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FXUS63 KEAX 191753 AFDEAX

Area Forecast Discussion National Weather Service Kansas City/Pleasant Hill MO 1253 PM CDT Sun May 19 2024

KEY MESSAGES

- Isolated Shower/Storms Northern Missouri This Afternoon

- Congealed Convective System Late Tonight Early Monday; Conditional Severe Wind Threat

- Severe Storms Forecast Tuesday

DISCUSSION
Issued at 340 AM CDT Sun May 19 2024

Widespread precipitation is expected across our forecast area starting late tonight and continuing through Monday. The severe threat for both late tonight and throughout the day Monday are conditional and contain high degrees of uncertainty. Overall, ensemble probabilities for precipitation are high, over 90 percent chances for measurable precipitation across most of the forecast area, and most points hold around a 40 percent chance for exceeding 0.50 inches of rainfall. Synoptically, persistent mid-level southwesterly flow with strong vorticity maxima will provide multiple opportunities of favorable kinematics. The big uncertainties for our area will be thermodynamic recovery from Sunday into Monday. This will largely depend on how potential MCS behaves Sunday Night. If our area is to see any severe winds or hail from MCS, the MCS will be largely dependent on cold pool dynamics maintaining it.

This morning, mid-level ridge axis has cleared the area. Low-level flow continues to provide warm air advection into the region, keeping temperatures generally in the mid to upper 60s, with a few 70s still being reported between 07-08 UTC. Strong PV anomaly continues to sit over the Pacific Northwest, with a 2.0+ PVU as low as 700mb. The troughing pattern continues, creating brisk southwesterly flow across the Central CONUS. A stronger short-wave and associated surface cyclone has lifted into Canada, but the trailing cold front made it about two-thirds of the way southeast into our forecast area before stalling. As of this morning, a mid- level vorticity maxima has been ejecting from the Front Range into the High Plains. This has briefly provided H5 height rises into the lower Missouri River Valley early this morning, which has helped stall the cold front in its current position. In western Kansas, the dCVA associated with this vorticity maxima has resulted in surface cyclogenesis, and has been deepening over the past few hours.
Surface pressure falls are slowly occurring eastward, and will continue to do so through the afternoon hours, This will provide backing to lower-level winds, and should begin to push the thermal boundary back north as a warm front later this afternoon. With the pressure falls expanding eastward and thermal boundary in place, convergence may increase along the boundary for areas primarily north of Hwy. 36 this afternoon which could force a few showers or even thunderstorms. With flow southwesterly between 700-600mb, an EML will likely be present this afternoon above the boundary layer, which will result in steep lapse rates. If the subtle height rises through this morning are enough to keep skies clear, boundary layer destabilization could support a few stronger updrafts along the warm front. However, the better kinematic support for deep layer shear will still be much further west over Central Kansas. This will make it difficult for storms along the warm front this afternoon to organize, thus limiting the severe threat. The stronger EML may also result in capping of near surface parcels, thus limiting severe potential this afternoon in our northern CWA The main concern for Sunday Night into early Monday morning will be how convection over Central Kansas evolves. Over the Central Plains, the EML will be quite strong, along with robust boundary layer mixing in the presence of deepening surface cyclone. Dryline will also be in play in far western Kansas late this afternoon. Plenty of sources of low- level convergence in the Central Plains for initiation of storms. With drier air aloft and stronger boundary layer mixing creating inverted-v soundings in the lowest part of the troposphere, along with increasing wind shear with the mid-level vort max, convection likely congeals as low-level jet ramps up and allows strong segments, with some bowing structure to it, to develop in Central Kansas. Over the Central Plains, CAPE should be high enough to support this for a bit. However, CAPE values quickly dwindle after sunset from far eastern Kansas into Central Missouri. HRRR mean SBCAPE values are just a tad under 2000 J/kg by 0400z, and by 0600z, when the favorable kinematics and mid-level vort max are passing through, mean HRRR CAPE values are under 1000 J/kg which generally would not be favorable for supporting a late Spring early Summer time MCS.
However, if the shear and MCS cold pool vorticity remain in balance, the system could continue into our area. Current downshear Corfidi vector estimates indicate a strong healthy MCS could be moving at 50+ kts. Propagation speed alone could get near severe criteria for wind gusts. With that being said, this is all conditional on an MCS holding up. CAM guidance since 00z indicates the MCS breaking down as it crosses the Hwy. 75 corridor, essentially as it outruns its instability axis. HRRR QPF mean values quickly drop-off as it enters our area as well.
Simulated radar reflectivity fields appear to indicate the system becoming outflow dominant into the early morning hours of Monday, which would greatly limit the severe threat with the system. Overall, current feeling is that it is a 50/50 coin toss on how organized this system is as it rolls through. Will need to watch trends closely through the afternoon, and radar observations may be the best indication. If the system breaks apart and does not materialize the wind and hail threats, we may still see efficient rainfall that could present some hydrology issues, especially if the system slows down. However, HRRR does not provide much concern with hydro though, as probability matched mean QPF values have a few pockets of 1.25 inches, with widespread 0.75 to 1.00 inch elsewhere. Most areas should be able to handle this, as long as it is spread out over a period of a few hours.

Monday late morning and through the afternoon, H5 vort max should be exiting the area, moving favorable kinematic forcing out of the area. There is still potential for lingering precipitation from overnight MCS to be ongoing. Another short-wave trough and vorticity maxima ejects out of the Front Range will the PV anomaly still sits over the Northern Rockies Region. This will provide more deepening for the surface cyclone in western Kansas and should enhance southerly flow into the lower Missouri River Valley. This will provide stronger theta-e advection and send surface dewpoints into the upper 60s across most of the forecast area. The short-wave trough will briefly provide H5 height rises at some point on Monday which should limit large scale ascent through the afternoon.
However, will need to keep an eye out on outflow boundary activity across the area left over form remnant MCS, and may need to remain on the lookout for remnant MCV that could greatly modify the mesoscale environment. Perhaps stronger differential heating along one of these boundaries provides a greater source of convergence that can overcome the lack of large scale synoptic ascent through the afternoon, and locally increase wind shear. Some model guidance does destabilize the boundary layer again, resulting in MLCAPE values near 2500 J/kg. If new initiation occurs Monday afternoon into evening, there would be potential for a few severe storms.
However, this is very conditional, thus leading to low confidence in the occurrence of severe weather. There are several possible mesoscale scenarios that could evolve on Monday.

Tuesday remains to be the most robust synoptic scale support our forecast area will have through this multi-day stretch of convective activity. A stronger short-wave trough and robust vorticity maximum ejects out of the Front Range and phases once again with surface cyclone over the High Plains. The PV anomaly over the Pacific Northwest is finally progged to start moving eastward with broader jet streak developing, moving the system further east. The short- wave trough begins to develop a negative tilt and lifts into the Central Plains by mid-afternoon. As the cyclone shifts eastward, surface pressure falls become more rapid and will start to back surface winds into the lower Missouri River Valley, and provide stronger theta-e advection into our region. There is still uncertainty with how early the trough begins to lift and where this will place the best mid-level kinematic support, but overall ascent will be widespread across the Central CONUS that it should bring stronger storms to much of the area. With 700-600mb flow transporting a stronger EML into the region, mid-level lapse rates will steepen through the afternoon. Model soundings indicate this combination along with boundary layer destabilization to yield MLCAPE values potentially in excess of 3000 J/kg, and amongst NBM members holds a 50 percent chance to achieve this. If the jet streak approaches our area, the warm sector could experience 0-6km bulk shear values between 50-60 kts. A cold front will start moving across the Central Plains during this time, further increasing convergence across our area. This may be enough develop a few discrete storms across a strong warm sector Tuesday afternoon into early evening, especially if the trough does not lift too early providing stronger synoptic scale ascent. Overall veering wind profile and longer, looped, hodographs could support a few supercells capable of damaging winds and large hail. A conditional tornado threat could be realized if the surface winds acquire a southeasterly direction, providing better potential for low-level streamwise vorticity ingest. It is still a bit far out to call for this though, and will need to monitor how Monday activity, if any, alters the environment. If the trough starts to lift early and synoptic scale ascent is not as strong, then convection initiation on Tuesday will have to wait a few more hours until the cold front comes through and pushes up on the warm unstable boundary layer. In this scenario, deep layer shear is still strong but the vector is oriented parallel to it, resulting in quick upscale growth. However, the strong kinematics and stronger mid-level lapse rates could provide potential for a few stronger bowing like segments along the cold front, presenting a damaging wind threat with potential for strong vertical pressure perturbation gradients to develop. The vort max is progged to clear the area by late Tuesday Night into early Wednesday morning, with the cold front surging ahead and strong surface anti-cyclone moving in behind it. As for hydro issues, the system will likely be progressive enough, but, if heavier rainfall occurs with Monday convection, may start to see some flooding issues. Current ensembles though keep greater QPF and excessive rainfall potential further north of our area closer to the warm front. Along the cold front, while training storms in a boundary relative sense are possible, the front should likely be progressive enough to limit this threat.

Wednesday should see a brief break from precipitation and thunderstorm activity, but more short-waves are possible toward end of next week with elevated probabilities for accumulating rainfall.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/
Issued at 1239 PM CDT Sun May 19 2024

Currently VFR at all terminals under mostly clear skies with southerly winds around 10 knots. These conditions should generally persist through the afternoon and early evening hours.
A squall line is likely to impact the terminals around 4z tonight, with moderate rain lowering visibility to around 3SM.
This squall line will also bring gusty WSW winds, with the initial surge of winds on the leading edge of the line potentially as strong as 50 knots. Storms and breezy winds may linger through around 6z, with some light rain potentially lingering through around 10z. Guidance suggests the potential for additional shower development in the 13z to 17z time window, especially in the vicinity of STJ.

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

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