Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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903 FXUS66 KOTX 170947 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 247 AM PDT Sat Aug 17 2024 .SYNOPSIS... Showers and thunderstorms will occur this evening through the overnight hours. The area of greatest concern is central Washington with the possibility of strong outflow winds and lightning. Isolated thunderstorms is possible for eastern WA and portions of the north Idaho Panhandle as well. Temperatures will be quite warm on Saturday with dry and breezy northeast winds across the Columbia Basin, West Plains, and southeast Washington. Unsettled weather will continue near the Cascades on Sunday with drier weather expected for Monday and Tuesday. Showery and cooler weather returns by midweek. && .DISCUSSION... Today through Sunday Night: Quiet weather through the afternoon as a brief shortwave ridge sets up across the region. Skies will be sunny and temperatures will be in the mid 80s to lower 90s, which is 4 to 8 degrees above average for mid August. A northeast pressure gradient has set up and breezy winds in the afternoon with gusts up to about 20 mph will occur across portions of the Columbia Basin. All eyes turn to this evening and overnight. The low pressure sitting off the coast will push a wave up Oregon this afternoon and into Washington this evening and overnight. Precipitable water values increase to 150-170% of normal as the wave moves up. Both the NAM and GFS are showing good forcing and elevated instability moving through the region. The best chance of showers and thunderstorms will be across central WA, but cannot rule out some elevated thunderstorms across portions of eastern WA and north ID as well. E WA/N ID has a 20-40% chance of seeing some sprinkles with breezy winds and lightning as the elevated instability moves north through the night. Further west across central WA they have the better potential of seeing brief heavy rain, lightning and stronger wind gusts. Some of the high resolution models are indicating a strong gust front coming out of the line of convection moving north into our area this evening. Right now they show is fizzling as it moves into the Columbia Basin and encounters the NE winds. However, the potential does exist that these strong winds coming out of the convection will move into the Columbia Basin, Wenatchee area and Waterville Plateau. Have kept patchy blowing dust in the forecast for this evening and overnight for the Columbia Basin. The convection will head north through the night and should exit by sunrise for much of the region. The exception is the Cascades where some of the high res models keep small showers and thunderstorms going through the day. Sunday will see mostly sunny skies and cooler temperatures. Winds will be south to southwesterly following the weather system passing through. Breezy afternoon winds with gusts 15-25 mph is expected across portions of the Columbia Basin, Okanogan Valley, Waterville Plateau and onto the west plains. Monday through Friday: The upcoming week will feature general upper level trough over the Pacific NW as the main upper level ridge lies to the east over the Rockies/Great Plains. This pattern will keep most of the heat levels down for the Inland NW although increase the threat of showers, thunderstorms, and gusty winds. For Monday, the circulation off the WA weakens although allows for a mild southwest flow into the region. Anticipate very warm temperatures for Monday with highs in the 80s to lower 90s, and this looks to be the warmest day of the week, before a weak cold front pushes through eastern WA into north ID with gusty westerly winds especially in lee of the Cascades and Columbia Basin. There is a 10-20% chance for showers and thunderstorms in the far northern Cascades and north ID with spotty precipitation Monday late afternoon and through the evening hours. By Tuesday and Tuesday night, the remains of the upper trough swing through the Inland NW accompanied with locally gusty winds, seasonal temperatures, and afternoon showers and thunderstorms in the northern Cascades. With the passage of the upper trough through Tuesday night, theres a 20-30% of light showers persisting into Wednesday with refreshingly cool temperatures in the 70s to lower 80s. By Thursday into Friday, another area of low pressure develops off the WA coast. Slight upper level ridging will help bring temperatures rebound back to seasonal levels in the 80s. Models differ on the track of this feature with it either slowly sinking southward along the west coast or weakening as it pushes inland, which would affect the convection coverage and temperatures. /rfox. && .AVIATION... 06Z TAFS: Rain showers will continue to diminish tonight. Any shower activity is expected t be along the Canadian Border. Saturday will be relatively quiet through the afternoon. An incoming system will begin to impact the MWH area with gusty winds around 25 MPH near the end of the TAF period. Models are indicating a wind shift from North to South as the system passes. The shift is expected overnight Saturday. It will also bring increasing chance of showers. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence for VFR conditions for the TAF period. Moderate confidence for increasing winds for MWH toward the end of the TAF period. Alternate scenario will be the timing of the system speeding or slowing down. /JDC ----------------------- 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 89 59 85 57 88 58 / 0 40 0 0 0 10 Coeur d`Alene 87 57 84 56 88 56 / 0 40 0 0 0 20 Pullman 89 54 82 51 82 51 / 0 20 0 0 10 10 Lewiston 97 65 92 63 92 62 / 0 10 0 0 10 0 Colville 87 49 84 46 89 48 / 0 50 0 0 0 10 Sandpoint 84 54 82 52 87 53 / 0 40 0 0 0 20 Kellogg 86 59 82 59 87 58 / 0 30 0 0 10 20 Moses Lake 94 59 85 55 88 55 / 0 50 0 0 0 0 Wenatchee 91 65 84 63 88 61 / 0 80 10 0 0 0 Omak 92 63 90 57 92 59 / 0 80 10 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$