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Thursday April 9, 2020

Assignment: Predict the snow depth at the end of the day (inches) for Bangor, ME (KBGR)

We haven't tried a snow forecast yet, and we're quickly running out of winter. So let's try forecasting Thursday's snow for Bangor, Maine. The measurement is the depth (inches) of snow on the ground at the end of the day. It looks like a tricky forecast, because there should be rain first, possibly changing to snow late in the day. The temperature is expected to be marginal, maybe in the 40's dropping into the 30's late. It would be a good idea to look around for snow forecasts, first on the National Weather Service page (look for the Forecast Discussion link at the bottom of the page!), and then maybe the Weather Channel, Weather Underground, etc.

Question: The NWS measures the snow depth at sites like Bangor, but they also measure the liquid equivalent (rain plus melted snow and ice). The average ratio of snow depth to the liquid equivalent is about 10 (10 inches of snow equals about 1 inch of liquid when melted), but it is varies a lot. Why is that?

What Happened?

Six inches of snow is pretty impressive for this time of year, and more than the NWS was expecting. The temperature dropped quickly into the mid- and low-30's, and it looks like it snowed very steadily through the evening and into the next morning. The density and texture of snow depends strongly on temperature and a couple of other things, so sometimes it's dry and powdery (higher ratio of snow depth to liquid depth, maybe 15 or more) and other times it's very wet (lower ratio, 5 or less). Here's a nice web page that talks about the snow to liquid equivalent issue.

Forecasts for Bangor, ME (KBGR)
Forecaster Snow depth, inches (error) Comment Day Score
OBSERVED 6 Snow FINAL.
Reference
PERSISTENCE (0)
MOS
GFS-MOS-06-DAY02 0 (-6) 1.6
NAM-MOS-12-DAY02 0 (-6) 1.6
GFS-MOS-12-DAY02 0 (-6) 1.6
GFS-MOS-00-DAY01 2.2 (-3.8) 2.1
GFS-MOS-06-DAY01 2.2 (-3.8) 2.1
GFS-MOS-12-DAY01 2.2 (-3.8) 2.1
GFS-MOS-00-DAY00 2.2 (-3.8) 2.1
NAM-MOS-00-DAY01 3.8 (-2.2) 2.5
GFS-MOS-18-DAY01 3.8 (-2.2) 2.5
GFS-MOS-18-DAY02 6.8 (0.8) 2.9
NAM-MOS-12-DAY01 6.8 (0.8) 2.9
NAM-MOS-00-DAY00 5.2 (-0.8) 2.9
StokesEarlyCollegeHigh-Mr.Price-SpringEarth/Env.Sciences
1. EmilyV15 5 (-1) 2.8
1. Jasper15 5 (-1) 2.8
3. Lizzie15 4 (-2) 2.6
4. Austin15 3 (-3) The snow will stack unlike the rain which must spread out first 2.3
4. T-Dawg15 3 (-3) 2.3
4. Shyann15 3 (-3) 2.3
7. Keith15 2.7 (-3.3) 2.3
7. Dorothy15 2.7 (-3.3) 2.3
9. Sara15 2.4 (-3.6) 2.2
9. Anna15 2.4 (-3.6) 2.2
11. Grace15 2.1 (-3.9) 2.1
11. Alex15 2.1 (-3.9) 2.1
11. Gus15 2.1 (-3.9) 2.1
14. Miles15 2 (-4) 2.1
15. Hannah15 1.9 (-4.1) 2.0
16. Eavenly15 1.5 (-4.5) 1.9
17. Joscelyn15 1.2 (-4.8) It's gonna snow 1.9
18. Shelby15 1 (-5) 1.8
18. Autumn15 1 (-5) 1.8
18. Josh15 1 (-5) Because water put together is just one big body and does not have any space between drops but with snow its crystals and allows some air between its like a collection of separate solids. 1.8
21. Django15 0 (-6) up isn't down, my guy? that's? 1.6
22. Elizabeth15 14.3 (8.3) 1.0
23. EmilyS15 31 (25) 0
Open
1. kendra15 2.2 (-3.8) 2.1