Sunrise 5:48 AM   Sunset 8:33 PM Moonrise 4:56 PM   Moonset 3:10 AM

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FXUS63 KDMX 200924 AFDDMX

Area Forecast Discussion National Weather Service Des Moines IA 424 AM CDT Mon May 20 2024

KEY MESSAGES

- Generally non-severe MCV associated convection lingers into the morning east, then chances temporarily diminish later in the day

- More storms expected tonight into early Tuesday morning. Severe storms possible, mainly a wind treat.

- Peak severe potential Tue afternoon with another round of storms. Tornadoes, damaging wind, and hail all possible.
Enhanced Risk of severe weather (3/5).

- Break from precip follow midweek, but additional chances return late in the week

DISCUSSION
Issued at 424 AM CDT Mon May 20 2024

Little change in the overall weather pattern is anticipated through the period with relatively lower amplitude and progressive flow bringing systems of varied strength through the Midwest every few days keeping us active. At onset this morning, the parent short wave and combined generative MCV continues to swirl along the IA/MO border with the last of the healthy forward flank convection exiting the area to the east.
Non-severe showers and a few storms are then expected to linger for several more hours before a temporary break with little to no precip in the MCV's subsident wake into at least early afternoon.

Some regeneration may occur during the late afternoon and especially early evening hours northwest however as the current NE/SD boundary sags into the state. This may start what could be an active night with 2-3K J/kg MLCAPEs building into the state, and effective shear increasing as well as the western long wave trough nears and mid level flow increases. This convection may persist and expand into the night, fueled by increasing low level moisture transport through the MO Valley. This may also be reinforced by an advancing MCS generated from what was High Plains peak heating convection as it maintains intensity from the low level jet associated moisture transport and convergence crossing NE into IA. Hail and especially damaging wind appear to the primary threats with 00Z HRRR high wind probs quite high into IA, even several hours past daybreak. Highly anomalous moisture parameter space, coupled with the strong moisture transport, suggests locally heavy rainfall is possible with isolated several inch maxes.

The CAM consensus suggests a brief break toward midday, but then the airmass recovers quickly into the afternoon as what is now a short wave off the Baja coast reaches the MO Valley and intensifies. Strong synoptic scale forcing should aid continued low level theta-e advection into the warm sector and also what is expected to be a line of storms forming along the associated cold front, with more widespread weaker precip to the north and west along the deformation zone. The precip should form into discrete supercells initially shortly after onset with the latest RAP suggesting uncapped 3000+ J/kg MLCAPEs with 50-60kts of deep shear normal to the boundary. Thermodynamic questions do remain however with recovery potentially delayed by the morning convection, possibly resulting in the genesis region being pushed farther east than depicted by hi res guidance. While confidence in supercells is fairly high, confidence in tornadoes is certainly there, but less. Examination of several CAM soundings suggests a spectrum of possibilities. While all have strong 500m shear, some seem more effective than others ranging from alarming SRH and streamwise vorticity values and high percentages of ingest, which could certainly be enhanced depending on remnant outflow boundaries, to less favorable crosswise SR ingest in broader SSW surface wind. It is curious that various CAM 0-3km updraft helicity tracks during the afternoon are not as ominous as one might think with a few tracks but not numerous ones, unlike what was depicted on 26 Apr. Nevertheless, large hail and damaging wind expected, along with the potential for tornadoes considering the overall severe weather parameter space.

Any convection should exit by early evening leading to more tranquil weather and seasonal temps for the next few days.
Albeit not as deep as our Tuesday system, our active pattern will cycle another northern Plains trough passage Friday bringing additional chances for showers and storms.
Deterministic GFS solutions aren't overly enthusiastic on severe weather potential, with weaker instability and deep shear. However 00Z 19 May CSU GEFS based machine learning solutions do reflect at least some severe potential, especially south. Other weaker waves will keep at least some precip chances into the forecast through the weekend as well.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
Issued at 1144 PM CDT Sun May 19 2024

A line of showers and storms continues east of I-35 early this morning and is expected to move out of the area over the next few hours. However, a large cluster of additional showers and storms are expected to lift north across the state after 06z, which will allow for active weather to continue through much of the morning. Periods of lower ceilings and reduced visibilities from heavier rainfall with these storms may allow for MVFR conditions at times. A drying period looks to occur by late morning through the afternoon, before additional showers and storms look to move into the area towards the evening. Specific mention of timing and location of storms Monday evening remain unclear and will largely depend on the previous storm evolution, which will be monitored closely. Winds will gradually shift south/southwesterly with slightly breezy winds through the daylight hours.

DMX WATCHES/WARNINGS/ADVISORIES
None.

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Des Moines, IA,