781
FXUS63 KDMX 112324
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
624 PM CDT Tue Jun 11 2024

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Few isolated storms possible before sunset northeast, but
  severe threat remains low this afternoon/early evening.

- Strong to severe storms possible Wednesday afternoon and
  evening especially north and east.

- Additional storms, possibly severe, expected south Thursday
  as well.

- Continued warming into midweek as highs reach into the 90s.

- Slightly cooler/drier Friday but heat and storm chances return
  for the weekend.

&&

.DISCUSSION...
Issued at 354 PM CDT Tue Jun 11 2024

Rest of Today:

Scattered showers this morning fizzled out by about midday leaving
mostly clear skies through much of central Iowa except for some
budding cu this afternoon. Surface boundary connected to the main
trough over southern Canada continues to move through the area this
afternoon into evening but overall chances for any isolated storm
development remain fairly low, around 20% or less with dew points
well into the 60sF as many models suggested not being realized. As
of 3 PM, dew points were in the 50s to low 60sF at a few sites with
temperatures in the 80s. These overall lower levels of moisture
should continue to help limit any storm development, though won`t
completely rule out an isolated storm with gusty winds or small hail
mainly in the far northeast, but overall chances for any severe
weather remain low this afternoon into early evening with any storm
development chances waning completely by around sunset. Temperatures
tonight will be warmer than this morning and generally in the upper
50s to 60s.

Wednesday/Thursday:

Wednesday will be noticeably warm and humid as warm air advection
amplifies with the thermal ridge moving through the region and H850
temperatures nearing +20C or more by Wednesday afternoon. This heat
will be paired with surging moisture as dew points reach towards or
well into the 60sF which translates to high temperatures in the
upper 80s to 90s and heat indices in the low to mid 90s for many. A
few theta-e advection induced showers or storms are possible in the
morning to early afternoon mainly north but moisture may once again
be an issue with this early day activity with forecast soundings
looking fairly dry. Attention then turns to the the main shortwave
and associated frontal boundary that will be dropping south through
MN through the day with storms, some severe, possible in two rounds
Wednesday, the first in the later afternoon to evening, and the
second close on the heels of the first, but in the later evening to
early overnight. Some questions remain on the placement of the
storms, especially in the coverage of storms to the south and west,
but storm chances are highest, >60% chance, over northeast areas, as
this is the most likely area to see storms given current CAM trends
and overall parameter space. The extent of capping could be the
limiting factor in portions of central and western Iowa where
afternoon H700 temperatures look to be near +10 to +12C which can be
tough to overcome. As noted in the previous discussion, the overall
parameter space is pretty good with the warm, humid environment
surging MLCAPE values into the 1000-2000+ J/kg range per NAM
and RAP soundings in portions of northern Iowa with storm
relative inflow around 25-35 knots and overall bulk shear of
30-40+ knots. Strong to severe storms are possible with damaging
wind gusts (DCAPEs over 1000 J/kg with lower level dry air in
soundings) and large hail (elongated hodographs) the primary
threats. Won`t completely rule out the possibility of a tornado
if everything can come together with boundary interactions given
increasing helicity values into the early evening, but overall
LCLs are high which would be a limiting factor. Heavy rain may
also occur, especially in areas that see multiple rounds of
storms like the northeast, where rain amounts may near 2-3+
inches, as noted in the 24 hour QPF HREF localized probability
matched mean. Progressive nature of storms should overall limit
hydro issues, but will certainly keep an eye on this with
potential for higher rainfall rates.

Although storms wane by the early overnight, additional showers are
possible Thursday morning with the location of the front towards
southern Iowa the location for new storm development on Thursday
afternoon to evening in another warm, humid, and unstable
environment as highs climb into the 80s to 90s with heat indices in
the upper 90s over far southern Iowa. Storm threats will better be
determined based on location of the front and timing, but severe
storms may again be possible with wind hail, and will even need to
watch the tornado potential depending on how the mesoscale
details evolve.

The overall take away for Wednesday and Thursday is to monitor the
forecast for updates with a SPC Day 2 Slight Risk (Level 2 of 5)
Wednesday north, with a Day 2 Marginal Risk (Level 1 of 5) extending
through much of the rest of the area, and a Day 3 Marginal Risk
(Level 1 of 5) over far southern Iowa on Thursday.

Friday and Beyond:

A small reprieve is expected on Friday with slightly cooler
temperatures, though still in the 80s, and lower dew points.
Additional storm chances return for the weekend with more building
heat as temperatures climb into the upper 80s to 90s again on Sunday
and Monday with upper 90s heat indices south.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 622 PM CDT Tue Jun 11 2024

VFR conditions currently prevail and are forecast through the
TAF period. Forecast uncertainty increases after 18z Wednesday
as model guidance suggests a complex of showers and storms will
dive southeast out of Minnesota. Confidence is low wrt the track
and timing of this thunderstorm activity, however the highest
chances currently reside just north/east of our northern
terminals KMCW and KALO. Opted to leave any mention out of
their respective TAFs for now, however that will be closely
monitored as additional guidance becomes available.

&&

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

&&

$$

DISCUSSION...KCM
AVIATION...Martin