What the forecast actually says — NWS Area Forecast Discussions, decoded into plain English.
Area Forecast Discussion · National Weather Service Omaha (OAX) · issued Friday, September 11 at 5:34 AM CDT.
Revised in 3 passages since the 11:35 PM discussion. See every revision.
Messages
Gusty 25 to 30 mph winds expected for most areas Friday with highs in the mid to upper 80s. 15-20% chance for some storms Friday evening, some of which could be severe with large hail and strong wind gusts.
Active pattern continues with more storm chances this weekend into much of next week. Some storms could be severe Saturday evening and again Monday.
Highs reach the 70s to low 80s Saturday and Sunday, followed by a brief warm up Monday, then cooling down to the 60s to low 70s Tuesday through Thursday.
Short Term
03z RAP objective analysis reveals weak H5 ridging across the Northern Plains, while to the west, a shortwave trough over western Wyoming has spun up a surface low. The 1017 mb surface high which brought our fantastic weather on Thursday has finally pushed off to the east, resulting in a pressure gradient setting up across much of Nebraska into the Dakotas. This will result in south southwesterly winds gradually increasing into the early morning hours Friday. Increased PBL mixing by the late morning and afternoon to just around H8 where a 30 to 40 knot LLJ is should help bring some more momentum downward, resulting in frequent gusts of 35 to 40 mph across far northeast Nebraska. Expect slightly lower gusts of 25 to 30 mph for the remainder of the area. Highs warm to the upper 80s to low 90s with a few passing clouds.
By late Friday afternoon into the evening hours, will see the surface cold front swing through the forecast area while the parent low tracks over eastern SD into southwest MN. Forcing along the frontal feature combined with weak large scale forcing for ascent from the H5 wave could spark some convection. Model guidance indicates an instability plume of 1,500 to 2,500 J/kg overspreading much of northeast Nebraska Friday evening, and with 0-6 km shear of 30 to 35 knots, can't rule out seeing strong to severe convection. However, newest 00z hires CAMs seem to struggle developing much convection in the forecast area.
Forecast BUFKIT soundings suggest some convective cap of 150 to 200 J/kg remaining in the low levels, and with the bulk of large scale forcing for ascent tied to the stronger H5 wave in the eastern Dakotas and MN, convection may struggle to get going across our area. If we can manage to get convection, the main threat would likely be damaging wind gusts given low level dry air noted by soundings and also large hail with steep H7-H5 lapse rates approaching 8 C/km. More redevelopment is plausible into early Saturday morning, particularly across the southern half of the forecast area as H8 WAA lingers there along with another weak H5 wave traversing the westerly flow. With this update, have kept chance of rain at 15 to 20% from 00z to 11z Saturday given the low confidence in storms developing, and have confined the chance of rain to the frontal area.
Saturday will see the surface frontal feature linger across the border in Kansas and Missouri. Looking aloft, could still see some remnant WAA driven forcing in the late morning hours that could spark more convection (chance of rain of 15 to 30% primarily over southeast Nebraska into southwest Iowa). By the late afternoon, will see more instability pool near and along that frontal zone. RAP forecast soundings along the southern Nebraska/Kansas border area show instability ranging from 1,500 to 2,000 J/kg, but some convective cap/capping is seen too. Large scale forcing still appears to lack around this timeframe too with subtle H5 height rises progged over the area, which could limit the storm threat. If storms can develop, the 0-6 km bulk shear of around 30 knots could promote a few strong storms in that general vicinity capable of strong wind gusts and large hail as we'll have fairly long hodographs and steep H7-H5 lapse rates near 8 C/km. At this time, chance of rain remain at 20 to 30% along and south of Interstate 80. Expect cooler highs in the mid 70s, while highs near 80F are forecast in southeast Nebraska into southwest Iowa. 30 to 40% precipitation chances continue into the overnight hours into Sunday as another H5 impulse moves through and H8 LLJ WAA/moisture advection persists.
Long Term
Rainy conditions should carry over into Sunday with areawide chance of rain of 60 to 80% forecast as the H8 baroclinic zone swings northeastward.
By Monday morning, should see an intensifying shortwave trough eject from the Montana/Alberta area east northeast toward the Dakotas/Manitoba. The feature will spawn another surface low that tracks north of the area, while the surface front swings through most of the Northern Plains. Ahead of the frontal feature, expect gusty 30-35 mph southwesterly winds across the area. A plume of 500-1,000 J/kg of instability will also overspread the area, and combined with surface convergence along the front, could see more convection develop. Strong to severe convection could develop, but it's worth noting that the bulk of 0-6 km shear is located near to just behind the frontal boundary and not collocated in the best plume of instability. Better H7-H5 midlevel forcing appears once again focused in the eastern Dakotas and Minnesota area. Some guidance does hint at a subtle wave trekking through the Central Plains during the day which could help provide more large scale lift. At this time, chance of rain of 60 to 80% are forecast for most of southeast Nebraska into western Iowa Monday evening into Tuesday.
chance of rain chances continue into Wednesday and Thursday as we remain in a zonal to slightly southwesterly flow and continued disturbances ride it. Temperatures in the long term will range from the 70s to low 80s Sunday, followed by a brief warm up Monday to the 80s and low 90s, then cooling down to the 60s to low 70s (yay, fall!) Tuesday through Thursday.
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