Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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995 FXUS63 KOAX 041122 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 622 AM CDT Thu Jul 4 2024 .KEY MESSAGES... - Scattered showers and thunderstorms are expected to develop across far eastern Nebraska and Iowa this afternoon. A storm or two may be strong to severe, though the bulk of this activity should be east and south of the region. - Another system will bring the chance for scattered strong to potentially severe thunderstorms Saturday evening. - Ridging out west will largely keep things drier next week, though occasional chances for isolated afternoon thunderstorms will be possible. && .DISCUSSION... Issued at 304 AM CDT Thu Jul 4 2024 Today and Tomorrow... A cold front currently extending from central South Dakota into central Nebraska is expected to sweep across the region late this morning into early this afternoon. By noon, this front should roughly be in line with the Missouri River. By this time, scattered showers and thunderstorms are expected to begin developing along and head of the front. Modest instability on the order of 1000-2000 J/kg and bulk shear ranging from 50 to 60 knots will help these storms organize fairly quick. With the progressive movement of this front, activity should quickly push east of the region by mid-afternoon. Nonetheless, there will be a period this afternoon, likely between noon and 4 PM, where scattered strong thunderstorms may develop (40 to 50 percent chance of rain), primarily across southwest Iowa. The primary hazards with these storms will be hail up to the size of quarters and wind gusts up to 60 mph. Behind this front, there will be some residual instability due to steep lapse rates aloft. As such, there is a low chance (20 percent) of isolated showers developing across northeast Nebraska between 3 PM and 10 PM this afternoon and evening. Any convection that is able to develop will be diurnally driven and should dissipate shortly after sundown. Tomorrow, though the front should be well to the east and south of our area, the upper-level disturbance will still linger over the northern Plains and upper Midwest. This will maintain steep lapse rates aloft via cold air advection. As such, there will be enough instability to again result in diurnally driven showers developing across northeast Nebraska and into west-central Iowa. The coverage, if these develop, will be isolated (any given location seeing a 15 to 25 percent chance of rain). Saturday and Sunday... The upper level pattern beginning this weekend will favor ridging over the western CONUS. As such, northwesterly flow aloft will prevail over the Plains. To our northwest, a shortwave trough from Alberta will dive southeast over the central CONUS. At the surface, a cold front is expected to stretch somewhere from central South Dakota into central Nebraska by midday on Saturday. The airmass ahead of the front is expected to destabilize by the afternoon, with CAPE ranging from 1500 to 2500 J/kg. As such, scattered thunderstorms (40 to 50 percent chance of rain) are expected to develop across eastern Nebraska by early afternoon. With bulk shear likely exceeding 40 knots, convection that is able to develop and mature will likely become organized to some degree, bringing the threat for strong to severe thunderstorms for much of the area. While there are still some questions with regards to when storms will initiate and the mode of convection that will be favored, confidence is growing in scattered strong thunderstorms traversing the region Saturday afternoon and evening. There are some slower model solutions that suggest the front will stall across southeast Nebraska into south-central Iowa. As such, a potential second day of thunderstorms would be possible Sunday afternoon across portions of southeast Nebraska and southwest Iowa. These storms, however, are not expected to be severe at this time should they develop in our area. Monday through Wednesday... The ridge that is forecast out west is expected to amplify next week, pushing disturbances diving southeast out of Canada east of our area for the most part. This will keep conditions seasonal and dry, with highs in the mid to upper 80s. Nonetheless, there is still a signal amongst medium-range guidance that suggest embedded low-amplitude disturbances may periodically traverse the northern Plains. Should PVA ahead of these disturbances coincide with peak diurnal heating across our area, isolated thunderstorms may develop. Uncertainty in timing and magnitude of these disturbances precludes any further discussion on specific days of concerns. The main takeaway for this part of the discussion is that though next week will likely be much drier than the last few weeks, there will still be a day or two with low end precipitation chances. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 622 AM CDT Thu Jul 4 2024 A cluster of thunderstorms has recently developed over south- central NE within a zone of locally stronger instability and minimal capping, per objective analysis. There is a fair amount of uncertainty in how that convection will evolve this morning given the poor handling of it by the models, and that instability decreases with eastward extent into eastern Nebraska. For now, -TSRA will not be included in the forecast. However, TEMPO groups for -SHRA will be maintained. The forecast will indicate prevailing VFR conditions with winds increasing to 12+ kt by late morning at KOFK, and early to mid afternoon at KOMA and KLNK. The winds are expected to diminish by around 8 PM (05/01z). && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Darrah AVIATION...Mead