Atmospheric Rivers are a Frequent Source of Moisture Transport in Severe Convective Storm Environments

May 6, 2026

A new paper entitled “Atmospheric Rivers are a Frequent Source of Moisture Transport in Severe Convective Storm Environments” was recently published in the American Geophysical Union’s Geophysical Research Letters. This research included contributions from co-authors Samuel Bartlett (CW3E), Jason Cordeira (CW3E), Chris Davis (NSF National Center for Atmospheric Research & University of Massachusetts, Amherst), and Jana Houser (The Ohio State University).

Atmospheric rivers (ARs) are well known for their contributions to precipitation and flooding across the U.S. The co‐occurrence of conditional instability, vertical wind shear, and abundant lower‐tropospheric moisture is well documented in connection with severe convection across the Central and Southeast U.S. The influence of the low‐level jet stream and precipitable water in fostering severe convective environments is also well documented; however, their combination as manifest in the form of ARs is relatively unexplored.

This study investigates the co‐existence of synoptic‐scale environments containing ARs and severe convection over the U.S. during both the warm and cool seasons. Additionally, the utility of the “AR framework” as a diagnostic and predictive insight into days that produce severe convection is also explored. This framework may offer added value in operational forecasting by highlighting broad‐scale moisture structures that precede severe convective storms. ARs may represent a complementary (not replacement) tool for established severe weather diagnostics, especially in the Southeast U.S., where ARs frequently co‐occur with dynamic environments favorable for severe weather.

The relationship between ARs the the potential for severe thunderstorms and tornadoes is analyzed in both the warm and cool seasons during a 20-year period from 2004 to 2023. A statistical analysis of severe thunderstorm and tornado warnings issued by the National Weather Service (NWS) and AR events as defined by the tARget v4 algorithm is performed for each NWS County Warning Area. These statistical analyses are performed in two ways, first using the “warning perspective” (i.e. was the warning issued during an AR event?) and secondly using the “AR perspective (i.e. did an AR have any warnings issued during the event?). These two perspectives facilitate answers to the following two questions: (a) What fraction of severe thunderstorm and/or tornado warnings occur with synoptic‐scale environments characterized by ARs, and (b) What fraction of ARs contain one or more severe thunderstorm and/or tornado warnings?

The statistical analysis of the “warning perspective” (Figure 1) demonstrates that a majority of warnings over the Southeastern and Eastern U.S. are associated with ARs, especially tornado warnings (Figure 1a.). Conversely, analysis from the “AR perspective” (Figure 2) shows that a minority of AR events feature severe thunderstorm warnings or tornado warnings, with higher fractions in the warm season except for tornado warnings over the Southeastern U.S.

In summary, at many locations across the Central and Eastern U.S., ARs appear as a practically necessary, but not sufficient, factor related to the potential for severe convective storms and the issuance of a tornado warning in the cool season. Our interpretation is that in order for conditions to occur that result in a cool‐season tornado warning, moisture must be transported rapidly into a region before the passage of a cold front. This rapid moisture “return” is best accomplished with a strong LLJ, which also presents an environment favorable for tornado formation provided at least some conditional instability can be realized. A strong AR, however, does not guarantee sufficient destabilization to create conditional instability; hence the AR may be a necessary factor, but not a sufficient factor for creating an environment with severe convective storm potential.

This research supports the “Atmospheric Rivers and Extreme Precipitation Research, Prediction, and Applications” priority area of the CW3E’s 2025-2029 Strategic Plan. In particular, it fulfills the key objectives to 1) expand research and forecast verification efforts on ARs and the different storm types responsible for extreme precipitation and 2) Work with strategic partners in atmospheric sciences to improve the understanding of atmospheric rivers and their associated impacts.

Figure 1. The fraction of (a, c, e) tornado and (b, d, e) severe thunderstorm warnings associated with ARs defined using the tARget method by (a, b) year, (c, d) cool season, and (e, f) warm season (shaded). Figure 3 from Bartlett et al. 2026b.

Figure 2. The fraction of ARs defined by tARget featuring (a, c, e) tornado and (b, d, e) severe thunderstorm warnings by (a, b) year, (c, d) cool season, and (e, f) warm season (shaded). Figure 4 from Bartlett et al. 2026b.

Acknowledgements:

This research was supported at CW3E (authors SB and JC) by the Cooperative Institute for Research to Operations in Hydrology (CIROH) with funding under award NA22NWS4320003 from the NOAA Cooperative Institute Program and by projects supporting AR Reconnaissance activities such as the California Department of Water Resources AR Program (Phase IV: 4600014942 and Phase V: 4600015671), U.S. Army Corps of Engineers Forecast Informed Reservoir Operations program (Phase III: W912HZ-24-2-0001 P00001), and the NOAA CIMEAS AR Reconnaissance Project No. NA20OAR4320278. Author (JH) acknowledges support from the NOAA CIMEAS AQPI project No. NA20OAR4320278 at CW3E and the work of Kamran Chowdhury, whose preliminary case studies relating spatial distributions of severe storm reports and concurrent atmospheric rivers contributed to the inspiration, formulation and execution of the current study. Statements, findings, conclusions, and recommendations are those of the authors(s) and not necessarily reflect the opinions of NOAA. Author (CD) was supported by the NSF National Center for Atmospheric Research, which is a major facility sponsored by the U.S. National Science Foundation under Cooperative Agreement No. 1852977.

Citation:

Bartlett, S. M., Cordeira, J. M., Houser, J. B., & Davis, C. A. (2026). Atmospheric Rivers Are a Frequent Source of Moisture Transport in Severe Convective Storm Environments. Geophysical Research Letters, 53(8). https://doi.org/10.1029/2025GL120738