Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 121059
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
559 AM CDT Mon Apr 12 2021

.UPDATE...
For 12Z Aviation.

&&

.SHORT TERM...
/Updated at 0256 AM CDT Mon Apr 12 2021/
Through Tuesday.

High pressure over the region today will slide southeast over the
next 24 hours. Meanwhile a larger, stronger high pressure system
will slide east across the Ohio Valley. This high will force a cold
front down from the north/northeast on Tuesday afternoon. Right now
moisture appears limited so will stay with with non mentionable PoPs
for the afternoon, but would not be out of the question for a
renegade shower/storm to develop during the peak heating of the day
across the north with the front and southwest with the added
southerly flow ahead of the front.

16

.LONG TERM...
/Updated at 0339 AM CDT Mon Apr 12 2021/
Tuesday night through Sunday.

A trifecta of upper lows will be located across the northern
stream to start the period, over the interior Northwest, upper
Midwest, and east of the Canadian Maritimes. Meanwhile a zonally
oriented ridge will be located across the Canadian provinces.
Quasi-zonal but broadly anticyclonic flow will remain across the
southern CONUS with various convectively-generated shortwaves. At
the surface, a continental cold front will be stalling across
northwest Alabama, while a marine front will extend from the
ArkLaMiss southeastward to the northern Gulf. An isolated shower
or storm will be possible during the evening hours near the
stalled continental front. The main focus for convective activity
will be back over the ArkLaTex near a convectively
generated/enhanced shortwave where a wave of weak low pressure
will be developing at the triple point between the two fronts,
but there is a slight chance of showers/storms developing ahead of
this feature across our western counties after midnight. An MCS
is expected to be developing by Wednesday morning over the
ArkLaMiss and will move east-southeastward on Wednesday along the
instability gradient associated with the marine front. The
expected track of the MCS is expected to keep any surface-based
instability and severe storm/flooding potential closer to the
coast, with instability over Central Alabama being more elevated
in nature. The wave of low pressure is also not expected to
undergo much in the way of deepening until it passes the area and
reaches the Carolinas. Increased rain chances across the south to
likely with a little less confidence in rain chances further north
depending on to what extent the MCS causes these areas to be "cut-
off" from the best moisture and lift. But still think most areas
will see measurable rain with a saturated column and additional
lift from the cold front as it pushes southeastward with height
falls also occurring as the Upper Midwest upper low sinks
southeastward across the Great Lakes.

Rain chances mainly decrease from southwest to northeast by
Wednesday evening, but some small rain chances may linger across
the south into Thursday morning as another weak shortwave may
temporarily enhance post-frontal rains. Otherwise a dry post-
frontal air mass will move into the area. Trended temperatures
towards the NBM 25th percentile for Thursday and Friday due to
cold air advection. Will have to monitor the progression of the
surface ridge axis Thursday night and mid and high level clouds
moving in, as typically cooler areas in the northeastern valleys
could reach the 30s if decent radiational cooling develops.

For the extended portions of the forecast, a strengthening ridge
along the West Coast will favor a longwave trough developing over
the eastern CONUS. This will cause the remnants of the Northwest
upper low as well as a northern stream shortwave to move towards
the area towards the Friday/Saturday timeframe. Timing of various
shortwaves moving through the longwave trough is uncertain but
will result in periods of rain chances and near normal to below
normal temperatures. With high pressure in control at the surface
maintaining generally off-shore flow at the surface, these rain
chances will be mainly of the stratiform over-running variety,
with no instability present.

32/Davis


&&

.AVIATION...
12Z TAF Discussion.

Clear skies and unrestricted visibility will continue across
central Alabama terminals through the next 24 hours. Calm winds at
night and westerly winds between 7 and 10 kts during the day.

16

&&

.FIRE WEATHER...

Drier air remains in place through much of the daytime hours on
Tuesday, with RH values in the 25-35 percent range today and
30-40 percent range on Tuesday. Westerly winds will become
southerly on Tuesday, with speeds at or below 12mph both days.
Wetting rains return Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     82  51  81  53  71 /   0   0  10  10  50
Anniston    82  54  82  55  73 /   0   0  10  10  50
Birmingham  83  55  82  57  71 /   0   0  10  10  50
Tuscaloosa  84  55  82  57  70 /   0   0  10  20  60
Calera      82  55  82  57  71 /   0   0  10  10  60
Auburn      82  56  82  58  73 /   0   0  10  10  60
Montgomery  84  55  85  58  73 /   0   0  10  20  70
Troy        85  55  86  59  76 /   0   0  10  10  60

&&

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

&&

$$



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