Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 10 2025 08:43:17 AWUS01 KWNH 100843 FFGMPD NEZ000-101400- Mesoscale Precipitation Discussion 0634 NWS Weather Prediction Center College Park MD 442 AM EDT Thu Jul 10 2025 Areas affected...Central Nebraska... Concerning...Heavy rainfall...Flash flooding possible Valid 100840Z - 101400Z SUMMARY...A few hours of oblique WAA training band, poses narrow axis of 2-3" totals and possible localized flash flooding. DISCUSSION...GOES-E WV and EIR loop depicts a progressive arc of thunderstorms driven by an slightly above average but compact shortwave over-topping the larger scale ridge ahead of the main northern stream wave back over the Wyoming Rockies. While the shortwave is sliding eastward, along with typical nocturnal cyclonic turning, the LLJ is responding with continued 40-45kts of southerly slowly veering southwesterly 850mb winds. This also aligns with the western gradient of an enhanced moisture from central KS through the Sandhills of NEB. Being on the western edge of the convective line, there has been lingering unstable air associated with the moisture axis remaining across a similar area with MUCAPE values of 2000+ J/kg extending into KS. The passage of the convective line also established a NNW to SSE boundary across central NEB that now aligns from Nuckolls to Brown county.=20 VWP and surface observations show, LLJ remains more southerly not having fully veered to the southwest, but strength of winds and intersection with the boundary provide strong deep layer convergence and isentropic ascent maximizing further northwest along the boundary near Brown to Loup County. As such, thunderstorms have been greatest cross this area; but with 700-500mb steering flow nearly parallel and opposite to the LLJ and boundary; cells have a favorable orientation to repeat. This orientation will shift slightly from NNW to SSE to more NW to SE with time as the 700-500mb flow shifts eastward with the exiting shortwave into central IA; but there will be sufficient overlap in time and space for favorable repeating. As this time, a limiting factor toward flash flooding is the overall available moisture. Surface Tds in the 60s are sufficient, CIRA LPW shows deepest moisture, particularly above 700mb is shifting eastward with the shortwave and the upstream gradient is very tight allowing for greater overall dry air entrainment. Still, with 1-1.5"/hr rates and potential for 2-4 hours of repeating, totals of 2-3" are possible. The other limiting factor is proximity to the Sandhills itself, where favorable infiltration of those lower rates are likely to mitigate much flooding potential north of Valley and Custer county.=20 However, as LLJ veers more southwesterly, the expansion of stronger boundary layer moisture convergence southward along the training line, places counties southward where FFG values are less than 1.5/hr and 3hr values are 2-2.5". While Hi-Res CAMs are less aggressive with the overall totals and trend toward quick evaporation of the line; this is a known negative bias where WAA, particularly orthogonal isentropic ascent tends to 'over-perform' the forecast guidance. Each HRRR run is also a bit more aggressive toward increasing convection, as well, providing some increased confidence this bias is once again plausible. So, while not particularly high-end, nor over a great areal extent, there is sufficient observational trends that an incident or two of localized flash flooding due to 2-3" totals is possible through early morning.=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-iWjdIqZQga1Vaa0bltm29zJcHfLLwGNX1UkreFTecMJC92-gNrw7o9_ARI8EKE_KbmI= boRkjSjE6P4AeKIUrWfQKG0$ for graphic product... ATTN...WFO...GID...LBF...OAX... ATTN...RFC...KRF...NWC... LAT...LON 42559933 42289852 41679780 41149742 40499787=20 40529880 41529964 42299979=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .