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Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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184 FXUS63 KOAX 222059 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 359 PM CDT Sat Jun 22 2024 .KEY MESSAGES... - Flooding of the Missouri River tributaries in southeast South Dakota and northwest Iowa will lead to increased water flow into the Missouri River downstream of Sioux City. Flood warnings are in effect along the Missouri from Decatur to Rulo beginning early next week. - There is less than a 5% chance of severe thunderstorm development in southeast Nebraska through early evening, with damaging winds the primary hazards. - The hottest temperatures so far this year are expected Monday and possibly Tuesday, with heat index readings of 100 to 110. - There will be additional storm chances next week, with occasional severe weather and heavy rainfall possible, particularly on Tuesday and Friday. && .DISCUSSION... Issued at 358 PM CDT Sat Jun 22 2024 Quasi-zonal flow prevails across the northern plains this afternoon, with a short wave feature moving eastward into the Great Lakes region. An attendant frontal boundary is slowing moving through the forecast area, so far only marked by a windshift and slightly cooler temperatures. Diabatic heating will allow SB/MUCAPE to increase into the 1500-2500 J/kg range by late afternoon with bulk shear 30-35kt. Diabatic forcing combined with weak large scale forcing and low level convergence may be sufficient to develop isolated thundestorms late this afternoon, generally south and east of Harlan IA to Omaha- Council Bluffs to Pawnee City line. Given bulk shear values on the low side, it may be difficult to storms to sustain updrafts, thus any storm that reaches severe limits may collapse producing isolated damaging wind gusts. The front is expected to move south of the forecast area early this evening, effectively ending the severe weather threat. The rest of the evening will be characterized by clearing skies and light northwest winds, with temperatures falling into the 60s. Sunday through Tuesday: Upper level riding amplifies as aforementioned short wave feature carves a long wave trough across the eastern U.S. bisecting southern tier H5 dome. The sensible weather effect across the forecast area is a dramatic increase in temperatures, especially Monday. Temperatures on Sunday will be about 5 degrees above normal, with upper 80s and lower 90s expected, and heat indicies in the mid 90s. Monday will be the sizzler of the week, with high temperatures in the upper 90s to lower 100s and heat indicies 100 to 110. There still is some spread in the forecast guidance, with half the at least one of the ensemble clusters indicating less ridging. 75+% confidence in heat headlines being issued in the next 24 hours. Tuesday, the signal is a little mixed. A vortex moving across the central Canadian provinces has a slight reflection in the form of a diffuse upper level disturbance that moves across the central plains Monday night into Tuesday, dragging another weak cold front across the region. Synoptic models and medium range ensemble clusters indicate the development of a MCS that will move across the area, mainly affecting northeast Nebraska and western Iowa. Convective cloud debris and cooling from the passage of the front may impact the level of warming, except for southeast Nebraska and southwest Iowa. Still, NBM 25-75% temperatures near or above 90 in most locations. Redevelopment of storms along the front later in the afternoon appears possible, which could further limit temperatures. Rainfall amounts do not appear excessive at this time, with model QPF a quarter inch or less, thus would not expect flooding situation to be exacerbated. However, precipitable water values will be in the 75% of climatology, thus isolated heavy rainfall may be possible. Wednesday Through Saturday: A relatively quiet weather day on Wednesday, with slightly above average temperatures and no precipitation expected. A large scale trough develops across the western U.S. coast Thursday, with medium range deterministic and ensembles ejecting systems quickly eastward Friday and Saturday across the northern U.S. and southern central Canada. One or more convective complexes will affect the area, with the possibility of severe weather and heavy rainfall, with the grand ensemble indicating a 20 to 40% probability of sufficient CAPE and shear for severe weather on Friday. Temperatures will trend slightly above average Wednesday through Friday, with more seasonable temperatures on Saturday. Similarly the probability of 1 inch or greater rainfall occuring somewhere across the region is 30 to 50%. The additional rainfall could delay the recession of the Missouri river if realized. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1248 PM CDT Sat Jun 22 2024 MVFR ceilings at FL020-025 will linger until 19z-20z at KOFK, with diurnal mixing and frontal passage leading to VFR ceiling FL040, and gradually becoming scattered. VFR conditions will prevail at KLNK and KOMA with SCT to BKN clouds at FL040-060. Front moving across the forecast area will cause southwest to westerly winds 10 to 20 with gusts up to 25kt to veer to a northwesterly direction between 20z and 22z. Any remaining low clouds will dissipate by 00z-01z with northwest winds slackening below 10kts, then becoming light and variable after 08z. There is a 15 to 25% probability of MVFR visibilities 3SM to 5SM developing 10z-12z, but will leave out for now. && .HYDROLOGY... Issued at 358 PM CDT Sat Jun 22 2024 Flood warnings have been posted along the Missouri River downstream from Sioux City to Rulo. The successive river forecasts during the past 24-36 hours have lagged the onset of flooding and crests, forecasts are tracking with observations more closely. This will be the first time since 2020 that the Missouri has been in flood along its entire reach in the HSA. Additionally flooding is occurring along Ponca Creak from its headwaters to Verdel, with some indications that the river could recrest again based on the National Water Model. River levels also are above action stage along the Platte between Schuyler and North Bend, Loup upstream of Columbus and Clear Creek. Fortunately there will be no precipitation in the short-term to affect rivers in the next 24-48 hours, but precipitation Tuesday and onward could impact the recession of the Missouri, and cause other area rivers to rise from Wednesday onward. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Fortin AVIATION...Fortin HYDROLOGY...Fortin