We started November 2019 bitterly cold, then winter 2019-2020 was mild and void of meaningful snow in D.C. Fast forward to Spring 2020 and temperatures in April were well below normal. We aren’t out of the woods yet as more record-shattering cold is coming for the upcoming Mother’s Day Weekend. Frost and Freeze Advisories may be issued this weekend and several storms will likely bring accumulating snows to the mountains from West Virginia to northern New England.
The image below (courtesy Pivotal Weather) shows the 500mb height anomalies. 500 mb height anomalies show where troughs and ridges are located in the atmosphere (a river of air). Red colors indicate ridging (blocking) and blue/purple colors indicate where the atmosphere is much thinner due to the presence of a very deep trough of low pressure. *Notice towards the end of the image below how the dark reds build across Greenland and northern Canada (indicative of blocking). Blocking allows the jet stream to buckle south and for the polar vortex to become dislodged southward into the lower 48. Bottom line – don’t put away your winter coats!
The dark blue and purple colors diving southeast across the Great Lakes, Mid-Atlantic and New England are indicative of a piece of the polar vortex breaking free from the arctic and a deep trough (dip in the jet stream) getting cut off below blocking over Greenland. If this pattern had materialized during the Winter we would have been digging out from feet of snow. For the upcoming weekend this pattern will bring temperatures down to 30 degrees below average! Pretty impressive for early May! So how cold will it get?