Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 221857

Area Forecast Discussion
National Weather Service Birmingham AL
157 PM CDT Fri Sep 22 2017

Through Tonight.

Isolated to scattered convection has already developed generally
along and south of the I-20 corridor early this afternoon. Weak
lift associated with the mid and upper level trough/elongated
upper low will continue to aid some of this convective development
along with leftover mesoscale boundary interactions. Have raised
PoPs a bit higher over the eastern counties, as low-level easterly
flow is pushing air parcels up and over the higher ridgetops. More
robust cu development was already observed on visible satellite.
This also lines up well with high-res guidance that has the most
development in our central and eastern counties as well. Have
raised highs a degree or two for a few locations this afternoon,
but temperature forecast is generally on track. Expect convection
to dissipate after sunset as typical for summer convection, even
though technically this is the first day of astronomical fall.
Humid conditions will continue during the overnight hours tonight,
with patchy fog expected once again in valley locations and near
major rivers and lakes.


Saturday through Thursday.

On Saturday, we have a rather busy looking upper air setup. A
piece of energy breaks off from a deteriorating Jose to over the
Northern Gulf of Mexico as Maria continues to trudge northward
out of the Caribbean toward the East Coast. At the same time a
deep trough digs across the Western US leaving a confined area of
weak upper ridging near the Mid MS River Valley into the Great
Lakes and NE US. Our result over C AL will be low diurnally
influenced pops with still status quo temperatures.

By Sunday, the upper energy from Jose fizzles further while the
low over the Northern Gulf retrogrades toward MS/LA, and Maria
moves further northward further constricting the weak ridging to
NE US while the West Coast system slowly moves over the Rockies.
On Monday we see Jose gone, absorbed into Maria. The system over
the Rockies starts to open up pulling the energy over the southern
states into it. Only weak flow remains over the Eastern US as
Maria monopolizes the flow. The result for C AL Sunday into Monday
will be only low pops south/southwest with better chances near
the Gulf Coast.

Tuesday into Wednesday, the main low associated with the Rockies
system moves northeast toward Manitoba. At the same time, ridging
fills in over the Gulf behind Maria and starts to creep around
into E Conus. During this time, we trend drier across Central
Alabama. By the latter half of the week, we see some divergence
in solutions as to weather we get a shortwave breaking off of the
main Rockies trough as the low pulls away across Canada and a
TX/Mexico ridge set up. Or we could get a somewhat flattening out
of the ridge but another low digging into the Northern Plains
from Canada. Either way, across C AL by the end of the forecast
Thursday, we remain on the dry side in advance of a slowly
approaching surface front across the US now that Maria is moving



18Z TAF Discussion.

Nothing noted on radar at the moment, but a nice cumulus field has
developed. Look for scattered convection today, but expected
coverage still only warrants VCTS mention for the afternoon hours.
As is typical in the summertime, activity will diminish this
evening. Winds will be easterly around 5 kts.

Widespread fog is not anticipated overnight. However, some patchy
fog is possible near bodies of water and in areas that receive
rain today.




Isolated to scattered showers and storms are expected through
Saturday. Rain chances trend lower Sunday and Monday. Relative
humidity values only drop into the upper 40s and 50s. Transport
winds remain rather light which will keep dispersion values too.


Gadsden     66  86  65  85  64 /  20  20  10  10  10
Anniston    67  85  66  84  65 /  20  20  10  10  10
Birmingham  69  87  68  86  67 /  20  20  10  10  10
Tuscaloosa  70  89  69  87  67 /  20  20  10  20  10
Calera      69  86  68  86  67 /  20  20  10  10  10
Auburn      68  85  67  84  67 /  30  20  10  10  10
Montgomery  71  89  69  88  68 /  30  20  10  20  10
Troy        67  86  67  86  66 /  20  20  10  20  10




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