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Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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358 FXUS63 KDMX 021811 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 111 PM CDT Tue Jul 2 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - Threat for severe and flash flooding continues today - Break on the way for Wednesday - More spotty showers/storms from Friday through Monday. Rainfall not expected to be significant, but outdoor activities may be impacted from time to time. && .DISCUSSION... Issued at 330 AM CDT Tue Jul 2 2024 .Short Term /Today through Wednesday/... Confidence Short Term: Medium to High Everything reaching the peak from early morning through around 02z this evening; including early morning heavy rainfall and potential for some flash flooding. Then this afternoon, the continued risk of severe storms and more heavy rainfall and potentially some flash flooding, rises in rivers and areal flooding. Late evening synoptic surface map shows two pronounced areas of warm air advection tied to weak lows and two warm fronts pushing north into Iowa/Minnesota. A trough of low pressure through the eastern Dakotas will eventually pass east later today and exit the region. The northern most low over southern North Dakota has a warm front over northern Iowa/southeast Minnesota. This has been responsible for the first round of moderate to heavy rainfall that has already lifted northeast over our border counties into southeast Minnesota this morning. The southern most low is situated over southeast Nebraska with a warm front extending southeast over northeast Kansas and into southwest Missouri. This has been the overachiever early this morning with a stronger cluster of storms in southeast Nebraska. This has already dropped 3 to 5 inches of rainfall and is edging east into southwest/western Iowa. Though most of the storms have been lessening in intensity the past few hours, rainfall efficiency will likely remain high through around 12 to 15z. The current HRRR runs suggest a more southerly propagation of the cluster to our west and due to that have added Madison Co to the early day FF.A. Since the low level jet is driving much of the overnight convection, this should begin to weaken this morning with lingering efficient showers/iso storms into the late morning hours. As we move into the afternoon hours, the southern low will to track toward southern Iowa with the warm front edging into or tracking near the border. With PWATS still running 2 to 2.5 inches this afternoon and evening over the east, warm cloud depths still over 4kft and ample support from the low and low level jet, heavy rainfall will again be possible. Severe storms will also be possible over the south and we again have a similar SPC forecast for slight/enhanced risk of storms over the southeast two thirds. The greatest risk will be wind nearer the Iowa Missouri border with hail and a smaller risk of a few tornadoes. Though rainfall has not been as prolific over the southeast, east and up toward the Waterloo area in the most recent past, there is still some signal that these areas may see amounts of 2 to 3 inches today with locally higher rainfall. Have added another Flash Flood Watch over the southeast third of the area today from 20z to 03z. Most of the convection will have exited the region by 01 to 02z, but some lingering hydro issues may still be ongoing. Today will see highs in the mid to upper 70s north with lower to mid 80s in the south. Tonight the low and boundary will scour out the moisture and bring cooler air into the region. Mins will dip to the lower 60s north to the upper 60s south. Tomorrow will be pleasant as a ridge of high pressure builds in behind the system and brings milder air back to the area. Highs will be warmer with readings in the mid to upper 80s. .Long Term /Wednesday Night through Monday/... Confidence: Medium to High There is reasonable confidence moving forward. Little has changed in the forecast. By Wednesday night, another lee side trough will approach the region with showers and storms edging into southern and western Iowa toward sunrise the 4th. There is some agreement with the GFS and EC in terms of the initial morning convection diminishing toward midday, but the GFS is tending to hold onto the afternoon convection into the evening across the east slightly longer than the Euro. Depending on the timing of the later day storms, some holiday festivities Thursday evening may be delayed east of I35. Will need to wait and see. Though there are breaks from time to time from Thursday night through Monday, a shift to northwest flow will bring several waves and weak fronts southeast through the region. Brief periods of showers and some thunderstorms can be expected each day. Spotty quarter to half inch rains may occur with the passing systems and should not really add much to our current hydro situation, but the passing showers and occasional storms will likely interfere with a few outdoor plans. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 110 PM CDT Tue Jul 2 2024 Widespread hazards occur this afternoon into tonight with areas of MVFR to IFR conditions, particularly in and near convection. Surface winds from the south to southeast are expected but may approach or exceed 50kts near stronger storms. The convection is expected to depart by late evening with improving conditions late tonight into Wendesday morning with VFR categories returning. Surface winds also become west to northwest late tonight into Wednesday morning. && .HYDROLOGY... Issued at 300 AM CDT Tue Jul 2 2024 A Flood Watch is in effect for parts of central and north central Iowa to noon today which covers both the potential for flash flooding and new or renewed river flooding. We have added a second Flood Watch for both the potential of flash flooding and a possible impacts on rivers. The second watch begins at 20z and goes through 03z in the east/southeast. The current river forecasts, which includes 48 hrs of forecast precipitation, do slow the fall along the West Fork Des Moines river. Rises are forecast across most other basins including the East Fork Des Moines, Des Moines, Winnebago, Shell Rock, Cedar and Iowa River basins including a return to Minor Flood stage at Mason City, Shell Rock, Cedar Falls and Waterloo, Stratford and Des Moines at SE 6th. Heavy rain is currently drifting east northeast from near I80 in western Iowa and may set up this morning across the area between I80 and US30, west of I35. This may bring additional impacts to these areas including the Saylorville Lake storage, which is currently forecast to reach 880 ft by the Corps of Engineers. This afternoons area of heavy rainfall is expected over south central to southeast Iowa, over to around Highway 63. Note, the QPF utilized by the RFCs for these forecasts may be on the low end and shifted to far northwest which may lead to some locations forecast being underdone. Rivers/streams and soil moisture in that part of the state are in better shape and can handle heavy rainfall compared to the recently impacted north. At this time, no streams are forecast to reach flood stage. However, there will still be a threat for some localized flash flooding, urban flooding and if enough rain falls, some areal flooding later today. && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch through late tonight for IAZ017-025>028-033>039- 044>050-057>062-070>075-081>086-092>097. && $$ DISCUSSION...Donavon AVIATION...Cogil HYDROLOGY...REV