DISCUSSION
through next weekend.

Water vapor satellite imagery depicts a very dry airmass over the Western and Southwestern US as a nearly 600dm high looms overhead.
The dryness is confirmed by our morning sounding, having just 0.25" of precipitable water which places it below the 10th percentile of climatology for this time of year. These dry conditions appear to be permitting more overnight recovery than anticipated, with lows this morning 1-4 degrees below the forecast. However, the limited overnight recovery is brief, with temperatures reaching 105 degrees in Vegas just after 10 AM this morning. This places us ~2 degrees ahead of schedule compared to yesterday's observations, and on track for ~115 degrees this afternoon. Today will be the hottest day of the year so far, but that title is expected to be usurped tomorrow and possibly the days to follow. Heat won't be confined to the Las Vegas Valley, however, as new Excessive Heat Warnings go into effect for Lincoln and northern Mohave Counties today, and the existing warnings remain in effect for the rest of the lower elevations in our CWA Combined with the Heat Advisories now in effect for the Sierra, Spring, Sheep, and White Mountains, all of our zones have some form of heat headline out through Wednesday. Temperatures will challenge daily records in many locations, with all-time records threatened at a few sites (mainly Las Vegas and Barstow). The historic warmth is producing widespread major to extreme HeatRisk (levels 3 and 4 on a scale to 4). These conditions now appear likely to persist through at least Friday as model guidance continues to delay the potential return of monsoonal moisture.

Heading into the weekend, ensemble guidance shows southerly flow developing over the lower Colorado River Valley as we become sandwiched between a high near the Four Corners and a weak trough/cutoff low off the CA Coast. This southerly flow then advects moisture up towards the I-15 corridor. However, the position of the aforementioned synoptic features is going to be crucial to our prospects of precipitation and "ending" this heat wave. Shifts of 50- 100 miles east/west could shut off the moisture tap, leaving us hot and dry. Latest GEFS shows 1"+ PWAT probabilities ranging from 10- 20% along the I-15 corridor to over 50% near Lake Havasu on Saturday. On Sunday, these probabilities along I-15 increase to 20- 40%. We'll be monitoring trends in the these probabilities as well as the positions of the upper-level high and upstream trough/cutoff low over the coming days.

AVIATION
For Harry Reid...Variable winds begin to take a northeasterly direction in the early afternoon, shifting to the southeast later in the afternoon. By this evening, southwesterly winds should be in place. Early tomorrow morning, variable winds return. Speeds should be less than 10 knots throughout the forecast period. Temperatures decrease to less than 100 degrees tonight around 07Z, increasing to over 100 degrees by 16Z tomorrow morning.

For the rest of southern Nevada, northwest Arizona and southeast California...Diurnal winds with speeds of less than 10 knots are expected at most locations. Moderately gusty westerly winds may develop at KDAG starting this evening, lasting through the night.
Occasional gusts of less than 20 knots cannot be ruled out this evening at KBIH. Highs in the 110s will occur in the afternoon today and tomorrow at all terminals except for KBIH.

CLIMATE
Numerous climate locations have a forecast high temperature and/or forecast warm low temperature within 3 degrees of the daily record.

The table below shows the daily record maximum temperature and the year the record was last set. An asterisk (*) denotes which records are in jeopardy (within 3 degrees of the forecast).

MAX SAT, JUL 6 SUN, JUL 7 MON, JUL 8 TUE, JUL 9 Record(Yr) Record(Yr) Record(Yr) Record(Yr)

Las Vegas 115(2007)* 116(2017)* 114(2021)* 116(2021)* Bishop 105(2021)* 107(2021)* 109(2021)* 108(2021)* Needles 120(1922)* 122(2017) 120(2017)* 120(2021)* Daggett 115(2007)* 116(1989)* 114(2021)* 113(2021)* Kingman 108(2017)* 112(2017) 108(2017)* 111(2021)* Desert Rock 111(2007)* 111(2017)* 108(2017)* 111(2021)* Death Valley 127(2007)* 129(2007)* 128(1913)* 130(2021)*

The table below shows the daily record warm minimum temperature and the year the record was last set. An asterisk (*) denotes which records are in jeopardy (within 3 degrees of the forecast).

WARM MIN SAT, JUL 6 SUN, JUL 7 MON, JUL 8 TUE, JUL 9 Record(Yr) Record(Yr) Record(Yr) Record(Yr)

Las Vegas 90(1957) 93(2018) 92(2017)* 93(2021)* Bishop 67(1985) 72(2014) 70(1991) 72(1975)
Needles 97(1903) 95(1942) 95(2018) 95(2021)
Daggett 83(2007)* 80(2018)* 84(2021)* 85(2017)* Kingman 79(1981) 80(1917) 84(2014) 82(2017)* Desert Rock 83(1992)* 82(1981) 81(2021) 86(1985)
Death Valley 99(2013) 101(2021)* 105(1921) 104(2021)

SPOTTER INFORMATION STATEMENT
Spotters are encouraged to report any significant weather or impacts according to standard operating procedures.