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 2024-11-02.

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 9% 5% 5% 5% 4 6% 7% 30%	102004
	Night	14% 11% 4 9% 5% 5% 4 4 5% 7% 32%	96956
Transparency	Day	51% 6% 11% 20% 10% 1	101768
	Night	51% 5% 11% 20% 11% 1	96813
Seeing	Day	20% 10% 28% 24% 13% 5%	14946
	Night	20% 10% 29% 29% 12% 1	23917

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% 18% 8% 13% 6% 4 4 3 3 5% 20%	2613
	11th to 20th	Day	11% 19% 9% 21% 7% 5% 4 4 6% 5% 9%	2840
	21st to end	Day	21% 20% 7% 13% 6% 6% 4 3 3 4 11%	3124
February	1st to 10th	Day	15% 18% 4 13% 9% 7% 6% 4 4 5% 14%	1710
	11th to 20th	Day	13% 14% 7% 15% 8% 4 5% 4 6% 6% 19%	1663
	21st to end	Day	16% 15% 6% 12% 7% 4 4 3 5% 6% 22%	1529
March	1st to 10th	Day	20% 15% 6% 9% 6% 4 4 3 3 5% 26%	3387
	11th to 20th	Day	11% 14% 6% 10% 6% 5% 5% 4 5% 6% 28%	3480
	21st to end	Day	16% 12% 4 10% 6% 5% 5% 3 5% 6% 29%	3815
April	1st to 10th	Day	17% 14% 5% 8% 5% 4 4 4 6% 7% 27%	2187
	11th to 20th	Day	19% 11% 3 7% 4 4 3 3 4 6% 35%	2398
	21st to end	Day	20% 11% 4 8% 4 5% 4 3 4 6% 32%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 3 6% 8% 33%	4108
	11th to 20th	Day	16% 9% 3 8% 6% 5% 4 4 6% 8% 30%	4198
	21st to end	Day	13% 5% 2 5% 4 4 4 4 6% 8% 45%	4837
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% 15% 4 8% 5% 5% 4 4 6% 6% 30%	1663
	11th to 20th	Day	14% 17% 4 9% 6% 4 6% 4 7% 7% 22%	1520
	21st to end	Day	18% 18% 7% 9% 5% 6% 3 4 6% 6% 18%	1520
December	1st to 10th	Day	15% 19% 7% 14% 7% 6% 5% 4 4 5% 13%	1520
	11th to 20th	Day	18% 18% 7% 13% 7% 6% 5% 3 5% 4 15%	1906
	21st to end	Day	28% 21% 6% 15% 7% 4 3 2 3 4 7%	2772
January	1st to 10th	Night	17% 17% 7% 16% 7% 6% 5% 3 4 5% 15%	4332
	11th to 20th	Night	14% 16% 7% 16% 9% 6% 6% 5% 6% 5% 11%	4120
	21st to end	Night	21% 15% 9% 15% 6% 4 4 3 4 5% 15%	4532
February	1st to 10th	Night	15% 16% 6% 11% 8% 5% 6% 4 5% 6% 19%	2470
	11th to 20th	Night	13% 13% 6% 11% 7% 5% 5% 4 5% 7% 23%	2403
	21st to end	Night	15% 13% 4 12% 7% 4 5% 4 6% 6% 23%	1922
March	1st to 10th	Night	16% 10% 3 9% 5% 5% 5% 3 4 6% 33%	3452
	11th to 20th	Night	11% 10% 3 9% 5% 4 4 4 6% 8% 35%	3479
	21st to end	Night	15% 10% 3 8% 5% 4 4 3 5% 5% 38%	3817
April	1st to 10th	Night	19% 10% 3 8% 6% 4 4 4 5% 7% 32%	1992
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 3 5% 7% 36%	1747
	21st to end	Night	14% 10% 3 8% 5% 4 4 4 5% 8% 34%	1710
May	1st to 10th	Night	17% 7% 2 6% 4 3 4 3 5% 8% 40%	2833
	11th to 20th	Night	13% 8% 3 8% 5% 5% 5% 4 6% 6% 36%	2695
	21st to end	Night	10% 5% 1 5% 3 4 3 3 6% 9% 51%	2738
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 6% 6% 27%	2519
November	1st to 10th	Night	14% 10% 3 8% 5% 4 5% 4 5% 7% 35%	2436
	11th to 20th	Night	15% 14% 4 10% 6% 5% 6% 4 6% 6% 24%	2660
	21st to end	Night	18% 13% 5% 9% 6% 5% 5% 4 5% 7% 22%	2660
December	1st to 10th	Night	18% 18% 6% 12% 6% 6% 5% 3 5% 6% 15%	2660
	11th to 20th	Night	14% 19% 6% 12% 6% 5% 4 4 5% 5% 18%	3288
	21st to end	Night	27% 21% 7% 11% 6% 5% 4 3 3 4 10%	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	67% 6% 9% 12% 7%	2614
	11th to 20th	Day	76% 5% 8% 7% 3	2840
	21st to end	Day	78% 5% 6% 7% 3 1	3124
February	1st to 10th	Day	71% 5% 8% 12% 4	1710
	11th to 20th	Day	64% 5% 8% 15% 7% 1	1672
	21st to end	Day	63% 4 10% 14% 7% 1	1529
March	1st to 10th	Day	62% 4 9% 19% 5% 1	3390
	11th to 20th	Day	55% 6% 12% 19% 7% 1	3480
	21st to end	Day	54% 6% 10% 17% 11% 2	3815
April	1st to 10th	Day	55% 5% 11% 17% 11% 1	2187
	11th to 20th	Day	50% 5% 11% 21% 12% 1	2398
	21st to end	Day	54% 4 10% 19% 11% 2	2470
May	1st to 10th	Day	48% 6% 12% 20% 12% 2	4120
	11th to 20th	Day	49% 8% 13% 22% 7% 1	4202
	21st to end	Day	37% 6% 12% 22% 19% 5%	4837
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	50% 5% 11% 18% 14% 1	1914
	11th to 20th	Day	55% 5% 12% 18% 9%	1900
	21st to end	Day	63% 4 11% 15% 6%	2076
November	1st to 10th	Day	53% 6% 11% 21% 8% 1	1663
	11th to 20th	Day	58% 6% 13% 14% 8% 1	1520
	21st to end	Day	65% 5% 13% 13% 4	1520
December	1st to 10th	Day	72% 5% 9% 10% 4	1520
	11th to 20th	Day	73% 6% 8% 9% 4	1906
	21st to end	Day	81% 5% 6% 6% 1	2772
January	1st to 10th	Night	69% 8% 8% 10% 4 1	4332
	11th to 20th	Night	72% 7% 9% 8% 3	4120
	21st to end	Night	74% 4 8% 11% 4 1	4532
February	1st to 10th	Night	66% 4 8% 16% 5%	2470
	11th to 20th	Night	60% 5% 10% 17% 8%	2405
	21st to end	Night	61% 3 12% 16% 8%	1922
March	1st to 10th	Night	51% 5% 13% 23% 7% 1	3462
	11th to 20th	Night	45% 6% 14% 22% 12% 1	3480
	21st to end	Night	47% 6% 7% 23% 16% 2	3817
April	1st to 10th	Night	53% 4 8% 19% 14% 1	1992
	11th to 20th	Night	48% 5% 9% 20% 17% 2	1747
	21st to end	Night	49% 4 9% 20% 15% 3	1710
May	1st to 10th	Night	43% 5% 11% 20% 16% 5%	2840
	11th to 20th	Night	45% 8% 13% 23% 9% 2	2696
	21st to end	Night	30% 6% 14% 24% 23% 3	2739
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	44% 4 10% 25% 16% 1	2266
	11th to 20th	Night	50% 5% 11% 24% 10% 1	2280
	21st to end	Night	57% 4 10% 18% 11% 1	2519
November	1st to 10th	Night	48% 6% 11% 22% 12% 1	2436
	11th to 20th	Night	58% 6% 12% 16% 7% 1	2660
	21st to end	Night	61% 5% 15% 14% 5% 1	2660
December	1st to 10th	Night	70% 5% 9% 12% 4	2660
	11th to 20th	Night	66% 6% 11% 13% 4	3288
	21st to end	Night	79% 6% 7% 7% 2	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	25% 19% 30% 17% 7% 1	207
	11th to 20th	Day	24% 17% 40% 15% 3 1	270
	21st to end	Day	28% 12% 36% 19% 4	297
February	1st to 10th	Day	27% 16% 41% 12% 4	270
	11th to 20th	Day	24% 21% 39% 14% 1	270
	21st to end	Day	34% 24% 30% 10% 2	225
March	1st to 10th	Day	26% 14% 34% 19% 6%	426
	11th to 20th	Day	25% 13% 35% 18% 7% 1	460
	21st to end	Day	28% 13% 33% 19% 7% 1	506
April	1st to 10th	Day	22% 17% 32% 22% 6% 2	460
	11th to 20th	Day	30% 14% 27% 16% 9% 4	452
	21st to end	Day	27% 10% 33% 20% 8% 2	460
May	1st to 10th	Day	24% 8% 27% 24% 11% 5%	463
	11th to 20th	Day	19% 7% 27% 25% 15% 7%	487
	21st to end	Day	15% 4 28% 28% 17% 7%	529
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	28% 12% 31% 22% 6% 1	525
November	1st to 10th	Day	22% 22% 27% 20% 8% 1	264
	11th to 20th	Day	26% 19% 30% 17% 6% 2	180
	21st to end	Day	25% 14% 38% 19% 3	180
December	1st to 10th	Day	33% 17% 32% 13% 4 1	180
	11th to 20th	Day	27% 25% 29% 15% 3 1	180
	21st to end	Day	31% 18% 37% 12% 2	198
January	1st to 10th	Night	24% 16% 36% 17% 6% 1	760
	11th to 20th	Night	28% 16% 30% 22% 3	760
	21st to end	Night	20% 12% 36% 25% 6%	836
February	1st to 10th	Night	23% 16% 36% 23% 2	760
	11th to 20th	Night	22% 15% 34% 23% 5%	743
	21st to end	Night	23% 18% 35% 21% 3	628
March	1st to 10th	Night	19% 14% 37% 23% 6%	760
	11th to 20th	Night	20% 15% 36% 22% 7% 1	760
	21st to end	Night	22% 11% 33% 25% 9% 1	836
April	1st to 10th	Night	23% 12% 33% 26% 6%	760
	11th to 20th	Night	22% 10% 33% 25% 9% 1	623
	21st to end	Night	19% 7% 33% 33% 7% 1	570
May	1st to 10th	Night	18% 5% 31% 29% 15% 2	570
	11th to 20th	Night	18% 4 26% 36% 15% 1	496
	21st to end	Night	11% 4 27% 38% 19% 1	411
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% 31% 27% 5%	836
November	1st to 10th	Night	20% 12% 27% 29% 10% 1	745
	11th to 20th	Night	24% 13% 33% 20% 8% 1	760
	21st to end	Night	27% 11% 33% 23% 6%	760
December	1st to 10th	Night	28% 16% 31% 20% 4	760
	11th to 20th	Night	25% 18% 36% 18% 4	760
	21st to end	Night	31% 14% 33% 19% 3	836

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