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 2024-11-02.

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%	101897
	Night	7% 9% 4 9% 6% 5% 5% 4 6% 8% 35%	97158
Transparency	Day	42% 8% 16% 24% 10% 1	101638
	Night	44% 8% 15% 22% 9% 2	97063
Seeing	Day	12% 7% 26% 31% 19% 5%	15441
	Night	12% 6% 29% 37% 15% 2	24477

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 11% 5% 14% 7% 5% 5% 5% 7% 9% 28%	2219
	11th to 20th	Day	5% 10% 4 10% 7% 6% 7% 8% 9% 7% 28%	2199
	21st to end	Day	5% 9% 4 11% 6% 5% 5% 5% 7% 8% 36%	2730
February	1st to 10th	Day	8% 14% 4 12% 8% 6% 6% 4 5% 7% 26%	1545
	11th to 20th	Day	6% 14% 5% 11% 7% 6% 6% 6% 7% 6% 25%	1665
	21st to end	Day	4 13% 6% 13% 8% 6% 7% 6% 5% 7% 25%	1475
March	1st to 10th	Day	4 12% 6% 13% 8% 7% 6% 4 6% 6% 26%	3159
	11th to 20th	Day	8% 9% 3 7% 5% 4 4 3 6% 10% 40%	3489
	21st to end	Day	10% 20% 6% 14% 5% 4 4 4 4 6% 23%	3825
April	1st to 10th	Day	9% 14% 3 7% 6% 5% 6% 4 7% 7% 31%	2360
	11th to 20th	Day	11% 12% 3 9% 5% 5% 6% 5% 7% 7% 31%	2440
	21st to end	Day	13% 10% 3 8% 6% 5% 6% 4 7% 8% 31%	2470
May	1st to 10th	Day	20% 11% 4 7% 4 5% 5% 4 5% 6% 30%	4375
	11th to 20th	Day	11% 8% 3 7% 5% 5% 5% 5% 7% 9% 34%	4694
	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	13% 9% 3 7% 5% 4 3 3 5% 7% 41%	1971
	11th to 20th	Day	9% 7% 3 7% 5% 5% 5% 4 6% 8% 41%	1800
	21st to end	Day	8% 11% 4 8% 5% 5% 5% 5% 6% 7% 36%	1881
November	1st to 10th	Day	10% 18% 5% 10% 5% 5% 5% 3 5% 7% 27%	1506
	11th to 20th	Day	8% 14% 3 10% 6% 5% 4 3 6% 6% 34%	1482
	21st to end	Day	6% 11% 3 11% 7% 5% 5% 4 8% 9% 32%	1330
December	1st to 10th	Day	7% 12% 7% 10% 7% 7% 6% 5% 5% 5% 28%	1330
	11th to 20th	Day	3 11% 5% 15% 7% 5% 6% 5% 5% 8% 29%	1682
	21st to end	Day	3 8% 4 10% 4 4 4 4 5% 7% 46%	2442
January	1st to 10th	Night	3 14% 5% 13% 7% 7% 7% 5% 6% 10% 24%	4726
	11th to 20th	Night	4 9% 4 13% 7% 6% 7% 5% 6% 9% 30%	4699
	21st to end	Night	4 11% 4 11% 5% 4 5% 5% 7% 9% 33%	4954
February	1st to 10th	Night	6% 12% 5% 12% 7% 6% 5% 3 6% 8% 29%	2634
	11th to 20th	Night	5% 13% 5% 11% 6% 7% 6% 5% 6% 8% 27%	2402
	21st to end	Night	4 10% 5% 11% 6% 6% 6% 5% 7% 7% 33%	1977
March	1st to 10th	Night	3 9% 5% 16% 9% 7% 6% 5% 6% 7% 27%	3715
	11th to 20th	Night	7% 7% 3 7% 6% 6% 6% 5% 7% 9% 37%	3490
	21st to end	Night	7% 19% 7% 16% 6% 5% 6% 5% 6% 6% 17%	3828
April	1st to 10th	Night	11% 11% 5% 8% 6% 7% 5% 3 6% 8% 30%	1818
	11th to 20th	Night	9% 12% 5% 9% 6% 6% 6% 4 6% 9% 29%	1691
	21st to end	Night	10% 10% 4 9% 5% 6% 5% 3 7% 8% 34%	1710
May	1st to 10th	Night	22% 11% 4 7% 4 4 4 3 5% 6% 28%	2587
	11th to 20th	Night	10% 6% 2 8% 5% 6% 6% 6% 8% 9% 34%	2199
	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	11% 8% 2 7% 4 4 5% 4 6% 8% 41%	2209
	11th to 20th	Night	8% 8% 3 9% 5% 6% 5% 4 6% 8% 39%	2379
	21st to end	Night	6% 9% 4 9% 5% 4 6% 5% 7% 9% 35%	2717
November	1st to 10th	Night	10% 15% 4 8% 5% 4 5% 3 6% 7% 32%	2575
	11th to 20th	Night	5% 9% 4 10% 7% 6% 6% 4 7% 8% 33%	2696
	21st to end	Night	6% 10% 3 10% 7% 6% 6% 4 6% 9% 32%	2850
December	1st to 10th	Night	7% 13% 4 12% 7% 6% 5% 4 5% 8% 30%	2850
	11th to 20th	Night	4 11% 4 12% 7% 7% 6% 5% 6% 8% 30%	3510
	21st to end	Night	4 8% 3 8% 5% 6% 5% 4 6% 8% 44%	5214

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	49% 9% 13% 20% 8% 1	2219
	11th to 20th	Day	47% 8% 15% 13% 15% 2	2220
	21st to end	Day	42% 9% 15% 28% 6%	2730
February	1st to 10th	Day	55% 6% 14% 15% 9% 1	1545
	11th to 20th	Day	55% 8% 14% 15% 7% 1	1674
	21st to end	Day	56% 6% 11% 17% 10%	1475
March	1st to 10th	Day	53% 8% 15% 14% 9%	3159
	11th to 20th	Day	37% 9% 19% 23% 12%	3490
	21st to end	Day	60% 8% 11% 15% 5%	3825
April	1st to 10th	Day	48% 9% 17% 16% 8%	2360
	11th to 20th	Day	48% 8% 13% 22% 8% 1	2440
	21st to end	Day	48% 9% 15% 20% 8% 1	2470
May	1st to 10th	Day	53% 8% 12% 22% 5%	4375
	11th to 20th	Day	41% 11% 15% 25% 9%	4698
	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	43% 5% 17% 24% 10% 1	1971
	11th to 20th	Day	38% 9% 16% 26% 10% 1	1800
	21st to end	Day	45% 8% 13% 23% 11% 1	1881
November	1st to 10th	Day	56% 7% 12% 17% 6% 2	1506
	11th to 20th	Day	49% 7% 13% 22% 8% 1	1482
	21st to end	Day	46% 9% 16% 20% 8% 1	1330
December	1st to 10th	Day	55% 7% 13% 16% 7% 2	1330
	11th to 20th	Day	51% 9% 15% 20% 4 1	1684
	21st to end	Day	36% 6% 12% 25% 16% 5%	2442
January	1st to 10th	Night	50% 10% 13% 20% 5% 1	4726
	11th to 20th	Night	49% 7% 11% 17% 14% 2	4740
	21st to end	Night	44% 8% 14% 25% 8% 1	4954
February	1st to 10th	Night	52% 7% 12% 19% 10% 1	2634
	11th to 20th	Night	51% 8% 13% 15% 11% 1	2403
	21st to end	Night	46% 7% 14% 21% 10% 1	1977
March	1st to 10th	Night	50% 8% 14% 20% 6%	3715
	11th to 20th	Night	38% 10% 22% 21% 9% 1	3490
	21st to end	Night	64% 10% 10% 12% 4 1	3828
April	1st to 10th	Night	50% 7% 16% 16% 11% 1	1818
	11th to 20th	Night	49% 7% 13% 22% 8% 1	1691
	21st to end	Night	45% 9% 14% 23% 8% 2	1710
May	1st to 10th	Night	55% 6% 11% 20% 6% 1	2587
	11th to 20th	Night	38% 13% 15% 24% 10%	2199
	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	40% 7% 16% 24% 12% 1	2209
	11th to 20th	Night	41% 7% 16% 23% 10% 3	2379
	21st to end	Night	43% 9% 15% 25% 7% 1	2717
November	1st to 10th	Night	49% 7% 13% 21% 9% 1	2575
	11th to 20th	Night	45% 8% 16% 19% 10% 1	2696
	21st to end	Night	46% 9% 18% 19% 6% 2	2850
December	1st to 10th	Night	52% 7% 12% 20% 8% 1	2850
	11th to 20th	Night	47% 10% 20% 18% 5%	3507
	21st to end	Night	36% 7% 13% 24% 15% 4	5214

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% 28% 30% 19% 11%	180
	11th to 20th	Day	7% 7% 33% 29% 19% 4	180
	21st to end	Day	10% 8% 26% 32% 19% 6%	198
February	1st to 10th	Day	12% 9% 26% 34% 13% 5%	193
	11th to 20th	Day	9% 6% 30% 34% 17% 4	270
	21st to end	Day	7% 6% 26% 38% 18% 5%	287
March	1st to 10th	Day	12% 6% 32% 32% 15% 4	460
	11th to 20th	Day	9% 6% 30% 35% 16% 5%	460
	21st to end	Day	11% 8% 32% 27% 17% 4	506
April	1st to 10th	Day	11% 13% 34% 29% 9% 3	460
	11th to 20th	Day	12% 10% 30% 28% 17% 2	452
	21st to end	Day	17% 11% 28% 28% 14% 2	460
May	1st to 10th	Day	16% 11% 21% 27% 20% 5%	565
	11th to 20th	Day	12% 7% 24% 33% 20% 4	675
	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% 11% 3	330
November	1st to 10th	Day	20% 8% 26% 31% 12% 3	273
	11th to 20th	Day	15% 11% 30% 29% 12% 2	252
	21st to end	Day	8% 7% 31% 32% 11% 11%	180
December	1st to 10th	Day	7% 6% 31% 31% 17% 8%	180
	11th to 20th	Day	8% 6% 37% 33% 14% 2	180
	21st to end	Day	8% 5% 22% 36% 23% 7%	198
January	1st to 10th	Night	10% 7% 33% 35% 14% 2	950
	11th to 20th	Night	11% 6% 32% 37% 13% 2	950
	21st to end	Night	11% 9% 30% 37% 12% 2	889
February	1st to 10th	Night	10% 9% 25% 34% 19% 2	760
	11th to 20th	Night	10% 4 33% 38% 14% 1	744
	21st to end	Night	8% 4 21% 41% 20% 5%	628
March	1st to 10th	Night	9% 4 32% 36% 15% 4	760
	11th to 20th	Night	9% 6% 30% 38% 15% 2	760
	21st to end	Night	13% 7% 27% 36% 16% 1	836
April	1st to 10th	Night	14% 6% 29% 34% 14% 2	665
	11th to 20th	Night	13% 9% 32% 35% 11% 1	563
	21st to end	Night	15% 6% 28% 37% 13% 1	570
May	1st to 10th	Night	16% 8% 26% 34% 14% 1	518
	11th to 20th	Night	12% 6% 29% 35% 17% 1	374
	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% 12% 1	836
November	1st to 10th	Night	17% 7% 31% 34% 9% 1	901
	11th to 20th	Night	9% 9% 37% 31% 11% 2	950
	21st to end	Night	9% 5% 35% 37% 13% 1	950
December	1st to 10th	Night	11% 7% 30% 34% 15% 3	950
	11th to 20th	Night	10% 6% 33% 37% 11% 2	950
	21st to end	Night	11% 4 31% 36% 15% 3	1045

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