493
FXUS63 KDMX 241802
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
102 PM CDT Mon Jun 24 2024

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Heat Advisory expanded slightly east today for heat indices
  around 105 degrees this afternoon.

- Conditional severe weather threat late this evening with
  damaging winds being the primary threat. Greatest potential in
  the northeast, but storms will be possible across the rest of
  the state as the evening progresses.

- More severe weather possible Tuesday with hail, winds and a
  tornado or two possible. Heavy rain to become the focus in the
  south through the night.

- More rain and storm chances late Thursday.

&&

.DISCUSSION...
Issued at 342 AM CDT Mon Jun 24 2024

The nocturnal jet reached across western Iowa overnight and formed
scattered thunderstorms along the instability axis and just ahead of
the EML. As these wane with sunrise, the EML will encompass
generally the Western half of the state this afternoon, capping
it with a 14C H700 temperature. 25C+ temperatures at H850 will
cover the western third of the state and help boost temperatures
well into the 90s. As mentioned in the previous discussion, dew
points in the 70s signal that there`s enough moisture in the
air to prevent a warming push to 100 degrees F, but nonetheless,
temperatures across the west will be hot and muggy. Have
expanded the Heat Advisory east to account for additional areas
that could see heat indices push 105 degrees F by this
afternoon.

As sunset occurs, the air column starts to cool and two factors
leading to precipitation are in play for the state this evening.
First will be the shortwave in Minnesota with an associated surface
low in southwest Minnesota Monday evening. This low will track to
the east-northeast after 7pm with its cold front tailing back into
Iowa. Lots of uncertainty is associated with the storm potential
along the front in Iowa. Better potential lies further north and
east closer to the main area of forcing and, more notably, cooler
temperatures. Still, have preserved some PoP mentions in this area,
especially since anything that does manage to go will be strong to
severe in the early evening. Very large CAPE values are in place and
increasingly favorable shear as you venture north and east. The
primary threat will be damaging winds with storms today as storms
have around 1300 J/kg of DCAPE at their disposal thanks to the dry
subcloud layer. Damaging winds so strong, in fact, that some CAM
guidance brings gusts exceeding 60kts with it. This is a highly
conditional outcome given how capped the atmosphere is going to be,
but worth noting as a possibility. Another facet of the night is an
MCS forming off the nocturnal jet in the evening, but keep in mind
that this MCS has the potential to tap into the very same
environment, especially early in its lifespan. Again, highly
conditional and highly uncertain if this MCS will even form beneath
the cap. The Slight Risk for today has been purposely expanded
across much of the state to account for uncertainty with the best
potential in northeast Iowa. Trends will be monitored through the
day.

Next, the one (or two) thunderstorm complexes will shove the
boundary into central Iowa on Tuesday. 40kts of deep layer shear
along and north of it, abundant instability to the south of it.
Another shortwave will approach from the west, but will once again
face the conditional factor of the cap through the afternoon. Storms
are likely to fire late in the day, highest confidence in the south.
Lower confidence during the afternoon hours as the front sinks
through the state. At least hail and winds will be possible through
the full duration and tornadoes would be possible immediately along
the boundary if storms initiate during the day. Trends will be
monitored. Heat indices around 105 degrees will be possible in the
south, but have decided to forego issuing a Heat Advisory due to so
many mesoscale features that will augment the environment and
influence the placement of the front.

A brief pause in precipitation will commence Wednesday and last
through much of Thursday, but Gulf moisture returns to the region
late Thursday into Friday. PWATs will be in excess of 2 inches in
the Midwest. An axis of heavy rain will be found somewhere nearby
that night, but details remain too uncertain this far out from the
event. What can be said is it is likely (>60%) that much of the
state will see rain Thursday night.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1257 PM CDT Mon Jun 24 2024

Mostly VFR conditions for much of the period with convection
edging along the north and east portions of the forecast area.
Convection may begin to increase in coverage toward the end of
the forecast period, mainly along the KDNS-KDSM-KCID corridor.
Surface winds remains south to southwest this afternoon with the
gustiness decreasing this evening as mixing decreases. Winds
begin to switch to the northeast across northern Iowa by the end
of the period as a weak boundary dives into the state.

&&

.HYDROLOGY...
Issued at 346 PM CDT Sat Jun 22 2024

Major to historic flooding continues along portions of the Des
Moines River above Saylorville Lake. River observations today have
trended slightly higher than forecasts, which has resulted in an
increase in expected crests at multiple sites. This includes ESVI4,
EMTI4, and HBTI4, which are all either currently exceeding or
forecasted to exceed their record crests. Consequently, with the
greater volume of water coming downstream, we are now anticipating
greater impacts to areas along the main stem of the Des Moines River
above Saylorville, with FODI4 now forecast to crest at 19.5 ft which
is the 3rd highest crest on record for that site. Likewise, the
forecasted lake elevation at Saylorville Lake is now just over 875
ft.

Looking ahead to potential rainfall through the week, the most
immediate concern for heavier rainfall will be Tuesday, as most of
the rainfall on Monday is expected to avoid our forecast area.
Fortunately for those being impacted by river flooding in northern
Iowa, the higher QPFs currently favor southern Iowa, and even if
heavier rainfall develops north, it will quickly drop south with the
front. That being said, any heavy rainfall could still delay
improvement to flood conditions, if only briefly. Additional shower
and thunderstorm chances are expected again Thursday night into
Friday with more details provided on this in the coming days.

Make sure to stay up to date on the latest forecasts and river
information, and use extreme caution in flooded areas.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for IAZ004-005-015-
023-024-033>035-044>046-057-058-070-071-081-082-092>094.

&&

$$

DISCUSSION...Jimenez
AVIATION...Cogil
HYDROLOGY...Dodson