Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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590 FXUS63 KDMX 260739 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 239 AM CDT Sun May 26 2024 .KEY MESSAGES... - Showers and storms to continue through the morning with a waning severe weather threat. A few thunderstorms possible southwest this afternoon. - Additional rain chances Monday and Tuesday. Some Monday storms could be strong in the east. - Midweek dry period with seasonal temperatures with rain returning Thursday night. On and off rain through next weekend. && .DISCUSSION... Issued at 225 AM CDT Sun May 26 2024 Convection progressively coated the state overnight, overrunning the surface warm front found in Missouri. 00z upper air analysis placed the nocturnal jet into central Iowa, bringing plenty of upgliding moisture into the state with mostly elevated thunderstorms with sparse hail reports. Expect instability to wane southward through the night as the MCS in Kansas takes over and sinks southeast, which will largely diminish severe weather chances for us. Otherwise, showers and storms will form from the jet-influenced theta-e advection, the passing shortwave, and the left exit region of the upper level jet. Southern Iowa can expect amounts between a half inch to an inch of rain with higher amounts with thunderstorms. The HREF probability matched mean QPF has a max along the H850 warm front between the Highway 20 and Highway 30 corridors where localized amounts nearing 2 inches will be possible. Rain and cloud cover will focus more south through the day Sunday under the influence of the deformation axis and pressure trough, finally exiting after sunset. Enough instability will remain for these to become thunderstorms, but northwesterly winds will inhibit the amount of moisture available. CAA will keep highs in northern Iowa near 70 for the day. Southern Iowa will be in the mid 70s. Additional rain will be possible along passing waves on Monday and Tuesday. CAMs build in an instability axis along the cold front on Monday, bringing thunderstorm chances mostly east. Effective shear at 40kts could organize some of the storms and produce hail and gusty winds. Tuesday`s rain will be focused north. A tightening pressure gradient and dry boundary layer will make for a breezy Monday with 30 mph gusts possible in the west. Upper level ridging will build in by midweek and spare the state from rain until Thursday night when upper level troughing influences the weather pattern again through next weekend. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1126 PM CDT Sat May 25 2024 While end of VFR conditions remains expected across all sites, the extent and duration of non-VFR has trended downward as hi- res models grapple with ongoing convection in Nebraska/Kansas/Missouri. Trend has been such that northward extent and duration of TSRA/SHRA have been less robust. Guidance has also eased a bit on the areal extent and duration of IFR ceilings. With all that in mind, have attempted to target best opportunity windows for prevailing thunder and vicinity mentions otherwise. Also have not fully dropped the hammer on IFR ceilings with current/upstream obs tending to be higher than guidance would suggest. VFR conditions then return late in the period. && .HYDROLOGY... Issued at 243 PM CDT Sat May 25 2024 The latest river forecasts utilizing QPF over the next 24 hours (7am Sat-7am Sun) mainly suggest either steady or falling river levels. Even higher end QPF simulations based on recent HEFS 30% exceedance probabilities yield similar results as sites either have 1) sufficient storage capacity, or 2) are already at such elevate flows that more appreciable precip would be needed for additional rises. The only exception to this would be locations below Lake Red Rock where the combination of runoff and Corps of Engineer releases may bring more significant within bank rises, or potentially minor flooding. Ottumwa may reach minor Flood Stage Sunday night, but confidence is medium at best and is dependent on rainfall and future reservoir release changes, so a River Flood Watch has been issued for Ottumwa for the time being until confidence in flooding increases. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Jimenez AVIATION...Curtis HYDROLOGY...Small