Archive for December 16th, 2012
Rain has moved into the Birmingham Metro and across much of Central Alabama. No severe storms anywhere in Alabama right now. The heaviest rain is falling along and north of Interstate 20. Heavier pockets of rain are west of downtown from Adamsville back towards the Samantha community in northern Tuscaloosa County. Another are of heavier rain is east of downtown from near Moody towards Piedmont. The rain should continue to drift off to the southeast and is one of several rounds of showers and storms we can expect today. More storms will develop later this afternoon, and then the main threat of severe weather for us will be overnight tonight. Any and all rain that falls today will be very beneficial as many areas continue to be running rainfall deficits.
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Central Alabama is in for a period of active weather through Monday. This morning we find a lines of thunderstorms lying across the Tennessee River Valley from near Chattanooga to about Columbus, MS. This line was slowly moving eastward while individual storms in the line were moving fairly rapidly northeastward. We also find ourselves in one of those somewhat difficult environments with low CAPE and fairly high shear with slightly better conditions for severe weather resting closer to the Gulf Coast. But SPC has placed a slight risk for Day 1 across the Southeast from about Tuscaloosa southwestward to Baton Rouge and the Louisiana Gulf Coast. For Day 2, the slight risk area shifts eastward stretching from about Dothan northeastward into the southeast corner of North Carolina.
CAPE values indicating instability are generally at or below 500 joules per kilogram with higher values hugging the Gulf Coast. But shear values are relatively high generally along and south of the Interstate 59 corridor. So we face several issues. The first issue is that the weather is likely to come in two waves, the first one coming this morning into the afternoon as one upper short wave kicks out across the area. The second coming later tonight and into the early morning hours of Monday focused south of Birmingham. The threat for today is primarily in two forms, damaging wind and flash flooding. I’m already seeing some potential for flash flooding to develop with the slow progression of the line of storms currently going on. In the second round later tonight, we have to add the threat of isolated tornadoes to the two already mentioned.
This will be a good day to stay indoors and enjoy a good book even though it is going to be mild with temperatures climbing into the mid and upper 60s across the area. Monday will be one of those days where we don’t see much temperature change until the colder air arrives late in the day pushing temperatures rapidly into the 40s – probably after dark.
We get a couple of days off with Tuesday and Wednesday being dry days with cooler temperatures. But the next system should be poised to bring rain and perhaps another round of severe storms to the area on Thursday. Current thinking is that it will be another low CAPE scenario, so it will bear watching. The upper trough with this system is sharper than the current one, so I expect to see colder conditions as we head into the weekend. Colder being a relative term since we will actually drop back to values more typical of the middle of December with lows in the lower 30s and highs in the middle 50s.
Looking into voodoo country, the GFS continues to be consistent with a progressive pattern. Christmas Day looks mild and dry with another weather producing trough around the 27th and yet another one around the 30th.
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James Spann will be back with the next edition of the Weather Xtreme Video. Stay tuned to the Blog for the latest updates as this weather situation unfolds. You can catch my forecast on ABC 3340 at 5 and 10 pm this eveningGodspeed.
The Storm Prediction Center’s first severe weather outlook of the day didn’t include Birmingham, as James noted earlier.
But the 7 a.m. update did nudge the severe weather risk eastward a bit, as you can see in this graphic from the College of DuPage. This graphic compares the current one with the last one issued.
Here is a close up of where the actual line lies on the update using the MyWARN app:
Where the line is isn’t important, because the main point is that there is a severe weather threat across Central Alabama through early Monday morning.
Brian Peters will be along shortly with a detailed discussion and Weather Xtreme video; here are some notes on what to expect today…
*LOTS OF RAIN: Heavy rain is already in place this morning over Northwest Alabama… see the radar below…
This batch of heavy and and storms will slowly drop southward this morning. The storms are not severe, and severe weather is not expected this morning. But, the rain will be heavy at times.
The 4km NAM is projecting 1-2 inches of rain over this part of Alabama through tomorrow morning, and no doubt some spots will get more, potentially leading to some localized flooding problems.
*SEVERE WEATHER? SPC has actually removed most of Alabama from the severe weather threat today; just a a few west-central counties are involved…
However, there seems to be a window for some late night problems over Alabama as shear increases along with the low level jet. Below is the projected radar reflectivity at 4:00 a.m. Monday…
The main window for severe weather will come from midnight tonight until 8:00 a.m. tomorrow, primarily along and south of I-20. This is a fairly marginal threat due to limited instability, but with the projected low level shear a few tornadoes can’t be ruled out, so this will be a night when you want to be sure your NOAA Weather Radio or smart phone app is properly programmed and ready for action.
More details soon…