I'm sure most everyone noticed the nice haze-free conditions today. It definitely didn't feel like fall today, but the sky resembled it. The reason for this (the tropical air mass over the state) has been mentioned several times already in the forecast and in the blog. I figured, though, that it might be interesting to take a little closer look into summertime haze, and how a tropical air mass can help alleviate it.

First of all, most of my understanding of this process came from reading a paper by Stephen Corfidi of the SPC. In it he gives a detailed overview of summertime haze in the eastern U.S.

Haze is a common phenomenon in the Southeast during the summer. The whole process of how haze forms is fairly complicated, but basically haze is tiny droplets of condensed air pollutants These pollutants are both natural and man-made (anthropogenic), and they are mostly sulfates. There is some debate over whether anthropogenic pollutants are the primary reason for haze, but that is beside the point of this post.

Most people associate haze with warm, humid air moving in from the Gulf of Mexico, but in reality, research has shown that the air in which summertime haze usually forms is modified continental polar air. This continental air brings in both anthropogenic pollutants from Midwest factories and natural pollutants. Many times the air mass has an inversion at 850mb or so, and this traps the pollutants and the low level moisture in a very shallow boundary layer. This is the perfect recipe for haze.

A true maritime tropical air mass, though, is another story. Every now and then during the summer, a "surge" of true tropical air will rush into the Southeast. That is what is currently happening with the low pressure system over eastern Texas. As the system moves inland, it is bringing tropical air with it. Tropical air is more humid than continental air, of course, and that is one ingredient needed for haze. Yet, tropical air is much cleaner than continental air. An air mass that has been over water for days does not accumulate the type of particulates that a mass over land does. Also, a tropical air mass usually lacks an inversion, so the boundary layer is fairly deep, and any pollutants in the air are mixed into a much larger volume of air. So, all of this combined makes for haze-free conditions and a beautiful blue sky (between the clouds).

Drew McCombs
ABC 33/40 Weather Intern
abc3340wx2@gmail.com

The Wednesday afternoon map discussion video is on the web, and also available on iTunes:

http://www.jamesspann.com/

Thanks to everyone for their input on the new video format this morning... I am still tinkering with settings and web server locations... I hope to have everything set for good next week. This is a great time to play with all of this since the weather tends to be fairly inactive in mid-summer, unless we have a big tropical system to deal with.

NICE VISIBILITY: I think everyone has noticed the lack of haze today as the pure tropical air takes over. Visibility is almost like a fall day, and we have been watching rain shafts on the SKYCAMs today... very nice. As I write this a nice cluster of showers is moving into the Birmingham metro area from the west; they dropped 0.06" in Tuscaloosa as they passed through a little earlier this afternoon. Not much lightning with these tropical showers.

MUGGY DAYS: Our disturbance over the far western Gulf will move slowly northward over the next day or so, but the general track of the moisture is in our direction. The GFS hints now that the deepest moisture won't arrive until Friday and Saturday, and for now those seem to be the days with the potential for the greatest coverage of showers and storms. The GFS also hints the best rain totals will come over the northern third of the state, in this kind of airmass a shower is possible almost anytime, anywhere. You can even have nocturnal showers around here.

WEEKEND PEEK: An upper ridge will be building over Alabama this weekend, which will offset to some degree the high amount of low level moisture. Showers and storms might decrease a bit by Sunday and Monday, but trying to determine the aerial coverage of summer showers and storms is almost possible many days in advance. The ole broad-brush will be used for now as we indicate typical summer weather conditions into early next week. Highs should be close to 90, with lows in the 70 to 73 degree range.

The good news is that there is no sign of any runaway heat in coming weeks; we have to wonder if the worst of the summer heat is behind us. Of course, we still have a long way to go this summer.

I have a line of people here needing me to do various things... will have to keep this one short... might make a longer post shortly!

Scattered showers continue over NW Alabama at mid-afternoon. At 2:40, most of them were in the Florence-Russellville-Moulton-Huntsville area.

Further south, Scattered showers were growing over East Tuscaloosa and SW Jefferson County mainly along the Jefferson-Tuscaloosa County line. These showers were traveling NE up I-20/59 and headed toward Bessemer and Birmingham.

All of the showers in the state were moving NE. Not a great deal of lightning so far.

Not too much going on around Alabama early this afternoon with some patches of light rain down south.

However, a group of showers moving toward the NE has spread into NW Alabama, mainly across Franklin, Marion and Winston Counties. The heavier showers were along the Marion-Franklin County line, mostly north of Hamilton.

Those showers are part of a large tropical air mass spreading up from coastal Texas and South Louisiana.

FIRST--A QUICK ALABAMA UPDATE
At 10 o'clock this morning, very little precipitation in Alabama. Only some scattered patches of light rain across the central part of the state. Have you noticed the sharper visibility this morning. We are in a semi-tropical airmass from our great friend--the Gulf of Mexico.

WEATHER BY THE NUMBERS

* 2.21 inches is how much rain fell overnight at Lake Charles, La.

* 1.70 was the Houston total--thanks to a big glob of tropical moisture

* 1.13 inches in Phoenix last night in a big desert storm

* 7 inches is the normal rain amount for Phoenix in an entire year

* 99 mph was the wind gust recorded at the Phoenix Airport Control Tower last night. Lots of power outages

* 104 is the forecast high in Wichita and Wichita Falls, Tex., today as the Plains heat up again

* 126 was the high in Death Valley yesterday. Their Tuesday morning low was 100

* 119 was the high in Bullhead City, Ariz.

* 118 was the high in Needles, Calif.

* 117 days is the average number of days with rain each year in Birmingham

* 36 days is the average number of such days for Phoenix and Los Angeles

* 20 inches is the rainfall shortfall so far this year in New orleans and Baton Rouge

* 18 inches is the total for New Orleans so far this year

* 38.72 inches is the Birmingham total so far (for comparision)

* 7.17 inches is all the rain that has fallen at Black Creek, NE of Gadsden in the last three months. Vic Bell reports that is 10 inches less than had fallen at this time last year.

* 2.18 inches of rain is all that has fallen since April 25 (three months 5 miles north of Gaylesville in NE Alabama, reported by Ron Haltermon. He wonders if their close proximity to Lookout Mountain could be the reason. They are also located in the west slope of Laurel Mountaiin (Is that also known as Dirtseller Mountain...actually a SW to NE ridge)

* 3 cups is all the coffee I have had today...the lowest count since records began in 1938 when I had my first cup.

* 0 is the number of sausage balls or Pop Tarts last 3 months.

* 162 is the number of consecutive days that Marble Bar, in West Australia had 100 degrees or hotter once.

* 87 is the average high temperature in July for Jerusalem, about 4 degrees cooler than Birmingham

* 27th of July was the date of the first named storm in the 2000 tropical season

* 10 names storms in only 35 days after that (an explosion) between August 19 and September 22. Lesson from that: The slow start this season does not mean we will not have an active season.

...enough of this. Much of this information is probably of little or no interest...outta here...

The Wednesday morning map discussion video is on the web, and avalable on iTunes:

http://www.jamesspann.com/

Note the location on the server has changed... just follow the link on the page above to see the video.

Once again, we are rendering the map discussion videos now in the QuickTime format. With the iPod craze in recent years, Quicktime (which is included with iTunes) is installed on 95 percent of computers in the nation, so you shouldn't have to do anything to your system for the videos to play. If by chance you don't have QT, you can get it as a free download here:

http://www.apple.com/quicktime/download

I will be adjusting the exact video files in coming days for the best quality and the best load time. It is all a learning process as I move from the Windows platform over to the OS X environment. And, I will write a post by the end of the week on the journey. I have always been a computer/radio type geek and enjoy stuff like this....

MOIST AIR: A good feed of tropical moisture in the high levels continues over the southern two-thirds of Alabama this morning. Water vapor satellite images shows this moisture coming from our tropical disturbance over the southern tip of Texas, and we even have a few showers in progress this morning over West Alabama's Sumter, Greene, and Hale counties. A few scattered showers and storms should fire up during the day, but the GFS is not as wet as it was yesterday. Most of the good moisture feed for the moment is in the high levels, but low level dewpoints should steadily increase as we go through the rest of the week.The GFS now identifies our best coverage of showers and storms on Friday and Saturday and goes nuts with POPs on both of those days (POP=probability of precipitation).

Bottom line is that we will go with the broad brush approach and mention scattered showers and storms on a daily basis through the rest of the week and into the weekend, with the best chance of rain during the afternoon. But, in a pure tropical airmass you can't rule out a stray morning shower or two, like the ones we have this morning over West Alabama.

Temperatures should be pretty close to normal for late July; daily highs around or just above 90 degrees for most spots. Yesterday, Muscle Shoals soared to 97 and was the state hot spot. The air was much drier up there, allowing it to heat more effectively.

TROPICS: While our system over the far western Gulf probably won't get a name, it is stirring up a fuss this morning. A tornado warning is in effect as I write this for Vermilion and Cameron parishes in Louisiana, and a few counties along the central Texas coast are under flash flooding warnings. Elsewhere, not much is happening with just a weak wave just east of the Leeward Islands.

Way out in the Pacific, people in Hawaii are breathing a little easier as Daniel has been downgraded to a tropical storm as it approaches the islands. Looks like the core of the system will pass a little to the south of Hawaii. Dry air is wrapping in the system and it should continue to weaken. The Big Island of Hawaii might get some rain, but no major problems are likely.

WEATHER PARTY: Don't forget to bookmark our latest site, weatherparty.com:

http://www.weatherparty.com/

Lots of great weather news and information over there; be sure and register and you can vote on the links to determine what goes on the front page. And, of course, you submit links as well. This is one of those sites where the readers determine what goes on the main page. I check it out often.

WEATHER BRAINS: We posted this week's WeatherBrains episode yesterday; I love the interview with Dr. John Knox as he discusses the legendary J.B. Elliott. Be sure and listen when you have some time:

http://www.weatherbrains.com/

I should have the next map discussion video posted on time today around 3:30...