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FXUS63 KEAX 211826 AFDEAX

Area Forecast Discussion National Weather Service Kansas City/Pleasant Hill MO 126 PM CDT Tue May 21 2024

KEY MESSAGES

- Chances for strong to severe storms this afternoon and evening continue across MO and KS. Storms are expected to start out as discrete cells before merging into a line of storms. All hazards are possible including damaging winds, large hail, and tornadoes.

- Storm chances will be greatly influenced by the position of the cold front and timing of storm initiation. Severe risk is significantly reduced behind the front.

MESOSCALE
Issued at 127 PM CDT Tue May 21 2024

Satellite imagery shows an area of agitated cumulus overspreading much of far eastern KS and western MO.
Observations show the cold front progressing into eastern KS.
Some convection has initiated across SE Nebraska; however, the 18Z TOP sounding shows a little bit of a CAP left curtailing development further south at this time. This CAP is expected to erode as daytime heating continues. SPC mesoanalysis shows nearly 1000-2000 J/kg CAPE gain in the past 3 hours mostly due to daytime heating. Bulk shear remains above 50kts with 0-1 helicity of 100-150 m2/s2. All of these factors keep expectations for storm modes unchanged. Initial discrete storms are anticipated before storms congeal into a line across central MO. All severe hazards including large hail, damaging winds, and tornadoes are possible.

Uncertainties remain as to where the front will be when initiation takes place; however, trends in obs and CAMs suggest storms starting to form within the next 1-3 hours.

DISCUSSION
Issued at 107 PM CDT Tue May 21 2024

Short Term (Today-Tonight)

A small line of elevated storms moved across far northern MO during the morning hours. Its concentration further north and quick progression through the region does not look to impact the short term forecast. Warm air and moisture advection into the region continues ahead the approaching cold front. This destabilizes the atmosphere substantially with some CAMs already projecting CAPE values around 3000-4000 J/kg. Bulk shear above 50kts and midlevel lapse rates greater than 8 C/km further increase confidence in the potentially volatile environment. Storms are already beginning to form across far SE Nebraska. Now, it is just a matter of how fast the cold front progresses across eastern KS and how long it takes for storms to initiate across the cold front.

Confidence is high that storms will form within the warm sector ahead of the front; however, exactly where the front will be as storms initiate is still in question. Short term model guidance varies in the timing of convective initiation and the position of the front. Citing two, the NAMnest initiates convection across eastern KS pushing eastward into central MO through the evening.
Conversely, the HRRR suggests the front progressing further eastward with storm initiation possible along and east of the I-35 corridor.
If the cold front progresses further eastward, those behind the front may not see any storms regardless if there are within the outlined risk areas.

Where models have been persistently agreeing is in the expected storm modes and evolution of the system. Confidence is high that storms are expected to start as discrete cells before congealing into a line of storms across central and eastern MO. These discrete cells are expected to bring chances for large hail (2+ inches), damaging winds, and tornadoes. These threats are expected to continue even as storms begin to linearize. Once the line becomes fully organized, the primary threat transitions to damaging winds.
However, embedded brief tornadoes remain possible. Please ensure you have multiple methods for receiving weather information; especially during the late evening hours.

Longer Term (Extended Forecast)

The long term forecast remains persistent. A reinforcing vort max will move through the Midwest on Wednesday, which may keep storm chances in our southern fringes during the afternoon/evening. More likely, though, is that storms will stay south of the region Wednesday and Wednesday night (70 percent chance). After the warm weather today, temperatures will be much more seasonal on Wednesday in the wake of the system.

The pattern late this week into this weekend remains unsettled, with general quasi-zonal or southwesterly low-amplitude flow in place. Multiple perturbations will eject from a broad large- scale trough in the West, leading to multiple chances for convection through the holiday weekend. Ensembles are gradually converging on a relatively higher threat Thursday night and Friday as well as Sunday. With an open Gulf and relatively fast flow in proximity to the perturbations, at least some severe threat exists with each of these passing systems. Notably, the CSU machine-learning probabilities provide nearly daily chances of severe weather from Thursday through Monday for the region.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
Issued at 1232 PM CDT Tue May 21 2024

Isolated to scattered thunderstorms are expected to develop after 20Z quickly developing into a line of thunderstorms. There is a question as to whether storms will be developed in the KC metro, so went with a few hours of vicinity. Gusty winds are expected to persist through the afternoon hours, subsiding with sunset this evening.

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

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