Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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058 FXUS63 KDMX 170448 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1148 PM CDT Mon Sep 16 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Above normal temperatures and mostly dry conditions continue for the next few days. - Multiple chances for showers and storms over the latter half of the week, and particularly late week into this weekend. The timing of precip chances and threat of severe weather is uncertain at this time. && .DISCUSSION... Issued at 215 PM CDT Mon Sep 16 2024 Synoptic pattern remains dominated by rex blocking with a ridge over a broad upper low out east and a deep trough to the west. With little movement to the wave train aloft, the weather over Iowa is relatively unchanged with above normal temps and humidity for mid-September and mostly dry conditions. Widespread shallow cumulus has developed once again with diurnal boundary layer heating. Some of this convection could be deep enough to produce a brief shower or two before the boundary layer cools again this evening. A weak shortwave moving out of the central Rockies spurs additional showers/storms west of the area later today into tonight. This activity should be in a state of decay as it progresses eastward toward the western edge of the CWA by Tuesday morning, as primary forcing mechanisms and low level moisture transport remain focused to our west. Kept mention of ~20% chance PoPs for some of our far western counties, however ensemble data would suggest even lower probabilities for any measurable precip. A large upper low pivots northeast out of the desert southwest toward mid-week, eventually taking on a negative tilt before occluding over eastern Montana. Models continue to paint light QPF over the state Wednesday, although key forcing mechanisms and moisture convergence are still displaced well to our west. Thus trending toward a drier forecast for Wednesday except for possibly our far western counties. A more probable window for precip arrives Thursday into Thursday night as the upper low begins to crest and suppress the ridge as it moves into south central Canada and attendant sfc boundary pushes into the state. Above normal temperatures likely continue through at least the middle of the week, although cloud/precip coverage could hinder peak heating potential. Substantial model differences hamper confidence wrt to the timing and magnitude of precip chances toward late week and into the weekend. While models unanimously agree that another upper low will emerge from the western US late in the week, there has been little run-to-run and cross-model consistency with the evolution of the upper low as it traverses the central conus. 12z GFS now advertises a more progressive open wave while the EC is prefers a slower, more wrapped up circulation. Substantial ensemble spreads also provide little clarity to the forecast at that time range. The latest NBM is loaded up with higher chance PoPs Friday night into Saturday, but this may be overdone as some guidance suggests our most likely window for rain holds off until Sunday into Monday. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1145 PM CDT Mon Sep 16 2024 VFR conditions prevail through the period. Winds are currently light out of the south southeast but increase out of the same direction after sunrise tomorrow, with a few gusts in the north and west nearing 20 kts. There is an off chance for a sprinkle or two to pass over KFOD, but any impacts should be minimal. Fog still seems unlikely at TAF sites this morning, but will continue to monitor for any changes in this trend. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Martin AVIATION...Dodson