Wyoming Infrared Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wyoming Infrared Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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 5% 2 6% 4 4 5% 4 7% 8% 53%	117748
	Night	2 4 2 5% 3 3 4 3 6% 8% 60%	119767
Transparency	Day	15% 44% 7% 15% 13% 5%	117494
	Night	13% 42% 9% 17% 14% 4	119611
Seeing	Day	10% 22% 32% 23% 11% 2	16231
	Night	6% 20% 36% 27% 10% 1	26417

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 3 10% 5% 4 3 3 5% 8% 56%	3638
	11th to 20th	Day	3 3 8% 7% 6% 6% 5% 7% 9% 47%	3755
	21st to end	Day	3 2 6% 6% 4 4 4 6% 8% 59%	4510
February	1st to 10th	Day	4 3 8% 6% 4 4 4 8% 10% 48%	1800
	11th to 20th	Day	3 3 6% 5% 5% 5% 4 7% 9% 51%	1840
	21st to end	Day	1 5% 2 7% 4 4 6% 5% 7% 9% 51%	1650
March	1st to 10th	Day	1 8% 4 8% 4 3 4 4 6% 8% 52%	4564
	11th to 20th	Day	1 8% 3 5% 3 3 5% 4 6% 11% 52%	5000
	21st to end	Day	2 6% 2 5% 4 5% 5% 5% 8% 11% 48%	5739
April	1st to 10th	Day	3 8% 3 5% 4 5% 5% 5% 7% 8% 47%	2400
	11th to 20th	Day	5% 10% 2 7% 5% 6% 5% 4 6% 9% 40%	2371
	21st to end	Day	5% 10% 3 7% 6% 6% 5% 5% 6% 8% 40%	2341
May	1st to 10th	Day	6% 15% 4 8% 6% 5% 6% 4 6% 7% 33%	4183
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 5% 8% 9% 43%	4388
	21st to end	Day	4 4 2 5% 5% 5% 6% 5% 8% 9% 48%	4825
June	1st to 10th	Day	4 4 1 5% 5% 5% 5% 5% 8% 9% 49%	2660
	11th to 20th	Day	5% 3 1 4 3 3 4 4 8% 8% 55%	2660
	21st to end	Day	2 3 1 5% 4 4 6% 4 7% 8% 57%	2660
July	1st to 10th	Day	3 4 1 4 3 4 5% 5% 7% 7% 56%	4430
	11th to 20th	Day	3 3 1 5% 5% 5% 7% 6% 7% 9% 49%	4430
	21st to end	Day	4 3 1 5% 4 5% 5% 5% 7% 7% 53%	4712
August	1st to 10th	Day	4 4 1 6% 5% 5% 7% 5% 8% 10% 46%	4092
	11th to 20th	Day	3 4 2 5% 4 6% 6% 5% 7% 8% 51%	3857
	21st to end	Day	4 3 1 4 4 4 5% 4 7% 7% 58%	4180
September	1st to 10th	Day	4 3 1 4 5% 3 4 3 5% 5% 61%	2280
	11th to 20th	Day	4 3 1 4 4 4 4 4 6% 6% 61%	2280
	21st to end	Day	5% 4 1 4 3 3 3 3 4 5% 65%	2049
October	1st to 10th	Day	3 3 1 3 2 3 2 3 4 4 73%	3170
	11th to 20th	Day	4 4 1 4 3 4 5% 4 6% 7% 58%	3150
	21st to end	Day	3 7% 3 4 3 3 4 3 5% 7% 59%	3351
November	1st to 10th	Day	2 4 1 4 3 3 4 3 6% 8% 62%	1763
	11th to 20th	Day	2 5% 2 4 3 4 3 3 5% 8% 61%	1770
	21st to end	Day	1 4 2 6% 4 4 4 4 5% 9% 57%	1600
December	1st to 10th	Day	2 2 6% 3 3 3 2 4 6% 70%	2620
	11th to 20th	Day	1 2 1 5% 2 3 3 3 7% 10% 63%	3026
	21st to end	Day	1 7% 3 6% 4 4 5% 4 6% 9% 52%	4004
January	1st to 10th	Night	4 4 9% 4 3 4 4 6% 8% 55%	6327
	11th to 20th	Night	2 1 4 5% 4 4 5% 8% 9% 57%	6269
	21st to end	Night	3 2 5% 3 4 4 4 5% 6% 64%	6468
February	1st to 10th	Night	4 2 6% 4 4 4 4 7% 9% 56%	2600
	11th to 20th	Night	1 3 2 5% 4 4 4 4 6% 9% 58%	2446
	21st to end	Night	1 4 2 6% 4 3 4 3 6% 8% 58%	1980
March	1st to 10th	Night	1 7% 3 7% 4 4 3 3 4 7% 57%	5296
	11th to 20th	Night	1 8% 3 4 3 2 3 2 5% 7% 61%	5000
	21st to end	Night	3 7% 2 6% 3 4 4 3 6% 9% 54%	5224
April	1st to 10th	Night	2 7% 2 5% 4 3 4 4 6% 7% 57%	2000
	11th to 20th	Night	5% 8% 2 6% 3 4 4 4 6% 8% 50%	1977
	21st to end	Night	5% 9% 3 6% 3 3 3 3 5% 7% 53%	1955
May	1st to 10th	Night	5% 10% 2 6% 4 4 5% 4 5% 7% 48%	2781
	11th to 20th	Night	7% 6% 2 4 3 3 5% 4 7% 9% 51%	2517
	21st to end	Night	4 3 2 4 2 4 3 5% 8% 9% 57%	2762
June	1st to 10th	Night	3 2 1 2 3 4 4 4 7% 10% 62%	1520
	11th to 20th	Night	3 3 1 4 2 3 4 4 5% 8% 64%	1520
	21st to end	Night	3 3 1 3 3 3 2 3 6% 7% 66%	1520
July	1st to 10th	Night	2 2 1 3 3 3 4 4 5% 7% 65%	2540
	11th to 20th	Night	1 2 2 2 3 4 5% 8% 11% 62%	2540
	21st to end	Night	2 2 1 4 3 3 4 4 6% 9% 62%	2847
August	1st to 10th	Night	3 3 1 4 3 3 5% 4 8% 11% 55%	2847
	11th to 20th	Night	2 2 2 4 3 5% 5% 4 8% 11% 54%	2982
	21st to end	Night	3 4 2 5% 4 4 4 4 6% 8% 57%	3487
September	1st to 10th	Night	4 4 1 3 2 3 3 2 5% 7% 64%	1900
	11th to 20th	Night	3 3 1 4 3 3 3 3 4 7% 67%	1900
	21st to end	Night	4 4 1 3 2 2 2 3 5% 5% 68%	2124
October	1st to 10th	Night	3 3 1 2 2 1 2 2 3 4 77%	3800
	11th to 20th	Night	3 5% 2 3 2 3 3 3 5% 8% 62%	3778
	21st to end	Night	3 6% 2 4 2 2 2 2 4 6% 67%	4174
November	1st to 10th	Night	2 4 1 3 2 2 3 3 6% 8% 65%	2535
	11th to 20th	Night	1 4 2 3 3 3 3 3 6% 8% 64%	2626
	21st to end	Night	1 6% 2 5% 3 2 4 3 6% 9% 60%	2800
December	1st to 10th	Night	2 1 3 2 2 3 3 4 6% 72%	4570
	11th to 20th	Night	1 3 1 4 3 3 3 3 6% 8% 67%	5181
	21st to end	Night	1 7% 3 6% 4 4 5% 3 6% 8% 54%	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	20% 34% 11% 18% 15% 2	3639
	11th to 20th	Day	25% 36% 12% 10% 14% 3	3755
	21st to end	Day	12% 32% 14% 18% 20% 4	4510
February	1st to 10th	Day	8% 65% 10% 8% 7% 3	1800
	11th to 20th	Day	8% 64% 6% 15% 6% 2	1849
	21st to end	Day	8% 64% 5% 12% 10% 1	1650
March	1st to 10th	Day	20% 31% 7% 21% 14% 7%	4564
	11th to 20th	Day	18% 34% 10% 23% 14% 1	5000
	21st to end	Day	17% 33% 15% 27% 6% 1	5739
April	1st to 10th	Day	11% 64% 6% 11% 6% 1	2400
	11th to 20th	Day	15% 64% 3 9% 7% 2	2374
	21st to end	Day	16% 65% 4 11% 4	2341
May	1st to 10th	Day	31% 43% 6% 7% 10% 3	4183
	11th to 20th	Day	16% 45% 10% 18% 10% 1	4392
	21st to end	Day	14% 43% 8% 15% 17% 3	4825
June	1st to 10th	Day	7% 67% 6% 9% 8% 2	2660
	11th to 20th	Day	8% 67% 5% 8% 9% 3	2660
	21st to end	Day	9% 64% 4 9% 10% 3	2660
July	1st to 10th	Day	12% 37% 5% 11% 19% 16%	4361
	11th to 20th	Day	18% 38% 6% 14% 13% 10%	4355
	21st to end	Day	14% 37% 5% 11% 14% 19%	4563
August	1st to 10th	Day	17% 42% 8% 17% 9% 8%	4078
	11th to 20th	Day	17% 40% 7% 10% 17% 8%	3896
	21st to end	Day	15% 39% 5% 12% 17% 13%	4179
September	1st to 10th	Day	10% 60% 4 8% 13% 5%	2280
	11th to 20th	Day	7% 60% 5% 10% 13% 4	2280
	21st to end	Day	9% 60% 3 9% 15% 5%	2049
October	1st to 10th	Day	6% 36% 3 8% 24% 23%	3170
	11th to 20th	Day	15% 39% 5% 21% 16% 4	3150
	21st to end	Day	16% 38% 5% 24% 16% 1	3351
November	1st to 10th	Day	9% 58% 7% 15% 10% 2	1763
	11th to 20th	Day	8% 58% 6% 14% 12% 2	1770
	21st to end	Day	11% 60% 5% 12% 10% 2	1600
December	1st to 10th	Day	9% 36% 7% 30% 17% 1	2620
	11th to 20th	Day	8% 34% 14% 30% 13%	3024
	21st to end	Day	22% 30% 9% 19% 15% 5%	4004
January	1st to 10th	Night	22% 31% 12% 19% 11% 4	6327
	11th to 20th	Night	18% 35% 13% 12% 17% 4	6269
	21st to end	Night	14% 32% 14% 18% 18% 4	6468
February	1st to 10th	Night	8% 65% 11% 8% 6% 2	2600
	11th to 20th	Night	7% 64% 8% 13% 6% 2	2447
	21st to end	Night	8% 62% 6% 12% 10% 3	1980
March	1st to 10th	Night	21% 31% 6% 19% 17% 7%	5296
	11th to 20th	Night	18% 30% 7% 20% 23% 2	5000
	21st to end	Night	19% 35% 14% 26% 7%	5224
April	1st to 10th	Night	10% 63% 7% 12% 8% 1	2000
	11th to 20th	Night	12% 63% 6% 11% 8% 1	1977
	21st to end	Night	13% 64% 5% 13% 5%	1955
May	1st to 10th	Night	19% 44% 7% 14% 14% 2	2781
	11th to 20th	Night	13% 45% 11% 21% 6% 3	2518
	21st to end	Night	12% 42% 8% 21% 17% 1	2762
June	1st to 10th	Night	3 66% 8% 11% 9% 2	1520
	11th to 20th	Night	6% 65% 6% 11% 9% 3	1520
	21st to end	Night	8% 64% 4 10% 11% 4	1520
July	1st to 10th	Night	10% 36% 5% 13% 19% 16%	2500
	11th to 20th	Night	9% 37% 8% 22% 15% 10%	2492
	21st to end	Night	11% 36% 6% 17% 15% 15%	2758
August	1st to 10th	Night	15% 38% 13% 18% 10% 6%	2838
	11th to 20th	Night	16% 40% 13% 14% 11% 6%	3009
	21st to end	Night	19% 38% 6% 10% 20% 8%	3487
September	1st to 10th	Night	7% 60% 4 11% 12% 6%	1900
	11th to 20th	Night	6% 60% 5% 11% 12% 6%	1900
	21st to end	Night	8% 60% 4 9% 14% 5%	2124
October	1st to 10th	Night	5% 36% 3 8% 29% 19%	3800
	11th to 20th	Night	13% 37% 7% 19% 20% 3	3778
	21st to end	Night	12% 37% 6% 24% 18% 3	4174
November	1st to 10th	Night	9% 58% 7% 14% 11% 2	2535
	11th to 20th	Night	7% 58% 5% 15% 12% 3	2626
	21st to end	Night	12% 59% 5% 15% 8% 2	2800
December	1st to 10th	Night	7% 38% 8% 30% 16% 2	4570
	11th to 20th	Night	9% 34% 13% 31% 12% 1	5182
	21st to end	Night	21% 30% 10% 19% 16% 3	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	12% 32% 33% 16% 7% 1	300
	11th to 20th	Day	10% 41% 33% 14% 3	300
	21st to end	Day	5% 35% 42% 14% 3 1	330
February	1st to 10th	Day	20% 45% 28% 6% 1	300
	11th to 20th	Day	18% 41% 29% 11% 1	300
	21st to end	Day	16% 41% 33% 8% 2	249
March	1st to 10th	Day	10% 39% 34% 14% 2 1	325
	11th to 20th	Day	13% 30% 36% 18% 4	500
	21st to end	Day	14% 36% 32% 14% 3	550
April	1st to 10th	Day	14% 34% 37% 13% 2	500
	11th to 20th	Day	16% 34% 33% 13% 4	492
	21st to end	Day	16% 25% 33% 20% 6% 1	481
May	1st to 10th	Day	19% 22% 30% 20% 8% 1	567
	11th to 20th	Day	15% 14% 31% 26% 13% 2	675
	21st to end	Day	10% 14% 30% 27% 16% 2	734
June	1st to 10th	Day	5% 11% 30% 31% 18% 5%	680
	11th to 20th	Day	8% 14% 37% 28% 11% 2	680
	21st to end	Day	5% 11% 33% 31% 18% 2	680
July	1st to 10th	Day	6% 7% 23% 35% 26% 4	671
	11th to 20th	Day	3 5% 29% 36% 23% 5%	668
	21st to end	Day	7% 5% 22% 36% 24% 6%	685
August	1st to 10th	Day	9% 5% 37% 35% 13% 2	487
	11th to 20th	Day	5% 6% 33% 34% 18% 4	477
	21st to end	Day	6% 9% 31% 33% 17% 4	539
September	1st to 10th	Day	7% 10% 30% 32% 17% 4	490
	11th to 20th	Day	6% 14% 37% 26% 13% 4	490
	21st to end	Day	7% 18% 30% 24% 15% 6%	321
October	1st to 10th	Day	8% 17% 31% 26% 12% 5%	300
	11th to 20th	Day	10% 30% 29% 21% 6% 4	300
	21st to end	Day	11% 33% 36% 15% 4 1	330
November	1st to 10th	Day	8% 39% 33% 15% 4 1	300
	11th to 20th	Day	14% 34% 39% 11% 2	300
	21st to end	Day	9% 35% 39% 13% 4	300
December	1st to 10th	Day	14% 38% 32% 10% 5% 1	300
	11th to 20th	Day	17% 40% 33% 10% 1	300
	21st to end	Day	15% 41% 28% 11% 3 1	330
January	1st to 10th	Night	6% 31% 41% 15% 5% 1	1000
	11th to 20th	Night	5% 38% 39% 13% 4	968
	21st to end	Night	4 28% 48% 16% 4	880
February	1st to 10th	Night	7% 34% 46% 10% 4	800
	11th to 20th	Night	4 32% 41% 19% 3	784
	21st to end	Night	6% 37% 41% 14% 2	660
March	1st to 10th	Night	2 29% 44% 19% 5%	800
	11th to 20th	Night	8% 18% 41% 29% 5% 1	800
	21st to end	Night	7% 20% 47% 21% 4 1	770
April	1st to 10th	Night	8% 19% 45% 25% 3	600
	11th to 20th	Night	12% 18% 40% 24% 5%	593
	21st to end	Night	10% 15% 36% 29% 10% 1	587
May	1st to 10th	Night	13% 11% 34% 30% 11% 1	570
	11th to 20th	Night	14% 6% 28% 33% 18% 1	561
	21st to end	Night	5% 9% 29% 37% 18% 1	617
June	1st to 10th	Night	4 6% 28% 40% 21% 1	570
	11th to 20th	Night	6% 8% 32% 41% 13%	570
	21st to end	Night	5% 4 25% 46% 20% 1	570
July	1st to 10th	Night	5% 3 17% 43% 31% 1	555
	11th to 20th	Night	2 2 18% 49% 28% 2	552
	21st to end	Night	3 1 12% 48% 33% 2	624
August	1st to 10th	Night	5% 2 13% 53% 26% 1	567
	11th to 20th	Night	4 2 18% 51% 24% 2	564
	21st to end	Night	3 2 18% 44% 30% 2	627
September	1st to 10th	Night	6% 2 22% 45% 21% 3	570
	11th to 20th	Night	6% 5% 22% 47% 17% 3	570
	21st to end	Night	5% 10% 28% 37% 18% 3	627
October	1st to 10th	Night	7% 11% 34% 35% 11% 1	760
	11th to 20th	Night	7% 17% 36% 29% 10% 1	760
	21st to end	Night	8% 19% 45% 21% 5% 2	866
November	1st to 10th	Night	5% 25% 45% 20% 5% 1	975
	11th to 20th	Night	8% 32% 43% 16% 2	1000
	21st to end	Night	5% 26% 49% 17% 3	1000
December	1st to 10th	Night	7% 36% 40% 14% 3	1000
	11th to 20th	Night	8% 32% 42% 15% 2	1000
	21st to end	Night	8% 37% 38% 14% 4	1100

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