A Summer Of Upper Level Lows Creates Strange Weather, We Are Experiencing The Latest Now

Upper level forecast map from NOAA for this
evening. One upper low spinning over northern
New England, and another northwest of Washington
State heading southward toward northern California.

 This is ending up being the summer of odd upper level cut-off low pressure systems that are all promoting strange, and sometimes dangerous weather here and elsewhere in the nation. 

An upper level cut off low is a storm in the upper levels of the atmosphere that's separated - or cut off- from the jet stream. 

Since the jet stream isn't there to push them along, these upper level lows - which are really pools of cool air aloft - tend to meander and move slowly. That, in turn, causes sometimes extended periods of unsettled, bad, or even dangerous weather. 

The latest of these upper lows is over us now.  I wouldn't say what we're experiencing this time is especially dangerous, though it does have its hazards.

Our current upper low is over-performing, as so many weather systems have lately. It's stronger and more persistent than many previous forecasts indicated. It's producing more rain than prior predictions hinted at too.  It's pretty damn chilly under this thing, too. 

Some places around Vermont will have near record low high temperatures today. Burlington missed that record by just two degrees Tuesday, as it only reached a high of 62 degrees. Burlington won't break that record today.  The lowest high temperature on this date was 58 degrees in 1982.  It was already 58 degrees as of 

I had said for the past several days that the rain with this system would fall far short of creating any flood risks. 

It turns out that it actually might cause issues, but the risk is pretty low. The upper low is pretty much right over us, which means any showers that get going today will move very slowly. 

This afternoon, the contrast between the meager (and I do mean meager) warmth near the surface and the very cold air aloft will give the showers a convective feel. Instead of the bland gray overcast with light rain we had this morning, things will evolve into tall billowing clouds which could produce local downpours. 

NOAA's Weather Prediction Center has actually put us under a marginal risk of excessive rains or local flash floods today. 

I still don't think this will end up being a major issue, though. There might be local, minor problems, but as you've surely noticed, we're lacking the deep tropical humidity that can lead to torrential downpours. So we're not going to have flood havoc today. 

Satellite view of a cut-off low centered over central
New England on the evening of July 29. This 
system would go on to cause a devastating flood
in the Northeast Kingdom of Vermont
several hours after this pic was taken. 

But since scattered afternoon downpours might have such a slow forward motion, we'll have local issues with ponding of water on roads, and minor washouts here and there, especially where recently repaired roads and driveways haven't been packed down and stabilized yet after prior flood damage. 

OTHER CUT OFF LOWS

Other upper level cut off lows have caused strangeness, and worse, scary danger here and elsewhere this summer. 

It was a meandering upper level low that tapped into deep tropical moisture that unleashed horrendous downpours on the Northeast Kingdom back on July 30.  We all know the calamity that caused. Don't worry, nothing like that will happen today in Vermont. This is a completely different situation. 

A more recent upper level low (related to the one we're dealing with now) contributed to dangerous flooding in and near Toronto last Saturday and deadly flooding in Connecticut on Sunday. 

Yet another cut off low is heading southward along the Pacific Northwest coast. It promises to briefly interrupt a very hot, dry summer in California and probably will lead to a very rare summer snowfall up high in the Sierra Nevada mountains. Snow levels could go as low as 7,600 feet above sea level.

Strong, dry winds ahead of this system are likely to stir up California, Nevada and Oregon forest fires today, making them especially dangerous. 

I'm not sure whether these upper lows are related to climate change or not.  Likely not. But the torrential rains associated with some of them probably are. As the atmosphere warms, it can hold more moisture. Meaning that when you get "perfect" setups, like July 30 over the Northeast Kingdom, it means the downpours end up being heavier than they would have been decades ago. Meaning bigger disasters. 

As for our that upper level cut off low meandering overhead in Vermont today, it will get a push to move slowly to the northeast and out of our hair by Thursday night. By Friday and the weekend, we should be back to our regularly scheduled, late summer warm but not hot weather.