Highly Uncertain Forecast South and East of DC

It is premature to post a snow map until Sunday morning in the Washington Region as until the exact track is pinned down we have precipitation type issues (where does the rain/snow line set up) during the event.

For those of you north and west of Washington and Baltimore the latest forecast modeling is still showing a significant snow storm. For those of you south and east, this could still wind up being a significant storm. 

The latest European operational model from overnight brings the “540 line” right into the District, meaning if this latest operational is correct (I will remind you that many of the ensembles keep the “540 line” south and east of Washington) the northern and western suburbs receive the heaviest snowfall accumulations while areas south and east get slop (wet snow) going over to a mix and ending as light snow.

Latest 00z operational European model showing 2am Tuesday (Monday night):

  • Notice the 540 line (blue line labeled 540)… that is the “rain/snow” line.

Latest 00z operational European model showing 8am Tuesday:

  • “540 line” could make it all the way to Baltimore and Dulles, of course in these areas the “damage will have been done” during the overnight when heavy snow would have already accumulated in these areas with snow-covered roadways. 

Latest 00z operational European model showing Noon Tuesday:

  • Storm is pulling away and colder air is rushing in as winds have now shifted to the north-north-west but the high-march sun angle is now helping to warm the atmosphere and best lift is now in the Philadelphia Area. 

Here is what has people pulling their hair out this morning:

  • So if last night’s latest operation model (the images I just showed you above) are absolutely 100% accurate in track (that’s a far stretch of the imagination)… this is how much snow could fall (notice how the southern and eastern outer suburbs get shafted while the northern and western suburbs are having a snow party)

Okay so now some of you (and I know who you are) are immediately jumping to the conclusion that “it’s over” … “Tim is forecasting a bust”. I am not forecasting a bust, I am saying that until we have an exact track ironed out… any shift back to the east even by as little as 25 miles is going to bring significant snowfall back into areas south and east of 95.  We simply do not know. Let me show you what I mean by looking at the latest Ensembles:

Latest European showing probability of 3″ or more:

  • Please notice the 70 to 80 percent probability of 3″ or more in locations that the latest operational showed zero accumulation… (southern Maryland for example) … now you can see my point (I hope). 

Latest European showing probability of 6″ or more:

Let’s take a look at the latest suggested track from the European Ensembles:

  • Here was yesterday’s European Ensemble showing potential locations of where the Nor’easter will be sitting at 8AM Tuesday with some of the “L’s” in eastern North Carolina and others just offshore.


  • The exact track is going to have significant impacts on how much snow falls in our area.  Any track further east keeps the boundary layer (850mb) at or below freezing. 

Here is the last night’s latest forecast ensemble from the European:

  • The entire DC Metropolitan Region is still in the “game” for significant snow… that is the bottom line. 

European Snowfall Accumulation Potential (based on the latest Ensembles)

Yesterday’s 12z run:

Last night’s 00z run:

  • Not a lot of change within the ensemble mean… good news for now. 

Let’s look at the latest Global Forecast System (GFS) Ensembles


GFS Ensemble showing precipitation type and track around 2AM Tuesday:

  • Notice how some have heavy snow in our southern and eastern immediate burbs while others show a mix.

The image below shows the latest GFS Ensemble showing potential Snowfall accumulation:

For my faithful Snow plow operator followers, the DC Area airport hubs finally issued a travel advisory yesterday for Tuesday so people are all scrambling to change flights to Monday.  

If you are a snow plow operator north and west of Baltimore or DC … it’s safe to say that right now your services are certainly going to be needed.  

If you plow snow in southern Maryland, Fredericksburg or the northern Neck of Virginia … I’d at least be ready as one operation run is meaningless until we start seeing the ensembles shifting to a rainy solution south and east of DC. 



4 thoughts on “Highly Uncertain Forecast South and East of DC

  1. Hey Tim,
    I grew up in Spotsy. I learned along time ago from an old park service guy that the climate between DC to the NW and DC to the S and SE are different. There is historical reasons for that different. Not to say on any given day that assumption cannot be challenged, certainly it can. The climatic zone between Humid Subtropical and Humid Continental is well established. When I hear all the noise about this storm and that storm (from weather services) and the uncertainty I think the resolution is in the climate zones. If you look at the maps with this storm that you have posted it is evident and clearly reenforces that zonal differential. Over that last few days there have been forecast that reflected a eight inch snow in King George VA. When I saw that I had to smile…now its coming around to maybe an inch with a good amount of rain before and during. That is more historically supportive. Just an observation.

    I really enjoy the data and analysis you provide. Good job, keep it coming.


  2. The latest GFS keeps the storm on a “perfect” track, just off shore and if that is correct, the immediate DC area should be almost all snow (it could briefly mix with sleet especially east of the city, but still be a major storm).

    Even Richmond starts as snow, so places in southern MD should get a few hours of accumulating snow. Even there , I don’t believe it will not be a non-event.

    Rapid 500 mb height falls (cooling aloft) during the storm and heavy precip rates should largely compensate for low level warming. One worry is the unusually warm Bay and ocean temperatures after such a mild winter. On the other hand, that might just increase instability and possibly trigger thundersnow.

    I don’t believe this will be a typical March “slop storm” as temperatures should be at least a little below freezing. Also, most of the snow falls at night and thus while most of snow is falling, we won’t be fighting the March sun.

    I believe 6-10″ is a pretty safe bet, even in the immediate southern and eastern suburbs. 12-18″ not far north and west of DC.

    I would assume at this time frame, the GFS should be pretty locked in, as it usually is 60-72 hours prior to a major coastal storm. The upper air solution is not that complex and the GFS has been remarkably consistent. Of course, If the progs go haywire, like bringing the storm inland, all bets are off, but I believe that is unlikely.

    Those are my bullish thoughts from my pea sized brain, for whatever they are worth! No school on Tuesday if I am right!

  3. Interesting thing about the Euro ensemble means is that the 0z is actually slightly snowier than the 12z was. Also, with a few exceptions, the GFS ensembles look good. I have hope that this will work out well (big snow) for the entire DC region. Please keep the updates coming.

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