10-11 January 2011 Winter Storm: Key Points Very cold air mass plunged far south, making conditions in northern AL, GA, and SC conducive for snow Very dry air to the north over NC and VA prevented much of the precipitation from reaching the ground until Monday afternoon; heaviest amounts were to the south, which is climatologically unusual By the time the lower troposphere was sufficiently moist, dry air aloft was beginning to cut off dendrite formation; some moderate snow bands still formed across SC and NC, resulting in quick bursts of snow late Monday Dry air aloft and “warm” cloud tops, coupled with a moistened lower troposphere, resulted in persistent freezing drizzle Monday night into Tuesday morning Storm failed to strengthen off the Southeast coast; a likely culprit was the system upstream over the Plains, which may have robbed the east coast system of its energy

An unusual snowfall distribution…

00 UTC Monday

06 UTC Monday Strongly negative AO/NAO with the polar jet displaced far to the south Long-wave trough to the west with short-wave trough moving through the Deep South

12 UTC Monday Snow is reaching the ground in GA and SC by early Monday morning

Very dry air mass over mid-Atlantic, VA, and NC prevents snow from reaching the ground

12 UTC Monday

Blue line = 0 deg isotherm

00 UTC Monday: GSO Cold, dry column at GSO before event begins

00 UTC Monday: BMX Warm nose and FZRA at Birmingham early in the event

00 UTC Monday: FFC Narrow warm nose and sleet at Atlanta

15 UTC Monday

UTC Monday Dry air to the north eroding the leading edge of precipitation in central NC

18 UTC Monday

1815 UTC Monday Dry slot moving across the Deep South is cutting off moisture in the dendritic growth zone

2138 UTC Monday “Banded” structure to the precipitation across the Carolinas

21 UTC Monday Snow begins to reach the ground in central NC

2215 UTC Monday

00 UTC Tuesday

700 mb Southwesterly flow at 700mb helps warm up the low-levels

Dry air aloft (above 700 mb) beginning to starve the dendritic zone of moisture

06 UTC Tuesday Freezing drizzle overnight in central NC due lack of dendrites, “warm” cloud tops, and moist lower troposphere

12 UTC Tuesday: GSO

Did the upstream long- wave trough steal some of this storm’s energy???

UTC Tuesday 1 and 2 above correspond to the soundings on the next slides

1 Note the dramatic subsidence inversion and mb thickness values!

2