Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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582 FXUS63 KDMX 281753 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1253 PM CDT Sun Apr 28 2024 ...Updated for the 18z Aviation Discussion... .KEY MESSAGES... - More showers and storms today. A few may be strong to severe, but the threat looks highly conditional at this time. - Storm chances return Tuesday along with the potential for strong to severe storms. Forecast trending wetter through the middle of the week. && .DISCUSSION... Issued at 252 AM CDT Sun Apr 28 2024 Shower and storm chances persist again today as an upper low slowly moves toward the northern Plains. While the primary moisture/instability axis will remain well south, some moisture is pulled back westward toward the low and will help support scattered to widespread precip. Hires guidance suggests the greatest coverage occurs this afternoon into the early evening hours. Severe threat today looks highly conditional as instability looks limited due to precip/cloud cover. Deeper convection that develops this afternoon over eastern KS/northern MO could dribble into southern Iowa and pose a threat for hail and gusty winds before weakening. Still cannot rule out potential for a few weak tornadoes, although again instability is a significant limiting factor. Ambient vorticity increases as upper and sfc lows both pass near or west of the forecast area. Sfc pressure field generally weakens and winds try to veer from se to sw through the day. It will likely take appreciable clearing and the development of more robust low level instability to generate enough stretching to support a quick spin up. Will need to monitor trends through the day, but at this time the threat looks low. Conditions dry out Monday as deep layer subsidence increases behind the departing upper low. Moisture wrapping around the backside of the system will promote broken to overcast cloud cover especially early in the day, and will help hold highs in the upper 50s north to mid 60s south. Forecast activity picks right back up through the middle to latter portions of the week as a series of shortwaves follow an upper jet streak traversing the central Rockies into the local region. Moisture returns northward on Tuesday ahead of an approaching surface front. Precip chances ramp up by mid to late day as showers and storms develop within the vicinity of the front. SBCAPE builds to near 1000-2000 J/kg and effective shear ~40-50 kts, which would be sufficient to support more organized strong to severe storm activity. This idea is backed by the CSU ML output that paints lower end severe probs over the cwa. Front stalls out just south of the area and is lifted back northward on Wednesday as models have trended more progressive with successive waves. The baroclinic zone serves as the general focus for additional rounds of showers and storms by late Wednesday through Thursday. While widespread heavy rain does not likely, there is a signal in the models for a potential axis of heavier QPF amounts, likely associated with training deeper convection. Precip potential becomes more uncertain as a deeper upper low pulls out of the central Rockies late in the week. Euro camp is more progressive and considerably drier by the end of the week, whereas the more sluggish GFS/GEFS solutions would favor more precip chances into Friday. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1250 PM CDT Sun Apr 28 2024 Messy TAF period ongoing with smattering of VFR through IFR conditions, generally from south to north across the TAF sites. While some improvement remains likely this afternoon in/around KMCW/KALO, where IFR currently prevails, degradation returns to all sites as a couple possible waves of showers/thunder move through this evening into overnight and expected spread of stratus field behind frontal passage and as the upper/surface low slide northeastward. Most prolonged IFR conditions around KFOD/KMCW, with more likely MVFR KDSM/KALO/KOTM during latter half of the period. Winds will be shifting from current southerly to easterly winds to westerly by/after 12z. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Martin AVIATION...Curtis