Bill's Doghouse Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bill's Doghouse Observatory clear sky chart from 2005-11-06 to 2026-06-01.

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	14% 9% 4 8% 5% 4 4 4 5% 7% 34%	131672
	Night	14% 10% 4 8% 5% 4 4 3 5% 7% 35%	131655
Transparency	Day	47% 6% 11% 22% 13% 1	135287
	Night	47% 5% 10% 22% 14% 2	136113
Seeing	Day	17% 10% 27% 24% 16% 7%	17609
	Night	18% 9% 29% 29% 14% 2	27473

By Month

Percentage Cloud Cover SE (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	16% 14% 8% 14% 7% 4 4 3 5% 6% 20%	4691
	11th to 20th	Day	10% 13% 6% 16% 9% 9% 6% 4 3 3 20%	4710
	21st to end	Day	18% 15% 7% 14% 6% 5% 5% 4 4 4 19%	5584
February	1st to 10th	Day	18% 15% 6% 10% 6% 4 4 3 4 5% 25%	2058
	11th to 20th	Day	16% 12% 4 12% 6% 5% 5% 3 4 6% 27%	2048
	21st to end	Day	16% 14% 5% 11% 5% 3 4 3 4 5% 31%	1730
March	1st to 10th	Day	19% 15% 7% 9% 5% 4 3 2 4 4 29%	4580
	11th to 20th	Day	12% 10% 3 7% 4 3 4 4 5% 8% 40%	4991
	21st to end	Day	17% 11% 4 9% 5% 4 4 4 5% 7% 30%	5716
April	1st to 10th	Day	16% 12% 3 8% 5% 4 4 3 6% 6% 32%	2520
	11th to 20th	Day	17% 9% 3 7% 4 4 4 4 5% 6% 37%	2500
	21st to end	Day	19% 8% 3 7% 4 4 4 4 4 7% 35%	2730
May	1st to 10th	Day	20% 10% 3 8% 5% 5% 5% 4 6% 7% 28%	5992
	11th to 20th	Day	18% 9% 3 7% 4 4 4 4 5% 7% 35%	5991
	21st to end	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 10% 31%	6576
June	1st to 10th	Day	11% 7% 2 6% 5% 5% 5% 5% 6% 8% 41%	2791
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 43%	2800
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	2800
July	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 4 7% 10% 41%	6360
	11th to 20th	Day	9% 6% 2 7% 4 4 5% 5% 8% 11% 39%	6360
	21st to end	Day	10% 7% 3 8% 5% 5% 6% 5% 7% 8% 35%	6588
August	1st to 10th	Day	7% 5% 2 6% 5% 4 5% 4 6% 9% 46%	4234
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 11% 39%	4081
	21st to end	Day	7% 4 2 5% 3 4 5% 3 6% 9% 51%	4312
September	1st to 10th	Day	11% 6% 2 6% 3 5% 4 3 5% 7% 48%	2335
	11th to 20th	Day	10% 5% 2 5% 3 4 4 4 7% 9% 48%	2200
	21st to end	Day	15% 6% 2 5% 4 3 3 3 5% 6% 47%	2200
October	1st to 10th	Day	12% 5% 3 6% 5% 3 4 3 3 7% 50%	2200
	11th to 20th	Day	13% 7% 2 5% 3 4 5% 4 6% 7% 45%	2056
	21st to end	Day	20% 11% 3 7% 4 3 3 3 5% 7% 34%	1980
November	1st to 10th	Day	9% 7% 2 6% 4 3 4 3 5% 6% 50%	1852
	11th to 20th	Day	16% 12% 4 7% 5% 3 4 3 5% 6% 34%	1890
	21st to end	Day	19% 13% 4 9% 4 4 3 3 4 6% 31%	1890
December	1st to 10th	Day	15% 13% 4 9% 4 3 3 3 4 5% 37%	3020
	11th to 20th	Day	17% 15% 6% 11% 5% 5% 4 3 4 5% 24%	3236
	21st to end	Day	25% 19% 8% 10% 5% 4 3 3 4 6% 13%	4070
January	1st to 10th	Night	14% 15% 7% 14% 6% 5% 5% 3 5% 5% 21%	8232
	11th to 20th	Night	10% 16% 7% 16% 7% 6% 5% 4 4 4 20%	8280
	21st to end	Night	18% 12% 4 8% 5% 5% 4 4 5% 7% 27%	8603
February	1st to 10th	Night	19% 12% 5% 10% 5% 5% 4 3 5% 5% 28%	2560
	11th to 20th	Night	15% 12% 5% 10% 5% 4 4 3 5% 7% 31%	2458
	21st to end	Night	18% 13% 4 9% 5% 3 3 3 5% 6% 31%	2076
March	1st to 10th	Night	20% 13% 3 6% 3 3 3 2 4 5% 38%	5493
	11th to 20th	Night	12% 7% 3 6% 4 5% 4 3 5% 7% 44%	5189
	21st to end	Night	18% 9% 3 8% 5% 4 4 3 6% 7% 34%	5499
April	1st to 10th	Night	15% 10% 3 7% 4 4 4 3 5% 7% 37%	2100
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 3 5% 7% 39%	2067
	21st to end	Night	16% 8% 3 7% 5% 4 5% 4 6% 7% 36%	1890
May	1st to 10th	Night	19% 11% 3 8% 5% 5% 5% 3 5% 7% 29%	4123
	11th to 20th	Night	16% 8% 3 6% 4 4 4 3 5% 9% 38%	4122
	21st to end	Night	14% 8% 2 7% 5% 4 4 3 5% 9% 39%	4520
June	1st to 10th	Night	10% 6% 2 5% 5% 4 4 3 5% 6% 48%	1605
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 10% 47%	1600
	21st to end	Night	6% 4 2 6% 4 4 6% 4 7% 11% 45%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	3618
	11th to 20th	Night	8% 6% 2 5% 4 4 5% 4 7% 10% 46%	3617
	21st to end	Night	9% 7% 2 6% 5% 5% 5% 4 7% 11% 38%	4269
August	1st to 10th	Night	8% 6% 2 6% 4 4 5% 3 5% 9% 49%	2915
	11th to 20th	Night	7% 7% 2 6% 5% 4 5% 4 6% 8% 45%	2964
	21st to end	Night	4 3 1 6% 4 4 5% 4 7% 8% 54%	3586
September	1st to 10th	Night	10% 6% 2 5% 4 4 4 3 5% 7% 50%	2044
	11th to 20th	Night	8% 4 1 5% 3 3 4 3 5% 7% 55%	2200
	21st to end	Night	13% 6% 2 5% 5% 3 4 3 5% 6% 48%	2200
October	1st to 10th	Night	9% 4 2 6% 3 4 4 3 5% 6% 56%	2200
	11th to 20th	Night	15% 7% 3 6% 4 3 4 3 4 6% 45%	2340
	21st to end	Night	17% 7% 3 6% 4 4 4 3 5% 6% 40%	2860
November	1st to 10th	Night	13% 8% 3 6% 3 3 4 3 5% 6% 47%	2666
	11th to 20th	Night	15% 10% 3 7% 5% 4 4 3 5% 7% 38%	2730
	21st to end	Night	19% 14% 4 9% 4 4 4 3 4 5% 30%	2730
December	1st to 10th	Night	16% 11% 4 8% 5% 4 4 3 4 6% 36%	4380
	11th to 20th	Night	19% 15% 6% 11% 5% 4 4 3 4 5% 25%	5169
	21st to end	Night	26% 18% 6% 11% 5% 4 4 3 4 4 16%	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	65% 4 10% 16% 5%	4692
	11th to 20th	Day	69% 3 8% 10% 8% 2	4710
	21st to end	Day	69% 3 8% 13% 6% 2	5584
February	1st to 10th	Day	62% 4 9% 14% 10% 1	2058
	11th to 20th	Day	59% 4 9% 18% 9%	2058
	21st to end	Day	55% 6% 10% 20% 8% 2	1730
March	1st to 10th	Day	60% 3 6% 18% 11% 1	4580
	11th to 20th	Day	42% 4 10% 31% 11% 1	4991
	21st to end	Day	53% 6% 13% 18% 8% 2	5718
April	1st to 10th	Day	51% 6% 11% 19% 12% 1	2520
	11th to 20th	Day	47% 5% 11% 23% 10% 3	2500
	21st to end	Day	48% 5% 11% 23% 10% 2	2730
May	1st to 10th	Day	53% 8% 11% 18% 10%	6027
	11th to 20th	Day	48% 6% 11% 24% 11%	5995
	21st to end	Day	43% 8% 14% 23% 11% 1	6590
June	1st to 10th	Day	39% 6% 12% 25% 16% 2	2791
	11th to 20th	Day	37% 6% 12% 24% 19% 2	2800
	21st to end	Day	36% 9% 16% 20% 16% 4	2800
July	1st to 10th	Day	38% 6% 11% 25% 19% 1	6291
	11th to 20th	Day	36% 9% 17% 24% 14% 1	6285
	21st to end	Day	42% 8% 14% 20% 13% 2	6401
August	1st to 10th	Day	31% 7% 17% 30% 13% 1	4221
	11th to 20th	Day	36% 8% 13% 29% 13%	4120
	21st to end	Day	27% 7% 14% 31% 17% 4	4311
September	1st to 10th	Day	36% 6% 11% 24% 18% 4	2335
	11th to 20th	Day	32% 6% 11% 25% 23% 4	2200
	21st to end	Day	38% 4 9% 24% 24% 1	2200
October	1st to 10th	Day	25% 4 8% 29% 32% 2	3590
	11th to 20th	Day	31% 5% 10% 28% 24% 2	3324
	21st to end	Day	41% 3 10% 23% 20% 2	3180
November	1st to 10th	Day	35% 4 12% 28% 17% 3	1852
	11th to 20th	Day	51% 4 9% 20% 12% 3	1890
	21st to end	Day	55% 4 10% 21% 9% 2	1890
December	1st to 10th	Day	51% 3 10% 25% 10%	3020
	11th to 20th	Day	63% 5% 9% 17% 6%	3233
	21st to end	Day	73% 5% 8% 10% 4	4070
January	1st to 10th	Night	64% 5% 9% 15% 7%	8233
	11th to 20th	Night	67% 4 7% 11% 9% 2	8280
	21st to end	Night	56% 4 10% 21% 8% 1	8603
February	1st to 10th	Night	59% 4 10% 17% 9% 1	2560
	11th to 20th	Night	53% 4 11% 18% 12% 1	2459
	21st to end	Night	55% 4 11% 17% 10% 2	2076
March	1st to 10th	Night	50% 3 7% 26% 12% 2	5493
	11th to 20th	Night	39% 5% 12% 27% 16% 2	5189
	21st to end	Night	49% 5% 10% 26% 9% 1	5499
April	1st to 10th	Night	46% 6% 10% 24% 13% 2	2100
	11th to 20th	Night	44% 5% 10% 20% 16% 4	2067
	21st to end	Night	45% 7% 10% 23% 12% 3	1890
May	1st to 10th	Night	54% 8% 9% 18% 9% 2	4150
	11th to 20th	Night	44% 6% 12% 26% 11% 1	4123
	21st to end	Night	40% 8% 15% 23% 11% 3	4528
June	1st to 10th	Night	35% 5% 11% 25% 21% 3	1605
	11th to 20th	Night	34% 6% 13% 24% 20% 3	1600
	21st to end	Night	30% 8% 15% 24% 18% 4	1600
July	1st to 10th	Night	33% 6% 11% 27% 17% 5%	3580
	11th to 20th	Night	33% 7% 17% 27% 15% 1	3572
	21st to end	Night	39% 7% 14% 24% 14% 3	4143
August	1st to 10th	Night	31% 7% 15% 32% 13% 1	2904
	11th to 20th	Night	35% 6% 13% 27% 18% 1	2991
	21st to end	Night	27% 7% 13% 28% 22% 3	3586
September	1st to 10th	Night	33% 6% 11% 23% 20% 7%	2044
	11th to 20th	Night	28% 6% 10% 26% 27% 4	2200
	21st to end	Night	36% 6% 10% 23% 23% 3	2200
October	1st to 10th	Night	21% 3 7% 28% 38% 2	3590
	11th to 20th	Night	29% 3 10% 23% 33% 1	3811
	21st to end	Night	35% 4 8% 26% 24% 4	4610
November	1st to 10th	Night	38% 4 10% 23% 22% 3	2666
	11th to 20th	Night	45% 4 9% 23% 16% 3	2730
	21st to end	Night	58% 4 10% 19% 9% 1	2730
December	1st to 10th	Night	50% 3 11% 23% 12%	4380
	11th to 20th	Night	62% 4 10% 16% 8% 1	5171
	21st to end	Night	72% 4 8% 11% 4	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	23% 17% 34% 21% 4 1	330
	11th to 20th	Day	22% 23% 34% 16% 5%	330
	21st to end	Day	27% 16% 33% 19% 4 1	363
February	1st to 10th	Day	27% 13% 37% 19% 5%	330
	11th to 20th	Day	25% 20% 34% 18% 4	330
	21st to end	Day	24% 18% 38% 17% 2	273
March	1st to 10th	Day	23% 20% 37% 17% 3	330
	11th to 20th	Day	25% 17% 34% 17% 5% 1	493
	21st to end	Day	28% 16% 32% 18% 6%	594
April	1st to 10th	Day	22% 15% 33% 20% 8% 2	540
	11th to 20th	Day	21% 16% 31% 20% 10% 3	532
	21st to end	Day	23% 12% 34% 21% 9% 1	540
May	1st to 10th	Day	22% 13% 32% 22% 8% 3	543
	11th to 20th	Day	20% 9% 31% 20% 14% 6%	567
	21st to end	Day	16% 5% 25% 26% 16% 12%	617
June	1st to 10th	Day	12% 5% 26% 30% 21% 6%	721
	11th to 20th	Day	13% 4 23% 30% 23% 7%	730
	21st to end	Day	11% 5% 26% 29% 21% 8%	730
July	1st to 10th	Day	12% 3 15% 27% 25% 18%	721
	11th to 20th	Day	8% 3 19% 33% 23% 13%	718
	21st to end	Day	10% 3 15% 28% 29% 14%	649
August	1st to 10th	Day	9% 2 14% 28% 30% 17%	526
	11th to 20th	Day	13% 3 17% 27% 26% 13%	519
	21st to end	Day	8% 4 11% 29% 33% 14%	583
September	1st to 10th	Day	10% 4 18% 24% 32% 12%	530
	11th to 20th	Day	10% 1 12% 29% 30% 18%	530
	21st to end	Day	18% 8% 18% 22% 24% 10%	530
October	1st to 10th	Day	12% 4 22% 32% 20% 10%	530
	11th to 20th	Day	12% 13% 31% 26% 15% 3	504
	21st to end	Day	28% 12% 35% 21% 4	363
November	1st to 10th	Day	16% 13% 34% 22% 12% 3	330
	11th to 20th	Day	24% 15% 30% 21% 8% 2	330
	21st to end	Day	27% 11% 37% 21% 4	330
December	1st to 10th	Day	19% 18% 41% 16% 5% 1	330
	11th to 20th	Day	23% 14% 39% 19% 4 1	330
	21st to end	Day	29% 16% 35% 16% 4	363
January	1st to 10th	Night	24% 13% 35% 23% 5%	1050
	11th to 20th	Night	25% 15% 39% 18% 3	1050
	21st to end	Night	22% 12% 39% 23% 4	996
February	1st to 10th	Night	24% 10% 37% 26% 2	840
	11th to 20th	Night	22% 13% 39% 24% 2	823
	21st to end	Night	23% 12% 40% 22% 2	692
March	1st to 10th	Night	24% 12% 35% 23% 6%	840
	11th to 20th	Night	21% 13% 35% 24% 6% 1	840
	21st to end	Night	24% 11% 34% 26% 5% 1	886
April	1st to 10th	Night	18% 12% 37% 26% 7% 1	630
	11th to 20th	Night	18% 11% 33% 29% 8% 1	623
	21st to end	Night	20% 7% 40% 23% 10% 1	630
May	1st to 10th	Night	22% 8% 35% 27% 8%	630
	11th to 20th	Night	18% 5% 25% 33% 16% 3	621
	21st to end	Night	11% 4 23% 38% 22% 2	683
June	1st to 10th	Night	12% 3 23% 40% 22%	600
	11th to 20th	Night	11% 4 18% 43% 22% 2	600
	21st to end	Night	7% 3 22% 38% 28% 2	600
July	1st to 10th	Night	10% 2 11% 35% 34% 7%	585
	11th to 20th	Night	10% 4 12% 39% 30% 5%	582
	21st to end	Night	10% 1 11% 41% 34% 3	657
August	1st to 10th	Night	9% 2 11% 40% 35% 4	597
	11th to 20th	Night	6% 3 11% 40% 34% 6%	594
	21st to end	Night	6% 2 12% 36% 37% 6%	660
September	1st to 10th	Night	12% 3 12% 36% 32% 5%	644
	11th to 20th	Night	10% 2 13% 34% 34% 6%	800
	21st to end	Night	14% 5% 21% 34% 23% 4	800
October	1st to 10th	Night	11% 5% 24% 34% 22% 5%	800
	11th to 20th	Night	18% 10% 29% 28% 14% 1	800
	21st to end	Night	21% 10% 35% 26% 9%	880
November	1st to 10th	Night	17% 9% 34% 28% 12% 1	820
	11th to 20th	Night	19% 15% 32% 27% 7% 1	840
	21st to end	Night	25% 12% 29% 27% 7%	840
December	1st to 10th	Night	24% 10% 38% 22% 5%	840
	11th to 20th	Night	26% 9% 35% 25% 5% 1	945
	21st to end	Night	31% 14% 31% 21% 3	1155

Page generated at 2026-05-29 01:53:28. Version ac07

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