425
AWUS01 KWNH 210745
FFGMPD
WIZ000-MNZ000-IAZ000-211330-

Mesoscale Precipitation Discussion 0295
NWS Weather Prediction Center College Park MD
344 AM EDT Tue May 21 2024

Areas affected...Central to Northeast IA...Adj Southeast MN...Adj
Southwest WI...

Concerning...Heavy rainfall...Flash flooding possible

Valid 210745Z - 211330Z

SUMMARY...Slow moving warm-advection thunderstorms with potential
training/mergers pose localized 2-4" totals and possible flash
flooding into early morning.

DISCUSSION...Regional RADAR mosaic depicts a shortwave/MCV across
north-central IA, well ahead of approaching stronger MCV and
associated synoptic scale height-falls.  The wave has strengthened
by latent heat release from earlier convection but also some
upper-level increasing diffluent pattern across IA between the
northern stream jet over the Dakotas and along the northeast edge
of the sub-tropical stream as it anticyclonically curves southeast
across the central MS River Valley.   At the surface the cold
front from prior exiting shortwave has stabilized air across much
of southern WI and northern IL before returning northward across E
IA and reaching a surface inflection near Ames, IA before dropping
southwest again into NEB.  A broad low-level jet has developed
with 40-45kts of southerly to south-southwesterly 850mb flow
across much of the eastern Plains into MO/IA; though a tighter
core may be responding the aforementioned shortwave/MCV in
northern IA.  As such, GOES-E and RADAR have show a marked
increase in WAA convection in proximity to the front and
along/east of the shortwave.  Source region ascending parcels
remain quite unstable with 1500-2000 J/kg of MUCAPE across much of
central IA, though rapidly diminishes east of the River into WI
where values drop to be below 500 J/kg east of the Driftless area.


Moisture is fairly deep with mid to upper 60s Tds south of the
front and total PWAT values over 1.5"; though per CIRA LPW, these
values are mainly driven from below 700mb.  As such, moisture flux
should be strong enough for efficient rainfall production in the
lower layers for intense showers capable of 1.5-1.75"/hr.
Duration will be key for locally intense rainfall, though upstream
redevelopment from isentropic ascent may allow for some
training/mergers to occur particularly from the SW to E quadrants
of the MCV across central to northeast IA.  Spots of 2-4" are
probable and given 1hr/3hr FFG values of ~1.5"/<2.25"
respectively, scattered incidents of flash flooding are considered
possible.  The stable air to the east should limit downstream
potential as well as reducing forward speed/propagation in that
duration.

Additionally, approaching shortwave/MCV may bring another round of
thunderstorms from SE NEB into SW IA and the SW edge of this MPD
increasing risk toward 14-15z.  For further information, please
refer to MPD 294 issued at 0703z and subsequent MPDs issued later
this morning.

Gallina

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...ARX...DMX...DVN...MPX...

ATTN...RFC...MBRFC...NCRFC...NWC...

LAT...LON   43829193 43519104 42859056 42159079 41489212
            41119421 41749498 42859477 43779343