Forecasters: ? (NWS) and Morris Weisman (NCAR)

Strong southerly winds overnight have advected low-level moisture back into the region, with surface dew points between 55 and 57 F this morning. A trough line is also quite evident this morning, extending from east-central Colorado northward through western Nebraska. West of this line, low and mid-level flow is developing a west to northwest component, and surface dew points are drying. This trough is expected to be located near Goodland by evening, in conjunction with a well formed dry line. East of this dry line position, dew points will remain in the mid-to-upper 50's, which, along with daytime heating, will create moderate-to strongly unstable conditions, with LIs between -4 and -8. Isolated convective storms are expected to trigger along the trough/dry line by early-to-mid afternoon in west-central and southwest Nebraska, and propagate into the northern or northeastern portion of the STEPS domain by late afternoon or evening. Vertical wind shear values will be just sufficient to support some supercell activity, with LP storms also a possibility. If supercells develop, expected cell motions will be to the south or southwest at 10-15 mph today.

A weak cold front passes through the STEPS region overnight, stabilizing most of the region, but return moisture should be sufficient to generate convection along the front range by late tomorrow. The chances of significant convection reaching the research area tomorrow, however, are small.

Continued strong southerly winds tomorrow night will lead to significant moisture return and increasing convective potential on Monday.

Based on the forecast, we have more ingredients to work with today than in the past several days. Radars will come up at noon. We will update T-28, EFM, hailstone van and mobile mesonet at noon as well. Problem today might be temptation to bite on early convection, leaving us unable to respond to possible early evening (stronger) convection. Since we have not had much activity this week, we will be aggressive in pursuing any reasonable storm that presents itself to us. However, the T-28 is willing to fly two missions and 6 EFM's will be carried by NSSL, so we indeed could cast a larger observational net with regard to time.

[Radar images]

Overview: Extensive dual-Doppler scanning and mobile mesonet data were collected on a well defined dry line (or trough line) in the west dual-Doppler lobe formed by S-pol and CHILL. Convection developed along the northern edge of the Doppler coverage and was eventually observed by NSSL5 (two EFM ascents), the mobile mesonet, and the T-28. Due to storm location, radar coverage was mainly with S-pol/Goodland dual-Doppler pair, with CHILL supporting with sector and RHI scans. This storm had characteristics of a low precip supercell, but appeared more as a low precipitation, rather weak unicell storm. No CG's were observed by NLDN, despite 60 kV/m fields (reported by NSSL5) and reports of "frequent" IC lightning. Polarimetric signatures suggested the absence of mixed phase conditions, with surface hail. Very little phase shift, suggesting only modest rain fell during a good portion of the storm's lifetime. Rapid scan was obtained from 1730 UTC to 0300 UTC (4 June).

Dual-Doppler scanning on dry line feature was concentrated between 1820 to 2245 UTC. Then sector scans were set up after 2045 UTC to observe developing convection. 2310 UTC-decision made to target developing echo with T-28 and EFM/mobile mesonet. These facilities were well positioned and obtained quality data. T-28 made 4 penetrations between 0000 UTC (4 June) to 0100. Data suggested numerous penetrations of developing clouds. Main precip core was penetrated and particles were limited to graupel no larger than 5 mm (via telemetered data). NSSL5 had two ascents, one into core and one into rear flank. This will be a very interesting storm to analyze from the point of view of storm electrification. Why were there no CG's (as depicted by NLDN data)? How large was the IC flash rate? This should be a good case for relating storm kinematics, microphysics and electrification in a low CG producer. Precipitation shaft was very narrow, and consistent with dry mid level air this storm had to work with. Storm was in range of 3-D LMA.

LMA data collection extended from 2257 UTC 3 June to 0110 UTC 4 June. First lightning at roughly 2257 UTC. Flash rates were 1 flash/10 sec at 2305 UTC, peaking at 1 flash/5 sec at 2358 UTC. Based on qualitative inspection of the LMA record by NMIMT, this storm was deemed to be a "significant" lightning producer.

Addendum: There were 6 passes by the T-28 at 2 different altitudes, roughly 6 and 6.6 km MSL. Temperatures were about -8 and -14 C. Although we did not know it in real time, precipitation particle sizes ranged up to 1 cm. There was graupel near new and old updraft cores, and rimed aggregates and smaller rimed single crystals in other portions. There were not many pristine small ice crystals in the regions sampled. The electric field structure was reasonably simple, and there was evidence of lightning at a frequency of about one or more flashes per minute. Peak updrafts were about 10 m/s.