Archive for October, 2011

Final Snowfall Totals
October 30, 2011

By Meteorologist Mike Skurko

Here are the official snowfall totals for Saturday’s storm.  These numbers come from trained spotters for the National Weather Service.  The 32.0 inches in Peru, MA was the highest in New England, followed by 31.4 inches in Jaffrey, NH and 30.8″ in Plainfield, MA.

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The 540 Line
October 24, 2011

By Meteorologist Mike Skurko

In our last entry we looked at the potential for snow in western Massachusetts late Thursday.  At this point, that possibility still exists.  I wanted to discuss a little further about the topic of atmospheric thicknesses…something that I pointed out on a computer model that would indicate the potential for snow.

A little Meteorology 101…whenever the air cools, it contracts.  When air is warmed, it expands.  Weather models can quantify how much the air expands and contracts by taking a look at pressure levels.  About 20,000 feet up is the “500-millibar pressure level”…which is the height where the atmospheric pressure is about half of the pressure at the surface (which is roughly 1000 millibars).  When the air cools…the 500mb pressure level falls because the air contracts.  When the air warms…the 500mb pressure level rises higher because the air is expanding.

The title of this blog “The 540 Line” refers to the difference in height between the 500mb pressure level and the 1000mb pressure level (which is roughly the surface).  If the difference between these two pressure levels is 5400 meters…then the 540 Line gets placed there on a weather map (5400 meters is technically converted to 540 decameters)

In the early days of forecasting and weather research, a group of meteorologists found that for areas located on this 540 Line…it snowed 50% of the time there was precipitation.  Thus this 540 Line has been used as a benchmark for assessing where that rain/snow line will be in forecasting winter storms.  If you ever read through weather forums and more advanced technical discussions…the 540 Line is often one of the first forecasting tools mentioned for assessing a winter storm.

Taking a look at this computer model below, this is a projection of 8PM Thursday night.  I’ve circled the 540 and traced the 540 Line in orange.  You can see how it goes right through Massachusetts, while ample precipitation is still hanging around.  Could this be our 50% chance of snow?

Snowflakes possible in a few days
October 23, 2011

By Meteorologist Mike Skurko

It’s true…we’re looking into a very real possibility of our first snowflakes in western Massachusetts this week.  The image below is a computer model from the National Weather service for 2 AM Friday (very late Thursday night).  As you’ll notice on our 7 day forecast, this will be the low pressure system responsible for the scattered rain showers Wednesday and Thursday.

When the low passes through New England, it will wrap in significantly cold air behind it.  The dotted red and dotted blue lines represent “atmospheric thicknesses”…basically the smaller the thickness value is, the colder the air will be.  The thickness values coming in behind the low are very capable of producing snow.  If enough precipitation is still behind the low when that cold air settles in…SNOW!  Those shaded areas of green and blue represent precipitation, which you can see are still lingering across western Massachusetts into the overnight hours.

Now one other note…there is much more to snow and wintry mix forecasting than those thickness values.  We also need to look at some vertical profiles/cross-sections of the atmosphere for a better idea if and when it will be cold enough at the surface for snow to stick.  Those more detailed computer models start coming in about 72 or 84 hours from a particular event.  Stay tuned!

World Series & Weather
October 19, 2011

By Meteorologist Mike Skurko

A few weeks ago, we looked at some of the anomalies between weather and the upcoming NFL season (see the entry from September 8).  I thought we’d give the World Series a try as well…who has the edge? Warmer vs. colder cities?  Wetter vs. drier cities?

First for temperatures, I looked at the annual average temperature for each city that has played in a World Series.   In the 107 World Series played in the modern era, the colder city has won 47 times and the warmer city has won 44 times (16 World Series have been contested against teams from the same city).  This includes three straight wins by the cooler city…Philadelphia in ’08, New York in ’09, and San Francisco in ’10.  Looking at this year’s matchup between Texas and St. Louis would give this “cooler” edge to St. Louis.

Looking at annual precipitation it’s even closer.  The wetter city has won 46 times and the drier city has won 45 times (again, 16 World Series being played by teams from the same city).  This would also give a slight edge to St. Louis, which averages about four more inches of rain per year than the Dallas-Fort Worth area.

Therefore, if these weather odds gave any indication of the winner, the slight edge would go to the St. Louis Cardinals.  But because these numbers are so close, it wouldn’t be surprising if Texas forces them to game 7.  I guess the World Series really could be dubbed the “Fall Classic” since the cooler, wetter city has won a few more championships.

Fall colors close to peak
October 17, 2011

By Meteorologist Mike Skurko

The fall foliage is currently hitting its peak color across the Berkshires, and there should be more peak coloring spreading across western Massachusetts in the days to come.  Weather-wise, we have a lot of rain on tap for Wednesday, but high pressure should return for the weekend…perhaps our best weekend for leaf watchers across the Pioneer Valley.  Conditions will be seasonal and sunny, and much more of western Massachusetts will be hitting their peak fall colors.

Doomsday Comet Misses Earth
October 16, 2011

By Meteorologist Mike Skurko

From time to time, some astronomy may sneak into our Weather Blog.  That is the case tonight as the “Doomsday Comet” approached our planet today…or at least what was left of it.

The Comet Elenin passed within 22 million miles of earth, but perhaps as more of a trail of debris instead of a still-intact comet.  According to NASA, the 2 to 3-mile wide comet was likely broken up in August by a huge solar storm, as astronomers had trouble locating the comet’s exact position after that.

For space standards, Comet Elenin was rather mundane.  It was the internet that began to spiral its devastating possibilities into the “Doomsday Comet” among conspiracy theorists.  Some say this comet was actually a run-away planet named Niburu.  Even the comet’s discoverer, Russian astronomer Leonid Elenin did not believe any of these claims, or that it would have any impact on Earth.

Perhaps the biggest conspiracy story about the doomsday prophecy of this comet comes from the name itself.  If Elenin was spelled out as E.L.E.N.I.N, some thought this stood for “Extinction Level Event, Niburu is Near.”  [Do you remember that name “ELE” or “Extiction Level Event” from the movie “Deep Impact”?]  Well, even though Elenin was a miss, a new doomsday comet will probably find another story for conspiracy theorists soon.

Why so windy?
October 15, 2011

By Meteorologist Mike Skurko

Some Meteorology 101 for you tonight…this afternoon’s wind gusts got above 30 mph at times, peaking at 33 mph at both Chicopee and Westfield.  The reason for the windy conditions is a phenomenon known as the “pressure gradient force”.  It is what governs the movement of air through our atmosphere.

Generally speaking, the large-scale movement of air will flow in the direction so that low pressure is to its left, and high pressure to its right.  For example, if a low is to the west and a high is to the east, the air will flow to the north.  The opposite…if a low is to the east and a high is to the west…means the air will flow to the south (from the air’s perspective, this would keep low pressure to its “left side”).  This is established through some complicated physics that boils down to these general principles…known as the pressure gradient force.

As today’s surface map below shows, low pressure has been stationed to our north, while high pressure sits to our south.  This means the air in between the two systems will be moving from west-to-east on the map…so the low is to the air’s “left side” as it is traveling.

The speed of the air is determined by the magnitude of the pressure gradient force.  The more drastic the pressure changes over a shorter space…the larger the pressure gradient force is…and thus the larger the wind speed is.  As you’ll notice on the surface map, there are many gray circles that tighten in on the low pressure center in Canada.  Each one of those rings represents a different pressure value.  Because they are so tightly packed, that means the pressure is changing very drastically in these broader regions.  This large pressure gradient force here in the Northeast is why we were so windy today.

Origins of Indian Summer
October 14, 2011

By Meteorologist Mike Skurko

Earlier this week, we enjoyed a nice stretch of weather here across New England…many calling it an Indian Summer.  But what does that actually mean?  What qualifies a stretch of weather as an Indian Summer?

The exact origin of an Indian Summer is unknown, but the earliest recorded reference to this term was by French-American writer St. John de Crevecoeur in 1778:

“Sometimes the rain is followed by an interval of calm and warmth which is called the Indian Summer…it arrives about the middle of November, although snows and brief freezes often occur long before that date.”

There are a few different theories as to why the name Indian Summer was coined.  Some speculate the Native Americans would use this brief period of warmth to do some extra hunting and gathering before winter. Others say that Europeans dubbed it an Indian Summer because it was a “fool’s summer,” teasing people with the warmer weather so late in the year (Europe and Native Americans didn’t get along). Another possibility has been linked to the fairer weather at this time of year in the Indian Ocean, when ships leaving America or Europe would load up more cargo to take advantage of the calmer seas so late in the year.

In the present day, the American Meteorological Society defines an Indian Summer as:

“A period in mid or late-autumn of abnormally warm weather, generally clear skies, sunny but hazy days, and cool nights.  At least one killing frost and preferably a substantial period of normally cool weather must precede this warm spell in order for it to be considered a true ‘Indian summer.'”

The definition is very general, as it does not include any specific thresholds for dates or temperatures. For western Massachusetts, I’d say we fit the definition when high temperatures a few days ago were in the mid-80s.  That would easily qualify as “abnormally warm”.  We also had “generally clear skies” and at least one killing frost beforehand (October 6th and 7th).  It is also possible to have another Indian Summer if we see another one of those abnormally warm stretches later this month, or even in November.

Columbus’ weather discoveries
October 10, 2011

By Meteorologist Mike Skurko

Christopher Columbus is credited with discovering America…but did you know he may also be responsible for two important weather discoveries?  Now I want to note, these reports are centuries old and likely contain missing/conflicting details, but the broader discoveries seem to hold merit among historians.

First, it is believed that Columbus made the first documentation of the Atlantic circulation.   In the tropics, the winds blow from east to west (known as the trade winds…the reason hurricanes move in that direction as well).  In the north Atlantic, the flow is from west to east.  See the image below, and focus on the gray arrows:

Columbus used this to his advantage on his voyages across the Atlantic.  When he left Spain, he sailed south to position his ships in the trade winds. On his return, he took a more northerly route to use the north Atlantic westerly winds.  Columbus’ records show  his route was not a direct line to the Indies and back, it was more of a circle…following this Atlantic circulation.

Second, there is speculation that Columbus made the first documentation of tropical cyclones.  Returning to Spain from his first voyage in 1492, Columbus’ ships encountered two storms near the Azores.  From his descriptions of the size, intensity, and characteristics of these storms, they may have been tropical storms or hurricanes.  Another, more definitive, report of a hurricane came in the West Indies during Columbus’ second voyage in 1495.

Can it frost above 32 degrees?
October 7, 2011

By Meteorologist Mike Skurko

Temperatures plummeted across western Massachusetts both Thursday morning and this morning.  However, not all locations that received frost officially dropped to 32 degrees, and the definition for issuing a frost advisory (see previous blog entry) doesn’t even need it to.  How can this be?  How can the temperature stay above freezing, but widespread areas of frost still occur?

All official temperatures are observed about 6 feet off the ground.  Accordingly, most forecast models across the world make predictions for temperatures 2 meters off the ground, not directly on the surface. That means the forecast may call for a low of 35 degrees, the official temperature will actually be 35 degrees, but the grass on your lawn is at 30 degrees…cold enough to generate frost, even though the “official” temperature was above freezing.

This can especially happen on clear, calm nights (like our last two) by a process known as radiation cooling.  On a clear and calm night, the ground quickly loses the heat it absorbed during the day.  Since cold air is denser than warm air, a pocket of cold air will sink below a pocket of warm air*. Thus, the earth can cool off more than the air just a few feet above, as that coldest pocket of air remains at the lowest point to the ground.

*[On a side note…This is why cold air from a cold front undercuts the warm air ahead of it, causing it to rise and grow into thunderstorms]