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 2026-09-14.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 40%	154152
	Night	7% 9% 4 9% 6% 5% 5% 4 6% 8% 36%	145705
Transparency	Day	41% 6% 16% 26% 10% 1	153849
	Night	44% 6% 15% 23% 10% 1	145591
Seeing	Day	12% 7% 25% 31% 19% 5%	17916
	Night	12% 6% 28% 38% 15% 2	26863

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	4 12% 7% 17% 8% 6% 5% 4 5% 7% 25%	4125
	11th to 20th	Day	3 9% 5% 10% 6% 6% 6% 6% 8% 7% 33%	4119
	21st to end	Day	4 9% 4 11% 5% 5% 5% 4 6% 8% 40%	5080
February	1st to 10th	Day	7% 13% 4 12% 9% 6% 6% 4 5% 8% 26%	1709
	11th to 20th	Day	6% 13% 5% 11% 7% 7% 6% 5% 7% 6% 26%	1845
	21st to end	Day	3 13% 6% 13% 8% 6% 6% 5% 6% 8% 26%	1625
March	1st to 10th	Day	3 10% 5% 12% 7% 6% 6% 4 7% 10% 31%	4652
	11th to 20th	Day	6% 11% 4 10% 6% 5% 5% 4 6% 9% 36%	5109
	21st to end	Day	10% 18% 6% 13% 5% 5% 5% 4 5% 6% 22%	5607
April	1st to 10th	Day	9% 13% 3 7% 6% 5% 6% 4 7% 7% 31%	2608
	11th to 20th	Day	11% 12% 3 8% 5% 5% 5% 5% 7% 8% 31%	2700
	21st to end	Day	13% 10% 3 8% 5% 5% 5% 4 6% 8% 32%	2730
May	1st to 10th	Day	13% 8% 2 5% 4 4 5% 4 6% 8% 41%	8120
	11th to 20th	Day	13% 10% 3 8% 6% 5% 6% 4 7% 8% 30%	8755
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 7% 39%	9649
June	1st to 10th	Day	15% 7% 3 7% 4 5% 5% 4 7% 8% 35%	3150
	11th to 20th	Day	19% 8% 3 7% 5% 5% 6% 5% 6% 8% 29%	3150
	21st to end	Day	11% 4 2 5% 4 4 5% 5% 8% 10% 42%	3150
July	1st to 10th	Day	7% 4 2 5% 3 4 4 4 6% 9% 52%	8820
	11th to 20th	Day	10% 4 2 5% 4 4 5% 4 7% 9% 47%	8820
	21st to end	Day	6% 4 2 4 3 3 3 3 5% 8% 59%	9569
August	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 4 6% 9% 48%	6430
	11th to 20th	Day	9% 6% 3 6% 4 5% 5% 4 6% 9% 43%	5925
	21st to end	Day	8% 4 2 4 3 3 3 3 6% 8% 56%	6570
September	1st to 10th	Day	11% 6% 2 6% 3 3 4 4 5% 7% 49%	2630
	11th to 20th	Day	15% 6% 2 5% 4 3 4 3 5% 7% 46%	2234
	21st to end	Day	8% 6% 3 5% 3 5% 4 4 6% 8% 47%	2200
October	1st to 10th	Day	8% 6% 3 8% 5% 5% 4 4 5% 8% 43%	3383
	11th to 20th	Day	6% 6% 2 7% 5% 5% 5% 4 7% 10% 43%	3075
	21st to end	Day	8% 9% 3 6% 5% 4 5% 4 6% 7% 43%	3200
November	1st to 10th	Day	9% 17% 5% 11% 5% 5% 5% 3 5% 7% 27%	1658
	11th to 20th	Day	8% 14% 3 10% 6% 5% 4 3 6% 6% 34%	1638
	21st to end	Day	6% 12% 3 12% 7% 5% 4 4 7% 8% 30%	1470
December	1st to 10th	Day	9% 12% 5% 9% 6% 6% 6% 5% 6% 6% 28%	2360
	11th to 20th	Day	7% 10% 4 15% 8% 6% 5% 4 6% 7% 27%	2712
	21st to end	Day	2 8% 4 10% 5% 5% 5% 4 6% 8% 43%	3575
January	1st to 10th	Night	4 13% 6% 14% 8% 7% 6% 4 6% 8% 23%	8768
	11th to 20th	Night	3 10% 4 10% 6% 6% 6% 5% 6% 9% 37%	8779
	21st to end	Night	3 9% 5% 11% 6% 5% 6% 5% 6% 8% 36%	9156
February	1st to 10th	Night	5% 12% 5% 12% 7% 6% 5% 4 7% 8% 28%	2910
	11th to 20th	Night	5% 12% 5% 12% 6% 6% 6% 5% 7% 8% 27%	2662
	21st to end	Night	4 10% 5% 11% 6% 6% 6% 5% 7% 8% 32%	2178
March	1st to 10th	Night	3 8% 4 13% 8% 7% 6% 5% 7% 10% 30%	5462
	11th to 20th	Night	5% 8% 4 9% 6% 6% 7% 5% 7% 10% 32%	5110
	21st to end	Night	7% 18% 6% 15% 6% 5% 5% 4 6% 6% 20%	5610
April	1st to 10th	Night	11% 11% 4 8% 6% 6% 5% 4 6% 8% 31%	2009
	11th to 20th	Night	9% 11% 5% 9% 6% 6% 6% 4 6% 9% 29%	1871
	21st to end	Night	10% 10% 4 9% 5% 6% 5% 3 7% 8% 34%	1890
May	1st to 10th	Night	14% 9% 3 7% 5% 4 4 4 6% 7% 36%	4815
	11th to 20th	Night	13% 7% 3 9% 5% 6% 6% 5% 7% 9% 30%	4105
	21st to end	Night	11% 8% 3 9% 6% 6% 6% 4 7% 8% 33%	4522
June	1st to 10th	Night	15% 9% 4 7% 5% 6% 5% 5% 7% 9% 30%	1470
	11th to 20th	Night	14% 8% 3 9% 7% 7% 5% 4 8% 10% 27%	1470
	21st to end	Night	10% 6% 2 7% 5% 5% 5% 4 7% 9% 41%	1470
July	1st to 10th	Night	5% 4 2 5% 5% 4 5% 4 7% 8% 51%	4140
	11th to 20th	Night	7% 4 2 5% 4 5% 5% 4 6% 9% 48%	4140
	21st to end	Night	7% 4 2 5% 3 3 4 4 6% 9% 52%	4499
August	1st to 10th	Night	9% 6% 2 7% 5% 4 3 4 6% 7% 46%	3717
	11th to 20th	Night	10% 6% 2 8% 5% 6% 6% 5% 7% 10% 35%	4141
	21st to end	Night	7% 3 2 4 4 4 4 4 7% 9% 51%	4578
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 4 5% 8% 48%	1986
	11th to 20th	Night	13% 7% 2 5% 4 3 3 3 6% 8% 47%	2233
	21st to end	Night	8% 6% 3 5% 3 4 4 3 7% 9% 48%	2200
October	1st to 10th	Night	9% 6% 2 6% 4 4 4 4 6% 8% 46%	3810
	11th to 20th	Night	6% 7% 3 7% 4 5% 5% 5% 7% 9% 43%	4072
	21st to end	Night	6% 7% 3 7% 5% 5% 6% 5% 7% 9% 40%	4600
November	1st to 10th	Night	9% 15% 4 8% 5% 4 5% 3 6% 7% 32%	2839
	11th to 20th	Night	5% 9% 4 11% 7% 6% 6% 4 7% 8% 33%	2980
	21st to end	Night	6% 11% 4 10% 7% 6% 6% 5% 6% 9% 31%	3150
December	1st to 10th	Night	6% 13% 5% 12% 7% 6% 6% 4 6% 9% 26%	5040
	11th to 20th	Night	7% 12% 5% 13% 7% 7% 6% 5% 7% 8% 22%	5700
	21st to end	Night	3 7% 3 9% 6% 6% 5% 4 6% 9% 40%	7623

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	57% 5% 10% 19% 9%	4125
	11th to 20th	Day	46% 5% 16% 16% 16% 2	4140
	21st to end	Day	42% 5% 17% 30% 7%	5081
February	1st to 10th	Day	55% 5% 13% 16% 10% 1	1709
	11th to 20th	Day	54% 7% 13% 17% 9% 1	1854
	21st to end	Day	54% 6% 11% 19% 10%	1625
March	1st to 10th	Day	46% 6% 16% 20% 11%	4652
	11th to 20th	Day	44% 7% 14% 23% 13%	5110
	21st to end	Day	60% 6% 11% 16% 6%	5607
April	1st to 10th	Day	48% 8% 17% 17% 8% 1	2608
	11th to 20th	Day	48% 8% 14% 22% 8% 1	2700
	21st to end	Day	47% 8% 14% 21% 8% 1	2730
May	1st to 10th	Day	40% 5% 10% 29% 13% 3	8120
	11th to 20th	Day	48% 6% 11% 25% 8%	8759
	21st to end	Day	41% 6% 15% 28% 10%	9650
June	1st to 10th	Day	44% 8% 15% 22% 10% 1	3150
	11th to 20th	Day	50% 8% 15% 19% 7% 1	3150
	21st to end	Day	35% 9% 21% 26% 7% 1	3150
July	1st to 10th	Day	29% 4 19% 33% 14% 1	8746
	11th to 20th	Day	35% 4 18% 28% 12% 3	8739
	21st to end	Day	25% 3 16% 32% 18% 5%	9362
August	1st to 10th	Day	32% 5% 18% 32% 11% 2	6412
	11th to 20th	Day	37% 3 25% 27% 6%	5964
	21st to end	Day	27% 4 18% 38% 13% 1	6569
September	1st to 10th	Day	33% 7% 16% 27% 12% 4	2630
	11th to 20th	Day	38% 6% 15% 29% 10% 2	2234
	21st to end	Day	33% 8% 17% 27% 12% 3	2200
October	1st to 10th	Day	39% 3 21% 27% 9% 1	3383
	11th to 20th	Day	35% 5% 19% 29% 11% 2	3075
	21st to end	Day	40% 5% 9% 34% 10% 1	3200
November	1st to 10th	Day	56% 7% 12% 17% 7% 2	1658
	11th to 20th	Day	49% 7% 14% 22% 8% 1	1638
	21st to end	Day	49% 9% 15% 19% 8% 1	1470
December	1st to 10th	Day	54% 5% 19% 16% 4 1	2360
	11th to 20th	Day	56% 6% 16% 18% 4 1	2714
	21st to end	Day	39% 5% 12% 27% 14% 3	3575
January	1st to 10th	Night	56% 6% 12% 16% 8% 1	8769
	11th to 20th	Night	44% 4 17% 20% 13% 2	8820
	21st to end	Night	45% 4 18% 25% 7%	9156
February	1st to 10th	Night	52% 6% 12% 19% 11% 1	2910
	11th to 20th	Night	50% 7% 12% 17% 12% 1	2663
	21st to end	Night	47% 7% 14% 21% 11% 1	2178
March	1st to 10th	Night	45% 7% 20% 19% 9%	5462
	11th to 20th	Night	43% 8% 17% 24% 7% 1	5110
	21st to end	Night	62% 7% 10% 15% 5% 1	5610
April	1st to 10th	Night	49% 7% 15% 17% 11% 1	2009
	11th to 20th	Night	50% 7% 13% 22% 8% 1	1871
	21st to end	Night	45% 8% 13% 24% 8% 2	1890
May	1st to 10th	Night	46% 4 9% 25% 13% 2	4812
	11th to 20th	Night	47% 7% 13% 24% 9%	4105
	21st to end	Night	46% 8% 14% 25% 6% 1	4526
June	1st to 10th	Night	49% 8% 13% 20% 9%	1470
	11th to 20th	Night	51% 10% 12% 18% 7% 1	1470
	21st to end	Night	37% 8% 19% 26% 8% 1	1470
July	1st to 10th	Night	31% 4 22% 28% 15% 1	4105
	11th to 20th	Night	33% 5% 17% 32% 10% 3	4098
	21st to end	Night	29% 4 15% 31% 17% 3	4401
August	1st to 10th	Night	37% 5% 15% 31% 11% 1	3710
	11th to 20th	Night	43% 4 23% 25% 5% 1	4168
	21st to end	Night	29% 4 17% 38% 10% 2	4578
September	1st to 10th	Night	33% 7% 15% 25% 13% 6%	1986
	11th to 20th	Night	36% 6% 15% 27% 12% 4	2233
	21st to end	Night	32% 6% 16% 28% 15% 2	2200
October	1st to 10th	Night	36% 4 19% 27% 12% 1	3810
	11th to 20th	Night	37% 5% 16% 29% 11% 2	4072
	21st to end	Night	39% 6% 14% 33% 8% 1	4600
November	1st to 10th	Night	50% 6% 13% 21% 9% 1	2839
	11th to 20th	Night	46% 7% 17% 19% 10% 1	2980
	21st to end	Night	48% 8% 17% 19% 6% 2	3150
December	1st to 10th	Night	55% 5% 19% 16% 5% 1	5040
	11th to 20th	Night	56% 7% 19% 14% 4	5697
	21st to end	Night	39% 5% 12% 26% 15% 3	7623

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% 5% 29% 31% 20% 9%	220
	11th to 20th	Day	7% 8% 33% 33% 17% 3	220
	21st to end	Day	9% 7% 26% 34% 19% 5%	242
February	1st to 10th	Day	11% 8% 27% 32% 15% 6%	237
	11th to 20th	Day	8% 6% 28% 35% 18% 4	330
	21st to end	Day	7% 6% 26% 38% 18% 5%	341
March	1st to 10th	Day	10% 6% 31% 32% 17% 4	540
	11th to 20th	Day	10% 5% 31% 34% 15% 4	540
	21st to end	Day	13% 8% 33% 26% 16% 3	594
April	1st to 10th	Day	11% 13% 31% 29% 11% 4	540
	11th to 20th	Day	14% 11% 30% 28% 17% 2	532
	21st to end	Day	17% 11% 25% 29% 14% 4	540
May	1st to 10th	Day	14% 11% 22% 27% 19% 5%	656
	11th to 20th	Day	14% 7% 23% 33% 19% 4	775
	21st to end	Day	16% 5% 22% 28% 22% 6%	844
June	1st to 10th	Day	16% 8% 26% 31% 17% 2	780
	11th to 20th	Day	20% 8% 26% 30% 13% 3	780
	21st to end	Day	14% 3 25% 29% 23% 7%	780
July	1st to 10th	Day	9% 4 19% 33% 26% 8%	771
	11th to 20th	Day	12% 5% 21% 31% 25% 7%	768
	21st to end	Day	6% 4 19% 33% 28% 9%	849
August	1st to 10th	Day	10% 4 23% 32% 23% 9%	573
	11th to 20th	Day	9% 3 20% 33% 28% 7%	557
	21st to end	Day	8% 9% 20% 29% 24% 11%	627
September	1st to 10th	Day	15% 6% 24% 31% 19% 6%	570
	11th to 20th	Day	18% 6% 21% 27% 22% 6%	543
	21st to end	Day	11% 10% 31% 29% 15% 3	530
October	1st to 10th	Day	15% 5% 24% 33% 18% 6%	404
	11th to 20th	Day	12% 8% 33% 30% 12% 6%	330
	21st to end	Day	13% 11% 33% 30% 11% 2	363
November	1st to 10th	Day	19% 8% 25% 34% 12% 3	330
	11th to 20th	Day	16% 9% 29% 30% 13% 2	308
	21st to end	Day	10% 6% 28% 35% 13% 9%	220
December	1st to 10th	Day	10% 5% 29% 33% 17% 6%	220
	11th to 20th	Day	10% 7% 35% 32% 14% 2	220
	21st to end	Day	7% 5% 24% 34% 24% 7%	242
January	1st to 10th	Night	9% 6% 33% 36% 14% 2	1050
	11th to 20th	Night	11% 6% 34% 36% 12% 1	1050
	21st to end	Night	11% 8% 30% 38% 11% 1	982
February	1st to 10th	Night	10% 8% 25% 36% 19% 2	840
	11th to 20th	Night	10% 4 32% 40% 14% 1	824
	21st to end	Night	8% 5% 22% 41% 20% 4	692
March	1st to 10th	Night	9% 4 32% 37% 15% 4	840
	11th to 20th	Night	9% 6% 32% 38% 15% 2	840
	21st to end	Night	13% 6% 28% 36% 15% 1	924
April	1st to 10th	Night	15% 6% 28% 34% 15% 2	735
	11th to 20th	Night	13% 9% 32% 35% 10% 1	623
	21st to end	Night	15% 7% 27% 37% 14% 1	630
May	1st to 10th	Night	15% 9% 26% 35% 14% 1	572
	11th to 20th	Night	13% 6% 29% 35% 17% 1	414
	21st to end	Night	20% 5% 22% 32% 20% 1	455
June	1st to 10th	Night	19% 8% 25% 35% 10% 2	420
	11th to 20th	Night	15% 5% 33% 31% 16%	420
	21st to end	Night	12% 4 25% 37% 18% 2	420
July	1st to 10th	Night	8% 2 17% 50% 22% 1	410
	11th to 20th	Night	10% 3 21% 46% 19% 1	408
	21st to end	Night	6% 3 18% 46% 24% 2	460
August	1st to 10th	Night	10% 2 22% 42% 21% 3	423
	11th to 20th	Night	10% 2 18% 46% 22% 1	624
	21st to end	Night	8% 5% 20% 44% 22% 1	693
September	1st to 10th	Night	12% 4 21% 44% 17% 1	673
	11th to 20th	Night	16% 5% 17% 41% 19% 1	812
	21st to end	Night	10% 6% 30% 39% 14% 2	800
October	1st to 10th	Night	15% 4 27% 37% 16% 2	800
	11th to 20th	Night	12% 5% 32% 37% 12% 2	800
	21st to end	Night	11% 8% 34% 35% 12% 1	880
November	1st to 10th	Night	17% 7% 32% 34% 9% 1	994
	11th to 20th	Night	9% 9% 36% 32% 11% 2	1050
	21st to end	Night	9% 5% 33% 38% 12% 1	1050
December	1st to 10th	Night	12% 7% 31% 34% 14% 2	1050
	11th to 20th	Night	11% 6% 33% 36% 11% 2	1050
	21st to end	Night	11% 4 30% 37% 15% 3	1155

Page generated at 2026-09-11 02:11:53. Version ac07

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