Forecasters: Michael Skipper (NWS/GLD) and Jim Johnson (NWS/DDC)

The 1200 UTC analysis indicated a 60KT+ 250mb jet streak which went unforecast by the 00Z ETA and NGM but was handled by the Aviation model. The morning environment was contaminated by convective feedback with 850mb, 700mb, and 500mb levels on the upstream sounding at DDC unrepresentative of the synoptic scale regime. Other convection was east of GLD with outflow from it working its way west into the GLD area. Vertical shear was not strong through the deep layer. The main polar boundary was along the KS, NE border at 14Z with the boundary layer airmass to the south of it well worked over by the nocturnal convection.

As the upper-level jet streak approaches from the southwest we expect falling pressures in the lee slopes with 55 to 65 surface dewpoints working back westward against the high terrain. There should be ample low level focus combined with diurnal heating to begin plumes (or bubbles?) of convective ascent in the afternoon near or within the STEPS domain. If there is descent of the upper jet streak by evening in the area, shear should be sufficient for an isolated supercell. Until the airmass re-stratifies and the boundary layer forcing becomes more clear, no point location of convective initiation is clear. The nowcaster will monitor this for positioning.

The aviation model was prefered for the later periods with Tuesday afternoon promising to be perhaps the best day yet as a vigorous upper wave drives a polar cold front south into the domain with rapidly strengthening cyclogenesis drawing in high CAPE air and producing a strongly sheared environment. Confidence in this is above average.

Based on the forecast, storms are expected in our area late this afternoon and and evening. Our initial plans will be the following: mobile mesonet will deploy to Idalia at 1 PM local. 18 Z and probably 21 Z soundings will be taken from Limon and Goodland to monitor expected moisture influx from the east and trough development to the west. Radars will come up in surveillance at noon local. NSSL5 will standby in Goodland. T-28 will also be on standby for possible late afternoon launch. All facilities are fully operational.

[Radar images]

We studied what basically could be described as an asymmetric MCS. This system approached from the west and passed through both the western and eastern dual-Doppler lobes. Convective elements in the line were quite intense and produced flash rates to 1/second (near 2224 UTC). Numerous positive strikes were observed by NLDN. Horizontally propagating flashes into the trailing stratiform region (from the convective line) were indicated by the interferometer (near 2224 UTC).

Observational highlights of the event included:

T-28 made multiple penetrations in developing and mature convection from roughly 2145 to 2245 UTC. Observed liquid water contents peaked at 1.5 g/m3, at -8 C. Heavy icing was picked up by the aircraft. Copious large particles were detected on most penetrations. T-28 studied two convective elements in the line while coordinated dual-Doppler scanning was conducted in the western lobe.

NSSL5 launched a total of five EFM's, with good data obtained on four of these flights. Balloons were launched in the vicinity of the T-28 passes. EFM's were obtained in the leading anvil, core (two flights) and post core environments. This should provide a very nice cross section of the E-field structure. Interferometer reported the horizontally propagating flashes near the time of the balloon ascents.

Mobile mesonet appeared to obtain a great dataset. Originally they sampled the well defined gust front of this system along an east-west line along route 36, just west of Idalia. Then they shifted their east most probes to a position east of Idalia, and north-south along 385 to study the gust front and convective passage in more detail. Numerous gustnadoes were observed by the probes.

Hailstone van got a core penetration near Joes CO where we received a report of 3/4 hail at 2143 UTC from a NWS spotter.

Dual-Doppler coverage was continued in east lobe after NSSL, mesonet and T-28 left the event. Doppler observed very strong rear inflow jet, as well as a well defined gust front. Peak outflows were 50 knots. This MCS was one of three MCS strung out along a N-S line. The southern most MCS was in the OK panhandle, and was the most intense of the three. Our MCS was the second in this N-S line, while the third MCS was situated in western Nebraska. This latter system was more of a parallel-stratiform system. MCSs #1 and #2 were more of the asymmetric MCS type with the stratiform region to the north of the bowed convective line.

RHI and PPI coverage was continued from 0030 (12 June) to approximately 0130 UTC (12 June) to document large stratiform region that was producing large horizontally propagating flashes at a rate of 1 per 5 minutes. Possibly a sprite producing case.

MGLASS soundings were obtained at Limon and Goodland at 18 and 21 UTC. Also, a post convective sounding was taken at Flagler at approximately 2245 UTC. A pre-storm sounding was also obtained at Goodland at approximately this same time. These soundings should have provided excellent documentation of this system.