Mesoscale Precipitation Discussion 0486
NWS Weather Prediction Center College Park MD
1116 PM EDT Fri Jun 21 2024

Areas affected...Central to Central Eastern Nebraska...Central
Western Iowa...

Concerning...Heavy rainfall...Flash flooding likely

Valid 220315Z - 220800Z

SUMMARY...Flanking cold front thunderstorms may train with spots
of 2-4" resulting in likely scattered incidents of flash flooding.

DISCUSSION...Regional RADAR depicts a line of stronger
thunderstorms along the effective cold front to the strengthening
surface wave and MCS to the north.  Very strong southerly, fairly
orthogonal surface flow at 20-25kts and located along a narrow
stripe of enhanced surface moisture with Tds in the mid to upper
60s is driving the very strong vertical ascent.  Overshooting tops
break through the canopy of -65 to -70C with spots reaching -80C. 
Instability is modest and starting to cap a bit, but the strength
of the flux convergence is overcoming this capping to release the
1500-2000 J/kg of SBCAPEs likely driven by those higher Tds. 
Additionally, the area remains in a favorable location for
peripheral divergence/outflow to the north of the larger synoptic
polar jet.  As such, the cluster is maintaining and appears to
have some short-term (3-4hr) longevity before LLJ veers and
flattens to the orientation of the convective line. 

Given total moisture of 1.75" and strength of flux, rates of 2"/hr
are likely with occasional short duration upticks to 2.5-3"
possible.  The concern remains in the potential for training as
deep layer steering is a bit north of parallel to the line
orientation but strength of inflow may counter act this with
southern component of propagation.  As such, a streak of 2-4" is
likely with a spot of 5" not completely ruled out over the next
3-4hrs across central to east-central NEB and perhaps into far
western IA, but that is much less certain. Given spots of 2-3"
have already fallen, flash flooding is considered likely for the
next few hours.

Gallina

ATTN...WFO...DMX...FSD...GID...LBF...OAX...

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

LAT...LON   42439588 42409476 41849457 41299514 40699714
            40419951 40640009 41259985 41819810