Three dog Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Three dog Observatory clear sky chart from 2005-11-06 to 2026-03-18.

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	20% 14% 5% 9% 5% 5% 4 3 5% 6% 23%	131261
	Night	19% 14% 5% 10% 5% 5% 4 3 5% 6% 23%	130537
Transparency	Day	62% 6% 11% 15% 6% 1	134688
	Night	61% 6% 12% 15% 6% 1	135222
Seeing	Day	29% 15% 29% 19% 7% 1	19935
	Night	29% 15% 31% 19% 5%	26863

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	18% 22% 8% 13% 5% 4 3 3 4 4 17%	4122
	11th to 20th	Day	18% 19% 8% 14% 5% 5% 4 3 4 4 16%	4659
	21st to end	Day	7% 13% 5% 11% 10% 8% 7% 4 5% 6% 22%	5157
February	1st to 10th	Day	16% 15% 4 12% 6% 5% 6% 4 6% 7% 19%	1680
	11th to 20th	Day	19% 21% 5% 13% 7% 4 4 4 4 4 16%	1896
	21st to end	Day	14% 14% 5% 13% 7% 7% 5% 4 4 5% 23%	1730
March	1st to 10th	Day	16% 14% 5% 15% 8% 6% 4 3 4 5% 19%	4574
	11th to 20th	Day	19% 18% 7% 12% 6% 5% 4 3 3 4 19%	4911
	21st to end	Day	24% 19% 9% 12% 5% 4 3 2 3 3 16%	5690
April	1st to 10th	Day	19% 19% 7% 12% 6% 5% 5% 3 4 5% 16%	2400
	11th to 20th	Day	23% 17% 5% 8% 3 4 3 3 5% 5% 24%	2557
	21st to end	Day	22% 20% 6% 8% 5% 4 4 3 4 4 20%	2600
May	1st to 10th	Day	27% 22% 6% 9% 4 4 3 2 3 4 16%	6110
	11th to 20th	Day	20% 17% 5% 9% 5% 5% 4 3 4 5% 22%	6524
	21st to end	Day	26% 17% 3 6% 4 4 3 3 4 5% 24%	7428
June	1st to 10th	Day	32% 15% 4 6% 5% 4 4 4 4 5% 18%	3000
	11th to 20th	Day	27% 12% 3 7% 4 5% 4 3 5% 5% 24%	3000
	21st to end	Day	24% 11% 3 7% 5% 6% 5% 4 5% 7% 24%	3000
July	1st to 10th	Day	18% 12% 4 8% 5% 5% 5% 4 5% 7% 27%	6800
	11th to 20th	Day	12% 7% 3 8% 6% 6% 6% 5% 7% 10% 29%	6717
	21st to end	Day	19% 9% 3 7% 5% 5% 5% 4 6% 7% 30%	6927
August	1st to 10th	Day	20% 10% 3 8% 6% 5% 6% 4 6% 7% 25%	4564
	11th to 20th	Day	18% 9% 3 6% 4 4 4 3 6% 6% 37%	4184
	21st to end	Day	20% 8% 2 7% 4 4 4 4 6% 8% 33%	4675
September	1st to 10th	Day	21% 7% 3 6% 4 4 5% 4 5% 8% 33%	2400
	11th to 20th	Day	27% 9% 3 7% 4 5% 5% 3 4 6% 27%	2200
	21st to end	Day	18% 10% 4 8% 4 5% 4 3 4 8% 31%	2200
October	1st to 10th	Day	22% 11% 3 7% 4 3 4 3 4 7% 30%	2157
	11th to 20th	Day	24% 14% 2 8% 5% 4 5% 4 5% 7% 22%	1825
	21st to end	Day	25% 18% 4 6% 5% 4 5% 3 5% 5% 20%	1980
November	1st to 10th	Day	23% 18% 4 8% 6% 5% 6% 3 4 5% 18%	1850
	11th to 20th	Day	22% 17% 5% 8% 4 4 5% 3 4 6% 22%	1641
	21st to end	Day	24% 17% 5% 9% 5% 4 4 3 3 5% 20%	1470
December	1st to 10th	Day	13% 12% 5% 8% 5% 4 4 4 6% 6% 32%	2360
	11th to 20th	Day	19% 13% 5% 13% 6% 5% 4 4 4 7% 19%	2698
	21st to end	Day	18% 15% 6% 16% 7% 5% 4 3 5% 5% 16%	3575
January	1st to 10th	Night	16% 20% 7% 12% 5% 5% 4 3 4 5% 18%	8802
	11th to 20th	Night	13% 20% 8% 14% 6% 5% 5% 4 5% 5% 15%	8254
	21st to end	Night	7% 13% 5% 11% 7% 7% 7% 4 6% 7% 26%	9056
February	1st to 10th	Night	16% 14% 5% 12% 8% 5% 5% 4 5% 5% 21%	2940
	11th to 20th	Night	19% 18% 5% 12% 6% 5% 5% 4 4 4 18%	2604
	21st to end	Night	14% 15% 4 11% 7% 4 4 3 5% 6% 27%	2076
March	1st to 10th	Night	19% 13% 4 11% 6% 5% 5% 4 6% 6% 21%	5486
	11th to 20th	Night	18% 16% 6% 13% 7% 6% 5% 4 4 5% 16%	5203
	21st to end	Night	23% 16% 5% 12% 5% 4 4 3 4 6% 19%	5238
April	1st to 10th	Night	24% 18% 6% 8% 4 4 3 3 4 5% 22%	2000
	11th to 20th	Night	25% 16% 4 7% 4 4 4 2 4 5% 25%	1793
	21st to end	Night	26% 17% 5% 7% 4 4 3 3 4 6% 23%	1800
May	1st to 10th	Night	33% 19% 6% 8% 3 3 2 2 4 4 15%	3848
	11th to 20th	Night	24% 18% 7% 11% 4 4 3 2 3 4 21%	3388
	21st to end	Night	30% 13% 4 6% 3 4 4 3 5% 6% 22%	3468
June	1st to 10th	Night	34% 13% 3 6% 4 4 4 3 5% 5% 19%	1400
	11th to 20th	Night	29% 10% 3 6% 4 4 4 4 5% 7% 25%	1400
	21st to end	Night	22% 13% 4 8% 6% 6% 5% 3 5% 6% 24%	1400
July	1st to 10th	Night	20% 10% 4 10% 5% 4 5% 3 6% 7% 25%	3179
	11th to 20th	Night	11% 9% 3 9% 6% 5% 6% 5% 7% 8% 31%	3259
	21st to end	Night	21% 10% 3 7% 4 4 4 3 5% 7% 31%	3948
August	1st to 10th	Night	14% 8% 3 8% 6% 4 5% 4 6% 8% 34%	2596
	11th to 20th	Night	17% 9% 3 7% 4 3 4 4 5% 6% 39%	2872
	21st to end	Night	21% 8% 3 6% 4 4 5% 3 4 7% 36%	3234
September	1st to 10th	Night	22% 8% 3 6% 4 3 3 3 5% 5% 38%	1997
	11th to 20th	Night	25% 11% 2 6% 4 4 4 3 4 6% 30%	2200
	21st to end	Night	22% 11% 3 7% 4 4 4 4 5% 6% 30%	2200
October	1st to 10th	Night	24% 11% 3 7% 4 4 3 3 5% 6% 30%	2242
	11th to 20th	Night	25% 13% 3 7% 4 4 4 3 4 6% 27%	2573
	21st to end	Night	27% 16% 3 7% 4 3 4 3 4 5% 24%	2860
November	1st to 10th	Night	22% 17% 4 8% 6% 5% 4 4 5% 6% 19%	2668
	11th to 20th	Night	25% 14% 5% 8% 5% 4 4 3 5% 6% 20%	2977
	21st to end	Night	21% 18% 5% 9% 5% 4 4 3 6% 6% 19%	3150
December	1st to 10th	Night	14% 13% 4 10% 6% 5% 4 4 5% 6% 29%	5050
	11th to 20th	Night	19% 15% 6% 14% 6% 5% 4 3 4 6% 18%	5731
	21st to end	Night	16% 13% 6% 17% 6% 5% 4 4 4 5% 18%	7645

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	70% 5% 11% 11% 3	4123
	11th to 20th	Day	70% 6% 8% 9% 6%	4688
	21st to end	Day	59% 5% 10% 16% 6% 3	5157
February	1st to 10th	Day	64% 7% 12% 10% 6% 1	1680
	11th to 20th	Day	70% 7% 9% 10% 4	1903
	21st to end	Day	62% 7% 9% 13% 8% 1	1730
March	1st to 10th	Day	66% 5% 7% 12% 9% 1	4578
	11th to 20th	Day	69% 5% 7% 9% 7% 2	4911
	21st to end	Day	74% 4 6% 10% 6%	5690
April	1st to 10th	Day	70% 6% 9% 10% 4 1	2400
	11th to 20th	Day	62% 6% 9% 14% 7% 1	2557
	21st to end	Day	67% 6% 7% 12% 8%	2600
May	1st to 10th	Day	73% 5% 8% 10% 3 1	6122
	11th to 20th	Day	64% 6% 9% 16% 6%	6528
	21st to end	Day	62% 5% 11% 17% 5%	7428
June	1st to 10th	Day	69% 7% 8% 12% 4	3000
	11th to 20th	Day	61% 8% 11% 16% 4	3000
	21st to end	Day	59% 9% 10% 14% 7% 1	3000
July	1st to 10th	Day	57% 4 12% 20% 6%	6725
	11th to 20th	Day	49% 6% 17% 23% 5%	6635
	21st to end	Day	53% 5% 16% 22% 4	6730
August	1st to 10th	Day	57% 8% 15% 17% 4	4550
	11th to 20th	Day	48% 6% 14% 20% 11% 1	4223
	21st to end	Day	49% 6% 15% 25% 5%	4675
September	1st to 10th	Day	48% 7% 12% 23% 8% 1	2400
	11th to 20th	Day	58% 7% 13% 16% 5%	2200
	21st to end	Day	52% 7% 17% 17% 6%	2200
October	1st to 10th	Day	59% 5% 12% 17% 6%	3511
	11th to 20th	Day	61% 5% 11% 18% 5%	2960
	21st to end	Day	66% 5% 10% 10% 8% 1	3191
November	1st to 10th	Day	67% 8% 11% 10% 3	1850
	11th to 20th	Day	63% 7% 11% 12% 6% 1	1641
	21st to end	Day	66% 7% 12% 9% 5% 1	1470
December	1st to 10th	Day	51% 5% 10% 24% 10%	2360
	11th to 20th	Day	65% 6% 19% 7% 3	2697
	21st to end	Day	68% 6% 10% 14% 2	3575
January	1st to 10th	Night	67% 5% 11% 12% 4	8802
	11th to 20th	Night	69% 7% 10% 10% 4	8300
	21st to end	Night	54% 6% 12% 14% 12% 2	9056
February	1st to 10th	Night	63% 6% 12% 13% 6% 1	2940
	11th to 20th	Night	68% 6% 10% 11% 4 1	2608
	21st to end	Night	56% 6% 12% 16% 8% 1	2076
March	1st to 10th	Night	61% 6% 9% 13% 8% 2	5495
	11th to 20th	Night	68% 8% 8% 8% 6% 1	5204
	21st to end	Night	66% 5% 11% 13% 5%	5238
April	1st to 10th	Night	64% 6% 8% 13% 9% 1	2000
	11th to 20th	Night	62% 4 9% 17% 7% 1	1793
	21st to end	Night	63% 6% 9% 13% 9% 1	1800
May	1st to 10th	Night	74% 4 7% 12% 3	3853
	11th to 20th	Night	68% 5% 8% 12% 7%	3389
	21st to end	Night	62% 6% 11% 16% 5%	3469
June	1st to 10th	Night	66% 8% 11% 10% 5%	1400
	11th to 20th	Night	58% 8% 13% 16% 5%	1400
	21st to end	Night	60% 8% 10% 15% 6% 1	1400
July	1st to 10th	Night	59% 5% 14% 19% 3	3146
	11th to 20th	Night	50% 5% 15% 21% 8%	3217
	21st to end	Night	54% 5% 16% 22% 4	3831
August	1st to 10th	Night	46% 9% 18% 22% 5%	2585
	11th to 20th	Night	46% 6% 16% 23% 9% 1	2899
	21st to end	Night	49% 5% 15% 26% 5%	3233
September	1st to 10th	Night	47% 7% 14% 23% 9% 1	1997
	11th to 20th	Night	55% 7% 13% 16% 8% 1	2200
	21st to end	Night	54% 7% 14% 18% 7%	2200
October	1st to 10th	Night	61% 5% 15% 14% 5% 1	3671
	11th to 20th	Night	60% 4 15% 15% 7%	4187
	21st to end	Night	59% 4 13% 17% 7% 1	4610
November	1st to 10th	Night	66% 8% 10% 11% 4	2668
	11th to 20th	Night	64% 7% 13% 14% 3	2977
	21st to end	Night	65% 7% 12% 11% 5%	3150
December	1st to 10th	Night	55% 5% 8% 21% 11%	5050
	11th to 20th	Night	69% 5% 14% 8% 4	5733
	21st to end	Night	66% 7% 11% 14% 2	7645

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% 22% 33% 15% 5%	430
	11th to 20th	Day	24% 23% 33% 17% 3	430
	21st to end	Day	27% 21% 32% 16% 3	473
February	1st to 10th	Day	25% 24% 30% 15% 4	430
	11th to 20th	Day	29% 22% 34% 12% 2 1	426
	21st to end	Day	21% 23% 36% 15% 4 1	355
March	1st to 10th	Day	23% 23% 37% 13% 3	430
	11th to 20th	Day	28% 18% 29% 17% 7% 1	421
	21st to end	Day	36% 21% 23% 15% 3 2	488
April	1st to 10th	Day	28% 23% 29% 16% 3	500
	11th to 20th	Day	33% 13% 29% 19% 5% 1	675
	21st to end	Day	32% 16% 29% 18% 4 1	700
May	1st to 10th	Day	38% 13% 24% 17% 6% 2	703
	11th to 20th	Day	30% 13% 28% 18% 9% 2	724
	21st to end	Day	34% 12% 29% 19% 4 1	790
June	1st to 10th	Day	39% 11% 24% 15% 9% 1	730
	11th to 20th	Day	32% 12% 26% 20% 9% 1	730
	21st to end	Day	27% 11% 27% 22% 10% 3	730
July	1st to 10th	Day	28% 10% 27% 23% 9% 2	720
	11th to 20th	Day	20% 11% 29% 29% 11% 1	718
	21st to end	Day	24% 10% 26% 29% 9% 1	795
August	1st to 10th	Day	23% 9% 28% 26% 11% 3	725
	11th to 20th	Day	23% 8% 26% 25% 15% 2	717
	21st to end	Day	24% 9% 29% 24% 12% 3	803
September	1st to 10th	Day	23% 12% 31% 23% 10% 1	532
	11th to 20th	Day	36% 11% 28% 20% 4	420
	21st to end	Day	22% 21% 35% 16% 5% 2	420
October	1st to 10th	Day	24% 19% 34% 17% 5% 2	420
	11th to 20th	Day	35% 11% 27% 17% 8% 2	420
	21st to end	Day	32% 19% 26% 16% 6% 2	462
November	1st to 10th	Day	37% 18% 30% 13% 2	425
	11th to 20th	Day	35% 21% 24% 15% 4 1	430
	21st to end	Day	37% 20% 30% 11% 1	430
December	1st to 10th	Day	25% 18% 34% 17% 5% 1	430
	11th to 20th	Day	29% 26% 30% 12% 3	430
	21st to end	Day	24% 21% 30% 18% 6% 1	473
January	1st to 10th	Night	27% 18% 32% 17% 4 1	950
	11th to 20th	Night	24% 24% 33% 15% 4	950
	21st to end	Night	23% 22% 37% 15% 3	1045
February	1st to 10th	Night	26% 20% 35% 16% 4	950
	11th to 20th	Night	30% 22% 33% 12% 3	894
	21st to end	Night	22% 15% 39% 17% 7% 1	692
March	1st to 10th	Night	27% 20% 34% 14% 4 1	840
	11th to 20th	Night	24% 17% 30% 22% 6%	690
	21st to end	Night	32% 17% 30% 17% 4	660
April	1st to 10th	Night	32% 19% 28% 16% 4 1	600
	11th to 20th	Night	32% 11% 34% 18% 5% 1	594
	21st to end	Night	33% 11% 33% 19% 3	600
May	1st to 10th	Night	36% 10% 25% 22% 7% 1	600
	11th to 20th	Night	34% 11% 28% 19% 8%	592
	21st to end	Night	35% 10% 31% 18% 5%	649
June	1st to 10th	Night	40% 10% 23% 24% 3	600
	11th to 20th	Night	37% 8% 24% 24% 7% 1	600
	21st to end	Night	28% 9% 32% 23% 8%	600
July	1st to 10th	Night	24% 8% 33% 28% 7% 1	586
	11th to 20th	Night	21% 9% 31% 33% 5%	582
	21st to end	Night	24% 8% 30% 31% 7%	656
August	1st to 10th	Night	22% 6% 30% 31% 10% 1	598
	11th to 20th	Night	23% 5% 29% 32% 10%	592
	21st to end	Night	23% 8% 28% 30% 9% 1	660
September	1st to 10th	Night	26% 7% 35% 26% 7%	600
	11th to 20th	Night	29% 13% 31% 24% 3	600
	21st to end	Night	31% 13% 32% 21% 4	600
October	1st to 10th	Night	32% 10% 32% 21% 4	624
	11th to 20th	Night	34% 12% 28% 20% 6%	883
	21st to end	Night	36% 15% 25% 18% 6% 1	1001
November	1st to 10th	Night	33% 20% 29% 14% 3	930
	11th to 20th	Night	35% 16% 30% 14% 5% 1	950
	21st to end	Night	33% 20% 31% 14% 2	950
December	1st to 10th	Night	28% 18% 34% 15% 4 1	950
	11th to 20th	Night	32% 23% 32% 12% 2	950
	21st to end	Night	24% 20% 31% 18% 5% 1	1045

Page generated at 2026-03-15 03:23:55. Version ac07

Copyright © 2026 Attilla Danko.