Greeley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greeley clear sky chart from 2005-11-06 to 2025-10-19.

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% 5% 2 5% 4 4 5% 4 6% 8% 52%	135433
	Night	6% 6% 2 6% 4 4 4 3 5% 7% 53%	131709
Transparency	Day	27% 6% 11% 24% 23% 9%	130367
	Night	29% 5% 11% 24% 23% 7%	127781
Seeing	Day	8% 6% 20% 34% 24% 8%	16977
	Night	8% 4 24% 47% 15% 1	26912

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	2 8% 3 8% 4 3 3 3 4 8% 53%	3638
	11th to 20th	Day	2 6% 3 8% 5% 5% 5% 4 7% 7% 49%	3640
	21st to end	Day	1 6% 2 5% 3 4 4 3 5% 6% 59%	4492
February	1st to 10th	Day	4 8% 4 6% 5% 4 4 4 6% 7% 49%	1800
	11th to 20th	Day	2 7% 3 6% 5% 5% 4 4 5% 9% 51%	1929
	21st to end	Day	3 8% 3 6% 3 4 3 5% 5% 6% 54%	1650
March	1st to 10th	Day	5% 8% 2 4 3 3 4 3 5% 7% 56%	4500
	11th to 20th	Day	5% 6% 2 6% 4 4 5% 3 6% 8% 50%	4860
	21st to end	Day	5% 7% 2 6% 4 4 5% 5% 6% 10% 45%	5870
April	1st to 10th	Day	8% 6% 2 4 4 4 4 4 6% 8% 50%	2400
	11th to 20th	Day	11% 8% 2 6% 4 4 4 3 6% 8% 44%	2371
	21st to end	Day	10% 7% 2 6% 4 4 5% 4 6% 9% 42%	2400
May	1st to 10th	Day	10% 7% 3 7% 5% 5% 5% 3 5% 6% 46%	5845
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 5% 8% 10% 45%	6291
	21st to end	Day	9% 5% 2 5% 4 5% 5% 4 6% 9% 44%	6925
June	1st to 10th	Day	5% 5% 1 4 4 4 5% 5% 7% 11% 51%	2800
	11th to 20th	Day	6% 3 2 5% 3 4 5% 5% 7% 9% 51%	2800
	21st to end	Day	4 3 1 4 4 3 5% 5% 8% 10% 53%	2800
July	1st to 10th	Day	4 3 1 4 3 4 5% 4 7% 10% 55%	6339
	11th to 20th	Day	3 2 1 5% 4 6% 6% 6% 9% 11% 47%	6340
	21st to end	Day	4 3 2 6% 5% 5% 6% 5% 7% 8% 49%	6903
August	1st to 10th	Day	8% 3 2 5% 5% 6% 6% 6% 8% 10% 42%	5808
	11th to 20th	Day	2 3 1 4 3 4 5% 5% 7% 10% 56%	5366
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 7% 9% 48%	5984
September	1st to 10th	Day	5% 3 1 4 3 3 4 3 5% 8% 62%	2400
	11th to 20th	Day	5% 2 1 5% 4 3 4 3 5% 7% 60%	2360
	21st to end	Day	7% 4 1 2 3 2 3 3 3 6% 65%	2200
October	1st to 10th	Day	5% 3 1 2 2 2 2 2 3 5% 74%	3334
	11th to 20th	Day	5% 5% 1 5% 3 3 3 3 4 6% 62%	3230
	21st to end	Day	6% 6% 1 4 3 3 3 2 5% 8% 58%	3255
November	1st to 10th	Day	4 5% 2 5% 4 3 4 3 5% 8% 58%	1763
	11th to 20th	Day	3 8% 2 3 3 4 3 3 5% 8% 59%	1800
	21st to end	Day	3 6% 3 4 3 3 3 4 5% 8% 57%	1690
December	1st to 10th	Day	2 5% 1 4 3 3 3 3 4 6% 66%	2620
	11th to 20th	Day	2 5% 2 4 3 3 3 3 5% 7% 63%	3026
	21st to end	Day	4 7% 3 7% 5% 5% 5% 4 5% 7% 49%	4004
January	1st to 10th	Night	4 11% 3 7% 4 4 4 3 6% 7% 48%	6327
	11th to 20th	Night	1 6% 3 10% 5% 4 4 3 5% 7% 52%	6340
	21st to end	Night	2 7% 3 7% 4 3 3 3 4 6% 57%	6518
February	1st to 10th	Night	4 9% 4 7% 4 4 4 4 5% 6% 51%	2600
	11th to 20th	Night	4 9% 3 7% 6% 5% 5% 4 5% 6% 48%	2356
	21st to end	Night	3 9% 2 7% 3 3 3 2 5% 5% 57%	1980
March	1st to 10th	Night	5% 10% 3 7% 4 3 3 2 4 5% 53%	5374
	11th to 20th	Night	8% 8% 2 5% 3 3 4 3 4 6% 54%	5119
	21st to end	Night	9% 9% 3 7% 4 4 4 3 6% 7% 44%	5086
April	1st to 10th	Night	7% 9% 2 6% 3 3 4 4 5% 6% 52%	2000
	11th to 20th	Night	12% 7% 3 6% 4 4 4 3 6% 6% 45%	1977
	21st to end	Night	15% 8% 2 6% 4 4 4 4 5% 7% 43%	2000
May	1st to 10th	Night	11% 7% 3 7% 4 5% 4 3 6% 7% 42%	4132
	11th to 20th	Night	9% 5% 2 6% 4 5% 5% 4 6% 8% 44%	3620
	21st to end	Night	12% 7% 2 5% 3 4 4 4 6% 7% 46%	3972
June	1st to 10th	Night	7% 3 2 4 4 4 3 4 6% 10% 54%	1600
	11th to 20th	Night	6% 2 1 4 4 4 4 4 5% 7% 59%	1600
	21st to end	Night	5% 4 1 6% 4 3 4 3 7% 9% 55%	1600
July	1st to 10th	Night	4 3 1 4 4 4 4 4 7% 8% 57%	3640
	11th to 20th	Night	4 3 1 5% 4 4 5% 5% 9% 11% 50%	3640
	21st to end	Night	4 4 2 6% 4 5% 6% 5% 8% 9% 47%	3970
August	1st to 10th	Night	9% 4 1 5% 5% 5% 5% 4 8% 9% 45%	3987
	11th to 20th	Night	3 4 2 6% 4 4 5% 5% 7% 10% 51%	4483
	21st to end	Night	7% 5% 2 6% 4 4 5% 5% 7% 9% 44%	4993
September	1st to 10th	Night	6% 3 2 5% 4 3 4 3 5% 8% 58%	2000
	11th to 20th	Night	6% 4 1 4 3 3 5% 4 4 6% 60%	2038
	21st to end	Night	7% 3 1 4 2 3 4 2 5% 6% 62%	2200
October	1st to 10th	Night	7% 3 1 3 2 2 3 2 3 5% 68%	3849
	11th to 20th	Night	6% 4 2 5% 3 4 4 3 5% 7% 56%	3874
	21st to end	Night	7% 6% 1 5% 3 3 3 2 4 7% 60%	4269
November	1st to 10th	Night	4 5% 2 4 3 3 4 3 5% 7% 60%	2535
	11th to 20th	Night	4 5% 2 5% 3 3 3 2 5% 6% 61%	2600
	21st to end	Night	4 7% 2 5% 4 3 2 3 5% 7% 58%	2705
December	1st to 10th	Night	2 5% 2 4 3 3 3 3 3 5% 67%	4570
	11th to 20th	Night	2 5% 2 5% 3 3 3 3 6% 8% 60%	5181
	21st to end	Night	5% 10% 3 6% 4 4 4 3 5% 7% 48%	6974

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	30% 4 9% 33% 18% 6%	3639
	11th to 20th	Day	31% 6% 11% 23% 24% 6%	3640
	21st to end	Day	25% 5% 10% 26% 25% 9%	4492
February	1st to 10th	Day	34% 5% 12% 25% 18% 5%	1800
	11th to 20th	Day	29% 6% 9% 29% 22% 4	1939
	21st to end	Day	29% 4 10% 24% 23% 10%	1650
March	1st to 10th	Day	27% 4 8% 18% 32% 10%	4500
	11th to 20th	Day	31% 5% 12% 22% 25% 5%	4860
	21st to end	Day	30% 7% 14% 34% 13% 2	5870
April	1st to 10th	Day	30% 6% 13% 24% 19% 8%	2400
	11th to 20th	Day	37% 5% 12% 22% 17% 7%	2374
	21st to end	Day	35% 7% 12% 25% 19% 2	2400
May	1st to 10th	Day	35% 6% 11% 26% 17% 4	5845
	11th to 20th	Day	31% 8% 10% 21% 21% 8%	6295
	21st to end	Day	32% 9% 14% 24% 19% 3	6926
June	1st to 10th	Day	24% 9% 19% 24% 17% 7%	2800
	11th to 20th	Day	26% 7% 11% 19% 23% 13%	2800
	21st to end	Day	22% 7% 12% 22% 24% 13%	2800
July	1st to 10th	Day	21% 7% 7% 18% 30% 16%	6271
	11th to 20th	Day	25% 8% 12% 25% 19% 11%	6265
	21st to end	Day	29% 7% 10% 18% 19% 17%	6705
August	1st to 10th	Day	34% 8% 14% 20% 16% 8%	4223
	11th to 20th	Day	25% 7% 12% 19% 23% 14%	3882
	21st to end	Day	23% 5% 10% 20% 25% 17%	4311
September	1st to 10th	Day	20% 4 8% 23% 26% 18%	2400
	11th to 20th	Day	22% 4 8% 21% 27% 16%	2360
	21st to end	Day	21% 5% 7% 21% 35% 12%	2200
October	1st to 10th	Day	16% 3 5% 17% 34% 25%	3334
	11th to 20th	Day	23% 4 9% 27% 27% 9%	3230
	21st to end	Day	25% 3 6% 27% 30% 9%	3255
November	1st to 10th	Day	23% 5% 12% 25% 25% 10%	1763
	11th to 20th	Day	24% 4 8% 26% 31% 7%	1800
	21st to end	Day	25% 3 10% 24% 28% 9%	1690
December	1st to 10th	Day	19% 4 8% 34% 27% 8%	2620
	11th to 20th	Day	21% 4 8% 34% 28% 5%	3024
	21st to end	Day	34% 4 11% 24% 20% 7%	4004
January	1st to 10th	Night	35% 5% 12% 25% 18% 5%	6327
	11th to 20th	Night	31% 5% 11% 22% 24% 6%	6340
	21st to end	Night	28% 5% 10% 25% 25% 6%	6518
February	1st to 10th	Night	33% 5% 13% 25% 20% 4	2600
	11th to 20th	Night	35% 5% 11% 26% 19% 4	2356
	21st to end	Night	30% 3 8% 24% 25% 11%	1980
March	1st to 10th	Night	32% 4 8% 16% 33% 8%	5374
	11th to 20th	Night	31% 5% 11% 16% 29% 8%	5119
	21st to end	Night	38% 6% 13% 28% 13% 2	5086
April	1st to 10th	Night	32% 5% 10% 25% 19% 7%	2000
	11th to 20th	Night	37% 5% 13% 21% 18% 5%	1977
	21st to end	Night	39% 5% 11% 25% 17% 3	2000
May	1st to 10th	Night	37% 8% 12% 26% 13% 4	4131
	11th to 20th	Night	34% 8% 15% 21% 16% 6%	3621
	21st to end	Night	35% 9% 17% 23% 12% 4	3972
June	1st to 10th	Night	24% 7% 22% 29% 13% 6%	1600
	11th to 20th	Night	24% 7% 14% 22% 21% 12%	1600
	21st to end	Night	25% 7% 12% 26% 25% 7%	1600
July	1st to 10th	Night	23% 6% 10% 25% 28% 8%	3600
	11th to 20th	Night	25% 7% 19% 25% 19% 5%	3592
	21st to end	Night	29% 8% 14% 19% 20% 9%	3856
August	1st to 10th	Night	37% 8% 16% 20% 14% 4	2896
	11th to 20th	Night	29% 9% 15% 22% 16% 10%	3243
	21st to end	Night	26% 6% 15% 21% 23% 9%	3597
September	1st to 10th	Night	24% 6% 11% 21% 22% 16%	2000
	11th to 20th	Night	22% 5% 11% 24% 23% 15%	2038
	21st to end	Night	23% 4 9% 22% 30% 12%	2200
October	1st to 10th	Night	20% 3 7% 17% 31% 22%	3849
	11th to 20th	Night	26% 5% 10% 25% 26% 8%	3874
	21st to end	Night	25% 3 7% 27% 27% 10%	4269
November	1st to 10th	Night	23% 5% 11% 25% 26% 10%	2535
	11th to 20th	Night	24% 4 9% 27% 28% 8%	2600
	21st to end	Night	27% 4 8% 25% 29% 7%	2705
December	1st to 10th	Night	20% 4 9% 36% 26% 5%	4570
	11th to 20th	Night	23% 3 7% 37% 26% 3	5182
	21st to end	Night	35% 4 9% 24% 24% 4	6974

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	7% 6% 14% 45% 23% 5%	300
	11th to 20th	Day	7% 8% 18% 47% 17% 3	300
	21st to end	Day	4 5% 25% 48% 13% 5%	330
February	1st to 10th	Day	6% 7% 29% 46% 9% 3	300
	11th to 20th	Day	5% 5% 31% 44% 14% 1	300
	21st to end	Day	6% 8% 25% 47% 11% 2	249
March	1st to 10th	Day	6% 9% 21% 40% 18% 5%	300
	11th to 20th	Day	11% 10% 27% 33% 15% 4	438
	21st to end	Day	10% 13% 31% 32% 13% 2	550
April	1st to 10th	Day	13% 13% 27% 30% 14% 3	500
	11th to 20th	Day	16% 17% 27% 27% 9% 3	492
	21st to end	Day	14% 14% 27% 26% 14% 4	500
May	1st to 10th	Day	13% 9% 26% 31% 17% 4	674
	11th to 20th	Day	16% 6% 18% 30% 24% 6%	725
	21st to end	Day	10% 8% 21% 29% 24% 7%	789
June	1st to 10th	Day	5% 4 15% 34% 30% 11%	730
	11th to 20th	Day	7% 4 22% 35% 26% 6%	730
	21st to end	Day	5% 4 20% 34% 28% 9%	730
July	1st to 10th	Day	7% 2 14% 29% 35% 13%	721
	11th to 20th	Day	3 2 13% 33% 36% 14%	718
	21st to end	Day	5% 2 13% 27% 40% 13%	794
August	1st to 10th	Day	6% 3 15% 33% 32% 12%	543
	11th to 20th	Day	3 3 16% 32% 32% 15%	517
	21st to end	Day	5% 2 17% 32% 32% 12%	583
September	1st to 10th	Day	5% 2 15% 33% 30% 14%	530
	11th to 20th	Day	4 3 20% 26% 34% 12%	490
	21st to end	Day	9% 2 14% 25% 28% 21%	330
October	1st to 10th	Day	11% 5% 13% 27% 27% 18%	330
	11th to 20th	Day	4 6% 18% 40% 21% 11%	324
	21st to end	Day	10% 6% 22% 34% 22% 7%	330
November	1st to 10th	Day	6% 7% 22% 38% 17% 9%	300
	11th to 20th	Day	7% 8% 17% 42% 22% 4	300
	21st to end	Day	6% 5% 18% 48% 19% 4	300
December	1st to 10th	Day	5% 7% 21% 38% 24% 5%	300
	11th to 20th	Day	6% 5% 19% 56% 14% 1	300
	21st to end	Day	6% 7% 24% 45% 14% 3	330
January	1st to 10th	Night	7% 4 26% 49% 12% 2	1000
	11th to 20th	Night	5% 5% 32% 48% 10%	1000
	21st to end	Night	6% 3 29% 51% 11%	904
February	1st to 10th	Night	7% 5% 36% 45% 8% 1	800
	11th to 20th	Night	7% 4 33% 48% 7%	784
	21st to end	Night	8% 5% 37% 46% 4	660
March	1st to 10th	Night	6% 5% 32% 48% 9%	800
	11th to 20th	Night	9% 5% 28% 44% 13%	800
	21st to end	Night	10% 6% 33% 43% 8%	710
April	1st to 10th	Night	11% 7% 37% 41% 5%	600
	11th to 20th	Night	14% 9% 30% 40% 7%	593
	21st to end	Night	18% 7% 26% 37% 12%	600
May	1st to 10th	Night	15% 6% 26% 40% 14%	600
	11th to 20th	Night	17% 4 21% 40% 16% 1	591
	21st to end	Night	10% 5% 24% 42% 18% 1	650
June	1st to 10th	Night	7% 3 19% 47% 24% 1	600
	11th to 20th	Night	6% 3 23% 53% 15%	600
	21st to end	Night	6% 2 19% 51% 21% 1	600
July	1st to 10th	Night	7% 3 13% 44% 32% 1	585
	11th to 20th	Night	3 1 13% 50% 31% 2	582
	21st to end	Night	5% 2 8% 47% 36% 2	657
August	1st to 10th	Night	6% 1 14% 46% 32% 1	597
	11th to 20th	Night	3 2 12% 53% 29% 1	594
	21st to end	Night	6% 1 12% 48% 32% 1	660
September	1st to 10th	Night	8% 2 16% 46% 26% 3	600
	11th to 20th	Night	8% 3 15% 48% 25% 2	600
	21st to end	Night	7% 3 20% 49% 21% 1	600
October	1st to 10th	Night	12% 3 19% 43% 21% 2	755
	11th to 20th	Night	7% 3 25% 46% 19% 1	792
	21st to end	Night	10% 5% 21% 49% 13% 2	923
November	1st to 10th	Night	5% 3 25% 51% 14% 1	975
	11th to 20th	Night	6% 6% 26% 53% 8% 1	1000
	21st to end	Night	7% 5% 24% 50% 13% 1	1000
December	1st to 10th	Night	6% 4 27% 53% 10%	1000
	11th to 20th	Night	7% 5% 27% 53% 9% 1	1000
	21st to end	Night	8% 5% 27% 51% 8% 1	1100

Page generated at 2025-10-15 23:50:26. Version ac07

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