Strengthening high pressure suppressed thunderstorm development and brought two days of excessive heat to portions of the Mojave Desert.
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The episode as NWS VEF wrote it up.
Strengthening high pressure suppressed thunderstorm development and brought two days of excessive heat to portions of the Mojave Desert.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Las Vegas, NV wrote its last area forecast discussion before the first event at Aug 15, 9:00 AM PST, 2 hours earlier.
Area Forecast Discussion National Weather Service Las Vegas NV 1000 AM PDT Sun Aug 15 2021 .SYNOPSIS...A strong area of high pressure centered over northwest Nevada will lead to above normal temperatures through Monday. A lingering moist and unstable air mass will continue to produce isolated afternoon thunderstorms over the mountains of southern Nevada and southeast California, with greater storm coverage over northwest Arizona through Tuesday. Cooler temperatures and a slow drying trend are expected to spread over the region after Tuesday. && .UPDATE...Moisture and instability, along with the overall pattern, have not changed much in the past 24 hours and the expectation for thunderstorm development is similar to Saturday afternoon and evening. Isolated thunderstorms that initiate over Lincoln County and central Nye counties (SB CAPE values around 500 J/kg) will be steered toward the southwest by clockwise flow around the 500mb high centered over northwest Nevada. Higher moisture and instability resides over Mohave County, and more surface heating is available today to prime the air mass for thunderstorms moving in from the rim country late this afternoon and evening. No need for immediate changes to the going forecast trends for these expectations. The high over northwest Nevada is also driving smoke from the northern California wildfires farther south and restricted visibilities of 4-5 have made it into the northern Owens Valley. The weather grids will be updated with the 12Z HRRR Smoke forecast. - Adair && .PREV DISCUSSION...147 AM PDT .SHORT TERM...through Monday night. Early morning satellite and radar loops showed scattered to broken mid level debris clouds over much of our CWA once again, along with isolated weak radar returns which were likely producing brief light showers at most. Surface obs showed light winds and seasonably warm temperatures areawide, with dewpoints mostly in the 50s and 60s southeast of I-15 and mostly in the 30s and 40s farther northwest. First concern will be the heat. Excessive Heat Warning still looks good, with Heat Risk values of 3 and 4 covering most of the warned zones today and Monday. Farther north, zones 14 and 15 are of growing concern as splotches of 3 and 4 have been increasing in coverage for today and Monday with each passing forecast. Coverage is not great enough to warrant a Warning, so will hoist a Heat Advisory for today and tomorrow, which will also match with WFO LKN's Advisory for northern Nye County. Second concern will be thunderstorms. High resolution models are showing similarities to yesterday, with development beginning in the early afternoon on the higher terrain, then the focus shifting to Mohave County later in the afternoon as storms roll in from the east. 850- 300 mb bulk shear magnitude is forecast to increase over Mohave Co in the late afternoon, so there could be an isolated severe storm before convection fizzles around midnight. Monday looks like a relatively down day for storms, with less coverage and less organization than yesterday or today. By Monday night, things will begin to change as a trough of low pressure swings into British Columbia and the Pacific Northwest states, suppressing the big dome of high pressure over our area. More on that in the long term section. .LONG TERM...Tuesday through Saturday. The setup is now looking less favorable for deeper moisture to be drawn into our region ahead of the aforementioned approaching trough though lingering moisture should remain over part of southern Nevada and northwest Arizona and maybe eastern San Bernardino County. There should still be sufficient instability over these areas for afternoon thunderstorms Tuesday and possibly again Wednesday and this is reflected by the latest NBM PoPs which indicate more than just terrain-based storms. However, the ECMWF and GEFS ensemble means have been digging the base of the trough a little deeper resulting a drier southwest flow which could scour moisture out to the east during the Tuesday-Wednesday period followed by a persistent dry west to northwest flow Thursday into next weekend. The ensemble-based NBM PoPs are a little slow at indicating this drying trend so far, but temperatures decrease several degrees after Tuesday under the influence of the trough and PoPs will likely trend downward over the next few model runs if ensembles continue to dig the trough slightly farther south. && .AVIATION...For McCarran...Light easterly winds expected this afternoon that will once again shift to the southeast through the evening. These southeast winds are expected to range from 8 to 10 kts, but gusts 15 to 25 kts from the southeast are possible with storm development between 3 and 5Z. Confidence at this time is not high enough to include in the TAF. Winds will become light and variable overnight. Otherwise, scattered to broken mid and high level clouds expected. For the rest of southern Nevada, northwest Arizona and southeast California...Light and diurnal winds are expected today across the region with scattered to broken mid and high clouds over the Mojave Desert and few clouds elsewhere. Gusty south-southeast winds possible at KIGM, KEED, KIFP, KHND, and KLAS between 00Z and 05Z as isolated storm formation moves through the Peach Springs corridor. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant weather or impacts according to standard operating procedures. && SHORT TERM...Morgan LONG TERM...Adair AVIATION...Varian For more forecast information...see us on our webpage: https://weather.gov/lasvegas or follow us on Facebook and Twitter
The national radar mosaic for the moment the first event began.
1 excessive heat. Local standard time, as filed.
Excessive Heat Warning criteria were reached two days in a row.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Nevada in 2021Every state in 2021This day in weather historyWarnings in Nevada, August 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 981088.