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 2024-01-17.

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	5% 6% 2 4 3 2 3 3 4 6% 61%	74830
	Night	4 6% 2 4 3 2 3 3 4 6% 63%	75001
Transparency	Day	24% 5% 9% 21% 25% 16%	74539
	Night	23% 4 9% 22% 27% 16%	74814
Seeing	Day	10% 13% 31% 29% 14% 3	14094
	Night	8% 6% 23% 35% 24% 4	23747

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	11% 9% 3 5% 3 2 3 5% 5% 8% 46%	1519
	11th to 20th	Day	6% 8% 3 4 6% 3 4 4 4 7% 52%	1556
	21st to end	Day	7% 10% 4 6% 3 3 4 4 5% 8% 46%	1782
February	1st to 10th	Day	7% 9% 3 7% 3 1 3 4 5% 6% 52%	1756
	11th to 20th	Day	5% 8% 5% 8% 4 2 3 3 3 6% 53%	1750
	21st to end	Day	7% 11% 5% 9% 6% 2 3 4 3 4 44%	1480
March	1st to 10th	Day	5% 13% 6% 9% 4 3 4 4 5% 7% 40%	1800
	11th to 20th	Day	5% 13% 4 8% 6% 4 4 4 4 7% 42%	1885
	21st to end	Day	7% 12% 5% 8% 3 2 4 3 4 6% 46%	2359
April	1st to 10th	Day	6% 8% 5% 5% 4 3 4 5% 4 7% 49%	2160
	11th to 20th	Day	7% 10% 5% 4 3 2 4 3 4 6% 53%	2129
	21st to end	Day	6% 10% 3 3 3 2 4 3 6% 8% 53%	2160
May	1st to 10th	Day	4 9% 3 3 2 2 3 3 4 7% 60%	2258
	11th to 20th	Day	4 8% 3 3 3 2 4 4 4 6% 60%	2301
	21st to end	Day	6% 9% 3 3 4 2 3 4 4 7% 55%	2672
June	1st to 10th	Day	4 5% 2 3 4 2 3 4 4 7% 63%	2520
	11th to 20th	Day	2 2 1 2 2 1 2 3 3 5% 78%	2520
	21st to end	Day	2 2 1 2 2 2 2 2 2 4 80%	2520
July	1st to 10th	Day	1 1 1 2 2 1 3 3 4 5% 77%	2520
	11th to 20th	Day	3 2 1 3 3 1 2 3 3 5% 75%	2520
	21st to end	Day	2 2 2 3 3 2 3 4 5% 6% 67%	2656
August	1st to 10th	Day	2 2 1 2 3 1 3 3 3 4 77%	2167
	11th to 20th	Day	2 1 1 2 3 2 2 3 4 5% 76%	2122
	21st to end	Day	2 2 1 1 1 2 1 3 3 4 80%	2376
September	1st to 10th	Day	2 1 1 2 2 2 2 3 3 5% 77%	2160
	11th to 20th	Day	4 2 1 2 2 1 2 3 2 5% 76%	2081
	21st to end	Day	2 4 1 2 2 2 2 3 4 5% 74%	1980
October	1st to 10th	Day	4 6% 2 2 3 2 3 2 4 4 68%	1926
	11th to 20th	Day	4 3 2 2 3 2 3 4 4 4 70%	1800
	21st to end	Day	5% 3 1 2 2 2 2 3 4 4 72%	1926
November	1st to 10th	Day	4 7% 3 5% 3 2 4 3 4 6% 59%	1674
	11th to 20th	Day	6% 5% 1 2 3 2 3 3 5% 6% 64%	1710
	21st to end	Day	5% 6% 2 5% 4 1 3 3 4 7% 60%	1710
December	1st to 10th	Day	8% 8% 2 4 3 2 3 3 3 7% 55%	1653
	11th to 20th	Day	12% 14% 4 7% 4 3 5% 4 4 5% 39%	1928
	21st to end	Day	5% 9% 6% 7% 4 3 4 5% 5% 8% 44%	2794
January	1st to 10th	Night	9% 10% 3 4 3 2 4 4 5% 6% 52%	2646
	11th to 20th	Night	5% 7% 3 4 4 2 4 4 5% 7% 54%	2539
	21st to end	Night	7% 10% 3 5% 2 2 3 4 4 7% 53%	2574
February	1st to 10th	Night	7% 8% 3 5% 3 2 3 3 4 6% 55%	2201
	11th to 20th	Night	5% 8% 4 6% 3 2 3 3 4 8% 56%	2098
	21st to end	Night	7% 8% 4 8% 5% 2 4 3 4 5% 51%	1776
March	1st to 10th	Night	5% 11% 4 8% 5% 2 4 3 5% 6% 47%	2160
	11th to 20th	Night	3 9% 6% 7% 5% 3 4 5% 4 8% 47%	2070
	21st to end	Night	5% 11% 4 6% 3 2 3 3 5% 6% 52%	1996
April	1st to 10th	Night	6% 8% 3 5% 4 2 3 4 4 7% 54%	1800
	11th to 20th	Night	5% 8% 3 4 4 2 2 3 5% 6% 58%	1779
	21st to end	Night	3 6% 2 4 3 2 3 4 6% 7% 62%	1800
May	1st to 10th	Night	2 5% 2 4 3 2 3 4 4 7% 64%	1701
	11th to 20th	Night	4 6% 1 3 3 2 3 2 4 6% 67%	1594
	21st to end	Night	3 5% 2 3 4 2 2 3 3 7% 68%	1599
June	1st to 10th	Night	3 3 1 3 3 1 2 4 3 7% 70%	1440
	11th to 20th	Night	1 1 2 2 1 2 2 4 5% 80%	1440
	21st to end	Night	1 1 1 1 1 1 2 2 3 3 85%	1440
July	1st to 10th	Night	1 1 2 2 1 1 2 2 3 85%	1440
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 4 78%	1440
	21st to end	Night	3 2 1 3 2 2 3 4 3 5% 72%	1657
August	1st to 10th	Night	1 2 1 2 1 1 2 2 2 4 82%	1770
	11th to 20th	Night	1 1 1 2 2 1 2 2 2 4 84%	1780
	21st to end	Night	2 1 1 1 2 1 2 1 1 2 86%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 3 87%	1800
	11th to 20th	Night	2 2 1 1 1 1 2 2 3 2 84%	1877
	21st to end	Night	2 2 1 2 2 1 1 3 3 4 80%	1980
October	1st to 10th	Night	3 3 2 2 2 1 3 3 3 5% 74%	2029
	11th to 20th	Night	3 2 1 1 2 2 2 3 4 5% 75%	2160
	21st to end	Night	4 2 1 2 2 1 2 2 3 4 77%	2430
November	1st to 10th	Night	3 6% 2 4 2 1 3 3 4 6% 65%	2405
	11th to 20th	Night	5% 4 2 3 2 2 3 3 5% 8% 63%	2470
	21st to end	Night	5% 5% 3 4 3 3 4 4 4 7% 59%	2470
December	1st to 10th	Night	8% 8% 2 4 3 2 3 4 4 7% 55%	2522
	11th to 20th	Night	10% 17% 3 5% 4 3 3 3 5% 6% 40%	3276
	21st to end	Night	5% 8% 3 6% 5% 4 5% 6% 7% 8% 42%	4862

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	35% 5% 11% 24% 19% 6%	1519
	11th to 20th	Day	30% 6% 10% 22% 19% 13%	1556
	21st to end	Day	37% 5% 9% 19% 20% 10%	1782
February	1st to 10th	Day	33% 3 10% 22% 19% 12%	1756
	11th to 20th	Day	34% 4 9% 21% 23% 8%	1760
	21st to end	Day	44% 4 9% 21% 18% 5%	1480
March	1st to 10th	Day	44% 7% 9% 18% 16% 6%	1800
	11th to 20th	Day	41% 6% 10% 20% 18% 5%	1885
	21st to end	Day	40% 6% 16% 21% 13% 4	2359
April	1st to 10th	Day	36% 5% 14% 23% 16% 5%	2160
	11th to 20th	Day	34% 6% 12% 24% 20% 5%	2132
	21st to end	Day	29% 6% 17% 28% 17% 2	2160
May	1st to 10th	Day	26% 5% 12% 33% 21% 3	2258
	11th to 20th	Day	26% 5% 12% 31% 22% 3	2304
	21st to end	Day	28% 7% 12% 31% 19% 3	2672
June	1st to 10th	Day	21% 7% 13% 26% 26% 7%	2520
	11th to 20th	Day	10% 4 9% 25% 35% 17%	2520
	21st to end	Day	10% 3 4 17% 40% 26%	2520
July	1st to 10th	Day	9% 4 4 13% 30% 39%	2451
	11th to 20th	Day	12% 5% 6% 15% 34% 29%	2445
	21st to end	Day	15% 5% 11% 18% 23% 29%	2508
August	1st to 10th	Day	12% 4 5% 11% 31% 37%	2152
	11th to 20th	Day	9% 5% 5% 14% 35% 31%	2122
	21st to end	Day	9% 3 4 13% 38% 32%	2376
September	1st to 10th	Day	9% 4 8% 13% 31% 36%	2160
	11th to 20th	Day	11% 4 7% 21% 32% 25%	2081
	21st to end	Day	14% 3 6% 22% 37% 19%	1980
October	1st to 10th	Day	20% 3 8% 17% 30% 23%	1926
	11th to 20th	Day	17% 3 8% 22% 30% 21%	1800
	21st to end	Day	16% 3 6% 22% 35% 19%	1926
November	1st to 10th	Day	27% 4 9% 21% 27% 12%	1674
	11th to 20th	Day	21% 4 9% 24% 29% 13%	1710
	21st to end	Day	26% 3 8% 18% 29% 15%	1710
December	1st to 10th	Day	30% 3 8% 22% 22% 14%	1653
	11th to 20th	Day	46% 6% 8% 14% 16% 9%	1928
	21st to end	Day	35% 7% 11% 21% 18% 8%	2794
January	1st to 10th	Night	32% 5% 8% 26% 21% 8%	2646
	11th to 20th	Night	28% 4 9% 22% 23% 14%	2539
	21st to end	Night	32% 4 9% 18% 24% 13%	2574
February	1st to 10th	Night	31% 3 6% 24% 23% 13%	2201
	11th to 20th	Night	29% 5% 8% 22% 25% 12%	2099
	21st to end	Night	37% 3 10% 21% 22% 8%	1776
March	1st to 10th	Night	38% 5% 8% 19% 21% 8%	2160
	11th to 20th	Night	34% 5% 12% 19% 21% 8%	2070
	21st to end	Night	33% 5% 14% 28% 15% 5%	1996
April	1st to 10th	Night	30% 4 13% 27% 18% 8%	1800
	11th to 20th	Night	27% 5% 13% 26% 21% 9%	1779
	21st to end	Night	21% 6% 16% 35% 20% 2	1800
May	1st to 10th	Night	20% 5% 14% 31% 27% 4	1701
	11th to 20th	Night	20% 4 10% 39% 23% 4	1595
	21st to end	Night	19% 5% 15% 33% 25% 3	1599
June	1st to 10th	Night	15% 5% 13% 27% 34% 5%	1440
	11th to 20th	Night	7% 5% 8% 26% 36% 17%	1440
	21st to end	Night	7% 2 5% 16% 41% 29%	1440
July	1st to 10th	Night	7% 1 3 13% 35% 41%	1400
	11th to 20th	Night	10% 4 6% 17% 36% 28%	1392
	21st to end	Night	14% 5% 7% 18% 28% 28%	1565
August	1st to 10th	Night	9% 2 6% 15% 33% 35%	1761
	11th to 20th	Night	7% 2 3 21% 35% 31%	1780
	21st to end	Night	9% 1 2 14% 40% 33%	1980
September	1st to 10th	Night	6% 2 3 14% 38% 38%	1800
	11th to 20th	Night	9% 3 5% 23% 37% 23%	1877
	21st to end	Night	10% 3 6% 21% 40% 21%	1980
October	1st to 10th	Night	14% 4 7% 20% 31% 25%	2029
	11th to 20th	Night	13% 3 6% 21% 32% 24%	2160
	21st to end	Night	12% 3 5% 22% 38% 20%	2430
November	1st to 10th	Night	21% 4 9% 23% 27% 17%	2405
	11th to 20th	Night	20% 3 9% 22% 31% 16%	2470
	21st to end	Night	26% 3 8% 18% 28% 16%	2470
December	1st to 10th	Night	30% 4 10% 18% 24% 14%	2522
	11th to 20th	Night	44% 5% 9% 16% 18% 9%	3276
	21st to end	Night	34% 7% 11% 19% 21% 8%	4862

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	27% 20% 24% 20% 6% 3	180
	11th to 20th	Day	17% 15% 27% 23% 15% 3	240
	21st to end	Day	15% 16% 28% 26% 12% 3	374
February	1st to 10th	Day	16% 18% 29% 23% 12% 3	401
	11th to 20th	Day	16% 21% 31% 20% 11% 1	415
	21st to end	Day	19% 22% 33% 18% 7%	346
March	1st to 10th	Day	20% 21% 34% 19% 5% 1	420
	11th to 20th	Day	19% 20% 30% 19% 10% 2	420
	21st to end	Day	21% 21% 36% 17% 5%	462
April	1st to 10th	Day	15% 19% 30% 27% 7% 1	420
	11th to 20th	Day	19% 21% 32% 22% 6% 1	412
	21st to end	Day	11% 16% 33% 24% 13% 3	420
May	1st to 10th	Day	12% 17% 28% 29% 13% 2	423
	11th to 20th	Day	16% 14% 22% 29% 16% 3	448
	21st to end	Day	14% 12% 24% 27% 19% 5%	485
June	1st to 10th	Day	6% 11% 26% 27% 24% 5%	450
	11th to 20th	Day	4 10% 27% 34% 19% 6%	450
	21st to end	Day	2 9% 26% 39% 20% 4	450
July	1st to 10th	Day	2 3 28% 39% 22% 4	446
	11th to 20th	Day	3 4 25% 40% 21% 7%	444
	21st to end	Day	3 4 30% 40% 17% 6%	487
August	1st to 10th	Day	2 7% 39% 37% 11% 4	447
	11th to 20th	Day	3 7% 34% 35% 18% 4	437
	21st to end	Day	2 5% 35% 39% 16% 2	495
September	1st to 10th	Day	3 8% 39% 36% 14% 1	450
	11th to 20th	Day	7% 13% 34% 36% 10% 1	450
	21st to end	Day	6% 12% 35% 33% 13% 1	450
October	1st to 10th	Day	6% 17% 36% 28% 12% 1	450
	11th to 20th	Day	5% 13% 34% 34% 12% 1	450
	21st to end	Day	9% 13% 31% 33% 12% 2	441
November	1st to 10th	Day	7% 17% 27% 26% 18% 4	270
	11th to 20th	Day	9% 13% 27% 33% 15% 3	270
	21st to end	Day	9% 15% 30% 26% 17% 3	270
December	1st to 10th	Day	15% 12% 30% 26% 14% 2	243
	11th to 20th	Day	13% 13% 33% 24% 15% 2	180
	21st to end	Day	19% 17% 29% 19% 13% 4	198
January	1st to 10th	Night	15% 10% 29% 22% 18% 6%	760
	11th to 20th	Night	10% 9% 33% 31% 13% 5%	746
	21st to end	Night	14% 10% 30% 28% 15% 3	792
February	1st to 10th	Night	14% 7% 29% 31% 16% 3	720
	11th to 20th	Night	11% 12% 26% 31% 16% 4	704
	21st to end	Night	15% 8% 30% 33% 11% 2	592
March	1st to 10th	Night	13% 9% 31% 32% 13% 3	720
	11th to 20th	Night	10% 11% 25% 30% 23% 2	720
	21st to end	Night	12% 8% 29% 35% 14% 1	792
April	1st to 10th	Night	11% 5% 27% 41% 14% 2	720
	11th to 20th	Night	9% 8% 28% 33% 19% 3	711
	21st to end	Night	8% 7% 28% 34% 19% 4	720
May	1st to 10th	Night	5% 5% 24% 40% 22% 4	621
	11th to 20th	Night	7% 3 23% 38% 26% 3	531
	21st to end	Night	6% 5% 22% 32% 31% 4	437
June	1st to 10th	Night	3 2 16% 40% 34% 4	360
	11th to 20th	Night	1 1 17% 43% 35% 4	360
	21st to end	Night	1 1 15% 38% 41% 5%	360
July	1st to 10th	Night	1 8% 40% 45% 6%	350
	11th to 20th	Night	2 1 7% 39% 45% 6%	348
	21st to end	Night	2 1 8% 30% 51% 7%	475
August	1st to 10th	Night	2 1 15% 37% 43% 3	696
	11th to 20th	Night	1 8% 40% 47% 4	712
	21st to end	Night	3 9% 39% 45% 5%	792
September	1st to 10th	Night	2 1 11% 39% 42% 6%	720
	11th to 20th	Night	2 2 14% 45% 31% 6%	720
	21st to end	Night	3 2 16% 40% 33% 6%	720
October	1st to 10th	Night	4 2 22% 44% 22% 6%	720
	11th to 20th	Night	5% 3 24% 37% 25% 6%	720
	21st to end	Night	5% 4 20% 36% 26% 9%	792
November	1st to 10th	Night	9% 4 19% 39% 24% 6%	740
	11th to 20th	Night	7% 5% 27% 38% 20% 3	760
	21st to end	Night	7% 6% 30% 36% 16% 4	760
December	1st to 10th	Night	13% 8% 28% 36% 13% 3	760
	11th to 20th	Night	17% 8% 29% 32% 12% 2	760
	21st to end	Night	14% 13% 31% 27% 13% 1	836

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