The biggest threat of the season is almost here and already virtually all of the weather outlets have downsized their predictions pointing to a bust scenario being more likely. Currently the National Weather Service believes 5-7 inches will fall in Baltimore and 4-6 inches in DC:

This is because significant mixing with sleet is being portrayed by the models due to their belief the storm is going to directly hug the coast now as it passes by us. Here’s a loop from the High Resolution Rapid Refresh (HRRR) model showing an extended period of sleet for I95 in the Mid-Atlantic. This is one such possibility, but usually the sleet band is slightly thinner than what is being portrayed:

But there’s still room for both boom and bust – the first flurries started flying around 6pm in the Baltimore area, a solid three hours ahead of model forecasts, so already the storm is behaving a little different than expected. It may mean nothing, but no storm has ever gone exactly as a model predicted even at event time. And interestingly, the “expect at least this much” (10 percentile) and “potential for this much” (90 percentile) graphics have changed to both lower and raise totals across the area.

The 10 percentile graphic shows nothing for the I95 corridor now:

But the 90 percentile graphic shows an even larger area of 18+ inches intersecting with the Baltimore City line:

So while the National Weather Service has lowered expectations overall, there’s actually more uncertainty in their forecast than there was yesterday.

As for the models, the 12z euro gave 7 inches down the I95 line:

The 18z GFS gives 4-6 inches:

The 12z Canadian gives big amounts, but much of this is sleet being translated as snow on the map:

As for my forecast if I could change it, I would downsize too with a few inches of snow followed by significant sleet. Wednesday is going to be very cold behind this system with temperatures not getting above freezing, a rarity for mid-March. That’s all I’ve got.

I issue a final forecast 24 hours prior to the beginning of an anticipated snow storm. Beyond that is just nowcasting IMO.

  • Directly along I95 from DC to Baltimore: 4-8 inches with the lighter amounts the further south/east one lives
  • North and west of I95 from Owings Mills to Rockville to Centreville: 8-12 inches
  • Northeastern MD (Harford and Cecil counties): 9-13 inches
  • Southern Anne Arundel county, southern and eastern PG county, north, central and western Charles County: 2-4 inches
  • Southeastern Charles, Calvert, and St. Mary’s counties: 0-2 inches

There’s no real changes in amounts or my thought process from my previous forecast. It’s a certainty that schools will be closed everywhere Tuesday except southern MD given the hype. As for OPM, I’m not sure what their thinking will be. Timing of first snow flakes will be sometime between just after rush hour Monday and prior to 11pm. Heaviest precipitation rates will be between midnight¬†and 8am Tuesday and in those spots where it is snowing, rates could be two inches per hour or slightly higher for several hours.

A storm like this makes me happy I’m not a professional meteorologist. The issues noted in my previous post could lead to a very sharp gradient of snow totals and it’s within the realm of possibility that gradient could be quite large. It’s possible that someone somewhere along the I95 corridor ends up with a few inches of slush while someone 5 miles to the north and west as the crow flies receives 18 inches, although I don’t think the difference will ultimately be that dramatic over such a short distance. The 12z GFS showed no mixing of precipitation for the I95 corridor and the 18z was very similar:

But I find it unlikely to be entirely snow for everyone except southern MD like it shows. Our local National Weather Service agrees that mixing is a distinct possibility over the I95 corridor:

The 12z Canadian showed sleet for a time along the I95 corridor and I find that to be the most likely scenario and sleet would cut down on the accumulation totals:

The 12z euro gave 8-10 inches over the I95 corridor, because it was the strongest bomb of them all with its coastal front overtaking the I95 corridor as well:

Additional Notes:

  • Even if the moderate snow totals in my forecast were to verify, it still wouldn’t bring this winter up to normal snow fall. The map below shows the paltry snow for our area this winter down at the bottom.

  • As with any storm undergoing bombogenesis, thundersnow is possible. I wouldn’t be surprised if there are a couple of reports on social media of thunder being heard if the bombing occurs like the models say it will.
  • If an area of convective snow breaks out in our area, I wouldn’t be surprised if the National Weather Service upgraded to a blizzard warning. Right now most of the models keep the wind gusts just under blizzard criteria, but convection would bring stronger winds down to the surface. This scenario (where the NWS was originally not going to issue blizzard warnings, but then had to) happened in the third blizzard of the 2009-2010 season. The 12z euro’s wind gusts would meet blizzard criteria for portions of the area if snow were falling.
  • I finally bought a semi-professional weather station a few weeks ago when AcuRite had a good deal going. I figured today was as good as any day to set it up with the possible snow storm coming. It’s supposed to be able to connect to weather underground but the wunderground site is giving me no response when trying to create a site. I’ll try again tomorrow, but I’m not concerned whether it’s on wunderground or not.

For the record, the local NWS “most likely” scenario at the time of this writing (6:00pm, 03/12) is:

And the “expect at least this much” and “potential for this much” are:

 

The mid-day model runs diverged fairly significantly with the snow possibility for Monday night into Tuesday. First up was the GFS, which had a coastal hugger and inland track once it got up to northern New England. The hugging of the coast resulted in the rain/mix line going over top of the I95 corridor for the Mid-Atlantic in the middle/end of the storm resulting in what would likely be a 6 or 8 inch slop when it was all said and done. The Canadian came in next and its 12z run took the storm east with virtually no snow for the I95 corridor in the Mid-Atlantic. The euro then came in splitting the difference and giving all snow to the I95 corridor and southern MD with accumulations likely over a foot.

Out of the three, I find the GFS and euro scenarios to be the most likely with the Canadian being the more unlikely of the three. In fact, the Canadian’s upper level energy was weaker than the other two and its model run formed a rather odd looking double barrel of low pressure oriented north-south out over the Atlantic. It was odd given the scenario and the surface low pressures splitting like this and weaker upper level energy may have been a result of the model initializing poorly. The 18z GFS was nearly identical to the 12z run, but it made a small step towards the euro’s solution in the upper levels of its model run.

Perhaps the best sign for snow lovers is the euro ensembles that came in the middle of the afternoon. The ensembles gave Baltimore a 50% chance of a foot of snow or more. This is a quite high probability this far out and would be a huge fail for the euro model suite if no snow were to fall for Baltimore.

My decision on whether I think snow is a probability or not will come Saturday afternoon.