Active Research Projects
Active research topics within our research group are listed below, which have been funded through support from NSF, NASA, DOE, and NOAA. To address these topics, we employ a multi-scale approach using a combination of long-term reanalysis datasets, field campaign observations, operational and idealized model output, and representative case studies. By investigating the antecedent environments and flow evolutions associated with high-impact weather events, as well as the relative forecast predictability of these events, our research efforts offer the potential to better inform future forecasts of high-impact weather.
Upper-Level Jet Streak Dynamics
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The upper-level jet streams are among the most recognizable structures within the Earth’s atmosphere. These narrow, rapidly-flowing air currents circumnavigate the globe at an altitude of ~12 km and play an important role in dictating surface weather conditions. Our group is leading efforts to (1) understand the dynamical and thermodynamic processes that facilitate the development of polar-subtropical jet superposition events and their subsequent influence on the development of high-impact weather and (2) evaluate how North Pacific jet stream variability impacts weather conditions across North America.
Relevant publications on polar-subtropical jet superpositions:
Relevant publications on North Pacific jet stream variability and downstream weather conditions:
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(a) Idealized cross section along A–A′, as indicated in (c), through separate polar and subtropical jets. Wind speed (gray shading with darker shades of gray identifying stronger wind speeds), potential temperature (red lines every 5 K), and the 2-PVU contour (thick yellow line). The polar jet (PJ) and subtropical jet (SJ) are labeled accordingly. (b) As in (a), but for an idealized cross section along B–B′, as indicated in (c), through a jet superposition. (c) Conceptual model summarizing the development of a jet superposition. The locations of the polar jet (PJ), subtropical jet (SJ), and superposed jet are labeled accordingly. Figure and caption from Winters and Martin (2020; their Fig. 1).
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Synoptic-Scale Flow Predictability
Composite mean 250-hPa wind speed (m s−1) is shaded in the fill pattern, 250-hPa geopotential height is contoured in black every 120 m, and 250-hPa geopotential height anomalies are contoured in solid red and dashed blue every 30 m for positive and negative values, respectively, 4 days following the initiation of (a) a jet extension, (c) a jet retraction, (e) a poleward shift, and (g) an equatorward shift regime. Composite anomalies of mean sea level pressure are contoured in solid and dashed black every 2 hPa for positive and negative values, respectively, and 850-hPa temperature anomalies are shaded in the fill pattern every 1 K, 4 days following the initiation of (b) a jet extension, (d) a jet retraction, (f) a poleward shift, and (h) an equatorward shift regime. The numbers in the bottom right of each panel indicate the number of cases included in each composite. Stippled areas represent locations where the 250-hPa geopotential height anomalies or 850-hPa temperature anomalies are statistically distinct from climatology at the 99% confidence level. Figure and caption from Winters et al. 2019, their Fig. 5.
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Multi-scale atmospheric processes (i.e., from the local scale to the planetary scale) that conspire to produce extreme weather events can be challenging to predict, which limits the delivery of timely and accurate warnings to stakeholders. Our group is investigating the factors that (1) influence the predictability of the North Pacific jet stream on medium-range (7-10-day) to subseasonal (2-4 week) timescales, and (2) impact the predictability of midlatitude cyclones and their attendant surface impacts across the continental U.S.
Relevant publications on North Pacific jet stream predictability:
Relevant publications on predictability of midlatitude cyclones and their impacts:
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Colorado Front Range Extreme Weather
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Colorado experiences as wide range of extreme weather events, including extreme cold-air outbreaks, heat waves, blizzards, floods, and downslope windstorms. Our group is performing analyses to better understand the characteristics of Colorado Front Range extreme weather events, the variability and synoptic-to-mesoscale flow patterns that contribute to their development, and how they may change in a future climate.
Relevant publications on Colorado Front Range extreme weather:
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Self-Organizing Map of MSLP anomalies (shading; hPa). Each SOM node is labeled from [0, 0] to [3, 3] at the top left along with the overall frequency of that node at the top right (percentage of ETCs in a given node out of all N = 4723 ETCs). The five SOM clusters are outlined in colored boxes: 1) Mississippi River Valley anticyclone in brown, 2) Canadian anticyclone in red, 3) Northern Plains cyclone in light blue, 4) Central Plains cyclone in yellow, and 5) Southern Plains cyclone in purple. Figure and caption from Larson and Winters 2025, their Fig. 7.
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High-Latitude Atmospheric Rivers
a Present-day average annual AR frequency among all 40 ensemble members in CESM2 (1980–2014). b Model AR frequency bias (CESM2 minus MERRA-2 reanalysis) in the present (1980–2014). c Future AR frequency difference in CESM2 (2066–2100 minus 1980–2014) when future AR detection is solely based on the present-day vIVT threshold. d Future AR frequency difference in CESM2 (2066–2100 minus 1980–2014) when the present-day threshold for AR detection is scaled by the ensemble mean relative increase in IWV. In b, c, d, stippling indicates regions where the mean difference in AR frequency exceeds the standard deviation among the 40 CESM2 ensemble members. Figure and caption from Maclennan et al. 2025, their Fig. 2.
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Atmospheric rivers are defined as long, narrow corridors of extreme moisture transport that can contribute to the development of extreme precipitation events. Our group has led efforts to understand factors that contribute to the development of atmospheric rivers at polar latitudes, their attendant impacts, and how they may change in the future. Such work has important implications as polar regions undergo rapid transformations as the climate warms.
Relevant papers on high-latitude atmospheric rivers:
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