Sunrise 6:11 AM   Sunset 8:12 PM Moonrise 12:00 AM   Moonset 7:58 AM

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FXUS63 KDMX 282012 AFDDMX

Area Forecast Discussion National Weather Service Des Moines IA 312 PM CDT Sun Apr 28 2024

KEY MESSAGES

* Another opportunity for a few strong storms today, mainly W/SW, but threat scaled back overall

* Briefly quiet Monday, then additional threats for some strong to severe storms return to the area Tuesday and possibly again Wednesday.

DISCUSSION
Issued at 308 PM CDT Sun Apr 28 2024

Largely been a cloudy and more dreary day across the area thus far with mostly cloudy skies and periodic showers streaming across the area.

While the overall severe threat remains on the lower end of the spectrum, there are a couple of items of note that may yet yield a stronger storm or two and/or a weak tornado or two. RAP/HRRR and CAMs in general, have struggled to pin down existing shower/storm activity back west as well as the stratus deck evolution across the state today, with all holding onto stratus into mid to late afternoon before more rapid erosion. By about 18z, about the southern two-thirds of Iowa had already seen a good amount of erosion of the stratus deck, resulting in some filtered sun through a relatively thin mid-level cloud deck. This may help develop more favorable conditions for a stronger storm or two, including potential for marginally supportive to supportive low level CAPE for a landspout or weak tornado or two as the upper/surface lows move through. However, existing shower activity ahead of the more vigorous convection near surface front muddy the waters once again.
While HRRR has struggled some, it has had a consistent trend in upping SBCAPE values along/ahead of the surface front with recent runs suggesting potential for around/above 1500 J/kg versus <1000 J/kg in morning runs. Similar trends have been seen in the SPC RAP mesoscale analysis in 0-3km CAPE and associated NST parameter space.
Deeper layer shear largely remains messy, marginal, and predominantly unidirectional, limiting organization, large hail, and damaging wind threats. At this point, the suggested main threat may be a few weak tornadoes/landspouts associated with any more vigorous convection along the surface front and nearer the core of the low this afternoon and evening before the lowest levels stabilize. This would point to west-central into northwest Iowa this afternoon into the evening.

Monday will be on the quieter and side as the upper and surface lows pull off to the northeast and westerly winds prevail. A few low level instability driven showers may be seen north.

Temperatures quickly rebound Tuesday with southerly flow increasing ahead of a shortwave trough and developing surface low. Expect highs to soar back towards the upper 70s and lower 80s. Moisture does not quite rebound in a similar fashion, but consistent signal for SB/MUCAPE values to approach 2000 J/kg in a corridor over eastern Nebraska into western Iowa by the afternoon and evening. Wind profiles will be supportive for some organized convection with fair curvature and effective shear values in excess of 40kts within various guidance. Hail and damaging winds appear to be the primary threats at this time, though a tornado would remain possible with storms near/along the surface cold front. Into Wednesday, additional chances for showers and storms present themselves as a warm front quickly lifts back northward ahead of upper level shortwave and developing surface low across the Front Range. Guidance this afternoon has trended northward with the warm frontal placement by the evening/overnight, so details remain in flux for both strong/severe potential and any heavy rain threat. Activity looks to be most robust with increasing LLJ activity Wednesday night.

Temperatures ease through the remainder of the week too with highs back into the lower 60s return by Friday. Also rounding out the week, discrepancy remains among flagship deterministic models and ensemble suites with Euro solutions still favoring a much more rapid upper trough passage while GFS/GEFS remain slower and would prolong shower/storm opportunities to end the week.

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.

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Des Moines, IA,