Wintry Mix Thursday - Friday

Good evening everyone! We have a threat for a wintry mix from Thursday to Friday, mainly north of DC metro. Models have been trending south and colder for the past day or two. The highest ice will be near the mason dixon line. Unlike the other ice event that busted, this is a cold air damming event, which tends to be undermodeled. This will not be a snow threat, and the main focus of this will be ice and sleet. Although precipitation onset could be snow, almost all of it will turn into sleet/ice quickly. Precipitation onset has been delayed a few hours to after sunset, which would lead to a better environment for ice to accumulate. Main roads most likely won't be a problem, however secondary roads and sidewalks could have some slick spots, especially north of I-70 and in higher elevation areas such as Damascus. A potential delay is possible on Friday, but I won't make a prediction until we get into the event and surface obs.

Now, I will show what some model simulations are for this storm. 

 

RGEM/RDPS:

This is the RGEM model. It has done quite well this winter. The location of the ice accumulation is realistic, and fits with climatology. However, ice totals are still definitely overdone. The RGEM would give us a scenario for a delay, as ZR lasts in Damascus for until 11a-12p. This solution matches up more with surface temperatures. It has shifted south and colder compared to its last run.

 

Euro:

 

Euro is a bit more conservative with the ice totals, but still overdone in some places. It has shifted south and colder compared to its previous run. For Friday 1a, it gives Germantown rain on ptype map, when it should be ZR as temperatures are 32, supporting freezing rain. The Euro and RGEM line more up with my thinking and climatology on where ice accumulations will be.

About the NAM. It has a cold bias and spits out a very cold solution, with ice accumulation for even southern parts of our region. Although it does do well with CAD, it is quite unreasonable. Ground temps will not cool instantly, and NAM assumes it does. As I said earlier, it has a cold bias, so it is also unreasonable in the ptype solution it puts out. Even with later onset time, I just don't see it happening. 

 

Here is my first call ice map:

 

I will have an update with a school prediction for Friday and with mesoscale models + surface obs tomorrow.