Long Range Weather Forecast Discussion November 21-December 1
James Munley
Long Range Weather Forecast Discussion November 21-December 1
220 PM EST Tue. Nov. 18, 2025
Nov. 21-25: A ridge, trough, ridge, and trough pattern is expected from the eastern Pacific to the Northeast. The flow is generally zonal with an upper low in the Southwest.
An upper low is forecast to track from the Southwest to the south-central states by Friday, along with the associated surface low and frontal systems. Height falls, moisture, and instability with a return flow into the frontal boundary will result in heavy rain and strong thunderstorms across the south-central states. This activity will spread eastward and weaken over the weekend. There will be a moderate risk of excessive rainfall. The next upper trough in the southern stream flow will form an upper low near California on Friday before moving east. The system is expected to be slow-moving, bringing additional rain to Southern California. Rainfall could be excessive. The WPC gives it a marginal risk. As the system progresses east, rainfall will be less across the lower Ohio and Tennessee Valleys, and also with the convection across the Lower Mississippi Valley.
Nov. 26-30: Models have done an about-face in the flow since yesterday. Today, a trough is forecast to slide into the East. The GFS and the ECMWF depict a broad trough across the nation. The ensembles depict a ridge in the West.
Above-normal temperatures are forecast for the West Coast and parts of the Great Basin. Anomalies are expected to be near 4°F. Below-normal temperatures are forecast from the eastern Rockies to the Great Lakes, the Midwest, the Tennessee Valley, to the Gulf Coast. Anomalies are expected to be near 6°F.
Above-normal precipitation is forecast for most of California, the Northwest, and western Montana. The probability of occurrence is nearly 40 percent. Below-normal precipitation is forecast for most of the northern Plains, the upper Mississippi Valley, the southern Plains, the middle and lower Mississippi Valley, the Midwest, the Ohio and Tennessee Valleys, the Southeast, the Mid-Atlantic, and the Northeast. The probability of occurrence is nearly 40 percent.
Dec. 1-5: The GFS and the ECMWF are indicating an amplified flow with a strong ridge in the West and a deep trough in the East. The ECMWF weeklies are the opposite, with a trough in the West and a ridge in the East. There will be a trough across eastern Asia at this time.
Little change is expected in the temperature anomaly forecast from the previous period.
Below-normal precipitation is forecast for central and northern California, the Northwest, the central and eastern Gulf Coast States, the Southeast, the Mid-Atlantic, and the Northeast. The probability of occurrence is 35 percent.
Jim Munley
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