575
FXUS63 KDMX 141141
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
641 AM CDT Sun Jul 14 2024

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Few areas of non-severe storms and gusty winds that may impact
  the area early this morning.

- Hot and humid conditions continue area-wide today and then
  south again tomorrow, with heat indices of 100 to 105F.

- Shower and thunderstorms chances continue tonight into Monday,
  a few of which could be strong to severe. Gusty winds and
  heavy rainfall will be the main threats with storms.

&&

.UPDATE...
Issued at 550 AM CDT Sun Jul 14 2024

Recent trends in short range guidance, particularly the HRRR and
RAP, have started to indicate thunderstorm development over the
northeastern portions of the forecast area this afternoon and
evening. These storms will be induced by the remnants of the
overnight MCS in southern South Dakota, which continues to
produce isolated thunderstorms and strong winds in northwest
Iowa/southeast South Dakota this morning. As this feature
tracks east through the day, it will eventually reach a more
unstable air mass in northeast IA where cooler temperatures
aloft may allow for surface based convection to develop. Weak
low level flow and LCLs around 1000m should help to limit
tornadic development, barring any stretching along a remnant
boundary. However, high DCAPE values and large amounts of
instability will make damaging winds and hail a threat,
especially if storms can utilize every bit of the marginal 25 to
35 kt bulk shear values.

&&

.DISCUSSION...
Issued at 351 AM CDT Sun Jul 14 2024

We continue to watch multiple areas of convection early this morning
as weak waves  kick off thunderstorms along the periphery of the
upper level high in the southwest CONUS. Fortunately, much of the
convection to the north of the state looks as if it will mostly stay
to our east and the MCS that produced 80 mph winds previously
tonight over South Dakota has since weakened as its drawn nearer to
the state, likely due to weaker kinematics ahead of it to keep the
cold pool in balance, as well as the 12C 700 mb temperatures it
resides in. Weve also seen a few storms develop along the leading
edge of the LLJ in southern IA/northern MO tonight, but these have
stayed sub-severe. Therefore, barring any additional development
with the MCS to our west or along the outflow from storms to our
north, not expecting anything other than a few storms this morning.
That being said, some gusty winds may accompany these features as
they move into warm, dry environments.

In addition to storms lingering into the morning hours, the heat
will continue to build in today, leading to another hot and humid
day for much of the state. Observed highs yesterday underperformed
the forecast by 1 to 3 degrees across the area, likely due to a
combination of 850 hPa temperatures being a bit cooler than
expected, as well as some patchy cumulus/shower activity through the
afternoon hours. Likewise, having the warm layer aloft could be
limiting how deep of mixing can occur, which would then translate to
surface temperatures. Fortunately, it seems guidance has picked up
on the slightly cooler 850 hPa temperatures, which has therefore
brought NBM highs down a tad from yesterday. On the flip side,
dewpoints overperformed yesterday, which kept apparent temperatures
over 100F, albeit still slightly lower than forecast. Keeping these
trends in mind, have tweaked high temperatures and dewpoints
slightly, but still anticipating hotter temperatures today with
slightly better mixing. That being said, the aforementioned MCS and
additional convection through the morning hours will likely have
some effect on highs today. Even if the precipitation dissipates
prior to arriving here, residual cloud cover will still likely drift
over the state in the morning. Therefore, because of the uncertainty
with convection today, decided to maintain the same area of counties
for the heat advisory.

As we get into tonight, more chances for storms will be possible as
the upper high begins to break down and the upper trough to the
north drops down into the region. Guidance is again fairly messy
with the progression of storms tonight, with convection first
developing with the better forcing to our north tonight and then
potentially dropping into the state Monday morning. Confidence is
low in these storms impacting the forecast area, but the mostly
likely area would be northern Iowa with strong winds being the main
concern. Confidence is then higher in the occurrence of convection
associated with the frontal passage Monday afternoon. These storms
could be more area wide, but the warm layer aloft will likely
inhibit widespread storm development. Strong winds will be the
primary concern with the afternoon storms as well, thanks to the
high bases and dry low levels. Locally heavy rainfall could
also become a concern with 2"+ PWATs, but storms should be
fairly progressive as the front pushes south. A supercell would
be needed to produce any larger hail, as any small hail will
melt as it falls. Finally, the tornado threat should be low, as
LCLs will be around 1500m or higher.


Not to be overshadowed by the storm chances, temperatures on Monday
will again be quite warm, primarily over southern Iowa where the
boundary will be arriving a bit later in the day. Theres potential
for Monday to also be the warmest of the three, with 850 hPa
temperatures nearing 30C ahead of the front. That being said,
Mondays highs will suffer from the same uncertainty of previous
days and be dependent on both location of the front, as well as any
convection/outflow boundaries that result from it. Regardless, those
that avoid these features on Monday could see heat indices exceeding
105F and potentially even approaching 110F. After Monday,
temperatures return to more normal values and high pressure overhead
mellows out the pattern through the week.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 636 AM CDT Sun Jul 14 2024

There`s quite a lot going on across the area this morning, with
multiple areas of showers and thunderstorms producing low cigs
and sporadic wind gusts. First, the area thunderstorms and
associated outflow in northwest Iowa will continue south and
east, likely impacting KFOD and KDSM. This will likely bring
a brief increase to winds as well as shift to northwesterly. Low
clouds may also accompany, but confidence is low. The other area
of storms is over KALO and KMCW, which is also producing gusty
north northeasterly winds and low cloud cover. The cloud cover
should improve, but breezy winds could linger.

As we get further into the day, convection is expected to
diminish, but redevelopment is possible in the afternoon, mainly
at KALO. Storms will be scattered and location of development is
tricky, so have just included VCSH for the most likely period at
KALO and will amend if need be. Elsewhere, skies should clear
some through the day with light to breezy winds across the
south. Additional storms are possible north overnight and into
tomorrow morning, but have left these out of TAFs for now.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM this afternoon to 8 PM CDT this
evening for IAZ004-015-023-024-033>035-044>048-057>062-070>075-
081>086-092>097.

&&

$$

UPDATE...Dodson
DISCUSSION...Dodson
AVIATION...Dodson