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Western US weather

Following unusual May downpours, more opportunities for rain coming to the Southwest

By Brian Thompson , AccuWeather meteorologist
5/13/2019, 6:46:15 AM

Over the past several days, a large upper-level low brought some rounds of heavy downpours to parts of the Southwest that do not typically see much in the way of rain in May. That may not be the last gasp of rain, as more appears to be on the way later this week.

Here are some rainfall stats from the past several days:

Las Vegas - 0.71 of an inch from Thursday into Friday, which already makes it the fifth wettest May on record.

San Diego - 0.40 of an inch for the month, which is triple the average for the month. Unlike Las Vegas, San Diego does occasionally have rainy spells in May. The city received 2.39 inches in May 2015.

Tucson - 1.21 inches from Saturday into Sunday, more than five times the normal for the month. It is currently the second-wettest May on record, behind only the 1.34 inches recorded in 1931.

Flagstaff and Grand Canyon National Park have picked up 1.55 and 1.76 inches of rain, respectively, so far this month, which is two to three times more than average.

Opportunities for rain in the Southwest are usually few and far between by this time of year, but it looks like another storm will bring rain to the West Coast later on this week, and perhaps a couple of more beyond that.

The Pacific Northwest will get started a little earlier with the next system, as a front-running system arrives Tuesday into Tuesday night, bringing some mostly light, but needed, rain.

Seattle and Portland have not recorded any rain this month and it's been a dry few months overall. Any rainfall now is beneficial with wildfire season just around the corner.

An initial wave of energy will trigger rain across Northern California (especially north of the Bay Area) and Oregon during the day on Wednesday.

Western Blog 5/13

Then, as a massive trough reaches the West Coast by Wednesday night and Thursday, rain chances will spread across virtually the entire West Coast.

The European model has been persistent with this thinking for the past several days, showing a significant rain event (at least by May standards) across California. The GFS has been trending toward this solution as well.

Unusual May Storm 5/13

The most significant rain from Wednesday night into Thursday is likely to set up across portions of California. One bull's-eye looks to be in the foothills east of the Sacramento Valley eastward into the Sierra. The Northern California coast will be another spot that could get hit pretty hard, from Mendocino northward through Eureka and Crescent City. These areas are the most likely to have 1 to 3 inches of rain through Thursday night if persistent plumes of rain develop.

With the cold air aloft, there can be some isolated thunderstorms that could even produce small hail.

The European has hinted at the potential for some heavier rain as far south as the San Gabriels and some of the hills east of the L.A. Basin. Amounts could exceed an inch in some areas.

Right now, it looks like closer to 0.50 of an inch or so in the L.A. Basin, with 0.25 of an inch or less expected toward San Diego. These numbers could certainly change given the exact track of the storm.

The San Francisco area could easily have over an inch of rain through Thursday night, where there has been no measurable rain so far this month.

Farther north, amounts through Friday generally look to be under an inch from Seattle to Portland. There will be some locally higher amounts in the Cascades and in some spots east of the Cascades in Oregon toward Burns.

In the Desert Southwest, the area hit hardest by the recent round of downpours, this storm system will not produce the same kind of results. Rainfall in Las Vegas should be on the lighter side with just a few showers. Toward Phoenix and Tucson, it should remain dry as the system scoots by to the north.

Snow levels could drop as low as 6,000 or 7,000 feet for a time, which could introduce the opportunity for accumulating snow in some of the higher terrain.

The energy helping to bring the rain chances to the West Thursday will move eastward and ultimately help spawn severe weather in the Plains by Friday and Saturday .

The amazing thing is that there still may be more opportunities for rain. Both the European and GFS hint at another storm system next weekend and another one around the 21st. Here's a look at the next large trough the GFS is showing this weekend:

Western Blog 2 5/13


We'll discuss those chances a little more later in the week as the details become a little more clear.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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