Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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572 FXUS63 KDMX 010500 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1200 AM CDT Mon Jul 1 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - A few showers and storms possible Monday. The threat for severe weather is low. - Storms expected Monday night with a strip of heavy rain possible over parts of northern Iowa. - Strong to severe storms possible over central and southern Iowa Tuesday. Locally heavy rain may occur. && .DISCUSSION... Issued at 241 PM CDT Sun Jun 30 2024 A large area of surface high pressure is encompassing much of the Upper Midwest today. Cool temperatures, low humidity and mostly sunny skies are common under this system this afternoon. A broad region with a rich moisture plume remains across much of the south central and southeast CONUS and this clips into central Kansas and southern Missouri. This moisture plume will begin to return northward on the backside of the current high pressure system once it begins to depart towards the central Great Lakes tonight and into Monday. For central Iowa, very dry air below 800 mb, that is being reinforced by the surface high, will remain in place into through much of the day Monday though it will be gradually moistening through that layer from west to east. Theta-e advection will begin to overtop this dry layer, again from west to east, beginning tonight and will begin to bring some elevated instability into central Iowa during the day. This will likely lead to some convective bubbling above the dry layer over western and central Iowa Monday, possibly not too dissimilar to what is ongoing over parts of Nebraska and north central Kansas today. Mid-level cloudiness will be on the increase as well and that will help keep temperatures seasonably cooler once again with high temperatures in the upper 60s to mid 70s. A short wave trough will approach the area from the west Monday night with lead short wave energy arriving into Iowa. This will help tilt a strong low level jet into northwest/north central Iowa allowing the deeper moisture axis with 2 inch plus PWAT values and 850 mb dew points of 16C or greater to arrive. Warm cloud depths over 14 kft highlighted by saturating profiles in a warm environment, will aid in warm rain processes. There will be the potential for training of precipitation/storms as the mean storm motions will be near parallel to a slow moving boundary thus a strip of heavy rainfall could occur, most likely south of where the previous very heavy rain fell last week. The 850-300 mb mean wind flow if 40 to 50 kts so that could be a limiting factor to heavy rainfall. Surface based convective development is expected along the descending boundary on Tuesday. While most guidance would suggest this boundary will be over central Iowa Tuesday afternoon though the exact location of the boundary may be influenced by the previous convection to the north and any potential outflow. The deep layer shear and in particular speed shear, is better Tuesday and would be supportive of some organized convection including a few supercells along the potential for splitting cells. Supercell motions would move storms off of the boundary meaning any organized activity could limit the training potential. Severe storms will be possible with the primary threats being large hail and damaging winds. A reprieve in the weather arrives for Wednesday followed for more active weather potential for the 4th of July holiday. The system arriving for Thursday is fairly pronounced with a closed low moving into the Northern Plains and may present the potential for more severe weather. Another strong upper level system arrives over the weekend followed by the upper flow devolving into a long wave trough next Sunday and into the following week. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1155 PM CDT Sun Jun 30 2024 VFR conditions expected to continue overnight through much of the daytime hours Monday, though clouds will be on the increase overnight into Monday morning. Although a few showers remain possible around midday west to central, confidence in showers impacting KFOD or KDSM remains lower than 50% needed for mentions in the TAFs due to dissipating nature of showers and encountering dry air. Higher confidence in rain or storms moving in towards the end of the TAF period northwest to southeast with mentions included in future issuances. Light winds overnight will become out of the southeast and increase on Monday morning with gusty conditions expected by Monday afternoon into Monday night. && .HYDROLOGY... Issued at 250 PM CDT Sun Jun 30 2024 Reference the main forecast discussion above for finer details about two potential rounds of heavy rain that may occur Monday night and Tuesday. Heavy rain over northern Iowa is possible Monday night with the other over central and southern Iowa Tuesday afternoon and evening. Most streams over northern Iowa have crested and are beginning to descend from last weeks heavy rainfall. In addition, many storage areas are beginning to lower and dry since these past events and are available for some water storage again. Areas along the parts of the Des Moines River and in particular the recent record crests along the West Fork of the Des Moines would take a significant amount of rain to return to those levels and at this point, the heavy rainfall should be south of the previous location. Despite the expected heavy rain potential upcoming, nothing showing up in the HEFS and other ensemble forecast that would suggest significant additional flooding even in the 10th percentile forecasts. This rainfall may prolong flooding at some locations. One area to watch is the Saylorville Lake area storage as additional heavy rainfall upstream could cause more rises there than currently forecast, which does not use future rainfall. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Donavon AVIATION...KCM HYDROLOGY...Donavon