Your favorites:

Coon Rapids, Iowa Weather Forecast Discussion

351
FXUS63 KDMX 212347
AFDDMX

Area Forecast Discussion National Weather Service Des Moines IA 647 PM CDT Sun Sep 21 2025

...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Chance of thunderstorms north late this afternoon into tonight, but better chances across southern Minnesota. Marginal Risk of severe weather, with large hail the primary threat.

- Some fog redevelopment early Monday morning, but dense fog less likely than this morning.

- Another round of thunderstorms around Monday evening into Monday night, initiating in western-to-northern Iowa then moving southward into southwestern-to-central Iowa. There is again a risk of severe weather, with damaging winds and large hail the primary threats.

&&

.DISCUSSION... Issued at 200 PM CDT Sun Sep 21 2025

A weak surface ridge is sliding across Iowa today, providing a brief spell of quiet weather. Conditions were conducive for the formation of fairly widespread stratus and dense fog early this morning, but these have largely dissipated as insolation has increased and skies are now partly to mostly sunny across the service area. This will not hold for long, however, as thunderstorms return to the forecast as early as this evening. A 500 MB low remains centered over the northern half of Minnesota with one more shortwave trough rounding its southwestern periphery later today and tonight. Meanwhile, at the surface a broad low pressure trough has developed along the lee of the Rockies with a stationary boundary gradually developing from near the Nebraska panhandle northeastward into western Minnesota, effectively providing the northwestern terminus of the aforementioned weak surface high over Iowa. Around this evening, upper-level forcing for ascent from the approaching shortwave will overlie the surface boundary just after peak heating, allowing for destabilization to be utilized for convective initiation. This will occur northwest of our forecast area, likely over southwestern Minnesota or far eastern South Dakota, with any storms sinking east southeast with the shortwave and boundary tonight. Modest instability (CAPEs near 1000 J/kg), 0-6 KM Bulk Shear of 25-35 KT, and fairly steep mid-level lapse rates will support a Marginal Risk of large hail around the SD/MN/IA tri-state region, possibly bleeding into our northwestern counties as outlined by SPC. However, with a steady northward trend in convective area forecasts today, will cap POPs in our area at around 50% and confined to our northern sections. There is also an area of light rain showers over northeastern Kansas that will translate east northeastward this afternoon into tonight and have maintained 20-30% POPs in our southern counties to account for this, but instability is much lower there and thunderstorms will be sparse or non-existent with no impacts anticipated.

Some fog and stratus redevelopment is possible tonight as Iowa remains within a moist airmass characterized by dewpoints in the upper 50s to lower 60s. Winds will once again be light, but slightly more organized with the weak surface high departing. It remains to be seen how much any storms/convective outflow will be able to penetrate into our area as well. Will advertise a couple hours of patchy fog in the official forecast, but overall conditions are not as favorable as this morning and the probability of dense fog is lower overall.

During the day on Monday, modest low-level warm air advection will translate into somewhat higher temperatures, peaking around 80 degrees. Destabilization will be more significant, with CAPE of 2000-2500 J/kg predicted by Monday afternoon and evening when thunderstorms are likely to initiate along the surface boundary, which by then should reside somewhere from western into north central Iowa. While deep-layer shear will be a bit weaker on Monday evening, perhaps only around 20 KT in the 0-6 KM layer, the strong instability will still support a risk of large hail and damaging winds. The lack of storm organization or a balanced cold pool could result in storms congealing into less severe clusters thereafter, as they head southward into central and southwestern Iowa. However, there is certainly support for another severe weather risk as outlined by SPC in their Day 2 Outlook.

By Tuesday another 500 MB low will be sinking over Colorado, and subsequently slide eastward across Kansas and Missouri on Wednesday and Thursday. It will then interact with the previous 500 MB low, the one over Minnesota today, which will by then be weaker and stationary/retrograding over the Great Lakes region. Long-range models differ in their solutions for this evolution, but overall we can expect continuing rain chances Tuesday/Wednesday, mainly over southern Iowa as the second upper low slides by to our south. Thereafter things may trend drier, but it depends on the interaction between the upper lows occurring nearby. Confidence in such details decreases with time in this scenario, but in any event, given the nature and location of the systems the overall threat of severe weather appears low from Tuesday onward.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 634 PM CDT Sun Sep 21 2025

Not a ton of change in thinking from 18z TAFs, with main aviation concerns being a low probability (30% or less) for a shower or isolated storms tonight, mainly near KFOD and KMCW. Given low confidence, still keeping mention out of TAFs at this time. The remainder of the area should remain dry overnight, turning the concern to more fog and stratus potential into Monday morning. Fog and low stratus looks most likely at KDSM, KALO, and KOTM, although KMCW and KFOD may see restrictions as well. Visibilities down to a mile or less are possible, but will be less widespread than Sunday morning. Stratus could develop below 1000kft, leading to a period of IFR conditions. Fog should begin to dissipate shortly after sunrise, but the MVFR to IFR ceilings may linger through the morning hours. Regardless, improvement to VFR is expected by mid-day.

Later Monday afternoon and into the evening there will be more chances for showers and storms, mainly north and west. That said, this mostly occurs at the end of this TAF period and after, so have held off on any mention in the 00z TAFs.

&&

.DMX WATCHES/WARNINGS/ADVISORIES... None.

&&

$$

DISCUSSION...Lee AVIATION...Dodson

NWS DMX Office Area Forecast Discussion

WeatherForYou.com, LLC is not responsible for any damages or problems caused by this service. Current weather conditions are obtained from the closest government operated station, a personal station contributing to the PWSweather.com network or from the Meteorological Assimilation Data Ingest System (MADIS). Some weather information is powered by XWeather. WeatherForYou.com, NOAA, AerisWeather and their data providers disclaim liability of any kind whatsoever, including, without limitation, liability for quality, performance, merchantability and fitness for a particular purpose arising out of the use or inability to use the data. Like all things, this site belongs to Jesus Christ ... He just trusts us to maintain it. If you have any questions or comments please use the suggestion box.

Copyright © 1999 - 2025, WeatherForYou.com LLC. All rights reserved.