The RWFS (which uses a 10:1 ratio) predicted over 2 inches total of snow accumulation
(Fig. 10.47). This over-forecast may be attributable to two things. First, the forecast
called for snow an extra 7 - 10 hours longer than actually occurred. Second, the actual
snow:liquid ratio for the case was probably closer to 5:1 at these surface temperatures,
which would put the predicted total closer to 1-1.5 inches. Predicted snow depths,
applying both 10:1 and 5:1 ratios to the observations from the METAR and LAPS data
are also shown on this graph, resulting in 0.25 0.5 inches of snow.
SN Depth Comparison for Feb 20, 2004
3
AMW OB
RA
SN
2.5
2
1.5
1
AMW METAR OB (10:1)
0.5
AMW METAR OB (5:1)
AMW METAR w/woFSL (10:1)
AMW METAR w/woFSL (5:1)
AMW RWIS w/woFSL (10:1)
AMW RWIS w/woFSL (5:1)
0
0 2 4 6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18 20 22 0
Feb 20, 2004
Feb 21, 2004
Fig. 10.47. Snow depth (inches) time-series comparison of the Ames
METAR observations versus the RWFS forecast for both the METAR and
RWIS sites using a ratio of 5:1 and 10:1.
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