Ranchita Canyon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ranchita Canyon Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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	4 3 1 3 2 2 3 2 4 6% 70%	139724
	Night	6% 4 1 3 2 2 3 2 4 6% 66%	139621
Transparency	Day	17% 4 7% 18% 28% 25%	134745
	Night	20% 4 8% 19% 26% 23%	135580
Seeing	Day	6% 5% 16% 31% 29% 13%	17313
	Night	6% 3 12% 37% 35% 7%	26958

By Month

Percentage Cloud Cover SW (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	9% 5% 1 4 3 3 3 4 5% 7% 55%	4961
	11th to 20th	Day	5% 4 1 3 3 3 3 3 4 5% 65%	5340
	21st to end	Day	9% 5% 2 6% 4 4 4 4 6% 9% 48%	5843
February	1st to 10th	Day	13% 6% 2 4 3 3 4 3 5% 6% 53%	1954
	11th to 20th	Day	10% 5% 2 6% 3 4 4 3 5% 7% 51%	2050
	21st to end	Day	11% 7% 2 5% 2 3 5% 4 5% 7% 50%	1730
March	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 5% 8% 9% 40%	4742
	11th to 20th	Day	9% 4 2 4 3 3 4 3 5% 6% 57%	5110
	21st to end	Day	8% 6% 2 6% 4 4 4 5% 7% 8% 45%	5866
April	1st to 10th	Day	8% 5% 1 4 3 3 3 3 5% 8% 56%	2413
	11th to 20th	Day	6% 5% 2 4 3 4 3 4 5% 7% 59%	2369
	21st to end	Day	5% 4 1 3 3 3 4 3 4 7% 64%	2400
May	1st to 10th	Day	2 2 1 2 1 2 2 1 3 5% 78%	5440
	11th to 20th	Day	1 1 1 3 2 2 2 2 3 5% 78%	5732
	21st to end	Day	1 1 1 2 1 1 2 2 3 6% 80%	6902
June	1st to 10th	Day	2 2 1 2 2 2 3 2 5% 8% 71%	2800
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 86%	2800
	21st to end	Day	1 1 1 1 1 2 2 3 87%	2800
July	1st to 10th	Day	1 1 2 3 92%	6319
	11th to 20th	Day	1 1 1 1 1 1 2 2 4 85%	5997
	21st to end	Day	1 1 1 1 2 2 4 5% 83%	6402
August	1st to 10th	Day	1 1 1 1 1 1 3 4 87%	5563
	11th to 20th	Day	1 1 1 1 2 3 91%	5364
	21st to end	Day	1 1 1 1 1 1 1 2 4 87%	5984
September	1st to 10th	Day	1 1 1 2 1 2 2 4 86%	2400
	11th to 20th	Day	2 1 1 2 1 2 1 2 2 5% 81%	2395
	21st to end	Day	2 2 1 2 2 2 2 3 4 5% 77%	2200
October	1st to 10th	Day	1 1 1 2 2 2 2 2 4 5% 77%	3281
	11th to 20th	Day	2 2 1 2 2 2 2 2 5% 4 76%	3261
	21st to end	Day	3 3 1 4 2 2 3 3 3 6% 69%	3558
November	1st to 10th	Day	4 4 1 4 4 2 3 3 5% 7% 64%	1956
	11th to 20th	Day	8% 3 2 4 3 4 3 3 5% 5% 61%	1890
	21st to end	Day	7% 4 2 4 4 2 3 3 5% 6% 60%	1890
December	1st to 10th	Day	6% 5% 2 5% 3 3 3 3 5% 7% 58%	2812
	11th to 20th	Day	16% 5% 2 4 3 2 4 3 6% 7% 48%	3108
	21st to end	Day	13% 8% 2 6% 3 4 5% 4 7% 12% 37%	4092
January	1st to 10th	Night	13% 7% 2 4 3 2 2 2 4 7% 54%	7930
	11th to 20th	Night	6% 4 1 3 2 2 3 2 4 7% 64%	7650
	21st to end	Night	11% 6% 2 7% 4 4 4 3 6% 7% 47%	8371
February	1st to 10th	Night	12% 6% 1 5% 4 3 4 3 5% 5% 53%	2664
	11th to 20th	Night	10% 4 1 4 2 3 3 3 5% 9% 56%	2458
	21st to end	Night	8% 6% 2 5% 4 3 3 3 3 6% 56%	2076
March	1st to 10th	Night	11% 9% 2 6% 4 4 4 4 5% 7% 43%	5366
	11th to 20th	Night	7% 6% 2 4 3 3 3 3 5% 7% 58%	5110
	21st to end	Night	11% 8% 2 5% 3 3 3 3 4 7% 50%	5349
April	1st to 10th	Night	6% 5% 1 4 3 3 3 3 5% 8% 60%	2010
	11th to 20th	Night	4 4 2 5% 2 2 2 2 3 5% 67%	1979
	21st to end	Night	3 4 1 4 3 2 4 2 3 6% 67%	2000
May	1st to 10th	Night	1 2 1 2 2 1 2 2 3 5% 80%	4560
	11th to 20th	Night	1 1 2 5% 2 1 2 2 3 5% 75%	4179
	21st to end	Night	1 1 1 1 1 1 2 2 2 3 86%	3972
June	1st to 10th	Night	2 2 1 3 2 2 2 3 5% 5% 75%	1600
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 4 87%	1600
	21st to end	Night	1 1 2 1 1 2 3 90%	1600
July	1st to 10th	Night	1 1 2 2 93%	3640
	11th to 20th	Night	1 1 1 2 1 2 4 88%	3959
	21st to end	Night	1 1 1 3 2 2 2 2 5% 5% 76%	4472
August	1st to 10th	Night	1 1 1 1 1 1 2 3 88%	4258
	11th to 20th	Night	1 1 1 1 2 3 91%	4506
	21st to end	Night	1 1 1 1 1 2 3 89%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 87%	2000
	11th to 20th	Night	2 2 1 2 1 1 2 1 2 3 82%	2005
	21st to end	Night	1 2 1 2 2 1 2 1 3 3 82%	2200
October	1st to 10th	Night	2 2 1 2 1 2 2 2 3 5% 81%	3914
	11th to 20th	Night	2 2 1 2 1 2 2 2 5% 5% 76%	3897
	21st to end	Night	3 3 1 3 2 1 2 2 4 5% 74%	4253
November	1st to 10th	Night	3 4 1 4 3 2 2 3 4 6% 70%	2561
	11th to 20th	Night	5% 4 2 4 3 3 3 3 5% 7% 62%	2730
	21st to end	Night	6% 5% 2 5% 3 2 4 3 6% 7% 58%	2730
December	1st to 10th	Night	6% 3 1 3 3 4 4 4 5% 7% 60%	4585
	11th to 20th	Night	14% 7% 1 4 3 3 4 4 7% 9% 43%	5316
	21st to end	Night	11% 8% 3 7% 5% 5% 6% 5% 7% 9% 35%	7106

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	27% 7% 14% 29% 16% 7%	4962
	11th to 20th	Day	22% 4 7% 12% 25% 30%	5340
	21st to end	Day	31% 6% 10% 16% 25% 12%	5843
February	1st to 10th	Day	33% 4 8% 19% 22% 14%	1954
	11th to 20th	Day	32% 5% 9% 21% 24% 8%	2060
	21st to end	Day	31% 5% 12% 23% 23% 6%	1730
March	1st to 10th	Day	33% 8% 13% 18% 23% 4	4742
	11th to 20th	Day	26% 6% 12% 32% 16% 8%	5110
	21st to end	Day	32% 7% 13% 28% 16% 4	5866
April	1st to 10th	Day	26% 5% 12% 26% 22% 9%	2413
	11th to 20th	Day	23% 6% 11% 27% 25% 8%	2372
	21st to end	Day	19% 5% 10% 29% 28% 8%	2400
May	1st to 10th	Day	11% 2 8% 25% 38% 16%	5440
	11th to 20th	Day	9% 4 6% 28% 42% 11%	5735
	21st to end	Day	8% 2 6% 27% 49% 9%	6904
June	1st to 10th	Day	12% 4 10% 21% 35% 18%	2800
	11th to 20th	Day	7% 2 4 13% 42% 33%	2800
	21st to end	Day	6% 2 3 9% 34% 47%	2800
July	1st to 10th	Day	2 1 1 5% 22% 69%	6251
	11th to 20th	Day	5% 2 2 6% 23% 61%	5925
	21st to end	Day	6% 3 3 14% 33% 42%	6217
August	1st to 10th	Day	7% 2 2 10% 33% 46%	4047
	11th to 20th	Day	4 1 2 6% 29% 59%	3880
	21st to end	Day	5% 1 1 10% 30% 52%	4311
September	1st to 10th	Day	6% 2 3 10% 31% 48%	2400
	11th to 20th	Day	9% 2 3 18% 41% 27%	2395
	21st to end	Day	10% 2 4 18% 37% 29%	2200
October	1st to 10th	Day	10% 2 4 13% 24% 46%	3281
	11th to 20th	Day	12% 3 6% 20% 37% 23%	3261
	21st to end	Day	17% 2 4 15% 35% 27%	3558
November	1st to 10th	Day	20% 3 9% 21% 30% 17%	1956
	11th to 20th	Day	25% 4 10% 23% 25% 14%	1890
	21st to end	Day	25% 4 8% 20% 25% 18%	1890
December	1st to 10th	Day	26% 4 6% 19% 27% 17%	2812
	11th to 20th	Day	34% 5% 13% 20% 18% 9%	3108
	21st to end	Day	37% 9% 17% 21% 11% 4	4092
January	1st to 10th	Night	31% 6% 13% 24% 20% 6%	7930
	11th to 20th	Night	21% 5% 7% 14% 27% 27%	7650
	21st to end	Night	35% 6% 8% 18% 22% 11%	8371
February	1st to 10th	Night	32% 4 8% 19% 23% 14%	2664
	11th to 20th	Night	26% 4 11% 24% 26% 9%	2459
	21st to end	Night	29% 4 10% 25% 24% 7%	2076
March	1st to 10th	Night	36% 8% 11% 20% 22% 4	5366
	11th to 20th	Night	25% 6% 14% 28% 19% 8%	5110
	21st to end	Night	31% 6% 15% 27% 17% 3	5349
April	1st to 10th	Night	23% 5% 14% 28% 19% 11%	2010
	11th to 20th	Night	21% 3 12% 29% 26% 10%	1979
	21st to end	Night	18% 4 9% 29% 32% 8%	2000
May	1st to 10th	Night	10% 3 9% 31% 31% 16%	4557
	11th to 20th	Night	10% 4 6% 25% 39% 15%	4180
	21st to end	Night	6% 2 6% 27% 49% 10%	3972
June	1st to 10th	Night	11% 4 12% 20% 35% 18%	1600
	11th to 20th	Night	6% 1 4 16% 40% 33%	1600
	21st to end	Night	4 1 2 9% 36% 49%	1600
July	1st to 10th	Night	2 1 1 4 21% 72%	3600
	11th to 20th	Night	4 2 2 6% 19% 67%	3909
	21st to end	Night	9% 3 4 14% 28% 42%	4345
August	1st to 10th	Night	7% 1 2 10% 31% 49%	3092
	11th to 20th	Night	3 1 1 4 26% 65%	3256
	21st to end	Night	4 1 2 8% 29% 55%	3608
September	1st to 10th	Night	6% 2 3 8% 28% 52%	2000
	11th to 20th	Night	10% 2 3 16% 36% 34%	2005
	21st to end	Night	9% 2 3 16% 38% 31%	2200
October	1st to 10th	Night	9% 2 4 11% 26% 47%	3914
	11th to 20th	Night	12% 2 6% 22% 34% 24%	3897
	21st to end	Night	15% 3 4 16% 39% 24%	4253
November	1st to 10th	Night	17% 3 7% 22% 32% 20%	2561
	11th to 20th	Night	21% 4 11% 21% 26% 18%	2730
	21st to end	Night	25% 4 11% 17% 26% 17%	2730
December	1st to 10th	Night	23% 4 7% 20% 31% 15%	4585
	11th to 20th	Night	35% 7% 12% 19% 17% 9%	5316
	21st to end	Night	43% 9% 14% 21% 9% 4	7106

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	15% 7% 24% 32% 19% 3	303
	11th to 20th	Day	12% 5% 20% 32% 24% 7%	430
	21st to end	Day	11% 4 20% 34% 24% 7%	473
February	1st to 10th	Day	13% 7% 21% 30% 23% 6%	464
	11th to 20th	Day	13% 12% 20% 33% 19% 3	535
	21st to end	Day	10% 9% 22% 37% 19% 3	446
March	1st to 10th	Day	13% 11% 23% 34% 18% 1	540
	11th to 20th	Day	13% 8% 21% 30% 21% 5%	540
	21st to end	Day	10% 12% 25% 31% 19% 4	594
April	1st to 10th	Day	11% 8% 24% 28% 21% 9%	505
	11th to 20th	Day	7% 11% 23% 32% 21% 7%	492
	21st to end	Day	3 9% 23% 31% 21% 12%	500
May	1st to 10th	Day	7% 8% 23% 31% 24% 8%	503
	11th to 20th	Day	3 7% 21% 34% 24% 11%	528
	21st to end	Day	4 8% 17% 34% 25% 13%	573
June	1st to 10th	Day	2 5% 15% 33% 30% 16%	530
	11th to 20th	Day	1 3 19% 32% 29% 15%	530
	21st to end	Day	1 1 13% 30% 30% 25%	530
July	1st to 10th	Day	7% 36% 35% 23%	526
	11th to 20th	Day	2 4 27% 38% 29%	524
	21st to end	Day	1 4 30% 38% 27%	575
August	1st to 10th	Day	1 1 9% 31% 36% 21%	527
	11th to 20th	Day	1 7% 26% 39% 26%	517
	21st to end	Day	2 1 5% 24% 42% 27%	583
September	1st to 10th	Day	2 10% 26% 38% 25%	530
	11th to 20th	Day	3 2 12% 29% 39% 16%	530
	21st to end	Day	2 3 11% 27% 42% 15%	530
October	1st to 10th	Day	3 3 15% 32% 34% 13%	530
	11th to 20th	Day	3 3 17% 30% 35% 12%	530
	21st to end	Day	4 4 13% 29% 39% 11%	583
November	1st to 10th	Day	3 7% 14% 26% 41% 9%	432
	11th to 20th	Day	8% 6% 13% 35% 29% 8%	330
	21st to end	Day	7% 3 18% 36% 30% 6%	330
December	1st to 10th	Day	11% 5% 15% 32% 32% 5%	258
	11th to 20th	Day	8% 9% 13% 31% 28% 11%	220
	21st to end	Day	17% 9% 18% 32% 20% 4	242
January	1st to 10th	Night	15% 3 15% 42% 21% 5%	840
	11th to 20th	Night	9% 1 13% 45% 27% 4	840
	21st to end	Night	13% 3 14% 44% 24% 2	924
February	1st to 10th	Night	14% 4 12% 41% 25% 4	840
	11th to 20th	Night	11% 4 18% 40% 23% 4	824
	21st to end	Night	10% 4 15% 50% 18% 2	692
March	1st to 10th	Night	11% 5% 18% 43% 20% 2	840
	11th to 20th	Night	10% 4 15% 39% 28% 5%	840
	21st to end	Night	10% 6% 18% 38% 26% 3	924
April	1st to 10th	Night	6% 7% 19% 38% 27% 3	804
	11th to 20th	Night	5% 6% 19% 35% 28% 5%	791
	21st to end	Night	4 5% 24% 32% 27% 8%	800
May	1st to 10th	Night	3 4 18% 40% 28% 7%	800
	11th to 20th	Night	4 3 18% 37% 33% 5%	645
	21st to end	Night	3 4 15% 40% 33% 6%	433
June	1st to 10th	Night	2 2 10% 42% 41% 4	400
	11th to 20th	Night	1 1 12% 41% 41% 5%	400
	21st to end	Night	1 5% 39% 48% 8%	400
July	1st to 10th	Night	1 3 26% 63% 7%	390
	11th to 20th	Night	1 1 13% 63% 22%	523
	21st to end	Night	1 1 1 13% 63% 22%	657
August	1st to 10th	Night	1 3 25% 56% 14%	695
	11th to 20th	Night	3 24% 60% 13%	792
	21st to end	Night	1 2 19% 62% 16%	880
September	1st to 10th	Night	1 1 3 25% 57% 14%	800
	11th to 20th	Night	3 2 6% 35% 45% 10%	800
	21st to end	Night	1 1 8% 30% 50% 9%	800
October	1st to 10th	Night	4 1 8% 36% 42% 8%	800
	11th to 20th	Night	4 3 9% 37% 40% 8%	800
	21st to end	Night	5% 2 8% 38% 37% 10%	880
November	1st to 10th	Night	4 2 12% 38% 38% 6%	820
	11th to 20th	Night	6% 3 10% 48% 30% 5%	840
	21st to end	Night	6% 2 12% 47% 28% 5%	840
December	1st to 10th	Night	10% 3 13% 43% 28% 4	840
	11th to 20th	Night	13% 3 11% 48% 23% 3	840
	21st to end	Night	13% 5% 17% 45% 18% 2	924

Page generated at 2026-03-29 23:18:40. Version ac07

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