Hopewell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hopewell Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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% 6% 2 6% 4 4 5% 4 6% 8% 42%	126911
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	123786
Transparency	Day	38% 8% 12% 23% 16% 4	130509
	Night	38% 7% 12% 23% 18% 4	128257
Seeing	Day	18% 12% 26% 24% 14% 5%	16360
	Night	17% 10% 30% 30% 12% 1	25939

By Month

Percentage Cloud Cover SE (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% 4 1 4 4 4 4 4 4 5% 50%	3809
	11th to 20th	Day	14% 8% 3 6% 3 3 3 3 4 4 48%	4060
	21st to end	Day	15% 7% 3 6% 4 3 3 3 4 6% 44%	4466
February	1st to 10th	Day	14% 7% 3 6% 5% 5% 4 4 6% 5% 39%	1800
	11th to 20th	Day	19% 7% 2 5% 4 4 4 3 5% 7% 39%	1780
	21st to end	Day	18% 8% 2 5% 5% 5% 4 3 5% 5% 41%	1650
March	1st to 10th	Day	18% 6% 2 5% 5% 4 4 3 4 6% 42%	4935
	11th to 20th	Day	10% 6% 2 6% 3 4 4 3 4 7% 50%	4980
	21st to end	Day	16% 7% 2 6% 4 4 4 3 6% 7% 40%	5500
April	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 6% 6% 42%	2400
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 3 5% 6% 47%	2374
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 6% 41%	2400
May	1st to 10th	Day	18% 7% 3 6% 4 4 6% 4 7% 10% 31%	5852
	11th to 20th	Day	22% 6% 2 6% 4 4 5% 4 6% 10% 31%	6036
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 6% 9% 39%	6934
June	1st to 10th	Day	11% 5% 2 6% 5% 4 4 5% 7% 8% 43%	2800
	11th to 20th	Day	11% 5% 3 6% 5% 4 5% 4 7% 9% 41%	2800
	21st to end	Day	8% 4 2 5% 5% 3 5% 5% 7% 10% 45%	2800
July	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 5% 7% 10% 43%	6360
	11th to 20th	Day	8% 6% 2 7% 5% 6% 7% 6% 9% 12% 31%	6004
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	6424
August	1st to 10th	Day	16% 5% 3 6% 4 5% 5% 4 8% 10% 34%	4234
	11th to 20th	Day	9% 4 2 6% 5% 5% 7% 5% 8% 9% 40%	4043
	21st to end	Day	11% 4 1 5% 4 4 5% 4 6% 8% 49%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 4 7% 47%	2400
	11th to 20th	Day	13% 5% 2 5% 4 4 3 3 5% 7% 49%	2395
	21st to end	Day	22% 7% 2 6% 4 4 4 3 5% 5% 38%	2088
October	1st to 10th	Day	16% 5% 2 5% 4 3 4 3 5% 6% 49%	2000
	11th to 20th	Day	16% 5% 1 5% 4 3 4 3 4 5% 50%	2000
	21st to end	Day	14% 6% 2 5% 3 3 2 3 4 6% 51%	2200
November	1st to 10th	Day	12% 5% 2 4 4 3 4 3 5% 7% 52%	1994
	11th to 20th	Day	14% 6% 2 4 3 3 4 3 5% 5% 50%	1835
	21st to end	Day	15% 6% 2 4 4 4 4 4 4 7% 47%	1680
December	1st to 10th	Day	11% 5% 2 5% 4 3 4 3 6% 6% 51%	2616
	11th to 20th	Day	19% 7% 2 6% 3 3 4 3 5% 6% 43%	2990
	21st to end	Day	18% 7% 3 6% 4 4 4 4 5% 7% 37%	3960
January	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 5% 6% 51%	6119
	11th to 20th	Night	14% 7% 2 4 3 3 3 3 4 5% 53%	5900
	21st to end	Night	16% 7% 2 6% 3 3 3 2 4 5% 49%	6490
February	1st to 10th	Night	15% 7% 2 7% 4 4 5% 4 6% 5% 41%	2600
	11th to 20th	Night	19% 7% 2 6% 4 3 3 3 5% 6% 43%	2504
	21st to end	Night	16% 8% 3 6% 4 3 4 3 4 6% 43%	1977
March	1st to 10th	Night	17% 5% 2 5% 4 3 4 3 4 6% 47%	4918
	11th to 20th	Night	10% 7% 3 5% 4 3 4 3 5% 7% 50%	4980
	21st to end	Night	11% 7% 2 6% 4 4 5% 4 5% 7% 44%	5431
April	1st to 10th	Night	15% 7% 3 6% 5% 4 4 4 5% 6% 41%	2000
	11th to 20th	Night	13% 6% 1 5% 5% 4 4 4 5% 8% 45%	1975
	21st to end	Night	16% 5% 1 5% 3 4 4 5% 6% 7% 44%	2000
May	1st to 10th	Night	21% 9% 3 7% 4 5% 5% 4 5% 8% 29%	4084
	11th to 20th	Night	25% 7% 2 6% 4 4 5% 4 5% 8% 30%	3854
	21st to end	Night	17% 6% 2 6% 4 5% 5% 4 6% 8% 36%	3920
June	1st to 10th	Night	10% 5% 3 6% 4 4 4 4 7% 9% 44%	1600
	11th to 20th	Night	13% 5% 3 5% 4 5% 6% 4 5% 8% 42%	1600
	21st to end	Night	8% 4 2 6% 4 5% 5% 4 7% 10% 44%	1600
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 6% 5% 7% 10% 40%	3598
	11th to 20th	Night	9% 9% 3 9% 6% 6% 6% 6% 7% 10% 29%	3934
	21st to end	Night	8% 6% 3 7% 5% 5% 5% 5% 8% 10% 41%	4427
August	1st to 10th	Night	16% 6% 2 7% 5% 6% 5% 5% 6% 9% 33%	2915
	11th to 20th	Night	9% 7% 2 8% 6% 6% 5% 4 6% 8% 38%	2970
	21st to end	Night	12% 5% 2 5% 3 4 4 3 5% 8% 49%	3586
September	1st to 10th	Night	14% 6% 2 5% 4 5% 4 4 6% 6% 46%	2000
	11th to 20th	Night	11% 6% 2 5% 4 5% 4 3 5% 7% 49%	2000
	21st to end	Night	21% 7% 2 6% 4 4 4 3 5% 5% 38%	2311
October	1st to 10th	Night	19% 6% 2 5% 3 3 3 3 4 5% 48%	2400
	11th to 20th	Night	15% 5% 1 4 3 3 3 3 4 6% 52%	2400
	21st to end	Night	14% 5% 2 5% 3 4 3 3 5% 6% 51%	2640
November	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 4 6% 54%	2520
	11th to 20th	Night	14% 6% 2 4 3 3 3 4 5% 7% 50%	2783
	21st to end	Night	13% 4 2 5% 4 4 4 4 6% 6% 48%	2940
December	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 5% 7% 54%	4609
	11th to 20th	Night	20% 6% 2 5% 4 4 4 3 4 6% 41%	5205
	21st to end	Night	17% 7% 2 6% 4 4 5% 4 6% 8% 37%	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	34% 4 7% 26% 21% 8%	3810
	11th to 20th	Day	38% 5% 8% 21% 17% 11%	4060
	21st to end	Day	41% 6% 9% 27% 15% 3	4466
February	1st to 10th	Day	43% 7% 12% 24% 12% 2	1800
	11th to 20th	Day	44% 4 11% 21% 17% 2	1789
	21st to end	Day	44% 5% 12% 20% 15% 4	1650
March	1st to 10th	Day	41% 5% 9% 20% 16% 8%	4935
	11th to 20th	Day	32% 6% 10% 25% 20% 6%	4980
	21st to end	Day	42% 7% 10% 18% 17% 7%	5500
April	1st to 10th	Day	39% 6% 12% 19% 18% 5%	2400
	11th to 20th	Day	37% 6% 11% 21% 20% 6%	2374
	21st to end	Day	41% 8% 10% 22% 15% 4	2400
May	1st to 10th	Day	45% 10% 16% 18% 10% 2	5887
	11th to 20th	Day	46% 9% 12% 24% 8% 1	6040
	21st to end	Day	38% 9% 14% 21% 15% 1	6949
June	1st to 10th	Day	34% 9% 15% 23% 16% 1	2800
	11th to 20th	Day	37% 10% 14% 23% 14% 2	2800
	21st to end	Day	30% 11% 16% 24% 17% 2	2800
July	1st to 10th	Day	33% 11% 18% 20% 14% 4	6290
	11th to 20th	Day	39% 12% 17% 23% 7% 1	5932
	21st to end	Day	36% 8% 10% 23% 21% 1	6240
August	1st to 10th	Day	42% 9% 18% 24% 7%	4221
	11th to 20th	Day	35% 11% 13% 27% 14% 1	4082
	21st to end	Day	32% 7% 15% 27% 17% 2	4312
September	1st to 10th	Day	36% 8% 13% 18% 21% 5%	2400
	11th to 20th	Day	34% 6% 9% 28% 20% 3	2395
	21st to end	Day	46% 7% 10% 19% 15% 2	2088
October	1st to 10th	Day	35% 5% 7% 18% 29% 5%	3260
	11th to 20th	Day	25% 4 7% 28% 25% 10%	3240
	21st to end	Day	22% 3 10% 30% 26% 8%	3538
November	1st to 10th	Day	32% 4 13% 24% 21% 5%	1994
	11th to 20th	Day	34% 6% 10% 22% 21% 5%	1835
	21st to end	Day	37% 6% 11% 27% 17% 2	1680
December	1st to 10th	Day	33% 6% 12% 27% 17% 4	2616
	11th to 20th	Day	42% 4 15% 26% 10% 3	2986
	21st to end	Day	42% 8% 15% 21% 14% 1	3960
January	1st to 10th	Night	33% 5% 8% 25% 25% 5%	6119
	11th to 20th	Night	33% 4 9% 24% 23% 7%	5900
	21st to end	Night	38% 4 9% 28% 18% 3	6490
February	1st to 10th	Night	42% 7% 14% 22% 14% 2	2600
	11th to 20th	Night	42% 4 10% 21% 17% 5%	2506
	21st to end	Night	42% 5% 10% 21% 16% 5%	1977
March	1st to 10th	Night	37% 6% 9% 24% 15% 8%	4918
	11th to 20th	Night	32% 6% 12% 23% 21% 6%	4980
	21st to end	Night	38% 6% 9% 22% 20% 5%	5431
April	1st to 10th	Night	42% 7% 9% 19% 19% 4	2000
	11th to 20th	Night	36% 7% 12% 20% 19% 5%	1975
	21st to end	Night	37% 9% 12% 24% 14% 4	2000
May	1st to 10th	Night	51% 8% 13% 16% 8% 4	4111
	11th to 20th	Night	50% 8% 11% 20% 10% 1	3855
	21st to end	Night	43% 9% 14% 22% 9% 2	3927
June	1st to 10th	Night	34% 10% 13% 24% 17% 2	1600
	11th to 20th	Night	37% 10% 15% 23% 14% 2	1600
	21st to end	Night	33% 8% 17% 22% 18% 3	1600
July	1st to 10th	Night	38% 11% 17% 17% 15% 3	3560
	11th to 20th	Night	46% 13% 17% 16% 8% 1	3886
	21st to end	Night	36% 9% 15% 23% 18%	4297
August	1st to 10th	Night	45% 9% 16% 21% 8% 1	2904
	11th to 20th	Night	40% 8% 12% 24% 14% 1	2997
	21st to end	Night	32% 6% 13% 30% 17% 2	3586
September	1st to 10th	Night	38% 7% 10% 21% 19% 5%	2000
	11th to 20th	Night	34% 6% 10% 25% 22% 3	2000
	21st to end	Night	48% 7% 10% 18% 15% 3	2311
October	1st to 10th	Night	39% 5% 10% 20% 21% 5%	3920
	11th to 20th	Night	24% 4 11% 22% 31% 8%	3899
	21st to end	Night	22% 4 9% 31% 26% 7%	4252
November	1st to 10th	Night	32% 4 10% 25% 22% 6%	2520
	11th to 20th	Night	35% 5% 8% 24% 22% 6%	2783
	21st to end	Night	35% 5% 11% 25% 20% 4	2940
December	1st to 10th	Night	31% 5% 13% 28% 21% 2	4609
	11th to 20th	Night	43% 5% 12% 19% 16% 4	5208
	21st to end	Night	42% 9% 15% 19% 14% 1	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	26% 29% 28% 15% 2	247
	11th to 20th	Day	31% 23% 29% 16% 2	300
	21st to end	Day	21% 26% 35% 13% 4 1	330
February	1st to 10th	Day	23% 26% 35% 13% 4	300
	11th to 20th	Day	37% 24% 32% 6% 2	327
	21st to end	Day	26% 20% 32% 20% 2	414
March	1st to 10th	Day	23% 22% 31% 22% 3	500
	11th to 20th	Day	23% 22% 32% 17% 5% 2	500
	21st to end	Day	21% 18% 35% 19% 6% 1	550
April	1st to 10th	Day	24% 21% 28% 20% 6% 1	500
	11th to 20th	Day	16% 19% 28% 22% 12% 3	492
	21st to end	Day	23% 13% 33% 19% 11% 2	500
May	1st to 10th	Day	21% 16% 29% 19% 11% 4	503
	11th to 20th	Day	20% 9% 31% 22% 15% 4	527
	21st to end	Day	19% 6% 24% 26% 18% 7%	573
June	1st to 10th	Day	11% 6% 28% 28% 21% 7%	530
	11th to 20th	Day	13% 7% 23% 31% 19% 7%	530
	21st to end	Day	8% 5% 23% 33% 22% 8%	530
July	1st to 10th	Day	11% 3 15% 32% 26% 13%	525
	11th to 20th	Day	5% 2 17% 32% 31% 12%	524
	21st to end	Day	11% 2 18% 33% 27% 9%	576
August	1st to 10th	Day	13% 4 17% 27% 27% 12%	526
	11th to 20th	Day	13% 4 16% 31% 24% 11%	519
	21st to end	Day	9% 3 18% 33% 23% 15%	583
September	1st to 10th	Day	15% 6% 21% 26% 18% 14%	530
	11th to 20th	Day	14% 5% 18% 29% 23% 12%	530
	21st to end	Day	27% 10% 21% 24% 15% 4	530
October	1st to 10th	Day	19% 6% 20% 26% 19% 8%	530
	11th to 20th	Day	16% 14% 25% 27% 15% 3	530
	21st to end	Day	16% 13% 33% 25% 10% 3	583
November	1st to 10th	Day	15% 12% 34% 26% 11% 3	502
	11th to 20th	Day	19% 14% 33% 23% 9% 2	375
	21st to end	Day	20% 23% 30% 20% 7% 1	220
December	1st to 10th	Day	18% 19% 38% 20% 4 1	204
	11th to 20th	Day	23% 18% 33% 20% 7%	200
	21st to end	Day	25% 17% 32% 20% 6% 1	220
January	1st to 10th	Night	21% 18% 40% 19% 3	800
	11th to 20th	Night	22% 14% 35% 25% 4	800
	21st to end	Night	19% 15% 43% 22% 2	880
February	1st to 10th	Night	19% 14% 41% 24% 3	800
	11th to 20th	Night	25% 19% 38% 16% 2	783
	21st to end	Night	24% 16% 38% 19% 3	660
March	1st to 10th	Night	19% 17% 40% 23% 3	800
	11th to 20th	Night	22% 16% 35% 21% 5% 1	800
	21st to end	Night	18% 16% 40% 21% 4	880
April	1st to 10th	Night	19% 17% 38% 22% 4	800
	11th to 20th	Night	16% 14% 35% 28% 7% 1	791
	21st to end	Night	19% 10% 32% 32% 8%	800
May	1st to 10th	Night	21% 8% 27% 32% 12%	625
	11th to 20th	Night	21% 5% 26% 35% 11% 1	517
	21st to end	Night	15% 3 22% 40% 19% 1	433
June	1st to 10th	Night	9% 4 24% 42% 20% 1	400
	11th to 20th	Night	13% 5% 20% 41% 19% 1	400
	21st to end	Night	8% 3 21% 49% 18% 2	400
July	1st to 10th	Night	11% 2 20% 38% 26% 4	390
	11th to 20th	Night	6% 2 14% 37% 37% 3	527
	21st to end	Night	9% 2 15% 42% 29% 4	657
August	1st to 10th	Night	11% 3 12% 42% 31% 2	597
	11th to 20th	Night	10% 4 13% 42% 30% 2	650
	21st to end	Night	10% 3 15% 42% 26% 4	880
September	1st to 10th	Night	16% 3 17% 34% 27% 4	800
	11th to 20th	Night	12% 3 16% 37% 29% 3	800
	21st to end	Night	23% 4 21% 33% 18% 1	800
October	1st to 10th	Night	20% 4 21% 30% 20% 5%	800
	11th to 20th	Night	16% 10% 27% 33% 14% 1	800
	21st to end	Night	16% 10% 32% 30% 12%	880
November	1st to 10th	Night	14% 9% 34% 32% 11% 1	820
	11th to 20th	Night	17% 12% 34% 29% 7% 1	840
	21st to end	Night	15% 13% 35% 29% 8%	840
December	1st to 10th	Night	21% 11% 37% 24% 6%	809
	11th to 20th	Night	19% 10% 40% 27% 5%	800
	21st to end	Night	20% 12% 34% 31% 3	880

Page generated at 2025-11-30 01:00:57. Version ac07

Copyright © 2025 Attilla Danko.