Scientific Forecaster Discussion
fxus64 kbmx 291720
Area forecast discussion
National Weather Service Birmingham Alabama
1220 PM CDT sun Mar 29 2020
for 18z aviation.
A deep upper low was located just west of Lake Michigan while a
shortwave ridge was amplifying over Colorado and this extended
south into West Texas. A trough extended from western Nevada south
into southeast California.
A cold front extended from central Georgia southwest to near
Mobile, Alabama. A warm front extended from a surface low over
Southeast Michigan and extended southeast through Pennsylvania and
into Virginia. Persistent surface high pressure located over the
southwest Atlantic Basin continued to nose westward across much
of the Florida Peninsula.
/updated at 1030 am CDT sun Mar 29 2020/
Effective cold front which is primarily denoted by a wind shift
from southwest to west/northwest along with a sharp drop in dew
point values, extended roughly along the I-85 corridor from
southern Chambers County southwest across far southeast Montgomery
County. A boundary associated with some clouds and light radar
returns roughly extended from northeast to southwest roughly
along the I-59 corridor. Kept pop's highest across the southeast
in proximity of the surface front while tapering pops lower back
northwest to the second boundary location.
Isolated shower activity accompanies the front with less activity
back to the northwest currently. Maintained a small chance for an
isolated thunderstorm or two southeast as we move into early
afternoon but overall potential remains low.
Drier air will continue to move into the state from the west
through the day today with fair skies expected across the
northern half of the forecast area.
Dry conditions are expected overnight despite gradual increasing
clouds from the west as the cold front stalls to the southeast of
our forecast area. The front will begin to lift northward as a
warm front during the daytime hours Monday. Will maintain the
potential for a few showers Monday afternoon due to isentropic
lifting processes across our area as the front approaches from the
/updated at 0343 am CDT sun Mar 29 2020/
Monday night through Tuesday.
There have been no significant changes to our expectations
concerning the severe threat on Tuesday. Early Tuesday morning, an
upper trough is progged to move over the Midwest while associated
surface cyclogenesis occurs over the arklatex. Guidance has been
fairly consistent in tracking the surface low west to east through
essentially the center of Alabama, although a couple models
continue to show a slight southward trend in the positioning of
the low which would limit the overall threat to locations south of
the forecast area if that trend continues. A warm front will be
lifted to just north of the Montgomery area early Tuesday morning
in response to the approaching system. Warm, moist southerly flow
with dewpoints in the mid to upper 60s will surge to as far north
as Clanton, allowing for SBCAPE of ~1000 j/kg across the
Montgomery area and south by Tuesday afternoon. Strong deep-layer
shear will be supportive for organized updrafts given sufficient
instability. This will be a quick moving system with rain chances
decreasing across the area by mid to late afternoon as the low
moves into Georgia. Therefore, the window for severe weather
should be fairly small, primarily late morning to early afternoon,
where the highest instability should align with strongest wind
shear before the favorable dynamics quickly shifts to the mid-
Atlantic by late afternoon. Will introduce a slight risk for areas
generally along and south of the I-85 & US 80 corridor due to the
consistent threat potential which has been observed over the past
several days, but adjustments may be necessary to the
confidence/threat level in future updates, especially depending on
the track of the low and northern extent of the warm sector.
Primary threats include damaging winds and quarter-size hail. A
tornado or two will be possible, as supported by veering low-level
winds and curved forecast hodographs, before flow becomes
unidirectional by the afternoon.
Wednesday through Saturday.
Low-level ridging quickly builds across the Mississippi Valley by
midweek as the mid-level low moves into the Atlantic. Mean 1000-
500mb relative humidity values ~20-40% accompanied by strong height rises will
allow for clearing skies on Wednesday with northwesterly cool air
advection supporting highs ranging from the mid 60s north to near
70f south. Rain chances will begin to rise again towards the end of
the week. An elongated upper low, extending from western Canada into
the upper plains, will develop a surface low over portions of
Oklahoma and Kansas on Thursday. The low will rapidly track towards
the upper Midwest with a weak cold front trailing into the lower
Mississippi Valley and southerly low-level flow returning across the
region. At the same time, a weak mid-level impulse embedded in the
westerly flow aloft will develop along the Louisiana coast and
provide additional lift as it moves eastward across the deep south
to start the weekend. Without a focused area of forcing and dry air
occasionally in the mix, did not go higher than chance pops for
Friday or Saturday, but the occasional showers and cloud cover will
keep temperatures near average for this time of year.
18z taf discussion.
VFR conditions are expected to prevail through this cycle.
The surface cold front have cleared all our terminal locations in
central Alabama. Expect west to northwest winds up to 10 kts at
most sites this afternoon. There will remain potential for a few
rain showers or perhaps a ts at our southern terminals through late
afternoon but probabilities are too low to include at any
location. Few to scattered clouds in the mid to high levels are expected
as a southwest flow aloft prevails.
The cold front is expected to stall across the Florida Panhandle
into far southeast Alabama tonight before returning northward as a
warm front during the day on Monday. Expect broken to overcast skies with
bases gradually descending thorough the day but bases should
remain above restrictive criteria. Chances for rain showers will increase
from west to east later in the day with growing ts potential with
time but these chances are too low to include at any site through
this cycle period.
Expect some lingering showers and a few thunderstorms across the
eastern counties early this morning. Drier and cooler low level
air will move in behind the cold front through the day, and rh's
will drop into the 35-45 percent range north, and 45-50 percent
south. Rain-free and slightly cooler conditions will continue
through Monday with afternoon rh's ranging from 30-40 percent,
but rain becomes widespread on Tuesday as a low pressure system
moves into the area.
Preliminary point temps/pops...
Gadsden 76 52 73 52 65 / 30 10 10 70 100
Anniston 77 54 74 54 67 / 40 10 10 60 100
Birmingham 77 55 74 55 69 / 20 10 10 80 90
Tuscaloosa 78 56 75 56 72 / 20 10 20 80 90
Calera 77 56 75 55 70 / 30 10 10 70 90
Auburn 78 57 76 57 72 / 30 10 10 20 100
Montgomery 80 58 79 60 78 / 40 10 10 40 100
Troy 82 59 81 62 78 / 30 0 10 10 100