An “omega” blocking pattern in the upper atmosphere across Canada will play a major role in the unfolding scenario for early next week. One climate index that we follow that gives an indication as to the strength of the blocking pattern is the Arctic Oscillation (AO). The AO index measures the difference in relative pressures between the Arctic and mid-latitudes and it plummeted yesterday to historically low values (-5.6) and it may even break a record with today’s reading.
Looking ahead to early next week, a “primary” low pressure system will head towards the Ohio Valley on Sunday after dumping heavy snow on the southern Rockies and central Plains, but as a result of the atmospheric roadblock that this system will encounter, the low will grind to a halt and transfer its energy to a developing “secondary” Mid-Atlantic coastal low. That coastal low will spread precipitation into the I-95 corridor from DC-to-Philly-to-NYC later Sunday into Monday and, while some of it will likely be in the form of rain, accumulating snow is also a real threat given this type of pattern; especially, in the northern and western suburbs and in higher elevation locations. Yesterday, we suggested the possibility that the GFS model run would shift somewhat in its forecast for the northward extent of the "primary" low pressure system and indeed the latest 12Z model run has made a change from 24 hours ago. The “primary” low is now forecasted to reach only as far north as West Virginia as compared to the previously somewhat unrealistic location way up in northwestern Pennsylvania. This seemingly subtle shift makes an important difference in parts of the Mid-Atlantic with respect to precipitation type as it yields a slightly colder solution which is critical given the expected marginally cold conditions. The blocking pattern across Canada may prevent the coastal low from riding up the New England coastline so, as of now, significant precipitation is more of a threat for DC, Philly and NYC as compared to Boston and Portland (but still some time for that kind of detail to change).
On another note, for those interested in viewing the cherry blossoms in DC, given the expected continuing cold pattern, it looks like the peak may not occur until the 1st week of April. Last year, the peak occurred around March 20th in a month that was far different than this year and much warmer than normal.
Finally, here are some interesting snowfall amounts for this winter season (up till now) for many cities with New England leading the way:
Worcester, MA 108.9” Portland, ME 97.8” Syracuse, NY 96.5” Erie, PA 94.1" Gray, ME 92.3” Concord, NH 83.2” Deluth, MN 78.3" Flagstaff, AZ 68.3" Madison, WI 66.9" Binghamton, NY 66.5” Bridgeport, CT 64.3” Boston, MA 63.1” Hartford, CT 56.9” Buffalo, NY 55.6" Denver, CO 46.9" Islip, LI NY 46.5” Providence, RI 46.3” Scranton, PA 33.6” Chicago, IL (O'hare) 29.9" Newark, NJ 29.5” Central Park, NY 26.1” JFK Airport, NY 17.6” Atlantic City, NJ 12.3" Philly Airport, PA 7.2” BWI Airport, MD 4.8" Reagan National, DC 1.7”