Whitin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitin Observatory clear sky chart from 2005-11-06 to 2025-07-06.

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	18% 7% 2 6% 4 4 4 4 5% 7% 38%	119539
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 40%	119269
Transparency	Day	44% 6% 11% 22% 15% 3	123117
	Night	44% 5% 12% 21% 16% 3	123852
Seeing	Day	24% 16% 33% 19% 7% 2	15884
	Night	22% 14% 33% 24% 6%	24796

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	11% 8% 2 8% 4 4 5% 3 5% 7% 44%	3597
	11th to 20th	Day	13% 8% 3 5% 3 4 4 3 4 5% 48%	3570
	21st to end	Day	17% 8% 2 5% 3 4 4 3 6% 5% 43%	3960
February	1st to 10th	Day	19% 7% 3 6% 5% 4 4 4 6% 5% 37%	1874
	11th to 20th	Day	13% 8% 3 6% 5% 4 6% 3 6% 6% 40%	1948
	21st to end	Day	18% 9% 3 6% 4 4 5% 2 5% 5% 38%	1650
March	1st to 10th	Day	21% 12% 2 6% 3 4 4 3 5% 5% 35%	4476
	11th to 20th	Day	15% 8% 2 6% 4 5% 4 4 6% 7% 39%	4784
	21st to end	Day	26% 9% 3 6% 4 4 4 4 6% 6% 30%	5775
April	1st to 10th	Day	20% 9% 3 7% 4 4 4 3 4 6% 37%	2400
	11th to 20th	Day	19% 7% 2 5% 4 4 4 3 5% 7% 38%	2388
	21st to end	Day	21% 6% 2 7% 4 4 5% 3 6% 6% 37%	2600
May	1st to 10th	Day	29% 11% 3 7% 4 3 4 3 4 6% 25%	5886
	11th to 20th	Day	20% 9% 4 8% 5% 4 5% 4 4 7% 32%	5944
	21st to end	Day	19% 7% 3 7% 4 4 4 4 5% 8% 35%	6949
June	1st to 10th	Day	19% 6% 2 6% 4 4 4 5% 6% 8% 34%	2800
	11th to 20th	Day	16% 7% 2 6% 5% 5% 4 4 6% 8% 38%	2800
	21st to end	Day	16% 6% 2 7% 4 5% 5% 4 6% 8% 36%	2800
July	1st to 10th	Day	13% 7% 2 6% 6% 5% 6% 5% 7% 8% 35%	4510
	11th to 20th	Day	11% 6% 2 7% 4 5% 5% 4 6% 9% 40%	4440
	21st to end	Day	17% 7% 3 7% 5% 4 4 4 5% 8% 35%	4814
August	1st to 10th	Day	15% 6% 3 8% 5% 6% 5% 5% 7% 8% 33%	4142
	11th to 20th	Day	13% 8% 3 6% 5% 5% 5% 4 6% 7% 38%	3989
	21st to end	Day	7% 4 2 5% 4 5% 6% 4 7% 8% 47%	4180
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 4 5% 6% 47%	2274
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 4 6% 51%	2090
	21st to end	Day	19% 6% 2 5% 4 3 3 3 6% 6% 44%	2090
October	1st to 10th	Day	24% 5% 2 4 4 3 4 3 4 6% 41%	2090
	11th to 20th	Day	15% 6% 2 5% 4 3 4 3 4 6% 48%	1862
	21st to end	Day	20% 7% 2 5% 4 4 4 3 4 6% 42%	1881
November	1st to 10th	Day	16% 6% 2 5% 4 4 3 2 4 4 50%	1761
	11th to 20th	Day	18% 7% 2 4 3 4 3 2 5% 5% 48%	1800
	21st to end	Day	19% 6% 3 5% 4 3 4 4 5% 6% 43%	1800
December	1st to 10th	Day	15% 8% 2 4 3 3 3 3 4 4 49%	2669
	11th to 20th	Day	20% 6% 2 4 3 3 3 3 3 5% 48%	2986
	21st to end	Day	21% 10% 3 7% 4 4 3 3 4 5% 38%	3960
January	1st to 10th	Night	14% 7% 2 5% 3 3 3 3 5% 6% 49%	6349
	11th to 20th	Night	14% 9% 3 8% 5% 4 4 3 4 6% 40%	6315
	21st to end	Night	15% 11% 3 7% 5% 4 4 3 4 5% 38%	6996
February	1st to 10th	Night	17% 9% 2 6% 4 4 4 3 5% 5% 39%	2523
	11th to 20th	Night	15% 9% 3 6% 5% 4 4 4 4 7% 39%	2338
	21st to end	Night	18% 9% 2 6% 4 5% 3 3 5% 5% 41%	1980
March	1st to 10th	Night	24% 9% 2 5% 4 4 3 3 4 6% 37%	5364
	11th to 20th	Night	16% 11% 3 7% 4 4 4 4 5% 5% 39%	5173
	21st to end	Night	25% 9% 3 5% 4 3 4 3 5% 4 33%	5156
April	1st to 10th	Night	19% 8% 2 7% 4 4 4 3 5% 6% 37%	2000
	11th to 20th	Night	20% 7% 2 6% 4 4 4 3 4 6% 39%	1960
	21st to end	Night	20% 8% 3 6% 5% 3 4 3 4 5% 40%	1800
May	1st to 10th	Night	30% 10% 3 7% 4 3 3 3 5% 6% 26%	4054
	11th to 20th	Night	18% 8% 3 8% 5% 6% 6% 5% 6% 7% 28%	3991
	21st to end	Night	20% 8% 3 8% 4 4 4 4 5% 7% 33%	3926
June	1st to 10th	Night	16% 8% 3 6% 5% 5% 4 4 5% 7% 37%	1600
	11th to 20th	Night	18% 6% 3 6% 4 4 4 4 6% 8% 36%	1600
	21st to end	Night	15% 7% 1 5% 4 5% 4 4 5% 9% 41%	1600
July	1st to 10th	Night	11% 6% 3 7% 6% 5% 5% 5% 8% 10% 35%	2560
	11th to 20th	Night	11% 7% 3 7% 5% 4 4 4 6% 10% 39%	2520
	21st to end	Night	15% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	2739
August	1st to 10th	Night	19% 7% 3 8% 5% 5% 5% 4 7% 7% 31%	2755
	11th to 20th	Night	10% 7% 3 8% 5% 6% 6% 4 7% 8% 37%	2835
	21st to end	Night	8% 4 1 4 3 4 4 4 5% 8% 55%	3476
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 6% 47%	1905
	11th to 20th	Night	15% 6% 1 4 3 3 4 3 4 5% 53%	2090
	21st to end	Night	18% 6% 2 6% 4 3 3 4 5% 5% 43%	2090
October	1st to 10th	Night	21% 6% 2 6% 4 3 4 3 4 5% 43%	2090
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 5% 6% 48%	2317
	21st to end	Night	21% 7% 3 5% 4 3 3 3 5% 6% 39%	2717
November	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 5% 5% 49%	2537
	11th to 20th	Night	18% 7% 2 6% 3 3 3 3 4 4 47%	2600
	21st to end	Night	17% 6% 2 5% 4 3 4 3 4 6% 45%	2600
December	1st to 10th	Night	18% 8% 2 5% 4 3 4 3 4 6% 43%	4509
	11th to 20th	Night	22% 8% 3 6% 4 3 3 3 4 4 41%	5208
	21st to end	Night	17% 10% 3 6% 4 3 3 3 4 6% 40%	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	39% 5% 7% 28% 19% 2	3598
	11th to 20th	Day	38% 5% 11% 22% 20% 5%	3600
	21st to end	Day	42% 4 11% 22% 19% 2	3960
February	1st to 10th	Day	46% 5% 15% 18% 14% 2	1874
	11th to 20th	Day	43% 7% 11% 22% 15% 3	1957
	21st to end	Day	47% 5% 10% 20% 15% 3	1650
March	1st to 10th	Day	50% 4 10% 16% 11% 9%	4479
	11th to 20th	Day	41% 8% 14% 26% 10% 2	4784
	21st to end	Day	53% 5% 7% 15% 14% 7%	5775
April	1st to 10th	Day	48% 5% 9% 18% 16% 4	2400
	11th to 20th	Day	43% 6% 11% 20% 17% 3	2388
	21st to end	Day	46% 6% 9% 19% 17% 4	2600
May	1st to 10th	Day	59% 6% 13% 12% 8% 1	5897
	11th to 20th	Day	51% 7% 14% 16% 10% 2	5948
	21st to end	Day	45% 7% 11% 22% 13% 1	6949
June	1st to 10th	Day	45% 7% 13% 23% 11% 1	2800
	11th to 20th	Day	43% 7% 13% 19% 16% 2	2800
	21st to end	Day	44% 7% 13% 21% 14% 1	2800
July	1st to 10th	Day	44% 8% 11% 21% 14% 2	4440
	11th to 20th	Day	39% 7% 15% 24% 13% 2	4365
	21st to end	Day	47% 7% 12% 20% 13% 2	4661
August	1st to 10th	Day	46% 9% 16% 21% 8% 1	4128
	11th to 20th	Day	42% 8% 13% 26% 10% 1	4028
	21st to end	Day	31% 8% 12% 30% 18% 1	4180
September	1st to 10th	Day	36% 7% 10% 24% 20% 2	2274
	11th to 20th	Day	35% 4 8% 28% 22% 3	2090
	21st to end	Day	41% 4 9% 21% 22% 2	2090
October	1st to 10th	Day	40% 5% 10% 24% 18% 4	3480
	11th to 20th	Day	31% 4 7% 28% 26% 4	3065
	21st to end	Day	32% 4 11% 29% 20% 3	3081
November	1st to 10th	Day	39% 3 13% 25% 17% 2	1761
	11th to 20th	Day	39% 4 8% 23% 22% 3	1800
	21st to end	Day	41% 5% 13% 26% 12% 2	1800
December	1st to 10th	Day	39% 3 14% 28% 14% 1	2669
	11th to 20th	Day	40% 3 14% 18% 19% 6%	2986
	21st to end	Day	49% 5% 8% 20% 14% 4	3960
January	1st to 10th	Night	34% 4 10% 33% 16% 2	6349
	11th to 20th	Night	45% 4 12% 21% 14% 4	6360
	21st to end	Night	48% 4 10% 16% 17% 4	6996
February	1st to 10th	Night	46% 5% 13% 21% 13% 2	2523
	11th to 20th	Night	46% 5% 10% 20% 16% 4	2340
	21st to end	Night	46% 4 8% 23% 16% 4	1980
March	1st to 10th	Night	49% 4 9% 16% 16% 7%	5374
	11th to 20th	Night	45% 7% 16% 17% 13% 2	5174
	21st to end	Night	53% 4 5% 12% 19% 7%	5156
April	1st to 10th	Night	47% 5% 10% 19% 15% 3	2000
	11th to 20th	Night	47% 5% 9% 20% 17% 3	1960
	21st to end	Night	46% 6% 10% 18% 17% 4	1800
May	1st to 10th	Night	58% 7% 14% 11% 8% 2	4060
	11th to 20th	Night	51% 9% 15% 15% 8% 2	3992
	21st to end	Night	50% 8% 14% 18% 10% 1	3927
June	1st to 10th	Night	46% 7% 13% 21% 12% 1	1600
	11th to 20th	Night	45% 7% 13% 22% 13% 1	1600
	21st to end	Night	40% 9% 13% 24% 14% 1	1600
July	1st to 10th	Night	42% 8% 14% 21% 15%	2520
	11th to 20th	Night	40% 8% 16% 24% 13% 1	2472
	21st to end	Night	47% 7% 11% 19% 14% 1	2651
August	1st to 10th	Night	50% 8% 14% 18% 9% 1	2745
	11th to 20th	Night	42% 9% 15% 24% 10%	2862
	21st to end	Night	26% 6% 16% 28% 23% 1	3476
September	1st to 10th	Night	38% 6% 11% 24% 19% 1	1905
	11th to 20th	Night	33% 5% 10% 23% 26% 2	2090
	21st to end	Night	41% 6% 9% 21% 20% 2	2090
October	1st to 10th	Night	39% 5% 14% 23% 16% 2	3480
	11th to 20th	Night	27% 4 10% 27% 30% 3	3853
	21st to end	Night	34% 4 12% 30% 19% 2	4467
November	1st to 10th	Night	37% 5% 11% 23% 20% 4	2537
	11th to 20th	Night	40% 4 10% 22% 21% 4	2600
	21st to end	Night	40% 4 14% 26% 14% 2	2600
December	1st to 10th	Night	42% 5% 12% 27% 13% 1	4509
	11th to 20th	Night	46% 4 15% 14% 20% 1	5208
	21st to end	Night	45% 5% 8% 23% 16% 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% 24% 30% 15% 4	200
	11th to 20th	Day	29% 22% 37% 10% 3	200
	21st to end	Day	26% 23% 35% 12% 4	220
February	1st to 10th	Day	30% 19% 33% 16% 2	412
	11th to 20th	Day	28% 23% 37% 11% 1	496
	21st to end	Day	27% 19% 35% 16% 3	414
March	1st to 10th	Day	30% 20% 32% 15% 3	500
	11th to 20th	Day	29% 22% 31% 14% 4 1	500
	21st to end	Day	31% 21% 33% 8% 7% 1	550
April	1st to 10th	Day	33% 23% 25% 13% 5% 1	500
	11th to 20th	Day	30% 23% 30% 11% 4 1	492
	21st to end	Day	27% 19% 33% 16% 2 1	500
May	1st to 10th	Day	33% 23% 28% 12% 3 1	503
	11th to 20th	Day	24% 19% 38% 13% 6% 1	527
	21st to end	Day	20% 14% 37% 22% 6% 1	573
June	1st to 10th	Day	22% 14% 38% 19% 6% 2	530
	11th to 20th	Day	18% 16% 38% 21% 6% 1	530
	21st to end	Day	16% 15% 37% 23% 8% 1	530
July	1st to 10th	Day	19% 9% 33% 28% 10% 1	505
	11th to 20th	Day	16% 8% 33% 29% 11% 3	484
	21st to end	Day	13% 8% 39% 31% 7% 1	532
August	1st to 10th	Day	12% 10% 33% 33% 10% 2	486
	11th to 20th	Day	16% 8% 34% 27% 14% 2	479
	21st to end	Day	13% 10% 33% 27% 13% 5%	539
September	1st to 10th	Day	19% 10% 29% 25% 14% 3	490
	11th to 20th	Day	20% 11% 28% 19% 13% 9%	490
	21st to end	Day	23% 12% 30% 22% 8% 4	490
October	1st to 10th	Day	28% 12% 26% 21% 10% 5%	490
	11th to 20th	Day	19% 17% 32% 21% 8% 3	435
	21st to end	Day	27% 14% 34% 17% 8% 1	429
November	1st to 10th	Day	23% 15% 34% 17% 9% 3	395
	11th to 20th	Day	27% 20% 32% 16% 5% 1	400
	21st to end	Day	28% 20% 29% 17% 6% 1	400
December	1st to 10th	Day	25% 20% 35% 17% 2	243
	11th to 20th	Day	32% 25% 32% 9% 3	200
	21st to end	Day	24% 20% 36% 14% 4 2	220
January	1st to 10th	Night	23% 18% 38% 18% 2	800
	11th to 20th	Night	27% 18% 36% 17% 2	800
	21st to end	Night	21% 19% 36% 20% 4	880
February	1st to 10th	Night	24% 17% 36% 22% 2	800
	11th to 20th	Night	24% 18% 40% 16% 1	783
	21st to end	Night	25% 19% 34% 19% 3	660
March	1st to 10th	Night	26% 17% 36% 18% 4	800
	11th to 20th	Night	23% 18% 37% 18% 4	800
	21st to end	Night	25% 18% 35% 18% 4	880
April	1st to 10th	Night	26% 19% 31% 20% 4	800
	11th to 20th	Night	24% 20% 34% 18% 5%	776
	21st to end	Night	25% 17% 36% 20% 2	600
May	1st to 10th	Night	29% 16% 32% 20% 4	600
	11th to 20th	Night	20% 16% 40% 20% 4	576
	21st to end	Night	20% 10% 35% 29% 5% 1	433
June	1st to 10th	Night	20% 8% 37% 29% 7%	400
	11th to 20th	Night	18% 7% 40% 29% 6%	400
	21st to end	Night	16% 7% 37% 34% 6%	400
July	1st to 10th	Night	13% 4 35% 37% 10%	380
	11th to 20th	Night	13% 4 33% 40% 10%	368
	21st to end	Night	14% 5% 32% 40% 8%	416
August	1st to 10th	Night	12% 6% 34% 38% 10%	523
	11th to 20th	Night	12% 6% 31% 39% 11%	589
	21st to end	Night	15% 5% 24% 40% 14% 2	836
September	1st to 10th	Night	16% 6% 32% 34% 12%	760
	11th to 20th	Night	17% 8% 27% 28% 18% 2	760
	21st to end	Night	22% 8% 25% 31% 12% 2	760
October	1st to 10th	Night	23% 11% 26% 26% 12% 2	760
	11th to 20th	Night	19% 12% 31% 24% 12% 1	760
	21st to end	Night	25% 14% 33% 22% 6%	836
November	1st to 10th	Night	18% 14% 33% 26% 8% 1	780
	11th to 20th	Night	23% 19% 32% 19% 7%	800
	21st to end	Night	23% 19% 33% 19% 5% 1	800
December	1st to 10th	Night	25% 18% 34% 19% 4	800
	11th to 20th	Night	25% 18% 31% 22% 3	800
	21st to end	Night	25% 16% 35% 21% 3	880

Page generated at 2025-07-03 01:30:15. Version ac07

Copyright © 2025 Attilla Danko.