Updraft: December 30, 2008 Archive

Water to snow

Posted at 7:09 AM on December 30, 2008 by Craig Edwards

Meteorologists are particularly challenged to accurately predict snow amounts well before the first flakes have fluttered down. Many factors are considered when assessing the environment for forecasting accumulating snow. Take the dynamic and synoptic meteorology classses in college and you'll find it is not as easy as it looks. But you can still try it at home.

One of the things we try to determine is the temperature in the snow growth area, between five thousand and ten thousand feet. Studies have shown that an ideal temperature in this region, for high quality snowflakes, is about five degrees.

We also try and determine the snow to water ratio that will be measured on the ground. A standard ratio is thrteen to one in our region. Last night's snowfall was about twenty to one. If we had received a quarter inch of moisture in the Twin Cities, it would have translated to about five inches of fresh snow.

Follow the snowfall observations throughout the day at the Chanhassen NOAA web site.

Snowfall reports...click on previous version for more reports

CE
naturesmessenger.com

Remarkable system

Posted at 4:46 PM on December 30, 2008 by Paul Huttner

Crash scene at Highway 52 and 494 in the southeast metro typifies another snowy commute.

It's getting a little old for metro commuters. Another rush hour with snow-slicked freeways is here. 2008 is going out with a flurry of snow systems here in Minnesota.

This latest system is remarkable in many ways.

1) It's been a prolific snow producer for much of central Minnesota into Wisconsin.
-Rush City has piled up 14.5" of new snow.
-Little Falls measures 14" of powder.
-Cambridge is shoveling 9.5" tonight.
-Hillman in Morrison County takes the cake with 15.7"!

Snowfall totals

2) This system had a sharp cutoff on the southern edge of the snowfall for most of the event. That's why we're seeing a big "snowfall gradient" over very short distances from north to south.

3) The sharp cutoff made for a high degree of forecast difficulty with this storm. The southern edge of lift or "upglide" that produces the right environment for producing snow was right over the metro last night and early today. That made it a tough call for us to pinpoint snow amounts in the metro. That's why we give a range. The state of the science often will not allow us to forecast snow amounts to the inch. If this system had tracked another 50 miles south, we'd be buried here in the metro.

I'll give us a "B" grade on forecasting this system. On the good side we locked onto the system well, there was no surprise it was going to snow. We also hit the highest amounts north of the metro. And the 2" to 4" forecast we put out for the metro, with 3" to 6"+ north of the metro was not bad. A little lower on the south side (Eden Prairie 1.6", Airport around an inch) and a bit higher on the north side. (Andover 4.8")

Snow was slow to get going in the metro last night and this morning, and we actually underestimated the prolific burst that produced over a foot in some places. Maybe we could get as high as a B+ with this system given the high degree of difficulty.

Can't wait for the next one!

PH