FXUS63 KDMX 210503 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1203 AM CDT Sun Jun 21 2026 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Widespread showers and thunderstorms (60-100% chance) develop tonight and continue into Sunday. The primary threat is heavy rainfall and possible flooding, mainly across the southern half of Iowa. There is also a very low risk of severe weather across far southern Iowa tonight and Sunday. - Slightly below average temperatures are forecast for most of next week with highs in the 70s to lower 80s. - There will be several chances for showers/thunderstorms, but the overall severe and heavy rainfall risk is low. && .SHORT TERM /THROUGH MONDAY/... Issued at 128 PM CDT Sat Jun 20 2026 Heavy rainfall and possible flooding is the primary concern this period. Tonight into Sunday will be a cool, wet period. Current upper air analysis depicted northwest flow over the Corn Belt, with an upper shortwave moving across the Intermountain West. At the sfc, weak high pressure was centered over IA and was slowly retreating ewd as sfc low pressure deepens over over CO/NE. Persistent elevated convection has been ongoing for much of the day across central NE, invof the plume of deeper moisture at 925/850mb. The remainder of the afternoon and into the evening hours will remain dry as the sfc high is slow to budge. Highs have been pleasant in the 70s. We will see increasing high clouds /cirrus blowoff/ from the west, but the deeper moisture will not begin to arrive until the inception of the 30-50kt LLJ after 03-06Z tonight. The first question is how the evening convection over Nebraska evolves. Current CAM suite is now in decent agreement showing the convective activity diving sewd from north-central NE towards the Missouri River valley between 22Z and 03Z. Current indications suggest this will stay well west of the DMX CWA, following the MUCAPE gradient. The more significant surge of low to mid level moisture/theta-E wont arrive in our area until after 06Z until the plume of +12C 850mb dewpoints and higher PWATs from 1-5-2.0" overspreading at least the southern half of Iowa. Model soundings show several factors favorable for heavy rainfall including deep saturation, strong moisture advection, and high freezing levels from 10-12k feet. The one limiting factor is instability. Due to poor mid-level lapse rates, MUCAPE values are generally below 250 J/kg, with models struggling to show even the typical tall, skinny CAPE profile usually associated with heavy rainfall. Thus, it appears more likely we'll see a prolonged period of moderate rainfall and thus lower rainfall rates, due to the limited convective elements. Comparing the latest QPF solutions, the global ensembles/NBM continue to indicate a 40-80% chance of exceeding 2" of rainfall from I-80 and southward and about 5-10% of exceeding 5". The CAMS and HREF continue to highlight that same region of southern Iowa, with the HREF mean indicating about 1.5 to 3.0" of rainfall, with the LPMM guidance higher, showing a few pockets of 2.0" to 4.0". Individual CAMS like the 3km NAM further indicate the possible ceiling of this event, showing a few basins picking up 6 or 7" of rainfall. Based on heavy rainfall climatology, these really robust QPF values would be favored much further south, nearer to the greater instability axis. The one parameter that did stand out today is the Extreme Forecast Index, which ramped up and continued to highlight the area along the IA/MO border. No change to Flash Flood guidance, although we did have another day of drying. So, where does all this leave us? The current expectation is a fairly widespread area of 1-2 inches, locally 3" of rainfall from I-80 south, including the Des Moines metro area. Amounts will taper as you go north, down to less an 0.5" near the MN border. If things come together, there is a higher ceiling of QPF (2" to 4"+), especially near the MO border. For this reason, we have coordinated the issuance of a Flood Watch for the far southern tier of Iowa counties, and also included Monroe and Wapello counties, where they saw the most rainfall from the events last week. For a further description of river flooding, see the Hydro section below. Finally, in term of severe weather, the risk continues to diminish, primarily due to a lack of instability (as noted above). If anything, perhaps we could see an isolated water loaded downburst. The majority of the precip will depart by late in the day Sunday, although a few light showers could linger early into the overnight. Lows will be cool in the 50s, and with all the moisture, will need to watch for fog development. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Issued at 128 PM CDT Sat Jun 20 2026 After the precipitation event ends Sunday night, the synoptic pattern next week will feature a predominately northwest upper flow regime, due to ridging out west, and a mean trough over the far northern CONUS. The latest 12Z model guidance indicates that several shortwaves will propagate through the mean flow, but as per usual, the timing and amplitudes of individual shortwaves is more uncertain attm. There is reasonable confidence that Tuesday night and early Wednesday, and Friday have the highest potential for more organized precipitation. Due to the NW flow regime, limited low level moisture return is expected, thus instability profiles appear mostly meager. As such the threat for severe weather next week appears low attm. However, it is June, and with stronger wind profiles and colder temperatures aloft, we'll need to watch for any sneaky severe threats. Finally temperatures next week look to stay below late June averages, with highs generally in the mid-upper 70s, maybe a few 80 by late week, we'll take that all things considered. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1203 AM CDT Sun Jun 21 2026 Showers will move through the area later tonight into Sunday, with TSRA possible at times mainly at DSM/OTM. Low ceilings will also spread in with the rain, again primarily at DSM/OTM where a period of IFR is likely Sunday morning. Have indicated these trends in the 06Z TAFs, but amendments are likely overnight and Sunday based on short-term radar and observational trends. && .HYDROLOGY... Issued at 128 PM CDT Sat Jun 20 2026 See the main portion of the discussion for the meteorology of the event. Flash flood guidance remains mostly unchanged with 6 hr FFG guidance generally 2.5" to 4". In terms of river flooding, little change in thinking. The latest guidance from the National Water Model, HEFS, and contingency forecasts, still suggest that the forecast NWS QPF (or most likely amounts of generally 1.5" to 3.0") would lead to within bank rises on several rivers, mainly across central and southern Iowa. However, river flooding could become an issue, but only if rainfall amounts on the higher end of the current guidance occur. This would generally require widespread QPF amounts in the 4" to 5" range (e.g. highest 10% of QPF members). This would likely cause several rivers to hit minor flooding, with moderate or greater flooding also a possibility. This would be most likely across southern Iowa, perhaps extending nwd into central Iowa if the higher QPF shifts nwd (unlikely at this time). && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch from 4 AM CDT early this morning through this evening for IAZ085-086-092>097. && $$ SHORT TERM...Fowle LONG TERM...Fowle AVIATION...Lee HYDROLOGY...Fowle