La Nina Storm Strikes The East

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Now that tropical cyclone season is winding down we enter the next persistent issue for meteorological winter 2020-21 which is La Nina storms. La Nina storms produce three types of high impact weather certainly evident in the SUN/MON forecast.

Highlight: La Nina Storm Batters East.

Fig. 1-4: NOAA/WPC depiction of an East U.S. La Nina storm to start the week.

La Nina Storm 1: Now that tropical cyclone season is winding down we enter the next persistent issue for meteorological winter 2020-21 which is La Nina storms. La Nina storms produce three types of high impact weather certainly evident in the SUN/MON forecast. First, severe thunderstorms affect the Southeast States ahead of the cold front which extends south from the intensifying storm center. Second, La Nina storms tends to be “inside runners” so the East is faced with heavy rain and high wind. Third, the strong upper trough invites cold air from Canada into the back side of the storm and the Ohio Valley/Great Lakes region sits in the heavy snow zone with these storms. The Ohio Valley snow could extend as far south as northern Georgia and allows cold north wind to push anomalous chill south to the Gulf Coast and into the Florida Peninsula. The storm-induced chill moderates crossing the Appalachians into the East/Northeast States. So…expect severe storms today/tonight from southeast Louisiana to coastal Carolinas, heavy rain from the Southeast U.S. to the Mid-Atlantic States and developing heavy snows in the Ohio Valley (Fig. 1-2). High wind shifts from offshore across New England later tomorrow along with the heavy rain (Fig. 3). The storm is slow to wind down on Tuesday as New England stays stormy and heavy snows linger in Ohio (Fig. 4). Jackpot rainfall? Roanoke to Washington/Baltimore to Connecticut where 1-3 in. of rain is possible. Jackpot snowfall? 8-18 in. of snow is forecast in the Cleveland to Erie stretch (Fig. 5-6). Maximum wind gusts? Long Island and southeast New England tomorrow evening…25-40 mph sustained with gusts 55-65 mph.

Fig. 5-6: ECMWF 48-hour snowfall forecast valid to 7AM EST Wednesday.

Next storm? Models are in disagreement however ECM indicates a second storm moving out of the Gulf of Mexico next weekend and then up the East Coast to just off the New England coast Sunday evening December 6th (Fig. 7). The GFS (model) takes the storm out to sea well to the south. The ECM forecast also indicates a modified arctic air mass shifting into the Upper Midwest/Midwest States to start next week. Support for this storm (indicated by presence of negative phase North Atlantic oscillation) is not great for the storm itself but is improving for the following cold air mass.

Fig. 7: ECM depiction of a potential Northeast coastal storm next weekend.