The precipitation type was an important parameter for this case. For forecasts without
the FSL models in the mix the predicted precipitation type went briefly from snow to
freezing drizzle before the time of observed rain and then back to snow around the time
of the actual snow (Fig. 10.45). When the FSL models were included, the precipitation
type was initially expected to be rain and then freezing rain for a few hours. At about the
time that the observations changed from rain to snow, the forecast precipitation type also
changed over to snow and remained so for the rest of the predicted event. It is again seen
that the snow prediction lasted much longer then the observations indicated for both with
and without FSL models. As was mentioned above, the NWS forecast also had a mix of
precipitation but the timing of the phase change was also hard to identify.
PType Comparison for Feb 20, 2004
7
AMW OB
RA
SN
FZDZ 6
FZRA 5
4
3
2
SN
RA/SN
AMW METAR OB
RWIS WFSL
1
RA
RWIS woFSL
Seg 3 wFSL
Seg 3 woFSL
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
Time (UTC)
Fig. 10.45. Precipitation type comparison between the Ames METAR
observations and the RWFS forecasts of type both with and without FSL at
the RWIS site and Segment 3 (along I-35, north of Ames).
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