Area Forecast Discussion
Issued by NWS Des Moines, IA

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354 FXUS63 KDMX 230912 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 412 AM CDT Sun Jun 23 2024 .KEY MESSAGES...
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- Dry Sunday with low chance thunderstorms west late tonight. - Heat Advisory in effect for the west Monday afternoon with severe chances ramping up later that evening. Wind and hail are the primary threats. - Additional severe weather chances Tuesday evening with similar threats. Storms will continue into the overnight hours. - Additional rain and storm chances return to the region Thursday.
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&& .DISCUSSION...
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Issued at 408 AM CDT Sun Jun 23 2024 Overnight surface analysis showed a surface high across Nebraska and a series of weak boundaries dropping southeast across Iowa. The surface high will preserve the drier air today, keeping precipitation out of the forecast for the day and making it feel less muggy outside. Highs will be in the 80s with some temperatures approaching 90 in the southwest. A shortwave will develop off of the northern High Plains and move into the upper Midwest through the day. A few thunderstorms will form on the back side of the departing high tonight as the LLJ angles in the western part of the state. CAPE values over 1500 J/kg will be available, but with weak flow. Models aren`t keen on precipitation primarily because of the questionable amount of available moisture. Soundings look relatively dry save for the midlevels. Have added in some precipitation mentions across the west and central through the night to cover the non-zero possibility of enough moisture being present. A thermal ridge will approach from the west on Monday. A front originating from the cyclone in the Dakotas will be positioned somewhere across the state. The EML will blanket at least the western half of the state by Monday afternoon with the cap inhibiting CI until the column cools in the evening. With H850 temperatures over 25C filling in the western half of the state and dew point values in the 70s, muggy conditions will resume, this time with higher confidence in warmer temperatures, driving up the heat indices. Currently expecting heat indices across far western Iowa behind the front to meet and exceed 105 degrees F. In coordination with neighboring offices, have issued a Heat Advisory Monday afternoon to cover the heat concerns for the afternoon. Adjustments possible in upcoming issuances depending on the progression of the thermal ridge. The nocturnal jet initiates an MCS somewhere in Nebraska that evening, moving into southern Iowa through the night. Some initiation is possible along the cold front later on in the night in the northeast. Better shear can be found closer to the main upper level feature near Canada with profiles across the state fairly unidirectional. Still, with ample MUCAPE available, cannot rule out severe winds and hail with storms along the front. The MCS will have DCAPE values near 1000 J/kg to work with, but will quickly become outflow dominant in an environment with weak shear. A boundary will stall somewhere across the northern part of the state Tuesday with cause for concern for more severe weather, again primarily with severe winds and hail. Soundings have an inverted-v PBL and CAPE in excess of 2000 J/kg, but again with relatively weak flow. South of the boundary, heat indices may reach the 100s once again, but will be dependent on the aftermath of the MCS. Trends for Tuesday will be monitored. High pressure behind the departing system will keep temperatures lower and conditions dry, but upcoming will be another wide open Gulf moisture plume into the Midwest region (and possibly into Iowa) late Thursday and into Friday. There is consensus among ensemble members of there being 99th percentile to climatological max values of precipitable water in the state. To give an idea for what values look like in that percentile, operational GFS has PWAT values of 2.3"+. GEFS QPF M-climate percentiles for 24 hours are in the upper 90s for Friday. Of course, details can change this far out, but given the recent heavy rain the state has experienced, it`s worth keeping an eye on trends for rain at the end of this week.
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&& .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1249 AM CDT Sun Jun 23 2024 MVFR to locally IFR stratus to affect KMCW and KALO for the next 6 to 8 hours, lifting to VFR after sunrise. Low confidence fog possible at KFOD, but have left out of TAF due to low confidence at this time. VFR conditions to prevail for much of the daytime and evening hours tomorrow. && .HYDROLOGY... Issued at 346 PM CDT Sat Jun 22 2024 Heavy rainfall in northeastern Iowa last night has led to flooding on multiple area rivers, primarily along the Des Moines River and Cedar River basins. As of right now, hydrographs are either on track or slightly less than what was expected yesterday. Those that have fallen below the forecasted rises are mainly along the Cedar/Winnebago Rivers which missed out on some of the heavier rainfall that was previously expected through that basin. This is most notable at MCWI4, which will see a significant downward trend from the previous forecasted crest of major flood stage to a now forecasted moderate flood stage. That being said, precipitation fallen in the basins and water routing down from Minnesota along the Cedar River, will still result in moderate to major flooding in areas along the Cedar River, notably at CCYI4, JANI4, and CEDI4, among other sites also seeing minor flooding on the Cedar River and it`s tributaries. Further west, river forecasts are mostly on track, with major flooding already ongoing at ESVI4 on the West Fork Des Moines River. Rises at ESVI4 have slowed some, but not expecting much improvement at this time with more water upstream still to be routed down. Forecasted crests of moderate and major flooding downstream at EMTI4 and HBTI4, respectively. HBTI4 is also forecasted to near and exceed the flood of record of 15.4ft. Flooding is also ongoing along the East Fork Des Moines River, with moderate flooding at AGNI4 and minor flooding forecasted at DAKI4. Consequently, flooding is likely along the main stem of the Des Moines River north of Des Moines as water routes downstream. This will lead to significant rises at Saylorville Lake, with an estimated lake elevation of just over 870 ft. Additional showers and thunderstorms are expected over portions of northeast Iowa this evening, which may slightly delay improvement on rivers. Those along the Cedar River basins will be most affected by any rainfall tonight, while those further west should mostly get a break. That being said, more rainfall is forecast at the beginning of next week so will continue to monitor the impacts these may have on area rivers. Make sure to stay up to date on the latest forecasts and river information, and use extreme caution in flooded areas. && .DMX WATCHES/WARNINGS/ADVISORIES...
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Heat Advisory from 1 PM to 8 PM CDT Monday for IAZ033-044-045- 057-070-071-081-082-092-093.
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&& $$ DISCUSSION...Jimenez AVIATION...Jimenez HYDROLOGY...Dodson