The ole wedge.

The flow of very cold air down the eastern slopes of the Appalachian Mountains into east Alabama. These ‘back door” cold fronts have given me fits for many years, but you have to deal with them. A nice wedge will set up over the eastern half of Alabama today, and as rain moves into the state our task at hand is to define where and when freezing rain will fall, and the problems that result from the ice. It might be a situation tonight when the bridges become icy over the eastern suburbs of Birmingham in places like Trussville, Moody, and Leeds, but no bridge ice forms at all over places like Bessemer and Pelham. I expect the temperature at the Birmingham Airport to hover around 33 degrees for much of the night. The bottom line is that ice is likely on bridges late tonight and early tomorrow for east Alabama making driving a little tricky. The good news is that most folks will be at home and sleeping in on a cold and rainy day, and we don’t have to deal with school closings.

The rest of the good news is that the ground is relatively warm, so road surfaces will be wet. And, the raindrops will be falling through a layer of much warmer air just off the surface, which means it will take a little longer than usual for ice to form. And, those “warm” raindrops can actually keep surface temperatures up a little. I do expect many of you in east Alabama to see some ice in the trees and on power lines late tonight, but I just don’t think we have much of a chance for any significant power outages.

But, I caution you, these wedge events are very difficult to forecast. I have seen some brilliant meteorologists brought to their knees by events like tonight, so be watching for quick changes in our forecast package. Looks like a long, but exciting day in the weather office. And, more than likely a long night ahead tonight. Lets get the coffee pot ready!

The affternoon video update is on the server:

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

Lets take a big deep breath and look at whats going on.

First off, I do believe there needs to be an open discussion in the weather community about what is a "winter storm" in Alabama. I was in Anniston doing a speech this morning, and as expected I noticed several people, including a number of senior adults with limited mobility, making plans for being stranded for multiple days. These people were making arrangements for runs to the grocery store for supplies, and trying to find relatives who would open their homes as "shelter". All of this was triggered by the winter storm watch message early this morning. This situation does not warrant that extreme level of preparation. It is a short term problem.

Once again, I do not fault anyone at the LOCAL NWS office. They do a wonderful job and we appreciate their work. I just don't agree on the criteria for a winter storm. This event tomorrow night does not meet the "James Spann" winter storm criteria in my mind. It is a situation where bridge icing can be a very real problem, but not much beyond that. Our friends up north would almost find this laughable that such a fuss is being stirred up.

No real change in the thinking since thing morning. Here are the highlights:

*Rain moves into Alabama from the west tomorrow, and cold air moves in from the east courtesy of the wedge. Rain could initially evaporate before reaching the ground, and that cooling could very well keep us in the 30s all day tomorrow. It will not be a pleasant day.

*Rain will be widespread tomorrow night over all of Alabama. During that time, temperatures should drop into the 29 to 32 degree range over eastern counties in the wedge, and bridge icing is likely. As J.B. mentioned, the general infrastructure and the soil is quite warm, so roads should only be wet. The bridges will be the problem. Some ice should also collect in trees and on power lines, but we do not expect enough accumulation for trees to fall, or for widespread power outages.

*The rain will be falling through a warm layer just off the surface, and those raindrops will take some time to freeze. Those warm rain drops can also keep temperatures from dropping to forecast levels. A very real possibility, and I have seen that happen many times before.

*The greatest chance of bridge icing will come from about 10:00 tomorrow night through 8:00 Saturday morning, and mainly east of a line from Huntsville to Pell City to Alexander City.

*It is a close call for Birmingham. We might see some bridge icing in Trussville and Moody, but none at all for Bessemer and Hoover. I expect the Birmingham Airport will get down to the 33 degree level and hold there most of the night.

Having said all of the above, wedge events are very difficult to forecast and deal with. Be ready for quick forecast changes. I have formally appointed J.B. Elliott as our official wedge officer.

Watch the video for the longer range stuff... still some potential for a powerhouse Gulf oF Mexico storm in the February 6-9 time frame. Very interesting stuff.

+ New 12Z model data generally supports the forecasts that are current. The ETA, now called the NAM, positions a high from New York to Charlotte at 12Z (6AM) Saturday with rain over virtually all of Alabama (best amounts over East-Central Alabama) Temperatures at that time 30-32 so the risk of light freezing rain still out there...mostly east and NE Alabama.

+ The infrastructure still relatively warm so the possibility of icing may be mainly on bridges and overpasses but not entirely.

+ The "wedge" plays a big part in this as cold air spills down from the East Coast high pressure area on the east side of the mountains and then spreads westward across South Carolina and Georgia into Alabama...this sets up a temperature profile of colder east/warmer west. It is sometimes called a "backdoor cold front" and it is difficult to deal with.

+ I feel sure that God created the "wedge" to keep us honest and to remind us weather humans who's in charge.

+ A few spot forecasts if you are traveling east of Alabama:

ATLANTA
Good chance of light rain and freezing rain Friday night continuing Saturday morning. Low Friday night about 28, high Saturday afternoon 38.

GREENVILLE-SPARTANBURG
A mix of snow and sleet Saturday morning with a mix of freezing rain, sleet and snow in the afternoon...continuing Saturday night. Moderate snow accumulations possible. Low/high Saturday 25/32.

CHARLOTTE
Chance of snow mixed with sleet Saturday. High near 32. Mix of freezing rain and sleet Saturday night, temperatures hoovering near freezing.

+ Be sure and check James Spann's video update later this afternoon + his additional posts here...also the afternoon discussion on the 3340 weather page around 2:30 or so.

The Thursday morning video update is on the server:

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

HMMMMM.

The NWS in Birmingham has issued a winter storm watch for counties east of Birmingham for tomorrow night and Saturday morning. I have absolutely no issues with my friends down there... they really do a wonderful job, but I have to wonder about the CRITERIA for a winter storm watch and warning in Alabama. With the exception of a few years in Dallas in the 1980s, I have lived here all my life and have a pretty good grasp on how people react to winter weather situations here.

When most people hear winter storm watch, they begin to head to the stores and buy "you know what", and expect a long duration snow or ice event.

This thing tomorrow night and Saturday morning will indeed bring a good chance of bridge icing, but I would consider it more of a temporary nuisance instead of a "winter storm". The ground is very warm, and roads will be just wet. Bridges will be the issue. And, yes, some ice could accumulate on trees and power lines, but I don't expect it to be enough to create widespread power outages. I notice NWS offices in Huntsville and Atlanta opted not to go with a winter storm watch.

The main window for bridge icing over east Alabama will come from about 10:00 Friday night through 8:00 Saturday morning, and mainly east of a line from Huntsville to Pell City to Alexander City. Some of the models are hinting at some 30 degree temperatures maybe earlier that 10:00, so that timing and the line might have to be adjusted. Dealing with a wedge is not easy at all, and like J.B. says, I tend to run for the hills when it comes into play. But, that is not an option and we will be at work looking at it closely.

Latest model data backs off on the idea of strong storms early next week, holding the main system back west of El Paso. Then, when it comes out, the GFS is locking on to the idea of a major storm forming in the Gulf of Mexico, then roaring up the Atlantic coast in the Feb 6-9 time frame. Very interesting.. watch the video for details.

Speaking over in Anniston this morning; will be back in the office by early afternoon for the afternoon video update and a good look at the 12Z model runs!