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Area Forecast Discussion
Issued by NWS Spokane, WA
Issued by NWS Spokane, WA
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790 FXUS66 KOTX 141128 AFDOTX Area Forecast Discussion National Weather Service Spokane WA 428 AM PDT Wed Aug 14 2024 .SYNOPSIS... The Inland Northwest will be between weather systems today before the next low pressure system swings through Thursday into Friday. Thunderstorms Thursday afternoon into Thursday night will bring the potential for gusty outflow winds. This will be followed by wetter showers and thunderstorms on Friday particularly across the Idaho Panhandle and northern mountains. Daytime temperatures will be near normal through the week. && .DISCUSSION... Today and Tonight: Low pressure will pull away from the region with decreasing showers and clouds dissipating today over the southeast portion of the region. Higher heights building in over the region will result in benign weather conditions with sunny skies other than some fair weather cumulus over the mountains by the afternoon. Thursday through Friday night: Weather will turn unsettled again with the next upper level low pressure system making its impact. This low pressure system is situated out over the eastern Pacific at around 133W/37N early this morning. It`s progged to eject northeastward across the Inland Northwest Thursday into Thursday night. Best dynamics looks to shift across extreme eastern Washington and over the Idaho Panhandle. The National Blend of Models indicates between 500-700 J/kg of surface based CAPE over the Northeast Blue Mountains, and into the southern to central Idaho Panhandle as the shortwave rounds into the area Thursday afternoon. The deterministic NAM and Canadian model guidance suggest a potential for closer to 1000 J/kg of surface based CAPE. There is convective inhibition to contend with, but there should be enough dynamics to overcome this. The atmosphere will be unstable out across the Palouse, Spokane Area, and into the Upper Columbia Basin as well, but CAPE will be weaker further out into the basin. The NAM also indicates around 25 kts of bulk shear in the 0-6 km layer over the Panhandle. This is marginal for seeing stronger thunderstorms. What is potentially concerning is the amount of Downdraft CAPE (or DCAPE). Surface temperatures Thursday will warm into the mid to upper 80s with an inverted V model sounding profile with DCAPEs on the order of 1000 J/kg. This combined with marginal potential for stronger storms moving north across the Idaho Panhandle may result in strong outflow winds from initial developing convection. The UW- WRF also shows this potential producing outflows from convection across this area. Potential for stronger outflow winds will be less over eastern Washington with instability lacking, but not completely out of the question. Vertical profiles moisten up through the night on Thursday night Friday. P-Wats increase up to near an inch with showers and thunderstorms expected to become increasingly more wet. Nocturnal convection Thursday night looks marginal for lightning. Thunderstorms should become less numerous heading into the midnight hour on Thursday with precipitation potentially taking on more of a stratiform band across the Idaho Panhandle with internal convective elements into Friday morning. Then the question becomes how much in the way of surface based convection do we see Friday afternoon. If the timing is right, I believe we`ll see the atmosphere destabilize with isolated to scattered thunderstorms developing over the northern mountains as the deformation band clears north into Canada. The NBM shows between 300-500 J/kg of surface based CAPE across these northern zones for Friday afternoon. Thunderstorms will be slow moving and contain heavy rain. Both the NAM and GFS model sounding profiles exhibit a moist sounding through the vertical profile. This is an indication that convection will contain the potential for very heavy rain. Highest risk areas will extend from the north Cascades over to the Northern Panhandle. This looks like a good set up for flash flooding and/or debris flows, and particularly so near burn scars and in steep terrain. Temperatures on Friday will cool into the mid 70s to mid 80s. /SVH Saturday through Wednesday: We will continue to live in the in between of a low off the west coast and a ridge over the rockies/northern plains. Saturday, 54% of the ensembles suggest the low will be closer to the coast with a wave moving up in the broad south to southwesterly flow aloft. Closer to the surface, winds will become upslope into the Cascades during the afternoon and evening hours. There is a 30-40% chance of showers for portions of central WA with a 20-30% chance of thunderstorms. Showers and thunderstorms could continue through the night, though instability is pretty weak. During the late afternoon/evening hours is the best chance in the extended forecast for portions of eastern WA and north ID to see showers as well, tho the probability is only about 20%. The remainder of the forecast period has the best chance of showers and/or thunderstorms along the Cascades and the US/Canadian border most days. No significant concerns in the forecast. Temperatures will be warmest Saturday, in the 80s to around 90 which is several degrees above average, and then temps start to cool a degree or two each day thereafter. By next Wednesday temps will be at or a few degrees below average. No significant wind events are being indicated in the models, but we could see gusts Sunday onward of 15-20 mph each afternoon and/or evening across portions of central WA onto the Palouse and Spokane area. /Nisbet && .AVIATION... 12Z TAFS: The Inland Northwest will be in between systems today. Look for light winds and mainly clear skies east of the Cascades. Fire activity in Washington has decreased in recent days with several fires in the Cascades receiving some rain. If no new fires develop, visibility should be VFR across central and eastern Washington as well as north Idaho Wednesday and Wednesday night. FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: Confidence is high for VFR conditions. /GKoch ----------------------- 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 84 56 87 59 81 56 / 0 0 0 30 30 10 Coeur d`Alene 82 55 85 58 78 55 / 0 0 0 40 50 10 Pullman 80 50 81 51 78 52 / 0 0 10 40 30 10 Lewiston 89 62 88 63 86 63 / 0 0 10 50 20 10 Colville 84 46 87 47 80 45 / 0 0 0 20 40 20 Sandpoint 81 52 84 55 75 51 / 0 0 10 40 60 20 Kellogg 79 59 83 58 75 58 / 0 0 10 60 60 10 Moses Lake 86 54 87 56 84 56 / 0 0 0 20 10 10 Wenatchee 86 63 87 62 83 62 / 0 0 10 10 20 10 Omak 91 60 92 61 87 59 / 0 0 0 10 40 20 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. && $$