What Is A “Bomb Cyclone”?

Discussion: Traditionally, a “bomb cyclone” is a low-pressure system deepening (strengthening) by more than 24 MB over a 24-hour period. The definition usually applies to middle/upper middle latitude. Although a “bomb cyclone” is not a tropical cyclone, these systems can reach category-1 hurricane force on the Saffir Simpson Scale. The NWS Boston Forecast Office mentioned potential deepening by 40 MB over a 24-hour period of tonight into Saturday for this weekend’s Northeast U.S. Blizzard qualifying this storm as a “bomb cyclone”. Minimum surface pressure should dip to the 965 MB just east of New England late tomorrow (Fig. 1) certainly qualifying this storm as having hurricane wind speed intensity. A Hurricane Force Wind Warning is in effect to the east of the New England and northern Mid-Atlantic shoreline.

The NWS Boston Forecast Office has updated their southern New England snowfall forecast (Fig. 2) which includes up to two feet well inland and revised higher to 24-30 in. on the “South Shore”. Wind gusts of 50-60 mph (possibly higher in favored areas) will cause fantastic blowing and drifting of snow likely exceeding 6 feet. Peak wind is around midday tomorrow for southern New England coastal areas with wind speeds sustained in the 30-40 mph range with gusts to 70 mph (Fig. 3). This type of wind may ease only slightly afternoon and evening. The maximum wind in the Mid-Atlantic coastal region is tomorrow morning around 9AM with sustained wind in the 25-35 mph range at the coast and gusts to 50-60 mph (Fig. 4).

This storm is very cold…incoming arctic air coupled with severe wind chill. At the coast, astronomical high tide running 1-2 feet above normal coupled with wind previously described leads to flooding and beach erosion. Snowfall rates can be 3-4 in. per hour. Coupled with wind, visibility is near zero for this storm during heavy snow.

Fig. 1: The ECM ENS maintains a snowy pattern in the Black Sea region to Turkey

Fig. 2: Latest NWS Boston snowfall forecast for the Jan. 28-30 storm.

Fig. 3: Peak wind speeds for the coast of southeast New England.

Fig. 4: Peak wind speeds for the coast of the Mid-Atlantic States.