Wednesday Afternoon Vermont Freeze Update: Possibly Worse Than Earlier Forecasts

Visible satellite view this afternoon. Those big choppy
clouds over northeastern Vermont, Quebec, northern
New Hampshire and Maine represent the core of the 
coldest air aloft. Notice the smaller clouds in western
and southern Vermont signaling the coldest air
aloft is departing. But the clear skies in New
York will move in, creating perfect conditions
for a frigid, possibly record breaking cold night. 

 We should start this with a caveat: It's always really tricky to predict the severity of a weird cold snap, even hours before it happens. Especially the nighttime temperatures. Any number of factors could make things worse than forecast, or not as bad as forecast. 

You don't know which way it'll go until after it happens. 

That said, some signs late this afternoon are kind of pointing to lower temperatures than previously forecast. Record lows are a now more likely. The record low tomorrow in Burlington is 29 degrees. Earlier forecast pegged tonights low at 33 degrees. Now, they're saying it'll get to 30 in Burlington. 

In Montpelier, earlier forecasts had lows in the upper 20s. Now, the forecast low is 24 in Montpelier, The record low is 28 degrees in Montpelier, so they should beat that. 

For one thing, it was cloudier today than originally expected. There were even snow flurries in many, many towns across northern and central Vermont. We didn't see any accumulation, but the snow flakes in the air weren't necessarily making people happy. 

The clouds held afternoon temperatures down below what they would have reached had there been more sunshine. 

At 4 p.m. today, around the time of day when the high temperature is set, it was still only 39 degrees in Montpelier. Burlington was at 46 degrees, compared to a normal high of 70 degrees. 

All this means that temperatures won't have as far to fall to reach the freezing point, and could go lower than what was forecast. 

Another problem is the reason why the clouds hung tough. An upper level pool of very cold air, some of the coldest upper air temperatures on record for this time of year, lingered stubbornly, centered over the middle of Quebec. 

The instability caused by this cold pool helped create the clouds and flurries. The cold upper level gyre started moving out more slowly than forecast, so temperatures high up aren't recovering as fast as they would have had this stupid thing moved faster. 

That will help encourage colder overnight temperatures. 

However, the cold pool is now moving away in time for cold high pressure with clear skies and light winds to move in this evening, and stay put all night through dawn tomorrow. Those are perfect conditions for temperatures to fall as low as the possibly can. 

Here's yet another reason to think we're at risk for particularly low temperatures. We have been really dry lately. Over the past two weeks, for instance, Burlington has had just 0.02 inches of rain. If rainfall had been normal, we'd have gotten at least 1.5 inches during that period. 

When the ground is wet, that adds humidity to the atmosphere, making it harder for temperatures at night to fall as low as they otherwise would. Dry ground is not providing much humidity, so that's not a factor. This is a big reason why deserts often have torrid afternoons and chilly nights.

There's also some wildfire smoke aloft due to those fires in Alberta. The smoke would slightly make daytimes cooler by blocking a little sunlight. But unlike clouds, smoke does not prevent temperatures from crashing on clear, calm nights.  

Here's one thing to hope for: If the wind keeps stirring all night, that would hold temperatures up a bit. 

I am worried now about apple crops and such. The blooms on these trees start to die when temperatures reach 29 or lower.  Some areas will get that cold. Luckily, apple orchards on the Champlain Islands will very likely stay warm enough to avoid that scenario.

 We might even see areas where newly leafed out trees actually lose many of their leaves. That happens when the temperature hits 26 or so, or lower. Nice green leaves could wilt or turn black and then fall off. Which is depressing. 

Unless a particular tree is already in rough shape they'll recover and sprout new leaves if this happens. There won't be any long term harm. But, as in my case, the leaves - early this year - are affording me privacy from the road and neighbors. If it gets bad tonight, I'll now have to wait until at least mid-June for that privacy to return. 

We won't know exactly where temperatures bottom out until around 6 or 7 tomorrow morning. It might take until afternoon until we know the extend of frost damage.