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Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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288 FXUS63 KOAX 140543 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1243 AM CDT Wed Aug 14 2024 .KEY MESSAGES... - There is a 60-80% chance of thunderstorms tonight into early Wednesday. Greatest threat will be localized flooding, but hail and damaging winds will also be possible (5-15%). - Severe storms are possible Wednesday afternoon and evening (10-20% chance). Large hail, damaging winds, and localized heavy rain and flooding will be the primary hazards. - Continued small shower and storm chances will persist into the Thursday (15-20% chance), but the overall trend will be toward drier, seasonably warm weather over the weekend. && .DISCUSSION... Issued at 1243 AM CDT Wed Aug 14 2024 Storm development was well underway in southeast NE as of 12:30 AM with low level moisture transport pointing into the area. Farther west a strong to severe bowing segment was producing 60+ mph winds across southwest into south-central NE. Latest CAMs continue to suggest this bow will eventually push east-northeast and somewhat weaken through the early morning hours. However, wondering if it won`t stay a little farther south than guidance indicates and follow the MUCAPE gradient progged to set up across southeast NE (roughly near and south of Omaha). Still, the primary upper level forcing does look to take more of a northeasterly track. Guessing the answer will be somewhere in the middle. Either way, the elevated instability along with fairly strong 0-3 km shear should yield a continued threat of severe weather...moreso wind with the bow, but maybe some large hail with any initially discrete storms ahead of the bow on the nose of the low level jet. In addition, heavy rain and localized flooding will be possible with these storms just given the orientation of ongoing storms and potential for repeat rounds. Also, if heavy rain falls on the narrow band of 1-2" that fell 2 nights ago from the Omaha metro toward Red Oak, IA, impacts could increase. When all is said and done, thinking there should be a decent band of of 1-2 inches with localized 3+ inch amounts. The question will be just exactly where it sets up. Most precip with the overnight MCS should pass off to our east by mid-morning, but clouds and perhaps a few light showers could linger into the afternoon ahead of a surface low pushing northeast out of KS. The exact track of the surface low and resultant clearing of clouds will play a large role in severe weather potential for the afternoon and evening. Latest guidance continues to suggest we see some clearing in the southern 2-3 rows of counties in southeast NE and far southwest IA by early afternoon, with HREF mean SBCAPE values in the 2500-3000 J/kg range. While deep layer shear could be somewhat limited (around 30 kts of 0-6 km), low level shear will increase in the evening as the low level jet strengthens. This will result in decent low level hodograph curvature and yield some tornado threat to go along with the threat for damaging winds and large hail. In addition, while storms do look like they`ll be fairly progressive, the environment is set up pretty well for efficient rain-producing storms with precipitable water values near or over 2 inches and warm cloud depths nearing 4 km. Should we get any degree of training storms or if they move over areas that received recent heavy rainfall, flooding could develop. Timing of the greatest threat currently looks to be roughly 5 PM to midnight. Precip should exit to the east by early Thursday morning immediately followed by a cold front and then additional weak shortwave energy during the afternoon. Guidance suggests some at least some decent elevated instability could be in place as the shortwave moves through along with 30-40 kts of 0-6 km shear. This could lead to a few additional stronger to isolated severe storms (5-10% chance), but higher chances should remain to our east ahead of the cold front where there will be much more instability. By Friday morning, a cutoff low is progged to develop over MN/WI/the Great Lakes with guidance in good agreement that associated precip on the back side remains just to our northeast (though wouldn`t completely rule out a few sprinkles Friday). We`ll remain under northwest flow aloft while upper level ridging amplifies just to our west. Do expect an overall drier pattern heading into the weekend, though guidance does show a few weak bits of shortwave energy sliding through the eastern side of the ridge, bringing us at least some small periodic precip chances (10-20%) through the weekend and into early next week. Otherwise, high temperatures should remain pretty steady in the 80s. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1129 PM CDT Tue Aug 13 2024 A line of thunderstorms currently ongoing across southeast Nebraska will move into northeast Nebraska (KOFK), east-central Nebraska (KOMA) and southwest Iowa tonight after 07Z. These storms will have the potential for heavy rain, wind gusts up to 60 knots, and hail up to the size of quarters. As of now, the highest chances for thunderstorms appears to be just north of KLNK, so have refrained from a TEMPO TSRA group for now. There is still a 30 to 40 percent chance of thunderstorms in Lincoln, so will monitor to see if TAFs need to be amended to include this. Otherwise, a deck of low stratus has developed across eastern Nebraska and southwest Iowa (all TAF sites). Ceilings are lower than what current guidance has suggested, so have manually brought ceilings down in the TAFs. A scattered deck of IFR ceilings is expected to build in tonight. Have kept these out of TAFs for now, but if observations shows more robust IFR cloud cover moving into terminal areas, will amend the TAFs accordingly. Lastly, there will be another chance for scattered strong to severe thunderstorms (KLNK and KOMA) tomorrow evening. Have denoted the more likely time frame to see precipitation with a SHRA FM group. After the round of thunderstorms tonight, will likely have a TEMPO TSRA group included in the KLNK and KOMA TAFs to start narrowing down the timing for this second round of storms. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...CA AVIATION...Darrah