Who Left the Fridge Open?

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We might be asking that question for the next few days as it appears the longwave pattern across the U.S. will tilt toward a configuration that places a trough axis over the eastern U.S. on average, allowing fairly deep penetration of cold air into the southeast and leaving us with temperatures that run well below normal through Thursday or Friday.

Within that pattern, however, there will be some ripples, one coming in the form of a short-wave ridge aloft that helps to intensify a surface high over the northeastern U.S. and southeast Canada tomorrow into Wednesday. That feature will combine with a departing "Clipper" type low later tonight and tomorrow to set us into a cold low level northerly flow that will initially bring lots of sunshine and highs in the low to mid 40s (about ten degrees below normal) for Tuesday. On Wednesday, though, surface low pressure ahead of a reinforcing trough dropping into the plains states will develop in something of a two-pronged approach, one intensifying across the midwest, the other near the Gulf Coast, with moisture flowing into our state from the south and west during the day, bringing an increase in cloud cover and eventually a good chance of precipitation.

Timing will be critical here, because if clouds thicken rapidly on Wednesday we may see temperatures max out in the in the mid 30s to around 40, and could potentially see precipitation initially in the form of mixed rain and snow around midnight Wednesday into early Thursday morning. From there, we continue to see some disagreement among computer projections as to how rapidly warmer air from the south and southeast will infiltrate the region and how stubbornly a low-lying layer of cold dry air will hang on over the Piedmont. Most models imply that the Triangle and areas south and east will pretty quickly warm enough for a principally rain event, perhaps with a period of freezing rain late Wednesday night. At this time, any ice or snow accumulation appears to be minimal, with notable glazing likely confined to the vicinity of the Triad and surrounding areas, while rainfall amounts remain uncertain but at least appear on track to be significant.

In the longer term, medium range outlooks from the Climate Prediction Center show a trend toward below normal temperatures and normal to above normal precipitation for the next week or two, while the longer range winter outlook remains non-commital, with an "equal chance" regime. Of note is that for the past couple of weeks we've seen a moderately negative phase of the North Atlantic Oscillation. Although our predictive ability regarding this feature ( is fairly poor, it is forecast to moderate to a neutral or slightly positive phase over the next week or two, which may imply some general moderation of temperatures over the eastern U.S. through the latter part of December. Time will tell...