Cushing Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cushing Observatory clear sky chart from 2005-11-06 to 2025-03-12.

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	13% 9% 3 8% 5% 5% 4 4 5% 7% 36%	109096
	Night	12% 10% 4 9% 5% 4 4 4 5% 6% 37%	110060
Transparency	Day	46% 6% 13% 24% 10% 1	112678
	Night	47% 6% 12% 23% 12% 1	114618
Seeing	Day	17% 10% 30% 26% 13% 4	16440
	Night	16% 9% 32% 32% 11% 1	26535

By Month

Percentage Cloud Cover SE (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	9% 13% 5% 18% 7% 5% 4 3 4 5% 27%	3617
	11th to 20th	Day	6% 11% 7% 13% 8% 8% 8% 7% 8% 5% 20%	3620
	21st to end	Day	6% 18% 8% 12% 5% 4 5% 3 5% 6% 30%	4395
February	1st to 10th	Day	8% 13% 4 10% 6% 5% 5% 5% 6% 6% 32%	1800
	11th to 20th	Day	7% 12% 5% 10% 5% 6% 4 4 5% 6% 36%	1754
	21st to end	Day	10% 12% 4 11% 6% 5% 4 4 5% 8% 33%	1560
March	1st to 10th	Day	11% 11% 4 8% 5% 5% 4 3 5% 7% 39%	3409
	11th to 20th	Day	9% 10% 3 8% 5% 5% 4 3 5% 8% 40%	3491
	21st to end	Day	20% 13% 4 11% 5% 5% 4 3 5% 5% 25%	3899
April	1st to 10th	Day	17% 12% 3 7% 5% 5% 4 3 5% 6% 34%	2280
	11th to 20th	Day	20% 13% 3 7% 5% 4 4 2 4 6% 31%	2254
	21st to end	Day	21% 11% 3 7% 5% 5% 4 3 4 5% 31%	2465
May	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 5% 6% 40%	4333
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 5% 7% 43%	4399
	21st to end	Day	19% 7% 2 8% 5% 4 5% 4 6% 7% 34%	4824
June	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 6% 7% 45%	2660
	11th to 20th	Day	13% 7% 3 6% 5% 5% 5% 4 6% 9% 37%	2660
	21st to end	Day	12% 5% 2 5% 5% 4 6% 5% 8% 10% 39%	2660
July	1st to 10th	Day	11% 5% 2 6% 4 5% 6% 5% 7% 10% 38%	4440
	11th to 20th	Day	6% 3 1 4 3 3 4 3 5% 9% 58%	4440
	21st to end	Day	8% 4 2 4 4 4 4 4 6% 9% 50%	4813
August	1st to 10th	Day	13% 6% 2 5% 3 5% 5% 4 6% 9% 43%	4150
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 6% 8% 43%	4041
	21st to end	Day	11% 6% 3 7% 5% 4 5% 3 6% 7% 44%	4313
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 3 5% 7% 47%	2280
	11th to 20th	Day	12% 6% 2 5% 4 5% 4 3 5% 7% 46%	2280
	21st to end	Day	16% 6% 2 5% 4 3 5% 3 5% 7% 44%	1982
October	1st to 10th	Day	17% 7% 2 6% 3 4 4 4 6% 8% 41%	1900
	11th to 20th	Day	17% 13% 3 7% 4 5% 4 3 5% 5% 36%	1900
	21st to end	Day	18% 12% 3 8% 5% 3 3 3 4 6% 35%	2024
November	1st to 10th	Day	11% 15% 4 8% 5% 4 3 3 5% 6% 34%	1653
	11th to 20th	Day	13% 15% 7% 11% 6% 5% 5% 3 4 5% 26%	1600
	21st to end	Day	14% 13% 4 8% 5% 5% 5% 4 5% 6% 32%	1600
December	1st to 10th	Day	8% 14% 5% 16% 13% 6% 5% 3 4 5% 21%	2610
	11th to 20th	Day	12% 16% 8% 10% 6% 4 5% 3 4 5% 27%	3008
	21st to end	Day	18% 21% 7% 19% 6% 4 3 2 3 3 13%	3982
January	1st to 10th	Night	9% 10% 6% 15% 9% 5% 4 3 5% 5% 30%	6348
	11th to 20th	Night	7% 11% 5% 12% 8% 6% 9% 8% 8% 6% 20%	6360
	21st to end	Night	8% 19% 7% 11% 6% 4 4 3 5% 5% 30%	6582
February	1st to 10th	Night	7% 11% 6% 10% 7% 6% 5% 3 5% 6% 35%	2600
	11th to 20th	Night	6% 11% 4 10% 6% 6% 5% 4 5% 6% 38%	2533
	21st to end	Night	12% 13% 3 8% 5% 5% 5% 3 5% 5% 35%	2070
March	1st to 10th	Night	9% 9% 2 7% 5% 4 4 3 5% 7% 46%	3693
	11th to 20th	Night	9% 9% 3 10% 6% 4 5% 3 5% 6% 40%	3497
	21st to end	Night	25% 12% 4 11% 4 3 3 2 3 4 30%	3732
April	1st to 10th	Night	17% 11% 4 7% 5% 4 4 3 4 6% 35%	1900
	11th to 20th	Night	21% 11% 3 6% 4 3 3 3 4 5% 36%	1875
	21st to end	Night	18% 11% 3 6% 5% 4 5% 4 5% 6% 34%	1711
May	1st to 10th	Night	15% 8% 3 7% 5% 4 4 4 5% 5% 40%	2570
	11th to 20th	Night	15% 5% 2 5% 2 3 3 3 5% 7% 51%	2506
	21st to end	Night	14% 7% 2 7% 5% 5% 4 4 6% 7% 39%	2743
June	1st to 10th	Night	12% 6% 2 5% 5% 3 5% 4 6% 8% 46%	1520
	11th to 20th	Night	10% 5% 2 5% 5% 5% 4 4 6% 7% 47%	1520
	21st to end	Night	8% 5% 1 5% 4 5% 4 5% 7% 8% 47%	1432
July	1st to 10th	Night	12% 4 2 4 4 3 4 4 6% 9% 47%	2530
	11th to 20th	Night	4 2 1 4 3 3 4 4 7% 9% 58%	2530
	21st to end	Night	6% 3 1 4 3 3 4 4 5% 8% 59%	2750
August	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 6% 49%	2787
	11th to 20th	Night	14% 5% 2 5% 3 3 5% 4 5% 7% 46%	2798
	21st to end	Night	12% 7% 2 7% 4 4 4 3 5% 6% 45%	3347
September	1st to 10th	Night	9% 4 1 5% 4 4 4 4 5% 7% 53%	1900
	11th to 20th	Night	9% 4 1 6% 2 4 4 3 6% 7% 54%	1900
	21st to end	Night	14% 5% 1 5% 3 4 4 3 4 6% 50%	2174
October	1st to 10th	Night	14% 7% 2 5% 4 3 4 2 5% 6% 49%	2280
	11th to 20th	Night	17% 10% 2 6% 4 4 4 3 4 6% 41%	2280
	21st to end	Night	18% 11% 3 7% 4 4 4 3 5% 5% 35%	2572
November	1st to 10th	Night	15% 11% 3 7% 4 4 4 4 6% 6% 38%	2645
	11th to 20th	Night	14% 13% 5% 12% 6% 4 3 3 4 5% 32%	2800
	21st to end	Night	13% 11% 4 10% 6% 4 3 4 5% 6% 34%	2800
December	1st to 10th	Night	6% 12% 5% 14% 9% 8% 5% 4 4 6% 26%	4580
	11th to 20th	Night	11% 17% 6% 14% 6% 4 5% 6% 5% 4 21%	5199
	21st to end	Night	21% 17% 7% 16% 5% 4 3 3 3 3 18%	6996

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	59% 5% 8% 18% 9%	3618
	11th to 20th	Day	61% 5% 8% 17% 9%	3620
	21st to end	Day	56% 6% 14% 17% 7%	4395
February	1st to 10th	Day	50% 6% 13% 21% 9% 1	1800
	11th to 20th	Day	48% 5% 12% 25% 9% 1	1763
	21st to end	Day	50% 5% 13% 20% 10% 1	1560
March	1st to 10th	Day	45% 6% 14% 22% 11% 1	3409
	11th to 20th	Day	43% 5% 14% 29% 10% 1	3491
	21st to end	Day	60% 6% 9% 19% 5%	3899
April	1st to 10th	Day	51% 5% 11% 19% 13% 1	2280
	11th to 20th	Day	55% 4 10% 18% 12% 2	2254
	21st to end	Day	55% 5% 11% 20% 8%	2465
May	1st to 10th	Day	43% 6% 12% 24% 13% 1	4373
	11th to 20th	Day	39% 7% 13% 26% 12% 2	4403
	21st to end	Day	47% 8% 11% 23% 10% 1	4837
June	1st to 10th	Day	35% 7% 15% 30% 12% 1	2660
	11th to 20th	Day	42% 8% 14% 23% 13% 1	2660
	21st to end	Day	36% 9% 17% 28% 9% 1	2660
July	1st to 10th	Day	38% 8% 18% 23% 12%	4371
	11th to 20th	Day	23% 6% 17% 37% 16% 1	4365
	21st to end	Day	29% 7% 16% 30% 18%	4662
August	1st to 10th	Day	37% 7% 14% 29% 12% 1	4135
	11th to 20th	Day	37% 7% 14% 34% 8%	4080
	21st to end	Day	40% 6% 16% 25% 12% 1	4312
September	1st to 10th	Day	35% 7% 13% 34% 11%	2280
	11th to 20th	Day	36% 8% 17% 31% 8%	2280
	21st to end	Day	40% 6% 13% 32% 9% 1	1982
October	1st to 10th	Day	31% 5% 11% 35% 18%	3160
	11th to 20th	Day	42% 4 10% 27% 16% 2	3140
	21st to end	Day	47% 4 16% 25% 8%	3314
November	1st to 10th	Day	50% 6% 12% 19% 12% 1	1653
	11th to 20th	Day	61% 5% 12% 14% 7% 1	1600
	21st to end	Day	52% 7% 16% 19% 5% 2	1600
December	1st to 10th	Day	67% 5% 10% 13% 4	2610
	11th to 20th	Day	58% 5% 10% 19% 7%	3005
	21st to end	Day	77% 5% 6% 7% 5%	3982
January	1st to 10th	Night	56% 5% 10% 18% 11%	6348
	11th to 20th	Night	60% 6% 11% 13% 10%	6360
	21st to end	Night	56% 6% 12% 20% 6%	6582
February	1st to 10th	Night	49% 6% 13% 21% 10% 1	2600
	11th to 20th	Night	47% 6% 14% 23% 9% 1	2534
	21st to end	Night	50% 6% 13% 20% 10% 1	2070
March	1st to 10th	Night	39% 6% 13% 24% 17% 2	3693
	11th to 20th	Night	44% 6% 11% 24% 14% 1	3497
	21st to end	Night	60% 4 8% 18% 10%	3732
April	1st to 10th	Night	50% 6% 7% 20% 16% 2	1900
	11th to 20th	Night	51% 5% 8% 20% 14% 2	1875
	21st to end	Night	49% 7% 10% 20% 14% 2	1711
May	1st to 10th	Night	44% 7% 12% 19% 17% 1	2595
	11th to 20th	Night	33% 6% 10% 29% 20% 3	2507
	21st to end	Night	41% 8% 14% 22% 14% 1	2751
June	1st to 10th	Night	35% 7% 15% 28% 13% 2	1520
	11th to 20th	Night	35% 7% 15% 23% 19% 2	1520
	21st to end	Night	31% 9% 15% 29% 13% 3	1432
July	1st to 10th	Night	32% 8% 20% 25% 13% 1	2490
	11th to 20th	Night	21% 7% 12% 39% 18% 2	2482
	21st to end	Night	24% 7% 14% 33% 20% 2	2662
August	1st to 10th	Night	34% 6% 13% 29% 15% 3	2778
	11th to 20th	Night	36% 6% 13% 32% 11% 1	2825
	21st to end	Night	39% 7% 15% 27% 10% 2	3347
September	1st to 10th	Night	29% 7% 14% 34% 14% 1	1900
	11th to 20th	Night	29% 7% 17% 33% 14%	1900
	21st to end	Night	36% 6% 12% 32% 12% 1	2174
October	1st to 10th	Night	25% 4 7% 37% 24% 4	3800
	11th to 20th	Night	38% 5% 12% 23% 21% 1	3779
	21st to end	Night	48% 4 12% 24% 11%	4232
November	1st to 10th	Night	46% 6% 13% 23% 11% 1	2645
	11th to 20th	Night	55% 5% 12% 17% 10% 1	2800
	21st to end	Night	50% 6% 15% 22% 6% 1	2800
December	1st to 10th	Night	58% 7% 15% 16% 3	4580
	11th to 20th	Night	63% 5% 9% 16% 6%	5201
	21st to end	Night	71% 4 8% 12% 4	6996

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	14% 11% 38% 23% 11% 4	300
	11th to 20th	Day	14% 12% 39% 28% 7%	300
	21st to end	Day	15% 11% 39% 23% 11% 2	330
February	1st to 10th	Day	16% 16% 42% 20% 6%	300
	11th to 20th	Day	14% 16% 41% 20% 7% 1	300
	21st to end	Day	16% 17% 42% 23% 2	249
March	1st to 10th	Day	16% 16% 42% 18% 6% 2	300
	11th to 20th	Day	19% 10% 38% 26% 5% 2	273
	21st to end	Day	24% 13% 29% 21% 10% 2	344
April	1st to 10th	Day	24% 14% 34% 22% 5% 1	460
	11th to 20th	Day	26% 12% 27% 25% 10% 1	452
	21st to end	Day	27% 12% 30% 19% 10% 2	645
May	1st to 10th	Day	19% 15% 31% 24% 10% 2	653
	11th to 20th	Day	18% 12% 27% 27% 13% 3	675
	21st to end	Day	18% 10% 27% 26% 14% 4	734
June	1st to 10th	Day	12% 6% 27% 32% 18% 4	680
	11th to 20th	Day	14% 9% 34% 30% 11% 2	680
	21st to end	Day	15% 7% 29% 29% 15% 6%	680
July	1st to 10th	Day	10% 6% 19% 30% 25% 11%	671
	11th to 20th	Day	9% 6% 26% 28% 22% 9%	668
	21st to end	Day	6% 3 26% 36% 19% 9%	739
August	1st to 10th	Day	11% 4 24% 31% 23% 6%	676
	11th to 20th	Day	14% 5% 20% 30% 23% 8%	665
	21st to end	Day	12% 7% 24% 31% 21% 5%	620
September	1st to 10th	Day	13% 6% 28% 32% 15% 5%	490
	11th to 20th	Day	12% 6% 28% 31% 19% 3	490
	21st to end	Day	20% 11% 28% 23% 13% 5%	306
October	1st to 10th	Day	18% 12% 31% 19% 14% 6%	300
	11th to 20th	Day	19% 20% 31% 24% 6% 1	300
	21st to end	Day	24% 18% 35% 15% 7% 1	330
November	1st to 10th	Day	21% 16% 34% 21% 7% 2	300
	11th to 20th	Day	23% 15% 38% 17% 7%	300
	21st to end	Day	23% 13% 39% 20% 5%	300
December	1st to 10th	Day	18% 11% 41% 20% 9%	300
	11th to 20th	Day	23% 16% 35% 22% 4	300
	21st to end	Day	31% 10% 36% 19% 3 1	330
January	1st to 10th	Night	14% 10% 36% 31% 9% 1	1000
	11th to 20th	Night	16% 8% 39% 28% 8% 1	1000
	21st to end	Night	17% 9% 37% 29% 6% 1	1100
February	1st to 10th	Night	12% 11% 41% 27% 8% 1	1000
	11th to 20th	Night	10% 12% 42% 27% 8% 1	979
	21st to end	Night	17% 11% 35% 27% 9% 1	750
March	1st to 10th	Night	16% 13% 37% 26% 7% 1	705
	11th to 20th	Night	17% 9% 40% 27% 6%	575
	21st to end	Night	22% 11% 29% 26% 9% 2	627
April	1st to 10th	Night	21% 12% 35% 25% 6%	570
	11th to 20th	Night	26% 10% 29% 27% 7% 1	563
	21st to end	Night	23% 8% 29% 31% 8% 1	570
May	1st to 10th	Night	19% 11% 31% 32% 6% 1	570
	11th to 20th	Night	17% 6% 32% 32% 11% 2	561
	21st to end	Night	13% 9% 27% 37% 13% 1	617
June	1st to 10th	Night	14% 5% 28% 40% 11% 1	570
	11th to 20th	Night	10% 6% 32% 43% 9%	570
	21st to end	Night	10% 5% 23% 43% 17% 2	570
July	1st to 10th	Night	5% 3 22% 42% 26% 2	555
	11th to 20th	Night	7% 3 25% 42% 22% 1	552
	21st to end	Night	6% 2 21% 46% 22% 3	624
August	1st to 10th	Night	9% 3 14% 53% 20% 2	567
	11th to 20th	Night	13% 3 19% 37% 24% 3	564
	21st to end	Night	13% 3 23% 37% 22% 2	627
September	1st to 10th	Night	10% 5% 23% 43% 16% 3	570
	11th to 20th	Night	10% 5% 29% 37% 17% 2	570
	21st to end	Night	15% 8% 33% 29% 14% 1	664
October	1st to 10th	Night	19% 8% 28% 31% 13% 1	760
	11th to 20th	Night	20% 12% 32% 29% 6% 1	760
	21st to end	Night	24% 10% 30% 28% 8%	836
November	1st to 10th	Night	20% 11% 32% 30% 7% 1	889
	11th to 20th	Night	21% 11% 34% 27% 7% 1	1000
	21st to end	Night	18% 14% 37% 24% 7%	1000
December	1st to 10th	Night	16% 12% 32% 31% 8% 1	1000
	11th to 20th	Night	20% 10% 37% 25% 8% 1	1000
	21st to end	Night	25% 10% 34% 25% 6% 1	1100

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