Archive for July, 2011

July in review
July 31, 2011

By Meteorologist Mike Skurko

July was hot and dry to say the least.  We had ten 90-degree days this month, which isn’t that far from the seven that we average every July.  However, we had a bunch of warm days in between too.  Our average high this month registered 87.3 degrees, about 2.4 degrees above normal.  Even our average low of 64.6 degrees was about 2.3 degrees above normal.

For rainfall we had a very dry month, but are still in a surplus of precipitation for the year.  July only recorded 1.72 inches of rain, while normally we have 3.67 inches for the month.  This puts our precipitation totals 1.95 inches below normal for July, but we’re still 6.13 inches above normal for the entire year…thanks mostly to a very active winter and a very rainy spring.

[Source Bradley Int’l.]

Sunspots Return!
July 29, 2011

By Meteorologist Nick Morganelli

Solar scientists study the sun and watch for changes. They also monitor solar weather. The sun does have an atmosphere of which most of that is the layer called the chromosphere. We see part of the sun’s atmosphere during a total solar eclipse. This is the corona just beyond the chromosphere.

We also look for sunspots on the sun’s surface or photosphere.  What are these dark irregularly shaped areas? They are highly magnetic areas with a north and a south pole and are thousands of degrees cooler than adjacent areas of the sun’s surface. Theses spots can expand and contract and are directly linked to the sun’s energy output. When sunspots are active, the sun sends more energy towards earth. The number of spots change in what we call solar cycles. Solar cycles last from about 9 to 14 yrs. The solar minimums are usually brief, lasting only a few years. This is when sunspots are few or none are seen. However, in the 17th century the sun plunged into a 70 yr. minimum of spotlessness known as the Maunder Minimum which remains to be fully understood.   When sunspots are visible, there is an increase in solar flares or Coronal Mass Ejections. These ‘explosions’ hurl charged particles at the earth in the order of one million miles per hour. In about 3 days, they reach earth and are drawn towards our magnetic poles, which by the way protect us from many harmful effects of the sun including these flares. These are the particles that excite atoms in the upper atmosphere to create the Northern and Southern Lights, or auroras. There’s so much to the sun that we continue to study. Too bad we cannot land on it. That just might answer a lot of questions….. My favorite website to monitor the sun’s weather is http://www.spaceweather.com

Microbursts
July 28, 2011

By Meteorologist Mike Skurko

Last night, the National Weather Service classified the recent storm damage in Wilbraham as a result of a microburst, not a tornado.  You may have heard the term microburst before, but let’s talk about what it is exactly.  The definition of a microburst is an intense downdraft of air that hits the ground and spreads out in all directions causing straight-line wind damage.

In a thunderstorm, updrafts are pockets of warm buoyant air that help the storm clouds grow vertically.  A downdraft is just the opposite…pockets of cooler air that will sink back down towards the ground.  When heavy rains encounter dry air, this will cause significant evaporation and cool the air quickly.  If this occurs rapidly enough and the mass of cold air becomes large enough, it will accelerate quickly to the ground (cold air is denser than warm air and will always want to sink).  This pocket of cooler air will slam into the ground and propagate outward.

Imagine dropping a pebble into water.  The pebble hitting the water would be the downdraft hitting the surface.  The ripples would be a visual of the fast-moving winds propagating out in all directions.  Those winds from a microburst can be as strong as small tornados.  In the case of Wilbraham, the peak winds from this downburst were estimated at 90 to 100 mph in the Tinkham Road area.  If you recall the sun was out and it was a pretty dry day right before those storm clouds arrived, helping that microburst develop.

The National Weather Service can survey the damage and determine whether a storm produced a microburst or a tornado.  For a microburst, the winds are all moving outward from a central point…and thus the trees will all fall in that same direction.  For a tornado, the trees would fall inwards and create a spiral pattern from the twister’s rotating winds.

Doppler radar and tornados, part II
July 27, 2011

By Meteorologist Mike Skurko

Yesterday, a tornado warning was issued for eastern Hampden County at about 4:30pm when National Weather Service Doppler radar indicated a tornado.  I also looked at the Doppler radar signatures of this storm yesterday, and yes it was a textbook tornado signature on the radar.  Now many televisions stations have a Doppler radar, but do you know exactly what a Doppler radar is?  If you think it’s the shades of color indicating rain showers and thunderstorms…you’re wrong.  In fact, a Doppler radar has little to do with detecting precipitation at all.

A Doppler radar is used to measure wind speed and direction.  It utilizes the Doppler Effect, the phenomenon that makes the sound of a car change its pitch as it passes by.  The frequency of the car’s sound wave is higher as it approaches you and lower as it moves away from you.  The same principle can apply to the wind.  A Doppler radar will send out a signal, which then gets reflected back by rain and rainclouds.  A Doppler radar can tell if the winds (and the storm cloud) are coming toward the radar or going away from the radar based on the changes in frequency that get reflected back.

If there is a drastic change in wind direction over a very small area, that may indicate a rotating cloud. Imagine a plate sitting on a table…if you want to rotate the plate, you have to push it on one side in one direction and pull the other side in the other direction.  So, a true “Doppler radar” has only two colors – green and red.  Green indicates motion toward the radar, while red indicates motion away from the radar.  Different shades of green and red will depict different wind speeds.

That is what happened just east of Chicopee on Tuesday – a significant red spot appeared next to a significant green spot.  Since both were associated with a strong thunderstorm, it is assumed that a strong rotation is occurring around a small central point.  Therefore the tornado warning was issued.

While our CBS3 Pinpoint Doppler radar (and any other station’s “Doppler radar”) does have the capability to detect these velocity fields, we rarely use a true “Doppler radar” image on air. The image of showers and thunderstorms on any nightly newscast is just a general precipitation radar. The images produced by a Doppler radar are very hard to interpret by the general public (as you can imagine by the explanation above).  In fact, at Penn State University, I had entire classes devoted to interpreting radar imagery.

Here is a sample of a true Doppler radar image from the National Weather Service from a tornado outbreak in Arkansas:

Doppler radar and tornados
July 26, 2011

By Meteorologist Mike Skurko

During this afternoon’s tornado warning, we repeatedly mentioned on-air that there was yet to be an official confirmed funnel cloud on the ground.  Right after we finished our 4pm newscast, the National Weather Service in Boston issued a statement at 4:28pm which said:  NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO.  So this asks the question if conditions are capable of producing a tornado, why isn’t it just a watch instead of a warning?

The reason is due to the limitations and complications of radar technology…so bear with me on the explanation.  The National Weather Service was 100% correct in issuing a warning in this case.

A Doppler radar has the ability to detect a rotation within the clouds of a thunderstorm.  If the rotation is strong enough, a funnel cloud may be forming. The radar is tilted slightly up and out to the sky, giving it the ability to detect those thunderstorm clouds and any rotation within the cloud.  However, the radar is not able to “see” anything occurring down at the ground.  It would useless to point the radar at the ground because there are no clouds there, and buildings/trees/etc. would get in the way.

Therefore in the case of a tornado, the radar has no idea if a funnel cloud has actually touched the ground.  All it knows is that there is a rotation up in the clouds.  Whether the tornado is touching the ground or not, the image on the radar will still look exactly the same.  The National Weather Service will then issue the warning, because there is a possibility that the tornado is actually occurring.  There is no time to wait for an official confirmation.  If they do receive confirmation, they will change their bulletins to say “a tornado has been spotted…”

Introducing our new weather blog
July 25, 2011

By Meteorologist Mike Skurko

Hello Western Mass!  It’s time to open up the official CBS3 Pinpoint Weather Blog.  There are so many interesting aspects to weather that we can’t cover in our newscasts…whether it’s more discussion about our weather in the Pioneer Valley, interesting weather phenomenon across the country, or fun facts and figures…you can find our team of meteorologists writing about them here.

From time to time, we’ll also use this blog to educate about the weather.  Why the sky is blue, how hurricanes form, and why cold fronts trigger thunderstorms are just some of the topics you will be able to find here.  Weather myths, weather in sports, and weather in pop culture will also be discussed.

Keep checking back here for the latest CBS3 Pinpoint Weather Blog entries…or follow us on Facebook and Twitter, where we will also post our latest entries for you to enjoy.

“Tonight’s forecast…dark.” – George Carlin