Scientific Forecaster Discussion
fxus64 kbmx 242056
Area forecast discussion
National Weather Service Birmingham Alabama
356 PM CDT Mon Jun 24 2019
for fire weather.
There are several surface boundaries across central Alabama this
afternoon, the most prominent being a surface trough entering
western areas. This boundary was the surface reflection of an
upper trough moving overhead. As mentioned below, instability
ahead of this boundary is moderately unstable with ml cape 2500,
SBCAPE 4000, downdraft cape near 1000 east half, and surface dew
points in the low to mid 70s. Mid and high level cloudiness has
restricted surface isolation somewhat and overall moisture
convergence along any said boundary is somewhat lacking. The lapse
rates are not quite as high as previous days due to slightly
warmer temps aloft. The latest visible satellite imagery has the
cumulus field stunted in many places. Effective bulk shear has
decreased slightly but still is near 20-25kts. 3 hour Theta E
change and dew point change actually indicate a decrease across
central Alabama. With all of this said, it appears the opposing
factors are winning out, at least temporarily this time. The radar
and satellite presentations have very little indication of any
area developing stronger storms in the next hour or so. The latest
run of the hrrr has the 925-850mb wind Max decreasing with time
and pulling into eastern Tennessee. Therefore, every second that
ticks away decreases our chances of any severe storms. Due to
level of conditional instability present, will hold onto the
severe threat through early this evening. The trough will move
eastward and pass east of I-65 by 3-4 PM and into Georgia this
evening. Due to the wide range of solutions in the latest model
output, will slightly drop overall pop into the 50-60 range where
the highest pops are northeast.
The latest model solutions are in fair agreement concerning the
extended period. A short wave trough moves into the area on
Wednesday creating a weakness in the overall ridging. We then
undergo a change into cyclonic flow aloft thereafter as a slow
transitioning Rex block sets up.
Previous short-term discussion:
Currently evaluating the severe potential for this afternoon.
There are several factors that either support or oppose the
development of severe storms:
Supporting factors...a large outflow boundary has pushed into
western Alabama this morning, the remnant of a much larger and
robust line of storms from last night. While the more active
portion of this boundary has become limited to Gulf Coast, its
mere presence in our area may provide the focus for later
development. Storm Prediction Center mesoanalysis already shows sbcapes in excess of
3000 j/kg, and MLCAPES of 1500-2500 j/kg. Winds ahead of the
outflow boundary are steady out of the south to southwest, and low
level moisture is quite rich, with surface dewpoints in the mid
70s. Synoptically, an upper level shortwave trough will continue
to move through the Ohio and Tennessee River valleys through the
afternoon, providing some larger scale lift (more so in the
northern portion of our area).
Opposing factors...as mentioned above, the active part of the
outflow boundary this morning was limited to the Gulf Coast. In
West Alabama, while there was a discernible temperature and
dewpoint gradient across the boundary, the surface pressure field
has largely equalized, which in turn is limiting convergence along
it in our area. Also, while CAPES are indeed impressive given the
time of day, they have not exactly increased appreciably in the
past few hours. Extensive cloud cover probably has a lot to do
with that. Finally, there is the timing factor. The longer it
takes for convection to re-fire in our area, the farther east the
outflow boundary is able to get, which would limit the severe
Course of action...we may be able to trim off the severe weather
potential on the western side of our area, based on the position
of the outflow boundary and relative stability behind it. Based on
radar and satellite trends, forecasts of cape, and model output,
we may need to extend the slight risk area further south. Finally,
also based on model trends and ongoing weather, we can probably
also adjust the ending time sooner by a few hours.
Will have updated graphics out within the next hour (by 1600z).
/issued at 430 am CDT/
Wednesday through Sunday.
The ridge will begin to retreat some on Wednesday and could place
central Alabama back in the northwesterly flow aloft and see yet
another mesoscale convective system work into the area late morning and slide through during
the day. Right now looking at just general thunderstorms with this
activity but will need to monitor to see if the threat for winds
will be on the increase as we get closer. A ridge will begin to
build back into the region on Tuesday and then amplify on Wednesday.
However, moisture will remain and we will likely see isolated to
scattered showers/storms on Tuesday through Thursday.
On Thursday afternoon, the Main Ridge will break down to our west
and easterly flow will begin to become predominate across the area.
This will provide a little bit more in bulk moisture in place across
the area beginning Thursday night and increasing Friday. Wet
conditions will persist through the weekend
With the Summer time temperatures and afternoon heating, any storm
good be on the strong side. But predictability is too low to mention
anything for next week at this time. On a whole look for near normal
temperatures through next week, with above normal rain chances,
especially as we head into the weekend.
18z taf discussion.
Remnant outflow from convection this morning in eastern
Mississippi is currently making its way through central Alabama.
Behind the boundary, low-level clouds have been largely non-
existent with only a deck of high level clouds from tcl to toi.
Expectations right now are for thunderstorms to develop this
afternoon in eastern Alabama along this boundary generally east
of bhm. Therefore, confidence was too low to include thunderstorms in the vicinity at most
sites. The exceptions were anb and asn where cumulus development
is observed on vis satellite within the convergent zone along the
boundary. Left thunderstorms in the vicinity in the forecast for both of the mentioned
terminals and will amend as necessary if development this
afternoon is more widespread than expected. In addition,
southwesterly pressure gradient winds are gusty this afternoon
with gusts up to 20 knots observed. Ceilings will continue to rise
overnight with winds becoming calm across the area. As a result,
patchy fog is possible before sunrise with brief lowering of
visibility expected at most sites as early as 08z. Terminals
should generally remain in MVFR to VFR criteria through the
A hot and humid airmass will remain in place. Rain chances
continue through tonight as a frontal boundary moves through the
area. Less coverage is expected on Tuesday and Wednesday. However,
rain chances remain in the forecast each day with humidity values
fairly high. We are not expected to reach critical fire weather
conditions any day this week.
Preliminary point temps/pops...
Gadsden 68 89 66 87 67 / 20 30 20 30 20
Anniston 69 90 67 88 68 / 30 20 20 30 20
Birmingham 71 91 70 89 70 / 20 30 20 50 20
Tuscaloosa 71 92 70 90 71 / 20 30 30 40 20
Calera 69 90 68 88 68 / 20 30 30 30 20
Auburn 71 90 70 89 70 / 40 20 20 20 20
Montgomery 71 92 70 92 70 / 30 30 30 30 20
Troy 70 91 69 91 69 / 40 30 30 20 20