Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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194 FXUS63 KDMX 250344 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1044 PM CDT Fri May 24 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Some additional showers and storms this afternoon over eastern Iowa - Returning chances for showers and storms late Saturday into Sunday; some strong to severe storms possible - Additional active weather into early next week && .DISCUSSION... Issued at 253 PM CDT Fri May 24 2024 After a busy morning with a QLCS passing across Iowa, which has weakened significantly as it tracks into Lake Michigan early this afternoon, conditions quieted down by mid to late morning outside of a few lingering storms across the eastern parts of the state. As of this afternoon, radar returns over the past hour or so have shown redevelopment of additional showers and storms along the frontal boundary, which is draped from southwest to northeast over eastern Iowa. A favorable environment with MUCAPEs around 1000-1500J/kg and favorable shear and lapse rates could allow for a few storms to potentially become strong at times, though the better severe potential lies further east where more favorable conditions reside. Small hail and gusty winds look to be the main hazards, along with a few heavy downpours at times. Breezy west/southwest winds this afternoon will shift more northwesterly and are expected to gradually decrease, along with skies clearing out from west to east this evening. With plentiful radiational cooling and the aforementioned NW flow, overnight lows are expected to fall into the 40s across the state. High pressure quickly passing across the region will allow for dry and quiet weather to remain into Saturday, before exiting the area ahead of a shortwave and deepening low pressure system tracking across Nebraska/Kansas into Missouri through the day. Increasing theta-e advection along with southwesterly flow and resultant warm air advection per guidance is expected to stream into the state throughout the day, with increasing chances for showers and storms by Saturday evening and into Sunday. Looking closer into the environment during this timeframe, steep lapse rates, effective shear values around 30-40+ kts are highlighted over southern Iowa, though CAPE values are on the lower end below 1000J/kg. While more favorable environmental conditions are looking likely into Missouri, the highest potential for strong the severe storms are expected over portions of southern Iowa where a Slight risk is highlighted per SPC guidance, while a Marginal risk covers the central into portions of southern Iowa. In terms of rainfall, model soundings have shown PWAT values up to 1.25-1.50 inches along with deep warm cloud depths, which would allow for a higher end potential for heavy widespread rainfall across the state. Showers and storms are expected to largely continue through Sunday morning, while model members are a bit less agreeable on when and where the rain ends, as a few members depict a lingering boundary remaining over southern Iowa that may allow for continued chances for showers and storms. Widespread rainfall amounts with the late Saturday into Sunday system look to bring widespread 1-2 inch amounts, with a few locally higher amounts possible as well. Into early next week, models indicate continued potential for active weather, though details regarding location and impact remain more uncertain. In general, guidance shows a positively tilted trough and associated developing low pressure system pivoting across the upper midwest, with a few embedded waves dropping into the state which look to bring continued chances for showers and storms. In specific terms, the NAM generally shows developing activity over largely the northeast half of Iowa Monday afternoon to evening and into Tuesday, while the GFS and Euro depict more widespread activity across Iowa through the same time periods. Overall, the severe potential looks low end at this time, along with generally lower end rainfall amounts, though will be watching closely for any changes. Upper level ridging looks to follow by midweek, with some quieter weather looking to result from this. Temperatures through the week generally are expected to be rather mild, with highs in the 70s and lows in the 50s. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1038 PM CDT Fri May 24 2024 VFR conditions remain expected through this TAF period. Winds will continue to ease overnight as area of high pressure moves in. Will cause all sites to have period of light VRB winds before settling out of the S and eventually SE through the latter half or more of the period predominantly around 10kts. Mid to high level cloud cover will increase latter portions of the period, but remain well within VFR territory. && .HYDROLOGY... Issued at 253 PM CDT Fri May 24 2024 An active hydro pattern continues and is expected to continue over the next several days at least for rivers and larger streams. With forecast rainfall last night into early this morning and during the day today coming in a little higher than what was expected yesterday, a flood watch was issued for much of the CWA for last night through this afternoon. That flood watch will expire this afternoon as the showers and storms gradually migrate east. Locally heavy rainfall this morning led to decent runoff and some localized flooding issues mainly across the southeastern CWA. Elevated SAC-SMA soil saturation values have increased across the southeastern CWA. Values are in the 40 to 60% range across the eastern CWA roughly bounded by IA 92, US 218, US 20 and I-35. In the western CWA they are also elevated in the Audubon-Jefferson County area. When soil saturation values exceed 50% the flash flood concern increases markedly. Thankfully with a relative lack of heavy rain in the forecast for the next couple days the flash flood threat will subside. In spite of the decrease in flash flood concerns, river flooding continues on some streams in the CWA and will continue over the next several days. River flooding continues or is forecast across portions of the Cedar, Iowa, Des Moines and Raccoon River basins as well as their tributaries. Further analysis of observed rainfall trends have led to decreases in the forecasts this afternoon for parts of the Des Moines River basin above Saylorville Lake. Below Saylorville Lake and Lake Red Rock, changes to outflow plans by the U.S. Army Corps of Engineers at both locations has led to adjustments at some locations as well. As is usual this time of year, the river forecasts take into account 24 hrs of QPF. Additional rainfall is in the forecast beyond Saturday. Looking beyond 24 hrs using our QPF ensemble hydrographs, the Hydrologic Ensemble Forecast System (HEFS) and National Water Model (NWM), the most likely scenario in most places is that the rain over the next several days will slow the fall of area rivers and possibly result in secondary crests. Those secondary crests should be lower than the levels we saw earlier this week. It is not outside the realm of possibility, however, that some locations may see higher crests than we saw earlier this week--but again that would be heavily dependent on future rainfall. If the rainfall comes in higher than forecast then we would see long, broad crests and/or higher secondary crests. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Bury AVIATION...Curtis HYDROLOGY...Zogg