National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KDMX 261743
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1243 PM CDT Fri Apr 26 2024

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

.KEY MESSAGES...

- Multiple rounds of showers and storms today. Severe threat is
  low with morning activity. Severe storms likely late this
  afternoon and evening with all severe hazards in play,
  including the potential for a few stronger tornadoes and very
  large hail.

- Widespread showers and storms develop again by Saturday
  evening and persist into Sunday. Severe storms possible again
  Saturday evening with a threat of very large hail and
  tornadoes. Severe threat becomes more uncertain Saturday night
  into Sunday. Heavy rainfall of 2-3"+ likely in some areas.

&&

.DISCUSSION...
Issued at 304 AM CDT Fri Apr 26 2024

The start of a period of very active weather is beginning to
unfold as the first in a series of upper lows is pushing into
the central Plains. A broad wing of thermal forcing has fueled
widespread shower and thunderstorm development to our south and
west. So far dry air has done some work to erode this activity
as it pushes north and east into the CWA, but over the next few
hours the precipitation should begin to win out and become more
widespread as it steadily tracks north and east this morning.
Effective shear of 30-40+ kts may support a few transient
stronger cores capable of producing small hail, but overall the
severe threat should remain low through the morning hours due
to limited instability.

A window for a more robust severe threat opens by mid to late
afternoon within an increasingly unstable warm sector sandwiched
between a sfc warm front and dryline. CIN erodes as a large
scale ascent associated with a now negatively tilted upper low
overspreads the warm sector. Nearly all high-res model guidance
initiates deep convection along the dryline in SE Neb/NE Kan
between 21z-00z. Recent model guidance has trended a bit later
and further west with initial development, but previous thoughts
on the extent of the severe weather threat remain mostly
unchanged as the environment will be supportive of all severe
hazards as the storms quickly race north and east into western
Iowa by late afternoon and evening. This includes the potential
for a few stronger tornadoes as the LLJ intensifies and 0-3km
SRH subsequently increases to near 300 m2/s2. The mode likely
evolves into more of a QLCS structure as storms push toward
central Iowa by mid to late evening. Low-level shear profiles
are more than sufficient to support a continuing QLCS tor
threat, however storms eventually begin to outrun the primary
instability axis and sbcape wanes with eastward extent and
models try to nocturnally stabilize the boundary layer.

Lead upper low is quick to exit the area and leads to a lull in
activity for the better part of the overnight hours into
Saturday morning. Instability quickly builds Saturday morning
and afternoon within a warm and increasingly humid environment
along and south of a sharp warm front draped over central Iowa.
Isolated convection is possible by early afternoon, but
background synoptic support is weak to non-existent at that time.
That changes in a hurry by the evening hours as the second
upper low kicks off the Rockies along with a rapidly maturing
attendant surface low. Strong upper level divergence will
support widespread shower and storm development, including the
potential for another round of severe storms along and south of
the warm front. Very large hail looks to be the primary threat
as storm relative ECAPE exceeds 3000 J/kg in most model
soundings. The tornado threat is a bit more uncertain as surface
winds are rather relaxed within the pressure trough associated
with the warm front, but shear profiles just off the surface
remain favorable with 0-1 shear between 10-20 kts and looping
hodographs in the lowest 3km.

Strong synoptic support and a steady northward stream of Gulf
moisture fuels widespread showers/storms through the night and
into Sunday. The setup looks increasingly favorable for some
heavier rainfall amounts, particularly near the waffling warm
frontal boundary as it remains parallel to the mean steering
flow aloft. HREF PMM product advertises 2-3" of rain central
and south with locally higher amounts by Saturday night, with
additional rainfall likely into Sunday. Certainly welcome for
drought stricken fields, but could cause issues if the higher
amounts and periods of intense rates are realized in urban
areas. The extent of the severe weather threat becomes
considerably uncertain Saturday night into Sunday due to the
successive periods of convection and models struggling to handle
the evolution of mesoscale details with time.

Pattern remains on the active side next week as multiple shortwaves
pass through the mean synoptic flow. This will lead to additional
windows for showers and storms. Ensemble output suggests Wed-Thu as
the most likely time period as a shortwave crosses the northern
Plains. Temperatures next week generally run above normal with most
days featuring highs in the 70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1240 PM CDT Fri Apr 26 2024

Messy aviation period with potential for multiple rounds of
showers and storms through around 06z for some sites. Have
attempted to denote periods of most likely prevailing
TSRA/SHRA, with VCTS/VCSH in less certain periods. Regardless,
much of the time will be IFR with ceilings at/around 1kft or
below until some improvement moves in after 00z as it lifts NE
through the TAF sites. Period of quieter overall conditions
flight category improvements after 06z. Additional
showers/storms expected Saturday, but outside of current TAF
period.

&&

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

&&

$$

DISCUSSION...Martin
AVIATION...Curtis