Roofer Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roofer Observing Site clear sky chart from 2005-11-06 to 2026-02-01.

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	12% 6% 2 6% 4 4 4 4 5% 8% 46%	127569
	Night	12% 6% 2 5% 3 3 3 3 5% 7% 50%	124710
Transparency	Day	38% 2 10% 23% 20% 8%	131247
	Night	35% 2 10% 21% 21% 11%	129095
Seeing	Day	14% 8% 22% 27% 22% 7%	16613
	Night	15% 8% 26% 33% 17% 2	26577

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	14% 8% 3 6% 3 3 3 2 5% 6% 49%	4167
	11th to 20th	Day	13% 6% 2 5% 2 2 3 2 4 8% 53%	4170
	21st to end	Day	27% 9% 2 6% 3 2 2 2 2 4 41%	4587
February	1st to 10th	Day	21% 8% 3 6% 4 3 3 2 4 6% 41%	1889
	11th to 20th	Day	20% 9% 3 6% 4 3 3 3 4 5% 39%	1949
	21st to end	Day	20% 8% 2 6% 3 3 3 3 4 5% 44%	1766
March	1st to 10th	Day	16% 10% 3 7% 4 3 3 3 4 6% 41%	4936
	11th to 20th	Day	14% 6% 2 5% 4 3 4 3 4 6% 49%	4980
	21st to end	Day	16% 8% 3 6% 4 4 4 3 5% 6% 41%	5462
April	1st to 10th	Day	13% 7% 3 7% 6% 4 4 4 5% 6% 40%	2200
	11th to 20th	Day	13% 8% 3 6% 5% 5% 4 3 5% 7% 41%	2319
	21st to end	Day	11% 7% 2 6% 5% 5% 5% 4 6% 6% 43%	2400
May	1st to 10th	Day	18% 8% 3 7% 4 4 4 3 6% 8% 34%	5811
	11th to 20th	Day	11% 6% 3 7% 5% 5% 5% 4 5% 7% 41%	5862
	21st to end	Day	11% 6% 2 8% 5% 6% 6% 5% 7% 10% 35%	6434
June	1st to 10th	Day	5% 5% 2 5% 6% 6% 5% 5% 7% 10% 44%	2600
	11th to 20th	Day	5% 5% 2 5% 4 5% 7% 4 7% 10% 47%	2600
	21st to end	Day	4 5% 2 6% 5% 6% 6% 6% 9% 11% 41%	2600
July	1st to 10th	Day	8% 6% 2 6% 5% 5% 6% 5% 8% 12% 37%	5900
	11th to 20th	Day	4 3 1 4 4 4 5% 5% 8% 12% 49%	5900
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 5% 6% 8% 43%	6422
August	1st to 10th	Day	2 1 1 2 2 3 3 3 6% 8% 70%	4234
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 11% 60%	4121
	21st to end	Day	5% 3 2 6% 4 6% 6% 6% 9% 10% 43%	4193
September	1st to 10th	Day	7% 5% 2 7% 5% 5% 5% 5% 5% 7% 48%	2200
	11th to 20th	Day	9% 6% 2 6% 4 4 6% 5% 5% 8% 45%	2200
	21st to end	Day	6% 4 1 5% 4 4 4 4 6% 8% 55%	2200
October	1st to 10th	Day	5% 4 1 5% 3 3 3 3 4 7% 62%	2100
	11th to 20th	Day	12% 4 2 4 3 3 3 2 5% 5% 58%	2000
	21st to end	Day	13% 5% 1 4 3 3 3 2 3 5% 58%	2200
November	1st to 10th	Day	11% 7% 2 5% 4 3 4 3 5% 6% 51%	2058
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 4 5% 54%	2100
	21st to end	Day	16% 7% 3 6% 4 4 3 3 5% 5% 44%	1911
December	1st to 10th	Day	20% 6% 2 5% 3 3 3 3 4 5% 47%	3030
	11th to 20th	Day	19% 8% 3 6% 4 3 3 3 5% 6% 41%	3481
	21st to end	Day	14% 9% 3 6% 4 4 4 3 4 4 46%	4587
January	1st to 10th	Night	16% 6% 2 5% 3 3 3 2 3 4 54%	6018
	11th to 20th	Night	13% 5% 1 4 2 2 3 2 4 5% 59%	6030
	21st to end	Night	27% 9% 2 6% 3 2 3 2 3 5% 39%	6633
February	1st to 10th	Night	18% 7% 2 6% 4 3 3 3 3 5% 46%	2529
	11th to 20th	Night	20% 8% 3 6% 3 3 3 2 3 4 46%	2338
	21st to end	Night	20% 6% 1 5% 3 3 3 2 4 4 47%	1861
March	1st to 10th	Night	19% 9% 2 5% 4 4 3 3 4 5% 42%	4919
	11th to 20th	Night	13% 6% 2 5% 3 3 3 4 5% 6% 49%	4980
	21st to end	Night	15% 9% 3 7% 4 3 3 3 4 5% 45%	5467
April	1st to 10th	Night	12% 6% 2 6% 4 4 3 4 5% 7% 48%	2200
	11th to 20th	Night	11% 7% 2 5% 3 3 4 4 6% 8% 46%	2030
	21st to end	Night	12% 6% 2 5% 4 4 4 2 6% 7% 50%	2000
May	1st to 10th	Night	15% 11% 3 8% 4 3 3 3 6% 8% 35%	4084
	11th to 20th	Night	9% 6% 3 7% 4 5% 5% 4 6% 7% 43%	4053
	21st to end	Night	10% 6% 2 6% 4 5% 5% 4 7% 11% 41%	4443
June	1st to 10th	Night	5% 3 1 5% 3 4 4 3 6% 10% 56%	1800
	11th to 20th	Night	4 3 1 3 2 3 3 3 6% 11% 62%	1800
	21st to end	Night	4 4 2 4 4 4 5% 5% 6% 10% 54%	1800
July	1st to 10th	Night	5% 4 2 6% 5% 6% 6% 5% 7% 13% 41%	4078
	11th to 20th	Night	2 3 1 4 3 3 5% 3 6% 13% 57%	4077
	21st to end	Night	6% 6% 2 6% 3 3 5% 5% 7% 10% 48%	4449
August	1st to 10th	Night	1 1 1 1 2 1 2 2 4 9% 77%	2926
	11th to 20th	Night	2 2 1 3 3 3 4 3 6% 12% 60%	2933
	21st to end	Night	4 4 1 4 3 5% 5% 4 7% 11% 52%	3699
September	1st to 10th	Night	6% 5% 2 5% 4 4 4 4 6% 8% 52%	2200
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 4 6% 7% 49%	2200
	21st to end	Night	6% 4 1 5% 3 3 3 3 5% 8% 60%	2200
October	1st to 10th	Night	5% 3 1 3 2 3 4 3 4 6% 67%	2280
	11th to 20th	Night	12% 4 1 3 2 2 3 2 3 5% 62%	2400
	21st to end	Night	13% 4 1 4 3 2 2 2 3 4 61%	2640
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 4 6% 57%	2460
	11th to 20th	Night	9% 6% 2 5% 4 3 3 3 5% 5% 55%	2520
	21st to end	Night	15% 7% 3 5% 3 3 3 3 4 6% 48%	2704
December	1st to 10th	Night	19% 8% 2 5% 3 3 3 3 4 5% 45%	4380
	11th to 20th	Night	17% 9% 3 6% 4 3 3 2 3 5% 45%	4946
	21st to end	Night	15% 7% 2 5% 3 2 3 2 3 4 53%	6633

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	40% 1 4 26% 25% 4	4168
	11th to 20th	Day	33% 1 3 22% 28% 12%	4170
	21st to end	Day	52% 1 3 13% 18% 14%	4587
February	1st to 10th	Day	47% 2 5% 15% 21% 11%	1889
	11th to 20th	Day	49% 2 6% 16% 19% 9%	1959
	21st to end	Day	45% 2 5% 16% 18% 13%	1766
March	1st to 10th	Day	47% 1 5% 13% 22% 12%	4936
	11th to 20th	Day	39% 1 5% 14% 19% 22%	4980
	21st to end	Day	46% 1 7% 22% 18% 5%	5464
April	1st to 10th	Day	45% 4 8% 20% 14% 10%	2200
	11th to 20th	Day	44% 3 9% 17% 19% 9%	2319
	21st to end	Day	41% 3 7% 20% 23% 6%	2400
May	1st to 10th	Day	50% 2 10% 24% 12% 3	5849
	11th to 20th	Day	43% 2 11% 18% 24% 2	5866
	21st to end	Day	44% 2 12% 23% 16% 2	6447
June	1st to 10th	Day	34% 4 15% 31% 15% 2	2600
	11th to 20th	Day	31% 4 13% 31% 17% 4	2600
	21st to end	Day	34% 6% 14% 28% 16% 2	2600
July	1st to 10th	Day	38% 4 27% 26% 5%	5836
	11th to 20th	Day	28% 3 21% 35% 13% 1	5831
	21st to end	Day	38% 4 16% 30% 12% 1	6240
August	1st to 10th	Day	13% 3 12% 41% 30% 1	4220
	11th to 20th	Day	18% 3 22% 43% 11% 2	4160
	21st to end	Day	34% 6% 18% 27% 13% 2	4192
September	1st to 10th	Day	36% 4 12% 21% 18% 9%	2200
	11th to 20th	Day	38% 4 12% 22% 17% 8%	2200
	21st to end	Day	28% 4 9% 24% 21% 15%	2200
October	1st to 10th	Day	15% 2 5% 14% 23% 41%	3425
	11th to 20th	Day	19% 2 3 21% 33% 22%	3240
	21st to end	Day	28% 1 2 22% 35% 12%	3538
November	1st to 10th	Day	35% 3 7% 20% 25% 10%	2058
	11th to 20th	Day	34% 2 7% 20% 23% 14%	2100
	21st to end	Day	44% 2 5% 20% 19% 10%	1911
December	1st to 10th	Day	42% 1 7% 19% 24% 7%	3030
	11th to 20th	Day	46% 1 6% 13% 24% 10%	3479
	21st to end	Day	44% 1 4 15% 28% 8%	4587
January	1st to 10th	Night	38% 1 4 22% 27% 8%	6018
	11th to 20th	Night	30% 1 4 18% 35% 13%	6030
	21st to end	Night	52% 1 2 13% 17% 15%	6633
February	1st to 10th	Night	43% 2 4 15% 19% 16%	2529
	11th to 20th	Night	45% 2 6% 15% 20% 12%	2338
	21st to end	Night	42% 2 7% 15% 18% 16%	1861
March	1st to 10th	Night	47% 1 4 12% 21% 13%	4919
	11th to 20th	Night	38% 2 6% 15% 17% 22%	4980
	21st to end	Night	45% 1 7% 17% 21% 9%	5467
April	1st to 10th	Night	37% 4 8% 20% 18% 12%	2200
	11th to 20th	Night	36% 3 10% 20% 18% 13%	2030
	21st to end	Night	36% 3 10% 19% 26% 7%	2000
May	1st to 10th	Night	50% 1 9% 24% 12% 3	4111
	11th to 20th	Night	42% 3 12% 18% 22% 2	4054
	21st to end	Night	39% 2 15% 28% 12% 3	4452
June	1st to 10th	Night	24% 5% 17% 31% 20% 2	1800
	11th to 20th	Night	19% 4 17% 35% 20% 5%	1800
	21st to end	Night	27% 5% 16% 30% 20% 3	1800
July	1st to 10th	Night	35% 3 28% 28% 5%	4035
	11th to 20th	Night	22% 3 25% 37% 13% 1	4026
	21st to end	Night	32% 5% 19% 30% 13% 1	4320
August	1st to 10th	Night	9% 3 14% 35% 36% 4	2916
	11th to 20th	Night	19% 3 23% 42% 11% 2	2960
	21st to end	Night	28% 5% 21% 30% 14% 2	3699
September	1st to 10th	Night	31% 4 15% 22% 18% 10%	2200
	11th to 20th	Night	34% 4 14% 21% 18% 8%	2200
	21st to end	Night	24% 3 11% 24% 25% 13%	2200
October	1st to 10th	Night	14% 2 5% 16% 20% 44%	3722
	11th to 20th	Night	17% 1 3 21% 33% 26%	3899
	21st to end	Night	24% 1 3 20% 35% 17%	4252
November	1st to 10th	Night	31% 2 8% 20% 25% 13%	2460
	11th to 20th	Night	32% 2 7% 21% 24% 15%	2520
	21st to end	Night	40% 2 7% 18% 22% 11%	2704
December	1st to 10th	Night	43% 1 5% 18% 25% 7%	4380
	11th to 20th	Night	45% 1 6% 11% 24% 13%	4947
	21st to end	Night	37% 1 4 16% 30% 11%	6633

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	25% 17% 34% 19% 4 2	330
	11th to 20th	Day	24% 16% 34% 20% 5%	330
	21st to end	Day	27% 19% 33% 16% 5%	363
February	1st to 10th	Day	27% 17% 34% 18% 3	300
	11th to 20th	Day	36% 22% 27% 12% 3	300
	21st to end	Day	29% 24% 35% 9% 3	249
March	1st to 10th	Day	27% 16% 36% 16% 5%	300
	11th to 20th	Day	25% 21% 37% 14% 3	300
	21st to end	Day	21% 18% 38% 17% 6%	330
April	1st to 10th	Day	23% 17% 40% 16% 4	300
	11th to 20th	Day	22% 17% 32% 19% 10%	437
	21st to end	Day	16% 15% 35% 25% 8% 1	500
May	1st to 10th	Day	16% 12% 36% 27% 8% 1	678
	11th to 20th	Day	14% 9% 27% 32% 14% 3	725
	21st to end	Day	12% 8% 27% 32% 18% 4	789
June	1st to 10th	Day	7% 3 17% 37% 27% 9%	730
	11th to 20th	Day	6% 3 18% 38% 28% 6%	730
	21st to end	Day	6% 3 12% 33% 35% 11%	730
July	1st to 10th	Day	7% 2 10% 31% 35% 15%	721
	11th to 20th	Day	3 1 6% 38% 38% 13%	718
	21st to end	Day	5% 2 5% 32% 44% 12%	794
August	1st to 10th	Day	4 1 4 27% 51% 13%	726
	11th to 20th	Day	7% 1 3 32% 45% 13%	691
	21st to end	Day	9% 1 4 19% 45% 22%	516
September	1st to 10th	Day	6% 11% 30% 36% 17%	330
	11th to 20th	Day	6% 2 10% 27% 36% 18%	330
	21st to end	Day	8% 3 12% 35% 28% 14%	330
October	1st to 10th	Day	5% 3 19% 37% 30% 6%	330
	11th to 20th	Day	9% 9% 25% 30% 20% 6%	330
	21st to end	Day	22% 11% 25% 26% 13% 3	363
November	1st to 10th	Day	18% 5% 31% 28% 15% 3	330
	11th to 20th	Day	15% 14% 33% 26% 9% 2	330
	21st to end	Day	20% 17% 32% 20% 10% 1	330
December	1st to 10th	Day	22% 9% 38% 17% 12% 2	330
	11th to 20th	Day	28% 14% 32% 20% 6% 1	330
	21st to end	Day	21% 15% 36% 22% 5% 1	363
January	1st to 10th	Night	21% 12% 34% 27% 6%	1050
	11th to 20th	Night	23% 13% 31% 25% 7%	1050
	21st to end	Night	22% 12% 33% 28% 5%	1155
February	1st to 10th	Night	23% 13% 32% 27% 4	929
	11th to 20th	Night	28% 12% 34% 23% 3	784
	21st to end	Night	24% 16% 36% 21% 3	541
March	1st to 10th	Night	23% 13% 33% 26% 5%	600
	11th to 20th	Night	18% 14% 38% 24% 6%	600
	21st to end	Night	15% 12% 42% 26% 4	660
April	1st to 10th	Night	15% 12% 40% 28% 6%	600
	11th to 20th	Night	15% 14% 37% 25% 9% 1	593
	21st to end	Night	17% 9% 38% 25% 10% 1	600
May	1st to 10th	Night	11% 11% 40% 29% 8% 1	600
	11th to 20th	Night	12% 9% 31% 33% 14% 1	591
	21st to end	Night	8% 5% 31% 37% 18% 2	650
June	1st to 10th	Night	7% 2 16% 41% 31% 4	600
	11th to 20th	Night	5% 3 21% 48% 21% 3	600
	21st to end	Night	5% 2 15% 44% 30% 6%	600
July	1st to 10th	Night	4 2 12% 42% 35% 5%	585
	11th to 20th	Night	3 9% 52% 31% 5%	582
	21st to end	Night	4 2 7% 46% 36% 5%	657
August	1st to 10th	Night	3 1 6% 46% 40% 5%	597
	11th to 20th	Night	6% 1 6% 48% 34% 6%	594
	21st to end	Night	6% 1 6% 38% 41% 7%	660
September	1st to 10th	Night	9% 1 9% 39% 37% 6%	600
	11th to 20th	Night	12% 1 5% 38% 40% 5%	600
	21st to end	Night	8% 2 12% 38% 37% 5%	600
October	1st to 10th	Night	5% 3 14% 44% 29% 5%	680
	11th to 20th	Night	13% 5% 24% 38% 18% 3	800
	21st to end	Night	15% 7% 29% 31% 16% 2	880
November	1st to 10th	Night	15% 5% 25% 36% 18% 2	820
	11th to 20th	Night	12% 10% 29% 37% 12%	840
	21st to end	Night	19% 10% 28% 28% 13% 1	1024
December	1st to 10th	Night	20% 9% 31% 30% 9%	1050
	11th to 20th	Night	24% 9% 29% 31% 7%	1050
	21st to end	Night	22% 11% 30% 29% 8%	1155

Page generated at 2026-01-29 00:21:42. Version ac07

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