Area Forecast Discussion
Issued by NWS Des Moines, IA

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000 FXUS63 KDMX 021131 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 531 AM CST Tue Mar 2 2021 ...Updated 12z Aviation... .DISCUSSION.../Today through Monday/ Issued at 310 AM CST Tue Mar 2 2021 Amplified thermal ridge over the Rocky Mountains has been in control of the weather for most of the central CONUS over the past 24 hours. Iowa has been in northwest flow downstream from the ridge axis, and this has allowed surface high pressure to develop. There have been some passing high clouds noted on satellite imagery, but subsidence has prevented cloud cover from becoming thick and creating low ceilings. A trough over the Pacific Ocean will approach the western CONUS this afternoon, and its downstream impacts will be a deamplification of the thermal ridge. However, this will continue to result in downslope flow across the Front Range and into the High Plains. With another short-wave trough and surface cyclone moving across the southern Canadian Prairie Provinces, surface to H85 flow will turn west-southwesterly across the eastern Plains and upper Midwest this afternoon. This will result in moderate WAA from the warmer airmass in the High Plains were the downslope will be allowing for adiabatic compression heating. For today, this will boost temperatures for southern and western potions of the forecast area. This should send afternoon highs into the 50s. Eastern and northeastern Iowa will remain cooler this afternoon as a pocket of cooler air moves along with the center of high pressure. Eastern Iowa also will not be in the stronger southwesterly flow where WAA is prominent. Winds will be a bit breezy especially for areas along and west of Interstate 35 today. Winds near the top of the mixed layer look to be around 35 kts. A few gusts up to 30 kts are possible this afternoon. One helpful factor though is that there is no CAA, and not much other forcing that would promote rapid momentum transport toward the ground. Wednesday, trough over the Pacific makes land-fall, and most of the 00z guidance is in agreement that progression of this feature will stall as through becomes a weak cut-off low. WAA will start again over much of the central CONUS, resulting in another ridge amplification that will control much of the weather. Wednesday into Thursday, Iowa sits downstream from the ridge axis in a favorable location of AVA, leading to subsidence that will allow high pressure to again develop at the surface and keep skies mostly clear. West- southwest flow near H85 will continue to provide warmer air from the High Plains that was a response to preceding downslope flow off the Front Range. Temperatures will gradually increase as the warmer air slowly pushes further toward the northeast throughout Iowa. Temperatures will range from the upper 50s south and southwest on Wednesday, with mid 40s in the northwest. Thursday, the mid 50s will push further northeast. Thursday night, closed H5 low begins to propagate across the Four Corners Region and surface lee cyclogenesis begins in response to this forcing in the southern Rockies. This will reinforce south- southwesterly flow across Iowa Friday and into Saturday. Currently, even though there are minor timing discrepancies, both GFS and ECMWF keep the bulk of any forcing away from Iowa, and there is not much QPF in the ensemble suites. Kansas, Oklahoma, and Missouri could see some thunderstorm activity with this. But for Iowa, will maintain a dry, warm forecast heading into the weekend. Toward the end of the weekend and next week Monday, another thermal ridge will slide across the area, keeping temperatures seasonably warm. The pattern does look to become more active by next week Tuesday and Wednesday, which could present some precipitation chances. && .AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/ Issued at 529 AM CST Tue Mar 2 2021 Mostly clear skies expected through the TAF period. MVFR cloud bases are possible Wednesday afternoon, however, cloud cover may only be scattered by that time. The main issue to focus on for today will be gusty winds, resulting in LLWS at most of the terminal sites this afternoon. Winds should eventually diminish by the evening. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION...Krull AVIATION...Krull

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