We have a bad habit of throwing out weather terms here often without good explanation. On a day like today, we are not overly concerned about severe weather because of low CAPE values. What in the world is CAPE anyway?

CAPE stands for Convective Available Potential Energy. Here is the “geek” definition: A cumulative measure of the positive buoyant energy (in J/kg) a rising parcel of air would have between its Level Of Free Convection (LFC) and the Equilibrium Level (EL). CAPE is a vertically integrated quantity as well as a fundamental indicator of the potential intensity of deep, moist convection. So, what does all of that mean?

A high value of CAPE simply means the air is unstable, and air parcels are buoyant and can rise easily through the atmosphere. These rising air columns can mean rapid thunderstorm formation if there is no capping inversion and there is adequate moisture. So, what is a capping inversion? We often simply call it a cap; a layer of warmer air aloft which prevents air parcels from rising above the cap level. Caps can been easily seen on upper air soundings.

So, what is an upper air sounding? Weather balloons are launched from many locations around the nation at least twice daily (the Alabama location is the Shelby County Airport, about 20 miles south of downtown Birmingham). The balloons have a weather instrument packet attached called a radiosonde, and this measures weather parameters like temperature, humidity, and pressure on the balloon ascent.

As the balloon rises, the atmosphere thins and the pressure outside the balloon decreases allowing the balloon to expand and eventually break. This usually happens within two hours of the launch at elevations of 80,000 to 120,000 feet. Upper air data from the radiosonde reports serves as input for the computer models we use on a daily basis.

The Tuesday afternoon web video update is on the server:

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

I also should note I put some new digital pictures from viewers on our cool pictures page:

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

Rain is already showing up nicely on our radar over south Alabama, and it will reach us sooner or later. But, at 2:00 the dewpoint in Birmingham is 29, so the rain sure won't be reaching the ground here within the next 3 to 5 hours at least. Light rain should become rather widespread late tonight as a warm front pushes northward from the Gulf.

SEVERE WEATHER? Severe weather potential for north Alabama tomorrow sure looks rather low at this point. Like I wrote here this morning, I just don't see us getting high dewpoints in here so quickly. Yes, we will have periods of rain tomorrow, and probably some thunder and lightning, but the real maritime tropical air needed for severe weather should be confined to south Alabama, especially south of U.S. 84 (Monroeville to Dothan).

Here are our severe weather parameters for midday tomorrow:

SB CAPE 445
Lifted Index -1.4
SWEAT Index 271
2M AGL Dewpoint 60
0 to 3 km Helicity 207
850 mb wind speed 48 kts
500 mb wind speed 61 kts

Those numbers are based on the NAM, and they sure don't look very impressive. I do note the 850 wind speed of 48 kts is pretty decent, but the GFS (the model I used on the video) was more in the 25 to 30 knot range.

Rainfall around one-half inch are likely late tonight and tomorrow. The NAM is showing 0.50", while the GFS shows 0.39". Both models have backed down a bit from earlier rain totals.

REST OF THE WEEK: Nice spring weather is ahead for Wednesday, Thursday, and Friday.

THE WEEKEND: Another storm system to deal with. No doubt a few showers and possibly a thunderstorm will be around n scattered spots on Saturday, but the more organized storms will hold off until Saturday night and Sunday. Good news for NASCAR fans is that the 12Z GFS is a little faster with the system, giving some hope that the main band of storms might be over in time for the big race Sunday. But, no promises this early in the game. It also looks like strong to severe storms will be possible over the weekend. We will continue to fine tune the forecast as we go along.

Thanks to the first graders at Valley Elementary for being such a good audience today! And, thanks for the BIG COOKIE!

Didn't snow quite as much as expected in the Great Smoky Mountains over the weekend. Gatlinburg did not report any measurable snow. There were some nice amounts higher up than Gatlinburg and elsewhere in East Tennessee and Western North Caroliona:

1 inch on Newfound Gap with a low temperature of 18
4 inches atop Mt. Leconte with a low of 9
4 inches at Beech Mountain, N. C., with a low of 16
9 inches on Mount Mitchell, N. C., with a low of 12.

In Extreme NE Tennessee, they called this weekend's snow the "Tulip Toppling Snowstorm." Some amounts:

4 inches at Mountain City
5 inches at Trade
2 to 3 inches in Shady Valley
2 inches in Butler
8 inches on Stone Mountain

Don't know if the mountain laurel and rhododendron is in bloom in that area. If it is, can you imagine the great photo ops!!

In more northern areas, there was very heavy snow over parts of Ohio and Michigan.

This is a composite list of low temperatures Sunday morning and Monday morning. We list the coldest of the two mornings at each location, so these lows could have been on either morning. In a few cases there may be two listings for the same area...but from a different source. Also see the notes at the end of this list.

As might be expected, the old faithful, Valley Head, was the coldest in the state. Valley Head has a long history of being the state cold spot and had the state record for many years until the -27 occurred at New Market NE of Huntsville. Valley Head had 18 below in 1905 and that was the state record for a long time.

Here is the list from over the weekend:

28 in Valley Head
29 at Little River Canyon and DeSoto State Park
30 at Ft. Payne Airport, Sardis Springs, Russell Cave, Hamilton, Jacksonville,
Black Creek
31 in Pinson, Collinsville, High Top, Wedowee, Gaylesville, Sterrett
32 at Addison, Gadsden Airport, Cullman Airport, Florette, Hartselle,
Vinemont, Owens Crossroads, Nauvoo, Clay, Union Grove, atop Mt.
Cheaha
33 at Mentone, Russellville, Scottsboro, Valley (Lee County), Hazel Green,
Ashland, Dearmanville, Heflin, Cottondale, Crumly Chapel
34 in Leeds, Albertville, Parish, Anniston, Meridianville, Muscle Shoals,
Centreville, Jasper, Wadley, Athens
35 in Huntsville, Clanton, Fayette, Helena, Ashville, Jasper, Huffman,
Inverness, Vincent, Hueytown, Smoke Rise
36 in Decatur, Guntersville, Alexander City, Auburn, Alexander City
37 in Childersburg, Birmingham Airport
38 at Montgomery, Troy, Union Springs, Calera, Tuscaloosa, Livingston,
Marion
39 in Talladega

EXTRA NOTES:
.....32 with a nice frost at Clay Sunday morning.
.....at Black Creek, Vic Bell reports a heavy frost with his low of 30

There were widespread reports of hail in Alabama Friday, however, wind damage was more isolated. It appears that the worst wind damage occurred in Randolph County adjacent to the Georgia border. We got a report from Wedowee at midday indicating a possible tornado. However, NWS meteorologists from the Birmingham office did a storm survey Saturday and determined that it was a severe thunderstorm. Here is the text of their report:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
1007 PM CDT SAT APR 23 2005

...STRAIGHT LINE WIND DAMAGE IN RANDOLPH COUNTY ON FRIDAY
...APRIL 22...

NATIONAL WEATHER SERVICE METEOROLOGISTS SURVEYED DAMAGE ACROSS
CENTRAL RANDOLPH COUNTY TODAY. THIS DAMAGE WAS THE RESULT OF A
STRAIGHT LINE WIND EVENT...ASSOCIATED WITH A SEVERE THUNDERSTORM...
THAT OCCURRED ON FRIDAY...APRIL 22.

IN THE CITY OF WEDOWEE...THE FIRST STATE BANK LAKE WEDOWEE OFFICE
BUILDING HAD ITS ROOF BLOWN OFF. MULTIPLE TREES WERE ALSO DOWNED
ACROSS THE CITY. FIVE MILES NORTH OF WEDOWEE...ON U.S. 431...SOME
MINOR STRUCTURAL BUILDING DAMAGE WAS ALSO OBSERVED AT A MARINA...
ALONG WITH MINOR DAMAGE AND DISPLACEMENT OF A FEW BOATS. BOTH OF
THESE EVENTS OCCURRED AROUND 1230 PM CDT.

IN THE TOWN OF NEW HOPE...ONE HOME HAD ITS ROOF BLOWN OFF...AND TWO
BUILDINGS RECEIVED MAJOR STRUCTURAL DAMAGE. A BARN WAS COMPLETELY
DESTROYED. NUMEROUS TREES WERE ALSO UPROOTED AND SNAPPED. NO INJURIES
OR DEATHS OCCURRED WITH BOTH OF THESE EVENTS.

A SEVERE THUNDERSTORM WARNING WAS IN EFFECT FOR RANDOLPH COUNTY FROM
1212 PM CDT TO 1245 PM CDT ON FRIDAY.

For most of North and Central Alabama, it was a degree or two colder this morning than Sunday morning. Here are some lows reported so far. Later this morning, we will have a more complete list and discuss where the coldest spots were over the two day chill:

29 at Little River Canyon in Desoto State Park
30 at Fort Payne Airport
31 in Pinson
32 at Gadsden Airport and atop Mt. Cheaha
33 at Mentone and at Valley (Lee County)
34 at Cottondale, Leeds, Albertville, Parrish, Anniston, Meridianville, Muscle Shoals
35 in Huntsville
36 in Decatur and Cullman Airport
37 at Auburn, Birmingham and Muscle Shoals
38 at Shelby County Airport, Montgomery and Troy
39 at Tuscaloosa
40 in Evergreen

Our expanded list later this morning will include reports from NWS cooperative observers and 3340 weather watchers. All of the coop oberver list is usually not available under about 10.

A few notes from Sunday morning...
.....Low of 32 in Nauvoo was accompanied by considerable frost
.....Vic Bell reported a low of 31 with widespread light frost at Black Creek in NE Etowah County.
.....Where I live in the NE edge of Trussville, I did not see any frost either morning. We live in a valley anbd our low temperatures on clear still nights are very close to those in Pinson.

The Monday morning web video is on the server:

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

As I write this my thermometer is showing 38 degrees. Which means it is really hard to get excited about severe weather possibilities tomorrow. SPC has all of Alabama in a slight risk of severe storms, but the dry air extends well southward into the Gulf, and it will take some time to get 60 degree plus surface dewpoints back in here....

TODAY: A warming trend begins this afternoon as the weekend chill becomes a memory. J.B. Elliott will post morning lows on here later today; the wind is calm and I am sure some of the colder valleys have some frost, and I would not be shocked for some of those places to report a low of 32 or 33. But, most places stayed well above freezing. Clouds return late in the day, and some rain should arrive after midnight tonight.

TOMORROW: Rain and storms are likely. It won't rain all day, and the best chance of thunder will come tomorrow afternoon. The lack of true maritime tropical air and rather unidirectional wind profiles suggest a marginal severe weather threat. Rain amounts of one inch are possible, and some spots might even see a little more than one inch. Should not be enough for any flooding problems.

WEDNESDAY THROUGH FRIDAY: Some beautiful spring weather, with sunny mild days and clear nights.

THE WEEKEND: Moisture begins to return on Saturday, and showers are possible. Unfortunately Sunday looks like we could have the potential for either severe thunderstorms or heavy rain with a deep surface low to the north, and the Gulf of Mexico wide open. Not the best news in the world for NASCAR fans since this is race weekend in Talladega. It won't rain all day Sunday, but the weather could be pretty rough. We will fine tune the forecast as we roll along this week...

Headed out to see the kids at Valley Elementary in Pelham later today, and will be in the office for the afternoon update by 3:00.