FXUS66 KOTX 301142 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 442 AM PDT Mon Sep 30 2024 .SYNOPSIS... Many residents of eastern Washington and north Idaho will wake up to temperatures in the 30s this morning. Readings this afternoon will rebound into the 60s. A cold front Tuesday night will bring breezy winds Tuesday afternoon through Wednesday. There is a chance of showers Friday and Friday night. Above average temperatures and dry weather is likely for the weekend into next week. && .DISCUSSION... Monday: Following Sunday’s cold front, the Inland Northwest is now under a very dry air mass this morning. Dew points are 18 to 25 degrees lower than at this time yesterday, and with lighter winds and clear skies, temperatures have dropped significantly overnight. Early risers will feel the chill as they head out, with many locations seeing temperatures in the 30s for the first time this season. Although these temperatures aren’t unusual for this time of year, the contrast will be noticeable. The afternoon will bring beautiful weather as an upper level ridge begins to move in from the west. Tuesday and Wednesday: The upper level ridge continues to shift eastward and flatten early Tuesday as a deep low in the Gulf of Alaska moves into the northern British Columbia coast. Temperatures early Tuesday morning will be cold again across the northern valleys with a 90 percent chance for temperatures below freezing for locations such as Colville, Chewelah, Priest River. Models are showing a modest moisture plume directed into British Columbia with the low, but the placement will be far enough south with moisture across northern Washington and far north Idaho. Clouds associated with this moisture across our northern zones will create a subtle north to south temperature gradient across eastern Washington and north Idaho with places under the cloud cover remaining cooler (highs in the 60s and low 70s) and the southern zones experiencing modest warming with clear skies and the ridge (highs in the low to mid 70s). As the low moves into British Columbia, a cold front will approach the Washington coast by early Tuesday. Winds will increase from the south and southwest ahead of the front, with model soundings showing limited mixing up to 850 mb and low level warm air advection. Sustained winds of 10-20 mph are expected across central and eastern Washington, with a 40-60% chance of gusts exceeding 30 mph in the Cascades, Okanogan Valley, Waterville Plateau, and Upper Columbia Basin. Winds will remain breezy overnight, shifting westward as the front moves across eastern Washington Tuesday night into Wednesday. Behind the front, better mixing and a 110-120 kt upper level jet diving into eastern Washington and northern Idaho on Wednesday will support breezier conditions than Tuesday, with a 60-80% chance of gusts over 30 mph in the lee of the Cascades, Waterville Plateau, Upper Columbia Basin, and Blue Mountains. Unfortunately, strong zonal winds and dry low levels will limit precipitation across the Inland Northwest, with only a 10% chance of 0.01 inches over northern Idaho Tuesday evening. Wednesday’s temperatures will be about 5 degrees cooler than Tuesday. While the winds won’t be as strong as Sunday, the continued dryness may cause localized visibility reductions due to blowing dust around recently worked fields. /vmt Thursday and Friday: There is good model agreement that the Polar Jet will retreat northward Thursday. As a high pressure expands over the western United States, look for mostly clear skies and lighter winds Thursday and Thursday night for Washington and north Idaho. Gardeners can expect morning lows in the 30s across much of the Inland Northwest both Thursday and Friday mornings. The only precipitation chances the NBM generates late in the week into the weekend occurs late in the day Friday into Saturday morning. There are enough ensemble members that resemble the operational ECMWF and Canadian for a 20 percent chance of showers for the Cascades, the Idaho Panhandle, and the eastern third of Washington. We will be keeping a close eye on a potential frontal passage Friday. The evening run of the deterministic ECMWF predicts another wind and dust event Friday. While there aren't enough ensemble members from the GFS and Canadian to nudge the NBM toward strong winds on Friday, the mean wind gust from the 50 ECMWF members has increased from 20 mph to nearly 30 mph over the last 2 runs. And the number of ECMWF ensembles generating 40 mph gusts for Spokane has increased from 4 members (Sat morning run) to 12 members (Sat evening run). The ECMWF has 50 total members. Saturday through Monday: Saturday's temperature forecast carries the highest uncertainty of the 7 day forecast. A frontal passage similar to the operational ECMWF would result in highs in the 60s for Saturday while a ridge solution similar to the GFS would lead to 70s and low 80s. The NBM is somewhere in the middle with low to mid 70s for Saturday. By Sunday and Monday, there is decent model agreement that the Polar Jet will be north of the border with above average temperatures. And the 8 to 14 Day Outlook from the Climate Prediction Center calls for a high probability of warmer than average temperatures into the second week of October. So gardeners that cover their plants this week may be able to keep their flowers and vegetables growing for another couple of weeks. /GKoch && .AVIATION... 12Z TAFS: Dry northwest flow aloft will gradually shift westerly as an upper level ridge moves into the region. VFR conditions will continue through the period under clear skies. Surface winds will generally be light and terrain driven. Mid to high clouds will move into eastern Washington Monday night ahead of an approaching cold front. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions. && .PRELIMINARY POINT TEMPS/POPS... Spokane 63 39 71 43 66 37 / 0 0 0 0 0 0 Coeur d'Alene 61 38 69 43 66 37 / 0 0 0 0 0 0 Pullman 60 36 70 45 64 36 / 0 0 0 0 0 0 Lewiston 66 43 77 53 74 44 / 0 0 0 0 0 0 Colville 63 31 67 28 66 28 / 0 0 0 10 0 0 Sandpoint 59 35 63 39 65 34 / 0 0 0 10 0 0 Kellogg 58 41 68 47 62 40 / 0 0 0 10 0 0 Moses Lake 65 38 72 42 69 37 / 0 0 0 0 0 0 Wenatchee 64 42 75 47 67 43 / 0 0 0 0 0 0 Omak 67 43 70 41 69 39 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Freeze Warning until 8 AM PDT this morning for Central Panhandle Mountains-Idaho Palouse-Northern Panhandle. Frost Advisory until 8 AM PDT this morning for Coeur d'Alene Area-Lewis and Southern Nez Perce Counties. WA...Freeze Warning until 8 AM PDT this morning for Northeast Mountains-Okanogan Highlands-Washington Palouse. Frost Advisory until 8 AM PDT this morning for Moses Lake Area- Okanogan Valley-Spokane Area-Upper Columbia Basin- Waterville Plateau. && $$