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 2024-03-06.

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 8% 7% 4 5% 5% 5% 7% 29%	79044
	Night	15% 11% 5% 8% 7% 3 5% 5% 5% 7% 30%	80460
Transparency	Day	54% 5% 11% 19% 10% 1	78757
	Night	54% 5% 11% 19% 10% 1	80283
Seeing	Day	20% 10% 28% 24% 13% 5%	13956
	Night	20% 10% 29% 29% 11% 1	23152

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% 11% 8% 3 4 4 3 5% 20%	2613
	11th to 20th	Day	12% 18% 9% 19% 9% 4 5% 5% 5% 5% 9%	2840
	21st to end	Day	21% 19% 8% 12% 7% 4 5% 4 3 4 11%	3124
February	1st to 10th	Day	16% 17% 5% 10% 11% 5% 7% 5% 4 5% 15%	1710
	11th to 20th	Day	13% 12% 9% 13% 9% 4 6% 5% 5% 6% 19%	1663
	21st to end	Day	16% 14% 6% 10% 9% 3 4 4 5% 6% 22%	1529
March	1st to 10th	Day	14% 12% 5% 9% 7% 4 5% 5% 4 6% 27%	1998
	11th to 20th	Day	13% 12% 7% 7% 7% 4 5% 5% 4 6% 30%	1980
	21st to end	Day	17% 12% 5% 8% 7% 4 4 4 4 6% 29%	2178
April	1st to 10th	Day	17% 12% 6% 7% 5% 3 4 4 6% 7% 27%	2071
	11th to 20th	Day	19% 10% 3 7% 4 3 4 4 5% 7% 35%	2270
	21st to end	Day	21% 10% 4 7% 5% 3 4 3 4 7% 32%	2340
May	1st to 10th	Day	18% 8% 3 6% 6% 4 5% 4 5% 8% 33%	2340
	11th to 20th	Day	17% 8% 3 6% 6% 3 4 4 5% 7% 36%	2362
	21st to end	Day	13% 5% 3 4 6% 3 5% 5% 7% 9% 40%	2725
June	1st to 10th	Day	14% 5% 3 6% 6% 4 5% 5% 6% 8% 38%	2520
	11th to 20th	Day	11% 6% 2 5% 6% 3 5% 6% 6% 9% 40%	2651
	21st to end	Day	13% 5% 2 6% 5% 3 5% 6% 6% 9% 40%	2700
July	1st to 10th	Day	8% 4 2 5% 6% 3 6% 6% 7% 9% 44%	2700
	11th to 20th	Day	11% 6% 3 5% 6% 4 7% 6% 7% 10% 36%	2443
	21st to end	Day	10% 6% 3 6% 6% 4 6% 5% 7% 9% 39%	2547
August	1st to 10th	Day	9% 5% 2 6% 6% 4 6% 7% 7% 11% 37%	2327
	11th to 20th	Day	9% 5% 3 7% 7% 4 6% 6% 7% 10% 36%	2303
	21st to end	Day	12% 7% 3 6% 5% 4 5% 6% 6% 8% 39%	2526
September	1st to 10th	Day	11% 7% 2 5% 6% 4 6% 6% 7% 9% 36%	2151
	11th to 20th	Day	12% 6% 3 4 5% 3 5% 5% 7% 9% 42%	1980
	21st to end	Day	15% 7% 3 7% 6% 4 4 5% 6% 8% 35%	1980
October	1st to 10th	Day	18% 10% 3 7% 6% 3 4 5% 5% 6% 33%	1814
	11th to 20th	Day	22% 10% 4 8% 6% 4 4 6% 5% 7% 27%	1800
	21st to end	Day	23% 13% 3 7% 7% 4 5% 5% 5% 6% 21%	1967
November	1st to 10th	Day	13% 13% 4 7% 6% 4 5% 4 6% 7% 31%	1654
	11th to 20th	Day	15% 15% 5% 8% 7% 3 5% 6% 7% 7% 22%	1520
	21st to end	Day	18% 16% 8% 9% 5% 5% 4 5% 6% 6% 19%	1520
December	1st to 10th	Day	15% 18% 8% 13% 8% 5% 6% 5% 4 5% 13%	1520
	11th to 20th	Day	18% 16% 8% 12% 8% 4 6% 4 4 4 15%	1906
	21st to end	Day	29% 20% 6% 13% 8% 3 3 3 3 4 7%	2772
January	1st to 10th	Night	17% 16% 7% 14% 8% 5% 5% 5% 4 5% 15%	4332
	11th to 20th	Night	14% 14% 8% 14% 11% 5% 6% 6% 6% 5% 11%	4120
	21st to end	Night	21% 14% 9% 13% 8% 3 4 4 4 5% 15%	4532
February	1st to 10th	Night	15% 14% 7% 10% 9% 4 6% 5% 5% 6% 19%	2470
	11th to 20th	Night	13% 12% 6% 10% 8% 4 6% 5% 5% 7% 23%	2403
	21st to end	Night	15% 12% 5% 11% 9% 3 5% 5% 5% 7% 23%	1922
March	1st to 10th	Night	14% 8% 3 8% 7% 4 6% 5% 5% 7% 33%	2065
	11th to 20th	Night	13% 11% 4 7% 7% 3 4 4 6% 6% 34%	1979
	21st to end	Night	16% 10% 4 7% 5% 3 5% 4 4 5% 35%	2178
April	1st to 10th	Night	19% 8% 4 7% 6% 3 4 5% 5% 7% 32%	1888
	11th to 20th	Night	16% 8% 3 6% 6% 4 4 5% 4 8% 37%	1654
	21st to end	Night	14% 10% 4 7% 5% 3 5% 5% 5% 8% 34%	1620
May	1st to 10th	Night	16% 7% 3 6% 5% 3 4 4 5% 8% 38%	1620
	11th to 20th	Night	15% 6% 2 6% 5% 2 5% 5% 5% 7% 41%	1531
	21st to end	Night	9% 5% 2 4 4 3 4 4 6% 9% 51%	1550
June	1st to 10th	Night	11% 5% 3 4 5% 3 4 5% 6% 7% 45%	1440
	11th to 20th	Night	9% 4 3 5% 5% 3 5% 5% 7% 9% 44%	1303
	21st to end	Night	10% 4 2 6% 5% 3 4 6% 5% 8% 46%	1260
July	1st to 10th	Night	5% 3 2 4 4 3 4 4 6% 10% 57%	1260
	11th to 20th	Night	9% 4 3 3 4 3 5% 4 6% 9% 50%	1509
	21st to end	Night	8% 5% 2 6% 5% 2 4 5% 6% 9% 48%	1771
August	1st to 10th	Night	8% 4 2 6% 5% 3 4 4 6% 9% 49%	1611
	11th to 20th	Night	6% 5% 3 4 5% 3 4 5% 7% 10% 48%	1598
	21st to end	Night	8% 5% 2 5% 6% 3 5% 4 7% 8% 47%	1811
September	1st to 10th	Night	10% 7% 2 5% 6% 4 5% 4 6% 8% 45%	1807
	11th to 20th	Night	11% 4 2 4 4 3 3 5% 4 7% 53%	1980
	21st to end	Night	15% 7% 3 5% 6% 4 4 4 5% 7% 41%	1980
October	1st to 10th	Night	15% 8% 3 6% 6% 3 4 4 4 7% 39%	2146
	11th to 20th	Night	19% 10% 3 6% 6% 3 5% 4 5% 8% 32%	2160
	21st to end	Night	23% 9% 3 7% 8% 3 5% 5% 5% 6% 26%	2386
November	1st to 10th	Night	14% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	2422
	11th to 20th	Night	16% 13% 4 9% 6% 4 6% 5% 6% 7% 24%	2660
	21st to end	Night	18% 12% 6% 9% 6% 3 6% 5% 5% 7% 22%	2660
December	1st to 10th	Night	18% 17% 8% 11% 7% 4 6% 4 5% 6% 15%	2660
	11th to 20th	Night	14% 18% 7% 11% 7% 4 5% 5% 5% 6% 19%	3288
	21st to end	Night	27% 20% 8% 10% 7% 4 4 4 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	59% 4 12% 18% 7% 1	2001
	11th to 20th	Day	56% 4 9% 18% 10% 2	1980
	21st to end	Day	56% 4 9% 17% 11% 2	2178
April	1st to 10th	Day	55% 5% 11% 17% 11% 1	2071
	11th to 20th	Day	50% 4 12% 21% 13% 1	2270
	21st to end	Day	54% 4 10% 19% 11% 2	2340
May	1st to 10th	Day	50% 4 10% 23% 12% 1	2340
	11th to 20th	Day	47% 5% 11% 24% 11% 2	2366
	21st to end	Day	40% 6% 14% 24% 14% 2	2725
June	1st to 10th	Day	43% 5% 12% 24% 15% 1	2520
	11th to 20th	Day	41% 6% 13% 24% 15% 2	2651
	21st to end	Day	41% 5% 12% 26% 16%	2700
July	1st to 10th	Day	34% 6% 12% 27% 18% 3	2626
	11th to 20th	Day	40% 6% 13% 27% 13% 1	2368
	21st to end	Day	40% 7% 12% 25% 15% 2	2405
August	1st to 10th	Day	38% 7% 17% 27% 10% 2	2314
	11th to 20th	Day	41% 6% 17% 25% 11% 1	2303
	21st to end	Day	42% 6% 12% 26% 13% 1	2526
September	1st to 10th	Day	42% 6% 14% 25% 11% 1	2151
	11th to 20th	Day	38% 5% 14% 29% 14% 1	1980
	21st to end	Day	46% 6% 12% 26% 10% 1	1980
October	1st to 10th	Day	52% 5% 11% 17% 14% 1	1814
	11th to 20th	Day	57% 5% 12% 18% 8% 1	1800
	21st to end	Day	64% 5% 11% 14% 6%	1967
November	1st to 10th	Day	52% 6% 11% 21% 8% 1	1654
	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% 6% 11% 22% 9% 1	2075
	11th to 20th	Night	51% 4 10% 22% 11% 2	1980
	21st to end	Night	52% 4 7% 21% 14% 3	2178
April	1st to 10th	Night	52% 4 9% 20% 14% 1	1888
	11th to 20th	Night	47% 5% 9% 20% 17% 2	1654
	21st to end	Night	49% 4 9% 20% 15% 3	1620
May	1st to 10th	Night	45% 5% 9% 24% 15% 2	1620
	11th to 20th	Night	42% 5% 11% 25% 14% 4	1532
	21st to end	Night	31% 5% 16% 27% 18% 4	1551
June	1st to 10th	Night	37% 5% 11% 28% 17% 3	1440
	11th to 20th	Night	35% 6% 13% 26% 18% 2	1303
	21st to end	Night	36% 5% 14% 25% 18% 1	1260
July	1st to 10th	Night	24% 6% 11% 31% 24% 4	1225
	11th to 20th	Night	30% 6% 13% 30% 19% 2	1462
	21st to end	Night	33% 5% 14% 28% 17% 3	1672
August	1st to 10th	Night	32% 6% 16% 32% 13% 2	1600
	11th to 20th	Night	30% 6% 15% 32% 15% 2	1598
	21st to end	Night	34% 6% 13% 31% 15% 2	1811
September	1st to 10th	Night	38% 5% 13% 27% 15% 2	1807
	11th to 20th	Night	31% 5% 12% 32% 19% 1	1980
	21st to end	Night	43% 5% 12% 27% 12%	1980
October	1st to 10th	Night	45% 4 11% 24% 15% 1	2146
	11th to 20th	Night	51% 5% 11% 23% 9% 1	2160
	21st to end	Night	59% 4 9% 17% 11% 1	2386
November	1st to 10th	Night	48% 6% 11% 22% 12% 1	2422
	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% 33% 20% 7%	406
	11th to 20th	Day	25% 12% 35% 19% 7% 1	420
	21st to end	Day	29% 13% 32% 19% 7% 1	462
April	1st to 10th	Day	21% 18% 31% 22% 7% 2	420
	11th to 20th	Day	29% 13% 26% 17% 10% 4	412
	21st to end	Day	27% 10% 33% 20% 9% 2	420
May	1st to 10th	Day	25% 9% 28% 23% 10% 6%	423
	11th to 20th	Day	19% 8% 28% 26% 14% 6%	447
	21st to end	Day	15% 4 27% 29% 17% 8%	485
June	1st to 10th	Day	16% 8% 26% 32% 14% 4	450
	11th to 20th	Day	15% 8% 25% 32% 16% 4	581
	21st to end	Day	15% 6% 29% 33% 13% 4	630
July	1st to 10th	Day	9% 5% 21% 29% 26% 9%	621
	11th to 20th	Day	16% 3 23% 27% 20% 11%	461
	21st to end	Day	11% 3 23% 36% 19% 8%	488
August	1st to 10th	Day	11% 4 18% 29% 24% 15%	446
	11th to 20th	Day	13% 2 16% 31% 22% 16%	439
	21st to end	Day	15% 4 19% 29% 20% 12%	495
September	1st to 10th	Day	13% 6% 21% 28% 21% 12%	450
	11th to 20th	Day	12% 4 19% 26% 27% 12%	450
	21st to end	Day	18% 8% 25% 25% 14% 10%	450
October	1st to 10th	Day	23% 10% 23% 22% 16% 7%	450
	11th to 20th	Day	24% 13% 33% 23% 7% 1	450
	21st to end	Day	30% 11% 32% 21% 5% 1	482
November	1st to 10th	Day	21% 23% 28% 20% 8% 1	261
	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% 24% 6%	743
	11th to 20th	Night	20% 14% 36% 22% 8% 1	720
	21st to end	Night	22% 10% 32% 26% 9% 1	792
April	1st to 10th	Night	22% 13% 32% 27% 6%	720
	11th to 20th	Night	21% 11% 33% 25% 9% 1	590
	21st to end	Night	19% 7% 33% 33% 7% 1	540
May	1st to 10th	Night	18% 5% 32% 28% 15% 2	540
	11th to 20th	Night	19% 4 27% 35% 14% 1	470
	21st to end	Night	11% 4 28% 38% 19% 1	389
June	1st to 10th	Night	14% 3 28% 42% 13% 1	360
	11th to 20th	Night	12% 5% 28% 42% 14%	360
	21st to end	Night	13% 4 26% 41% 16%	360
July	1st to 10th	Night	5% 1 19% 52% 22% 2	350
	11th to 20th	Night	11% 3 21% 40% 21% 4	438
	21st to end	Night	10% 2 19% 47% 19% 3	591
August	1st to 10th	Night	10% 1 15% 45% 26% 4	537
	11th to 20th	Night	9% 2 14% 42% 30% 4	534
	21st to end	Night	11% 2 21% 35% 27% 4	623
September	1st to 10th	Night	13% 4 21% 35% 23% 4	720
	11th to 20th	Night	12% 4 19% 36% 25% 5%	720
	21st to end	Night	19% 6% 20% 31% 19% 5%	720
October	1st to 10th	Night	19% 6% 26% 28% 19% 3	720
	11th to 20th	Night	24% 9% 29% 28% 9% 2	720
	21st to end	Night	28% 10% 30% 27% 5%	792
November	1st to 10th	Night	20% 12% 27% 30% 10% 1	740
	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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