River Flood Warning 50, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
721 AM CDT Fri May 24 2019

.DISCUSSION.../Today through Thursday/
Issued at 613 AM CDT Fri May 24 2019

Convective trends remain the primary forecast focus and will
remain so through the Memorial Day weekend into at least the
middle of next week. Overall the models are in decent agreement
through that time with a continued active pattern. Southwest flow
aloft will transition to minor ridging late in the weekend and
then back to southwest flow again early next week allowing for
only brief breaks from convection.

At onset, the situation is volatile with tremendous 0-1km
shear/SRH across southern Iowa just north of a northern MO warm
front. Objective analysis suggests the instability environment is
marginal, but radar trends suggests otherwise with a very healthy
QLCS advancing into the forecast area in strong effective shear.
Thus expect the MCS to maintain itself for a while at least with
all modes of severe weather possible. The only thing holding the
severe potential back for now seems to be the lack of cold pool
generation and/or getting rooted low enough.

Later today the warm front and weak surface low over eastern NE
are expected to advance northward through IA with a considerable
airmass changes across the state. It will be humid with MLCAPEs
reaching around 2K j/kg with 40-50kts of 0-6km shear. The surface
flow will be broad southwesterly, with little convergence, but the
lingering thermal discontinuity across NE/KS early this morning
should advance into the state and potentially aid convective
initiation. This will combine with any remnant MCVs from overnight
convection upstream and other weak synoptic waves in the
southwest flow to trigger additional convection over central and
southeast IA with severe weather possible, This will likely
transition into a heavy rain threat into the night south and east.
There will be strong 850MB moisture transport into the convection
and with the mean wind parallel to the convective axis, and
opposite the low level inflow, the convection may train over
similar areas with minimal Corfidi Vectors as well. Precipitation
waters will be approaching 2 inches with 3.5km warm cloud depths
so 1-3 inch rains are certainly possible, with locally higher
amounts much like occurred this morning. Thus have issued a Flash
Flood Watch to account for this possibility.

The convection should exit to the south and east and weaken into
Saturday morning, but a weak synoptic front will linger SW to NE
across the state again Saturday. The thermodynamic environment
will be even greater by peak heating with MLCAPEs pushing 3K j/kg
and 50kts of deep shear. Thus additional severe weather with large
hail and damaging winds are possible. Low level winds appear too
weak and veered for much tornado potential. The heavy rain threat
does not appear as great with this round however as the deeper
moisture will be pushed just to the south and east with the low
level jet into the night veering to WNW into the early morning
hours and staying south.

This should lead into a break Sunday before a more coherent short
wave lifts into the MO Valley Sunday Night into Monday. We will
then see another repeat cycle of nocturnal, possibly severe, MCS
and then potentially additional peak heating severe convection
into Monday. The tornado potential will be in or near Iowa, but
dependent on where the warm front lays out. This will likely
transition into yet another round of nocturnal convection Monday
Night with more heavy rain potential. Large scale forcing
attendant to the long wave trough is expected to produce
significant convective into Tuesday and Tuesday Night before there
is finally some light at the end of the tunnel toward drying out
and a flip to NW flow into the end of the next work week.

&&

.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 649 AM CDT Fri May 24 2019

Showers and thunderstorms embedded within stratus will continue to
produce varied conditions early this morning with anywhere from
VFR to LIFR possible, thus confidence is low. Once the convection
exits some MVFR stratus will linger before additional showers and
storms are anticipated by later this afternoon and tonight,
especially across the southeast third of the state. Generally VFR
conditions are anticipated here, but there is some MVFR or less
and thunder possible. Due to the duration of the precip potential,
have opted to omit that mention until the likely time window can
be narrowed.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 4 PM CDT this afternoon through Saturday
morning for IAZ050-061-062-072>075-081>086-092>097.

&&

DISCUSSION...Small
AVIATION...Small

Hazardous Weather Outlook
National Weather Service Des Moines IA
421 AM CDT Fri May 24 2019

IAZ050-061-062-072>075-081>086-092>097-250930-
Tama-Jasper-Poweshiek-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
421 AM CDT Fri May 24 2019

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

A Flash Flood Watch is in effect for this area. Please refer to
the National Weather Service website at weather.gov/desmoines for
further details.

Thunderstorms are expected throughout today. A few storms may be
strong to severe, with large hail and damaging winds the primary
threat. Heavy rainfall may lead to flash flooding and river
flooding.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Outside of a brief break around Sunday, periodic thunderstorm
chances are expected into early next week, including Memorial
Day. Severe weather primarily in the form of large hail, damaging
wind gusts, and moderate to heavy rainfall will be possible at
times. Flash flooding and river flooding risks will increase
through the weekend.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed off and on through the Memorial Day
weekend, especially today, Saturday, and Monday.

IAZ004>007-015>017-023>028-033>039-044>049-057>060-070-071-250930-
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-Audubon-Guthrie-Dallas-Polk-Cass-Adair-
421 AM CDT Fri May 24 2019

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Thunderstorms are possible today, especially towards central and
to southeastern Iowa. A few storms may be strong to possibly
severe, with large hail and damaging winds the main threats. Heavy
rainfall may also increase flash flooding and river flooding
risks.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Outside of a brief break around Sunday, periodic thunderstorm
chances are expected into early next week, including Memorial
Day. A few storms may be strong to possibly severe. Flash
flooding and river flooding risks will increase through the
weekend.

A River Flood Warning remains in effect for the West Fork Des
Moines River near Estherville for the foreseeable future. Please
refer to the National Weather Service website at
weather.gov/desmoines for further details.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed off and on through the Memorial Day
weekend, especially today, Saturday, and Monday.

Kotenberg

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