"Pulse" Storms Make For Gorgeous Summer Skies

A small, isolated storm formed over the Adirondacks around
sunset last evening, as seen looking toward the southwest
from St. Albans, Vermont. 

One of the many things I like about summer is the sky is far more interesting and beautiful than in the winter.

Summer is the time of year when scattered showers and thunderstorms are more likely, without those dreary, boring overcast skies that come in the colder seasons.

Such was the case last evening when isolated thunderstorms erupted over mountainous terrain of northern Vermont and the Adirondacks of New York.

These dramatic looking, but usually harmless and brief thunderstorms often form during these hot, humid days.

There's really no weather systems to create updrafts that would form organized lines of clusters of long lasting storms.    But the atmosphere in these conditions is primed for storms, if only there were a trigger.

That trigger is the mountains. The strong June sun helps creates updrafts that also help cause light local breezes.  If things line up just right, one of these breezes hits a mountain slope and is forced to rise.

That breeze going up the side of a mountain can be just enough to trigger a storm.  That upslope breeze becomes a rapidly rising column of air, which forms almost immediately into a towering thunderstorm, the kind we saw here and there last evening. They go from nothing to immense, often in just minutes

Since these clouds are so tall, they can be seen from very far away. People in the Burlington area saw a gorgeous white tower erupt to the northeast early Friday evening. That storm was near Greensboro, almost 50 miles away as the crow flies.

Beautiful isolated storm last evening in
northern Vermont. Photo via Twitter
by Charlie of Mystery Springs
@SlowWaterMvmnt

Unlike in some hot spells, when haze obscures the best views, the skies Friday were more clear, making the beautiful storms more striking.  They were isolated, so looking east, the low angle sun turned the clouds brilliant white, surrounded by a deep blue background.

Some lucky bastard up near Greensboro was probably treated to a brief downpour for their garden, and maybe a lightning strike or two.

These so-called "pulse" storms die pretty much as fast as they form.  Remember, there's no real weather system, or cold front, or boundary to continue the updraft.

Once they move beyond that mountain that caused the initial updraft in the first place, the storm collapses. The process from initiation to dissipation can take less than an hour.

I did say these pulse storms are usually harmless. But there is one moment - when they're dying - when they can become momentarily dangerous.  The storm collapses, often in a very localized gush of wind and heavy rain.

This collapse could become a very local microburst, in which wind is strong enough to cause damage in a very small area.  One end of a street might have fallen trees from this type, while a mile away, there was just a gentle breeze.

Timing out these collapses is hard, and since they're so local and quick, they're often over and done with by the time the National Weather Service can issue a storm warning.

On some occasions, a pulse storm can keep forming in the same location all afternoon and evening, and just not move. In those cases, you can get a small area of dangerous flash flooding while immediate surrounding areas remain dry.

These two hazards only sometimes happen. More often than not, a pulse storm will quickly collapse and die with no danger involved. That's why they're called pulse storms. They quickly form, then quickly fade. It was just a quick pulse.

After we lost the Greensboro storm last evening, a couple others formed in the Adirondacks, contributing to a gorgeous sunset as the orange light lit up the towering clouds to our west and south.

If you missed these beautiful storms last night, not to worry. The weather pattern is kind of stuck in this hot, humid, still and featureless set up.  This will favor more scattered, slow moving and brief "pulse" storms today, Sunday and Monday.

They tend to start forming in the early to mid afternoon on these hot days, and fade with the setting sun.  The storms tend to avoid large valleys, so we in the dusty Champlain Valley will just be bystanders, begging in vain for just a little rain from these brief showers.

A weak cold front will approach us during the upcoming mid to late week.  That will provide enough forcing for more sustained, and somewhat more widespread showers and storms starting perhaps on Tuesday and continuing into Wednesday.