Hanover
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hanover 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	16% 9% 3 9% 5% 5% 5% 4 6% 7% 32%	143914
	Night	16% 10% 4 9% 6% 5% 5% 4 5% 6% 31%	138309
Transparency	Day	50% 6% 12% 21% 11% 1	147410
	Night	51% 6% 11% 19% 11% 1	142902
Seeing	Day	25% 17% 28% 19% 9% 3	17133
	Night	23% 14% 27% 27% 9% 1	25983

By Month

Percentage Cloud Cover NE (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	9% 10% 7% 20% 8% 5% 5% 4 4 5% 23%	4661
	11th to 20th	Day	9% 14% 5% 15% 8% 6% 5% 3 5% 6% 25%	4650
	21st to end	Day	9% 12% 6% 10% 6% 5% 5% 4 6% 7% 31%	5124
February	1st to 10th	Day	13% 12% 5% 9% 6% 6% 4 4 5% 7% 29%	1859
	11th to 20th	Day	10% 12% 5% 12% 7% 5% 4 4 5% 6% 29%	2048
	21st to end	Day	15% 12% 4 10% 7% 5% 3 3 4 6% 31%	1730
March	1st to 10th	Day	18% 14% 4 13% 6% 5% 4 3 4 3 26%	4576
	11th to 20th	Day	14% 11% 5% 9% 5% 4 4 4 5% 6% 32%	4761
	21st to end	Day	21% 11% 4 9% 5% 4 4 3 4 6% 29%	6055
April	1st to 10th	Day	20% 12% 3 8% 4 4 4 3 5% 5% 33%	2520
	11th to 20th	Day	17% 10% 3 7% 5% 4 5% 4 6% 6% 33%	2494
	21st to end	Day	22% 9% 3 8% 5% 5% 3 3 5% 6% 32%	2722
May	1st to 10th	Day	27% 12% 3 8% 5% 4 5% 4 5% 5% 22%	7639
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 5% 7% 30%	8178
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 6% 7% 30%	9060
June	1st to 10th	Day	19% 8% 3 8% 6% 5% 5% 4 7% 7% 29%	2940
	11th to 20th	Day	17% 7% 3 6% 5% 5% 4 4 5% 8% 36%	2940
	21st to end	Day	19% 8% 3 8% 6% 5% 6% 4 6% 8% 29%	2940
July	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 5% 7% 10% 34%	8280
	11th to 20th	Day	8% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	8280
	21st to end	Day	14% 7% 2 6% 5% 5% 5% 4 7% 8% 38%	8993
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 6% 5% 7% 8% 33%	4603
	11th to 20th	Day	14% 8% 3 9% 5% 5% 6% 4 7% 8% 31%	4205
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 5% 7% 9% 40%	4420
September	1st to 10th	Day	12% 6% 2 6% 5% 4 4 5% 5% 8% 45%	2400
	11th to 20th	Day	12% 6% 2 6% 4 4 3 3 5% 6% 49%	2245
	21st to end	Day	16% 5% 2 6% 5% 4 4 3 6% 8% 42%	2200
October	1st to 10th	Day	20% 7% 2 8% 5% 4 3 3 5% 6% 36%	2180
	11th to 20th	Day	15% 8% 3 7% 6% 5% 4 4 5% 7% 37%	1916
	21st to end	Day	23% 12% 3 8% 4 4 5% 3 5% 5% 29%	1980
November	1st to 10th	Day	14% 9% 3 7% 4 4 5% 3 7% 6% 38%	1851
	11th to 20th	Day	16% 11% 3 7% 5% 4 4 4 5% 6% 34%	1890
	21st to end	Day	18% 12% 4 9% 5% 4 5% 4 4 6% 29%	1780
December	1st to 10th	Day	15% 13% 4 14% 7% 6% 5% 3 6% 7% 20%	2680
	11th to 20th	Day	19% 14% 3 9% 5% 4 4 3 4 5% 29%	3066
	21st to end	Day	19% 13% 5% 11% 5% 4 4 3 4 5% 27%	4048
January	1st to 10th	Night	11% 11% 8% 17% 7% 5% 4 3 5% 5% 24%	8234
	11th to 20th	Night	10% 13% 6% 17% 8% 6% 5% 4 5% 6% 19%	8235
	21st to end	Night	11% 10% 4 10% 8% 8% 7% 4 7% 6% 27%	9057
February	1st to 10th	Night	13% 12% 4 9% 7% 6% 6% 4 6% 7% 28%	2755
	11th to 20th	Night	10% 9% 5% 11% 7% 6% 5% 5% 6% 6% 29%	2458
	21st to end	Night	12% 10% 4 12% 6% 4 4 4 5% 6% 31%	2076
March	1st to 10th	Night	20% 12% 3 9% 5% 5% 4 4 5% 6% 27%	5484
	11th to 20th	Night	14% 13% 4 9% 6% 5% 5% 3 4 6% 31%	5418
	21st to end	Night	22% 12% 4 8% 4 4 3 3 4 5% 29%	5102
April	1st to 10th	Night	20% 10% 3 8% 5% 5% 4 3 5% 6% 32%	2100
	11th to 20th	Night	19% 12% 2 7% 5% 3 4 3 5% 5% 34%	2075
	21st to end	Night	19% 9% 3 7% 5% 4 5% 3 4 6% 36%	1896
May	1st to 10th	Night	27% 12% 4 8% 4 4 3 3 4 6% 23%	5259
	11th to 20th	Night	17% 9% 3 8% 5% 5% 4 4 6% 7% 30%	4725
	21st to end	Night	19% 8% 3 7% 5% 4 5% 4 6% 8% 32%	5114
June	1st to 10th	Night	19% 6% 3 6% 5% 5% 5% 4 6% 7% 33%	1680
	11th to 20th	Night	19% 6% 3 6% 5% 4 4 5% 5% 6% 37%	1680
	21st to end	Night	16% 6% 3 8% 6% 4 5% 4 6% 8% 35%	1680
July	1st to 10th	Night	11% 7% 2 6% 5% 5% 6% 5% 7% 10% 37%	4680
	11th to 20th	Night	11% 6% 3 6% 5% 4 4 4 6% 7% 42%	4680
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 7% 45%	5084
August	1st to 10th	Night	18% 10% 3 7% 5% 3 4 3 4 7% 35%	2733
	11th to 20th	Night	13% 8% 3 8% 4 4 5% 4 6% 8% 38%	3059
	21st to end	Night	10% 6% 2 6% 3 4 4 4 8% 9% 45%	3677
September	1st to 10th	Night	13% 5% 3 6% 3 3 4 3 6% 7% 49%	2000
	11th to 20th	Night	13% 5% 2 6% 3 4 3 3 5% 6% 50%	2154
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 7% 45%	2200
October	1st to 10th	Night	20% 6% 3 7% 4 4 4 4 5% 7% 36%	2218
	11th to 20th	Night	17% 10% 3 6% 5% 5% 4 3 5% 7% 36%	2483
	21st to end	Night	22% 11% 2 7% 4 5% 4 3 5% 7% 30%	2860
November	1st to 10th	Night	14% 9% 4 8% 5% 5% 4 4 5% 6% 37%	2667
	11th to 20th	Night	16% 10% 3 6% 6% 5% 4 3 6% 6% 35%	2730
	21st to end	Night	16% 11% 4 9% 5% 4 4 4 5% 7% 30%	2838
December	1st to 10th	Night	14% 14% 6% 14% 8% 5% 5% 3 5% 6% 19%	4720
	11th to 20th	Night	22% 12% 4 9% 5% 4 4 3 4 5% 27%	5348
	21st to end	Night	19% 14% 5% 11% 6% 4 4 3 5% 5% 22%	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	60% 5% 9% 20% 5%	4662
	11th to 20th	Day	57% 6% 10% 16% 10% 2	4680
	21st to end	Day	50% 5% 9% 21% 13% 2	5124
February	1st to 10th	Day	54% 6% 12% 17% 9% 2	1859
	11th to 20th	Day	53% 6% 10% 19% 10% 2	2057
	21st to end	Day	55% 5% 10% 17% 12% 1	1730
March	1st to 10th	Day	62% 5% 7% 12% 9% 6%	4579
	11th to 20th	Day	47% 8% 14% 18% 9% 3	4761
	21st to end	Day	55% 5% 5% 14% 17% 3	6055
April	1st to 10th	Day	54% 4 9% 19% 12% 3	2520
	11th to 20th	Day	49% 7% 9% 18% 15% 2	2494
	21st to end	Day	53% 5% 8% 19% 13% 2	2722
May	1st to 10th	Day	62% 6% 9% 14% 8% 1	7651
	11th to 20th	Day	52% 7% 13% 18% 9% 1	8182
	21st to end	Day	50% 6% 11% 22% 9% 1	9061
June	1st to 10th	Day	52% 7% 11% 19% 10%	2940
	11th to 20th	Day	47% 7% 12% 19% 14% 2	2940
	21st to end	Day	51% 7% 12% 18% 10% 1	2940
July	1st to 10th	Day	44% 6% 16% 23% 11%	8210
	11th to 20th	Day	37% 6% 16% 29% 12% 1	8205
	21st to end	Day	43% 5% 14% 27% 11%	8795
August	1st to 10th	Day	47% 7% 15% 20% 11%	4589
	11th to 20th	Day	48% 7% 15% 23% 7%	4244
	21st to end	Day	38% 6% 16% 26% 13% 1	4420
September	1st to 10th	Day	36% 7% 13% 28% 15% 1	2400
	11th to 20th	Day	36% 5% 10% 28% 20% 1	2245
	21st to end	Day	39% 7% 12% 26% 14% 2	2200
October	1st to 10th	Day	47% 5% 9% 22% 16% 1	3557
	11th to 20th	Day	44% 4 13% 25% 14% 1	3093
	21st to end	Day	43% 4 9% 30% 12% 2	3180
November	1st to 10th	Day	42% 7% 14% 21% 14% 1	1851
	11th to 20th	Day	49% 5% 11% 16% 17% 2	1890
	21st to end	Day	55% 6% 16% 16% 7% 1	1780
December	1st to 10th	Day	62% 5% 13% 15% 5%	2680
	11th to 20th	Day	56% 5% 8% 16% 13% 1	3066
	21st to end	Day	58% 4 7% 15% 13% 3	4048
January	1st to 10th	Night	61% 5% 10% 15% 7% 1	8234
	11th to 20th	Night	61% 7% 10% 11% 9% 2	8280
	21st to end	Night	55% 6% 8% 15% 13% 3	9057
February	1st to 10th	Night	53% 7% 10% 19% 10% 1	2755
	11th to 20th	Night	51% 8% 11% 20% 10% 1	2460
	21st to end	Night	50% 7% 11% 20% 9% 3	2076
March	1st to 10th	Night	56% 4 9% 14% 13% 3	5494
	11th to 20th	Night	52% 7% 15% 15% 10% 2	5419
	21st to end	Night	55% 6% 6% 14% 18% 3	5102
April	1st to 10th	Night	54% 5% 9% 17% 14% 1	2100
	11th to 20th	Night	50% 6% 9% 20% 14% 1	2075
	21st to end	Night	49% 5% 10% 17% 16% 3	1896
May	1st to 10th	Night	62% 5% 10% 13% 9% 1	5265
	11th to 20th	Night	52% 7% 12% 20% 8% 1	4726
	21st to end	Night	50% 7% 12% 23% 9% 1	5115
June	1st to 10th	Night	48% 8% 11% 20% 12%	1680
	11th to 20th	Night	46% 8% 14% 19% 12% 1	1680
	21st to end	Night	47% 8% 13% 21% 11% 1	1680
July	1st to 10th	Night	42% 6% 18% 23% 10%	4640
	11th to 20th	Night	40% 5% 13% 26% 15%	4632
	21st to end	Night	40% 5% 14% 32% 10% 1	4967
August	1st to 10th	Night	50% 6% 13% 20% 10% 1	2723
	11th to 20th	Night	44% 6% 19% 21% 10%	3086
	21st to end	Night	33% 6% 19% 28% 13% 1	3677
September	1st to 10th	Night	35% 6% 15% 28% 16% 1	2000
	11th to 20th	Night	34% 5% 12% 29% 19% 1	2154
	21st to end	Night	38% 7% 12% 27% 16% 2	2200
October	1st to 10th	Night	48% 5% 13% 22% 10% 1	3621
	11th to 20th	Night	43% 4 12% 24% 15% 2	4045
	21st to end	Night	45% 5% 10% 29% 10% 1	4610
November	1st to 10th	Night	47% 6% 11% 22% 12% 2	2667
	11th to 20th	Night	47% 6% 11% 21% 14% 1	2730
	21st to end	Night	52% 7% 14% 20% 8%	2838
December	1st to 10th	Night	65% 5% 11% 16% 3	4720
	11th to 20th	Night	58% 5% 9% 13% 15% 1	5348
	21st to end	Night	61% 5% 7% 15% 8% 3	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	26% 23% 26% 18% 6%	220
	11th to 20th	Day	31% 25% 30% 11% 1 1	220
	21st to end	Day	26% 26% 30% 13% 6%	242
February	1st to 10th	Day	30% 27% 30% 11% 2	331
	11th to 20th	Day	28% 26% 30% 14% 2	536
	21st to end	Day	29% 23% 30% 15% 3	446
March	1st to 10th	Day	31% 20% 32% 15% 3	540
	11th to 20th	Day	33% 23% 28% 11% 4 1	540
	21st to end	Day	35% 21% 25% 11% 6% 2	594
April	1st to 10th	Day	37% 20% 25% 11% 6% 1	540
	11th to 20th	Day	34% 22% 24% 12% 6% 1	532
	21st to end	Day	31% 22% 27% 11% 7% 1	540
May	1st to 10th	Day	36% 21% 24% 12% 5% 2	543
	11th to 20th	Day	24% 18% 33% 18% 5% 2	567
	21st to end	Day	22% 15% 33% 20% 8% 1	617
June	1st to 10th	Day	23% 13% 34% 19% 10% 1	570
	11th to 20th	Day	21% 16% 32% 20% 9% 2	570
	21st to end	Day	22% 16% 32% 18% 9% 2	570
July	1st to 10th	Day	17% 12% 33% 23% 12% 3	565
	11th to 20th	Day	14% 10% 33% 30% 11% 2	564
	21st to end	Day	16% 8% 37% 25% 11% 3	620
August	1st to 10th	Day	13% 11% 28% 27% 17% 3	566
	11th to 20th	Day	16% 10% 28% 25% 13% 8%	559
	21st to end	Day	13% 14% 25% 27% 16% 5%	619
September	1st to 10th	Day	16% 12% 25% 25% 15% 7%	530
	11th to 20th	Day	15% 13% 23% 22% 17% 11%	530
	21st to end	Day	16% 14% 29% 22% 12% 7%	530
October	1st to 10th	Day	25% 13% 23% 20% 13% 6%	530
	11th to 20th	Day	23% 17% 22% 26% 9% 2	483
	21st to end	Day	35% 13% 24% 20% 7%	462
November	1st to 10th	Day	27% 18% 23% 20% 12% 1	425
	11th to 20th	Day	32% 18% 24% 18% 7% 1	430
	21st to end	Day	35% 18% 26% 15% 5% 1	320
December	1st to 10th	Day	30% 22% 26% 16% 5%	220
	11th to 20th	Day	34% 24% 30% 8% 4	220
	21st to end	Day	33% 19% 28% 14% 5%	242
January	1st to 10th	Night	23% 19% 33% 22% 3	840
	11th to 20th	Night	25% 19% 29% 23% 3	840
	21st to end	Night	21% 19% 35% 21% 4 1	924
February	1st to 10th	Night	23% 18% 34% 22% 3	840
	11th to 20th	Night	21% 19% 36% 22% 2	823
	21st to end	Night	24% 18% 32% 23% 3	692
March	1st to 10th	Night	26% 17% 31% 23% 3	840
	11th to 20th	Night	26% 19% 28% 23% 5%	840
	21st to end	Night	29% 17% 26% 21% 7% 1	924
April	1st to 10th	Night	27% 20% 26% 22% 5%	840
	11th to 20th	Night	26% 21% 24% 22% 6%	831
	21st to end	Night	26% 16% 30% 22% 5%	636
May	1st to 10th	Night	30% 12% 29% 23% 6%	630
	11th to 20th	Night	19% 13% 31% 30% 7%	450
	21st to end	Night	20% 9% 26% 34% 11% 1	455
June	1st to 10th	Night	21% 8% 27% 34% 10%	420
	11th to 20th	Night	20% 11% 26% 32% 11%	420
	21st to end	Night	17% 7% 24% 41% 10%	420
July	1st to 10th	Night	14% 6% 21% 44% 14%	410
	11th to 20th	Night	15% 5% 21% 41% 16% 1	408
	21st to end	Night	13% 5% 21% 43% 17% 1	460
August	1st to 10th	Night	14% 4 17% 43% 21% 1	459
	11th to 20th	Night	14% 6% 24% 36% 18% 2	680
	21st to end	Night	15% 6% 21% 35% 21% 2	917
September	1st to 10th	Night	14% 9% 24% 32% 19% 2	800
	11th to 20th	Night	16% 7% 20% 31% 22% 4	800
	21st to end	Night	18% 8% 23% 31% 19% 2	800
October	1st to 10th	Night	26% 9% 18% 29% 17% 2	800
	11th to 20th	Night	23% 12% 23% 31% 11% 1	800
	21st to end	Night	29% 14% 25% 24% 8%	880
November	1st to 10th	Night	22% 17% 25% 27% 9%	820
	11th to 20th	Night	24% 16% 28% 23% 8% 1	840
	21st to end	Night	25% 17% 27% 25% 6%	840
December	1st to 10th	Night	24% 18% 32% 22% 4	840
	11th to 20th	Night	27% 19% 29% 21% 4	840
	21st to end	Night	29% 19% 31% 18% 4	924

Page generated at 2026-08-27 04:07:11. Version ac07

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