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Area Forecast Discussion
Issued by NWS Las Vegas, NV
Issued by NWS Las Vegas, NV
507 FXUS65 KVEF 172055 AFDVEF Area Forecast Discussion National Weather Service Las Vegas NV 155 PM PDT Wed Jul 17 2024 .SYNOPSIS...High pressure to the east will move overhead by the weekend resulting in excessively hot temperatures and increasing Heat Risk. Isolated to scattered thunderstorm activity will remain possible each day with the best storm coverage expected across northwest Arizona. A deeper push of moisture into the area next week could bring higher storm chances while well above normal temperatures could extend excessively hot conditions through the middle of the week. && .DISCUSSION...Thursday and Friday. No changes were made to the Excessive Heat Watch in place for Friday and the weekend. Monsoon moisture increases on Thursday becoming more widespread with precipitable water values between 130% and 180% of normal for this time of year. Much of the region is forecast to be weakly unstable due both to the increasing daytime temperatures and to the moisture increase. Higher instability is forecast over the central and southern portions of Mohave County, the Colorado River Valley, and the far southern portions of San Bernardino County where the HREF gives a increasing probability of CAPE exceeding 500 j/kg in the afternoon. The WPC day 2 outlook for excessive rainfall captures much of Mohave County with the exception of the southwest portion of the county. These areas will have the highest potential for localized flash flooding on Thursday. Moisture becomes trapped under high pressure that is forecast to move over the area on Friday. Isolated to scattered thunderstorms are forecast to continue across portions of Lincoln, Clark, Mohave, and eastern San Bernardino counties where conditions are forecast to be more unstable. Thunderstorm development in our western areas will need to rely on daytime heating and topographic lift in absence of any other lifting mechanism. Our western valley locations are likely to have little to no convection Friday with storms tied to the higher terrain. Otherwise, expect generally light winds with afternoon breezes both days and temperatures around 5 degrees above normal. An Excessive Heat Watch goes into effect on Friday across our southern/southeastern areas where we could see localized major Heat Risk. Saturday and Sunday... The Excessive Heat Watch expands to include much of the area over the weekend. High pressure settles over the area resulting in more widespread major to extreme Heat Risk this weekend. High temperatures are forecast to be around 2-3 degrees warmer while overnight lows will be warmer overall, providing less overnight relief from the heat. The high will trap moisture beneath it leading to a chance of thunderstorms each day. Warmer temperatures aloft that are associated with high pressure will initially cap convection until daytime heating and topographic lift work to allow storms to develop over the mountains. Eventually, storms will roll off the higher terrain into the valleys. Better chances for storms will continue over our central and eastern areas while limited convection is forecast in our western areas where more stable conditions are expected. Monday through Wednesday... Temperatures are forecast to remain hot with areas of major to extreme Heat Risk continuing. It`s likely that heat products will be needed for this period how that will look is the question. Ensemble systems are forecasting an increase in moisture and thunderstorm coverage early in the week which could help mitigate the impacts from Heat Risk. In general, areas south of the I-15 drop back into the widespread moderate Heat Risk category Monday through Wednesday with major Heat Risk more localized. Major to extreme Heat Risk continues for areas north of the I-15 including the Las Vegas Valley. More detailed information regarding heat risk for the upcoming week will provided in the days ahead. Regarding monsoon activity, low grade recycling of thunderstorms is expected with daily storm activity forecast to be fairly widespread. && .AVIATION...For Harry Reid...Winds will be a headache this evening. There are three possibilities: easterly outflow winds from thunderstorms in Arizona, strong south to southwest outflow winds from thunderstorms in extreme southern Nevada, and light easterly winds shifting to light southerly with no outflow influence. There is also a very low (10%) chance of these outflow winds kicking off thunderstorm development near the terminal this evening. Thursday is likely to be similar, with thunderstorms over the mountains in the approach corridors and a low (20%) chance of a thunderstorm at the terminal. For the rest of southern Nevada, northwest Arizona and southeast California...Expect a slight uptick in thunderstorm coverage this afternoon versus yesterday, with the highest chances (40-50%) in Mohave County. Storms here are likely to produce outflow winds moving west, possibly into San Bernardino and Clark counties. Thunderstorm chances will increase and expand across much of the Mojave Desert and southern Great Basin Thursday, with the main concerns again being erratic, gusty winds as well as low ceilings and terrain obscuration. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ DISCUSSION...Salmen AVIATION...Morgan For more forecast information...see us on our webpage: https://weather.gov/lasvegas or follow us on Facebook and Twitter