Rare Asperitas Clouds Announce Frigid Vermont Cold Front, Freeze Warnings Coming For Tonight

Relatively rare Undulatus Asperitas clouds over 
St. Albans, Vermont Tuesday. These preceded a 
cold front that will give us a nasty spring
freeze tonight. 

 Our big cold front that came through yesterday did manage to give us weather nerds a treat. 

Rather rare Undulatus Asperitas clouds appeared overhead, just ahead of the cold front. 

This is a "new" cloud in that they've only gotten their own meteorological classification in 2015, when the World Meteorological Organization agreed to classify this previously poorly documented cloud.

Us weather geeks get pretty wound up when we see these clouds because they're pretty rare, and nobody agrees on how they form, unlike most other cloud types. 

You need unstable air to create these clouds, but the air is often unstable. In most cases, those clouds don't form. For some reason on Tuesday, they appeared.

As the British Met Office tells us, many scientists think they are associated with thunderstorms. However, the  Asperitas clouds   have been spotted often enough when no thunderstorms were nearby.  Yesterday in Vermont  was an example. No thunderstorms were nearby when they appeared. 

The clouds are often associated with rain, and a few light showers came through not long after they appeared. Video of these clouds from Tuesday is at the bottom of this post. 

THE COLD FRONT

That cold front meant business yesterday, Temperatures in some parts of Vermont crashed by 20 degrees in an hour. Ahead of the front, temperatures were near 70. A little behind it, readings were in the mid and upper 40s. 

Temperatures continued to drift down overnight and by this morning, some people were near freezing. I noticed a bit of ice on my truck in St. Albans, Vermont early today. 

It will not warm up much today, with highs in the 45 to 52 degree range with gusty north winds. 

There's still a wildfire hazard today. The cold front deposited very little rain, and some places didn't get any at all. An overcast over northern Vermont early this morning should break up later. In the meantime, I wouldn't be at all surprised if a few places are seeing a snow flurry or two this morning. But that won't amount to anything. Thank goodness for that. We don't want a snowstorm. However, rain would be nice, and it's not in the cards. 

Very dry air and those gusty winds will ensure the underbrush out there remains pretty parched. Any fires that start could spread really fast, so be aware and be careful with any flames. 

The Vermont Department of Forest, Parks and Recreation rates today's fire danger as very high, which is a pretty rare designation covering the entire state. 

THE FREEZE

If anything, forecasts for tonight's subfreezing temperatures have gotten a little worse. Above freezing temperatures will probably be limited to the immediate shores of Lake Champlain. By the time you read this, the National Weather Service in South Burlington will have issued a freeze warning for the entire state except the Northeast Kingdom.

The NEK is not in the warning because the growing season is not considered to have started yet out there. 

If you haven't done so already, bring your sensitive plants inside. I do worry that in some colder areas that already have leafed out trees, those leaves will get damaged. That would leave things looking pretty ugly into June, as we'll have to wait until blackened and wilted leaves are replaced by new ones,

This won't be a widespread problem, but I wouldn't be surprised to see a few spots have this issue.

Temperatures also now look marginal for fruit crops in the Champlain Valley.  As I said yesterday, blooms on apple trees can hang in there if the temperature stays above 29 degrees. Other fruit crops can survive temperatures down to about 30. It will be close in some areas. 

Thankfully, it will rapidly warm up during the day Thursday, with temperatures bumping up into the 60s. 

We can hope for some rain this weekend, but unfortunately, it doesn't look like much.  There's another chance of frost early next week, but that still looks less widespread or as intense as tonight's freeze.

VIDEO:

Here's a video I shot of the asperitas clouds over St. Albans, Vermont on Tuesday. Part of the video even features a guided tour of the clouds courtesy of a hawk.  End of the video shows cold wind gusts that dropped the temperature from about 70 to 50 in a little over an hour. If you don't see an image below, click on this link to view the video. Otherwise, click on image below to watch: