Dutchman's Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dutchman's Hill 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	4 5% 2 4 3 4 4 4 6% 7% 58%	100969
	Night	5% 6% 2 5% 4 4 4 4 5% 7% 55%	98259
Transparency	Day	22% 6% 11% 21% 24% 16%	100734
	Night	26% 6% 10% 20% 23% 15%	98083
Seeing	Day	6% 7% 21% 33% 25% 8%	15086
	Night	7% 4 18% 44% 25% 2	25274

By Month

Percentage Cloud Cover SW (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	4 8% 2 7% 3 4 5% 4 5% 6% 50%	2858
	11th to 20th	Day	4 7% 3 6% 3 4 4 4 6% 7% 55%	2860
	21st to end	Day	7% 8% 3 6% 3 4 4 3 5% 6% 51%	3146
February	1st to 10th	Day	4 7% 3 6% 4 2 3 4 5% 6% 56%	1710
	11th to 20th	Day	5% 9% 2 6% 5% 4 4 3 4 6% 51%	1720
	21st to end	Day	4 10% 3 7% 4 3 4 4 5% 6% 51%	1598
March	1st to 10th	Day	4 8% 2 4 3 3 4 3 6% 7% 56%	3444
	11th to 20th	Day	5% 9% 3 7% 4 4 5% 3 6% 7% 45%	3490
	21st to end	Day	5% 8% 3 8% 5% 4 4 3 5% 8% 47%	3825
April	1st to 10th	Day	4 4 2 4 4 4 4 5% 5% 6% 58%	2270
	11th to 20th	Day	2 5% 2 5% 3 3 4 4 5% 8% 58%	2251
	21st to end	Day	4 4 1 4 4 4 4 4 6% 6% 60%	2280
May	1st to 10th	Day	4 3 1 3 3 3 4 3 4 6% 64%	3974
	11th to 20th	Day	3 4 1 5% 4 5% 5% 4 7% 8% 54%	4071
	21st to end	Day	2 2 1 3 2 2 3 3 4 6% 72%	4690
June	1st to 10th	Day	3 2 1 3 3 3 3 3 5% 7% 67%	2660
	11th to 20th	Day	2 2 1 2 2 2 4 2 3 5% 74%	2660
	21st to end	Day	2 2 1 4 3 3 4 4 6% 7% 65%	2660
July	1st to 10th	Day	3 2 1 3 2 3 3 3 5% 6% 68%	4176
	11th to 20th	Day	2 1 1 3 4 5% 6% 6% 9% 12% 52%	4110
	21st to end	Day	3 3 1 4 4 4 5% 5% 8% 9% 54%	4454
August	1st to 10th	Day	4 3 2 5% 5% 6% 6% 6% 11% 13% 41%	4092
	11th to 20th	Day	2 3 1 3 3 4 5% 4 8% 11% 54%	3877
	21st to end	Day	3 3 1 4 3 5% 6% 6% 9% 10% 51%	4180
September	1st to 10th	Day	6% 4 2 4 4 4 4 3 7% 8% 55%	2280
	11th to 20th	Day	5% 3 2 4 3 3 4 4 6% 7% 61%	2252
	21st to end	Day	6% 3 1 3 3 2 3 2 4 5% 69%	2012
October	1st to 10th	Day	6% 3 1 4 3 4 3 3 5% 6% 61%	1900
	11th to 20th	Day	4 3 1 3 2 2 2 2 3 4 74%	1900
	21st to end	Day	4 3 1 3 3 3 2 2 3 6% 70%	2090
November	1st to 10th	Day	4 3 1 2 2 2 3 2 3 6% 71%	1869
	11th to 20th	Day	3 3 1 3 2 2 3 3 5% 6% 69%	1758
	21st to end	Day	5% 7% 2 5% 3 3 2 3 4 6% 61%	1539
December	1st to 10th	Day	6% 8% 3 5% 3 3 3 2 4 7% 57%	1520
	11th to 20th	Day	7% 8% 2 6% 4 4 5% 4 5% 8% 47%	1926
	21st to end	Day	5% 9% 3 6% 4 3 3 3 5% 5% 52%	2867
January	1st to 10th	Night	4 8% 4 11% 5% 4 4 3 4 5% 48%	4097
	11th to 20th	Night	5% 10% 2 5% 3 3 3 3 4 6% 56%	4110
	21st to end	Night	7% 9% 3 7% 4 3 3 3 5% 7% 49%	4521
February	1st to 10th	Night	5% 9% 2 4 3 3 2 3 4 6% 59%	2470
	11th to 20th	Night	7% 8% 2 5% 4 3 3 3 5% 6% 54%	2345
	21st to end	Night	7% 10% 2 5% 3 2 3 2 3 5% 57%	1854
March	1st to 10th	Night	4 8% 2 5% 4 4 4 3 5% 7% 54%	3430
	11th to 20th	Night	9% 11% 3 7% 5% 4 4 3 5% 6% 44%	3490
	21st to end	Night	4 6% 2 6% 5% 4 5% 4 6% 7% 50%	3828
April	1st to 10th	Night	5% 5% 2 5% 4 4 5% 3 6% 6% 54%	1910
	11th to 20th	Night	6% 5% 2 6% 3 4 4 4 4 5% 58%	1877
	21st to end	Night	5% 5% 2 4 4 3 4 3 4 6% 60%	1900
May	1st to 10th	Night	5% 3 2 3 3 3 2 3 4 6% 67%	2992
	11th to 20th	Night	4 5% 2 5% 4 4 5% 4 6% 6% 55%	2834
	21st to end	Night	4 4 1 3 2 3 3 3 4 5% 68%	2893
June	1st to 10th	Night	3 3 1 3 2 4 3 3 5% 7% 66%	1520
	11th to 20th	Night	4 3 1 4 3 3 3 2 4 5% 70%	1520
	21st to end	Night	4 2 1 4 3 4 4 4 6% 9% 58%	1520
July	1st to 10th	Night	3 3 2 4 3 4 4 4 5% 6% 62%	2787
	11th to 20th	Night	2 3 2 6% 5% 5% 7% 8% 10% 11% 41%	2860
	21st to end	Night	4 5% 2 6% 5% 5% 6% 5% 8% 10% 43%	3109
August	1st to 10th	Night	4 5% 2 8% 7% 7% 7% 7% 10% 10% 32%	2847
	11th to 20th	Night	4 4 2 6% 6% 6% 7% 5% 8% 10% 42%	2960
	21st to end	Night	4 5% 2 8% 5% 6% 7% 6% 9% 11% 37%	3487
September	1st to 10th	Night	5% 4 2 7% 5% 5% 6% 5% 8% 8% 45%	1900
	11th to 20th	Night	6% 3 2 5% 3 4 4 3 4 6% 60%	1924
	21st to end	Night	5% 3 1 3 3 2 3 2 3 4 69%	2166
October	1st to 10th	Night	9% 4 1 4 3 3 4 3 3 5% 61%	2280
	11th to 20th	Night	5% 3 1 3 2 2 3 2 3 5% 71%	2280
	21st to end	Night	4 3 2 3 2 3 3 2 4 5% 70%	2508
November	1st to 10th	Night	5% 3 1 2 2 2 3 3 5% 5% 70%	2244
	11th to 20th	Night	3 3 1 3 2 2 2 2 3 5% 74%	2400
	21st to end	Night	7% 7% 1 3 3 2 2 3 4 6% 61%	2638
December	1st to 10th	Night	7% 6% 2 5% 3 3 3 2 5% 5% 59%	2660
	11th to 20th	Night	7% 9% 2 5% 4 5% 4 3 5% 7% 49%	3271
	21st to end	Night	8% 9% 3 6% 3 3 3 2 4 6% 54%	4827

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	29% 8% 17% 28% 17% 2	2859
	11th to 20th	Day	27% 6% 19% 32% 12% 2	2860
	21st to end	Day	31% 8% 14% 29% 16% 2	3146
February	1st to 10th	Day	27% 5% 14% 26% 20% 7%	1710
	11th to 20th	Day	33% 4 9% 27% 24% 3	1729
	21st to end	Day	31% 6% 8% 17% 30% 8%	1598
March	1st to 10th	Day	22% 6% 8% 24% 32% 8%	3444
	11th to 20th	Day	29% 10% 11% 27% 18% 5%	3490
	21st to end	Day	29% 9% 10% 22% 26% 5%	3825
April	1st to 10th	Day	23% 5% 8% 20% 29% 16%	2270
	11th to 20th	Day	21% 5% 8% 19% 29% 18%	2254
	21st to end	Day	21% 5% 8% 20% 30% 16%	2280
May	1st to 10th	Day	18% 5% 7% 15% 29% 27%	3974
	11th to 20th	Day	19% 9% 12% 20% 24% 16%	4074
	21st to end	Day	11% 4 6% 10% 37% 32%	4690
June	1st to 10th	Day	15% 4 7% 17% 28% 29%	2660
	11th to 20th	Day	12% 4 5% 10% 22% 47%	2660
	21st to end	Day	16% 5% 7% 14% 24% 35%	2660
July	1st to 10th	Day	16% 5% 8% 10% 20% 42%	4112
	11th to 20th	Day	16% 8% 12% 28% 25% 10%	4041
	21st to end	Day	21% 9% 16% 25% 19% 11%	4314
August	1st to 10th	Day	25% 12% 21% 20% 12% 10%	4078
	11th to 20th	Day	20% 8% 17% 19% 16% 19%	3916
	21st to end	Day	22% 9% 16% 19% 23% 10%	4179
September	1st to 10th	Day	24% 6% 10% 15% 22% 21%	2280
	11th to 20th	Day	20% 7% 9% 17% 24% 24%	2252
	21st to end	Day	18% 4 6% 17% 31% 24%	2012
October	1st to 10th	Day	22% 6% 10% 17% 24% 21%	1900
	11th to 20th	Day	15% 2 4 15% 41% 22%	1900
	21st to end	Day	16% 4 8% 23% 36% 12%	2090
November	1st to 10th	Day	15% 2 8% 26% 39% 10%	1869
	11th to 20th	Day	16% 2 8% 30% 37% 6%	1758
	21st to end	Day	26% 3 7% 28% 27% 8%	1539
December	1st to 10th	Day	28% 4 13% 29% 21% 5%	1520
	11th to 20th	Day	33% 7% 12% 29% 17% 2	1924
	21st to end	Day	30% 7% 12% 20% 24% 8%	2867
January	1st to 10th	Night	34% 8% 10% 28% 19% 2	4097
	11th to 20th	Night	28% 6% 15% 31% 17% 3	4110
	21st to end	Night	33% 6% 12% 30% 16% 3	4521
February	1st to 10th	Night	26% 4 12% 28% 22% 8%	2470
	11th to 20th	Night	30% 4 9% 23% 26% 8%	2346
	21st to end	Night	28% 3 7% 19% 31% 12%	1854
March	1st to 10th	Night	22% 8% 9% 23% 32% 8%	3430
	11th to 20th	Night	36% 9% 9% 19% 20% 7%	3490
	21st to end	Night	25% 8% 11% 25% 26% 5%	3828
April	1st to 10th	Night	26% 5% 7% 19% 27% 16%	1910
	11th to 20th	Night	25% 4 7% 14% 29% 21%	1877
	21st to end	Night	23% 5% 7% 17% 31% 17%	1900
May	1st to 10th	Night	16% 5% 7% 15% 37% 22%	2992
	11th to 20th	Night	22% 9% 11% 21% 20% 17%	2835
	21st to end	Night	14% 5% 7% 10% 31% 32%	2893
June	1st to 10th	Night	17% 4 8% 15% 21% 35%	1520
	11th to 20th	Night	16% 4 5% 9% 18% 48%	1520
	21st to end	Night	21% 5% 8% 14% 18% 34%	1520
July	1st to 10th	Night	22% 6% 9% 7% 11% 44%	2742
	11th to 20th	Night	26% 11% 14% 24% 15% 10%	2806
	21st to end	Night	30% 11% 14% 19% 13% 12%	3011
August	1st to 10th	Night	38% 13% 17% 11% 10% 12%	2838
	11th to 20th	Night	32% 9% 15% 13% 11% 21%	2987
	21st to end	Night	33% 9% 13% 19% 15% 11%	3487
September	1st to 10th	Night	29% 7% 13% 16% 14% 20%	1900
	11th to 20th	Night	24% 5% 8% 16% 19% 28%	1924
	21st to end	Night	18% 4 6% 13% 30% 29%	2166
October	1st to 10th	Night	23% 7% 8% 13% 23% 26%	2280
	11th to 20th	Night	17% 4 5% 12% 34% 28%	2280
	21st to end	Night	17% 3 6% 20% 37% 17%	2508
November	1st to 10th	Night	16% 3 7% 22% 39% 14%	2244
	11th to 20th	Night	14% 3 6% 27% 40% 10%	2400
	21st to end	Night	25% 3 6% 24% 33% 10%	2638
December	1st to 10th	Night	28% 4 11% 28% 24% 5%	2660
	11th to 20th	Night	32% 7% 13% 28% 18% 2	3272
	21st to end	Night	31% 6% 11% 20% 24% 8%	4827

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	14% 3 27% 34% 19% 3	270
	11th to 20th	Day	10% 8% 31% 27% 22% 2	270
	21st to end	Day	7% 4 23% 38% 22% 6%	297
February	1st to 10th	Day	4 10% 28% 37% 17% 3	270
	11th to 20th	Day	12% 6% 30% 38% 13% 1	270
	21st to end	Day	11% 13% 33% 32% 10% 1	253
March	1st to 10th	Day	8% 12% 31% 30% 16% 2	460
	11th to 20th	Day	7% 13% 29% 30% 16% 5%	460
	21st to end	Day	10% 22% 33% 22% 12% 1	506
April	1st to 10th	Day	9% 16% 32% 27% 13% 3	460
	11th to 20th	Day	8% 22% 34% 24% 12% 1	452
	21st to end	Day	6% 18% 32% 32% 12% 1	460
May	1st to 10th	Day	7% 14% 34% 29% 14% 1	463
	11th to 20th	Day	4 10% 30% 31% 19% 6%	488
	21st to end	Day	4 9% 26% 35% 22% 3	651
June	1st to 10th	Day	4 4 16% 38% 35% 4	680
	11th to 20th	Day	3 5% 19% 37% 27% 8%	680
	21st to end	Day	2 3 17% 41% 33% 4	680
July	1st to 10th	Day	4 1 13% 33% 38% 11%	526
	11th to 20th	Day	3 1 7% 30% 35% 24%	484
	21st to end	Day	3 1 7% 29% 39% 21%	531
August	1st to 10th	Day	4 1 10% 34% 36% 14%	487
	11th to 20th	Day	3 2 13% 36% 33% 13%	477
	21st to end	Day	4 1 11% 35% 35% 13%	539
September	1st to 10th	Day	7% 1 12% 29% 35% 17%	490
	11th to 20th	Day	4 1 18% 36% 32% 9%	490
	21st to end	Day	7% 4 19% 28% 29% 13%	412
October	1st to 10th	Day	4 7% 18% 25% 31% 15%	300
	11th to 20th	Day	5% 10% 16% 31% 26% 12%	300
	21st to end	Day	5% 8% 15% 32% 30% 10%	330
November	1st to 10th	Day	8% 7% 20% 34% 24% 6%	273
	11th to 20th	Day	3 6% 20% 38% 24% 9%	270
	21st to end	Day	8% 9% 22% 31% 21% 9%	270
December	1st to 10th	Day	10% 6% 20% 40% 17% 6%	270
	11th to 20th	Day	7% 7% 24% 39% 19% 4	270
	21st to end	Day	15% 9% 24% 36% 13% 2	297
January	1st to 10th	Night	10% 2 20% 44% 21% 2	760
	11th to 20th	Night	9% 3 22% 43% 22% 2	760
	21st to end	Night	10% 3 21% 42% 21% 3	836
February	1st to 10th	Night	10% 3 25% 47% 13% 2	760
	11th to 20th	Night	10% 3 24% 48% 13% 1	744
	21st to end	Night	11% 4 27% 47% 10%	628
March	1st to 10th	Night	7% 5% 27% 47% 14% 1	760
	11th to 20th	Night	8% 6% 21% 43% 21% 1	760
	21st to end	Night	8% 7% 27% 43% 15% 1	836
April	1st to 10th	Night	7% 8% 29% 45% 11%	580
	11th to 20th	Night	7% 9% 29% 41% 15%	563
	21st to end	Night	7% 6% 29% 42% 16%	570
May	1st to 10th	Night	6% 5% 24% 49% 16%	570
	11th to 20th	Night	6% 5% 20% 48% 20% 1	561
	21st to end	Night	6% 6% 22% 45% 21% 1	617
June	1st to 10th	Night	5% 2 17% 52% 24%	570
	11th to 20th	Night	4 3 17% 47% 28% 1	570
	21st to end	Night	3 2 11% 51% 33% 1	570
July	1st to 10th	Night	4 1 9% 47% 39% 2	555
	11th to 20th	Night	5% 6% 36% 49% 4	552
	21st to end	Night	5% 2 7% 32% 49% 5%	624
August	1st to 10th	Night	2 1 6% 32% 52% 7%	567
	11th to 20th	Night	5% 2 9% 38% 44% 4	564
	21st to end	Night	4 1 7% 41% 42% 4	627
September	1st to 10th	Night	6% 1 10% 42% 40% 2	570
	11th to 20th	Night	5% 2 10% 47% 33% 3	594
	21st to end	Night	6% 2 13% 42% 34% 4	760
October	1st to 10th	Night	9% 3 16% 44% 27% 2	760
	11th to 20th	Night	5% 3 13% 50% 27% 2	760
	21st to end	Night	5% 4 16% 44% 27% 4	836
November	1st to 10th	Night	6% 3 12% 49% 27% 4	748
	11th to 20th	Night	4 4 19% 46% 23% 4	880
	21st to end	Night	10% 4 19% 39% 24% 3	950
December	1st to 10th	Night	9% 4 20% 47% 19% 1	950
	11th to 20th	Night	13% 5% 22% 39% 21% 1	950
	21st to end	Night	12% 5% 25% 42% 16% 1	1012

Page generated at 2024-10-30 11:19:22. Version ac07

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