Sunrise 5:59 AM   Sunset 8:30 PM Moonrise 4:56 PM   Moonset 3:17 AM

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FXUS63 KEAX 200938 AFDEAX

Area Forecast Discussion National Weather Service Kansas City/Pleasant Hill MO 438 AM CDT Mon May 20 2024

KEY MESSAGES

- Isolated to scattered showers and storms possible today, but timing and overall coverage are highly uncertain.

- There is an enhanced risk of severe thunderstorms on Tuesday across the entire region, with all severe hazards possible.
Currently, the greatest chances for severe weather are generally east of Interstate 35.

- Locally heavy rainfall may occur with storms on Tuesday night, especially south of Interstate 70. A few instances of flooding may occur (about a 20 percent chance).

- The pattern remains active later this week through Memorial Day weekend.

DISCUSSION
Issued at 337 AM CDT Mon May 20 2024

Busy night here with the severe storms that moved through the KC metro during the late evening hours. Unfortunately, this abridged the forecast process quite a bit tonight, so main focus of the morning update was on the first 48 hours.

Objective 00z upper-air analysis indicated a broad trough in western North America, with an elongated 250-mb jet streak from the Great Basin to the Upper Great Lakes. Meanwhile, a southern-stream anticyclonic jet streak extended from the Baja region to western Texas, with difluent flow in the Missouri Valley. A midlevel perturbation was present in the central Plains, collocated with regionally strong 850-mb southerly flow.
Evening soundings exhibited environments quite supportive of the severe storms that moved through Kansas and western Missouri, with substantial CAPE and deep-layer shear atop fairly dry low- and midlevels (resulting in highly favorable DCAPE). A strong bow echo developed in southern Kansas and raced eastward into the CWA during the late evening, producing substantial wind damage in the KC metro and surrounding areas before dissipating as nocturnal stabilization continued and cold-pool dynamics gradually waned as outflow outpaced the existing convection.
The mesoscale convective system (MCS) developed a very pronounced mesoscale convective vortex (MCV), which traversed the northwestern half of our CWA overnight (and has now progressed into southern Iowa as of 4 am).

The immediate forecast question today is to what degree the MCS has curbed our region's ability to generate new convection. The progression of the MCV to our north and northeast suggests its influence in our region may be confined to our far eastern counties. However, as diurnal heating and destabilization commence, the presence of the MCV and associated convergence/lift may provide additional support to generate convection with relatively little diabatic heating. Based on current progression of the MCV, think chances of convective regeneration in our CWA associated with it are diminishing, and PoPs have been lowered somewhat in the eastern CWA today (after the remnant precipitation from the MCS traverses to eastern Iowa/Missouri early this morning).

However, convection-allowing models (CAMs) have been reasonably consistent in developing convection early this morning in eastern Kansas, supported by isentropic ascent on the poleward side of the nocturnally maximized low-level jet. Less consistent is the progression and persistence of this convection through the day, with the latest HRRR simulations, for example, anywhere from keeping convection mostly to our west before its dissipation to lingering it into at least mid-afternoon in northern/western Missouri. Given some support from the NAM Nest, higher PoPs are warranted in the western half of the CWA today (generally 30 to 60 percent).

Confidence lowers further during the late afternoon and evening, with at least some hints of scattered convection developing in northern/central Missouri. CAMs are all over the place regarding coverage, specific geographic placement, and timing. Thus, maintenance of some low PoPs through the overnight hours is warranted (primarily north of I-70). Sufficient capping should be in place farther south to keep these areas mostly dry tonight.

Multiple rounds of convection will be occurring to our north from this afternoon through Tuesday morning, in the stronger southwesterly mid- and upper-level flow. However, on Tuesday, a strong vort max will eject from the western U.S. trough northeastward into the central Plains. This will translate into eastern South Dakota and Nebraska and adjacent portions of Minnesota and Iowa during the afternoon. Large-scale ascent attendant to the shortwave trough will result in the development of convection in advance of the progressive vort max. The southern-stream jet streak will advance to Kansas and Missouri during the afternoon, providing upper divergence support via the left-exit region to areas mostly to our north. Such forcing weakens farther south into our CWA, casting some uncertainty on when convection develops along the approaching front given a strong elevated mixed layer and associated capping. Development should occur from north to south, with gradually sparser coverage with southern extent. With this in mind, there is a chance that the northwestern portions of the CWA see little in the way of convection from the Tuesday system, with probabilities increasing as one gets farther east from I-35.

Regarding the overall environment, severe weather is certainly supported, with moderate to strong buoyancy (MLCAPE > 2000 J/kg), strong deep-layer and low-level shear (0-6 km bulk wind differences exceeding 50 kt; effective SRH exceeding 150 J/kg), and increasingly orthogonal upper flow to the approaching front (more supportive of discrete/supercellular storms, at least initially). The primary limiting factor is strength of capping, as mentioned above, and also how quickly storms congeal/grow upscale. Even if upscale growth is rapid, a severe MCS with an environment supportive of QLCS tornadoes would be present.

Another consideration is heavy rain potential. With gradually diminished forcing on the southern side of the system/front, convection may tend to become more oriented parallel to upper flow, especially during the evening/overnight hours. CAMs are hinting at upward propagation becoming favored on the south side of the developing MCS, which may lead to a favored zone of training storms and potential flash flooding. This threat looks greatest south of I-70 at this time. We will be monitoring this potential closely as the event approaches.

A reinforcing vort max will move through the Midwest on Wednesday, which may keep storm chances lingering through the day in our eastern and southern CWA, especially. Otherwise, there should be a brief period of quiet weather Wednesday and Wednesday night. Yes, brief. The wavetrain of vorticity maxima in favorable zonal to southwesterly upper flow continues thereafter, with frequent bouts of active weather apparent Thursday right through the holiday weekend.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
Issued at 1216 AM CDT Mon May 20 2024

A convective complex developed across Kansas Sunday evening and will continue to move ENE through Missouri through the morning hours of Monday. The strongest storms have pushed well east and north of the terminals, but lingering wrap around storms will persist for a few hours this morning across the KC terminals with MVFR to VFR conditions expected to prevail. Otherwise, winds will need watching as the center of the low moves through this morning.

EAX WATCHES/WARNINGS/ADVISORIES
MO...None.
KS...None.

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