FXUS66 KOTX 051104 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 304 AM PST Tue Mar 5 2024 .SYNOPSIS... Afternoon showers will return once more Tuesday afternoon, then retreat to the Idaho Panhandle for Wednesday and Thursday. Temperatures will remain below average with very chilly mornings through Friday morning, then trend to near normal values for the weekend with the return of widespread precipitation. && Tuesday: The Inland Northwest is under a broad northwest flow this morning as a shortwave along the Washington and Oregon border and a stationary front associated with a broad upper level low over western Canada sits along the Washington and Idaho northern borders. With the upper level to the south in Oregon, the strongest forcing with this shortwave will mostly be outside of our forecast area. Recent SPC mesoanalysis shows some upper level forcing glancing the southernmost areas with light reflectivities showing up on radar across the lower Columbia Basin and areas south of Pullman. Snow amounts will be less than a half inch with no impacts expected for the Tuesday commute. The potential for snow showers will return this afternoon, although coverage will be much less and showers should be less intense compared to Monday. Warmer temperatures moving in aloft will result in relatively more stable mid-level lapse rates and less surface based CAPE this afternoon. The best chances for shower development will be across the Washington and Idaho Palouse, the Blues, and the central Panhandle mountains. High resolution models keep showers south of Spokane, but I would not be surprised if there was some isolated development in the vicinity of the Spokane and CdA metro areas. Any showers will be capable of a brief burst of moderate snow or snow pellets, but will be short lived. The less widespread shower coverage combined with the dry air should help dry out roads and side walks, lessening the chances for black ice Tuesday night and Wednesday morning. Wednesday and Thursday: Drier, northwest flow will shove the cold pool aloft to the east with small chances for afternoon showers limited to the Idaho Panhandle mountains. The influx of drier air will keep skies cloud free for very sunny afternoons, but very cold overnight low temperatures. Fog development will be possible in the northern valleys Wednesday morning. /vmt Friday: Temperatures will begin to trend warmer on Friday as our cool upper level trough is finally replaced by a shortwave ridge. High pressure won't be around long, but it will provide the Inland Northwest with a day of dry weather Friday. By the afternoon, there is good model agreement that rain will be spreading into Vancouver Island with our next frontal system. For eastern Washington and north Idaho, morning sunshine is expected to give way to increasing mid and high clouds during the afternoon. Look for afternoon highs to be near average for early March ranging from the low 40s in far north Idaho to the mid to upper 40s in the Columbia Basin, central Washington, Spokane area, and Palouse. Saturday: The front will move inland on Saturday bringing increasing chances of light precipitation to Washington, Oregon, and north Idaho. The front will weaken and shear apart as it crosses the Cascades and encounters a formidable high pressure ridge over the Rocky Mountains. Chances of measureable precipitation during the day Saturday from the National Blend of Models (NBM) range from 15 percent for Wenatchee and Moses Lake to 40 percent for the mountainous terrain of northeast and north central Washington. With morning temperatures in the 20s and low 30s, some of the light precipitation Saturday morning may fall as snow. Given the light precipitation amounts and marginally warm temperatures, the NBM probabilities for any measurable snow Saturday morning is 10 percent or less for Spokane, Pullman, Colville, Sandpoint, Omak, and most all other lowland communities in north Idaho and northeast Washington. By the afternoon, south winds of 10 to 15 mph will push high temperatures into the mid to upper 40s with readings as high as the low 50s in the L-C Valley. Sunday through middle of next week: The Polar Jet will become increasingly active over the Pacific Northwest early next week. There are some differences in the timing and strength of shortwaves embedded within the active onshore flow, but there is good ensemble agreement that our mountains will receive periods of light to moderate snow early next week while our lowlands experience rain. Last week's heavy mountain snow was important for adding to our mountain snowpack, but mountains of north Idaho, northeast Washington, and the Cascades are roughly at about 70 percent of normal for early March. Our snowpack for the season typically peaks in early April, so the snow we receive the next several weeks will be important for our water supply this summer. Unfortunately, the ensembles are advertising the arrival of a potentially prolonged warmer and drier pattern by late next week. /GKoch && .AVIATION... 06Z TAFS: Bands of snow showers producing light accumulations will continue across North Idaho and around Newport, WA through 09z then dissipate. Patchy fog will be possible across the valleys of NE WA and N ID with a 10% chance for visibility to fall to 1/2SM around Deer Park, Felts Field, and Geiger. Confidence was too low to include in the 06z TAFS. There will be increasing clouds along the WA-OR border with light snow developing. There is a 30% chance for the light snow to buckle northward into Lewiston and Pullman for a few hours Tuesday morning before decreasing. Afternoon instability will be focused over SE WA and the lower ID Panhandle Tuesday afternoon with convective snow showers. Local MVFR conditions or lower will be possible under any showers with the greatest risk focusing south of I-90 over the Palouse, L-C Valley, and Camas Prairie. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is low confidence for restrictions and snow for Lewiston and Pullman given uncertainty how far north the shield of snow will buckle. It is possible ceilings are lower around Lewiston and Pullman if the snow is more organized. The air mass will begin warming aloft tomorrow so although one more afternoon of convective snow showers are expected, there is moderate confidence that these will not be as deep and intense as activity on Sunday and Monday with a lower threat for restrictions. This is reflected in the Lewiston and Pullman TAFS. ------------------------ 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 39 21 40 21 40 23 / 20 0 0 0 0 0 Coeur d'Alene 36 19 37 19 39 19 / 20 0 10 0 0 0 Pullman 38 22 39 22 39 23 / 20 0 10 0 0 0 Lewiston 43 28 45 28 45 27 / 20 0 0 0 0 0 Colville 39 15 39 16 41 19 / 0 0 0 0 0 0 Sandpoint 35 18 36 19 38 19 / 20 0 10 0 10 0 Kellogg 37 22 37 19 37 19 / 20 10 30 0 10 0 Moses Lake 44 24 44 24 45 26 / 0 0 0 0 0 0 Wenatchee 43 23 42 25 44 28 / 0 0 0 0 0 0 Omak 42 22 42 22 44 27 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$