150 FXUS63 KDMX 131721 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1221 PM CDT Fri Jun 13 2025 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Drier period Friday into Saturday with chances no higher than 30% over eastern or northern Iowa. - Active period of weather starting later Sunday into next week. While lacking specifics (timing, location, hazards) due to low predictability, strong to severe storms and locally heavy rainfall will be possible at times over the region. - Staying warm and humid through the period. && .UPDATE... Issued at 251 AM CDT Fri Jun 13 2025 Primary weather concerns today and Saturday will be anchored on the warm front that will waver along and north of the Iowa/Minnesota border. This afternoon that boundary is expected to be pushed north of the area when diurnal heating destabilizes things enough for convective development, though a few thunderstorms may skim far northern Iowa. These storms should remain sub-severe with modest instability and little shear to help organize storms. Saturday will be a near repeat with storms developing along the boundary with diurnal heating. The boundary will need to be watched closely for where this sets up, but the northern couple rows of Iowa counties are expected to see a few scattered storms. Instability is marginally increase on Saturday but overall severe chances remain low. A shortwave brings a more organized chance for showers and storms to northwest Iowa on Sunday. This will kick off what is shaping up to be an active week across Iowa. After what has been a quiet start to the warm season locally, now is a good time to dust off those severe weather preparedness skills. Several robust shortwaves will move across the area, riding the northern warm front, as is often the case with this set up. Right now waves look to be times as Monday into the Monday overnight, Tuesday into the Tuesday overnight and Wednesday, and a final quick moving wave on Friday. Monday and especially Tuesday into Wednesday are the most robust waves at this time and will likely bring severe weather to the state. With this several days out there are a number of details that are uncertain. What is known is that severe storms and heavy rain look likely through this window. Multiple rounds of heavy rain could present hydrologic concerns if they set up over similar locations on consecutive nights. This forecast will be fine tuned with additional details supplied as more data comes available in the coming days. && .DISCUSSION... Issued at 208 PM CDT Thu Jun 12 2025 Iowa resides between two areas of forcing early this afternoon with a shortwave trough passing north of the state and a broad, closed low moving ever so slowly near the Ozarks. The passing north shortwave trough is also located closer to the surface warm front, which is currently from near Estherville to south of Waterloo, though the effective warm front is a bit north of that. There is some speed and directional shear over northern Iowa in the forecast soundings that results in marginal at best amounts of deep and effective shear. Forecast soundings also show a bit more surface based instability (SBCAPE) to around 1500 J/kg per latest SPC mesoanalysis. This may allow for a few stronger storms around severe limits to develop mid-afternoon around the Iowa-Minnesota border that may scrape the far northern part of our forecast area. The severe wind gust signal that was seen yesterday in the convective allowing models (CAMs) is not present today so the marginal risk from the Storm Prediction Center seems quite reasonable. Any activity is expected to dissipate by mid-evening. Farther south over central and southern Iowa, the flow below 500mb is quite weak with speeds generally around or less than 10 knots resulting in little if any deep or effective shear. CAPE profiles are skinny, but yield around 500 to 1000 J/kg of instability with steep low level lapse rates. As was the case yesterday, soundings show plenty of dry air in the mid-levels as well as sub-cloud resulting in downdraft CAPE values between 800 and 900 J/kg. As temperatures rise to near the convective temperature in the next hour or two, isolated storms are expected to develop. Storms may grow somewhat quickly due to the low level lapse rates, but will be unable to organize with the weak shear and be of an airmass variety. Thus, any hail will be small, sub-severe with dry air entraining into the downdraft resulting in gusty, sub-severe winds of around 30 to 35 knots per CAMs. This activity should diminish after sunset in the early evening hours. Mid-level ridging will build into Iowa Friday into this weekend as the shortwave trough moves east and the closed low over the Ozarks continues its slow trudge into the Ohio Valley. At the surface, a front will pass and stall south of the state. This should provide a period of drier conditions Friday into the day Saturday with chances for showers and storms at no more than 30% and mainly over eastern or northern Iowa. The ridge begins to retreat late this weekend into early next week with initially northwesterly flow that becomes more flattened allowing shortwaves to overtop it. This will allow the stalled boundary south of the state to return northward and place Iowa back into the warm sector early next week. While lacking specifics on hazard types (e.g. hail, wind, tornado, flash flood), timing, and location, it does look like there will be appreciable instability and shear plus favorable efficient rainfall parameters for strong to severe storms and at least locally heavy rainfall somewhere over the region at times from later Sunday into a good chunk of next week. The severe potential continues to be supported by various machine learning/artificial intelligence (ML/AI) probabilities with the higher probabilities around Tuesday and Wednesday. While not as high, the machine learning probabilities for excessive rainfall also point to some risk over the region with WPC`s days 4 and 5 excessive rainfall outlooks covering some portion of Iowa. Beyond the storm chances, it will be a mid- June week with highs well into the 80s and dewpoints in the 60s. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1221 PM CDT Fri Jun 13 2025 Cumulus clouds have developed over central Iowa early this afternoon and any MVFR ceilings should rise into lower end VFR in the next few hours. The next concern will be ceiling and patchy visibility restrictions moving in from the east around and after midnight. Primarily MVFR ceilings are expected at the terminals, though IFR ceilings are looking increasingly likely at OTM. Patchy fog is forecast to move in toward sunrise for a few hours with the highest confidence at OTM, but could briefly affect DSM. This will be something to monitor in future cycles. Conditions will return to VFR by the end of the period. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hagenhoff DISCUSSION...Ansorge AVIATION...Ansorge