Thursday, June 21, 2012

Dew Point vs. Relative Humidity: FIGHT!

Welcome back! Hopefully you're reading this in a cool place, out of the searing heat that has taken up shop over the eastern United States! But I hope you're finding a way to enjoy the heat too! As I said in the last post, that's why we invented pools! 

Now, heat is one thing. Humidity is what makes a heat wave especially tough to deal with. All of that water vapor in the air makes it hard to breathe, hard to cool off, and just downright uncomfortable. It is also during these hot spells that you start hearing a lot about the relative humidity and the dew point when you watch your local weather reports. But what does that all mean, and which one is a better measure of just how humid it is out there? That's what we're about to find out. Let the debate begin! Dew point temperature vs. relative humidity! DING! DING!

First up, what the heck is the dew point? It is the temperature to which you would need to cool the air in order to saturate it. In simple terms, it is the temperature at which dew would form if the air were cooled off. As such, it is a direct measure of the amount of water vapor in the air, and thus a direct measure of just how humid it is. The higher the dew point temperature, the more humid and moist the air is. Dew point is a parameter that always exists with the day-to-day weather. The reason we tend to talk about it more during hot weather is because it causes far more dangerous and noticeable effects in warmer air than in cold. For some more details on those detrimental effects, see my previous post "Summer Arrives by Kicking in the Front Door." For reference, here's an index for the ambient dew point and the comfort level.

Source: http://home.comcast.net/~rodmanjd/weatherlink/archives.htm

So what about the other player, relative humidity (RH)? We hear about it year-round, but what exactly are you being told when you see a relative humidity of, say, 79% ? In all honesty, not a whole lot. The first problem with relative humidity is right in the name. It is a "relative" value, and is actually dimensionless, acting simply as a percentage. But a percentage of what? Relative humidity is formally defined as the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Confusing, right? The best I can do to clarify that definition is to that the RH tells you how much water vapor is in the air relative to how much would be there if the air were cooled to the dew point. (Doesn't really clarify things does it?) Another problem with relative humidity is that it is not an absolute figure. That is, it is not a tangible figure that you can feel, touch, or measure. It is simply a mathematical ratio and a function of moisture content and temperature; the second half of the formal definition relies on temperature. As confusing as that may sound, does anything about that jump out at you? Since RH is a function of moisture content and temperature, it actually relies partly on the dew point! So when all is said and done (thanks for hanging in there, by the way...), relative humidity does not directly indicate the amount of water in the air. It does not tell you how humid the air actually is.

Then why even mention the relative humidity in a weather forecast or report? That's more of an opinion question, and is left more to the discretion of individual meteorologists. Some use it, some don't. (Personally, I don't care for it in my own forecasts.)

So they've duked it out, exchanged some haymakers, and left a black eye or two, but who comes out on top when it comes to measuring how humid the air actually is? Dew point looks like our clear winner! So, the next time hot weather rolls in to town, if you want to know how humid it is, look up the dew point temperature and see where it falls on the comfort index! After all, Summer has only just begun!

Thanks for reading!

Until next time...

Tuesday, June 19, 2012

Summer Arrives by Kicking in the Front Door!

Hello everyone, and welcome back!

This is just about as fitting as it gets! Summer officially begins on June 20 at 7:09 PM, and will it ever feel the part! We're staring down the barrel of what will likely be the first heat wave of the year in many parts of the eastern United States, though we don't expect it to be an official heat wave here in New York and New England. However you spin it, we are looking at some seriously hot weather! With that in mind, let's talk heat safety!

When dealing with excessive heat and humidity, it is immensely important to know your limits and the limits of the human body. Normal body temperature usually sits at 98.6°F and is generally considered the optimal temperature for the body to conduct its metabolic processes. The harder the body works, the hotter it gets, and the body needs to be able to cool itself through processes such as sweating in over to avoid overheating. This cooling process becomes increasingly difficult as the heat and humidity rises, as high humidity impairs the body's ability to cool through sweating. When the air is dry, water evaporates from the body more readily and thus cools the body more efficiently. On humid days, the presence of more water vapor in the air tends to limit the amount of water that evaporates away from us, and causes the body to hold on to heat. Add to that increased heat from the environment, and it doesn't take much for our bodies to start to overheat, causing a condition called hyperthermia (the opposite of hypothermia, where the body loses too much heat and begins to shut down). In such cases, heat exhaustion or heat stroke can quickly develop, and can be deadly if not treated in a timely fashion. Before we go on, here's a list of heat-related ailments and their symptoms:

SUNBURN: Redness and pain. In severe cases swelling of skin, blisters, fever, headaches.


HEAT EXHAUSTION: Heavy sweating; weakness; cold, pale, clammy skin; thready pulse; fainting and vomiting but may have normal temperature. 

HEAT STROKE (or sunstroke): High body temperature (106° F or higher), hot dry skin, rapid and strong pulse, possible unconsciousness. 

So, how to protect yourself and loved ones when hot weather rolls in to your area? Well it's all pretty basic stuff, but the simple things can go a very long day!
  • Limit strenuous outdoor activities, such as yard work and exercise to the early morning or late evening  when daytime heating is at a minimum.
  • Stay hydrated! Avoid alcoholic beverages, soda, or other caffienated drinks. 
  • Dress in lightweight clothes and light colors. Brighter colors tend to reflect heat and sunlight, rather than dark colors which absorb them.
  • Dial back your protein intake. The body has to work harder to digest meat and other high-protein foods, which in turn can raise your body temperature. 
  • Spend more time in air conditioning out of the sun, or have a cool shady spot to retreat to. A/C is your best friend during periods of extreme heat!
  • Don't forget the pets! Limit their walks or time outdoors to morning or evening if possible. Keep them in a cool place with A/C or a fan and make sure to keep them hydrated too!
After all of that, don't forget that you can have some fun on hot days! (Just do it safely!) That's what the pool, the beach, or the sprinklers are for, right? Hang in there, and stay cool!

I'll leave you with the forecast and some other important info about the impending heat...
Heat Advisories have been issued for the Hudson and Mohawk Valleys of New York  from 12:00 PM - 8:00 PM Wednesday. Temperatures are expected to each the mid 90s with heat index values over 100°

Heat would be one thing, but the humidity really makes things difficult to deal with. Dew point temperatures are expected to be in the upper 60s to low 70s, which means an oppressive air mass. All the more reason to stay cool!
Regional forecast for Wednesday, June 20.
Here's a bonus look at the 7-Day Forecast for the greater Capital Region. Record highs on Wednesday and Thursday in Albany are 97° so we will certainly be in the ballpark. Humidity drops on Friday!

Until next time!

Monday, June 4, 2012

Astronomical Lightning Round

Hello and welcome back! There certainly has not been a shortage of weather headlines in recent weeks. Tornadoes, tropical storms, severe thunderstorms, wildfires have dominated the news and even prompted the word "biblical" to pop up. (I think that's a bit over the top, but I guess that's how you grab attention...anyway) While a lot has been going on here on Earth, space has been putting on shows of its own in rapid-fire succession! And we're not done yet! We've seen two eclipses in the last 3 weeks, and we're in for one more event, and this one is once in a lifetime! We'll get to that in a little bit...

Every year here on Earth, we are treated to four eclipse events, 2 lunar and 2 solar. Lunar eclipses occur when the Moon moves through Earth's shadow as it orbits the planet, while a solar eclipse occurs when the Moon moves between the Earth and the Sun. As you'd probably expect, lunar eclipses are much easier to view than solar eclipses since you need special eyewear to be able to look at the Sun. In fact, the Sun's light can be even more damaging to your eyes during a total solar eclipse, but that's a topic for another day!

It all started back on the evening of May 20 with the year's first eclipse event. Unfortunately due to the way things just happened to play out, we missed this event here in the eastern U.S., but folks in the west were treated to what is called an annular solar eclipse. So called because the Moon does not completely block out the Sun, but rather it leaves a ring of fire around its edges, as long as you are in the right location on Earth to see it. Luck will come our way eventually, but here's a little sampling of what we missed.






Jacob Thumberger in Gail, TX was in exactly the right place to catch the height of the eclipse.





Folks in Minnesota got lucky right as the sun was setting and caught at least a partial solar eclipse!
And here's a great timelapse of photos taken in California!

I would love to tell you that we'll get our chance during this year's second solar eclipse, but we will miss out on that one too. Only people in the southern hemisphere will be able to witness it. We may have to wait until sometime in 2013!

So that was all well and good. We missed that solar eclipse solely because it didn't begin until after the Sun had already set here in the east. Unfortunately, we were robbed again just this morning (June 4)! June's full moon, known as the "strawberry moon," came along with the first lunar eclipse of the year. This was only a partial eclipse with only 38% of the Moon falling under Earth's shadow at its climax. By astronomical conditions, we would have been able to see it right before sunrise here in the eastern U.S., but the weather here withing our own atmosphere had other plans. With our stubborn weekend storm system still sitting and spinning over the region, overcast skies never even offered us a chance to sneak a peek at the moon. Areas that were clear enough to see it though, caught quite a show!

Dennis Mammana took this shot from Borrego Springs, California at the height of the eclipse. Earth's shadow only made a glancing blow, but made for a great snapshot!

OK, so we're 0 for 2 thus far, but we've got one more celestial event coming up on the evening of June 5 that in this case will literally be once in a lifetime! This time around, it doesn't even involve our Moon, but rather the planet Venus! Shortly before sunset tomorrow, Venus will move across the face of the Sun in what is known as a transit event. Since Venus is obviously much farther away than our moon, it will not block out the Sun, but rather appear as a visible dark dot moving across the solar disk. These transits are rare events that occur in pairs, over 100 years apart. June 5th's transit will be the second in the latest pair, following the last one in 2004. Tomorrow's event is being called once in a lifetime since the next one won't occur until the year 2117! 

Here in our area, the transit will begin shortly after 6:00 PM and will take a little over 7 hours. That in mind, we will have just about 2 1/2 hours for viewing in our area, assuming the weather cooperates. Now, like anything involving the Sun, you don't want to look directly at it without protective gear. A popular item would be to use #14 welder's glass, if you can get your hands on some. But in any event, use caution when trying to view this event. (Let's hope the weather breaks just long enough to give us a chance. Skies are expected to be mostly cloudy here in New York and New England.)




This shot was taken a few weeks ago as Venus began its trip toward the upcoming transit. When seen through a telescope, Venus goes through phases just like our Moon.













And a shot of the 2004 Venus transit taken by the Dutch Open Telescope in the Canary Islands.










So happy hunting tomorrow evening! Keep your fingers crossed for clearer skies! 

Thanks for reading!

Until next time...