Stampede
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stampede clear sky chart from 2005-11-06 to 2025-09-19.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	11% 12% 5% 11% 7% 6% 6% 5% 6% 7% 24%	132149
	Night	5% 10% 5% 13% 8% 7% 6% 5% 6% 7% 28%	125676
Transparency	Day	55% 11% 14% 14% 5% 1	131770
	Night	50% 10% 14% 15% 8% 3	125634
Seeing	Day	18% 12% 22% 25% 17% 6%	19763
	Night	13% 10% 20% 28% 23% 6%	23626

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	1 9% 3 8% 7% 7% 6% 4 6% 7% 42%	1819
	11th to 20th	Day	1 7% 4 9% 7% 7% 8% 6% 8% 10% 35%	1808
	21st to end	Day	1 5% 3 12% 10% 11% 10% 6% 9% 8% 25%	2726
February	1st to 10th	Day	1 10% 5% 8% 5% 6% 6% 5% 6% 8% 41%	1248
	11th to 20th	Day	1 10% 5% 14% 7% 7% 6% 5% 9% 8% 28%	1494
	21st to end	Day	2 9% 7% 14% 9% 7% 7% 4 7% 6% 28%	1360
March	1st to 10th	Day	1 8% 7% 20% 9% 7% 7% 5% 7% 6% 24%	4357
	11th to 20th	Day	1 8% 5% 14% 12% 10% 9% 6% 7% 7% 22%	4640
	21st to end	Day	2 10% 6% 13% 6% 5% 6% 5% 7% 8% 32%	5969
April	1st to 10th	Day	3 14% 7% 12% 7% 7% 6% 5% 7% 7% 25%	2532
	11th to 20th	Day	3 12% 6% 12% 8% 5% 6% 4 7% 7% 31%	2766
	21st to end	Day	4 9% 3 8% 7% 6% 7% 5% 8% 8% 35%	2984
May	1st to 10th	Day	6% 16% 4 12% 7% 6% 6% 5% 7% 7% 25%	7260
	11th to 20th	Day	7% 15% 4 10% 6% 5% 5% 4 5% 6% 31%	7734
	21st to end	Day	11% 13% 4 12% 7% 6% 6% 5% 7% 8% 22%	8911
June	1st to 10th	Day	16% 12% 4 10% 8% 7% 7% 6% 8% 7% 16%	3754
	11th to 20th	Day	18% 10% 4 10% 7% 6% 5% 5% 6% 7% 22%	4000
	21st to end	Day	18% 10% 4 9% 8% 6% 7% 5% 7% 7% 20%	4000
July	1st to 10th	Day	21% 12% 4 9% 6% 5% 5% 4 6% 7% 22%	8574
	11th to 20th	Day	17% 10% 4 11% 7% 6% 7% 5% 7% 9% 19%	8160
	21st to end	Day	20% 14% 5% 11% 7% 7% 5% 4 5% 5% 18%	8572
August	1st to 10th	Day	23% 15% 4 11% 6% 6% 5% 4 5% 6% 16%	5206
	11th to 20th	Day	20% 13% 4 11% 6% 6% 6% 5% 7% 7% 15%	4856
	21st to end	Day	20% 15% 5% 13% 7% 6% 5% 4 5% 6% 15%	5038
September	1st to 10th	Day	19% 13% 4 10% 6% 7% 6% 4 6% 6% 20%	2561
	11th to 20th	Day	20% 15% 5% 9% 6% 6% 6% 4 5% 6% 19%	2375
	21st to end	Day	15% 20% 5% 10% 6% 5% 3 4 5% 6% 21%	2024
October	1st to 10th	Day	8% 18% 6% 12% 5% 4 4 4 5% 6% 28%	3067
	11th to 20th	Day	4 12% 5% 18% 9% 7% 5% 4 5% 8% 24%	2740
	21st to end	Day	5% 19% 6% 12% 7% 7% 6% 4 6% 6% 22%	2539
November	1st to 10th	Day	3 16% 4 13% 8% 8% 5% 4 5% 6% 26%	1269
	11th to 20th	Day	5% 11% 7% 15% 9% 8% 7% 3 4 5% 26%	1040
	21st to end	Day	4 11% 6% 13% 6% 8% 5% 5% 8% 8% 26%	865
December	1st to 10th	Day	2 9% 3 11% 10% 6% 7% 5% 7% 10% 30%	1155
	11th to 20th	Day	2 11% 6% 13% 7% 5% 7% 6% 7% 9% 28%	1134
	21st to end	Day	1 6% 3 10% 7% 6% 6% 4 8% 7% 42%	1612
January	1st to 10th	Night	1 6% 4 11% 7% 5% 5% 4 6% 7% 43%	8146
	11th to 20th	Night	1 9% 4 11% 7% 6% 6% 5% 6% 9% 35%	8110
	21st to end	Night	1 5% 3 11% 10% 12% 9% 5% 7% 7% 30%	8258
February	1st to 10th	Night	2 8% 4 12% 8% 5% 6% 4 6% 6% 39%	3150
	11th to 20th	Night	2 8% 4 12% 8% 7% 8% 5% 8% 11% 28%	2793
	21st to end	Night	2 11% 6% 18% 10% 6% 6% 4 6% 5% 27%	2268
March	1st to 10th	Night	1 11% 7% 16% 7% 6% 5% 5% 6% 6% 30%	5497
	11th to 20th	Night	1 6% 5% 17% 11% 10% 10% 7% 7% 6% 19%	5315
	21st to end	Night	3 9% 4 12% 7% 6% 7% 5% 7% 8% 31%	4962
April	1st to 10th	Night	3 15% 6% 13% 8% 5% 6% 5% 8% 8% 23%	1865
	11th to 20th	Night	3 12% 4 11% 6% 4 5% 5% 7% 9% 34%	1583
	21st to end	Night	5% 8% 4 7% 5% 5% 5% 4 8% 10% 39%	1414
May	1st to 10th	Night	4 12% 4 10% 7% 7% 7% 6% 9% 10% 24%	2720
	11th to 20th	Night	8% 11% 4 9% 5% 6% 7% 4 7% 6% 35%	2158
	21st to end	Night	10% 10% 4 9% 6% 6% 6% 6% 9% 8% 26%	1986
June	1st to 10th	Night	13% 13% 3 9% 8% 8% 7% 5% 7% 7% 20%	645
	11th to 20th	Night	18% 11% 4 8% 7% 5% 4 4 5% 8% 27%	400
	21st to end	Night	18% 8% 3 10% 6% 7% 6% 5% 6% 10% 22%	400
July	1st to 10th	Night	19% 14% 4 10% 7% 5% 5% 4 6% 7% 20%	1403
	11th to 20th	Night	15% 13% 4 12% 6% 5% 6% 4 7% 6% 21%	1820
	21st to end	Night	26% 15% 5% 13% 6% 4 4 2 4 4 16%	2283
August	1st to 10th	Night	22% 14% 4 9% 6% 5% 6% 4 6% 5% 17%	1954
	11th to 20th	Night	18% 11% 5% 13% 7% 7% 6% 5% 6% 7% 16%	2200
	21st to end	Night	20% 17% 5% 11% 6% 5% 5% 4 5% 5% 16%	2871
September	1st to 10th	Night	19% 11% 3 9% 7% 6% 6% 4 7% 6% 22%	1836
	11th to 20th	Night	20% 15% 5% 10% 6% 5% 5% 3 5% 7% 19%	1982
	21st to end	Night	16% 20% 5% 10% 6% 5% 5% 3 5% 5% 20%	2154
October	1st to 10th	Night	7% 17% 5% 11% 6% 5% 6% 5% 6% 8% 23%	3896
	11th to 20th	Night	5% 16% 7% 17% 8% 6% 5% 4 6% 7% 20%	4188
	21st to end	Night	5% 15% 5% 15% 9% 7% 6% 3 5% 7% 23%	5020
November	1st to 10th	Night	4 14% 6% 14% 7% 5% 5% 4 5% 6% 29%	3027
	11th to 20th	Night	4 13% 7% 15% 11% 8% 6% 4 4 5% 23%	3359
	21st to end	Night	3 10% 5% 13% 9% 7% 7% 5% 7% 7% 29%	3534
December	1st to 10th	Night	3 8% 3 10% 7% 7% 6% 6% 8% 11% 30%	6001
	11th to 20th	Night	2 12% 7% 14% 7% 6% 6% 4 7% 8% 28%	7070
	21st to end	Night	1 6% 5% 13% 8% 6% 6% 6% 7% 8% 34%	9408

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	38% 9% 12% 18% 14% 9%	1819
	11th to 20th	Day	37% 12% 19% 20% 8% 4	1820
	21st to end	Day	48% 8% 10% 12% 14% 8%	2726
February	1st to 10th	Day	39% 8% 11% 18% 16% 9%	1248
	11th to 20th	Day	48% 12% 15% 13% 9% 3	1500
	21st to end	Day	52% 8% 11% 15% 12% 2	1360
March	1st to 10th	Day	54% 7% 8% 17% 12% 2	4357
	11th to 20th	Day	50% 10% 12% 15% 12% 1	4640
	21st to end	Day	44% 12% 12% 13% 16% 2	5969
April	1st to 10th	Day	55% 10% 13% 14% 7%	2532
	11th to 20th	Day	49% 11% 14% 15% 8% 2	2766
	21st to end	Day	44% 10% 14% 22% 9%	2984
May	1st to 10th	Day	52% 12% 14% 18% 5%	7260
	11th to 20th	Day	48% 12% 12% 21% 7%	7737
	21st to end	Day	52% 13% 17% 16% 4	8912
June	1st to 10th	Day	60% 15% 14% 10% 1	3754
	11th to 20th	Day	59% 12% 14% 13% 3	4000
	21st to end	Day	59% 14% 17% 9%	4000
July	1st to 10th	Day	58% 10% 20% 11%	8484
	11th to 20th	Day	57% 10% 18% 14% 1	8061
	21st to end	Day	63% 11% 14% 9% 2	8330
August	1st to 10th	Day	67% 9% 15% 8% 1	5187
	11th to 20th	Day	62% 13% 15% 9% 1	4904
	21st to end	Day	67% 12% 12% 8% 1	5037
September	1st to 10th	Day	63% 12% 14% 10% 1	2561
	11th to 20th	Day	64% 12% 13% 10%	2375
	21st to end	Day	63% 10% 11% 14% 2	2024
October	1st to 10th	Day	56% 8% 9% 19% 6% 1	3067
	11th to 20th	Day	56% 11% 15% 15% 3 1	2740
	21st to end	Day	60% 10% 12% 15% 2 1	2539
November	1st to 10th	Day	57% 10% 11% 14% 5% 3	1269
	11th to 20th	Day	58% 7% 13% 15% 6% 1	1040
	21st to end	Day	52% 9% 17% 13% 8% 1	865
December	1st to 10th	Day	46% 9% 15% 22% 6% 1	1155
	11th to 20th	Day	47% 10% 16% 17% 6% 3	1136
	21st to end	Day	34% 9% 19% 11% 22% 6%	1612
January	1st to 10th	Night	35% 9% 13% 22% 11% 10%	8146
	11th to 20th	Night	40% 11% 18% 20% 9% 2	8160
	21st to end	Night	46% 8% 10% 11% 14% 10%	8258
February	1st to 10th	Night	43% 6% 9% 17% 16% 8%	3150
	11th to 20th	Night	45% 10% 15% 15% 12% 3	2798
	21st to end	Night	56% 7% 9% 15% 10% 2	2268
March	1st to 10th	Night	52% 5% 8% 17% 15% 3	5497
	11th to 20th	Night	51% 11% 14% 11% 10% 2	5317
	21st to end	Night	43% 12% 14% 16% 13% 2	4962
April	1st to 10th	Night	53% 10% 14% 16% 7% 1	1865
	11th to 20th	Night	43% 12% 18% 17% 8% 2	1583
	21st to end	Night	35% 11% 14% 28% 11%	1414
May	1st to 10th	Night	46% 12% 16% 22% 4	2717
	11th to 20th	Night	41% 12% 13% 25% 9%	2158
	21st to end	Night	46% 13% 18% 19% 4	1986
June	1st to 10th	Night	58% 14% 13% 13% 2	645
	11th to 20th	Night	54% 11% 16% 17% 2	400
	21st to end	Night	57% 15% 19% 9%	400
July	1st to 10th	Night	61% 10% 18% 10% 1	1384
	11th to 20th	Night	57% 11% 15% 17%	1796
	21st to end	Night	68% 9% 13% 8% 1	2221
August	1st to 10th	Night	65% 12% 18% 4 1	1948
	11th to 20th	Night	62% 14% 16% 8%	2218
	21st to end	Night	68% 12% 15% 6%	2871
September	1st to 10th	Night	59% 13% 16% 10% 1	1836
	11th to 20th	Night	65% 9% 13% 12% 1	1982
	21st to end	Night	65% 10% 10% 13% 2	2154
October	1st to 10th	Night	56% 9% 12% 18% 4	3896
	11th to 20th	Night	61% 10% 11% 14% 3 1	4188
	21st to end	Night	57% 10% 13% 17% 3 1	5020
November	1st to 10th	Night	55% 9% 12% 18% 5% 2	3027
	11th to 20th	Night	62% 8% 11% 13% 6%	3359
	21st to end	Night	51% 9% 13% 16% 8% 2	3534
December	1st to 10th	Night	44% 9% 15% 22% 9% 1	6001
	11th to 20th	Night	49% 9% 16% 15% 7% 4	7067
	21st to end	Night	40% 12% 17% 10% 16% 5%	9408

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 12% 18% 32% 20% 12%	100
	11th to 20th	Day	7% 3 31% 33% 18% 8%	100
	21st to end	Day	9% 12% 20% 31% 22% 6%	315
February	1st to 10th	Day	4 9% 24% 26% 25% 13%	300
	11th to 20th	Day	10% 18% 23% 26% 16% 8%	362
	21st to end	Day	8% 15% 30% 26% 15% 5%	331
March	1st to 10th	Day	7% 13% 28% 30% 19% 4	400
	11th to 20th	Day	6% 10% 23% 33% 23% 5%	441
	21st to end	Day	8% 13% 27% 30% 17% 6%	660
April	1st to 10th	Day	9% 16% 31% 24% 16% 4	640
	11th to 20th	Day	10% 12% 24% 30% 19% 5%	690
	21st to end	Day	10% 7% 23% 31% 24% 5%	700
May	1st to 10th	Day	13% 13% 26% 30% 15% 3	703
	11th to 20th	Day	11% 13% 26% 28% 17% 6%	789
	21st to end	Day	19% 14% 24% 23% 16% 5%	1006
June	1st to 10th	Day	18% 11% 22% 25% 18% 6%	1060
	11th to 20th	Day	18% 8% 19% 25% 23% 7%	1130
	21st to end	Day	19% 8% 19% 24% 21% 9%	1130
July	1st to 10th	Day	21% 12% 22% 25% 16% 4	997
	11th to 20th	Day	29% 11% 19% 22% 15% 5%	912
	21st to end	Day	24% 11% 20% 24% 15% 6%	972
August	1st to 10th	Day	28% 15% 23% 18% 12% 4	726
	11th to 20th	Day	31% 15% 21% 21% 10% 2	715
	21st to end	Day	33% 16% 20% 20% 9% 1	803
September	1st to 10th	Day	27% 17% 23% 17% 11% 4	678
	11th to 20th	Day	33% 19% 21% 16% 9% 2	611
	21st to end	Day	26% 11% 19% 20% 17% 7%	390
October	1st to 10th	Day	25% 17% 23% 17% 12% 5%	390
	11th to 20th	Day	10% 8% 22% 27% 21% 11%	390
	21st to end	Day	14% 10% 19% 26% 22% 8%	429
November	1st to 10th	Day	11% 10% 19% 28% 21% 11%	343
	11th to 20th	Day	8% 12% 20% 26% 27% 7%	140
	21st to end	Day	9% 13% 18% 29% 21% 10%	100
December	1st to 10th	Day	9% 13% 25% 24% 23% 6%	100
	11th to 20th	Day	8% 12% 22% 30% 22% 6%	100
	21st to end	Day	10% 14% 22% 36% 12% 6%	110
January	1st to 10th	Night	6% 8% 20% 31% 27% 9%	1000
	11th to 20th	Night	9% 7% 23% 34% 21% 6%	1000
	21st to end	Night	9% 9% 23% 34% 21% 5%	1043
February	1st to 10th	Night	5% 8% 24% 30% 24% 9%	900
	11th to 20th	Night	8% 15% 24% 31% 19% 4	884
	21st to end	Night	9% 14% 22% 29% 23% 3	701
March	1st to 10th	Night	6% 12% 21% 37% 20% 4	700
	11th to 20th	Night	5% 5% 18% 32% 31% 8%	699
	21st to end	Night	7% 11% 18% 25% 28% 11%	660
April	1st to 10th	Night	10% 12% 26% 28% 19% 6%	600
	11th to 20th	Night	8% 10% 18% 28% 27% 8%	593
	21st to end	Night	9% 5% 14% 32% 33% 7%	545
May	1st to 10th	Night	11% 9% 17% 28% 29% 7%	400
	11th to 20th	Night	9% 12% 20% 31% 25% 3	232
	21st to end	Night	12% 11% 21% 26% 26% 4	217
June	1st to 10th	Night	16% 12% 19% 27% 25% 2	200
	11th to 20th	Night	22% 7% 12% 27% 28% 5%	200
	21st to end	Night	19% 7% 13% 22% 35% 5%	200
July	1st to 10th	Night	22% 9% 17% 24% 23% 5%	195
	11th to 20th	Night	31% 8% 18% 21% 19% 3	194
	21st to end	Night	28% 7% 20% 21% 20% 4	304
August	1st to 10th	Night	30% 13% 15% 21% 18% 4	398
	11th to 20th	Night	28% 11% 22% 21% 15% 3	468
	21st to end	Night	31% 12% 15% 19% 19% 5%	660
September	1st to 10th	Night	26% 14% 21% 18% 16% 5%	600
	11th to 20th	Night	30% 15% 18% 18% 13% 6%	594
	21st to end	Night	26% 10% 12% 26% 20% 6%	605
October	1st to 10th	Night	24% 15% 17% 20% 18% 5%	727
	11th to 20th	Night	15% 10% 17% 26% 25% 8%	860
	21st to end	Night	13% 10% 17% 32% 22% 6%	946
November	1st to 10th	Night	10% 9% 19% 31% 24% 7%	880
	11th to 20th	Night	12% 7% 19% 31% 24% 8%	900
	21st to end	Night	8% 10% 22% 28% 26% 7%	967
December	1st to 10th	Night	10% 15% 22% 25% 20% 8%	1069
	11th to 20th	Night	9% 9% 21% 30% 23% 8%	1200
	21st to end	Night	8% 13% 18% 31% 22% 9%	1285

Page generated at 2025-09-15 21:49:13. Version ac07

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