Sunrise 6:27 AM   Sunset 8:09 PM Moonrise 9:20 PM   Moonset 6:09 AM

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FXUS63 KTOP 251949 AFDTOP

Area Forecast Discussion National Weather Service Topeka KS 249 PM CDT Thu Apr 25 2024

KEY MESSAGES

- Several rounds of thunderstorms are expected to move across the area through Sunday.

- There is a risk for severe weather each day, with the greatest risk including tornadoes on Saturday.

- Multiple rounds of heavy rain could lead to isolated flooding.

DISCUSSION
Issued at 249 PM CDT Thu Apr 25 2024

19Z water vapor imagery showed an upper trough over the Great Basin with a shortwave lifting through the four corners region.
At the surface, low pressure was noted in southeast CO with a warm/stationary front extending through southwest KS and north central OK. Persistent moisture advection over this boundary has maintained the elevated showers and thunderstorms across the forecast area today.

The main focus of the forecast is on the potential for severe weather in the coming days. 12Z model consistency is good with an upper low lifting into central NEB Friday morning with a second upper low coming out into the western plains Saturday night and Sunday morning. The warm sector with dewpoints in the lower and middle 60s is expected to lift into northeast KS by Friday afternoon as the initial upper low lifts to the northwest of the forecast area with a dry line developing by the afternoon. This warm moist airmass remains over the area through Saturday night and becomes somewhat modified by Sunday afternoon. Though there is still expected to be some moisture lingering across northeast and east central KS Sunday afternoon. Good environmental shear is progged with a strong wind field forecast through the weekend and the setup for severe storms just doesn't move out of the area until Sunday evening.

The MCS this afternoon is expected to continue to propagate southeast along the axis of MUCAPE that extends northeast of the surface warm front. With this having worked over the environment a little, think there may be a break from the deep moist convection into the evening, but the CAMs hint at the redevelopment of showers through the evening. The main point of uncertainty through the evening is where new convection develops. The HRRR has been consistent in thunderstorms developing more over northwest KS within the low level convergence area northeast of the surface low. This would tend to keep storms mainly north of the forecast area through the late evening. However by the early morning hours, PVA with the shortwave should cause development to become more widespread and move east through the morning. These storms look to be mainly elevated with a hail and damaging wind risk, but there does appear to be a narrow axis of surface based instability advecting north through the morning. If storms develop in this axis of surface based instability, the risk for a tornado or two will be higher.

By Friday afternoon, forecast soundings from the NAM and RAP show MUCAPE around 3500 J/kg just ahead of the dryline. Good turning in the low level winds are progged to create SRH around 200 m2/s2. More of the models are starting to show a signal for convective initiation along the dryline in northeast KS though there remains some uncertainty given the lack of convection from the HRRR this far south. Supercell thunderstorms would be favored with the potential for very large hail and perhaps a strong tornado into the evening across northeast KS thanks to increasing SRH with the strengthening low level jet. This risk may move east and north of the forecast area by mid evening with shortwave ridging overspreading the area.

This should lead to a break in the thunderstorm activity heading into Saturday with the dryline retreating west. The setup for Saturday looks ominous with forecast soundings showing a capped boundary layer with large amounts of CAPE (3000 to 4000 J/kg) within the warm sector east of the dryline. Again good environmental shear would support supercell thunderstorms and as the low level jet increases in the early evening, SRH also increases to around 300 m2/s2. So the concern for Saturday afternoon and evening is for tornadoes, some potentially strong. Shortwave energy is progged to be lifting over the dryline through peak heating and could be the trigger for thunderstorm development.

By Sunday, the upper low should be to the north of the forecast area but a diffuse boundary may still be over eastern KS acting as a focus for renewed convection. Models are not as strong with the instability and deep layer shear looks to be a little weaker too. So severe risks may be a little more marginal. Repeated rounds of heavy rainfall could cause some flooding problems before the weekend is over. But confidence in the location of the thunderstorms and where heavy rain develops is a little to low to pinpoint with a watch at this time. Right now the heaviest rainfall is forecast for parts of east central KS, but this could change depending on the short term evolution of the storms.

For next week, the pattern becomes a little more zonal with shortwave energy passing through the plains mid-week. With a frontal boundary in the area, there looks to be another chance for showers and thunderstorms Tuesday through Thursday.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
Issued at 1149 AM CDT Thu Apr 25 2024

There is good agreement among the models for continues southerly return flow advecting moisture into the area. So confidence in IFR CIGS moving in is good. CAMs show this initial cluster of storms moving through the terminals early this afternoon with activity becoming more isolated by early evening. A shortwave lifting through NE KS is expected to cause additional TS development by the early morning hours of Friday. CIGS may improve Friday as a surface low lifts north, but this looks to be after 18Z.

TOP WATCHES/WARNINGS/ADVISORIES
None.

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