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Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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454 FXUS66 KOTX 121801 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 1101 AM PDT Mon Aug 12 2024 .SYNOPSIS... There will be a couple more days of showers and thunderstorms for some of the region, followed by a brief lull around mid-week, before additional shower and thunderstorm chances arrive heading into the end of the week. In the near term, the focus for thunderstorms will be over the Cascade and northern mountains, as well as over southeastern Washington into the southern Panhandle tonight through Monday night. Lightning from thunderstorms will be capable of starting new fires. Daytime temperatures will begin the week slightly warmer than normal but should drop to average or slightly below by midweek. && DISCUSSION... Today through Tuesday night: A compact upper level low is swinging across north-central Washington early this morning. A vorticity maximum moving across the northern Cascades is interacting with between 200-300 J/kg of MUCAPE to force thunderstorms in the area. These storms are slow moving to the north and contain brief heavy rain, small hail, along with frequent lightning. The prognoses is for this low to slowly track into the Okanogan Highlands this afternoon. Model guidance suggests between 500-800 J/kg of surface based CAPE to work with in the Cascades over to the Okanogan Highlands, Northeast Mountains and Idaho Panhandle. Thunderstorms are expected to expand in coverage as lower levels destabilize this afternoon under the cold pool. Steering flow will be weak and P-wats on the order of 0.9+ inches. Concerns with thunderstorms today will be two fold: flooding/debris flows near burn scars and new fire starts from lightning strikes. Good news is that rain from thunderstorms will act to extinguish new fire starts. Will maintain the red flag warning over the Cascades to the Okanogan Highlands. There is also some mid level instability to contend with across southeast Washington into the Central Panhandle Mountains. Instability is fairly weak with out much in the way of dynamics to get convection going. I expect that these areas will mainly just see ACCAS and virga this morning. A better chance for nocturnal convection will come Monday night into Tuesday morning over southeast Washington into the southern and central Idaho Panhandle. The NAM is suggesting better MUCAPEs on the order of up to 400-500 J/kg and a shortwave disturbance pushing northeast out of northern California and southern Oregon. I went ahead and maintained a 15-30% chance for higher based thunderstorms. These storms will be moving fast, thus be drier and may be a higher threat for lightning caused fires. Winds will be generally breezy through the Cascade gaps and out over the basin sustained at 10-15 mph and gusts up to around 25 mph. Winds will increase this afternoon and remain breezy through Monday night into Tuesday. Temperatures will cool to near normal by Tuesday with highs in the upper 70s to the mid 80s. /SVH Wednesday through Sunday: Weak high pressure of the mid part of the week becomes altered as a large upper area of low pressure intensifies and digs southward off the coast toward the end of the week and remains more or less in the same area over the weekend. The end result will be a warming trend peaking on Thursday. Benign conditions under weak high pressure Wednesday give way to a warm southwesterly flow increasing moisture and instability and allowing for a more unsettled Thursday evening and beyond. Pops for showers and thunderstorms and a bit more cloud cover is likely to result in slightly cooler temperatures after they peak Thursday and more or less continue on as such through the weekend as the offshore upper area of low pressure remains in place and allows for continued moisture, instability, and small trigger disturbances to be steered overhead in a southwest to northeast or south to north trajectory across Eastern Washington and North Idaho. /Pelatti && .AVIATION... 18Z TAFS: A compact upper level low pressure system will track from the Cascades into northeast Washington today. Widely scattered thunderstorms are expected near airports from the Methow Valley (KS52), Omak (KOMK), Colville (KCQV), and Bonners Ferry (K65S). An axis of mid level instability across southeast Washington to the Central Panhandle Mountains will result in mid to level clouds, including ACCAS cover, but mainly only expecting isolated showers. Westerly winds will increase through the Cascades late this afternoon with gusts of 15-20 kts at KEAT expected into the evening. Nocturnal thunderstorms are expected to push northeast out of northeast Oregon Monday night into Tuesday morning. These storms may impact the Pullman/Moscow (KPUW) and Lewiston (KLWS) airports after 06Z. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high for VFR conditions. High confidence for thunderstorms over the Cascades and northern mountains today. Low confidence for thunderstorms elsewhere across the region, including nocturnal thunderstorms Monday night into Tuesday morning in the vicinity of KPUW and KLWS. ----------------------- 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 88 56 80 53 83 56 / 0 10 10 0 0 0 Coeur d`Alene 86 55 79 52 81 54 / 20 10 20 0 0 0 Pullman 83 52 75 47 79 51 / 20 20 20 0 0 0 Lewiston 93 63 85 60 88 61 / 20 20 40 0 0 0 Colville 87 47 83 45 83 46 / 20 20 10 0 0 0 Sandpoint 83 52 79 50 80 51 / 20 10 10 0 0 0 Kellogg 83 57 76 54 79 58 / 20 20 20 10 0 0 Moses Lake 89 56 84 53 85 55 / 0 0 0 0 0 0 Wenatchee 88 62 85 61 86 64 / 10 10 10 0 0 0 Omak 92 61 89 59 90 60 / 30 20 10 10 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...Flood Watch through this evening for Okanogan Highlands-Okanogan Valley-Upper Columbia Basin-Western Okanogan County. Red Flag Warning until 8 PM PDT this evening for East Washington North Cascades (Zone 698)-Methow Valley (Zone 704)-Okanogan Highlands and Kettle Mountains (Zone 699)-Okanogan Valley (Zone 703). Red Flag Warning until noon PDT today for East Portion of North Cascades National Park/Lake Chelan National Recreation Area (Zone 697)-East Washington Central Cascades (Zone 696). && $$