Another Major Winter Storm to Affect the Area Much of This Week

The latest GOES-WEST satellite image continues to show a rather complex weather pattern developing over the Pacific and west coast currently. There is a rather large cold area of low pressure off the Pacific northwest coast and a rather large area of subtropical moisture entraining to the southwest of this low. In addition, storm systems are beginning to undercut the ridge in the north central Pacific. All of this leads to a rather complex, but potentially very wet weather forecast over the next 5-7 days.

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The latest 500mb heights over the US continues to show a rex-block type of pattern over the northwestern US, with a trough extending east into the Great Lakes area. Another closed low has developed well north of Hawaii underneath the ridge that extends well into Alaska toward the arctic region. The general area of below normal heights continues to suggest a rather active pattern will continue over much of the US over the next 5-7 days, especially along the west coast of California and Nevada.

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Next, a look at the 250mb wind pattern, you can see the same ridge noted above, with westerlies associated with the polar jet beginning to undercut this ridge, while splitting ahead of the Gulf of Alaska ridge. Looking further east, the flow is rather disorganized at this time with the polar jet located over the northern tier of states and the subtropical jet located well south from Hawaii trough Mexico into the southeastern US.

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A look ahead to the weather outlook, persistence has played a major role in the weather pattern this winter, with another round of heavy valley rain and very heavy snow expected for much of the northern and central Sierra and far western Nevada. Another atmospheric river is likely to set up over northern and central California over the next several days, with almost ideal orographic flow over the Sierra into western Nevada through at least Thursday. Snow levels will be rather tricky, but at this time they look to be around 5,000 to 6,000 feet, but some areas may see lower snow levels if heavy precipitation develops in the lower valleys of Reno/Carson City. There is still some uncertainty with snow levels, so this may change over the next day or two. Best educated guess at this time, would be higher snow levels to near 7,000 at times.

For the sake of brevity, I only show a few of the operational runs of the forecast precipitation models. At any rate, a look at the WPC blended model continues to indicate precipitation amounts of 6+ inches over the Sierra crest, tapering to 2-4 inches over the Tahoe Basin and 1-3 inches over the Carson City area over the next 7 days.

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The 12Z ECMWF has trended wetter, with 6+ amounts over the northern and central Sierra crest. Amounts in the Lake Tahoe Basin are similar in the 2-4-inch range, while the Carson City area has a bit more shadowing with 1-2 inches over the next 7 days.

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Finally, the 18Z GFS model is very wet with amounts in the 10+ inch range over the next 7 days. There is quite a bit more shadowing east of the Sierra crest with amounts tapering to 2-6-inch range and the Carson City area in the 1-2-inch range. I think for now, the WPC blend has a good handle on precipitation amounts for the near term, while the GFS is too wet, and the ECMWF is a bit too dry on total amounts over the next week.

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For snowfall amounts in the Sierra, the Reno National Weather Service has put together a graphic on the expected snowfall amounts for that region.

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Given all the forecast models scenarios, we still look to be in for a major winter storm for the Sierra and a possible significant rain event for the lower valleys around the Carson City area.

Looking ahead to this weekend, another possibly significant storm may affect the region from Saturday through Monday with additional valley rain/snow and more mountain snow. The active pattern looks to continue through possibly the second week of March with a return to colder storm systems. Hopefully we can move through this winter/spring season without significant flooding.

R.  Sandberg