Dodie's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dodie's Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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 6% 8% 45%	126233
	Night	14% 6% 2 5% 3 3 3 3 5% 7% 49%	123098
Transparency	Day	36% 4 10% 21% 18% 9%	129976
	Night	35% 4 11% 21% 19% 11%	127418
Seeing	Day	13% 6% 19% 28% 25% 9%	16035
	Night	15% 6% 25% 36% 17% 2	25867

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	17% 10% 3 5% 3 3 3 2 4 5% 44%	4077
	11th to 20th	Day	16% 5% 2 4 3 2 3 3 5% 5% 52%	4080
	21st to end	Day	27% 9% 2 5% 2 2 2 1 3 5% 40%	4651
February	1st to 10th	Day	21% 7% 3 5% 3 3 3 3 4 5% 43%	2000
	11th to 20th	Day	20% 8% 3 5% 3 3 3 2 3 6% 43%	1949
	21st to end	Day	18% 8% 2 5% 4 2 3 3 4 5% 46%	1675
March	1st to 10th	Day	13% 6% 3 6% 4 4 3 3 5% 6% 48%	4936
	11th to 20th	Day	14% 6% 2 6% 4 4 3 3 4 5% 48%	4980
	21st to end	Day	17% 8% 2 7% 4 3 3 3 5% 5% 43%	5462
April	1st to 10th	Day	15% 8% 3 6% 4 4 4 4 5% 6% 41%	2200
	11th to 20th	Day	14% 8% 3 8% 5% 4 4 3 4 6% 41%	2186
	21st to end	Day	14% 7% 3 6% 4 4 5% 3 5% 6% 43%	2505
May	1st to 10th	Day	19% 8% 3 6% 5% 4 5% 4 6% 7% 34%	5862
	11th to 20th	Day	10% 6% 2 7% 4 3 5% 4 6% 8% 44%	5862
	21st to end	Day	10% 7% 3 7% 5% 5% 6% 5% 8% 9% 35%	6434
June	1st to 10th	Day	5% 4 2 5% 4 5% 5% 5% 7% 10% 49%	2600
	11th to 20th	Day	6% 4 3 6% 4 4 4 5% 7% 10% 47%	2600
	21st to end	Day	5% 6% 2 6% 6% 6% 6% 5% 8% 10% 39%	2600
July	1st to 10th	Day	9% 6% 3 7% 6% 5% 5% 4 7% 9% 39%	5900
	11th to 20th	Day	6% 5% 2 6% 4 4 6% 5% 7% 13% 43%	5900
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 11% 41%	6422
August	1st to 10th	Day	2 1 1 2 2 3 3 3 6% 9% 68%	4234
	11th to 20th	Day	3 2 1 4 3 3 5% 4 8% 13% 54%	3992
	21st to end	Day	4 3 2 6% 4 5% 6% 5% 8% 11% 46%	4048
September	1st to 10th	Day	7% 6% 2 8% 6% 6% 6% 3 5% 7% 45%	2200
	11th to 20th	Day	9% 6% 3 7% 5% 5% 5% 4 7% 7% 42%	2178
	21st to end	Day	6% 5% 2 5% 4 6% 5% 5% 7% 7% 49%	2090
October	1st to 10th	Day	6% 4 2 4 3 4 4 4 5% 7% 57%	2090
	11th to 20th	Day	13% 5% 2 4 3 3 5% 2 4 6% 54%	1914
	21st to end	Day	11% 5% 1 4 3 3 3 3 4 5% 58%	2090
November	1st to 10th	Day	13% 7% 2 5% 4 3 4 3 5% 6% 46%	1958
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 4 5% 52%	1939
	21st to end	Day	16% 8% 2 6% 4 4 3 3 4 7% 44%	1800
December	1st to 10th	Day	26% 7% 3 6% 4 3 3 3 4 5% 37%	2940
	11th to 20th	Day	19% 7% 2 5% 4 3 3 3 4 6% 43%	3391
	21st to end	Day	14% 7% 2 5% 3 3 3 2 4 4 53%	4488
January	1st to 10th	Night	19% 7% 2 5% 2 3 3 2 4 5% 49%	5888
	11th to 20th	Night	13% 4 1 3 2 2 3 3 3 5% 61%	5900
	21st to end	Night	29% 6% 2 5% 3 2 2 2 3 5% 39%	6356
February	1st to 10th	Night	19% 8% 2 5% 4 2 3 3 3 6% 46%	2400
	11th to 20th	Night	21% 6% 2 5% 3 2 3 2 3 6% 47%	2338
	21st to end	Night	21% 7% 2 5% 4 3 3 2 4 5% 44%	1955
March	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 7% 44%	4919
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 4 5% 48%	4980
	21st to end	Night	18% 9% 2 6% 4 3 4 2 4 6% 42%	5467
April	1st to 10th	Night	13% 7% 2 5% 5% 4 4 3 5% 7% 45%	2200
	11th to 20th	Night	15% 7% 3 5% 5% 3 3 3 6% 7% 45%	2160
	21st to end	Night	14% 8% 2 5% 3 3 3 3 5% 7% 46%	1890
May	1st to 10th	Night	22% 8% 3 7% 4 4 4 3 5% 7% 33%	4053
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 4 6% 8% 46%	4053
	21st to end	Night	12% 8% 2 6% 4 5% 5% 4 7% 9% 38%	4443
June	1st to 10th	Night	4 3 1 4 2 3 3 4 6% 10% 60%	1800
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 9% 57%	1800
	21st to end	Night	4 4 2 5% 4 4 4 5% 8% 9% 51%	1800
July	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 6% 10% 43%	4078
	11th to 20th	Night	5% 4 2 4 4 4 5% 4 7% 12% 51%	4077
	21st to end	Night	7% 5% 2 5% 5% 4 5% 4 7% 9% 47%	4449
August	1st to 10th	Night	1 1 1 2 2 2 3 2 5% 8% 73%	2926
	11th to 20th	Night	2 3 1 3 3 3 4 4 7% 12% 58%	3048
	21st to end	Night	3 3 1 4 3 4 4 4 8% 11% 55%	3851
September	1st to 10th	Night	7% 5% 2 5% 5% 4 4 4 6% 8% 51%	2200
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 5% 7% 49%	2178
	21st to end	Night	7% 4 2 5% 3 4 4 4 6% 8% 53%	2090
October	1st to 10th	Night	4 3 1 4 2 3 3 3 4 7% 64%	2090
	11th to 20th	Night	12% 4 1 5% 3 2 3 3 4 5% 57%	2247
	21st to end	Night	13% 4 2 4 3 2 3 2 3 5% 61%	2508
November	1st to 10th	Night	13% 5% 2 4 3 4 4 3 4 6% 52%	2340
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 4 6% 54%	2458
	21st to end	Night	17% 5% 2 4 4 3 4 2 4 7% 48%	2600
December	1st to 10th	Night	24% 9% 3 5% 4 4 3 3 4 4 39%	4250
	11th to 20th	Night	18% 8% 3 5% 3 2 2 2 3 5% 48%	4816
	21st to end	Night	16% 6% 2 4 2 2 2 2 3 4 56%	6490

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	44% 3 4 21% 19% 9%	4078
	11th to 20th	Day	35% 2 5% 18% 24% 15%	4080
	21st to end	Day	50% 2 3 10% 23% 14%	4651
February	1st to 10th	Day	45% 3 6% 12% 20% 14%	2000
	11th to 20th	Day	45% 3 7% 18% 17% 11%	1959
	21st to end	Day	42% 3 7% 17% 17% 14%	1675
March	1st to 10th	Day	38% 2 6% 19% 17% 18%	4936
	11th to 20th	Day	39% 3 6% 9% 16% 26%	4980
	21st to end	Day	44% 3 7% 19% 20% 7%	5464
April	1st to 10th	Day	44% 4 8% 17% 15% 13%	2200
	11th to 20th	Day	44% 3 7% 16% 19% 11%	2186
	21st to end	Day	41% 4 7% 21% 20% 8%	2505
May	1st to 10th	Day	48% 5% 10% 20% 13% 4	5900
	11th to 20th	Day	37% 5% 12% 20% 21% 6%	5866
	21st to end	Day	41% 6% 11% 27% 13% 2	6447
June	1st to 10th	Day	28% 6% 15% 28% 20% 3	2600
	11th to 20th	Day	30% 7% 12% 27% 19% 5%	2600
	21st to end	Day	37% 8% 14% 24% 15% 2	2600
July	1st to 10th	Day	40% 7% 20% 28% 5% 1	5836
	11th to 20th	Day	32% 6% 21% 29% 11% 1	5831
	21st to end	Day	35% 7% 17% 26% 13% 2	6240
August	1st to 10th	Day	14% 4 13% 41% 27% 1	4220
	11th to 20th	Day	20% 5% 25% 37% 10% 2	4031
	21st to end	Day	28% 10% 19% 23% 17% 2	4047
September	1st to 10th	Day	39% 6% 10% 20% 16% 9%	2200
	11th to 20th	Day	39% 6% 12% 20% 18% 5%	2178
	21st to end	Day	32% 5% 10% 21% 17% 14%	2090
October	1st to 10th	Day	16% 3 7% 13% 22% 38%	3480
	11th to 20th	Day	21% 2 8% 19% 31% 19%	3154
	21st to end	Day	26% 3 5% 21% 30% 15%	3428
November	1st to 10th	Day	37% 5% 8% 19% 20% 12%	1958
	11th to 20th	Day	35% 3 8% 17% 21% 16%	1939
	21st to end	Day	41% 3 8% 17% 18% 13%	1800
December	1st to 10th	Day	51% 2 6% 15% 17% 8%	2940
	11th to 20th	Day	43% 4 7% 12% 23% 12%	3389
	21st to end	Day	36% 2 4 18% 25% 14%	4488
January	1st to 10th	Night	40% 2 4 19% 22% 12%	5888
	11th to 20th	Night	28% 2 4 18% 32% 17%	5900
	21st to end	Night	50% 2 3 11% 20% 14%	6356
February	1st to 10th	Night	42% 3 6% 13% 19% 17%	2400
	11th to 20th	Night	41% 3 6% 17% 18% 14%	2338
	21st to end	Night	44% 2 6% 15% 17% 15%	1955
March	1st to 10th	Night	40% 3 8% 17% 18% 14%	4919
	11th to 20th	Night	40% 3 8% 12% 14% 24%	4980
	21st to end	Night	45% 4 7% 17% 18% 10%	5467
April	1st to 10th	Night	38% 4 9% 18% 17% 14%	2200
	11th to 20th	Night	39% 4 10% 16% 16% 15%	2160
	21st to end	Night	39% 4 9% 22% 17% 9%	1890
May	1st to 10th	Night	51% 4 9% 19% 12% 5%	4080
	11th to 20th	Night	35% 5% 12% 22% 19% 8%	4054
	21st to end	Night	41% 5% 15% 28% 11% 1	4452
June	1st to 10th	Night	20% 5% 20% 32% 21% 3	1800
	11th to 20th	Night	22% 6% 16% 32% 20% 5%	1800
	21st to end	Night	27% 7% 18% 29% 16% 2	1800
July	1st to 10th	Night	36% 8% 25% 26% 4	4035
	11th to 20th	Night	26% 7% 23% 33% 10%	4026
	21st to end	Night	31% 8% 21% 26% 11% 3	4320
August	1st to 10th	Night	10% 4 16% 44% 25% 1	2916
	11th to 20th	Night	18% 5% 32% 32% 10% 1	3075
	21st to end	Night	22% 10% 24% 29% 14% 2	3851
September	1st to 10th	Night	31% 7% 16% 23% 16% 8%	2200
	11th to 20th	Night	34% 7% 14% 23% 16% 6%	2178
	21st to end	Night	28% 6% 15% 20% 17% 14%	2090
October	1st to 10th	Night	15% 3 7% 17% 18% 40%	3480
	11th to 20th	Night	18% 3 8% 18% 31% 22%	3733
	21st to end	Night	23% 2 5% 23% 30% 17%	4120
November	1st to 10th	Night	33% 4 9% 19% 21% 13%	2340
	11th to 20th	Night	32% 4 9% 19% 20% 16%	2458
	21st to end	Night	38% 3 8% 19% 17% 15%	2600
December	1st to 10th	Night	51% 3 5% 16% 17% 9%	4250
	11th to 20th	Night	41% 3 8% 10% 23% 16%	4817
	21st to end	Night	34% 2 5% 16% 30% 13%	6490

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	21% 10% 34% 27% 7% 1	300
	11th to 20th	Day	24% 11% 28% 28% 7% 2	300
	21st to end	Day	24% 12% 34% 19% 10% 2	330
February	1st to 10th	Day	29% 10% 27% 23% 9% 1	300
	11th to 20th	Day	27% 14% 33% 18% 7% 1	300
	21st to end	Day	30% 10% 37% 20% 2	249
March	1st to 10th	Day	21% 14% 35% 24% 6% 1	300
	11th to 20th	Day	17% 16% 36% 23% 6% 1	300
	21st to end	Day	18% 11% 39% 23% 8% 1	330
April	1st to 10th	Day	19% 17% 37% 21% 6% 1	300
	11th to 20th	Day	18% 16% 32% 22% 12% 1	304
	21st to end	Day	20% 10% 33% 26% 10% 1	605
May	1st to 10th	Day	17% 9% 36% 27% 11%	703
	11th to 20th	Day	16% 8% 26% 32% 15% 3	725
	21st to end	Day	11% 5% 26% 36% 20% 2	789
June	1st to 10th	Day	7% 2 11% 42% 31% 8%	730
	11th to 20th	Day	7% 2 14% 42% 29% 5%	730
	21st to end	Day	6% 3 10% 33% 34% 14%	730
July	1st to 10th	Day	8% 4 6% 29% 38% 14%	721
	11th to 20th	Day	5% 2 5% 27% 47% 14%	718
	21st to end	Day	4 2 5% 26% 49% 15%	794
August	1st to 10th	Day	3 1 2 23% 52% 19%	726
	11th to 20th	Day	5% 2 27% 47% 19%	614
	21st to end	Day	5% 2 4 21% 33% 36%	423
September	1st to 10th	Day	7% 1 8% 22% 38% 24%	330
	11th to 20th	Day	6% 5% 23% 41% 25%	324
	21st to end	Day	12% 2 5% 22% 36% 24%	300
October	1st to 10th	Day	4 1 8% 29% 43% 15%	300
	11th to 20th	Day	11% 1 19% 33% 28% 8%	300
	21st to end	Day	18% 8% 23% 25% 20% 6%	330
November	1st to 10th	Day	19% 7% 19% 32% 18% 6%	300
	11th to 20th	Day	18% 6% 25% 28% 18% 5%	300
	21st to end	Day	18% 11% 34% 22% 11% 4	300
December	1st to 10th	Day	21% 5% 32% 24% 13% 5%	300
	11th to 20th	Day	26% 11% 28% 25% 9% 1	300
	21st to end	Day	18% 10% 37% 22% 11% 2	330
January	1st to 10th	Night	21% 9% 30% 32% 8%	1000
	11th to 20th	Night	21% 11% 28% 32% 8%	1000
	21st to end	Night	23% 9% 29% 32% 6%	1044
February	1st to 10th	Night	24% 12% 30% 29% 6%	800
	11th to 20th	Night	25% 9% 35% 26% 4	784
	21st to end	Night	25% 12% 39% 21% 2	635
March	1st to 10th	Night	20% 11% 39% 28% 3	600
	11th to 20th	Night	21% 10% 36% 30% 4	600
	21st to end	Night	16% 9% 42% 28% 3 1	660
April	1st to 10th	Night	15% 10% 42% 30% 3	600
	11th to 20th	Night	18% 10% 41% 26% 4	593
	21st to end	Night	16% 10% 40% 26% 8% 1	600
May	1st to 10th	Night	16% 7% 43% 28% 6%	600
	11th to 20th	Night	13% 6% 34% 35% 11% 1	591
	21st to end	Night	11% 4 32% 38% 15%	650
June	1st to 10th	Night	4 2 20% 46% 27% 1	600
	11th to 20th	Night	5% 2 26% 51% 16% 1	600
	21st to end	Night	5% 3 14% 45% 30% 4	600
July	1st to 10th	Night	8% 1 8% 48% 31% 4	585
	11th to 20th	Night	4 1 9% 51% 34% 2	582
	21st to end	Night	4 2 8% 48% 37% 2	657
August	1st to 10th	Night	1 6% 52% 37% 4	597
	11th to 20th	Night	5% 1 5% 50% 34% 5%	594
	21st to end	Night	4 1 4 37% 45% 8%	660
September	1st to 10th	Night	7% 2 7% 42% 38% 5%	600
	11th to 20th	Night	10% 2 5% 38% 41% 4	594
	21st to end	Night	8% 2 11% 37% 38% 4	570
October	1st to 10th	Night	5% 1 11% 48% 31% 5%	570
	11th to 20th	Night	13% 4 20% 42% 20% 2	727
	21st to end	Night	13% 6% 27% 32% 20% 2	836
November	1st to 10th	Night	15% 4 21% 40% 19% 1	780
	11th to 20th	Night	13% 6% 26% 38% 16% 1	858
	21st to end	Night	20% 8% 28% 30% 13% 1	1000
December	1st to 10th	Night	20% 8% 26% 34% 12% 1	1000
	11th to 20th	Night	24% 9% 27% 32% 8% 1	1000
	21st to end	Night	20% 8% 30% 34% 8%	1100

Page generated at 2025-09-16 00:49:13. Version ac07

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