Check out the Monday Night Football game up in Nashville... light snow is falling! Also keeping an eye on the Hytop NWS radar... looks like that light snow could very well get into extreme northeast Alabama after midnight...

About to post the morning forecast package shortly.

The afternoon video is on the web server now:

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

No real change in our thinking; low 20s tomorrow morning, then Wednesday morning average lows in the upper teens. Coldest valleys between 10 and 15, ridge tops between 20 and 25. We stay in the 30s all day tomorrow.

Have added snow flurries to the forecast on Sunday thanks to a strong impulse rounding the base of the trough. Not much moisture, but a few flakes are certainly possible.

Next week still looks very cold as we approach Christmas, but I just can't define any specific snow threat right now. Interesting to note the GFS accumulated snow graphic has one inch on the ground here on Christmas day (it is in the video)... That will probably change a number of times over the next few days.

There are many, many people who look at the model output statistics from the primary American global model, the Global Forecast System (GFS). These products give you highs and lows out to seven days for points all around the nation. You can see them (for Birmingham) here:

http://www.nws.noaa.gov/cgi-bin/mos/getmex.pl?sta=KBHM

By design, the GFS MOS skews toward climatology in the day 4 through 7 period, meaning highs in the 50s and lows in the 30s this time of the year. Rarely does it pick up on major weather changes, which is why often you need to toss those numbers out the window. Sure, there are days when we DO have highs in the 50s and lows in the 30s. But, in a high amplitude pattern like this, with a tap to the Yukon, forecasting 50s and 30s at the longer range can be a disaster.

Last Thursday (December 9) the GFS MOS was spitting out the usual 50s and 30s for Alabama, valid tomorrow (Tuesday December 14). To be exact, the GFS MOS product last Thursday has a high of 50 and a low of 30 for Birmingham on Tuesday December 14 (I had to dig through the archives to find it).

Looks like the actual high tomorrow will be close to 39, and the early morning low close to 23... a good TEN degree bust.

Lets look back at last Thursday's actual forecasts.

Here is a quote from our blog on Thursday December 9 (check it out on the calendar to see it yourself:

"Next Tuesday, I don't think we will reach 40. By Wednesday morning, lows in the 20 to 25 degree range should be common."

So, you see, it is a GOOD thing to depart from the GFS MOS 50s/30s thing somtimes if you want a GOOD forecast. I was not cold enough on the morning lows.

Lets give the local NWS office some credit... they were not as bold as us, but at least they lowered the GFS numbers as well last Thursday. Here was their state forecast from December 9:

STATE FORECAST FOR ALABAMA
NATIONAL WEATHER SERVICE BIRMINGHAM AL
500 PM CST THU DEC 09 2004

.TONIGHT...MOSTLY CLOUDY. A SLIGHT CHANCE OF SHOWERS. PATCHY FOG
AFTER MIDNIGHT. LOWS IN THE LOWER TO MID 50S.
.FRIDAY...PARTLY CLOUDY. A SLIGHT CHANCE OF SHOWERS...MAINLY NORTH.
HIGHS IN THE LOWER 50S TO MID 60S.
.FRIDAY NIGHT...MOSTLY CLOUDY. A SLIGHT CHANCE OF SHOWERS...MAINLY
NORTH. LOWS IN THE UPPER 30S.
.SATURDAY...PARTLY CLOUDY. HIGHS 48 TO 55.
.SUNDAY...PARTLY CLOUDY. LOWS 30 TO 40. HIGHS 50 TO 60.
.MONDAY...PARTLY CLOUDY. LOWS 38 TO 42. HIGHS 48 TO 60.
.TUESDAY...MOSTLY SUNNY. LOWS 28 TO 35. HIGHS 45 TO 55.


What I don't understand is how some weather operations blindly buy into the 50s/30s stuff beyond the third day. Amazing.

And, please let me say I will be dead wrong at times when I depart from the beloved GFS MOS, but my object here is to be CORRECT, not to throw out some watered down forecast that drifts back to the 50s and 30s every time.

Have I vented enough? I love this blog, because you can click on any calendar day and go back to see what we ACTUALLY SAID. I do get tired of being blamed for bad forecasts thrown out by other people. Sure, we will be wrong at times, but at least we are accountable and stand by our products.

Thanks for taking the time to read this rant. Now, back to the regular blog material, and enjoy the cold weather! Headed out to Mountain Brook to speak to the kids at Crestline Elementary school, and then back in the office where I will knock out the afternoon video update.

The morning video is posted to the server:

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

I am often torn between writing a technical discussion of weather here, or a general discussion for the public. I will lean toward the latter, but when I do get technical I will do my best to explain.

No change in my message since last week:

*VERY cold for the latter half of December

*I will be very surprised if we get through the rest of the month without at least one snow or ice threat.

We will be in the 30s all day tomorrow, and by Wednesday morning the coldest valleys will be in the 10 to 15 degree range, with 15 to 22 for everyone else.

Just about six days ago the stastical guidance from the main American global computer model, the GFS (Global Forecast System), had forecast highs in the 50s and lows in the 30s for Tuesday. Later today I will write about the GFS "50s and 30s" problem beyond three days! Sometimes it doesn't have a clue in those longer time frames, and I don't understand people who follow it blindly.

Another shot of cold air comes in here over the coming weekend, and once again, the GFS is out to lunch on the 50s and 30s. I am not sure we will get as cold as tomorrow and Wednesday (it is possible), but it will be very cold. And, a couple of impluses rotating through the base of the upper trough might squeeze out a few snow flurries here over the weekend. The stronger one comes through on Sunday, and might be enough to make the ground white over the northeast corner of Alabama, especially over 1,500 feet in places like Mentone. The problem is that the vort max will be starved for moisture. I will probably revise the forecast to include flurries on Sunday... and hold off on anything stronger until we see more model runs this week.

Christmas week: The fun and games begin again with yet another surge of cold air moving in. The high up in Canada early next week shows up as almost 1050 mb, and could very feature the coldest air of this series of cold air blasts. As the new surge of cold air arrives, a strong impulse moving through the upper air flow tries to spin up a storm system that would bring the risk of snow to parts of the deep south in the December 22-24 time frame. Then, after that system departs, there is some risk we get in a cold airmass like we saw here in late December 1983 or 1989.

REMEMBER: There is no way to forecast a specific event beyond seven days. These are just ideas based on the pattern and observed surface and upper air weather across North America (and beyond). Do not go out and tell people James Spann is forecasting a white Christmas. I am not right now. All I am saying is there is a chance. And, perhaps the best chance here in 15 years.