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Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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520 FXUS66 KOTX 181157 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 455 AM PDT Thu Jul 18 2024 .SYNOPSIS... Strong high pressure will begin to amplify over the Inland Northwest during this period continuing our string of hot weather which began around July 5th. The heat will likely peak this weekend with widespread triple digit high temperatures and possible records. There are hints the heat will finally relent by the middle of next week. && .DISCUSSION... Today...Slow moving upper level shortwave, currently centered just north of Spokane will continue to eject slowly NE during the next several hours. Isolated thunderstorms will still be possible near the shortwave as well as along a narrow band stretching from Lookout Pass toward Lewiston. Most of the lightning will occur in northern portions of Pend Oreille County as well as northern Bonner and Boundary Counties in an area of the greatest instability (MUCAPE values in excess of 500 j/kg, and weak forcing from the shortwave. Otherwise we expect to see the upper level ridge rebounding today as a trough rebuilds just west of 130w. This amplification will bring several degrees of warming compared to what we experienced yesterday. That equates to highs in the mid 90s to 104 for most valley locations. However unlike yesterday where we saw partial relief from variable cloud cover, today should be much sunnier and thus potentially feel hotter. Based on these temperatures we decided to expand the heat advisories into north Idaho to join the rest of eastern Washington. These will be in effect at least through the weekend. Tonight through Friday night...The offshore trough will begin to nudge toward the Cascades. This could bring a slight cooling trend to the Cascade Crest area, but little cooling elsewhere. Highs will once again peak in the mid 90s to the lower 100s with little cloud cover. Meanwhile overnight lows will be in the mid 50s and 60s. From a fire weather perspective, the daytime relative humidity values will drop into the teens to lower 20s with poor overnight recoveries in the mountains and mid-slopes. This suggests any ongoing fires (or new ones from this lightning event) have the potential to exhibit strong growth. The sunshine today will also potentially perk up local fires in the Cascades and the numerous ones over Oregon. This will result in increased smoke production, but for now the HRRR smoke models are keeping most of the surface based smoke near the Pioneer fire north of Chelan. The only saving grace is winds will be relatively light for most locations save the Wenatchee Valley and Waterville Plateau late this afternoon and evening when we could see wind gusts possibly up to 20 to 25 mph. fx Saturday to Wednesday: The region will continue to warm through this weekend as a ridge amplifies over the northern Rockies, before it starts to lose influence heading into the new work week and temperatures start to moderate, maybe even closer to seasonal norms. Highs push into the 100s over much of the region Saturday and Sunday, with Sunday being the warmest day. By Monday an onshore flow begins to push cooler air up toward the Cascade crest and knock temperatures down a couple degrees everywhere, though still with highs largely in the 100s. Models hint at the chance for showers Monday and Tuesday as the offshore trough starts to push inland. However 2/3 of the models keep the better chances around the fringes of our CWA, so the forecast largely remains dry. If chances are increased, right now the chances remain best near the Cascades though north-central WA. Winds start to increase as the trough shifts inland too, especially near the Cascades and central WA. Models are still marginal or very localized where wind speeds and RH may converge to product critical fire weather conditions from Monday through Wednesday, but it definitely will be monitored. Highs trend toward the 90s and even upper 80s by midweek. /Solveig && .AVIATION... 12Z TAFS: Upper level disturbance over extreme NE WA will continue to track slowly NE through 16z. This should take any chance of precipitation into W MT by that time. For the remainder of the Inland NW expect VFR conditions to prevail as high pressure builds into the region. The only exception will be some hazy conditions this AM near KPUW from smoke and brief MVFR visibilities. We should also see increasing smoke from the regional fires this afternoon/evening, including the Pioneer Fire near Lake Chelan. The HRRR smoke model suggests this will drift N-NW late today and tonight and should remain out of the KEAT area. fx FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: With the exception of smoke near wildfires confidence is high for continued VFR conditions. ----------------------- 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 98 64 98 65 102 66 / 0 0 0 0 0 0 Coeur d`Alene 95 62 96 63 99 65 / 0 0 0 0 0 0 Pullman 93 58 94 59 98 63 / 0 0 0 0 0 0 Lewiston 103 70 103 70 107 71 / 0 0 0 0 0 0 Colville 97 54 97 54 100 56 / 0 0 0 0 0 0 Sandpoint 93 58 94 58 99 60 / 0 0 0 0 0 0 Kellogg 92 67 95 68 98 71 / 0 0 0 0 0 0 Moses Lake 100 62 100 61 104 68 / 0 0 0 0 0 0 Wenatchee 101 70 99 69 103 76 / 0 0 0 0 0 0 Omak 102 65 102 65 106 68 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Heat Advisory until 10 PM PDT Sunday for Central Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse-Lewiston Area- Northern Panhandle. WA...Heat Advisory until 10 PM PDT Sunday for Central Chelan County- Lower Garfield and Asotin Counties-Moses Lake Area- Northeast Mountains-Okanogan Highlands-Okanogan Valley- Spokane Area-Upper Columbia Basin-Washington Palouse- Waterville Plateau-Wenatchee Area-Western Okanogan County. && $$