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Stormy Weather for Northern U.S., Alaska and Hawaii

A powerful storm system will produce a swath of heavy snow and high winds across the Northern U.S. on Sunday from the northern Plains to the Upper Great Lakes. Meanwhile, a major winter storm will hammer the Alaskan West Coast and Western Interior on Sunday with blizzard warnings in effect. Finally, a developing Kona low will produce numerous hazards for Hawaii through early this week. Read More >

Overview -  Atmospheric River - January 26-29,2021 

Heavy Rains and Strong Winds Returned to the Bay Area and the Central Coast

Water year 2020-2021 was off to an active start in terms of storms generating over the Pacific and moving toward America's Western coastline; however, the La Niña pattern in place kept the storm tracks heading toward Seattle, Portland, and the Pacific Northwest. Any rain received near San Francisco was at the tail end of the system. This resulted in quick, weak frontal systems that only brought light showers to the North Bay, with even less to the South Bay and the Central Coast. Only getting weak fronts kept the Bay Area well below normal precipitation levels and dreaming of a major soaking rain.

And then the plume of moisture from the tropical Pacific began to move northward and two magical words were added to the Forecast Discussion: "atmospheric river". (AR)  Atmospheric River refresher

As an upper level trough moved over the Bay Area bringing strong winds and light showers Sunday, January 24, 2021, a ridge of high pressure was sitting over the southeastern Pacific. The anti-cyclonic rotation of the high pressure pushed a large swath of moisture northward toward Alaska. This moisture would ride around the central high and sink southward toward San Francisco January 26-29, 2021. This "colder" AR is atypical for  ARs that impact California.  ARs are generally "warmer" and have a more direction connection to Hawaii or the sub-tropics resulting in higher snow levels. The approach of such a large amount of moisture prompted Flash Flood Watches in place for most 2020 burn scars around the area as heavy rain could trigger debris flows and mud slides.

Light rain reached the North Bay and San Francisco on Tuesday, January 26, 2021, in the evening. Enough lingering cold air resulted in lower snow levels with accumulating snow over the higher peaks in the Bay Area. In fact, snow levels were low enough that low elevation snow occurred over the Northern Sacramento Valley. As another upper level low started to sink southward, pushing the tropical moisture to San Francisco, a narrow cold-frontal rainband (NCFR) developed on the leading edge that prompted Flood Advisories in the North Bay and a Flash Flood Warning over the Walbridge burn scar. The band moved quickly southward prompting further Flash Flood Warnings over the CZU Lightning Complex, River, Carmel, and Dolan burn scars. High Wind Warnings for higher elevations and a Wind Advisory for valley locations were issued as southerly winds ahead of the NCFR intensified. Gusts in the valleys reached 25-35 mph with higher peaks reaching gusts from 60-80 mph Tuesday evening through Wednesday morning.

While rain around the Bay Area tapered off behind the NCFR, it slowed over the Big Sur Coast as it began to encounter higher pressure located west of San Diego. The moisture "hose" was turned on and it was pointed straight at the Central Coast. The main band of precipitation then began to retrograde through the day on Wednesday into Thursday once again reaching the Santa Cruz Mountains. The wavering moisture plume resulted in steady moderate to heavy rain from Big Sur to Santa Cruz on Wednesday and Thursday. As the low pressure moved southward down the coast, the main moisture plumed moved south and inland to the Central Valley bringing snow to the high Sierra, leaving scattered showers around the Bay Area and the Central Coast Thursday evening into Friday.

This atmospheric river was the strongest storm of the water year thus far. For total precipitation amounts, see the tab below. Despite this heavy rain, the result keeps much of the Bay Area 40% to 60% of normal precipitation for the water year. While it certainly made a chunk in the deficit, summer remains just around the corner with the hope of more rain before the dry season arrives.

 

CW3E also included a thorough write up here

https://cw3e.ucsd.edu/cw3e-event-summary-26-29-january-2021/

 

Composed by: MMehle and DKing

Satellite loop
Satellite loop showing the evolution of the Atmospheric River impacting the Bay Area and Central Coast.

Direct Link to Radar Loop

Debris/Mud Flows and Flooding

Mudflows near the River Fire burn scars covered roadways and trapped animals at local ranches. Heavy rain caused flooding near the Carmel Lagoon, which by Thursday the 28th was breached. Debris flows in Big Sur resulted in the closure of Highway 1, as mud covered pockets of roadway. By Thursday the 28th, a section of Highway 1 near Rat Creek collapsed and fell into the Pacific.

Debris Flow

Debris Flow into house Debris Flow against fence Highway 1 fell into the ocean landslide

Home impacted by mud flow along River Rd, Salina, CA

Photo by @mcrfd

Property impacted by mud flow near the River Fire burn area.

Photo by NWS Employee

Highway 1 near Rat Creek.

Photo by Heath Johnston  @calransD5

Landslide near Soledad, CA

Photo by @BrianEmfinger

Youtube Videos

 

 

Flooding

Hydrograph showing flooding in Carmel Carmel River flowing into ocean Flooded home in Carmel by the Sea River runoff from Soquel River
Water coming out of the Carmel River is backing up at the Carmel Lagoon near Carmel River State Beach. A flood warning has been issued.  Carmel River flowing into the  ocean. Flooded home in Carmel by the Sea Animation showing a before and after of Soquel Creek
  River runoff into the Pacific Flooded home in Carmel by the Sea  
  Big Sur Coast creeks flowing into the ocean. Flooded home in Carmel by the Sea  

Local Storm Report - Debris Flow

Local Storm Report
National Weather Service San Francisco CA
621 AM PST Wed Jan 27 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0340 PM     Debris Flow      13 SE Livermore         37.56N 121.58W
01/28/2021                   Alameda            CA   Law Enforcement  

            Landslide blocking roadway on MM Mines Rd. 

0100 PM     Debris Flow      4 WSW Soledad           36.41N 121.39W
01/28/2021                   Monterey           CA   Public           

            Video shows debris flow damage along portion 
            of River Rd at Fort Romie Rd. 

0424 AM     Debris Flow      3 NE Scotts Valley      37.08N 121.98W
01/28/2021                   Santa Cruz         CA   Law Enforcement  

            Mud/Dirt/Rock in 2nd LN BTWN JARVIS AND 
            SUGARLOAF. 

0840 PM     Debris Flow      30 ENE Soledad          36.60N 120.83W
01/27/2021                   San Benito         CA   Law Enforcement  

            Mudslide on Panoche Road. 

0646 PM     Debris Flow      2 N Aromas              36.90N 121.64W
01/27/2021                   Santa Cruz         CA   Law Enforcement  

            Rockslide on SR-129 and Rogge Lane. 

0528 PM     Debris Flow      8 SE San Jose           37.23N 121.75W
01/27/2021                   Santa Clara        CA   Law Enforcement  

            Mud/dirt/rocks in roadway at Metcalf Rd and 
            Monterey Hwy. 

0501 PM     Debris Flow      2 NE Bolinas            37.93N 122.68W
01/27/2021                   Marin              CA   Law Enforcement  

            Rockslide onto roadway at SR-1 near Bolinas. 

0309 PM     Debris Flow      7 WNW Gonzales          36.56N 121.55W
01/27/2021                   Monterey           CA   Broadcast Media  

            Mudslide on River Road 1/2 mile NW of 
            Chualar River Rd. Photos show damage to 
            nearby homes and structures. 

0300 PM     Debris Flow      23 S Carmel Valley Vill 36.15N 121.67W
01/27/2021                   Monterey           CA   Public           

            Video shows debris flow in Anderson Canyon 
            this afternoon. Exact timing unknown, 
            estimated between 2 and 4 pm. 

0239 PM     Debris Flow      13 WNW Monte Rio        38.52N 123.25W
01/27/2021                   Sonoma             CA   Law Enforcement  

            Mudslide on SR-1 and Fort Ross Rd. 

1130 AM     Debris Flow      35 SE King City         35.80N 120.75W
01/27/2021                   Monterey           CA   Law Enforcement  

            Mudslide on US-101 S and Camp Roberts, 
            closure of road. 

1040 AM     Debris Flow      27 SW Greenfield        36.05N 121.59W
01/27/2021                   Monterey           CA   Public           

            Mudslide onto HWY 1 at mile marker 27. 

1037 AM     Debris Flow      7 SSE Salinas           36.59N 121.61W
01/27/2021                   Monterey           CA   Fire Dept/Rescue 

            mudslide from the River Fire burn scar. 

1057 PM     Debris Flow      10 NE Yountville        38.50N 122.25W
01/26/2021                   Napa               CA   Public           

            Rock slide blocking roadway near 2000 Capell 
            Valley Rd. 


&&

$$


Atmospheric River January 26-29, 2021

Tropical moisture from over the Pacific moved eastward and set up along the Central Coast. This this provided strong winds with reports of snow at higher elevations, a few lightning strikes, but the main impacts were from the copious amounts of heavy precipitation causing ponding and urban flooding as well as debris flows in Monterey County. Flash Flood watches were issued ahead of the event, while Flash Flood Warnings for the Walbridge, CZU Lightning Complex, River, Carmel, and Dolan burn scars were issued during the event as heavy rain rates increased. Event total precipitation totals ranged from 1.5 inches to 2.5 inches in the North Bay Valleys with the higher elevations of the North Bay Mountains received between 3 inches to 6 inches. Downtown San Francisco received 2 to 3  inches. The East Bay ranged between 2 inches to 4 inches, the South Bay 2 inches to 3 inches with the Santa Cruz mountains receiving 8 to 10 inches. By far the most rain was down the Central Coast. Monterey Valleys saw 3 to 4.5 inches with the Big Sur Coast getting between 10 and 13 inches.   But it was the higher elevations of the Santa Lucia's that received between 15 inches and 20 inches.

Flash Flood Watch Flood Advisory Flash Flood Warning

Lead Up to the AR Flash Flood Watches were issued.

Persistent rainfall led to urban and small stream flooding.

Flash Flood Warning issued for Dolan Fire Burn Area

Excessive Rainfall Outlook Excessive Rainfall Outlook Rainfall totals graphic

WPC issued a high risk potential for flash flooding along the Central Coast Jan 27, 2021

WPC issued a high risk potential for flash flooding along the Central Coast Jan 28, 2021

48 hour rainfall totals ending Jan 28, 2021

Rainfall Totals graphic 7 day rainfall total  

48 hour rainfall totals ending Jan 28, 2021

Estimated rainfall totals

 


Snow

Low Snow Levels Snow Above Big Sur Snow in Sonoma county
Initial rain bands reaching northwest Sonoma county with the profiling radar near Cazadero showing the moistening of the lower atmosphere. This device measures and estimates an observed snow level of 2620 feet right now (highlighted in lower right).

Light snow accumulations above Big Sur.  

Photo By L Pantilat

1,300ft elevation on Geysers Road above the Alexander Valley, Sonoma County Tuesday evening.

Photo by @kentphotos

 

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0740 PM     Snow             6 W Saratoga            37.26N 122.12W
01/26/2021  E4.0 inch        Santa Cruz         CA   Law Enforcement  

            Snow reported on SR 9 and SR 35, 3 to 5 
            inches. 

 


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