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Area forecast discussion 
National Weather Service Birmingham Alabama 
1138 PM CST Wed Feb 20 2019 


Update... 
for 06z aviation. 


&& 


Short term... 
through tonight. 


Showers and thunderstorms continue to track across central Alabama 
this afternoon, but thankfully the deeper moisture and higher dew 
points have stayed to our south today along with our warm front. 
Thus, we did not reach the severe potential that we initially 
through we would reach. Dew points ranged today from the upper 
40s northeast (with a cad wedge helping to keep that area cooler) 
to the lower 60s in the south. The deeper moisture (higher 60s dew 
points) did not come to materialize. We also kept socked in with 
low stratus that helped to keep temperatures down. We did have 
enough moisture and lift for some elevated convection today, but 
only a few strong storms accompanied it. The main threats have 
been heavy rain and lightning. The heavy rain should taper down 
during the evening hours, but there still should remain the need 
for a higher band of rain chances. This will be due to our surface 
cold frontal boundary remaining across the area. It is expected 
to stall and then meander back to the north as we head into 
Thursday as a warm front. Overnight low temperatures for tonight 
will range greatly from the northwest to the southeast with 
respect to which side of the boundary you lie. Readings will vary 
little in the southeast with lows expected in the middle 60s 
(generally southeast of the I-85 corridor) as they will remain in 
the warmer airmass. While readings in the far northwest are 
expected to range through the 40s behind the front. In between we 
will see a large temperature gradient with the moving boundary. 


08 


Long term... 
/previous discussion issued at 404 am CST Wed Feb 20 2019/ 
Thursday through Tuesday. 


Height rises will occur aloft on Thursday as ridging temporarily 
builds in over the eastern Continental U.S. Ahead of a closed low near Las 
Vegas. The surface front will remained stalled out near the I-85 
corridor during the day. However, southwest flow returns aloft 
ahead of the trough out west, causing the 925/850mb front to lift 
northward. Associated frontogenesis/isentropic lift/overrunning 
will maintain the Post-frontal precipitation area and cause it to 
begin to shift northward. While overall rainfall amounts should be 
lower, the presence of some weak elevated instability suggests 
any ongoing flooding could be aggravated, and the Flood Watch will 
continue to be in effect. Cams also suggest scattered 
thunderstorm development south of the front with daytime heating 
of an unstable air mass. This could pose a conditional 
strong/isolated severe storm risk over our far southeast counties 
where hail/gusty winds would be possible given sufficient deep 
layer shear, while the stronger low-level shear stays north of the 
boundary. 


On Friday, continued southerly low-level flow should cause the 
surface front northward as a warm front. The front will continue to 
serve as a focus for precipitation along and north of it. The 
NAM/European model (ecmwf) push the front north of the area while the GFS is slower 
to push it north and is wetter. If the wetter solution wins out, 
then an extension may be needed to the watch. A similar 
conditional risk for a strong/isolated severe risk to Thursday 
will exist over a greater portion of the area, but if the 
NAM/European model (ecmwf) solution wins out then we may remain capped on Friday 
afternoon with warm/dry air aloft. Also of note will be the 
warming trend in temperatures with readings near 80 in our 
southern counties. 


Attention then turns to the potent shortwave trough and associated 
deepening surface low tracking from the Southern Plains to the Great 
Lakes, and the associated cold front. There remains some model-to- 
model and run to run differences in the tilt/amplitude/timing of 
this shortwave that will be key in determining the magnitude of the 
event. The stronger upper-level forcing remain well northwest of the 
area but there are some decent height falls. The somewhat weaker 
upper-level forcing could help storms stay discrete longer, but 
could also limit the areal coverage of severe storms or prevent them 
from occurring at all this far south given capping concerns/warmer 
700mb temperatures. A Stout warm sector will be present with this 
system, with mid to upper 60s dew points and temperatures in the mid 
to upper 70s, resulting in potential cape values of 1000-1500 j/kg 
with favorable lapse rates. 70kt southwesterlies at 500mb and a 50 
kt 850 mb jet would suggest the potential for supercells to form 
ahead of a qlcs. Latest model trends are a bit quicker with this 
system, suggesting storms may move through at a time when the 
atmosphere is more unstable. Srh is certainly supportive of a 
tornado threat. Storm Prediction Center has expanded the 15%/slight risk southeastward 
to include areas along and north of I-59, and we will follow suit 
in our graphics and begin to trend the severe weather potential statement confidence number 
upward. Again, the possible forcing issues remain one potential 
limiting factor, but looking at the moisture and quantitative precipitation forecast depicted by 
the models suggests thunderstorms should develop this far south. 
This rainfall could also cause additional flooding concerns. 


Conditions finally dry out Sunday afternoon through Monday. Rain 
chances return to the forecast Monday night and Tuesday, however. 
Rainfall amounts currently look to be on the lighter side with an 
overrunning situation as a weak wave of low pressure moves along the 
Gulf Coast. 


32/Davis 




&& 


Aviation... 
06z taf discussion. 


Even with the complex frontal structure we have across central 
Alabama tonight, will hold on to the IFR ceilings/vis in many 
locations overnight. The boundary stalls in south central Alabama 
and only moves very slowly northward. Therefore, many locations 
north will remain IFR throughout. The southern locations may 
touch MVFR and then drop back down after 00z. 


Mixture of LIFR/dense fog to start off several locations. 
Additionally, the next upper impulse and associated upward motion 
has already started back in Mississippi. Therefore, showers and 
thunderstorms will be in the terminals overnight and into 
Thursday. The southern terminals may get a reprieve before more 
activity develops on Thursday. At any rate, restrictions rule this 
package with a mix of ceilings/vis/rain/thunder. Wind direction 
will be an issue also as the current frontal structure has north 
winds in the north and south winds in the south. This appears to 
remain the directions. Luckily, winds at most sites are light. 


75 


&& 


Fire weather... 


A prolonged period of rainfall will continue through the end of the 
week, with a strong storm system expected over the weekend. Very wet 
conditions are expected, especially across the northern half of the 
area. There are no fire weather concerns at this time. 


&& 


Preliminary point temps/pops... 
Gadsden 51 56 51 67 57 / 90 90 80 80 80 
Anniston 55 57 54 72 58 / 100 80 80 70 70 
Birmingham 53 57 55 71 63 / 90 90 80 70 70 
Tuscaloosa 54 57 55 72 63 / 90 90 80 70 60 
Calera 56 60 56 73 62 / 90 70 80 70 70 
Auburn 58 74 61 75 61 / 80 60 70 40 50 
Montgomery 63 75 63 80 64 / 100 60 70 50 30 
Troy 67 76 65 80 63 / 50 60 50 30 20 


&& 


Bmx watches/warnings/advisories/... 
dense fog advisory until 9 am CST Thursday for the following 
counties: Autauga...Barbour...Bibb...Bullock...Chambers... 
Chilton...Clay...Cleburne...Coosa...Dallas...Elmore...Hale... 
Lee...Lowndes...Macon...Marengo...Montgomery...Perry...Pike... 
Randolph...Russell...Shelby...Talladega...Tallapoosa. 


Flood Watch through late Thursday night for the following 
counties: Bibb...Blount...Calhoun...Cherokee...Clay...Cleburne... 
Etowah...Fayette...Jefferson...Lamar...Marion...Pickens... 
Shelby...St. Clair...Talladega...Tuscaloosa...Walker...Winston. 



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