Sunrise 6:13 AM   Sunset 8:10 PM Moonrise 11:35 PM   Moonset 7:06 AM

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FXUS63 KDMX 270807 AFDDMX

Area Forecast Discussion National Weather Service Des Moines IA 307 AM CDT Sat Apr 27 2024

KEY MESSAGES

- Another round of severe weather is possible over southern into central Iowa later this afternoon and evening. All severe weather hazards are possible, but large hail and damaging winds are the primary threats.

- Showers and storms are likely tonight into Sunday. Additional severe weather is possible Sunday afternoon and evening, but the extent of the threat is uncertain at this time.

- Weather pattern remains active into next week with more shower and storm chances Tuesday/Tuesday night and again late in the week.

DISCUSSION
Issued at 300 AM CDT Sat Apr 27 2024

We have transitioned into a quieter period overnight as the upper low responsible for yesterday's severe weather outbreak has pushed north and east of the area. Subsidence on the backside of the departing low has cleared out most cloud cover and precipitation, although the lull will be short lived as another potent upper wave is already churning through the four corners region and ready to take aim on the Plains states later today.
A warm frontal boundary draped over southwestern and through central Iowa serves as the focus for additional convective development. Hires models percolate isolated showers and storms early in the day as instability builds along and south of the front, but this will likely have a tough time overcoming mean deep layer subsidence. Much more robust convective initiation holds off until 20z-22z as vigorous deep layer ascent overspreads the increasingly unstable warm sector. Most of the 00z model suite has honed in on nw MO into sw IA for initial development. These storms may quickly become severe as they work within a favorable environment for large hail and damaging wind gusts. Sounding analysis suggests a few tornadoes cannot be ruled out with the initial development into southern Iowa given 0-1km SRH ~100-200 m2/s2, looping hodographs, plentiful CAPE within the lowest 3km.

Convective evolution becomes increasingly uncertain into the evening hours. A few hires members (HRRR/ARW) quickly grow upscale and race the storms east, while others (NAM/FV3) take a more northerly trajectory and eventually push the storms north of the warm frontal boundary and into a less favorable environment for severe weather over northern Iowa. Redevelopment through the night is also poorly handled as some models favor the mesoscale storm outflow over MO into SE Iowa, while others favor the synoptic warm front bisecting the CWA In either case, strong background upper level divergence should support at least scattered shower and storm activity over the forecast area tonight into Sunday as the upper low pushes toward the Dakotas. Another window for a severe weather risk including hail and a few tornadoes may materialize Sunday afternoon and evening as the surface low moves and attendant dryline move into western Iowa. The extent of the threat will hinge on precip/clouds clearing out and allowing the boundary layer to destabilize.

Pattern remains active into next week as models show multiple waves traversing through the region. After another break in storm chances on Monday, the atmosphere quickly reloads with return moisture ahead of an approaching upper wave and surface frontal boundary.
Showers and storms are looking increasingly likely as the front passes through Tuesday evening and night. Latest NBM PoPs are likely too aggressive into Wednesday and may need to be trimmed back if current trends continue. The next system is quick on its heels as another shortwave digs into the central Rockies, leading to additional shower/storm chances later in the week.
Models begin to diverge with pattern evolution by this point, and ensemble data is noisy and does not provide many clues for honing in on a particular time period for higher PoPs.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
Issued at 1229 AM CDT Sat Apr 27 2024

Shower and storm activity continues to wind down and gradually push east. Brief downpours and sporadic gusty winds possible at KALO through 07z. Then conditions dry out as we have a lull in storm activity. Many terminals also improve to VFR, except for those into eastern and northern Iowa where model guidance suggests MVFR or lower cigs will hold strong through the night and into Saturday. Additional TSRA activity develops over southern Iowa around or after 20z and quickly moves north.
Timing of impacts at specific terminals remains a bit uncertain at this time, but the storms will be capable of producing hail and gusty winds in addition to periods of heavy rainfall. Future updates should better capture the timing and periodic categorical restrictions from tsra activity.

DMX WATCHES/WARNINGS/ADVISORIES
None.

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