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It's cool, it's hot.... It's fall! Plus an awesome look at Igor
Submitted by Tim Buckley on Tue, 09/14/2010 - 8:24am.
This time of year can often be a difficult one for your wardrobe. Cool mornings with hot afternoons are typical as we start to head into fall - and that's just what we're seeing now.
Take today for example. Many areas dropped down to near 60 degrees this morning, a refreshing start which was the coolest morning for many areas since a cool spell around July 4th. This afternoon, we'll be up into the low 90's in most areas - making for around a 30 degree temperature difference between our high and our low. This is often referred to as a 'diurnal range' by meteorologists, and 30 degrees is a large diurnal range for sure.
During the summer, our diurnal ranges tend to be smaller - in our area typically in the 15 to 20 degree range. This has a lot to do with the level of humidity present in the air. If you think about it, the more water content present in the air, the harder it is to heat it up or cool it down. Just like it takes a longer time to bring water to a boil than it does to heat up air to that same temperature.
On the flip side, if you have low water content in the air, it becomes easier to heat it up or cool it down. So, low humidity climates tend to have the highest temperature ranges. In deserts, it's not uncommon to have diurnal ranges of 40 or 50 degrees compared to 10-15 degrees in the tropics.
Right now, the low humidity in the area is allowing these large temperature swings to happen, which is typical as we head into September and October. Dewpoints in the 50's will make for nights in the 60's and highs in the 90's in some places over the next few days, meaning it is possible to have a cool morning and a hot afternoon. Adjust your wardrobe accordingly!
Now onto the ominous Hurricane Igor, who is still alive and well on this Tuesday starting off the day again as a healthy Category 4 storm. The good news today is that we're starting to see the beginning signs of a curve to the north, with some motion to the WNW. Heading into the next few days the forecast calls for more of a northwesterly track as a trough of low pressure picks up Igor and helps to steer him around the sub-tropical ridge.
Igor has certainly been a photogenic hurricane so far. It's almost textbook with its symmetric structure, its well defined consistent eye-wall and shear size. One of the best ways to look at a storm is through visible satellite images which actually show you the texture of the cloud tops. Check out this awesome looping image courtesy of the University of Wisconsin.
This is such a great shot because it slows down the loop to one minute intervals letting you get a slow motion look at the storm. You can really see it's spinning siphoning structure with the rain bands feeding the energy into the inner eye wall. Not to mention a great look at the eye itself, which is showing what some meteorologists call a 'stadium effect'.
Of course we can enjoy looking at images like these as long as the storms stay far away from a landfall near us. At this point that looks to be the case with Igor, and that's good news.
That's all for now.
By: Tim Buckley