Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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794 FXUS66 KOTX 260457 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 957 PM PDT Sat May 25 2024 .SYNOPSIS... Dry weather returns on Sunday and Monday with temperatures warming back into 70s and 80s. A return of wet weather is expected to return Tuesday onward, with temperatures trending cooler. && .DISCUSSION... Tonight: A weather disturbance is moving across southern British Columbia producing scattered showers across northern WA and the ID Panhandle this afternoon. Showers will continue through the evening hours. There is a 20-30 percent chance of thunderstorms through sunset mainly along the Canadian border. The pressure gradient from Seattle to Wenatchee is currently 7.8mb and will continue to be near that value through the afternoon before the gradient begins to relax around sunset. Windy conditions will occur across the Cascade gaps onto the Waterville Plateau and Columbia Basin. The NBM is showing a 30 to 50% chance of gusts to 30 mph for the Columbia Basin and Wenatchee area. Probabilities are higher- 60-75% chance for the Waterville Plateau and northern Grant county. Clouds will partially thin and/or dissipate overnight. Some of the colder valleys could see some frost. Main areas of concern are NE WA and north Idaho, like around Colville, Priest Lake, Republic and Deer Park. Probabilities of frost for these locations is 45-60%. NBM is also showing lower probabilities of 15-20% around Spirit Lake/Athol, Wilbur/Davenport, Moscow/Troy areas. Sunday and Sunday Night: The weather disturbance will move over the Continental divide and a broad ridge will begin to set up across the region. There is still a 20-25% chance of showers in the afternoon right along the Canadian border. Instability is not as strong, so no thunderstorms in the forecast. Winds will be lighter and temperatures will be a couple of degrees warmer. The afternoon will see partly to mostly cloudy skies. Temperatures Sunday night/Monday morning will be warmer than the previous day as the ridge builds in and there will be more cloud cover. /Nisbet Monday to Saturday: High pressure will keep the area dry and mild Monday, before a cold front moves in with rain and t-storm chances, increased winds and a cooling trend; by late week the shower chance retreat to the mountains. First on Monday the ridge axis will shift toward the northern Rockies. This will leave the area in a mild southwest flow and high clouds spilling in ahead of the next system and some afternoon cumulus build-ups, particularly around the mountains. Highs are forecast to be in the 70s, with some low 80s in the deeper basin and L-C valley. Then Monday night and Tuesday impulses start to ride in ahead of the approaching cold front. Overnight into early Tuesday this will bring an increase in clouds, with limited shower chances coming onto the Cascade crest and the Blue Mountains to southern Palouse/lower ID Panhandle. Ensembles show about a 20-40% chance of measurable precipitation (>=0.01 inches) in these areas, so I raised PoPs here slightly compared to the NBM. Some guidance expands that risk a bit further northeast toward the Spokane/CdA area before sunrise but confidence is too low (less than 10%) to add to the forecast. Heading into Tuesday through Tuesday night precipitation chances expand over much of the region as the cold front and upper trough push in, drawing on deeper moisture and instability. The highest will be in the afternoon and evening over the southeast WA through the central Panhandle. The lowest risk will be over the lower lee of the Cascades and deeper Columbia Basin. Accompanying the general precipitation threat will be thunderstorm chances, with models painting the best instability over southeast WA through the central Panhandle. SBCAPE values could between 100-800 J/kg. However models are not in great agreement yet over where the better instability will lay. Still there is decent 0-6KM shear at 40-50kts and PWATs rising to around 0.70 to 1.0 inches (150-170% of normal). So locally heavier rain and strong t-storms will be possible, especially in these area, with gusty winds and hail. We will have to watch for localized hydrology issues such as ponding of water or debris flow/rock slides. The River Forecast Center does show some rises on mainstem river, but all of them are currently forecast to stay below action stage. However we will have keep eye on smaller creeks and streams. By Wednesday the area will be dominated by long-wave trough with a second upper shortwave coming into the region in the afternoon evening. This will continue precipitation chances through much of the region. but by this time drier air infiltrates the region, with PWAT decreasing to around 0.25 to 0.45 inches (70-80-% of normal). Unstable lapses rates and bit of SBCAPE remains over the region. So showers will be possible, with embedded t-storm chances. The potential for stronger storms will be lower, with less instability and overall less shear. But some isolated stronger storms are not out of the question over the SE CWA. Expect breezy winds to develop for Tuesday and Wednesday, especially near the Cascades into central WA. Gusts of 15-35 mph in the afternoon and evening hours, with that higher range closer to the Cascades. Thursday to Saturday the upper trough gradually shifts east while a ridge starts to build in from the west (ahead of another system that approaches toward the latter part of next weekend). How quickly all this occurs is not agreed on. Shower chances will continue around the mountains through this period, expanding to include the eastern third of WA Thursday afternoon under the still exiting trough. Temperatures will be above normal Monday and Tuesday, though temperatures Tuesday could be held back in the clouds and precipitation are more dominant the forecast. Expect cooler than normal conditions on Wednesday and Thursday, then a return to slightly above normal temperatures. /Solveig && .AVIATION... 06Z TAFS: VFR conditions for TAF sites for the next 24 hours. Gusty winds have begun to subside but will remain breezy through the night across the Basin and Palouse, including GEG/PUW/MWH/EAT. These breezy winds will continue through Sunday afternoon before subsiding Sunday evening. A weak ridge will begin to build over eastern Washington Sunday, but moist upslope flow into the Cascades will continue to support precipitation and mountain obscuration through Sunday afternoon. There is a 15-25% chance for showers to develop across northeast Washington and far north Idaho Sunday afternoon, with the best chance over the mountains. Warming temperatures aloft will limit cumulus vertical growth, so the potential for lightning is very low (less than 5%). FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence for VFR conditions to continue across the TAF Sites. ----------------------- 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 65 44 73 51 75 / 10 0 0 0 0 20 Coeur d`Alene 39 62 45 72 50 73 / 30 0 0 0 0 30 Pullman 38 62 43 71 50 73 / 10 0 0 0 10 20 Lewiston 44 71 49 81 57 81 / 10 0 0 0 10 20 Colville 34 65 38 72 43 73 / 40 10 0 0 0 40 Sandpoint 39 61 44 70 48 71 / 50 10 10 0 0 50 Kellogg 41 58 44 71 52 74 / 30 10 0 0 10 40 Moses Lake 41 72 44 78 52 78 / 0 0 0 0 0 0 Wenatchee 46 68 47 76 55 73 / 10 0 0 0 0 10 Omak 40 71 44 75 50 75 / 10 10 0 0 0 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$