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 2026-06-16.

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%	137584
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 44%	134453
Transparency	Day	37% 6% 12% 23% 18% 4	141182
	Night	38% 5% 11% 23% 18% 4	138927
Seeing	Day	18% 11% 27% 25% 14% 5%	17092
	Night	17% 10% 29% 29% 13% 1	26714

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 6% 4 4 4 3 5% 6% 47%	4961
	11th to 20th	Day	14% 8% 2 6% 3 3 3 3 3 4 52%	5280
	21st to end	Day	14% 6% 2 6% 4 4 4 3 5% 6% 45%	5780
February	1st to 10th	Day	13% 7% 2 7% 5% 4 5% 3 5% 6% 41%	1890
	11th to 20th	Day	19% 7% 3 5% 4 3 4 2 5% 6% 41%	1896
	21st to end	Day	18% 8% 2 6% 5% 4 4 3 5% 6% 38%	1730
March	1st to 10th	Day	18% 6% 2 6% 4 4 4 4 5% 7% 40%	5031
	11th to 20th	Day	12% 6% 2 5% 3 4 4 3 5% 6% 51%	5090
	21st to end	Day	17% 6% 2 7% 4 4 4 4 5% 7% 41%	5632
April	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 7% 46%	2520
	11th to 20th	Day	12% 6% 2 5% 4 3 4 3 5% 6% 48%	2494
	21st to end	Day	16% 6% 2 5% 5% 4 4 3 6% 7% 41%	2520
May	1st to 10th	Day	16% 7% 3 6% 4 5% 5% 4 7% 8% 36%	7490
	11th to 20th	Day	18% 6% 2 5% 4 3 4 4 6% 10% 38%	7856
	21st to end	Day	21% 5% 2 6% 4 3 4 3 6% 7% 38%	9045
June	1st to 10th	Day	11% 4 2 5% 5% 5% 4 4 6% 10% 45%	2940
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 5% 6% 9% 43%	2870
	21st to end	Day	8% 3 2 5% 5% 6% 5% 4 7% 10% 45%	2800
July	1st to 10th	Day	7% 5% 2 6% 5% 4 5% 5% 7% 11% 43%	6360
	11th to 20th	Day	9% 6% 2 7% 6% 5% 7% 6% 10% 13% 29%	6000
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 42%	6424
August	1st to 10th	Day	15% 5% 2 7% 5% 5% 5% 4 7% 12% 33%	4234
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 9% 40%	3993
	21st to end	Day	9% 4 2 5% 3 4 4 4 7% 8% 50%	4312
September	1st to 10th	Day	14% 4 2 5% 4 4 4 4 6% 8% 47%	2400
	11th to 20th	Day	12% 6% 2 4 3 3 3 4 6% 8% 49%	2400
	21st to end	Day	21% 7% 2 6% 4 4 4 4 5% 6% 36%	2092
October	1st to 10th	Day	16% 5% 2 5% 4 4 4 3 4 6% 49%	2000
	11th to 20th	Day	17% 4 2 4 3 3 4 3 4 6% 52%	2000
	21st to end	Day	14% 5% 2 5% 3 3 3 3 4 7% 51%	2200
November	1st to 10th	Day	12% 4 1 4 4 4 4 3 5% 6% 53%	1992
	11th to 20th	Day	14% 6% 1 3 3 3 3 3 6% 6% 51%	1874
	21st to end	Day	16% 5% 2 5% 4 3 3 3 4 5% 50%	1680
December	1st to 10th	Day	12% 5% 2 5% 3 4 4 4 5% 7% 49%	2680
	11th to 20th	Day	17% 8% 2 5% 3 3 3 2 4 6% 46%	3070
	21st to end	Day	16% 7% 2 6% 5% 4 4 3 6% 7% 40%	4048
January	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 6% 6% 47%	7915
	11th to 20th	Night	14% 7% 2 5% 3 2 2 2 4 5% 54%	7680
	21st to end	Night	14% 6% 3 6% 4 4 4 3 4 5% 49%	8401
February	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 6% 6% 43%	2730
	11th to 20th	Night	20% 7% 2 6% 4 3 3 2 4 5% 43%	2608
	21st to end	Night	15% 8% 3 5% 4 4 4 3 5% 6% 44%	2076
March	1st to 10th	Night	16% 6% 2 5% 4 3 4 3 4 5% 48%	5039
	11th to 20th	Night	12% 6% 3 4 3 3 4 4 5% 7% 50%	5090
	21st to end	Night	12% 7% 2 6% 4 4 4 4 4 6% 46%	5527
April	1st to 10th	Night	15% 7% 3 5% 4 3 4 3 5% 7% 44%	2100
	11th to 20th	Night	11% 5% 2 5% 6% 3 4 3 5% 7% 49%	2075
	21st to end	Night	17% 4 1 5% 4 3 5% 3 6% 8% 43%	2100
May	1st to 10th	Night	17% 9% 2 7% 5% 4 5% 3 5% 8% 34%	5418
	11th to 20th	Night	19% 7% 2 6% 3 4 4 4 5% 8% 38%	5000
	21st to end	Night	23% 7% 2 7% 4 4 4 3 5% 8% 33%	5108
June	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 5% 6% 10% 43%	1680
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 5% 6% 8% 41%	1640
	21st to end	Night	9% 5% 1 5% 5% 5% 5% 5% 8% 10% 44%	1600
July	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 5% 7% 10% 40%	3598
	11th to 20th	Night	11% 7% 3 8% 6% 6% 6% 6% 7% 10% 30%	3953
	21st to end	Night	7% 6% 2 7% 6% 5% 6% 4 9% 9% 39%	4427
August	1st to 10th	Night	16% 6% 3 8% 5% 5% 4 5% 6% 9% 32%	2915
	11th to 20th	Night	11% 6% 3 9% 6% 5% 6% 5% 6% 8% 36%	3021
	21st to end	Night	11% 5% 2 5% 4 3 4 3 5% 8% 50%	3586
September	1st to 10th	Night	15% 5% 2 5% 4 4 5% 4 5% 7% 46%	2000
	11th to 20th	Night	11% 5% 3 6% 5% 4 4 3 4 8% 48%	2000
	21st to end	Night	21% 7% 2 6% 4 3 4 3 5% 7% 37%	2303
October	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 4 5% 47%	2400
	11th to 20th	Night	16% 5% 2 6% 3 3 3 3 5% 6% 50%	2400
	21st to end	Night	14% 5% 2 5% 3 4 4 3 5% 6% 50%	2640
November	1st to 10th	Night	12% 6% 2 4 4 3 3 2 4 5% 54%	2524
	11th to 20th	Night	15% 6% 2 4 4 3 4 3 4 6% 50%	2744
	21st to end	Night	12% 4 1 5% 4 4 4 4 5% 7% 50%	2940
December	1st to 10th	Night	10% 5% 2 5% 3 4 3 3 5% 6% 54%	4720
	11th to 20th	Night	21% 6% 2 5% 3 4 4 3 4 5% 42%	5345
	21st to end	Night	16% 6% 2 5% 4 4 4 4 5% 7% 41%	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% 4 9% 24% 19% 7%	4962
	11th to 20th	Day	37% 3 5% 20% 23% 11%	5280
	21st to end	Day	40% 4 7% 30% 15% 3	5780
February	1st to 10th	Day	43% 4 11% 25% 14% 3	1890
	11th to 20th	Day	44% 4 7% 23% 18% 4	1905
	21st to end	Day	45% 4 12% 18% 16% 4	1730
March	1st to 10th	Day	42% 5% 9% 20% 16% 8%	5031
	11th to 20th	Day	34% 4 9% 25% 21% 7%	5090
	21st to end	Day	42% 5% 11% 18% 17% 7%	5632
April	1st to 10th	Day	36% 6% 11% 21% 20% 6%	2520
	11th to 20th	Day	35% 5% 12% 21% 21% 6%	2494
	21st to end	Day	41% 6% 10% 24% 14% 4	2520
May	1st to 10th	Day	43% 8% 12% 21% 16% 1	7524
	11th to 20th	Day	39% 7% 12% 27% 14% 1	7860
	21st to end	Day	44% 7% 11% 19% 17% 3	9061
June	1st to 10th	Day	34% 7% 14% 26% 17% 2	2940
	11th to 20th	Day	34% 8% 14% 25% 17% 2	2870
	21st to end	Day	31% 8% 15% 25% 18% 2	2800
July	1st to 10th	Day	32% 10% 20% 20% 13% 5%	6290
	11th to 20th	Day	39% 12% 20% 22% 6% 1	5928
	21st to end	Day	35% 8% 13% 22% 22% 1	6240
August	1st to 10th	Day	43% 8% 16% 26% 7%	4221
	11th to 20th	Day	37% 8% 14% 26% 14% 1	4032
	21st to end	Day	29% 7% 16% 28% 18% 2	4312
September	1st to 10th	Day	34% 7% 14% 20% 20% 5%	2400
	11th to 20th	Day	33% 5% 9% 28% 21% 4	2400
	21st to end	Day	47% 5% 10% 19% 17% 2	2092
October	1st to 10th	Day	35% 5% 7% 19% 30% 5%	3260
	11th to 20th	Day	26% 3 7% 26% 29% 10%	3240
	21st to end	Day	22% 3 9% 28% 26% 12%	3538
November	1st to 10th	Day	32% 4 10% 27% 22% 5%	1992
	11th to 20th	Day	34% 5% 9% 23% 22% 6%	1874
	21st to end	Day	37% 4 10% 26% 20% 3	1680
December	1st to 10th	Day	34% 6% 11% 27% 18% 5%	2680
	11th to 20th	Day	41% 3 14% 26% 13% 4	3066
	21st to end	Day	42% 5% 13% 23% 16% 1	4048
January	1st to 10th	Night	37% 4 10% 23% 22% 4	7916
	11th to 20th	Night	35% 3 6% 22% 25% 9%	7680
	21st to end	Night	39% 3 6% 29% 19% 4	8401
February	1st to 10th	Night	41% 5% 10% 24% 18% 2	2730
	11th to 20th	Night	44% 3 8% 21% 18% 6%	2610
	21st to end	Night	41% 4 10% 21% 17% 6%	2076
March	1st to 10th	Night	38% 4 7% 24% 19% 8%	5039
	11th to 20th	Night	32% 5% 10% 24% 23% 7%	5090
	21st to end	Night	38% 5% 9% 22% 20% 6%	5527
April	1st to 10th	Night	39% 6% 9% 20% 22% 4	2100
	11th to 20th	Night	35% 5% 11% 22% 21% 5%	2075
	21st to end	Night	38% 6% 11% 25% 14% 5%	2100
May	1st to 10th	Night	48% 7% 12% 21% 10% 3	5447
	11th to 20th	Night	43% 7% 12% 24% 13% 1	5001
	21st to end	Night	50% 6% 10% 18% 13% 2	5115
June	1st to 10th	Night	35% 8% 12% 26% 17% 2	1680
	11th to 20th	Night	38% 9% 15% 22% 14% 2	1640
	21st to end	Night	34% 8% 16% 20% 19% 3	1600
July	1st to 10th	Night	39% 10% 18% 18% 13% 2	3560
	11th to 20th	Night	47% 11% 19% 17% 7% 1	3905
	21st to end	Night	37% 9% 15% 21% 17%	4297
August	1st to 10th	Night	46% 8% 16% 21% 8% 1	2904
	11th to 20th	Night	43% 9% 12% 22% 14% 1	3048
	21st to end	Night	33% 5% 11% 29% 20% 1	3586
September	1st to 10th	Night	36% 7% 11% 22% 17% 6%	2000
	11th to 20th	Night	35% 5% 10% 26% 22% 3	2000
	21st to end	Night	46% 6% 12% 17% 15% 3	2303
October	1st to 10th	Night	40% 5% 9% 20% 20% 6%	3920
	11th to 20th	Night	25% 4 9% 22% 32% 9%	3899
	21st to end	Night	22% 4 8% 31% 27% 9%	4252
November	1st to 10th	Night	34% 4 9% 25% 23% 6%	2524
	11th to 20th	Night	36% 4 8% 22% 23% 7%	2744
	21st to end	Night	33% 4 10% 26% 22% 4	2940
December	1st to 10th	Night	31% 4 10% 29% 22% 4	4720
	11th to 20th	Night	44% 4 11% 19% 16% 5%	5348
	21st to end	Night	40% 6% 15% 23% 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	25% 21% 31% 18% 5%	275
	11th to 20th	Day	27% 26% 28% 17% 2	330
	21st to end	Day	22% 21% 38% 16% 4	363
February	1st to 10th	Day	24% 20% 37% 14% 5%	330
	11th to 20th	Day	30% 26% 32% 11% 2	383
	21st to end	Day	26% 19% 31% 21% 3	446
March	1st to 10th	Day	22% 19% 35% 20% 4	540
	11th to 20th	Day	24% 19% 34% 18% 5% 1	540
	21st to end	Day	23% 15% 37% 18% 5% 1	594
April	1st to 10th	Day	22% 18% 33% 20% 6% 1	540
	11th to 20th	Day	17% 16% 31% 23% 11% 3	532
	21st to end	Day	21% 13% 31% 25% 9% 2	540
May	1st to 10th	Day	22% 14% 33% 19% 10% 3	543
	11th to 20th	Day	19% 12% 30% 23% 14% 3	567
	21st to end	Day	21% 6% 24% 22% 21% 6%	617
June	1st to 10th	Day	11% 5% 28% 28% 20% 7%	570
	11th to 20th	Day	11% 7% 23% 34% 18% 7%	550
	21st to end	Day	9% 4 21% 35% 22% 8%	530
July	1st to 10th	Day	11% 4 16% 31% 27% 11%	525
	11th to 20th	Day	5% 2 13% 35% 32% 13%	524
	21st to end	Day	11% 3 14% 35% 26% 11%	576
August	1st to 10th	Day	14% 3 17% 30% 27% 10%	526
	11th to 20th	Day	13% 4 16% 31% 25% 11%	519
	21st to end	Day	10% 3 18% 31% 22% 15%	583
September	1st to 10th	Day	17% 3 20% 26% 19% 16%	530
	11th to 20th	Day	14% 3 17% 31% 24% 11%	530
	21st to end	Day	27% 7% 24% 27% 9% 5%	530
October	1st to 10th	Day	21% 6% 19% 28% 18% 8%	530
	11th to 20th	Day	18% 13% 23% 26% 16% 3	530
	21st to end	Day	16% 13% 33% 26% 9% 3	583
November	1st to 10th	Day	15% 10% 34% 25% 13% 2	500
	11th to 20th	Day	20% 12% 37% 20% 10% 1	414
	21st to end	Day	22% 17% 29% 20% 11%	220
December	1st to 10th	Day	20% 15% 37% 21% 5% 1	220
	11th to 20th	Day	21% 13% 35% 24% 7%	220
	21st to end	Day	27% 13% 33% 19% 7%	242
January	1st to 10th	Night	20% 18% 38% 21% 3	840
	11th to 20th	Night	21% 16% 35% 24% 4	840
	21st to end	Night	19% 16% 40% 22% 2	924
February	1st to 10th	Night	21% 13% 38% 25% 3	840
	11th to 20th	Night	25% 19% 37% 17% 1	823
	21st to end	Night	21% 18% 37% 22% 2	692
March	1st to 10th	Night	20% 15% 38% 24% 3	840
	11th to 20th	Night	22% 16% 36% 20% 5% 1	840
	21st to end	Night	18% 16% 39% 23% 5%	924
April	1st to 10th	Night	17% 19% 38% 21% 4	840
	11th to 20th	Night	15% 12% 35% 29% 8%	831
	21st to end	Night	18% 10% 32% 31% 8%	840
May	1st to 10th	Night	21% 9% 32% 27% 10% 1	696
	11th to 20th	Night	18% 6% 31% 31% 15%	543
	21st to end	Night	18% 4 21% 35% 20% 1	455
June	1st to 10th	Night	9% 4 24% 41% 21% 1	420
	11th to 20th	Night	14% 4 20% 39% 21% 1	410
	21st to end	Night	10% 3 19% 47% 21% 1	400
July	1st to 10th	Night	10% 3 17% 38% 27% 4	390
	11th to 20th	Night	8% 2 13% 37% 34% 6%	533
	21st to end	Night	9% 1 16% 42% 28% 4	657
August	1st to 10th	Night	12% 2 12% 39% 30% 4	597
	11th to 20th	Night	13% 3 13% 41% 27% 4	675
	21st to end	Night	12% 3 15% 36% 29% 6%	880
September	1st to 10th	Night	17% 2 17% 33% 27% 5%	800
	11th to 20th	Night	12% 3 17% 35% 29% 4	800
	21st to end	Night	24% 5% 18% 33% 19% 1	800
October	1st to 10th	Night	20% 5% 20% 29% 23% 4	800
	11th to 20th	Night	17% 10% 28% 29% 16% 1	800
	21st to end	Night	16% 10% 32% 28% 13% 1	880
November	1st to 10th	Night	16% 10% 31% 30% 12% 2	820
	11th to 20th	Night	18% 13% 33% 28% 8%	840
	21st to end	Night	15% 13% 36% 26% 9% 1	840
December	1st to 10th	Night	20% 13% 36% 24% 8%	840
	11th to 20th	Night	20% 11% 38% 26% 5%	840
	21st to end	Night	20% 12% 33% 31% 4	924

Page generated at 2026-06-13 02:31:38. Version ac07

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