FXUS66 KOTX 191818 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 1118 AM PDT Fri Jul 19 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 through Sunday Night: Excessive Heat is the main story as temperatures increase even further across the region. Models are in good agreement that a strong upper ridge will build over region into Saturday, and then remain strong with the ridge axis shifting to over North Idaho on Sunday. Initially with the ridge overhead, the warming will be due to subsidence associated with the ridge. On Sunday as the upper flow turn southerly on the back side of the upper ridge, temperatures increase even further. 850mb temperatures reach an impressive 30C, with widespread triple digit heat. The one factor that could knock temperatures down a few degrees is wildfire smoke coming up from Oregon. Either way, it will be very hot. Heat Advisories are in effect for most of the region on Friday, followed by Excessive Heat Warnings Saturday through Monday. For Sunday Night a mid level wave tracks into Central Washington on the back side of the ridge. The NAM is showing elevated CAPE of 100-300 J/KG with some lift as well. At this time instability parameters and atmospheric lift are not expected to be strong enough for any precipitation or thunderstorms, but a potential we will be keeping an eye on since any lightning would not be good news. The other potential concern on Sunday is the hot, dry, unstable atmosphere as the flow turns southerly, especially in the Cascades. The GFS shows dry adiabatic lapse rates up to near 15000 feet (deep layer of mixing), that could allow fires to get very active. JW Monday through Friday: Quite the pattern change is on the horizon as models are in solid agreement on a deep low moving into British Columbia and remaining nearly stationary through the work week. On Monday, as the upper level low strengthens in the Gulf of Alaska, increasing southwest flow into the PNW will allow an embedded shortwave to move across the region and initiate the breakdown of the ridge. Deterministic models are hinting at a pattern for high based thunderstorms with an increase in elevated moisture and instability across the region Sunday night into Monday. Probabilities below 15% in the NBM currently limit confidence in pinning down a specific area of interest, but this will be something to monitor. Depending how this shortwave pans out, temperatures may vary slightly on Monday compared to what is currently forecasted. Increasing onshore flow will tighten the cross-Cascade pressure gradient late Monday afternoon into the evening with breezy winds through the Cascade gaps with a 50-100 percent chance for sustained wind speeds above 20 mph. The center of the low will move into northern British Columbia on Tuesday, with a dry cold front sweeping across the Inland Northwest. While this will provide much needed relief from the heat, it will come at a cost as a cool down of this caliber is typically accompanied by a strong push of winds. With that said, we will need to monitor this period for critical fire weather conditions as models show a 60 to 100 percent chance for the lee of the Cascades to see sustained winds above 20 mph on Tuesday. Continued breeziness is expected as the center of the low parks itself in northern BC and additional shortwaves move across the region. Temperatures on Tuesday look to cool by about 10 degrees with gradual cooling through Friday. To put this duration of heat into perspective, if the current forecast for Spokane International (KGEG) pans out, we would have seen 20 consecutive days with a high temperature above 90 degrees, smashing the current record of 15 consecutive days. The NBM finally drops below 90 degrees on Thursday, but this could occur as early as Tuesday or Wednesday with 55 percent chance of a high below 90 both days. /vmt && .AVIATION... 18Z TAFS: A building upper level ridge will allow VFR conditions to continue through the period. The only exception will be some hazy conditions from smoke near wildfires that may reduce visibilities along Lake Chelan, and the Methow Valley. 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 64 101 66 106 69 / 0 0 0 0 0 0 Coeur d'Alene 95 60 98 64 103 68 / 0 0 0 0 0 0 Pullman 93 59 98 61 102 63 / 0 0 0 0 0 0 Lewiston 102 70 106 70 111 74 / 0 0 0 0 0 0 Colville 96 56 99 58 104 60 / 0 0 0 0 0 0 Sandpoint 93 54 97 58 101 64 / 0 0 0 0 0 0 Kellogg 93 65 96 67 101 71 / 0 0 0 0 0 0 Moses Lake 99 62 103 61 109 67 / 0 0 0 0 0 10 Wenatchee 98 68 102 73 107 74 / 0 0 0 0 0 0 Omak 102 64 105 67 110 72 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...Heat Advisory until 11 AM PDT Saturday for Central Panhandle Mountains-Coeur d'Alene Area-Idaho Palouse-Lewis and Southern Nez Perce Counties-Lewiston Area-Northern Panhandle. Excessive Heat Warning from 11 AM Saturday to 8 PM PDT Monday for Central Panhandle Mountains-Coeur d'Alene Area-Idaho Palouse-Lewis and Southern Nez Perce Counties-Lewiston Area- Northern Panhandle. WA...Heat Advisory until 11 AM PDT Saturday for Central Chelan County- Lower Garfield and Asotin Counties-Moses Lake Area- Northeast Blue Mountains-Northeast Mountains-Okanogan Highlands-Okanogan Valley-Spokane Area-Upper Columbia Basin- Washington Palouse-Waterville Plateau-Wenatchee Area- Western Okanogan County. Excessive Heat Warning from 11 AM Saturday to 8 PM PDT Monday for Central Chelan County-Lower Garfield and Asotin Counties-Moses Lake Area-Northeast Blue Mountains-Northeast Mountains-Okanogan Highlands-Okanogan Valley-Spokane Area- Upper Columbia Basin-Washington Palouse-Waterville Plateau- Wenatchee Area-Western Okanogan County. Heat Advisory from 11 AM Saturday to 8 PM PDT Monday for Western Chelan County. && $$