426 
FXUS64 KBMX 071710
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1110 AM CST Sat Dec 7 2019

.UPDATE...
For 18Z Aviation.

&&

.SHORT TERM...
/Updated at 0551 AM CST Sat Dec 07 2019/

The Dense Fog Advisory has been cancelled. Despite decreasing 
cloud cover since 3 am CST, visibilities have also improved with 
most areas above 3 miles. A few locations were still below 1 mile,
but certainly not enough fog to continue dense fog advisory. 

Previous short-term discussion:
/Updated at 0355 AM CST Sat Dec 07 2019/

Through Tonight.

The combination of a rain cooled air mass and partial clearing of 
clouds in some areas has led to the formation of patchy dense fog. 
Even though the dense fog is not widespread in areal coverage, there 
are several metropolitan areas that are experiencing very low 
visibilities. A dense fog advisory has been issued for all counties 
in central Alabama thru 9 am this morning. The advisory may be 
lifted in some counties where cloud cover has persisted overnight. A 
large cyclonic flow below 850 mb will keep moisture levels high 
enough for mostly cloudy skies to prevail, but with breaks in the 
clouds at times. The breaks in the clouds will allow for enough 
sunshine to push afternoon temperatures into the lower to middle 
60s. Much drier air aloft will advect into the area and keep rain 
free conditions. Low level pressure gradient will increase tonight 
as a surface high pushes down the mid-Atlantic states. This should 
hinder fog formation.  

58/rose

.LONG TERM...
/Updated at 0355 AM CST Sat Dec 07 2019/

Sunday through Friday.

Relatively active weather is expected across the CONUS for the 
upcoming work week as a result of several mid/upper-level shortwaves 
to traverse the country. This will produce a period a wet weather to 
begin overnight Sunday in the form of isolated light rain showers 
via the onset of low-level WAA across Central Alabama. This activity 
will gradually peak in coverage/intensity on Tuesday, and eventually 
clear the area to the southeast on Wednesday ahead of a stout cold 
front. Thereafter, a second round of wet weather is possible for the 
late Thursday through early Saturday timeframe.

By Sunday morning a rather complex upper-level pattern is progged to 
continue evolving across the country. A sharp trough is forecast to 
begin digging across the West Coast with a low amplitude/downstream 
jet streak positioning across the souther tier of the country. 
Through time the trough is expected to become more amplified with 
southwesterly flow aloft overspreading the Southeast with a sub-
tropical ridge near the northern Caribbean. By Tuesday morning this 
places favorable synoptic scale lift via the right entrance region 
of the jet streak to our north, as well as continuation of low-level 
WAA. Peak coverage of rainfall is forecast through Tuesday evening 
as additional forcing from the advancing shortwave provides PVA and 
a deformation axis from the TX Gulf Coast northeastward through the 
southern Appalachians. PWs are expected to rise to the 1.3-1.5" 
range during this time, which is plenty to support widespread rain 
chances. However, totals are forecast to remain at or below an inch 
at this time as convection remains quite limited due to little 
instability, even aloft. With the cold front forecast to continue 
southeastward across Central Alabama through the afternoon, 
aforementioned forcing aloft will provide needed support for over-
running rain showers through the evening. However, the Canadian 
airmass will not bring sub-freezing temperatures into the area 
until early Wednesday morning. By this time the trough axis passes
to our east & associated subsidence will signal the end of 
rainfall as the much cooler/drier airmass takes over with high 
pressure. Forecast details with this system will continue to be 
tweaked in the coming days. For now, any wintry precipitation that
may occur in the cold airmass will be negligible (as with the 
last case of isolated flurries).

After frontal passage on Wednesday, highs in the 40s/50s are 
forecast through the end of the forecast period. High pressure will 
keep weather conditions relatively quiet through around Friday 
whereas another potent shortwave is expected to approach from the 
west. This will support another period of wet weather as an 
associated low pressure system develops across the region. For now, 
PoPs have been truncated to <40% as forecast certainty remain low 
this far out.

40/Sizemore


&&

.AVIATION...
18Z TAF Discussion.

VFR conditions are expected through Sunday morning at all TAF
sites. Due to the winds remaining light...and increasing cloud
coverage...fog development is not expected at this time. After
sunrise Sunday...introduced MVFR ceilings at KMGM and KTOI due to
increasing moisture and chance for scattered showers through the 
rest of the TAF period. Only included VCSH for now due to
uncertainty in coverage and timing. 

24

&&

.FIRE WEATHER...

Overnight clearing of overcast ceilings led to many areas of fog
to develop across Central Alabama. This should improve throughout
this morning. Otherwise, mostly cloudy skies are expected to 
continue through today with best coverage across the south. A 
slight chance of light rain showers is forecast again on Sunday 
with more widespread rainfall expected Monday night into 
Wednesday. There are no fire weather concerns at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     62  44  58  49  68 /   0  10  20  50  40 
Anniston    65  46  59  50  70 /   0  10  20  50  30 
Birmingham  63  47  61  53  68 /   0  10  20  40  30 
Tuscaloosa  64  48  64  53  70 /   0  10  20  30  30 
Calera      65  47  61  52  69 /   0  10  20  40  20 
Auburn      63  46  58  52  69 /  10  10  20  40  30 
Montgomery  67  50  64  55  74 /  10  10  20  30  20 
Troy        65  49  64  55  74 /  10  10  20  30  20 

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None. 

&&

$$