Download Understanding Michigan snowfall

Understanding Michigan snowfall
Jim Keysor - NWS Gaylord
Presentation Outline Topics
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Background information on lake effect
Radar and lake effect snow
Wind direction and lake effect
Lake Enhanced snow
Elevation and snowfall
Snow-water ratio
Where to find information
Conclusion
Mean Lake/Air Temperatures
(for Lake Michigan at Muskegon)
Lake Effect
Snow
Lake Effect
Rain
Snow
Stable Season
70
60
°F
50
40
Lake
30
Air
20
J
F
M
A
M
J
J
A
S
Month
Air temperature
Lake temperature
O
N
D
So What Happens?
Imagine a cold air mass coming out of Wisconsin…moving across a relatively mild
Lake Michigan:
As the air near the water becomes
warm and moist…it becomes less
dense than the colder air above it.
This creates buoyancy…and causes
the air to rise.
As cold air moves
out
across
a
warmer body of
water…it picks up
heat and moisture.
Cold air
Heat and Moisture
Warm water
Formation of Lake Effect Precipitation
The moist, rising air eventually cools to saturation (the relative humidity reaches
100 percent). Continued lifting leads to cloud formation.
As these “bubbles” of buoyant
air rise, they cool. Eventually,
they cool to the point where its
humidity reaches 100%. At that
point,
condensation
occurs,
resulting in cloud formation.
Cold air
Heat and Moisture
Lake effect snow and radar
Heavy snow in Sault Ste. Marie, MI on this image
1”+ per hour snowfall 25‐30 dBZ
Radar and color curves
Surface wind, fetch and lake effect snow
Fetch is the distance that an air mass travels over a body of water. Generally
the longer the fetch, the more opportunity to pick up moisture/heat and
develop into more intense lake effect snow
Typical northwest flow lake effect snow bands
over Northern Michigan
Wind directions favorable for lake effect
snow for Northwest Lower Michigan
Wind directions favorable for lake effect
snow for Northwest Lower Michigan
Wind directions favorable for lake effect
snow for Northwest Lower Michigan
Wind directions favorable for lake effect
snow for Northwest Lower Michigan
Wind patterns when Lake Huron produces
lake effect snow
Lake Enhanced Snow
Lake enhanced snow is not “pure” lake effect, but is associated with
regular snow-producing weather features (typically Alberta clippers or
other low pressure systems) where the lake enhances snowfall.
7 am EST 21 January 2005
Heavier lake
enhanced snowfall
21-22 January 2005
Strong/cold northeast flow
off Lake Huron generated
enough instability and added
moisture to enhance snow
totals.
Lighter snowfall
associated with
storm system
L
8-10”
1-4”
4-6”
6-8”
January 22, 2005 Lake Enhanced Snow Event
Another Factor That Can Enhance Snowfall
Topography plays an important role in enhancing snowfall rates
associated with lake effect snow bands.
100 feet of elevation change can result in an 8 to 12 inch
increase in annual snowfall.
Lake elevation=560 ft MSL
Gaylord area=1400 ft MSL
Traverse City area=600 ft MSL
Snow to Water Ratio
Definition: Snow Water Ratio is a measure of how much water is
in the snow if you melted it.
• System snow generally has snow to water ratios of 10:1 or 12:1
• That means if you melt down 10 inches of snow, you get 1
inch of water
• Lake effect snow generally has snow to water ratios of 20:1 or
30:1
• That means it takes 20 inches of lake effect snow to get 1
inch of water
• The average snow to water ratio in northern Michigan based
on the past 30 years is 16:1
• Snow to water ratios vary throughout the season, across the
country and across northern Michigan
Average snow to water ratio’s across
the country
Notice the drier snow ratios in northern Michigan
Snow to water ratio’s in Michigan
30 Year study of average snow to water
ratio’s in northern Michigan
Finding daily snow ratio
information
NWS Gaylord forecasts the snow ratio everyday during the
winter months between November 1st and April 1st. You can
refer to our snow ratio forecasts to determine how wet the
snow is expected to be for an upcoming snow event.
Go to our homepage:
www.weather.gov/gaylord
Then click on the winter briefing page:
http://www.crh.noaa.gov/apx/?n=winterbriefing
How to find snow ratio information
www.weather.gov/gaylord
Winter Weather
Briefing Page
http://www.crh.noaa.gov/apx/?n=winterbriefing
Daily snow ratio information
On our NWS Winter Weather Briefing Page
RECREATIONAL FORECAST FOR NORTHERN LOWER MICHIGAN
NATIONAL WEATHER SERVICE GAYLORD MI
1100 AM EST SAT JAN 22 2011
MIZ008‐015‐222100‐
SAULT STE. MARIE...PARADISE...TAHQUAMENON FALLS AND ENGADINE‐
1100 AM EST SAT JAN 22 2011
SNOW DEPTH..........9 TO 11 INCHES. .TODAY...
SKY/WEATHER.........CLOUDY. SNOW. MAX TEMPERATURE(F)..7‐12. WIND................EAST AROUND 5 MPH. SNOW AMOUNT.........AROUND 1 INCH. WIND CHILL(F).......MINIMUM FOR THE PERIOD ‐22. SNOW RATIO..........DRY/NORMAL (17‐20 TO 1). A few other things you can find on our
webpage which you may find useful
www.weather.gov/gaylord
• Hourly snowfall accumulation forecasts
• Lake effect snow maps with favored wind directions
• Recorded hazardous weather briefings
Hourly forecast charts which show hourly
snowfall accumulation forecasts
www.weather.gov/gaylord
Lake effect maps which show targeted
areas with certain wind directions
How to find the Hazardous
Weather Briefing on our web page
www.weather.gov/gaylord
This will take you to a 2x
daily updated briefing
Weekly weather webinars
Every Tuesday at 11 am during the winter, NWS Gaylord
conducts winter webinars with road commissions, schools,
EM’s and MDOT in northern Michigan.
These webinars last about 10-15 minutes and include a
summary of expected weather hazards over the next 7
days. There is also the opportunity to ask questions.
If there is a specific storm in the near term, forecasters
will provide detailed information on timing, locations,
amounts.
If you would like to be included on these webinars, please
email me…
[email protected]
Winter Temperature Outlook
Winter Precipitation Outlook
Questions or want more information
Jim Keysor
Warning Coordination Meteorologist
NWS Gaylord
989-731-3384 Ext 726
[email protected]
www.weather.gov/gaylord