Forecasters: Mike Skipper (NWS) Llyle Barker (NWS/STEPS)
Today:Biggest challenge today will be to develop enough instability to initiate convection. ETA (12Z) does diminish area of low clouds to the east of the urban corridor by late morning as weak 700 mb short wave traverses area. Visible imagery at 15Z suggests that this may be beginning as clearing noted east of DIA. Mid-level winds are progged to reach 40-50 kts by 00Z with increasing SE flow in the boundary layer approaching 10-15 kts. This combination should provide sufficient shear for isolated supercells if thunderstorms do develop. Cooler (-12 to -13C) temperatures at 500 mb evident at GJT and RIW at 12z should also advect into STEPS area through the day adding to instability.
We expect thunderstorms to initiate just to the east of the front range urban corridor this afternoon then move east reaching near the STEPS domain's western edge around 4 PM. They should weaken as they move into the more stable air over the central and eastern portions of the domain. However, there may be targetable supercell storms on the western edge of the domain during the late afternoon.
Day 2: Reinforcing shot of cooler air is progged to move into STEPS domain area tonight as sfc ridge slides across Nebraska. Any convection hat does develop on day2 will likely remain south and west of domain.
Day 3: Return flow and good boundary is progged by 12Z ETA to move into the domain by afternoon setting up good conditions for targetable storms, particularly across the southern portions of the domain. Still plenty of uncertainty in timing.
| VARIABLE | Day 1: 1-4 pm | Day 1: 4-9 pm | Day 2 | Day 3 |
|---|---|---|---|---|
| Convective Potential |
1.5 | 2.5 | 1 | 2 |
| Storm Type | 2.5 | 2.5 | 2 | 2 |
| Triggering | 1 | 2 | 1 | 3 |
| Intuition | -0.5 | 0 | -1 | 0 |
| Total | 4.5 | 7 | 3 | 7 |
| SYSTEM | STATUS |
|---|---|
| Ops Center | Operational. |
| CHILL | Operational. |
| S-Pol | Operational. |
| LMA | Operational. |
| MGLASS | Operational. |
| T-28 | Operational. |
| Storm ballooning | Operational, but will target only +CG or hail-producing storms because of limited numbers of EFMs. |
| Mobile mesonet | Six vehicles are available. |
| Storm chase van | Operational as the primary precipitation verification vehicle. |
| YRFS | Operational. |
| NWS | Operational. |
Possible severe convection is expected to develop near the front range and, hopefully, advect into the STEPS observational domain. The mobile mesonets will deploy to the west from Goodland around noon (MDT) to observe the types of clouds that develop. The ballooning unit will be on standby, starting at 2pm, and will launch only in +CG or hail-producing storms. The DOWs will deploy along CO highway 59 north of US36 (DOW2) and south of US36 (DOW3) around 1pm. CHILL and S-Pol will be up by ~12-1pm for surveillance. The MGLASS will take an 18Z sounding at Flagler CO to find information about winds and cold-air advection aloft. Other soundings might be done farther east as the expected clearing moves eastward.
No targetable storms occurred in the STEPS domain. Only data collection involved sondes at 18 and 21 Z from Flagler only. Mesonet worked convection in various places to the far west of the STEPS domain. Storms remained at 150 km or greater from CHILL and S-pol.