![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Flash Flood Guidance
Issued by NWS
Issued by NWS
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
573 AWUS01 KWNH 170148 FFGMPD MNZ000-IAZ000-NEZ000-SDZ000-170600- Mesoscale Precipitation Discussion 0449 NWS Weather Prediction Center College Park MD 948 PM EDT Sun Jun 16 2024 Areas affected...eastern NE, southeast SD, far northwest IA, far southwest MN Concerning...Heavy rainfall...Flash flooding possible Valid 170147Z - 170600Z Summary...Showers and thunderstorms will slowly increase in coverage through the evening across Nebraska, and then expand into South Dakota late. Rainfall rates will steadily intensify to 1-2"/hr, which through training could produce 1-3" of rain. Flash flooding is possible. Discussion...A cold front analyzed by WPC draped from south-central MN southwest into southern NE is becoming a focus for convective development as noted via cooling cloud tops on the GOES-E IR imagery. Ascent along this front is being forced by low-level convergence and isentropic ascent as the 850mb winds from the south impinge into the front at 20-25kts. This ascent is occurring into favorable thermodynamics as reflected by SPC RAP analyzed MLCAPE as high as 4000 J/kg south of the front with a very sharp instability gradient along it, overlapped with PWs ranging from 1.1 inches north of the front to as high as 1.8 inches to the south. At the same time, a shortwave is ejecting out of western NE, while a jet streak lifting northeast into Manitoba and Ontario will more favorably place the diffluent RRQ over the region to additionally enhance ascent. The next few hours remain uncertain, but the past few runs of the HRRR have become increasingly aggressive with development along the cold front, which appears to be trending in the right direction based on current satellite. With synoptic ascent continuing to increase, and the LLJ surging to as high as 30-40 kts from the south, the overlap of ascent and thermodynamics should become even more robust resulting in widespread development across NE. Additionally, as the LLJ strengthens and veers subtly more to the SW, this will cause Corfidi vectors to locally back to cause some backbuilding along the front, resulting in slower cells with longer duration training as the 0-6km mean winds track parallel to the front. The HREF indicates rainfall rates have a 40-50% chance of exceeding 1"/hr, which through training should produce stripes of 1-3" of rainfall, with locally higher amounts possible, along the front. Farther to the north, the intensifying LLJ will help draw the higher moisture northward, and SREF 850-700mb moisture flux anomalies are progged to reach as high as +4 sigma into NE by 06Z. This will result in intense convergence of the moisture transport vectors along the nose of this LLJ, resulting in a secondary axis of elevated thunderstorm development. This axis is likely to become the primary mechanism for heavy rainfall and flash flooding overnight, but some development and training until 06Z could result in isolated flash flooding along this boundary before that time as well. In general, this will be a priming event across SD/MN with more significant flash flood potential occurring overnight. Weiss ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABR...DMX...FSD...GID...GLD...LBF...MPX...OAX... UNR... ATTN...RFC...MBRFC...NCRFC...NWC... LAT...LON 44379629 44009498 43449406 42739383 42299464 41929562 41289763 40569949 40200041 40210098 40690115 41360055 41959983 42449944 42870018 43230109 43860055 44229885