King George Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the King George Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	104786
	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	104215
Transparency	Day	37% 6% 13% 24% 17% 4	108423
	Night	38% 6% 11% 23% 18% 4	108717
Seeing	Day	17% 10% 26% 26% 16% 5%	15218
	Night	17% 10% 28% 29% 13% 2	24849

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	17% 6% 2 4 3 3 3 3 5% 6% 49%	2671
	11th to 20th	Day	16% 10% 2 6% 4 4 4 3 4 5% 42%	2840
	21st to end	Day	16% 10% 3 7% 4 4 3 4 4 6% 39%	3124
February	1st to 10th	Day	14% 8% 3 6% 5% 5% 5% 4 5% 7% 39%	1710
	11th to 20th	Day	18% 6% 3 4 4 3 4 3 6% 6% 43%	1738
	21st to end	Day	19% 7% 2 6% 4 5% 5% 3 5% 7% 38%	1570
March	1st to 10th	Day	22% 7% 3 5% 4 4 4 3 5% 7% 36%	3371
	11th to 20th	Day	10% 4 2 4 4 4 4 4 6% 7% 52%	3480
	21st to end	Day	21% 6% 2 5% 4 4 3 3 5% 6% 39%	3892
April	1st to 10th	Day	11% 6% 3 5% 3 4 5% 3 5% 8% 46%	2280
	11th to 20th	Day	12% 6% 2 6% 4 3 4 3 5% 6% 49%	2254
	21st to end	Day	16% 5% 3 5% 4 4 4 4 6% 6% 43%	2280
May	1st to 10th	Day	21% 8% 2 6% 4 5% 5% 4 6% 8% 31%	3952
	11th to 20th	Day	20% 7% 2 6% 4 3 4 4 6% 9% 34%	4256
	21st to end	Day	9% 4 1 6% 4 5% 5% 5% 6% 10% 45%	4823
June	1st to 10th	Day	10% 4 2 5% 6% 5% 4 4 6% 9% 45%	2660
	11th to 20th	Day	8% 4 2 6% 4 4 5% 5% 7% 10% 44%	2660
	21st to end	Day	8% 4 1 5% 5% 5% 6% 5% 8% 10% 44%	2660
July	1st to 10th	Day	5% 4 2 6% 4 4 6% 5% 9% 12% 43%	4440
	11th to 20th	Day	10% 5% 2 5% 4 5% 6% 5% 9% 12% 36%	4254
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 5% 7% 10% 35%	4466
August	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 5% 8% 11% 32%	4104
	11th to 20th	Day	9% 5% 2 7% 4 5% 6% 5% 8% 10% 39%	3831
	21st to end	Day	8% 5% 2 5% 4 4 5% 3 6% 10% 50%	4180
September	1st to 10th	Day	13% 4 2 6% 3 4 5% 3 5% 8% 47%	2280
	11th to 20th	Day	11% 6% 2 4 3 4 4 3 5% 8% 48%	2280
	21st to end	Day	19% 8% 3 5% 4 4 4 4 5% 7% 38%	2004
October	1st to 10th	Day	16% 6% 2 5% 3 3 3 3 5% 6% 48%	1900
	11th to 20th	Day	15% 5% 2 4 3 3 3 3 4 5% 53%	1900
	21st to end	Day	14% 5% 2 5% 3 3 3 3 5% 6% 52%	2090
November	1st to 10th	Day	11% 5% 1 4 4 3 3 3 4 7% 54%	1867
	11th to 20th	Day	14% 6% 2 3 4 3 3 4 5% 6% 51%	1800
	21st to end	Day	14% 6% 2 5% 4 4 3 3 4 5% 51%	1619
December	1st to 10th	Day	11% 6% 2 5% 3 3 4 3 6% 6% 49%	2600
	11th to 20th	Day	17% 8% 3 5% 4 2 3 2 4 7% 46%	2990
	21st to end	Day	14% 8% 3 6% 4 4 4 3 6% 8% 42%	3960
January	1st to 10th	Night	15% 8% 2 6% 4 3 3 2 4 6% 47%	4404
	11th to 20th	Night	17% 8% 2 6% 3 3 3 3 4 5% 46%	4120
	21st to end	Night	19% 9% 2 6% 4 3 3 2 4 4 43%	4532
February	1st to 10th	Night	15% 7% 2 6% 4 4 4 4 5% 6% 44%	2470
	11th to 20th	Night	19% 8% 2 5% 4 4 3 3 4 5% 44%	2327
	21st to end	Night	17% 8% 2 4 4 4 4 3 5% 5% 44%	1884
March	1st to 10th	Night	23% 8% 3 6% 4 3 4 3 4 5% 38%	3479
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 5% 8% 51%	3480
	21st to end	Night	16% 7% 3 6% 3 3 3 3 4 6% 46%	3739
April	1st to 10th	Night	15% 7% 2 4 4 4 4 4 4 8% 43%	1900
	11th to 20th	Night	11% 6% 3 6% 4 3 3 3 5% 6% 49%	1875
	21st to end	Night	17% 4 2 5% 4 3 4 4 6% 9% 43%	1900
May	1st to 10th	Night	21% 9% 2 7% 4 4 4 3 5% 7% 33%	2971
	11th to 20th	Night	21% 6% 3 7% 5% 4 5% 4 6% 6% 33%	2635
	21st to end	Night	9% 5% 2 5% 5% 4 5% 4 7% 11% 43%	2732
June	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 3 7% 10% 42%	1520
	11th to 20th	Night	11% 5% 2 6% 5% 4 4 4 7% 10% 42%	1520
	21st to end	Night	8% 5% 3 5% 5% 5% 5% 4 7% 11% 43%	1520
July	1st to 10th	Night	6% 5% 3 6% 5% 5% 6% 5% 9% 10% 40%	2520
	11th to 20th	Night	8% 5% 2 7% 6% 6% 6% 5% 8% 10% 38%	2702
	21st to end	Night	9% 8% 3 8% 6% 6% 6% 5% 7% 8% 34%	3087
August	1st to 10th	Night	15% 7% 3 7% 5% 4 6% 4 7% 9% 33%	2825
	11th to 20th	Night	9% 7% 3 8% 5% 5% 6% 4 7% 10% 35%	2966
	21st to end	Night	10% 5% 2 5% 4 3 4 3 5% 8% 51%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 4 3 4 6% 7% 45%	1900
	11th to 20th	Night	10% 6% 2 6% 4 3 5% 4 5% 8% 48%	1900
	21st to end	Night	21% 7% 2 6% 4 3 4 4 4 6% 38%	2173
October	1st to 10th	Night	17% 6% 2 5% 4 3 4 3 5% 6% 46%	2280
	11th to 20th	Night	15% 5% 2 6% 3 3 3 3 4 6% 50%	2280
	21st to end	Night	14% 5% 1 5% 3 4 4 3 5% 7% 49%	2508
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 4 5% 54%	2430
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 4 6% 49%	2600
	21st to end	Night	12% 5% 2 4 3 4 4 4 5% 7% 51%	2779
December	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 54%	4580
	11th to 20th	Night	20% 7% 2 6% 4 4 4 3 5% 6% 40%	5205
	21st to end	Night	15% 7% 2 5% 4 4 4 4 6% 8% 41%	6996

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 8% 32% 17% 4	2672
	11th to 20th	Day	43% 4 8% 20% 19% 5%	2840
	21st to end	Day	46% 5% 11% 22% 14% 2	3124
February	1st to 10th	Day	44% 6% 10% 25% 13% 2	1710
	11th to 20th	Day	41% 5% 8% 23% 19% 4	1747
	21st to end	Day	46% 5% 13% 16% 16% 4	1570
March	1st to 10th	Day	46% 7% 10% 20% 13% 4	3371
	11th to 20th	Day	29% 6% 8% 28% 23% 6%	3480
	21st to end	Day	44% 6% 11% 19% 17% 4	3892
April	1st to 10th	Day	35% 6% 11% 22% 20% 6%	2280
	11th to 20th	Day	35% 5% 11% 22% 21% 6%	2254
	21st to end	Day	39% 7% 12% 23% 14% 5%	2280
May	1st to 10th	Day	48% 9% 11% 20% 10% 2	3987
	11th to 20th	Day	44% 9% 14% 23% 8% 1	4260
	21st to end	Day	30% 9% 16% 25% 18% 3	4837
June	1st to 10th	Day	34% 8% 15% 27% 14% 2	2660
	11th to 20th	Day	33% 10% 15% 24% 18% 2	2660
	21st to end	Day	33% 9% 15% 23% 17% 2	2660
July	1st to 10th	Day	30% 10% 24% 18% 13% 5%	4370
	11th to 20th	Day	36% 8% 20% 26% 8% 1	4180
	21st to end	Day	41% 9% 14% 19% 16% 1	4324
August	1st to 10th	Day	44% 8% 17% 24% 7%	4091
	11th to 20th	Day	37% 7% 15% 26% 14% 1	3870
	21st to end	Day	29% 6% 16% 28% 18% 2	4180
September	1st to 10th	Day	35% 8% 13% 20% 19% 4	2280
	11th to 20th	Day	34% 6% 10% 26% 20% 4	2280
	21st to end	Day	45% 6% 9% 20% 16% 3	2004
October	1st to 10th	Day	36% 5% 8% 19% 28% 5%	3160
	11th to 20th	Day	25% 3 6% 23% 32% 11%	3140
	21st to end	Day	21% 3 10% 29% 26% 12%	3428
November	1st to 10th	Day	33% 3 11% 27% 22% 4	1867
	11th to 20th	Day	34% 4 11% 23% 22% 6%	1800
	21st to end	Day	35% 3 10% 27% 21% 3	1619
December	1st to 10th	Day	34% 4 10% 27% 18% 6%	2600
	11th to 20th	Day	41% 3 13% 26% 15% 3	2986
	21st to end	Day	39% 6% 14% 25% 16% 1	3960
January	1st to 10th	Night	39% 4 8% 25% 19% 5%	4404
	11th to 20th	Night	41% 4 8% 24% 19% 4	4120
	21st to end	Night	45% 4 7% 25% 17% 2	4532
February	1st to 10th	Night	41% 6% 10% 25% 16% 2	2470
	11th to 20th	Night	43% 4 7% 21% 19% 6%	2329
	21st to end	Night	41% 4 11% 21% 17% 6%	1884
March	1st to 10th	Night	47% 5% 9% 22% 15% 2	3479
	11th to 20th	Night	31% 5% 10% 26% 24% 4	3480
	21st to end	Night	39% 5% 9% 22% 20% 6%	3739
April	1st to 10th	Night	39% 5% 10% 19% 22% 5%	1900
	11th to 20th	Night	35% 5% 11% 21% 21% 6%	1875
	21st to end	Night	38% 6% 12% 25% 14% 5%	1900
May	1st to 10th	Night	49% 8% 11% 20% 10% 2	3001
	11th to 20th	Night	48% 9% 12% 21% 9% 1	2636
	21st to end	Night	33% 9% 17% 25% 14% 2	2739
June	1st to 10th	Night	36% 8% 13% 26% 16% 2	1520
	11th to 20th	Night	36% 9% 15% 23% 15% 2	1520
	21st to end	Night	34% 7% 16% 21% 20% 3	1520
July	1st to 10th	Night	36% 11% 22% 18% 11% 3	2480
	11th to 20th	Night	38% 8% 23% 23% 8% 1	2653
	21st to end	Night	45% 8% 14% 19% 13%	2988
August	1st to 10th	Night	45% 8% 17% 22% 8%	2814
	11th to 20th	Night	41% 8% 15% 22% 13% 1	2993
	21st to end	Night	32% 6% 11% 28% 22% 1	3476
September	1st to 10th	Night	37% 7% 13% 20% 16% 6%	1900
	11th to 20th	Night	34% 7% 10% 25% 22% 2	1900
	21st to end	Night	45% 7% 10% 17% 17% 4	2173
October	1st to 10th	Night	40% 5% 9% 20% 20% 6%	3800
	11th to 20th	Night	24% 3 9% 22% 32% 9%	3779
	21st to end	Night	22% 3 7% 32% 27% 10%	4120
November	1st to 10th	Night	35% 3 9% 26% 22% 5%	2430
	11th to 20th	Night	37% 4 9% 21% 22% 7%	2600
	21st to end	Night	33% 4 11% 26% 22% 4	2779
December	1st to 10th	Night	30% 3 11% 29% 23% 4	4580
	11th to 20th	Night	46% 4 11% 20% 14% 5%	5208
	21st to end	Night	39% 6% 14% 26% 14% 1	6996

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	22% 21% 34% 17% 6%	224
	11th to 20th	Day	27% 24% 29% 17% 2	270
	21st to end	Day	21% 20% 38% 16% 5%	297
February	1st to 10th	Day	22% 15% 38% 18% 6%	270
	11th to 20th	Day	25% 23% 35% 15% 2	345
	21st to end	Day	27% 17% 31% 20% 5%	382
March	1st to 10th	Day	20% 20% 34% 20% 6%	460
	11th to 20th	Day	22% 18% 34% 18% 6% 1	460
	21st to end	Day	22% 16% 35% 20% 5% 1	506
April	1st to 10th	Day	20% 17% 35% 21% 5% 2	460
	11th to 20th	Day	14% 14% 32% 27% 9% 4	452
	21st to end	Day	21% 13% 32% 24% 9% 2	460
May	1st to 10th	Day	22% 12% 30% 21% 12% 3	463
	11th to 20th	Day	20% 6% 29% 28% 13% 4	487
	21st to end	Day	17% 5% 22% 29% 21% 6%	529
June	1st to 10th	Day	11% 5% 26% 28% 23% 7%	490
	11th to 20th	Day	10% 6% 22% 35% 20% 7%	490
	21st to end	Day	10% 4 23% 34% 22% 6%	490
July	1st to 10th	Day	10% 3 14% 31% 29% 12%	485
	11th to 20th	Day	5% 2 11% 36% 33% 12%	484
	21st to end	Day	10% 3 16% 34% 27% 10%	532
August	1st to 10th	Day	12% 2 17% 33% 26% 11%	486
	11th to 20th	Day	11% 4 15% 33% 26% 12%	479
	21st to end	Day	10% 4 16% 29% 26% 15%	539
September	1st to 10th	Day	13% 3 20% 26% 22% 16%	490
	11th to 20th	Day	14% 3 19% 29% 24% 11%	490
	21st to end	Day	26% 8% 22% 25% 13% 5%	490
October	1st to 10th	Day	20% 6% 21% 27% 20% 7%	490
	11th to 20th	Day	18% 9% 23% 29% 17% 5%	490
	21st to end	Day	15% 12% 31% 27% 11% 4	539
November	1st to 10th	Day	15% 9% 31% 27% 14% 4	450
	11th to 20th	Day	17% 15% 34% 21% 12% 2	400
	21st to end	Day	21% 15% 32% 19% 13% 1	219
December	1st to 10th	Day	17% 16% 39% 21% 5% 3	200
	11th to 20th	Day	24% 13% 33% 22% 9% 1	200
	21st to end	Day	25% 13% 30% 21% 10% 1	220
January	1st to 10th	Night	20% 22% 35% 19% 3	785
	11th to 20th	Night	22% 18% 31% 24% 5%	760
	21st to end	Night	21% 17% 36% 24% 2	836
February	1st to 10th	Night	19% 14% 38% 25% 4	760
	11th to 20th	Night	25% 18% 39% 16% 2	743
	21st to end	Night	23% 18% 34% 23% 3	628
March	1st to 10th	Night	20% 16% 37% 24% 3	760
	11th to 20th	Night	23% 14% 35% 22% 6% 1	760
	21st to end	Night	19% 14% 39% 24% 4	836
April	1st to 10th	Night	19% 15% 38% 23% 4	760
	11th to 20th	Night	15% 11% 34% 30% 9%	751
	21st to end	Night	20% 10% 31% 30% 9%	760
May	1st to 10th	Night	20% 9% 31% 27% 12% 1	666
	11th to 20th	Night	15% 6% 28% 35% 14% 1	462
	21st to end	Night	15% 4 20% 36% 24% 1	411
June	1st to 10th	Night	11% 2 23% 40% 23% 1	380
	11th to 20th	Night	12% 4 18% 43% 21% 2	380
	21st to end	Night	8% 3 22% 45% 20% 3	380
July	1st to 10th	Night	9% 4 16% 37% 30% 5%	370
	11th to 20th	Night	4 2 14% 38% 35% 7%	471
	21st to end	Night	8% 2 16% 41% 29% 5%	624
August	1st to 10th	Night	12% 1 13% 40% 30% 4	567
	11th to 20th	Night	12% 3 15% 36% 28% 5%	667
	21st to end	Night	12% 3 14% 34% 31% 7%	836
September	1st to 10th	Night	16% 3 16% 35% 25% 6%	760
	11th to 20th	Night	12% 4 15% 36% 28% 5%	760
	21st to end	Night	23% 6% 21% 29% 19% 1	760
October	1st to 10th	Night	20% 5% 19% 31% 21% 4	760
	11th to 20th	Night	17% 12% 26% 28% 16% 1	760
	21st to end	Night	16% 12% 29% 27% 14% 2	836
November	1st to 10th	Night	16% 9% 29% 32% 12% 2	780
	11th to 20th	Night	20% 13% 32% 26% 9%	800
	21st to end	Night	15% 14% 33% 27% 10% 1	800
December	1st to 10th	Night	20% 16% 32% 22% 9% 1	800
	11th to 20th	Night	20% 12% 38% 25% 4	800
	21st to end	Night	20% 13% 32% 31% 5%	880

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