Keeble Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Keeble Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	14% 6% 2 6% 4 4 4 4 6% 8% 42%	101072
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	97900
Transparency	Day	38% 6% 13% 23% 17% 4	104715
	Night	38% 6% 11% 22% 18% 4	102397
Seeing	Day	18% 11% 27% 25% 14% 5%	15115
	Night	17% 10% 29% 30% 13% 1	24736

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	18% 5% 2 4 3 3 3 2 4 5% 51%	2746
	11th to 20th	Day	15% 8% 3 6% 4 4 4 3 5% 5% 44%	2840
	21st to end	Day	16% 10% 3 8% 4 4 4 3 5% 5% 39%	3124
February	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 5% 7% 40%	1710
	11th to 20th	Day	20% 7% 2 5% 3 3 4 4 6% 5% 42%	1724
	21st to end	Day	19% 7% 3 6% 5% 5% 4 3 5% 6% 37%	1570
March	1st to 10th	Day	21% 9% 2 8% 4 4 4 3 5% 6% 36%	3435
	11th to 20th	Day	10% 4 2 4 3 4 4 4 6% 7% 52%	3480
	21st to end	Day	21% 6% 2 6% 4 5% 4 3 5% 6% 38%	3841
April	1st to 10th	Day	10% 6% 2 6% 4 3 3 4 5% 7% 51%	2280
	11th to 20th	Day	12% 6% 2 4 4 4 4 3 4 8% 48%	2254
	21st to end	Day	15% 6% 2 6% 5% 4 4 3 5% 7% 42%	2280
May	1st to 10th	Day	17% 8% 2 8% 5% 5% 5% 4 6% 8% 31%	3974
	11th to 20th	Day	20% 7% 2 6% 4 4 5% 4 6% 9% 32%	4130
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 46%	4823
June	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 5% 10% 44%	2660
	11th to 20th	Day	11% 4 1 5% 5% 5% 5% 5% 7% 10% 43%	2660
	21st to end	Day	8% 5% 2 6% 5% 4 6% 5% 7% 11% 42%	2660
July	1st to 10th	Day	6% 4 2 6% 4 5% 5% 5% 9% 12% 41%	4415
	11th to 20th	Day	11% 5% 2 6% 5% 5% 6% 5% 8% 12% 36%	4120
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 5% 7% 10% 35%	4466
August	1st to 10th	Day	15% 8% 3 7% 5% 5% 5% 5% 8% 11% 29%	4104
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 4 7% 10% 39%	3853
	21st to end	Day	8% 4 2 5% 3 4 4 3 6% 11% 49%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 5% 5% 4 6% 7% 45%	2280
	11th to 20th	Day	12% 7% 2 6% 4 3 4 3 5% 8% 46%	2280
	21st to end	Day	21% 7% 2 6% 4 4 4 3 4 6% 38%	1987
October	1st to 10th	Day	15% 5% 2 6% 5% 4 3 3 4 7% 47%	1900
	11th to 20th	Day	16% 4 1 4 3 3 3 3 5% 5% 53%	1900
	21st to end	Day	14% 5% 2 5% 3 2 3 2 4 6% 53%	2090
November	1st to 10th	Day	13% 5% 2 4 3 4 3 3 5% 6% 53%	1859
	11th to 20th	Day	14% 6% 2 5% 3 3 3 2 4 7% 49%	1710
	21st to end	Day	15% 5% 2 4 4 3 3 3 4 5% 52%	1535
December	1st to 10th	Day	16% 7% 2 5% 4 4 4 4 6% 8% 42%	1520
	11th to 20th	Day	17% 6% 2 4 3 3 3 2 4 5% 51%	1910
	21st to end	Day	17% 7% 2 7% 5% 4 4 3 6% 7% 40%	2772
January	1st to 10th	Night	14% 8% 2 5% 3 4 3 3 5% 6% 47%	4195
	11th to 20th	Night	16% 7% 2 6% 4 3 3 3 4 5% 46%	4120
	21st to end	Night	20% 9% 3 6% 4 3 3 3 3 4 43%	4532
February	1st to 10th	Night	15% 7% 2 5% 4 3 4 4 6% 6% 42%	2470
	11th to 20th	Night	19% 7% 2 5% 4 3 3 3 4 6% 43%	2342
	21st to end	Night	17% 6% 3 6% 4 4 3 3 5% 5% 46%	1879
March	1st to 10th	Night	22% 7% 3 5% 4 3 4 3 5% 6% 38%	3418
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 51%	3480
	21st to end	Night	15% 8% 3 5% 3 3 4 2 3 5% 49%	3790
April	1st to 10th	Night	13% 8% 2 5% 5% 4 4 2 4 7% 45%	1900
	11th to 20th	Night	11% 6% 2 5% 3 4 4 4 5% 8% 49%	1875
	21st to end	Night	15% 6% 2 6% 4 3 4 4 6% 8% 44%	1900
May	1st to 10th	Night	18% 7% 3 7% 4 5% 4 3 5% 9% 34%	2948
	11th to 20th	Night	22% 8% 3 7% 4 4 4 3 5% 6% 33%	2759
	21st to end	Night	10% 4 2 6% 4 4 5% 4 7% 10% 43%	2732
June	1st to 10th	Night	10% 5% 2 5% 5% 6% 5% 5% 7% 9% 41%	1520
	11th to 20th	Night	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	1520
	21st to end	Night	8% 5% 3 5% 5% 5% 5% 5% 6% 10% 44%	1520
July	1st to 10th	Night	7% 4 2 7% 5% 6% 6% 5% 8% 10% 40%	2541
	11th to 20th	Night	9% 6% 2 6% 5% 5% 6% 5% 9% 11% 36%	2840
	21st to end	Night	11% 8% 3 9% 7% 7% 6% 6% 7% 7% 30%	3087
August	1st to 10th	Night	15% 7% 3 8% 5% 5% 5% 5% 7% 10% 31%	2825
	11th to 20th	Night	10% 7% 2 7% 5% 5% 6% 5% 7% 9% 37%	2943
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 8% 47%	3476
September	1st to 10th	Night	13% 5% 2 6% 5% 4 4 4 6% 7% 43%	1900
	11th to 20th	Night	12% 6% 1 6% 4 3 5% 3 6% 8% 47%	1900
	21st to end	Night	21% 9% 3 6% 4 4 3 3 5% 6% 37%	2188
October	1st to 10th	Night	15% 6% 2 6% 3 3 4 3 5% 6% 47%	2280
	11th to 20th	Night	15% 6% 2 5% 4 4 3 2 4 6% 49%	2280
	21st to end	Night	13% 5% 2 5% 4 3 3 2 4 6% 53%	2508
November	1st to 10th	Night	13% 6% 2 6% 4 4 2 3 4 5% 53%	2289
	11th to 20th	Night	14% 6% 3 5% 4 3 3 3 4 5% 50%	2470
	21st to end	Night	13% 4 2 4 3 4 4 4 5% 6% 50%	2644
December	1st to 10th	Night	17% 8% 2 6% 4 4 4 4 4 6% 42%	2660
	11th to 20th	Night	18% 6% 2 5% 4 3 3 3 5% 5% 46%	3285
	21st to end	Night	15% 8% 2 6% 4 4 4 4 5% 7% 41%	4884

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	35% 4 6% 33% 17% 5%	2747
	11th to 20th	Day	41% 5% 7% 20% 21% 5%	2840
	21st to end	Day	47% 4 10% 20% 15% 3	3124
February	1st to 10th	Day	42% 5% 11% 26% 14% 3	1710
	11th to 20th	Day	41% 5% 7% 23% 19% 5%	1733
	21st to end	Day	48% 5% 10% 16% 17% 4	1570
March	1st to 10th	Day	47% 6% 10% 17% 14% 5%	3435
	11th to 20th	Day	28% 6% 9% 25% 23% 9%	3480
	21st to end	Day	46% 5% 11% 18% 17% 3	3841
April	1st to 10th	Day	33% 5% 12% 23% 19% 8%	2280
	11th to 20th	Day	35% 5% 11% 21% 22% 6%	2254
	21st to end	Day	42% 5% 11% 23% 14% 5%	2280
May	1st to 10th	Day	47% 9% 13% 19% 10% 2	4010
	11th to 20th	Day	46% 9% 13% 22% 9% 1	4134
	21st to end	Day	31% 8% 17% 24% 19% 2	4837
June	1st to 10th	Day	35% 7% 17% 26% 14% 1	2660
	11th to 20th	Day	35% 9% 16% 23% 16% 1	2660
	21st to end	Day	34% 8% 16% 23% 17% 2	2660
July	1st to 10th	Day	32% 11% 23% 18% 11% 5%	4345
	11th to 20th	Day	38% 8% 23% 23% 7% 1	4051
	21st to end	Day	43% 9% 13% 19% 16% 1	4324
August	1st to 10th	Day	46% 8% 18% 21% 6%	4091
	11th to 20th	Day	38% 8% 16% 25% 14%	3892
	21st to end	Day	30% 6% 16% 28% 18% 2	4180
September	1st to 10th	Day	37% 7% 15% 16% 21% 4	2280
	11th to 20th	Day	37% 6% 9% 25% 19% 4	2280
	21st to end	Day	48% 5% 9% 20% 15% 4	1987
October	1st to 10th	Day	36% 5% 8% 19% 28% 5%	3160
	11th to 20th	Day	25% 4 6% 20% 33% 13%	3140
	21st to end	Day	20% 3 9% 29% 26% 13%	3428
November	1st to 10th	Day	32% 4 9% 25% 25% 4	1859
	11th to 20th	Day	36% 3 10% 21% 23% 7%	1710
	21st to end	Day	34% 4 7% 26% 24% 5%	1535
December	1st to 10th	Day	39% 5% 12% 25% 14% 5%	1520
	11th to 20th	Day	37% 3 8% 29% 16% 7%	1906
	21st to end	Day	42% 6% 10% 27% 14% 1	2772
January	1st to 10th	Night	37% 5% 8% 24% 20% 5%	4195
	11th to 20th	Night	41% 4 7% 22% 22% 4	4120
	21st to end	Night	46% 4 6% 23% 17% 5%	4532
February	1st to 10th	Night	40% 5% 11% 25% 17% 3	2470
	11th to 20th	Night	43% 4 6% 21% 19% 6%	2344
	21st to end	Night	41% 4 9% 21% 17% 7%	1879
March	1st to 10th	Night	46% 5% 8% 22% 17% 2	3418
	11th to 20th	Night	33% 5% 7% 20% 27% 7%	3480
	21st to end	Night	39% 4 8% 22% 22% 5%	3790
April	1st to 10th	Night	39% 5% 8% 18% 22% 6%	1900
	11th to 20th	Night	33% 5% 12% 22% 22% 6%	1875
	21st to end	Night	39% 6% 11% 23% 16% 5%	1900
May	1st to 10th	Night	46% 7% 15% 18% 11% 2	2978
	11th to 20th	Night	49% 8% 12% 21% 9% 1	2760
	21st to end	Night	33% 9% 18% 24% 15% 1	2739
June	1st to 10th	Night	37% 9% 14% 25% 15% 1	1520
	11th to 20th	Night	36% 10% 17% 21% 16% 1	1520
	21st to end	Night	33% 9% 14% 23% 18% 4	1520
July	1st to 10th	Night	36% 12% 19% 19% 11% 3	2501
	11th to 20th	Night	37% 10% 24% 21% 6% 1	2786
	21st to end	Night	49% 10% 12% 16% 12%	2988
August	1st to 10th	Night	46% 9% 16% 22% 7%	2814
	11th to 20th	Night	39% 10% 16% 22% 13%	2970
	21st to end	Night	33% 7% 11% 28% 19% 1	3476
September	1st to 10th	Night	38% 8% 15% 19% 15% 6%	1900
	11th to 20th	Night	35% 6% 10% 25% 21% 3	1900
	21st to end	Night	47% 6% 9% 18% 16% 4	2188
October	1st to 10th	Night	39% 5% 10% 19% 22% 5%	3800
	11th to 20th	Night	25% 3 8% 22% 31% 12%	3779
	21st to end	Night	21% 3 6% 31% 26% 13%	4120
November	1st to 10th	Night	35% 4 9% 22% 24% 5%	2289
	11th to 20th	Night	37% 4 8% 20% 23% 9%	2470
	21st to end	Night	33% 5% 9% 26% 22% 5%	2644
December	1st to 10th	Night	43% 5% 9% 23% 16% 4	2660
	11th to 20th	Night	39% 5% 10% 20% 21% 5%	3288
	21st to end	Night	41% 5% 11% 25% 16% 2	4884

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	28% 21% 33% 14% 4	247
	11th to 20th	Day	30% 27% 29% 10% 3	270
	21st to end	Day	24% 23% 39% 12% 1	297
February	1st to 10th	Day	21% 27% 37% 12% 3	270
	11th to 20th	Day	33% 23% 32% 11% 1	331
	21st to end	Day	30% 18% 31% 18% 3	382
March	1st to 10th	Day	23% 20% 33% 18% 5%	460
	11th to 20th	Day	22% 23% 34% 16% 4 1	460
	21st to end	Day	25% 15% 38% 16% 5% 1	506
April	1st to 10th	Day	22% 21% 31% 19% 7% 1	460
	11th to 20th	Day	18% 14% 35% 21% 8% 4	452
	21st to end	Day	22% 15% 35% 21% 6% 2	460
May	1st to 10th	Day	19% 16% 31% 22% 10% 2	463
	11th to 20th	Day	23% 8% 29% 27% 11% 2	487
	21st to end	Day	18% 5% 23% 32% 17% 5%	529
June	1st to 10th	Day	10% 6% 29% 30% 21% 4	490
	11th to 20th	Day	12% 6% 26% 34% 17% 6%	490
	21st to end	Day	10% 6% 26% 32% 21% 4	490
July	1st to 10th	Day	9% 3 18% 34% 28% 8%	485
	11th to 20th	Day	6% 2 16% 42% 26% 8%	484
	21st to end	Day	8% 4 23% 34% 22% 9%	532
August	1st to 10th	Day	12% 4 20% 31% 25% 8%	486
	11th to 20th	Day	11% 3 19% 32% 26% 9%	479
	21st to end	Day	9% 5% 17% 31% 23% 15%	539
September	1st to 10th	Day	14% 4 17% 29% 20% 15%	490
	11th to 20th	Day	15% 4 19% 30% 21% 11%	490
	21st to end	Day	30% 8% 21% 27% 11% 3	490
October	1st to 10th	Day	19% 7% 22% 27% 17% 8%	490
	11th to 20th	Day	17% 11% 24% 27% 18% 2	490
	21st to end	Day	15% 11% 34% 27% 9% 5%	539
November	1st to 10th	Day	17% 9% 33% 24% 12% 4	454
	11th to 20th	Day	17% 15% 32% 24% 11% 1	370
	21st to end	Day	20% 16% 32% 22% 9% 2	195
December	1st to 10th	Day	21% 19% 37% 14% 7% 1	180
	11th to 20th	Day	21% 17% 35% 17% 9% 1	180
	21st to end	Day	24% 18% 30% 18% 9% 2	198
January	1st to 10th	Night	22% 17% 39% 19% 3	760
	11th to 20th	Night	21% 17% 35% 23% 4	760
	21st to end	Night	21% 17% 38% 23% 2	836
February	1st to 10th	Night	19% 14% 38% 25% 3	760
	11th to 20th	Night	25% 20% 36% 17% 1	743
	21st to end	Night	22% 19% 35% 20% 3	628
March	1st to 10th	Night	20% 17% 36% 25% 3	760
	11th to 20th	Night	23% 18% 34% 19% 5% 1	760
	21st to end	Night	18% 16% 39% 23% 4	836
April	1st to 10th	Night	18% 19% 38% 21% 3	760
	11th to 20th	Night	14% 14% 38% 26% 8%	751
	21st to end	Night	18% 9% 37% 30% 6%	760
May	1st to 10th	Night	18% 11% 35% 28% 7%	656
	11th to 20th	Night	19% 5% 33% 32% 11% 1	534
	21st to end	Night	14% 2 23% 38% 22% 1	411
June	1st to 10th	Night	11% 2 23% 43% 21%	380
	11th to 20th	Night	11% 4 22% 38% 23% 2	380
	21st to end	Night	8% 3 22% 48% 18% 1	380
July	1st to 10th	Night	10% 3 18% 40% 27% 3	378
	11th to 20th	Night	5% 1 13% 42% 34% 6%	552
	21st to end	Night	8% 2 20% 42% 25% 4	624
August	1st to 10th	Night	12% 2 13% 43% 28% 3	567
	11th to 20th	Night	13% 5% 12% 42% 25% 3	657
	21st to end	Night	11% 2 15% 37% 30% 5%	836
September	1st to 10th	Night	15% 2 14% 37% 28% 5%	760
	11th to 20th	Night	14% 4 14% 36% 29% 3	760
	21st to end	Night	26% 4 20% 31% 18% 1	760
October	1st to 10th	Night	18% 4 22% 31% 22% 4	760
	11th to 20th	Night	17% 9% 27% 31% 14% 2	760
	21st to end	Night	15% 10% 30% 29% 14% 1	836
November	1st to 10th	Night	17% 8% 29% 31% 12% 3	755
	11th to 20th	Night	18% 12% 32% 29% 9% 1	760
	21st to end	Night	14% 13% 33% 30% 9% 1	760
December	1st to 10th	Night	21% 13% 35% 23% 8% 1	760
	11th to 20th	Night	20% 11% 34% 29% 6%	760
	21st to end	Night	20% 14% 30% 32% 4	836

Page generated at 2024-11-01 22:47:50. Version ac07

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