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 2026-05-02.

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%	131714
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	130800
Transparency	Day	37% 6% 12% 23% 17% 4	135307
	Night	38% 5% 11% 23% 18% 4	135277
Seeing	Day	17% 11% 26% 25% 15% 5%	16948
	Night	17% 11% 28% 29% 13% 2	26607

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	14% 5% 2 6% 4 4 4 4 5% 6% 48%	4879
	11th to 20th	Day	14% 8% 2 5% 3 3 3 2 3 4 52%	5280
	21st to end	Day	13% 7% 3 6% 4 4 4 4 4 6% 46%	5780
February	1st to 10th	Day	14% 7% 3 6% 5% 5% 5% 4 4 7% 41%	1890
	11th to 20th	Day	19% 7% 2 5% 3 3 4 3 6% 6% 41%	1926
	21st to end	Day	18% 7% 2 5% 4 5% 5% 3 5% 6% 39%	1730
March	1st to 10th	Day	18% 6% 2 5% 4 4 5% 4 5% 8% 40%	4951
	11th to 20th	Day	11% 6% 2 5% 3 3 4 3 5% 6% 51%	5090
	21st to end	Day	17% 6% 2 6% 4 5% 4 4 5% 7% 41%	5693
April	1st to 10th	Day	11% 6% 3 5% 3 4 5% 3 5% 8% 46%	2520
	11th to 20th	Day	12% 5% 2 6% 4 3 4 3 5% 7% 48%	2494
	21st to end	Day	15% 5% 3 5% 4 4 4 4 6% 7% 43%	2520
May	1st to 10th	Day	18% 7% 2 6% 4 5% 5% 4 6% 10% 32%	5688
	11th to 20th	Day	19% 6% 2 6% 4 4 4 4 7% 10% 33%	6106
	21st to end	Day	14% 5% 2 6% 4 4 5% 4 6% 9% 40%	6934
June	1st to 10th	Day	10% 4 2 5% 5% 5% 5% 4 6% 9% 45%	2800
	11th to 20th	Day	9% 4 2 6% 4 4 5% 5% 7% 10% 43%	2800
	21st to end	Day	8% 4 1 5% 5% 5% 5% 4 8% 10% 44%	2800
July	1st to 10th	Day	6% 5% 2 6% 4 4 5% 4 8% 12% 44%	6360
	11th to 20th	Day	9% 6% 2 8% 5% 6% 6% 5% 10% 13% 29%	6090
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 7% 11% 41%	6424
August	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 5% 8% 11% 32%	4234
	11th to 20th	Day	9% 5% 2 7% 4 5% 6% 5% 8% 10% 39%	3954
	21st to end	Day	8% 5% 2 5% 4 4 5% 3 6% 10% 50%	4312
September	1st to 10th	Day	14% 4 2 6% 3 4 5% 3 5% 8% 48%	2400
	11th to 20th	Day	12% 6% 2 4 3 4 4 3 5% 8% 48%	2400
	21st to end	Day	19% 8% 3 5% 4 4 4 4 5% 7% 38%	2109
October	1st to 10th	Day	16% 6% 2 5% 3 3 3 3 4 7% 49%	2000
	11th to 20th	Day	16% 6% 2 4 3 3 3 3 4 5% 53%	2000
	21st to end	Day	14% 5% 2 5% 3 3 3 3 5% 6% 52%	2200
November	1st to 10th	Day	11% 5% 1 4 4 3 3 3 4 7% 54%	1962
	11th to 20th	Day	14% 6% 2 4 4 3 3 4 5% 6% 51%	1890
	21st to end	Day	15% 6% 2 5% 4 4 3 3 4 5% 51%	1700
December	1st to 10th	Day	12% 6% 2 5% 3 3 4 3 6% 7% 49%	2680
	11th to 20th	Day	17% 8% 3 5% 4 3 3 2 4 7% 47%	3070
	21st to end	Day	14% 8% 2 6% 4 4 4 3 6% 8% 42%	4048
January	1st to 10th	Night	12% 7% 2 6% 3 3 4 4 6% 7% 46%	8011
	11th to 20th	Night	14% 7% 2 5% 3 3 3 2 4 4 53%	7680
	21st to end	Night	14% 6% 2 5% 4 4 4 3 4 6% 47%	8401
February	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 5% 6% 44%	2730
	11th to 20th	Night	19% 8% 2 5% 3 4 3 3 4 5% 44%	2579
	21st to end	Night	16% 8% 2 4 4 4 4 3 5% 6% 44%	2076
March	1st to 10th	Night	17% 6% 2 5% 3 3 3 3 4 6% 47%	5119
	11th to 20th	Night	11% 6% 2 4 3 3 3 3 5% 7% 51%	5090
	21st to end	Night	13% 7% 2 6% 4 4 4 4 5% 7% 46%	5480
April	1st to 10th	Night	15% 7% 2 5% 4 4 4 4 4 8% 44%	2100
	11th to 20th	Night	11% 5% 3 6% 4 3 3 3 5% 7% 49%	2075
	21st to end	Night	17% 4 2 5% 4 3 3 3 6% 8% 44%	2100
May	1st to 10th	Night	18% 9% 3 8% 4 5% 5% 4 6% 8% 32%	4272
	11th to 20th	Night	21% 6% 3 6% 4 4 4 4 6% 8% 32%	3771
	21st to end	Night	16% 8% 2 6% 5% 4 5% 4 6% 9% 36%	3920
June	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 4 7% 10% 42%	1600
	11th to 20th	Night	12% 5% 2 6% 5% 4 4 5% 7% 9% 41%	1600
	21st to end	Night	8% 5% 2 5% 5% 5% 5% 4 6% 12% 43%	1600
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 5% 8% 10% 38%	3598
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 5% 9% 11% 30%	3863
	21st to end	Night	7% 6% 2 7% 6% 6% 6% 5% 7% 10% 38%	4427
August	1st to 10th	Night	15% 7% 3 7% 5% 4 5% 4 7% 9% 34%	2915
	11th to 20th	Night	10% 7% 3 8% 5% 5% 6% 4 7% 10% 35%	3062
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	3586
September	1st to 10th	Night	13% 6% 2 6% 4 4 3 4 6% 7% 46%	2000
	11th to 20th	Night	11% 6% 2 6% 4 3 4 4 5% 8% 48%	2000
	21st to end	Night	21% 7% 2 6% 4 4 4 4 4 7% 37%	2287
October	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 5% 6% 47%	2400
	11th to 20th	Night	16% 4 2 6% 3 3 3 3 4 6% 50%	2400
	21st to end	Night	14% 5% 2 5% 4 4 4 3 5% 6% 49%	2640
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 4 5% 54%	2555
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 4 6% 49%	2730
	21st to end	Night	12% 5% 2 4 4 4 4 4 5% 7% 51%	2918
December	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 54%	4720
	11th to 20th	Night	20% 6% 2 6% 4 4 4 3 5% 6% 40%	5345
	21st to end	Night	15% 7% 2 5% 4 4 4 4 5% 8% 42%	7150

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	38% 3 8% 25% 19% 6%	4880
	11th to 20th	Day	37% 3 5% 19% 27% 9%	5280
	21st to end	Day	40% 4 8% 29% 16% 3	5780
February	1st to 10th	Day	42% 5% 11% 25% 14% 3	1890
	11th to 20th	Day	42% 5% 8% 22% 19% 4	1935
	21st to end	Day	45% 5% 12% 18% 16% 4	1730
March	1st to 10th	Day	41% 6% 9% 20% 17% 7%	4951
	11th to 20th	Day	32% 5% 9% 26% 21% 7%	5090
	21st to end	Day	42% 5% 12% 18% 18% 6%	5693
April	1st to 10th	Day	35% 6% 12% 21% 21% 6%	2520
	11th to 20th	Day	34% 5% 11% 23% 21% 6%	2494
	21st to end	Day	38% 6% 11% 25% 14% 5%	2520
May	1st to 10th	Day	45% 9% 15% 19% 12% 1	5720
	11th to 20th	Day	44% 8% 13% 24% 10% 1	6110
	21st to end	Day	38% 8% 14% 22% 16% 2	6949
June	1st to 10th	Day	34% 8% 15% 27% 15% 2	2800
	11th to 20th	Day	33% 10% 15% 23% 17% 2	2800
	21st to end	Day	33% 9% 15% 24% 18% 2	2800
July	1st to 10th	Day	32% 9% 22% 20% 14% 4	6290
	11th to 20th	Day	43% 10% 21% 20% 6% 1	6016
	21st to end	Day	34% 7% 14% 22% 21% 1	6240
August	1st to 10th	Day	43% 7% 17% 25% 7%	4221
	11th to 20th	Day	37% 7% 16% 26% 13% 1	3993
	21st to end	Day	29% 6% 16% 28% 19% 2	4312
September	1st to 10th	Day	35% 8% 14% 21% 19% 4	2400
	11th to 20th	Day	35% 6% 10% 26% 20% 4	2400
	21st to end	Day	46% 6% 10% 20% 15% 3	2109
October	1st to 10th	Day	36% 5% 8% 19% 28% 5%	3260
	11th to 20th	Day	25% 3 6% 23% 32% 11%	3240
	21st to end	Day	22% 3 9% 28% 26% 12%	3538
November	1st to 10th	Day	32% 3 11% 27% 22% 4	1962
	11th to 20th	Day	34% 4 11% 23% 22% 6%	1890
	21st to end	Day	36% 3 10% 27% 21% 3	1700
December	1st to 10th	Day	35% 4 11% 27% 18% 6%	2680
	11th to 20th	Day	40% 3 13% 26% 15% 3	3066
	21st to end	Day	39% 6% 14% 25% 15% 1	4048
January	1st to 10th	Night	37% 3 10% 23% 22% 5%	8012
	11th to 20th	Night	36% 3 5% 24% 24% 9%	7680
	21st to end	Night	39% 3 7% 29% 19% 4	8401
February	1st to 10th	Night	41% 5% 10% 24% 18% 2	2730
	11th to 20th	Night	44% 3 8% 21% 19% 5%	2581
	21st to end	Night	40% 4 11% 22% 17% 6%	2076
March	1st to 10th	Night	38% 4 8% 22% 19% 8%	5119
	11th to 20th	Night	32% 4 9% 24% 23% 7%	5090
	21st to end	Night	38% 5% 9% 23% 19% 6%	5480
April	1st to 10th	Night	39% 5% 10% 20% 21% 5%	2100
	11th to 20th	Night	35% 5% 11% 22% 21% 5%	2075
	21st to end	Night	37% 6% 12% 25% 15% 5%	2100
May	1st to 10th	Night	49% 7% 14% 19% 8% 3	4302
	11th to 20th	Night	48% 7% 12% 21% 11% 1	3772
	21st to end	Night	43% 7% 14% 23% 12% 1	3927
June	1st to 10th	Night	36% 8% 13% 25% 17% 2	1600
	11th to 20th	Night	37% 9% 15% 23% 14% 2	1600
	21st to end	Night	33% 7% 16% 21% 20% 3	1600
July	1st to 10th	Night	38% 11% 19% 17% 12% 3	3560
	11th to 20th	Night	45% 10% 23% 17% 5% 1	3817
	21st to end	Night	39% 8% 15% 21% 16%	4297
August	1st to 10th	Night	45% 8% 17% 23% 8%	2904
	11th to 20th	Night	41% 8% 15% 22% 13% 1	3089
	21st to end	Night	32% 6% 11% 28% 22% 1	3586
September	1st to 10th	Night	36% 7% 13% 21% 16% 6%	2000
	11th to 20th	Night	34% 7% 9% 26% 22% 2	2000
	21st to end	Night	46% 7% 11% 17% 16% 3	2287
October	1st to 10th	Night	39% 4 9% 20% 21% 6%	3920
	11th to 20th	Night	25% 3 9% 22% 32% 9%	3899
	21st to end	Night	23% 3 7% 31% 27% 10%	4252
November	1st to 10th	Night	34% 3 9% 25% 23% 5%	2555
	11th to 20th	Night	37% 4 9% 21% 22% 7%	2730
	21st to end	Night	33% 4 11% 26% 22% 4	2918
December	1st to 10th	Night	31% 3 11% 29% 22% 4	4720
	11th to 20th	Night	45% 4 11% 20% 15% 5%	5348
	21st to end	Night	39% 6% 14% 26% 14% 1	7150

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	24% 20% 33% 17% 6%	260
	11th to 20th	Day	27% 26% 30% 15% 2	330
	21st to end	Day	21% 21% 37% 17% 4	363
February	1st to 10th	Day	23% 17% 37% 17% 6%	330
	11th to 20th	Day	27% 24% 34% 13% 2	413
	21st to end	Day	27% 16% 31% 21% 4	446
March	1st to 10th	Day	21% 19% 34% 20% 6%	540
	11th to 20th	Day	22% 19% 34% 18% 6% 1	540
	21st to end	Day	22% 17% 37% 19% 5% 1	594
April	1st to 10th	Day	21% 17% 35% 21% 5% 1	540
	11th to 20th	Day	16% 15% 32% 26% 8% 3	532
	21st to end	Day	20% 12% 31% 25% 9% 2	540
May	1st to 10th	Day	21% 12% 32% 21% 11% 3	507
	11th to 20th	Day	20% 7% 28% 27% 13% 4	527
	21st to end	Day	18% 6% 24% 27% 20% 6%	573
June	1st to 10th	Day	11% 5% 27% 29% 22% 7%	530
	11th to 20th	Day	11% 6% 22% 34% 20% 7%	530
	21st to end	Day	9% 4 22% 33% 24% 7%	530
July	1st to 10th	Day	10% 4 14% 31% 29% 12%	525
	11th to 20th	Day	5% 2 11% 36% 33% 12%	524
	21st to end	Day	10% 3 15% 33% 29% 10%	576
August	1st to 10th	Day	13% 2 17% 33% 24% 10%	526
	11th to 20th	Day	13% 4 14% 32% 26% 11%	519
	21st to end	Day	10% 3 18% 29% 25% 15%	583
September	1st to 10th	Day	14% 3 21% 26% 21% 15%	530
	11th to 20th	Day	15% 4 19% 28% 24% 11%	530
	21st to end	Day	26% 8% 23% 25% 12% 5%	530
October	1st to 10th	Day	19% 6% 21% 27% 20% 8%	530
	11th to 20th	Day	19% 11% 23% 27% 16% 5%	530
	21st to end	Day	15% 14% 30% 26% 10% 3	583
November	1st to 10th	Day	15% 11% 32% 26% 13% 4	485
	11th to 20th	Day	17% 16% 33% 21% 11% 2	430
	21st to end	Day	22% 15% 30% 19% 13% 1	240
December	1st to 10th	Day	18% 16% 38% 21% 5% 2	220
	11th to 20th	Day	24% 13% 33% 22% 8%	220
	21st to end	Day	24% 14% 32% 19% 10% 1	242
January	1st to 10th	Night	20% 22% 34% 20% 3	840
	11th to 20th	Night	22% 19% 32% 23% 5%	840
	21st to end	Night	20% 18% 37% 23% 2	924
February	1st to 10th	Night	20% 15% 38% 24% 3	840
	11th to 20th	Night	26% 19% 38% 16% 1	823
	21st to end	Night	22% 18% 35% 22% 2	692
March	1st to 10th	Night	20% 16% 36% 24% 3	840
	11th to 20th	Night	22% 15% 34% 23% 6%	840
	21st to end	Night	18% 15% 39% 23% 4	924
April	1st to 10th	Night	20% 16% 38% 23% 4	840
	11th to 20th	Night	14% 13% 34% 30% 9%	831
	21st to end	Night	19% 10% 32% 30% 8%	840
May	1st to 10th	Night	19% 10% 31% 27% 12% 1	706
	11th to 20th	Night	16% 7% 28% 35% 14% 1	486
	21st to end	Night	16% 5% 20% 34% 23% 1	433
June	1st to 10th	Night	11% 3 23% 41% 22% 1	400
	11th to 20th	Night	13% 4 19% 42% 20% 2	400
	21st to end	Night	8% 4 21% 44% 21% 3	400
July	1st to 10th	Night	10% 3 16% 37% 29% 5%	390
	11th to 20th	Night	5% 2 14% 38% 34% 7%	497
	21st to end	Night	7% 2 15% 41% 30% 5%	657
August	1st to 10th	Night	12% 1 14% 40% 29% 4	597
	11th to 20th	Night	13% 3 15% 36% 28% 5%	703
	21st to end	Night	12% 3 14% 34% 30% 6%	880
September	1st to 10th	Night	15% 3 17% 35% 25% 5%	800
	11th to 20th	Night	12% 4 15% 37% 27% 5%	800
	21st to end	Night	24% 6% 21% 30% 19% 1	800
October	1st to 10th	Night	20% 5% 18% 30% 22% 5%	800
	11th to 20th	Night	18% 12% 26% 27% 16% 1	800
	21st to end	Night	16% 13% 29% 27% 14% 1	880
November	1st to 10th	Night	16% 10% 29% 32% 12% 2	820
	11th to 20th	Night	20% 14% 33% 25% 8%	840
	21st to end	Night	15% 15% 33% 27% 9% 1	840
December	1st to 10th	Night	20% 16% 32% 22% 9% 1	840
	11th to 20th	Night	20% 13% 38% 25% 4	840
	21st to end	Night	20% 13% 32% 30% 5%	924

Page generated at 2026-04-29 02:21:43. Version ac07

Copyright © 2026 Attilla Danko.