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 2025-05-26.

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	15% 11% 4 10% 6% 5% 5% 4 5% 7% 29%	114829
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 7% 31%	114412
Transparency	Day	52% 5% 11% 19% 10% 1	118453
	Night	52% 5% 11% 20% 12% 1	118953
Seeing	Day	20% 11% 28% 23% 13% 5%	15586
	Night	20% 10% 29% 28% 11% 1	24687

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	11% 16% 7% 20% 7% 4 5% 3 4 5% 20%	3735
	11th to 20th	Day	10% 19% 8% 24% 8% 8% 4 3 5% 4 7%	4026
	21st to end	Day	17% 17% 7% 17% 7% 6% 4 3 4 5% 12%	4466
February	1st to 10th	Day	15% 18% 4 13% 9% 7% 6% 4 4 5% 15%	1800
	11th to 20th	Day	13% 14% 7% 14% 9% 5% 5% 4 5% 6% 18%	1753
	21st to end	Day	16% 15% 6% 12% 7% 4 4 3 5% 6% 21%	1607
March	1st to 10th	Day	18% 12% 5% 12% 8% 4 3 3 3 5% 26%	4859
	11th to 20th	Day	11% 12% 5% 9% 5% 5% 5% 4 6% 8% 29%	4980
	21st to end	Day	17% 13% 5% 11% 5% 5% 4 3 4 5% 28%	5465
April	1st to 10th	Day	17% 14% 5% 8% 5% 4 4 4 6% 7% 27%	2302
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 5% 7% 35%	2526
	21st to end	Day	19% 10% 4 8% 4 5% 4 3 4 7% 32%	2600
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 3 6% 8% 33%	4238
	11th to 20th	Day	16% 10% 3 8% 6% 5% 4 4 6% 8% 30%	4332
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 8% 44%	4907
June	1st to 10th	Day	14% 6% 3 6% 5% 5% 5% 4 7% 8% 37%	2660
	11th to 20th	Day	11% 7% 2 6% 6% 4 5% 5% 6% 9% 38%	2799
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 5% 6% 9% 39%	2850
July	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 6% 8% 10% 37%	4760
	11th to 20th	Day	10% 5% 2 5% 5% 5% 5% 5% 7% 9% 41%	4279
	21st to end	Day	9% 6% 2 6% 5% 6% 6% 4 7% 9% 41%	4466
August	1st to 10th	Day	15% 7% 2 6% 4 4 5% 4 7% 10% 35%	4104
	11th to 20th	Day	10% 7% 3 8% 5% 5% 6% 5% 7% 10% 35%	4044
	21st to end	Day	8% 6% 2 7% 5% 6% 6% 5% 6% 9% 39%	4442
September	1st to 10th	Day	11% 7% 2 6% 5% 6% 6% 5% 7% 8% 38%	2270
	11th to 20th	Day	11% 7% 3 5% 4 4 5% 4 7% 8% 43%	2090
	21st to end	Day	15% 7% 3 8% 5% 5% 5% 4 7% 8% 34%	2090
October	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 6% 6% 34%	1914
	11th to 20th	Day	21% 10% 3 9% 5% 4 4 4 4 7% 29%	1900
	21st to end	Day	22% 13% 3 9% 6% 5% 6% 4 5% 6% 21%	2076
November	1st to 10th	Day	13% 14% 4 8% 6% 5% 4 4 6% 6% 31%	1743
	11th to 20th	Day	14% 17% 4 9% 6% 4 5% 4 7% 7% 23%	1600
	21st to end	Day	17% 18% 7% 10% 5% 6% 4 4 6% 6% 18%	1600
December	1st to 10th	Day	18% 20% 7% 14% 8% 6% 6% 5% 5% 4 10%	2600
	11th to 20th	Day	22% 19% 7% 12% 7% 5% 4 3 4 3 15%	2986
	21st to end	Day	26% 20% 6% 14% 6% 4 4 2 3 4 11%	3960
January	1st to 10th	Night	13% 14% 6% 18% 7% 6% 5% 4 5% 5% 18%	6196
	11th to 20th	Night	11% 15% 7% 19% 11% 6% 6% 5% 5% 5% 10%	5859
	21st to end	Night	16% 14% 8% 15% 6% 5% 5% 3 5% 6% 18%	6490
February	1st to 10th	Night	15% 15% 6% 11% 8% 5% 6% 4 5% 6% 19%	2600
	11th to 20th	Night	13% 13% 6% 12% 7% 5% 5% 4 5% 7% 23%	2533
	21st to end	Night	14% 13% 4 13% 7% 4 5% 4 6% 6% 23%	2020
March	1st to 10th	Night	13% 9% 3 9% 8% 5% 5% 4 5% 6% 31%	4980
	11th to 20th	Night	9% 9% 3 9% 5% 5% 5% 4 7% 9% 35%	4979
	21st to end	Night	18% 10% 3 7% 4 4 4 3 4 5% 36%	5467
April	1st to 10th	Night	19% 10% 3 9% 6% 4 4 4 5% 7% 31%	2097
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 4 5% 7% 35%	1840
	21st to end	Night	14% 10% 3 8% 5% 4 5% 4 5% 8% 35%	1800
May	1st to 10th	Night	17% 7% 2 6% 4 3 4 3 5% 8% 40%	2923
	11th to 20th	Night	13% 8% 3 8% 5% 5% 5% 4 6% 7% 36%	2781
	21st to end	Night	11% 5% 1 5% 3 4 3 3 6% 9% 51%	2784
June	1st to 10th	Night	11% 6% 2 5% 5% 4 4 4 7% 7% 44%	1520
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 4 7% 9% 43%	1375
	21st to end	Night	10% 5% 2 6% 4 4 4 5% 5% 8% 46%	1330
July	1st to 10th	Night	6% 4 2 5% 4 4 4 3 6% 10% 53%	2210
	11th to 20th	Night	9% 5% 2 4 3 4 4 3 6% 9% 52%	2660
	21st to end	Night	6% 5% 2 6% 4 4 4 5% 6% 8% 48%	3087
August	1st to 10th	Night	11% 6% 2 7% 4 4 4 3 6% 8% 46%	2825
	11th to 20th	Night	10% 7% 3 6% 4 4 4 4 6% 9% 44%	2785
	21st to end	Night	8% 6% 2 5% 4 4 5% 3 6% 8% 49%	3181
September	1st to 10th	Night	9% 6% 2 5% 5% 6% 4 3 6% 8% 46%	1908
	11th to 20th	Night	10% 4 1 4 4 4 3 4 5% 7% 54%	2090
	21st to end	Night	16% 7% 3 6% 5% 5% 4 3 5% 6% 39%	2090
October	1st to 10th	Night	15% 8% 3 7% 4 4 4 3 5% 7% 40%	2266
	11th to 20th	Night	18% 10% 3 7% 5% 4 5% 3 5% 8% 34%	2280
	21st to end	Night	22% 9% 3 8% 6% 5% 5% 4 5% 6% 27%	2519
November	1st to 10th	Night	14% 10% 3 8% 5% 4 5% 5% 5% 7% 35%	2553
	11th to 20th	Night	15% 15% 4 10% 6% 5% 6% 4 6% 6% 24%	2800
	21st to end	Night	19% 13% 5% 10% 6% 5% 5% 4 5% 7% 21%	2800
December	1st to 10th	Night	13% 18% 8% 14% 8% 6% 6% 4 5% 5% 13%	4580
	11th to 20th	Night	14% 21% 7% 12% 6% 5% 4 4 4 5% 19%	5208
	21st to end	Night	23% 20% 7% 11% 5% 5% 4 3 4 4 14%	6996

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	67% 5% 7% 11% 9%	3736
	11th to 20th	Day	81% 4 7% 6% 3	4060
	21st to end	Day	75% 5% 8% 7% 6%	4466
February	1st to 10th	Day	70% 5% 8% 13% 4	1800
	11th to 20th	Day	65% 5% 8% 14% 7% 1	1762
	21st to end	Day	64% 4 10% 14% 7% 1	1607
March	1st to 10th	Day	61% 4 12% 16% 6% 1	4862
	11th to 20th	Day	52% 5% 15% 19% 7% 2	4980
	21st to end	Day	58% 5% 9% 17% 10% 1	5465
April	1st to 10th	Day	55% 5% 11% 17% 11% 1	2302
	11th to 20th	Day	50% 5% 11% 21% 12% 1	2526
	21st to end	Day	53% 4 10% 19% 11% 2	2600
May	1st to 10th	Day	48% 5% 12% 20% 12% 3	4250
	11th to 20th	Day	49% 8% 13% 22% 7% 1	4336
	21st to end	Day	37% 6% 12% 21% 19% 4	4907
June	1st to 10th	Day	43% 6% 11% 24% 14% 1	2660
	11th to 20th	Day	40% 6% 13% 24% 16% 2	2799
	21st to end	Day	42% 5% 12% 25% 15%	2850
July	1st to 10th	Day	39% 6% 14% 25% 15% 2	4686
	11th to 20th	Day	35% 6% 12% 34% 12% 1	4204
	21st to end	Day	38% 7% 12% 23% 18% 1	4324
August	1st to 10th	Day	42% 6% 13% 24% 14% 1	4091
	11th to 20th	Day	42% 6% 16% 26% 9%	4083
	21st to end	Day	39% 7% 11% 32% 11% 1	4442
September	1st to 10th	Day	41% 6% 14% 27% 11% 1	2270
	11th to 20th	Day	37% 5% 13% 29% 16% 1	2090
	21st to end	Day	47% 6% 12% 25% 9% 1	2090
October	1st to 10th	Day	42% 5% 12% 22% 18% 1	3174
	11th to 20th	Day	42% 5% 13% 23% 18%	3140
	21st to end	Day	53% 5% 15% 21% 7%	3402
November	1st to 10th	Day	52% 6% 12% 21% 8% 1	1743
	11th to 20th	Day	59% 5% 13% 14% 9% 1	1600
	21st to end	Day	66% 5% 12% 13% 4	1600
December	1st to 10th	Day	76% 5% 8% 7% 4	2600
	11th to 20th	Day	74% 4 7% 10% 5%	2986
	21st to end	Day	78% 6% 5% 7% 5%	3960
January	1st to 10th	Night	64% 7% 7% 15% 6% 1	6196
	11th to 20th	Night	74% 7% 8% 8% 3	5900
	21st to end	Night	68% 4 8% 11% 8% 1	6490
February	1st to 10th	Night	66% 4 9% 16% 5%	2600
	11th to 20th	Night	60% 5% 10% 17% 8%	2535
	21st to end	Night	61% 3 11% 16% 8%	2020
March	1st to 10th	Night	52% 5% 13% 19% 10% 2	4990
	11th to 20th	Night	43% 6% 17% 22% 11% 1	4980
	21st to end	Night	50% 5% 7% 19% 17% 2	5467
April	1st to 10th	Night	54% 4 8% 19% 14% 1	2097
	11th to 20th	Night	49% 5% 8% 20% 17% 2	1840
	21st to end	Night	48% 4 10% 20% 16% 3	1800
May	1st to 10th	Night	44% 5% 11% 20% 16% 5%	2930
	11th to 20th	Night	45% 8% 13% 23% 10% 2	2782
	21st to end	Night	31% 6% 13% 24% 23% 3	2785
June	1st to 10th	Night	38% 5% 11% 27% 17% 3	1520
	11th to 20th	Night	35% 6% 13% 26% 18% 2	1375
	21st to end	Night	36% 5% 14% 25% 18% 1	1330
July	1st to 10th	Night	27% 5% 13% 28% 21% 6%	2175
	11th to 20th	Night	30% 5% 13% 33% 18% 1	2613
	21st to end	Night	32% 7% 13% 27% 18% 3	2988
August	1st to 10th	Night	37% 5% 13% 27% 17% 2	2814
	11th to 20th	Night	37% 6% 16% 27% 13% 1	2812
	21st to end	Night	33% 6% 12% 33% 16% 1	3181
September	1st to 10th	Night	36% 5% 12% 28% 17% 2	1908
	11th to 20th	Night	29% 5% 12% 32% 20% 1	2090
	21st to end	Night	45% 5% 11% 27% 12%	2090
October	1st to 10th	Night	34% 3 8% 29% 24% 1	3786
	11th to 20th	Night	43% 4 13% 24% 16% 1	3779
	21st to end	Night	43% 4 14% 27% 12%	4143
November	1st to 10th	Night	48% 6% 11% 22% 12% 1	2553
	11th to 20th	Night	58% 6% 11% 16% 8% 1	2800
	21st to end	Night	62% 5% 15% 13% 4 1	2800
December	1st to 10th	Night	72% 6% 10% 10% 3	4580
	11th to 20th	Night	67% 5% 8% 11% 8% 1	5208
	21st to end	Night	74% 5% 8% 8% 5%	6996

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	23% 20% 33% 17% 7% 1	230
	11th to 20th	Day	23% 19% 40% 14% 3 1	300
	21st to end	Day	27% 15% 37% 17% 4	330
February	1st to 10th	Day	27% 18% 39% 12% 4	300
	11th to 20th	Day	26% 22% 37% 14% 1	300
	21st to end	Day	33% 22% 31% 12% 2	249
March	1st to 10th	Day	26% 14% 35% 19% 6%	464
	11th to 20th	Day	25% 14% 34% 18% 7% 1	500
	21st to end	Day	29% 14% 32% 19% 6% 1	550
April	1st to 10th	Day	24% 17% 31% 21% 6% 1	500
	11th to 20th	Day	29% 16% 26% 16% 10% 4	492
	21st to end	Day	26% 10% 33% 21% 8% 2	500
May	1st to 10th	Day	24% 9% 29% 23% 10% 5%	503
	11th to 20th	Day	19% 8% 28% 24% 14% 7%	527
	21st to end	Day	16% 4 29% 28% 17% 7%	549
June	1st to 10th	Day	16% 8% 26% 30% 14% 4	490
	11th to 20th	Day	14% 8% 26% 32% 16% 4	629
	21st to end	Day	15% 6% 30% 32% 13% 4	680
July	1st to 10th	Day	10% 6% 22% 30% 24% 9%	671
	11th to 20th	Day	15% 3 24% 27% 21% 11%	501
	21st to end	Day	11% 3 22% 35% 21% 9%	532
August	1st to 10th	Day	12% 5% 18% 28% 23% 14%	486
	11th to 20th	Day	13% 2 19% 29% 22% 15%	479
	21st to end	Day	14% 4 19% 29% 21% 12%	539
September	1st to 10th	Day	12% 7% 22% 26% 20% 13%	490
	11th to 20th	Day	11% 3 18% 25% 28% 14%	490
	21st to end	Day	18% 8% 25% 26% 15% 9%	490
October	1st to 10th	Day	22% 10% 24% 23% 16% 6%	490
	11th to 20th	Day	23% 12% 32% 23% 8% 2	490
	21st to end	Day	29% 12% 31% 22% 6% 1	525
November	1st to 10th	Day	20% 24% 28% 19% 8% 1	290
	11th to 20th	Day	25% 19% 32% 18% 6% 2	200
	21st to end	Day	24% 17% 39% 18% 4	200
December	1st to 10th	Day	35% 18% 31% 12% 5% 1	200
	11th to 20th	Day	28% 24% 31% 14% 3 1	200
	21st to end	Day	32% 18% 35% 11% 3	220
January	1st to 10th	Night	24% 17% 36% 17% 6% 1	800
	11th to 20th	Night	27% 17% 31% 22% 3	800
	21st to end	Night	20% 13% 37% 24% 6%	880
February	1st to 10th	Night	23% 17% 36% 23% 2	800
	11th to 20th	Night	23% 16% 34% 22% 5%	783
	21st to end	Night	22% 18% 35% 21% 3	660
March	1st to 10th	Night	19% 15% 37% 23% 6%	800
	11th to 20th	Night	19% 15% 36% 22% 7% 1	800
	21st to end	Night	22% 11% 33% 25% 9% 1	880
April	1st to 10th	Night	23% 13% 32% 26% 6%	800
	11th to 20th	Night	22% 11% 32% 25% 9% 1	656
	21st to end	Night	19% 8% 33% 33% 7% 1	600
May	1st to 10th	Night	19% 5% 31% 29% 14% 2	600
	11th to 20th	Night	18% 4 26% 35% 15% 1	522
	21st to end	Night	12% 4 28% 37% 18% 1	423
June	1st to 10th	Night	16% 2 28% 41% 12% 1	380
	11th to 20th	Night	11% 5% 28% 42% 14%	380
	21st to end	Night	13% 4 27% 40% 16%	380
July	1st to 10th	Night	5% 1 20% 52% 21% 2	370
	11th to 20th	Night	11% 3 21% 40% 22% 4	464
	21st to end	Night	10% 3 18% 46% 20% 3	624
August	1st to 10th	Night	10% 1 15% 44% 26% 4	567
	11th to 20th	Night	9% 2 14% 42% 29% 4	564
	21st to end	Night	11% 2 20% 35% 28% 4	658
September	1st to 10th	Night	12% 4 21% 35% 22% 4	760
	11th to 20th	Night	11% 4 18% 35% 27% 5%	760
	21st to end	Night	20% 6% 20% 31% 19% 5%	760
October	1st to 10th	Night	19% 6% 26% 28% 19% 2	760
	11th to 20th	Night	23% 9% 28% 28% 10% 2	760
	21st to end	Night	27% 10% 30% 27% 5%	836
November	1st to 10th	Night	20% 12% 28% 29% 10% 1	780
	11th to 20th	Night	24% 14% 32% 21% 8% 1	800
	21st to end	Night	27% 12% 33% 23% 6%	800
December	1st to 10th	Night	28% 17% 31% 20% 5%	800
	11th to 20th	Night	24% 19% 35% 18% 4	800
	21st to end	Night	30% 14% 33% 20% 3	880

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