377 FXUS63 KOAX 291738 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1238 PM CDT Tue Sep 29 2020 ...Updated Aviation Forecast Discussion... .DISCUSSION... Issued at 353 AM CDT Tue Sep 29 2020 Forecast Summary: One day of above-normal temperatures today will be followed by cooler-than-normal temps through the weekend as a couple of shots of cooler air plunge through the Plains. The coldest day of the week should be Thursday, with temperatures dropping well into the 30s Thursday night when our first real shot of widespread frost and spotty freezing temperatures are likely. Saturday brings the only substantial chance for precipitation through early next week. Today through Friday: Upper flow pattern features a strong ridge in the West from northwest Mexico into the Pacific Northwest, and a deep trough to our east extending from the Great Lakes into East Texas. Strong northerly flow resides in between these features, with a 120-140kt 300mb jet extending from southern Manitoba into eastern Nebraska. A slight eastward shift of trough and jet is forecast today, allowing mid level heights to rise and promote a nice warm advection pattern at the surface. Westerly low level flow and warmer 850 temps suggest highs rising well into the 70s in eastern Nebraska, and likely just above 70 in western Iowa. West to northwest winds are likely to gust to around 35 mph or higher this afternoon as deep mixing occurs. Wind profilers suggest speeds are a bit higher than models indicate now, so have increased speeds through much of the day all areas. The strong winds combined with mixing induced low humidities suggest very high fire danger in some spots across eastern Nebraska this afternoon. Current fuel status indicates widespread uncontrollable fires are not likely, so will refrain from any fire weather headlines at the moment. A wind shift will drop through the area later tonight as a mid level shortwave rotates into the southern Great Lakes. Highs Wednesday will swing to just below normal as cold advection continues through the day. And that cool advection is accelerated Thursday when 850 temperatures drop below 4C. Highs may not reach 60 in much of our area on Thursday. Winds diminish under mainly clear skies for Friday morning when surface high pressure settles over the Mid Missouri Valley. Decent radiational cooling should allow for some spots to drop into the lower 30s, and perhaps lower, with areas of frost likely most of eastern Nebraska and southwest Iowa. Winds turn southerly rather quickly Friday as surface high slides east. A nice 30-degree warmup from morning lows should put most spots back into the 60s. Saturday through Monday: A significant shortwave will induce surface cyclogenesis in the western Plains on Saturday. Only modest-at-best moisture return is expected, but strength of system suggests areas of showers and even isolated thunderstorms are a good bet. ECMWF is most bullish in showing widespread rains across eastern Nebraska and southwest Iowa, but most other mid-range models have a decent precipitation signal in or close to our area as well. Currently have rather low precip chances in the forecast, but confidence is increasing for rain on Saturday. A brief cooldown will follow this system for Sunday, with a return to warm advection to start next week. Have highs in the 60s this weekend, then closer to the lower 70s on Monday. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1234 PM CDT Tue Sep 29 2020 VFR conditions to prevail for the TAF period. Wind speeds are beginning to increase across the area as wind gusts near 20 kts have been observed at several sites. Wind gust should peak near 25 kts. Winds will rotate over the afternoon from westerly to northwesterly. By 23Z, wind gusts should begin to diminish. After 01Z, winds should settle to less than 10 kts. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Dergan AVIATION...Fajman