169
FXUS64 KHUN 251140
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
640 AM CDT Sat May 25 2024

...New AVIATION...

.NEAR TERM...
(Today)
Issued at 359 AM CDT Sat May 25 2024

As an outflow boundary moves in from the west this morning, an
unorganized line of storms has formed in the Mississippi Valley.
Guidance from CAMs shows the line weakening as it moved into our
area and dissipating. However, development behind it is likely
due to lingering stratiform rainfall creating a temperature-
driven boundary.

Threats through this afternoon will include the following: Heavy
rainfall/localized flooding (medium confidence) Damaging
winds(medium confidence) hail (low confidence) and a tornado or
two (very low). Tornadoes remain a very low confidence threat
throughout the day. In the morning to early afternoon hours, we
remain capped with sufficient shear in place. However, there is a
low chance this cap can be overcome and allow an increased low
level streamwise vorticity to support a potential tornado threat.
As we move into the afternoon hours, wind shear decreases
significantly and the possible tornado threat decreases as well.
Therefore, it is a conditional threat depending on if the cap is
able to erode while there is enough environmental wind shear to
support the formation of one or two tornadoes. Heavy rainfall and
damaging winds will be our primary concerns through tonight. Any
storms that form are forecast to move slowly and have a potential
for backbuilding. PWATs in these storms are forecast to be around
1.7-1.75", which is exceeding the 90th percentile sounding
climatology per BMX. Model soundings support DCAPE values around
800-1,000 J/kg this morning into the late afternoon/evening hours,
supporting a damaging wind threat. As we move into the afternoon
hours, low level lapse rates increase to around 8.0 C/km as
atmospheric mixing occurs, supporting the potential for strong
downdrafts. Due to the high PWATs and possible waterloading, hail
has been kept as a low confidence threat.

While this morning`s storms are more unorganized linear clusters
and we are able to time them, this afternoon`s storms will likely
be a different story for timing. Their timing depends on where the
secondary boundary sets up, however, we are currently thinking
this will be somewhere around 12-14Z (7-9 AM CDT). After this
secondary cluster, we will be looking at more of a pop up
microburst situation through the evening hours. On the other hand,
there is also a low chance that redevelopment does not occur and
we are able to get through the day without any strong to severe
storms throughout the TN Valley. We will be closely monitoring
this mesoscale-driven situation. Storm total rainfall through
tonight is forecast to be less than an inch, however, higher
amounts are likely in areas that receive rainfall during these
sporadic, additional rounds.

&&

.SHORT TERM...
(Tonight through Tuesday)
Issued at 359 AM CDT Sat May 25 2024

The potential for microbursts will continue into the evening
hours before subsiding with the loss of diurnally driven
instability around sunset. Overnight, a break in rainfall will
take place for most of the TN Valley. However, low chances (around
30% or less) have been kept in due to lingering showers.

Sunday into Monday, high sfc pressure off the southern coast of
Florida will cause southerly winds to advect moisture from the
Gulf to the Tennessee Valley. This will support increased dew
points and subsequently an increased heat risk (to be discussed at
the end of this short term section) ahead of a cold front. A
slight risk (level 2/5) is in place for most of the area
(primarily north of the TN River). Timing continues to shift
later, however, it is looking like storms will move in from the NW
around 1 AM CDT and continue southeastward through noon. These
storms will bring risks of damaging winds (medium confidence),
heavy rainfall/localized flash flooding (medium confidence), hail
(medium confidence), and one or two tornadoes (low confidence).
Forecast soundings currently have us capped overnight, however,
there is sufficient shear in place as well as low level
streamwise vorticity to support a relatively higher tornado risk
if that cap is broken. Steep mid level lapse rates (7-8 C/km) and
MUCAPE around 1700-1900 J/kg will also support a hail risk.
DCAPE around 900-1100 J/kg also exists in these model soundings,
accompanied by sufficient shear to warrant a damaging wind risk.
We will continue to monitor this system closely.

As mentioned previously, high dew points will contribute to an
increased, moderate heat risk with high temperatures forecast to
reach the low 90s Sunday. During this time, heat will affect
individuals most sensitive to heat, especially those without
effective cooling and/or adequate hydration. Max heat indices
during this period will be around 95-99 degrees F.

Overnight Monday into Tuesday, dry weather returns (PoPs 10% or
less) as high pressure filters in from the northwest and lows
drop into the 60s before rising back into the low to mid 80s
during Tuesday afternoon.

&&

.LONG TERM...
(Tuesday night through Friday)
Issued at 359 AM CDT Sat May 25 2024

Sfc high pressure allows for dry weather to settle over the
region through the mid week. Upper level shortwaves will allow a
very low chance of showers (10% or less) during this time,
however, confidence is low in this occurring. High temperatures
during this period are forecast to be in the 80s with overnight
lows in the 50s/60s.

&&

.AVIATION...
(12Z TAFS)
Issued at 640 AM CDT Sat May 25 2024

A line of storms will continue to push eastward out of the area
this morning. Additional development is possible later this
afternoon and evening but confidence in timing and placement
remains too low to warrant more than a PROB30 at this time.
Otherwise, VFR conditions prevail.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...None.
TN...None.
&&

$$

NEAR TERM...HC
SHORT TERM....HC
LONG TERM....HC
AVIATION...30