Table Rock
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Table Rock clear sky chart from 2005-11-06 to 2025-10-04.

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	4 7% 3 7% 5% 5% 5% 4 5% 7% 48%	135339
	Night	3 7% 3 7% 5% 5% 5% 4 6% 7% 48%	131368
Transparency	Day	35% 3 8% 22% 20% 11%	130103
	Night	35% 4 10% 23% 20% 8%	127602
Seeing	Day	10% 17% 30% 26% 13% 4	15659
	Night	8% 12% 23% 34% 20% 3	24785

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 11% 6% 16% 8% 8% 6% 5% 7% 6% 24%	3639
	11th to 20th	Day	3 9% 5% 12% 5% 5% 5% 5% 5% 7% 40%	3640
	21st to end	Day	4 12% 4 10% 5% 6% 5% 4 5% 6% 41%	4004
February	1st to 10th	Day	4 11% 5% 12% 7% 6% 6% 4 7% 7% 31%	1756
	11th to 20th	Day	3 13% 6% 12% 7% 6% 6% 5% 7% 7% 29%	1910
	21st to end	Day	1 11% 4 13% 9% 7% 7% 6% 8% 7% 28%	1650
March	1st to 10th	Day	2 10% 5% 12% 7% 7% 5% 4 6% 8% 34%	4518
	11th to 20th	Day	1 12% 4 10% 6% 6% 6% 4 6% 7% 39%	4679
	21st to end	Day	2 13% 5% 13% 8% 7% 7% 6% 7% 7% 25%	5969
April	1st to 10th	Day	6% 11% 4 11% 7% 8% 6% 4 6% 6% 30%	2400
	11th to 20th	Day	5% 11% 4 9% 7% 6% 5% 4 5% 6% 37%	2369
	21st to end	Day	5% 11% 4 9% 5% 5% 5% 3 6% 7% 40%	2556
May	1st to 10th	Day	6% 8% 4 6% 5% 4 4 4 5% 6% 50%	6042
	11th to 20th	Day	7% 7% 2 6% 5% 5% 5% 4 5% 7% 48%	6277
	21st to end	Day	5% 7% 2 6% 4 4 5% 4 6% 7% 49%	6902
June	1st to 10th	Day	9% 7% 3 9% 6% 6% 5% 4 6% 8% 37%	2800
	11th to 20th	Day	7% 7% 2 7% 6% 5% 4 4 6% 7% 46%	2800
	21st to end	Day	4 3 1 4 4 4 4 4 5% 6% 60%	2800
July	1st to 10th	Day	2 2 1 3 2 3 3 3 4 5% 73%	6319
	11th to 20th	Day	1 2 1 2 2 2 3 2 3 4 79%	6320
	21st to end	Day	2 2 1 3 3 4 5% 4 6% 7% 63%	6880
August	1st to 10th	Day	4 3 2 5% 4 4 5% 4 6% 8% 55%	6210
	11th to 20th	Day	2 2 1 4 3 3 3 2 4 4 71%	5612
	21st to end	Day	4 4 2 5% 3 3 4 3 4 5% 63%	5984
September	1st to 10th	Day	2 2 1 4 4 2 4 3 5% 6% 67%	2400
	11th to 20th	Day	5% 4 2 5% 4 4 4 3 5% 7% 56%	2310
	21st to end	Day	3 6% 2 7% 4 3 3 3 4 6% 58%	2200
October	1st to 10th	Day	4 5% 2 5% 3 3 3 2 3 5% 65%	3369
	11th to 20th	Day	4 6% 2 6% 4 4 4 4 6% 8% 50%	3112
	21st to end	Day	6% 8% 3 8% 5% 5% 6% 5% 7% 7% 40%	3101
November	1st to 10th	Day	7% 11% 3 10% 6% 5% 7% 4 5% 8% 34%	1764
	11th to 20th	Day	4 9% 4 10% 9% 7% 6% 6% 8% 8% 30%	1795
	21st to end	Day	3 8% 3 9% 5% 6% 6% 6% 7% 9% 38%	1600
December	1st to 10th	Day	2 7% 3 7% 5% 5% 4 4 5% 7% 51%	2620
	11th to 20th	Day	4 12% 4 12% 8% 8% 7% 5% 8% 8% 24%	3028
	21st to end	Day	4 9% 4 11% 9% 7% 7% 6% 7% 9% 26%	4004
January	1st to 10th	Night	4 11% 6% 16% 8% 8% 7% 5% 7% 7% 22%	6306
	11th to 20th	Night	4 10% 5% 9% 4 4 4 5% 5% 7% 42%	6320
	21st to end	Night	3 10% 4 10% 6% 5% 5% 4 5% 6% 42%	6952
February	1st to 10th	Night	2 9% 3 11% 8% 7% 6% 5% 7% 8% 33%	2640
	11th to 20th	Night	3 9% 4 9% 7% 6% 7% 5% 7% 9% 33%	2378
	21st to end	Night	3 8% 3 9% 7% 8% 8% 5% 8% 8% 33%	1980
March	1st to 10th	Night	2 7% 4 8% 6% 5% 5% 4 8% 11% 40%	5376
	11th to 20th	Night	2 7% 4 9% 6% 6% 7% 5% 7% 8% 40%	5317
	21st to end	Night	2 9% 4 10% 8% 7% 8% 6% 8% 9% 30%	5006
April	1st to 10th	Night	4 7% 3 8% 6% 5% 7% 5% 8% 9% 37%	2000
	11th to 20th	Night	3 10% 4 8% 5% 4 4 4 6% 7% 45%	1979
	21st to end	Night	5% 8% 3 6% 6% 5% 5% 5% 8% 9% 41%	1842
May	1st to 10th	Night	5% 8% 3 7% 4 4 4 3 5% 6% 52%	3926
	11th to 20th	Night	3 6% 3 5% 4 4 4 4 5% 5% 56%	3616
	21st to end	Night	5% 7% 3 5% 4 4 4 3 4 6% 57%	3972
June	1st to 10th	Night	6% 8% 2 7% 5% 4 5% 5% 7% 9% 44%	1600
	11th to 20th	Night	5% 5% 2 5% 4 5% 5% 4 5% 7% 54%	1600
	21st to end	Night	2 3 1 4 4 3 3 3 4 7% 66%	1600
July	1st to 10th	Night	2 2 1 3 2 2 3 2 3 5% 76%	3640
	11th to 20th	Night	2 1 2 2 2 3 4 83%	3640
	21st to end	Night	3 2 1 4 3 3 4 3 5% 5% 66%	3970
August	1st to 10th	Night	2 2 1 4 3 4 4 4 7% 8% 61%	3582
	11th to 20th	Night	1 1 1 3 2 2 3 3 3 5% 75%	4244
	21st to end	Night	3 4 2 4 3 3 3 3 4 5% 66%	5015
September	1st to 10th	Night	2 3 1 2 2 3 3 3 3 5% 73%	2000
	11th to 20th	Night	3 2 2 4 3 4 4 4 5% 7% 61%	2089
	21st to end	Night	4 4 2 5% 3 2 3 3 6% 6% 62%	2200
October	1st to 10th	Night	3 3 1 3 3 4 3 2 3 5% 69%	3673
	11th to 20th	Night	3 5% 2 6% 3 4 4 4 6% 8% 55%	3824
	21st to end	Night	3 6% 4 8% 5% 5% 6% 5% 6% 8% 45%	4457
November	1st to 10th	Night	4 9% 3 8% 7% 6% 5% 4 7% 7% 39%	2535
	11th to 20th	Night	3 9% 3 9% 7% 6% 6% 6% 8% 8% 34%	2601
	21st to end	Night	3 8% 3 9% 6% 6% 5% 5% 7% 8% 40%	2800
December	1st to 10th	Night	3 6% 3 6% 4 4 4 4 5% 8% 54%	4560
	11th to 20th	Night	4 12% 5% 13% 8% 7% 7% 5% 7% 8% 22%	5176
	21st to end	Night	4 11% 4 12% 8% 7% 8% 6% 7% 8% 25%	6952

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	58% 5% 8% 18% 11% 1	3639
	11th to 20th	Day	43% 3 12% 28% 12% 2	3640
	21st to end	Day	46% 3 9% 14% 18% 10%	4004
February	1st to 10th	Day	50% 4 16% 19% 9% 1	1756
	11th to 20th	Day	51% 5% 11% 19% 11% 3	1920
	21st to end	Day	52% 6% 12% 17% 11% 2	1650
March	1st to 10th	Day	49% 3 7% 21% 15% 5%	4518
	11th to 20th	Day	43% 3 10% 29% 14%	4679
	21st to end	Day	53% 5% 11% 23% 8%	5969
April	1st to 10th	Day	51% 4 11% 23% 9% 2	2400
	11th to 20th	Day	45% 3 11% 23% 15% 3	2372
	21st to end	Day	42% 5% 10% 26% 17% 1	2556
May	1st to 10th	Day	37% 2 6% 28% 26% 3	6042
	11th to 20th	Day	34% 3 8% 26% 23% 6%	6280
	21st to end	Day	32% 3 8% 36% 17% 3	6904
June	1st to 10th	Day	43% 4 9% 29% 14% 1	2800
	11th to 20th	Day	36% 2 8% 26% 23% 5%	2800
	21st to end	Day	23% 2 7% 26% 31% 11%	2800
July	1st to 10th	Day	14% 3 3 14% 25% 41%	6251
	11th to 20th	Day	12% 2 3 9% 21% 54%	6245
	21st to end	Day	17% 5% 5% 18% 29% 25%	6681
August	1st to 10th	Day	25% 3 4 15% 28% 25%	4524
	11th to 20th	Day	16% 3 5% 15% 40% 20%	4059
	21st to end	Day	18% 2 4 26% 26% 24%	4311
September	1st to 10th	Day	18% 2 4 23% 31% 22%	2400
	11th to 20th	Day	28% 4 6% 22% 27% 14%	2310
	21st to end	Day	29% 2 7% 26% 25% 11%	2200
October	1st to 10th	Day	24% 3 6% 19% 38% 10%	3369
	11th to 20th	Day	32% 3 12% 29% 21% 3	3112
	21st to end	Day	40% 5% 10% 23% 21% 1	3101
November	1st to 10th	Day	47% 4 11% 24% 12% 1	1764
	11th to 20th	Day	48% 6% 16% 21% 8% 1	1795
	21st to end	Day	41% 6% 12% 24% 13% 4	1600
December	1st to 10th	Day	34% 5% 9% 30% 22% 1	2620
	11th to 20th	Day	58% 5% 15% 16% 6%	3028
	21st to end	Day	56% 4 13% 18% 9%	4004
January	1st to 10th	Night	56% 4 10% 20% 10% 1	6306
	11th to 20th	Night	40% 3 10% 29% 16% 3	6320
	21st to end	Night	46% 3 9% 15% 15% 11%	6952
February	1st to 10th	Night	45% 7% 16% 21% 10% 1	2640
	11th to 20th	Night	43% 7% 16% 19% 13% 3	2379
	21st to end	Night	45% 6% 14% 18% 13% 3	1980
March	1st to 10th	Night	38% 4 9% 22% 21% 6%	5376
	11th to 20th	Night	39% 4 9% 30% 17%	5317
	21st to end	Night	47% 7% 13% 26% 6% 1	5006
April	1st to 10th	Night	38% 5% 13% 30% 11% 2	2000
	11th to 20th	Night	37% 4 13% 29% 15% 2	1979
	21st to end	Night	35% 6% 14% 27% 17% 1	1842
May	1st to 10th	Night	31% 2 6% 31% 26% 4	3923
	11th to 20th	Night	26% 4 11% 31% 28% 1	3616
	21st to end	Night	28% 2 11% 42% 16%	3972
June	1st to 10th	Night	35% 6% 13% 32% 13% 1	1600
	11th to 20th	Night	28% 3 11% 32% 22% 5%	1600
	21st to end	Night	21% 2 9% 32% 28% 8%	1600
July	1st to 10th	Night	14% 1 3 16% 25% 41%	3600
	11th to 20th	Night	7% 2 3 12% 27% 49%	3592
	21st to end	Night	21% 3 3 19% 32% 22%	3857
August	1st to 10th	Night	19% 3 5% 17% 33% 22%	2601
	11th to 20th	Night	13% 2 4 18% 43% 20%	3069
	21st to end	Night	15% 3 4 26% 30% 23%	3608
September	1st to 10th	Night	15% 3 4 24% 30% 24%	2000
	11th to 20th	Night	22% 2 9% 23% 28% 15%	2089
	21st to end	Night	22% 2 7% 27% 29% 13%	2200
October	1st to 10th	Night	20% 2 7% 20% 39% 12%	3673
	11th to 20th	Night	26% 3 18% 23% 28% 3	3824
	21st to end	Night	33% 4 13% 24% 23% 2	4457
November	1st to 10th	Night	42% 5% 12% 23% 16% 2	2535
	11th to 20th	Night	45% 6% 14% 22% 12%	2601
	21st to end	Night	40% 5% 14% 19% 18% 4	2800
December	1st to 10th	Night	28% 5% 10% 28% 26% 3	4560
	11th to 20th	Night	59% 5% 11% 18% 7% 1	5176
	21st to end	Night	55% 4 11% 18% 11% 1	6952

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	15% 22% 28% 20% 12% 5%	200
	11th to 20th	Day	11% 17% 37% 16% 17% 3	200
	21st to end	Day	10% 13% 37% 26% 10% 3	220
February	1st to 10th	Day	13% 30% 33% 17% 4 2	356
	11th to 20th	Day	13% 30% 33% 17% 6% 1	475
	21st to end	Day	14% 26% 30% 24% 6%	414
March	1st to 10th	Day	14% 25% 34% 20% 7%	500
	11th to 20th	Day	13% 24% 31% 21% 9% 2	500
	21st to end	Day	15% 28% 30% 21% 6% 1	550
April	1st to 10th	Day	17% 24% 26% 19% 10% 3	500
	11th to 20th	Day	15% 25% 29% 18% 9% 3	492
	21st to end	Day	12% 23% 34% 21% 8% 2	500
May	1st to 10th	Day	12% 23% 30% 22% 9% 4	503
	11th to 20th	Day	20% 20% 28% 16% 12% 3	528
	21st to end	Day	15% 13% 23% 29% 16% 4	573
June	1st to 10th	Day	12% 16% 26% 25% 15% 6%	530
	11th to 20th	Day	12% 18% 35% 22% 11% 2	530
	21st to end	Day	4 14% 32% 29% 16% 5%	530
July	1st to 10th	Day	3 10% 38% 32% 14% 3	526
	11th to 20th	Day	2 10% 34% 35% 15% 3	524
	21st to end	Day	2 7% 31% 37% 19% 4	575
August	1st to 10th	Day	6% 7% 28% 36% 16% 6%	527
	11th to 20th	Day	3 8% 26% 32% 22% 9%	517
	21st to end	Day	5% 10% 26% 32% 19% 8%	583
September	1st to 10th	Day	3 9% 28% 34% 18% 8%	530
	11th to 20th	Day	6% 13% 24% 32% 18% 7%	530
	21st to end	Day	7% 13% 31% 26% 18% 5%	530
October	1st to 10th	Day	12% 16% 26% 24% 18% 5%	503
	11th to 20th	Day	8% 17% 31% 23% 16% 5%	466
	21st to end	Day	12% 20% 25% 26% 14% 3	330
November	1st to 10th	Day	15% 20% 25% 27% 12% 2	300
	11th to 20th	Day	11% 17% 29% 29% 11% 3	297
	21st to end	Day	11% 13% 31% 31% 13% 2	200
December	1st to 10th	Day	14% 13% 29% 22% 15% 8%	200
	11th to 20th	Day	15% 22% 37% 18% 8% 1	200
	21st to end	Day	12% 22% 32% 22% 10% 2	220
January	1st to 10th	Night	9% 15% 27% 30% 18% 2	800
	11th to 20th	Night	12% 15% 26% 27% 19% 2	800
	21st to end	Night	8% 11% 24% 35% 19% 3	880
February	1st to 10th	Night	8% 18% 30% 29% 12% 2	800
	11th to 20th	Night	8% 16% 27% 31% 15% 3	784
	21st to end	Night	11% 15% 28% 31% 13% 2	660
March	1st to 10th	Night	6% 15% 27% 34% 16% 2	800
	11th to 20th	Night	9% 14% 26% 32% 17% 2	800
	21st to end	Night	9% 18% 27% 31% 13% 1	880
April	1st to 10th	Night	8% 16% 26% 32% 15% 2	800
	11th to 20th	Night	9% 15% 30% 27% 15% 4	791
	21st to end	Night	7% 17% 28% 33% 14% 2	642
May	1st to 10th	Night	11% 13% 29% 29% 16% 2	530
	11th to 20th	Night	11% 10% 19% 32% 25% 3	394
	21st to end	Night	10% 9% 22% 33% 23% 4	433
June	1st to 10th	Night	9% 9% 22% 35% 23% 2	400
	11th to 20th	Night	5% 15% 26% 35% 17% 2	400
	21st to end	Night	4 5% 19% 46% 25% 2	400
July	1st to 10th	Night	2 4 20% 50% 22% 3	390
	11th to 20th	Night	1 2 23% 53% 21%	388
	21st to end	Night	2 2 18% 48% 29% 2	438
August	1st to 10th	Night	4 3 15% 47% 29% 3	398
	11th to 20th	Night	1 2 18% 41% 31% 6%	669
	21st to end	Night	3 5% 18% 40% 30% 4	880
September	1st to 10th	Night	4 3 15% 40% 34% 4	800
	11th to 20th	Night	3 5% 15% 37% 31% 9%	800
	21st to end	Night	6% 9% 18% 30% 30% 7%	800
October	1st to 10th	Night	8% 8% 21% 33% 26% 5%	772
	11th to 20th	Night	8% 11% 17% 35% 21% 7%	760
	21st to end	Night	7% 11% 22% 36% 17% 6%	836
November	1st to 10th	Night	9% 12% 22% 37% 18% 2	780
	11th to 20th	Night	12% 13% 22% 34% 16% 3	800
	21st to end	Night	8% 15% 23% 32% 17% 6%	800
December	1st to 10th	Night	10% 12% 23% 33% 18% 4	800
	11th to 20th	Night	11% 15% 24% 34% 14% 3	800
	21st to end	Night	13% 18% 28% 29% 11% 1	880

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