Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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087 FXUS63 KOAX 020543 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1243 AM CDT Tue Jul 2 2024 .KEY MESSAGES... - Severe thunderstorms and flash flooding will be possible this evening and overnight tonight. The primary severe hazard looks to be damaging winds,but there is potential for tornadoes and some hail. The most likely area to experience wind gusts greater than 75 mph or a tornado will be south and west of a line from Ord to Norfolk to Fremont to Lincoln to Beatrice, and the most likely time will be between 7 PM and midnight. - Another round of strong to severe thunderstorms will be possible tomorrow afternoon, primarily across southeast Nebraska and southwest Iowa. All severe hazards will again be possible with the primary risk being damaging straight-line winds. - Unsettled weather continues through the week and into the weekend, with almost daily chances for thunderstorms. The 4th of July features a good chance for thunderstorms, mainly focused between 10 PM Wednesday and 9 PM Thursday. && .DISCUSSION... Issued at 319 PM CDT Mon Jul 1 2024 There is a lot going on around the region at 3 PM. Much of the local forecast area is chilly, locked in to low cloud cover with temperatures in the upper 60s to mid 70s with a stiff southeast breeze. However, we don`t have to look very far south to find a zone of warm moist air lifting in this direction...and just a bit farther south to find an area of very hot and muggy conditions also lifting north. A very impressive warm front extended from just north of Goodland to north of Hill City to just south of Concordia to near Emporia KS. To the south, temperatures in the upper 90s to lower 100s with dewpoints in the upper 60s to middle 70s. In the 50 mile zone north of this front, cloud cover clears and temperatures quickly climb into the middle to upper 80s with dewpoints in the low 70s. And north of that zone, the cool but increasingly moist boundary layer airmass remains. Over the next 6 hours, this front will continue to lift north, along with the substantial instability that exists within the frontal zone. While there is a very strong cap in place north of the front, it is likely to erode somewhat into the evening. The question is just how much that cap will erode, and if the intensity of boundary layer destabilization will overcome any remaining semblance of the cap aloft. The near-frontal zone...that 40-50 miles north of the true surface front, will feature very large cyclonically curved hodographs in the lowest 1km, with favorable deep layer shear for supercell storm mode. Even if linear convection interacts with this frontal zone as it moves in from the west, the high-end low level and deep layer shear would seem to favor some development of isolated intense wind gusts and tornadoes. Additionally, as the night progresses, additional moisture will be advected over the top of any stable layer in eastern NE and western IA, developing increasing MUCAPE. Do expect the near-surface layer to remain stable well to the north of that frontal zone, but the thermal profiles may still allow for some momentum transfer to the surface from storms with elevated inflow sectors. Furthermore, as expected, the moisture content locally will become quite impressive with PWAT of 2-2.5 inches across much of the forecast area and substantial warm cloud depth. The LLJ will continue to focus moisture influx into the local area with at least some instability recharge over the top of any outflow and frontal boundaries suggesting multiple rounds of thunderstorms possible. So what will happen. Well, there is high confidence in the storms that have developed over extreme northwest KS this afternoon continuing to cluster and build to the east northeast. Additional near-frontal convection immediately in advance of this cluster should favor at least some growth on the southern fringes amidst the very unstable and strongly sheared near- frontal zone. Believe that this cluster of storms will approach the Albion and Columbus areas between 7 and 8 PM, and may extend southward toward I-80 with eastward progression toward places like Lincoln and Fremont by closer to 10 PM. This cluster of storms appears to have damaging winds as the primary hazard, although with some hail potential as well. The possibility of significant (75+ mph) damaging winds is also there along with a chance for some QLCS tornado development...and that chance seems to be highest with southward extent of the line, closer to the very unstable and highly sheared frontal zone. Some model guidance has maintained a more northerly track to the abundance of convection, but given the nature of the lifting frontal zone, believe that this cluster will at least try to favor some periods of eastward or even east southeastward propagation into the instability axis...until it outruns the instability which should happen with eastward progression across our forecast area. There is also the question of weather the northward lifting frontal zone itself will foster isolated intense supercell convection. There is currently an increasing cumulus field along the front, and it seems to be a good chance for one or two storms to develop along this front. Now, whether they are able to move into our local forecast area is another question...but if any isolated storms are able to develop in north central KS and move northeast within the frontal zone long enough to mature, would expect to see some enhanced tornado potential prior to around 9 PM or so. The biggest question is if the cap and inhibition are enough to limit that sustained storm from developing. Finally, as the night progresses, that initial cluster of storms will lay out some semblance of a "cold pool" which looks likely to act as a focus for further convective development near and north of the boundary. As previously mentioned, some convective recharge should allow for additional rounds of storms to develop and move over the same areas, probably leading to isolated 3-5 inch rainfall amounts. There is still some uncertainty in the exact location of this favored band of training, but have issued a flood watch to encompass the parts of the forecast area with the greatest chance for repeat thunderstorms and flash flooding. Tuesday morning will probably feature showers and a few thunderstorms lingering in the frontal zone, and perhaps some lingering flooding concerns in that same area. Things become more interesting by early afternoon as there should be some heating in the warm sector producing surface based convection as early as noon. Will also see some decent instability lingering north of the surface front for several hours, so could thus have a couple rounds of storms. The main focus will be on fresh development between noon and 2 PM, probably in southeast NE into southwest IA. The deep shear will be conducive to supercell development, likely transitioning into clusters or bowing segments. The low level shear should not be as impressive as today, but may still suffice for at least a low end tornado threat. The main hazard though will probably be damaging winds, with at least a few hours of some potential for hail. As we get deeper into the afternoon, by 4-6 PM, most all of this activity should push east of the forecast area. Dry conditions are expected until Wednesday evening when the next short wave trough enters the Plains states. This should support another round of storms across the region during the overnight hours and then one more as the main trough axis and front cross the region during the day on Independence Day. The day as a whole should not be a constant rain-out, but with periods of storms possible. The current indications are also that the front will clear through the entire forecast area by approximately 9 PM. And while that is very tight timing for the many outdoor evening activities planned, please know that this forecast is still a few days out and the exact timing is rather uncertain. Here`s hoping for a fast front to clear natures fireworks out of the area before dusk. The first few days of the forecast have provided more than enough to look at in terms of impactful weather, and the longer term forecast has remained largely the same for now. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1243 AM CDT Tue Jul 2 2024 Showers and storms will continue to push through the area tonight and bring MVFR to potential IFR conditions at time, though the severe weather threat should largely be over for the night. Outside of storms, expect VFR conditions at LNK and OMA through the morning and IFR ceilings at OFK, but additional showers and storms look to develop toward mid day. Confidence is fairly low on exact timing and there is some potential they stay south of the TAF sites, but consensus says scattered storms will develop near at least LNK and OMA. By this evening, expect any lower clouds to exit with mid to high clouds remaining. Otherwise, expect winds to be out of the southeast to south before becoming northwesterly behind departing showers and storms. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Flood Watch until 7 AM CDT this morning for NEZ012-015>018- 030>034-042>045-050>053-065>067. IA...Flood Watch until 7 AM CDT this morning for IAZ043-055-056-069- 079. && $$ DISCUSSION...Barjenbruch AVIATION...CA