Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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583 FXUS66 KOTX 131002 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 302 AM PDT Mon May 13 2024 .SYNOPSIS... An approaching system will deliver breezy conditions Monday, especially closer to the Cascades and western Columbia Basin. A chance for showers will come to the Cascade crest, northeast Washington and the northern Idaho Monday, lingering over Idaho Tuesday. Temperatures will cool for Monday and Tuesday, rebound around midweek, then decrease again later in the week as the next shower and breezy winds chances come in. && .DISCUSSION... Monday: A dry, shortwave trough is currently moving across the northwest early this morning, evident on satellite imagery as a band of high level clouds pushing across the northwest. A tightening cross-Cascade pressure gradient is bringing breezy northwest winds through the Cascade gaps with sustained winds of 15 to 25 mph currently being observed. Expect these winds strengthen through Monday morning, peaking in the afternoon and the early evening across central Washington with wind gusts up to 45 mph. The National Blend of Models is giving the higher elevations across the Waterville Plateau a 60% chance to see wind gusts over 45 mph. Other locations in central Washington such as Wenatchee, Bridgeport, Malott, and Ephrata are carrying a 30-40% chance for wind gusts over 45 mph. Winds will also increase across far eastern Washington and north Idaho through Monday afternoon, but are not expected to be strong compared to central Washington. As the shortwave passes through far eastern Washington and north Idaho in the late morning and afternoon, areas across the northeast Washington and the north Idaho mountains will see chances for showers and thunderstorms. Model soundings indicate the best chances for lightning to be for areas closer to the Canadian border, where the steepest mid level lapse rates and orographic lift enhance the potential Monday afternoon. Another shortwave moving through late Monday afternoon will continue the chances for showers and isolated thunderstorms into the evening for these areas. Temperatures today will be about 5 to 10 degrees cooler compared to Sunday with widespread highs in the 70s. Some lower locations in the Columbia Basin and the L-C Valley could peak slightly above 80. Tuesday: Chances for showers will continue across north Idaho early Tuesday on the backside of the shortwave as the upper level ridge begins to rebound from the west. Winds will begin to shift to the north early Tuesday morning and funnel down the Okanogan Valley through Tuesday afternoon with sustained wind speeds of 10-20 mph and gusts of 25-30 mph. They will shift back to the west-northwest Tuesday evening with another breezy evening through the Cascade gaps. /vmt Wednesday and Thursday: Temperatures will rebound Wednesday as a warm ridge of upper level high pressure builds off the West Coast, and summer-like temperatures may persist into Thursday. The medium range models bring a shortwave over the top of the ridge Wednesday night into Thursday leading to differences in the Thursday forecast including the timing of a cold front. Confidence is relatively high that Wednesday will feature partly to mostly sunny skies with high temperatures ranging from the mid 70s across the Idaho Panhandle to the mid 80s in central/north central Washington. With differences in frontal timing Thursday, a few of the ensemble members make Thursday the warmest day of the week while others suggest Thursday will be about 10 degrees cooler than Wednesday. Guidance from the National Blend of Models (NBM) illustrates the spread in the ensembles with the 90th percentile generating highs in the mid 80s to low 90s while the 10th percentile has highs in the mid 60s to mid 70s. Chances are good that Thursday will be breezy whether is warm/breezy ahead of the front or cool/breezy behind the front. Friday through Sunday: The forecast Friday into the weekend becomes more complicated with a developing split flow pattern by the end of the week. With the southern branch of the Polar Jet along the Mexican border and the northern branch carving into the Northern Rockies there is a good deal of variability in the medium range models. The NBM forecasts daytime temperatures cooling into the 60s and 70s Friday, Saturday and Sunday with a 20 to 30 percent chance of showers over the mountainous terrain of north Idaho, northeast Washington, and the northern Cascades. This is a "middle of the road" forecast while the evening run of the GFS is an example of a statistical outlier. The deterministic GFS drags an upper low south through Washington and Oregon Saturday and Sunday. Fewer than 15 percent of the GFS, ECMWF, and Canadian ensembles look similar to the chilly and rainy GFS next weekend. /GKoch && .AVIATION... 06Z TAFS: A pair of cold fronts push through the region over the next 24 hours. The first front has pushed into W WA and will swing across the forecast area overnight. A second front arrives Monday evening 00-03z with more of a northwest orientation. Winds will remain breezy through the night with gusts near 30kts possible especially in the Cascade gaps. There will be a small risk for marginal LLWS in advance of the front. The front first front will deliver little to no precipitation. The second front will bring a 20-40% chance for showers across far NE WA and N ID mainly north of a line from Kellogg to Colville. North Idaho has a 15% chance of thunder after 18z Mon. Generally VFR skies are expected region-wide outside some mountain obscrns on the higher peaks. The main impact for most terminals will be gusty west to southwest winds. Wind gusts of 20-30 mph are anticipated for most terminals between 19-03z Monday afternoon-evening. KEAT could experience a few periods of winds closer to 40 mph which were added as a tempo group. /sb FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high confidence for gusty winds with a transition in air masses occurring in the next 24 hours. Confidence is low for rainfall in NE WA and N ID and general pilots should be aware of virga showers producing gusty, erratic winds. Winds could decouple sooner than expected for sites after sunset leading to lower confidence for exact wind speeds. ----------------------- 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 74 47 74 48 79 53 / 0 10 0 0 0 0 Coeur d`Alene 72 46 71 47 76 51 / 10 10 0 0 0 0 Pullman 70 46 69 48 74 51 / 0 10 0 0 0 0 Lewiston 79 52 76 52 83 56 / 0 10 0 0 0 0 Colville 76 44 76 45 81 47 / 20 20 0 0 0 0 Sandpoint 72 47 70 46 74 49 / 20 30 10 0 10 10 Kellogg 69 49 67 50 73 53 / 10 20 10 0 0 10 Moses Lake 79 48 81 50 86 53 / 0 0 0 0 0 0 Wenatchee 74 50 79 54 83 57 / 0 0 0 0 0 0 Omak 79 48 81 50 85 53 / 10 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$