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 2024-04-25.

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	5% 8% 4 8% 7% 4 5% 5% 6% 7% 43%	83232
	Night	4 7% 4 7% 6% 4 6% 6% 6% 8% 42%	85955
Transparency	Day	41% 3 9% 22% 18% 7%	82936
	Night	39% 4 11% 23% 17% 6%	85772
Seeing	Day	10% 17% 29% 26% 14% 4	13743
	Night	8% 11% 23% 35% 20% 4	23101

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	4 11% 6% 16% 10% 6% 8% 6% 7% 6% 20%	2539
	11th to 20th	Day	4 13% 7% 14% 9% 4 6% 4 5% 7% 27%	2540
	21st to end	Day	5% 16% 6% 11% 8% 6% 7% 6% 5% 7% 24%	2794
February	1st to 10th	Day	4 10% 6% 10% 8% 4 6% 5% 6% 8% 32%	1668
	11th to 20th	Day	3 12% 6% 11% 7% 4 6% 7% 7% 8% 29%	1812
	21st to end	Day	2 9% 6% 12% 10% 5% 8% 7% 7% 8% 26%	1570
March	1st to 10th	Day	3 11% 6% 11% 9% 5% 6% 6% 6% 7% 31%	3138
	11th to 20th	Day	2 8% 3 7% 5% 3 5% 5% 5% 6% 51%	3260
	21st to end	Day	4 14% 7% 12% 10% 6% 8% 7% 6% 6% 22%	4165
April	1st to 10th	Day	7% 10% 5% 10% 8% 6% 7% 6% 6% 6% 29%	2280
	11th to 20th	Day	5% 10% 5% 8% 8% 5% 6% 5% 5% 6% 36%	2249
	21st to end	Day	5% 11% 4 7% 6% 4 5% 4 6% 7% 40%	2352
May	1st to 10th	Day	5% 7% 4 7% 7% 3 5% 6% 7% 7% 42%	2398
	11th to 20th	Day	10% 8% 3 7% 6% 4 6% 6% 6% 8% 34%	2477
	21st to end	Day	11% 10% 4 8% 8% 5% 6% 6% 6% 6% 30%	2723
June	1st to 10th	Day	10% 6% 4 8% 8% 4 6% 5% 6% 7% 36%	2520
	11th to 20th	Day	7% 6% 3 6% 6% 3 5% 5% 5% 7% 46%	2520
	21st to end	Day	4 3 2 4 4 2 4 5% 5% 6% 60%	2520
July	1st to 10th	Day	2 2 1 3 3 2 4 5% 5% 7% 65%	2520
	11th to 20th	Day	2 2 1 3 3 2 3 3 3 5% 74%	2520
	21st to end	Day	2 2 1 3 3 2 3 3 4 5% 73%	2741
August	1st to 10th	Day	4 3 2 4 4 3 5% 5% 7% 7% 59%	2507
	11th to 20th	Day	2 2 1 3 3 2 3 4 4 5% 70%	2231
	21st to end	Day	2 3 1 3 3 2 3 4 4 6% 69%	2376
September	1st to 10th	Day	2 2 1 3 4 2 3 3 4 6% 69%	2160
	11th to 20th	Day	5% 4 2 4 5% 3 4 4 5% 7% 58%	2080
	21st to end	Day	3 7% 2 7% 5% 3 3 3 4 6% 56%	1980
October	1st to 10th	Day	8% 8% 4 7% 5% 3 3 3 4 6% 50%	1890
	11th to 20th	Day	5% 6% 2 6% 5% 3 5% 5% 6% 9% 50%	1778
	21st to end	Day	7% 8% 3 8% 6% 4 4 5% 6% 7% 42%	1782
November	1st to 10th	Day	7% 10% 4 8% 7% 4 6% 6% 5% 8% 35%	1674
	11th to 20th	Day	4 8% 5% 7% 10% 6% 7% 7% 8% 8% 31%	1706
	21st to end	Day	4 7% 4 8% 6% 5% 6% 7% 7% 9% 38%	1520
December	1st to 10th	Day	4 10% 6% 9% 7% 4 6% 6% 6% 9% 32%	1520
	11th to 20th	Day	5% 11% 4 10% 9% 6% 7% 6% 8% 8% 26%	1928
	21st to end	Day	3 8% 6% 11% 10% 5% 7% 7% 6% 9% 27%	2794
January	1st to 10th	Night	3 10% 6% 15% 10% 6% 8% 8% 8% 8% 20%	4406
	11th to 20th	Night	6% 14% 8% 11% 6% 3 5% 6% 6% 7% 27%	4420
	21st to end	Night	4 13% 6% 11% 8% 5% 6% 6% 6% 8% 27%	4862
February	1st to 10th	Night	3 8% 4 10% 9% 5% 7% 6% 6% 8% 34%	2508
	11th to 20th	Night	4 8% 5% 8% 7% 4 8% 7% 7% 9% 34%	2256
	21st to end	Night	3 7% 3 9% 8% 7% 8% 7% 8% 8% 32%	1884
March	1st to 10th	Night	2 7% 5% 8% 7% 4 5% 6% 7% 9% 38%	3736
	11th to 20th	Night	2 7% 4 7% 6% 3 5% 5% 6% 7% 48%	3716
	21st to end	Night	2 9% 5% 9% 10% 6% 9% 9% 8% 9% 26%	3488
April	1st to 10th	Night	5% 7% 4 7% 7% 4 7% 6% 7% 9% 37%	1900
	11th to 20th	Night	3 9% 5% 8% 5% 4 5% 5% 6% 8% 43%	1879
	21st to end	Night	5% 7% 3 6% 6% 4 6% 6% 7% 9% 40%	1705
May	1st to 10th	Night	4 6% 2 6% 4 4 5% 5% 7% 9% 48%	1558
	11th to 20th	Night	6% 5% 4 6% 6% 4 6% 6% 7% 8% 42%	1416
	21st to end	Night	8% 8% 4 5% 6% 3 5% 5% 7% 9% 41%	1552
June	1st to 10th	Night	7% 7% 3 7% 6% 3 5% 6% 7% 9% 41%	1440
	11th to 20th	Night	5% 4 2 5% 5% 3 6% 4 5% 7% 53%	1440
	21st to end	Night	3 3 1 3 5% 2 4 4 4 7% 65%	1440
July	1st to 10th	Night	2 2 1 3 3 2 3 3 4 7% 69%	1440
	11th to 20th	Night	1 1 2 1 2 3 3 5% 80%	1440
	21st to end	Night	1 3 1 2 2 2 3 3 4 5% 75%	1576
August	1st to 10th	Night	3 3 1 3 3 3 3 4 7% 7% 63%	1432
	11th to 20th	Night	1 1 1 2 2 1 3 3 3 6% 77%	1668
	21st to end	Night	2 2 1 2 3 2 3 3 5% 6% 72%	1980
September	1st to 10th	Night	2 3 1 2 2 2 2 3 3 5% 76%	1800
	11th to 20th	Night	2 2 1 3 3 3 4 5% 5% 7% 64%	1879
	21st to end	Night	4 4 2 4 4 2 3 4 6% 6% 61%	1980
October	1st to 10th	Night	5% 6% 2 3 4 3 4 4 5% 7% 57%	2065
	11th to 20th	Night	4 5% 3 5% 4 2 4 4 6% 8% 53%	2182
	21st to end	Night	4 6% 3 7% 7% 3 6% 7% 6% 8% 45%	2574
November	1st to 10th	Night	5% 8% 4 7% 7% 5% 6% 6% 7% 7% 38%	2405
	11th to 20th	Night	3 8% 3 8% 8% 5% 6% 7% 8% 8% 35%	2470
	21st to end	Night	3 7% 4 9% 7% 4 6% 6% 7% 7% 41%	2660
December	1st to 10th	Night	4 8% 5% 8% 7% 5% 5% 6% 7% 8% 36%	2660
	11th to 20th	Night	4 10% 5% 10% 9% 5% 7% 7% 7% 8% 27%	3276
	21st to end	Night	4 9% 4 10% 9% 6% 7% 8% 8% 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	41% 5% 10% 25% 17% 1	2352
May	1st to 10th	Day	39% 3 9% 32% 15% 2	2398
	11th to 20th	Day	46% 3 12% 26% 12% 1	2480
	21st to end	Day	52% 4 10% 24% 10% 1	2724
June	1st to 10th	Day	45% 4 10% 28% 12% 1	2520
	11th to 20th	Day	36% 2 8% 26% 22% 5%	2520
	21st to end	Day	24% 2 6% 26% 31% 11%	2520
July	1st to 10th	Day	19% 3 4 19% 28% 26%	2451
	11th to 20th	Day	14% 2 4 15% 31% 34%	2445
	21st to end	Day	15% 2 1 11% 35% 36%	2589
August	1st to 10th	Day	23% 3 3 22% 29% 20%	2490
	11th to 20th	Day	17% 3 3 20% 36% 21%	2231
	21st to end	Day	17% 2 4 21% 37% 18%	2376
September	1st to 10th	Day	17% 2 4 23% 31% 24%	2160
	11th to 20th	Day	26% 3 5% 22% 28% 15%	2080
	21st to end	Day	30% 2 8% 26% 23% 11%	1980
October	1st to 10th	Day	36% 4 9% 23% 23% 6%	1890
	11th to 20th	Day	32% 3 10% 30% 21% 4	1778
	21st to end	Day	39% 5% 13% 22% 19% 2	1782
November	1st to 10th	Day	47% 4 12% 24% 12% 1	1674
	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	36% 6% 14% 26% 16% 1	1705
May	1st to 10th	Night	31% 4 10% 38% 16% 1	1558
	11th to 20th	Night	38% 3 15% 30% 13%	1416
	21st to end	Night	38% 4 17% 31% 10%	1552
June	1st to 10th	Night	36% 6% 15% 32% 10%	1440
	11th to 20th	Night	29% 3 12% 33% 20% 4	1440
	21st to end	Night	21% 2 9% 32% 28% 7%	1440
July	1st to 10th	Night	18% 2 5% 25% 28% 23%	1400
	11th to 20th	Night	9% 2 5% 21% 32% 31%	1392
	21st to end	Night	14% 2 2 14% 37% 31%	1488
August	1st to 10th	Night	18% 3 5% 26% 30% 17%	1424
	11th to 20th	Night	11% 2 4 24% 34% 25%	1668
	21st to end	Night	13% 2 4 25% 37% 19%	1980
September	1st to 10th	Night	14% 2 3 25% 30% 26%	1800
	11th to 20th	Night	20% 2 8% 24% 30% 16%	1879
	21st to end	Night	23% 2 7% 28% 27% 12%	1980
October	1st to 10th	Night	27% 3 11% 26% 25% 8%	2065
	11th to 20th	Night	28% 3 14% 24% 27% 4	2182
	21st to end	Night	34% 4 16% 21% 21% 4	2574
November	1st to 10th	Night	43% 5% 12% 23% 16% 2	2405
	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	13% 22% 32% 22% 9% 2	437
May	1st to 10th	Day	11% 21% 30% 24% 9% 4	423
	11th to 20th	Day	21% 19% 28% 16% 13% 4	448
	21st to end	Day	16% 12% 23% 30% 15% 4	485
June	1st to 10th	Day	12% 15% 26% 25% 16% 6%	450
	11th to 20th	Day	12% 18% 33% 23% 12% 2	450
	21st to end	Day	3 12% 32% 30% 18% 6%	450
July	1st to 10th	Day	3 8% 37% 35% 15% 2	446
	11th to 20th	Day	2 9% 32% 36% 16% 4	444
	21st to end	Day	2 6% 31% 38% 18% 4	487
August	1st to 10th	Day	6% 6% 26% 39% 17% 6%	447
	11th to 20th	Day	3 5% 24% 33% 24% 10%	437
	21st to end	Day	4 10% 26% 33% 19% 8%	495
September	1st to 10th	Day	4 8% 27% 35% 19% 7%	450
	11th to 20th	Day	7% 11% 23% 33% 18% 8%	450
	21st to end	Day	7% 13% 30% 27% 19% 4	450
October	1st to 10th	Day	12% 16% 25% 24% 19% 5%	450
	11th to 20th	Day	8% 17% 29% 23% 17% 6%	428
	21st to end	Day	11% 19% 24% 27% 15% 4	297
November	1st to 10th	Day	14% 20% 26% 29% 11% 1	270
	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% 16% 27% 33% 14% 2	595
May	1st to 10th	Night	9% 13% 29% 30% 17% 3	478
	11th to 20th	Night	11% 8% 18% 33% 27% 4	354
	21st to end	Night	11% 8% 21% 32% 23% 4	389
June	1st to 10th	Night	9% 9% 22% 34% 24% 2	360
	11th to 20th	Night	6% 13% 25% 36% 19% 2	360
	21st to end	Night	3 4 18% 48% 27% 1	360
July	1st to 10th	Night	2 3 18% 51% 22% 3	350
	11th to 20th	Night	1 2 20% 53% 24%	348
	21st to end	Night	2 1 16% 49% 30% 2	394
August	1st to 10th	Night	4 3 14% 46% 30% 3	358
	11th to 20th	Night	2 2 14% 42% 34% 7%	600
	21st to end	Night	3 4 18% 41% 31% 4	792
September	1st to 10th	Night	4 3 15% 39% 34% 4	720
	11th to 20th	Night	3 4 14% 38% 33% 9%	720
	21st to end	Night	6% 8% 17% 30% 31% 7%	720
October	1st to 10th	Night	8% 8% 20% 33% 27% 5%	720
	11th to 20th	Night	8% 11% 17% 34% 22% 8%	720
	21st to end	Night	7% 11% 21% 37% 18% 6%	792
November	1st to 10th	Night	9% 11% 22% 38% 18% 2	740
	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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