Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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172 FXUS63 KOAX 171952 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 252 PM CDT Sun Sep 17 2017 .SHORT TERM...(Tonight through Wednesday) Issued at 251 PM CDT Sun Sep 17 2017 More active weather will continue, with a roller coaster of temperatures. Subjective 12Z upper-air analysis indicates an upper- level ow centered near the MB/SK border, with 500mb height falls centered in noe northwestern Great Lakes. Another shortwave trough was evident in the Pacific Northwest through the Baja, along with a weak remnant wave in the mid-Atlantic. An 850mb cold front extended from a now in western ON through the mid-MS river valley and toward the TX/OK panhandles, with much of the moisture shunted ahead of it. Surface high at 19Z was centered near the SD-MN and NE-IA border area, with temperatures well below normal today. Main forecast concern is shower/thunderstorm potential this evening through Monday across the area, with another brush of the northern CWA possible on Tuesday night. Mid-level flow and moisture already are returning to the High Plains, with advection returning eastward this evneing. As a weak but broad upper-level shortwave passes through the central Plains, showers and a few embedded thunderstorms should develop later this evening from southeast to central NE, spreading northeastward through the night and continuing on Monday, before finally shunting away to the east later Monday. MUCAPE profile is not very impressive, with weak 500-1000 J/kg MUCAPE possible tonight through Monday morning, perhaps around 1000-1500 J/kg in the southeastern CWA by afternoon, and skinny CAPE profile. Clouds and rain will hold temperatures down again on Monday, despite a return of warm air advection. In wake of the Monday showers/storms, rising 500mb heights should keep things quiet on Monday night and Tuesday as a deeper upper- level trough digs into the Rockies. With continued warm air advection, temperatures on Tuesday should pop well above normal again. An ejecting shortwave trough on Tuesday night across the Dakotas will bring another round of thunderstorms, but do think the activity will struggle to get southward into northeast NE/northwest IA as the upper-level support pulls away to the north and with rather substantial mid-level cap. If it did sneak into the area, there is some potential for storms to be on the strong to severe side. Associated cold front will bring a return to near-normal temperatures to the area on Wednesday. .LONG TERM...(Wednesday night through Sunday) Issued at 251 PM CDT Sun Sep 17 2017 A deep upper-level low is progged to dig into the Rockies late this week and through the weekend (and likely beyond), with an upper- level high parked over the Great Lakes. The persistent pattern will keep the central US under an active weather regime, with the potential for several consecutive days of moderate rainfall slowly moving across the area from Saturday into early next week. Temperatures are likely to be quite a bit above normal to our east, below normal to our west, and something in between here in the middle, with rainier days likely to be on the cooler side. ECMWF is quite a bit slower than GFS to bring the slow-moving front and associated moderate to heavy rainfall into the area. Ultimately, the weekend looks cool and rainy, with well above normal temperatures on Thursday and Friday ahead of the digging low and advancing front, along with dry weather on Thursday and potentially on Friday, depending on the speed of the advancing front. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1209 PM CDT Sun Sep 17 2017 Surface high pressure will quickly build through the area today with strengthening warm advection already yielding a growing cloud shield to the immediate west. A low-amplitude perturbation will emerge from the Rockies tonight, combining with the warm-advection pattern to foster numerous showers and thunderstorms which will affect the area from after midnight until about midday Monday. Ceilings will gradually lower from south to north with prevail MVFR conditions anticipated late tonight into Monday morning at all three TAF sites. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Mayes LONG TERM...Mayes AVIATION...Mead

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