Serious flooding risk in Southern California on Wednesday, as much of the country gears up for one of the warmest Christmases on record

In brief: Flooding swamped parts of northern California yesterday, as attention focuses to a potential serious and significant flooding risk in the LA Basin in SoCal on Wednesday. Meanwhile, snow levels will drop enough to get some good snows in the Sierra. Elsewhere, it will be the warmest Christmas on record in many parts of the country with a pretty crazy warm weather pattern anchored over the Central U.S.

NorCal flooding

Atmospheric river moisture pounded parts of California over the weekend, delivering widespread rains generally north of I-80. 13 inches of rain was reported in the Sierra near Serene Lake, just west of Sugar Bowl Ski Resort (which is temporarily closed but expecting snow tomorrow night). Over 11 inches fell just south of Storrie, CA as well, north of I-80 in Plumas County. Same story for Strawberry Valley in northeast Yuba County.

Multi-sensor rainfall estimates over the last 48 hours in northern California with 10″+ in parts of the Sierra and heavy rain outside the north end of the Sacramento Valley. (NOAA NSSL)

In the Redding area, flooding was particularly bad. A fairly common feature (the Shasta County convergence zone) set up near or just north of the city last night. If you track the radar loop below, you’ll be able to see a pencil thin area of heavy rain that setup for several hours near “KRDD,” or Redding.

Radar loop from about 10 AM to 10 PM on Sunday of heavy rain impacting northern California. (College of DuPage)

This led to significant flooding in the Redding area, where only 1.44 inches officially fell yesterday. But the airport is just south of the city, so it missed the heaviest precip, which was probably closer to 3 to 6 inches with isolated higher amounts.

48-hour rainfall totals in the Redding area. (NOAA)

Unfortunately, one fatality was reported from the flooding.

“High risk” for damaging SoCal flooding

Today, showery weather dominates parts of central and northern California. The next firehose of moisture will increase tomorrow, aimed at northwestern California to start, but dropping south into the Bay Area tomorrow evening and into SoCal tomorrow night and Christmas Eve morning. A second wave of storminess will follow Wednesday night and Christmas morning. These systems are going to cause some serious flood concerns in parts of California. Given the trajectory of moisture perpendicular to the west-east mountains in the LA Basin, this is going to dump a lot of rain. And it looks like minimal to no snow for the San Gabriels or San Bernardino Mountains during the peak of the precipitation.

A “high” risk, Level 4/4 for excessive rainfall and flooding is now posted for Christmas Eve in the mountains and burn scar areas of the LA Basin in Southern California. (NOAA WPC)

A high risk was issued this afternoon for Southern California for flash flooding for Wednesday. High risks are well correlated to flood damage, and the fact that they’re confident enough to update the day 3 outlook to high is slightly concerning. There are three main elements of flooding concerns: Urban flooding in the LA Metro, debris flow issues from burn scars, particularly the Eaton and Palisades fire footprints, and flooding due to torrential rain in the mountains and hills. Overall, this looks like a serious flooding setup in SoCal, and it should be taken very seriously.

Forecast rain totals over the next 5 days show over 6 inches in Los Angeles, and double digit rain totals in the mountains. (Pivotal Weather)

In addition to the heavy rain in Southern California, wind gusts over 40 mph are possible in some of the valleys and higher gusts up to 80 mph or so in the mountains.

And then there’s the snow. While the SoCal mountains will be dusted only at the end of the event, the Sierra will see snow levels down to 4,500 feet or so, which will allow for several feet of snow to accumulate, including perhaps as much as 4 to 8 feet above 5,500 feet.

A major snowstorm for the Sierra above 4,500-5,500 feet. (NWS Sacramento)

Precip will continue into Friday across the state with colder air. Overall, this will be the highest impact storm of the season so far in much of California.

Warmest Christmas ever for many

Well, the good news is that a little bit quieter weather is on the way after the system flushes out of Cali this weekend. Atmospheric river events may pick back up again toward New Years, starting up in the Northwest or British Columbia, then tracking southward with time again.

Meanwhile, the focus is on warm weather, record warm weather. Dozens of record highs will fall this week, with Christmas Day clocking in as one of the warmest on record in many parts of the country.

Forecast record or near-record highs on Christmas Day, with nearly 50 locations between the Southeast and the Rockies expected to see record warmth. (NOAA WPC)

Some of these records will be obliterated, including Wichita (record: 68° in 2019, forecast 76°), Childress, TX (record 77° in 1971, forecast 84°), and Kansas City (record: 67° in 1922, forecast 73°). In addition to record highs, nearly 70 locations are forecast to have their warmest low temperatures on Christmas morning on record. My favorite? Harrison, Arkansas, which is forecast to be 61° on Christmas morning, 12 degrees warmer than the previous record set in 2019 (records going back to 1892). Oklahoma City isn’t far off, expecting to break their warmest record minimum temperature by 10 degrees on Christmas morning. If you like your Christmas’s feeling like Christmas, try again next year. Or go to the Dakotas or New England.

Christmas morning lows across the country. (Pivotal Weather)

Newsy bits

Indonesia: A weird situation in southeast Asia, which has been battered this autumn by floods. A lot of humanitarian aid being sent to parts of Indonesia has either had to be returned or diverted elsewhere because of government issues. Suffice to say, people are not happy. (Asia News Network)

Washington State: Much like we saw in Alaska after the remnants of Halong earlier this autumn, federal money earmarked for disaster has been held up by the Trump Administration, including $182 million in Washington State for flood mitigation. This has been a bit of a theme of late. To be clear, this probably would not have helped with the recent flooding, but it serves as a reminder that vital work for mitigation around the country is being held up for ambiguous reasons. (NBC News)

Colorado River: We aren’t getting any closer to a deal on cuts to water in the differing, sometimes warring basins on the Colorado River. It seems like this is either headed for litigation, a federal directive, or some sort of temporary stopgap measure to buy a little more time. Either way, this does not bode well for anyone. (Inside Climate News)

Florida: A new paper published in AGU’s Geophysical Research Letters by a group of heavy hitting tropical meteorologists discusses the recent increase in Florida Gulf Coast landfalling hurricanes, while there has been a void of much action on the East Coast of Florida. The authors believe that the combination of climate mode variability from teleconnection patterns via El Niño/La Niña, the North Atlantic Oscillation, and the Atlantic Multidecadal Oscillation can explain a significant amount of the Gulf variance but not the Atlantic Coast variance. Basically, a combination of bad seasonal and annual scale factors likely increased the odds of Gulf Coast impacts from tropical systems in Florida. (AGU)

U.S.: A preprint from scientists at Villanova examines geospatial risk of tropical systems in the U.S. As it turns out Harris County, TX (Houston) and Cameron County, TX (Brownsville) have the highest disaster risk from hurricanes in the country. Several counties in Florida, as well as much of New York City ranks high on this list, much due to socioeconomic factors, vulnerability, and resilience. (Research Square)

Wild weather in the West leading into Christmas, with warm weather dominating almost everywhere else

In brief: A major series of atmospheric river-driven storms will impact the West heading into next week, this time focusing more on California. The storm system that hits Tuesday night and Wednesday may be particularly significant there. Elsewhere, windy weather will have a hold on the Front Range & Foothills today in Colorado with dangerous fire weather possible. Warm weather is in control for most places for a good bit of the rest of 2025.

Western Weather is wild!

The last couple posts have been heavily policy-related matters (though I do want to point you to a later night update yesterday from Alan Gerard’s Balanced Weather), so let’s focus mostly on actual weather today, because the West is in for it. The firehose is turned on and will not turn off anytime soon. However, it will take aim at differing parts of the West Coast at different times. The heaviest precipitation will exit Oregon today and push into Northern California while weakening. This leads to a generally calmer day Saturday across the West. On Saturday night and Sunday, the moisture plume revs back up, aiming primarily at parts of southern Oregon and northern California, north of the Bay Area.

That continues Monday, with perhaps a slight downtrend in precip intensity. By later Tuesday and into Christmas Eve, it appears that a significant storm is going to deliver a multitude of hazards to California, including flooding rains, mudslide risk, debris flow risk, strong winds, and extremely heavy snow in the Sierra. This comes in two or three “waves” of action continuing into Christmas Day. Each one gets slightly colder, so snow levels will slowly drop through the event as well. Things reset next Friday and Saturday with a focus on British Columbia, before perhaps the next plume aims at the Northwest again on the following Sunday or Monday before New Year’s.

The key point: The most significant impact of this multi-day atmospheric river event will probably occur Tuesday night through Thursday, focused primarily on California.

The atmospheric river plume that hits California next week is currently forecast to be of high-end strong to low-end extreme intensity. (Center for Western Weather and Water Extremes)

You can see from the chart above that estimates atmospheric river “intensity” for the Bay Area that the intensity picks up today, Sunday, and Tuesday night into Wednesday, with the strongest of the event occurring then (pushing into category 5 level intensity). Let’s talk about total precipitation expected in California. Snow-wise, it looks like a solid 3-to-6-foot type snow event for the High Sierra, with the potential for higher or lower amounts depending on the exact setup that unfolds, but let’s go with that estimate right now as a placeholder based on the most recent data. Liquid-wise? We’re looking at perhaps as much as 15 to 20 inches of liquid equivalent in the northernmost Sierra and just south of the Shasta area.

Forecast rain totals from the Weather Prediction Center for the next week in California exceed 20 inches in some of the high terrain in northern California. (Pivotal Weather)

Expect a flurry of watches, warnings, and advisories to be issued in the next couple days, and expect travel across California to be impacted by this series of storms, especially Sunday into Wednesday.

Front Range & Foothills windstorm

Another round of particularly powerful winds will occur today across the West, with a focus on Colorado again for perhaps the most significant impacts. A combination of low humidity and wind gusts in excess of 70 to 80 mph will be possible primarily west of the immediate Denver and Colorado Springs metros. Red flag warnings are posted in these areas with extremely high fire risk.

A ‘particularly dangerous situation’ for damaging wind and wildfire risk exists today in the Foothills northwest of Denver. (NWS Denver)

Additional wind events seem likely on Sunday and Wednesday as well, though hopefully slightly less intense than today. Precipitation looks to be at a premium in the Front Range and Urban Corridor, with perhaps some good snows possible in northwest Colorado this weekend and later next week, especially for Steamboat and Winter Park.

Warmth continues

The rest of the country looks generally warm over the next 6 to 10 days, with average temperatures well above normal and a flurry of new record highs expected.

Winter cold will take a hiatus through about New Years unless you live in New England, the higher terrain of the West, the Pac Northwest, or Alaska. (NOAA CPC)

Will the pattern change at all as we roll into 2026? We’ll see. For now, just buckle up for a wild ride out West and a warm one for most everywhere else.

Newsy bits

Whatcom County, WA: In Washington, the governor toured damage in Whatcom County from the recent record flooding that occurred in that area. As is often the case, a lot of good things were said after local, state, and tribal officials met, but the real test will be if any of it leads to changes.

Fraser Valley, BC: Meanwhile, over the border in British Columbia, the province’s premier echoed frustration with Canadian federal government inaction on the repeated flooding that is occurring there due to overflow from the Nooksack River into the Sumas Prairie and eventually Fraser Valley. The premier also spoke to Washington’s governor. It appears any concrete relief is going to have to occur with cooperation between the U.S. and Canadian governments.

Denver & Phoenix: Denver and Phoenix have little in common, being on opposite ends of the Colorado River politics spectrum and in different basins of the river entirely. The two cities are scrambling to future-proof their water supplies as the basin’s crunch deepens and negotiators have missed recent deadlines on how to share a shrinking river that 40 million people depend on. Both cities are quietly embracing solutions, from reservoirs to grass removal and planning for the potential of water cuts.

Mount Dora, FL: An update on flood damage from a very localized major flooding event earlier this autumn that occurred north of Orlando.

As atmospheric river events bear down on the West Coast, U.S. weather research that helps public safety and the economy continues to be credibly threatened

In brief: Today we have some commentary on a developing story, where the Trump Administration is planning to dismantle one of the premiere atmospheric research centers in the world. Also, we focus back in the West, where more atmospheric river problems lie ahead.

National Center for Atmospheric Research

I want to start today’s post with a quick note on a story that broke yesterday evening. USA Today reported (and OMB head Russ Vought confirmed) that the Trump Administration would direct the National Science Foundation to dismantle the National Center for Atmospheric Research, or NCAR. The plan is to fully close the historic Mesa Lab in Boulder, CO.

I cannot begin to tell you what a bad, bad, bad decision this is. Objectively so. This will absolutely cripple and devastate weather research in the U.S. While the administration claims that NCAR is “one of the largest sources of climate alarmism in the country,” (it isn’t) almost any climate and weather research done in this country is underpinned in some way, shape or form by NCAR. The administration also claims that vital weather research activities will be “moved to another entity or location,” which seems a bit sus to me given many examples of them causing chaos by dismantling things without adequate replacements or contingency plans. But it also completely misses the forest for the trees. The reason the work done by NCAR has been so critical and important to the science and to industry (and thus the American people) is because of NCAR acting as a (very effective) cog in the weather enterprise wheel. This needlessly breaks up an organization at taxpayer expense for no other reason than they don’t like it. NCAR is not an inefficient organization, nor do they do anything but advance atmospheric science research. In other words, there’s no real value derived by anyone in dismantling the organization.

Just as a slight relevant example from my recent past, and this is something that happens a lot all around the country. At a previous job, we sent another meteorologist to NCAR to take part in a discussion forum with leaders from both there and in the field at large to learn and discuss ways we could incorporate machine learning techniques to potentially improve seasonal or sub-seasonal forecasting (S2S). It would be important to note here that both seasonal and sub-seasonal forecasting is very much a climate-related research topic. Grant proposals, 16-to-45-day models, etc. will use the word “climate” to describe the research here. Nothing about that work is involved in climate change. Since the Trump administration gets uncomfortable about particular words and phrases, they probably see “climate” and assume the worst, when in reality a lot of the “climate research” is actually working to help improve forecasts for the economic and societal benefit of the country — not for pedaling alarmism. Go figure. Meetings like these happen a lot, and it ultimately leads to economic and human benefit, as well as uncovers new avenues of research to travel down.

Anyway, suffice to say, this is a terrible decision that will have significant negative consequences for the country and the economy over the long-term, long after these people leave office. That’s why I am writing about it here. Two organizations within government atmospheric research would be devastating to lose, not that others would not but these two are particularly critical: NOAA’s OAR (Office of Atmospheric Research) and NCAR. The Administration has now tried to gut or is in the process of gutting both of them at zero meaningful taxpayer savings and plenty of meaningful negative consequences for the American public and economy. I must question how that fits a so-called America first agenda.

On to the weather

The big story over the next several days into next week will be another atmospheric river event on the West Coast. Note that NCAR does work to support atmospheric river reconnaissance research that helps improve forecasts of these events. This event is taking aim at the Pacific Northwest right now, where we have numerous watches and warnings posted for flooding (thankfully not as bad as last week), heavy snow, blizzard conditions, and strong winds. In fact, the footprint of wind advisories and high wind warnings is tremendous, extending from the Northwest into the Northern Rockies and Northern Plains.

A whole lotta wind out there! (Pivotal Weather)

One specific area to watch closely today will be the Front Range in Colorado where gusts of 70 to 90 mph will be possible in the higher terrain and wind-prone bases of the foothills. Winds could gust as high as 50 to 60 mph in the Denver area as well later today.

(NWS Denver/Boulder)

Wind gusts on the Plains will be nothing to sneeze at either, with widespread 50 to 70 mph gusts in the Dakotas, Montana, and Wyoming, along with stronger winds at higher elevations.

Maximum forecast wind gusts through tomorrow in the Northern Plains. (Pivotal Weather)

Meanwhile, back on the West Coast, thankfully snow levels are lower with this event than we saw last week. So for Washington that means less rain running off into the swollen river basins. Currently, no rivers in Washington are forecast to hit major flooding levels over the next few days, with several back into moderate flooding. Better news for sure.

River forecasts are all below major flooding across western Washington with this event, thanks in part to lower snow levels. Localized issues may still crop up. (NOAA NWC)

In case you missed it, there was a story that dropped about the Skagit River, and this is a great example of the economic and societal value of weather forecasts. The Army Corps took over dam operations from area utilities that use dams for hydropower. By taking over operations and impounding the water rather than releasing it, about 4 to 5 feet (!) of water was kept out of the river, which prevented an already bad situation from turning into an absolute catastrophe. None of this would have been possible without good coordination, good forecasts, and quick action. This is an example of the value and benefit of weather forecasts and when government agencies and partners perform at their best.

Moving southward, the next target of the atmospheric river will be Oregon. Heavy rain and mountain snows will move in tomorrow through Saturday.

Heavy rain is likely in Oregon, and while mountain snows may drop down to pass levels, there will still be a lot of water being flushed through the system. (Pivotal Weather)

Snow levels will be low today, rise tomorrow, and lower again on Friday. While there may be snow down to pass levels, a lot of water is going to be pushed through the river systems here that are already fairly elevated. So there is some legitimately localized serious flooding risk in these areas.

For California, the next few days will see varying levels of moisture move in, heaviest in far northern California on Friday and for parts of northern and central California on Sunday. The bigger story may be what’s coming next week, where a major storm could overtake all of California, including SoCal. This is highlighted on the 8-to-14-day hazards outlook from Tuesday, showing Christmas Eve, Christmas Day, and Friday in play for a potentially significant rainstorm and Sierra snowstorm.

Potential for a very significant western U.S. storm next week, particularly in California where heavy Sierra snow and flooding all the way into SoCal will be possible. (NOAA CPC)

So, things are busy! Folks in Cali will want to pay attention to next week’s storm, as it does have the potential to be a serious one.

Elsewhere, record warmth is a story. We’re expecting multiple days of records threatened here in Houston, with highs in the 80s next week. The interior West and even parts of the Northeast (Friday) will see record warmth tomorrow into next week. More to come.

Water does not care about your geopolitical borders

I wrote a bit about the flooding this past week in Washington State over at The Eyewall. It was pretty bad. In some places, it was at record levels, others the worst since 1990, and so on. I neglected to look much at how the heavy precip and flooding was impacting Oregon. Or British Columbia.

The Nooksack River sources in North Cascades National Park on Mt. Shuksan. It flows north and then west, eventually dumping into Bellingham Bay off Puget Sound. Because of the topography in that region, when the Nooksack River floods badly, it spills north into the Sumas River. The Sumas sources in Whatcom County, Washington and flows around past the Nooksack and dumps into the Fraser River in British Columbia northeast of Abbotsford.

As is often the case, the reason this is a problem is because of what we chose to do many years ago. This whole area is a leftover flat plain from glacial retreat that acts as a floodplain for the rivers. It is called the Sumas Prairie, but it actually used to be a lake. In the 1920s, the lake was diked and drained. This opened up a bunch of fertile land for farming, as well as reduced flooding on the Fraser River in Canada. But it also is a former lakebed, and water was there for a reason. Thus, in floods like this, the lake is attempting to refill, except now people live where a lake once sat. Essentially, the Nooksack watershed gets higher than the Sumas watershed, and water essentially “spills” downhill into the Sumas, which flows from Washington into Canada.

Maps have borders. Nature does not.

After the bad flooding in 1990, a cross-border group was created to propose flood mitigation measures, specifically near Everson, WA where the Nooksack overflows into the Sumas Prairie. Some modeling efforts were undertaken, some solutions proposed but as time wore on and urgency disappeared, nothing happened, and the effort sort of ended in 2011. After 2021 flooding, the effort was revived. The rub is that a solution that could help alleviate flooding in British Columbia and in Everson would probably cause disastrous effects downriver from there. So, you could fix one problem only to create new ones.

After this event, there will be renewed momentum to try and address this, but the problem is complicated. Some possible ways of solving the problem will take years and are quite costly. Other problems are similar in nature to problems we’ll have to address with respect to dams, which is sediment buildup. In the case of the Nooksack, the river has been constrained for years, when in reality it used to expand and contract. This has allowed for sediment to remain constrained and build up over years, reducing the capacity of the river to hold water, which is challenging even when we don’t factor in that atmospheric river events in the Northwest are becoming stronger. More water from the sky, less capacity to hold water on the ground, a natural floodplain, more flooding. It’s an extremely complex problem underpinned by pretty simple math.

This is not a problem isolated to Washington and British Columbia. On the other side of the countries, flooding problems led to the International Joint Commission (created from the 1909 Boundary Waters Treaty to investigate and come up with joint solutions for U.S.-Canada water challenges) to propose solutions to flooding on the Lake Champlain-Richelieu River basin shared between Quebec, Vermont and New York. The IJC has not yet been involved with the issues in Washington and British Columbia.

Borders exist on this map but as a secondary feature to the water basins themselves.

Locally in my world, there’s an issue right now between Harris County and Montgomery County in Texas. A proposed development in Montgomery County west of a particularly flood prone community in the Houston area (Kingwood in Harris County) forced a Harris County precinct commissioner to push out a high-level resolution requesting that Montgomery County ensure the development adopts Harris County’s minimum drainage standards. Montgomery County has generally weaker standards for developments than does Harris County. In this instance, their choices could directly impact the outcomes for people that do not live in their jurisdiction.

In Canada, Abbotsford’s mayor is not happy with Canada’s federal government or with their neighbors in Washington. In addition to the issues around Lake Champlain and the Richelieu, the IJC did adjudicate and come up with a bunch of recommendations after the horrific 1997 Red River of the North flood that impacted the Upper Midwest and Manitoba. In 2017, they issued a report showing how a good chunk of the effort had succeeded. In Asia, there have been and will continue to be tensions over how countries, in particular China and India manage substantial quantities of water that source in their regions and flow into other nations. In Africa, dam building on the Nile in Ethiopia has created significant tension downstream in Egypt where they believe they have superior water rights on the river.

At what point does it become one community’s responsibility to ensure an adjacent one is not negatively impacted by decisions they make? Look at the Colorado River for one. This is less about flooding and more about water rights, but there are substantial tensions between the upper and lower basins (not to mention tribal nations) over this question. These are not easy problems to solve. But they do require coordination and cooperation. We have that to some degree with the Colorado River, which is governed by the 1922 Colorado River Compact. But when you have a patchwork of requirements and regulations rather than a single agency overseeing an entire region it can make for difficulties, such as in Southeast Texas, where decisions made in rapidly growing counties can impact many neighborhoods in the Houston area. The counties bordering Harris County have grown by nearly 1 million people in the last 15 years. Harris County itself has grown by nearly a million people in that same time. The growth is likely to continue. A formalized regional regulatory approach to flooding in this area is not currently in progress.

But these are the things we’re going to need to be thinking about as flooding likely continues to worsen. Climate change will get the oxygen for a lot of these issues. And it’s obviously a major factor. But it’s not just climate change. In the case of the Sumas/Nooksack flooding, it’s pretty much because we chose to drain a lake in the 1920s that existed for this specific reason, and we decided to constrain the flow of the river leading to sediment buildup and less room for water. In the Houston area we are eradicating prairie and former farmland in differing jurisdictions with differing requirements for building and quickening runoff. In the Colorado River, we are sharing a scarce resource and have dammed the river up. Rather than treating the Washington-British Columbia problems as an unfortunate circumstance from an extreme weather event, it should be a (yet another) wake-up call about some of the decisions we make as people in charting our growth.