Mountain Storms Monday, with Possible Valley Drifters

It’s about time I have something to write about here locally!

Over the last several days, monsoonal moisture in the desert southwest has been slowly sliding northward as an upper level ridge centered in the Great Basin and the remnants of Tropical Storm Douglas about 500 miles off the southern California coast force monsoonal moisture and bands of mid/upper level instability and lift northward. Showers and thunderstorms have been widespread throughout AZ, southern NV, southern California, and the southern sierra the last several days. One surge of moisture in the form of decaying thunderstorms in southern Nevada will spread north through the night tonight into Monday, and will help with lift and weak forcing to get thunderstorms developing in the sierra, northern mountains, and coastal range. It also appears this surge of moisture northward overnight into the day Monday could be enough to moisten parts of the valley enough to possibly support storms in the higher elevations to drift west to northwest into the foothills and valley without dying out.

Water vapor satellite imagery combined with 500mb heights from 9:40pm Sunday. You can pick out the area of storms/moisture in southern Nevada, which will slide north/northwest overnight into Sunday. You can also see some spiraling in clouds and moisture off the southern California coast in association with lower heights, which is the remnant low of TS Douglas.

While general instability will be weak, MUCAPE increases to 100 – 150 j/kg after 4 – 6pm into the overnight hours Monday in the valley. If anything does drift into the valley, it’ll be quite elevated, and precipitation may be sparse due to very dry low-levels, thus any thunderstorms in the lower elevations could produce dry lightning. In the higher elevations, patchy inverted-v soundings mean you can’t rule out some dry lightning, but generally things will moisten up compared to previous days so most storms in the higher elevations should produce at least some wetting rain, but even then with elevated storms you especially can’t rule out lightning striking outside precipitation cores.

Models are always very sketchy when it comes to valley convection during monsoonal events, and this is no different. Sure, some low to moderate reflectivity values show up in high resolution forecast models, but most models have no precipitation despite the reflectivity being progged. I’ll probably post a quick update to the beginning of this post Monday morning mainly regarding the valley convection to see if it still looks possible. No real need to re-look the mountain chances, it’s pretty much a given at this point.

In addition to convective chances, it’ll be a hot day Monday – with highs in the 101 to 110 depending where you’re at in the valley, which could vary quite a bit depending on cloud cover.

4km NAM’s forecast 2-meter temperatures valid for around 4pm Monday afternoon.

Tuesday could be an even more active day in the mountains compared to Tuesday as instability increases a bit more compared to previous days.