Courtright Reservoir
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Courtright Reservoir clear sky chart from 2005-11-06 to 2026-04-17.

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	3 6% 2 4 2 3 3 2 4 5% 66%	139961
	Night	3 6% 2 4 2 3 3 2 4 6% 66%	139657
Transparency	Day	21% 4 7% 20% 27% 21%	135016
	Night	21% 3 8% 20% 28% 20%	135577
Seeing	Day	10% 14% 32% 28% 13% 3	17086
	Night	8% 6% 25% 35% 22% 4	26721

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	5% 11% 4 5% 3 3 3 3 4 6% 54%	4722
	11th to 20th	Day	3 7% 1 4 3 3 3 3 3 5% 66%	4962
	21st to end	Day	4 8% 3 6% 3 3 4 3 5% 10% 52%	5843
February	1st to 10th	Day	7% 10% 4 8% 2 2 3 3 5% 5% 50%	2049
	11th to 20th	Day	4 10% 5% 8% 4 3 3 3 3 6% 51%	2050
	21st to end	Day	6% 12% 4 9% 5% 3 3 3 4 5% 46%	1730
March	1st to 10th	Day	4 12% 5% 14% 3 4 4 4 5% 7% 38%	4618
	11th to 20th	Day	3 12% 4 7% 3 4 4 3 4 7% 49%	4880
	21st to end	Day	4 13% 6% 10% 4 4 4 3 4 5% 44%	6070
April	1st to 10th	Day	5% 8% 4 6% 3 4 4 3 4 6% 52%	2520
	11th to 20th	Day	6% 11% 3 5% 3 3 4 2 4 5% 53%	2442
	21st to end	Day	5% 10% 3 4 3 3 4 3 5% 8% 52%	2400
May	1st to 10th	Day	4 7% 2 4 2 2 3 2 3 4 67%	5694
	11th to 20th	Day	2 7% 2 3 2 3 3 2 3 5% 68%	5841
	21st to end	Day	2 4 1 2 2 3 3 2 3 5% 73%	6786
June	1st to 10th	Day	3 5% 1 4 3 3 3 3 5% 7% 63%	2800
	11th to 20th	Day	2 2 2 1 2 2 2 3 5% 79%	2800
	21st to end	Day	2 2 1 2 2 2 2 1 3 3 81%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 3 88%	6319
	11th to 20th	Day	1 2 1 2 2 2 2 2 3 4 79%	6320
	21st to end	Day	1 1 1 2 2 2 2 2 4 5% 80%	6668
August	1st to 10th	Day	1 1 1 1 1 1 1 1 2 2 87%	5389
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 88%	5364
	21st to end	Day	2 2 1 2 2 2 3 3 4 6% 74%	5984
September	1st to 10th	Day	2 1 1 2 2 2 3 3 3 5% 77%	2400
	11th to 20th	Day	4 3 1 2 2 2 2 2 2 5% 75%	2311
	21st to end	Day	2 4 1 2 2 3 2 2 4 5% 74%	2200
October	1st to 10th	Day	2 4 1 2 2 3 3 2 4 4 72%	3504
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 3 76%	3261
	21st to end	Day	3 4 1 3 3 4 4 3 4 6% 66%	3462
November	1st to 10th	Day	4 7% 3 5% 2 3 4 2 4 6% 61%	1854
	11th to 20th	Day	6% 6% 1 3 3 3 3 3 4 6% 61%	1890
	21st to end	Day	5% 6% 2 5% 3 2 3 2 4 6% 60%	1890
December	1st to 10th	Day	5% 5% 1 4 2 3 3 3 4 7% 64%	2938
	11th to 20th	Day	9% 12% 3 5% 3 3 3 2 5% 6% 48%	3108
	21st to end	Day	7% 11% 5% 7% 3 3 4 3 5% 10% 43%	4092
January	1st to 10th	Night	5% 11% 3 5% 2 2 2 3 4 6% 57%	8172
	11th to 20th	Night	4 7% 2 4 2 2 3 3 4 6% 63%	7994
	21st to end	Night	3 8% 3 6% 3 4 4 4 6% 8% 52%	8371
February	1st to 10th	Night	7% 10% 3 6% 3 3 3 3 5% 6% 53%	2568
	11th to 20th	Night	4 9% 4 6% 4 3 4 2 4 8% 52%	2458
	21st to end	Night	6% 8% 3 7% 4 3 4 2 5% 5% 51%	2076
March	1st to 10th	Night	3 11% 5% 10% 4 3 4 3 6% 6% 45%	5496
	11th to 20th	Night	2 8% 3 6% 4 5% 4 4 4 7% 52%	5335
	21st to end	Night	4 13% 4 8% 3 4 4 3 5% 7% 46%	5146
April	1st to 10th	Night	5% 9% 3 6% 3 3 3 4 4 7% 54%	2100
	11th to 20th	Night	4 9% 3 5% 3 3 2 3 5% 6% 58%	2039
	21st to end	Night	3 7% 1 4 3 2 3 3 5% 6% 61%	2000
May	1st to 10th	Night	1 5% 2 4 2 3 2 2 3 5% 71%	4293
	11th to 20th	Night	2 4 1 2 2 2 2 2 4 5% 74%	4074
	21st to end	Night	1 3 1 2 2 1 1 1 2 4 82%	4075
June	1st to 10th	Night	2 4 1 3 2 2 3 3 4 7% 70%	1600
	11th to 20th	Night	1 1 2 2 2 2 2 4 5% 81%	1600
	21st to end	Night	1 1 1 1 1 1 1 2 3 3 86%	1600
July	1st to 10th	Night	1 1 1 1 1 2 93%	3640
	11th to 20th	Night	1 1 2 1 2 2 2 2 3 83%	3640
	21st to end	Night	1 1 1 1 1 2 2 2 4 85%	4188
August	1st to 10th	Night	1 1 1 1 1 2 1 2 3 87%	4439
	11th to 20th	Night	1 1 1 1 1 1 2 92%	4506
	21st to end	Night	1 1 1 2 2 2 2 2 2 3 82%	5015
September	1st to 10th	Night	1 1 1 1 1 1 2 1 2 3 87%	2000
	11th to 20th	Night	2 3 1 2 1 2 1 1 3 2 82%	2087
	21st to end	Night	2 2 1 2 1 2 2 2 3 4 80%	2200
October	1st to 10th	Night	2 2 1 1 1 1 2 1 2 4 83%	3691
	11th to 20th	Night	2 2 1 2 2 2 2 2 3 4 79%	3897
	21st to end	Night	2 2 1 2 3 3 3 2 3 5% 75%	4346
November	1st to 10th	Night	3 6% 1 4 2 3 2 2 4 6% 66%	2665
	11th to 20th	Night	5% 4 2 4 3 3 3 2 5% 8% 61%	2730
	21st to end	Night	5% 7% 2 5% 3 4 3 3 4 6% 59%	2730
December	1st to 10th	Night	4 5% 1 3 2 3 3 3 5% 6% 64%	4464
	11th to 20th	Night	7% 13% 2 5% 3 3 3 3 6% 10% 44%	5316
	21st to end	Night	5% 8% 2 6% 5% 6% 6% 5% 7% 9% 41%	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	32% 3 12% 23% 21% 9%	4723
	11th to 20th	Day	22% 5% 6% 13% 22% 33%	4962
	21st to end	Day	29% 5% 8% 20% 24% 14%	5843
February	1st to 10th	Day	35% 3 10% 20% 19% 13%	2049
	11th to 20th	Day	36% 5% 8% 20% 22% 8%	2060
	21st to end	Day	41% 4 9% 23% 17% 6%	1730
March	1st to 10th	Day	42% 6% 8% 17% 17% 9%	4618
	11th to 20th	Day	33% 5% 13% 30% 13% 7%	4880
	21st to end	Day	41% 6% 12% 23% 13% 4	6070
April	1st to 10th	Day	34% 5% 14% 23% 18% 5%	2520
	11th to 20th	Day	33% 6% 11% 25% 19% 5%	2445
	21st to end	Day	30% 7% 16% 28% 17% 2	2400
May	1st to 10th	Day	22% 4 8% 35% 27% 4	5694
	11th to 20th	Day	18% 4 9% 32% 31% 6%	5844
	21st to end	Day	15% 4 6% 30% 39% 5%	6787
June	1st to 10th	Day	19% 7% 13% 28% 27% 7%	2800
	11th to 20th	Day	10% 4 8% 25% 36% 18%	2800
	21st to end	Day	10% 3 4 16% 40% 28%	2800
July	1st to 10th	Day	5% 2 2 7% 20% 66%	6251
	11th to 20th	Day	9% 3 3 8% 26% 52%	6245
	21st to end	Day	8% 2 4 14% 32% 39%	6474
August	1st to 10th	Day	9% 3 3 10% 41% 34%	3920
	11th to 20th	Day	5% 3 3 8% 30% 51%	3880
	21st to end	Day	8% 2 3 12% 35% 41%	4311
September	1st to 10th	Day	8% 4 7% 14% 34% 33%	2400
	11th to 20th	Day	12% 4 6% 20% 34% 24%	2311
	21st to end	Day	13% 3 5% 22% 37% 20%	2200
October	1st to 10th	Day	15% 2 4 13% 39% 26%	3504
	11th to 20th	Day	15% 2 4 15% 38% 26%	3261
	21st to end	Day	20% 3 4 21% 37% 16%	3462
November	1st to 10th	Day	25% 4 8% 22% 29% 13%	1854
	11th to 20th	Day	24% 4 8% 24% 27% 12%	1890
	21st to end	Day	27% 3 8% 19% 29% 15%	1890
December	1st to 10th	Day	23% 2 6% 25% 25% 20%	2938
	11th to 20th	Day	36% 4 10% 21% 19% 9%	3108
	21st to end	Day	37% 5% 13% 21% 16% 8%	4092
January	1st to 10th	Night	30% 3 12% 23% 21% 11%	8172
	11th to 20th	Night	23% 3 5% 13% 25% 31%	7994
	21st to end	Night	30% 4 7% 18% 22% 19%	8371
February	1st to 10th	Night	33% 3 5% 23% 21% 15%	2568
	11th to 20th	Night	32% 5% 8% 21% 24% 11%	2459
	21st to end	Night	34% 3 10% 22% 22% 9%	2076
March	1st to 10th	Night	38% 4 7% 17% 22% 12%	5496
	11th to 20th	Night	30% 4 9% 31% 18% 8%	5335
	21st to end	Night	37% 5% 17% 22% 14% 5%	5146
April	1st to 10th	Night	30% 4 12% 26% 20% 8%	2100
	11th to 20th	Night	27% 5% 12% 27% 21% 8%	2039
	21st to end	Night	22% 6% 16% 34% 20% 2	2000
May	1st to 10th	Night	16% 3 11% 39% 26% 5%	4290
	11th to 20th	Night	13% 4 11% 35% 33% 4	4075
	21st to end	Night	9% 3 6% 34% 44% 4	4075
June	1st to 10th	Night	15% 5% 13% 30% 33% 5%	1600
	11th to 20th	Night	7% 5% 7% 26% 35% 20%	1600
	21st to end	Night	6% 2 4 15% 42% 30%	1600
July	1st to 10th	Night	3 1 1 6% 20% 69%	3600
	11th to 20th	Night	8% 3 2 9% 31% 47%	3592
	21st to end	Night	6% 2 3 18% 33% 38%	4070
August	1st to 10th	Night	8% 2 4 16% 38% 32%	3223
	11th to 20th	Night	4 1 2 13% 28% 53%	3256
	21st to end	Night	8% 1 2 10% 39% 40%	3608
September	1st to 10th	Night	6% 2 3 15% 39% 35%	2000
	11th to 20th	Night	10% 3 5% 22% 37% 23%	2087
	21st to end	Night	10% 2 5% 22% 39% 22%	2200
October	1st to 10th	Night	9% 2 4 13% 42% 30%	3691
	11th to 20th	Night	11% 2 3 13% 37% 33%	3897
	21st to end	Night	14% 2 3 17% 45% 19%	4346
November	1st to 10th	Night	20% 3 8% 23% 28% 17%	2665
	11th to 20th	Night	22% 3 8% 21% 31% 15%	2730
	21st to end	Night	27% 3 7% 19% 28% 16%	2730
December	1st to 10th	Night	22% 2 7% 23% 25% 20%	4464
	11th to 20th	Night	36% 4 10% 20% 22% 8%	5316
	21st to end	Night	36% 5% 13% 17% 19% 9%	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	26% 19% 25% 21% 6% 2	220
	11th to 20th	Day	15% 14% 29% 24% 15% 3	299
	21st to end	Day	14% 15% 29% 27% 11% 3	473
February	1st to 10th	Day	19% 19% 27% 22% 11% 2	514
	11th to 20th	Day	19% 21% 33% 17% 9% 1	535
	21st to end	Day	16% 20% 37% 20% 7%	446
March	1st to 10th	Day	21% 20% 36% 18% 5% 1	540
	11th to 20th	Day	18% 20% 32% 19% 10% 2	540
	21st to end	Day	20% 21% 37% 16% 5% 1	594
April	1st to 10th	Day	15% 18% 31% 27% 8% 1	540
	11th to 20th	Day	18% 21% 31% 24% 7% 1	517
	21st to end	Day	10% 16% 33% 24% 14% 2	500
May	1st to 10th	Day	12% 17% 30% 26% 13% 2	503
	11th to 20th	Day	16% 15% 23% 27% 16% 3	528
	21st to end	Day	12% 12% 25% 28% 19% 4	573
June	1st to 10th	Day	5% 10% 25% 31% 23% 5%	530
	11th to 20th	Day	5% 10% 31% 33% 16% 5%	530
	21st to end	Day	2 9% 29% 37% 18% 4	530
July	1st to 10th	Day	2 6% 31% 36% 21% 4	526
	11th to 20th	Day	3 5% 28% 38% 20% 7%	524
	21st to end	Day	3 5% 33% 37% 17% 6%	575
August	1st to 10th	Day	2 9% 39% 34% 11% 4	527
	11th to 20th	Day	3 8% 37% 32% 16% 4	517
	21st to end	Day	3 7% 37% 36% 15% 3	583
September	1st to 10th	Day	3 9% 40% 34% 13% 1	530
	11th to 20th	Day	7% 14% 34% 34% 9% 2	530
	21st to end	Day	6% 15% 36% 30% 12% 1	530
October	1st to 10th	Day	7% 18% 35% 27% 12% 1	530
	11th to 20th	Day	8% 14% 35% 31% 11% 1	530
	21st to end	Day	9% 14% 34% 32% 10% 2	523
November	1st to 10th	Day	7% 17% 29% 26% 16% 4	330
	11th to 20th	Day	13% 14% 29% 28% 12% 3	330
	21st to end	Day	11% 14% 32% 25% 16% 2	330
December	1st to 10th	Day	13% 11% 30% 27% 15% 3	297
	11th to 20th	Day	15% 13% 31% 24% 14% 4	220
	21st to end	Day	22% 16% 29% 20% 11% 3	242
January	1st to 10th	Night	16% 11% 31% 20% 17% 5%	840
	11th to 20th	Night	9% 11% 35% 30% 12% 4	840
	21st to end	Night	13% 12% 34% 26% 13% 2	924
February	1st to 10th	Night	15% 9% 31% 28% 14% 2	840
	11th to 20th	Night	12% 13% 30% 28% 14% 3	824
	21st to end	Night	13% 10% 35% 30% 9% 2	692
March	1st to 10th	Night	14% 10% 34% 29% 11% 2	840
	11th to 20th	Night	9% 12% 29% 28% 20% 2	840
	21st to end	Night	12% 8% 31% 35% 13% 1	924
April	1st to 10th	Night	11% 7% 28% 40% 13% 1	840
	11th to 20th	Night	9% 9% 30% 32% 17% 3	815
	21st to end	Night	7% 7% 28% 36% 18% 4	800
May	1st to 10th	Night	6% 5% 26% 39% 20% 3	689
	11th to 20th	Night	7% 4 24% 38% 25% 2	591
	21st to end	Night	6% 4 23% 35% 28% 4	485
June	1st to 10th	Night	3 2 18% 43% 32% 4	400
	11th to 20th	Night	1 2 22% 41% 31% 4	400
	21st to end	Night	1 1 19% 39% 37% 5%	400
July	1st to 10th	Night	1 12% 41% 41% 5%	390
	11th to 20th	Night	2 1 7% 43% 42% 5%	388
	21st to end	Night	2 1 11% 33% 47% 6%	529
August	1st to 10th	Night	2 1 16% 39% 40% 2	774
	11th to 20th	Night	1 11% 39% 44% 3	792
	21st to end	Night	2 11% 39% 43% 4	880
September	1st to 10th	Night	2 1 12% 42% 39% 5%	800
	11th to 20th	Night	3 2 16% 45% 29% 6%	800
	21st to end	Night	3 3 20% 40% 30% 6%	800
October	1st to 10th	Night	5% 3 21% 45% 21% 5%	800
	11th to 20th	Night	5% 3 27% 36% 23% 5%	800
	21st to end	Night	5% 4 24% 36% 24% 8%	880
November	1st to 10th	Night	8% 4 22% 39% 22% 6%	820
	11th to 20th	Night	8% 6% 30% 35% 18% 3	840
	21st to end	Night	8% 8% 32% 34% 15% 3	840
December	1st to 10th	Night	12% 8% 30% 35% 11% 3	840
	11th to 20th	Night	16% 8% 32% 31% 11% 2	840
	21st to end	Night	15% 14% 33% 25% 12% 1	924

Page generated at 2026-04-13 23:44:26. Version ac07

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