MWN Lightning Round: On heat, haze, and high-latitude auroras

It's once again time for the MWN Lightning Round, in which we hit a few different topics in rapid succession and let you get on about your day, armed with insightful new information!

Heat Builds as High Pressure Expands

A hot day was once again tempered just a bit by thunderstorm-induced cloud cover today, although high humidity values still pushed the heat index over the century mark this afternoon. With a large upper-level ridge continuing to expand the next two days, fewer storms are expected, thus we expect highs to reach their full potential in the mid to upper 90s. Combined with dewpoints in the 70s, we'll see heat index values near or exceed the danger level of 105° Tuesday and Wednesday. Practice the heat safety tips below and check out our complete guide to staying safe on a Memphis summer day!

Remember also that successive hot days have a cumulative effect and heat illness can occur more quickly in the same heat when there is less opportunity to recover from previous days. Overnight lows in the upper 70s can provide little relief.

Walk Like an Egyptian - in the Saharan Dust

If our previous article on a lone thunderstorm casting a shadow into Alabama wasn't enough to convince you, we have another example of how weather hundreds (or thousands!) of miles away can affect an area.

You may have noticed on your way home from work today that the sun seemed filtered and the sky hazy when looking off in the distance. Although there was a veil of high cirrus clouds from earlier thunderstorms, there also was a noticeable haze. It wasn't just summertime urban air pollution you were seeing. In fact, it was a thin veil of dust from the Saharan desert!

The dust was transported across the Atlantic Ocean into the southern U.S. on trade winds. This is the same dust that is sometimes mentioned in Atlantic tropical discussions as a deterrent to tropical organization. The dust was even mentioned in today's air quality forecast discussion issued by the Shelby County Health Department:

A combination of local emission sources and transported Saharan dust are creating very hazy skies as the particles are easily remaining suspended in the very humid conditions over the Mid-South. 

We've written one other time about dust that actually accumulated on vehicles and outdoor objects - that was April 2014 from dust storms in the Central Plains. This dust has a much more exotic origin and won't be enough to create a coating, but is reducing visibility just a bit. The image below shows the concentration of Saharan dust over the Atlantic Ocean and into Central America and the southern U.S.

Saharan dust thickness at 7pm Monday is shown in this model graphic from WxBell Analytics.

Storms Originating on the Sun Reach Earth

Another long-distance connection - this one farther than the Sahara to the Mid-South - is occurring today as well. A geomagnetic storm on the sun hurled multiple coronal mass ejections (CMEs) at the Earth over the past couple of days. Today, the strongest of these reached our magnetic field and prompted space weather warnings indicating a blackout of low-frequency radio waves over North America. The "Planetary K-Index" is a scale used to measure the strength of these waves, which are then tied to expected impacts. The index spiked this afternoon at a magnitude 8. This is strong enough to have some effect on power grids, radio waves, and communication with aircraft, as well as on orbiting spacecraft.

The Planetary K-Index spiked at a level 8 this afternoon as a strong CME bounced off the earth's magnetic field.
Image courtesy SWPC.

In addition, strong CMEs tend to produce more vivid aurora borealis, which can be seen further south from the poles as they get stronger. Some northern U.S. locations could have a decent chance of seeing the aurora tonight if skies are clear. While there is some chance of aurora dipping farther south, it is highly unlikely we'll see the northern lights in the Mid-South.

An aurora map produced by KATV meteorologist Ryan Vaughan (@ryanvaughan on Twitter) indicates a low probability of  aurora viewing into the central U.S.

More really cool graphics, animations, and information can be found on the Space Weather Prediction Center's homepage.

Erik Proseus
MWN Meteorologist

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The Top 11 of '11: Mid-South weather stories from MWN (part 1)

Everybody does Top 10 lists to end the year (or daily if your name is David Letterman), so MWN decided we should too.  Only once we put together the list of Top 10 Mid-South weather stories of 2011, the list was 10+1, or 11 if you are up on your 1st grade math!  So we decided that since it was 2011 we were talking about, we'd make an exception and call it the "Top 11 of '11".  No word yet on whether there will be 12 next year... so without further delay we bring you (in true Letterman fashion, counting down from 11) the first 3:

"The Top 11 of '11" - Mid-South Weather Stories from MemphisWeather.net

# 11. Aurora Borealis appears in Mid-South skies
On the evening of October 24 around 9pm, I was checking my Twitter feed when people started reporting seeing a red glow in the sky across the southern states, including many Mid-South locations.  Reports from NC to AR, including locations as far south as northern AL and MS, were flooding my feed of mainly weather and news accounts. Quick sleuthing and some timely and informative tweets pointed to the event being a rare Aurora Borealis, which resulted from a coronal mass ejection from the sun early that afternoon. The image below was one that I highlighted in a blog post that evening that further described the event, including what causes the Aurora and why it was red.  While not unprecedented, it has been years since the Aurora has been visible this far south in the U.S.  Perhaps more of this type of solar activity will be possible as the lately-dormant sun enters an active sunspot period that peaks in a little over a year?

Aurora captured in Corning, AR on October 24, 2011

# 10. MWN at the forefront of social media nowcasting
While not a "weather event," one of the facets of weather reporting that has taken off in the past year is the explosion in nowcasting the weather via social media.  Nowcasting is very-short-term forecasting, most often encompassing only the next 1-4 hours.  More and more, operational meteorologists, broadcast professionals, and even enthusiasts are turning to Facebook and Twitter to update their audience on current weather events and solicit reports, particularly during severe weather episodes.  Even the National Weather Service has begun using social media.

MWN is proud to have been at the forefront of this new style of weather reporting, having started nowcasting for the Memphis metropolitan area nearly three years ago in the spring of 2009.  Thanks to some wild weather in greater Memphis this past year (more on these events as we continue the countdown) and momentum generated during our first couple of years on social media, MWN's nowcasting service quickly became well-known.  We are proud to say that we went "wall-to-wall" for every severe and winter event in 2011 and the growth in our follower-ship responded accordingly, tripling on both Facebook and Twitter!  Thank you for trusting us to keep you updated, safe, and informed during hazardous (and even placid) weather conditions!

• AP story on nowcasting, featuring MWN's Erik Proseus and David Drobny of Nashville
• "Tennessee Matters" interview with Erik on nowcasting, which was heard on the Tennessee Radio Network (MP3)
• MWN nowcasting on Facebook and Twitter

Exposure produced by MemphisWeather.net tweets on February 25, 2011

# 9. Addition of key team members helps MWN expand it's presence
There will be plenty of weather events in our Top 11 (in fact, we're saving many of the top spots just for those), but one other weather "story" for MemphisWeather.net this year was the addition of a few individuals to our team that allowed us to grow exponentially and expand our product and service offerings that directly benefit you.

• Though not employed by MWN, one of the best decisions I made in early 2011 was contracting with Ben Deming (@bendeming) to design and code our first-ever mobile applications.  Ben possesses a very broad skill set that allowed him to develop not only our iPhone app, but also an Android app, and assist with other minor software and server-related issues.
• Late this summer, a decision was made that, to continue to keep up the ambitious pace that MWN had grown to, we needed some help. The search began for individual with basic meteorology knowledge that was also teachable, interested in social media, and a good communicator, among other things.  It didn't take long to find the person who has evolved into my right hand man - social media nowcaster and blogger, Kevin Terry (@jterry0).  Kevin quickly embraced the mission of MWN, took over a sizable part of the nowcasting requirements, and allowed me to work on expanding MWN's presence through new services and marketing efforts.  Kevin will remain with MWN through at least June 2012.
• Though those are the two individuals I deal with most often, there are certainly others whose contributions have allowed MWN to rapidly expand this year.  They include: Wayne Randall, owner of IT company Nextek, whose generous offer of server space in his data center ensures the reliable delivery of products and services to MWN; Amy Howell (@howellmarketing) and Alys Drake (@alysdrake) of world-class marketing firm Howell Marketing Strategies, who assist in making sure the MWN story is told; and countless others in Memphis and Mid-South social media and business circles who help us disseminate our words and information to the masses - you know who you are, and we thank you!

Those are the first 3 of the "Top 11 of '11"! We'll reveal a couple more each day through New Year's Eve here on the MWN Blog  (and I promise they won't be weighted nearly as heavily on MWN but much more about actual weather events!).  What Mid-South weather event do you think should be #1 this year?

Rare Aurora Borealis (Northern Lights) visible over parts of the Mid-South

Parts of the region have the pleasure of experiencing a very rare Aurora Borealis, or Northern Lights, this evening.  We have seen reports from northeast AR, west and middle TN, northeast MS, north AL, NC, VA, and many places in the northeast U.S.

This particular aurora event was caused, according to SpaceWeather.com, by a coronal mass ejection (CME) that occurred around 1pm CDT today [10-24-11] and hit the Earth's magnetic field. The website states that "according to analysts at the Goddard Space Weather Lab, the impact caused a strong compression of Earth's magnetic field" and subsequent geomagnetic storm.  A CME (often associated with a solar flare) is an explosion on the Sun that happens when energy is suddenly released, producing a burst of radiation. Strong flares can reach the Earth's magnetic field, like the one today.  There is plenty of additional information for science "geeks" (like me!) at SpaceWeather.com and on Wikipedia (including animations and video).

It is very rare to see the Northern Lights this far south and red auroras are somewhat rare as well.  The red color is not completely understood, but scientists believe that they occur much higher above the Earth than typical geomagnetic storms (300-500km) and sometimes occur during intense geomagnetic storms. [More technical details on red auroras can be found here.]  The picture below was taken by Jay Malone in Corning, AR on Monday evening. Enjoy!

Photo of Aurora Borealis over Corning, AR on 10/24/11, courtesy Jay Malone

Did you see the aurora?  Let us know below, or send any pictures to photos@memphisweather.net.

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