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National Weather Service
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Fri Dec 12 2025
Valid 12Z Mon Dec 15 2025 - 12Z Fri Dec 19 2025
...Potentially hazardous cold temperatures across the Midwest to Southeast Monday...
...Additional atmospheric rivers to impact the Pacific Northwest for much of next week...
...Overview...
Into next week, the pattern aloft will mainly be transitioning to quasi-zonal flow over the lower 48, though with multiple shortwaves causing potentially impactful weather. Rounds of energy will direct atmospheric rivers into the Pacific Northwest, causing additional concerns for heavy rain and flooding, along with some mountain snow. Shortwaves and frontal systems continuing east could lead to at least modest precipitation chances across the northern tier as well as to the Midwest/Mississippi Valley towards midweek and toward the eastern U.S. Thursday. Temperature-wise, cold mean northwest flow and high pressure at the surface will lead to much below average temperatures across the Midwest to Ohio Valley to Southeast into Monday, but most of the lower 48 should warm up to above normal as the upper-level pattern flattens as the week progresses.
...Guidance/Predictability Assessment...
Model guidance begins the period Monday in reasonably good agreement with the overall pattern, consisting of exiting troughing in the western Atlantic, cold surface high pressure behind, and ridging across the south-central U.S. into the Great Basin, while southern stream troughing is present atop southern California/northern Mexico into the Four Corners region. The 12/18Z GFS runs were on the slower side in moving the southern stream trough eastward Tuesday-Wednesday, but the 00Z GFS has sped up some and aligns better with other guidance. The WPC forecast used a multi-model blend favoring the 12Z ECMWF for the early period.
There are increasing detail differences in the models from midweek and beyond that could have sensible weather impacts. First, the 12Z and new 00Z CMC both seem to be out of phase with the ECMWF and GFS runs (and their AI counterparts) across the northern tier by early Wednesday, with the CMC not showing a shortwave in the Great Lakes. Then behind this feature, models do show another shortwave moving across the U.S./Canada border along with a surface low. Guidance generally shows this mid-upper feature deepening and broadening a bit more into a notable trough moving across the Midwest and then the East later next week. However, GFS runs are the exception. GFS runs have been showing more Northeast Pacific energy entering the Northwest by Wednesday-Thursday, which shunts the Midwest trough eastward more quickly (not to mention the impacts of timing of another potential AR coming into the Northwest). Even the AI-GFS is more agreeable with guidance other than the GFS. Recent GFS runs have been consistent with each other but interestingly, GFS runs from a day or two ago were more like the current model consensus. Thus for the latter half of the period, reduced the proportion of the deterministic guidance, especially the GFS, in favor of the ensemble means. The means comprised about half the blend Day 6 and more Day 7 amid the increasing spread.
...Weather/Hazards Highlights...
Into Monday, another atmospheric river is forecast to take aim at the Pacific Northwest. This AR should be shorter lived than this extreme recent event. However, there looks to be strong IVT moving into Washington and Oregon especially early Monday. One limiting factor should be that this should be oriented more southwesterly rather than completely orthogonal to the terrain. However, antecedent conditions will be quite sensitive to additional rainfall. A Slight Risk has been added to the Day 4/Monday ERO for flooding concerns. Moist inflow (though not as strong) should continue into Tuesday. Higher IVT looks to get renewed late Tuesday, but farther south toward northern California, which has not been near as wet lately. Thus for Day 5/Tuesday, show a Marginal Risk in the ERO as a starting point. Yet another AR seems likely to impact the Northwest by Thursday.
On Monday, lake effect snow is possible in the cold westerly flow pattern behind the exiting upper trough. Then as impulses move out of the Northwest across the northern tier, rain and snow could spread across the northern Plains around Tuesday-Wednesday and into the Great Lakes region Wednesday-Thursday. Farther south, some Gulf moisture return is possible for light to moderate rain across eastern Texas into the Lower and Middle Mississippi Valley for Tuesday and Wednesday. By Thursday these systems are likely to interact and spread broadening precipitation chances across the eastern third of the U.S. Most of this precipitation is likely to be rain except in the Great Lakes to interior Northeast.
Cold high pressure will spread much below normal temperatures across the Midwest, Ohio and Tennessee Valleys, and all the way to the Gulf Coast early Monday, with temperatures 15 to 30 degrees below normal. A few record lows are possible, and wind chills may dip as low as the teens as far south as the southeastern Atlantic and Gulf Coasts Sunday night/Monday morning. However, upper level ridging over the West will allow temperatures to reach 15F to 25F above seasonal averages, spreading east across much of the lower 48 for midweek and beyond, creating a December thaw.
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