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Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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687 FXUS65 KRIW 161731 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1131 AM MDT Tue Jul 16 2024 .KEY MESSAGES... - Seasonable temperatures across the Cowboy State today with isolated showers and thunderstorms possible this afternoon. - Gusty outflows of 30-40+ mph will be possible once again nearby any developing storms. - Near seasonable temperatures and daily chance for afternoon showers and thunderstorms look to continue through the remainder of the week. && .DISCUSSION... Issued at 245 AM MDT Tue Jul 16 2024 Yesterday was quite the eventful and unsettled day across the Cowboy State, especially in parts of Fremont and Natrona Counties. Widespread showers and thunderstorms developed during the early afternoon. A robust storm moved through the central CWA starting in Lander and moving all the way into Casper. Severe wind gusts were recorded in Lander with the airport recording a gust of 66 mph. This storm produced widespread strong wind gusts of 55+ mph which led to some downed trees and power lines in parts of Fremont County. Fortunately, things are looking much quieter this morning with a few lingering weak showers moving through parts of the CWA. Similar to yesterday temperatures are expected to be warm but seasonable with highs in the low to upper 80s and highs in the low 90s across parts of the Bighorn Basin. Showers and thunderstorms are possible once again this afternoon but are expected to be more isolated in nature and remaining mainly across central and western parts of the CWA. A weakening area of high pressure will continue to retreat to the south for the first half of the week. This is largely due to a longwave trough digging across the central CONUS, bringing with it an active northern stream that aids in suppressing the high to the south. As a result of this shift, westerly/northwesterly flow is expected to develop, which will aid in funneling moist pacific air into the region. PWAT values are forecast to remain above normal over the next few days with amounts ranging from 0.75 to 1.00 inches. This flow combined with daytime heating and Pacific moisture will create daily chances for showers and thunderstorms. The main concern with any convection will be strong gusty outflows and brief heavy downpours. Soundings for today are showing a drier overall profile compared to Monday with a lower dewpoint depression. This means that some storms may be capable of producing outflow winds but weaker in nature compared to yesterday. Storms will likely be able to produce isolated outflows of 30 to 40 mph with a few gusts near 50 mph possible. One thing to monitor will be upper steering flow today as models are indicating a rather stagnant flow. This would lead to storms stalling over one place or moving very slowly. Due to the above normal PWAT values there is some concern for heavy downpours over a brief period of time in the locations where storms develop. CAM`s are showing most of the convection being limited to the high elevation mountain ranges in the central and western part of the CWA. There are some models showing these storms being able to move off the mountains but due to the drier sounding profiles, storms will likely weaken quickly over lower elevations. Overall, showers and thunderstorms are possible this afternoon but will be more isolated and restricted mainly to higher elevations. This does not mean some lower elevations will not see a shower or two. The best chance for showers in the lower elevations look to be along the eastern slopes of the Wind River Range, western valleys, and the Green River Basin. Precipitation chances in these locations range from 20-40%. Thunderstorms are looking very isolated, with the areas mentioned before having the best chance of seeing some with a 10-30% chance. The majority of the CWA will likely remain dry today but there is still the concern for some strong outflow winds developing from the storms over the higher elevations. Showers and thunderstorms will gradually dissipate by the evening with a few lingering showers possible into the early morning Wednesday. Due to the suppression of the high to the south and the development of the potent northerly stream, unsettled weather is expected to occur daily through the Wednesday. Pacific moisture along with westerly/northwesterly flow will create daily chances for afternoon showers and thunderstorms. Temperatures will also remain around seasonable values with highs in the 80s to low 90s. The second half of the week still has a lot of uncertainty as models differ on the possible outcomes. Models are starting to lean towards the high south of the region being pushed west over the Great Basin for the second half of the week. This will leave Wyoming sandwiched in between a large upper level low over the Hudson Bay and the upper level high along the West Coast. Overall, temperatures look to remain warm but still around seasonable values. Unsettled weather will prevail through the remainder of the week with daily chances of afternoon showers and thunderstorms. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1130 AM MDT Tue Jul 16 2024 An axis of upper-level high pressure remains just to the west of Wyoming today, keeping warm, yet somewhat moist and unstable air over the area. Mostly clear skies during the morning are giving way to convective development by noon, with thunderstorms starting over the eastern slopes of the Wind Rivers and Wyoming range. Convection will focus today over west-central WY into the Wind River Basin and southern Absarokas, and extend down to Sweetwater County. Not as certain at KJAC but have included vicinity showers in case some storms move around that airspace. Winds are generally light, though thunderstorm outflows could exceed 30 kts. As such, VFR conditions generally expected, with brief MVFR is storms directly impact terminals. Showers are expected to linger in the early evening hours, especially at KPNA and KLND around the Wind Rivers. Winds will decrease overnight, though skies should remain partly cloudy for some areas. A couple of forecast models are indicating an area of light showers early Wednesday morning over northwest WY, possibly bringing some rain to KCOD around sunrise. The high pressure axis shifts slightly eastward on Wednesday which should bring showers and thunderstorms to areas along and east of the divide. SW WY should remain mostly dry, though can`t rule out an isolated storm or two. WNW winds will continue over SW WY, while east of the divide will see NE to E winds Wed afternoon, with stronger ENE winds pushing southwestward into KRKS Wed evening. Finally, smoke concentrations are increasing over the area due to regional fires, but not yet enough to reduce visibilities at the TAF sites. Will continue to monitor and adjust forecasts as necessary. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... Air Quality Alert until 1 PM MDT this afternoon for WYZ010-023- 024-027. && $$ DISCUSSION...Dziewaltowski AVIATION...McDonald