The big question - what will happen Friday? This winter thus far has been a challenge to forecast, and I am not yet sure why. Part of the blame goes to the models, but I also see patterns forming this winter I had not seen in previous winters. Something for me to research come spring. I will leave the discussion to the end. Here is how I see it:
TIMING: The snow should start after noon, most likely 3'ish or so. The heaviest precip probably after 6:00pm. The storm should end around midnight.
PRECIP: All snow.
ACCUMULATION: Let me put it this way. On average most of us in central MD should see about 2" while those closer to the PA line and in S MD could see a couple inches more. These numbers are dependent upon my concerns listed below. Localized heavier snow bands possible.
CONCERNS: The bulk of this storm will occur around the evening rush hour. During the day the streets will warm enough that the first snow flakes will melt on contact. That water will then freeze as the snow piles on and the temp cools. Thus the bottom layer of snow on the road will be a thin sheet of ice.
WHAT CAN GO WRONG? In summary, here is what is happening. There are 2 Low pressure systems moving into the area. The air is relatively dry, although it will moisten. The southern Low comes in well before the northern Low. For snow lovers, we would want both of those to merge, or phase, and become one very strong Low with the potential to dump a lot of snow. But alas, it won't happen. Two major concerns of mine: too much dry air which will evaporate the snow as it falls (virga) and the creation of a dry slot between the 2 Lows as their energies are pulled apart from each other. Both of these scenarios contributed to the last 2 storm busts.
BUT ... Given the cold temps in place, moisture on the way, and recent history of these clipper systems over performing (stronger and more snow than indicated by the models), I am feeling confident that we can expect a couple inches of snow from this system. Thursday morning showed the over-performance, and this system is similar. So, I think 2" is conservative with those N and S of Baltimore receiving more. If the dry slot happens then we could see no snow. If the southern Low re-forms over the Atlantic in good timing and position we would see more snow. Both of those factors cannot easily be forecast.
I expect the NWS to issue a winter weather advisory for Friday, but thus far none have been issued. Follow me daily on Twitter (@wxmanmd) for weather updates and info. I will have another update as needed on Friday.