758 FXUS65 KVEF 060942 AFDVEF Area Forecast Discussion National Weather Service Las Vegas NV 242 AM PDT Mon Sep 6 2021 .SYNOPSIS...Dry weather and seasonably warm temperatures expected to continue through midweek. Chances of monsoonal moisture returning have diminished as the ridge of high pressure continues to build over the Desert Southwest. && .DISCUSSION...Today through next Sunday. The forecast through midweek has changed quite drastically in the last 24 hours. Originally, the area of high pressure bringing us unseasonably warm temperatures was going to continue to grow over the Great Basin through the holiday weekend before weakening and retreating east due to an incoming Pacific Northwest trough. This trough would shift the upper level flow from the south, allowing moisture to funnel up the Colorado River Valley from northern Mexico. Additionally, there was a glimpse of moisture flux from a tropical system approaching the Baja at the same time, which would bring widespread precipitation chances to the Desert Southwest, and drop temperatures. However, updated ensemble forecasts indicate that the area of high pressure will actually continue to intensify over the Desert Southwest, essentially winning in the fight between Pacific NW Trough and Desert Ridge. This dominating ridge of high pressure will extend up the western United States through the first half of the work week, which would raise heights enough to prevent a strong, digging trough... thus preventing an upper level shift from the south. The center of the high pressure will remain too far west over the course of the week to facilitate moisture transport indicative of monsoon season. What does this mean? Less chance of rain; hotter temperatures. Forecast high temperatures on Wednesday have increased quite a bit due to the lack of moisture, so the Excessive Heat Warning has been extended another day for the entire warned area. There was consideration of added the Owens Valley to a warning as well as our northern zones to a Heat Advisory; however, I decided to hold off due to HeatRisk values failing to reach criteria... let me explain. Though Bishop, CA is forecast to tie or break record high temperatures in the afternoon, the evening will cool off substantially. For context, the high in Bishop on Sunday was 100F with a morning low of 50F, so a diurnal range of 50 degrees. Though record high temperatures are possible in the Owens Valley, warm temperatures will not be maintained through a 24 hour period like the remainder of the warned zones where records are possible for both afternoon highs and warm morning lows. Warm morning lows are often the reason for heat-related illness in populations experiencing homelessness, as the body is unable to adequately cool off at night. Northern zones were not included in Heat Advisories for similar reasons. Records and forecast temperatures through Wednesday are highlighted below in the CLIMATE section. Guidance has trended considerably drier in the longer range period as a result. Forecast precipitation chances are now obsolete on Wednesday, and have been reduced by 2/3rds on Thursday from the forecast 24 hours ago. There will still be a modest increase in precipitable water for the latter half of the week, thanks to a tropical system in the mouth of the Gulf of California and a more favorable southerly flow regime, but the quantity of moisture will be limited. PoPs for Thursday and Friday look to favor the higher terrain and northwest Arizona at this time. With the decrease in moisture, warmer temperatures are likely to continue, with afternoon highs averaging 3-5 degrees above normal through the weekend. && .CLIMATE...Numerous locations have the potential to tie or break record high and warm low temperatures through Wednesday. The table below shows the record high temperature, the year the record was last set, and the forecast temperature for all of our climate sites. MAX HIGH MONDAY, SEPT 6 TUESDAY, SEPT 7 WEDNESDAY, SEPT 8 Record(Yr)/Fcst Record(Yr)/Fcst Record (Yr)/Fcst Las Vegas 114(2020)/107 108(1977)/108 110(1979)/107 Bishop 104(2020)/101 102(2020)/103 100(1979)/103 Needles 120(2020)/108 117(2020)/112 115(2018)/110 Barstow-Daggett 116(2020)/107 109(2020)/108 108(2018)/109 Kingman 110(2020)/100 107(2020)/101 105(1915)/101 Desert Rock 109(2020)/102 102(1979)/104 102(2018)/105 Death Valley 123(2020)/118 121(1932)/119 120(2018)/120 The table below shows the record warm low temperature, the year the record was last set, and the forecast temperature for all of our climate sites. WARM LOW MONDAY, SEPT 6 TUESDAY, SEPT 7 WEDNESDAY, SEPT 8 Record(Yr)/Fcst Record(Yr)/Fcst Record (Yr)/Fcst Las Vegas 84(2020)/81 84(2020)/82 81(2018)/83 Bishop 61(1950)/52 63(2020)/55 63(2020)/55 Needles 88(2019)/82 88(2012)/83 87(1986)/84 Barstow-Daggett 83(2020)/76 82(2020)/77 78(1974)/78 Kingman 77(1917)/71 72(1949)/71 84(1914)/72 Desert Rock 78(1989)/70 74(2020)/72 75(2012)/73 Death Valley 96(2013)/87 98(1913)/89 92(1979)/91 && .AVIATION...For McCarran...Another day with wind speeds generally staying 6 knots or less, though an easterly direction will be possible in the afternoon hours. A more definitive southwest direction overnight with speeds 6-10 kts possible. No operationally significant cloud cover. For the rest of southern Nevada, northwest Arizona and southeast California...Wind speeds generally less 10 knots favoring typical diurnal trends can be expected across the Mojave Desert and southern Great Basin through tonight. No operationally significant cloud cover expected. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && $$ DISCUSSION...Varian/Outler CLIMATE...Varian AVIATION...Pierce For more forecast information...see us on our webpage: https://weather.gov/lasvegas or follow us on Facebook and Twitter