Area Forecast Discussion
Issued by NWS Birmingham, AL
FXUS64 KBMX 241151
Area Forecast Discussion
National Weather Service Birmingham AL
651 AM CDT Mon Apr 24 2017
For 12Z Aviation.
Today and Tonight.
An upper low was currently centered over north Alabama. Low clouds
covered much of the state with patchy drizzle or light rain being
reported over the northern half, close to the upper level
circulation. Light rain or drizzle will be confined to mainly areas
east of I-65 this morning, with low clouds lingering across most of
central Alabama. Clearing likely to begin across west Alabama by
late morning and spreading eastward as the upper low tracks into
Georgia. However, some counties closer to the Georgia state line may
not see much sunshine today. With clearing skies this evening and
winds becoming calm, patchy fog will certainly be a possibility and
will include in this forecast.
Tuesday through Monday.
Upper-level ridging builds into the area today ahead of a deepening
trough over the Great Plains. Winds will shift from the north to
more westerly, then from the south late in the afternoon. A surface
low develops as part of the larger trough over the Southern Plains
early Wednesday. Models disagree with the track of the surface low
and evolution of the trough as we go into Thursday. The GFS has the
trough digging further south into the Ozarks with a stronger vort
max at the base of the trough. The ECMWF has a less-amplified trough
moving more quickly into the Great Lakes region. Both models stretch
a cold front down through the Mississippi River Valley and moving
eastwards through Central AL on Thursday. Instability is forecast to
be in excess of 2000 J/kg and sufficient 0-6km Bulk Shear is
expected for organized storms. However, the upper-level jet is well
to the north and west of the area, which limits the upper level
support. The biggest question will be the timing of the front as it
moves through and whether or not the trough digs south, leading to
height falls. For now, will leave mention of severe threat out of
the HWO and continue to monitor trends in the models. Would not be
surprised to see at least see a few strong storms across the area
Along with any potential severe threat, models have 1.7-
1.8" PWATS, which is well above the climatological maximum for this
time of year. NAEFS and GEFS show PWAT above the 99th percentile as
well, which adds confidence in the potential for heavy rain in any
storms that do develop on Thursday, regardless of the severe
Southerly flow returns quickly after the frontal passage as low-
level ridging builds in under generally zonal flow aloft on Friday,
leading to above normal temperatures. The ECMWF hints at a warm
front surging northward late Friday ahead of a developing trough in
the Plains. This could lead to some shower activity along our
northern counties Friday afternoon, so have mentioned slight chance
or chance of rain/thunderstorms north of I-80.
The next system takes shape on Saturday as a surface low develops
over the Southern Plains as a trough digs into the Central US.
Models are in decent agreement with the surface low moving
northeastward into the Great Lakes region Sunday and into Monday,
stretching a cold front down through the Mississippi River Valley.
Here in Central AL, expect an increase in southerly flow ahead of
the deepening trough and temperatures remaining well above normal
for this time of year. For now, models disagree on exactly when the
cold front pushes through Central AL just beyond the extended
forecast period (late Monday into Tuesday). Will continue to monitor
this system for timing and any severe potential in the coming days.
12Z TAF Discussion.
A deep closed upper low over north Alabama was producing
widespread low clouds across Alabama. The cigs across central
Alabama were in the 1000-2000 ft agl range. Patchy light or
drizzle possible across east-central Alabama before 17z, but
vsbys should stay above 5 miles and did not include any pcpn in
Tafs. Cigs will gradually rise throughout the day. Difficult to
pinpoint when clearing will occur at each site, but the overall
trend will be clearing from west to east. With clearing skies and
light winds overnight, patchy fog likely areawide. Confidence too
low this early in the forecast period to include vsby
Very small rain chances today as an upper low moves overhead.
Northerly flow persists before shifting back from the south on
Tuesday. Critical fire weather conditions are not expected at this
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 69 50 82 54 84 / 20 0 0 0 0
Anniston 70 53 82 57 84 / 20 0 0 0 0
Birmingham 71 54 84 60 85 / 20 0 0 0 0
Tuscaloosa 73 53 83 57 85 / 10 0 0 0 0
Calera 71 54 83 59 84 / 10 0 0 0 0
Auburn 68 55 80 59 83 / 10 0 0 0 0
Montgomery 74 55 85 59 87 / 10 0 0 0 0
Troy 72 53 83 57 84 / 10 0 0 0 0