More storms eye California, western US into Memorial Day weekend
By Alex Sosnowski, AccuWeather senior meteorologist
May 20, 2019, 4:46:44 AM EDT
Additional storms bearing rain, locally gusty thunderstorms and high-elevation snow will take aim at California and the balance of the western United States into the Memorial Day weekend.
"A block in the jet stream is forcing storms to take a much more southern route onshore into western North America than usual for the latter part of May," according to AccuWeather Senior Meteorologist Brett Anderson.
The first storm in the series brought disruptive snow and record-setting rainfall to California last Wednesday into Thursday.
The second storm brought more rain and mountain snow to California on Sunday. In the wake of this system, dry conditions will briefly take hold across most of the state on Monday.
Yet another storm is anticipated to roll ashore later Monday into Tuesday.
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While that storm may move in over Oregon at first, indications are that it will slowly wobble southward along the West coast much of the week.
During a blocking pattern, the jet stream can become so convoluted that the normal west-to-east motion of storms and fair weather systems may stop. Some areas may have an extended period of unsettled or sunny conditions as a result.
There is a chance that the storm early this week may then crawl slowly inland or spread out over much of the interior West during the Memorial Day weekend with showers and thunderstorms, as well as lower-than-average temperatures.
During the cloudiest and rainiest days in the pattern, high temperatures across the interior West may average 15-20 degrees below normal. Along the coast, highs of 5-10 degrees below average are likely on the wettest days.
Given the time of the year and the power of the May sun, it will not rain the entire stretch through the end of May, and there will be intervals of clear skies. However, pinpointing these episodes beyond a few days in advance would be futile.
The relentlessly wet pattern will produce rainfall that could end up being five to 10 times that of average for May in some locations.
In San Francisco, this month has been the wettest May since 2005, when 1.15 inches fell. So far, 1.88 inches has fallen in the city. Rainfall this month may surpass that of 1998, when 2.37 inches fell.
Typically in May, rainfall ranges from a few hundredths of an inch in the southeastern deserts to a couple of inches in the northwestern part of the state.
In addition to throwing a wrench into outdoor plans, the rainfall could be significant enough to trigger isolated incidents of mudslides in recent burn scar areas, as well as the potential for flash and urban flooding.
The rounds of rain will slow travel on the roads and at the airports.
At the coast, the stormy pattern over the Pacific is likely to produce occasional rough surf. Waters may be rough for some novice pleasure boaters.
There is also the risk of a waterspout forming in the conditions anticipated. A locally severe thunderstorm with hail or a brief tornado cannot be ruled out in the ongoing pattern.
The long-duration wet weather can pose a problem for vineyards in the form of the spread of fungus.
There are some positive impacts from the wet pattern.
The frequent bouts of rain will help to clean pollen and other pollutants out of the air that would normally be building up at this time.
The ongoing rain will add to the flow rate and water levels of streams and rivers and will continue to fill reservoirs.
In portions of the Northwest, where dryness was evolving until a week ago, according to the United States Drought Monitor, the pattern will continue to ease drought concerns in the short term.
The rain will delay the onset of the wildfire season in the West in general.
However, in the long term, the extra moisture this spring will continue to spur the growth of brush that will inevitably dry out later this summer and become fuel for wildfires.
Property owners are urged to keep after the growth of weeds, high grass and other brush that will be brought on by the rain this past winter and over the remainder of this month.
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