Drought monitor improves for the Black Hills region

Two main themes that will influence our fall and early winter weather will be our severe to extreme drought conditions and a high likelihood of La Niña conditions in the Pacific Ocean

Doing a long range forecast for the Black Hills is easier than a short range forecast.

If you need to read that again slowly, I understand.

The Northern Plains and the front range are heavily influenced by overall global patterns as opposed to somewhere like San Francisco or New Orleans, which can have local features overcome global trends more easily. A good example is counting on a summer thunderstorm at 2 p.m. every single day in New Orleans, while morning fog in San Francisco is almost a guarantee, barring large-scale systems.

In the Black Hills, there is no guarantee of an afternoon thunderstorm in the summer or an overnight frost in the winter – it’s all heavily influenced by jet stream dynamics and lumbering air masses that cross our area like a congested metropolitan intersection. We can look through the history books and see global climate patterns and what their influence on our “weather traffic” has historically been.

This year, two main themes will be our severe to extreme drought conditions and a high likelihood of La Niña conditions in the Pacific Ocean.

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The latest drought monitor through October 21 showcases steady improvements thanks to our October winter storm. We can still recognize the glaring deficits we see in precipitation, particularly north and west of the Black Hills. This data is not perfect; there are many ranchers and producers east of Rapid City who claim to be almost 8-12” below normal, while Rapid City only boasts a deficit of 1”-2”.

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Precipitation from October 6, 2020 to October 6, 2021 focused mainly on the Central and Southern Black Hills. Far eastern South Dakota and eastern Nebraska did very well, while northeast Wyoming and north central/northwestern South Dakota sees some glaring differences. October storm added to these totals, but aren’t pictured in the above map.

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Much of the above average precipitation you see through last winter, spring, and summer on this map in the Black Hills was due to the March blizzard of 2021, dumping over two feet of heavy, wet snow while leaving little to no precipitation in northeastern Wyoming and northwestern South Dakota. Even six months later – this event has shaped the entire region’s water table.

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Can current drought impact future weather?

The short answer is yes – and it lies in the simple measurement of much-ignored dew points and soil moisture.

As a note, dew point is the actual measurement of water in the atmosphere – not relative humidity. RH is how close water vapor is to condensing from a gas to a liquid (tiny water droplets).

Most Pacific systems that survive the journey across the inter-mountain west bring little moisture, it gets wrung out like a towel by the Rocky Mountains. Most of this moisture that survives the journey is at the mid-levels (thousands of feet up) and not at the surface. Add dry surface conditions, and you’re looking at a recipe for dry thunderstorms and passing virga (evaporating rain). The journey from cloud to ground is too far, and the dry surface conditions evaporate rain before it can make it.

This can cause dry feedback loops at the local level that perpetuate dry conditions. One valley has 45° dew points while the next valley has 55° dew points. Which valley is more likely to receive rainfall out of the same storm? The one with less dry conditions – so how to you break drought?

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Figure 1 – La Nina, NOAA

Larger, broader systems must impose their will on local conditions – so you need global patterns on your side.

La Niña could be the climatological phenomenon that helps break that cycle. Cold waters in the central Pacific favor patterns that push blocking warm air masses of high pressure into the Gulf of Alaska. This can dislodge areas of colder weather and force it south. This turns the jet stream into a roller coaster for the West coast and the front range. When a trough is forced down into the West, it can bring up Gulf moisture from the south.

Roller coaster jet stream = lots of passing systems and fronts.

Traditionally, La Niña’s have brought colder and wetter winters to the northern plains, so that bodes well for those hoping for a little relief. The bad news is last winter was also technically a La Niña season, and it was one of the warmer and drier winters we saw. What we have going for us this year, is the signature is stronger and more pronounced.

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So far, the 90-day outlook through December shows that any chance of La Niña imposing colder than normal conditions on the Northern Plains may have to wait for Jan-Feb-March to really kick in. You’ll of course have variations as individual systems knock down the temperature for a day or two, but to support and overall colder pattern over weeks at a time you need robust support from global weather patterns.

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The same could be said for the 90-day outlook for precipitation. Barring October 14-16, our overall dry conditions may continue through Thanksgiving before more consistent support for south-to-north moving systems can bring significant moisture to the area. Once again, the Gulf of Mexico supplies most of our moisture in any given year – so we need multiple dives of cold, dry Canadian air into the west, to facilitate the yin-yang of warm, moist air to move upward into the Northern Plains. As soon as we can observe consistent signatures of warm areas of high pressure pushing into the Gulf of Alaska, we can have more confidence that the overall dry pattern has at the very least been stalled.

A bitterly cold, wet winter is the bet this particular meteorologist would make. Historical La Niña years have traditionally brought such conditions to the Northern Plains – and half of climatology and meteorology is being able to see patterns and forecasting based upon those patterns.

It may take a few months to get the La Niña train going, but I believe once the cold train gets moving it’ll be hard to stop.

Stay safe out there,

Brant

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