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 2024-02-25.

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% 7% 3 5% 5% 3 5% 5% 6% 7% 50%	78589
	Night	6% 8% 3 5% 5% 3 4 4 5% 6% 51%	80770
Transparency	Day	30% 3 9% 24% 23% 12%	78309
	Night	31% 2 10% 25% 22% 10%	80572
Seeing	Day	9% 11% 26% 32% 19% 3	14321
	Night	9% 5% 19% 40% 24% 4	24636

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 8% 7% 4 5% 5% 6% 9% 41%	2762
	11th to 20th	Day	4 13% 4 6% 7% 4 6% 5% 6% 6% 39%	2860
	21st to end	Day	4 10% 3 6% 5% 3 4 4 5% 6% 50%	3146
February	1st to 10th	Day	4 10% 4 7% 7% 3 5% 5% 5% 7% 40%	1710
	11th to 20th	Day	6% 11% 4 7% 5% 4 5% 5% 6% 6% 40%	1665
	21st to end	Day	5% 10% 6% 10% 7% 4 5% 4 4 5% 41%	1533
March	1st to 10th	Day	7% 12% 3 7% 6% 3 5% 5% 5% 6% 41%	1980
	11th to 20th	Day	4 9% 3 6% 5% 4 5% 5% 4 8% 46%	1980
	21st to end	Day	5% 12% 4 7% 7% 3 5% 5% 5% 6% 41%	2178
April	1st to 10th	Day	7% 9% 3 7% 5% 3 5% 4 5% 7% 45%	2146
	11th to 20th	Day	6% 9% 3 7% 7% 4 6% 5% 5% 7% 41%	2131
	21st to end	Day	5% 7% 3 6% 6% 4 6% 6% 6% 8% 44%	2178
May	1st to 10th	Day	7% 7% 4 7% 6% 4 7% 6% 7% 7% 40%	2340
	11th to 20th	Day	5% 7% 2 5% 6% 3 6% 6% 7% 7% 44%	2322
	21st to end	Day	5% 6% 3 5% 5% 3 5% 5% 6% 8% 48%	2724
June	1st to 10th	Day	4 4 2 4 4 2 4 5% 6% 8% 58%	2520
	11th to 20th	Day	4 4 2 3 5% 2 3 3 5% 6% 62%	2520
	21st to end	Day	2 3 1 3 4 3 4 4 5% 7% 64%	2520
July	1st to 10th	Day	3 4 2 5% 5% 3 4 5% 6% 10% 53%	2516
	11th to 20th	Day	3 4 2 4 5% 4 6% 7% 8% 9% 49%	2340
	21st to end	Day	5% 4 2 4 6% 5% 7% 7% 9% 11% 39%	2545
August	1st to 10th	Day	7% 5% 2 5% 7% 4 7% 7% 8% 8% 41%	2328
	11th to 20th	Day	4 3 2 4 5% 4 5% 5% 6% 7% 57%	2277
	21st to end	Day	4 4 2 5% 6% 4 6% 6% 7% 8% 50%	2376
September	1st to 10th	Day	6% 3 1 3 4 3 4 4 6% 4 60%	2160
	11th to 20th	Day	5% 4 2 4 4 2 5% 5% 5% 6% 59%	2113
	21st to end	Day	6% 3 1 4 3 2 2 4 4 5% 65%	1920
October	1st to 10th	Day	9% 4 2 4 4 2 4 4 4 7% 55%	1800
	11th to 20th	Day	4 3 1 4 3 2 3 3 6% 6% 65%	1800
	21st to end	Day	6% 5% 2 4 3 2 4 3 5% 5% 61%	1980
November	1st to 10th	Day	4 5% 3 4 4 2 3 3 4 5% 61%	1840
	11th to 20th	Day	7% 6% 2 4 4 2 3 4 4 6% 59%	1619
	21st to end	Day	5% 8% 2 4 4 3 4 3 4 6% 56%	1520
December	1st to 10th	Day	7% 10% 4 7% 5% 2 4 4 4 5% 48%	1520
	11th to 20th	Day	6% 10% 4 7% 5% 3 4 4 5% 7% 44%	1926
	21st to end	Day	5% 9% 4 6% 6% 3 4 5% 5% 7% 46%	2794
January	1st to 10th	Night	4 8% 4 8% 7% 3 5% 4 5% 6% 45%	4221
	11th to 20th	Night	5% 15% 5% 7% 6% 3 5% 4 6% 6% 39%	4110
	21st to end	Night	5% 12% 3 5% 4 3 4 4 4 5% 49%	4521
February	1st to 10th	Night	4 10% 3 6% 6% 3 3 5% 6% 6% 47%	2470
	11th to 20th	Night	6% 10% 3 7% 6% 4 5% 4 5% 6% 44%	2402
	21st to end	Night	4 10% 4 8% 6% 3 5% 4 5% 7% 45%	1814
March	1st to 10th	Night	7% 9% 4 7% 5% 3 4 5% 4 5% 47%	1980
	11th to 20th	Night	5% 7% 4 5% 5% 3 5% 5% 5% 6% 51%	1980
	21st to end	Night	6% 11% 4 8% 7% 3 5% 5% 5% 6% 40%	2178
April	1st to 10th	Night	8% 11% 4 8% 5% 3 4 3 4 6% 44%	1814
	11th to 20th	Night	7% 9% 4 6% 6% 4 4 5% 5% 6% 45%	1777
	21st to end	Night	8% 8% 3 6% 5% 3 5% 5% 6% 5% 46%	1778
May	1st to 10th	Night	9% 8% 3 6% 5% 3 5% 6% 4 7% 43%	1620
	11th to 20th	Night	8% 6% 2 5% 5% 3 5% 5% 6% 8% 48%	1569
	21st to end	Night	8% 6% 3 6% 5% 3 5% 4 5% 6% 51%	1552
June	1st to 10th	Night	3 3 2 4 3 3 4 5% 5% 7% 60%	1440
	11th to 20th	Night	6% 5% 2 4 3 2 4 3 5% 5% 62%	1440
	21st to end	Night	2 3 1 3 4 3 4 4 5% 7% 64%	1440
July	1st to 10th	Night	4 3 1 3 5% 3 6% 5% 6% 7% 56%	1440
	11th to 20th	Night	3 2 1 5% 5% 3 6% 6% 7% 11% 51%	1619
	21st to end	Night	4 4 3 5% 6% 4 7% 8% 7% 10% 42%	1773
August	1st to 10th	Night	4 4 3 5% 6% 3 6% 6% 8% 9% 46%	1611
	11th to 20th	Night	5% 4 2 3 4 2 4 4 6% 10% 55%	1624
	21st to end	Night	5% 3 3 4 4 3 5% 5% 6% 8% 53%	1980
September	1st to 10th	Night	5% 4 2 4 3 3 4 4 4 6% 60%	1800
	11th to 20th	Night	6% 4 1 3 3 2 3 3 6% 6% 62%	1844
	21st to end	Night	7% 3 2 3 3 2 3 2 3 4 67%	2038
October	1st to 10th	Night	9% 5% 1 3 3 2 3 4 4 6% 59%	2160
	11th to 20th	Night	5% 4 1 2 3 2 3 4 4 5% 67%	2160
	21st to end	Night	7% 7% 2 4 3 2 3 3 3 6% 62%	2376
November	1st to 10th	Night	4 6% 3 4 3 2 3 3 4 5% 62%	2220
	11th to 20th	Night	6% 6% 2 4 3 2 4 3 4 5% 61%	2555
	21st to end	Night	7% 8% 3 4 4 2 4 3 5% 5% 54%	2660
December	1st to 10th	Night	7% 9% 4 5% 4 3 3 4 4 5% 51%	2660
	11th to 20th	Night	7% 11% 3 7% 6% 4 4 4 5% 7% 42%	3271
	21st to end	Night	6% 11% 4 6% 5% 3 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	41% 2 7% 26% 20% 5%	1533
March	1st to 10th	Day	39% 1 7% 29% 23% 2	1980
	11th to 20th	Day	31% 2 8% 35% 18% 5%	1980
	21st to end	Day	38% 2 7% 29% 19% 5%	2178
April	1st to 10th	Day	34% 2 7% 24% 23% 10%	2146
	11th to 20th	Day	36% 3 7% 22% 25% 7%	2134
	21st to end	Day	32% 3 6% 25% 27% 7%	2178
May	1st to 10th	Day	36% 2 6% 21% 26% 9%	2340
	11th to 20th	Day	31% 3 7% 26% 24% 9%	2325
	21st to end	Day	29% 2 6% 18% 30% 14%	2724
June	1st to 10th	Day	22% 2 4 21% 30% 22%	2520
	11th to 20th	Day	21% 2 4 11% 24% 38%	2520
	21st to end	Day	18% 2 1 14% 27% 38%	2520
July	1st to 10th	Day	24% 4 6% 13% 19% 33%	2447
	11th to 20th	Day	27% 3 9% 21% 21% 21%	2271
	21st to end	Day	32% 5% 13% 21% 17% 11%	2404
August	1st to 10th	Day	35% 4 11% 17% 16% 17%	2313
	11th to 20th	Day	25% 3 6% 18% 26% 23%	2277
	21st to end	Day	27% 4 7% 19% 24% 19%	2376
September	1st to 10th	Day	24% 3 5% 14% 25% 29%	2160
	11th to 20th	Day	24% 3 8% 18% 27% 21%	2113
	21st to end	Day	21% 2 3 18% 40% 17%	1920
October	1st to 10th	Day	27% 2 7% 24% 29% 11%	1800
	11th to 20th	Day	18% 2 4 27% 38% 12%	1800
	21st to end	Day	24% 2 9% 30% 29% 6%	1980
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% 21% 5%	1814
March	1st to 10th	Night	36% 1 8% 28% 26% 2	1980
	11th to 20th	Night	30% 2 6% 31% 25% 6%	1980
	21st to end	Night	39% 2 8% 28% 19% 4	2178
April	1st to 10th	Night	38% 2 7% 22% 21% 11%	1814
	11th to 20th	Night	38% 2 6% 21% 23% 11%	1777
	21st to end	Night	34% 3 6% 22% 28% 7%	1778
May	1st to 10th	Night	36% 3 8% 19% 26% 8%	1620
	11th to 20th	Night	31% 3 8% 24% 26% 7%	1570
	21st to end	Night	31% 3 7% 17% 28% 14%	1552
June	1st to 10th	Night	21% 2 5% 19% 30% 24%	1440
	11th to 20th	Night	22% 2 5% 12% 20% 38%	1440
	21st to end	Night	18% 2 2 14% 26% 39%	1440
July	1st to 10th	Night	23% 4 7% 14% 19% 34%	1400
	11th to 20th	Night	22% 3 10% 22% 19% 23%	1566
	21st to end	Night	30% 5% 17% 19% 16% 13%	1674
August	1st to 10th	Night	29% 5% 14% 18% 18% 16%	1602
	11th to 20th	Night	24% 2 10% 18% 21% 26%	1624
	21st to end	Night	26% 4 7% 16% 23% 24%	1980
September	1st to 10th	Night	24% 2 6% 15% 20% 34%	1800
	11th to 20th	Night	21% 2 9% 20% 22% 26%	1844
	21st to end	Night	22% 2 3 16% 37% 20%	2038
October	1st to 10th	Night	25% 3 5% 22% 28% 16%	2160
	11th to 20th	Night	18% 2 5% 23% 36% 15%	2160
	21st to end	Night	25% 1 6% 32% 30% 7%	2376
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	12% 17% 32% 29% 7% 2	228
March	1st to 10th	Day	15% 19% 30% 24% 10% 2	420
	11th to 20th	Day	13% 15% 32% 27% 11% 2	420
	21st to end	Day	17% 25% 34% 18% 6%	462
April	1st to 10th	Day	17% 18% 32% 23% 9% 1	420
	11th to 20th	Day	19% 26% 31% 16% 8% 1	412
	21st to end	Day	16% 19% 34% 22% 9%	420
May	1st to 10th	Day	14% 20% 33% 24% 9% 1	423
	11th to 20th	Day	11% 13% 29% 30% 16% 1	469
	21st to end	Day	11% 11% 27% 30% 19% 3	679
June	1st to 10th	Day	6% 9% 23% 36% 24% 3	630
	11th to 20th	Day	9% 10% 24% 35% 19% 4	630
	21st to end	Day	4 8% 22% 42% 21% 3	630
July	1st to 10th	Day	3 3 15% 39% 34% 5%	617
	11th to 20th	Day	5% 3 15% 43% 30% 5%	444
	21st to end	Day	7% 4 9% 44% 32% 4	487
August	1st to 10th	Day	7% 4 18% 40% 28% 4	447
	11th to 20th	Day	3 3 17% 43% 28% 5%	437
	21st to end	Day	6% 2 18% 43% 27% 5%	495
September	1st to 10th	Day	7% 4 21% 36% 25% 6%	450
	11th to 20th	Day	6% 7% 28% 36% 20% 4	450
	21st to end	Day	10% 8% 23% 32% 23% 4	390
October	1st to 10th	Day	11% 9% 22% 26% 24% 7%	270
	11th to 20th	Day	6% 10% 23% 34% 21% 6%	270
	21st to end	Day	9% 12% 27% 30% 20% 2	297
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	8% 8% 30% 45% 9% 1	610
March	1st to 10th	Night	11% 5% 28% 40% 14% 2	720
	11th to 20th	Night	7% 7% 20% 45% 20% 2	720
	21st to end	Night	11% 7% 26% 40% 14% 2	792
April	1st to 10th	Night	12% 7% 28% 40% 11% 1	554
	11th to 20th	Night	13% 11% 22% 38% 14% 2	533
	21st to end	Night	11% 7% 26% 36% 15% 4	540
May	1st to 10th	Night	13% 8% 21% 40% 16% 2	540
	11th to 20th	Night	11% 4 16% 39% 26% 5%	531
	21st to end	Night	10% 7% 20% 34% 25% 5%	584
June	1st to 10th	Night	5% 4 16% 41% 29% 5%	540
	11th to 20th	Night	7% 5% 18% 44% 23% 4	540
	21st to end	Night	4 2 14% 41% 35% 4	540
July	1st to 10th	Night	4 2 8% 33% 47% 6%	525
	11th to 20th	Night	2 1 5% 38% 47% 7%	522
	21st to end	Night	4 2 5% 32% 50% 7%	591
August	1st to 10th	Night	5% 2 6% 36% 46% 5%	537
	11th to 20th	Night	5% 1 7% 37% 43% 6%	534
	21st to end	Night	5% 1 8% 38% 39% 9%	594
September	1st to 10th	Night	7% 1 9% 38% 39% 6%	540
	11th to 20th	Night	6% 3 13% 37% 38% 4	584
	21st to end	Night	8% 3 16% 31% 35% 8%	720
October	1st to 10th	Night	9% 3 19% 37% 29% 3	720
	11th to 20th	Night	7% 3 18% 40% 29% 4	720
	21st to end	Night	9% 4 18% 39% 26% 4	792
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 2024-02-22 04:05:44. Version ac07

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