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 2024-01-17.

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% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	74712
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 44%	75123
Transparency	Day	25% 37% 8% 16% 11% 2	74423
	Night	26% 37% 7% 16% 12% 2	74931
Seeing	Day	17% 10% 26% 26% 16% 6%	13934
	Night	17% 10% 28% 29% 14% 2	23590

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% 7% 3 5% 4 3 4 4 6% 6% 44%	1584
	11th to 20th	Day	17% 8% 2 5% 4 2 3 4 5% 7% 42%	1674
	21st to end	Day	16% 6% 3 6% 5% 3 4 4 5% 6% 44%	1782
February	1st to 10th	Day	14% 8% 3 5% 5% 4 5% 5% 4 7% 38%	1620
	11th to 20th	Day	19% 5% 3 4 4 3 4 4 5% 6% 43%	1644
	21st to end	Day	19% 7% 2 5% 5% 3 6% 4 5% 7% 38%	1480
March	1st to 10th	Day	13% 6% 2 4 4 2 4 3 5% 6% 51%	1941
	11th to 20th	Day	17% 5% 2 4 5% 3 4 5% 5% 6% 44%	1980
	21st to end	Day	17% 7% 3 5% 6% 3 4 5% 5% 7% 39%	2214
April	1st to 10th	Day	11% 5% 3 4 4 3 5% 4 5% 8% 47%	2160
	11th to 20th	Day	12% 4 3 5% 5% 2 4 4 5% 7% 49%	2134
	21st to end	Day	16% 5% 3 4 4 3 5% 5% 6% 6% 43%	2160
May	1st to 10th	Day	15% 5% 2 4 4 3 5% 5% 5% 9% 41%	2263
	11th to 20th	Day	17% 5% 3 5% 4 3 4 6% 6% 9% 39%	2392
	21st to end	Day	12% 5% 2 5% 6% 3 5% 5% 6% 9% 42%	2725
June	1st to 10th	Day	11% 3 2 5% 6% 4 4 4 6% 10% 45%	2520
	11th to 20th	Day	9% 4 3 5% 5% 3 5% 6% 7% 10% 43%	2520
	21st to end	Day	8% 3 1 5% 5% 4 6% 6% 8% 9% 44%	2520
July	1st to 10th	Day	9% 5% 2 6% 5% 3 5% 6% 6% 10% 43%	2520
	11th to 20th	Day	5% 3 2 4 4 4 6% 6% 9% 13% 44%	2418
	21st to end	Day	9% 4 3 5% 6% 3 7% 6% 8% 11% 37%	2547
August	1st to 10th	Day	9% 5% 2 5% 6% 4 6% 7% 8% 11% 38%	2327
	11th to 20th	Day	11% 5% 3 6% 5% 3 6% 6% 7% 9% 38%	2188
	21st to end	Day	9% 6% 2 4 5% 4 5% 5% 6% 11% 43%	2376
September	1st to 10th	Day	14% 3 2 5% 4 3 5% 4 5% 8% 46%	2160
	11th to 20th	Day	10% 5% 2 4 4 3 4 4 5% 8% 49%	2160
	21st to end	Day	18% 7% 3 5% 4 3 4 5% 5% 7% 40%	1900
October	1st to 10th	Day	16% 6% 2 4 3 3 4 4 5% 7% 48%	1800
	11th to 20th	Day	16% 6% 2 4 4 2 3 3 4 5% 52%	1800
	21st to end	Day	14% 5% 2 5% 4 3 3 4 5% 6% 49%	1980
November	1st to 10th	Day	12% 5% 1 3 4 3 4 4 4 6% 54%	1772
	11th to 20th	Day	15% 5% 2 3 4 2 4 4 5% 5% 52%	1710
	21st to end	Day	15% 5% 2 4 5% 3 3 4 4 5% 51%	1539
December	1st to 10th	Day	16% 7% 2 4 4 2 5% 4 6% 7% 41%	1520
	11th to 20th	Day	16% 6% 2 4 4 2 3 3 4 7% 49%	1910
	21st to end	Day	16% 7% 3 5% 4 3 5% 4 6% 8% 38%	2772
January	1st to 10th	Night	17% 7% 2 5% 5% 2 3 3 4 7% 46%	2578
	11th to 20th	Night	16% 7% 3 6% 5% 3 4 4 5% 5% 40%	2430
	21st to end	Night	16% 6% 2 4 5% 2 4 4 4 5% 47%	2574
February	1st to 10th	Night	16% 6% 3 5% 5% 3 4 5% 4 6% 43%	2340
	11th to 20th	Night	18% 8% 3 4 4 3 3 3 4 5% 44%	2201
	21st to end	Night	18% 7% 2 4 4 3 4 3 5% 5% 44%	1776
March	1st to 10th	Night	14% 5% 3 4 4 2 4 3 4 6% 50%	2016
	11th to 20th	Night	19% 6% 2 4 4 3 3 4 6% 7% 43%	1980
	21st to end	Night	16% 6% 3 6% 4 3 4 5% 5% 7% 42%	2141
April	1st to 10th	Night	15% 6% 3 4 4 3 4 5% 4 8% 44%	1800
	11th to 20th	Night	12% 5% 3 6% 4 3 3 4 5% 7% 49%	1775
	21st to end	Night	18% 4 2 4 5% 2 3 4 5% 9% 44%	1800
May	1st to 10th	Night	15% 7% 2 5% 4 3 4 5% 6% 8% 40%	1711
	11th to 20th	Night	15% 5% 3 5% 6% 2 6% 5% 6% 8% 38%	1499
	21st to end	Night	13% 5% 2 5% 6% 3 5% 5% 6% 11% 40%	1550
June	1st to 10th	Night	11% 5% 3 4 5% 2 5% 4 7% 10% 43%	1440
	11th to 20th	Night	12% 4 3 6% 6% 3 4 5% 7% 9% 41%	1440
	21st to end	Night	9% 4 2 5% 5% 4 5% 5% 7% 11% 43%	1440
July	1st to 10th	Night	8% 5% 3 5% 6% 4 6% 6% 7% 10% 41%	1440
	11th to 20th	Night	5% 4 2 6% 6% 3 6% 6% 8% 10% 44%	1538
	21st to end	Night	7% 4 2 5% 6% 4 8% 6% 8% 10% 39%	1771
August	1st to 10th	Night	9% 5% 3 6% 5% 3 6% 7% 7% 9% 40%	1611
	11th to 20th	Night	10% 6% 3 6% 7% 4 6% 5% 7% 10% 36%	1695
	21st to end	Night	10% 5% 3 5% 6% 3 5% 6% 6% 10% 41%	1980
September	1st to 10th	Night	14% 6% 2 5% 5% 3 3 5% 6% 8% 45%	1800
	11th to 20th	Night	9% 5% 2 6% 5% 2 4 5% 5% 7% 49%	1800
	21st to end	Night	19% 7% 2 5% 5% 2 4 5% 5% 6% 40%	2057
October	1st to 10th	Night	17% 6% 2 5% 4 3 4 4 5% 6% 46%	2160
	11th to 20th	Night	16% 5% 2 5% 4 2 3 3 4 6% 49%	2160
	21st to end	Night	15% 5% 1 5% 4 3 4 4 5% 7% 48%	2376
November	1st to 10th	Night	13% 6% 3 4 4 2 3 3 4 5% 54%	2305
	11th to 20th	Night	15% 6% 3 4 3 2 3 3 4 6% 50%	2470
	21st to end	Night	12% 4 2 3 4 3 4 5% 4 7% 51%	2640
December	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 7% 42%	2660
	11th to 20th	Night	18% 5% 2 5% 4 3 4 4 5% 6% 44%	3285
	21st to end	Night	16% 7% 2 5% 5% 3 5% 5% 6% 8% 38%	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	24% 41% 7% 19% 9% 1	1585
	11th to 20th	Day	27% 40% 7% 15% 11% 1	1674
	21st to end	Day	26% 37% 6% 17% 11% 2	1782
February	1st to 10th	Day	29% 36% 7% 18% 9% 2	1620
	11th to 20th	Day	26% 37% 5% 18% 12% 2	1653
	21st to end	Day	30% 36% 7% 13% 10% 3	1480
March	1st to 10th	Day	20% 36% 8% 19% 14% 3	1941
	11th to 20th	Day	26% 37% 7% 14% 11% 5%	1980
	21st to end	Day	30% 37% 7% 13% 10% 2	2214
April	1st to 10th	Day	21% 36% 8% 14% 14% 5%	2160
	11th to 20th	Day	24% 35% 6% 14% 15% 6%	2134
	21st to end	Day	26% 37% 7% 16% 11% 4	2160
May	1st to 10th	Day	26% 38% 9% 13% 12% 1	2263
	11th to 20th	Day	27% 39% 9% 14% 10% 2	2396
	21st to end	Day	23% 38% 10% 18% 9% 1	2725
June	1st to 10th	Day	22% 38% 11% 18% 11% 1	2520
	11th to 20th	Day	24% 38% 10% 16% 10% 2	2520
	21st to end	Day	22% 39% 9% 17% 11% 2	2520
July	1st to 10th	Day	23% 39% 9% 16% 10% 3	2450
	11th to 20th	Day	20% 40% 11% 17% 10% 2	2344
	21st to end	Day	23% 42% 10% 15% 10% 1	2405
August	1st to 10th	Day	25% 39% 10% 18% 9%	2314
	11th to 20th	Day	27% 38% 9% 15% 10% 1	2188
	21st to end	Day	27% 38% 10% 15% 8% 3	2376
September	1st to 10th	Day	22% 37% 9% 13% 15% 4	2160
	11th to 20th	Day	21% 37% 7% 19% 14% 3	2160
	21st to end	Day	28% 38% 6% 11% 15% 3	1900
October	1st to 10th	Day	24% 36% 6% 16% 16% 2	1800
	11th to 20th	Day	25% 36% 5% 19% 13% 2	1800
	21st to end	Day	25% 37% 4 16% 16% 2	1980
November	1st to 10th	Day	17% 40% 7% 19% 15% 2	1772
	11th to 20th	Day	22% 39% 7% 16% 13% 3	1710
	21st to end	Day	24% 39% 7% 15% 13% 2	1539
December	1st to 10th	Day	24% 40% 8% 17% 10% 1	1520
	11th to 20th	Day	27% 32% 5% 23% 11% 3	1906
	21st to end	Day	32% 27% 10% 22% 9%	2772
January	1st to 10th	Night	25% 39% 7% 16% 12% 1	2578
	11th to 20th	Night	28% 40% 7% 13% 10% 1	2430
	21st to end	Night	27% 37% 6% 17% 13% 1	2574
February	1st to 10th	Night	27% 35% 6% 17% 14% 2	2340
	11th to 20th	Night	29% 37% 5% 14% 11% 4	2203
	21st to end	Night	28% 36% 6% 14% 12% 3	1776
March	1st to 10th	Night	22% 36% 6% 20% 14% 2	2016
	11th to 20th	Night	28% 37% 7% 14% 11% 2	1980
	21st to end	Night	29% 36% 6% 15% 10% 4	2141
April	1st to 10th	Night	27% 36% 7% 13% 14% 4	1800
	11th to 20th	Night	24% 36% 7% 12% 16% 5%	1775
	21st to end	Night	24% 37% 8% 18% 9% 4	1800
May	1st to 10th	Night	29% 37% 8% 14% 9% 2	1711
	11th to 20th	Night	28% 39% 8% 12% 11% 1	1500
	21st to end	Night	25% 39% 11% 16% 9% 1	1551
June	1st to 10th	Night	22% 39% 9% 19% 10% 1	1440
	11th to 20th	Night	26% 38% 9% 17% 9% 2	1440
	21st to end	Night	25% 37% 10% 13% 13% 2	1440
July	1st to 10th	Night	24% 41% 12% 13% 7% 3	1400
	11th to 20th	Night	23% 39% 11% 15% 10% 1	1489
	21st to end	Night	22% 40% 12% 16% 9%	1672
August	1st to 10th	Night	23% 39% 11% 18% 8%	1600
	11th to 20th	Night	30% 38% 9% 14% 8% 1	1695
	21st to end	Night	30% 37% 11% 14% 7% 2	1980
September	1st to 10th	Night	25% 36% 7% 13% 13% 5%	1800
	11th to 20th	Night	22% 38% 5% 17% 17% 2	1800
	21st to end	Night	28% 37% 7% 11% 14% 4	2057
October	1st to 10th	Night	25% 36% 5% 18% 14% 3	2160
	11th to 20th	Night	26% 36% 6% 17% 12% 2	2160
	21st to end	Night	25% 37% 5% 16% 15% 3	2376
November	1st to 10th	Night	20% 40% 4 17% 15% 3	2305
	11th to 20th	Night	24% 39% 7% 15% 13% 3	2470
	21st to end	Night	23% 39% 6% 16% 13% 3	2640
December	1st to 10th	Night	23% 40% 5% 17% 12% 1	2660
	11th to 20th	Night	29% 32% 6% 15% 15% 3	3288
	21st to end	Night	32% 26% 12% 20% 9% 1	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	21% 20% 34% 18% 7%	212
	11th to 20th	Day	28% 24% 29% 17% 2	258
	21st to end	Day	22% 20% 37% 16% 5%	264
February	1st to 10th	Day	24% 16% 39% 14% 6%	240
	11th to 20th	Day	25% 22% 36% 16% 1	311
	21st to end	Day	28% 18% 31% 19% 4	346
March	1st to 10th	Day	19% 21% 35% 20% 5%	420
	11th to 20th	Day	22% 18% 33% 20% 6% 1	420
	21st to end	Day	22% 17% 35% 19% 6% 1	462
April	1st to 10th	Day	20% 17% 34% 22% 6% 2	420
	11th to 20th	Day	14% 14% 31% 27% 9% 4	412
	21st to end	Day	21% 13% 31% 25% 8% 2	420
May	1st to 10th	Day	21% 12% 31% 21% 12% 3	423
	11th to 20th	Day	19% 6% 31% 27% 14% 4	447
	21st to end	Day	18% 5% 21% 28% 21% 6%	485
June	1st to 10th	Day	12% 4 25% 29% 23% 7%	450
	11th to 20th	Day	11% 7% 22% 33% 19% 7%	450
	21st to end	Day	10% 4 23% 34% 23% 7%	450
July	1st to 10th	Day	11% 3 15% 29% 29% 13%	445
	11th to 20th	Day	4 2 11% 36% 34% 13%	444
	21st to end	Day	10% 2 15% 34% 27% 10%	488
August	1st to 10th	Day	11% 2 16% 33% 27% 11%	446
	11th to 20th	Day	12% 4 13% 32% 27% 13%	439
	21st to end	Day	10% 4 16% 28% 26% 16%	495
September	1st to 10th	Day	14% 2 20% 25% 22% 17%	450
	11th to 20th	Day	13% 4 19% 29% 25% 11%	450
	21st to end	Day	24% 7% 23% 26% 14% 5%	450
October	1st to 10th	Day	20% 6% 20% 27% 21% 7%	450
	11th to 20th	Day	19% 8% 24% 28% 18% 4	450
	21st to end	Day	16% 13% 31% 27% 11% 3	495
November	1st to 10th	Day	16% 9% 30% 26% 15% 4	415
	11th to 20th	Day	17% 15% 33% 21% 13% 2	370
	21st to end	Day	19% 15% 31% 20% 14% 1	199
December	1st to 10th	Day	18% 16% 37% 21% 6% 3	180
	11th to 20th	Day	24% 13% 32% 22% 9% 1	180
	21st to end	Day	25% 13% 30% 20% 11% 1	198
January	1st to 10th	Night	21% 21% 35% 20% 4	760
	11th to 20th	Night	22% 18% 31% 24% 5%	748
	21st to end	Night	20% 18% 37% 23% 2	792
February	1st to 10th	Night	20% 15% 38% 23% 4	720
	11th to 20th	Night	25% 18% 39% 16% 2	703
	21st to end	Night	23% 18% 35% 22% 2	592
March	1st to 10th	Night	19% 16% 38% 23% 3	720
	11th to 20th	Night	23% 13% 35% 23% 6% 1	720
	21st to end	Night	19% 14% 39% 24% 5% 1	792
April	1st to 10th	Night	19% 15% 38% 24% 4	720
	11th to 20th	Night	15% 11% 33% 31% 10%	711
	21st to end	Night	21% 10% 30% 29% 9%	720
May	1st to 10th	Night	19% 9% 32% 27% 12% 1	631
	11th to 20th	Night	16% 6% 29% 35% 14% 1	438
	21st to end	Night	16% 3 19% 36% 24% 2	389
June	1st to 10th	Night	11% 2 23% 39% 23% 1	360
	11th to 20th	Night	13% 4 18% 42% 21% 2	360
	21st to end	Night	8% 3 21% 45% 21% 3	360
July	1st to 10th	Night	9% 3 17% 35% 30% 5%	350
	11th to 20th	Night	4 2 13% 37% 36% 7%	445
	21st to end	Night	7% 2 16% 40% 30% 5%	591
August	1st to 10th	Night	11% 1 12% 40% 31% 4	537
	11th to 20th	Night	13% 3 14% 36% 29% 5%	631
	21st to end	Night	12% 3 14% 33% 31% 7%	792
September	1st to 10th	Night	16% 3 15% 34% 26% 6%	720
	11th to 20th	Night	11% 4 15% 36% 28% 5%	720
	21st to end	Night	22% 5% 22% 30% 20% 1	720
October	1st to 10th	Night	20% 5% 18% 31% 22% 4	720
	11th to 20th	Night	18% 11% 26% 28% 16% 1	720
	21st to end	Night	17% 13% 29% 27% 14% 2	792
November	1st to 10th	Night	16% 9% 29% 32% 12% 2	740
	11th to 20th	Night	19% 13% 32% 26% 9%	760
	21st to end	Night	15% 14% 32% 28% 10% 1	760
December	1st to 10th	Night	21% 15% 31% 22% 10% 1	760
	11th to 20th	Night	20% 12% 39% 25% 4	760
	21st to end	Night	20% 13% 32% 31% 5%	836

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