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 2024-10-25.

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 8% 5% 5% 5% 4 6% 7% 32%	101278
	Night	17% 10% 3 8% 5% 5% 4 4 5% 6% 32%	97532
Transparency	Day	49% 7% 12% 20% 11% 1	101036
	Night	50% 7% 12% 19% 11% 1	97394
Seeing	Day	24% 17% 28% 19% 9% 3	14803
	Night	22% 14% 27% 27% 9% 1	23705

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	12% 11% 4 11% 6% 6% 5% 4 5% 6% 30%	2517
	11th to 20th	Day	13% 14% 6% 12% 8% 6% 5% 3 4 5% 23%	2520
	21st to end	Day	15% 14% 7% 11% 6% 5% 5% 4 5% 6% 23%	2772
February	1st to 10th	Day	14% 12% 5% 8% 6% 6% 4 4 5% 7% 29%	1681
	11th to 20th	Day	10% 12% 5% 11% 7% 5% 4 4 6% 6% 28%	1848
	21st to end	Day	16% 12% 4 9% 6% 5% 3 3 4 6% 31%	1570
March	1st to 10th	Day	20% 17% 4 11% 6% 4 3 3 4 4 24%	3116
	11th to 20th	Day	14% 13% 6% 10% 5% 5% 4 4 5% 6% 28%	3256
	21st to end	Day	18% 12% 4 10% 5% 4 4 3 4 6% 30%	4134
April	1st to 10th	Day	20% 12% 3 8% 4 4 3 2 5% 5% 34%	2280
	11th to 20th	Day	18% 9% 3 7% 5% 4 5% 4 6% 6% 34%	2254
	21st to end	Day	22% 9% 3 8% 5% 4 3 3 5% 6% 30%	2462
May	1st to 10th	Day	24% 11% 4 8% 5% 4 4 4 5% 5% 27%	4106
	11th to 20th	Day	17% 9% 3 8% 6% 5% 6% 4 6% 8% 30%	4382
	21st to end	Day	12% 6% 2 5% 5% 5% 5% 4 7% 9% 40%	4837
June	1st to 10th	Day	19% 8% 3 8% 6% 5% 5% 4 6% 7% 29%	2660
	11th to 20th	Day	17% 7% 3 6% 5% 5% 4 4 5% 8% 36%	2660
	21st to end	Day	19% 8% 3 8% 6% 5% 6% 4 7% 7% 28%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	9% 6% 2 7% 6% 6% 6% 5% 8% 10% 34%	4440
	21st to end	Day	15% 8% 2 6% 5% 5% 5% 5% 6% 8% 35%	4814
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 6% 5% 7% 8% 32%	4329
	11th to 20th	Day	14% 8% 3 9% 6% 5% 6% 4 7% 8% 30%	3951
	21st to end	Day	9% 6% 3 7% 5% 4 5% 5% 7% 9% 40%	4180
September	1st to 10th	Day	12% 6% 2 5% 5% 4 4 5% 5% 8% 44%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 3 3 5% 6% 48%	2133
	21st to end	Day	15% 5% 2 6% 5% 4 4 3 6% 8% 42%	2090
October	1st to 10th	Day	21% 7% 3 8% 5% 4 4 3 5% 6% 34%	2071
	11th to 20th	Day	14% 8% 3 7% 6% 5% 4 4 5% 7% 37%	1820
	21st to end	Day	24% 12% 2 8% 4 4 5% 3 5% 5% 28%	1825
November	1st to 10th	Day	14% 9% 3 7% 4 4 4 3 7% 7% 39%	1671
	11th to 20th	Day	17% 10% 3 7% 5% 4 4 4 5% 6% 34%	1710
	21st to end	Day	18% 11% 4 9% 4 4 5% 4 4 6% 31%	1611
December	1st to 10th	Day	20% 14% 3 10% 6% 5% 5% 3 4 7% 23%	1520
	11th to 20th	Day	21% 14% 3 8% 4 3 4 3 4 6% 30%	1906
	21st to end	Day	24% 14% 5% 12% 5% 4 4 3 4 4 22%	2772
January	1st to 10th	Night	14% 12% 4 9% 5% 5% 5% 3 6% 6% 31%	4429
	11th to 20th	Night	11% 13% 6% 14% 8% 6% 5% 4 5% 5% 22%	4440
	21st to end	Night	19% 14% 5% 11% 6% 6% 4 3 5% 4 23%	4884
February	1st to 10th	Night	13% 12% 4 9% 6% 6% 5% 4 6% 7% 27%	2493
	11th to 20th	Night	11% 10% 5% 11% 7% 6% 5% 5% 6% 6% 28%	2218
	21st to end	Night	13% 10% 4 12% 6% 4 4 4 5% 6% 32%	1884
March	1st to 10th	Night	23% 13% 3 8% 5% 4 4 3 5% 5% 27%	3724
	11th to 20th	Night	14% 14% 4 9% 6% 5% 5% 3 4 5% 30%	3703
	21st to end	Night	20% 13% 4 8% 4 4 3 3 5% 5% 32%	3481
April	1st to 10th	Night	19% 10% 3 8% 5% 5% 4 3 5% 6% 33%	1900
	11th to 20th	Night	18% 11% 2 8% 5% 3 4 3 5% 5% 35%	1875
	21st to end	Night	20% 9% 3 6% 5% 4 5% 3 4 6% 34%	1716
May	1st to 10th	Night	26% 11% 3 9% 4 4 3 4 5% 6% 25%	2834
	11th to 20th	Night	17% 10% 3 10% 6% 6% 5% 3 6% 6% 28%	2541
	21st to end	Night	15% 6% 2 6% 5% 4 5% 5% 6% 9% 39%	2738
June	1st to 10th	Night	19% 6% 3 7% 5% 6% 5% 4 7% 7% 31%	1520
	11th to 20th	Night	19% 6% 3 6% 5% 4 4 5% 5% 6% 39%	1520
	21st to end	Night	16% 6% 3 8% 6% 5% 5% 4 6% 7% 35%	1520
July	1st to 10th	Night	12% 5% 2 6% 5% 6% 6% 5% 7% 9% 36%	2520
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 4 6% 7% 40%	2520
	21st to end	Night	14% 7% 2 6% 5% 4 4 4 6% 7% 40%	2739
August	1st to 10th	Night	19% 10% 3 8% 5% 3 4 3 4 7% 34%	2569
	11th to 20th	Night	13% 8% 3 8% 4 4 5% 5% 6% 8% 37%	2873
	21st to end	Night	10% 5% 2 6% 3 4 4 4 7% 9% 45%	3476
September	1st to 10th	Night	13% 5% 2 6% 3 3 4 3 6% 7% 48%	1900
	11th to 20th	Night	14% 5% 2 6% 3 4 3 3 5% 6% 50%	2046
	21st to end	Night	14% 6% 2 5% 4 4 4 3 5% 7% 45%	2090
October	1st to 10th	Night	21% 7% 3 7% 4 4 4 4 5% 7% 34%	2107
	11th to 20th	Night	17% 10% 3 6% 5% 5% 4 3 5% 7% 36%	2359
	21st to end	Night	22% 11% 2 7% 5% 5% 4 3 5% 6% 30%	2637
November	1st to 10th	Night	15% 8% 3 8% 5% 5% 4 4 5% 6% 37%	2407
	11th to 20th	Night	16% 9% 3 6% 6% 5% 4 3 6% 6% 36%	2470
	21st to end	Night	17% 10% 4 9% 5% 4 4 4 5% 7% 31%	2567
December	1st to 10th	Night	18% 14% 4 11% 7% 4 5% 4 5% 5% 23%	2660
	11th to 20th	Night	20% 12% 3 8% 5% 4 4 4 5% 7% 28%	3288
	21st to end	Night	23% 14% 6% 12% 5% 4 4 3 4 4 21%	4884

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	50% 7% 12% 25% 6% 1	2518
	11th to 20th	Day	59% 9% 11% 16% 5% 1	2520
	21st to end	Day	59% 7% 11% 15% 6% 1	2772
February	1st to 10th	Day	55% 6% 13% 17% 8% 2	1681
	11th to 20th	Day	53% 7% 10% 18% 10% 2	1857
	21st to end	Day	54% 5% 10% 17% 13% 1	1570
March	1st to 10th	Day	63% 5% 8% 11% 10% 2	3119
	11th to 20th	Day	50% 10% 12% 14% 11% 2	3256
	21st to end	Day	53% 7% 6% 14% 17% 3	4134
April	1st to 10th	Day	53% 4 9% 20% 12% 3	2280
	11th to 20th	Day	48% 7% 10% 19% 15% 1	2254
	21st to end	Day	54% 6% 8% 17% 13% 2	2462
May	1st to 10th	Day	58% 7% 10% 17% 7% 1	4120
	11th to 20th	Day	50% 10% 14% 16% 9% 2	4386
	21st to end	Day	37% 9% 14% 25% 14% 1	4837
June	1st to 10th	Day	52% 8% 12% 18% 10%	2660
	11th to 20th	Day	46% 7% 11% 20% 14% 2	2660
	21st to end	Day	52% 8% 12% 17% 10% 1	2660
July	1st to 10th	Day	42% 7% 13% 22% 15% 1	4370
	11th to 20th	Day	41% 8% 18% 25% 9%	4365
	21st to end	Day	45% 6% 13% 23% 12% 1	4661
August	1st to 10th	Day	48% 7% 15% 20% 10%	4315
	11th to 20th	Day	49% 7% 15% 23% 6%	3990
	21st to end	Day	38% 6% 15% 26% 13% 1	4180
September	1st to 10th	Day	37% 7% 13% 28% 15% 1	2280
	11th to 20th	Day	37% 5% 10% 28% 19% 1	2133
	21st to end	Day	39% 7% 13% 26% 13% 2	2090
October	1st to 10th	Day	51% 6% 9% 20% 13% 2	2071
	11th to 20th	Day	45% 6% 14% 25% 9% 1	1820
	21st to end	Day	57% 6% 10% 16% 9% 2	1825
November	1st to 10th	Day	41% 8% 15% 20% 15% 1	1671
	11th to 20th	Day	49% 6% 12% 17% 15% 2	1710
	21st to end	Day	53% 7% 17% 16% 7% 1	1611
December	1st to 10th	Day	61% 6% 13% 13% 7%	1520
	11th to 20th	Day	55% 6% 10% 16% 12% 1	1906
	21st to end	Day	65% 6% 8% 13% 8%	2772
January	1st to 10th	Night	49% 8% 13% 19% 9% 1	4429
	11th to 20th	Night	56% 10% 11% 14% 7% 1	4440
	21st to end	Night	62% 7% 9% 13% 7% 1	4884
February	1st to 10th	Night	54% 7% 11% 17% 9% 1	2493
	11th to 20th	Night	51% 8% 10% 19% 11% 1	2220
	21st to end	Night	49% 8% 12% 20% 9% 3	1884
March	1st to 10th	Night	58% 5% 10% 15% 10% 2	3734
	11th to 20th	Night	51% 9% 10% 17% 11% 2	3704
	21st to end	Night	51% 7% 7% 13% 19% 4	3481
April	1st to 10th	Night	53% 5% 9% 18% 14% 2	1900
	11th to 20th	Night	49% 6% 9% 21% 14% 1	1875
	21st to end	Night	50% 6% 10% 17% 14% 3	1716
May	1st to 10th	Night	59% 7% 10% 15% 8% 1	2840
	11th to 20th	Night	54% 11% 11% 15% 8% 1	2542
	21st to end	Night	40% 9% 15% 21% 13% 2	2739
June	1st to 10th	Night	49% 8% 12% 18% 11% 1	1520
	11th to 20th	Night	45% 8% 14% 19% 12% 2	1520
	21st to end	Night	47% 8% 13% 20% 11% 1	1520
July	1st to 10th	Night	42% 7% 16% 21% 13%	2480
	11th to 20th	Night	41% 6% 15% 26% 12%	2472
	21st to end	Night	44% 6% 11% 27% 11% 1	2651
August	1st to 10th	Night	51% 6% 13% 21% 10%	2559
	11th to 20th	Night	44% 6% 19% 20% 10%	2900
	21st to end	Night	33% 6% 20% 28% 13% 1	3476
September	1st to 10th	Night	35% 6% 15% 28% 15% 1	1900
	11th to 20th	Night	35% 5% 12% 29% 18% 1	2046
	21st to end	Night	37% 7% 12% 27% 15% 2	2090
October	1st to 10th	Night	49% 6% 11% 21% 10% 2	2107
	11th to 20th	Night	47% 7% 13% 23% 9% 1	2359
	21st to end	Night	54% 6% 11% 19% 8% 1	2637
November	1st to 10th	Night	46% 6% 12% 21% 12% 2	2407
	11th to 20th	Night	46% 6% 11% 21% 14% 1	2470
	21st to end	Night	51% 7% 14% 20% 8%	2567
December	1st to 10th	Night	60% 7% 10% 17% 5%	2660
	11th to 20th	Night	55% 7% 12% 14% 11% 1	3288
	21st to end	Night	63% 6% 9% 17% 5%	4884

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	27% 22% 26% 19% 7%	180
	11th to 20th	Day	32% 26% 28% 12% 1 1	180
	21st to end	Day	21% 26% 31% 16% 7%	198
February	1st to 10th	Day	30% 28% 29% 11% 3	273
	11th to 20th	Day	27% 26% 31% 14% 2	456
	21st to end	Day	30% 21% 29% 17% 3	382
March	1st to 10th	Day	29% 18% 33% 16% 3	460
	11th to 20th	Day	32% 22% 29% 12% 5% 1	460
	21st to end	Day	32% 21% 25% 12% 7% 3	506
April	1st to 10th	Day	35% 19% 26% 12% 7% 2	460
	11th to 20th	Day	32% 21% 24% 14% 7% 1	452
	21st to end	Day	31% 21% 28% 12% 7% 1	460
May	1st to 10th	Day	33% 22% 25% 13% 6% 2	463
	11th to 20th	Day	22% 16% 34% 20% 5% 2	487
	21st to end	Day	19% 15% 33% 23% 9% 1	529
June	1st to 10th	Day	23% 14% 36% 17% 10% 1	490
	11th to 20th	Day	19% 16% 30% 22% 11% 2	490
	21st to end	Day	23% 16% 32% 18% 10% 2	490
July	1st to 10th	Day	16% 12% 33% 23% 12% 4	485
	11th to 20th	Day	13% 9% 34% 30% 12% 3	484
	21st to end	Day	16% 8% 38% 26% 11% 2	532
August	1st to 10th	Day	13% 12% 29% 25% 17% 3	486
	11th to 20th	Day	17% 9% 28% 25% 14% 8%	479
	21st to end	Day	13% 14% 25% 25% 17% 6%	539
September	1st to 10th	Day	17% 11% 24% 25% 15% 7%	490
	11th to 20th	Day	16% 13% 22% 21% 17% 10%	490
	21st to end	Day	15% 14% 29% 22% 12% 8%	490
October	1st to 10th	Day	26% 13% 24% 20% 12% 5%	490
	11th to 20th	Day	22% 17% 23% 27% 10% 3	447
	21st to end	Day	36% 13% 22% 21% 8%	411
November	1st to 10th	Day	23% 16% 23% 23% 13% 1	365
	11th to 20th	Day	31% 18% 23% 19% 7% 1	370
	21st to end	Day	32% 17% 26% 17% 6% 1	271
December	1st to 10th	Day	30% 23% 27% 14% 6%	180
	11th to 20th	Day	32% 24% 31% 9% 4	180
	21st to end	Day	35% 20% 25% 15% 5% 1	198
January	1st to 10th	Night	23% 17% 34% 24% 3	760
	11th to 20th	Night	25% 18% 29% 23% 3	760
	21st to end	Night	21% 18% 34% 22% 4	836
February	1st to 10th	Night	23% 17% 35% 22% 3	760
	11th to 20th	Night	20% 19% 35% 23% 2	743
	21st to end	Night	24% 18% 31% 24% 3	628
March	1st to 10th	Night	26% 16% 30% 24% 4	760
	11th to 20th	Night	24% 19% 28% 24% 5%	760
	21st to end	Night	28% 16% 26% 22% 7% 1	836
April	1st to 10th	Night	25% 19% 27% 24% 5%	760
	11th to 20th	Night	24% 21% 24% 24% 7%	751
	21st to end	Night	27% 15% 30% 22% 5%	576
May	1st to 10th	Night	28% 13% 28% 24% 6% 1	570
	11th to 20th	Night	20% 12% 29% 31% 7%	407
	21st to end	Night	18% 9% 26% 35% 12% 1	411
June	1st to 10th	Night	21% 8% 28% 32% 10%	380
	11th to 20th	Night	19% 10% 24% 33% 12%	380
	21st to end	Night	18% 8% 25% 40% 9% 1	380
July	1st to 10th	Night	15% 5% 20% 44% 15% 1	370
	11th to 20th	Night	15% 5% 20% 42% 17% 2	368
	21st to end	Night	14% 6% 19% 44% 16% 1	416
August	1st to 10th	Night	15% 4 17% 42% 21% 1	415
	11th to 20th	Night	14% 6% 24% 36% 18% 3	614
	21st to end	Night	15% 6% 20% 35% 22% 2	836
September	1st to 10th	Night	14% 9% 24% 32% 19% 2	760
	11th to 20th	Night	17% 7% 21% 29% 22% 4	760
	21st to end	Night	17% 8% 24% 30% 19% 2	760
October	1st to 10th	Night	27% 9% 18% 29% 16% 2	760
	11th to 20th	Night	23% 12% 23% 31% 11% 1	760
	21st to end	Night	29% 14% 26% 23% 8%	812
November	1st to 10th	Night	20% 16% 25% 28% 10%	740
	11th to 20th	Night	24% 15% 29% 24% 8% 1	760
	21st to end	Night	25% 16% 26% 26% 7% 1	760
December	1st to 10th	Night	24% 18% 32% 22% 4	760
	11th to 20th	Night	26% 18% 30% 21% 4	760
	21st to end	Night	29% 18% 31% 19% 3	836

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