Boundary temperatures and snowfall rates will be the two main things to watch tomorrow as a nice looking vort. max passes over the region. Precipitation will start off as rain for most/all of the region tomorrow, with the back end of the system changing over to a heavy, wet snow. The strong vort. max will help dynamically cool the air as decent rates form up along the back part of the storm, but with the boundary layer temperatures remaining at or above freezing, it will be hard to get a lot of that snow to stick.
Then there is the disagreement between the models. The Euro continues to run drier and further south compared to a host of other models, which is somewhat concerning considering it has never really been on board with the snow totals that I have forecast. Given the non-consensus of the models along with the temperature issues, risks to the forecast are more to the down side throughout the region, though some of the models do still show some upward potential with this storm. All in all, it will just be something that needs to be nowcasted as the bands of snow develop and try to overcome above freezing surface temperatures.
Much more aggressive with the totals this time around, but there is still more upside risk than downside to the forecast.
I went with a rough 50/50 blend of the GFS and Euro, with some personal touches here and there. NAM’s still out to lunch with it’s QPF and snow totals, so I didn’t even bother with it. There’s going to be some winners and losers in the low-end/mix areas as the details work themselves out. The bulk of the snow across northern MD, southern PA and southern NJ will be during the back part of the storm. The front-end could start off as snow/mix/rain in these same areas and could/should flip to rain at some point before transitioning to snow to end the storm.
Just going to start off by saying that forecast confidence is lower than normal. Miller B type storm will form up late tomorrow into Friday and will initially cause mixing/temp issues across the more southern areas. As the coastal intensifies, banding on the back edge of the system could bring locally higher totals from central PA to NJ, NY and maybe even down into northeast MD and northern DE. There’s plenty of risk in either direction, especially across central PA into NJ and NYC/LI.
I didn’t try too hard to figure out contouring based on strict temperature and boundary layer issue areas since there is not enough certainty to really go into that much detail yet. That’s a job that is best saved for tomorrow’s update.
While the severe weather outbreak will be more focused on the southern states, I did this write-up just for folks in the Mid-Atlantic.
A widespread strong to severe wind event appears to be unfolding over the eastern half of the U.S. Tuesday into Wednesday, with isolated tornadoes also a threat, which is mostly across parts of the Southeast. The Mid-Atlantic has some opportunity for both on Wednesday, with the main threat obviously being a line of strong to severe winds.
We will be battling marginal lapse rates and pre-frontal clouds/rain, as we normally do in these early year setups. Very strong winds aloft (50-60 kt jet at 925mb!) suggests any sort of convection will bring down strong to severe level winds. With the strong forcing associated with the cold front, I don’t see much of a problem getting those winds to the surface. The only issue would be if a stable layer at the surface can linger ahead of the front, but that appears to be just a minor problem as the lift from the front should overcome the stable layer (if there is indeed a stable layer).
With dewpoints climbing into the lower 60s ahead of the front, we should be able to see a fairly strong frontal passage with widespread strong to severe winds. The main thing I’m watching now is the potential of a secondary low formation, which the NAM has (though that can’t be relied upon at this point). The Euro also develops a secondary low, but it comes later and further north than the NAM. If this secondary low develops before the front comes through, and if it’s far enough south, it will be able to back the winds more at the surface and would provide a greater risk for tornadoes in the Mid-Atlantic.
Somewhat higher confidence in the QPF totals brought about an expansion of the 2-4″ area. The GFS/NAM continue to suggest a snow hole in the northern VA and DC region, which remains a slight risk to the low side. Overall, I think risks are more to the high side, with localized 2-4″ totals possible within the 1-2″ contour. Likewise, the 2-4″ contour could see localized totals of 4-8″ (which is more so for the Appalachians than anywhere else).
Certainly a new breed of winter storm for this winter as we now have plenty of cold air in place, but moisture will be lacking in most areas. The good news is most of the Mid-Atlantic will see high snow ratios around 15-20:1, giving the event more bang for the buck.
Risks are more to the low side at the moment, with the current forecast leaning more towards the wetter European solutions. The NAM and GFS have been fairly insistent on a DC snow hole where accumulations are less than an inch. While entirely possible, I still think there’s enough QPF for most to get around an inch. Some of those east of the mountains in PA and NJ have a shot at 2-3″ if the higher-end QPF verifies.
Confidence is lower than normal with this storm due to the QPF issues and because the energy that will create this system is still somewhat offshore in the Pacific Northwest, so it is not getting sampled as well as it would if it was onshore.
A quick update before I head into work… shifted the forecast further south overall and tightened up the contouring in areas that have slightly higher confidence than the initial forecast.
This results in a virtual no-show north of DC aside from some flakes in the air to a dusting. Southern VA into northern NC will get rocked as the vort. max pushes through. There is a risk of this shifting even further south according to some of the hi-res models.