Twin Dogs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Dogs Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	17% 10% 4 9% 6% 5% 5% 4 5% 6% 29%	130463
	Night	16% 11% 4 9% 6% 5% 5% 4 5% 6% 30%	130467
Transparency	Day	55% 6% 12% 18% 9% 1	133919
	Night	54% 6% 12% 18% 9% 1	135099
Seeing	Day	25% 18% 31% 17% 7% 1	17437
	Night	23% 16% 31% 22% 7%	25676

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	12% 15% 6% 14% 8% 5% 6% 4 4 6% 20%	4190
	11th to 20th	Day	10% 16% 7% 16% 9% 6% 5% 4 5% 5% 17%	4650
	21st to end	Day	5% 8% 5% 14% 7% 7% 6% 6% 7% 7% 27%	5124
February	1st to 10th	Day	9% 13% 5% 11% 9% 7% 6% 4 5% 6% 24%	1827
	11th to 20th	Day	13% 15% 5% 12% 8% 5% 5% 4 5% 6% 22%	1841
	21st to end	Day	12% 12% 3 10% 8% 7% 4 4 5% 6% 29%	1650
March	1st to 10th	Day	22% 17% 5% 10% 5% 4 3 3 4 5% 23%	4494
	11th to 20th	Day	16% 16% 5% 10% 7% 5% 4 3 5% 6% 23%	4980
	21st to end	Day	20% 16% 5% 11% 5% 4 4 3 4 5% 24%	5466
April	1st to 10th	Day	22% 15% 3 9% 6% 4 4 3 4 5% 25%	2409
	11th to 20th	Day	20% 12% 3 8% 6% 4 4 3 4 6% 31%	2572
	21st to end	Day	25% 12% 2 7% 4 3 3 3 5% 5% 31%	2600
May	1st to 10th	Day	20% 12% 4 9% 6% 5% 4 3 5% 5% 25%	5886
	11th to 20th	Day	26% 10% 3 7% 5% 4 4 3 4 5% 28%	6223
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 4 6% 8% 28%	7451
June	1st to 10th	Day	22% 8% 3 7% 5% 4 5% 3 6% 7% 27%	3000
	11th to 20th	Day	20% 6% 3 7% 6% 6% 5% 4 6% 7% 31%	3000
	21st to end	Day	24% 10% 3 8% 6% 5% 4 4 5% 6% 25%	3000
July	1st to 10th	Day	16% 6% 3 8% 6% 6% 6% 5% 7% 9% 28%	6820
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	6619
	21st to end	Day	12% 5% 2 7% 4 5% 5% 4 8% 9% 40%	6926
August	1st to 10th	Day	15% 6% 2 7% 6% 6% 6% 5% 7% 8% 31%	4312
	11th to 20th	Day	16% 8% 3 9% 6% 6% 6% 4 6% 8% 27%	4175
	21st to end	Day	17% 6% 3 7% 5% 4 5% 4 7% 8% 36%	4675
September	1st to 10th	Day	14% 7% 3 7% 4 4 5% 3 5% 7% 41%	2365
	11th to 20th	Day	15% 6% 3 6% 4 4 3 2 5% 6% 47%	2200
	21st to end	Day	17% 6% 3 7% 4 4 4 3 5% 7% 40%	2200
October	1st to 10th	Day	17% 9% 3 7% 4 4 5% 3 4 6% 38%	2115
	11th to 20th	Day	20% 10% 4 8% 5% 5% 4 4 5% 5% 31%	1945
	21st to end	Day	25% 11% 3 8% 5% 4 4 3 4 6% 28%	1980
November	1st to 10th	Day	17% 12% 4 9% 6% 5% 4 4 5% 5% 29%	1851
	11th to 20th	Day	19% 12% 4 9% 6% 5% 5% 4 5% 6% 26%	1697
	21st to end	Day	20% 15% 4 9% 5% 5% 4 3 3 5% 26%	1629
December	1st to 10th	Day	17% 15% 4 10% 5% 4 3 3 5% 6% 27%	2350
	11th to 20th	Day	17% 11% 5% 9% 7% 5% 5% 4 5% 5% 29%	2688
	21st to end	Day	18% 12% 5% 13% 6% 5% 4 3 4 5% 25%	3553
January	1st to 10th	Night	10% 15% 6% 13% 8% 7% 6% 4 6% 6% 19%	8713
	11th to 20th	Night	10% 16% 6% 13% 9% 7% 6% 4 5% 6% 19%	8235
	21st to end	Night	4 10% 5% 11% 7% 6% 7% 5% 7% 7% 30%	9057
February	1st to 10th	Night	9% 13% 5% 11% 6% 6% 4 4 6% 6% 30%	2792
	11th to 20th	Night	11% 16% 5% 11% 7% 6% 5% 4 5% 6% 25%	2554
	21st to end	Night	12% 15% 3 7% 7% 5% 4 4 4 5% 34%	1980
March	1st to 10th	Night	20% 13% 4 11% 5% 5% 6% 3 3 5% 25%	5331
	11th to 20th	Night	16% 12% 5% 9% 6% 6% 5% 4 6% 7% 25%	4979
	21st to end	Night	23% 14% 4 8% 4 3 3 3 4 5% 29%	5466
April	1st to 10th	Night	21% 13% 4 7% 5% 4 4 3 4 4 31%	1988
	11th to 20th	Night	20% 11% 3 7% 4 4 3 3 5% 7% 32%	1778
	21st to end	Night	26% 11% 3 7% 4 4 3 3 4 5% 31%	1800
May	1st to 10th	Night	23% 12% 3 6% 4 3 4 4 5% 6% 30%	4054
	11th to 20th	Night	25% 9% 3 8% 5% 4 5% 3 5% 5% 29%	3705
	21st to end	Night	17% 7% 2 5% 4 3 4 4 5% 8% 40%	3446
June	1st to 10th	Night	23% 9% 3 5% 4 5% 5% 4 6% 7% 30%	1400
	11th to 20th	Night	16% 6% 2 5% 4 4 5% 4 7% 8% 40%	1400
	21st to end	Night	23% 9% 2 8% 5% 4 4 4 6% 6% 30%	1400
July	1st to 10th	Night	14% 7% 2 6% 5% 5% 5% 4 6% 8% 37%	3160
	11th to 20th	Night	15% 6% 2 6% 4 4 6% 4 7% 8% 38%	3336
	21st to end	Night	10% 5% 2 7% 4 5% 6% 5% 6% 7% 42%	3926
August	1st to 10th	Night	18% 6% 2 7% 5% 5% 5% 4 6% 6% 36%	2804
	11th to 20th	Night	13% 7% 3 8% 5% 5% 5% 5% 7% 8% 34%	2872
	21st to end	Night	17% 5% 2 5% 4 4 4 3 4 5% 45%	3223
September	1st to 10th	Night	14% 5% 2 6% 4 4 4 4 5% 8% 45%	2030
	11th to 20th	Night	15% 6% 2 5% 3 4 4 3 5% 6% 48%	2200
	21st to end	Night	16% 6% 2 5% 4 3 3 3 5% 5% 47%	2200
October	1st to 10th	Night	19% 7% 2 6% 4 3 3 3 4 7% 42%	2284
	11th to 20th	Night	19% 8% 2 7% 4 5% 4 3 6% 6% 36%	2451
	21st to end	Night	21% 10% 3 7% 4 5% 4 3 5% 7% 32%	2860
November	1st to 10th	Night	18% 11% 3 8% 5% 4 4 4 6% 7% 30%	2667
	11th to 20th	Night	18% 11% 3 9% 5% 4 5% 4 5% 7% 30%	2921
	21st to end	Night	19% 11% 4 10% 6% 5% 5% 4 5% 6% 25%	2987
December	1st to 10th	Night	14% 12% 5% 10% 7% 6% 5% 3 6% 6% 26%	5060
	11th to 20th	Night	21% 11% 3 9% 6% 5% 5% 4 5% 5% 27%	5741
	21st to end	Night	18% 13% 4 11% 7% 4 4 3 5% 5% 26%	7667

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	67% 4 10% 14% 5%	4191
	11th to 20th	Day	70% 5% 6% 13% 5%	4680
	21st to end	Day	56% 5% 8% 14% 16%	5124
February	1st to 10th	Day	59% 6% 10% 15% 9% 2	1827
	11th to 20th	Day	61% 6% 11% 14% 6% 1	1849
	21st to end	Day	54% 7% 9% 20% 9% 2	1650
March	1st to 10th	Day	64% 5% 7% 9% 12% 4	4497
	11th to 20th	Day	61% 6% 14% 11% 6% 1	4980
	21st to end	Day	64% 4 5% 16% 9% 2	5466
April	1st to 10th	Day	62% 5% 8% 14% 8% 3	2409
	11th to 20th	Day	54% 6% 10% 17% 11% 2	2572
	21st to end	Day	55% 5% 8% 17% 12% 3	2600
May	1st to 10th	Day	58% 7% 8% 16% 10% 1	5897
	11th to 20th	Day	56% 8% 12% 15% 8% 2	6227
	21st to end	Day	51% 8% 11% 18% 12%	7451
June	1st to 10th	Day	54% 8% 11% 15% 10% 1	3000
	11th to 20th	Day	50% 7% 13% 18% 11% 2	3000
	21st to end	Day	58% 8% 11% 15% 8% 1	3000
July	1st to 10th	Day	52% 4 15% 19% 9%	6745
	11th to 20th	Day	48% 4 16% 26% 5%	6538
	21st to end	Day	41% 5% 16% 30% 7%	6728
August	1st to 10th	Day	48% 7% 17% 19% 8%	4298
	11th to 20th	Day	54% 6% 16% 19% 5%	4214
	21st to end	Day	45% 6% 16% 22% 11%	4675
September	1st to 10th	Day	42% 7% 14% 25% 13%	2365
	11th to 20th	Day	39% 5% 13% 27% 15%	2200
	21st to end	Day	43% 7% 12% 26% 12%	2200
October	1st to 10th	Day	53% 3 13% 25% 6%	3440
	11th to 20th	Day	54% 4 11% 24% 6%	3148
	21st to end	Day	50% 4 16% 18% 12%	3180
November	1st to 10th	Day	56% 6% 13% 17% 7%	1851
	11th to 20th	Day	58% 7% 12% 15% 7%	1697
	21st to end	Day	61% 6% 14% 15% 3	1629
December	1st to 10th	Day	60% 4 15% 12% 9%	2350
	11th to 20th	Day	59% 4 10% 15% 9% 2	2688
	21st to end	Day	61% 7% 11% 10% 10% 1	3553
January	1st to 10th	Night	66% 7% 10% 11% 5%	8713
	11th to 20th	Night	66% 5% 11% 12% 6%	8280
	21st to end	Night	53% 5% 8% 19% 15% 1	9057
February	1st to 10th	Night	54% 6% 11% 17% 10% 1	2792
	11th to 20th	Night	60% 6% 10% 16% 7% 1	2557
	21st to end	Night	53% 5% 11% 18% 11% 2	1980
March	1st to 10th	Night	63% 5% 7% 13% 11% 1	5341
	11th to 20th	Night	58% 7% 15% 12% 8% 1	4980
	21st to end	Night	58% 3 5% 18% 14% 1	5466
April	1st to 10th	Night	56% 5% 8% 15% 13% 3	1988
	11th to 20th	Night	52% 5% 10% 18% 14% 1	1778
	21st to end	Night	55% 5% 8% 18% 12% 1	1800
May	1st to 10th	Night	53% 7% 11% 16% 12% 1	4060
	11th to 20th	Night	54% 8% 12% 18% 7% 1	3706
	21st to end	Night	41% 9% 16% 21% 13%	3447
June	1st to 10th	Night	52% 7% 13% 19% 9% 1	1400
	11th to 20th	Night	41% 9% 15% 22% 12% 2	1400
	21st to end	Night	55% 7% 12% 17% 9% 1	1400
July	1st to 10th	Night	47% 3 21% 24% 5%	3125
	11th to 20th	Night	45% 5% 20% 26% 5%	3294
	21st to end	Night	41% 5% 21% 24% 8%	3809
August	1st to 10th	Night	49% 6% 15% 24% 6%	2794
	11th to 20th	Night	46% 8% 21% 17% 8%	2899
	21st to end	Night	42% 6% 16% 23% 13% 1	3223
September	1st to 10th	Night	37% 7% 16% 27% 12% 1	2030
	11th to 20th	Night	37% 7% 16% 27% 13%	2200
	21st to end	Night	39% 7% 13% 26% 14% 1	2200
October	1st to 10th	Night	48% 3 12% 29% 8% 1	3739
	11th to 20th	Night	48% 4 12% 28% 7%	3987
	21st to end	Night	45% 4 19% 19% 12%	4610
November	1st to 10th	Night	52% 8% 14% 20% 6%	2667
	11th to 20th	Night	53% 7% 14% 15% 10% 1	2921
	21st to end	Night	59% 7% 14% 13% 5%	2987
December	1st to 10th	Night	62% 4 12% 18% 5%	5060
	11th to 20th	Night	59% 5% 10% 17% 9%	5742
	21st to end	Night	61% 6% 10% 15% 8%	7667

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	28% 26% 33% 9% 4	220
	11th to 20th	Day	35% 19% 30% 10% 5%	220
	21st to end	Day	21% 22% 38% 12% 6% 1	242
February	1st to 10th	Day	22% 24% 32% 14% 6% 2	367
	11th to 20th	Day	25% 25% 34% 13% 2	434
	21st to end	Day	24% 24% 33% 15% 4	414
March	1st to 10th	Day	28% 21% 33% 15% 4	500
	11th to 20th	Day	26% 25% 29% 12% 7% 1	500
	21st to end	Day	31% 23% 25% 16% 4 1	550
April	1st to 10th	Day	31% 26% 26% 12% 3 2	500
	11th to 20th	Day	32% 21% 28% 14% 5%	492
	21st to end	Day	33% 22% 31% 10% 3 1	500
May	1st to 10th	Day	34% 17% 32% 14% 4	503
	11th to 20th	Day	31% 17% 29% 17% 6% 1	586
	21st to end	Day	27% 21% 29% 18% 5%	790
June	1st to 10th	Day	26% 17% 31% 18% 6% 1	730
	11th to 20th	Day	24% 19% 26% 22% 8% 1	730
	21st to end	Day	25% 15% 33% 20% 7%	730
July	1st to 10th	Day	19% 15% 34% 22% 9%	720
	11th to 20th	Day	18% 12% 34% 25% 9% 1	634
	21st to end	Day	15% 12% 40% 23% 9% 1	576
August	1st to 10th	Day	16% 11% 33% 25% 10% 3	526
	11th to 20th	Day	18% 10% 30% 27% 12% 2	519
	21st to end	Day	22% 14% 27% 22% 12% 3	583
September	1st to 10th	Day	17% 15% 33% 20% 11% 4	530
	11th to 20th	Day	20% 12% 27% 24% 11% 5%	530
	21st to end	Day	20% 18% 31% 16% 11% 5%	530
October	1st to 10th	Day	19% 17% 30% 20% 10% 4	483
	11th to 20th	Day	31% 17% 27% 14% 9% 2	420
	21st to end	Day	32% 20% 29% 14% 5%	462
November	1st to 10th	Day	31% 22% 27% 15% 4	425
	11th to 20th	Day	29% 20% 30% 14% 6% 1	430
	21st to end	Day	38% 18% 30% 11% 3 1	379
December	1st to 10th	Day	26% 25% 28% 15% 5%	220
	11th to 20th	Day	34% 23% 30% 10% 3 1	220
	21st to end	Day	33% 23% 25% 14% 4 1	242
January	1st to 10th	Night	23% 22% 36% 17% 3	928
	11th to 20th	Night	25% 21% 30% 19% 4	840
	21st to end	Night	15% 21% 38% 22% 4	924
February	1st to 10th	Night	17% 25% 35% 18% 6%	840
	11th to 20th	Night	25% 25% 30% 17% 4	804
	21st to end	Night	23% 18% 38% 17% 3	660
March	1st to 10th	Night	22% 19% 38% 19% 3	800
	11th to 20th	Night	25% 18% 32% 18% 7% 1	800
	21st to end	Night	24% 17% 34% 20% 5%	880
April	1st to 10th	Night	30% 18% 30% 18% 4 1	784
	11th to 20th	Night	26% 18% 31% 19% 6%	594
	21st to end	Night	34% 16% 25% 20% 6%	600
May	1st to 10th	Night	25% 14% 33% 23% 4	600
	11th to 20th	Night	27% 13% 30% 21% 8% 1	514
	21st to end	Night	23% 13% 33% 24% 6%	433
June	1st to 10th	Night	27% 8% 29% 29% 7% 1	400
	11th to 20th	Night	18% 9% 27% 36% 11%	400
	21st to end	Night	27% 7% 31% 28% 8%	400
July	1st to 10th	Night	17% 8% 35% 28% 11%	390
	11th to 20th	Night	15% 6% 33% 36% 10%	388
	21st to end	Night	17% 6% 29% 36% 11% 1	438
August	1st to 10th	Night	17% 5% 29% 37% 12%	525
	11th to 20th	Night	14% 6% 30% 35% 15%	592
	21st to end	Night	13% 9% 30% 34% 13% 1	660
September	1st to 10th	Night	16% 10% 31% 31% 12%	746
	11th to 20th	Night	19% 11% 26% 30% 14% 2	800
	21st to end	Night	20% 12% 29% 26% 13%	800
October	1st to 10th	Night	22% 13% 30% 26% 9% 1	800
	11th to 20th	Night	24% 13% 33% 20% 9%	800
	21st to end	Night	28% 19% 29% 19% 5%	880
November	1st to 10th	Night	26% 19% 32% 19% 4	820
	11th to 20th	Night	28% 18% 29% 19% 5% 1	941
	21st to end	Night	27% 20% 29% 19% 4	950
December	1st to 10th	Night	27% 17% 35% 16% 4 1	950
	11th to 20th	Night	29% 20% 31% 16% 3	950
	21st to end	Night	29% 21% 30% 16% 4 1	1045

Page generated at 2026-02-13 01:42:15. Version ac07

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