Transcript Lake Superior

Lake Superior
North Shore Climate
Jim Zandlo
State Climatology Office
DNR-Waters 2006
Superior Climate
• 2005-06 snow season
• Dry summer, low lake
Superior Climate
• 2005-06 snow season
– More-or-less ‘normal’ precipitation
• spring runoff was (probably) more-or-less ‘normal’
– Snowfall pattern very similar to 4-year
SnowRules! result
– climate.umn.edu/SnowRules then
click on 2005-06 map
A slow start in NE (again) …
Snowfall Dec 13-19, 2005
… right past ‘normal’ snow depth
Snowfall Nov 2005 – Apr 2006
Grand Marais
Wolf Ridge
Grand Marais
Wolf Ridge
Two Harbors
Two Harbors
Snowfall
Four season average
2002-06
Superior Climate
• 2005-06 snow season
– Snowfall transect updated
• Fraction of median (was fraction of max)
• Log-of-distance spreads out values close to
Lake Superior
– climate.umn.edu/SnowRules then
click on 2005-06 map
Superior Climate
• 2005-06 snow season
• Dry summer
– Low Lake Superior
– Basic hydrology
• GLERL time series
Superior Climate
• 2005-06 snow season
• Dry summer
– Near record low water levels (1925-26)
on Lake Superior
– Basic hydrology
• Summer is primary recharge period for
Lake Superior
• GLERL time series
• What happens next?
Lake Level:
A range of almost 4 feet in the
observational record.
Basic Lake Hydrology
Lake level =
old lake level
+ precipitation on lake
+ runoff from surrounding land (flow in)
- lake evaporation
- flow out at outlet (Sault Saint Marie, MI)
+/- groundwater flow
Geography and General Hydrology
- large,
‘state-sized’ watershed
- ‘narrow’ along American shore
Water for runoff, cisterns
Water coming in …
Runoff 37%
Diversion 4%
Deposition
0.2%
Evaporation 43%
Precipitation 59%
on lake
St. Mary’s River 57%
…must go out
(most of the time)
Water coming in …
Runoff 1.8 ft
Runoff 1.7 ft
Precipitation 3.1 ft
Diversion 0.2 ft
Deposition
0.2%
Precipitation 2.7 ft
…varies
Year ending 11/1985
had 10% more
water
Runoff 1.1 ft
Precipitation 2.6 ft
Year ending Feb
2001 had 15% less
water
Water coming in …
Runoff 1.8 ft
Runoff 1.7 ft
Precipitation 3.1 ft
Diversion 0.2 ft
Deposition
0.2%
Precipitation 2.7 ft
…varies
Year ending 11/1985
had 10% more
water
Runoff 1.1 ft
Precipitation 2.6 ft
Year ending Feb
2001 had 15% less
water
Water coming in …
Runoff 1.8 ft
Runoff 1.7 ft
Precipitation 3.1 ft
Diversion 0.2 ft
Deposition
0.2%
Precipitation 2.7 ft
…varies
Year ending 11/1985
had 10% more
water
Runoff 1.1 ft
Precipitation 2.6 ft
Year ending Feb
2001 had 15% less
water
Superior Climate
Future developments?
(What happens next?)
Lake Superior evaporation …
Lake Superior evaporation …
is not the same as evapotranspiration
from nearby land surfaces
NOAA Buoys
-meteorological parameters
-sea measurement
-wave info
-water temperature
-
Lake Evaporation equation
• Evaporation = factor * D
‘factor’ varies with weather, surface
conditions, etc.
‘D’ is the difference in vapor pressure
between two different air masses
• If this year’s atmospheric humidity was
essentially ‘normal’ (don’t know yet) then
using the above equation, evap would
have been about 0.5 foot more than
‘normal’ this Aug-Oct.
Lake Evaporation equation
• September water at
9+°F ’above normal’ has cooled to a little
more than 5+°F by Oct 23. The water will
tend toward 32°F (and be ‘more normal’) as
winter progresses.
• If water temperature becomes ‘normal’ by midwinter, an additional
0.2 feet or more than ‘normal’ can be
expected to evaporate from the lake this winter.
Where will it actually end up?
Lake Level:
A range of almost 4 feet in the
observational record.
Winter 2006-07 Outlook
(a strong ‘el nino’ influence)
Let it snow!
Varley
Lake Superior
North Shore Climate
(thermochrons)
Jim Zandlo
State Climatology Office
DNR-Waters 2006
Thermochrons, transects
Thermochrons, the dime sized devices that measure and store thousands
of temperatures, are being used throughout the SnowRules! study area to
gather temperatures where the snow falls, namely on snowboards. They
are also being used to get air and water temperatures at a few other
locations. See the data at climate.umn.edu/SnowRules
f
° F at 5/28/2006 12:00
Let it snow!
Let it snow!
Superior Climate
• 2005-06 snow season
• Dry summer
– Near record low water levels (1925-26)
on Lake Superior
– Basic hydrology
• Summer is primary recharge period for
Lake Superior
• GLERL time series
• What happens next?
Let it snow!
Lake Level:
A range of almost 4 feet in the
observational record.
Superior Climate
• Geography and Hydrology
• Summarizing the observations
–
–
–
–
–
–
Normal Temperature
Satellite-based measurements
Is it ‘elevation’ or ‘the lake’
Normal Precipitation
Snowfall patterns
Temperature versus snow
Great Lakes Hydrology (climate)
• Basin maps: limited detail
• Balance of incoming/outgoing
– Superior evaporation smaller fraction of
precipitation than other great lakes
• Lake levels are ‘integrator’
Cold!
Cool
Dry
Evapo-transpiration
Evapotranspiration
Runoff
Lake Level:
A range of almost 4 feet in the
observational record.
Hydrology is ‘forced’ by climate
• How do patterns arise?
– ‘weather patterns’
– cool/warm water nearby
– topography
• (Water flows downhill)
• topo temp evap runoff
– All the above interacting (!)
• What do patterns of ‘climate’
variables look like?
Wind – winter transect
Hibbing
Grand Marais airport
Grand Marais shore
• Inland: mostly N-NW or S-SW
• Shore: strong tendency to ‘follow’
• Can transport air masses across the
shoreline
Wind – winter along shore
Two Harbors
Silver Bay
Grand Marais shore
• ‘Everywhere’ along shore has strong
tendency for ‘along shore’ winds in winter
Wind – seasons at Grand Marais
Tendency to be ‘along shore’ less in summer
Air moisture (air mass)
Normal Temperature
winter(DJF)
spring(MAM)
summer(JJA)
fall(SON)
• Biggest near shore influences near equinoxes
– Land near seasonal extremes
– Lake ‘lags’ land by a month or two
• Detail limited by 25-mile NWS observer spacing
Satellite-based ice observations
• Most of Minnesota
averages less than
2 months.
• Much of north
shore not until Feb
• ‘ice out’ by early to
mid-March
20 years of
buoy data at
red circle.
No midwinter buoy
data is
available.
Commonly open water in mid-winter means a
large wet surface near 32 degrees is often near
the north shore anytime during winter.
Land versus ‘sea’
Two Harbors and
Grand Marais
temps ‘buoyed
up’ in winter,
‘anchored’ to
lower values in
summer.
Water maximum
lags land
maximum.
Land versus ‘sea’
Shore virtually
identical in
winter to MSP
150 miles south!
At Babbitt about
6 F cooler than
MSP year-round.
Temperature is also affected by elevation. Some of the steepest
gradients of the Great Lakes are along Minnesota’s north shore.
Thermochrons, transects
Thermochrons are dime sized devices that measure and store
thousands of temperatures. A contact sensor is later used to
download the data.
‘Board’ versus ‘air’
Sea breeze by day …
Land breeze at night
Normal Precipitation
winter(DJF)
spring(MAM)
summer(JJA)
fall(SON)
• Everywhere in Minnesota…
– Summer is wettest
– Winter is driest
• North shore ‘bands’ most apparent fall, winter
– Warmer lake provides energy and moisture
Snow fraction peak
Tettegouche SP transect
Let it snow!