3. I want to remove the mystery
of Colorado weather.
4. Hi, I’m Joel Gratz.
I grew up in Pennsylvania,
ski raced and instructed,
then moved to Colorado
after college.
5. And I started to
miss powder days due to
inaccurate forecasts.
6. So I learned how to forecast in
Colorado, and started to share.
Dec 2007
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2008-2009
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2009-2010
245,000 pageviews
2010-2011
1,315,000 pageviews
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2013-2014
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14. It snowed in Aspen during September.
Of the past 22 Septembers
with snow, 19 of the
ensuing winters have been
average or above.
- Cory Gates, AspenWeather.net
15. Perhaps there’s
another clue.
!
We set a snowfall record
in April and a rainfall
record in September for
Boulder. Does this tell us
anything about winter
snow in the mountains?
16. Each line shows amount of snow on the ground for various weather
stations, during winters after heavy precipitation in Boulder.
160%
150%
140%
130%
120%
110%
100%
Dec 1
Jan 1
Feb 1
Mar 1
April 1
17.
18.
19.
20.
21. Colorado
SNOTEL Snow Water Equivalent (SWE)
% of Normal
Feb 27, 2014
UPPER
GREEN
112
129
110 148
159
76
117
Steamboat Springs 111
Current SWE
% of 1981-2010
Median
WHITE-YAMPA
137
147
133
117
119 126
136
182
152
144
> 160%
130
98
188
126
Fort Collins
131
NORTH
PLATTE
141 191
164
70
140-160%
162
90
117
105
120-139%
118
100-119%
60-79%
98
COLORADO
HEADWATERS
80-99%
87
111
95
98
40-59%
128
Denver
123
147
110
144
152 149
132 150
141
70
Leadville
119 153
109
121
145
126
158
124 122
Grand Junction
SMOKY HILL
148
Colorado Springs
116
1-39%
67
123
GUNNISON
Gunnison
0%
136
76
Unavailable*
Provisional Data
Subject to Revision
REPUBLICAN
SOUTH PLATTE
130
123
UPPER ARKANSAS
Pueblo
UPPER
COLORADO-DOLORES
140
25
76
73 101
82
LOWER
SAN JUAN
67
58
81
106
85
99
70
89
114
97
122
87
79
72
138
95
88
95
RIO GRANDE
HEADWATERS
Alamosa
68
Durango
UPPER
SAN JUAN
72
47
39
94
10
UPPER CIMARRON
86 47
69
Prepared by the
USDA/NRCS National Water and Climate Center
Portland, Oregon
http://www.wcc.nrcs.usda.gov/gis/
0
10 20
40
60
80
Miles
100
* Data unavailable at time of posting or unavailable long-term normal.
52. WEATHER 101: Five ways to get high
U is for undercut.
Cold front moving left-to-right
Cold Air
Warm Air
http://www.clker.com/cliparts/e/4/9/a/12401693261710228990Kliponius_Mountain_in_a_Cartoon_Style.svg.med.png
53. WEATHER 101: Five ways to get high
D is for dynamic.
This is complicated - it’s all physics.
Jet Stream
(river of fast air)
30,000ft
300mb
Induces upward motion by “pulling” surface air
upward into the void left by the fast-moving air
above. Similar to opening a car window while
moving and having a piece of paper “sucked” out.
http://www.clker.com/cliparts/e/4/9/a/12401693261710228990Kliponius_Mountain_in_a_Cartoon_Style.svg.med.png
54. WEATHER 101: Five ways to get high
D is for dynamic.
This is complicated - it’s all physics.
18,000ft
500mb
Vorticity
counter-clockwise
spin
As vorticity centers (“vort max”)
move, they induce upward
motion in front and downward
motion behind.
http://www.clker.com/cliparts/e/4/9/a/12401693261710228990Kliponius_Mountain_in_a_Cartoon_Style.svg.med.png
55. SNOW in CO: What winds to watch?
As a standard, winds are forecast (and measured) at 850mb,
700mb, 500mb, 300mb, and 250mb.
JET STREAM
30,000ft
300mb
VORTICITY
18,000ft
500mb
OROGRAPHIC
10,000ft
700mb
5,000ft
850mb
57. Mountains = Precipitation
Indian Peaks /
RMNP
Park Range
Flattops
Gore
Ten Mile &
Mosquito
Grand
Mesa
Elk
Mtns
N&S
San Juans
Sawatch
Sangre de
Christo
East
San Juans
67. The best snow requires...
• Lots of moisture
• Temperatures between about 0-10F
where the lift is taking place (usually
mountain top, but sometimes higher)
• Best wind for
Crested Butte = West-southwest
Irwin = SW through NW
