Blueberry Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blueberry Hill Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	16% 7% 2 6% 4 4 4 4 6% 7% 40%	119479
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 43%	118726
Transparency	Day	41% 6% 12% 22% 16% 3	123052
	Night	40% 5% 11% 23% 17% 4	123315
Seeing	Day	21% 14% 29% 22% 11% 3	15767
	Night	19% 11% 31% 29% 10% 1	25067

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	13% 8% 2 5% 3 2 3 3 5% 5% 51%	3597
	11th to 20th	Day	14% 8% 3 8% 5% 4 3 3 4 5% 44%	3593
	21st to end	Day	19% 9% 3 6% 4 3 3 2 4 5% 42%	4466
February	1st to 10th	Day	15% 8% 3 7% 5% 4 4 3 6% 6% 40%	1800
	11th to 20th	Day	17% 8% 2 5% 5% 4 5% 3 4 6% 41%	1943
	21st to end	Day	17% 8% 4 5% 5% 3 4 3 5% 5% 40%	1650
March	1st to 10th	Day	21% 7% 2 5% 3 3 3 3 3 5% 46%	4476
	11th to 20th	Day	11% 8% 3 6% 4 4 5% 4 6% 6% 45%	4883
	21st to end	Day	17% 6% 2 6% 3 4 4 3 5% 6% 43%	5867
April	1st to 10th	Day	17% 8% 3 6% 4 4 5% 3 5% 6% 40%	2400
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 6% 7% 42%	2374
	21st to end	Day	16% 6% 2 6% 5% 4 4 4 6% 7% 40%	2400
May	1st to 10th	Day	24% 9% 3 6% 4 4 4 4 5% 8% 29%	5792
	11th to 20th	Day	24% 8% 3 6% 4 4 4 3 5% 6% 34%	6290
	21st to end	Day	19% 6% 3 6% 4 4 5% 4 6% 8% 36%	6949
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	2786
	11th to 20th	Day	11% 7% 2 6% 5% 5% 4 5% 6% 9% 39%	2660
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 5% 6% 8% 41%	2660
July	1st to 10th	Day	8% 5% 2 6% 7% 7% 7% 6% 9% 10% 34%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 10% 36%	4440
	21st to end	Day	11% 8% 3 8% 7% 6% 6% 5% 7% 8% 30%	4800
August	1st to 10th	Day	18% 7% 3 8% 5% 5% 5% 5% 7% 8% 30%	4045
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 9% 37%	3730
	21st to end	Day	9% 6% 2 6% 4 4 5% 6% 7% 9% 42%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 3 5% 7% 44%	2280
	11th to 20th	Day	12% 6% 2 5% 3 4 4 3 5% 7% 49%	2223
	21st to end	Day	18% 7% 2 7% 4 4 4 3 5% 5% 40%	2090
October	1st to 10th	Day	18% 6% 3 6% 3 3 3 3 4 6% 44%	1948
	11th to 20th	Day	16% 5% 2 4 3 3 4 3 4 6% 50%	1900
	21st to end	Day	17% 5% 2 5% 3 3 3 3 4 6% 47%	1990
November	1st to 10th	Day	13% 6% 2 4 4 3 3 3 4 7% 52%	1761
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 5% 6% 47%	1800
	21st to end	Day	15% 6% 2 5% 4 4 4 3 4 7% 46%	1720
December	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 6% 8% 45%	2600
	11th to 20th	Day	20% 10% 3 4 3 3 3 2 3 5% 45%	2986
	21st to end	Day	16% 6% 2 5% 3 4 5% 4 6% 7% 41%	3960
January	1st to 10th	Night	14% 6% 2 4 3 3 3 3 5% 6% 51%	6349
	11th to 20th	Night	15% 7% 2 6% 3 3 3 3 4 5% 48%	6289
	21st to end	Night	17% 8% 3 6% 3 3 4 3 4 6% 42%	6490
February	1st to 10th	Night	16% 9% 2 6% 4 3 4 3 4 6% 42%	2600
	11th to 20th	Night	18% 8% 3 5% 4 4 3 3 5% 6% 41%	2341
	21st to end	Night	18% 8% 3 7% 3 3 3 3 5% 5% 42%	1980
March	1st to 10th	Night	18% 9% 2 5% 4 3 3 2 4 5% 45%	5364
	11th to 20th	Night	12% 10% 3 6% 3 3 3 3 4 6% 48%	5071
	21st to end	Night	16% 7% 3 7% 4 4 4 3 5% 5% 42%	5064
April	1st to 10th	Night	17% 8% 3 6% 4 4 3 3 4 6% 41%	2000
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 4 7% 42%	1975
	21st to end	Night	17% 7% 2 5% 3 4 4 3 5% 7% 45%	2000
May	1st to 10th	Night	20% 9% 3 8% 4 4 4 4 6% 8% 28%	4146
	11th to 20th	Night	22% 8% 3 7% 5% 3 3 3 5% 7% 33%	3632
	21st to end	Night	21% 7% 3 6% 4 4 3 4 5% 9% 36%	3926
June	1st to 10th	Night	14% 6% 2 6% 4 4 5% 3 6% 8% 43%	1598
	11th to 20th	Night	9% 8% 2 7% 6% 4 5% 4 6% 7% 43%	1520
	21st to end	Night	8% 6% 2 5% 5% 6% 6% 5% 8% 11% 40%	1520
July	1st to 10th	Night	7% 6% 3 8% 6% 5% 6% 6% 8% 10% 35%	2520
	11th to 20th	Night	10% 7% 2 6% 4 4 5% 4 8% 11% 38%	2520
	21st to end	Night	14% 8% 2 7% 5% 5% 5% 4 7% 8% 35%	2739
August	1st to 10th	Night	21% 6% 2 7% 4 5% 5% 4 6% 7% 32%	2850
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 3 5% 8% 43%	3097
	21st to end	Night	9% 5% 2 4 4 4 4 4 5% 8% 49%	3476
September	1st to 10th	Night	13% 7% 2 6% 4 5% 4 4 5% 6% 45%	1900
	11th to 20th	Night	10% 6% 2 4 3 4 3 3 5% 7% 53%	1957
	21st to end	Night	19% 6% 2 6% 4 3 4 3 5% 7% 41%	2090
October	1st to 10th	Night	18% 7% 2 6% 3 4 4 2 6% 6% 44%	2228
	11th to 20th	Night	14% 4 2 4 3 3 4 3 4 6% 51%	2280
	21st to end	Night	17% 6% 2 5% 3 3 3 3 4 5% 48%	2606
November	1st to 10th	Night	11% 5% 2 6% 4 4 3 2 4 6% 53%	2537
	11th to 20th	Night	16% 6% 3 5% 4 3 3 3 4 5% 48%	2600
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 7% 45%	2677
December	1st to 10th	Night	14% 7% 2 5% 3 4 3 3 5% 6% 48%	4580
	11th to 20th	Night	22% 7% 2 5% 3 3 3 3 4 7% 40%	5208
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 6% 42%	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 9% 26% 23% 3	3598
	11th to 20th	Day	42% 5% 8% 23% 17% 5%	3623
	21st to end	Day	46% 4 11% 24% 14% 2	4466
February	1st to 10th	Day	44% 4 13% 25% 12% 1	1800
	11th to 20th	Day	44% 5% 10% 23% 15% 2	1952
	21st to end	Day	45% 5% 9% 22% 14% 5%	1650
March	1st to 10th	Day	41% 4 9% 24% 15% 8%	4479
	11th to 20th	Day	37% 5% 10% 27% 16% 5%	4883
	21st to end	Day	42% 5% 9% 16% 23% 6%	5867
April	1st to 10th	Day	43% 7% 10% 20% 15% 5%	2400
	11th to 20th	Day	39% 6% 14% 22% 16% 3	2374
	21st to end	Day	41% 7% 10% 20% 19% 4	2400
May	1st to 10th	Day	52% 6% 15% 17% 9% 1	5803
	11th to 20th	Day	50% 5% 10% 22% 12% 1	6294
	21st to end	Day	44% 7% 11% 23% 14% 1	6949
June	1st to 10th	Day	40% 9% 12% 22% 15% 1	2786
	11th to 20th	Day	40% 8% 13% 25% 12% 2	2660
	21st to end	Day	38% 8% 13% 23% 16% 2	2660
July	1st to 10th	Day	41% 10% 16% 19% 13% 2	4370
	11th to 20th	Day	41% 7% 18% 20% 13% 1	4365
	21st to end	Day	47% 7% 11% 19% 14% 1	4647
August	1st to 10th	Day	50% 7% 13% 20% 9% 1	4032
	11th to 20th	Day	40% 7% 14% 24% 13% 1	3766
	21st to end	Day	33% 7% 13% 26% 18% 2	4180
September	1st to 10th	Day	39% 7% 12% 18% 21% 3	2280
	11th to 20th	Day	34% 5% 11% 23% 24% 3	2223
	21st to end	Day	46% 6% 8% 18% 20% 2	2090
October	1st to 10th	Day	37% 3 11% 17% 28% 5%	3234
	11th to 20th	Day	25% 3 10% 23% 32% 7%	3140
	21st to end	Day	26% 3 13% 26% 27% 5%	3254
November	1st to 10th	Day	33% 4 13% 27% 20% 3	1761
	11th to 20th	Day	38% 4 9% 24% 22% 3	1800
	21st to end	Day	38% 5% 13% 30% 12% 2	1720
December	1st to 10th	Day	38% 4 16% 26% 14% 2	2600
	11th to 20th	Day	44% 4 10% 29% 11% 2	2986
	21st to end	Day	40% 6% 12% 23% 18% 2	3960
January	1st to 10th	Night	35% 3 8% 25% 22% 7%	6349
	11th to 20th	Night	39% 4 10% 24% 17% 7%	6334
	21st to end	Night	44% 3 9% 23% 18% 3	6490
February	1st to 10th	Night	44% 4 14% 23% 13% 2	2600
	11th to 20th	Night	44% 4 9% 21% 18% 5%	2343
	21st to end	Night	43% 5% 8% 22% 18% 5%	1980
March	1st to 10th	Night	42% 4 8% 23% 13% 10%	5374
	11th to 20th	Night	38% 5% 14% 25% 14% 5%	5072
	21st to end	Night	44% 4 8% 16% 24% 5%	5064
April	1st to 10th	Night	45% 5% 10% 19% 18% 5%	2000
	11th to 20th	Night	43% 5% 10% 20% 19% 3	1975
	21st to end	Night	39% 6% 11% 20% 21% 5%	2000
May	1st to 10th	Night	52% 7% 13% 17% 10% 2	4152
	11th to 20th	Night	51% 5% 11% 17% 14% 1	3633
	21st to end	Night	45% 6% 13% 21% 13% 2	3927
June	1st to 10th	Night	39% 8% 12% 21% 19% 2	1598
	11th to 20th	Night	39% 9% 13% 25% 13% 2	1520
	21st to end	Night	35% 9% 16% 23% 15% 2	1520
July	1st to 10th	Night	41% 10% 19% 18% 11% 2	2480
	11th to 20th	Night	38% 7% 19% 24% 10% 1	2472
	21st to end	Night	45% 6% 15% 19% 14% 1	2651
August	1st to 10th	Night	50% 7% 19% 15% 9% 1	2840
	11th to 20th	Night	39% 6% 13% 30% 12% 1	3127
	21st to end	Night	32% 6% 11% 28% 21% 2	3476
September	1st to 10th	Night	39% 7% 12% 19% 20% 3	1900
	11th to 20th	Night	31% 5% 12% 24% 24% 4	1957
	21st to end	Night	43% 6% 9% 21% 19% 2	2090
October	1st to 10th	Night	37% 5% 11% 23% 22% 2	3722
	11th to 20th	Night	24% 3 9% 28% 30% 6%	3779
	21st to end	Night	26% 3 11% 31% 25% 4	4292
November	1st to 10th	Night	33% 4 12% 25% 22% 5%	2537
	11th to 20th	Night	40% 4 9% 22% 21% 5%	2600
	21st to end	Night	37% 5% 12% 26% 17% 2	2677
December	1st to 10th	Night	37% 4 12% 30% 14% 3	4580
	11th to 20th	Night	44% 3 11% 23% 14% 4	5208
	21st to end	Night	44% 5% 11% 20% 18% 3	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	29% 21% 33% 14% 4 1	200
	11th to 20th	Day	34% 25% 26% 13% 1	205
	21st to end	Day	27% 25% 28% 14% 4 1	330
February	1st to 10th	Day	26% 27% 32% 12% 3	300
	11th to 20th	Day	33% 21% 33% 11% 2	491
	21st to end	Day	29% 21% 32% 15% 3	414
March	1st to 10th	Day	27% 20% 31% 17% 4	500
	11th to 20th	Day	22% 25% 35% 13% 4 2	500
	21st to end	Day	27% 21% 31% 16% 5% 1	550
April	1st to 10th	Day	27% 22% 32% 13% 5% 1	500
	11th to 20th	Day	24% 18% 33% 16% 7% 2	492
	21st to end	Day	27% 17% 30% 19% 5% 2	500
May	1st to 10th	Day	31% 17% 28% 15% 8% 2	503
	11th to 20th	Day	23% 12% 35% 19% 8% 2	527
	21st to end	Day	21% 8% 25% 25% 17% 4	573
June	1st to 10th	Day	17% 10% 29% 26% 15% 3	526
	11th to 20th	Day	14% 11% 31% 26% 15% 3	490
	21st to end	Day	12% 8% 30% 32% 14% 4	490
July	1st to 10th	Day	13% 4 23% 32% 21% 7%	485
	11th to 20th	Day	8% 5% 25% 33% 23% 6%	484
	21st to end	Day	12% 8% 27% 33% 16% 5%	532
August	1st to 10th	Day	13% 4 25% 33% 18% 8%	486
	11th to 20th	Day	13% 5% 22% 31% 22% 7%	479
	21st to end	Day	13% 4 26% 29% 18% 10%	539
September	1st to 10th	Day	16% 8% 28% 22% 18% 9%	490
	11th to 20th	Day	13% 6% 27% 31% 15% 9%	490
	21st to end	Day	25% 11% 24% 24% 11% 5%	490
October	1st to 10th	Day	25% 9% 24% 23% 13% 6%	490
	11th to 20th	Day	19% 13% 27% 26% 12% 4	490
	21st to end	Day	18% 13% 35% 20% 11% 2	486
November	1st to 10th	Day	15% 13% 36% 22% 12% 2	395
	11th to 20th	Day	24% 16% 33% 20% 7%	400
	21st to end	Day	23% 15% 34% 19% 8% 1	320
December	1st to 10th	Day	26% 23% 36% 9% 8%	200
	11th to 20th	Day	35% 17% 31% 14% 5%	200
	21st to end	Day	29% 15% 31% 18% 6% 1	220
January	1st to 10th	Night	21% 20% 35% 20% 4	800
	11th to 20th	Night	25% 16% 33% 23% 4	800
	21st to end	Night	19% 17% 39% 23% 2	880
February	1st to 10th	Night	21% 16% 38% 24% 2	800
	11th to 20th	Night	26% 20% 37% 16% 1	783
	21st to end	Night	24% 21% 34% 19% 2	660
March	1st to 10th	Night	23% 17% 36% 21% 4	800
	11th to 20th	Night	22% 17% 36% 19% 6% 1	800
	21st to end	Night	21% 12% 42% 20% 5%	880
April	1st to 10th	Night	22% 18% 37% 18% 5%	800
	11th to 20th	Night	20% 13% 37% 26% 4	791
	21st to end	Night	20% 13% 34% 27% 5%	800
May	1st to 10th	Night	20% 12% 34% 26% 7%	640
	11th to 20th	Night	19% 12% 36% 28% 5%	425
	21st to end	Night	18% 5% 24% 40% 12% 1	433
June	1st to 10th	Night	17% 4 29% 39% 10% 1	400
	11th to 20th	Night	11% 4 28% 43% 14%	380
	21st to end	Night	9% 4 26% 47% 13%	380
July	1st to 10th	Night	10% 5% 22% 44% 19% 1	370
	11th to 20th	Night	7% 4 21% 47% 20% 2	368
	21st to end	Night	10% 3 25% 44% 17%	416
August	1st to 10th	Night	11% 2 18% 47% 20% 3	579
	11th to 20th	Night	12% 4 18% 40% 25% 2	750
	21st to end	Night	13% 4 17% 40% 24% 2	836
September	1st to 10th	Night	16% 3 24% 36% 18% 3	760
	11th to 20th	Night	13% 5% 20% 34% 24% 4	760
	21st to end	Night	23% 5% 21% 34% 17% 1	760
October	1st to 10th	Night	21% 6% 27% 27% 16% 3	760
	11th to 20th	Night	16% 10% 27% 33% 13% 1	760
	21st to end	Night	20% 9% 34% 26% 11%	836
November	1st to 10th	Night	14% 9% 36% 28% 12% 1	780
	11th to 20th	Night	19% 15% 30% 28% 8% 1	800
	21st to end	Night	17% 15% 35% 26% 7% 1	800
December	1st to 10th	Night	25% 14% 34% 20% 6% 1	800
	11th to 20th	Night	20% 16% 34% 25% 5%	800
	21st to end	Night	21% 14% 34% 28% 3	880

Page generated at 2025-06-07 10:28:19. Version ac07

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