Broad upper low, situated over the far NW US, pushed eastwards during the afternoon hours and onwards. A sharp 100-120 kt high-level jet also translated to the east over the N-C Rockies with the favorable left exit region approaching our area of interest over NW Dakota at 19Z onwards. The airmass composite image was helpful in pinpointing the position of the jet max as a sharp moisture gradient evolved (roughly extending from Oregon to Wyoming). Initiation over far NW Dakota also awaited the approach of the “ozone-rich” airmass (purple) as it overtook the eastward progressing dryline between 19-22Z, fostered by reports of surface dewpoints in the mid 50s beneath rapidly drying mid/upper levels.

The first image captured at 1900Z:

and the second one at 2200 Z with initiation already underway/building SE-wards:

Helge

There has been little action so far along the dryline across South Dakota so far this afternoon, despite MLCAPE peaking at 2500-3000J/kg and good convergence along the dryline and a possible dryline bulge per the SPC Mesoscale Analysis at 22Z:

Last night’s 00Z NSSL-WRF SimSat product indeed shows some isolated development along the dryline across northern South Dakota close to 00Z:

As of 23Z, a few showers have developed across central South Dakota, near the small dryline bulge, but no lightning has been observed yet.

Isolated thunderstorm development was possible over far SW Texas mainly due to intense diabatic heating (with temperature readings in the lower 90s). Roughly 30kt deep layer shear and 1 kJ/kg SBCAPE overlap were supportive for strong to severe pulsating storms. Rapid to explosive development occurred south of Pecos (isolated in nature) with UAH-CI product showing high probabilities for initiation at 1945Z (not shown) with cloud top cooling of -38K/15 min present at 2010Z. Cloud top cooling peaked at -46K/15 min at 2015Z. Would not be surprised to see an isolated large hail report with that storm (up to 60 dBz present).

Helge