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Tuesday 1/7/20 Disco snow event


MountainGeek
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This is a legitimate event for us. The 500 pattern looks good. Ridge out west is in the right place, the 500 trough is deepening as it crosses the Appalachians, heights falling as it crosses to our south, coastal even pops closer to the Delmarva. It has room to become more than what it is but rates will be there. I’m usually pessimistic on here, but this is a threat. West of 95 has a legit shot at 2-4, with 1-2 from about Fairfax to DC. Wouldn’t be surprised if someone in the subforum got 5”. 

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Forecast wet bulb temperature profiles definitely look colder at low levels than a few days ago, with 18z NAM and GFS profiles below 0C everywhere above the immediate surface layer (see BWI forecast sounding below). A deformation zone between 800-600 mb is aligned relative to the temperature gradient such that there will be frontogenesis-induced lift within this region. Vertical motion in this layer will have pretty good overlap with temperatures favorable for dendritic growth, with the subsequent aggregation of these dendrites producing relatively large, low-density ice particles. These low-density particles should help to increase snow-liquid equivalent ratios, though surface temperatures at or slightly above freezing could counteract these enhanced ratios somewhat. It will be interesting to follow this tomorrow, and I kind of wish I had planned ahead to telework!

 

691177353_Screenshotfrom2020-01-0620-36-21.thumb.png.a909352ad0a61d733b098cf9279676cf.png

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1 minute ago, heavy_wx said:

Forecast wet bulb temperature profiles definitely look colder at low levels than a few days ago, with 18z NAM and GFS profiles below 0C everywhere above the immediate surface layer (see BWI forecast sounding below). A deformation zone between 800-600 mb is aligned relative to the temperature gradient such that there will be frontogenesis-induced lift within this region. Vertical motion in this layer will have pretty good overlap with temperatures favorable for dendritic growth, with the subsequent aggregation of these dendrites producing relatively large, low-density ice particles. These low-density particles should help to increase snow-liquid equivalent ratios, though surface temperatures at or slightly above freezing could counteract these enhanced ratios somewhat. It will be interesting to follow this tomorrow, and I kind of wish I had planned ahead to telework!

 

691177353_Screenshotfrom2020-01-0620-36-21.thumb.png.a909352ad0a61d733b098cf9279676cf.png

I don’t understand 90% of this but I think I like it!

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2 minutes ago, heavy_wx said:

Forecast wet bulb temperature profiles definitely look colder at low levels than a few days ago, with 18z NAM and GFS profiles below 0C everywhere above the immediate surface layer (see BWI forecast sounding below). A deformation zone between 800-600 mb is aligned relative to the temperature gradient such that there will be frontogenesis-induced lift within this region. Vertical motion in this layer will have pretty good overlap with temperatures favorable for dendritic growth, with the subsequent aggregation of these dendrites producing relatively large, low-density ice particles. These low-density particles should help to increase snow-liquid equivalent ratios, though surface temperatures at or slightly above freezing could counteract these enhanced ratios somewhat. It will be interesting to follow this tomorrow, and I kind of wish I had planned ahead to telework!

 

691177353_Screenshotfrom2020-01-0620-36-21.thumb.png.a909352ad0a61d733b098cf9279676cf.png

I agree it's one of those events where dynamics will win out, increase those ratios and give that area more than advertised. We'll see will surely be fun to watch tomorrow.

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28 minutes ago, ers-wxman1 said:

This is a legitimate event for us. The 500 pattern looks good. Ridge out west is in the right place, the 500 trough is deepening as it crosses the Appalachians, heights falling as it crosses to our south, coastal even pops closer to the Delmarva. It has room to become more than what it is but rates will be there. I’m usually pessimistic on here, but this is a threat. West of 95 has a legit shot at 2-4, with 1-2 from about Fairfax to DC. Wouldn’t be surprised if someone in the subforum got 5”. 

Talk about luck...the western ridge is transient, in place for all of 12 hours basically but it traverses the perfect location at exactly the right time. Along with a good vort track. The whole pattern is junk but if you only look at the conus for that one moment frozen in time it looks close to the pna ridge +AO snow composite. 

2E502F76-34BE-4919-B891-8C06F19D791B.thumb.png.d76bce0561496a4863b99738aa396995.png

 

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Clear and plummeting temps since 5pm with dews coming up at only 25% ratio. Already made up a lot of ground toward getting temps right. 

Looks like it will get  cloudy at right time snd sun effect with clouds right now is zero.

couple of normal naysayers like it and that’s encouraging.

Lets sharpen up our obs skills

to start, right now I’m 40/19 and brilliantly clear 

 

 

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