Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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848 FXUS66 KOTX 152228 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 328 PM PDT Thu Aug 15 2024 .SYNOPSIS... Showers and thunderstorms will continue through this evening and overnight across eastern Washington and north Idaho. Thunderstorms Thursday will bring the potential for gusty outflow winds. Thunderstorms will return on Friday across the northern mountains with concerns for flash flooding over burn scars. More showers and thunderstorms are possible late Saturday afternoon and night for central WA. Temperatures will be warmer on Saturday with dry and breezy northeast winds across the Columbia Basin, West Plains, and southeast Washington. && .DISCUSSION... Tonight and Friday: An upper level trough in eastern Oregon will move northward into eastern Washington and north Idaho late this afternoon and evening. Weak impulses rotating around the main trough has allowed for thunderstorm development over the central Panhandle mountains this afternoon. As the main trough over eastern Oregon moves north into the region, there will be another round of showers and thunderstorms to move into the central Panhandle and southeast Washington later this evening and move into the CdA/Spokane area overnight. The biggest concern with convection will be lightning and gusty outflow winds. Models are showing DCAPE (downdraft CAPE) between 800-900 J/kg for the Camas Prairie, into southeast Washington, and across much of the Central Panhandle Mountains. Wind gusts up to 40 mph will be possible with stronger convective cells. Convection then looks to transition into more of a stratiform precipitation with isolated lightning overnight as instability decreases across the Northern Panhandle into the Northeast Mountains and Okanogan Highlands. On Friday, models indicate 500-1000 J/kg of surface based CAPE from the east slopes of the northern Cascades and across the northern mountains for Friday afternoon and evening. Model soundings are showing moist and unstable profiles with very slow storm motions. Forcing does not look to be overly strong with convection being focused over the mountains where orographic influences aid in development. Thunderstorms that development will be slow moving with concerns for flash flooding and debris flows in and around the burn scars in the North Cascades. The best potential for showers do look to be for areas north Lake Chelan in Chelan County and Okanogan County. Saturday: A deep upper level low will move toward the Pacific Northwest coast late Friday night and early Saturday morning. This will pump up the upper level ridge across eastern Washington and north Idaho with temperatures warming into the upper 80s and 90s across much of the region. Models are showing a surface low to move northward across eastern Washington and north Idaho Saturday evening. This will bring showers and thunderstorms across the western and central Washington Saturday evening into Sunday. With the placement of the surface low, thinking far eastern Washington and north Idaho will miss out on precipitation chances. Breezy northeast winds will set up across eastern Washington and north Idaho with this low with an 70 to 100 percent chance for sustained winds above 15 mph across the Waterville Plateau through the Columbia Basin and into the West Plains and the Snake River area. RHs in the upper teens to low 20s on Saturday will elevate fire concerns across these areas. As this low moves northward, these areas will see a distinct wind shift to the southwest overnight Saturday into Sunday. /vmt Sunday through Thursday: The majority of the extended forecast will see low pressure to our west along the coast and a ridge just to the east of the Inland Northwest. Chances for showers/thunderstorms will linger into Sunday across the Cascades and northern mountains. Forecast then looks to turn drier for Monday through early Wednesday. Chances for storms return Wednesday afternoon through Thursday, though confidence in the pattern is far from set in stone. Daytime temps near daily normals through much of the extended, though Monday looks the warmest with temps around 5 degrees above average. Best chances for gusty winds will be near any thunderstorms that develop through the period, though locally breezy winds are anticipated Sunday across central Washington. /KD && .AVIATION... 00Z TAFS: An upper level shortwave will bring showers and thunderstorms across eastern Washington and north Idaho through the evening and overnight. Some of these thunderstorms may become strong with gusty outflow winds up to 40 kts impacting airports in extreme eastern Washington namely KLWS- KPUW. Thunderstorms will also be capable of heavy rain that brings a brief period of MVFR conditions after 01Z. Moderate rain with lowering ceilings is expected across the northern Idaho Panhandle into northeast Washington overnight into Friday morning. Isolated embedded thunderstorms will be possible overnight as well. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions today across the majority of the TAF period. The exception will be for locations under heavy showers where brief MVFR conditions are possible. Moderate to high confidence for thunderstorms at KLWS and KPUW this evening and moderate confidence for thunderstorms across KGEG-KSFF-KCOE. ----------------------- 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 59 80 56 90 59 83 / 50 40 0 0 30 0 Coeur d`Alene 57 78 54 87 57 82 / 60 70 10 0 20 0 Pullman 52 78 52 90 53 81 / 60 20 0 10 10 0 Lewiston 62 86 62 97 64 90 / 60 10 0 0 10 0 Colville 50 79 44 87 48 83 / 30 60 20 0 30 10 Sandpoint 55 73 51 84 55 81 / 60 80 10 0 20 10 Kellogg 58 74 57 88 59 81 / 90 70 10 0 20 0 Moses Lake 56 83 55 93 57 83 / 20 10 0 20 50 0 Wenatchee 62 83 62 90 63 81 / 10 10 0 20 60 10 Omak 62 87 59 93 62 88 / 20 50 10 10 50 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Flash Flood Watch from Friday morning through Friday evening for Central Chelan County-Okanogan Highlands-Okanogan Valley- Upper Columbia Basin-Wenatchee Area-Western Chelan County- Western Okanogan County. && $$