Hoback
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hoback clear sky chart from 2005-11-06 to 2026-08-30.

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	4 11% 4 8% 4 4 4 4 5% 7% 45%	153973
	Night	4 12% 4 9% 4 4 4 3 5% 7% 45%	145795
Transparency	Day	38% 6% 11% 20% 17% 8%	148706
	Night	39% 6% 12% 21% 15% 6%	142071
Seeing	Day	15% 19% 32% 24% 9% 2	18154
	Night	12% 11% 26% 35% 15% 1	27648

By Month

Percentage Cloud Cover SW (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	2 23% 10% 17% 6% 5% 5% 3 4 4 20%	4937
	11th to 20th	Day	2 10% 5% 14% 6% 3 3 3 4 5% 45%	5340
	21st to end	Day	2 16% 6% 10% 5% 4 4 3 5% 6% 39%	5844
February	1st to 10th	Day	4 22% 9% 16% 6% 4 4 3 6% 5% 22%	1890
	11th to 20th	Day	2 23% 9% 15% 7% 4 4 2 4 5% 24%	1845
	21st to end	Day	4 20% 8% 18% 7% 5% 4 3 4 4 23%	1672
March	1st to 10th	Day	3 20% 7% 14% 5% 4 3 3 4 5% 33%	4992
	11th to 20th	Day	3 19% 7% 10% 5% 4 3 3 4 5% 37%	5110
	21st to end	Day	5% 25% 8% 13% 7% 5% 5% 3 5% 5% 20%	5607
April	1st to 10th	Day	7% 18% 7% 11% 6% 4 3 3 5% 6% 30%	2415
	11th to 20th	Day	6% 15% 5% 12% 7% 5% 4 3 5% 6% 30%	2633
	21st to end	Day	7% 17% 5% 10% 5% 5% 4 4 5% 8% 29%	2730
May	1st to 10th	Day	6% 10% 2 6% 4 4 5% 4 6% 7% 45%	7626
	11th to 20th	Day	5% 9% 3 7% 5% 5% 5% 5% 7% 8% 41%	7775
	21st to end	Day	8% 9% 4 7% 4 5% 5% 4 6% 7% 41%	9026
June	1st to 10th	Day	9% 7% 2 6% 4 4 4 5% 7% 9% 42%	2940
	11th to 20th	Day	7% 7% 2 7% 4 5% 4 4 6% 6% 49%	3093
	21st to end	Day	2 2 1 4 3 4 4 4 6% 7% 62%	3150
July	1st to 10th	Day	1 2 1 3 3 3 5% 4 6% 7% 64%	8819
	11th to 20th	Day	1 2 1 4 3 4 5% 4 5% 7% 64%	7916
	21st to end	Day	2 3 1 5% 4 5% 6% 5% 7% 9% 55%	8304
August	1st to 10th	Day	2 2 1 4 3 4 5% 4 7% 8% 59%	5909
	11th to 20th	Day	2 2 1 3 3 4 4 4 6% 8% 63%	5928
	21st to end	Day	4 4 2 5% 3 4 4 3 5% 7% 59%	6504
September	1st to 10th	Day	4 3 1 4 4 4 4 3 5% 6% 62%	2380
	11th to 20th	Day	6% 5% 2 6% 3 5% 4 3 4 6% 56%	2200
	21st to end	Day	7% 5% 2 5% 3 3 3 3 4 5% 60%	2200
October	1st to 10th	Day	6% 7% 2 5% 3 3 3 2 3 4 63%	3320
	11th to 20th	Day	6% 9% 2 5% 4 3 4 3 5% 5% 54%	3250
	21st to end	Day	5% 14% 4 7% 4 4 3 3 5% 7% 42%	3518
November	1st to 10th	Day	11% 15% 6% 9% 4 3 4 2 4 6% 37%	1842
	11th to 20th	Day	8% 18% 4 11% 4 4 4 3 4 6% 35%	1680
	21st to end	Day	2 17% 7% 12% 5% 4 3 3 5% 5% 37%	1680
December	1st to 10th	Day	3 14% 6% 10% 5% 4 3 3 3 6% 44%	2700
	11th to 20th	Day	4 20% 8% 16% 7% 4 4 2 4 6% 25%	3106
	21st to end	Day	4 20% 7% 15% 6% 5% 5% 4 5% 8% 23%	4092
January	1st to 10th	Night	3 20% 10% 19% 7% 5% 5% 4 4 5% 19%	8039
	11th to 20th	Night	1 12% 6% 15% 6% 4 4 4 4 5% 38%	7650
	21st to end	Night	2 18% 6% 9% 4 3 4 3 5% 8% 38%	8370
February	1st to 10th	Night	4 21% 9% 15% 7% 5% 5% 3 4 5% 23%	2730
	11th to 20th	Night	4 20% 10% 14% 6% 4 3 3 4 3 29%	2662
	21st to end	Night	4 18% 8% 18% 8% 5% 4 2 4 5% 26%	2131
March	1st to 10th	Night	3 21% 7% 14% 4 3 3 2 3 5% 35%	5121
	11th to 20th	Night	3 14% 5% 9% 5% 4 4 3 5% 8% 40%	5110
	21st to end	Night	6% 18% 7% 11% 6% 5% 5% 4 5% 6% 27%	5610
April	1st to 10th	Night	6% 17% 5% 9% 5% 3 4 3 5% 7% 36%	2205
	11th to 20th	Night	6% 12% 5% 9% 6% 5% 5% 4 6% 5% 37%	1932
	21st to end	Night	7% 12% 3 7% 4 4 5% 3 5% 7% 42%	1890
May	1st to 10th	Night	6% 12% 3 5% 3 3 3 3 5% 6% 51%	5321
	11th to 20th	Night	5% 6% 2 6% 4 4 4 3 5% 8% 53%	5101
	21st to end	Night	6% 7% 2 5% 3 3 4 4 7% 9% 50%	5181
June	1st to 10th	Night	7% 7% 2 6% 4 4 5% 3 7% 10% 46%	1680
	11th to 20th	Night	6% 5% 2 4 3 3 3 4 5% 8% 56%	1520
	21st to end	Night	2 2 1 3 2 3 3 2 5% 7% 68%	1470
July	1st to 10th	Night	1 1 1 3 2 3 4 4 6% 7% 68%	4140
	11th to 20th	Night	1 1 2 2 3 4 4 6% 9% 68%	5037
	21st to end	Night	1 2 1 4 3 4 4 4 7% 9% 61%	5805
August	1st to 10th	Night	2 2 1 3 3 3 4 4 6% 9% 64%	4123
	11th to 20th	Night	1 2 1 3 3 3 4 4 6% 8% 65%	4141
	21st to end	Night	5% 3 2 5% 3 3 3 3 5% 7% 62%	4671
September	1st to 10th	Night	4 3 2 4 2 3 3 3 5% 5% 66%	2015
	11th to 20th	Night	6% 4 2 5% 3 3 3 4 5% 8% 57%	2200
	21st to end	Night	8% 5% 2 3 3 2 2 2 3 6% 64%	2200
October	1st to 10th	Night	7% 5% 2 4 2 2 2 2 3 5% 66%	3870
	11th to 20th	Night	7% 8% 3 6% 3 4 4 2 5% 6% 53%	3898
	21st to end	Night	5% 11% 3 6% 3 3 4 4 5% 7% 49%	4278
November	1st to 10th	Night	10% 13% 4 8% 3 4 4 3 5% 5% 40%	2665
	11th to 20th	Night	7% 15% 4 10% 4 5% 5% 3 6% 6% 36%	2930
	21st to end	Night	4 14% 6% 10% 6% 4 3 4 5% 7% 38%	2940
December	1st to 10th	Night	3 13% 5% 14% 5% 4 2 2 3 4 44%	4710
	11th to 20th	Night	4 20% 9% 14% 5% 4 5% 3 4 6% 26%	5321
	21st to end	Night	3 22% 8% 15% 6% 5% 4 3 4 6% 23%	7128

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	64% 8% 11% 10% 6%	4940
	11th to 20th	Day	41% 5% 19% 20% 10% 4	5340
	21st to end	Day	44% 6% 14% 23% 11% 3	5844
February	1st to 10th	Day	64% 7% 12% 13% 4 1	1890
	11th to 20th	Day	63% 6% 12% 12% 5% 2	1854
	21st to end	Day	64% 6% 7% 15% 6% 1	1672
March	1st to 10th	Day	54% 5% 10% 17% 10% 4	4992
	11th to 20th	Day	49% 7% 11% 24% 9% 1	5110
	21st to end	Day	64% 8% 11% 14% 3	5607
April	1st to 10th	Day	54% 8% 12% 18% 7% 1	2415
	11th to 20th	Day	53% 7% 12% 18% 9% 1	2636
	21st to end	Day	52% 8% 12% 21% 6%	2730
May	1st to 10th	Day	33% 7% 13% 30% 15% 2	7626
	11th to 20th	Day	35% 8% 11% 26% 17% 4	7778
	21st to end	Day	38% 8% 12% 28% 14%	9027
June	1st to 10th	Day	36% 8% 16% 24% 14% 2	2940
	11th to 20th	Day	33% 7% 10% 20% 22% 8%	3093
	21st to end	Day	19% 5% 9% 23% 33% 11%	3150
July	1st to 10th	Day	16% 5% 6% 16% 31% 26%	8746
	11th to 20th	Day	17% 4 7% 18% 26% 28%	7842
	21st to end	Day	22% 6% 8% 17% 32% 15%	8120
August	1st to 10th	Day	22% 6% 8% 16% 30% 18%	4338
	11th to 20th	Day	20% 5% 7% 23% 31% 14%	4327
	21st to end	Day	19% 5% 8% 20% 30% 19%	4723
September	1st to 10th	Day	22% 5% 9% 18% 31% 14%	2380
	11th to 20th	Day	29% 6% 10% 23% 25% 8%	2200
	21st to end	Day	28% 4 11% 26% 26% 5%	2200
October	1st to 10th	Day	28% 4 6% 20% 32% 10%	3320
	11th to 20th	Day	32% 5% 10% 33% 15% 5%	3250
	21st to end	Day	41% 6% 15% 27% 11%	3518
November	1st to 10th	Day	49% 5% 13% 21% 9% 2	1842
	11th to 20th	Day	50% 6% 18% 17% 8% 1	1680
	21st to end	Day	50% 6% 15% 20% 9% 1	1680
December	1st to 10th	Day	42% 7% 23% 20% 6% 2	2700
	11th to 20th	Day	60% 6% 18% 12% 3	3104
	21st to end	Day	58% 6% 11% 12% 7% 5%	4092
January	1st to 10th	Night	64% 9% 8% 15% 4	8040
	11th to 20th	Night	47% 6% 19% 19% 7% 2	7650
	21st to end	Night	44% 6% 12% 24% 12% 2	8370
February	1st to 10th	Night	64% 7% 11% 12% 5%	2730
	11th to 20th	Night	60% 6% 10% 15% 8% 1	2663
	21st to end	Night	61% 6% 10% 14% 6% 3	2131
March	1st to 10th	Night	54% 4 10% 17% 11% 4	5121
	11th to 20th	Night	41% 8% 14% 26% 11% 1	5110
	21st to end	Night	54% 11% 13% 19% 3	5610
April	1st to 10th	Night	47% 9% 14% 18% 10% 2	2205
	11th to 20th	Night	45% 9% 14% 21% 9% 1	1932
	21st to end	Night	39% 10% 16% 25% 10%	1890
May	1st to 10th	Night	32% 7% 10% 32% 19% 1	5319
	11th to 20th	Night	26% 7% 11% 28% 22% 6%	5102
	21st to end	Night	27% 8% 15% 33% 15% 1	5182
June	1st to 10th	Night	33% 9% 17% 24% 15% 3	1680
	11th to 20th	Night	26% 7% 13% 24% 23% 8%	1520
	21st to end	Night	15% 5% 9% 24% 32% 14%	1470
July	1st to 10th	Night	14% 4 7% 17% 34% 25%	4105
	11th to 20th	Night	12% 4 8% 17% 30% 29%	4989
	21st to end	Night	18% 5% 9% 21% 31% 17%	5677
August	1st to 10th	Night	20% 5% 7% 15% 36% 18%	3018
	11th to 20th	Night	21% 5% 9% 26% 25% 15%	3018
	21st to end	Night	16% 4 8% 21% 33% 19%	3383
September	1st to 10th	Night	19% 5% 7% 19% 32% 18%	2015
	11th to 20th	Night	25% 6% 11% 23% 26% 10%	2200
	21st to end	Night	24% 4 9% 28% 29% 5%	2200
October	1st to 10th	Night	22% 4 8% 25% 35% 6%	3870
	11th to 20th	Night	34% 4 8% 32% 16% 5%	3898
	21st to end	Night	33% 7% 14% 31% 14% 1	4278
November	1st to 10th	Night	46% 7% 13% 22% 9% 2	2665
	11th to 20th	Night	48% 8% 16% 20% 8% 1	2930
	21st to end	Night	46% 7% 14% 21% 10% 2	2940
December	1st to 10th	Night	45% 5% 19% 24% 5% 2	4710
	11th to 20th	Night	58% 7% 17% 14% 4	5322
	21st to end	Night	61% 6% 9% 14% 6% 4	7128

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% 14% 30% 26% 7% 1	330
	11th to 20th	Day	12% 18% 38% 20% 11% 1	330
	21st to end	Day	11% 17% 38% 28% 6% 1	363
February	1st to 10th	Day	26% 27% 30% 14% 3	330
	11th to 20th	Day	22% 28% 29% 18% 4	330
	21st to end	Day	21% 30% 30% 15% 4	388
March	1st to 10th	Day	23% 27% 33% 13% 4 1	540
	11th to 20th	Day	20% 26% 31% 19% 4	540
	21st to end	Day	22% 28% 32% 15% 2	594
April	1st to 10th	Day	25% 24% 29% 16% 5% 1	540
	11th to 20th	Day	23% 26% 32% 14% 4 1	532
	21st to end	Day	24% 22% 25% 20% 7% 1	540
May	1st to 10th	Day	17% 20% 31% 22% 9% 1	543
	11th to 20th	Day	18% 19% 31% 21% 10% 1	630
	21st to end	Day	20% 13% 27% 25% 13% 3	844
June	1st to 10th	Day	11% 18% 27% 28% 14% 3	780
	11th to 20th	Day	13% 22% 37% 21% 8%	780
	21st to end	Day	7% 15% 33% 28% 14% 2	780
July	1st to 10th	Day	4 10% 33% 36% 16% 2	771
	11th to 20th	Day	2 13% 43% 26% 14% 1	643
	21st to end	Day	4 11% 39% 32% 12% 2	619
August	1st to 10th	Day	6% 13% 41% 29% 9% 1	567
	11th to 20th	Day	5% 10% 38% 28% 15% 4	557
	21st to end	Day	5% 15% 34% 28% 13% 3	620
September	1st to 10th	Day	5% 15% 33% 30% 13% 4	530
	11th to 20th	Day	12% 16% 33% 25% 10% 4	530
	21st to end	Day	9% 17% 29% 27% 14% 3	530
October	1st to 10th	Day	13% 17% 29% 23% 15% 4	367
	11th to 20th	Day	17% 22% 21% 24% 13% 4	330
	21st to end	Day	19% 20% 28% 26% 6% 2	363
November	1st to 10th	Day	24% 19% 28% 20% 7% 3	330
	11th to 20th	Day	17% 22% 33% 23% 5% 2	330
	21st to end	Day	13% 18% 35% 26% 8%	330
December	1st to 10th	Day	21% 17% 28% 22% 12% 1	330
	11th to 20th	Day	22% 20% 35% 17% 5%	330
	21st to end	Day	26% 18% 29% 18% 7% 2	363
January	1st to 10th	Night	15% 14% 30% 32% 8% 1	992
	11th to 20th	Night	12% 14% 32% 29% 11% 2	840
	21st to end	Night	14% 9% 34% 34% 8% 1	924
February	1st to 10th	Night	17% 15% 36% 26% 6%	840
	11th to 20th	Night	14% 16% 33% 29% 8% 1	824
	21st to end	Night	14% 16% 37% 27% 6%	692
March	1st to 10th	Night	14% 18% 30% 30% 7% 1	840
	11th to 20th	Night	11% 15% 29% 34% 11%	840
	21st to end	Night	14% 14% 31% 31% 9%	924
April	1st to 10th	Night	14% 15% 28% 32% 10% 1	735
	11th to 20th	Night	14% 15% 30% 32% 9%	623
	21st to end	Night	14% 10% 26% 35% 14% 1	630
May	1st to 10th	Night	15% 9% 23% 36% 17% 1	630
	11th to 20th	Night	12% 8% 26% 33% 20% 1	621
	21st to end	Night	16% 8% 20% 37% 17% 1	683
June	1st to 10th	Night	10% 11% 23% 32% 22% 1	630
	11th to 20th	Night	9% 11% 27% 39% 14%	470
	21st to end	Night	3 3 16% 49% 25% 2	420
July	1st to 10th	Night	2 14% 51% 31% 1	410
	11th to 20th	Night	2 3 16% 51% 28%	592
	21st to end	Night	2 2 13% 51% 30% 1	690
August	1st to 10th	Night	6% 2 14% 51% 26% 2	627
	11th to 20th	Night	3 3 13% 52% 28% 2	624
	21st to end	Night	5% 4 18% 42% 29% 2	687
September	1st to 10th	Night	6% 4 15% 43% 30% 2	615
	11th to 20th	Night	8% 3 20% 38% 28% 4	800
	21st to end	Night	10% 5% 17% 38% 26% 4	800
October	1st to 10th	Night	14% 7% 21% 36% 20% 2	800
	11th to 20th	Night	14% 10% 20% 35% 19% 2	800
	21st to end	Night	13% 10% 21% 42% 11% 3	880
November	1st to 10th	Night	18% 12% 26% 32% 11% 1	820
	11th to 20th	Night	16% 14% 33% 31% 6% 1	1040
	21st to end	Night	13% 13% 28% 35% 10% 1	1050
December	1st to 10th	Night	18% 13% 31% 31% 6%	1050
	11th to 20th	Night	18% 15% 32% 29% 6%	1050
	21st to end	Night	19% 16% 31% 24% 8% 1	1155

Page generated at 2026-08-27 02:07:14. Version ac07

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