Tornadoes and Hail in Iowa, March 31, 2023

Area Forecast Discussion
National Weather Service Des Moines IA
643 AM CDT Fri Mar 31 2023

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

.DISCUSSION.../Today through Thursday/
Issued at 421 AM CDT Fri Mar 31 2023

Key Messages:

- Moderate Risk for Severe Weather Today!
- Strong winds today and even stronger tonight.
- Snow expected over northern Iowa tonight. Still monitoring the
  potential for moderate accumulations with significant blowing
  snow.
- Severe weather risk may return Tuesday.

Definitely a multi-faceted storm system to impact central Iowa over
the next 30 hours which is bringing a multitude of forecast
challenges, each of which could bring significant impacts to the
area.

A 992 mb surface low pressure is tracking northeast on schedule
though central Nebraska with the warm front extending northeast into
northwest Iowa then eastward along the IA/MN border while the upper
low is still further west and just moving into far western Nebraska.
There are two distinct strong short waves to contend with today and
the interaction and phasing of the two will play a significant role
in the evolution and timing of severe weather potential today. The
southern short wave that is still well southwest near New Mexico but
it will race northeast this morning and by early afternoon will
catch up with the northern short wave, lead to phasing and will
likely cause a quick deepening of the surface low and also cause the
surface low to jog to the north a bit. The impact of this is the
north jump of the low likely will delay the boundary passage by 2-3
hrs and lead to convective development further west around mid
afternoon. That boundary will then race east and may cross the
Mississippi River by 00z. Note due to the delayed timing, have
cancelled the Fire Weather Watch.

Severe Weather Mode:
The SPC moderate risk was expanded westward to near Interstate 35
for today due the delay mentioned above. There is the potential
for a few strong storms or even supercells in the warm section
ahead of the southern short wave over parts of southeast Iowa.
That could bring some severe weather potential for early
afternoon. For the convection along the boundary, damaging wind
gusts are still the threat with the most confidence and gusts over
70 mph are likely with some of the storms. A lot of speed shear
with this system with fairly straight hodographs with storm
motions nearly parallel to the hodographs. Hodographs are still
displaying some convex areas below 3 km which would inhibit right
mover updrafts a bit. The initial convection will be cellular and
potentially supercellular. The speed shear suggests splitting
supercells early with the left movers moving nearly north so could
get some mergers with other storms. The unknown there is if any
early mergers will be constructive or destructive to the right
movers they interact with. Sometimes that can promote quick
tornadogenesis. Large hail is certainly possible also. Storms
will be moving at 50+ mph and as mentioned previously, these fast
storm motions would promote the potential for EF-2 tornadoes. The
limiting factor remains the lack of backed flow away from just
east of the surface low. Back flow and a greater chance for
tornadoes may end up in the northeast quadrant of Iowa. Overall,
this will all quickly go linear and lead to mesovortex potential
with line normal 0-3 km shear in the 30-40 kt range. This
transition to linear also go resemble a serial derecho before it
is done assuming it last long enough to the east. Finally there is
a hail potential with the initial storms that should diminish
with the linear transition.

Snow Potential North:
The potential for snow over northern Iowa does appear to be
increasing. This system will remain quite dynamic into the
overnight and there are signs the snow could be convective into
northern Iowa. There are numerous deterministic models that have
shifted the heavier snow farther south and clipping into northern
Iowa. Cross sections and profiles do suggest strong vertical
ascent through the dendritic growth zone. The 00z HREF probs for 1
inch per hour or greater snow is now nudging into northern Iowa
as well. For now, have placed a Winter Weather Advisory into far
northern Iowa for 1-3 inches of snow along with blowing snow with
the potential for 50 mph winds. The worst case scenario is the
heavy snow line dips 20 miles south than currently forecast and
this becomes a blizzard event into northern Iowa. Continue to
monitor this situation.

Strong wind potential:
Strong southerly winds are expected ahead of the boundary today
into southern Iowa with gusts over 45 mph likely. There is the
potential for higher gusts behind the boundary passage with the
first wave of cold advection and stronger mixed layer winds
immediately behind the boundary. There is not strong support that
there will be 50+ knots available within the mixed layer at this
time so any synoptic 58+ mph winds should be limited, note that
does not include the severe storm wind potential. The wind should
subside slightly into the evening before another wave of strong
winds arrive with the primary cold front sometime between 04-12z.
That period seems to have a greater chance for high wind criteria
to occur with the 58+ mph wind gusts with the mixing efficiency
still high with another strong pressure height rise push moving
through along with cold advection. So wind headlines are
complicated. Covered the afternoon wind with an advisory and just
ran that through the night. Further north, no wind headlines but
something will be needed and potentially the later night event
will still need to be covered with a High Wind Warning.

The wind will quickly subside on Saturday as high pressure arrives
by the afternoon. Though cooler, Saturday afternoon may actually be
quite nice out with highs in the 40s to low 50s. Another warmup
arrives for Sunday and Monday with highs back in the 60s to some 70s
for much of the area. Another strong system arrives for Tuesday and
this may become another severe weather threat for the state pending
temporal and spatial parameters that are still being resolved.

&&

.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 640 AM CDT Fri Mar 31 2023

A complex aviation forecast for the next 24 hrs. A mix of MVFR and
VFR conditions this morning with a warm front stalled across
northern Iowa. This makes the KFOD and KMCW forecast more
challenging for wind then precipitation type. Overall expect
thunderstorms, with some severe, to develop this afternoon and
sweep quickly northeast. Strong westerly winds will follow into
the overnight. The precipitation will switch to snow overnight
over northern Iowa and may move south into central Iowa late.
Still possible for blowing snow near KMCW as well.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 11 PM this evening to 7 AM CDT
Saturday for IAZ004>007.

Wind Advisory from 1 PM this afternoon to 7 AM CDT Saturday for
IAZ044>050-057>062-070>075-081>086-092>097.

&&

DISCUSSION...Donavon
AVIATION...Donavon

Hazardous Weather Outlook
National Weather Service Des Moines IA
359 AM CDT Fri Mar 31 2023

IAZ017-025>028-036>039-010900-
Cerro Gordo-Wright-Franklin-Butler-Bremer-Hamilton-Hardin-Grundy-
Black Hawk-
359 AM CDT Fri Mar 31 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

There is an Enhanced to Moderate Risk of severe storms this
afternoon. Damaging winds and tornadoes are the primary concerns
with hail as a secondary threat. Storms will be moving quickly at
over 50 mph.

Strong west to northwest winds are expected tonight with gusts of
55 mph possible. Falling snow may also occur overnight and the
combination of snow and winds may restrict visibilities from time
to time.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed this afternoon.

IAZ015-016-023-024-033>035-010900-
Palo Alto-Hancock-Pocahontas-Humboldt-Sac-Calhoun-Webster-
359 AM CDT Fri Mar 31 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Scattered thunderstorms remain possible today with a few stronger
storms this afternoon before ending.

Strong west winds are forecast by tonight with gusts over 50 mph
possible.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is unlikely today.

IAZ047>050-059>062-072>075-083>086-094>097-010900-
Boone-Story-Marshall-Tama-Dallas-Polk-Jasper-Poweshiek-Madison-
Warren-Marion-Mahaska-Clarke-Lucas-Monroe-Wapello-Decatur-Wayne-
Appanoose-Davis-
359 AM CDT Fri Mar 31 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

There is an Enhanced to Moderate Risk of severe storms this
afternoon. At this time, damaging winds and tornadoes are the
primary concerns with hail as a secondary threat. Storms will be
moving quickly at over 50 mph.

A very high grassland fire danger remains across the southern
half of Iowa, especially this afternoon into the early evening.
Any fires that occur may be difficult to control.

Very strong west to northwest winds are expected by later this
afternoon and persisting overnight. A Wind Advisory is in effect
for the area this afternoon and tonight. Please refer to the
National Weather Service website at weather.gov/desmoines for
further details.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed this afternoon.

IAZ044>046-057-058-070-071-081-082-092-093-010900-
Crawford-Carroll-Greene-Audubon-Guthrie-Cass-Adair-Adams-Union-
Taylor-Ringgold-
359 AM CDT Fri Mar 31 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Scattered thunderstorms are possible this afternoon. A few may
produce strong wind gusts before exiting the area.

A very high grassland fire danger remains across the southern
half of Iowa, especially this afternoon into the early evening.
Any fires that occur may be difficult to control.

Very strong west to northwest winds are expected by later this
afternoon and persisting overnight. A Wind Advisory is in effect
for the area this afternoon and tonight. Please refer to the
National Weather Service website at weather.gov/desmoines for
further details.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is possible this afternoon.

IAZ004>007-010900-
Emmet-Kossuth-Winnebago-Worth-
359 AM CDT Fri Mar 31 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Scattered thunderstorms remain possible today. A few storms may
have damaging wind gusts near the Interstate 35 corridor this
afternoon.

A combination of snow and strong winds are expected tonight
produce low visibilities. A Winter Weather Advisory is in effect
for the area tonight. Please refer to the National Weather
Service website at weather.gov/desmoines for further details.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed toward the Interstate 35 corridor
this afternoon.

Special Weather Statement
National Weather Service Des Moines IA
1027 AM CDT Fri Mar 31 2023

IAZ004>007-015>017-023-024-033-311730-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Sac-
Including the cities of Estherville, Algona, Forest City,
Lake Mills, Northwood, Manly, Emmetsburg, Garner, Britt, Kanawha,
Mason City, Clear Lake, Pocahontas, Laurens, Rolfe, Fonda,
Gilmore City, Humboldt, Sac City, Lake View, Odebolt, Wall Lake,
Schaller, and Early
1027 AM CDT Fri Mar 31 2023

...Areas of Fog in Northwest Iowa...

Areas of fog have developed across portions of northwest Iowa.
Fog may lower visibilities to under one mile, at times.

Motorists are advised to slow down and use low-beam headlights.
Allow for extra following distance.

Hagenhoff