701
FXUS63 KDMX 150455
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1155 PM CDT Fri Jun 14 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Prolonged period of elevated heat and humidity Sunday through
  Tuesday.

- Off and on chances for showers and storms this weekend into
  next week. Some chances for strong to severe storms and
  locally heavy rainfall Saturday mainly west/southwest during
  the late afternoon to evening.

&&

.DISCUSSION...
Issued at 335 PM CDT Fri Jun 14 2024

Rest of Today Through Sunday:

The lower dew points and humidity levels of today will be short
lived with a prolonged heat wave upcoming with upper-level ridging
dominating the overall pattern today and again on Sunday into early
next week. A shortwave lifting out of the southwest U.S. today will
be our main disruption in the overarching pattern as it nears and
crosses through the area early Saturday into Sunday. Initially this
will be in the form of showers or weak storms starting overnight as
theta-e advection increases west/southwest with general expectations
and model trends suggesting any showers/storms to be on a weakening
trend as they move eastward with time towards central Iowa during
the morning hours Saturday. It will also take time for profiles to
saturate with nearing 12kft of dry air in place prior to theta-e
advection increasing tonight making it so rain could hold off until
closer to early Saturday morning. Either way, instability remains
very minimal overnight so while cannot completely rule out some
lightning, not expecting anything in the way of severe storms
overnight/early Saturday. Some CAMs kick off new storms on Saturday
morning south behind the weakening first line which could
potentially muck up storm potential late Saturday afternoon into
evening in addition to how much clearing does or does not occur
behind the first main line. However, moisture, instability, and heat
should all be on the increase through the afternoon hours Saturday
as a warm front lifts into the area ahead of the approaching wave.
The question will be how much instability and will it be surfaced
based. On the high end, MLCAPEs could reach 3000-4000J/kg which
could easily help storms become severe. More likely instability
might be closer to 1000-2000 J/kg of MLCAPE paired with the more
marginal 25-35 knots of bulk shear. Soundings indicate steepening
low level lapse rates, especially southwest on Saturday afternoon,
with LCLs under 1000m, 0-1 SRH values near to over 200 m2/s2, which
would keep some tornado and large hail potential with any
initial supercells that are able to form, with some damaging
wind potential if any storms can congeal. Details are highly
dependent on morning activity and our degree of realized
instability, but the SPC Day 2 Slight (Level 2 out of 5)
captures the main threat area well. Although the severe threat
wanes with time into the evening hours as storms move eastward,
rain continues through the overnight into Sunday morning before
ending in the east early Sunday.

Will also have to monitor heavy rain amounts as pwats increase to be
near to over 1.5-2" by 00Z Sunday (Saturday night) with warm cloud
depths of 11-13kft. 24-hour HREF QPF Probability Matched Mean values
ending 12Z Sunday (Sunday morning) indicate localized areas of 1-3"
with isolated higher amounts possible. Highest QPF amounts look to
be over southwest into western Iowa, with a secondary localized area
over northern Iowa given the potential for repeated storms from
activity Saturday morning and Saturday evening into Sunday morning.

Some additional storms are possible on Sunday later in the day,
especially far north to northwest, but otherwise main story Sunday
will be the building heat and humidity as highs reach into the 90s
with heat indices in the mid 90s to nearing 100 in parts of central
to southern Iowa.

Monday and Beyond:

The new work week starts off with Iowa being sandwiched between an
amplifying ridge over the eastern U.S. and a digging trough over the
northwest U.S. keeping various degrees of ridging in place in the
otherwise southwest flow. Although there may be periodic storm
chances at times, conditions will remain hot and humid with highs
near to in the 90s and some areas approaching the upper 90s on
Monday. These hot temperatures will be paired with dew points in the
60s to maybe even low 70s at times sending the heat indicies to the
upper 90s, nearing 100 in parts of central to southern Iowa, on
Monday and Tuesday, with Monday being the hotter day. Little relief
is expected at night with lows in the 70s and challenging some high
minimum temperature records on Monday and Tuesday mornings. As
mentioned in the previous discussion, although heat indices remain
below heat advisory criteria, the duration of the heat event may
lead to heat headlines at some point, something we will continue to
monitor. On a positive note, the heat on Monday and Tuesday will be
paired with breezy to gusty winds that will help mitigate some of
how the heat feels. However, certainly prepare accordingly for the
multi-day above-normal summer heat by staying hydrated, limiting
outdoor activities in especially the heat of the day or by taking
breaks in the shade, and never leave pets or kids in a vehicle
unattended - look before you lock!

Although the south to southwest flow remains in place with the
otherwise eastern U.S. ridge and western U.S. trough dominating the
upper-level pattern, uncertainty increases significantly on
Wednesday and beyond in overall degree of heat remaining (whether it
be 80s or 90s) with the Euro suite hotter and drier and the GFS
suite slightly cooler and more active/wetter. One period of storm
chances we`ll continue to monitor is Tuesday night into Wednesday
though details remain sparse at this lead time.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1154 PM CDT Fri Jun 14 2024

Light winds out of the southeast expected tonight before picking
up and becoming gusty through the day tomorrow. A few light
showers will drift over northern Iowa this morning, before
additional rainfall is expected later in the morning and into
the afternoon. Low confidence in location of thunder this
afternoon and evening, so have left out of TAFs at this time.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...KCM
AVIATION...Dodson