Western US warmth could break records, raise flooding concerns
Unseasonably warm weather will challenge daily high temperature records and cause flooding concerns across the West.
A prolonged stretch of warm, dry weather is bringing summerlike vibes to the western United States this week. AccuWeather meteorologists say building heat will challenge daily record highs for the final week of April and cause flooding concerns as the massive snowpack that was built during the winter steadily melts away.
The weather pattern across much of the western part of the U.S. has been extremely active so far in 2023. Although the winter months are often referred to as "the wet season" in this part of the country, Mother Nature dished out an extraordinary amount of rain and snow — particularly in California — that broke snowfall records and busted yearslong droughts.
"Since late January, much of California has [had temperarures] below historical averages on the majority of days. Any time temperatures did go about the seasonal norm, it would be by only a few degrees and at most only for a couple of days," said AccuWeather Senior Meteorologist Heather Zehr.
A new weather pattern set up shop this week and brought a noticeable change for most of the western U.S. and providing the first extended stretch of significant warmth so far this year.
A strengthening area of high pressure near California and a northward bulge in the jet stream this week will allow the warmth to continue into Saturday without much interruption.
"Temperatures will not only be as much as 20 degrees above typical levels for the end of April; they will also challenge records in some places," Zehr explained.
Afternoon high temperatures are expected to be most extreme across parts of the Northwest into the central California Valley through Saturday.
So far this year, Seattle has averaged temperatures about 2.2 degrees below the historical average. This week, the city is forecast to surpass 70 degrees for the first time since Oct. 16. The forecast high in the upper 70s on Friday is about 15 degrees above Seattle's historical average for late April. Temperatures are likely to be only a couple of degrees shy of daily-high record temperatures.
In Portland, Oregon, AccuWeather meteorologists are predicting a high temperature in the upper 80s on Friday, which will shatter the record-high temperature of 82 from 1998. Such high temperatures are more akin to the months of June, July and August and haven't been reached in the city since mid-October.
For areas farther inland and to the south, temperatures are also expected to soar to near-record levels. Reno, Nevada, residents can expect temperatures to reach the middle 80s, challenging daily high records on both Friday and Saturday. Sacramento, California, is expected to have temperatures in the lower 90s on Friday and Saturday, which are almost 20 degrees above the historical averages for late April.
Along the California coastline, the expected warmth will not be quite as extreme. Cities like San Francisco has had high temperatures ranging from the upper 70s to the lower 80s from Tuesday to Thursday which is as much as 15 degrees F above the historical average.
One of the wettest winter seasons on record obliterated most of the drought conditions in California and other parts of the West. The moisture-laden storms unloaded whopping amounts of snow in mountainous areas and filled reservoirs with epic amounts of rain. That seemingly beneficial weather pattern over the past winter is now bringing other dangers, however.
The warmth is expected to melt some of the snow across the region, leading to rising river levels. Flooding concerns are already mounting in Yosemite National Park. Earlier this week, National Park Service officials said the park would close to the public on Friday and remain closed to the public at least until May 3 due to flooding issues.
For those seeking relief from the heat, AccuWeather meteorologists warn that it may be unsafe to take a dip in the water this time of year. Despite how warm the air might be, the water may still be dangerously cold, putting swimmers and adventurers at risk of cold water shock.
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The area of high pressure contributing to the abnormal warmth across the region is expected to start to break down early next week when a new storm arrives.
"The widespread warmup will quickly end this weekend as a large, slow-moving storm comes into the Pacific Northwest," explained Zehr.
Even though some showers may push across Washington, Oregon and Northern California from Sunday to Tuesday, no extensive wet weather is expected. Most areas are likely to get only a shower or two on a single day, rather than several days of steady rain.
The showers and associated clouds are likely to bring temperatures early next week back to more seasonable levels for early May.
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