Upper level flow shows continued SSW flow aloft over the region, thanks to deep troughing remaining over the West Coast. Overall forcing through the afternoon is on the weaker side of things, but models show an upper level jet streak nosing into the area. Scattered thunderstorm activity has already developed (below) to the south of Billings in northern WY, and is expected to expand in coverage through the afternoon. The DSS event is noted by the large yellow “B” over Billings.
The 14Z PHS forecast output (below) showed 19Z MUCAPE values across the area ranging roughly from 1000-2500 j/kg (with highest values in the eastern areas). Looking further into the mid-afternoon hours, outside of MUCAPE values creeping closer to 3000 j/kg in far NE portions of the CWA, the PHS overall didn’t show any notable changes in values. PHS values of 0-6km shear also matched up fairly well with SPC Mesoanalysis at 19Z, and had values increasing to around 35-40 kts through the afternoon.
Below is the 19Z MUCAPE via the SPC Mesoanalysis page.
LightningCast right around 19Z showed the 10% probability contour still about 40 miles SSW of Billings at its closest point (below).
LightningCast right around 20Z showed the 10% probability contour still about 30-35 miles W-SW of Billings at its closest point (below).
Around 2045Z, the 10% prob. contour reached the DSS event(below), but overall activity continues to be slow to push NNE. The LightningCast Time Series is included to show the trend up to this point.
Fast forward to roughly an hour later (~2140Z), there’s been a bit of a jump in the LightningCast Probability/TimeSeries (below), with the DSS event now sitting with a roughly 35% probability of lightning in the next hour.
A few minutes later, another jump up in probability – up to around 50%. Below is an image that has the GLM FED (colored pixels) included with the radar, LightningCast, and ENI Total Lighting Plot.
You likely have already been talking with the DSS contact point, but this jump up in the last ~10 mins may warrant another update, conveying that there is an increasing probability of lightning occurring in the next 60 mins.
Not surprisingly, the LightningCast probabilities have continued to increase, also shown in the time series. Image is from 2220Z.
What’s the best way to pass along this information to the DSS contact point?
With this type of event, where it’s slow to move in (driven more by the upper forcing vs the somewhat random quicker-developing activity that can occur in high CAPE/low shear and other types of environments) and no significant changes in the overall environment across the area, perhaps you could wait until it’s closer to 50% or more before expressing greater concern for the threat of lightning. In those instances where activity may be quicker to develop/strengthen, it’s not out of the question that values closer to the 25% contour would warrant greater concern. No matter the overall environment, I do believe the addition of a shorter-term probability (lightning within 30 mins) would be beneficial.