We had a very interesting “Weather Brains” podcast this week. This is our weekly thirty minute audio show all about weather; distributed free via iTunes and the Internet. The host is my old weather associate from the Channel 13 days in the early 1980s, David Black, and most weeks you hear from people like J.B. Elliott, Brian Peters, Bill Murray, Jason Simpson, John Oldshue, and myself.

This week’s episode somehow drifted onto the subject of using “probability of precipitation” in weather forecasts. These “POPs” are used by the National Weather Service, and some broadcast meteorologists. Long time readers know my dislike for POPs. People remember them, but very few understand them, and they usually lead to confusion. In fact, within the next two weeks I will write my annual post here about summer weather forecasting in Alabama, which includes a little about how the “chance of rain” parameter is pretty much useless on a summer afternoon here in the Deep South.

I learned during the podcast that even weather people really don’t understand “POP”. I think everyone on the show had a different idea about the definition of “POP”, but we were all in good agreement that they are horrible in a public forecast. I poked around and found this definition for “POP”:

"If a forecast for a given county says that there is a 40% chance of rain this afternoon, then there is a 40% chance of rain at any point in the county from noon to 6 p.m. local time. This point probability of precipitation is determined by the forecaster by multiplying two factors: Forecaster certainty that precipitation will form or move into the area X Areal coverage of precipitation that is expected."

Listen to the podcast here:

http://www.weatherbrains.com/

And, read the entire explanation of "POP" here:

http://www.utexas.edu/depts/grg/kimmel/nwsforecasts.html

For the third day in a row we have some great rainbow images captured by digital cameras across Alabama... the first four pictures below are from Rachel Jordan, who was in northeast Coosa County. They were taken around 7:00 this evening.











The final image below was taken by Shiela Limbaugh:

The Wednesday afternoon map discussion video is on the server:

http://www.jamesspann.com/

This will be our last really "cool" day for a while. Maybe until October. I hope you enjoyed the cool snap.

RIGHT NOW: As forecast, scattered showers are in progress across the state. I just cheked our SKYCAM site at Mt. Cheaha... 60 degrees, light rain falling, and a west wind of 12 mph. Check it out:

http://www.abc3340.com/static/skycams/skycamsmain.html

All of the showers will end later tonight.

TOMORROW/FRIDAY: The big warm-up begins. We go into the upper 70s tomorrow, and 80 are likely by Friday. Most of Alabama should be dry tomorrow, and any showers late Friday afternoon should be isolated, and mainly north of Birmingham.

THE WEEKEND: The 12Z GFS continues to trend dry for the weekend. Looks like we can safely forecast a good supply of sunshine on Saturday and Sunday with very warm afternoons. The GFS MOS actually pushes us into the upper 80s; that might be a tad agressive. But, no doubt the weather will finally feel like late May over the weekend. With dewpoints in the 60s and that kind of warmth, I guess you can't rule out an afternoon shower, but if they do form they should be very isolated.

NEXT WEEK: The week should begin with dry and warm weather, but showers and storms should increase by Wednesday and Thursday as the southern edge of the westerlies will be over North Alabama.

TROPICS: While there have been hints of an early season tropical storm in the Gulf on some GFS runs, it really doesn't show up on the latest run(12Z). The 2006 "official" hurricane season begins in 15 days.

RAINBOW WATCH: I expect more rainbows to show up this evening in the Alabama sky... if you have a cool weather picture send them here:

weatherpix@abc3340.com

The next map discussion video will be posted by 7:00 a.m. tomorrow!

The Wednesday morming map discussion video is on the server:

http://beta.abc3340.com/weather/video.hrb

Thanks for the great pictures from our blog readers last night... you see pictures posted anytime by selecting the "pictures" category on the blog:

http://www.jamesspann.com/bmachine/cat/wxtalk/15/Pictures

I expect to see more rainbow scenes this evening as the weather pattern remains the same... a big trough over the eastern U.S., and very cold air aloft over Alabama. Look for scattered showers and storms this afternoon and this evening; the chance of any one spot getting wet today is about one in four.

WARMER DAYS: Heights will slowly rise across Alabama over the latter half of the week, which means a warming trend. We expect highs in the upper 70s tomorrow, and low 80s by Friday, as the mercury finally gets back to normal levels for this time of the year. Today will be the 13th day in a row with below normal temperatures, and we have reached 80 on only two days so far this month.

We will watch a surface front approaching from the north on Friday, but for now it looks like the best chance of showers will stay in Tennessee.

THE WEEKEND: The GFS continues to look pretty dry for the weekend. The surface boundary to the north fizzles out, and little if any rain shows up on the 00Z run. For now, we have just the chance of a few scattered or isolated showers in the forecast for Sunday and Monday. Doesn't look like rain will be a problem. Highs will be in the low to mid 80s both days.

NEXT WEEK: At this time the weather for much of next week looks relatively dry and warm, with temperatures near normal. Toward the end of the week the westerlies (the main band of upper air winds over North America; the "stprm track" if you will) begins to lift northward as it usually does in late May. This will set the stage for warm and humid weather here, and the chance of "scattered, afternoon showers and thunderstorms", an almost daily part of our summer forecast routine.

TROPICS? The GFS continues to hint at some early season mischief in the Gulf of Mexico. Nothing to hang our hat on for now, but we will keep an eye on trends. Some runs have tried to develop a system down there in about 7 to 10 days, then drifting it northward in this direction. We will pretty much be watching developments over the Gulf between now and October. Tis the season.

I will have the afternoon video discussion posted by 3:30 this afternoon....