak waves of moisture periodically pass through the Pacific Northwest bringing spotty showers chances to the Inland Northwest. The best chances are generally over the mountains. Weak afternoon convection from daytime heating has around a 20-30% chance of generating an isolated thunderstorm. The pattern will allow temperatures to moderate to near normals. Highs will start in the 70s and climb into the 80s and low 90s by the weekend. Overnight lows will start in the 40s and climb into the upper 50s and 60s for Friday night. /JDC && .AVIATION... 12Z TAFS: Winds will increase this morning, with windy west- southwest winds for all TAF sites today. Sustained winds of 15-23 kts, with gusts to 28-35 kts are forecast over the region. A low pressure system moving into the area will also destablize the atmosphere with increasing showers through the day. There is also a 30-50% chance of thunderstorms over Northeast Washington into the Idaho Panhandle, with a 10-20% chance across the Columbia Basin down into the LC Valley and Palouse. KGEG/KSFF are on the fringe of the highest probabilities for thunderstorms with not enough confidence to include in a PROB30 group. Convection will come to an end after sunset with loss of daytime heating, with decreasing winds as well. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence in continued VFR conditions through 12z Sunday at the TAF sites. Increased boundary layer moisture into the Central Panhandle Mountains this morning due to rain showers leads to a 60% chance of MVFR conditions around Kellogg (HREF guidance) between 15-18z. JW ----------------------- 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 64 40 64 40 67 44 / 50 20 20 20 30 20 Coeur d`Alene 61 38 62 39 64 43 / 80 20 20 20 30 30 Pullman 60 36 60 38 61 40 / 50 20 20 20 30 20 Lewiston 71 44 70 46 70 48 / 30 0 20 20 30 20 Colville 62 32 58 34 67 37 / 90 40 50 30 50 30 Sandpoint 59 37 58 38 62 41 / 90 40 40 20 50 50 Kellogg 55 40 58 41 58 44 / 90 30 20 20 50 40 Moses Lake 69 40 68 44 73 45 / 10 0 20 20 10 10 Wenatchee 65 45 66 47 72 47 / 10 10 20 20 10 0 Omak 68 41 62 43 73 45 / 60 10 40 20 20 10 && .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. && $$