Severe Thunderstorm Warning 1, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
732 AM CDT Tue Apr 16 2024

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Several rounds of storms today. Severe weather possible
  throughout the day. Damaging winds, large hail and tornadoes
  all possible

- Strong synoptic winds today. Non-thunderstorm gusts to 50 mph
  or greater possible.

- Much colder to end the week.

&&

.DISCUSSION...
Issued at 427 AM CDT Tue Apr 16 2024

Elevated thunderstorms have begun to develop across parts of west
central, central and southern Iowa along a region of theta-e
advection. The strongest updrafts thus far in Iowa have been over
west central Iowa but thus far nothing has approached severe limits.
The main low level jet axis remains to the west of the areas from
eastern South Dakota and into eastern Kansas. Thunderstorm activity
over north central Kansas and south central Nebraska has evolved
into a QLCS with wind gusts and numerous meso vertices occurring.
This activity should turn more north/northeast and remain to the
west of the forecast area. Another region of thunderstorm
development has been occurring over southeast Kansas which is in
vicinity of the mid and upper level jet maxes and immediately ahead
of the strongest PV anomaly rotating around the upper low. This is
the activity that will be lifting rapidly north/northeast towards
the DMX CWA and should be near the southwest corner between 12-14z.
Additional thunderstorms will continue to develop ahead of this line.

The 500 mb low is moving into northwest Kansas early this morning
and will continue to deepen through 18z as it moves into eastern
Nebraska then will slowly begin to fill as it lifts further
northeast into northwest Iowa by late this afternoon. This track
does fit past composite analysis of past Iowa severe weather and
tornado outbreaks with some minor temporal differences. The one
differences if the more deep layer unidirectional flow that is
predominant much of the period. Model solutions are varying to some
degree on the strength of the low level flow and thus the low level
shear potential. The overall trends are suggesting a stronger low
level wind field at 850 mb and below that would promote better
turning in the low levels. At the surface, low pressure over western
Nebraska is gravitating southeast towards the approaching upper low.
The low will undergo a fujiwhara as it reorients with the upper low.
A plume of 60+ dewpoints has lifted into east central Nebraska and
this will continue to lift into central Iowa today.

Today's severe weather threat and how it will evolve still is not
completely clear cut. Will be referring this as 3 rounds of storm
potential. Round 1 is the current elevated storms that may have a
low end severe hail threat. Round 2 is the activity lifting
northeast out of Kansas and round 3 is potential storms to develop
along the pseudo dry line. We will focus on rounds 2 & 3. Round 2
may end up evolving into a linear/QLCS line this morning as the
storms motions are nearly parallel to the 0-3 km shear vector of 40-
50 kts. In addition, low level stretching is likely as 0-3 km CAPE
values increase to 50-100 J/kg this morning. Proximity soundings
would suggest that the storms may be slightly elevated but given the
forcing and the low level moisture advection, the storms may be
surface based and pose a damaging wind and QLCS tornado threat.
Round 3 which is expected to form along the pseudo dry line, could
see more discrete supercells development. Again, the overall profile
is more unidirection which may suggest more of a wind and hail
threat. The wind threat is further supported by the 0-3 km theta-e
differences over 25k suggesting the potential for sustained cold
pools. Will have to see how the low level wind field sets up for the
tornadic threat. The unidirection profiles may result in splitting
storms with the left movers possessing an enhanced hail threat if they
can sustain. Finally, storm motions today of around 45 kts does
increase the risk for EF2+ tornadoes as it further strengthens the
right forward moving portions of any tornadoes. Any storms today
will have the damaging wind threat with the strong winds just above
the surface.

Have added the entire area into the wind advisory today for the
synoptic wind. It is possible some areas approach 60 mph in non-
thunderstorm winds. Should have an increase this morning then again
as the pseudo dry moves through and deeper mixing occurs this
afternoon.

No major changes beyond that as the focus this morning was on the
near term. Precipitation ends on Wednesday but breezy to gusty winds
will persist. The big story in the extended is the cool down coming
and yes we will have frost and freezing temperatures back in
Iowa.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 637 AM CDT Tue Apr 16 2024

Several rounds of storms today at most sites before a boundary
passes through the area later this afternoon and early evening.
Additional showers and isolated storms are possible overnight,
mainly over northern Iowa. Strong and gusty synoptic winds are
expected today as well, the strongest winds will be this morning
and again this afternoon immediately behind fropa. Damaging wind
gusts are possible with any storms today. Cigs may become MVFR
or lower during the day today with some improvement behind the
boundary. Addition MVFR stratus is possible tonight.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 7 PM CDT this evening for IAZ004>007-
015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097.

&&

DISCUSSION...Donavon
AVIATION...Donavon

Hazardous Weather Outlook
National Weather Service Des Moines IA
425 AM CDT Tue Apr 16 2024

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-170930-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
425 AM CDT Tue Apr 16 2024

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

A Wind Advisory is in effect for the area. Please refer to the
National Weather Service website at weather.gov/desmoines for
further details.

Multiple rounds of thunderstorms are be expected today into
tonight with a Slight (2 out of 5) to Enhanced Risk (3 out of 5)
for severe weather. Large hail, damaging wind gusts, and a few
tornadoes will all be possible, along with locally heavy rainfall.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed at times today into tonight.

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