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Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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940 FXUS66 KOTX 142258 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 358 PM PDT Wed Aug 14 2024 .SYNOPSIS... The next weather system will move into the Inland Northwest from the southwest Thursday afternoon. Thunderstorms Thursday afternoon into Thursday night will bring the potential for gusty outflow winds. This will be followed by wetter showers and thunderstorms on Friday particularly across the Idaho Panhandle and northern mountains. Daytime temperatures will be near normal through the week. && .DISCUSSION... Tonight: The Inland Northwest is currently placed under a weak ridge as an upper level low off the Oregon coast begins to move inland. This weak ridge will bring another beautiful night across eastern Washington and north Idaho with clear skies, light winds, and cool temperatures. Thursday and Friday: The upper level low will move onshore Oregon late tonight and move northeastward into the Inland Northwest Thursday afternoon and evening. Thunderstorms will begin over eastern Oregon and shift northward to southeastern Washington and the southern Panhandle Thursday afternoon. Models are showing surface CAPE increasing to 500-1000 J/kg and across the Cascades, southeastern Washington and the Idaho Panhandle Thursday afternoon. The best chances for stronger thunderstorms will be focused across southeastern Washington and the southern Panhandle where the strongest lift and 25 to 30 knots of 0-6km bulk shear will aid in development. Precipitable water values climbing to over an inch Thursday and Friday will support wet thunderstorms. The biggest concerns will be for brief heavy rain, gusty outflow winds, and new fire starts for lightning strikes outside the strongest precipitation cores. Showers will shift northward across north Idaho and northeastern Washington overnight. Decreasing instability after sunset will reduce the risk for lightning but isolated strikes cannot be fully ruled out. Focus will shift to the north Cascades and northern mountains on Friday as a shortwave moves across eastern Washington. Models are showing slow storm motions combined with forecasted surface CAPE of 400 to 800 J/kg. Any storms that develop will bring the risk for lightning and heavy rainfall Friday afternoon and evening. Any showers that form over burn scars or recently burned areas will bring the threat for flash flooding or debris flows. /vmt Saturday through Tuesday: Heading into early Saturday morning, a large trough will establish itself just offshore while a ridge simultaneously sets up to our east over the Rockies. As a result, the Inland Northwest will be caught between the two in a stream of southwesterly flow. Warm, moist air flowing in out of the southwest will keep us in somewhat of an active, unstable pattern with chances for showers and thunderstorms through the weekend and into next week. What we don`t know yet is exactly how far offshore the trough will develop. The trough`s distance from the shore will play a big part in how warm our temperatures get, how much precip we`ll see, and where that precip will fall. Ensemble members are split 50/50 on whether the trough will be closer to shore or further away. If the trough is closer, temperatures will be a bit cooler, rainfall amounts will be higher, and chances for showers and thunderstorms will reach further east. If the trough sets up farther offshore, the ridge to our east will have a greater influence on our weather conditions. This means temperatures would be on the warmer side and we`d get less rainfall, especially in the eastern parts of the region. Saturday looks like the most active day with widespread chances for showers and thunderstorms. The highest chances will be over the Cascade Crest (70 percent chance of showers and 20 percent chance of thunderstorms). Central WA and Northern WA right along the Canadian border will have a 30 to 50 percent chance of showers and a 10 percent chance of thunderstorms. The rest of the region including Ritzville up to Spokane, Sandpoint, and Bonners Ferry will have around a 20 percent chance of showers and minimal thunderstorm chances. There is a possibility for storms to continue into Saturday night, but instability is not looking very impressive so it`s unlikely that storms will survive very long after the daytime heating subsides. Slight chances for showers and thunderstorms will pop up each afternoon Sunday into the first half of next week mainly over the Cascades and northern mountains. Winds will be breezy each afternoon with gusts in the 15 to 20 mph range, but no significant wind events are expected. /Fewkes && .AVIATION... 00Z TAFS: Weather will be quiet across the Inland Northwest this evening and Thursday morning. Look for generally light winds and terrain driven wind shifts with mainly clear skies east of the Cascades. Clouds will begin to increase from the south late Thursday morning as a weather system moves into eastern Washington and north Idaho Thursday afternoon. This will bring chances for thunderstorms across the Cascades and southeast Washington and southern Panhandle Thursday afternoon. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high for VFR conditions at TAF sites for the next 24 hours. There is low confidence thunderstorms will make it into LWS by 00Z tomorrow, with better chances after 00Z. ----------------------- 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 56 87 59 81 56 88 / 0 0 30 20 10 10 Coeur d`Alene 54 86 58 78 54 86 / 0 10 50 40 10 10 Pullman 48 81 52 78 51 87 / 0 10 50 20 10 10 Lewiston 62 89 63 87 62 95 / 0 20 50 20 10 10 Colville 47 88 49 80 44 86 / 0 0 20 30 10 10 Sandpoint 49 84 55 73 51 82 / 0 10 50 50 20 10 Kellogg 59 83 58 75 57 85 / 0 20 70 60 10 10 Moses Lake 54 87 56 84 55 88 / 0 0 20 10 0 20 Wenatchee 63 87 63 83 62 85 / 0 10 20 10 10 30 Omak 59 93 62 87 59 90 / 0 0 20 30 10 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$