Area Forecast Discussion

KEY MESSAGES

*Dry and seasonable conditions continue through Thursday.

*Precipitation chances and cooler temperatures return to the region late this week and continue through the weekend.

DISCUSSION

Per latest water vapor imagery and 500 hPa analysis, quasi-zonal flow persists over much of the west, maintaining quiescent conditions across the region. Temperatures today through Thursday will remain close to seasonal normals, with dry conditions and intermittent afternoon breezes forecast. Temperatures each day will top out in the 70s and 80s for lower elevations with 60s in the mountains, and overnight lows dropping into the 40s and 50s for most.

Flow aloft will transition southwesterly late Thursday ahead of a trough taking shape off of the West Coast. Concurrently, a fetch of moisture associated with Tropical Storm Vance will move northward up the Colorado River Valley, resulting in a return of precipitation chances across Mohave County and portions of Clark and Lincoln Counties as early as Thursday night, persisting through Saturday. The aforementioned trough will continue deepening along the West Coast, developing into a split flow scenario with a secondary shortwave developing over southern California while the core of the trough remains over the Pacific Northwest. This evolution will limit the winds that are generally expected with these systems, though as the trough axes move over the region during the weekend, precipitation chances become widespread Saturday evening through Sunday. There is uncertainty regarding precipitation amounts, with the current forecast ranging from around a tenth to a half inch across lower elevations and up to an inch in the mountains and localized areas in Mohave County. This will likely change, dependent on the trajectory of the moisture plumes associated with TS Vance and the incoming trough, as well as the amplitude and trajectory of the trough itself. Mountain snow is another expectation with this weekend's system, mainly over the Sierra and the Spring Mountains. Currently, snow levels look to remain around 8500 feet or above for a majority of the event, with minor snow accumulations expected before precipitation moves out of the region Sunday night. Cooler, dry, and breezy conditions will then follow for Monday, with highs around 5 to 10 degrees below normal. For those keeping track, the last time Las Vegas had measurable rain on Halloween was all the way back in 1987, when a record rainfall for the day of 0.25 inch was observed. So stay tuned, and start planning ahead for potentially soggy trick-or-treating!

AVIATION...For Harry Reid...For the 00Z Forecast Package

Winds have switched to the S-SW for the remainder of the evening with gusts upwards of 20 kts persisting through sunset. Speeds diminish to 8 knots or less for the overnight period. VFR conditions will prevail through the TAF period, however expect increasing high clouds with bases AOA 20kft AGL tonight into tomorrow. A similar diurnal wind pattern is expected again tomorrow with light easterly flow in the morning becoming S-SW around 21-22z.

For the rest of southern Nevada, northwest Arizona and southeast California...For the 00Z Forecast Package...Winds will follow typical diurnal directional trends today and tomorrow. Winds have turned southerly at most locations this afternoon with the exception of KDAG which will see W-SW winds pick up after 00z. Gusty W-SW winds persist at KDAG through around 05z before becoming WNW around 10 kt through the rest of the overnight hours. Elsewhere, lighter winds return for the overnight period becoming variable at times. VFR conditions will prevail through the TAF period, with SCT high clouds overspreading the area from west to east tonight. A similar diurnal wind pattern is expected again tomorrow with a shift to S winds in the 19-21z timeframe with gusts under 20 kt.

SPOTTER INFORMATION STATEMENT

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