Active week of weather across West with heavy rain, thunderstorms and snow
An active week of weather is underway across the western U.S. with one storm system moving across California right now. Another storm system is set to move into the Northwest and across California Wednesday through Friday.
The storm system impacting California this afternoon (Monday afternoon) is a potent upper-level low with plenty of cold air aloft with it. It has already brought some thunderstorms to the San Joaquin Valley, most notably in Sacramento and areas to the north.
This afternoon's thunderstorms and mountain snow are being driven by a strong upper-level low shown above that is moving over the state. Model shown is 18Z GFS.
This afternoon several thunderstorms slowly moved through Sacramento and brought a long-duration hail event, which quickly piled up in the streets and looked like a few inches of snow had fallen!
A road in Sacramento covered with inches of sleet and hail. (Photo/Sacramento Fire)
A modeled sounding for the Sacramento area (KSAC) this afternoon showed plenty of cold air aloft and instability for thunderstorms to develop. The freezing level was quite low and all of these providing ingredients for thunderstorms with hail.
There were also a couple thunderstorms that spawned funnel clouds north of Sacramento Monday afternoon.
The storm system is also bringing heavy snowfall to the Sierra. There's already been several reports of around a foot of fresh snow from this storm.
As this upper-level low dives southward through Tuesday, the threat for showers and even thunderstorms will increase across Southern California. Some of them can be heavy and produce brief downpours and even small hail. Snow levels will also drop, falling to 2,500 to 3,000 feet at their lowest. Snow will impact travel through I-5 near the Grapevine and there can be some snow in the Antelope Valley. Above 3,500 feet, there can be a few inches of fresh snow.
This storm will exit Tuesday night and the focus will then turn to the next upper-level low that will drop into the Northwest Wednesday and southward into California by Thursday and Friday.
The next upper-level low will arrive in the Northwest Wednesday and will slide southward Thursday and Friday. This one will be larger and stronger so impacts will be greater. Model shown is 18Z GFS 500 mb for Wednesday.
Models show a stronger and larger system with this one so we can expect more mountain snow and the threat for heavy rain from Washington to northern California. Enough rain can fall to produce flooding and mudslides, especially across northern California.
This one should produce a few feet of snow for the Sierra and a foot or two in the Cascades and Bitterroots by the time it is all said and done. A round of snow will spread farther east into Montana, Wyoming and the Wasatch Range in Utah as well towards the end of the week.
As the system moves southward Thursday night and Friday, rain chances will increase for Southern California which will be largely welcomed.
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