Unsettled weather over the next few days as monsoon moisture builds over the region. This will bring scattered thunderstorm chances over the mountains with Valley shower and thunderstorm chances at times. Mountain thunderstorm chances continue mid-week onward but should not be as widespread. Cooler the next few days with warm temperatures returning by mid-week.
Discussion
We will continue to be in an unsettled weather pattern the next few days as high pressure over the four corners region and low pressure over the Pacific push deep monsoon moisture into northern California. Short waves will spin around the high and that will be the main forcing to kick off activity. There is still quite a bit of uncertainty with the forecast on how widespread activity will be with these short waves.
The first short wave will be pushing out of southern NV this morning into the afternoon. Models tonight are keeping this wave further east than previous runs. This will keep the better forcing to the east. We will also see quite a bit of mid-level clouds with this short wave. This will make it tough for instability to build in and will keep activity more limited.
Still looking at isolated shower and thunderstorm chances over the Valley and foothills with isolated to scattered shower and thunderstorm chances over the mountains. If we do see less cloud cover and more instability build in activity will be a bit more widespread.
Precipitable water values push to an impressive 1.0 to 2.0″ over the region today. This will bring a heavy rain threat with any thunderstorm activity over the mountains. Dry air below the mid-level moisture will limit heavy rain in the Valley and foothills but a brief heavy shower isn’t out of the question if more intense cells happen to develop.
By the evening most activity will diminish with just a few lingering showers over the mountains into the overnight. Another short wave will move over the area Tuesday morning into the afternoon. This will once again bring shower and thunderstorm chances mainly to the mountains during the afternoon. Mid-level clouds will once again make it tough for instability to build in and will limit activity.
Moisture won’t be an issue on Tuesday either as this short wave will pull in some moisture from Tropical Storm Frank. Heavy rain will be an issue with any thunderstorms that happen to develop.
The ridge will push back west for the middle and late part of the week bringing the return of hot temperatures. Widespread lower 100s can be expected in the lower elevations.
Forcing will be weak but higher moisture levels will remain in place and that will bring a few afternoon and evening thunderstorms over the mountains.
Extended Discussion (Friday through Monday)
Ensembles continue to show Four Corners ridging and an upper level low over the Pacific. Afternoon and evening thunderstorm chances continue late week into the weekend with breezy onshore winds at times. Temperatures will be seasonal throughout the period.