There will be heavy rainfall and severe convection along the U.S.-Canada border

Widespread high-temperature weather will affect the United States

It is forecasted that from June 20 to 23, influenced by the eastward movement of a low vortex over the northeastern Pacific Ocean and the subtropical high (Figure 1), southern Canada, the Great Lakes region, and northern United States will experience moderate to heavy rainfall. Specifically, parts of southern Alberta, Ontario, southern Quebec in Canada, northern Montana, and northeastern Minnesota in the United States are expected to see heavy rain or torrential downpours, with cumulative precipitation reaching 60 to 130 millimeters (Figure 2). Affected by the warm and moist jet stream at the base of the low vortex, some areas in southern Manitoba and southern Ontario in Canada, as well as northern Minnesota and eastern Nebraska in the United States, will also experience severe convective weather, including short-term intense rainfall, thunderstorms with strong winds, hail, and tornadoes (Figure 3).

Additionally, influenced by the eastward and northward movement of the subtropical high-pressure system, high temperatures are expected to emerge from west to east over the next ten days in the southwestern and central-eastern United States, southeastern Canada, and northern Mexico. Specifically, southeastern Canada will experience daily maximum temperatures exceeding 32°C, with localized areas surpassing 35°C, which is 4 to 6°C higher than the long-term average for this period. In the southwestern, central, and eastern coastal regions of the United States, daily maximum temperatures are anticipated to exceed 37°C. Southern Nebraska, northern Kansas, western North Carolina, and western South Carolina will see daily maximum temperatures surpassing 40°C (Figure 4).

Figure 1. Average Geopotential Height at 500 hPa (contours, units: dagpm) and Wind Field at 850 hPa (wind barbs, units: m/s) from June 20 to 23, 2025

Figure 2. Forecasted Accumulated Precipitation from June 20 to 23, 2025 (Unit: mm)

Figure 3. Forecast of 850 hPa Wind Field (wind barbs, unit: m/s) and K-Index (shaded, unit: °C) at 00:00 UTC on June 23, 2025

Figure 4. Forecast of Daily Maximum Temperatures from June 20 to June 28, 2025 (Unit: °C)

Author: Huo Da                                 Reviewer: Ma Jie 

English reviewer:Wang Yi                                                                       Issue approver:Dai Kan