March 20, 2018

The East Braces for Another Snowstorm While the West Prepares for Flooding Rains

This winter sure decided to go out with a bang. Two storms will bookend the United States with big disruptions to major cities along both the eastern and western coasts. The fourth nor'easter this month looks like it'll bring significant snows to the Mid-Atlantic and Northeast to herald the start of astronomical spring. The extent of the heavy snow looks like it'll be farther south than the previous atmospheric cha-cha slide of snowstorms, finally giving Washington D.C. the snow it's missed all season. Meanwhile, on the other side of the country, a major storm system approaching California will give the Golden State some much needed rainfall. The rain will be heavy enough that flooding could be a serious issue in some communities.

Eastern Snow

It's pretty rare to have four significant nor'easters in one month—let alone when that month is March—but here we are talking about more than a foot of snow on the first day of spring. Heavy snow will fall between Tuesday night and Thursday evening from the mountains of North Carolina through Maine. The heaviest snow looks like it'll fall in a large swath from Virginia to Massachusetts, but the amount and extent of the big totals will change as forecasters and models fine-tune the forecasts.

The above snowfall map shows all the different forecasts issued by individual National Weather Service offices as of 3:00 PM Eastern, giving you an overview of what each office thinks will happen in their regions. These maps usually look like a mismatched jigsaw puzzle during a big event like this, reflecting differing opinions between forecasters at different offices, but there seems to be tight agreement in the snowfall totals across the Mid-Atlantic and Northeast for this storm.

It's worth noting that some private forecasts (like those issued by The Weather Channel and local news outlets) are coming in higher than what the National Weather Service is showing, especially on the southern extent of the heavy snowfall around Washington D.C. Any northward or southward change in the track of the storm will shift the axis of heavy snow accordingly.

It's currently snowing around the Washington D.C. area right now, but don't be fooled—this isn't the storm yet. The precipitation right now is what's left of the storm system that brought destructive severe thunderstorms to parts of the southeast on Tuesday. The big snowstorm will develop tonight and work its way up the coast through Thursday.

Rain should change over to snow in central North Carolina and Virginia late Tuesday night or early Wednesday morning. The snow will gradually increase in intensity up the Interstate 95 corridor on Wednesday and taper off on Wednesday night around D.C. The storm will move out of Philadelphia and New York city by Thursday morning, and it should finally end for coastal New England on Thursday evening.

It's pretty late in the year for a snowstorm like this. Ian Livingston reports that it would be one of the largest snowstorms this late in the year on record in Washington D.C. Temperatures hovering within a few degrees of freezing for the duration of the event will help the snow stay heavy and wet, adding weight to trees and power lines and making it hard to shovel. The weight of the snow plus the force of gusty winds (possibly exceeding 40 MPH in spots) could lead to downed trees and power outages. Trees that have buds and leaves on them already will experience additional stress.

West Coast Rain

The focus on eastern snow is often well-deserved given how many people live in areas that are easily ground to a halt when there's even a modest snowfall, but the West Coast deserves some love, too. They haven't really had much weather over the past few months that warrants warning, but it looks like the first significant storm in a long time is about to roll across California and bring much-needed rain they haven't seen this winter.

A large low-pressure system swirling in the eastern Pacific Ocean is tapping into deep tropical moisture as it heads toward California. Water vapor imagery from this afternoon shows a deep plume of moisture heading toward California straight from Hawaii—this feature is often called the "Pineapple Express" in weather coverage. Heavy rain will begin on Tuesday night and continue on and off in waves over the next couple of days.

The Weather Prediction Center is calling for at least an inch or more of rain for just about every part of California save for the deserts in the southeastern corner of the state. Los Angeles could see two inches of rain with much higher totals in the higher elevations between there and Monterrey. There's so much moisture associated with this system that some parts of the Sierras could see more than five feet of snow over the next couple of days. Northwestern California is also on track to see a few inches of rain from this storm, but the lack of drought or flooding concerns there makes this more of a dreary nuisance than an urgent problem.

Flash flood watches are in effect for much of southern California and the Sierra Nevada foothills in anticipation of rain heavy enough to trigger flooding and mudslides. The threat for flooding and mudslides is greatest in areas with burn scars from recent wildfires.

Drought


They're hurting for rain in some parts of California. The drought isn't nearly as bad as it was a few years ago, but much of the southern and central part of the state are in a moderate or a severe drought as of last week's drought monitor.

Los Angeles has only seen about three inches of rain since the beginning of October, which is just a fraction of the amount they would typically see during the wet season. The city could see several months worth of rain in just a few days with this upcoming storm.

Elsewhere, the drought is getting worse across the Southwest and the Plains states as storm systems keep skirting around this region of the country. Oklahoma went from no drought conditions in the beginning of September to 42% of the state under a severe, exceptional, or extreme drought as of last week's update.

[Maps: Dennis Mersereau | Visible Satellite: NOAA | Water Vapor: NASA/MSFC | Rainfall Graph: xmACIS2]

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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I ran Gawker's The Vane for two years and I've contributed to Mental Floss, Forbes, Popular Science, and the Washington Post's Capital Weather Gang. I also teamed up with Outdoor Life to write a book called The Extreme Weather Survival Manual, which came out in October 2015.

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