Day 1 Convective Outlook: April 25, 2024

Summary:
Scattered severe thunderstorms are anticipated from late this afternoon into tonight across parts of the central and southern Great Plains. Threats include very large hail, severe wind gusts, and a couple of strong tornadoes.

Locations:

  • Central and Southern Great Plains: Focused particularly across eastern Colorado, the northeast Texas Panhandle, and northwest Kansas.

Threats:

  • Very Large Hail: Expected to occur with storm activity.
  • Severe Wind Gusts: Accompanying the thunderstorms.
  • Tornadoes: Most likely with any robust supercells in the early evening.

Timing:

  • Peak Activity: Initiation by late afternoon, continuing into the overnight hours.

Discussion

  • Weather Patterns: A short-wave trough off the Southern California/Baja Peninsula coast is progressing towards the Southern High Plains, influencing severe weather potential. A 70+ kt 500 mb speed max accompanying the trough is expected to reach central Kansas by early Friday morning.
  • Atmospheric Dynamics:
    • Surface Features: A lee surface low will reposition into eastern Colorado by late afternoon. This will coincide with the jet’s left exit region enhancing lift as surface temperatures in eastern Colorado breach convective temperatures around 21Z.
    • Moisture and Instability: Surface dew points reaching 60°F have spread into the northeast Texas Panhandle early this morning, advancing into northwest Kansas ahead of expected supercell initiation. Forecast soundings suggest favorable shear and buoyancy for organized rotating updrafts.
    • Storm Development: The dry line across eastern Colorado into northwest Kansas will be the primary focus for storm initiation. Initial storm mode is expected to be supercellular, with very large hail and a couple of tornadoes. Activity further south will be more isolated.
  • Overnight Potential:
    • Strengthening Low-Level Jet (LLJ): The LLJ will intensify along the I-35 corridor from North Texas into Nebraska during the overnight hours, aiding in the eastward spread and development of convection in western Kansas.
    • Southern Plains Activity: A secondary area of convection is anticipated to develop over west/northwest Texas during the late evening. Despite some initial inhibition, large-scale height falls will erode this inhibition, facilitating thunderstorm development. Supercellular activity is likely initially, with potential for upscale growth into an MCS-type cluster moving northeast across the Southern Plains.
  • Practical Tips:
    • Target Area: Focus is on the vicinity of the dry line where convective initiation is most probable in NW Kansas. Watch for rapidly changing conditions as storms could quickly transition from supercellular to a more linear MCS-type structure.

Technical Breakdown

Initial storms should form by mid-afternoon under the divergent flow of the upper jet in NW KS and NE Colorado. However, the low-level thermodynamics in this region are, well, they’re really lacking. I don’t want to discount the low-lying weird things up here, but this seems like we should call it a hail and a low tornado threat zone.
Storms will become more widespread into the evening hours in that zone, and any storms that interact with a frontal zone likely to be draped in the area could pose a risk of a brief tornado before crossing into the stable low-level air. Further south, models differ on where the southern extent of storm activity will be. At first glance, this seems strange given the outlook — so let’s talk about it.
A dryline draped across the Plains this afternoon isn’t sharpening up that quickly on some models because the upper energy is (tell me if you’ve heard this before this year) lagging way behind. The surface map at 6 p.m. is pretty much perfectly terrible if you want storms on the dryline, with S/SE winds on both sides of the dryline. In the face of strong capping, the lack of surface convergence alone can spell doom for dryline storms.
But when you pull a sounding for that same time frame, you also see another problem emerge: there is a distinct lack of mid-level lift, and, in fact, it seems there may be a tendency to have subsident air in the mid-levels at peak heating over the dryline today. So, if you are doing the math, you have a lack of surface convergence, a lack of large-scale lift, and a cap that will require lots of mixing to get through. So, are storms possible?
You can see the dryline gradient tightens up nearer to sunset due to the upper wave finally moving in. But this poses a twofold problem. First, storms will form right as surface heating ceases and cooling begins. Without an extremely strong lift, the cap will be nearly impossible for updrafts to defeat. The key today I think is how fast this gradient tightens up. If it does so at peak heating, I think you can bust through everything with isolated storms from SW KS into the Panhandle — if it waits until 5-6 p.m. then I think you can find a good spot for another beautiful cloudless sunset photo in SW KS or the Texas Panhandle. The other obvious problem is that a storm moving east off the dryline will move into increasingly capped air. Through the night, strong moist advection and upper lift will work in tandem to weaken the cap, so tornadoes are possible throughout the night as storms fire despite the daytime odds of storms being a bit lower. If a storm fires further south in SW KS or the Northern Panhandles, a tornado risk is certainly there if the storm remains surface-based and robust.
So, while storm development from the Northern Texas Panhandle through Western Kansas is a question mark, we do expect fully that storms will fire in the Southern Panhandle/West Texas and move east through the night with a hail and tornado risk.