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 2024-10-25.

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	3 5% 2 6% 4 4 5% 4 7% 8% 51%	101381
	Night	2 5% 2 5% 3 3 4 4 6% 8% 58%	97670
Transparency	Day	14% 50% 7% 13% 11% 5%	101127
	Night	12% 51% 9% 15% 10% 4	97514
Seeing	Day	10% 21% 32% 23% 11% 2	15636
	Night	6% 20% 36% 27% 11% 1	25637

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 9% 5% 4 4 4 6% 8% 54%	2538
	11th to 20th	Day	4 2 7% 5% 6% 7% 6% 8% 12% 43%	2613
	21st to end	Day	4 2 6% 4 4 4 4 6% 8% 57%	3146
February	1st to 10th	Day	4 4 8% 7% 5% 4 4 8% 10% 47%	1710
	11th to 20th	Day	3 3 6% 5% 5% 5% 4 7% 9% 52%	1745
	21st to end	Day	1 5% 2 7% 4 4 6% 5% 8% 9% 49%	1570
March	1st to 10th	Day	1 4 3 8% 4 4 5% 5% 8% 10% 49%	3180
	11th to 20th	Day	1 10% 3 4 4 3 5% 4 6% 9% 51%	3490
	21st to end	Day	2 7% 2 7% 5% 5% 6% 5% 8% 11% 42%	4000
April	1st to 10th	Day	3 8% 3 5% 4 5% 5% 5% 7% 8% 47%	2280
	11th to 20th	Day	6% 10% 2 7% 5% 6% 6% 4 7% 9% 39%	2251
	21st to end	Day	5% 10% 3 7% 6% 6% 5% 5% 6% 8% 41%	2280
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	4 5% 2 4 3 4 4 4 6% 6% 57%	1900
	11th to 20th	Day	2 5% 1 4 3 3 3 3 6% 8% 61%	1900
	21st to end	Day	3 6% 3 4 3 3 4 3 6% 7% 58%	1977
November	1st to 10th	Day	1 4 1 3 3 3 4 3 6% 7% 64%	1673
	11th to 20th	Day	2 5% 2 4 3 4 3 3 5% 8% 60%	1682
	21st to end	Day	1 4 2 6% 5% 4 4 4 5% 8% 57%	1520
December	1st to 10th	Day	4 3 7% 5% 4 4 3 5% 9% 54%	1520
	11th to 20th	Day	1 3 1 6% 3 4 4 3 7% 11% 57%	1926
	21st to end	Day	1 8% 3 7% 5% 4 5% 4 5% 8% 51%	2794
January	1st to 10th	Night	4 3 9% 4 4 4 4 6% 9% 53%	4417
	11th to 20th	Night	2 1 3 3 3 4 6% 9% 11% 57%	4387
	21st to end	Night	1 4 2 6% 3 3 4 3 5% 7% 62%	4521
February	1st to 10th	Night	4 2 6% 4 4 4 4 8% 9% 56%	2470
	11th to 20th	Night	1 3 2 4 4 4 4 4 6% 9% 59%	2321
	21st to end	Night	1 4 2 7% 4 3 4 3 6% 9% 57%	1884
March	1st to 10th	Night	4 3 7% 3 4 4 3 5% 8% 57%	3682
	11th to 20th	Night	2 11% 3 5% 3 2 2 2 4 7% 58%	3490
	21st to end	Night	2 7% 2 5% 3 4 4 3 6% 10% 52%	3647
April	1st to 10th	Night	2 7% 2 5% 4 3 4 4 6% 8% 57%	1900
	11th to 20th	Night	6% 7% 2 6% 3 4 4 4 6% 8% 50%	1877
	21st to end	Night	5% 9% 3 6% 3 3 3 3 6% 6% 52%	1900
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	4 4 1 4 3 2 3 3 5% 6% 63%	2280
	11th to 20th	Night	3 4 1 3 2 3 3 2 4 7% 67%	2280
	21st to end	Night	4 7% 2 4 2 3 3 3 4 7% 61%	2464
November	1st to 10th	Night	2 3 1 3 2 2 3 3 6% 8% 66%	2405
	11th to 20th	Night	1 4 2 4 3 3 3 3 6% 8% 63%	2494
	21st to end	Night	1 6% 2 5% 3 2 4 3 6% 9% 59%	2660
December	1st to 10th	Night	1 4 2 4 3 3 4 4 6% 8% 62%	2660
	11th to 20th	Night	1 4 2 4 4 3 3 4 7% 11% 58%	3271
	21st to end	Night	1 8% 3 7% 4 4 5% 3 5% 8% 51%	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	18% 44% 10% 11% 15% 1	2539
	11th to 20th	Day	21% 48% 15% 8% 7% 1	2613
	21st to end	Day	10% 45% 16% 18% 10% 1	3146
February	1st to 10th	Day	8% 68% 9% 7% 6% 1	1710
	11th to 20th	Day	7% 66% 6% 14% 5% 2	1754
	21st to end	Day	8% 67% 5% 11% 8%	1570
March	1st to 10th	Day	15% 44% 9% 21% 9% 2	3180
	11th to 20th	Day	16% 46% 12% 21% 4 1	3490
	21st to end	Day	18% 45% 13% 21% 2 1	4000
April	1st to 10th	Day	10% 67% 7% 10% 5% 1	2280
	11th to 20th	Day	14% 67% 3 9% 6% 1	2254
	21st to end	Day	16% 66% 4 10% 4	2280
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	9% 61% 5% 10% 11% 6%	1900
	11th to 20th	Day	7% 60% 4 12% 13% 4	1900
	21st to end	Day	10% 61% 6% 13% 8% 2	1977
November	1st to 10th	Day	7% 61% 6% 15% 9% 2	1673
	11th to 20th	Day	7% 61% 6% 14% 10% 2	1682
	21st to end	Day	11% 62% 5% 11% 9% 1	1520
December	1st to 10th	Day	12% 62% 10% 9% 7% 1	1520
	11th to 20th	Day	7% 50% 9% 23% 10% 1	1924
	21st to end	Day	20% 39% 6% 15% 13% 6%	2794
January	1st to 10th	Night	19% 41% 12% 18% 8% 2	4417
	11th to 20th	Night	15% 47% 16% 11% 7% 4	4387
	21st to end	Night	13% 44% 18% 17% 6% 2	4521
February	1st to 10th	Night	8% 68% 10% 8% 5% 1	2470
	11th to 20th	Night	6% 67% 8% 12% 6% 2	2322
	21st to end	Night	7% 65% 6% 12% 8% 2	1884
March	1st to 10th	Night	15% 43% 7% 21% 12% 2	3682
	11th to 20th	Night	18% 42% 9% 23% 7% 1	3490
	21st to end	Night	16% 45% 13% 22% 4	3647
April	1st to 10th	Night	9% 66% 7% 10% 7% 1	1900
	11th to 20th	Night	11% 66% 5% 11% 6%	1877
	21st to end	Night	13% 65% 5% 12% 5%	1900
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	8% 60% 4 10% 11% 5%	2280
	11th to 20th	Night	6% 59% 4 12% 14% 5%	2280
	21st to end	Night	11% 61% 7% 12% 7% 2	2464
November	1st to 10th	Night	7% 60% 7% 13% 11% 2	2405
	11th to 20th	Night	7% 61% 5% 15% 9% 2	2494
	21st to end	Night	12% 62% 5% 13% 7% 2	2660
December	1st to 10th	Night	8% 62% 10% 12% 7% 1	2660
	11th to 20th	Night	8% 51% 10% 20% 10%	3272
	21st to end	Night	20% 40% 7% 15% 14% 4	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	10% 32% 34% 15% 7% 1	270
	11th to 20th	Day	10% 41% 31% 14% 3	270
	21st to end	Day	3 37% 43% 12% 3 1	297
February	1st to 10th	Day	16% 47% 30% 6% 1	270
	11th to 20th	Day	15% 43% 31% 10% 1	270
	21st to end	Day	16% 42% 34% 8%	225
March	1st to 10th	Day	10% 40% 34% 14% 2 1	294
	11th to 20th	Day	11% 29% 36% 19% 4	460
	21st to end	Day	13% 37% 33% 14% 3	506
April	1st to 10th	Day	14% 34% 37% 13% 3	460
	11th to 20th	Day	16% 35% 33% 13% 4	452
	21st to end	Day	16% 25% 33% 20% 5% 1	460
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% 16% 4 1	311
November	1st to 10th	Day	7% 40% 34% 13% 5% 1	270
	11th to 20th	Day	12% 33% 42% 12% 2	270
	21st to end	Day	7% 35% 40% 13% 4	270
December	1st to 10th	Day	14% 39% 32% 10% 4 1	270
	11th to 20th	Day	12% 41% 35% 11% 1	270
	21st to end	Day	14% 42% 27% 12% 4 1	297
January	1st to 10th	Night	6% 32% 40% 15% 6% 1	950
	11th to 20th	Night	5% 39% 39% 13% 5%	920
	21st to end	Night	3 29% 48% 15% 4	836
February	1st to 10th	Night	5% 33% 47% 10% 4	760
	11th to 20th	Night	3 32% 41% 20% 3	744
	21st to end	Night	5% 37% 41% 14% 2	628
March	1st to 10th	Night	2 30% 44% 19% 5%	760
	11th to 20th	Night	7% 17% 41% 30% 5% 1	760
	21st to end	Night	6% 20% 48% 21% 5% 1	732
April	1st to 10th	Night	8% 19% 45% 25% 2	570
	11th to 20th	Night	12% 18% 40% 24% 5%	563
	21st to end	Night	10% 15% 35% 28% 11% 1	570
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	9% 19% 44% 21% 5% 2	840
November	1st to 10th	Night	4 25% 46% 20% 5% 1	925
	11th to 20th	Night	7% 32% 43% 16% 2	950
	21st to end	Night	4 25% 49% 18% 3	950
December	1st to 10th	Night	7% 36% 39% 14% 2	950
	11th to 20th	Night	6% 33% 44% 15% 3	950
	21st to end	Night	7% 38% 37% 14% 4	1045

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