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If you hear a Virginia weather forecaster say we are currently experiencing CAD conditions, they aren't referring to some guy making untoward advances to a female.

CAD refers to a common weather phenomenon in our area know as Cold Air Damming, also known as "the cold wedge". It is a condition where warmer air is trying to push into our area from the southwest, but has a difficult time eroding the cold air, due to a damming effect from the Appalachians.

Yesterday and earlier today exhibited a classic example of this.  A warm front was approaching from NC, but stalled over our area. At one point the Short Pump area was hovering around 39 while it was in the 50s in Colonial Heights. 

Similarly, this morning when it was 39 in Short Pump, it was 48 in Blacksburg, an area that's generally 3 to 5 degrees cooler than us. See image below for a graphic representation of this from this morning. 

As you can see from the map warmer air had pushed up the western side of the Appalachians, but was having a hard time moving into central Virginia.

For this particular event, we were cold, but still above freezing. Sometimes when the entrenched air is a bit colder, this setup can cause some classic ice storms in our region, as the warmer air moves up and over the dammed-up cold air at the surface. The temps in the upper atmosphere can be in the 40s with precipitation falling as rain, and as it falls through the colder air, it can refreeze as sleet if the dammed-up cold air layer is thick, or freeze after it hits the ground (freezing rain) if the layer is thinner. 

Your Richmond area weather lesson of the day!

Follow me on Twitter at @HenricoWxGeek

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Edited by Henrico Weather
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Interesting look at the total snowfall over the last ten years (measured in feet). The Richmond area falls within the zone that saw 10 to 15 feet of snow for the decade. This is comparable to areas like central Kentucky, southern Indiana, southern Illinois, central Missouri and southern Kansas. 

Screenshot_20200101-223450_Twitter.jpg

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If you think this has been a lame winter in the Richmond area so far, you'd be factually correct. But we're in good company. The entire east and Ohio Valley are right there with us. Only central New England has seen a bumper crop of snowfall. In fact the 1 inch recorded at RIC to date, is ahead of Dulles, National, Baltimore, Harrisburg, Philadelphia and Wilmington. January still isn't looking good for snow lovers, but the pattern may change later in the month. 

Screenshot_20200106-083403_Twitter.jpg

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Great chart.  Thanks for posting.  It just takes one major snow storm to bring these totals above the norm.

Edited by Shakman

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Think winters have been pretty lame here in the Richmond area the last few years? Well, it's not just us. Globally, 3 out of the last 5 Januarys have set new records for warmth across the planet. This past January was the 2nd warmest since records have been kept. The chart below only goes back to 1980, but the records go back to the 1800s.

Looking forward to February, projections are for another unseasonably warm month. Prospects for cold weather and snow are very low. We are on course to have one of the lowest seasonal snow totals on record for our area.

 

IMG_20200204_090439.jpg

Edited by Henrico Weather
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Today is another great example of what I had described in a post up above about CAD (cold air damming) aka "The Wedge" (as in wedge of cold air), which is peculiar to our area. To refresh, this is a setup where cold air filters down from the northeast (known as a "backdoor cold front") on the east side of the Appalachians, and becomes entrenched, even as warmer air tries to push into the area from the south and southwest. The cold air dams up against the Appalachians and doesn't want to budge. This is a tough setup for forecasters, since it's difficult to know just where this cold air stands firm or gets eroded by the warmer air. It's evident in situations where we could get several inches of snow or ice here in Richmond, but just a short distance away, it could be in the 50s and 60s in Williamsburg and Va. Beach.

Unfortunately, today's CAD setup doesn't contain air cold enough for snow, but does keep us cold and wet. "The Wedge" can clearly be seen on the map below. Don't pay attention to the numbers shown in the circles, because there's some kind of glitch in the app, but just focus on the colors. You can see where the blue has settled in, and the oranges and yellows that are trying to push in, but can't make much progress. Here are some actual temps for reference:

Short Pump 42, Williamsburg 56, Virginia Beach 63, Elkins WV 56, Parsons WV 62.

Screenshot_20200206-111637_Wunderground.jpg

Edited by Henrico Weather
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2PM update on the post above: But once the cold air finally begins to move, it MOVES! Warmer air is pushing up in ernest, bringing heavy rain, thunderstorms and flash flooding. Temps in Short Pump have jumped up to near 50 and should continue to climb the rest of the afternoon. Just plain nasty, nasty weather. See 2PM radar capture below. 

Screenshot_20200206-141000_nbc12weather.jpg

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The satellite image below illustrates very well how Richmond is quite often on the battle line for snow events. Usually we are on the southern boundary, but sometimes the scenario is reversed and we end up on the northern extent of the event, as was the case yesterday.

If we are on the southern end, it's usually temperature related. If we are on the northern end, it's generally moisture related (as in lack of). Many times there is such a sharp gradient from no snow to a bunch of snow, you could literally cross from one to the other in the distance you could jog a half-marathon. 

The satellite image shows a clear delineation between snow and no snow in our area, with the line going  diagonally from SW to NE. Varina/Enon had accumulating snow, but the amounts dropped sharply to nothing as you went just a few miles west into central Chesterfield and Henrico. 

So, just remember to be kind to your local weather forecaster when their snow forecast doesn't quite pan out. It's darned near impossible to predict exactly where that boundary will set up, and a variance of just a few miles can make all the difference in the world. 

Screenshot_20200221-110352_Wunderground.jpg

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Going to the north, there is not much significant snowfall coverage until extreme northern PA into Upstate NY.    

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26 minutes ago, Shakman said:

Going to the north, there is not much significant snowfall coverage until extreme northern PA into Upstate NY.    

Yep. And almost all of Ohio, West Virginia and most of Connecticut, Rhode Island, Massachusetts, Indiana and Illinois have nothing to next-to-nothing on the ground. Truly exceptional for this time of year. 

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