Henderson, NV 89044 Weather

Key Messages

* Multiple rounds of rain and storms expected over the Sierra, Lower Great Basin and NW Arizona this afternoon through Thursday. Flash Flooding possible under repeated storm activity.

* Increasing confidence for a dry conditions and seasonable temperatures this weekend.

Discussion

Today through Next Monday.

An active weather pattern is setting up for the Desert Southwest this week as a strong trough slowly approaches the west coast impacting local weather through the end of the week. For this afternoon and tonight, mainly dry conditions expected for most desert valleys while the first round of the thunderstorms is expected over Inyo, southern Nye, and Esmeralda counties...more isolated convection possible in higher terrain further east. The entire area remains ahead of the approaching trough with strong upper level diffluence and enhanced lift from the left exit region of a 100 kt jet streak. Moisture advection northward is great for this time of year with PW of 0.7-1.00 inches engulfing the area. MUCAPE of 300-700 j/kg combined with 0-6km shear exceeding 50 kt will be more than sufficient for more organized clusters of showers and storms. DCAPE values 800-1000+ j/kg may also lead to a localized strong wind threat in a few storms this afternoon and evening on top of the heavy rain threat. Best forcing for ascent will be in the higher terrain of Inyo county and Death Valley, Southern and Western Nye County and Esmeralda County. At the moment confidence is not high enough in a widespread Flash Flood threat to warrant the issuance of any type of watch, however a low threat does exist in areas that see repeated rounds of storms. Lingering lighter shower activity may persist into the night due to such strong lift and upper level dynamics

For Wednesday the upper level low will be approaching the Central California Coast. Precipitation chances are higher across the board due to additional moisture and colder air aloft, but the same places will be favored in addition to Mohave County. A strong southerly 50kt low to mid level jet sets up bringing copious amounts of moisture northward into NW Arizona. As waves of energy rotate around the trough and into the region, expect showers and storms to begin developing early Wednesday morning across Mohave County and potentially Inyo and Esmeralda counties, with the most robust convection likely during the afternoon hours. Shear, instability, and moisture will be similar if not better than parameters on Tuesday, resulting in the same threat...flash flooding, gusty winds, heavy rain, and lightning. Highest confidence in any Flash Flooding is currently over Northern Mohave County where better lift and moisture availability should result in more robust storms; Therefore a Flash Flood Watch has been issued for that area Wednesday and Thursday. While showers and storms are expected Wednesday afternoon over Inyo, Esmeralda, and Nye counties, more isolated convective coverage should keep the flash flood threat lower. Outside of any convection, most of the Mohave Desert and its valleys should be fairly warm and dry with temperatures a few degrees above normal for this time of year.

Finally on Thursday, the upper low shifts inland into Central California and Nevada with the main vort max bringing widespread threat of showers and storms to much of the Lower great basin. Steep lapse rates and sufficient instability from cold air advection aloft will allow for convective showers and a few storms through the day on Thursday. This will likely be the best chance for any rainfall in the Mojave Desert valleys; however guidance has been consistent in showing a dry slot associated with the incoming trough keeping the majority of the precipitation away from the Mohave Desert and Colorado River Valley with a 40-70% chance of 0.10" of rain or less. Overall, best odds of precipitation impacts are in the southern Great Basin, Inyo County, and northern Mohave County where higher chances of total rainfall 1.00" exist. Outside of any storms, gusty south-southwest winds (20-40 mph) will accompany this system as well Thursday and Friday, but any impacts should be confined to the local lakes. Temperatures drop about 10 degrees from earlier in the week with widespread highs Thursday into the weekend in the 70s for desert valleys.

There is a minor wintry component of this system as snow levels bottom out around 8kft in the Sierra. However, precipitation will largely be done by the time colder air filters in , so any impacts are expected to be confined to elevations above 9kft where forecast snow totals range from 3-10" (the higher amounts near the crest).

By Saturday, ensemble guidance has the area firmly on the backside of the trough with a dry northerly flow that quickly scours out moisture and precipitation chances, and produces some gusty north winds. On Sunday and Monday, the flow weakens and becomes more zonal or southwesterly, keeping us dry with light winds and slightly below- normal temperatures.

Aviation

For Harry Reid...For the 00Z Forecast Package...Winds will continue to be generally light and diurnal through the day, with light-to-breezy southeasterly winds this afternoon around 8 kts and light southwesterly winds overnight. Gusty south-southeasterly winds pick up Wednesday afternoon with gust speeds topping out between 25 and 30 kts. FEW-SCT aoa 10 kft through the TAF period.

For the rest of southern Nevada, northwest Arizona and southeast California...For the 00Z Forecast Package...Light and diurnal winds in the Las Vegas Valley and Colorado River Valley continue through the day today, with gusty south-southeasterly winds picking up Wednesday afternoon to 30 kts. KBIH will continue to gust from the south-southeast this afternoon and Wednesday afternoon to 30 kts with the potential for gusts from variable directions due to vicinity thunderstorms. 30 percent chance of showers and thunderstorms over the KBIH terminal, with best chances between 01 and 05Z. Gusty east winds at KDAG to 25 kts this afternoon and Wednesday afternoon. FEW-SCT aoa 10 kft, though expect BKN aoa 8 kft with thunderstorm activity overhead.

Spotter Information Statement

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