Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 300504
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1204 AM CDT Thu Jun 30 2022

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

.SHORT TERM.../Tonight through Thursday night/
Issued at 237 PM CDT Wed Jun 29 2022

Key Messages:

*Gusty winds overnight into Thursday
*Chance of storms beginning Thursday evening

A warm front gradually drifted northward this afternoon, giving way
to gusty southerly winds advecting in warm, more moist air. An area
of low pressure to the northwest combined with a strong low-level
jet will preserve the gusty winds through the night tonight.
Soundings show a brief period of time where the top of the mixed
layer will have winds of over 40mph, but these values will cease to
be realized once the nocturnal inversion layer sets in place.
Persistent warm air advection from the strong southerlies will keep
low temperatures slightly warmer tonight.

The low to the west along with a tailing cold front will reach Iowa
by Thursday evening, however models continue to downplay chances for
convection in this timeframe. Soundings show capping, lots of low-
level dry air, and marginal deep layer shear in Iowa as the front
arrives Thursday evening. Convection will be more favorable in
portions of Kansas and Nebraska at the nose of the LLJ. However, the
weaker low-level convergence in Iowa may still produce localized
rain in spots overnight. Precip will gradually fill in more with the
return of daytime heating the next day as the boundary stalls over
southern Iowa. The recent HREF PMM for precip has the majority of
measurable rainfall overnight south of Interstate 80.

&&

.LONG TERM.../Friday morning through Wednesday/
Issued at 237 PM CDT Wed Jun 29 2022

Key Messages:

* Varied degrees of seasonal warmth and humidity
* Periodic chances for showers and storms

The general theme through the period includes fairly typical
summertime conditions as quasi-zonal flow gradually transitions to
upstream ridging early next week. This will keep intermittent
chances for showers and storms in the forecast, with a few favored
periods, and temperatures and humidities at or just above seasonal
normals.

At onset Friday morning, the weak front that is expected to drop
south through Iowa earlier that night should be positioned along or
just south of the IA/MO border. Low level convergence associated
with this feature, and some support from the trailing lobe of lift
far removed from the Ontario closed low will likely support
lingering convection south into the morning. The eventual evolution
of the current AZ to CO monsoonal tap into the MO Valley will result
in fairly deep saturation however, minimizing instability and lapse
rates. This along with unfavorable vertical shear profiles will keep
the severe weather potential low. The heavy rain potential in this
window does not look great either with the 925/850mb convergence
into MO.

The low level boundary and more elevated baroclinic zone are
expected to began slowly advancing northward through the MO Valley
Friday Night into Saturday keeping low end chances in the forecast.
Forcing mechanisms surface to aloft are fairly nondescript however
so this and the lack of noted instability or shear will keep any
organized potential low. With the exception of overnight Sunday into
the Forth of July, this looks to be the theme through the remainder
of the period as well. Neither the SLU CIPS Analogs or CSU machine
learning page suggest much in the way of severe weather potential
through the extended forecast.

The aforementioned early week window heading into the Forth may be
somewhat more substantial however with a short wave topping the
ridge and a strengthening low level jet into Nebraska, which return
humid conditions. There is better model consensus here for an MCS
developing with those features and moving through the MO Valley into
IA Monday the 4th, with the ECMWF suggesting associated boundaries
will continue to trigger convection into the night. Although the
signal isn`t too strong, this may be a window to watch for strong
storms and heavy rain potential with at least some increase in
instability and precipitable water, with light mean wind. The
convective potential continues into Tuesday and Wednesday, but the
confidence is low with little consensus in the degree of ridging and

&&

.AVIATION.../For the 06Z TAFS through 06Z Thursday night/
Issued at 1158 PM CDT Wed Jun 29 2022

VFR conditions expected to continue through Thursday afternoon.
Winds out of the south to southwest will remain gusty through the
overnight hours into Thursday afternoon with a tightening pressure
gradient and approaching front. Low level wind shear will impact
all but KOTM overnight as well. A few showers could be possible
across northern Iowa Thursday morning but dry air at the surface
kept from any mentions due to low confidence in showers reaching
the ground. Additional showers/storms are possible towards the end
of the TAF period.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Small/Jimenez
LONG TERM...Small
AVIATION...KCM


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