Table Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Table Mountain 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	8% 10% 3 7% 5% 4 4 3 5% 6% 44%	105351
	Night	9% 11% 4 8% 5% 4 4 4 5% 6% 41%	102306
Transparency	Day	37% 6% 11% 23% 17% 7%	105119
	Night	39% 7% 12% 23% 14% 5%	102184
Seeing	Day	14% 18% 29% 26% 10% 2	14380
	Night	12% 15% 25% 30% 16% 3	23337

By Month

Percentage Cloud Cover NW (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	12% 24% 8% 13% 6% 5% 4 4 4 5% 16%	2539
	11th to 20th	Day	12% 19% 7% 11% 6% 4 4 3 4 5% 24%	2516
	21st to end	Day	20% 18% 5% 10% 6% 5% 4 3 5% 6% 18%	2794
February	1st to 10th	Day	12% 18% 5% 11% 7% 4 5% 4 5% 6% 23%	1687
	11th to 20th	Day	11% 19% 6% 9% 5% 4 5% 3 5% 7% 27%	1665
	21st to end	Day	8% 17% 5% 12% 7% 5% 6% 5% 6% 6% 23%	1555
March	1st to 10th	Day	7% 14% 4 10% 6% 6% 5% 4 7% 6% 30%	3138
	11th to 20th	Day	7% 11% 4 7% 5% 4 3 3 5% 4 46%	3423
	21st to end	Day	11% 17% 6% 10% 6% 5% 6% 4 6% 6% 23%	4059
April	1st to 10th	Day	10% 15% 5% 10% 6% 5% 7% 5% 6% 6% 25%	2280
	11th to 20th	Day	8% 15% 5% 8% 6% 5% 5% 4 6% 7% 32%	2252
	21st to end	Day	7% 12% 3 8% 5% 5% 5% 5% 7% 9% 34%	2499
May	1st to 10th	Day	6% 9% 3 7% 5% 4 4 3 5% 6% 48%	4420
	11th to 20th	Day	6% 6% 2 5% 4 3 4 4 6% 7% 53%	4377
	21st to end	Day	10% 14% 4 8% 6% 5% 5% 3 5% 7% 32%	4813
June	1st to 10th	Day	11% 8% 3 7% 5% 5% 5% 4 7% 7% 38%	2660
	11th to 20th	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 8% 45%	2660
	21st to end	Day	6% 5% 2 4 4 3 4 4 6% 6% 56%	2660
July	1st to 10th	Day	2 2 1 3 2 2 3 2 3 3 78%	4420
	11th to 20th	Day	3 2 1 2 2 2 1 2 3 3 79%	4420
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 78%	4790
August	1st to 10th	Day	2 2 1 3 3 3 4 3 5% 6% 69%	4401
	11th to 20th	Day	2 3 1 3 2 3 4 3 6% 8% 64%	4089
	21st to end	Day	7% 6% 3 6% 3 3 3 3 4 5% 58%	4211
September	1st to 10th	Day	4 3 1 4 3 3 4 3 4 7% 65%	2280
	11th to 20th	Day	6% 6% 2 5% 5% 4 5% 4 5% 6% 51%	2280
	21st to end	Day	9% 6% 2 6% 4 4 4 3 6% 6% 50%	2042
October	1st to 10th	Day	7% 6% 2 5% 4 3 4 4 6% 9% 51%	3180
	11th to 20th	Day	11% 11% 4 8% 5% 5% 5% 3 6% 7% 36%	3161
	21st to end	Day	11% 11% 4 10% 5% 5% 5% 3 5% 6% 35%	3140
November	1st to 10th	Day	15% 16% 4 10% 6% 5% 5% 5% 5% 6% 25%	1661
	11th to 20th	Day	13% 17% 6% 12% 6% 5% 4 4 5% 5% 24%	1520
	21st to end	Day	12% 16% 5% 9% 5% 5% 4 5% 5% 7% 27%	1520
December	1st to 10th	Day	12% 16% 5% 9% 7% 5% 5% 3 4 5% 28%	1520
	11th to 20th	Day	13% 15% 5% 13% 7% 6% 6% 4 6% 6% 20%	1925
	21st to end	Day	12% 17% 6% 14% 8% 6% 6% 3 4 5% 20%	2794
January	1st to 10th	Night	13% 17% 8% 13% 6% 6% 5% 4 5% 5% 17%	4406
	11th to 20th	Night	13% 14% 6% 13% 6% 4 4 3 5% 9% 23%	4382
	21st to end	Night	17% 18% 5% 10% 6% 6% 5% 4 5% 6% 19%	4862
February	1st to 10th	Night	11% 18% 4 9% 7% 5% 5% 4 6% 6% 24%	2489
	11th to 20th	Night	10% 15% 3 8% 5% 5% 4 4 5% 6% 33%	2402
	21st to end	Night	9% 17% 7% 10% 6% 5% 5% 4 6% 6% 25%	1899
March	1st to 10th	Night	8% 13% 5% 9% 6% 5% 5% 5% 7% 8% 30%	3736
	11th to 20th	Night	6% 10% 4 8% 4 3 3 2 5% 6% 49%	3555
	21st to end	Night	7% 14% 5% 10% 7% 6% 6% 5% 7% 7% 28%	3593
April	1st to 10th	Night	9% 10% 4 7% 7% 6% 6% 6% 7% 8% 31%	1900
	11th to 20th	Night	8% 10% 3 8% 5% 4 4 3 6% 7% 41%	1879
	21st to end	Night	7% 10% 4 8% 4 6% 5% 3 5% 9% 39%	1677
May	1st to 10th	Night	6% 12% 3 5% 3 4 3 2 4 5% 51%	2540
	11th to 20th	Night	5% 7% 2 4 4 3 3 3 5% 5% 58%	2516
	21st to end	Night	4 11% 2 6% 5% 5% 5% 5% 7% 8% 41%	2762
June	1st to 10th	Night	9% 7% 2 6% 6% 5% 5% 5% 6% 6% 45%	1520
	11th to 20th	Night	7% 7% 2 7% 5% 4 4 4 5% 8% 48%	1520
	21st to end	Night	3 4 2 4 3 4 4 4 6% 7% 60%	1520
July	1st to 10th	Night	2 2 1 2 1 2 2 2 3 4 80%	2540
	11th to 20th	Night	1 1 2 1 2 2 2 3 4 82%	2540
	21st to end	Night	1 2 1 2 1 1 2 2 3 4 81%	2762
August	1st to 10th	Night	2 2 1 4 3 2 2 2 4 4 74%	2529
	11th to 20th	Night	2 2 1 3 3 3 3 3 5% 7% 68%	2743
	21st to end	Night	6% 6% 1 4 3 3 3 3 5% 5% 62%	3466
September	1st to 10th	Night	4 2 2 3 3 3 3 2 5% 7% 66%	1900
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 6% 6% 54%	1900
	21st to end	Night	6% 5% 2 5% 4 4 3 3 6% 8% 54%	2135
October	1st to 10th	Night	6% 6% 2 5% 4 4 5% 4 6% 7% 50%	3800
	11th to 20th	Night	10% 9% 3 8% 4 4 5% 4 5% 7% 41%	3777
	21st to end	Night	13% 11% 3 8% 5% 4 4 3 5% 6% 37%	4418
November	1st to 10th	Night	18% 12% 4 8% 4 4 4 4 6% 6% 28%	2516
	11th to 20th	Night	14% 15% 4 8% 6% 5% 4 4 5% 7% 29%	2660
	21st to end	Night	14% 13% 4 9% 6% 5% 5% 4 6% 6% 28%	2660
December	1st to 10th	Night	12% 15% 5% 8% 6% 4 5% 4 5% 7% 28%	2660
	11th to 20th	Night	15% 16% 5% 10% 6% 6% 5% 4 4 7% 21%	3280
	21st to end	Night	14% 15% 6% 13% 7% 5% 5% 3 5% 6% 21%	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	64% 11% 10% 11% 4 1	2539
	11th to 20th	Day	60% 6% 14% 16% 4 1	2540
	21st to end	Day	67% 4 14% 10% 4	2794
February	1st to 10th	Day	59% 6% 14% 16% 4 1	1687
	11th to 20th	Day	56% 6% 12% 17% 8% 1	1674
	21st to end	Day	55% 9% 11% 16% 8% 1	1555
March	1st to 10th	Day	45% 11% 8% 17% 16% 3	3138
	11th to 20th	Day	35% 7% 10% 41% 7%	3423
	21st to end	Day	55% 9% 12% 18% 6%	4059
April	1st to 10th	Day	53% 8% 12% 19% 7%	2280
	11th to 20th	Day	48% 6% 12% 21% 11% 2	2252
	21st to end	Day	43% 7% 12% 24% 13% 2	2499
May	1st to 10th	Day	33% 6% 9% 22% 24% 7%	4420
	11th to 20th	Day	27% 6% 14% 31% 20% 1	4380
	21st to end	Day	45% 9% 15% 24% 5%	4814
June	1st to 10th	Day	40% 6% 10% 28% 13% 3	2660
	11th to 20th	Day	32% 5% 14% 30% 17% 2	2660
	21st to end	Day	25% 5% 13% 31% 22% 4	2660
July	1st to 10th	Day	12% 3 5% 16% 30% 34%	4351
	11th to 20th	Day	13% 2 4 12% 28% 41%	4345
	21st to end	Day	12% 3 4 22% 38% 21%	4639
August	1st to 10th	Day	14% 4 7% 22% 34% 18%	4384
	11th to 20th	Day	16% 7% 12% 38% 21% 5%	4130
	21st to end	Day	28% 4 8% 27% 29% 4	4210
September	1st to 10th	Day	20% 3 9% 31% 28% 9%	2280
	11th to 20th	Day	32% 5% 12% 24% 22% 6%	2280
	21st to end	Day	33% 4 15% 26% 18% 4	2042
October	1st to 10th	Day	27% 7% 12% 35% 18% 1	3180
	11th to 20th	Day	40% 10% 13% 24% 14%	3161
	21st to end	Day	39% 12% 10% 23% 11% 6%	3140
November	1st to 10th	Day	55% 7% 11% 17% 8% 1	1661
	11th to 20th	Day	58% 8% 13% 15% 5% 1	1520
	21st to end	Day	54% 5% 14% 17% 8% 2	1520
December	1st to 10th	Day	57% 6% 12% 18% 7%	1520
	11th to 20th	Day	63% 6% 16% 11% 4	1928
	21st to end	Day	68% 5% 9% 12% 6%	2794
January	1st to 10th	Night	62% 9% 12% 11% 5% 1	4406
	11th to 20th	Night	54% 8% 11% 19% 7% 1	4420
	21st to end	Night	64% 5% 16% 11% 3 1	4862
February	1st to 10th	Night	56% 7% 16% 16% 5% 1	2489
	11th to 20th	Night	49% 6% 15% 20% 8% 2	2404
	21st to end	Night	55% 9% 10% 17% 9%	1899
March	1st to 10th	Night	43% 11% 9% 20% 14% 4	3736
	11th to 20th	Night	30% 9% 14% 39% 8%	3556
	21st to end	Night	48% 8% 15% 25% 4	3593
April	1st to 10th	Night	44% 8% 16% 22% 9%	1900
	11th to 20th	Night	40% 5% 14% 23% 15% 2	1879
	21st to end	Night	39% 7% 13% 26% 14% 1	1677
May	1st to 10th	Night	31% 8% 8% 24% 25% 5%	2540
	11th to 20th	Night	24% 6% 12% 37% 21% 1	2516
	21st to end	Night	31% 10% 19% 31% 7% 1	2762
June	1st to 10th	Night	35% 7% 13% 26% 15% 3	1520
	11th to 20th	Night	32% 5% 17% 31% 14% 2	1520
	21st to end	Night	22% 4 14% 35% 21% 5%	1520
July	1st to 10th	Night	10% 2 7% 19% 22% 41%	2500
	11th to 20th	Night	8% 2 6% 16% 26% 43%	2492
	21st to end	Night	7% 4 5% 23% 33% 27%	2674
August	1st to 10th	Night	13% 3 5% 19% 39% 21%	2521
	11th to 20th	Night	15% 6% 15% 37% 22% 6%	2768
	21st to end	Night	20% 7% 12% 27% 29% 6%	3466
September	1st to 10th	Night	19% 3 11% 28% 30% 9%	1900
	11th to 20th	Night	28% 5% 10% 27% 22% 8%	1900
	21st to end	Night	27% 5% 14% 31% 16% 7%	2135
October	1st to 10th	Night	26% 7% 10% 35% 20% 1	3800
	11th to 20th	Night	36% 10% 11% 27% 14% 2	3777
	21st to end	Night	38% 11% 10% 24% 14% 3	4418
November	1st to 10th	Night	52% 7% 11% 19% 10% 1	2516
	11th to 20th	Night	51% 8% 14% 19% 7% 1	2660
	21st to end	Night	53% 5% 13% 19% 9% 1	2660
December	1st to 10th	Night	54% 7% 13% 20% 6%	2660
	11th to 20th	Night	62% 6% 17% 11% 4	3276
	21st to end	Night	63% 5% 11% 13% 8%	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	18% 18% 26% 22% 16% 2	180
	11th to 20th	Day	24% 12% 27% 18% 14% 4	180
	21st to end	Day	19% 15% 25% 26% 12% 3	198
February	1st to 10th	Day	20% 27% 29% 18% 3 1	347
	11th to 20th	Day	22% 21% 34% 16% 5%	365
	21st to end	Day	18% 22% 33% 20% 6% 1	375
March	1st to 10th	Day	17% 26% 30% 20% 7% 1	460
	11th to 20th	Day	17% 23% 23% 26% 10% 1	460
	21st to end	Day	20% 25% 30% 20% 6%	506
April	1st to 10th	Day	25% 22% 27% 17% 7% 2	460
	11th to 20th	Day	18% 27% 29% 16% 7% 3	452
	21st to end	Day	17% 24% 31% 18% 8% 2	460
May	1st to 10th	Day	14% 18% 35% 26% 6% 1	463
	11th to 20th	Day	20% 13% 30% 23% 11% 2	488
	21st to end	Day	16% 16% 26% 28% 12% 2	529
June	1st to 10th	Day	13% 23% 30% 23% 9% 2	490
	11th to 20th	Day	13% 23% 35% 20% 7% 1	490
	21st to end	Day	9% 17% 30% 29% 13% 2	490
July	1st to 10th	Day	6% 14% 35% 36% 8% 1	486
	11th to 20th	Day	4 15% 36% 31% 11% 3	484
	21st to end	Day	3 11% 33% 36% 13% 4	531
August	1st to 10th	Day	6% 11% 29% 34% 17% 3	487
	11th to 20th	Day	4 9% 26% 39% 17% 6%	477
	21st to end	Day	7% 16% 29% 29% 16% 4	539
September	1st to 10th	Day	6% 12% 33% 31% 13% 4	490
	11th to 20th	Day	10% 14% 31% 30% 12% 2	490
	21st to end	Day	13% 19% 28% 27% 12% 1	490
October	1st to 10th	Day	17% 16% 26% 26% 13% 2	490
	11th to 20th	Day	19% 17% 25% 24% 12% 3	490
	21st to end	Day	20% 20% 25% 24% 8% 3	357
November	1st to 10th	Day	19% 24% 24% 27% 6%	258
	11th to 20th	Day	17% 23% 26% 17% 12% 6%	180
	21st to end	Day	13% 18% 24% 27% 13% 4	180
December	1st to 10th	Day	17% 22% 20% 20% 13% 8%	180
	11th to 20th	Day	17% 16% 26% 28% 11% 2	180
	21st to end	Day	18% 19% 21% 30% 11% 2	198
January	1st to 10th	Night	19% 21% 20% 25% 13% 2	760
	11th to 20th	Night	17% 17% 20% 28% 15% 2	760
	21st to end	Night	17% 14% 19% 31% 16% 3	836
February	1st to 10th	Night	16% 17% 27% 25% 14% 1	760
	11th to 20th	Night	15% 17% 23% 29% 14% 2	744
	21st to end	Night	17% 20% 22% 27% 13% 2	628
March	1st to 10th	Night	14% 18% 23% 30% 14% 1	760
	11th to 20th	Night	11% 17% 24% 30% 16% 2	760
	21st to end	Night	12% 21% 29% 26% 11% 1	836
April	1st to 10th	Night	14% 16% 28% 28% 13% 2	760
	11th to 20th	Night	11% 20% 30% 25% 12% 3	751
	21st to end	Night	10% 17% 34% 25% 12% 2	537
May	1st to 10th	Night	9% 18% 28% 29% 13% 2	380
	11th to 20th	Night	11% 11% 24% 31% 20% 3	374
	21st to end	Night	9% 10% 26% 36% 16% 3	411
June	1st to 10th	Night	9% 11% 32% 31% 15% 1	380
	11th to 20th	Night	9% 18% 34% 28% 11% 1	380
	21st to end	Night	5% 11% 33% 29% 20% 2	380
July	1st to 10th	Night	4 9% 29% 41% 17% 1	370
	11th to 20th	Night	1 8% 36% 36% 17% 1	368
	21st to end	Night	2 9% 29% 33% 27% 1	416
August	1st to 10th	Night	2 6% 23% 38% 28% 3	378
	11th to 20th	Night	3 3 21% 33% 32% 7%	519
	21st to end	Night	5% 11% 25% 32% 23% 4	817
September	1st to 10th	Night	5% 8% 24% 33% 26% 4	760
	11th to 20th	Night	7% 9% 20% 29% 28% 8%	760
	21st to end	Night	9% 11% 21% 33% 21% 5%	760
October	1st to 10th	Night	12% 9% 21% 33% 22% 3	760
	11th to 20th	Night	12% 14% 20% 29% 20% 5%	760
	21st to end	Night	17% 16% 24% 27% 13% 3	836
November	1st to 10th	Night	16% 16% 24% 33% 11% 1	760
	11th to 20th	Night	16% 19% 25% 25% 13% 3	760
	21st to end	Night	14% 18% 23% 27% 15% 3	760
December	1st to 10th	Night	16% 14% 24% 29% 14% 3	760
	11th to 20th	Night	18% 14% 26% 31% 10%	760
	21st to end	Night	17% 21% 23% 32% 7% 1	836

Page generated at 2024-11-02 23:11:16. Version ac07

Copyright © 2024 Attilla Danko.