279 FXUS63 KDMX 091817 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 117 PM CDT Tue Oct 9 2018 ...Updated for 18z Aviation Discussion... .SHORT TERM.../Today through Tonight/ Issued at 430 AM CDT Tue Oct 9 2018 Deep southerly flow will persist into the state through tonight as upper system finally begins to eject from the intermountain southwest. The deep flow of moisture and instability will continue during this period with the surface front stretching southwest to northeast through the center of the state although it will meander some. Large area of showers and embedded thunderstorms are expected to move north into the western half of the state this morning with a round of moderate to heavy rainfall. Meanwhile, the east should see more of a break by early afternoon. This will allow for modest destabilization into the afternoon along with a veering wind profile as the surface low begins to deepen. This should lead to another late afternoon/early evening round of strong to severe storms across the southeast half of the forecast area. Given the low LCLs, veering profile and some modest CAPE in the low levels, a few tornadoes seem possible once again in the slight risk area of storms. This threat will persist into the evening and maybe even longer than Monday evening given the increasing synoptic forcing and surface low moving toward the state. The convection will persist into the overnight with the surface low approaching and entering Iowa. The rainfall concerns will persist and are highlighted below in the Hydrology section. Temperatures today will move very little in the northwest behind the boundary with low status and periods of rain. Farther southeast in the warm sector, temperatures are likely to climb to near 80 by mid afternoon prior to convective development. .LONG TERM.../Wednesday through Monday/ Issued at 430 AM CDT Tue Oct 9 2018 Surface low will be near Des Moines at the beginning of this period along with ongoing pcpn over much of northern and eastern Iowa. However, subsidence will be increasing across the southwest during the morning along with strengthening cold advection. This will bring a halt to the showers across the south and west during the morning and elsewhere by early to mid afternoon. Highs in the east will likely be in the morning on Wednesday with strong cold advection developing during the day behind the cold front. Otherwise, breezy conditions are expected through the day into Wednesday evening as the cold advection continues. Much needed quiet weather is expected on Thursday as large Canadian surface ridge approaches the state. This will have some implications for frost/freeze on Thursday night with light winds and initially clear skies across the area. Frost is expected across the north and possibly central Iowa during the night as temperatures drop into the low to mid 30s. The limiting factor for frost farther south with be an increase in clouds overnight which will likely hamper radiational cooling and the frost potential. Both GFS and Euro have a weak shortwave approaching from the northwest late Thursday night into Friday with increasing clouds and some decent isentropic lift. However, moisture will be limited and the threat of precipitation will remain low. However, another shortwave will drop quickly southeast into the central United State by the weekend. This will have some interaction with Hurricane Sergio from the eastern Pacific and while the bulk of moisture from Sergio will remain to the south, it will help deepen the system. This will produce additional rain into Iowa from late Saturday into Sunday with highest amounts in the south. Both models are hinting at deformation precipitation crossing the state on Sunday night which would be a very cold rain with even the possibility of a few snow flakes on the northwest side of the precipitation area. Drier but cool conditions are then expected into early next week as broad northwest flow develops across the central United States. && .AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/ Issued at 114 PM CDT Tue Oct 9 2018 Messy TAF forecast continues. Expecting Thunder at all sites this afternoon through early tonight...timing dependent upon site. Vsbys will likely be 1 mile or less during heavy downpours. Given the speed of storms, periods of highly reduced vsbys would less than 1 hour. Precip to eventually move east of TAF sites by tomorrow afternoon. && .HYDROLOGY... Issued at 430 AM CDT Tue Oct 9 2018 Continued deep moist southerly flow into the state through tonight. PWATs will remain impressive and near the climatological max for this time of year. Western Iowa will be the focus into today for the heavier QPF but some translation slightly eastward is expected by afternoon closer to the instability axis where storms are forecast to fire. These storms will have higher precipitation rates and are expected to persist through the evening and into the overnight, albeit not as strong. Main concern here is that flash flooding may be more of a danger later today into tonight that has occurred with this system to this point given the heavy rainfall already received and the higher rates expected later today into this evening. Otherwise, widespread areal and river flooding continue to look likely through tonight into early Wednesday before the precipitation subsides. Thereafter, river flooding is expected to linger for quiet some time as the water gradually routes through the streams and rivers. The Flood Watch has been expanded to include the rest of the forecast after some moderate to heavy rains in those areas along with collaboration from surrounding sites. && .DMX WATCHES/WARNINGS/ADVISORIES... Flood Watch through Wednesday morning for IAZ004>007-015>017- 023>028-033>039-044>050-057>062-070>075-081>086-092>097. && $$ SHORT TERM...Cogil LONG TERM...Cogil AVIATION...Kotenberg HYDROLOGY...Cogil