cw3e-web - Center for Western Weather and Water Extremes

CW3E Subseasonal Outlook: 16 February 2024

February 16, 2024

Click here for a pdf of this information.

Summary provided by J. Wang, C. Castellano, Z. Yang, M. DeFlorio, and J. Kalansky; 16 February 2024

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E AR Update: 16 February 2024 Outlook

February 16, 2024

Click here for a pdf of this information.

Pair of Storms to Bring Precipitation to California

A pair of storms are forecast to impact the US West Coast during the next several days.
The first storm is an atmospheric river (AR) that makes landfall across the USWC on Fri 16 Feb.
The landfall orientation of the this AR is likely to be suboptimal for orographic precipitation, potentially limiting the precipitation potential of this system.
The second storm is a second AR that is forecast to make landfall alongside a low pressure system into central CA on Sun 18 Feb.
The second system taps into remnant moisture from the first system, which combined with the persistence of the stationary low pressure system off the CA coast, will result in a multi-day precipitation event for the state.
The NWS Weather Prediction Center (WPC) is forecast significant precipitation over the next 7 days along the northern and central CA coasts and in the Sierra Nevada.
The WPC Excessive Rainfall Outlook (ERO) indicates a Slight Risk (level 2 of 4, or at least 15% chance) for flooding over the northern CA coast with the first storm and along the northern and central CA coasts with the second storm.
The WPC ERO also indicates a Marginal Risk (level 1 of 4, or at least 5% chance) for flooding across broader areas.
The second storm is likely to bring heavy snowfall to the Sierra Nevada. The National Blend of Models (NBM) indicates very high probabilities (>90%) of snowfall accumulations exceeding 24”.

Click images to see loops of GFS IVT and IWV forecasts Valid 1200 UTC 16 February 2024 – 1200 UTC 21 February 2024

Summary provided by M. Steen, P. Iniguez, S. Bartlett and C. Castellano; 16 February 2024

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

For any unfamiliar terms, please refer to the American Meteorological Society Glossary.

CW3E Researcher Agniv Sengupta selected for AMS ECLA

February, 15 2024

CW3E scientist, Dr. Agniv Sengupta, was selected as a member of the American Meteorological Society’s Early-Career Leadership Academy Class of 2023. “The American Meteorological Society’s (AMS) Early Career Leadership Academy (ECLA) aims to build and sustain a diverse network of early career leaders in weather, water, and climate science. ECLA will bring together a select group of early career individuals—in particular, women and underrepresented minorities—for an immersion experience in leadership, such as creative problem-solving, conflict resolution, building trust, and enhancing communication skills. We seek early career individuals from a wide range of professions, interests, perspectives, cultures, and experiences.” (from AMS’s website ).

Group photo of the members of the 2023 AMS ECLA Cohort

This professional development program included four virtual leadership webinars and several peer mentoring calls, leading up to a three-day, in-person summit in Phoenix, Arizona. Webinars for the 2023 ECLA program began with participants taking an individual leadership assessment using the CliftonStrengths test. This assessment helped them identify personalized traits in strategic thinking, influencing, relationship building, and executing. The webinars also covered conflict management and resolution, as well as providing comprehensive diversity, equity, and inclusion (DEI) training with dedicated reading and writing exercises.

During the in-person workshop, participants heard from several invited keynote speakers who shared their leadership journeys and how they navigated various societal and professional challenges. The workshop also included sessions on constructing personal leadership styles, research ethics, team building, enhancing communication skills, and bystander practice and intervention using real-life scenarios.

Dr. Sengupta expresses his appreciation to the AMS for developing ECLA and to the Planning Committee for their hard work in creating an immersive experience for the cohort. He found the overall experience enriching as it provided fresh perspectives, insights into unique leadership styles, and a high-quality, diverse network of peers and mentors. Dr. Sengupta highly recommends this career development opportunity to early-career scientists interested in leadership positions in the future.

Photo of the peer-mentor group of Dr. Sengupta from the ECLA workshop

CW3E AR Update: 14 February 2024 Outlook

February 14, 2024

Click here for a pdf of this information.

Trio of Storms to Bring Precipitation to California

A trio of storms are forecast to make landfall over the US West Coast in the next 7 days.
The first storm is driven by a low pressure system that brings a burst of IVT to the USWC on Wed 14 Feb. This low pressure system persists off the PNW coast through Thu 15 Feb as the second AR propagates toward the USWC.
The second storm is an atmospheric river (AR) that makes landfall across the USWC on Fri 16 Feb. The landfall direction of the AR is likely to be suboptimal for precipitation, potentially limiting the precipitation potential of this system.
The ECMWF EPS is forecasting greater probabilities of IVT > 250 kg m-1 s-1 making landfall over the PNW with the second AR than the GEFS.
The third storm is a second AR that is forecast to make landfall alongside a low pressure system into central CA on Sun 18 Feb.
There is uncertainty amongst GEFS and EPS ensemble members regarding the duration and strength of AR conditions with the second and third ARs across CA.
The WPC is forecasting significant 7 day precipitation over the northern and central CA coasts and the Sierra Nevada.
The WPC Excessive Rainfall Outlook indicates a Slight Risk (level 2 of 4, or at least 15% chance) for flash flooding over the northern CA coast for the 24 hour period ending 4 AM PT Sun 18 Feb with the second AR.
The NWS WPC has issued Excessive Rainfall Outlooks highlighting the potential for flash flood conditions in various locations along the coast of California in association with precipitation during each of the three storms during this period.

Click images to see loops of GFS IVT and IWV forecasts Valid 1200 UTC 14 February 2024 – 0000 UTC 22 February 2024

Summary provided by M. Steen, S. Bartlett and P. Iniguez; 14 February 2024

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

For any unfamiliar terms, please refer to the American Meteorological Society Glossary.

Summary: Major CA Winter Storm (4-6 Feb 2024)

CW3E Event Summary: 4-6 February 2024

14 February 2024

Click here for a pdf of this information.

Major CA Winter Storm (4-6 Feb 2024)

Overall summary:

A strong atmospheric river (AR) impacted much of California on 4-6 Feb 2024.
It was an AR3 in the Santa Barbara base on the Ralph (2019) AR scale.

Precipitation impacts:

Widespread precipitation of 1-5” fell across most of California with 5-10” in the coastal mountains and Los Angeles Basin. Some areas of the San Gabriel Mountains received 10-15” of precipitation.
Los Angeles recorded one of its wettest multi-day stretches on record.
Heavy rain resulted in hundreds of mudslides and high flows on area rivers.
Year-to-date percent of normal snowfall increased by 10-20% across the Sierra Nevada mountains.

Wind and power outages:

- Storm produced widespread winds of 60+ mph across northern California with local peak wind gusts around the San Francisco Bay Area of 80-100 mph.
- Strong winds and wet soils felled hundreds of trees.
- A reported 1.4 million customers were without power at various points across the state.

IVT across the northeast Pacific Ocean during this event

Click image for animation (9MB).

IVT near the US West Cost during this event

Click image for animation (8MB).

Peak IVT values for this AR

Click image for video (YouTube).

AR Recon IOP 31 map

CW3E Radiosondes

MSLP analysis of bomb cyclone

Click image for animation (27MB).

Wind gust analysis

Click image for animation (15MB).

Peak wind gusts

Total precipitation and share of annual rainfall

Chance in WYTD percent of normal precipitation

Chance in WYTD percent of normal precipitation LA area

Rainfall statistics for downtown LA

Snowfall analysis

Summary of impacts

Images of trees toppled

Images of landslides

Images of flooding

River gage data for the Los Angeles River

Images of snowfall

Example of FIRO operations

Summary provided by: P. Iniguez, C. Castellano, J. Cordeira, , J. Kalansky, S. Roj, and M. Steen.

To sign up for email alerts when CW3E post new AR updates click here.

CW3E Event Summary: 26 January – 2 February 2024

13 February 2024

Click here for a pdf of this information.

Atmospheric Rivers Produce Heavy Precipitation from Alaska to Southern CA

A family of atmospheric rivers (ARs) brought heavy precipitation to portions of Alaska, British Columbia, the Pacific Northwest, and California during 26 Jan – 2 Feb.

The ARs:

AR #1 made landfall in Oregon on 26 Jan and produced at least 2–6 inches of precipitation in portions of western Washington and Oregon.
AR #2 made landfall in British Columbia and southeastern Alaska on 28 Jan and produced 6–12 inches of precipitation over Vancouver Island, the Coast Mountains, the Alaska Panhandle, and the St. Elias Mountains.
AR #3 produced AR4 conditions (based on the Ralph et al. 2019 AR Scale) along the southern Oregon coast and AR3 conditions in coastal Northern California.
AR #3 brought widespread precipitation to California, including 4–8 inches of rain in the Northern California Coast Ranges and western Transverse Ranges, and 1–3 feet of snow in the Sierra Nevada.
All three ARs were fed from a tropical moisture source referred to as a Tropical Moisture Export (TME).

Impacts:

Rain falling on moist soils caused minor-to-moderate riverine flooding in western Washington during the first AR.
The greatest hydrologic impacts occurred in British Columbia during the second AR, with significant flooding near Pemberton, BC.
Minor flooding and several landslides were reported in Northern California during the third AR
This family of ARs and nearby essential atmospheric features were sampled by the NOAA and the 53rd Weather Reconnaissance Squadron as part of the AR Recon field campaign.

Click images to see loops of West-WRF IVT/IWV analyses and forecasts Valid: 0000 UTC 26 January – 0900 UTC 2 February 2024

Summary provided by C. Castellano, S. Bartlett, J. Cordeira, P. Iniguez, J. Kalansky, M. Steen, and S. Roj; 13 Feb 2024

To sign up for email alerts when CW3E post new AR updates click here.

CW3E Seasonal Outlook: 9 February 2024

February 9, 2024

Click here for a pdf of this information.

Summary provided by Z. Yang, C. Castellano, J. Wang, M. DeFlorio, and J. Kalansky; 9 February 2024

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E Publication Notice: Impact of atmospheric rivers on Arctic sea ice variations

CW3E Publication Notice

Impact of atmospheric rivers on Arctic sea ice variations

February 5, 2024

A new paper titled “Impact of atmospheric rivers on Arctic sea ice variations” led by Linghan Li with co-authors Forest Cannon (Tomorrow.io), Matthew Mazloff (UCSD), Aneesh Subramanian (University of Colorado Boulder), Anna Wilson (CW3E), and Fred Martin Ralph (CW3E Director), was recently published in the European Geosciences Union’s journal The Cryosphere. This paper examines how atmospheric rivers (ARs) contribute to variations in Arctic sea ice, which has been rapidly decreasing especially in the summer in recent decades. The research first focuses on physical processes in two case studies of ARs in 2012 and 2020, then expands to a larger statistical analysis for 1981-2020 over the entire Arctic Ocean. This research contributes to the Atmospheric River Research and Applications, and the Monitoring and Projections of Climate Variability and Change Priority Areas in CW3E’s 2019-2024 Strategic Plan by adding to the understanding of the global impacts of atmospheric rivers and the relationship with climate change in polar regions.

Li uses hourly data at 0.25° × 0.25° resolution from ERA5, the most recent atmospheric reanalysis from ECMWF, to study causal relationships between ARs and decreases in sea ice concentration. In August 2012 and July 2020, ARs associated with large cyclones triggered rapid sea ice melt through modulating turbulent heat fluxes and winds. In a statistical analysis on weather timescales, Li finds a significant negative correlation between atmospheric moisture content and the rate of changes in sea ice concentration over almost the entirety of the Arctic Ocean (Figure 1, Figure 10 from Li et al. 2024). Ice concentration changes are also shown to be negatively correlated with northward winds and with latent and sensible heat fluxes. The work demonstrates how conditions associated with ARs play an important role in the changing Arctic sea ice cover.

Figure 1: (Figure 10 from Li et al. 2024) (a) Rank correlation between anomalies of IWV and sea ice concentration tendency. Only significant correlations are plotted. (b) Rank correlation between anomalies of northward wind and sea ice concentration tendency. (c) Rank correlation between anomalies of latent heat flux and sea ice concentration tendency. (d) Rank correlation between anomalies of sensible heat flux and sea ice concentration tendency.

Li, L., Cannon, F., Mazloff, M. R., Subramanian, A. C., Wilson, A. M., & Ralph, F. M. (2024). Impact of atmospheric rivers on Arctic sea ice variations. The Cryosphere, 18(1), 121-137. https://doi.org/10.5194/tc-18-121-2024

CW3E Subseasonal Outlook: 2 February 2024

February 2, 2024

Click here for a pdf of this information.

Summary provided by C. Castellano, J. Wang, Z. Yang, M. DeFlorio, and J. Kalansky; 2 February 2024

To sign up for email alerts when CW3E post new AR updates click here.

*Outlook products are considered experimental

CW3E AR Update: 2 February 2024 Outlook

February 2, 2024

Click here for a pdf of this information.

Strong Atmospheric River to Drive High-Impact Precipitation Event Over California

A strong AR and low pressure system are forecast to make landfall over Central CA Sun 4 Feb and progress down the CA coast through Mon 5 Feb.
There is uncertainty between the GFS and ECMWF deterministic models on the strength of the low pressure system and AR as well as the landfall location.
The GFS is forecasting the low pressure and AR to be stronger than the ECMWF and make landfall further north in CA.
The GEFS and West-WRF ensemble are forecasting AR3 conditions (based on Ralph et al. 2019 AR scale) over the central CA coast, with AR1/2 conditions in northern and southern CA.
This AR is forecast to bring significant precipitation to much of CA, including heavy rainfall along the central and southern CA coasts and heavy snowfall in the Sierra Nevada.
The WPC is forecasting greater than 6 inches of precipitation over the Sierra Nevada and Transverse Ranges over the next 7 days.
The WPC Excessive Rainfall Outlook indicates a Moderate Risk (level 3 of 4, or at least 40% chance) for flash flooding in Central CA coast for the 24 hour period ending 4 AM PT Mon 5 Feb and Los Angeles Metro Area for the 24 hour period ending 4 AM PT Tue 6 Feb.
NWS San Francisco has issued a high wind warning from the South Bay area to San Luis Obispo County for southerly wind gusts possibly exceeding 60 mph from 4am to 10pm Sunday 4 Feb