Area Forecast Discussion
Issued by NWS Las Vegas, NV
Issued by NWS Las Vegas, NV
855 FXUS65 KVEF 202054 AFDVEF Area Forecast Discussion National Weather Service Las Vegas NV 154 PM PDT Sat Jul 20 2024 .SYNOPSIS...Isolated showers and thunderstorms return today and Sunday afternoons and will favor the higher terrain. Meanwhile, an upper-level high pressure system will center itself overhead, resulting in persistent above-average temperatures. Monsoonal moisture will increase through the work week, resulting in muggy conditions and a return of widespread shower and thunderstorm chances each afternoon. && .SHORT TERM...Today and Sunday. The upper-level area of high pressure typically responsible for its monsoonal moisture flux into the Desert Southwest will shift overhead today. This position change will result in persistent above- average temperatures for the Mojave Desert. As such, the Excessive Heat Warning for southern Inyo, southern Nye, Clark, San Bernardino, and southern Mohave counties will continue through Sunday. With the high overhead, the moisture flux up the Colorado River Valley from northern Mexico is cut off. However, remnant moisture trapped beneath the high coupled with heat-driven instability and orographic lift will result in isolated thunderstorms in the higher terrain of the Mojave Desert and southern Great Basin each afternoon through the weekend. This reduction in Precipitable Water (PWAT) will help mitigate widespread flash flooding concerns, though there remains some risk of localized flash flooding beneath stronger cells, especially in cases of training or stationary storms. A slight increase in moisture Sunday afternoon will allow for increased coverage of thunderstorms across the southern Great Basin and eastern Mojave Desert. Of particular interest, Convection Allowing Models (CAMs) continue to highlight the occurrence of a thunderstorm outflow impacting the Las Vegas Valley and nearby lakes Sunday evening as a result of thunderstorms in southeastern Nevada and southwestern Utah. This is supported by a slight shift in the upper-level high, resulting in a northerly flow over southeastern Nevada and by HRRR forecast soundings calling for 2200 J/kg of DCAPE over southern Nevada. Associated with this outflow would be gusty winds between 25 and 35 mph and additional convection along the boundary. .LONG TERM...Monday through Friday. Southerly flow will return to the region through the week, resulting in an increase of monsoonal moisture and daily afternoon scattered showers and thunderstorms through Friday. Meanwhile, the center of the high pressure aloft continues to wobble around the western Mojave Desert, which will result in above-average temperatures persisting through the week. Though forecast temperatures are not expected to break records or approach readings experienced a few weeks ago, the added humidity will feel oppressive. HeatRisk indirectly incorporates humidity by analyzing diurnal spreads in temperature and unusually warm overnight low temperatures. With that in mind, HeatRisk doesn`t have widespread Major-to-Extreme HeatRisk, but rather focuses in the desert valleys. Will continue to wait to see how much of an impact this moisture has on temperatures before pulling the trigger on an extended heat-related headline at this time. && .AVIATION...For Harry Reid...Light north to east winds through mid afternoon. Still looking at the development of an isolated shower or thunderstorm west of the valley over the Spring Mountains/Red Rock Canyon between 19Z and 22Z. Outflow winds from the collapsing storm near Red Rock Canyon could shift the wind to a westerly direction after 22Z. Winds look to remain from a west-southwest direction this evening and overnight. Similar conditions expected Sunday with shower and thunderstorm formation staying along the higher terrain west and south of the valley. Outflow winds may impact the valley terminals with the potential for stronger outflow winds Sunday evening from the northeast. For the rest of southern Nevada, northwest Arizona and southeast California...Outside of the Las Vegas Valley, isolated thunderstorms expected over northwest Arizona, central Nevada and the vicinity of KBIH in the Owens Valley. Erratic, gusty winds up to 30 mph at KBIH possible between 21Z and 02Z. Ceilings will drop to 10-12 kft with thunderstorm activity. Winds will return to diurnal trends overnight before isolated thunderstorm chances return to the region Sunday afternoon with similar timing. Stronger east or northeast outflow winds are possible Sunday evening at KIFP and KEED as well as at the Las Vegas Valley TAF sites. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ DISCUSSION...Soulat AVIATION...Czyzyk For more forecast information...see us on our webpage: https://weather.gov/lasvegas or follow us on Facebook and Twitter