A Major East Coast Storm Followed by Cold East U.S. Medium-range Forecast

Highlight: East Coast storm brings heavy snow, ice, heavy rain, high wind and coastal flooding. Medium-range forecasts trend colder.

Fig. 1: Current NOAA/NWS weather watch, warning and advisories.

Storm discussion: A major storm moves north-northeast through the Atlantic Seaboard later today and Monday (Fig. 1). The storm is unusually intense (976 MB in northern New Hampshire by tomorrow evening) due to entrainment of moisture off the somewhat warmer than normal ocean surface of the Gulf of Mexico and western North Atlantic and the subsequent clash from arctic air from Quebec. A series of major hazards to the East U.S. is caused by this storm.

First, is the period of high wind as the storm approaches the Mid-Atlantic and Northeast U.S. Coast. East to southeast wind reaches >30-35 mph sustained with gusts routinely in the 50-60 mph range for 6-8 hours. This causes snow, sleet and some freezing rain during the first few hours of the storm to flip to all rain due to temperatures rises of 10-20F. Rainfall amount is in the 1-2 in. range along the Northeast Corridor and coupled with snowmelt leads to a flood risk. However, the largest flood risk is at the beach where storm surges in the 2-3-foot range are likely coupled with high waves that lead to significant coastal flooding and beach erosion. Fortunately, the storm is moving quick-enough so that the risk is 6-8 hours before wind turns south southwest (blowing offshore) after the storm has passed. The offshore wind will ease coastal water rise and flooding.

The high wind is an issue on approach of the storm for the Northeast Corridor tonight and trailing the storm as wind flips from east to southwest and west. The entire East has high wind issues on Monday after the storm has passed. Strong southwest to west wind has already developed across Georgia and Florida.

Fig. 2: ECM projects today/tomorrow storm profile.

Second, precipitation type featuring heavy freezing rain in the central South Carolina zone is a major hazard. Ice accretion over 0.5 in. occurs in this zone weighing down trees and power lines. There is limited warming for this zone before gusty cold westerlies generate tonight. Freezing rain also reaches the western half of North Carolina. During of any icing further north is too limited to allow for accretion.

Third, weighty snow and sleet mixed. Well inland snow will turn to a mix and 8:1 rain to snow ratio will lead to heavy accumulations on power lines and trees increasing the risk of significant loss of power. Heavy sleet will occur for a period of several hours from east-central North Carolina to east-central Virginia to Baltimore and northward through eastern Pennsylvania to west/central New England. Power outage risk increases due to the heavy sleet. Snowfall amount remains in the 6-20 in. range but is pushed slightly westward (Fig. 2).

A cold regime to follow: The weekend trend for the medium-range is colder. The 6-10-day/11-15-day forecasts are likely prohibitively cold for the East U.S. (Fig. 3-4) occurring at the peak cold of winter. During this time additional Northeast Corridor storms producing excessive snow away from the coast are expected. The gas population weight HDD forecast using a consensus of all models projects a frigid 251 HDD for next week (Fig. 5). The consensus forecast is colder than indicated Friday morning.

Fig. 3-4: Mega-cluster most likely temperature anomalies for the medium-range across the U.S.

Fig. 5: Using all models, the gas population weight HDD consensus forecast compared with 48 hours ago and the 30-year/10-year normal for the U.S. is indicated.