Sailing Colorado Lakes
….Or….how to integrate frustration into
your recreational time,
……………..and learn to enjoy it.
by
John McGinley
NOAA (retired)
You might be a Colorado
sailor if:
You’ve seen this….two downwind boats
on opposing courses
Slide 0
You’ve witnessed massed boats knocked down in every
compass direction….and then float there semi-submerged in a
dead calm
Every leg of a race is a beat
A major voyage is three miles
long and usually circular….
You’ve seen a tornado from
your boat
You’ve had a race like this!
5 min
1 hour
RC
Finish
Start
3 min
30 Sec
You’ve used your anchor as a
tactical tool, racing or cruising,
where there is no current or tide
yikes
So other than lake size what is
the weird thing about Colorado
sailing?…..THE WINDS
So let’s talk about winds in Colorado
The summer weather pattern. Winds in the
Plains are dominated by the Bermuda High;
mountains are dominated by monsoon and
local circulations: Denver sits between.
Monsoon
In Eastern Colorado we get four
main wind regimes
Westerly downslope - dangerous gusts
Post Cold Front Upslope – cloudy with showers
Mountain upslope breeze – light and crazy winds
Bermuda high southerlies - Denver Cyclone and
thunderstorms
Some days are dominated by downslope or
mountain wave flow; often prefrontal
Dryline
Reliable
Southerly
Winds
Downslope Day
Lenticular clouds
Strong Winds
Cap cloud
or
Foehn wall
Rotor
Dangerous winds
Lenticular Clouds
Lenticular Clouds
Weak Summer cold fronts.
Cool upslope with clouds.
Banding is possible near the Front Range.
Showers and thunderstorms likely.
Cloudy Upslope Day
Stratocumulus
steady winds
gusty winds
steady winds
Cloud Bands
Stratocumulus
Best sailing
Strong winds above
Looking down on cloud bands
Best Winds
Stratus and Stratocumulus
Stratus and Stratocumulus
Edge of cloud
steady
Bands
gusty
Mountain Upslope
Dryline (red-dash) is key feature separating
Bermuda High flow from mountain-disturbed flow - near the
Front Range we get a light upslope mountain breeze and
unpredictable winds. Winds are dominated by local effects.
SW
Monsoon
Reliable
Southerly
Winds
Mountain Breeze
Cold
Warm
Thermal
Good breeze
20-30 miles
Sunny Day – themals form
Cumulus cloud
also Invisible
The Infamous Thermal
Cat’s paws
0.5 to 2 miles
Looking down on a cumulus/
thermal . Moves along with
steering flow.
Best Winds
Steady Winds and Thermals
Cumulus cloud and winds
- find the edge of the cloud
Size relative to our
favorite lakes –
These things
Cherry
can
dominate
Creek
lake winds!
Chatfield
Carter
Cumulus clouds – visible
thermals
Cumulus clouds – visible tracer
of thermals
Cumulus cloud
Towering
cumulus cloud
Rain
Stormy Day
Hail
Cumulonimbus
Shelf Cloud
Outflow Gust front
Dryline sometimes is right on the Front
Range - forms what meteorologists call the
“DENVER CYCLONE”
The Monsoon Pattern from July to early
September. Storms develop over mountains
and move into the metro area if upper level
winds are right.
Monsoon
The US Monsoon
Thunderstorm Formation
40000ft
25000ft
8000ft
32F
Initiation stage:
Heat source
Trigger
Low level moisture
10-20 minutes: Towering Cu
Rain formation
Snow/Ice in top of cloud
Formation rain and downdraft
20-40 minutes: Anvil stage
Heavy rain, hail, lightning
Strong outflow/downburst
Shelf clouds
How Thunderstorms Move
Storm Movement:
Average of upper winds
Thunderstorm Outflow
Shelf Cloud and Outflow
Thunderstorms and outflows
Thunderstorms
Formation of downbursts
Evaporative
Cooling
Schematic of Downburst
Downburst example
Downburst example
Downburst example
Lightning with Thunderstorms
Charge in a Thunderstorm
Lightning with Thunderstorm
Sound travels about a mile in 5 sec.
Use this to determine how far away
strike is. Thunder rolls owing to height
of bolt.
20 sec
10sec
7sec
5sec
1 mile
A mast in a thunderstorm – a
target or not?
Cloud base
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Electrical field lines
Zap!!!
Cloud base
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Electrical field lines
Super Cell Thunderstorm
Super Cell Thunderstorm
Wall Cloud – Evidence of
Strong Rotating Updrafts
Wall Cloud – Dangerous for
Sailors
LAKE BREEZES
Do they happen here?
When breezes don’t form
• Lakes that are too small ( < 2 mi)
• Lakes dominated by gradient flow
• Winds on small lakes are controlled by
land effects as if the lakes aren’t there
On a Colorado lake, what you
see
What you
On asee…..
Clorado lake
what the
atmosphere
What
you
see sees
What you
see…..
So you
are subject to all the
Hey, is
that
combine on
starboard
or port?
small themals,
eddies, etc
What
you
see
that occur over land
Summary
Colorado is in a complex wind regime
Often times we’re an atmospheric backwater,
suffering all manner of intense local
circulations
Hazards are frequent: downslope,
thunderstorms with downbursts, outflows,
tornadoes and lightning
Winds on Colorado lakes behave just like
winds over bare ground – lots of thermals