Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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896 FXUS63 KDMX 190431 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1131 PM CDT Sat May 18 2024 ...Updated for the 06z Aviation Discussion... .KEY MESSAGES... - Progressive pattern to spark increasingly active thunderstorm pattern through the first half of next week. - Storms may become strong to severe along with heavy rain throughout the active period, but especially on Tuesday. - Temps to be overall seasonal, with Wednesday looking the coolest (65-70) through the period. && .DISCUSSION... Issued at 237 PM CDT Sat May 18 2024 Well-defined shortwave trough evident on satellite pix spinning west of Winnipeg early this afternoon; with the attendant surface front extending south thru Minnesota and just about 1/3 of Iowa. Air mass cools 10-15F in its wake, with upper 60s approaching the MO River. Temps ahead of the front have climbed into the mid-upper 80s; with dew points in the low 60s. Decent cap in place per forecast soundings; which is supported by limited cu at this point. Latest CAMs suggest that this inhibition will erode sufficiently tapping into 1500+ j/kg MLCAPE to get a few storms along front and generally south and east of DSM between 21-01z. Lack of sufficient deep layer shear will be limiting factor for convective organization. However, with DCAPEs in excess of 1000 j/kg, winds would be the primary thunderstorm hazard. Any storms that are able to develop will fall apart quickly by sunset. Front makes it into N MO for all of about 12 hours before lifting back north Sunday morning. Along the northward moving warm-front, isolated elevated convection will be moving thru Sunday morning into early afternoon. While severe threat with this activity appears minimal, it may briefly interrupt any outdoor activities. This activity shifts east and weakens thru the day. Meanwhile, thunderstorm round #2 will be in the process of developing across the plains as the next shortwave translates east, arriving into central Iowa Sunday evening. Initially discrete across the plains, these thunderstorms will congeal into a thunderstorm complex moving through Sunday night. Although greatest severe potential is with initial storms, deep layer shear remains 30-35 knots as thunderstorm complex moves through, which may be enough for severe potential lingering Sunday especially west of I-35. Sunday night will also be the beginning of a multi-day excessive rain threat, with deep warm cloud depths and PWATs of 1.5-2". That shortwave departs early Monday. Any gap will be short-lived as the atmosphere once again destabilizes during afternoon with SBCAPEs progd to be 2000-2500 j/kg with deep layer shear again of 30-40 knots. More heavy rain and severe storms will be possible Monday afternoon & evening. Greatest severe potential of the period comes on Tuesday afternoon as the next shortwave deepens as it emerges from the plains lifting thru Iowa and Minnesota during peak heating. As such, instabilities will be maximized at 3000 j/kg of progd SBCAPE along with deep layer shear in excess of 50 knots in areas. This is captured well in SPCs day 4 outlook. Temperatures will briefly cool on Wednesday, before rebounding by week`s end, with more thunderstorm chances returning. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1131 PM CDT Sat May 18 2024 Mainly clear skies are expected through sunrise, before cloud cover increases from west to east though VFR conditions are expected to remain. However, still expecting scattered showers and storms after 12z-15z Sunday morning, with the best potential for stronger storms into the afternoon to evening hours. Heavy rainfall at times may cause for reduced periods of visibilities at times, though would be relatively short lived. Uncertainty is still on the higher end given the scattered nature of the expected activity, so exact timing and location remains unclear. Winds are expected to gradually turn more southeasterly throughout the day, with increasing winds generally up to 10-15 knots. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Hahn AVIATION...Bury