Why Were Recent Vermont Storm Forecasts So Bad?

How it began: Forecast from the National Weather Service
issued Sunday afternoon for the storm that hit
Sunday night and continued into Monday. 

 We've had three pretty substantial winter storms here in Vermont since November 27. One of the storms, on December 4, was pretty well forecast. 

The other two storms, one on November 27 the other Sunday and yesterday, were not so well predicted.

The storm on November 27 was surprisingly ferocious. What was expected to be mostly a rain storm turned out to be a wet, sloppy snowstorm that cut power to as many as 34,000 Vermonters.

The most recent storm was supposed to be something of a monster. We were variously warned to expect Flooding, widespread heavy, wet snow, travel trouble, widespread power outages and strong winds.

Even just 12 hours before the storm hit, it was supposed to be bad. As we all know, it was just.... meh.

Are local meteorologists suddenly falling down on the job? Have all the computer forecasting models gone haywire?

Nope and nope.

Winter storms in New England are notoriously hard to predict. I don't think I've ever seen a Vermont snowstorm that played out precisely as forecast. More often than not, the storm predictions are quite accurate, but you're going to get a few surprises somewhere no matter what. 

However, two of the recent storm forecasts fell short. That was mostly due to very slight forecast inaccuracies that had big real-life effects

WHAT WENT WRONG?

In all three recent storms, temperatures hovered very close to the freezing mark. It's normally no big deal if you predict a temperature of say, 34 degrees and it ends up being 32 degrees. Close enough. When there's a lot of precipitation around, that ever so slight error in temperature can mean surprise snow, or an unforeseen wet washout. 

Both relatively poorly forecast storms were mostly a case of just slight errors in precipitation intensity. Those very minor mistakes had super noticeable effects.

In the November 27 case, the storm was stronger than forecast, which increased the intensity of the precipitation.  Heavier precipitation tends to cool the atmosphere more than lighter sprinkles and inconsequential snow.

Since temperatures were just a little above freezing at the start of the November 27 storm the extra oomph of moisture dropped temperatures just a degree or two below what had been expected. The result was that very unpleasant surprise snowstorm and power outages.

The storm Sunday and Monday had the opposite problem. The storm - and its associated precipitation - turned out to be less intense than expected.

It was still a very wet storm, especially for this time of year. Almost all of Vermont had at least an inch of rain and melted snow, and some places had two inches.

Still, it was less precipitation than expected, especially at the stage of the storm when rain was to change to snow.

There was lots of moisture available to the storm, so it did look like we were in for a lot of snow. What was to be an intense storm moving northward through eastern New England turned out be only of moderate strength. v

How it ended: Map of actual snow totals from 
storm that ending Monday afternoon. As you can
see, it was noticeably less than expected.

That means there was less lift in the air than anticipated, so the precipitation once temperatures fell to near the freezing mark wasn't so intense. 

 In the valleys, the temperature stayed up by a degree or so because of the less intense precipitation. So what was to have been a wet, heavy snow was just a yucky slush bomb.

For instance, in Burlington, the temperature stayed at 33 or 34 degrees for the entire snow event, so the National Weather Service measured just 1.9 inches of new snow. 

Even where it was a bit colder, at slightly higher elevations, an expected band of intense snow never materialized.  So most everybody got just four to seven inches of snow, with just a couple spots seeing eight or nine inches.  That was well short of the 12 to 18 inches that was expected.

Forecasters do get bonus points for accurately figuring out where the deepest snow would accumulate. It just didn't pile up as much as planned.

At least in this second wrong forecast, the effects of the storm weren't as bad as feared, so any frustration with an off prediction was tempered by relief things turned out OK.

The National Weather Service office in South Burlington also has a range of forecasts with each storm.  They offer what amounts to a 10 percent chance of storm over-performing, and a 10 percent chance of it under-producing.

This latest storm was just slightly larger than the 10 percent chance of a whiff - meaning lighter snow.

Of course, there is one success story in here. The December 4 storm played out pretty much as meteorologists expected.  Sure, there was a little more rain instead of snow in the valleys, but the forecast was fairly close. 

For the latest storm, there were still nearly 2,500 homes and businesses in Vermont without power as of 8 a.m. today. Even though the storm was less intense than forecast, it still had some real impacts,

As far as this week goes, the only weather trouble I see is the potential for briefly heavy snow showers this evening. That could make some slick spots on the roads, but accumulations should be under an inch for almost everybody, except maybe some spots in the northern Green Mountains.

Those of you who are frustrated by some winter storm forecasts that don't turn out as planned: Remember this: Forecasts as little as six or 12 hours before the storm will give you a general idea of what will happen. 

The storm will almost always turn out to be a little more intense, or a little less dramatic than the forecast indicates. If meteorologist say you will see four to eight inches of new snow, that's probably what will happen, but be prepared for a little more or a little less, just in case. 

Storms Unexpectedly Avoided Vermont Sunday; Meanwhile Canada Deals With Sat. Derecho

Chaotic looking clouds, but no real storms over 
northern Vermont Sunday. Despite forecasts, there
was a lack of severe weather in Vermont Sunday.

 It really did seem like Vermont was primed for severe weather on Sunday. As we all know, that didn't happen. 

An interesting part of this is that the storms were expected to be most focused in northern Vermont.  Instead, most of the activity that formed was south and east of us in the Hudson Valley of New York, southern New England and the Middle Atlantic States.

Maine also experienced some activity. 

A map of storm reports from Sunday shows almost nothing in northern New England, where the bulk of damaging storms was forecast. 

I am puzzling a bit over the lack of storms, though I have some ideas. First of all, we should be happy there weren't severe storms, as who wants to deal with the damage and problems they cause?  But still, the forecast was wrong, and I'm sure local meteorologists are analyzing why. 

I have training in meteorology but am not a full-blown meteorologist, so I tend to defer to the experts.  One thing I noticed late Sunday morning and afternoon was that the clouds that were in the sky had a sort of "stable" look to them, like there wasn't anything triggering a lift.  It made me wonder a little if the predicted storms would develop. I guess my gut was right in this instance.

I didn't mention this in my updates to this here blog thingy Sunday, as I didn't want to contradict the messaging coming from real meteorologists. Adding my doubts to a volatile forecast would have been confusing to readers. And perhaps some people would have let their guard down if I expressed my doubts. Then, had severe storms developed, there was a chance that whoever read my posts might be unprepared. 

Anyway, the rest of the ingredients were there. It was quite humid, as we well know. A cold front was approaching, which would have created lift in the atmosphere, creating that severe weather risk.

The thinking was a line of storms would form just ahead of the cold front, with renegade strong storms out ahead of it.  

The blue and occasional green dots on this map indicate
reports of severe thunderstorms Sunday. Note that northern
Vermont and New Hampshire, which were considered
the most likely target for severe weather Sunday,
had no reports of damaging winds or big hail

That is precisely what tried to happen. I saw pop up showers on radar quickly form in Vermont, mostly along the west slopes of the Green Mountains and then race eastward. But they didn't grow into severe storms and sort of just petered out on their way toward the Connecticut River Valley. 

Strong winds aloft can make thunderstorms worse. But under certain conditions, the strong winds can rip the top off thunderstorms, stopping them in their tracks. I wonder if that was part of the problem with Sunday's situation.

Meanwhile, that expected line of storms sort of, kinda formed in New York and crossed into Vermont in the late afternoon and evening. But there was no lightning and the showers were wimpy.  The line of basically sprinkles did produce a gust front with winds of 30 to 35 mph.

You might have noticed it turned a bit hazy during that period of northwest wind gusts. That was sort of a pollen haboob.  The gust front blew tons of pollen from trees and other plants.  Allergy sufferers in northern Vermont must have had a rough Sunday evening. 

I think this line of wannabe storms didn't materialize into something strong because stable air was running out ahead of the actual cold front, which was right behind this little gust front thingy.

On the bright side, the forecast for the today and tomorrow is easy. Just nice. High clouds might dim the sun at times today, but it will be refreshingly cool and dry, with highs in the low 60s.

The coldest hollows of the Northeast Kingdom and Adirondacks are at risk for some frost tonight, but the vast majority of us will be fine, garden wise. Tomorrow looks nice, too, with highs a little warmer, approaching a near-normal 70 degrees or so.

CANADA DERECHO

We in Vermont really dodged a bullet Saturday. True, there were some severe storms around. However, a deadly derecho in southeastern Canada missed us by a mere 100 miles or so. 

The derecho, which swept across some of the most populated regions of southern Ontario and Quebec, killed at least 8 people and caused widespread damage.  At least a half million people lost electricity. The storms were so powerful that some large metal transmission towers toppled in the winds, which gusted as high as 85 mph.  

Trees bend in hurricane force winds in this screen grab
of the derecho in Ontario Saturday.

The derecho originated in Michigan and swept through the Toronto metropolitan area and then on to Ottawa.  It weakened somewhat by the time it reached Montreal and Quebec City, but was still powerful enough to cause damage there. 

As in many derechos, the damage was concentrated in some towns while others got off with relatively light damage. The town of Uxbridge, north of Toronto, and Clarence-Rockland, east of Ottawa, suffered considerable damage to buildings, to the point where a number of homes in those communities are too damaged to be occupied.  

It might take a week or more to get power back to everyone in the derecho zone. 

Videos. As always, if you don't see the image of the video on your screen, click the hyperlinks. : 

The derecho sweeps into downtown Ottawa:

The title of this video is "Ottawa Rain Storm"  You're telling me!