


Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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676 FXUS63 KDMX 271121 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 621 AM CDT Fri Jun 27 2025 ...Updated for the 12z Aviation Discussion... .KEY MESSAGES... - `Cooler` today with highs in the 80s in most central Iowa towns - Chance of weakening storms and showers into northern Iowa late this evening or after midnight tonight - Additional storm chances later this weekend, particularly Sunday afternoon and evening, and at times mid to late next week. Severe and locally heavy rainfall risk on Sunday is low at this time. - Warm conditions around 90 degrees this weekend, but closer to climatological values in the 80s for late June next week. && .UPDATE... Issued at 325 AM CDT Fri Jun 27 2025 An active afternoon and evening has become more tranquil early this morning with Nighttime Microphysics RGB from the GOES-East satellite showing convection over northern Missouri into far southeastern Iowa with patchy high cloud blow off moving northeastward over the eastern half or so of Iowa. Low stratus clouds are also filling in over northern into parts of central Iowa with some hints of fog in the surface observations and a few webcam checks. With weak cold air advection behind the surface front as shown in the 925mb chart, highs today will be kept in the 80s with upper 70s over northeastern Iowa where the stratus clouds will linger and depart later in the day. As we head into tonight, attention will be on western Nebraska and South Dakota as a weak shortwave perturbation kicks off convection out that direction. The 0z convective allowing models (CAMs) are hinting that this will near Missouri River and possibly move into western Iowa as some weakening convection later this evening or overnight. The NamNest and ARW cores show this arriving late in the evening into western Iowa while the HRRR and RRFS brings this in later and over northern Iowa. Soundings point to these being elevated storms as they arrive, but with downdraft CAPE values over 1000 J/kg per GFS and HRRR forecast soundings, there could be a few wind gusts with guidance currently pointing to these being sub- severe. Most CAMs have whatever convection dissipating by sunrise Saturday and forecast is dry by that timeframe into the day Saturday, but the RRFS does fester some convection over northern Iowa. It will become breezy as the cold front, which will have stalled just south of the state, will return as a warm front on Saturday. Winds from the south will average 10 to 20 mph with gusts of 15 to 25 mph common and highs will be back within a few degrees of 90 in most places. As the sun sets Saturday evening, we`ll be keeping an eye to the north and northwest as convection develops along a cold front. Instability will not be in short supply and mid-level lapse rates will be steep, but any appreciable deep layer shear for storm organization Saturday night/early Sunday is closer to the boundary. Thus, activity is expected to stay mostly if not fully in Minnesota that develops along the front there with this idea supported by CAMs such as the 0z RRFS and 6z HRRR. The convection that develops over South Dakota may push into northern Iowa well after midnight if not closer to after daylight Sunday. Thus, may need to further trim and fine tune initial National Blend of Models guidance that seems aggressive on rain and storm chances over northern Iowa Saturday evening and night. && .DISCUSSION... Issued at 109 PM CDT Thu Jun 26 2025 Focus is on the developing activity this afternoon into evening. Midday surface analysis has the warm front hanging out over northern Iowa near the IA/MN border, continuing to become better defined with time. The surface low is ejecting out of eastern SD/NW IA/SE MN and will track across far northern IA/southern MN with time through the afternoon and evening hours. Adjacent to the low is a cool front extending southward through eastern NE and beyond. These features will all be drivers of our showers and storms through the afternoon and evening with storms having already been bubbling into midday over portions of west central Iowa with some showers ongoing in portions of northern Iowa and mostly clear skies to the east of the bubbling storms/showers. The warm sector south and east of the two boundaries is directly over the state where temperatures have warmed into the 80s where precipitation is not ongoing, with very moist and humid conditions as dew points are near-widespread in the 70s. This has translated to instability values (MLCAPE) of 1000-2500 J/kg over the area as of midday with soundings showing robust ECAPE values as we get into later this afternoon as well. Wind shear over much of central to southern Iowa remains weaker, but over north central into far northern Iowa bulk wind shear is much better, 30-40 knots. The farther north is also where LCLs are lowest and is generally where the better tornado environment exists, but is also highly conditional with rain ongoing over that same environment as of midday. The triple point between the fronts and surface low will remain a foci for any potential more discrete storms where the tornado potential would be highest with initial storm development given the low level CAPE and stretching potential in that vicinity. The caveat is how this environment recovers given the activity ongoing around midday. Further south along the front, generally expecting more linear convection with more broken storms the farthest south you go given the very weak shear. For portions of central into northern Iowa, storms along the line may pose a damaging wind threat, though will monitor for any potential spin ups as well the further north you go where the more favorable (though conditional) tornado environment exists. Not really expecting much in the way of hail given the overall environment, but some small, to maybe isolated marginally severe hail could be possible if a more robust storm is able to develop. Overall, storms are expected to develop in western Iowa and track east to southeast with time through the area, but CAMs are not necessarily capturing current trends well so confidence is decreased in how convection plays out through the afternoon. Besides the conditional tornado threat north, and wind threat with the line, will also continue to monitor our hydro situation as the environment remains favorable for efficient rainfall, as it has the last several days. Continue to expect 1-3" with localized higher 3"+ amounts, though again midday activity may affect how the rest of the afternoon/evening progress. By late tonight, storms will have cleared the area with a surface ridge moving over on Friday. This will bring a much-needed quiet day in terms of weather back to the area. Waves moving through our otherwise upper zonal flow will bring precipitation chances back to the forecast at times later in the weekend (Saturday night into Sunday) and again at times next week. Will continue to monitor the threat for any severe weather with uncertainty remaining on where storms may track into Sunday. Otherwise, temperatures remain warm in the 80s to 90s. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 620 AM CDT Fri Jun 27 2025 IFR and MVFR ceilings are common at terminals north of I-80 this morning as low stratus settles into the state. However, this stratus will begin to move to the northeast and to scatter later this morning with VFR conditions returning by early afternoon at all official forecast sites. The timing of this was slightly delayed in this issuance to account for the latest trends in guidance. VFR conditions will prevail as winds from the northwest become light and variable late this afternoon and evening with winds becoming from the southeast by the end of the period. && .HYDROLOGY... Issued at 109 PM CDT Thu Jun 26 2025 One final round of heavy rainfall and possible flash flooding is expected today before at least a short break in precipitation on Friday. However, as water is routed through the basins and river systems, river flooding concerns will persist well into next week. A broken line of storms is expected to develop along a cold front this afternoon and move from west to east across much of the CWA into this evening. As in past days, robust moisture content, high freezing levels and ample instability will again lead to efficient rain rates. However, this line of storms should be progressive, moving eastward around 30 mph. Many of the global models and CAMs are indicating widespread 1-2" rainfall amounts, but the progressive nature of the storms should prevent rainfall amounts from getting out of hand. The 26/12Z HREF 24hr PMM valid from 12z Thu to 12z Fri shows this nicely, with only sporadic amounts over 3" indicated. Flash flooding is a concern with the rainfall this afternoon into tonight however for now we have opted to not issue a flood watch for flash flooding because we think the current flash flood guidance (FFG) across our CWA is a little too low. Historically the FFG starts having a tougher time capturing reality in our region during this time of year, due to ag crops taking off in their growth. That issue is admittedly tempered with the recent heavy rainfall, however we still think the FFG is running a little low. Although some isolated flash flooding is possible, at this time we do not believe the flash flooding will become scattered (i.e., rise to the level of needing a watch). If the storms this afternoon and evening do more training than we presently expect, though, then the flash flood risk would increase. In terms of river flooding, we have returned to 24 hrs of QPF in our river forecasts. The river forecast updates today do not have any significant changes aside from some ups and downs within the same category. The main reasons for the forecast changes are mainly QPE vs QPF changes from last night was well as shifting of the QPF locations for today. It should also be noted that for many locations where action stage is forecast, those forecast crests are near flood stage. Due to increased confidence in the river flooding occurring, we have issued river flood watches for those locations where river flooding is forecast. The larger streams of most concern presently include the Cedar, Winnebago and Raccoon Rivers. For some locations, the elevated stages and river flooding is expected to continue well into next week. Additional rainfall is in the forecast for the Sunday timeframe. This rainfall may be locally heavy and may impact area rivers. Depending on the location of the rainfall, this rainfall has the potential to result in quicker rises, slightly higher crests or slower falls after the crests. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Ansorge DISCUSSION...05 AVIATION...Ansorge HYDROLOGY...05/Zogg