Katherine Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Katherine Hill Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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% 43%	108619
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	109953
Transparency	Day	37% 6% 12% 24% 17% 4	112260
	Night	38% 5% 11% 23% 19% 4	114452
Seeing	Day	18% 11% 26% 25% 15% 6%	15321
	Night	17% 10% 29% 29% 13% 1	25030

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	15% 5% 2 4 3 3 4 3 5% 6% 50%	3827
	11th to 20th	Day	14% 8% 2 6% 3 4 3 3 3 5% 49%	4060
	21st to end	Day	15% 7% 3 6% 4 4 4 3 4 5% 45%	4466
February	1st to 10th	Day	14% 8% 2 7% 5% 4 5% 3 5% 6% 39%	1800
	11th to 20th	Day	19% 7% 2 5% 4 4 3 2 5% 6% 42%	1803
	21st to end	Day	18% 8% 2 6% 5% 5% 4 3 5% 7% 37%	1570
March	1st to 10th	Day	22% 7% 2 6% 4 4 5% 3 4 7% 36%	3422
	11th to 20th	Day	11% 4 2 5% 4 4 5% 3 5% 6% 51%	3480
	21st to end	Day	21% 7% 2 6% 4 3 4 4 5% 7% 38%	3846
April	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 6% 7% 46%	2280
	11th to 20th	Day	12% 6% 2 5% 5% 3 4 3 5% 6% 48%	2254
	21st to end	Day	17% 6% 2 5% 5% 4 4 3 6% 6% 41%	2280
May	1st to 10th	Day	21% 7% 3 6% 4 5% 4 4 7% 8% 30%	4012
	11th to 20th	Day	22% 7% 2 6% 4 3 4 4 6% 9% 32%	4199
	21st to end	Day	11% 4 2 5% 4 4 5% 4 8% 9% 45%	4823
June	1st to 10th	Day	11% 4 2 5% 5% 5% 4 4 6% 10% 44%	2660
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 5% 6% 9% 43%	2660
	21st to end	Day	8% 3 2 5% 5% 6% 5% 4 7% 10% 44%	2660
July	1st to 10th	Day	5% 4 2 6% 5% 4 5% 5% 8% 12% 43%	4440
	11th to 20th	Day	10% 5% 2 5% 5% 4 6% 5% 9% 13% 36%	4192
	21st to end	Day	11% 6% 2 8% 6% 6% 5% 5% 7% 8% 36%	4466
August	1st to 10th	Day	15% 5% 2 7% 5% 5% 5% 5% 7% 12% 32%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 9% 40%	3868
	21st to end	Day	9% 4 2 5% 3 4 4 4 7% 8% 50%	4180
September	1st to 10th	Day	14% 4 1 6% 4 4 4 4 6% 8% 46%	2280
	11th to 20th	Day	11% 6% 2 4 3 4 3 4 6% 8% 49%	2280
	21st to end	Day	21% 6% 2 6% 3 4 4 4 5% 6% 37%	1987
October	1st to 10th	Day	17% 5% 2 5% 4 4 4 3 4 6% 47%	1900
	11th to 20th	Day	17% 4 2 4 3 3 4 3 4 6% 52%	1900
	21st to end	Day	14% 5% 2 5% 3 3 3 3 4 7% 51%	2090
November	1st to 10th	Day	12% 4 1 4 4 4 4 3 5% 6% 53%	1895
	11th to 20th	Day	15% 6% 1 3 3 3 3 3 5% 6% 51%	1785
	21st to end	Day	16% 5% 1 5% 4 3 3 3 5% 5% 50%	1600
December	1st to 10th	Day	12% 5% 2 5% 3 4 4 4 5% 7% 50%	2600
	11th to 20th	Day	18% 8% 2 5% 3 2 3 2 4 6% 46%	2990
	21st to end	Day	17% 6% 2 6% 5% 4 4 3 6% 7% 40%	3960
January	1st to 10th	Night	13% 6% 2 5% 3 4 3 3 4 5% 52%	6101
	11th to 20th	Night	13% 7% 2 5% 3 2 2 2 4 5% 54%	5900
	21st to end	Night	15% 7% 3 6% 4 3 3 2 4 5% 48%	6490
February	1st to 10th	Night	16% 7% 2 5% 4 4 4 3 6% 6% 42%	2600
	11th to 20th	Night	20% 7% 2 6% 4 3 2 2 4 5% 44%	2481
	21st to end	Night	16% 8% 3 5% 4 3 4 3 5% 6% 44%	1885
March	1st to 10th	Night	21% 7% 3 6% 4 3 4 3 5% 5% 39%	3428
	11th to 20th	Night	13% 5% 2 4 3 3 4 3 5% 8% 50%	3480
	21st to end	Night	15% 8% 2 6% 4 4 3 3 4 5% 47%	3771
April	1st to 10th	Night	15% 7% 2 5% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Night	11% 5% 2 6% 6% 3 4 3 5% 6% 50%	1875
	21st to end	Night	18% 4 1 5% 4 3 5% 4 6% 8% 43%	1900
May	1st to 10th	Night	21% 10% 2 7% 5% 4 4 3 5% 8% 32%	2910
	11th to 20th	Night	23% 9% 2 6% 4 4 4 4 5% 7% 33%	2690
	21st to end	Night	11% 4 2 6% 4 5% 5% 4 7% 10% 43%	2732
June	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 4 7% 11% 42%	1520
	11th to 20th	Night	11% 5% 2 7% 5% 5% 5% 5% 7% 8% 42%	1520
	21st to end	Night	9% 5% 1 5% 5% 5% 5% 5% 7% 10% 44%	1520
July	1st to 10th	Night	7% 5% 2 6% 5% 6% 5% 5% 7% 10% 42%	2520
	11th to 20th	Night	8% 5% 2 7% 6% 5% 5% 5% 7% 10% 39%	2764
	21st to end	Night	9% 7% 3 8% 6% 6% 6% 4 8% 8% 35%	3087
August	1st to 10th	Night	16% 6% 3 8% 5% 5% 4 5% 7% 9% 32%	2825
	11th to 20th	Night	10% 6% 3 9% 6% 5% 6% 5% 6% 8% 36%	2927
	21st to end	Night	11% 5% 2 5% 4 3 4 3 5% 8% 50%	3476
September	1st to 10th	Night	15% 5% 2 5% 4 4 5% 4 5% 7% 45%	1900
	11th to 20th	Night	11% 5% 3 5% 5% 3 3 3 4 8% 48%	1900
	21st to end	Night	21% 7% 2 6% 4 3 4 3 5% 7% 37%	2188
October	1st to 10th	Night	18% 5% 2 5% 4 4 4 3 4 6% 46%	2280
	11th to 20th	Night	16% 5% 2 6% 3 2 3 3 5% 6% 50%	2280
	21st to end	Night	14% 5% 2 5% 3 4 4 3 5% 6% 50%	2508
November	1st to 10th	Night	12% 6% 2 4 4 3 3 2 4 5% 54%	2401
	11th to 20th	Night	15% 6% 2 4 4 3 3 3 4 6% 50%	2613
	21st to end	Night	12% 4 1 4 4 4 4 4 5% 7% 50%	2800
December	1st to 10th	Night	10% 5% 2 5% 3 4 3 3 5% 6% 55%	4580
	11th to 20th	Night	21% 6% 2 5% 4 4 4 3 4 5% 41%	5205
	21st to end	Night	17% 6% 2 5% 4 4 4 4 5% 7% 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% 3 6% 25% 22% 9%	3828
	11th to 20th	Day	39% 4 6% 21% 20% 11%	4060
	21st to end	Day	42% 4 8% 26% 17% 3	4466
February	1st to 10th	Day	44% 5% 11% 25% 13% 2	1800
	11th to 20th	Day	43% 4 8% 23% 18% 4	1812
	21st to end	Day	46% 4 13% 15% 17% 4	1570
March	1st to 10th	Day	47% 5% 10% 20% 13% 5%	3422
	11th to 20th	Day	33% 4 8% 26% 24% 6%	3480
	21st to end	Day	46% 5% 11% 19% 15% 4	3846
April	1st to 10th	Day	36% 6% 11% 21% 19% 7%	2280
	11th to 20th	Day	35% 5% 11% 21% 21% 7%	2254
	21st to end	Day	41% 7% 10% 23% 15% 5%	2280
May	1st to 10th	Day	48% 8% 11% 20% 11% 1	4049
	11th to 20th	Day	46% 8% 12% 24% 9% 1	4203
	21st to end	Day	32% 9% 16% 24% 18% 2	4837
June	1st to 10th	Day	34% 7% 15% 27% 15% 1	2660
	11th to 20th	Day	34% 8% 13% 25% 17% 2	2660
	21st to end	Day	32% 8% 15% 25% 18% 2	2660
July	1st to 10th	Day	31% 11% 21% 19% 12% 6%	4370
	11th to 20th	Day	34% 9% 19% 28% 9% 1	4120
	21st to end	Day	42% 8% 12% 20% 18% 1	4324
August	1st to 10th	Day	43% 8% 16% 26% 7%	4091
	11th to 20th	Day	37% 8% 14% 27% 15% 1	3907
	21st to end	Day	29% 7% 16% 28% 18% 2	4180
September	1st to 10th	Day	35% 7% 13% 20% 20% 4	2280
	11th to 20th	Day	33% 5% 8% 28% 21% 4	2280
	21st to end	Day	46% 5% 9% 20% 18% 3	1987
October	1st to 10th	Day	36% 5% 7% 18% 30% 5%	3160
	11th to 20th	Day	25% 3 7% 26% 29% 10%	3140
	21st to end	Day	21% 3 9% 29% 26% 11%	3428
November	1st to 10th	Day	32% 4 10% 27% 22% 5%	1895
	11th to 20th	Day	34% 5% 10% 23% 22% 7%	1785
	21st to end	Day	36% 4 10% 26% 21% 3	1600
December	1st to 10th	Day	33% 6% 11% 27% 19% 5%	2600
	11th to 20th	Day	41% 3 14% 25% 13% 3	2986
	21st to end	Day	42% 5% 13% 23% 16% 1	3960
January	1st to 10th	Night	35% 3 7% 23% 27% 6%	6101
	11th to 20th	Night	34% 3 7% 24% 24% 8%	5900
	21st to end	Night	40% 3 7% 28% 19% 3	6490
February	1st to 10th	Night	41% 5% 11% 24% 17% 2	2600
	11th to 20th	Night	44% 3 7% 21% 19% 6%	2483
	21st to end	Night	41% 4 11% 21% 17% 6%	1885
March	1st to 10th	Night	46% 5% 8% 24% 14% 2	3428
	11th to 20th	Night	31% 5% 10% 25% 25% 4	3480
	21st to end	Night	39% 5% 8% 22% 20% 5%	3771
April	1st to 10th	Night	40% 6% 8% 19% 23% 4	1900
	11th to 20th	Night	35% 6% 11% 21% 22% 6%	1875
	21st to end	Night	39% 6% 11% 25% 13% 6%	1900
May	1st to 10th	Night	51% 7% 10% 19% 10% 3	2939
	11th to 20th	Night	49% 9% 11% 20% 9% 1	2691
	21st to end	Night	34% 8% 16% 26% 13% 3	2739
June	1st to 10th	Night	35% 8% 13% 27% 15% 2	1520
	11th to 20th	Night	37% 9% 15% 22% 14% 2	1520
	21st to end	Night	34% 8% 17% 20% 19% 3	1520
July	1st to 10th	Night	36% 10% 21% 18% 12% 3	2480
	11th to 20th	Night	38% 8% 20% 23% 9% 1	2713
	21st to end	Night	43% 9% 14% 19% 15%	2988
August	1st to 10th	Night	46% 8% 16% 21% 8% 1	2814
	11th to 20th	Night	43% 9% 11% 22% 14% 1	2954
	21st to end	Night	33% 5% 11% 29% 20% 1	3476
September	1st to 10th	Night	37% 8% 12% 20% 17% 6%	1900
	11th to 20th	Night	34% 5% 10% 25% 23% 3	1900
	21st to end	Night	45% 6% 12% 18% 16% 3	2188
October	1st to 10th	Night	40% 5% 9% 20% 19% 7%	3800
	11th to 20th	Night	24% 4 9% 22% 32% 9%	3779
	21st to end	Night	22% 4 8% 31% 26% 9%	4120
November	1st to 10th	Night	34% 4 9% 25% 23% 6%	2401
	11th to 20th	Night	36% 4 8% 22% 22% 7%	2613
	21st to end	Night	33% 4 10% 26% 22% 4	2800
December	1st to 10th	Night	31% 4 10% 29% 22% 4	4580
	11th to 20th	Night	45% 4 11% 19% 16% 5%	5208
	21st to end	Night	41% 6% 15% 23% 15% 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	25% 22% 30% 18% 4	250
	11th to 20th	Day	26% 25% 28% 18% 2	300
	21st to end	Day	21% 20% 38% 16% 4	330
February	1st to 10th	Day	23% 20% 37% 13% 6%	300
	11th to 20th	Day	29% 27% 31% 11% 2	350
	21st to end	Day	26% 19% 30% 21% 3 1	382
March	1st to 10th	Day	22% 19% 34% 20% 4	460
	11th to 20th	Day	22% 18% 35% 18% 5% 1	460
	21st to end	Day	23% 15% 36% 20% 6% 1	506
April	1st to 10th	Day	21% 19% 34% 20% 6% 1	460
	11th to 20th	Day	15% 16% 30% 25% 12% 3	452
	21st to end	Day	21% 14% 30% 24% 8% 2	460
May	1st to 10th	Day	22% 13% 31% 20% 11% 3	463
	11th to 20th	Day	19% 9% 31% 23% 14% 3	487
	21st to end	Day	18% 4 23% 25% 23% 7%	529
June	1st to 10th	Day	12% 5% 27% 27% 22% 7%	490
	11th to 20th	Day	11% 7% 22% 34% 19% 7%	490
	21st to end	Day	9% 4 22% 36% 20% 8%	490
July	1st to 10th	Day	11% 4 15% 30% 28% 12%	485
	11th to 20th	Day	5% 1 13% 35% 32% 13%	484
	21st to end	Day	11% 3 15% 35% 24% 11%	532
August	1st to 10th	Day	13% 3 16% 29% 28% 10%	486
	11th to 20th	Day	12% 4 16% 31% 25% 11%	479
	21st to end	Day	10% 3 17% 31% 23% 15%	539
September	1st to 10th	Day	17% 3 19% 25% 20% 17%	490
	11th to 20th	Day	14% 3 17% 30% 23% 12%	490
	21st to end	Day	27% 8% 24% 26% 10% 6%	490
October	1st to 10th	Day	22% 6% 19% 27% 18% 8%	490
	11th to 20th	Day	17% 12% 23% 28% 17% 4	490
	21st to end	Day	14% 12% 33% 27% 10% 4	539
November	1st to 10th	Day	16% 9% 32% 27% 14% 2	463
	11th to 20th	Day	19% 11% 37% 20% 11% 1	385
	21st to end	Day	21% 17% 30% 21% 12% 1	200
December	1st to 10th	Day	20% 16% 38% 21% 6% 2	200
	11th to 20th	Day	21% 13% 35% 24% 8%	200
	21st to end	Day	27% 13% 31% 21% 8%	220
January	1st to 10th	Night	21% 19% 37% 20% 3	800
	11th to 20th	Night	21% 15% 35% 25% 4	800
	21st to end	Night	19% 16% 40% 23% 2	880
February	1st to 10th	Night	21% 13% 39% 24% 3	800
	11th to 20th	Night	25% 19% 38% 16% 1	783
	21st to end	Night	22% 18% 35% 23% 2	629
March	1st to 10th	Night	20% 15% 38% 24% 3	760
	11th to 20th	Night	22% 16% 36% 20% 5% 1	760
	21st to end	Night	18% 15% 38% 24% 5%	836
April	1st to 10th	Night	17% 19% 39% 21% 4	760
	11th to 20th	Night	14% 11% 35% 30% 9%	751
	21st to end	Night	19% 11% 31% 30% 9%	760
May	1st to 10th	Night	21% 9% 30% 28% 11% 1	630
	11th to 20th	Night	18% 5% 30% 31% 16%	491
	21st to end	Night	16% 4 19% 37% 22% 1	411
June	1st to 10th	Night	10% 2 23% 42% 21% 1	380
	11th to 20th	Night	13% 4 21% 38% 23% 2	380
	21st to end	Night	10% 3 19% 48% 20% 1	380
July	1st to 10th	Night	9% 2 18% 38% 28% 4	370
	11th to 20th	Night	7% 2 13% 38% 34% 6%	505
	21st to end	Night	9% 1 16% 42% 28% 4	624
August	1st to 10th	Night	12% 2 12% 40% 31% 4	567
	11th to 20th	Night	12% 3 14% 41% 27% 4	641
	21st to end	Night	13% 3 13% 36% 29% 6%	836
September	1st to 10th	Night	18% 2 15% 33% 27% 5%	760
	11th to 20th	Night	12% 3 16% 35% 30% 4	760
	21st to end	Night	24% 5% 19% 32% 19% 1	760
October	1st to 10th	Night	20% 5% 20% 29% 21% 4	760
	11th to 20th	Night	16% 9% 28% 30% 16% 1	760
	21st to end	Night	16% 10% 32% 28% 13% 1	836
November	1st to 10th	Night	16% 10% 31% 30% 12% 2	780
	11th to 20th	Night	18% 13% 33% 28% 8%	800
	21st to end	Night	16% 12% 35% 26% 10% 1	800
December	1st to 10th	Night	20% 12% 35% 24% 9%	800
	11th to 20th	Night	20% 10% 39% 26% 5%	800
	21st to end	Night	19% 12% 33% 32% 4	880

Page generated at 2025-02-18 03:26:31. Version ac07

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