Area Forecast Discussion

KEY MESSAGES

- An increasingly synoptic supported heavy rain set up continues to evolve today, just hours following this dissipation of last night's heavy rain MCS.

- Heavy rains will again break out tonight, especially along and north of I-80 and near and south of Highway 20. This area is already saturated, and is broadly included in a Flood Watch until 7 AM Sunday.

- The Marginal risk for isolated severe storms was added back to the area by SPC, but this risk remains conditional and low in our area.

SHORT TERM /THROUGH TONIGHT/

Issued at 105 PM CDT Sat Sep 19 2026

The overnight MCS impacted nearly all locations along and north of I- 80 early today, resulting in widespread 1 to 4 inch rains, that were highest in our Highway 20 corridor. Since 10 AM, the intensity has decreased, along with coverage of heavy rains. In the mean time, clouds and scattered showers continue to move east over the area, as warm advection continues to force showers in a high PWAT atmosphere. Our freezing level on our 18Z sounding (just launched) is 13,900 ft! For September, that is remarkably high, and shows how anomalous this atmosphere is. SPC mesoscale analysis continues to show moisture transport aimed into Iowa and Illinois, with strong heating ongoing to our southwest in Missouri and Kansas. Thus, there will be ample MUCAPE and moisture to support another round of storms over our area.

Models are in good agreement showing a short wave over Kansas (seen on WV this morning), moving up over our region tonight. This will trigger storms to form, especially where the warm front to our west meet the outflow boundary. That point at 1230 PM this afternoon is located just southwest of Des Moines. Unfortunately, the trajectory of storms that form near that point will spread over the CWA, and much like last night, training storms are expected. Our ongoing forecast already had a good handle on that, though with WPC expanding the Moderate (Level 3 out of 4) westward along I-80 to our western counties I have expanded the Flood Watch into that area.

Tonight's storms could be capable of a brief window of strong to severe wind gusts, if the atmosphere over eastern Iowa can see some PM heating. That remains questionable with clouds and rain showers continuing to move over the area. In any case, by the time a multicell line is formed, an west to east band of thunderstorms with torrential rainfall of 1-2 per hour expected. Thus, much like last night, a broad axis of 1-3 inches is expected, with a maximum of 3- 5" possible within it. There is some threat that this could overlay last night's heavy axis in the north, and if so, higher level impacts would be expected. This morning, creeks along Highway 20 were reported to be high to just out of their banks, per EMA reports. Dubuque county did see some creek flooding along Catfish Creek and the Little Maquoketa River. Tonight, we may see some Flash flood warning containing "Considerable" wording, vs baseline warnings, as this situation is just hours removed from the rain this morning. Urban areas, including Cedar Rapids, Iowa City, Muscatine, and Quad Cities are included for metro areas for urban flooding potential.

LONG TERM /SUNDAY THROUGH FRIDAY/

Issued at 105 PM CDT Sat Sep 19 2026

Sunday...A cooler cloudy and post-frontal day with ongoing lift up and over the LLVL baroclinicity which should be settling off to the south of the DVN CWA. Increasing north to northeasterly boundary layer(BL) winds with some spotty rain will make for not a very nice day with a lot of the area held down in the 60s to low 70s. With the upper wave still moving acrs the area, suppose some isolated thunderstorms possible as well as nuisance funnels.

Monday through Friday...Quick look at the longer range suggests that the large upper low/wave currently centered over southern ID will roll eastward acrs the northern plains and toward the upper MS RVR Valley through Tuesday. This may keep cloudy, cooler weather going acrs the area as well as sctrd showers for the early next week period. As this upper wave fills and pulls off to the east, there may be a mid week precip lull until medium range ensemble indicated next passing trof brings the next precip chances by Thu night or next Friday. Cooler temp regime still looks to last much of the week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1207 PM CDT Sat Sep 19 2026

Widespread light to moderate rain showers continue over the entire area as of Noon today, leading to wet variable conditions throughout eastern Iowa and Illinois. We are all sitting just northeast of a sharp warm front in northern Missouri, where a hot sunny day is taking place, vs our rain filled and IFR ceiling plagued atmosphere to the north. The rest of the afternoon will see southeast winds at 10 to 15 mph gradually decrease in strength to around 5 mph this afternoon. The scattered showers are expected to decrease in coverage this afternoon, with mainly VFR weather for the mid afternoon to early evening hours, before another round of widespread thunderstorms develops near the I-80 to Highway 20 corridors this evening and continues overnight in a transition to widespread rains, much like last night and the night before. A cold front will slowly make its way south, leading to north winds by mid evening tonight, and with that and the rain, another prolonged period of IFR cigs are expected tonight lasting through Sunday morning, with occasional rain showers.

HYDROLOGY

Issued at 1040 AM CDT Sat Sep 19 2026

This mornings MCS brought widespread moderate to heavy rain to portions of the area mainly along and north of the Interstate 80 corridor counties. Rainfall amounts in this area were 2 to 4 inches with the heaviest rains falling along and east of of a Manchester to Maquoketa line. This has caused many area creeks to rise this morning and additional rainfall today and tonight increases the threat for flash flooding to occur especially in areas that saw the heaviest rainfall the last 3 days. A Flood Watch for flash flooding potential remains in effect for portions of eastern Iowa and northwest Illinois until 7 AM Sunday.

Widespread heavy rains are leading to rises on area rivers. The heaviest rains the last 3 days have fallen in the Maquoketa, Wapsipinicon, Rock, Pecatonica, English and Cedar River basins. This is leading to forecast rises above flood stage at many locations over the next several days. River flood watches have been issued at many locations on these rivers. Certainty will increase on potential flooding by tomorrow morning after the next round of storms moves across the area tonight into Sunday morning.

DVN WATCHES / WARNINGS / ADVISORIES

IA...Flood Watch through Sunday morning for IAZ040>042-051>054- 063>068-077-078. IL...Flood Watch through Sunday morning for ILZ001-002-007-009-015- 024. MO...None.