-- Discussion containing changed information from previous version are highlighted. --
171
FXUS63 KDMX 191723
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1223 PM CDT Wed Jun 19 2024

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

.KEY MESSAGES...

- On and off showers and thunderstorms today across much of
  central Iowa. The severe threat is low by locally heavy rain
  remains possible.

- The storm potential shifts to northern Iowa by Thursday
  afternoon. Locally heavy rainfall and a few strong storms are
  possible.

- More storms by Saturday.

&&

.DISCUSSION...
Issued at 404 AM CDT Wed Jun 19 2024

Showers and storms continue to move northeast across much of central
and north central Iowa while less activity is occurring over the
southeast. Several bands of 1 to 2 inches of precipitation have
fallen overnight and the precipitation continues to be efficient
with precipitation rates over 1 inch per hour in areas with radar
returns of 45 dBZ or greater and areas with 35 to 40 dBZ are
producing one quarter to one half inch precipitation rates. None of
these are of any hydrology concern at the moment. The moisture
transport into Iowa is slowing down early this morning. There are a
couple reasons for this. First surface and upper level high pressure
over the eastern CONUS is expanding eastward into the south central
CONUS. This ridging combined with the tropical system over the
western Gulf of Mexico, is the strong moisture transport into Texas
and routing it well west into eastern New Mexico and the
Texas/Oklahoma panhandles before turning back northeast towards
Iowa. Surface high pressure over the Dakotas and Minnesota is
also helping pinch off this moisture transport.

At the surface, the boundary has slowed down and is currently over
the southeast third of Iowa with the bulk of the precipitation now
post frontal which is where the main instability axis resides. The
mean storm motion flow utilizing the 850-300mb mean wind, remains
nearly parallel to the boundary and the instability axis, which will
keep the potential for numerous rounds of precipitation over the
same areas. The instability axis will not move much today and remain
over central and southern Iowa through the day before beginning to
lift back northward later tonight and into the day Thursday as the
upper ridge pivots and helps lift everything north. This will keep
on and off showers and storms in those areas today before the focus
shifts to the northern half of Iowa by Thursday afternoon. The axis
of more persistent precipitation this morning appears to be showing
its hand already with that axis setup 30 miles either side of a line
from near Waterloo to the Des Moines metro and back to the far
southwest part of the forecast area near Bedford. Parts of the
southwest half of that line could see another 1-2 inches today
despite the waning moisture advection today, due to the repeated
activity and efficient rainfall rates. Will be monitoring another
potential for heavy rain Thursday afternoon and night which could be
somewhere from northern Iowa to southern Minnesota pending how far
north the boundary returns. Not expecting any severe weather today.
A few severe storms with wind or hail could occur Thursday.


By Friday, the upper ridge will be progressing westward across the
southern CONUS. It will be suppressed a bit south on Friday as an
strong upper level system passes through the Northern Plains and by
Saturday that will translate in a brief switch to northwest flow
aloft that will help drop the surface boundary back into Iowa and
bring more chances for storms. The upper flow will then evolve into
a more westerly zonal flow Sunday through early next week. This
should result in mostly dry and warmer conditions for that period
before another system arrives mid next week. Of note, the NBM
temperatures remain much too warm for a large portion of the period.
Have lowered these in the first several days of the forecast but
these are currently untouched in the extended. The temperatures in
that period are in the 75-90th percentiles yet and the forecast low
to mid 90s next Tue are running 3-5 degrees above the NBM 50th
percentile, which for the past several days, has been much more
realistic and has represented the potential of the thermal vertical
profile much better.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
-- Changed Discussion --
Issued at 1220 PM CDT Wed Jun 19 2024

Nearly stationary front extends from southwest/northeast with
showers/possible iso thunder through late afternoon. Low cigs
well into MVFR range will continue near boundary. Tonight the
boundary lifts back north with periods of IFR/MVFR into
Thursday. Winds remain light during period. /rev
-- End Changed Discussion --

&&

.HYDROLOGY...
Issued at 415 AM CDT Wed Jun 19 2024

A few strips of rainfall of 1-2 inches occurred overnight which
appears to have been handled well with most streams. Most
responses on streams has mainly been from local runoff. All
streams with the exception of the upper basin of the West Fork
Des Moines river, are well within their banks and can handle a
fair amount of water and runoff yet before approaching minor
flood stage.

With the potential for localized heavy rainfall yet through
Thursday, cannot rule out localized flash flooding or at least
significant ponding but not expecting anything widespread at
this time. A few rivers may reach bankfull or possibly minor
flood stage again with the target being the West Fork Des Moines
River where the river is already running near bankfull at
Estherville and Emmetsburg.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...REV
HYDROLOGY...Donavon