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 2025-04-26.

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	5% 12% 4 9% 5% 4 4 3 5% 6% 43%	118519
	Night	4 13% 5% 10% 4 4 4 3 5% 6% 42%	118991
Transparency	Day	41% 6% 11% 19% 16% 7%	118269
	Night	42% 6% 12% 21% 14% 5%	118831
Seeing	Day	15% 19% 32% 23% 9% 2	16218
	Night	13% 11% 25% 35% 15% 1	25969

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 18% 10% 17% 7% 5% 5% 3 5% 5% 23%	3799
	11th to 20th	Day	3 13% 6% 19% 7% 4 4 4 4 5% 32%	4100
	21st to end	Day	2 20% 6% 10% 5% 4 4 3 4 6% 37%	4510
February	1st to 10th	Day	4 23% 9% 17% 6% 4 4 3 5% 5% 20%	1800
	11th to 20th	Day	3 23% 9% 15% 7% 3 4 2 4 5% 25%	1755
	21st to end	Day	4 20% 8% 19% 8% 5% 4 3 4 4 22%	1595
March	1st to 10th	Day	3 20% 7% 14% 5% 4 3 3 4 5% 33%	4884
	11th to 20th	Day	3 19% 7% 10% 5% 4 3 3 4 5% 37%	5000
	21st to end	Day	5% 25% 8% 13% 7% 5% 5% 3 4 5% 19%	5486
April	1st to 10th	Day	7% 18% 7% 12% 6% 4 3 3 6% 6% 29%	2300
	11th to 20th	Day	7% 16% 5% 12% 7% 5% 4 3 5% 6% 30%	2506
	21st to end	Day	7% 17% 5% 10% 5% 5% 4 4 5% 8% 30%	2537
May	1st to 10th	Day	9% 18% 4 9% 6% 5% 5% 4 5% 6% 28%	4110
	11th to 20th	Day	6% 7% 2 6% 5% 4 5% 5% 7% 8% 44%	4166
	21st to end	Day	8% 14% 5% 9% 5% 5% 4 4 5% 5% 35%	4825
June	1st to 10th	Day	10% 8% 2 6% 5% 4 4 5% 7% 9% 40%	2660
	11th to 20th	Day	8% 7% 3 7% 4 5% 4 4 6% 6% 46%	2798
	21st to end	Day	2 2 1 5% 3 4 4 4 5% 7% 63%	2850
July	1st to 10th	Day	2 2 1 3 2 2 3 3 5% 6% 72%	4740
	11th to 20th	Day	1 2 1 4 3 4 4 4 5% 7% 65%	4238
	21st to end	Day	3 3 1 4 4 4 5% 4 6% 7% 58%	4454
August	1st to 10th	Day	3 3 1 4 3 5% 6% 4 7% 8% 55%	4092
	11th to 20th	Day	2 2 1 4 3 4 4 4 5% 7% 63%	4028
	21st to end	Day	3 2 1 4 2 3 4 3 5% 6% 66%	4465
September	1st to 10th	Day	4 4 2 5% 4 4 4 3 5% 6% 62%	2261
	11th to 20th	Day	7% 5% 2 6% 3 4 4 3 4 6% 56%	2090
	21st to end	Day	7% 5% 2 5% 3 3 3 3 3 5% 60%	2090
October	1st to 10th	Day	6% 7% 2 5% 3 3 3 2 3 4 64%	3218
	11th to 20th	Day	6% 9% 2 5% 4 3 4 3 5% 5% 55%	3150
	21st to end	Day	5% 14% 4 8% 4 4 3 3 5% 7% 41%	3409
November	1st to 10th	Day	11% 15% 6% 9% 4 3 3 2 4 6% 37%	1753
	11th to 20th	Day	8% 18% 4 11% 4 4 4 2 4 7% 35%	1600
	21st to end	Day	2 17% 7% 12% 5% 4 3 3 5% 5% 36%	1600
December	1st to 10th	Day	3 13% 6% 10% 4 3 3 3 3 6% 45%	2620
	11th to 20th	Day	3 20% 8% 16% 7% 4 4 2 5% 6% 24%	3026
	21st to end	Day	4 20% 7% 15% 6% 5% 5% 4 5% 8% 23%	4004
January	1st to 10th	Night	2 15% 10% 19% 7% 5% 5% 4 5% 5% 23%	6207
	11th to 20th	Night	2 16% 8% 19% 8% 5% 4 4 4 5% 25%	5880
	21st to end	Night	3 21% 6% 9% 3 3 3 3 4 6% 38%	6468
February	1st to 10th	Night	4 21% 10% 16% 7% 5% 4 3 3 5% 22%	2600
	11th to 20th	Night	4 20% 10% 14% 6% 4 3 3 4 3 29%	2532
	21st to end	Night	4 19% 8% 18% 8% 5% 3 2 4 5% 25%	2033
March	1st to 10th	Night	3 21% 8% 14% 4 3 3 2 3 5% 35%	5009
	11th to 20th	Night	3 14% 6% 9% 5% 4 4 3 5% 8% 40%	5000
	21st to end	Night	6% 19% 8% 11% 6% 5% 5% 4 5% 6% 26%	5489
April	1st to 10th	Night	6% 16% 5% 9% 5% 3 4 3 5% 7% 35%	2100
	11th to 20th	Night	6% 13% 5% 9% 5% 5% 5% 3 6% 5% 37%	1839
	21st to end	Night	8% 12% 3 7% 4 3 5% 3 5% 7% 43%	1759
May	1st to 10th	Night	9% 20% 4 7% 3 4 4 3 5% 6% 36%	2860
	11th to 20th	Night	4 4 2 5% 4 3 4 4 7% 9% 54%	2723
	21st to end	Night	7% 11% 3 7% 4 4 5% 4 6% 7% 43%	2762
June	1st to 10th	Night	8% 7% 2 6% 4 4 5% 3 7% 10% 44%	1520
	11th to 20th	Night	7% 6% 2 4 3 4 3 4 5% 8% 53%	1376
	21st to end	Night	2 1 1 3 2 3 3 2 5% 7% 71%	1330
July	1st to 10th	Night	1 1 2 2 3 3 4 6% 6% 72%	2220
	11th to 20th	Night	1 1 2 2 2 3 3 6% 8% 71%	2697
	21st to end	Night	1 1 1 3 2 3 3 4 7% 8% 66%	3109
August	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 9% 60%	2847
	11th to 20th	Night	2 2 1 4 3 4 4 4 6% 8% 61%	2811
	21st to end	Night	3 2 1 3 2 2 2 2 5% 6% 72%	3201
September	1st to 10th	Night	4 3 2 4 2 3 3 3 5% 5% 67%	1914
	11th to 20th	Night	6% 4 2 5% 3 3 3 4 5% 8% 58%	2090
	21st to end	Night	8% 5% 2 3 3 1 2 2 3 6% 64%	2090
October	1st to 10th	Night	7% 5% 2 4 2 2 2 2 3 5% 67%	3752
	11th to 20th	Night	7% 7% 3 6% 3 4 4 3 5% 6% 54%	3778
	21st to end	Night	5% 11% 3 6% 3 3 4 4 5% 7% 48%	4145
November	1st to 10th	Night	11% 14% 4 8% 3 4 4 3 5% 5% 39%	2535
	11th to 20th	Night	7% 15% 4 9% 4 5% 5% 3 6% 6% 36%	2790
	21st to end	Night	4 15% 6% 10% 6% 4 3 4 5% 7% 38%	2800
December	1st to 10th	Night	3 13% 5% 14% 5% 4 3 2 3 4 45%	4570
	11th to 20th	Night	4 21% 9% 14% 5% 4 4 3 4 6% 26%	5181
	21st to end	Night	3 22% 8% 16% 6% 5% 4 3 4 6% 23%	6974

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	60% 9% 10% 13% 8%	3800
	11th to 20th	Day	54% 6% 13% 15% 8% 4	4100
	21st to end	Day	48% 5% 10% 21% 12% 3	4510
February	1st to 10th	Day	67% 7% 11% 12% 4 1	1800
	11th to 20th	Day	63% 6% 12% 12% 5% 2	1764
	21st to end	Day	66% 6% 7% 14% 5% 2	1595
March	1st to 10th	Day	54% 5% 10% 17% 10% 4	4884
	11th to 20th	Day	49% 7% 11% 24% 9% 1	5000
	21st to end	Day	65% 8% 11% 14% 2	5486
April	1st to 10th	Day	55% 8% 12% 16% 7% 1	2300
	11th to 20th	Day	54% 7% 12% 18% 8% 1	2509
	21st to end	Day	53% 8% 12% 22% 6%	2537
May	1st to 10th	Day	51% 9% 11% 20% 7% 1	4110
	11th to 20th	Day	30% 9% 13% 31% 13% 3	4169
	21st to end	Day	46% 8% 12% 25% 8%	4825
June	1st to 10th	Day	38% 8% 18% 25% 11% 1	2660
	11th to 20th	Day	36% 8% 11% 19% 19% 8%	2798
	21st to end	Day	19% 5% 9% 22% 33% 12%	2850
July	1st to 10th	Day	12% 4 6% 14% 35% 29%	4666
	11th to 20th	Day	17% 4 7% 12% 24% 36%	4164
	21st to end	Day	22% 6% 7% 15% 35% 16%	4314
August	1st to 10th	Day	23% 7% 8% 15% 31% 17%	4078
	11th to 20th	Day	20% 5% 7% 22% 32% 14%	4067
	21st to end	Day	18% 5% 7% 19% 31% 20%	4464
September	1st to 10th	Day	23% 5% 8% 17% 32% 14%	2261
	11th to 20th	Day	29% 6% 10% 22% 25% 8%	2090
	21st to end	Day	27% 4 11% 26% 26% 5%	2090
October	1st to 10th	Day	27% 4 6% 20% 32% 10%	3218
	11th to 20th	Day	31% 5% 10% 33% 16% 5%	3150
	21st to end	Day	41% 6% 15% 26% 11%	3409
November	1st to 10th	Day	50% 5% 13% 20% 10% 2	1753
	11th to 20th	Day	51% 6% 17% 17% 9% 1	1600
	21st to end	Day	51% 6% 14% 19% 9% 1	1600
December	1st to 10th	Day	41% 7% 23% 21% 6% 2	2620
	11th to 20th	Day	61% 6% 18% 12% 3	3024
	21st to end	Day	58% 6% 11% 12% 8% 5%	4004
January	1st to 10th	Night	59% 9% 9% 17% 5%	6207
	11th to 20th	Night	60% 7% 11% 14% 6% 3	5880
	21st to end	Night	47% 5% 12% 22% 12% 2	6468
February	1st to 10th	Night	66% 7% 10% 11% 6%	2600
	11th to 20th	Night	60% 6% 10% 15% 8% 1	2533
	21st to end	Night	62% 6% 10% 14% 5% 3	2033
March	1st to 10th	Night	54% 4 10% 17% 12% 4	5009
	11th to 20th	Night	41% 8% 13% 26% 11% 1	5000
	21st to end	Night	55% 11% 13% 19% 2	5489
April	1st to 10th	Night	48% 9% 14% 17% 10% 2	2100
	11th to 20th	Night	45% 9% 14% 21% 9% 1	1839
	21st to end	Night	39% 10% 17% 25% 10%	1759
May	1st to 10th	Night	46% 8% 12% 23% 11% 1	2860
	11th to 20th	Night	22% 9% 17% 35% 14% 2	2724
	21st to end	Night	36% 10% 13% 30% 10% 2	2762
June	1st to 10th	Night	34% 9% 18% 25% 12% 1	1520
	11th to 20th	Night	28% 7% 13% 23% 20% 8%	1376
	21st to end	Night	14% 5% 8% 24% 34% 15%	1330
July	1st to 10th	Night	11% 4 8% 14% 40% 23%	2185
	11th to 20th	Night	10% 3 5% 18% 32% 32%	2649
	21st to end	Night	13% 4 9% 21% 35% 17%	3011
August	1st to 10th	Night	20% 5% 8% 15% 35% 16%	2838
	11th to 20th	Night	20% 5% 8% 26% 25% 15%	2838
	21st to end	Night	15% 3 7% 21% 34% 20%	3201
September	1st to 10th	Night	19% 5% 7% 18% 32% 19%	1914
	11th to 20th	Night	24% 6% 11% 22% 26% 10%	2090
	21st to end	Night	24% 4 9% 28% 29% 6%	2090
October	1st to 10th	Night	22% 4 8% 25% 35% 7%	3752
	11th to 20th	Night	33% 4 8% 33% 16% 5%	3778
	21st to end	Night	34% 7% 14% 30% 15% 1	4145
November	1st to 10th	Night	47% 7% 13% 21% 10% 2	2535
	11th to 20th	Night	47% 8% 15% 20% 8% 1	2790
	21st to end	Night	47% 6% 14% 20% 10% 2	2800
December	1st to 10th	Night	45% 5% 20% 24% 5% 2	4570
	11th to 20th	Night	59% 7% 17% 14% 4	5182
	21st to end	Night	61% 6% 9% 14% 6% 4	6974

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% 13% 29% 28% 8% 1	300
	11th to 20th	Day	13% 18% 36% 20% 11% 1	300
	21st to end	Day	12% 17% 38% 27% 6% 1	330
February	1st to 10th	Day	27% 29% 30% 13% 2	300
	11th to 20th	Day	22% 28% 29% 18% 3	300
	21st to end	Day	21% 29% 30% 16% 4	359
March	1st to 10th	Day	22% 27% 33% 13% 4 1	500
	11th to 20th	Day	17% 27% 32% 19% 5%	500
	21st to end	Day	22% 27% 32% 15% 3	550
April	1st to 10th	Day	26% 24% 29% 16% 5% 1	500
	11th to 20th	Day	24% 26% 32% 14% 4 1	492
	21st to end	Day	24% 21% 26% 21% 7% 1	481
May	1st to 10th	Day	17% 22% 32% 21% 7% 1	463
	11th to 20th	Day	16% 18% 33% 22% 10% 1	544
	21st to end	Day	22% 12% 26% 24% 13% 3	734
June	1st to 10th	Day	11% 18% 26% 27% 14% 3	680
	11th to 20th	Day	14% 22% 36% 19% 9%	680
	21st to end	Day	5% 14% 34% 29% 15% 2	680
July	1st to 10th	Day	4 10% 32% 36% 15% 2	671
	11th to 20th	Day	3 14% 43% 26% 12% 1	555
	21st to end	Day	4 12% 38% 32% 12% 3	531
August	1st to 10th	Day	7% 13% 40% 31% 9% 2	487
	11th to 20th	Day	5% 11% 38% 28% 15% 4	477
	21st to end	Day	5% 16% 35% 28% 13% 3	539
September	1st to 10th	Day	5% 16% 33% 29% 13% 4	490
	11th to 20th	Day	12% 17% 33% 23% 10% 4	490
	21st to end	Day	10% 17% 30% 27% 14% 3	490
October	1st to 10th	Day	13% 17% 29% 22% 16% 3	335
	11th to 20th	Day	16% 20% 20% 26% 14% 4	300
	21st to end	Day	20% 20% 29% 25% 5% 1	330
November	1st to 10th	Day	24% 19% 27% 21% 6% 3	300
	11th to 20th	Day	17% 21% 33% 22% 5% 2	300
	21st to end	Day	13% 19% 35% 26% 7%	300
December	1st to 10th	Day	19% 15% 28% 24% 13% 1	300
	11th to 20th	Day	20% 21% 36% 18% 5%	300
	21st to end	Day	24% 19% 31% 18% 7% 2	330
January	1st to 10th	Night	14% 14% 30% 33% 8% 1	945
	11th to 20th	Night	13% 15% 30% 29% 11% 2	800
	21st to end	Night	15% 9% 33% 34% 9% 1	880
February	1st to 10th	Night	18% 15% 35% 26% 5% 1	800
	11th to 20th	Night	14% 16% 33% 30% 7% 1	784
	21st to end	Night	13% 16% 35% 28% 7%	660
March	1st to 10th	Night	14% 19% 30% 31% 7% 1	800
	11th to 20th	Night	11% 14% 27% 36% 12% 1	800
	21st to end	Night	15% 15% 30% 31% 10%	880
April	1st to 10th	Night	14% 16% 28% 31% 10% 1	700
	11th to 20th	Night	13% 15% 31% 31% 9%	593
	21st to end	Night	14% 9% 26% 34% 15% 1	587
May	1st to 10th	Night	16% 10% 22% 36% 16% 1	570
	11th to 20th	Night	12% 6% 25% 34% 22% 1	561
	21st to end	Night	17% 9% 20% 36% 18% 1	617
June	1st to 10th	Night	11% 12% 21% 32% 23% 1	570
	11th to 20th	Night	10% 11% 27% 38% 15%	426
	21st to end	Night	3 2 15% 50% 27% 3	380
July	1st to 10th	Night	2 15% 49% 33% 2	370
	11th to 20th	Night	2 3 16% 51% 28%	534
	21st to end	Night	2 2 13% 50% 31% 1	624
August	1st to 10th	Night	6% 2 14% 48% 28% 2	567
	11th to 20th	Night	3 3 12% 51% 29% 2	564
	21st to end	Night	5% 4 18% 41% 30% 2	627
September	1st to 10th	Night	6% 4 15% 43% 29% 2	584
	11th to 20th	Night	8% 3 20% 38% 28% 4	760
	21st to end	Night	11% 5% 18% 37% 25% 4	760
October	1st to 10th	Night	15% 7% 21% 36% 20% 2	760
	11th to 20th	Night	13% 10% 19% 36% 20% 2	760
	21st to end	Night	13% 10% 21% 41% 11% 3	836
November	1st to 10th	Night	18% 12% 25% 32% 12% 1	780
	11th to 20th	Night	16% 14% 32% 31% 6% 1	990
	21st to end	Night	13% 13% 28% 35% 10% 1	1000
December	1st to 10th	Night	18% 12% 32% 31% 6% 1	1000
	11th to 20th	Night	18% 14% 32% 30% 6%	1000
	21st to end	Night	18% 16% 31% 24% 8% 1	1100

Page generated at 2025-04-23 07:25:08. Version ac07

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