487 FXUS63 KDMX 161940 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 240 PM CDT Thu May 16 2024 .KEY MESSAGES... - Warm Friday and Saturday with highs in the 80s. - Isolated storms possible Saturday. - Several periods with storm chances from late Sunday through Tuesday night and again by late in the week. && .DISCUSSION... Issued at 237 PM CDT Thu May 16 2024 A few showers and isolated thunderstorms have developed across far southeast Iowa this afternoon along a weak frontal boundary that was ushering in drier air to the state. The drier air is resulting in the erosion of this mornings cumulus filed over central and north central parts of the state. This trend will continue as the as the boundary moves off the to the east. The precipitation over the far southeast will depart as well. High pressure ridge will move quickly across central Iowa this evening with the wind turning southerly already by midnight or shortly after. Friday will be warmer and dry with high temperatures in the low to mid 80s for most areas. The Gulf moisture will likely remain cutoff from Iowa through Saturday night with high pressure ridge cutting the flow off. The thermal ridge will move across Iowa on Saturday leading to another bump in temperatures with widespread highs in the 80s expected. A boundary will move into the region Saturday afternoon and evening while the parent short wave moves from Montana and into North Dakota. While it is possible that a few storms fire along the boundary, the lack of moisture available due to the Gulf flow shut off and it is possible the surface boundary undercuts the thermal ridge aloft, which would lead to capping. Those factors in addition to the lack of good forcing should keep any precipitation isolated to scattered at best. Another area of high pressure will quickly follow and settle over Iowa Saturday night and into Sunday morning. During this time, a strong upper level system will be dropping southeast into the Pacific Northwest which will tilt the upper flow to southwesterly. The switch to southwest flow will help allow the Gulf moisture to stream back northward. In addition, a strong short wave fragment originating from a close low off the southwest California coast, will eject out in the southwest flow and arrive into Iowa later Sunday. Timing of the short wave and also the arrival of the Gulf moisture will be the primary factors on thunderstorm timing for Sunday/Sunday night. Most likely scenario at this time is thunderstorms developing over western Iowa Sunday afternoon, then moving eastward Sunday night. Another strong short wave will be following this system by Monday afternoon or night with additional thunderstorm chances and those chances will persist until the main upper level energy to the west lifts out and clears the region, likely sometime Tuesday night. In addition to a few chances for severe weather during this time period, the heavy rainfall threat may return with a few periods with PWATS topping 1.50 inches along with several rounds of storms possible. A break in the weather should arrive by Wednesday and persist into at least early Thursday. Another potent upper low will be over the Pacific northwest early Thursday. This system will bring more weather to the state once it ejects out towards the region sometime towards the end of next week. With streams running above normal flows currently, will have to monitor the river flood potential as repeated rounds may bring renewed flooding. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1232 PM CDT Thu May 16 2024 Cumulus has developed across much of the area. While there still could be a localized brief MVFR cig, the cigs are rising with daytime mixing leading to cloud bases above 3 kft. In addition to the rising cigs, the clouds will begin to diminish in areal coverage by mid afternoon, except the far northeast. West wind today will become light tonight and transition to southerly by Friday morning. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Donavon AVIATION...Donavon