New Hamburg Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New Hamburg Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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% 10% 4 9% 6% 5% 5% 4 5% 7% 31%	150384
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 7% 31%	140986
Transparency	Day	51% 5% 11% 21% 11% 1	153965
	Night	51% 5% 10% 20% 12% 1	145495
Seeing	Day	20% 11% 28% 24% 13% 5%	17425
	Night	19% 10% 29% 29% 11% 1	26305

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	15% 15% 8% 20% 7% 4 4 3 4 4 16%	4841
	11th to 20th	Day	9% 21% 10% 23% 9% 9% 4 3 4 3 6%	5246
	21st to end	Day	14% 16% 6% 17% 9% 8% 6% 3 4 5% 11%	5780
February	1st to 10th	Day	14% 18% 4 13% 9% 7% 6% 4 4 5% 16%	1890
	11th to 20th	Day	13% 14% 7% 15% 9% 5% 5% 4 5% 6% 18%	1843
	21st to end	Day	15% 16% 6% 12% 7% 5% 5% 3 5% 6% 21%	1685
March	1st to 10th	Day	18% 12% 5% 12% 7% 4 3 3 3 5% 26%	4967
	11th to 20th	Day	12% 12% 5% 10% 5% 5% 4 4 6% 8% 29%	5090
	21st to end	Day	17% 13% 5% 11% 6% 5% 4 3 4 5% 27%	5586
April	1st to 10th	Day	17% 14% 5% 8% 5% 4 4 4 6% 7% 27%	2417
	11th to 20th	Day	18% 11% 3 8% 4 4 4 3 4 7% 34%	2654
	21st to end	Day	19% 10% 4 8% 5% 5% 4 3 4 7% 33%	2730
May	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 4 5% 7% 33%	7642
	11th to 20th	Day	15% 9% 3 8% 5% 5% 4 4 6% 8% 33%	7841
	21st to end	Day	17% 7% 2 5% 4 4 4 4 5% 7% 42%	9060
June	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 4 6% 8% 38%	2940
	11th to 20th	Day	11% 7% 2 7% 6% 5% 5% 5% 7% 9% 37%	3094
	21st to end	Day	13% 5% 2 7% 4 5% 5% 5% 6% 9% 39%	3150
July	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 5% 7% 9% 38%	8879
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 10% 46%	7993
	21st to end	Day	8% 5% 2 7% 4 5% 5% 4 6% 8% 45%	8340
August	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 6% 8% 37%	6014
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 37%	5951
	21st to end	Day	10% 6% 3 8% 5% 6% 6% 5% 7% 9% 36%	6459
September	1st to 10th	Day	10% 7% 2 6% 5% 6% 5% 5% 7% 8% 39%	2508
	11th to 20th	Day	10% 7% 3 5% 4 4 5% 4 7% 8% 44%	2310
	21st to end	Day	14% 8% 3 8% 5% 4 4 5% 6% 8% 34%	2288
October	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 6% 6% 36%	2015
	11th to 20th	Day	20% 10% 3 8% 5% 4 4 4 5% 7% 30%	2000
	21st to end	Day	22% 13% 3 9% 6% 5% 6% 4 5% 6% 22%	2185
November	1st to 10th	Day	13% 14% 4 8% 5% 5% 4 4 6% 7% 30%	1832
	11th to 20th	Day	14% 17% 4 9% 6% 4 5% 4 7% 7% 23%	1680
	21st to end	Day	16% 19% 7% 10% 5% 6% 4 4 6% 6% 17%	1680
December	1st to 10th	Day	18% 20% 7% 14% 8% 5% 6% 5% 5% 4 10%	2680
	11th to 20th	Day	21% 19% 7% 12% 7% 5% 5% 3 4 3 15%	3066
	21st to end	Day	26% 20% 6% 14% 6% 4 4 2 3 4 11%	4048
January	1st to 10th	Night	14% 14% 6% 19% 7% 6% 5% 4 5% 5% 16%	8039
	11th to 20th	Night	10% 18% 8% 18% 11% 7% 5% 4 5% 5% 9%	7639
	21st to end	Night	13% 13% 7% 15% 8% 7% 6% 4 5% 6% 17%	8401
February	1st to 10th	Night	14% 15% 6% 11% 8% 5% 5% 4 5% 6% 19%	2730
	11th to 20th	Night	13% 13% 6% 12% 7% 5% 5% 4 5% 7% 23%	2663
	21st to end	Night	14% 13% 5% 13% 7% 5% 5% 4 6% 6% 23%	2118
March	1st to 10th	Night	13% 10% 3 9% 8% 5% 5% 4 5% 6% 31%	5092
	11th to 20th	Night	9% 9% 3 9% 5% 5% 5% 4 7% 9% 34%	5089
	21st to end	Night	18% 10% 3 8% 4 4 4 3 4 5% 36%	5588
April	1st to 10th	Night	19% 9% 3 9% 6% 4 4 4 5% 7% 30%	2202
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 3 5% 7% 35%	1933
	21st to end	Night	14% 10% 3 8% 5% 4 5% 4 5% 8% 35%	1890
May	1st to 10th	Night	18% 7% 3 7% 4 4 4 3 5% 8% 38%	5257
	11th to 20th	Night	14% 9% 3 8% 5% 5% 5% 3 5% 6% 37%	5005
	21st to end	Night	18% 5% 2 5% 2 3 4 3 5% 7% 46%	5114
June	1st to 10th	Night	11% 6% 2 5% 5% 4 4 4 6% 7% 45%	1680
	11th to 20th	Night	8% 5% 3 6% 5% 5% 5% 4 7% 10% 42%	1519
	21st to end	Night	10% 5% 2 6% 4 4 4 5% 5% 8% 46%	1470
July	1st to 10th	Night	6% 5% 2 5% 4 4 5% 4 6% 10% 49%	4110
	11th to 20th	Night	8% 5% 2 5% 3 4 4 3 6% 10% 49%	4934
	21st to end	Night	8% 5% 2 6% 4 4 4 4 5% 7% 50%	5737
August	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 6% 7% 42%	4135
	11th to 20th	Night	9% 6% 3 6% 4 4 4 4 6% 8% 45%	4095
	21st to end	Night	10% 7% 2 6% 4 4 5% 4 7% 7% 44%	4619
September	1st to 10th	Night	9% 6% 2 5% 5% 6% 4 4 6% 8% 46%	2109
	11th to 20th	Night	9% 5% 1 4 4 4 3 4 5% 7% 55%	2310
	21st to end	Night	16% 7% 2 6% 5% 5% 4 3 5% 6% 41%	2289
October	1st to 10th	Night	15% 8% 3 7% 4 4 4 3 5% 7% 42%	2385
	11th to 20th	Night	18% 10% 3 7% 5% 4 4 3 5% 7% 34%	2400
	21st to end	Night	21% 9% 3 8% 6% 5% 5% 4 5% 6% 28%	2652
November	1st to 10th	Night	14% 10% 3 8% 5% 4 5% 4 5% 7% 35%	2684
	11th to 20th	Night	15% 15% 4 10% 6% 5% 6% 4 6% 7% 24%	2940
	21st to end	Night	19% 14% 6% 10% 6% 5% 5% 4 5% 7% 20%	2940
December	1st to 10th	Night	13% 18% 7% 14% 8% 6% 5% 4 5% 5% 13%	4720
	11th to 20th	Night	13% 20% 7% 12% 6% 5% 4 4 4 5% 19%	5348
	21st to end	Night	23% 20% 7% 11% 6% 5% 4 3 4 4 14%	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	71% 5% 6% 10% 8%	4842
	11th to 20th	Day	84% 3 5% 5% 3	5280
	21st to end	Day	75% 4 8% 7% 5%	5780
February	1st to 10th	Day	70% 4 7% 13% 5%	1890
	11th to 20th	Day	65% 5% 8% 15% 6% 1	1852
	21st to end	Day	64% 4 10% 14% 7% 1	1685
March	1st to 10th	Day	61% 4 12% 16% 6% 1	4970
	11th to 20th	Day	52% 5% 14% 19% 7% 2	5090
	21st to end	Day	58% 5% 9% 17% 10% 1	5586
April	1st to 10th	Day	56% 5% 11% 17% 11% 1	2417
	11th to 20th	Day	50% 4 11% 22% 12% 1	2654
	21st to end	Day	53% 4 10% 20% 11% 2	2730
May	1st to 10th	Day	49% 5% 11% 21% 11% 4	7651
	11th to 20th	Day	47% 6% 11% 21% 13% 1	7845
	21st to end	Day	42% 4 8% 25% 18% 3	9061
June	1st to 10th	Day	42% 5% 11% 24% 16% 1	2940
	11th to 20th	Day	41% 6% 13% 24% 15% 1	3094
	21st to end	Day	41% 5% 12% 26% 15%	3150
July	1st to 10th	Day	40% 6% 12% 25% 15% 1	8806
	11th to 20th	Day	31% 5% 11% 35% 16% 1	7918
	21st to end	Day	35% 6% 12% 27% 20% 1	8156
August	1st to 10th	Day	44% 5% 12% 20% 15% 3	6001
	11th to 20th	Day	40% 6% 17% 30% 7%	5990
	21st to end	Day	42% 7% 12% 30% 8% 1	6459
September	1st to 10th	Day	40% 6% 14% 27% 11% 1	2508
	11th to 20th	Day	36% 4 14% 29% 16% 1	2310
	21st to end	Day	47% 6% 12% 25% 11% 1	2288
October	1st to 10th	Day	41% 5% 11% 23% 18% 1	3275
	11th to 20th	Day	41% 5% 12% 23% 18%	3240
	21st to end	Day	53% 5% 14% 20% 8%	3511
November	1st to 10th	Day	52% 6% 12% 21% 8% 1	1832
	11th to 20th	Day	58% 5% 12% 14% 9% 1	1680
	21st to end	Day	66% 5% 12% 13% 4	1680
December	1st to 10th	Day	76% 5% 8% 7% 4	2680
	11th to 20th	Day	74% 4 7% 10% 5%	3066
	21st to end	Day	78% 5% 5% 7% 5%	4048
January	1st to 10th	Night	68% 6% 7% 13% 5%	8039
	11th to 20th	Night	75% 6% 6% 8% 4	7680
	21st to end	Night	68% 4 7% 12% 8%	8401
February	1st to 10th	Night	65% 4 8% 17% 6% 1	2730
	11th to 20th	Night	60% 5% 10% 18% 8%	2665
	21st to end	Night	61% 3 11% 16% 8%	2118
March	1st to 10th	Night	52% 5% 13% 19% 10% 2	5102
	11th to 20th	Night	44% 6% 17% 22% 11% 1	5090
	21st to end	Night	50% 5% 7% 19% 17% 2	5588
April	1st to 10th	Night	54% 4 9% 18% 14% 1	2202
	11th to 20th	Night	49% 5% 9% 20% 16% 2	1933
	21st to end	Night	47% 4 10% 20% 15% 3	1890
May	1st to 10th	Night	46% 5% 11% 16% 16% 6%	5264
	11th to 20th	Night	47% 7% 10% 22% 12% 2	5006
	21st to end	Night	38% 4 10% 25% 20% 2	5115
June	1st to 10th	Night	36% 5% 10% 27% 18% 3	1680
	11th to 20th	Night	35% 6% 13% 27% 17% 2	1519
	21st to end	Night	36% 5% 14% 24% 19% 1	1470
July	1st to 10th	Night	31% 5% 15% 28% 17% 3	4075
	11th to 20th	Night	31% 4 10% 31% 21% 2	4887
	21st to end	Night	33% 5% 10% 25% 23% 3	5606
August	1st to 10th	Night	41% 5% 11% 23% 15% 6%	4124
	11th to 20th	Night	36% 6% 17% 29% 12% 1	4122
	21st to end	Night	37% 6% 13% 31% 13% 1	4619
September	1st to 10th	Night	35% 6% 13% 29% 15% 2	2109
	11th to 20th	Night	29% 5% 12% 32% 21% 1	2310
	21st to end	Night	44% 5% 11% 26% 14% 1	2289
October	1st to 10th	Night	33% 3 8% 30% 24% 1	3905
	11th to 20th	Night	43% 4 12% 23% 16% 1	3899
	21st to end	Night	43% 4 14% 26% 12%	4276
November	1st to 10th	Night	48% 6% 10% 22% 12% 1	2684
	11th to 20th	Night	57% 6% 11% 16% 8% 1	2940
	21st to end	Night	63% 5% 14% 13% 4 1	2940
December	1st to 10th	Night	71% 6% 10% 10% 3	4720
	11th to 20th	Night	67% 5% 8% 12% 8% 1	5348
	21st to end	Night	73% 5% 8% 9% 5%	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% 20% 34% 15% 6% 1	253
	11th to 20th	Day	23% 21% 38% 14% 3 1	330
	21st to end	Day	26% 16% 37% 17% 4	363
February	1st to 10th	Day	25% 19% 38% 14% 4	330
	11th to 20th	Day	25% 22% 38% 15% 2	330
	21st to end	Day	30% 23% 33% 11% 3	273
March	1st to 10th	Day	26% 15% 34% 19% 6%	502
	11th to 20th	Day	26% 16% 32% 18% 6% 1	540
	21st to end	Day	28% 15% 33% 18% 6% 1	594
April	1st to 10th	Day	24% 18% 31% 20% 6% 1	540
	11th to 20th	Day	29% 16% 26% 16% 9% 4	532
	21st to end	Day	26% 10% 34% 21% 8% 2	540
May	1st to 10th	Day	24% 10% 30% 23% 9% 5%	543
	11th to 20th	Day	18% 9% 29% 25% 13% 6%	567
	21st to end	Day	16% 6% 30% 27% 15% 6%	617
June	1st to 10th	Day	15% 9% 28% 30% 14% 4	570
	11th to 20th	Day	14% 9% 29% 30% 14% 3	724
	21st to end	Day	14% 6% 30% 33% 12% 4	780
July	1st to 10th	Day	10% 6% 22% 31% 23% 8%	771
	11th to 20th	Day	14% 4 24% 28% 21% 10%	583
	21st to end	Day	10% 3 22% 35% 22% 8%	620
August	1st to 10th	Day	12% 4 18% 29% 23% 14%	566
	11th to 20th	Day	12% 2 20% 31% 21% 14%	559
	21st to end	Day	15% 5% 18% 31% 21% 11%	627
September	1st to 10th	Day	12% 7% 22% 25% 21% 13%	570
	11th to 20th	Day	11% 4 18% 25% 28% 14%	570
	21st to end	Day	17% 7% 24% 27% 16% 8%	562
October	1st to 10th	Day	21% 9% 23% 24% 17% 6%	530
	11th to 20th	Day	22% 13% 33% 23% 8% 2	530
	21st to end	Day	28% 12% 32% 22% 5% 1	568
November	1st to 10th	Day	22% 24% 28% 18% 7% 1	319
	11th to 20th	Day	25% 20% 30% 18% 6% 2	220
	21st to end	Day	24% 18% 38% 17% 3	220
December	1st to 10th	Day	33% 19% 30% 13% 5%	220
	11th to 20th	Day	27% 25% 30% 14% 3 1	220
	21st to end	Day	33% 19% 34% 12% 3	242
January	1st to 10th	Night	23% 17% 36% 17% 5% 1	840
	11th to 20th	Night	27% 18% 32% 21% 3	840
	21st to end	Night	20% 14% 37% 24% 6%	924
February	1st to 10th	Night	23% 17% 35% 23% 2	840
	11th to 20th	Night	22% 16% 35% 22% 5%	823
	21st to end	Night	22% 18% 35% 21% 3	692
March	1st to 10th	Night	19% 15% 37% 23% 6%	840
	11th to 20th	Night	21% 15% 35% 22% 7%	840
	21st to end	Night	22% 12% 33% 24% 8% 1	924
April	1st to 10th	Night	23% 13% 33% 25% 5%	840
	11th to 20th	Night	22% 11% 33% 25% 8% 1	689
	21st to end	Night	19% 8% 32% 34% 7%	630
May	1st to 10th	Night	18% 6% 32% 28% 14% 2	630
	11th to 20th	Night	18% 4 27% 35% 14% 1	548
	21st to end	Night	13% 4 29% 36% 17% 1	455
June	1st to 10th	Night	15% 2 29% 41% 13% 1	420
	11th to 20th	Night	11% 5% 29% 41% 13%	420
	21st to end	Night	13% 4 27% 41% 15%	420
July	1st to 10th	Night	5% 1 19% 52% 21% 1	410
	11th to 20th	Night	11% 3 22% 39% 22% 3	514
	21st to end	Night	10% 3 19% 47% 20% 2	690
August	1st to 10th	Night	11% 1 14% 44% 26% 3	627
	11th to 20th	Night	9% 2 13% 44% 28% 3	624
	21st to end	Night	12% 2 20% 34% 28% 3	728
September	1st to 10th	Night	12% 5% 21% 36% 23% 4	840
	11th to 20th	Night	11% 4 18% 36% 27% 5%	840
	21st to end	Night	19% 5% 20% 32% 19% 5%	833
October	1st to 10th	Night	18% 6% 26% 29% 20% 2	800
	11th to 20th	Night	23% 9% 29% 28% 10% 2	800
	21st to end	Night	26% 10% 31% 28% 5%	880
November	1st to 10th	Night	20% 13% 28% 29% 10% 1	820
	11th to 20th	Night	23% 15% 32% 21% 8% 1	840
	21st to end	Night	28% 12% 33% 22% 5%	840
December	1st to 10th	Night	27% 16% 31% 21% 5%	840
	11th to 20th	Night	24% 19% 36% 17% 4	840
	21st to end	Night	31% 14% 33% 19% 3	924

Page generated at 2026-09-26 04:18:43. Version ac07

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