Winter Storms and Northeasters Robert E. Davis University of Virginia Dept. of Environmental Sciences Virginia Mitigation Summit June 17, 2004

Nor’easters and Snowfall in Virginia Nor’easters Snow Nor’easter- generated snowfall Many Virginia snow events are not linked to nor’easters

WINTER STORM INGREDIENTS Cold Air Cold Air Damming 1. Sufficient cold air source H Cold Air Damning

WINTER STORM INGREDIENTS 2. Sufficient moisture Moist Air

WINTER STORM INGREDIENTS 3. Lifting mechanism (the “storm”) L winds

WINTER STORM INGREDIENTS Cold Air H L Moist Air

TIMING IS EVERYTHING Cold Air H L *Arrival of storm does not coincide with cold air *Warm air from Atlantic decreases vertical thickness of cold air mass

L L *Forward speed too fast *Low snow accumulations TIMING IS EVERYTHING

L L L *Track too far inland *Not enough moisture WINTER STORM INGREDIENTS

THE “SNOWMAKER” TRACK *Ideal track for producing snow in the Mid-Atlantic * * * Storm Track Heaviest snow frequency (Knappenberger and Michaels, 1993)

NOR’EASTERS L “A cyclonic storm of the east coast of North America, so called because the winds over the coastal area are from the northeast” (Glossary of Meteorology) *New England *gale force winds *winter *high waves *beach erosion

“Storms”

FACTORS THAT DETERMINE WAVE HEIGHTS IN DEEP WATER *wind speed *wind duration *fetch Wave height climatologies can be “hindcasted” from historical weather records

Storm Center Wave Approach Fetch

IMPORTANCE OF STORM TRACK

NOR’EASTER FORMATION REGIONS

Most Class IV and V storms form near the Bahamas or Florida Nor’easter Type by Class V IV I II III

NOR’EASTERS AND VIRGINIA SNOW H 1. New England High Cold air source Slows forward motion of storm Most major snowstorms in Virginia are caused by large nor’easters L L L L 2. Coastal storm Atlantic moisture Lifting mechanism Slow movement = more snow Slow movement = bigger waves

NOR’EASTER SEASONALITY

1) Boundary between warm, tropical and cold, polar air masses 2) Size and strength vary seasonally 3) Linked to mid-latitude storms at surface 4) Linked to storm tracks JET STREAM

JANUARY JULY IN WINTER, JET STREAM 1) EXPANDS 2) STRENGTHENS

Mid-latitude storms derive their energy from the jet stream

MID-LATITUDE STORM FORMATION REGIONS

JANUARY MIDLATITUDE STORM TRACKS

JULY MIDLATITUDE STORM TRACKS

PREFERRED WINTER STORM TRACKS L L L L L L L L L L Continental Track Coastal Track (After Hayden, 1981)

(Knappenberger and Michaels, 1993) “Snowmaker” track Golfer’s track

ASH WEDNESDAY STORM March, 1962 H Strong high to north Storm track off coast (Bahamas Low) Slow-moving Strong northeast winds to the north of storm Long fetch, strong winds from same direction for long duration

ASH WEDNESDAY STORM, MARCH, 1962 Snowfall (inches)

“STORM OF THE CENTURY” March, ; 7 a.m. EST

“Storm of the Century” Surface weather map 3/13/ p.m., EST

Mean Annual Snowfall

Record-Holding Snowfall Seasons

EL NINO AND NOR’EASTERS (ALL STORMS)

EL NINO AND NOR’EASTERS (STRONG STORMS)

EL NINO AND VIRGINIA PRECIPITATION EL NINO LA NINA

EL NINO AND VIRGINIA TEMPERATURE EL NINO LA NINA

VIRGINIA SNOWFALL (INCHES) JAN-MAR EL NINO STATUS El Nino La Nina EL NINO AND VIRGINIA SNOWFALL

Winter Storms and Northeasters Robert E. Davis University of Virginia Dept. of Environmental Sciences Virginia Mitigation Summit June 17, 2004 Thanks to: Chip Knappenberger Jerry Stenger Pat Michaels