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 2024-11-05.

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 8% 3 8% 5% 5% 5% 4 5% 6% 47%	105228
	Night	3 7% 3 8% 5% 5% 5% 4 6% 7% 46%	102493
Transparency	Day	36% 3 8% 21% 20% 12%	104972
	Night	36% 4 10% 23% 19% 8%	102338
Seeing	Day	10% 17% 30% 26% 13% 4	14501
	Night	7% 11% 23% 35% 20% 3	23669

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% 18% 8% 8% 7% 5% 7% 6% 20%	2539
	11th to 20th	Day	4 13% 7% 16% 7% 6% 5% 3 5% 6% 27%	2540
	21st to end	Day	5% 16% 5% 13% 7% 8% 6% 5% 5% 7% 23%	2794
February	1st to 10th	Day	4 11% 5% 11% 7% 6% 6% 4 7% 7% 32%	1668
	11th to 20th	Day	2 13% 6% 12% 6% 6% 6% 5% 7% 8% 29%	1812
	21st to end	Day	1 11% 4 14% 9% 7% 7% 6% 8% 7% 26%	1570
March	1st to 10th	Day	3 12% 5% 12% 7% 7% 6% 4 6% 7% 31%	3138
	11th to 20th	Day	2 9% 3 7% 4 5% 5% 4 5% 6% 51%	3260
	21st to end	Day	3 15% 6% 13% 8% 8% 7% 5% 6% 6% 22%	4165
April	1st to 10th	Day	6% 11% 4 11% 8% 8% 6% 4 6% 6% 29%	2280
	11th to 20th	Day	5% 11% 4 9% 8% 6% 6% 4 5% 6% 36%	2249
	21st to end	Day	5% 12% 4 9% 5% 5% 5% 4 6% 7% 39%	2428
May	1st to 10th	Day	7% 10% 5% 8% 6% 5% 4 4 5% 5% 41%	4220
	11th to 20th	Day	6% 5% 2 5% 3 4 4 4 5% 6% 56%	4377
	21st to end	Day	6% 10% 3 7% 6% 5% 5% 5% 6% 7% 40%	4813
June	1st to 10th	Day	9% 8% 3 9% 6% 6% 5% 4 6% 7% 36%	2660
	11th to 20th	Day	7% 7% 2 7% 5% 5% 4 4 6% 7% 46%	2660
	21st to end	Day	4 3 1 4 4 3 4 4 5% 6% 60%	2660
July	1st to 10th	Day	1 1 1 2 2 3 3 2 4 4 76%	4420
	11th to 20th	Day	2 2 1 3 2 3 3 2 4 4 74%	4420
	21st to end	Day	1 2 1 2 2 3 3 3 4 5% 73%	4790
August	1st to 10th	Day	4 3 1 5% 4 4 4 4 6% 8% 57%	4400
	11th to 20th	Day	3 2 1 4 3 3 4 3 4 5% 68%	3894
	21st to end	Day	3 3 1 4 2 3 3 3 4 5% 70%	4180
September	1st to 10th	Day	2 2 1 4 4 2 3 3 4 6% 69%	2280
	11th to 20th	Day	5% 4 2 5% 4 4 4 3 5% 7% 56%	2195
	21st to end	Day	3 6% 2 7% 4 3 3 3 4 6% 58%	2090
October	1st to 10th	Day	4 5% 2 5% 3 3 3 2 3 5% 65%	3335
	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%	1710
	11th to 20th	Day	4 9% 4 9% 9% 7% 6% 6% 8% 8% 30%	1706
	21st to end	Day	4 8% 3 9% 5% 6% 6% 5% 8% 9% 38%	1520
December	1st to 10th	Day	4 11% 5% 10% 7% 6% 6% 5% 7% 8% 32%	1520
	11th to 20th	Day	4 12% 4 11% 8% 8% 7% 5% 8% 7% 25%	1928
	21st to end	Day	3 9% 5% 12% 9% 7% 7% 5% 6% 8% 27%	2794
January	1st to 10th	Night	3 10% 6% 16% 8% 8% 8% 6% 8% 7% 19%	4406
	11th to 20th	Night	6% 15% 8% 12% 5% 5% 5% 4 6% 7% 27%	4420
	21st to end	Night	4 14% 6% 13% 7% 6% 6% 5% 6% 8% 27%	4862
February	1st to 10th	Night	2 9% 3 11% 8% 7% 6% 5% 7% 8% 34%	2508
	11th to 20th	Night	3 9% 4 9% 6% 6% 7% 5% 7% 9% 33%	2256
	21st to end	Night	3 8% 3 10% 7% 8% 8% 5% 8% 8% 32%	1884
March	1st to 10th	Night	2 8% 4 9% 7% 5% 6% 5% 7% 9% 38%	3736
	11th to 20th	Night	2 7% 4 7% 5% 4 5% 4 6% 7% 48%	3716
	21st to end	Night	2 9% 4 10% 9% 8% 8% 7% 8% 8% 26%	3488
April	1st to 10th	Night	5% 8% 3 9% 7% 6% 7% 5% 8% 9% 36%	1900
	11th to 20th	Night	3 10% 4 8% 5% 5% 5% 4 6% 7% 43%	1879
	21st to end	Night	5% 8% 3 6% 6% 5% 5% 5% 8% 9% 40%	1750
May	1st to 10th	Night	6% 10% 4 8% 4 5% 5% 3 6% 7% 40%	2742
	11th to 20th	Night	3 4 2 4 3 3 3 3 4 5% 64%	2516
	21st to end	Night	5% 9% 4 6% 5% 4 4 3 5% 7% 48%	2762
June	1st to 10th	Night	6% 8% 2 7% 5% 4 5% 5% 7% 9% 41%	1520
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 4 5% 7% 53%	1520
	21st to end	Night	3 3 1 4 4 3 3 3 4 7% 66%	1520
July	1st to 10th	Night	1 1 1 2 2 2 2 2 2 4 82%	2540
	11th to 20th	Night	1 1 2 2 2 3 3 4 4 78%	2540
	21st to end	Night	1 2 1 3 2 3 3 3 4 5% 73%	2761
August	1st to 10th	Night	2 3 1 4 3 3 4 4 7% 7% 63%	2529
	11th to 20th	Night	1 1 1 2 2 3 3 3 4 5% 75%	2948
	21st to end	Night	1 2 1 3 2 3 3 2 4 5% 73%	3498
September	1st to 10th	Night	2 3 1 2 2 3 2 2 3 5% 75%	1900
	11th to 20th	Night	3 3 2 4 3 4 4 4 5% 7% 61%	1984
	21st to end	Night	4 4 2 5% 3 2 3 3 6% 6% 62%	2090
October	1st to 10th	Night	3 3 1 3 3 4 3 2 3 4 70%	3640
	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	5% 9% 3 8% 7% 6% 5% 4 7% 7% 38%	2469
	11th to 20th	Night	3 9% 3 9% 7% 6% 6% 6% 8% 8% 35%	2470
	21st to end	Night	3 8% 3 9% 6% 5% 5% 5% 7% 7% 40%	2660
December	1st to 10th	Night	4 9% 4 9% 7% 6% 5% 5% 7% 8% 36%	2660
	11th to 20th	Night	4 10% 5% 12% 8% 7% 7% 5% 8% 8% 27%	3276
	21st to end	Night	4 10% 4 12% 8% 7% 8% 6% 7% 9% 27%	4862

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	60% 5% 9% 19% 6% 1	2539
	11th to 20th	Day	59% 3 11% 19% 7% 2	2540
	21st to end	Day	62% 4 12% 14% 6% 2	2794
February	1st to 10th	Day	50% 4 16% 20% 9% 1	1668
	11th to 20th	Day	51% 5% 12% 19% 11% 2	1822
	21st to end	Day	53% 6% 11% 17% 11% 2	1570
March	1st to 10th	Day	55% 3 7% 17% 17% 1	3138
	11th to 20th	Day	34% 2 9% 37% 18%	3260
	21st to end	Day	59% 3 9% 22% 8%	4165
April	1st to 10th	Day	52% 3 11% 22% 9% 2	2280
	11th to 20th	Day	46% 3 12% 21% 14% 3	2252
	21st to end	Day	42% 5% 10% 26% 17% 1	2428
May	1st to 10th	Day	44% 2 8% 26% 18% 3	4220
	11th to 20th	Day	29% 2 7% 27% 27% 9%	4380
	21st to end	Day	41% 2 8% 33% 13% 1	4814
June	1st to 10th	Day	45% 4 10% 28% 13% 1	2660
	11th to 20th	Day	36% 2 8% 26% 23% 5%	2660
	21st to end	Day	23% 2 6% 26% 31% 12%	2660
July	1st to 10th	Day	12% 2 3 11% 19% 53%	4351
	11th to 20th	Day	14% 3 4 10% 19% 50%	4345
	21st to end	Day	13% 3 2 12% 34% 36%	4639
August	1st to 10th	Day	24% 3 4 14% 29% 26%	4384
	11th to 20th	Day	16% 3 5% 15% 40% 20%	3933
	21st to end	Day	18% 2 4 26% 26% 24%	4179
September	1st to 10th	Day	17% 2 4 23% 31% 23%	2280
	11th to 20th	Day	27% 4 6% 22% 27% 15%	2195
	21st to end	Day	29% 2 8% 27% 24% 11%	2090
October	1st to 10th	Day	24% 3 6% 19% 38% 10%	3335
	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 12% 24% 12% 1	1710
	11th to 20th	Day	48% 5% 16% 22% 8% 1	1706
	21st to end	Day	41% 6% 13% 23% 14% 4	1520
December	1st to 10th	Day	50% 7% 13% 18% 10% 2	1520
	11th to 20th	Day	57% 3 13% 18% 9%	1928
	21st to end	Day	56% 3 12% 19% 9%	2794
January	1st to 10th	Night	56% 4 12% 21% 6%	4406
	11th to 20th	Night	55% 3 11% 21% 9% 2	4420
	21st to end	Night	59% 3 13% 17% 7% 2	4862
February	1st to 10th	Night	44% 7% 17% 22% 9% 2	2508
	11th to 20th	Night	43% 7% 16% 19% 12% 3	2257
	21st to end	Night	46% 6% 15% 19% 12% 3	1884
March	1st to 10th	Night	43% 3 9% 19% 23% 2	3736
	11th to 20th	Night	34% 3 9% 35% 19% 1	3716
	21st to end	Night	50% 5% 13% 24% 7% 2	3488
April	1st to 10th	Night	40% 5% 14% 29% 11% 2	1900
	11th to 20th	Night	39% 4 13% 27% 15% 2	1879
	21st to end	Night	35% 6% 14% 27% 17% 1	1750
May	1st to 10th	Night	39% 2 7% 31% 19% 2	2742
	11th to 20th	Night	23% 2 8% 31% 35% 1	2516
	21st to end	Night	34% 2 15% 38% 11%	2762
June	1st to 10th	Night	36% 6% 14% 32% 11% 1	1520
	11th to 20th	Night	28% 3 11% 32% 21% 5%	1520
	21st to end	Night	20% 2 9% 32% 28% 8%	1520
July	1st to 10th	Night	10% 1 3 14% 21% 52%	2500
	11th to 20th	Night	10% 2 4 13% 24% 48%	2492
	21st to end	Night	15% 2 2 11% 37% 32%	2674
August	1st to 10th	Night	20% 3 5% 16% 34% 23%	2521
	11th to 20th	Night	13% 2 4 19% 43% 19%	2975
	21st to end	Night	14% 3 4 26% 31% 23%	3498
September	1st to 10th	Night	14% 2 3 24% 31% 26%	1900
	11th to 20th	Night	22% 2 9% 24% 28% 15%	1984
	21st to end	Night	22% 2 7% 28% 28% 12%	2090
October	1st to 10th	Night	20% 2 6% 20% 39% 12%	3640
	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	43% 5% 12% 22% 16% 2	2469
	11th to 20th	Night	45% 6% 14% 23% 12%	2470
	21st to end	Night	40% 5% 14% 18% 19% 4	2660
December	1st to 10th	Night	44% 8% 14% 20% 11% 3	2660
	11th to 20th	Night	55% 4 12% 19% 9% 1	3276
	21st to end	Night	52% 3 12% 18% 13% 2	4862

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% 20% 28% 19% 13% 5%	180
	11th to 20th	Day	11% 16% 36% 17% 17% 3	180
	21st to end	Day	10% 13% 38% 28% 9% 3	198
February	1st to 10th	Day	12% 29% 35% 18% 5% 2	328
	11th to 20th	Day	12% 30% 32% 17% 7% 1	437
	21st to end	Day	13% 27% 31% 24% 6%	382
March	1st to 10th	Day	14% 25% 34% 20% 8%	460
	11th to 20th	Day	10% 23% 32% 23% 10% 2	460
	21st to end	Day	14% 27% 30% 22% 7%	506
April	1st to 10th	Day	17% 25% 25% 19% 11% 3	460
	11th to 20th	Day	14% 26% 29% 18% 10% 3	452
	21st to end	Day	12% 23% 33% 22% 8% 2	460
May	1st to 10th	Day	12% 22% 30% 23% 9% 4	463
	11th to 20th	Day	19% 19% 29% 17% 13% 4	488
	21st to end	Day	16% 12% 23% 29% 16% 4	529
June	1st to 10th	Day	12% 16% 26% 25% 15% 6%	490
	11th to 20th	Day	13% 18% 33% 22% 11% 2	490
	21st to end	Day	4 13% 32% 29% 17% 5%	490
July	1st to 10th	Day	3 10% 37% 33% 14% 2	486
	11th to 20th	Day	3 10% 33% 36% 16% 3	484
	21st to end	Day	2 7% 32% 37% 18% 4	531
August	1st to 10th	Day	6% 7% 27% 38% 17% 6%	487
	11th to 20th	Day	3 7% 26% 32% 23% 9%	477
	21st to end	Day	4 11% 26% 32% 18% 8%	539
September	1st to 10th	Day	3 9% 28% 34% 18% 8%	490
	11th to 20th	Day	7% 12% 24% 32% 18% 7%	490
	21st to end	Day	7% 13% 31% 27% 18% 4	490
October	1st to 10th	Day	11% 16% 26% 25% 18% 5%	490
	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% 26% 28% 11% 1	282
	11th to 20th	Day	7% 16% 28% 32% 12% 4	268
	21st to end	Day	9% 13% 32% 31% 13% 1	180
December	1st to 10th	Day	14% 14% 31% 22% 11% 8%	180
	11th to 20th	Day	14% 20% 38% 18% 8% 1	180
	21st to end	Day	9% 20% 33% 25% 12% 2	198
January	1st to 10th	Night	9% 14% 26% 30% 19% 2	760
	11th to 20th	Night	12% 14% 25% 27% 20% 3	760
	21st to end	Night	9% 11% 24% 34% 19% 4	836
February	1st to 10th	Night	8% 17% 30% 30% 13% 2	760
	11th to 20th	Night	8% 16% 26% 32% 16% 3	744
	21st to end	Night	10% 15% 28% 32% 13% 2	628
March	1st to 10th	Night	6% 15% 27% 34% 16% 2	760
	11th to 20th	Night	9% 12% 26% 33% 18% 2	760
	21st to end	Night	9% 18% 27% 32% 14% 1	836
April	1st to 10th	Night	8% 16% 26% 33% 16% 2	760
	11th to 20th	Night	8% 16% 29% 28% 15% 4	751
	21st to end	Night	8% 17% 27% 33% 14% 2	610
May	1st to 10th	Night	10% 13% 29% 29% 16% 2	504
	11th to 20th	Night	10% 9% 18% 33% 26% 3	374
	21st to end	Night	11% 9% 21% 32% 23% 4	411
June	1st to 10th	Night	9% 9% 23% 34% 23% 2	380
	11th to 20th	Night	5% 14% 25% 36% 18% 2	380
	21st to end	Night	4 4 19% 47% 25% 1	380
July	1st to 10th	Night	2 4 19% 51% 22% 3	370
	11th to 20th	Night	1 2 22% 53% 22%	368
	21st to end	Night	2 1 18% 48% 29% 2	416
August	1st to 10th	Night	4 2 15% 47% 29% 3	378
	11th to 20th	Night	2 2 16% 42% 32% 7%	635
	21st to end	Night	3 4 18% 40% 31% 4	836
September	1st to 10th	Night	4 3 15% 40% 34% 4	760
	11th to 20th	Night	3 5% 15% 37% 31% 9%	760
	21st to end	Night	6% 9% 18% 30% 30% 7%	760
October	1st to 10th	Night	8% 8% 20% 34% 26% 5%	760
	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% 23% 37% 18% 2	760
	11th to 20th	Night	11% 12% 22% 35% 17% 3	760
	21st to end	Night	7% 15% 23% 32% 17% 6%	760
December	1st to 10th	Night	10% 12% 24% 33% 18% 4	760
	11th to 20th	Night	10% 13% 24% 35% 14% 3	760
	21st to end	Night	12% 17% 28% 30% 11% 2	836

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