At 3 PM this afternoon, Memphis had the highest heat index reading in the entire United States.  Our heat index at that time was 109 degrees.  We didn’t have the highest temperature, but noone else felt as hot as we did!  It must be late July….Sorry if this is your first summer here!

Check out the map below of the United States Heat Index as of 3 PM

Last week as Hurricane Dolly was making its way on shore in southern Texas a question was posed by a reader of this blog regarding hurricane wind speeds.  Here’s the question:

off-topic question, but with new Hurricane Dolly, just wondering….how come the winds are reported only in 5 mph increments? Yesterday she was at 60, earlier today at 70, now at 75. Not that it would make any difference, but what if the actual winds were only 72 or 73 mph? Do they round it up? I mean technically, if winds never got above say, 73, they couldn’t categorize it as a hurricane, could they?

After reading the comment I realized that I knew wind speeds were reported in 5 mph increments and I thought I knew why but I wasn’t 100% sure.  So, I posed that question to the meteorologists at the National Hurricane Center in Miami.  Here’s their response:

Thanks for your e-mail. 

Winds speeds in the official advisory are posted in 5 mph increments as that is the highest degree of accuracy that we have at this time for measuring wind speed.

The Hurricane Specialists are in agreement that the margin error in a wind speed measurement is as high as ten percent.

Best regards,

Dennis Feltgen

Public Affairs Officer

Meteorologist

National Hurricane Center

Miami, Florida

So there you have it, the “official” answer to the question.  If you have a question regarding weather just leave it in the comment box below and we’ll answer it for you. 

We are currently tracking an MCS (Mesoscale Convective Complex) system diving down our way from Missouri.  There are a couple of thunderstorm watches associated with this storm complex.  I am hopeful, and cautiously optimistic most of the main energy will either weaken or move East of us.  It is, however, something to carefully watch overnight in case it were to hold together.  It is possible rain or thunderstorms could affect the Northern parts of our area.  You definitely want to check in with Ron Childers tomorrow morning for information on our latest forecast.

A heat advisory has been issued by the National Weather Service and it does include Memphis and Shelby county.  In fact, here is the graphic below straight from the website of the Weather Service.  The counties highlighted in Orange are included in the advisory.

When an advisory is issued it means heat index values could approach the danger level of 105 degrees.  I suspect this is the first advisory of many over the next several days or so.  Our hottest weather of the summer season is expected as High pressure in the Mid-levels of the atmosphere dominates and anchors itself over the Mid-South.  Drink lots and lots of water even if you are not thirsty. 

I hope you have a good rest of the weekend.

I got this today from NASA regarding the mysterious Aurora Borealis and Aurora Australis, aka Northern and Southern Lights.  Scientist have figured out way they occur.  I found this very interesting and thought I’d pass it along.

On a clear night over the far northern areas of the world, you may witness a hauntingly beautiful light display in the sky that can disrupt your satellite TV and leave you in the dark.

The eerie glow of the northern lights seems exquisite and quite harmless. Most times, it is harmless. The display, resembling a slow-moving ribbon silently undulating in the sky, is called the aurora. It is also visible in far southern regions around the South Pole.

Images above: These are photos of the aurora before and during a substorm. The left image is the typical appearance of the aurora before a substorm. During a substorm, the single auroral ribbon may split into several ribbons (middle image) or even break into clusters that race north and south (right image). Credit: Jan Curtis

Occasionally, however, the aurora becomes much more dynamic. The single auroral ribbon may split into several ribbons or even break into clusters that race north and south. This dynamic light show in the polar skies is associated with what scientists call a magnetospheric substorm. Substorms are very closely related to full-blown space storms that can disable spacecraft, radio communication, GPS navigation, and power systems while supplying killer electrons to the radiation belts surrounding Earth. The purpose of NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is to understand the physical instability (trigger mechanism) for magnetospheric substorms.

Just like meteorologists who study tornadoes to understand the most severe thunderstorms, space physicists study substorms for insight into the most severe space storms. “Substorm processes are fundamental to our understanding of space weather and how it affects satellites and humans in the magnetosphere,” said Vassilis Angelopoulos, THEMIS principal investigator at the University of California’s Berkeley Space Sciences Laboratory, in Berkeley, Calif. Scientists propose two possible triggers for substorms, but until now, there has been no way to distinguish between the two models.

Discerning between the two proposed substorm trigger mechanisms is difficult because the magnetosphere is so large. Over Earth’s night (solar wind down-stream) side, the solar wind stretches the magnetosphere far past the moon’s orbit, to form the geomagnetic tail. Substorms start from a small region in space inside the geomagnetic tail, but within minutes cover a vast region of the magnetosphere. However, the two proposed trigger mechanisms predict substorm onset in distinctly different locations within the geomagnetic tail, so the key to solving this mystery lies in identifying the substorm point of origin.

Down-stream alignments have been carefully planned to occur over North America once every four days. For about 15 hours surrounding the alignments, 20 ground stations in Canada and Alaska with automated all-sky cameras will document the aurora from Earth. The combined spacecraft and ground observations will give scientists the first comprehensive look at the phenomena from Earth’s upper atmosphere to far into space, enabling researchers to pinpoint where and when substorm initiation begins.

If you went for an early morning walk or jog or if you just went from your front door to your car for the drive to work, then you probably noticed that it wasn’t nearly as muggy as the last few mornings.  A weak cold front moved south of the Action News 5 coverage area yesterday and high pressure in the upper midwest built in behind the front.  This helped to take a big bite out of the humidity overnight.  The high will bring an east northeast wind to the area today which in turn ushers drier air into the region and that makes for a noticable dip in the humidity.  Afternoon highs will also be a bit cooler as afternoon highs in the lower nineties as opposed to the mid and upper nineties that we’ve endured for much of the week. 

Don’t get too accustomed to this break from the excessive heat and humidity as it will be making a comeback.  A warm front will push north through the region Friday.  This will return a southerly flow by Friday afternoon resulting in warm moist air advecting into the area.   The frontal passage will also likely trigger a few scattered showers and thunderstorms.  A warm and muggy pattern will settle in behind the warm front making for a swealtering weekend.  Highs Saturday will be in the mid to upper nineties and then Sunday we’ll have afternoon highs approaching the century mark.  With the heat of the day and increased moisture flowing into the Mid-South it is also possible that a few isolated afternoon or evening thunderstorms could pop up, however, most of the area and the weekend will be dry.  The hot, muggy, and mainly dry trend will continue through the middle of next week.   

In the tropics:  Hurricane Dolly came on shore in southern Padre Island, Texas Wednesday as a borderline category 1 category 2 hurricane with maximum sustained winds of 90 to 100 mph.  Many areas received 10 to 12 inches of rain with some areas getting as much as 20 inches of rain.  As of 10 AM EDT Dolly had been downgrade to a tropical storm with maximum sustained winds of 45 mph.  Dolly was still dumping a tremendous amount of rain on southern Texas and north central Mexico.  The storm will continue to produce torential rain in the area today as it makes a slow trek to the west and becomes a topical depression by late today or tonight. 

Elsewhere in the tropics a large area of low pressure is located in the open waters of the Atlantic about 650 miles west of the Cape Verde Islands.  At this time the system does not look to be favorable to strengthen into a tropical depression but will still be monitored closely as it moves westward toward the eastern Carribbean.

Get ready for searing heat on Monday as highs climb near the Century mark and heat index values exceed 100.  A heat advisory is in effect, as the danger level of 105 likely will be reached concerning the heat index.  The good news though, is a frontal boundary will likely break the heat late Tuesday and Wednesday and bring us better rain chances.  It doesn’t mean the heat is going away, it just means that the mercury won’t be quite as oppressive.  Here’s the front as it stands right now…

In a respect this is true, but when you are talking about temperatures in the middle and upper 90s the heat is a big factor.  But when you combine that kind of heat with relatively high humidity, a very uncomfortable heat index can “take the life out of you” this time of year.  How do we come up with the heat index? Check out this table below.

Expect the heat index tomorrow to climb above 100 degrees in many spots.  Slow it down if you will be outside for any length of time and always drink plenty of water.

Whenever we’re expecting high temperatures in the mid 90s, it makes me wonder who’s got it or had it worse than us. 

Let’s be real.  I’m certainly not whining about our conditions.  There are portions of the U.S. that hit triple digits with at least a small degree of regularity this time of year.

Almost three years to the day Las Vegas had one heckuva 24 hour period.  According to the National Weather Service in Las Vegas the low temperature for July 19, 2005 was 95 degrees!  The high temp hit 117 degrees (tied a record high), leading to an average temperature of 106 degrees.  I don’t know about you, but that’s hot enough to ponder a plunge into the fountains outside the Bellagio.

Closer to home, get ready for weekend temperatures in the mid 90s with heat indices slightly higher.  Not close to record highs, but Summer enough for me.

Have a great weekend.  See you on the air!

The Forecast:  The heat kicks in once again today as high pressure continues to keep the Mid-South hot and dry.  The incoming sunshine combined with a dry surface will push afternoon temperatures into the mid nineties today and tomorrow.  Dry air from the north and east has been filtering into the area for most of the week but that trend is about to change.  A southerly flow will return Friday.  This will bring Gulf moisture into the region gradually increasing humidity each day through the weekend and well into next week.  We’ve dealt with a dry heat for most of the week but as we get into the weekend the heat and humidity will combine make it feel much warmer even though afternoon highs will remain in the low to mid nineties.  The one positive aspect of the increasing humidity will be a slight increase in our chances for rain.  By the end of the weekend and into the beginning of next week we’ll likely see a few isolated to widely scattered showers and thunderstorms popping up during the late afternoon and early evening hours.  Even with those typical summertime pulse thunderstorms dotting the area, most of the daytime hours and most of the Mid-South will be hot, muggy, and dry. 

CODE ORANGE TODAY:  A light east wind along with dry weather has allowed the airmass over Shelby and the immediate surrounding counties to become a bit stagnant.  This allows pollutants to build in the atmosphere.  As a result,  ozone levels are expected to reach unhealthy limits again today.  This will primarily affect small children, the elderly, and people with breathing difficulties such as asthma and emphysema.  The best way to combat this will be to limit outdoor activity today especially during the later afternoon hours when ozone levels typically peak.

In the Tropics:  Bertha continues to trudge along.  Now a tropical storm, Bertha is located in the open waters of the Atlantic about 355 miles east of Bermuda.  Maximum sustained winds are 60 mph and the storm is moving southeast at 10 mph.  Bertha should make a turn to the north overnight and then move northeast into the colder waters of the Atlantic where it will likely die. 

In the Carribbean a couple of storms are being monitored.  One is in the western Carribbean near the Lesser Antilles.  This broad area of low pressure has become a bit more unorganized today but will still be monitored as the warm waters in the area could give it the fuel it needs to regroup.  Another system is off the coast of Honduras and Nicaragua.  It is producing torrential rain and has the potential to trigger major mudslides in the hilly coastal regions of the two counties.  Right now the storm system is a tropical wave, which is an elongated low pressure system that moves from east west over tropical water, but could be upgraded to a tropical depression before coming on shore overnight or tomorrow.  \

The waters in the Gulf of Mexico are warm but calm at this time and no tropical storms are expected through the weekend.  However, there is a low pressure system located over Central Florida this morning.  It is not likely to become a tropical system but it is producing a tremendous amount of rain over central and southern Florida.  Rainfall amount of three to five inches is likely in many locations today and tomorrow.