Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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900 FXUS63 KDMX 151901 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 201 PM CDT Wed May 15 2024 .KEY MESSAGES... - Showers and storm chances increase this evening into the overnight. Highest chances north. Severe threat low. - Active pattern continues this weekend into early next week. Threat for severe weather and heavy rainfall may develop Sunday night and again Monday night into Tuesday, although specific details remain uncertain at this time. && .DISCUSSION... Issued at 200 PM CDT Wed May 15 2024 19z GOES water vapor imagery shows an active split-flow pattern over the conus with several embedded lower amplitude waves. One such shortwave was noted crossing the northern Plains and will serve as the impetus for precip chances through the next 24 hours. At the surface a weak low pressure center was over eastern SD with a surface boundary extending south toward the MO River valley. Thermal forcing and meager moisture return ahead of the front will phase with the increasing kinematic ascent with the approaching upper wave to produce more scattered to widespread shower/storm activity later this afternoon into the evening over western Iowa, then pushing eastward late this evening and overnight. Highest chances (>50%) for rain will reside over the northern half of the cwa. The shear and instability parameter space is not overly supportive of organized strong to severe convection, but some sporadic small hail or gusty winds cannot be ruled out. Frontal boundary progression is sluggish and will only be over eastern Iowa by Thursday morning. Lingering showers/storms are possible into Thursday morning, but most hi-res guidance suggests afternoon redevelopment will occur east of the cwa. Most locations should be dry for the majority of the day with temps reaching into the 70s to near 80. GFS still wants to graze southern Iowa with light rain Friday as it brings an upper low much further north than other guidance. This is an outlier compared to most ensemble guidance and the NBM continues to trend in a dry direction. An active forecast continues over the weekend and into early next week as the synoptic pattern aloft gradually transitions to mean western troughing and southwesterly flow. Storms are possible as a frontal boundary pushes through Saturday, however much more organized robust chances likely evolve early next week as the Gulf opens up and deeper moisture streams northward. Details at that time range are still nebulous considering the typical model variances and likelihood for mesoscale processes to drive convective evolution, however models are keying on Sunday night and then again Monday night into Tuesday for the most probable windows. A threat for severe storms and heavy rainfall may develop, but will be more acutely determined in the days ahead. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1229 PM CDT Wed May 15 2024 VFR conditions currently prevail across the forecast area. -SHRA and some embedded -TSRA will move west to east over the state from late this afternoon through tonight. Highest chances generally reside across northern Iowa, so have included mention of -SHRA/VCTS for now to cover the potential, however the extent of categorical impacts, if any, will need to be further evaluated since confidence is low at this time. Low cigs push into MVFR range toward Thursday morning, but should not last long as improvement is noted in most model guidance by late morning or early afternoon. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Martin AVIATION...Martin