Long Range Weather Forecast Discussion May 15-29
James Munley
Long Range Weather Forecast Discussion May 15-29
358 PM EDT Tue. May 12, 2026
May 15-19: A trough is forecast in the West and a ridge across the eastern and central states.
A system is forecast to develop a coastal cyclogenesis. This will cause rain across New England. A Pacific upper-level low will move inland to the central states by Friday and cause cyclogenesis, bringing rain to the Midwest and Great Lakes. Shortwaves will track into the West and across the central states this weekend into early next week and bring precipitation across the Northwest and north-central Intermountain. A front along the Gulf Coast and Gulf moisture will cause rainfall that could be heavy later in the weekend and into next week.
May 20-24: A trough will be in the West and a ridge and a zonal flow across the eastern and central states. The ECMWF ensembles depict a trough, ridge, and trough pattern from the West to the East.
A system will develop in the Plains on Thursday with rain and storms across the southern Plains and snow in the higher elevations of the Rockies. The system progresses into the Mississippi Valley, causing rain and storms. The ECMWF is further south than the GFS. The system moves into the Midwest and the East on Friday and Saturday with rain. High pressure follows later in the weekend. By this time, a system enters the Northeast with rain and higher-elevation snow.
Above-normal temperatures are forecast for the country. Anomalies could be near 8°F across parts of the Mississippi Valley to the Mid-Atlantic.
Below-normal precipitation is forecast for parts of coastal California, northern California, most of the Northwest, the central and eastern Gulf Coast States, the Southeast, the Mid-Atlantic, and the Northeast. The probability of occurrence is up to 45 percent in the East. Above-normal precipitation is forecast for the Plains and the Mississippi Valley. The probability of occurrence is 35 percent.
May 25-29: Overall, guidance is in fair agreement on the flow for this period with a trough ridge and trough pattern.
Another system develops in the Plains on Monday and tracks to the East Coast by Tuesday and into Wednesday with rain. The southern extension of the front will cause possible heavy rain and storms across the South,
Above-normal temperatures are forecast from the Rockies to the Atlantic Coast. Anomalies could be near 6°F in some locations. A system moves into southwest Canada and could bring higher-elevation snow to the northern Rockies.
Below-normal precipitation is forecast for the northern Plains, most of the Mississippi Valley, to the Atlantic Coast. The probability of occurrence is 35-40 percent in parts of the East.
Jim Munley
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