Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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907 FXUS66 KOTX 131015 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 315 AM PDT Tue Aug 13 2024 .SYNOPSIS... Isolated showers and thunderstorms for southeast Washington and the Idaho Panhandle this morning then over the northern mountains of eastern Washington this afternoon. A break in showers and thunderstorms comes Wednesday before more unsettled conditions return late Thursday into the weekend. Daytime temperatures will be near normal through the week. && .DISCUSSION... Today and Tonight: The Inland Northwest remains under a baggy upper level trough of lower pressure. A shortwave disturbance riding northward in eastern Oregon early this morning will bring a 15-30% chance for showers and thunderstorms to extreme southeastern Washington and the southern to central Idaho Panhandle through the morning hours. Higher probabilities will be from the Northeast Blue Mountains, to the Camas Prairie and Central Panhandle Mountains, and then decreasing precipitously further northwest across the Palouse. The Spokane-Coeur d`Alene corridor will be on the northern fringe of the nocturnal convection. Surface based afternoon convection will mainly be confined to the northern mountains near the Canadian border. This includes the Cascades north of Lake Chelan, over the Okanogan Highlands, and Northeast Mountains. Bulk shear through the atmospheric column is non-existent, and surface based CAPE of up to 500 J/kg at best will yield weak pulse type thunderstorms. Lightning activity will be isolated. Slow moving thunderstorms will also result in rainfall that will limit the potential for new fire starts with lightning. Rainfall doesn`t look particularly heavy with modest P-Wat values near 0.9 inches. Limited instability should also result in thunderstorms decaying fairly quickly. Risk for flash flooding and/or debris flows isn`t particularly high. South to southwest winds will be a little breezy into the afternoon, but not to the point that impacts are expected. Wednesday and Wednesday night: Higher heights build into the region with an upper level low forming off of the coast of Oregon. This will act to stabilize the atmosphere with benign weather conditions. Sunny skies with temperatures warming slightly from the mid 70s and mid 80s on Tuesday to the low to upper 80s on Wednesday. /SVH Thursday through Tuesday: Longwave pattern shows a trough along or just off the west coast with a ridge towards the Rockies/northern Plains region. Forecast confidence is higher Thurs/Fri than the weekend and beyond. Thursday a low will move into Oregon and swing up into Washington early Friday. This will bring an increase in clouds along with a chance of rain and thunderstorms. The first area to watch will be southeast WA and the southern and central ID Panhandle (much like today). Showers with a 15-20% chance of thunderstorms moves in late Thursday afternoon and continues through the night as elevated instability moves into the region with enough moisture and forcing from the low pushing east of the Cascades. Friday morning a fair amount of the long term ensemble members are showing light rain for much of eastern Washington and the Idaho Panhandle. Have increased our chance of precip a bit for the Spokane/Palouse area and most of the Idaho Panhandle with much of the region having a 35-50% chance of rain. By the afternoon the chance of showers and thunderstorms extends into the Cascades and northern WA mountains. Highest probabilities of thunder will be Lake Chelan area northward to the Canadian border, along the US/Canadian border as well as the ID/MT border with a 25-30% chance. Saturday through Tuesday the models differ a bit with the placement of the low. The closer the low is to our area, the more likely to see near average temps or a few degrees cooler. If the low remains further west, that will allow more of the ridge to the east to influence and temperatures to be a few degrees above average. Currently 25-40% of the ensembles are suggesting the warmer solution, with 60% or more suggesting near average temperatures. Average temperatures for mid August is mid 80s to around 90. We look to have bouts of moisture in the south to southwesterly flow which will keep showers and thunderstorms in the forecast through at least the weekend. Best chance of thunderstorms will be in the Cascades and across northern WA/ID. /Nisbet && .AVIATION... 06Z TAFS: VFR conditions will prevail. Nocturnal thunderstorms are expected to push northeast out of northeast Oregon Tuesday morning. These storms may impact Lewiston (KLWS) after 12z. Models have trended slower and further south but Pullman still carries a small chance (10%) of a thunderstorm. Expecting another round of weak thunderstorms in far north-central and north-east Washington and north Idaho starting around 18-21z. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high for VFR conditions. Low confidence in nocturnal thunderstorms for 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 81 52 84 56 87 59 / 10 0 0 0 0 20 Coeur d`Alene 80 52 82 54 86 57 / 10 0 0 0 10 30 Pullman 75 47 80 50 81 53 / 20 0 0 0 10 30 Lewiston 85 60 88 62 90 64 / 40 0 0 0 10 40 Colville 84 44 84 45 87 49 / 10 0 0 0 0 20 Sandpoint 80 50 80 51 85 55 / 0 0 0 0 0 30 Kellogg 77 55 79 58 84 60 / 20 0 0 0 10 40 Moses Lake 84 52 85 55 88 57 / 0 0 0 0 0 10 Wenatchee 85 60 86 63 88 62 / 10 0 0 0 10 10 Omak 88 58 90 60 92 61 / 20 0 0 0 10 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$