Convection Embedded in an Atmospheric River: Exploring Precipitation Sensitivity to Convective Parameterizations

February 14, 2026

The paper titled “Convection Embedded in an Atmospheric River: Exploring Precipitation Sensitivity to Convective Parameterizations” was co-authored by Rosa Luna Niño (SIO/CW3E), Catherine M. Naud (Columbia University/GISS), Sasha Gershunov (SIO/CW3E), Juan A. Crespo (JPL/UCLA), Derek J. Posselt (JPL), and Luca Delle Monache (SIO/CW3E). It was recently published in the journal Monthly Weather Review. This work was supported by the NASA ROSES Project: Convection and Atmospheric Rivers (Award 80NSSC22K0603).

This work investigates the sensitivity of precipitation associated with an atmospheric river (AR) event to two convective parameterization schemes (Tiedtke and Grell–Freitas) using the Weather Research and Forecasting Model (WRF). The case study focuses on the 2019 Valentine’s Day Storm, a well-documented AR event that impacted the U.S. West Coast. The ensemble simulations consist of 64 simulations at 9-km horizontal resolution—a scale within the gray zone where some convection is resolved, but parameterization remains necessary.

Although total precipitation is dominated by the stratiform component, convective precipitation shows a clear sensitivity to the choice of scheme (Figure 1). Grell–Freitas produces more parameterized convective precipitation within the AR (Figure 1i), associated with higher low-level humidity, stronger winds, and larger IVT, which together create a more unstable environment. In contrast, Tiedtke produces more convective precipitation behind the AR (Figure 1h). Similar moisture amounts, but stronger low-level winds boost IVT, supporting the development of shallow convection in that area.

Figure 1. Accumulated (a)–(c) total, (d)–(f) stratiform, and (g)–(i) convective precipitation during 12–15 Feb 2019 according to ERA5 and WRF simulations groups using Tiedtke and Grell–Freitas convective schemes. Note the change in color bar between total/stratiform and convective precipitation. Figure 6 from Luna-Niño et al. (2026).

Observations from GPM-DPR confirm convective precipitation extending across the Pacific Ocean during the Valentine’s Day Storm, most notably along the area of high IVT within the AR. An alternative method using Ongoing Longwave Radiation and precipitation rates thresholds is applied to identify potentially convective precipitation that is not clearly resolved by the WRF Model at 9km. Using the alternative convective method, the overall pattern of convective precipitation is generally consistent between the Grell–Freitas and Tiedtke schemes (Figure 2). This agreement contrasts with the patterns of parameterized convective precipitation. The proposed approach to diagnosing embedded convection in ARs can be instrumental for global models or regional large ensembles approaching gray-zone resolution.

This research advances CW3E’s Strategic Plan by improving the understanding and prediction of atmospheric rivers that drive extreme precipitation and flooding along the US West Coast. Examining convection simulations at gray-zone resolutions strengthens regional forecasting capabilities and supports CW3E’s mission to enhance flood preparedness and resilience to hydroclimate extremes.

Figure 2. Accumulated convective precipitation based on the alternative methodology using thresholds for OLR and precipitation rates, during 12–15 February 2019, according to (a) Tiedtke, (b) Grell–Freitas, and (c) the difference between Tiedtke and Grell–Freitas. The black contours indicate the mean AR footprint (IVT > 250 kg m⁻¹ s⁻¹) of (a) Tiedtke, (b) Grell–Freitas, and (c) the WRF ensemble. Figure 13 from Luna-Niño et al. (2026).

Citation:

Luna-Niño, R., Naud, C. M., Gershunov, A., Crespo, J. A., Posselt, D. J., & Delle Monache, L. (2026). Convection Embedded in an Atmospheric River: Exploring Precipitation Sensitivity to Convective Parameterizations. Monthly Weather Review, 154(1), 3-20. https://doi.org/10.1175/MWR-D-25-0087.1