Figure 1. Special Weather Statement issued this morning by the Nome, Alaska, NWS office.
The METARs (see Figure 2) indicate the beginning and ending of the event. Several "special" METARs were issued that note the presence moderate snow and blowing snow concurrent with the lightning. The temperature was noted to be -2°C (28°F) during the thunderstorm.
Figure 2. Screenshot of METARs for Nome, Alaska, between 17:15 Z and 17:31 Z.
Figure 3. Upper air Skew T/Log P plot from Nome, Alaska, for February 24, 2015 (12 Z).
Just how rare of an occurrence is this? Surprisingly, it is not unprecedented. In fact there are 11 instances of thunderstorms in Nome with a temperature below freezing prior to today's occurrence. Figure 4 shows all of the hourly observations (1960-present) with snow and/or sub-freezing temperatures and a thunderstorm. Only 69 days in Nome have recorded a thunderstorm since 1960; the fact that 11 of those days were winter occurrences is remarkable. Even more amazing is that three instances occurred with a temperature of 2°F or colder!
Figure 4. Hourly observations from Nome, Alaska, that contain a thunderstorm and sub-freezing temperatures.