Moab Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Moab Observatory 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	3 4 1 4 3 3 4 3 6% 8% 60%	135005
	Night	4 5% 2 5% 3 3 4 3 5% 7% 57%	132212
Transparency	Day	22% 6% 10% 20% 25% 17%	129835
	Night	24% 6% 10% 21% 24% 15%	128385
Seeing	Day	7% 10% 26% 32% 20% 4	16401
	Night	7% 6% 21% 38% 25% 4	26630

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 7% 3 6% 5% 4 6% 5% 7% 10% 46%	4098
	11th to 20th	Day	3 5% 2 7% 5% 4 5% 4 7% 9% 50%	4100
	21st to end	Day	5% 6% 2 5% 4 4 4 3 5% 7% 56%	4510
February	1st to 10th	Day	4 6% 2 6% 4 4 4 4 9% 10% 46%	1800
	11th to 20th	Day	6% 8% 2 6% 5% 3 4 4 6% 8% 49%	1755
	21st to end	Day	6% 7% 3 4 3 4 4 3 6% 6% 52%	1698
March	1st to 10th	Day	3 8% 3 6% 4 4 4 3 4 7% 55%	4954
	11th to 20th	Day	4 11% 3 8% 4 4 4 4 6% 8% 44%	5000
	21st to end	Day	5% 10% 3 7% 5% 4 4 3 6% 7% 45%	5486
April	1st to 10th	Day	5% 5% 2 5% 4 3 3 3 5% 7% 59%	2315
	11th to 20th	Day	4 5% 2 5% 5% 4 4 4 5% 7% 56%	2371
	21st to end	Day	4 5% 2 4 4 3 3 3 5% 7% 59%	2513
May	1st to 10th	Day	5% 5% 2 5% 4 4 4 3 6% 8% 56%	5880
	11th to 20th	Day	3 3 1 5% 3 4 4 4 6% 7% 61%	5841
	21st to end	Day	3 3 1 3 3 2 3 3 4 7% 69%	6532
June	1st to 10th	Day	3 2 1 3 2 3 3 3 5% 8% 67%	2800
	11th to 20th	Day	2 3 1 3 3 2 3 3 4 5% 74%	2800
	21st to end	Day	2 2 1 3 2 2 3 2 4 5% 74%	2766
July	1st to 10th	Day	2 2 1 2 2 2 3 3 4 5% 75%	5879
	11th to 20th	Day	2 2 1 3 3 3 4 4 7% 10% 62%	5880
	21st to end	Day	2 1 1 3 2 3 4 4 6% 8% 67%	6401
August	1st to 10th	Day	2 1 1 3 3 4 4 4 7% 10% 62%	5779
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 7% 67%	5798
	21st to end	Day	4 2 1 4 4 4 4 4 7% 10% 55%	6072
September	1st to 10th	Day	4 2 1 3 3 3 3 3 6% 7% 65%	2400
	11th to 20th	Day	2 2 1 4 3 3 4 2 5% 6% 68%	2229
	21st to end	Day	3 2 1 3 2 2 2 3 3 5% 73%	2198
October	1st to 10th	Day	3 2 1 2 1 2 2 2 3 4 79%	3270
	11th to 20th	Day	5% 3 1 4 3 3 4 3 6% 9% 58%	3230
	21st to end	Day	3 3 1 2 2 2 2 3 5% 10% 67%	3438
November	1st to 10th	Day	4 4 1 3 3 2 2 2 5% 7% 66%	1959
	11th to 20th	Day	4 4 1 3 3 2 2 2 4 7% 68%	1758
	21st to end	Day	5% 6% 1 4 2 3 3 3 4 7% 62%	1600
December	1st to 10th	Day	3 5% 1 4 3 2 3 4 6% 12% 57%	2620
	11th to 20th	Day	4 5% 2 5% 4 4 4 4 8% 17% 44%	3026
	21st to end	Day	5% 9% 2 6% 4 5% 5% 4 6% 10% 44%	4249
January	1st to 10th	Night	3 8% 4 7% 4 4 4 3 5% 7% 52%	5867
	11th to 20th	Night	4 7% 2 5% 4 3 3 4 5% 9% 54%	5880
	21st to end	Night	5% 7% 3 6% 4 3 3 3 4 5% 56%	6468
February	1st to 10th	Night	3 6% 2 5% 3 4 4 4 6% 8% 54%	2600
	11th to 20th	Night	6% 8% 2 5% 3 4 4 3 6% 7% 52%	2532
	21st to end	Night	5% 8% 2 7% 4 4 3 4 5% 7% 51%	1928
March	1st to 10th	Night	4 9% 3 6% 4 4 4 3 4 6% 54%	4940
	11th to 20th	Night	5% 8% 2 6% 4 3 4 4 5% 8% 49%	5000
	21st to end	Night	6% 9% 3 7% 3 4 4 4 5% 7% 48%	5489
April	1st to 10th	Night	5% 7% 2 6% 4 4 4 3 5% 6% 54%	2083
	11th to 20th	Night	5% 6% 3 6% 4 5% 4 3 5% 6% 53%	1977
	21st to end	Night	6% 5% 2 5% 3 4 4 3 6% 7% 54%	1883
May	1st to 10th	Night	6% 6% 2 5% 4 4 4 4 5% 6% 54%	4100
	11th to 20th	Night	4 5% 2 5% 3 4 4 4 7% 7% 55%	4074
	21st to end	Night	5% 2 1 4 3 3 3 3 5% 7% 66%	4346
June	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 8% 61%	1600
	11th to 20th	Night	3 4 1 4 3 3 3 3 5% 7% 65%	1600
	21st to end	Night	2 2 1 4 3 2 3 4 5% 6% 68%	1627
July	1st to 10th	Night	2 2 1 3 3 4 4 4 6% 6% 66%	4100
	11th to 20th	Night	2 3 1 5% 5% 5% 7% 5% 8% 10% 50%	4100
	21st to end	Night	2 2 1 4 3 4 4 4 7% 10% 59%	4472
August	1st to 10th	Night	2 2 2 5% 4 5% 5% 5% 8% 9% 54%	4033
	11th to 20th	Night	3 2 1 4 3 4 4 3 6% 8% 62%	4051
	21st to end	Night	3 3 2 5% 5% 5% 5% 5% 7% 8% 52%	4905
September	1st to 10th	Night	4 3 1 3 3 2 4 3 6% 7% 64%	2000
	11th to 20th	Night	3 2 1 3 3 3 3 3 4 7% 66%	2168
	21st to end	Night	4 3 1 3 2 2 3 3 3 4 72%	2200
October	1st to 10th	Night	4 2 1 2 2 2 2 2 4 5% 75%	3920
	11th to 20th	Night	5% 4 1 5% 3 3 4 3 6% 7% 58%	3874
	21st to end	Night	5% 4 1 3 2 3 3 3 3 6% 68%	4120
November	1st to 10th	Night	3 4 1 3 3 3 3 2 5% 7% 66%	2340
	11th to 20th	Night	5% 4 1 3 3 2 3 3 4 5% 67%	2614
	21st to end	Night	6% 6% 2 4 3 2 3 3 4 6% 61%	2800
December	1st to 10th	Night	4 4 1 3 2 2 2 2 6% 9% 65%	4570
	11th to 20th	Night	4 5% 1 5% 4 3 4 4 6% 11% 53%	5181
	21st to end	Night	5% 7% 2 6% 4 4 4 3 5% 9% 50%	6770

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% 8% 20% 30% 11% 2	4099
	11th to 20th	Day	25% 9% 17% 25% 19% 5%	4100
	21st to end	Day	26% 8% 13% 26% 24% 3	4510
February	1st to 10th	Day	31% 10% 19% 20% 15% 5%	1800
	11th to 20th	Day	33% 6% 14% 23% 19% 4	1764
	21st to end	Day	31% 7% 9% 25% 22% 6%	1698
March	1st to 10th	Day	27% 5% 10% 22% 29% 8%	4954
	11th to 20th	Day	37% 8% 12% 22% 19% 4	5000
	21st to end	Day	37% 7% 9% 24% 20% 3	5486
April	1st to 10th	Day	26% 5% 9% 24% 25% 11%	2315
	11th to 20th	Day	26% 6% 11% 22% 25% 11%	2374
	21st to end	Day	24% 5% 10% 22% 32% 8%	2513
May	1st to 10th	Day	22% 9% 11% 17% 33% 8%	5880
	11th to 20th	Day	19% 6% 8% 19% 34% 15%	5844
	21st to end	Day	14% 5% 6% 14% 42% 18%	6533
June	1st to 10th	Day	16% 4 7% 16% 32% 26%	2800
	11th to 20th	Day	14% 3 5% 8% 23% 46%	2800
	21st to end	Day	13% 3 5% 10% 23% 46%	2766
July	1st to 10th	Day	13% 3 6% 7% 11% 61%	5816
	11th to 20th	Day	16% 4 7% 15% 27% 31%	5811
	21st to end	Day	14% 5% 8% 15% 24% 33%	6217
August	1st to 10th	Day	20% 8% 13% 25% 17% 18%	4208
	11th to 20th	Day	20% 6% 11% 15% 23% 24%	4197
	21st to end	Day	20% 6% 10% 18% 24% 21%	4375
September	1st to 10th	Day	19% 5% 8% 14% 24% 29%	2400
	11th to 20th	Day	17% 6% 9% 17% 23% 28%	2229
	21st to end	Day	16% 3 7% 13% 38% 22%	2198
October	1st to 10th	Day	12% 4 6% 13% 28% 37%	3270
	11th to 20th	Day	23% 4 8% 20% 35% 9%	3230
	21st to end	Day	16% 4 9% 30% 36% 6%	3438
November	1st to 10th	Day	19% 3 12% 29% 29% 8%	1959
	11th to 20th	Day	19% 4 9% 34% 30% 3	1758
	21st to end	Day	24% 6% 14% 28% 25% 4	1600
December	1st to 10th	Day	20% 5% 17% 37% 18% 2	2620
	11th to 20th	Day	27% 7% 26% 27% 13%	3024
	21st to end	Day	35% 8% 15% 18% 20% 4	4249
January	1st to 10th	Night	30% 7% 17% 27% 18% 2	5867
	11th to 20th	Night	24% 10% 16% 22% 26% 4	5880
	21st to end	Night	30% 6% 11% 24% 23% 5%	6468
February	1st to 10th	Night	28% 8% 17% 25% 17% 5%	2600
	11th to 20th	Night	30% 9% 12% 25% 20% 4	2533
	21st to end	Night	31% 6% 10% 25% 21% 7%	1928
March	1st to 10th	Night	29% 6% 8% 19% 25% 13%	4940
	11th to 20th	Night	31% 7% 10% 23% 22% 7%	5000
	21st to end	Night	32% 8% 9% 27% 22% 2	5489
April	1st to 10th	Night	30% 6% 8% 19% 26% 12%	2083
	11th to 20th	Night	31% 5% 8% 18% 26% 12%	1977
	21st to end	Night	26% 6% 9% 19% 30% 10%	1883
May	1st to 10th	Night	26% 7% 10% 16% 30% 11%	4097
	11th to 20th	Night	22% 6% 8% 17% 35% 12%	4075
	21st to end	Night	16% 5% 7% 15% 37% 21%	4346
June	1st to 10th	Night	19% 5% 6% 14% 31% 26%	1600
	11th to 20th	Night	18% 5% 7% 9% 18% 43%	1600
	21st to end	Night	15% 4 7% 10% 20% 45%	1627
July	1st to 10th	Night	16% 4 7% 9% 9% 55%	4055
	11th to 20th	Night	23% 6% 9% 13% 21% 29%	4046
	21st to end	Night	19% 5% 9% 12% 22% 34%	4344
August	1st to 10th	Night	29% 8% 11% 20% 14% 18%	2928
	11th to 20th	Night	24% 6% 11% 14% 16% 30%	2928
	21st to end	Night	22% 6% 9% 17% 19% 27%	3533
September	1st to 10th	Night	19% 5% 8% 14% 20% 34%	2000
	11th to 20th	Night	18% 4 10% 17% 20% 30%	2168
	21st to end	Night	18% 4 6% 11% 33% 29%	2200
October	1st to 10th	Night	13% 3 5% 12% 24% 42%	3920
	11th to 20th	Night	24% 4 8% 15% 37% 12%	3874
	21st to end	Night	20% 3 5% 29% 35% 9%	4120
November	1st to 10th	Night	20% 3 9% 23% 33% 12%	2340
	11th to 20th	Night	20% 4 8% 28% 35% 5%	2614
	21st to end	Night	26% 5% 9% 22% 30% 9%	2800
December	1st to 10th	Night	17% 5% 12% 42% 21% 3	4570
	11th to 20th	Night	26% 6% 15% 36% 16%	5182
	21st to end	Night	31% 7% 16% 23% 18% 5%	6770

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	11% 10% 28% 31% 15% 4	300
	11th to 20th	Day	9% 10% 26% 37% 17% 1	300
	21st to end	Day	5% 3 31% 39% 19% 3	330
February	1st to 10th	Day	10% 11% 34% 32% 11% 2	300
	11th to 20th	Day	11% 9% 37% 30% 12% 1	300
	21st to end	Day	10% 18% 30% 30% 11% 1	371
March	1st to 10th	Day	11% 16% 30% 29% 12% 2	500
	11th to 20th	Day	9% 14% 33% 28% 14% 2	500
	21st to end	Day	15% 19% 34% 23% 8% 1	550
April	1st to 10th	Day	12% 15% 32% 25% 12% 4	500
	11th to 20th	Day	12% 19% 37% 23% 7% 1	492
	21st to end	Day	10% 19% 32% 24% 13% 1	500
May	1st to 10th	Day	9% 13% 39% 27% 10% 1	503
	11th to 20th	Day	6% 13% 30% 31% 15% 3	528
	21st to end	Day	7% 15% 24% 30% 19% 5%	617
June	1st to 10th	Day	4 7% 24% 33% 29% 4	730
	11th to 20th	Day	4 11% 26% 34% 20% 4	730
	21st to end	Day	4 7% 27% 35% 24% 3	696
July	1st to 10th	Day	2 4 21% 40% 28% 6%	526
	11th to 20th	Day	3 2 18% 36% 35% 6%	524
	21st to end	Day	3 2 15% 37% 38% 5%	575
August	1st to 10th	Day	4 4 19% 39% 28% 5%	527
	11th to 20th	Day	3 3 18% 37% 30% 9%	517
	21st to end	Day	4 4 21% 34% 30% 7%	583
September	1st to 10th	Day	4 4 18% 34% 30% 10%	530
	11th to 20th	Day	4 12% 24% 33% 23% 5%	530
	21st to end	Day	6% 11% 20% 30% 25% 8%	528
October	1st to 10th	Day	12% 8% 20% 24% 23% 13%	330
	11th to 20th	Day	7% 13% 23% 29% 22% 6%	324
	21st to end	Day	8% 12% 24% 28% 25% 3	330
November	1st to 10th	Day	8% 13% 27% 29% 19% 4	300
	11th to 20th	Day	4 8% 33% 33% 19% 4	300
	21st to end	Day	9% 10% 25% 33% 22% 2	300
December	1st to 10th	Day	8% 9% 25% 34% 20% 4	300
	11th to 20th	Day	9% 7% 27% 38% 15% 4	300
	21st to end	Day	11% 11% 28% 36% 12% 2	330
January	1st to 10th	Night	8% 5% 19% 41% 23% 5%	800
	11th to 20th	Night	7% 5% 22% 38% 25% 4	800
	21st to end	Night	9% 3 22% 42% 20% 4	880
February	1st to 10th	Night	6% 7% 29% 40% 16% 3	800
	11th to 20th	Night	8% 6% 30% 38% 16% 2	784
	21st to end	Night	9% 8% 28% 42% 13% 1	660
March	1st to 10th	Night	9% 10% 26% 39% 16% 2	800
	11th to 20th	Night	7% 8% 25% 36% 24% 1	800
	21st to end	Night	7% 11% 30% 35% 15% 2	880
April	1st to 10th	Night	9% 11% 29% 35% 15% 1	683
	11th to 20th	Night	9% 11% 31% 33% 14% 2	593
	21st to end	Night	7% 14% 26% 33% 16% 5%	600
May	1st to 10th	Night	7% 10% 26% 39% 15% 2	600
	11th to 20th	Night	5% 6% 23% 40% 23% 3	591
	21st to end	Night	4 10% 26% 33% 24% 3	650
June	1st to 10th	Night	3 6% 21% 37% 32% 2	600
	11th to 20th	Night	5% 7% 23% 39% 25% 3	600
	21st to end	Night	2 4 18% 42% 31% 3	600
July	1st to 10th	Night	2 1 16% 33% 41% 5%	585
	11th to 20th	Night	3 1 9% 35% 45% 6%	582
	21st to end	Night	3 1 9% 35% 45% 7%	657
August	1st to 10th	Night	4 1 12% 36% 41% 6%	597
	11th to 20th	Night	4 2 11% 40% 36% 6%	594
	21st to end	Night	4 2 12% 38% 36% 8%	660
September	1st to 10th	Night	5% 1 11% 41% 35% 8%	600
	11th to 20th	Night	3 5% 17% 36% 33% 7%	768
	21st to end	Night	5% 5% 16% 34% 31% 10%	800
October	1st to 10th	Night	7% 5% 19% 39% 26% 4	800
	11th to 20th	Night	6% 5% 19% 39% 27% 5%	792
	21st to end	Night	7% 6% 20% 33% 28% 6%	836
November	1st to 10th	Night	5% 5% 21% 37% 28% 4	780
	11th to 20th	Night	5% 4 23% 42% 21% 5%	845
	21st to end	Night	9% 6% 21% 36% 23% 5%	1000
December	1st to 10th	Night	9% 4 20% 44% 21% 2	1000
	11th to 20th	Night	11% 4 22% 39% 21% 2	1000
	21st to end	Night	13% 5% 23% 39% 17% 3	1013

Page generated at 2025-10-15 23:50:24. Version ac07

Copyright © 2025 Attilla Danko.