FXUS65 KVEF 192008 AFDVEF Area Forecast Discussion National Weather Service Las Vegas NV 108 PM PDT Tue Aug 19 2025 .KEY MESSAGES... * A stretch of very hot conditions is expected beginning tomorrow and lasting into the upcoming weekend. Heat-related warnings and advisories are in place. * A return of Monsoonal moisture will result in an increase in chances for showers and thunderstorms, especially over the higher terrain. These will bring the potential for strong/potentially damaging winds and heavy rains/flash flooding. && .DISCUSSION... Short and medium range ensemble guidance is in very good agreement regarding a powerful Four Corners ridge of high pressure. This feature will intensify mid to late week. Given our abnormally dry conditions for mid-August, the subsidence associated with this feature will result in very hot conditions across much of the Desert Southwest. As such, Extreme Heat Warnings and Heat Advisories remain in effect beginning tomorrow and lasting into the weekend. With moisture set to return over the weekend, it would make sense that temperatures may cool slightly owing to increased cloud cover. However, as we are initially on the gradient of moisture return, it may take a day or two to see a response in temperatures. The increase in moisture will also bring about muggier than usual conditions, which will make temperatures feel hotter, and limit the potential for overnight cooling. This will promote a prolonged risk of heat exposure, especially for those who are sensitive to heat and/or do not have adequate access to cooling. The positioning of the aforementioned upper ridge will usher in a period of optimal south/southeast mid and upper level flow. This will finally allow meaningful moisture to return to the Desert Southwest late this week into the weekend, with perhaps the highest and most widespread chances for Monsoon thunderstorms we have seen in well over a month. Given the presence of upper ridging and large scale subsidence, conventional wisdom would favor the mountains and nearby higher terrain for greater coverage of showers and thunderstorms. That being said, ensemble guidance is quite bullish,even in the lower elevations, with precipitation. It is apparent that the ensembles may not be handling the rapid influx of moisture all that well. While thunderstorm outflow interactions can and do promote showers/storms in the lower elevations, coverage is generally more isolated in nature. Without much in the way of upper level forcing, it remains to be seen just how widespread our afternoon showers and storms are, but it will certainly be more active than it has in the last several weeks. With PWAT values some 150-200% of normal, and modest instability, the potential for locally heavy rains and flash flooding will also exist. Initial storms late this week may also pose a greater risk of damaging downburst winds given the extreme heat and dry/deeply mixed environment. Stay tuned and prepare for a return to our regularly scheduled Monsoon. && .AVIATION...For Harry Reid...For the 18Z Forecast Package... Winds largely remain diurnally driven through the period. Expect winds to gradually turn east/southeast by early afternoon with a southwest push this evening and overnight. Winds should generally remain 15 knots or less, although a period of gusts in the 15-20 knot range is apparent in the late afternoon to early evening. Winds will gradually diminish late this evening and overnight becoming variable. Another hot day is on tap with highs exceeding 100 degrees from 19z through 04z and highs peaking around 106 degrees. For the rest of southern Nevada, northwest Arizona and southeast California...For the 18Z Forecast Package...Winds will largely remain diurnal and 10-15 knots or less. The few exceptions will be KBIH, where gusty south/southeast winds will persist through the afternoon. Winds here will decrease after sunset, eventually becoming northwesterly overnight. KDAG will also experience its typical west/southwest gustiness. Each of these locations can expect a few gusts of 20-30 knots. Otherwise expect just a few passing mid and high level clouds through the period. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ DISCUSSION/AVIATION...Austin For more forecast information...see us on our webpage: https://weather.gov/lasvegas or follow us on Facebook and Twitter