Severe Thunderstorm Warning 36, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
340 AM CDT Fri Apr 22 2022

.DISCUSSION.../Today through Thursday/
Issued at 340 AM CDT Fri Apr 22 2022

Key Messages:
-- Storm chances into this morning with locally heavy rain and
   strong storms possible
-- Strong to severe storm Saturday, especially later in the day
-- Strong winds Saturday, windy today too
-- Warmer through Saturday, then cooler into early next week

Details: The longwave trough axis is nearing the western US
coastline early this morning with surface low pressure deepening
underway over eastern Colorado. This surface low has aided in a warm
front lifting northward over the state with SPC mesoanalysis showing
the warm air advection at varying low levels. This WAA has helped to
develop a line of showers from near Estherville back toward Waterloo
with additional showers and a few thunderstorms over central and
southern Iowa. This activity has all been just garden variety/well
below severe limits with effective shear not existent and low
amounts of MUCAPE per SPC mesoanalysis. Further west, GOES-East
imagery shows a convective cluster that has developed over south
central Nebraska where the parameter space is more favorable and
there has been a recent severe reports with 1" hail and 60 mph wind
gusts. Our effective shear as well as instability will be increasing
over the next few hours; however, forecast soundings show the CAPE
profile narrowing with additional saturation as precipitable water
values increase to 1.25 to at times 1.5 inches. Therefore, severe
risk may be lessening, but flash flood risk may increase later
this morning. Most convective allowing models show additional
development into central Iowa toward and after 9z this morning as
the Nebraska cluster is carried northeast and east. The total QPF
is quite murky and not a lot of confidence as recent runs (e.g.
1-5z) of the HRRR have backed off on the QPF amounts and pushed
the higher amounts north through 12z compared to the 00z/06z,
which were hammering areas either side of I-80/between Highway 20
and 30, respectively. Other recent deterministic runs are
generally under 2 inches with the 00z HREF probability matched
mean showing similar for a 6 hour total. As mentioned in last
night's discussion, there were a few models and ensemble members
that were topping 2 inches, but that seems even more in the
minority with present guidance. Now, additional rainfall is
expected between 12 and 18z that could for storm total top 2"
somewhere from around Des Moines to Waterloo to near I-80 and
points east. We have been mulling over the idea of a flash flood
watch since yesterday, but the corridor for any hydro issues looks
to be quite narrow at a county or two wide. In addition, mean
flow is around 30 knots should keep storms progressive. Will
continue to monitor incoming guidance and can raise a watch in
short order if the need arises.

Much of the convection from this morning will push north and east of
the state by this afternoon as elevated mixed layer overspreads the
state. This will keep a cap on any additional development later this
afternoon into tonight for much of our area. Additional elevated
storms may try to develop as the low level jet ramps up over 40
knots and if these storms do form, the likely hazard would be hail.
There will likely be a lull in activity later in the morning into
the early afternoon as the warm EML keeps activity limited. However,
as the cold front enters the forecast area later in the afternoon
into the evening, better convergence should help to develop updrafts
and storms. Shear will not be lacking near the front and a narrow
ribbon of modest instability should form. Strong storms capable of
gusty winds and hail would be the main concern as the front pushes
through. In addition on Saturday, strong southerly winds will
prevail with gusts above wind criteria. Experimental NBM is really
aggressive with gusts over 50 knots and forecast soundings show
winds at the top of the mixed layer around 50 knots across western
Iowa. However, typically in the warm sector this is not fully
realized. That said, the signal for strong wind and the need for a
wind advisory has been present for several days and confidence is
high enough to issue at this time.

Gusty winds in the cold air advection regime will prevail on Sunday
with the cool weather persisting in to early next week, though by
then the winds will have lessened. Rain chances look overall minimal
through Tuesday as a longwave trough stays over the area. As that
departs and ridging tries to build in midweek, a few chances may
result as shortwave troughs come through the flow.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1212 AM CDT Fri Apr 22 2022

Showers and storms will be the name of the game through much of
the overnight, yielding a fall back into MVFR/IFR and possibly
LIFR conditions. SHRA/TSRA activity will ramp up in coverage to
start the period, and generally linger within the area through 12z
to 15z before exiting E/NE. Ceilings will quickly drop down into
MVFR/IFR values, and potentially LIFR. Winds will also increase
out of the S, peaking in the afternoon when wind gusts in excess
of 30kts may be seen. Breezy conditions will linger through the
remainder of the period as well.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 10 AM to 7 PM CDT Saturday for IAZ004-005-015-
023-024-033>035-044>046-057-058-070-071-081-082-092-093.

&&

DISCUSSION...Ansorge
AVIATION...Curtis

Hazardous Weather Outlook
National Weather Service Des Moines IA
431 AM CDT Fri Apr 22 2022

IAZ006-007-016-017-025>028-036>039-047>050-059>062-072>075-
083>086-094>097-230945-
Winnebago-Worth-Hancock-Cerro Gordo-Wright-Franklin-Butler-Bremer-
Hamilton-Hardin-Grundy-Black Hawk-Boone-Story-Marshall-Tama-
Dallas-Polk-Jasper-Poweshiek-Madison-Warren-Marion-Mahaska-Clarke-
Lucas-Monroe-Wapello-Decatur-Wayne-Appanoose-Davis-
431 AM CDT Fri Apr 22 2022

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This morning and tonight

Rain showers and thunderstorms will continue through the morning
hours and are expected to diminish in the afternoon. Heavy
rainfall is possible. Some storms may be strong to severe with
hail being the primary threat.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Rain showers and thunderstorms are expected on Saturday. There is
a slight risk for severe storms on Saturday across much of the
area. Hail and damaging winds will be the main threats on
Saturday, though a tornado threat cannot be ruled out. Areas that
experienced heavy rainfall on Friday will be at increased risk for
flooding with additional rainfall on Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter reports will likely be needed over the next few days.

IAZ004-005-015-023-024-033>035-044>046-057-058-070-071-081-082-
092-093-230945-
Emmet-Kossuth-Palo Alto-Pocahontas-Humboldt-Sac-Calhoun-Webster-
Crawford-Carroll-Greene-Audubon-Guthrie-Cass-Adair-Adams-Union-
Taylor-Ringgold-
431 AM CDT Fri Apr 22 2022

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Rain showers and thunderstorms will continue through the morning
hours and are expected to diminish in the afternoon. Heavy
rainfall is possible. Some storms may be strong to severe with
hail being the primary threat.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

A Wind Advisory is in effect for the area from 10AM to 7PM CDT.
Please visit weather.gov/desmoines for more information.

Rain showers and thunderstorms are expected on Saturday. There is
a slight risk for severe storms on Saturday across much of the
area. Hail and damaging winds will be the main threats on
Saturday, though a tornado threat cannot be ruled out. Areas that
experienced heavy rainfall on Friday will be at increased risk for
flooding with additional rainfall on Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter reports will likely be needed over the next few days.

Dodson/Ansorge

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