Forecasters: Randy Coleman (NWS) Llyle Barker (NWS/STEPS)

Today:

Abundant low-level moisture advection is evident this morning with stratus caught up in 25-30 kt southerly flow at 200-400 ft AGL. This stratus is ahead of shortwave that is aiding formation of SW-NE line of cumulus across northwestern STEPS domain this morning. Although mid-level winds are a bit lighter behind this wave, profiler and RIW sounding suggest they will pick up again in association with a second wave moving southeast. This wave is aiding convection along the front range at 16Z. The stronger than progged low-level winds and moisture advection should lead to capes on the order of 2500 J/kg and 0-6km shear values around 50-55 kts by 00Z this evening near the center of the STEPS domain.

Although some activity may occur around midday in association with the first wave. The most targetable activity will likely be delayed until the second wave enters the area late this afternoon. The passage of the first wave will hopefully dissipate the stratus in place along the Kansas/Colorado border and allow strong insolation to add to the instability by late afternoon. Eta progged VGP values are around 0.27 just south of Goodland by 00Z and with moisture and low-level winds underestimated a rather larger area of VGPs of >.20 should cover much of the domain area.

Targetable supercells seem likely by late afternoon or early evening in the central portion of the STEPS domain.

Day 2:

Although weak shortwaves and decent low-level moisture should remain in place for Friday. A decreasing trend in 0-6km shear values begins to develop as 500 mb heights increase and winds decrease as ridge amplifies in to area. We will also see a gradual increase in 700 mb temperatures as ridge builds. This increase will likely postpone any activity that does develop until late in the day.

Day 3:

The trends discussed in day 2 continue with lowering shear and increasing cap. weak shortwaves moving along the top of the ridge and decent low-level moisture continue to be in place.

Forecast is for good chance of singificant convection in the STEPS domain. Radars will come up at noon. Mesonet will work north along highway 385, starting at noon. T-28 and EFM to stand by in Goodland starting at 1PM. We will take 18 and 21Z sondes at Goodland and Sterling in advance of short wave moving towards us in brisk northwest flow aloft. DOWs will deploy and plan to be up by 2PM.

[Radar images]

Well this was the event we have all been hoping for, and we got it! A tremendous supercell storm was in the east Doppler lobe for over two hours. Observations included excellent Doppler coverage by CHILL and S-Pol (great coordination on scans), four EFM launches, T-28 penetrations, excellent coverage by the mobile mesonet (with observations of a tornado) and supporting soundings measurements. LMA reported flash rates of 1 per second at times.

One particular highlight was the fact that the storm became a right mover near Wheeler around 2330 UTC. This behavior was accompanied by the onset of positive CG's and the occurrence of a tornado. The first tornado observation was noted around 2330 UTC, az/range of 57 degrees, 75 km from CHILL (reported by NSSL5). Prior to this time the storm produced only one positive CG, and was primarily an intracloud lightning producer. The storm was reported as having an inverted polarity structure prior to the turning and onset of positive CG's.

Near 2350 UTC, the storm featured a well-identified BWER with tops to 15 km. Ldr values as large as -15 db in the hail shaft. Reflectivites of 60 dBZ were maintained to 10 km AGL for a good deal of the time the storm was in the east lobe.

First EFM was launched near Wheeler into the mesocyclone. NSSL5 was then directed south and east and ended up setting up for further launches near Brewster KS. Second EFM launch was 3 mi. west of Brewster, again into mesocyclone. Third EFM was also into mesocyclone near 0045 UTC at Edson, KS. The fourth EFM was sent up into a strong core that was just north of I-70, with was north of the main core that the previous EFM's had been launched into. This storm was targeted since it was producing positive CG's and had a mesocyclone. If NNSL5 would have stuck with the southern storm that they had been working, they would have been directly in the path of the mesocyclone associated with the northern storm. This location was undesirable for obvious reasons, and hence the northern storm was selected. The Hailstone van set up near Brewster too, and got a great core penetration near 0030 UTC 30 June. There were numerous reports of hail exceeding golf ball size in this area. The manual hail catcher was used, but the software on the SDSMT hail box was not operative after several reboots.

T-28 penetrations were conducted between roughly 2240 and 2340 UTC, 29 June. A total of 6 passes were made. Pass 4 and 6 were most interesting, with a peak updraft of 33 m/s on one of these passes. Heavy rain, moderate hail and continuous lightning were observed on these passes. Unfortunately the engine on the T-28 seized just before landing and the aircraft is down for the rest of STEPS. The aircraft was able to land at the Goodland airport, thanks to the tremendous skill of pilot Tom Root. We are all thankful that Tom made it back to Goodland safely. The T-28 provided 14 flights for STEPS and performed very well.

The mobile mesonet got great observations including hail intercepts and a tornado siting.

Radar observations were ended around 0245 UTC 30 June, with CHILL examining the hailstorm as it moved off to the SE. To date this event marks the top case collected in STEPS.