2022-06-19 EVENT: WY/MT/SD/ND

[JamesCaruso]

I looked only briefly at the situation on this day, but was surprised to see SPC calling for northeast surface winds in the outlooks, as I did not see this on any of the models I looked at. Neither did I see northeast winds observed on the evening surface map - yet this supercell appeared to strengthen, and SPC was still talking about north/northeast winds in the MSD. What am I missing? There is a gap in surface observations in the immediate vicinity of the storm, but looking at the obs that are available in the surrounding areas, it’s hard to see how there could have been north or northeast winds in the area of the storm or the area outlined by the MSD, unless there is some local geographical influence?

Based on storm reports, this storm apparently sustained itself into extreme northwestern SD, where clearly surface winds were northwesterly. I could somewhat understand that, as dewpoints were high, and combined with southerly winds at higher levels perhaps there was still adequate shear? This scenario has to be fairly unusual… But in any case the bigger mystery to me is the specific mention of north/northeast surface winds, which I simply fail to see…

Comments, explanations, insights welcome, because I never want to stop learning!

 

[Ethan Schisler]

I'm assuming it is related to the topography. Since we don't have any METAR data in that area to confirm for us, I'm guessing there is a narrow tongue stretching back into WY/MT with moisture and E/NE winds. I remember seeing on mesoanlysis, moisture pooling just to the north/northeast of that storm. Perhaps this is what is being indicated in their MD, I'm not 100% certain though. I do know with upslope events, easterly winds and even northeasterly winds aren't super uncommon, especially in a post-frontal environment in Eastern CO.

I do see the one METAR in South Dakota that appears due easterly, so I'm guessing to the north in the area we see the "void" of observations, there is probably E/NE winds in there if we did have that data, in addition to modestly higher moisture. Those are just my guesses based on what I've looked at.

 

[Jesse Risley]

I went and looped a 12-hour surface map archive across that region starting late morning and continuing through the evening on that day. There was in fact northerly surface flow behind the front in nearby observation stations to the north and west of that region. I attached one image to this post.

There definitely is terrain enhancement across that region and studies have been done on the effect of the downstream Pine Ridge and surface flow on supercell and storm development (I can link you to a paper on that if you want it), but as near as I can tell as the front sagged south and had passed to the south of that immediate area by the time the MD came out surface flow became more northerly but also vacillated throughout the day in response to an associated area of low pressure that was just off to the east over in Western North Dakota by late evening (that appears to be impacting just off to the northeast). The eastward progression and depth of the low along with the front seems to be the biggest factors impacting surface flow throughout the day as I loop the surface map.

 

[GPhillips]

Here's a 5 PM CDT weather plot with all available ob networks plotted. The MCD came out at 552 PM CDT and likely would have been based on surface analyses/plots from 5 PM. Northerly/North-northwesterly describe the winds near and just north of the storm. Below is a plot two hours later at 7 PM. The winds over northwest South Dakota had veered to northerly as well.