Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 240435 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1135 PM CDT Wed May 23 2018 .SHORT TERM...(Tonight through Saturday) Issued at 332 PM CDT Wed May 23 2018 Thunderstorm chances tonight and especially Thursday afternoon and evening are the primary forecast concerns. Showers and thunderstorms that had pretty much dissipated this morning in central Nebraska had reformed this afternoon along mid level theta-e axis working into northeast Nebraska. Hi-res model output had not captured this activity in afternoon hourly runs. Storms are expected to continue tracking north-northeast this afternoon, and may linger in parts of northeast Nebraska during the evening before dissipating with loss of daytime heating. Second area of convection is possible late today and this evening, tied to weak mid level impulse lifting northeast from western NE/KS shown on water vapor satellite imagery and RAP 500mb analysis. Hi- res models were becoming more insistent on scattered storms developing in northwest Kansas and south central Nebraska, and tracking activity into our western CWA this evening. While shear is weak, modest instability should support storms through sunset before diminishing. Both these areas of storms are in an environment with weak shear, but instability on the order of 2000-2500 J/kg of MLCAPE may aid in low-end severe hail potential. Attention then turns to later tonight when low level jet increases to near 40kt from central into northeast Nebraska under southwest mid level flow regime. Nose of that jet is forecast over north central and northeast Nebraska between 06Z and 12Z in area where MUCAPE increases to 1500 J/kg based on NAM forecast soundings. Expect scattered convection to fire by 09Z and gradually work north and northeast through northeast Nebraska through mid morning. A lull in the action is likely a few hours either side of 18Z Thursday, allowing atmosphere to recharge from central into northeast Nebraska. Models suggest surface dew points in the mid and upper 60s combined with cooling mid level temperatures with approach of shortwave will push MLCAPE values potentially north of 3000 J/kg. Bulk shear looks modest at best, maybe around 25kt 0-6km, and low level convergence appears to lag instability. SPC has elevated our severe risk into the Slight category, and given instability, think that is reasonable if storms fire in our CWA. Convection is expected to continue much of the night Thursday night as shortwave gradually works through eastern Nebraska and southwest Iowa by Friday morning. Storms may linger a while longer in southeast Nebraska and southwest Iowa, and could re-fire Friday afternoon if instability is not swept southeast as per latest GFS indications. Otherwise a mainly warm forecast is in order as 850 temps climb into the lower and middle 20`s C range for Friday and Saturday. Many spots should reach 90 one or both of those days. .LONG TERM...(Saturday night through Wednesday) Issued at 332 PM CDT Wed May 23 2018 A fairly active setup appears to be forming for next week, at least in terms of chances for thunderstorms. Potential severity of convection will have to be determined at a later time, but it looks like we`ll have chances for storms much of the period Monday through Wednesday. Upper low moving through the western U.S. on Sunday will eventually open up and send several impulses through the Plains, with the timing of each impossible to time this far out as solutions are widely variable between model to model and run to run. However low level southerly flow should maintain a moist and warm atmosphere conducive for convection with each impulse. As far as temperatures are concerned, Sunday looks like the warmest day of the long term period under mid level ridging ahead of approaching low. Monday through Wednesday temperatures should average 85 to 90, but could vary based on convection and cloud cover day to day. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 1135 PM CDT Wed May 23 2018 Convection had ended to the west and north of KOFK at 05Z but some storms continue further west in north central Nebraska. Latest models show this area to drift slowly east through 18Z in tandem with instability axis. VFR conditions will prevail outside of convection through the period. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...Fobert

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