Will the day-before-the-day event be a sleeper for this system? I have a feeling it will be. Right now the SPC Enhanced risk areas are in Nebraska along the forecast warm front and in the Oklahoma and Texas panhandles along the dry line.
A strong low pressure system is forecast to develop in northeast Colorado to northwest Kansas. That will help pull moisture into Kansas, bringing mid-60's dew points in the western half of the state by late afternoon. A moderate cap should be in place, possibly delaying storm initiation until nearer sunset (let's say 6-7pm). All severe weather hazards are possible, not only from storms that may stay parked along the dryline for a couple hours, but from a developing cluster of storms forecast to bring threats into the early morning hours Saturday. In fact, there may be precipitation and even some small hail after sunrise for a few hours.
Friday night will be a time to ensure your weather alert radio has fresh batteries and to be sure to sleep with it on!
The first day of what looks to be almost a week of severe weather possibilities in the plains will feature an ENHANCED risk of severe weather over parts of Texas (dryline) and Nebraska (warm front). The western half of the state, while in only a SLIGHT risk area at this time, is shown with a significant risk level if severe storms occur.
In chaser parlance, we call this the “day-before-the-day” event.
Consensus is for low pressure to develop over the CO/KS/NE region, with a stationary front stretching from northern NE across IA, IL, OH and WV. Meanwhile, a sharp dryline will develop across western NE and KS into the eastern OK and TX Panhandles and west TX where it will remain overnight. Strengthening southerly winds over the Plains will bring mid 60s F dewpoints north across the entire warm sector, which will result in areas of strong instability. Lift related to these boundaries should result in a few concentrated areas of severe storms, with very large hail and few tornadoes possible.
Strong instability will develop along the dryline with daytime heating and dewpoints increasing into the mid 60s F. A capping inversion will exist east of the dryline, with development expected where heating is strongest. Ample deep-layer shear along with increasing SRH late in the day and overnight will support supercells capable of very large hail and a few tornadoes. Storms may not move very far east until overnight when a larger complex of storms is forecast from southwest TX into southwest OK, with all modes of severe possible.
Forecast Consideration 1: Dew Point temperature and surface wind.
We see upper-60’s dew points up into Nebraska and Iowa, and some 70’s pooling south of the warm front east of Omaha. The warm front can be seen by the area where wind switches from out of the south and southeast to out of the east. It’s a bit north of I-80 from North Platte to Des Moines.
The dryline is sharp, with 63 in Norton, 66 in Hays, 64 in Dodge City, while we’re looking at 32 at Ulysses and 37in Tribune and Goodland. We’ll position the dry line right along US 83 from Oakley south into Texas. Generally we target about 30 miles ahead of the dryline
Forecast Consideration 2: Wind profiles
700mb (about 9,000 feet above sea level or 3,500 feet above ground in that area); 500mb (about 12,000 feet above ground); 300mb (about 25,000 feet above ground); 200 mb (about 33,000 feet above ground).
What we’re seeing is something we haven’t had over the central US in some time. In all levels of the atmosphere, that kink representing the strong low over the Four Corners is pretty well aligned above and below. There is also divergence (the lines are narrower over the TX panhandle and further apart over northern KS).
Forecast Consideration 3: 700mb temperature
We look at the 700mb temperature to get a sense of how strong the capping inversion is. In the area of interest, 700mb temps are running about 8-9 degrees Celsius. In April this would leave us capped off and prevent most severe weather. By this time of year, though 8-9 degrees is getting almost ideal. It’s enough the cap will take some time to erode Friday afternoon, letting the moist air at the surface to heat and gain more energy. But it’s weak enough it should start to erode, I’m thinking in the 5-6pm CDT time frame.
Forecast Consideration 4: Skew-T and Hodograph
These are graphics based on a forecast vertical column profile (Skew-T) and a view from above the updraft (hodograph). It’s more complex than that, but we’ll roll with it…
First, my initial target is somewhere within a box bounded by Ness City, Dodge City, Dighton and Meade. So let’s say between K-4 on the north and US-56 on the south, K-23 on the west and US-283 on the east.
The associated Skew-T looks like this:
These things jump out at me:
- Surface wind: SE, 20-25 mph
- Lower wind: veering (more westerly with height) through about 15,000 ft.
Upper wind: slight backing (shift back to the east) at 15000 ft, then little to no directional change
- Wind speed with height: generally increasing through 30,000 ft
- LFC-LCL height (closer = easier to get convection going, closer to ground = more likely to be a surface-based storm): I’d rate these as acceptably close, but a little high up for a robust tornado risk. If they were at or below the 850mb line and right on top of one another, I’d be more wary of tornado risk. But this is a Skew-T that contains some tornado risk, and if a storm can get rooted on a subtle boundary there could be a strong tornado.
This is the hodograph (looking down from the top):
Wind in a hodograph works the opposite of how it does in everything else. Now a southeast wind will be along the 45-degree axis in the upper left quadrant. The further up the centerline a point is plotted, the higher the wind speed.
What we’re looking for to analyze tornado risk is a tracing in the upper panel that starts in the upper left quadrant and loops while getting a larger radius in the red segment. The larger the radius becomes, the more wind shear (twist) there is with height.
This tends to confirm a large hail risk as being higher than the tornado risk, despite how the panel is labeled in the lower left. Tornadoes are possible if this forecast verifies, but I believe very large hail to be the main risk.
What is a Day-before-the-Day event?
Typically, an event that gets this name has a “surprise” tornado or very large to giant hail. It’s a surprise because the main upper strength hasn’t come out onto the plains. If you go back and look at the 200mb graphic early in this outlook, you’ll see bright pinks along the west coast. Those will be in our area by Saturday evening.
There are two worrisome risks on a day-before-the-day event: the severe weather really ramps up shortly after dark and continues into the night. SPC notes that once storms initiate along the dry line they won’t move much until night time, and all severe risks are on the table well into the early morning hours.
Be sure your weather alert radio has good batteries. Sleep Friday night with it on.
- Tornadoes: 5 on a scale of 0 to 10. A strong tornado (EF2-5) is possible.
- Hail: 9 on a scale of 0 to 10. Numerous reports of 2” or larger hail.
- Wind: 7 on a scale of 0 to 10. Some straight-line wind above 70 mph.
- Flooding: Much of the risk area is in saturated areas. 6 on a 0 to 10 scale.
Steve Boleski, Nolan Banks, and Charlene Miller will join me for Friday’s chase.
NWS products for Friday:
Appears that dryline will remain well west of forecast area through at least early Friday evening. Temperatures cool just a bit Friday with increasing dew points and potentially more clouds.
Parameters are impressive: moderate to strong instability in eastern half of the area combined with deep layer shear of 30-40kts. Fairly strong upper system will be coming out of the Rockies with a slight negative tilt, although best forcing will north/west of the area. At the surface, cold front will be located across central Nebraska in the afternoon, north of the area, then sweep through Friday night. Model QPF, however, is quite sparse, with most of the precipitation well north of the area in the post frontal environment. The front, in fact, may turn out to be the primary forcing mechanism, with storms racing north with the mean flow, once again away from the area.
Fri is now the focus for high-end severe wx potential. A cap will be over the CWA…but it shouldn’t be strong enough to completely preclude initiation as 700 mb temps will be around 11C. Expect a few (maybe just a couple?) isolated thunderstorms to develop. With MLCAPE up to 3000 J/kg over most of the CWA…deep layer shear 30-35 kt…and 0-3 km SRH 100-150 m2/s2…expect severe supercells will be the primary convective mode. The models are surprisingly sparse with QPF Fri afternoon/evening. If that is correct…it means less competition/potential for storm mergers… and an increased threat for high-end severe wx…including very large hail and tornadoes…as long as storms form.
[C]onditions will support decent destabilization through the day with MUCAPE values upwards of 1000- 2000 J/kg by Friday night as the surface cold front tracks into central KS. A strong dryline will develop over far western KS, with storms likely developing along and ahead of the advancing cold front. Depending upon the exact timing of the eastward progression of this front into central KS, some of these strong to severe storms could extend into north central and central KS during the overnight hours.