Lookout Mountain Snow Report

573 FXUS63 KDMX 290848 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 348 AM CDT Tue Sep 29 2026 .KEY MESSAGES... - Showers and thunderstorms passing from west to east through the day today, followed by a brief lull in the afternoon and early evening. - Widespread, prolonged period of rainfall expected over Iowa from tonight through Wednesday and Thursday. Rainfall amounts of 2 to 4 inches likely, with higher amounts possible in areas that see less breaks from the rain. Flooding and flash flooding will be possible. - Rainfall chances ending north and northwest on Thursday, ending in the south Friday morning. Cooler and drier conditions into the weekend. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 336 AM CDT Tue Sep 29 2026 After finally getting to see some sunshine across Iowa today, cloud cover is already increasing from the west. These clouds are foreshadowing what will be a wet couple of days for Iowa. A slow moving 500 mb trough and remnants from tropical activity in the Pacific will bring a steady surge of moisture up into Iowa today through Thursday. Visible satellite and water vapor imagery highlight this broad mid and upper level moisture plume well, stretching up from Hurricane Polo in Baja California, up through New Mexico, Colorado, Kansas, Nebraska, the Dakotas and Minnesota. Through the day today, a northern stream 500 mb shortwave will push this moisture plume eastward into Iowa, while also providing weak synoptic ascent. The result will be rain chances beginning as soon as 9 to 10 am today in western Iowa, spreading across the area throughout the day. A small amount of instability will accompany this activity, but instability values generally under 1000 J/kg, poor lapse rates, and minimal shear should keep any thunderstorm activity below severe limits. Warm cloud processes and increasing layer moisture/precipitable water values will promote efficient rainfall with activity today, and really through the entirety of the event. Storms during the day today should generally be progressive enough to mitigate flash flood concerns, barring a poorly placed downpour over an urban area. However, with rainfall generally expected to continue into the overnight hours and beyond, flooding concerns will be increasing tonight through Wednesday. While today`s initial push of rain will generally be associated with the passing northern shortwave, the pattern quickly transitions to a broad theta-e advection/overrunning setup as Hurricane Polo lifts northward into the plains tonight and parks itself over Kansas on Wednesday. The coincident moisture from the hurricane remnants will overrun a cooler air mass over Iowa, keeping persistent rainfall over Iowa through Wednesday. The combination of anomalously high PWATs for this time of year (2"+), storm motions roughly parallel to the boundary, warm cloud processes, and persistent lift will result in a prolonged, widespread moderate to heavy rainfall over Iowa tonight through Wednesday night and potentially Thursday. It appears likely we will see one or multiple areas of 2 to 4 inch rainfall amounts falling from tonight through Wednesday night. Embedded within this band, locally higher amounts closer to 5 inches will be possible, especially in areas where convective processes drive up rain rates, or where breaks in the rain are minimal. That said, exactly where the axis of heaviest rainfall will occur is still somewhat up for debate as models continue to waver on QPF placement. On previous shifts, the heaviest band looked to setup from western into north central Iowa. On this shift, the QPF band has seemed to shift southward slightly, albeit not completely removed from northern Iowa. More on that in a second. Recent deterministic guidance, namely the GFS, ECMWF, and RRFS, are showing the highest QPF footprint roughly from southwest into central Iowa. This southerly trend is being picked up by the NBM as well, with the highest probabilities for exceeding 4" of rainfall (~40 to 50%) now from the southwest corner of Iowa up through Atlantic and Creston to roughly Ames and Des Moines. However, while the heaviest band is trending southward, the AI GFS and GFS output still show a second band along that Fort Dodge to Mason City line in north central Iowa. This band is in addition to the southern band, resulting from a northward push of the rainfall overnight Wednesday, before rain/storm activity is shunted back south and east again. That all to say, there is considerable uncertainty with the evolution of the rainfall and where the heaviest rain will fall. What is certain is that prolonged, widespread rainfall will be ongoing from tonight through Wednesday, and will likely lead to flooding and flash flooding concerns as water is added to the system. The Flood Watch remains in effect from this evening through Thursday evening, although have expanded it southeastward to account for the southeastward trend in the QPF. For more on flood concerns, see the hydro discussion below. Instability through Wednesday remains fairly low (under 1000 J/kg), which should help to negate severe weather concerns. However, will be watching how the pattern evolves Wednesday, as some better instability will be in place to our south and west in the warm sector of the low. It seems unlikely this will get too far up into Iowa, but a few stronger storms could certainly scrape southern Iowa if this pushes farther north Wednesday evening. At this time, the storm prediction center just has general thunder over the area, which is valid given the environment in our current guidance. && .LONG TERM /THURSDAY THROUGH MONDAY/... Issued at 336 AM CDT Tue Sep 29 2026 Moving into Thursday and Friday, the longwave trough deamplifies and largely shears out as an approaching northern stream wave aids in pushing this system away from the area. For sensible weather, this will mean the rain ending from early Thursday or perhaps as soon as Wednesday night over northwestern Iowa and our northwest forecast area. This drying trend moves slowly southeastward ending the rain in our southeastern forecast area by Friday morning.The approaching northern stream wave will move through Saturday and will bring a return of some clouds and atmospheric moisture return, but showers seem more limited and would certainly be progressive. Behind this system, northwesterly flow looks to take over and with a zone of high pressure moving in, this may spell a change as we continue into October with some drier conditions. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1145 PM CDT Mon Sep 28 2026 Impacts begin after 15z with the arrival of showers and perhaps a few thunderstorms into central Iowa. Exact timing is still unknown, though a long period of showers is highly certain, especially after 18z. Current trends indicate higher chances of showers at KDSM/KALO after 18z, and will be monitored for an addition of prevailing showers. Precip may decrease for a time into the evening and CIGs will likely lower at that time. Falls to LIFR CIGs, with fog potentially building in as well, appear to be possible but onset may be beyond 06z. && .HYDROLOGY... Issued at 336 AM CDT Tue Sep 29 2026 Primed antecedent conditions for water issues in parts of the state this week. September 2026 has thus far been the second wettest September on record for Des Moines, and this has led to saturated soils in central and southern Iowa. Both the 10 and 40cm soil moisture percentiles are high: over 80% from about Highway 20 and south, per NASA SPoRT. This means that less infiltration will occur with the heavy rain expected this week. Crops at this point in the year have dried and no longer add an absorption buffer in rural areas. Flash flood guidance is thus closer to accurate representation, sitting around 2 inches for 3 hour guidance and 2.5 to 3" for 6 hour. Looking at rivers, flows are well above normal in basins in central and southern Iowa: the Raccoon, North, Middle, South, Nodaway, and Thompson Rivers. These rivers are above the 95th percentile for the 14 day average streamflow anomalies. The Des Moines River south of Des Moines is much above normal (91-95th percentile) due to contribution from some of these listed basins. Further to the northeast, the Skunk, Ioway and Cedar basins are above normal with these rivers exceeding the 90th percentile as they route into eastern Iowa. Conversely, normal to even below normal flow can be found in northwest Iowa due to below-normal precipitation in this region. A concerning trend noted in the discussion above is the southern drift in the highest precipitation axis the next 2 nights as well as an added round of precipitation developing Thursday night. The precipitation now is progged to fall in central and southern Iowa; the most hydrologically vulnerable part of the area. This event is synoptic-driven with less thunderstorm activity, thus less mesoscale influence. This means that hydro issues will be less rate driven and more duration driven, and the QPF footprint is wide. Widespread rainfall amounts over 2 inches will be common for both Tuesday and Wednesday night, respectively. Flash flooding potential on night one will be more of a concern in urban areas, but rural areas will come into play once comparable, if not heavier, rain falls during round 2. HEFS guidance based on the 00z suite was not yet available at the time of this discussion, but would expect higher probabilities of minor flood stage on the North, Middle, South, and Thompson rivers. It should be noted that the HEFS 50th percentile trace was already above Minor Flood stage for the North and Middle Rivers. The medium range National Water Model supports this. The Raccoon Basin will now be primarily impacted past the confluence of its 3 stems on night 1, but more of the basin will be in play for night 2. By the time all this water routes into the main Raccoon, confidence is increasing for river levels above Minor Flood thresholds. The Medium Range NWM also supports this. The Skunk, Iowa and Cedar basins will be more in play with night 2 as the precipitation band axis centers more across central Iowa. Minor Flood Stage stage is simulated in HEFS and the NWM with Skunk River points reaching Moderate in some simulations. Not to be left out are the smaller, flashier basins around Ames and Des Moines (Walnut, Fourmile, Ioway). Their smaller footprint increases the odds of the broad QPF yielding a high QPF average of their basins. 6 hour headwater guidance is between 2 and 3 inches. Given the southern drift of round 1, the Walnut basin may see the most rain Tuesday night, but confidence is increasing that it will be below headwater guidance. That being said, any rainfall will lower headwater guidance ahead of round 2. All mentioned small basins are in play for Wednesday night, especially given local amounts over 3 inches are more likely that night. && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch from this evening through late Thursday night for IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>074- 081>083-092>094. && $$ SHORT TERM...Dodson LONG TERM...Ansorge AVIATION...De Bruin HYDROLOGY...Jimenez