Blueberry Pond Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blueberry Pond Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	18% 8% 2 6% 4 4 4 4 5% 7% 38%	126602
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 38%	125061
Transparency	Day	45% 4 11% 23% 14% 3	130110
	Night	47% 4 10% 22% 15% 2	129641
Seeing	Day	22% 12% 32% 22% 8% 3	16424
	Night	22% 11% 29% 27% 9% 1	25452

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	14% 6% 3 7% 6% 5% 5% 4 6% 6% 40%	3677
	11th to 20th	Day	14% 7% 3 6% 4 4 4 4 4 6% 45%	3618
	21st to end	Day	13% 11% 2 5% 3 3 3 3 4 4 47%	3960
February	1st to 10th	Day	17% 9% 2 7% 4 4 4 4 6% 6% 37%	1770
	11th to 20th	Day	13% 9% 3 7% 5% 6% 5% 4 5% 6% 39%	1948
	21st to end	Day	16% 11% 3 7% 4 4 5% 3 6% 6% 36%	1650
March	1st to 10th	Day	23% 11% 2 6% 5% 4 4 3 4 4 33%	4476
	11th to 20th	Day	18% 11% 2 7% 4 4 4 3 5% 6% 36%	4883
	21st to end	Day	27% 9% 2 6% 3 3 4 3 5% 6% 33%	5602
April	1st to 10th	Day	20% 10% 3 8% 4 3 4 4 4 6% 35%	2400
	11th to 20th	Day	19% 6% 2 6% 4 4 5% 4 5% 6% 39%	2472
	21st to end	Day	23% 8% 2 5% 4 3 4 3 5% 5% 36%	2600
May	1st to 10th	Day	33% 11% 3 7% 4 4 4 3 4 5% 23%	5886
	11th to 20th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 8% 29%	5946
	21st to end	Day	20% 6% 3 7% 5% 5% 4 4 6% 8% 33%	6949
June	1st to 10th	Day	21% 9% 2 6% 4 4 4 4 5% 8% 32%	2800
	11th to 20th	Day	16% 7% 2 6% 5% 4 4 4 5% 8% 39%	2800
	21st to end	Day	21% 7% 2 6% 5% 5% 4 4 6% 7% 32%	2800
July	1st to 10th	Day	17% 8% 3 7% 4 5% 5% 4 6% 9% 32%	6360
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 4 6% 9% 37%	6360
	21st to end	Day	17% 5% 2 5% 4 3 4 4 6% 8% 44%	6926
August	1st to 10th	Day	15% 6% 2 7% 4 4 5% 4 6% 9% 37%	4250
	11th to 20th	Day	16% 8% 3 7% 4 4 5% 4 6% 8% 35%	4175
	21st to end	Day	9% 4 2 5% 5% 4 5% 4 7% 9% 47%	4477
September	1st to 10th	Day	12% 4 1 5% 4 4 4 4 5% 8% 49%	2354
	11th to 20th	Day	12% 6% 1 5% 3 3 3 2 4 6% 55%	2200
	21st to end	Day	16% 6% 2 5% 3 3 4 4 5% 8% 45%	2200
October	1st to 10th	Day	18% 7% 2 7% 4 4 4 3 4 6% 42%	2200
	11th to 20th	Day	18% 6% 3 6% 3 4 4 3 4 6% 43%	1928
	21st to end	Day	22% 8% 2 5% 3 3 4 2 4 6% 40%	1980
November	1st to 10th	Day	17% 6% 2 4 4 3 4 3 5% 6% 46%	1851
	11th to 20th	Day	19% 5% 1 5% 4 3 4 3 6% 6% 46%	1890
	21st to end	Day	22% 8% 2 6% 3 2 3 3 4 6% 42%	1890
December	1st to 10th	Day	16% 10% 2 5% 3 3 4 5% 5% 7% 42%	2427
	11th to 20th	Day	19% 8% 2 4 2 3 3 2 4 5% 48%	2849
	21st to end	Day	21% 10% 3 6% 4 4 4 3 4 5% 35%	4048
January	1st to 10th	Night	12% 8% 3 7% 5% 4 4 3 6% 6% 43%	6489
	11th to 20th	Night	13% 10% 4 10% 5% 5% 5% 4 5% 5% 35%	6400
	21st to end	Night	15% 10% 3 7% 4 4 4 3 5% 5% 41%	6996
February	1st to 10th	Night	17% 9% 3 7% 5% 5% 4 4 5% 5% 36%	2623
	11th to 20th	Night	13% 11% 2 6% 5% 5% 4 3 5% 6% 40%	2338
	21st to end	Night	15% 10% 3 6% 4 4 3 3 5% 6% 40%	1980
March	1st to 10th	Night	26% 10% 3 7% 4 4 4 3 4 5% 31%	5364
	11th to 20th	Night	16% 10% 3 7% 5% 5% 5% 4 6% 6% 34%	5076
	21st to end	Night	25% 8% 3 6% 4 4 4 4 6% 6% 32%	5314
April	1st to 10th	Night	22% 10% 2 5% 4 4 4 3 5% 6% 35%	2000
	11th to 20th	Night	19% 6% 2 6% 4 4 5% 4 5% 6% 37%	1875
	21st to end	Night	22% 7% 2 6% 5% 4 4 4 4 6% 36%	1800
May	1st to 10th	Night	33% 8% 3 8% 4 4 4 3 5% 6% 23%	4054
	11th to 20th	Night	17% 11% 3 8% 6% 5% 5% 4 6% 7% 28%	3989
	21st to end	Night	18% 9% 4 9% 5% 4 5% 4 5% 7% 30%	3926
June	1st to 10th	Night	21% 8% 2 7% 5% 5% 4 5% 4 7% 32%	1600
	11th to 20th	Night	17% 7% 3 6% 4 3 4 4 6% 8% 39%	1600
	21st to end	Night	22% 7% 3 5% 5% 4 4 4 6% 7% 33%	1600
July	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 5% 6% 8% 35%	3600
	11th to 20th	Night	15% 9% 3 8% 4 4 5% 4 6% 8% 35%	3600
	21st to end	Night	12% 5% 1 5% 4 4 4 4 7% 8% 46%	3926
August	1st to 10th	Night	20% 7% 3 8% 5% 4 4 4 6% 7% 32%	2865
	11th to 20th	Night	16% 8% 3 7% 5% 4 5% 4 7% 8% 33%	2872
	21st to end	Night	11% 5% 2 6% 4 4 4 3 6% 8% 46%	3416
September	1st to 10th	Night	12% 6% 2 5% 4 4 3 3 5% 6% 49%	2045
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 6% 51%	2200
	21st to end	Night	15% 7% 2 5% 3 3 3 3 4 6% 48%	2200
October	1st to 10th	Night	18% 7% 2 6% 4 3 5% 4 5% 6% 41%	2200
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 5% 7% 42%	2468
	21st to end	Night	24% 6% 2 5% 4 3 4 3 5% 5% 38%	2860
November	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 5% 5% 45%	2667
	11th to 20th	Night	18% 6% 2 4 4 4 4 3 5% 6% 45%	2730
	21st to end	Night	17% 7% 3 5% 4 3 3 4 5% 6% 42%	2730
December	1st to 10th	Night	17% 11% 2 5% 4 4 4 3 5% 5% 39%	4968
	11th to 20th	Night	23% 7% 2 5% 4 3 3 3 4 5% 42%	5540
	21st to end	Night	21% 12% 3 7% 4 3 3 2 3 4 37%	7150

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	45% 3 8% 27% 16% 1	3678
	11th to 20th	Day	41% 3 12% 28% 14% 3	3648
	21st to end	Day	41% 3 9% 21% 20% 6%	3960
February	1st to 10th	Day	47% 4 11% 20% 15% 3	1770
	11th to 20th	Day	45% 5% 12% 20% 15% 4	1957
	21st to end	Day	48% 3 9% 22% 14% 4	1650
March	1st to 10th	Day	55% 3 8% 12% 14% 9%	4479
	11th to 20th	Day	48% 4 14% 20% 12% 3	4883
	21st to end	Day	52% 4 4 17% 17% 6%	5602
April	1st to 10th	Day	50% 4 7% 18% 16% 4	2400
	11th to 20th	Day	44% 5% 10% 24% 15% 3	2472
	21st to end	Day	50% 4 8% 19% 16% 4	2600
May	1st to 10th	Day	63% 5% 11% 14% 6% 1	5897
	11th to 20th	Day	53% 5% 13% 18% 9% 2	5950
	21st to end	Day	48% 6% 14% 21% 10% 1	6949
June	1st to 10th	Day	50% 5% 13% 23% 10%	2800
	11th to 20th	Day	42% 5% 13% 22% 16% 2	2800
	21st to end	Day	50% 6% 11% 22% 10% 1	2800
July	1st to 10th	Day	49% 4 13% 22% 12%	6290
	11th to 20th	Day	44% 4 14% 24% 13% 1	6285
	21st to end	Day	38% 4 14% 29% 15% 1	6728
August	1st to 10th	Day	44% 5% 17% 26% 8%	4236
	11th to 20th	Day	47% 4 16% 25% 8%	4214
	21st to end	Day	33% 5% 15% 27% 20% 1	4477
September	1st to 10th	Day	32% 6% 14% 29% 18% 1	2354
	11th to 20th	Day	32% 4 10% 29% 23% 2	2200
	21st to end	Day	38% 6% 9% 28% 18% 2	2200
October	1st to 10th	Day	45% 3 9% 24% 17% 2	3590
	11th to 20th	Day	35% 3 9% 31% 21% 1	3105
	21st to end	Day	36% 2 11% 27% 20% 3	3180
November	1st to 10th	Day	39% 4 13% 25% 17% 3	1851
	11th to 20th	Day	38% 4 9% 23% 21% 4	1890
	21st to end	Day	45% 4 15% 23% 13% 1	1890
December	1st to 10th	Day	43% 3 12% 30% 12% 1	2427
	11th to 20th	Day	40% 3 11% 21% 16% 9%	2850
	21st to end	Day	51% 3 8% 19% 14% 5%	4048
January	1st to 10th	Night	42% 3 10% 30% 13% 2	6489
	11th to 20th	Night	50% 5% 12% 20% 11% 2	6445
	21st to end	Night	46% 2 7% 21% 18% 6%	6996
February	1st to 10th	Night	49% 4 11% 19% 14% 3	2623
	11th to 20th	Night	45% 4 9% 21% 17% 4	2340
	21st to end	Night	45% 4 9% 23% 15% 5%	1980
March	1st to 10th	Night	56% 2 7% 13% 14% 7%	5374
	11th to 20th	Night	49% 4 15% 19% 10% 2	5077
	21st to end	Night	52% 4 4 15% 19% 5%	5314
April	1st to 10th	Night	50% 4 8% 20% 15% 4	2000
	11th to 20th	Night	46% 4 9% 21% 18% 2	1875
	21st to end	Night	50% 5% 10% 17% 15% 4	1800
May	1st to 10th	Night	63% 5% 11% 13% 7% 1	4060
	11th to 20th	Night	55% 5% 11% 20% 8% 1	3990
	21st to end	Night	54% 6% 11% 20% 9% 1	3927
June	1st to 10th	Night	51% 6% 10% 22% 11% 1	1600
	11th to 20th	Night	43% 6% 15% 20% 15% 2	1600
	21st to end	Night	49% 5% 13% 22% 10% 1	1600
July	1st to 10th	Night	47% 4 14% 22% 12%	3560
	11th to 20th	Night	48% 4 12% 22% 14%	3552
	21st to end	Night	36% 4 15% 32% 12% 1	3809
August	1st to 10th	Night	52% 5% 14% 21% 8% 1	2855
	11th to 20th	Night	47% 6% 14% 23% 11%	2899
	21st to end	Night	36% 4 14% 27% 18% 1	3416
September	1st to 10th	Night	36% 5% 10% 30% 17% 1	2045
	11th to 20th	Night	35% 4 9% 30% 20% 2	2200
	21st to end	Night	38% 5% 10% 29% 17% 2	2200
October	1st to 10th	Night	45% 4 12% 23% 16% 1	3590
	11th to 20th	Night	33% 3 9% 29% 25% 2	4030
	21st to end	Night	39% 2 10% 28% 18% 3	4610
November	1st to 10th	Night	40% 4 9% 27% 17% 2	2667
	11th to 20th	Night	41% 4 10% 24% 19% 3	2730
	21st to end	Night	42% 4 15% 22% 15% 2	2730
December	1st to 10th	Night	47% 3 8% 29% 12% 1	4968
	11th to 20th	Night	46% 3 11% 19% 19% 4	5540
	21st to end	Night	52% 2 9% 18% 17% 2	7150

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	27% 20% 28% 19% 5%	220
	11th to 20th	Day	26% 17% 31% 21% 5% 1	212
	21st to end	Day	20% 16% 39% 16% 8%	220
February	1st to 10th	Day	28% 13% 38% 18% 3	368
	11th to 20th	Day	24% 20% 40% 14% 2	496
	21st to end	Day	25% 15% 38% 18% 5%	414
March	1st to 10th	Day	27% 13% 39% 17% 3	500
	11th to 20th	Day	22% 20% 37% 17% 2 1	500
	21st to end	Day	27% 19% 31% 15% 5% 2	550
April	1st to 10th	Day	30% 16% 32% 16% 4 2	500
	11th to 20th	Day	26% 17% 33% 17% 6% 1	492
	21st to end	Day	30% 13% 32% 18% 4 2	500
May	1st to 10th	Day	30% 15% 30% 18% 5% 2	503
	11th to 20th	Day	21% 12% 39% 20% 7% 2	527
	21st to end	Day	22% 11% 34% 25% 7% 1	573
June	1st to 10th	Day	22% 8% 36% 24% 6% 3	530
	11th to 20th	Day	16% 13% 37% 22% 10% 2	530
	21st to end	Day	23% 8% 33% 25% 9% 2	530
July	1st to 10th	Day	20% 6% 32% 28% 12% 3	525
	11th to 20th	Day	16% 6% 32% 29% 13% 4	524
	21st to end	Day	15% 4 32% 31% 14% 4	576
August	1st to 10th	Day	13% 6% 28% 34% 15% 4	526
	11th to 20th	Day	18% 4 26% 30% 15% 7%	519
	21st to end	Day	13% 6% 30% 29% 14% 7%	583
September	1st to 10th	Day	15% 8% 30% 29% 14% 5%	530
	11th to 20th	Day	15% 8% 31% 24% 13% 8%	530
	21st to end	Day	18% 9% 32% 23% 12% 6%	530
October	1st to 10th	Day	22% 11% 23% 26% 13% 5%	530
	11th to 20th	Day	21% 12% 30% 23% 10% 4	426
	21st to end	Day	29% 13% 29% 22% 8%	462
November	1st to 10th	Day	25% 15% 28% 22% 9% 2	425
	11th to 20th	Day	24% 17% 31% 20% 6% 1	430
	21st to end	Day	29% 14% 30% 20% 6% 1	430
December	1st to 10th	Day	25% 15% 35% 16% 8% 1	251
	11th to 20th	Day	27% 17% 34% 16% 5%	220
	21st to end	Day	29% 18% 28% 19% 6%	242
January	1st to 10th	Night	23% 18% 35% 20% 4	840
	11th to 20th	Night	24% 19% 34% 19% 4	825
	21st to end	Night	19% 19% 38% 20% 3	880
February	1st to 10th	Night	24% 16% 36% 21% 3	800
	11th to 20th	Night	23% 18% 37% 19% 2	783
	21st to end	Night	22% 15% 35% 24% 5%	660
March	1st to 10th	Night	25% 17% 36% 21% 2	800
	11th to 20th	Night	23% 13% 34% 22% 7%	800
	21st to end	Night	26% 13% 32% 24% 5% 1	880
April	1st to 10th	Night	28% 12% 31% 25% 4	800
	11th to 20th	Night	23% 10% 35% 24% 8%	691
	21st to end	Night	26% 10% 29% 28% 6% 1	600
May	1st to 10th	Night	28% 7% 29% 27% 9% 1	600
	11th to 20th	Night	23% 7% 32% 29% 9% 1	574
	21st to end	Night	26% 6% 22% 32% 12% 1	433
June	1st to 10th	Night	25% 7% 20% 33% 13% 2	400
	11th to 20th	Night	20% 4 22% 36% 17% 1	400
	21st to end	Night	24% 5% 19% 38% 14%	400
July	1st to 10th	Night	19% 3 14% 45% 17% 2	390
	11th to 20th	Night	20% 3 16% 38% 21% 3	388
	21st to end	Night	16% 3 15% 42% 23% 2	438
August	1st to 10th	Night	15% 3 17% 44% 19% 2	560
	11th to 20th	Night	16% 4 16% 39% 22% 3	592
	21st to end	Night	16% 4 19% 38% 19% 3	775
September	1st to 10th	Night	15% 4 25% 35% 19% 2	800
	11th to 20th	Night	18% 6% 24% 28% 20% 4	800
	21st to end	Night	19% 6% 24% 33% 16% 2	800
October	1st to 10th	Night	21% 8% 22% 30% 18% 2	800
	11th to 20th	Night	20% 10% 31% 26% 12% 1	800
	21st to end	Night	28% 10% 30% 26% 7%	880
November	1st to 10th	Night	21% 11% 33% 26% 6% 2	820
	11th to 20th	Night	24% 14% 32% 22% 7% 1	840
	21st to end	Night	22% 18% 33% 22% 5%	840
December	1st to 10th	Night	26% 15% 36% 18% 5% 1	936
	11th to 20th	Night	25% 20% 32% 19% 4	903
	21st to end	Night	27% 14% 35% 20% 3	924

Page generated at 2026-01-14 01:14:27. Version ac07

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