645 
FXUS64 KBMX 181823
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
123 PM CDT Sat Aug 18 2018

.UPDATE...
For 18Z Aviation.

&&

.SHORT TERM...
Today and Tonight.

An upper level trough extending southward from the Ohio River
Valley will move across the region today. Ahead of this trough, 
moist isentropic lift has resulted in low stratus and light fog 
across Central Alabama this morning. Have already seen a couple 
short-lived showers north of I-20 over the last couple hours. 
Cannot rule out additional, isolated to scattered showers early 
through the early morning hours.

Southwesterly flow continues today, with PW values around 2
inches. This moist airmass combined with added forcing from the 
upper level trough will result in scattered to numerous showers 
and storms by this afternoon. Best coverage this morning will be 
across the north, and will maintain the 70% coverage areawide 
later today. For tonight, rain coverage decreases, but with 
persistent wet southwesterly flow will keep 40-50% coverage. 

Skies will remain partly to mostly cloudy today, and with
increased rain coverage this afternoon, highs will be in the mid 
to upper 80s. Tonight's temperatures will generally be in the low 
70s, but might see a few locations fall into the upper 60s across 
the northeast.

14

.LONG TERM...
Sunday through Friday.

A pattern of broad low-level confluence will combine with very
moist deep-layer west-southwest flow on Sunday as an upper-level
trough moves eastward off the coast of the Carolinas. This setup 
should be favorable for numerous showers and storms with rain 
chances in the 60-70 percent range. 

Models are in good agreement on Monday into Tuesday and indicate a 
well-organized system ejecting from the Central Plains toward the 
Great Lakes. Low-level convergence and moisture advection is 
expected over a wide area from the Gulf Coast to the Ohio Valley, 
and this should lead to high rain chances across Alabama. Where 
stronger upper-level support exists, some risk of organized severe
storms may be found to our north and west on Monday. This threat 
could shift toward our area on Tuesday but would require more 
deep-layer shear than currently indicated by the global models. 

A cold front may pass through our northern areas on Tuesday night 
into Wednesday and then begin to lose forward momentum across the
middle of the forecast area. However, the front may get shoved 
southward by a secondary shortwave rotating around the base of the
large-scale trough on Wednesday night. This would lead to a dry 
period on Thursday and Friday with much lower humidity and cooler 
mornings as high pressure moves in from the north.

87/Grantham


&&

.AVIATION...
18Z TAF Discussion.

Scattered to numerous showers and thunderstorms are expected to
impact each TAF site through the afternoon...with the greatest
chances around KMGM and KTOI. Any shower and thunderstorm that
moves over a TAF site will temporarily lower visibilities and
ceilings. Confidence is low on exactly where and when this
convection will move...so for now have included VCTS and will
update when confidence increases. Even though IFR ceilings are
expected to develop...enough low level moisture will be present
with a greater chance for calm winds tonight...so included MVFR
fog development in the early morning. Showers and thunderstorms 
are possible again Sunday...though with a focus more in the
afternoon.


24

&&

.FIRE WEATHER... 

Rain chances remain high through the weekend as a cold front
slowly approaches the forecast area and the airmass remains 
unseasonably wet. Low stratus and patchy fog will lift slowly this
morning, and expect similar conditions tonight/Sunday morning. 
There are no fire weather concerns at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     70  85  71  85  72 /  50  70  40  70  50 
Anniston    70  86  72  86  72 /  50  70  40  70  50 
Birmingham  72  87  74  87  74 /  50  70  40  70  50 
Tuscaloosa  73  88  74  89  74 /  40  70  40  70  40 
Calera      70  86  72  87  72 /  50  70  40  70  40 
Auburn      71  84  72  85  72 /  50  70  30  60  30 
Montgomery  73  89  74  90  73 /  50  70  30  60  30 
Troy        72  87  72  89  72 /  40  70  30  60  20 

&&

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

&&

$$