First Severe Winter Storm Ends Pleasant December Weather

Sunday was marked by the passage of a severe, rapidly developing frontal system. A wave of low pressure formed along a weak cold front that inched slowly south-southeastwards from Atlantic Canada. It was enhanced by a stream of faster jet stream winds and tropical Atlantic Moisture that was already in place from days of southerly winds in the area.

Saturday, in Bermuda, the morning started out overcast and slightly cool. The sun then broke through the clouds and allowed for a sunny, warm day with light winds. Clouds moved back over in the evening and overnight as the weak coldfront approached. However, the wave of low pressure was still developing.and it stalled the cold front to the north of Bermuda for a while on Sunday. It allowed the temperature to reach 74.3F around 10:00am rivalling a record high of 76F (1974). I recorded a high temperature of 73.7F for the day. Then a band of moderate to heavy showers with some squally gusts passed through immediately dropping temperatures to the mid 60s.   The airport observed a gust of 39mph with this squall line.

Radar Image of the showers ahead of the cold front

We continued to be in the Southerly flow for at least an hour after the first rain bands of the cold front passed. In Bermuda it isn’t often that you can observe a distinct frontal passage due to the moderating effects of the warm Atlantic ocean on the cold airmasses that follow cold fronts off of the American and Canadian coasts. However, this was not the case with this storm because it rapidly deepened along the front and was able to drag more cold air down; counteracting, to an extent, the moderating oceanic effects. Bermuda weather service did observe frontal passage (FROPA) at 11:35am when there was a 90degree wind shift from the west-southwest to the north-northwest.

However, although the surface front passed at 11:35am, the winds had shifted to a northerly direction, and temperatures had dropped at least 10F; the mid-upper level cold front had not yet passed and winds at that level were still from a southerly direction. Therefore only patchy areas of light-moderate rain were able to develop. By 7:30pm the mid-upper level coldfront passed and the troughiness that had developed behind it was able to bring fast moving squally, but scattered showers to the island.

Satellite Image of the Storm

Gales developed sharply in this post frontal troughiness and gusts were measured at 86mph (commissioner’s point), 52mph (Airport), and 45mph (my PWS – Devonshire). Overnight, the upper cold pocket was able to interact with the now slowly deepening surface trough to generate hail producing showers, many of them missed the island but most parts of the island experienced at least one of them.

As the humidities dropped behind the cold front, the showers were able to cool the air through evaporation and temperatures dropped to 55.9F ; just shy of a record low of 54F (1987). My personal weather station recorded a low temperature of 52.2F.  The gales were able to due considerable tree damage because the trees were still heavily in leaf as there hadn’t been any high winds yet.  The showers and gales decreased in intensity as the storm center moved away Monday leaving rough northerly swells behind; up to 5 feet inside the reef. The next day saw a tied record low of 54F and hail in the extreme early morning.


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