As if dealing with some of the intricacies and inherent uncertainties of the weather wasn’t enough, you occasionally have days like today, where everything suddenly shifts and it looks like that monster storm you discounted yesterday may not be dead after all. And you start to wonder what has happened in 12 hours to completely change your thinking. And then the Hydrometeorological Prediction Center issues its discussion on the models and says this:
PREFERENCE: EQUAL BLEND OF THE 06Z GFS/00Z ECMWF OR THE ENSEMBLE MEANS INITIALIZATION ERRORS IN NUMEROUS DIAGNOSTIC QUANTITIES...INCLUDING HEIGHT/VORTICITY FIELDS/RH...ARE EVIDENT IN BOTH THE 12Z NAM/GFS WITH SMALL BUT LIKELY SIGNIFICANT SHORTWAVE TROUGHS OVER SOUTH DAKOTA/NEBRASKA ALONG WITH SASKATCHEWAN/MANITOBA...WITH THESE AREAS ALSO NOT PARTICULARLY RESOLVED OR PREDICTED WELL BY THE 00Z ECMWF. THUS...THE SPECIFIC PREDICTIONS BY ALL DETERMINISTIC GUIDANCE ARE IN QUESTION...WITH THE RECOMMENDATION TO FOLLOW CONTINUITY...WITH THE FINAL OUTCOME MOST BELIEVED TO LIE BETWEEN THE 06Z GFS AND 00Z ECMWF...WITH ALL ENSEMBLE GUIDANCE INCLUDING THE SREF MEAN/GEFS MEAN/ECMWF ENSEMBLE MEAN ALSO CONSIDERED USEFUL TO ADDRESS THE CONTINUED UNCERTAINTY. THIS APPROACH DISREGARDS THE SUBSTANTIALLY DEEPER AND WESTWARD SHIFT OF THE 12Z GFS REGARDING THE POWERFUL LOW TRACKING UP THE EASTERN SEABOARD...AND TO A LESSER EXTENT THE 12Z NAM WHICH LIES NEAR THE FAST EDGE OF THE GUIDANCE WITH THE DEVELOPING LOW
In other words, trust NOTHING. In reality, it’s more or less that there was a problem initializing both the NAM (short range model) and GFS model that was serious enough to make them believe that their solutions showing a much further west and stronger storm should be discounted completely. Basically, when the model is run, it’s run off of a snapshot of the atmosphere taken at the beginning…the initialization. If that’s significantly incorrect, you better believe the rest of the run of the model is also incorrect. So you literally trash it.
That said, there still will be a storm, and it still could be significant for a couple places, primarily southeast Massachusetts again, as well as potentially southeast Virginia and northeast North Carolina. There’s really not much else to say, except you’ll just need to keep an eye on things to make sure they don’t change…a 50-100 mile shift either way will shift those already tight banded snowfall amounts in one direction or another. But frankly, I’m not too worried about this one. So your post-Christmas return rush and Monday for the most part look okay, unless you live on Cape Cod. Forecast map is below (the Comic Sans font for the title was done intentionally to emphasize how much of a joke this storm has been)…not planning to do a new one unless there’s a significant change. I was a little generous with how far inland the “coating-inch” zone was. That’s mainly to account for remaining uncertainty. Many areas may just see flurries that don’t really accumulate. Only area I didn’t really look too terribly closely at is SE Virginia. Really seems to be a toss up there as to how much will accumulate depending on timing and track…could be more or could be less. We’ll see. Merry Christmas!