Explaining Northern Michigan Snow(A “Big Picture” Viewpoint)

Explaining Northern Michigan Snow(A “Big Picture” Viewpoint)

2010 Winter Talk Series

BackgroundBackground

• If you’ve attended our Winter Talk series in the past, there’s a good chance you’ve seen us discuss the science of lake effect snow

• Lake effect snow is the single most important factor as to why some parts of Northern Michigan get so much more snow than others

• If you’ve attended our Winter Talk series in the past, there’s a good chance you’ve seen us discuss the science of lake effect snow

• Lake effect snow is the single most important factor as to why some parts of Northern Michigan get so much more snow than others

So: why does this map look like this?

Not to give away the answers, but…Not to give away the answers, but…

• Prevailing wind direction during cold air outbreaks

• “Fetch” and “effective fetch” lengths

• Elevation

• Proximity to a “warm” lake

• Ice cover

• Prevailing wind direction during cold air outbreaks

• “Fetch” and “effective fetch” lengths

• Elevation

• Proximity to a “warm” lake

• Ice cover

Prevailing WindsPrevailing Winds

• Lake effect snow will tend to develop over the Great Lakes, as long as the air is cold enough, and the water is warm enough

• Where the snow goes from there, depends on where the wind is blowing

• Thus, the “prevailing wind” – our most common wind direction – during periods of cold weather is crucial

• Lake effect snow will tend to develop over the Great Lakes, as long as the air is cold enough, and the water is warm enough

• Where the snow goes from there, depends on where the wind is blowing

• Thus, the “prevailing wind” – our most common wind direction – during periods of cold weather is crucial

Prevailing WindsPrevailing Winds

• Wind Rose for Pellston, MI (Nov-Feb)

• Dominance of Northwesterly direction

– Particularly when cold air is arriving!

• Wind Rose for Pellston, MI (Nov-Feb)

• Dominance of Northwesterly direction

– Particularly when cold air is arriving!

NW

W

N

E

SSW SE

NE

Prevailing Winds & FetchesPrevailing Winds & Fetches

• A “fetch” is the distance over which air is moving over water, for a given wind direction

– Generally speaking, the longer the fetch, the more snow the lake will be capable of generating

• Given that a northwest wind is our prevailing winter wind, what kind of fetch does that produce?

• A “fetch” is the distance over which air is moving over water, for a given wind direction

– Generally speaking, the longer the fetch, the more snow the lake will be capable of generating

• Given that a northwest wind is our prevailing winter wind, what kind of fetch does that produce?

Prevailing Winds & FetchesPrevailing Winds & Fetches

• The longest fetch, and heaviest snow, do NOT match up.

• The longest fetch, and heaviest snow, do NOT match up.

30

70

70

80

70

• So is there something we are we not accounting for?

• So is there something we are we not accounting for?

Fetches & Effective FetchesFetches & Effective Fetches

• Yes - there’s another lake up there!

• An airmass will retain “lake effect characteristics” on a short trip over land, IF there is little terrain (hills/mountains) to cross

• If this is the case, the result is a longer “effective fetch” due to the air crossing multiple lakes

• Yes - there’s another lake up there!

• An airmass will retain “lake effect characteristics” on a short trip over land, IF there is little terrain (hills/mountains) to cross

• If this is the case, the result is a longer “effective fetch” due to the air crossing multiple lakes

Fetches & Effective FetchesFetches & Effective Fetches

• As it turns out, the east half of the U.P. is As it turns out, the east half of the U.P. is narrow, and does not have many hillsnarrow, and does not have many hills

• The west half is “thicker” and much hillier, The west half is “thicker” and much hillier, and eliminates a Lake Superior contribution and eliminates a Lake Superior contribution to an effective fetchto an effective fetch

Fetches & Effective FetchesFetches & Effective Fetches

• Bingo!Bingo!

• The longest The longest effective fetch, effective fetch, and heaviest and heaviest snow, match up snow, match up nicely.nicely.

• In BOTH In BOTH Peninsulas!Peninsulas!

• But why is But why is the heaviest the heaviest snow snow inlandinland??• It’s lake It’s lake

effect; effect; shouldn’t it shouldn’t it be near the be near the lake? lake?

Cold air

Warm water

Stable air aloft

FrictionalConvergenceand Upslope

Heat and Moisture

Recall How Lake Effect FormsRecall How Lake Effect Forms

Precipitation

ElevationElevation

• Elevation plays 2 key Elevation plays 2 key rolesroles• Forced AscentForced Ascent• Colder TemperaturesColder Temperatures

Elevation – Forced AscentElevation – Forced Ascent

• Precipitation will be Precipitation will be generated/enhanced generated/enhanced when moist/unstable air when moist/unstable air is forced to ascendis forced to ascend• They know all about this They know all about this

in the mountain states in the mountain states out westout west

Elevation – Colder TemperaturesElevation – Colder Temperatures

• Top of hills usually Top of hills usually coldercolder

• May make the May make the difference between difference between rain and snowrain and snow

ElevationElevation• Conversely, precipitation will diminish/end as Conversely, precipitation will diminish/end as

air is forced to move air is forced to move downhilldownhill

• So snow showers will weaken as they move So snow showers will weaken as they move toward NE Lower Michigan and Lake Hurontoward NE Lower Michigan and Lake Huron

Elevation & “Warm” LakesElevation & “Warm” Lakes

• Most common early Most common early in the snow season, in the snow season, when coastal areas when coastal areas will be warmed by will be warmed by the warm lakethe warm lake• It’s common to see It’s common to see

rain in Charlevoix, rain in Charlevoix, and snow in Gaylordand snow in GaylordDec 1 2009Dec 1 2009

• Same rules apply Same rules apply to Eastern Upperto Eastern Upper

• But Superior is But Superior is colder, and colder, and doesn’t hinder doesn’t hinder coastal snow as coastal snow as much as Lake much as Lake MichiganMichigan

Elevation & “Warm” LakesElevation & “Warm” Lakes

• What about St What about St Ignace?Ignace?• Surrounded Surrounded

by water, but by water, but doesn’t get doesn’t get much snowmuch snow

• The prevailing The prevailing wind is the wind is the biggest biggest reason…reason…

Elevation & “Warm” LakesElevation & “Warm” Lakes

Ice CoverIce Cover

• Ice cover is another Ice cover is another reasonreason

• The Straits region The Straits region freezes over quickly freezes over quickly in a typical winterin a typical winter

• Ice-covered water Ice-covered water does NOT generate does NOT generate significant lake significant lake effect snoweffect snow

Jan 19 2009Jan 19 2009

The Home Stretch…The Home Stretch…

• Okay, we now have a handle on lake effect snow and its distribution

• But, what about snow that doesn’t originate from the lakes?

• Okay, we now have a handle on lake effect snow and its distribution

• But, what about snow that doesn’t originate from the lakes?

L

Typical Midlatitude CycloneTypical Midlatitude Cyclone

SNOW MIX

RA

IN

Typical Cyclone TracksTypical Cyclone Tracks

Midlatitude Cyclone SnowMidlatitude Cyclone Snow

• Numerous storm tracks pass east or even well east of the region

• If we look at a county that sees relatively little lake effect (e.g. Arenac), we probably can assume a typical “synoptic snowfall”

• ~40 inches per year

• Numerous storm tracks pass east or even well east of the region

• If we look at a county that sees relatively little lake effect (e.g. Arenac), we probably can assume a typical “synoptic snowfall”

• ~40 inches per year

In SummaryIn Summary

• Our snow comes from two sources

– Lake Effect

– Mid latitude cyclones

• Lake Effect depends on numerous microscale factors

– Fetch/effective fetch, elevation, lake temperature, ice cover, distance to shore, etc.

• Our snow comes from two sources

– Lake Effect

– Mid latitude cyclones

• Lake Effect depends on numerous microscale factors

– Fetch/effective fetch, elevation, lake temperature, ice cover, distance to shore, etc.

Any Questions???Any Questions???