Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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239 FXUS66 KOTX 222307 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 407 PM PDT Wed May 22 2024 .SYNOPSIS... Thursday will feature scattered afternoon showers and thunderstorms mainly across north Idaho as well as north central and northeast Washington. Friday, Saturday and Sunday will cool with highs in the 60s and low 70s with chances for afternoon and evening showers and thunderstorms. Memorial Day will be the warmest and driest day of the holiday weekend with afternoon temperatures well into the 70s. && .DISCUSSION... Tonight: Showers will become less numerous along the Canadian border this evening with the loss of afternoon destabilization. By 8 or 9 PM, most shower activity around Republic, Northport, and Metaline will dissipate. As daytime convection weakens, we should see a band of rain wrapping around our departing upper low. Through the night, the upper low and it`s associated band of rain will migrate south bringing an additional tenth to quarter inch of rain to Lookout Pass and the mountains of southern Shoshone county. Less than a tenth is advertised by the National Blend of Models (NBM) for Kellogg, Coeur d`Alene, St Joe, and Craigmont. It will be a chilly night for our northern valleys including places like Priest Lake, Metaline, Colville, and Republic. Mid and high clouds will follow our departing low. Valley locations that don`t fog in overnight will drop into the mid to upper 30s with some patchy frost. The rest of central/eastern Washington as well as the Idaho Panhandle will experience lows in the upper 30s to mid 40s. Thursday: There is good model agreement that an upper level disturbance embedded within our weak upper trough will aid in the development of showers thunderstorms along the Canadian border by late morning Thursday. Cells will move to the southeast between 20-25 mph during the afternoon and into the evening hours. With dewpoints in the 40s, surface based instability will be relatively weak. High Resolution Ensemble Forecast mean CAPE values are generally less than 200 J/Kg. With limited shear, thunderstorms that form should not be particularly strong. Chances for measureable precipitation from the NBM ranges from 50 to 70 percent in places like Republic, Colville, and Bonners Ferry to 20 to 30 percent in Omak, Winthrop, Grand Coulee, Davenport, Spokane and Coeur d`Alene. Moses Lake, Wenatchee, Ritzville, and Lewiston have a less than 10 percent chance for showers Thursday. Friday: The Inland Northwest will be in between systems on Friday...at least during the day. Afternoon and evening showers should be limited to mountainous terrain in the absence of any significant upper level support. Afternoon temperatures will range from the mid 60s in north Idaho and northeast Washington to the low 70s in the Columbia Basin, Okanogan Valley, and the L-C Valley. /GKoch Friday afternoon through Sunday: Models are in excellent agreement for an unsettled Memorial Day weekend for the Inland Northwest. The first wave Friday afternoon will bring the potential for weak thunderstorms in the Blue Mountains and Camas Prairie/Northern Panhandle. The second and stronger wave Saturday will bring additional chances for thunder in the northern mountains Saturday afternoon. The best chances (40-70%) for a wetting rain (0.10 or greater) Friday afternoon through Saturday afternoon are in the northern mountains, the eastern third of Washington, the Cascade Crest, Blue Mountains, and the ID Panhandle. Temperatures Friday and Saturday will be in the 60s and 70s. Sunday looks mostly dry except zonal flow aloft will promote weak shower development in the ID Panhandle mountains and near the Cascade crest. Temperatures Sunday will still be in the 60s and 70s. Monday through Wednesday: Models are also in excellent agreement of a substantial pattern change to warmer and drier weather Monday. Height rises downstream a deep Gulf of Alaska trough will send our high temperatures into the 70s and 80s early next week. There is a 10-20% chance of temperatures 90 degrees or greater in the deeper Columbia Basin southeast of Moses Lake by Tuesday if the ridge axis stays in the region. 60% of models briefly cool us off Tuesday with a shortwave. /Butler && .AVIATION... .AVIATION... 00Z TAFS: Afternoon instability showers will decrease through the evening in areas along the Canadian border. A band of rain organizing in west central Montana that is wrapping around low pressure dropping southward through the night will produce periods of rain over the central and southern Idaho Panhandle. The COE, LWS, and PUW TAFs have mention of light rain in the 05-11z time frame as this band sinks south. Moisture associated with this precipitation will likely result in 1500-2500ft ceilings across southeast Washington and the southern/central Idaho Panhandle where the HREF gives Pullman an 80 percent chance 2000ft ceilings between 12-18z. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: HREF probabilities for 2000-3000ft ceilings at Coeur d`Alene and Spokane are about 50 percent Thursday morning. There will be a good deal of dry northerly winds in the mid and upper levels suggesting clearing in the morning. Since GFS MOS produces a stratocumulus deck at Coeur d`Alene, and NAM/GFS soundings support that idea a BKN025 deck has been included. It wouldn`t be surprising to see similar conditions at SFF and GEG, and may need to be added later TAFs. /GKoch ----------------------- 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 64 45 68 46 63 / 20 20 20 10 20 30 Coeur d`Alene 40 60 44 67 45 60 / 40 30 20 10 30 50 Pullman 39 59 40 65 44 58 / 30 10 0 10 40 30 Lewiston 47 66 45 73 51 66 / 40 10 0 10 40 30 Colville 35 64 39 67 41 64 / 40 60 50 30 40 60 Sandpoint 38 58 43 64 44 58 / 70 50 60 40 40 60 Kellogg 42 57 44 64 47 56 / 70 30 40 30 50 60 Moses Lake 42 72 44 73 47 71 / 20 0 0 10 10 10 Wenatchee 47 71 47 71 49 67 / 20 10 0 10 10 10 Omak 43 72 44 72 46 70 / 50 30 10 10 20 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$