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Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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204 FXUS65 KRIW 150411 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1011 PM MDT Sun Jul 14 2024 .KEY MESSAGES... - Sunday afternoon and evening convection again has the potential to generate outflow wind gusts of 35 to 55 mph, although increasing moisture will lead to more rain-producing convection. - Northerly near-surface wind flow tonight and Monday morning allows smoke to filter as far south as central Wyoming, especially along the Interstate 25 corridor in Johnson and Natrona Counties. - Temperatures cool to seasonal averages Monday and Tuesday giving relief from the recent hot temperatures. - Typical summertime diurnal convection is anticipated through the coming week. && .DISCUSSION... Issued at 121 PM MDT Sun Jul 14 2024 Water vapor imagery depicts moisture from the southwest pushing into and then eastward across Wyoming early Sunday afternoon. Cloud cover waned over the central and southwest during the late morning allowing for better surface heating and the development of convection over the higher terrain. This convection is beginning to move off the mountains and into the basins. A dry sub-cloud base layer will again generate gusty outflow wind of 35 to 45 mph. However, surface dew points have crept up so rain will reach the ground with the stronger showers and storms. The greatest temperature-dew point spreads will be across the high southwest deserts where outflow gusts of 45 to 55 mph are possible. Drier mid-level air reaches the southwest Sunday evening leading to a decrease in coverage in that region prior to sunset. Shortwave energy over northern Nevada early Sunday afternoon is eventually caught up in westerly flow aloft and makes a right turn toward Wyoming tonight. While convection intensity and coverage diminishes around sunset, this shortwave and weak jet energy along the northern border enables at least isolated light showers to prevail over the northern-third of the forecast area tonight. A stronger shortwave over southern Canada tracks east late tonight and Monday morning causing near-surface flow on the backside to switch to the north along and east of the Continental Divide. Wildfire smoke that has been plaguing locations to our north Sunday should filter into northern and central Wyoming. As a result, Johnson and Natrona Counties could see reduced visibilities Monday morning before afternoon mixing improves smoke dispersal. The active northern stream flattens a dominant Four Corners high, which elongates over the southwest US to begin the week. Heights fall accordingly, and the aforementioned northerly push provides cooler, more seasonal temperatures across the forecast area Monday. Weakly cyclonic west-northwest flow and a persistent stream of mid- level moisture combine to generate more widespread showers and thunderstorms Monday afternoon and evening. The strongest storms would be in Johnson and Natrona Counties where instability and shear are greatest. These areas are highlighted in the SPC Day 2 Convective Outlook. The loss of solar heating brings an end to the convection Monday evening, with only a few lingering light showers around the Bighorns overnight. The only wind of consequence will be 15 to 25 mph west to northwest afternoon breezes over the southwest- quarter of the state. Seasonal temperatures continue Tuesday and Wednesday within west to northwest flow aloft. Mid-level moisture favors typical diurnal convection, with coverage greatest on Tuesday. The Four Corners high begins to amplify north toward the Northern Rockies Wednesday and builds through the remainder of the week. Temperatures climb to above seasonal averages, but not as warm as the heat at the end of this past week. Ensemble clusters generally show the high retrograding to the Desert Southwest by next weekend. This may cut-off the primary southerly flow of moisture, but blended model solutions seem to favor a dirty ridge. Thus, the trend of summertime diurnal convection persists. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1005 PM MDT Sun Jul 14 2024 A couple of showers will linger at KCOD and KWRL, mainly before 08Z. Any outflow with these lingering shower/thunderstorms could bring variable gusts 30 to 40 knots. Winds become lighter overnight, before increasing again Monday afternoon due to diurnal heating and thunderstorm outflows. Showers and thunderstorms are once again possible Monday afternoon and evening, with gusty outflow being the main concern. Most convection should end by around 04Z Tuesday. Smoke continues, mainly across the northern half of the area. VFR conditions are expected to remain for all terminals, though some mountain obscuration continues. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .FIRE WEATHER... Issued at 121 PM MDT Sun Jul 14 2024 Above normal Sunday afternoon temperatures combined with low relative humidity and the potential for gusty outflow wind from convection leads to continued elevated to near-critical fire weather conditions, especially in Zone 280. Scattered showers and storms through early Sunday evening will also produce rainfall, although wetting rain would be scarce. Scattered showers and thunderstorms ignite again Monday afternoon, with a 30 percent chance of wetting rain in the Absaroka and Wind River Mountains. Increasing dew points and cooler temperatures Monday and Tuesday lead to higher relative humidity both days along with improved overnight recovery. && .RIW WATCHES/WARNINGS/ADVISORIES... && $$ DISCUSSION...CNJ AVIATION...Hattings FIRE WEATHER...CNJ