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This is What "Bombogenesis" Looks Like on Model Data.

10:48 PM, Feb 7, 2013   |    comments
  • This is the NAM forecast for the 250mb level winds, often called the jet level, at 7pm Friday. The yellow shading indicates relatively stronger winds, and the green areas have weaker wind speeds. What you see on this map is a split between the wind maxima at the jet level, right over Long Island.
  • This is the NAM forecast for vertical velocity at 850mb at 7pm Friday.
  • This is the NAM forecast for vorticity at the 500mb level, often called the steering level, at 7pm Friday.
  • This is the NAM forecast for precipitation over a 3-hour period at 7pm Friday. This map also shows lines of constant thickness and lines of constant pressure.
    
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A big storm is making its way from the Southeastern United States up the East Coast tonight. While this storm is not expected to bring much wintry weather to the DC Metro, the forecast for New England calls for snow to be measured in feet instead of inches in some locations.

This storm has a textbook "Bombogensis" look on the forecast model data. This is a term I learned in college. It doesn't have a meaning in the dictionary, but it's a term meteorologists sometimes use for large (synoptic-scale) storms that intensify very rapidly.The NAM model's forecast projections from this morning have all the classic signs of true "Bombogenesis".

First up, the jet stream.

NAM forecast for the 250mb winds, valid 7pm Friday

?This is the NAM forecast for the 250mb level winds, often called the jet level, at 7pm Friday. The yellow shading indicates relatively stronger winds, and the green areas have weaker wind speeds. What you see on this map is a split between the wind maxima at the jet level, almost directly over Long Island. The space in between the jet maxima creates a relative vacuum in the upper atmosphere. The air underneath rushes upward in an attempt to fill this void, creating one of the essential elements of Bombogenesis: UPLIFT. 

Second, the 500mb map with absolute vorticity. 

This is the NAM forecast for vorticity at the 500mb level, often called the steering level, at 7pm Friday. The highly-shaded area just south of Connecticut shows an area of Positive Vorticity Advection (PVA). Vorticity is a measure of the amount of spin in the atmosphere. If an area is experiencing PVA, the amount of spin is increasing, and that will also lead to increased uplift.  

We should be able to see a measure of this increased uplift somewhere, right? Well, we can check the 850mb level:

 

Not coincidentally, we see a defined area of very strong uplift in the same region with the relatively slow winds at jet level and the positive vorticity advection. We would expect to see the surface area of low pressure form underneath the area of high vertical velocity (vvel). You can also clearly see some large vvel values over western Pennsylvania through the Maryland panhandle; these are in conjunction with the other part of the storm system moving across the Plains. As the secondary low traverses the Appalachians, it will lose some of its uplift.

So, all the elements are in place for Bombogenesis. What's the surface look like?

NAM forecast for precipitation over a 3-hour period at 7pm Friday; also shows lines of constant thickness and lines of constant pressure.

BAM! Notice that this is a map for 3-hour precip amounts, and the red shading is for up to 1" of liquid equivalent. If that were to all fall as snow (which it won't), it would be equal to about a foot of snow in just a 3-hour period! Also, check out the isobars, marked in light blue. They're really tightly packed near the center of the storm. Blizzard conditions are a certainty if this model prediction plays out.  

If this storm turns out to be "The Big One" as the NAM model indicates, then I believe meteorology students will be using this storm as a case study in the future... just as I did with the Blizzard of '96 when I was in school. Only time will tell if this storm is one for the record books!

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