textproduct: Des Moines

KEY MESSAGES

- Slight Risk for severe storms expended more to the west today. All modes of severe weather possible, with a locally higher tornado threat along the I-80 corridor.

- Enhanced Risk expanded for Friday, covering much of the eastern half of the state.

- Much cooler over the weekend with a hard freeze likely in northern Iowa Saturday night.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 130 PM CDT Wed Apr 15 2026

A nearly stationary frontal zone is draped across Iowa this afternoon, with the surface boundary stretching from around Glenwood to Des Moines to Elkader. South of the boundary, winds are gusty from the south southwest and temperatures are soaring into the 70s. North of the boundary, winds are light and variable and temperatures are holding in the upper 50s to 60s. A cluster of severe thunderstorms developed this morning in eastern Nebraska and has tracked east northeastward into our area, affecting areas between Highway 20 and Highway 30 and west of I-35 so far. However, farther south near the surface boundary the atmosphere remains undisturbed and very unstable, with strong deep layer shear moving overhead. As a mid-level trough approaches from the west this afternoon, it will generate additional storms along and south of the surface front that will carry an attendant threat for large hail, strong winds, and perhaps a few tornadoes. The storms will eventually clear our area to the east this evening, though a few weaker showers or storms may bubble up behind it as the mid-level trough moves overhead.

Later tonight through Thursday night, a 500 MB ridge will build across the region and provide a brief respite of quiet weather. Thursday will be mild and dry, with winds coming around to south and picking up later in the day. The strongest winds will be in our northwestern counties, farther from the departing ridge to the east, with speeds of 15 to 20 MPH and higher gusts up around Estherville and Storm Lake on Thursday afternoon. As temperatures warm to near 80 degrees in that area, RH will plummet to near or just below 30 percent, combining with the gusty winds to result in an elevated fire weather risk, mainly north of I-80 and west of I-35. On Thursday night relative humidity will characteristically increase after sunset, however winds will remain brisk through the night and support unseasonably warm low temperatures by Friday morning.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 105 PM CDT Wed Apr 15 2026

By Friday morning a deep longitudinal 500 MB trough will be crossing the U.S. Rockies, emerging over the High Plains late in the day. A surface low pressure trough will develop ahead of this system, stretching from around the Texas Panhandle northeastward across Kansas, Iowa, and toward Lake Superior by the middle of the day. A sharp baroclinic zone will develop along this trough, with gusty south breezes ahead of it and stronger north northwest winds behind it providing enhanced low-level convergence beneath a broad region of dynamic lift on the leading flank of the approaching 500 MB trough. Initially a low-level inversion will inhibit convective initiation, but by the afternoon near-surface warming and mixing will erode the cap and numerous thunderstorms will develop all along the frontal zone. SBCAPE of 3000-3500 J/KG and 0-6 KM Bulk Shear of 35-45 KT will support strong updrafts and a severe weather threat across a large area, particularly given the magnitude of forcing for ascent. Forecast soundings indicate a deep unstable layer and strong winds aloft (around 50 KT at 700 MB), but generally straight hodographs with little directional shear in the effective layer. Any surface-based storms will be able to tap into modest directional shear in the lowest levels, but the tornado threat remains uncertain due to a relative lack of backed surface winds - certainly any storms moving to the right of mean motion would carry an enhanced tornado threat. In any event, given the strength of the wind fields, linear nature of the convection along the frontal zone, and magnitude of instability in the hail growth zone, damaging wind gusts and large hail appear to be the primary threat at this time. If the storms are able to form an organized QLCS, then the tornado threat may increase accordingly. Overall, any areas of Iowa that are along or east of the front when convection initiates will see a significant threat of severe weather on Friday afternoon and evening. There is still some uncertainty in exactly where the front will lie when storms develop, but the eastern/southeastern half of Iowa appears most likely to be under this threat.

The cold front will sweep through on Friday night, ushering in considerably cooler weather for the upcoming weekend. High temperatures on Saturday will be about 25-30 degrees lower than on Friday, ranging in the mid-40s to lower 50s across our forecast area. Meanwhile, Friday night/Saturday morning lows will fall below freezing in our northern and western counties, though strong post- frontal winds should prevent any frost formation at that time. By Saturday night/Sunday morning a surface high pressure area will be building into Iowa from the northwest, sending temperatures lower and also diminishing winds. Lows will likely range in the mid/upper 20s north to lower 30s southeast, resulting in a hard freeze in some areas and potential frost across much of our service area, depending on wind speed and cloud cover. A large-scale broad ridging pattern will then set up from later Sunday into the first half of next week, supporting a few days of quieter weather with a gradual warming trend. There are some signs that a more active pattern may return from around the middle of next week onward, but that will be determined in the coming days.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1229 PM CDT Wed Apr 15 2026

Scattered thunderstorms will move through the area this afternoon and evening, resulting in sporadic periods of MVFR or lower conditions. Have targeted TEMPO/PROB30 groups around most likely time windows of impact, but amendments will be likely based on radar and observational trends. Once the storms clear to the east this evening, VFR conditions will prevail through the remainder of the TAF period, but at MCW/ALO there is potential for a period of low stratus and BR in the early morning hours Thursday.

HYDROLOGY

Issued at 119 PM CDT Tue Apr 14 2026

Multiple rounds of seasonally moderate to heavy rain this week will lead to renewed flooding concerns. Concerns will include possible renewed or additional river flooding as well as flash flooding.

Output from the GFS- and NBM-forced medium-range National Water Model (NWM) and the Hydrologic Ensemble Forecast System (HEFS) suggest the most likely scenario will be moderate to significant within-bank rises on many rivers and streams across the CWA over the next week, especially across the southeast half. Some locations may see minor river flooding as well. These rises will be due to the additive effect of multiple rounds of rainfall. If rainfall is higher than presently forecast then the risk of several locations seeing minor flooding and a few locations seeing moderate flooding will increase.

Flash flooding is less of a concern than river flooding, however the risk is nonzero. The additive effect of rain events will result in a slightly higher risk of flash flooding from Friday into Saturday. The most likely scenario through the end of this week will be ponding of water or low-end flash flooding especially in urban areas or areas that receive repeated heavy rainfall over a relatively short time period.

DMX WATCHES/WARNINGS/ADVISORIES

None.