Transcript Winter Storms and Northeasters

Winter Storms and Northeasters
Robert E. Davis
Dept. of Environmental Sciences
University of Virginia
Email: [email protected]
Virginia Mitigation Summit
June 17, 2004
Nor’easters and Snowfall in Virginia
Nor’easters
Snow
Nor’eastergenerated
snowfall
Many Virginia snow events are not linked to nor’easters
WINTER STORM INGREDIENTS
H
Cold Air
Cold Air Damning
Damming
1. Sufficient cold air source
WINTER STORM INGREDIENTS
Moist Air
2. Sufficient moisture
Moist Air
WINTER STORM INGREDIENTS
winds
L
3. Lifting mechanism
(the “storm”)
WINTER STORM INGREDIENTS
H
Cold Air
L
Moist Air
TIMING IS EVERYTHING
H
Cold Air
L
*Arrival of storm does
not coincide with cold air
*Warm air from Atlantic
decreases vertical thickness
of cold air mass
TIMING IS EVERYTHING
L
L
*Forward speed too fast
*Low snow accumulations
WINTER STORM INGREDIENTS
L
L
L
*Track too far inland
*Not enough moisture
THE “SNOWMAKER” TRACK
*Ideal track for producing
snow in the Mid-Atlantic
Heaviest snow frequency
*
*
*
Storm Track
(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
Wave
Approach
Fetch
Storm
Center
IMPORTANCE OF STORM TRACK
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NOR’EASTER FORMATION REGIONS
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I
IV
II
V
III
Nor’easter Type
by Class
Most Class IV and V
storms form near the
Bahamas or Florida
NOR’EASTERS AND VIRGINIA SNOW
L
L
L
H
1. New England High
•Cold air source
•Slows forward motion of storm
L
2. Coastal storm
•Atlantic moisture
•Lifting mechanism
•Slow movement = more snow
•Slow movement = bigger waves
Most major snowstorms in
Virginia are caused by
large nor’easters
NOR’EASTER SEASONALITY
JET STREAM
1) Boundary between
warm, tropical and
cold, polar air masses
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2) Size and strength
vary seasonally
3) Linked to mid-latitude
storms at surface
4) Linked to storm
tracks
JANUARY
JULY
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IN WINTER, JET STREAM
1) EXPANDS
2) STRENGTHENS
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Mid-latitude storms derive their energy from the jet stream
MID-LATITUDE STORM FORMATION REGIONS
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JANUARY MIDLATITUDE STORM TRACKS
JULY MIDLATITUDE STORM TRACKS
PREFERRED WINTER STORM TRACKS
L
L
L
L
L
L
Continental Track
L
L
L
(After Hayden, 1981)
L
Coastal Track
“Snowmaker” track
(Knappenberger and Michaels, 1993)
Golfer’s track
H
ASH WEDNESDAY STORM
March, 1962
•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, 13 1993; 7 a.m. EST
“Storm of the
Century”
Surface weather
map
3/13/1993
7 p.m., EST
Mean Annual Snowfall
Record-Holding Snowfall Seasons
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EL NINO AND NOR’EASTERS (ALL STORMS)
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EL NINO AND NOR’EASTERS (STRONG STORMS)
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EL NINO AND VIRGINIA PRECIPITATION
EL NINO
LA NINA
EL NINO AND VIRGINIA TEMPERATURE
EL NINO
LA NINA
EL NINO AND VIRGINIA SNOWFALL
VIRGINIA SNOWFALL (INCHES)
35
El Nino
La Nina
30
25
20
15
10
5
0
-8
-6
-4
-2
0
JAN-MAR EL NINO STATUS
2
4
Winter Storms and Northeasters
Robert E. Davis
Dept. of Environmental Sciences
University of Virginia
Email: [email protected]
Virginia Mitigation Summit
June 17, 2004
Thanks to:
Chip Knappenberger
Jerry Stenger
Pat Michaels