Thunder Snow in Nome

This morning the National Weather Service noted the occurrence two lightning strikes concurrent with snow in Nome – thunder snow. This is quite the event. Figure 1 shows the text of the Special Weather Statement that was issued by the NWS office in Nome. Since the event was observed by NWS personnel, we assume that the report is valid. Unfortunately the two closest lightning detectors to Nome are both non-operational at the moment so we cannot tell how widespread the event was.

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.

Thunder snow requires an unusual set of atmospheric occurrence to come together at just the right time. I am not a forecaster and am not qualified to provide context on the specific atmospheric dynamics at the time. However, for those out there more qualified than I am, here is the 12 Z (3 a.m.) upper air sounding from Nome this morning.

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.