UPDATE
Gusty winds were reported this afternoon across the region. Many areas reported gusts of 25 to 35 MPH with higher gusts to around 40 MPH reported in the western Mojave Preserve and the Barstow as well as in the Sierra terrain. As the sunsets, winds have been diminishing outside of the Barstow, CA area where gusts to 40 MPH continued. This trend will continue through the night with winds dropping off but impactful gusts to around 40 MPH in the western Mojave Desert. A wind advisory continues through early Thursday morning for the area where winds will likely stay up through the night. The Red Flag Warning will expire at 11PM which looks good based on the current wind trends slowly fall below levels where fire danger would be a significant concern.

Smoke from wildfires continues to stream into region. Winds aloft have turn more west to southwest so the plume of smoke stretched across southern Nevada has shifted slightly east. Haze and occasional visibility reductions have been reported in the Morongo Basin and Yucca Valley this evening where satellite showed the most intense and smoke plume was most robust. The HRRR smoke model shows this trend of the most dense smoke moving into the southern Colorado River Valley and Arizona tonight. Smoke will still hang over parts of southern Nevada though which will result in hazy skies at times tonight into Thursday morning.

-Nickerson-

PREVIOUS DISCUSSION
148 PM PDT Wed Sep 11 2024
SHORT TERM
Tonight through Friday

A low pressure system over the Pacific Northwest will move east into the Intermountain West tonight and tomorrow. A tight pressure gradient will result in gusty southerly to southwesterly winds through tonight, warranting a Red Flag Warning until 11 PM PDT Wednesday for sections of Nevada and Arizona, and a Wind Advisory for western San Bernardino County until 4 AM PDT Thursday. Winds decrease going into tomorrow morning as the trough tracks northeast and the pressure gradient relaxes. Lighter winds are expected to last through Friday. However, westerly to southwesterly flow will continue to funnel smoke from the Line, Airport, and Bridge fires in Southern California into the forecast area. Near surface smoke will remain in Clark, Mohave, and San Bernardino Counties through Thursday night per the 12Z HRRR smoke model, bringing reduced air quality, lower visibility, and smoky skies. The heaviest smoke should move into southern San Bernardino and Mohave Counties starting tonight with a push of westerly winds.

Temperatures decrease on Thursday following the passage of a surface cold front associated with the trough. Zonal flow on Friday will help maintain near average temperatures.

LONG TERM
Saturday through Wednesday

The interesting / least confident part of the forecast comes late- weekend into the start of next week. There continues to be an indication among ensemble members that tropical moisture will push northward up the Gulf of California over the weekend. There are a lot of variables to consider before deciding if this will have any direct impact on the forecast area, as models remain uncertain how organized this moisture will become as it pushes northward as well as what exact track it will take. That said, the NHC has formally noted this tropical disturbance off the western coast of Mexico by Colima with a 40% chance of cyclone formation in the next 48 hours.
Both the ECMWF ensemble and GEFS means show an associated increase in PWATs up the Colorado River Valley on Sunday and Monday, with the NBM subsequently increasing PoPs over Mohave County Sunday and the southern Great Basin and eastern Mojave Desert on Monday. That said, the ECMWF ensemble mean is not as enthused about bringing moisture as far north as Las Vegas as it was 24 hours ago. Timing will be key in this scenario as an additional trough will usher dry air into the southwestern United States late Monday into early Tuesday.

AVIATION
For Harry Reid...Southwest winds with occasional gusts to 30kts can be expected into this evening. Winds will decrease below 15kts overnight before shifting to the northwest Thursday morning between 14Z and 16Z. Winds may initially gust to 25kts with the wind shift, but speeds should decrease below 12kts by 20Z Thursday. Reduced visibilities to as low as 4SM due to smoke from the wildfires over Southern California will continue to move over the valley into tonight. While some occasional improvement to 6SM or greater is possible this afternoon and evening, the smoke is not expected to clear the area until after 16Z Thursday when the northwest winds move into the valley. Above the smoke layer near the surface, mainly clear skies with only FEW high clouds are expected.

For the rest of southern Nevada, northwest Arizona and southeast California...Gusty south-to-west winds are expected at most regional TAF sites into tonight, with the strongest winds anticipated across the western Mojave Desert, including KDAG, and in the Owens Valley, including KBIH. Speeds will decrease by Thursday morning with directions shifting to the northwest across northern areas of the region by late morning. Reduced visibilities to as low as 4SM due to smoke from the wildfires over Southern California will continue to move over Southern Nevada, Southeast California, and Northwest Arizona. While occasional improvement to 6SM or greater is possible this afternoon and evening, the smoke is not expected to clear northern areas until after 16Z Thursday. Southern areas, including KDAG, KEED, and KIFP, will see the smoke persist. Above the smoke layer near the surface, mainly clear skies with only FEW high clouds are expected.

FIRE WEATHER
The Red Flag Warning was extended to 11 PM PST/MST given a 50 to 80 percent chance of reaching criteria between 8 PM and 11 PM. Winds should relax later overnight, lessening the threat.
Dry conditions remain with the next opportunity for thunderstorms arriving early next week.

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