A thick deck of high cirrostratus clouds has overspread the area this afternoon. The high clouds are the outflow from a complex of thunderstorms over Mississippi.

This activity will spread into western sections of Alabama over the next couple of hours over Sumter and Pickens Counties. The rain and storms will move across the state during the evening hours.

The activity is moving northeast at a pretty good clip now, nearly 40 mph.

It will reach Tuscaloosa around 630 p.m and the Birmingham area before 8 p.m.

Some stronger storms are located in extreme southern Alabama. They have moved out of Mobile and Baldwin Counties into Washington and Escambia counties. This activity will also be spreading northward.

We don't expect any severe weather tonight, but you can look for decent amounts of lightning and thunder, along with some heavy rain.

The upper level disturbance causing the activity is over Central Mississippi. It will continue moving east northeast overnight.

Low pressure over southeastern Texas will move northeast over the next 36 hours, pushing a cold front our way. More thunderstorms will develop in the warm and unstable airmass over Alabama tomorrow. Some of them could be severe, with the main threat coming from high winds.

A quick mid-morning note...

SPC has much of central and south Alabama under a slight risk of severe weather tomorrow. Needless to say, lots of interest in the weather situation tomorrow with the final round of the Regions Charity Golf Classic ahead.

Here is a quick look at various severe weather parameters for tomorrow afternoon at Birmingham from the 12Z NAM:

Surface based CAPE: 1129
Lifted index: -1.9
0 to 3 km helicity: 92.9
SWEAT Index: 194
Temp/Dewpoint: 72/65
850 mb wind speed: 16 knots
500 mb wind speed: 47 knots

At first glance it sure looks like the best chance of severe storms will be over the southern half of the state; the NAM shows a surface low forming on a surface front over central Alabama, passing south of Birmingham. Instability values are marginal for severe weather along the I-20 corridor.

Bottom line: rain is likely after midnight tonight and during the day tomorrow. Some thunder is likely here, but for the moment we still believe the best chance of severe storms will be south of Birmingham, and perhaps south of Montgomery....

We will keep an eye on the situation... more updates later.

Mount Cheaha, the highest point in Alabama at 2407 feet above sea level, was visible on the WSR-88D radar located at the Shelby County Airport this morning. I grabbed this screen shot of the radar around 7:45 am and added an anotation to show the "echo" which is Mount Cheaha.

How does this happen? The radar beam is assumed to travel in a straight line, but in reality, atmospheric temperature and humidity profiles affect the radar beam. This means that the beam does not travel in a straight line, but bends. The bending can be upward (subrefraction) or downward (superrefraction). Today, the lowest beam in the radar volume scan is being bend downward just enough to strike Mount Cheaha and return some energy thus painting at "echo." Of course we know that echo is not rain but a geographic feature.

This situation illustrates a good point. If you were to look at radar alone, you might conclude that a small shower was occuring in the vicinity of Mount Cheaha. However, when you combine radar and satellite imagery or the sounding from the Birmingham radiosonde run, you would see that the correct conclusion is beam bending and no shower exists.

Special thanks to the NWS forecasters at Birmingham for noting this occurrence in their forecast discussion.

-Brian-

The Saturday video map discussion is on the server at:

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

Wow, I'm beginning to feel a lot like James Spann with as busy as I've gotten between all the various duties and responsibilities - and I'm supposed to be retired!! I've been providing weather support to a couple of outdoor festivals this weekend and there are some tough decisions to be made based on - you guessed it - the weather.

Interesting radar image this morning from the NWS at the Shelby County Airport. The radar is actually showing Mount Cheaha. The atmospheric temperature/moisture profile must be causing the radar beam to bend downward a bit resulting in an echo right where Mount Cheaha is located. I'll grab the image and make another post so you can see it.

Large mesoscale convective complex (MCC) occurring this morning over Southeast Texas. Rain likely to spread eastward today as the stalled frontal boundary along the Gulf coast begins to come back northward. Looks like Central Alabama should be dry but cloudy for the day with rain possible after midnight. Temperatures will be in the mid 70s.

Sunday looks wet as a disturbances moves through the zonal flow aloft. Would not be surprised to see one to two inches of rain and temperatures not climb much above 70. Of course, any breaks in the clouds would allow some sunshine and warm things up rapidly.

The weather pattern dries out on Monday and Tuesday, but moisture begins a comeback late Tuesday. The result should be a wet day on Wednesday. Drying occurs again on Thursday and continues into the first part of the weekend. Probably see temperatures return to near 80 by next Saturday.

Lots of activities today including the annual hamfest put on by the Birmingham Amateur Radio Club (BARC) at the Zamora Temple near the intersection of I-20 and I-459. Hamfests are gatherings of amateur radio operators for a chance to buy and sell equipment and swap handshakes or lies (hams sometimes better than fishermen in that department). There will also be forums about a number of topics including SKYWARN. I understand the SKYWARN Forum is set for 3 pm. I hope to make it out for that.

Have a great weekend.

-Brian-