Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 041945
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
245 PM CDT Mon Jul 4 2022

.DISCUSSION.../Tonight through Monday/
Issued at 243 PM CDT Mon Jul 4 2022

Key Messages:

- Heat headlines through Tuesday
- Several rounds of storms through Friday. Each will carry an
  attendant severe and heavy rain threat.

Thunderstorms have moved east fo the state early this afternoon.
Partly to mostly cloudy skies still remain along and north of
Interstate 80. The surface warm front is working northward into
central Iowa with temperatures near 90 in the Des Moines metro and
in the low to mid 90s into southern Iowa along with heat index
values in the 100 to 105 range.

Still monitoring thunderstorm chances over northern/northeastern
Iowa later this afternoon and evening while the increasingly strong
elevated mixed layer is arriving with the warm front to the south.
The capping and CIN over the northern areas is much weaker and may
erode enough for some convective development. Still there is a lack
of a triggering mechanism with the low level jet bent to the
east/northeast and only weak short wave fragments moving through.
Will keep low pops over that region and given the amount of
instability, a severe storm is possible should storms develop.

The warm front will continue to lift very slowly north tonight but
will stall over northern Iowa then slightly oscillate while
hanging for much of Tuesday. Expect heat index values in the 105
range for areas south of the boundary. Have expanded the Heat
Advisory another tier of counties northward, including all but the
MN border counties. Not expecting any expansion of heat headlines
for Wednesday as temperatures back off. Thunderstorms are
expected to develop near the South Dakota/Nebraska border during
the afternoon before beginning to roll east/southeast along the
instability max across northern Iowa. Damaging winds will be a
primary threat. Large hail is also a threat give the large/fat
CAPES conducive for updraft acceleration despite a deep melting
layer. Shear is lacking through the lower portion of the profile
but speed shear does exist above 500 mb which would help exhaust
the storm away from the surface updraft entry point. Heavy
rainfall is also a threat.

The boundary will sag into central Iowa by Wednesday and there will
be a threat for repeated training of storms in the vicinity of the
boundary. Warm rain processes look to be in place also with deep
saturated soundings with PWATS near 2.25"+ and warm cloud depths in
excess of 14 kft. A flash flood threat may develop after priming the
pump so to speak today and again Tue/Tuesday night with locally
heavy rainfall saturating the soil conditions. The repeated rounds
will eventually have an impact on local streams as well. The
boundary will remain in the central to southern Iowa area into at
least early Friday so even more storms will be possible and will
continue to carry an attendant heavy rain threat. At this time, a
break on Saturday and Sunday looks possible before the pattern
becomes active again for early next week.

&&

.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1223 PM CDT Mon Jul 4 2022

MVFR to local IFR cigs are over northern Iowa early this
afternoon. These conditions are expected to gradually improve from
south to north. VFR conditions will persist at KDSM/KOTM through
the period. Southerly winds will persist as well. Have left storms
out of the forecast at sites with potential diminishing during the
period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT Tuesday for IAZ033-044>046-057>060-
070>074-081>086-092>097.

Heat Advisory from noon to 8 PM CDT Tuesday for IAZ005-015>017-
023>028-034>039-047>050-061-062-075.

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon


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