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Wednesday April 4, 2018

Assignment: Predict the 24 hr minimum temperature (deg F) for Aberdeen, SD (KABR)

Tuesday morning's NWS forecast discussion for Aberdeen, South Dakota says "Our cold, wintry April continues. With highs in the upper teens to 20s, temperatures [are] 25 to 30 degrees below normal." The forecasts for Wednesday morning's low temperature go as low as 0 F, probably depending on cloud cover and wind speeds. Let's predict Aberdeen's Tmin and see if they reach 0. Aberdeen is in the northeast corner of South Dakota and is the third-largest city in the state. It's also the home of the first motel in the Super 8 motel chain. The name Super 8 came from the price they initially charged -- $8.88/night!

Question: The NWS discussion also says this: "An additional 1 to 5 inches of snow will be possible today, with the highest amounts mainly southwest of Pierre, and across our southeast counties along the Coteau De Prairies. Expecting SLRs of around 15-18:1, with some reduction possible due to the gusty winds." What do you think the abbreviation "SLR" means? Can you make a guess?

What Happened?

The temperature in Aberdeen really plunged after nightfall, dropping to -6 F, much lower than the MOS forecasts. Completely clear skies were favorable for radiative cooling, but the winds didn't die down, so it's a little surprising that it got that cold.

I think that SLR here refers to "Snow-Liquid Ratio", the ratio of the depth of snow to the depth of the melted liquid. The average ratio is about 10-to-1, but with heavy wet snow near 32 F it can be much lower, and with cold, dry conditions it can be a lot higher.

Forecasts for Aberdeen, SD (KABR)
Forecaster Tmin, deg F (error) Comment Day Score