Horseshoe Canyon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Horseshoe Canyon clear sky chart from 2005-11-06 to 2025-05-11.

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	9% 9% 3 8% 5% 5% 5% 4 6% 8% 38%	117255
	Night	7% 9% 4 10% 6% 6% 5% 4 6% 9% 34%	120414
Transparency	Day	42% 7% 16% 24% 10% 1	116996
	Night	45% 7% 15% 22% 9% 1	120319
Seeing	Day	12% 7% 26% 31% 19% 5%	16010
	Night	12% 6% 29% 37% 15% 2	25281

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	3 12% 7% 17% 8% 6% 4 4 5% 7% 27%	3179
	11th to 20th	Day	4 11% 4 10% 7% 6% 6% 7% 9% 8% 28%	3159
	21st to end	Day	5% 10% 4 10% 5% 5% 5% 5% 6% 8% 38%	3926
February	1st to 10th	Day	7% 13% 4 12% 9% 6% 6% 4 5% 7% 25%	1627
	11th to 20th	Day	6% 14% 5% 12% 7% 7% 6% 6% 7% 6% 24%	1755
	21st to end	Day	3 13% 6% 13% 8% 6% 6% 6% 5% 8% 26%	1550
March	1st to 10th	Day	3 10% 5% 12% 7% 6% 6% 4 7% 9% 31%	4552
	11th to 20th	Day	6% 11% 4 10% 6% 4 4 4 6% 9% 36%	4999
	21st to end	Day	10% 18% 6% 13% 5% 5% 5% 4 5% 6% 22%	5486
April	1st to 10th	Day	9% 13% 3 7% 6% 5% 6% 4 7% 7% 32%	2484
	11th to 20th	Day	11% 12% 3 8% 5% 5% 6% 5% 7% 7% 31%	2570
	21st to end	Day	13% 10% 3 7% 5% 5% 6% 4 7% 8% 32%	2600
May	1st to 10th	Day	20% 11% 4 7% 4 5% 5% 4 5% 6% 31%	4514
	11th to 20th	Day	11% 8% 3 7% 5% 5% 5% 5% 7% 9% 34%	4697
	21st to end	Day	16% 8% 3 9% 6% 6% 6% 5% 6% 6% 29%	5161
June	1st to 10th	Day	15% 7% 3 6% 5% 5% 5% 4 7% 8% 34%	2850
	11th to 20th	Day	20% 8% 3 7% 5% 5% 6% 5% 6% 8% 29%	2850
	21st to end	Day	9% 4 2 5% 4 4 5% 5% 8% 10% 43%	2850
July	1st to 10th	Day	7% 4 2 5% 4 4 4 4 7% 9% 51%	4740
	11th to 20th	Day	8% 3 1 5% 3 4 5% 3 7% 10% 52%	4740
	21st to end	Day	4 3 1 4 3 4 4 4 5% 9% 59%	5138
August	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 9% 43%	4390
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 45%	4028
	21st to end	Day	11% 4 2 5% 3 3 3 3 6% 7% 53%	4521
September	1st to 10th	Day	11% 5% 2 7% 3 3 4 4 5% 7% 49%	2380
	11th to 20th	Day	16% 7% 2 5% 4 3 4 3 5% 7% 45%	2090
	21st to end	Day	8% 7% 3 5% 3 5% 4 4 6% 8% 46%	2090
October	1st to 10th	Day	8% 6% 3 8% 5% 5% 4 4 6% 8% 43%	3280
	11th to 20th	Day	6% 6% 2 7% 5% 5% 5% 4 7% 10% 43%	2980
	21st to end	Day	8% 9% 3 6% 5% 5% 5% 4 5% 7% 43%	3101
November	1st to 10th	Day	9% 18% 5% 11% 5% 5% 5% 3 5% 7% 27%	1578
	11th to 20th	Day	8% 14% 3 10% 6% 5% 4 3 6% 6% 34%	1560
	21st to end	Day	7% 12% 3 12% 7% 5% 4 4 7% 8% 30%	1400
December	1st to 10th	Day	9% 12% 5% 9% 6% 6% 6% 5% 6% 6% 29%	2290
	11th to 20th	Day	7% 10% 4 16% 9% 6% 5% 4 5% 7% 27%	2642
	21st to end	Day	2 8% 4 10% 5% 5% 5% 4 6% 8% 44%	3498
January	1st to 10th	Night	3 14% 6% 14% 7% 7% 6% 4 6% 9% 23%	6766
	11th to 20th	Night	3 11% 4 12% 6% 6% 6% 5% 6% 9% 31%	6739
	21st to end	Night	3 10% 5% 10% 5% 5% 5% 4 6% 8% 38%	7072
February	1st to 10th	Night	6% 12% 5% 13% 7% 6% 5% 4 6% 8% 28%	2772
	11th to 20th	Night	5% 12% 5% 12% 7% 7% 6% 5% 7% 8% 27%	2532
	21st to end	Night	4 10% 5% 11% 6% 6% 6% 5% 7% 8% 33%	2077
March	1st to 10th	Night	3 8% 4 13% 8% 7% 6% 5% 7% 10% 30%	5342
	11th to 20th	Night	5% 8% 4 9% 6% 6% 6% 5% 7% 10% 32%	5000
	21st to end	Night	8% 18% 6% 15% 6% 5% 5% 4 6% 6% 20%	5489
April	1st to 10th	Night	10% 11% 4 8% 6% 6% 5% 3 6% 8% 32%	1913
	11th to 20th	Night	9% 11% 5% 9% 7% 6% 6% 5% 6% 9% 29%	1781
	21st to end	Night	10% 10% 4 9% 5% 6% 5% 3 7% 8% 34%	1800
May	1st to 10th	Night	22% 11% 4 7% 4 4 4 3 6% 6% 29%	2668
	11th to 20th	Night	10% 6% 2 8% 5% 6% 6% 6% 8% 9% 34%	2202
	21st to end	Night	16% 11% 4 11% 6% 7% 6% 5% 6% 6% 23%	2414
June	1st to 10th	Night	15% 9% 3 7% 5% 6% 4 5% 7% 9% 31%	1330
	11th to 20th	Night	15% 8% 3 8% 7% 6% 5% 3 8% 9% 27%	1330
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 7% 9% 42%	1330
July	1st to 10th	Night	7% 5% 2 7% 6% 5% 5% 4 7% 8% 45%	2220
	11th to 20th	Night	5% 3 2 5% 4 5% 6% 6% 8% 12% 45%	2220
	21st to end	Night	4 4 2 6% 4 4 4 4 7% 9% 52%	2414
August	1st to 10th	Night	9% 5% 2 6% 5% 4 4 4 7% 9% 45%	2537
	11th to 20th	Night	7% 4 2 6% 5% 6% 5% 5% 7% 11% 42%	2811
	21st to end	Night	9% 3 2 4 4 4 4 4 6% 10% 50%	3146
September	1st to 10th	Night	11% 5% 2 6% 4 3 4 4 5% 8% 48%	1796
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 6% 8% 45%	2090
	21st to end	Night	8% 6% 2 5% 4 4 4 3 7% 9% 47%	2090
October	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 6% 8% 46%	3693
	11th to 20th	Night	6% 7% 3 7% 4 5% 5% 5% 7% 9% 42%	3947
	21st to end	Night	6% 7% 3 7% 5% 5% 6% 5% 7% 9% 40%	4457
November	1st to 10th	Night	10% 15% 4 8% 5% 5% 5% 3 6% 7% 33%	2700
	11th to 20th	Night	5% 9% 4 11% 8% 6% 6% 4 7% 8% 33%	2838
	21st to end	Night	6% 11% 4 10% 7% 6% 6% 4 6% 9% 31%	3000
December	1st to 10th	Night	6% 13% 5% 12% 7% 6% 6% 4 6% 9% 26%	4890
	11th to 20th	Night	7% 12% 5% 13% 7% 7% 6% 5% 7% 8% 22%	5550
	21st to end	Night	3 7% 3 9% 6% 6% 5% 4 6% 9% 41%	7458

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	55% 6% 11% 19% 8% 1	3179
	11th to 20th	Day	48% 6% 14% 14% 16% 2	3180
	21st to end	Day	42% 6% 15% 29% 7%	3926
February	1st to 10th	Day	57% 5% 13% 15% 9% 1	1627
	11th to 20th	Day	55% 7% 13% 16% 8% 1	1764
	21st to end	Day	54% 6% 11% 18% 10%	1550
March	1st to 10th	Day	46% 6% 16% 20% 11%	4552
	11th to 20th	Day	43% 7% 14% 23% 13%	5000
	21st to end	Day	60% 7% 11% 16% 6%	5486
April	1st to 10th	Day	47% 9% 17% 18% 9%	2484
	11th to 20th	Day	48% 8% 13% 22% 8% 1	2570
	21st to end	Day	47% 9% 14% 20% 8% 1	2600
May	1st to 10th	Day	52% 8% 12% 22% 6% 1	4514
	11th to 20th	Day	41% 11% 15% 25% 9%	4701
	21st to end	Day	49% 10% 15% 19% 6% 1	5162
June	1st to 10th	Day	44% 9% 16% 21% 9% 1	2850
	11th to 20th	Day	50% 9% 15% 18% 6% 1	2850
	21st to end	Day	33% 10% 21% 26% 8% 2	2850
July	1st to 10th	Day	29% 6% 18% 28% 17% 2	4666
	11th to 20th	Day	28% 7% 16% 36% 12% 1	4659
	21st to end	Day	22% 6% 15% 30% 22% 5%	4976
August	1st to 10th	Day	36% 6% 16% 32% 9% 1	4372
	11th to 20th	Day	33% 5% 24% 31% 7% 1	4067
	21st to end	Day	30% 5% 22% 31% 11% 1	4520
September	1st to 10th	Day	32% 8% 17% 26% 12% 5%	2380
	11th to 20th	Day	40% 6% 15% 28% 9% 2	2090
	21st to end	Day	33% 8% 17% 27% 11% 3	2090
October	1st to 10th	Day	40% 3 21% 27% 8% 1	3280
	11th to 20th	Day	35% 5% 19% 28% 11% 2	2980
	21st to end	Day	41% 5% 9% 35% 10% 1	3101
November	1st to 10th	Day	56% 7% 12% 17% 6% 2	1578
	11th to 20th	Day	49% 7% 13% 21% 8% 1	1560
	21st to end	Day	49% 9% 15% 19% 8% 1	1400
December	1st to 10th	Day	54% 5% 19% 16% 4 1	2290
	11th to 20th	Day	56% 6% 16% 18% 3 1	2644
	21st to end	Day	39% 5% 11% 27% 14% 3	3498
January	1st to 10th	Night	55% 7% 13% 18% 5% 1	6766
	11th to 20th	Night	49% 5% 12% 17% 14% 2	6780
	21st to end	Night	43% 5% 16% 28% 8% 1	7072
February	1st to 10th	Night	52% 7% 12% 19% 10% 1	2772
	11th to 20th	Night	51% 8% 12% 16% 11% 1	2533
	21st to end	Night	46% 7% 15% 21% 11% 1	2077
March	1st to 10th	Night	45% 7% 20% 19% 9%	5342
	11th to 20th	Night	43% 8% 17% 24% 7% 1	5000
	21st to end	Night	62% 8% 10% 14% 5% 1	5489
April	1st to 10th	Night	49% 7% 15% 17% 12% 1	1913
	11th to 20th	Night	50% 7% 13% 21% 8% 1	1781
	21st to end	Night	44% 8% 14% 24% 8% 2	1800
May	1st to 10th	Night	54% 6% 11% 21% 7% 1	2668
	11th to 20th	Night	38% 13% 15% 24% 10%	2202
	21st to end	Night	55% 13% 12% 15% 4 1	2414
June	1st to 10th	Night	48% 9% 14% 20% 9%	1330
	11th to 20th	Night	51% 11% 13% 17% 7% 2	1330
	21st to end	Night	36% 9% 20% 26% 8% 1	1330
July	1st to 10th	Night	35% 7% 18% 23% 15% 2	2185
	11th to 20th	Night	29% 8% 17% 36% 8% 2	2178
	21st to end	Night	26% 5% 14% 30% 21% 4	2337
August	1st to 10th	Night	35% 6% 16% 30% 11% 1	2530
	11th to 20th	Night	34% 5% 23% 29% 7% 1	2838
	21st to end	Night	29% 5% 19% 34% 11% 2	3146
September	1st to 10th	Night	33% 8% 15% 24% 13% 7%	1796
	11th to 20th	Night	37% 6% 15% 26% 12% 4	2090
	21st to end	Night	32% 7% 17% 27% 15% 2	2090
October	1st to 10th	Night	36% 5% 19% 27% 13% 1	3693
	11th to 20th	Night	37% 5% 16% 29% 11% 2	3947
	21st to end	Night	39% 6% 14% 33% 7% 1	4457
November	1st to 10th	Night	49% 6% 13% 21% 9% 1	2700
	11th to 20th	Night	47% 8% 16% 19% 10% 1	2838
	21st to end	Night	48% 8% 18% 18% 6% 2	3000
December	1st to 10th	Night	55% 5% 19% 16% 5% 1	4890
	11th to 20th	Night	56% 7% 19% 14% 4	5547
	21st to end	Night	39% 5% 12% 26% 15% 3	7458

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% 6% 29% 30% 21% 10%	200
	11th to 20th	Day	7% 8% 32% 32% 19% 4	200
	21st to end	Day	10% 8% 25% 35% 18% 5%	220
February	1st to 10th	Day	11% 9% 27% 33% 13% 6%	215
	11th to 20th	Day	8% 6% 30% 35% 18% 3	300
	21st to end	Day	6% 6% 25% 39% 19% 5%	314
March	1st to 10th	Day	11% 6% 31% 31% 17% 4	500
	11th to 20th	Day	10% 6% 29% 34% 16% 5%	500
	21st to end	Day	12% 8% 31% 27% 17% 3	550
April	1st to 10th	Day	11% 13% 32% 29% 10% 4	500
	11th to 20th	Day	13% 11% 31% 27% 16% 2	492
	21st to end	Day	17% 11% 26% 29% 14% 3	500
May	1st to 10th	Day	15% 11% 21% 27% 20% 5%	611
	11th to 20th	Day	12% 7% 24% 33% 20% 4	676
	21st to end	Day	17% 6% 22% 26% 22% 6%	734
June	1st to 10th	Day	15% 8% 27% 30% 18% 2	680
	11th to 20th	Day	20% 8% 26% 30% 13% 3	680
	21st to end	Day	12% 3 26% 30% 21% 8%	680
July	1st to 10th	Day	9% 4 19% 34% 25% 9%	671
	11th to 20th	Day	11% 5% 20% 31% 26% 7%	668
	21st to end	Day	5% 4 19% 33% 29% 9%	739
August	1st to 10th	Day	9% 4 23% 33% 22% 8%	493
	11th to 20th	Day	9% 3 19% 35% 29% 6%	477
	21st to end	Day	9% 10% 22% 28% 22% 10%	539
September	1st to 10th	Day	13% 7% 26% 29% 19% 6%	490
	11th to 20th	Day	19% 6% 23% 28% 20% 4	490
	21st to end	Day	12% 11% 30% 28% 16% 3	490
October	1st to 10th	Day	16% 5% 25% 31% 18% 6%	371
	11th to 20th	Day	11% 7% 33% 30% 13% 6%	300
	21st to end	Day	14% 11% 32% 30% 12% 2	330
November	1st to 10th	Day	19% 8% 26% 32% 12% 3	300
	11th to 20th	Day	16% 10% 31% 29% 13% 1	280
	21st to end	Day	11% 7% 29% 33% 12% 10%	200
December	1st to 10th	Day	9% 6% 30% 32% 18% 7%	200
	11th to 20th	Day	9% 6% 35% 34% 15% 2	200
	21st to end	Day	7% 5% 21% 35% 24% 8%	220
January	1st to 10th	Night	9% 6% 33% 35% 14% 3	1000
	11th to 20th	Night	11% 6% 33% 37% 13% 2	1000
	21st to end	Night	11% 9% 30% 37% 12% 1	935
February	1st to 10th	Night	10% 9% 25% 36% 19% 2	800
	11th to 20th	Night	10% 4 33% 39% 14% 1	784
	21st to end	Night	8% 5% 22% 41% 20% 5%	660
March	1st to 10th	Night	9% 4 31% 36% 16% 4	800
	11th to 20th	Night	9% 6% 30% 38% 15% 2	800
	21st to end	Night	13% 6% 27% 36% 16% 1	880
April	1st to 10th	Night	14% 6% 29% 34% 15% 2	700
	11th to 20th	Night	12% 9% 32% 35% 10% 1	593
	21st to end	Night	15% 6% 28% 37% 14% 1	600
May	1st to 10th	Night	15% 8% 26% 34% 15% 1	545
	11th to 20th	Night	12% 6% 29% 35% 17% 1	375
	21st to end	Night	21% 5% 23% 32% 18% 1	411
June	1st to 10th	Night	18% 9% 25% 36% 10% 2	380
	11th to 20th	Night	16% 5% 33% 30% 16%	380
	21st to end	Night	11% 5% 26% 37% 19% 2	380
July	1st to 10th	Night	8% 2 18% 49% 22% 1	370
	11th to 20th	Night	9% 3 21% 46% 20% 2	368
	21st to end	Night	5% 3 19% 47% 24% 2	416
August	1st to 10th	Night	9% 2 23% 42% 21% 3	383
	11th to 20th	Night	10% 2 20% 46% 21% 1	564
	21st to end	Night	9% 5% 20% 43% 22% 1	627
September	1st to 10th	Night	12% 4 21% 44% 17% 2	609
	11th to 20th	Night	17% 5% 18% 41% 18% 1	760
	21st to end	Night	11% 6% 30% 38% 14% 2	760
October	1st to 10th	Night	15% 3 27% 37% 16% 2	760
	11th to 20th	Night	12% 5% 31% 37% 13% 2	760
	21st to end	Night	11% 8% 33% 36% 13% 1	836
November	1st to 10th	Night	17% 7% 31% 34% 9% 1	945
	11th to 20th	Night	10% 9% 37% 31% 11% 2	1000
	21st to end	Night	9% 5% 34% 37% 13% 1	1000
December	1st to 10th	Night	12% 7% 30% 34% 15% 2	1000
	11th to 20th	Night	11% 6% 32% 37% 12% 2	1000
	21st to end	Night	11% 4 30% 36% 16% 3	1100

Page generated at 2025-05-08 07:33:57. Version ac07

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