Grand Mesa Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grand Mesa Observatory clear sky chart from 2005-11-06 to 2024-10-24.

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 7% 2 6% 4 4 5% 4 6% 7% 50%	101130
	Night	5% 8% 3 6% 4 4 4 4 5% 6% 50%	97879
Transparency	Day	30% 3 8% 23% 23% 14%	100890
	Night	31% 2 9% 24% 22% 11%	97709
Seeing	Day	9% 11% 26% 32% 18% 3	15310
	Night	9% 5% 19% 40% 24% 4	25432

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	3 7% 4 9% 6% 6% 5% 4 6% 9% 41%	2762
	11th to 20th	Day	4 13% 3 7% 6% 5% 6% 4 6% 6% 39%	2860
	21st to end	Day	4 11% 3 7% 4 4 4 3 5% 6% 50%	3146
February	1st to 10th	Day	4 11% 4 8% 6% 5% 5% 4 6% 7% 40%	1710
	11th to 20th	Day	6% 11% 4 8% 5% 5% 5% 3 6% 6% 40%	1665
	21st to end	Day	5% 11% 5% 10% 6% 5% 4 3 4 5% 42%	1584
March	1st to 10th	Day	4 13% 4 9% 7% 5% 5% 4 5% 5% 40%	3444
	11th to 20th	Day	3 12% 4 10% 6% 5% 4 4 6% 6% 40%	3490
	21st to end	Day	5% 15% 5% 12% 7% 5% 4 4 5% 5% 34%	3825
April	1st to 10th	Day	7% 9% 3 8% 4 4 5% 3 5% 7% 46%	2266
	11th to 20th	Day	6% 9% 3 8% 6% 5% 6% 4 5% 6% 42%	2251
	21st to end	Day	4 8% 3 8% 5% 5% 6% 4 6% 7% 43%	2299
May	1st to 10th	Day	5% 9% 4 10% 6% 5% 6% 4 6% 6% 40%	4110
	11th to 20th	Day	4 5% 2 6% 5% 5% 5% 5% 7% 8% 49%	4120
	21st to end	Day	6% 6% 2 6% 3 4 4 4 6% 7% 52%	4825
June	1st to 10th	Day	4 4 2 5% 4 3 4 4 6% 8% 57%	2660
	11th to 20th	Day	4 4 2 4 4 3 3 3 5% 6% 63%	2660
	21st to end	Day	3 3 1 4 3 4 4 4 5% 7% 63%	2660
July	1st to 10th	Day	2 3 1 3 3 3 3 3 4 6% 69%	4412
	11th to 20th	Day	2 3 1 3 4 5% 6% 6% 11% 13% 47%	4110
	21st to end	Day	3 3 1 3 4 5% 4 5% 7% 8% 57%	4454
August	1st to 10th	Day	4 3 2 5% 5% 6% 8% 7% 11% 11% 39%	4092
	11th to 20th	Day	4 4 1 5% 5% 6% 6% 4 6% 7% 53%	3980
	21st to end	Day	5% 3 1 5% 5% 5% 5% 5% 7% 9% 51%	4180
September	1st to 10th	Day	6% 3 1 4 3 4 4 3 6% 5% 60%	2280
	11th to 20th	Day	4 4 1 4 3 4 5% 4 5% 6% 59%	2230
	21st to end	Day	6% 3 1 4 3 3 3 3 4 5% 66%	2026
October	1st to 10th	Day	8% 5% 2 5% 3 3 4 3 4 6% 57%	1900
	11th to 20th	Day	4 3 2 4 3 3 3 3 6% 7% 62%	1900
	21st to end	Day	6% 5% 2 5% 3 3 3 3 5% 4 61%	2010
November	1st to 10th	Day	4 5% 2 5% 4 3 3 3 4 5% 61%	1840
	11th to 20th	Day	6% 7% 2 5% 3 3 4 3 4 6% 58%	1619
	21st to end	Day	5% 9% 2 4 4 4 4 3 4 6% 56%	1520
December	1st to 10th	Day	7% 10% 4 8% 4 3 4 3 4 5% 48%	1520
	11th to 20th	Day	6% 11% 3 8% 5% 4 4 4 5% 7% 44%	1926
	21st to end	Day	5% 10% 4 7% 5% 4 4 4 5% 7% 45%	2794
January	1st to 10th	Night	4 8% 4 9% 5% 4 5% 3 6% 6% 45%	4221
	11th to 20th	Night	5% 16% 4 9% 4 4 4 4 5% 6% 39%	4110
	21st to end	Night	5% 12% 3 6% 4 4 4 3 4 5% 49%	4521
February	1st to 10th	Night	4 11% 3 7% 5% 4 4 4 6% 6% 46%	2470
	11th to 20th	Night	6% 11% 2 8% 5% 5% 5% 3 5% 6% 44%	2402
	21st to end	Night	4 11% 4 9% 5% 5% 4 3 5% 6% 45%	1866
March	1st to 10th	Night	4 10% 4 9% 5% 4 4 3 5% 6% 45%	3430
	11th to 20th	Night	4 11% 4 7% 5% 5% 5% 4 5% 6% 45%	3490
	21st to end	Night	5% 13% 5% 13% 7% 6% 5% 4 5% 5% 31%	3828
April	1st to 10th	Night	7% 11% 3 8% 5% 4 3 3 4 6% 45%	1914
	11th to 20th	Night	7% 10% 3 7% 6% 4 4 3 5% 5% 46%	1877
	21st to end	Night	8% 8% 2 7% 5% 4 5% 4 6% 5% 46%	1876
May	1st to 10th	Night	8% 10% 3 9% 5% 4 5% 4 4 6% 41%	2860
	11th to 20th	Night	6% 5% 2 6% 4 4 6% 6% 7% 8% 47%	2781
	21st to end	Night	8% 6% 2 6% 4 3 4 3 4 5% 55%	2762
June	1st to 10th	Night	3 4 2 4 3 4 4 4 5% 7% 60%	1520
	11th to 20th	Night	6% 5% 2 4 3 4 3 3 5% 5% 61%	1520
	21st to end	Night	3 3 1 3 4 4 3 4 5% 8% 62%	1520
July	1st to 10th	Night	2 2 1 3 3 4 4 3 4 4 68%	2540
	11th to 20th	Night	2 2 1 5% 3 5% 5% 5% 7% 11% 54%	2859
	21st to end	Night	2 4 2 5% 4 4 4 4 6% 7% 58%	3109
August	1st to 10th	Night	3 4 2 6% 6% 6% 8% 6% 10% 9% 40%	2847
	11th to 20th	Night	4 4 2 6% 5% 5% 6% 4 6% 8% 50%	2859
	21st to end	Night	5% 4 2 5% 3 5% 6% 5% 6% 8% 51%	3487
September	1st to 10th	Night	5% 4 2 4 3 4 3 4 5% 6% 61%	1900
	11th to 20th	Night	5% 4 1 4 3 3 3 2 5% 6% 62%	1947
	21st to end	Night	6% 4 1 4 3 2 3 2 3 4 68%	2152
October	1st to 10th	Night	8% 5% 1 4 3 3 3 3 4 6% 61%	2280
	11th to 20th	Night	5% 4 1 3 2 3 3 3 4 6% 65%	2280
	21st to end	Night	7% 7% 2 4 2 3 2 2 3 6% 62%	2412
November	1st to 10th	Night	4 6% 3 4 3 3 3 2 4 5% 62%	2220
	11th to 20th	Night	5% 7% 2 4 3 3 3 2 4 5% 61%	2555
	21st to end	Night	7% 8% 3 5% 4 4 3 3 5% 5% 54%	2660
December	1st to 10th	Night	7% 10% 3 6% 3 3 4 3 4 5% 51%	2660
	11th to 20th	Night	6% 11% 3 7% 5% 4 4 3 5% 8% 42%	3271
	21st to end	Night	6% 11% 4 8% 4 4 3 3 5% 7% 46%	4873

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	36% 2 16% 35% 11% 1	2763
	11th to 20th	Day	41% 2 19% 28% 10% 1	2860
	21st to end	Day	33% 2 18% 33% 13% 2	3146
February	1st to 10th	Day	38% 3 16% 26% 15% 2	1710
	11th to 20th	Day	39% 2 10% 28% 19% 3	1674
	21st to end	Day	40% 2 7% 26% 22% 5%	1584
March	1st to 10th	Day	39% 1 4 32% 21% 3	3444
	11th to 20th	Day	39% 1 8% 36% 13% 3	3490
	21st to end	Day	46% 1 5% 27% 17% 3	3825
April	1st to 10th	Day	33% 2 7% 26% 23% 10%	2266
	11th to 20th	Day	35% 3 7% 22% 25% 7%	2254
	21st to end	Day	32% 3 6% 25% 27% 6%	2299
May	1st to 10th	Day	37% 1 4 17% 32% 9%	4110
	11th to 20th	Day	28% 2 5% 26% 28% 11%	4123
	21st to end	Day	28% 1 4 17% 40% 10%	4825
June	1st to 10th	Day	22% 2 4 21% 31% 21%	2660
	11th to 20th	Day	21% 2 4 11% 25% 37%	2660
	21st to end	Day	18% 2 2 14% 27% 37%	2660
July	1st to 10th	Day	16% 3 4 9% 15% 53%	4343
	11th to 20th	Day	22% 3 8% 21% 26% 20%	4041
	21st to end	Day	21% 3 9% 18% 20% 29%	4314
August	1st to 10th	Day	30% 7% 17% 16% 15% 15%	4078
	11th to 20th	Day	29% 5% 8% 16% 24% 18%	4019
	21st to end	Day	26% 6% 9% 18% 23% 19%	4179
September	1st to 10th	Day	24% 3 5% 15% 26% 27%	2280
	11th to 20th	Day	23% 3 8% 18% 27% 21%	2230
	21st to end	Day	21% 2 3 18% 39% 17%	2026
October	1st to 10th	Day	26% 2 7% 23% 29% 13%	1900
	11th to 20th	Day	20% 2 4 26% 37% 11%	1900
	21st to end	Day	24% 2 9% 31% 29% 6%	2010
November	1st to 10th	Day	22% 2 7% 28% 35% 6%	1840
	11th to 20th	Day	24% 2 9% 36% 26% 3	1619
	21st to end	Day	26% 1 13% 33% 23% 4	1520
December	1st to 10th	Day	35% 2 18% 28% 15% 2	1520
	11th to 20th	Day	38% 3 10% 36% 13%	1924
	21st to end	Day	35% 3 15% 21% 23% 3	2794
January	1st to 10th	Night	38% 2 13% 34% 12%	4221
	11th to 20th	Night	43% 2 18% 28% 9% 1	4110
	21st to end	Night	36% 1 20% 30% 12% 1	4521
February	1st to 10th	Night	33% 4 15% 30% 16% 2	2470
	11th to 20th	Night	38% 2 10% 28% 20% 2	2403
	21st to end	Night	36% 2 7% 29% 23% 4	1866
March	1st to 10th	Night	36% 1 5% 33% 24% 2	3430
	11th to 20th	Night	39% 1 8% 32% 18% 3	3490
	21st to end	Night	48% 1 6% 26% 17% 2	3828
April	1st to 10th	Night	37% 1 6% 22% 22% 10%	1914
	11th to 20th	Night	38% 2 6% 21% 22% 12%	1877
	21st to end	Night	34% 2 6% 22% 28% 7%	1876
May	1st to 10th	Night	39% 2 5% 17% 28% 9%	2860
	11th to 20th	Night	30% 2 7% 27% 27% 8%	2782
	21st to end	Night	30% 2 4 15% 36% 14%	2762
June	1st to 10th	Night	21% 2 5% 19% 30% 24%	1520
	11th to 20th	Night	23% 2 5% 12% 21% 37%	1520
	21st to end	Night	18% 2 3 15% 25% 37%	1520
July	1st to 10th	Night	18% 3 5% 8% 14% 52%	2500
	11th to 20th	Night	19% 3 8% 26% 23% 21%	2806
	21st to end	Night	22% 4 11% 14% 22% 27%	3011
August	1st to 10th	Night	33% 7% 16% 14% 15% 16%	2838
	11th to 20th	Night	30% 5% 11% 14% 20% 19%	2886
	21st to end	Night	27% 6% 8% 14% 24% 21%	3487
September	1st to 10th	Night	23% 2 6% 15% 22% 32%	1900
	11th to 20th	Night	21% 2 9% 19% 24% 26%	1947
	21st to end	Night	21% 2 3 16% 37% 21%	2152
October	1st to 10th	Night	24% 3 5% 21% 29% 18%	2280
	11th to 20th	Night	19% 3 5% 24% 35% 14%	2280
	21st to end	Night	25% 1 6% 32% 29% 7%	2412
November	1st to 10th	Night	24% 2 7% 27% 33% 8%	2220
	11th to 20th	Night	23% 2 8% 35% 29% 4	2555
	21st to end	Night	30% 2 8% 29% 28% 4	2660
December	1st to 10th	Night	33% 2 16% 28% 20% 2	2660
	11th to 20th	Night	39% 3 10% 35% 13% 1	3272
	21st to end	Night	38% 2 14% 23% 21% 2	4873

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	16% 6% 29% 28% 14% 7%	270
	11th to 20th	Day	13% 8% 29% 34% 15% 1	270
	21st to end	Day	9% 6% 28% 40% 13% 4	297
February	1st to 10th	Day	7% 18% 34% 31% 9% 1	270
	11th to 20th	Day	13% 11% 38% 27% 10% 1	270
	21st to end	Day	13% 16% 31% 30% 7% 2	244
March	1st to 10th	Day	15% 19% 30% 25% 10% 2	460
	11th to 20th	Day	12% 16% 32% 27% 11% 2	460
	21st to end	Day	17% 24% 34% 17% 7%	506
April	1st to 10th	Day	16% 17% 33% 23% 9% 1	460
	11th to 20th	Day	17% 25% 32% 17% 7% 1	452
	21st to end	Day	15% 18% 35% 23% 9%	460
May	1st to 10th	Day	16% 19% 32% 24% 9% 1	463
	11th to 20th	Day	10% 13% 29% 31% 16% 1	511
	21st to end	Day	11% 11% 26% 30% 19% 3	734
June	1st to 10th	Day	5% 9% 23% 36% 24% 3	680
	11th to 20th	Day	9% 13% 24% 34% 17% 4	680
	21st to end	Day	5% 9% 24% 40% 20% 3	680
July	1st to 10th	Day	3 5% 17% 38% 32% 5%	666
	11th to 20th	Day	5% 3 15% 44% 29% 5%	484
	21st to end	Day	6% 5% 13% 43% 29% 4	531
August	1st to 10th	Day	6% 3 19% 41% 26% 3	487
	11th to 20th	Day	4 4 20% 41% 26% 5%	477
	21st to end	Day	6% 3 20% 41% 25% 4	539
September	1st to 10th	Day	7% 4 21% 38% 24% 6%	490
	11th to 20th	Day	7% 9% 29% 33% 18% 4	490
	21st to end	Day	9% 9% 24% 32% 22% 4	426
October	1st to 10th	Day	10% 8% 22% 27% 24% 8%	300
	11th to 20th	Day	5% 11% 26% 33% 19% 5%	300
	21st to end	Day	9% 11% 27% 30% 20% 2	306
November	1st to 10th	Day	9% 14% 26% 31% 19% 1	270
	11th to 20th	Day	5% 10% 34% 31% 15% 5%	270
	21st to end	Day	9% 12% 26% 30% 20% 4	270
December	1st to 10th	Day	9% 12% 31% 30% 14% 4	270
	11th to 20th	Day	7% 10% 32% 31% 16% 4	270
	21st to end	Day	11% 9% 33% 31% 13% 2	297
January	1st to 10th	Night	10% 4 19% 41% 22% 4	832
	11th to 20th	Night	9% 5% 21% 40% 21% 4	760
	21st to end	Night	12% 3 20% 42% 19% 3	836
February	1st to 10th	Night	9% 5% 24% 46% 14% 2	760
	11th to 20th	Night	9% 6% 28% 41% 14% 2	744
	21st to end	Night	7% 8% 30% 45% 9% 1	628
March	1st to 10th	Night	10% 6% 29% 39% 14% 2	760
	11th to 20th	Night	7% 7% 20% 44% 20% 1	760
	21st to end	Night	11% 8% 26% 39% 14% 2	836
April	1st to 10th	Night	12% 7% 29% 40% 11% 1	584
	11th to 20th	Night	12% 12% 23% 38% 13% 2	563
	21st to end	Night	11% 8% 26% 37% 14% 4	570
May	1st to 10th	Night	13% 9% 22% 39% 15% 2	570
	11th to 20th	Night	11% 4 16% 40% 25% 5%	561
	21st to end	Night	10% 7% 20% 35% 24% 5%	617
June	1st to 10th	Night	5% 4 15% 42% 29% 5%	570
	11th to 20th	Night	7% 5% 19% 43% 21% 4	570
	21st to end	Night	4 3 16% 39% 33% 4	570
July	1st to 10th	Night	4 2 11% 32% 45% 6%	555
	11th to 20th	Night	2 1 6% 39% 45% 7%	552
	21st to end	Night	4 2 8% 31% 47% 7%	624
August	1st to 10th	Night	5% 2 8% 36% 44% 5%	567
	11th to 20th	Night	5% 2 11% 36% 40% 6%	564
	21st to end	Night	5% 3 10% 37% 37% 8%	627
September	1st to 10th	Night	7% 1 10% 40% 37% 5%	570
	11th to 20th	Night	6% 4 15% 35% 36% 4	617
	21st to end	Night	8% 3 17% 32% 33% 7%	760
October	1st to 10th	Night	8% 3 19% 39% 28% 3	760
	11th to 20th	Night	7% 3 20% 39% 28% 4	760
	21st to end	Night	9% 4 18% 39% 25% 4	804
November	1st to 10th	Night	7% 5% 19% 40% 26% 3	740
	11th to 20th	Night	8% 4 23% 43% 19% 4	946
	21st to end	Night	10% 7% 20% 38% 21% 4	950
December	1st to 10th	Night	10% 5% 20% 44% 18% 2	950
	11th to 20th	Night	13% 5% 21% 39% 19% 2	950
	21st to end	Night	12% 6% 23% 45% 11% 2	1045

Page generated at 2024-10-21 00:20:00. Version ac07

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