Jeremy’s Quick Snow Thoughts

January 17th, 2013 at 7:16 pm by under Weather

Ok. Lots of folks are chiming-in about the 18Z NAM. So I thought I’d try and address it.  It does look impressive at face value.  I looked at the NAM’s FOUS data (numerical output), and if you look at it then it spits out something like 11 inches of snow with a 10-1 ratio.  However, you have to look at the time increments.  The NAM has a value at every 6 hours.  So the temperature in the lowest layers drops from the upper 30s in one increment to the lower 30s in another.  That is during the time of the heaviest precipitation.  BUT… the window for that to happen will likely be 2-3…maybe 4 hours.  In order to get the maximum snow out of that it would have to snow 2-4 inches per hour, and there would be no mix at all.  Well it will likely be 1-2 inches per hour at the most and there will be a mix in that 6 hour window.  Plus, there will definitely be melting for at least the beginning of all snow in the region. Richmond is in the low/mid 30s as I write this, but everywhere else is in the upper 30s to low 40s.   Richmond is seeing a mix already.  The snow will change over sooner between there and Williamsburg over to Gloucester and up to the Northern Neck.  So I wouldn’t be surprised if we have to increase the amounts there.  Maybe even 6 inches or more near Richmond.  We’ll see.  But Hampton Roads is still expecting a longer time with rain and mix.

Jeff Edmondson wrote an earlier blog that described the situation pretty well.  I have seen heavy snow overcome a warm ground around here several times.  But the heavy snow would have to come down right at the beginning for it to really stick and maximize the snowfall.  Plus there is a lot of standing water out there right now along with the warm ground.  I know the NAM has been looking very ominous (overall) for the past couple of days, but again I just don’t think the 6 hour increments can capture what is going to happen between midnight and 4 am very well.  Also, I spoke before about the thicknesses, and that the best ones won’t come through here until towards the end of the precip.  However, the temps at 850 mb (millibars) will be cold enough. So the question is:  Will the snow be heavy enough and last long enough to drag the cold air down to the surface and also overcome the warm ground?  The NAM is promising, but the hi-res version isn’t as impressive, and our Future Trak has also been sticking to its guns with mostly a mix in Hampton Roads.  Difficult forecast???  You bet!!  But it’s not so much because of the meteorology as it is the hyper-local weather and the climatology. 

Here is the latest National Weather Service forecast from their model.  It is running fairly close to Don Slater’s forecast tonight. 

NWS Snow Forecast (Model)

 He also highlighted that a lot of melting will occur in the metro area.  At least on the roads. 

 So I would love to write another 2-3 paragraphs here and do more analysis, but I have to get to bed in a little while.  I am going to be in at 4am along with Jeff.  I appreciate everyone’s input.  There are some very smart people out there.  I am actually very curious to see how tomorrow plays out.  Have a good night.

Meteorologist: Jeremy Wheeler

6 Responses to “Jeremy’s Quick Snow Thoughts”

  1. DA says:

    Jeremy, that’s funny I just wrote something similiar on the bottom of Jeff’s blog (19th comment) after seeing all the replys about the 18Z NAM. In case you hadn’t seen it, I’ll copy it here:

    I’m with Jeff and the WAVY team on this one. For those of you seeing 5-6″ on the NAM 18Z…you have to consider that the changeover probably won’t happen until ~06Z (1am EST) for the southside (maybe midnight for Hamp-NN). Sure a good chance of heavier rain by about 03Z (10pm) with some snow mixing in closer to midnight. So much of those amounts will be liquid. So you need to see what would fall beyond 06Z (6-hr precip ending at 12Z) or (3-hr precip ending at 09Z). Prior to 06Z, 850 temps = or > 0°C and 1000-850 thick > 1310. Too warm for pure snow. My guess is that about 0.10 liquid (~1 inch snow “IF”
    it sticks) (from what NAM shows..which is a model of course and not necessarily perfect by all means) during 06Z-09Z time frame (1am-4am) and then still only colder surfaces (parked cars, patios, grass). I wouldn’t be surprised if those big heavy flakes fall for about 30 minutes during changeover but will it stick at that time. Rapid drying occurs beyond 09Z as
    evident at 850mb so everything ends by 4am or so. A dusting to half inch was my thoughts (for VB/southside) since yesterday, (little more for the peninsula Hamp/NN folks maybe 1″ or 2″ at most). Also, look at the observations at RIC. They started reporing mix RASN at 2337Z (let’s call it 00Z) which matches well with 850 temps of < 0°C and 1310dm 1000-850 thickness. An hour later and still reporting a mix. Really, only thing to do now is sit and wait and see what happens.

    1. Jeremy Wheeler says:

      Thanks for the comment Dave. You have some good points. Richmond is in full changeover now. It’s probably melting up there for now, but I would bet that their forecast will have to be increased. One component I didn’t talk about earlier was the wind and wind direction. Right now it’s a northeast wind for most of Hampton Roads. That’s coming in off of the ocean. The winds will turn more from the north by probably midnight, but if the northeast wind holds longer, then that will also be a factor. I’m going to bed. See you in the morning. Jeremy W.

  2. carollavs says:

    Jeremy is so professional. Lol. I just don’t see how we would have enough snow to overcome the standing water we have out there right now either. From the comments on the other article seems to me we have a lot of southern people going through what I have named flake panic. As a Georgia girl I have been there myself. Lol lets all get some sleep!

  3. Wes says:

    Hey Jeremy, NN/Williamsburg airport is full snow, and has been since about 9:30. Appears to be sticking. We could see a big event from this if it sticks around.

  4. Matt says:

    Well played Wavy weather team. Town center of VB has not a trace of snow on anything. You guys seemed to be the only ones calling for this and you nailed it!!!

    1. Jeremy Wheeler says:

      Thanks Matt. Have a good one. Jeremy

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