000 
fxus64 kbmx 191813 
afdbmx 


Area forecast discussion 
National Weather Service Birmingham Alabama 
112 PM CDT Wed Jun 19 2019 


Update... 
for 18z aviation. 


&& 


Short term... 
today and tonight. 


An upper level vort Max over Mississippi has produced enough lift 
for the production of scattered showers and a few thunderstorms 
during the overnight hours, mainly along and south of I-20. The vort 
Max will track slowly eastward today and produce additional 
convective development later this morning and into the afternoon. 
Most of the development today will be along and east of I-65. 
Temperatures are forecast to climb into the lower 90s across West 
Alabama. Southwest low level winds will transport this warm and 
muggy air mass into the area of forcing associated with the vort 
Max. Surface based cape values will climb to near 2,500 j/kg this 
afternoon. Slightly higher mid level lapse rates over east 
Alabama will provide enough instability for a few strong to severe 
storms, and will include a marginal risk of severe storms for 
areas along and east of I-65. Damaging winds will be the main 
threat. 


Things get more complicated for the overnight period. An mesoscale convective system 
currently over eastern Oklahoma and North Texas will track east 
southeast today and into Mississippi this afternoon. This activity 
will likely weaken as it approaches West Alabama as it encounters 
subsidence on the western side of Alabama vort Max, but will need to 
monitor for severe potential. Another mesoscale convective system will track towards West 
Alabama later tonight and into Thursday. The models are not in good 
agreement with the evolution of this system, with some models 
showing it falling apart before reaching Alabama, and others holding 
it together. Low level jet will maintain itself across Mississippi 
overnight, so see little reason for the mesoscale convective system to weaken much before 
reaching northwest Alabama. Best potential for severe storms will be 
across the northwest counties, with damaging straight line winds the 
primary threat. 


58/rose 


Long term... 
/issued at 430 am CDT/ 


* a slight risk for severe weather on Thursday. 


* Heat indices of 100-105 f possible Friday through Sunday. 


Thursday. 


The advertised shortwave moving across the southern/Central Plains 
eastward into the eastern Continental U.S. Will bring two possible rounds of 
severe weather to central Alabama on Thursday. 


The first possible threat window opens ~1 am Thursday morning 
with a potential ongoing mesoscale convective system advancing eastward across northern 
Mississippi and into northern Alabama. This particular threat will 
carry the chance for damaging straight-line winds up to 60 mph as 
it moves into the forecast area. This scenario remains at low 
confidence at this time as the system could very well weaken 
before it arrives here, though MLCAPE ~2,000 j/kg and 30-40 kts 
eff. Bulk shear across its inflow region suggest maintenance of 
strong to severe characteristics if the system doesn't become too 
outflow dominate overnight. Nocturnal 925-850 mb winds ~30-40 kts 
also suggest the convective system will be actively replenished 
throughout its journey into our area. As a result, a slight risk 
has been placed across our northwest forecast area as a damaging 
straight-line wind threat may manifest in the early morning hours 
Thursday. 


Thereafter, effects from the possible early-morning mesoscale convective system will have 
implications for the second round of potential severe weather in the 
afternoon & evening. As the overall synoptic shortwave amplifies 
with eastward progression, height falls & cooling temperatures 
aloft will overspread our area with a remnant outflow/Theta-E 
gradient across central Alabama. Wherever this gradient 
establishes will generally determine the spatial area favorable for 
convective development in the afternoon. Convergence along this axis 
will need to be sufficient enough to overcome unfavorable synoptic 
scale subsidence as confluent flow aloft establishes behind the 
shortwave trough axis. If lift is sufficient, guidance has certainly 
maintained favorable thermodynamic variables (mlcape upwards of 
3,500 j/kg and ~7 c/km mid-level lapse rates) with deep-layer shear 
~30-40 kts for severe thunderstorm organization. Thunderstorms will 
be capable of large hail and damaging convective downbursts 
considering dcape 1,100-1,300 j/kg & 500 mb temperatures -9 to -10 
c. As the shortwave continues eastward into Georgia and the 
Carolinas, flow aloft will veer more northwesterly as upstream 
ridging amplifies. Because of varying scenarios of how severe 
threats may manifest in the next 24-48 hours, forecast confidence 
remains low with a marginal risk being maintained for Thursday 
afternoon & evening in our graphical products. Stay tuned for 
future forecast updates. 


Friday through Tuesday. 


In wake of the exiting shortwave Friday morning, the mid/upper-level 
pattern will transition to a longwave trough building across the 
intermountain west with resultant ridging developing along the 
Mississippi River valley. This ridge will continue to 
strengthen/amplify into the weekend as hot temperatures develop in 
the afternoons. To make matters worse, a humid, Gulf airmass will 
linger across the southeast. As such, heat indices are expected to 
increase to the 100-105 f range on the afternoons of Fri/Sat/sun. It 
appears the hottest afternoons will be Fri/Sat with some locations 
likely approaching criteria for a heat advisory. With this 
possibility now likely, will be mentioning in the severe weather potential statement and monitoring 
trends in temperatures & dewpoints in the next day or so. Looking 
ahead in to next week shows a relatively active pattern for this time 
of year to continue with the ridge axis now approaching the East 
Coast. Rain chances will be on the increase with the upstream trough 
and associated surface frontal boundary moving in from the northwest. 


40/sizemore 




&& 


Aviation... 
18z taf discussion. 


A tropical air mass is in place with isolated to scattered showers 
and tstms expected with daytime heating through early evening and 
again early Thursday morning as a front approaches the area. Vsbys 
will fall quickly in the heavier downpours, with vsbys less than one 
mile at times. Strong wind gusts are also possible with stronger 
storms. VFR cigs are expected through much of the period, although 
cannot rule out occasional MVFR heights with shower activity. 
Overnight, as the second round of storms moves through the area, 
expect cigs to fall into the 1500-2500ft range and remain low 
through the end of the forecast period. 


Winds will generally be from the southwest through the evening, then 
become southerly during the brief lull in convection. Winds then 
become southwesterly again when the second round of storms. Other 
than gusts with stronger storms, wind speeds will be around 10kts or 
less. 


14 


&& 


Fire weather... 


Rain and thunderstorm chances remain high through the next 48 hours, 
with an active upper-level pattern. Southerly flow and tropical air 
will keep relative humidity values at or above 60% percent with 
further recovery after peak heating subsides. Kbdi values remain 
high, but increased low-level moisture & recent rainfall will keep 
US from reaching critical fire weather criteria. Drier weather with 
hot afternoon temperatures are expected Friday through Sunday with 
heat indices likely exceeding 100 degrees. 


&& 


Preliminary point temps/pops... 
Gadsden 86 72 87 68 91 / 40 60 70 30 30 
Anniston 86 72 89 70 92 / 50 50 60 40 30 
Birmingham 88 74 90 72 93 / 40 60 60 40 30 
Tuscaloosa 92 75 92 73 95 / 30 50 60 40 30 
Calera 88 73 90 71 92 / 40 50 60 40 40 
Auburn 85 73 89 72 91 / 50 40 60 40 40 
Montgomery 90 75 93 73 95 / 40 30 60 40 40 
Troy 88 74 92 72 93 / 50 40 50 40 40 


&& 


Bmx watches/warnings/advisories/... 
none. 



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