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Flash Flood Guidance
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Issued by NWS
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800 AWUS01 KWNH 220317 FFGMPD IAZ000-NEZ000-220800- 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 ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...DMX...FSD...GID...LBF...OAX... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 42439588 42409476 41849457 41299514 40699714 40419951 40640009 41259985 41819810