Burke Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burke Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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% 3 7% 5% 4 5% 4 6% 7% 35%	101164
	Night	15% 9% 3 7% 4 4 4 4 5% 7% 37%	97799
Transparency	Day	24% 48% 6% 12% 7% 2	104893
	Night	24% 48% 6% 12% 8% 2	102209
Seeing	Day	21% 12% 21% 23% 16% 7%	15063
	Night	19% 9% 20% 31% 18% 2	25116

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	18% 14% 7% 10% 5% 3 4 2 4 6% 27%	2836
	11th to 20th	Day	17% 17% 8% 11% 8% 3 4 3 4 4 22%	2840
	21st to end	Day	18% 17% 4 8% 5% 4 4 3 4 5% 28%	3124
February	1st to 10th	Day	19% 12% 4 8% 4 3 5% 3 4 6% 31%	1733
	11th to 20th	Day	22% 12% 4 10% 4 4 3 2 4 6% 29%	1848
	21st to end	Day	23% 11% 4 8% 3 3 3 3 4 6% 32%	1570
March	1st to 10th	Day	20% 13% 3 6% 4 3 4 3 5% 6% 33%	3375
	11th to 20th	Day	14% 7% 3 7% 4 4 4 3 5% 6% 45%	3480
	21st to end	Day	18% 10% 2 6% 4 4 4 3 5% 6% 37%	3815
April	1st to 10th	Day	14% 8% 2 7% 5% 4 4 3 7% 7% 38%	2090
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 5% 6% 42%	2300
	21st to end	Day	16% 9% 3 6% 5% 4 5% 4 5% 6% 38%	2470
May	1st to 10th	Day	20% 9% 3 8% 6% 5% 5% 4 6% 7% 27%	4082
	11th to 20th	Day	18% 9% 3 8% 5% 6% 5% 4 6% 6% 29%	4081
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 10% 35%	4476
June	1st to 10th	Day	11% 7% 2 6% 5% 5% 5% 5% 7% 9% 36%	2470
	11th to 20th	Day	7% 7% 2 8% 7% 6% 6% 5% 9% 9% 33%	2470
	21st to end	Day	10% 6% 3 7% 6% 5% 5% 5% 7% 9% 36%	2470
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 6% 6% 10% 11% 36%	4120
	11th to 20th	Day	12% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	4120
	21st to end	Day	19% 10% 3 10% 7% 6% 6% 5% 6% 8% 20%	4466
August	1st to 10th	Day	12% 7% 3 8% 6% 6% 6% 6% 9% 11% 28%	4104
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 5% 8% 11% 35%	4044
	21st to end	Day	6% 3 1 4 3 4 4 4 6% 9% 56%	4279
September	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 5% 6% 9% 41%	2090
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 4 6% 9% 39%	2090
	21st to end	Day	15% 6% 2 7% 5% 5% 5% 4 6% 8% 39%	2090
October	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 5% 6% 48%	2027
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 5% 5% 50%	1900
	21st to end	Day	18% 8% 2 6% 3 3 3 3 4 6% 46%	2090
November	1st to 10th	Day	12% 7% 2 5% 4 3 3 3 5% 6% 51%	1807
	11th to 20th	Day	11% 10% 2 6% 4 4 4 3 5% 7% 43%	1710
	21st to end	Day	15% 8% 3 7% 4 4 3 4 5% 6% 42%	1710
December	1st to 10th	Day	21% 13% 4 8% 5% 3 4 3 4 5% 30%	1710
	11th to 20th	Day	16% 15% 4 7% 3 3 3 3 6% 8% 32%	2153
	21st to end	Day	17% 16% 6% 7% 4 5% 5% 4 5% 6% 24%	3124
January	1st to 10th	Night	19% 17% 6% 9% 4 4 4 3 5% 4 25%	4109
	11th to 20th	Night	21% 12% 4 10% 4 3 3 3 4 5% 33%	4120
	21st to end	Night	22% 12% 4 8% 5% 4 4 3 4 6% 29%	4532
February	1st to 10th	Night	18% 10% 3 8% 4 4 3 4 5% 7% 34%	2444
	11th to 20th	Night	22% 11% 4 8% 5% 4 4 3 4 6% 30%	2218
	21st to end	Night	23% 11% 4 8% 4 4 3 3 4 6% 30%	1884
March	1st to 10th	Night	23% 12% 3 7% 4 4 3 3 3 5% 32%	3465
	11th to 20th	Night	14% 6% 3 6% 4 3 3 3 5% 6% 45%	3480
	21st to end	Night	15% 7% 2 6% 4 5% 5% 4 5% 7% 42%	3817
April	1st to 10th	Night	14% 9% 3 7% 4 4 4 4 5% 7% 40%	2090
	11th to 20th	Night	14% 7% 2 7% 6% 4 4 4 5% 7% 41%	1843
	21st to end	Night	13% 7% 2 7% 5% 5% 5% 5% 5% 7% 41%	1710
May	1st to 10th	Night	18% 10% 4 8% 6% 5% 4 3 5% 7% 30%	2813
	11th to 20th	Night	19% 9% 4 7% 4 4 4 3 6% 8% 32%	2812
	21st to end	Night	9% 7% 3 9% 5% 5% 6% 5% 7% 10% 35%	3079
June	1st to 10th	Night	11% 6% 1 8% 4 4 6% 4 8% 10% 38%	1710
	11th to 20th	Night	6% 5% 2 6% 6% 6% 6% 5% 8% 10% 41%	1710
	21st to end	Night	11% 7% 2 6% 5% 5% 5% 4 7% 11% 37%	1710
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 5% 10% 11% 34%	2840
	11th to 20th	Night	10% 6% 2 7% 4 4 5% 4 6% 11% 40%	2840
	21st to end	Night	17% 10% 4 10% 7% 5% 5% 5% 6% 9% 23%	3087
August	1st to 10th	Night	12% 7% 3 7% 6% 5% 5% 5% 7% 11% 31%	2825
	11th to 20th	Night	13% 7% 2 7% 5% 5% 5% 4 7% 8% 36%	2785
	21st to end	Night	6% 4 1 4 3 4 4 5% 6% 9% 53%	3314
September	1st to 10th	Night	11% 6% 3 7% 5% 5% 4 3 5% 7% 43%	2090
	11th to 20th	Night	13% 6% 3 6% 4 4 4 4 6% 8% 43%	2090
	21st to end	Night	14% 6% 2 5% 4 4 3 4 6% 6% 45%	2090
October	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 49%	2152
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 4 6% 49%	2280
	21st to end	Night	15% 8% 2 5% 3 4 3 2 5% 7% 46%	2508
November	1st to 10th	Night	13% 7% 3 5% 3 3 4 3 4 5% 51%	2368
	11th to 20th	Night	15% 9% 2 6% 3 3 4 3 4 7% 44%	2470
	21st to end	Night	14% 10% 2 5% 3 3 4 4 4 5% 45%	2470
December	1st to 10th	Night	21% 13% 4 8% 5% 4 4 2 4 6% 29%	2470
	11th to 20th	Night	18% 11% 5% 9% 5% 3 3 3 4 5% 34%	3042
	21st to end	Night	17% 16% 5% 8% 5% 5% 4 4 5% 7% 23%	4532

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	36% 39% 3 10% 10% 2	2837
	11th to 20th	Day	44% 38% 3 8% 6%	2840
	21st to end	Day	39% 41% 3 8% 10%	3124
February	1st to 10th	Day	20% 65% 2 7% 6% 1	1733
	11th to 20th	Day	23% 63% 2 5% 6% 1	1858
	21st to end	Day	19% 65% 3 4 7% 1	1570
March	1st to 10th	Day	34% 43% 5% 9% 7% 2	3375
	11th to 20th	Day	19% 42% 4 19% 14% 3	3480
	21st to end	Day	25% 42% 4 17% 10% 2	3815
April	1st to 10th	Day	19% 66% 4 7% 5%	2090
	11th to 20th	Day	16% 65% 4 8% 5% 1	2300
	21st to end	Day	17% 64% 4 9% 5% 1	2470
May	1st to 10th	Day	35% 44% 6% 11% 3	4120
	11th to 20th	Day	31% 44% 6% 15% 4	4085
	21st to end	Day	22% 46% 10% 14% 6% 2	4489
June	1st to 10th	Day	15% 67% 6% 8% 4	2470
	11th to 20th	Day	15% 67% 6% 7% 4	2470
	21st to end	Day	17% 65% 7% 7% 5%	2470
July	1st to 10th	Day	21% 42% 17% 12% 7% 1	4055
	11th to 20th	Day	26% 38% 11% 22% 2	4051
	21st to end	Day	44% 38% 5% 9% 5%	4324
August	1st to 10th	Day	31% 42% 11% 13% 4	4091
	11th to 20th	Day	23% 41% 11% 18% 6% 2	4083
	21st to end	Day	12% 38% 14% 27% 9%	4279
September	1st to 10th	Day	14% 62% 6% 10% 5% 3	2090
	11th to 20th	Day	17% 62% 5% 9% 7% 1	2090
	21st to end	Day	17% 62% 7% 9% 4	2090
October	1st to 10th	Day	17% 38% 4 13% 23% 6%	3365
	11th to 20th	Day	14% 37% 5% 16% 11% 16%	3140
	21st to end	Day	15% 36% 3 23% 10% 12%	3428
November	1st to 10th	Day	19% 57% 3 10% 10% 1	1807
	11th to 20th	Day	17% 59% 2 8% 10% 3	1710
	21st to end	Day	19% 60% 3 9% 8% 1	1710
December	1st to 10th	Day	25% 60% 3 7% 3 2	1710
	11th to 20th	Day	25% 48% 3 9% 12% 2	2150
	21st to end	Day	39% 40% 6% 11% 4	3124
January	1st to 10th	Night	41% 40% 3 8% 7% 2	4109
	11th to 20th	Night	32% 39% 4 11% 12% 1	4120
	21st to end	Night	35% 42% 5% 10% 9% 1	4532
February	1st to 10th	Night	18% 65% 4 7% 6% 1	2444
	11th to 20th	Night	22% 64% 2 6% 4 1	2219
	21st to end	Night	19% 65% 3 6% 5% 2	1884
March	1st to 10th	Night	37% 42% 5% 10% 5% 1	3465
	11th to 20th	Night	18% 42% 5% 18% 11% 6%	3480
	21st to end	Night	22% 41% 6% 17% 12% 1	3817
April	1st to 10th	Night	17% 66% 4 8% 4 1	2090
	11th to 20th	Night	17% 66% 4 7% 5% 1	1843
	21st to end	Night	14% 65% 5% 10% 5%	1710
May	1st to 10th	Night	33% 44% 7% 12% 3	2840
	11th to 20th	Night	30% 44% 8% 16% 2	2813
	21st to end	Night	23% 47% 10% 13% 6% 1	3087
June	1st to 10th	Night	13% 67% 7% 7% 5% 1	1710
	11th to 20th	Night	11% 68% 8% 9% 3 1	1710
	21st to end	Night	15% 66% 7% 8% 4	1710
July	1st to 10th	Night	26% 42% 15% 13% 5%	2795
	11th to 20th	Night	22% 38% 15% 21% 3 1	2786
	21st to end	Night	44% 39% 5% 10% 3	2988
August	1st to 10th	Night	30% 42% 12% 14% 2	2814
	11th to 20th	Night	26% 41% 11% 16% 6%	2812
	21st to end	Night	12% 39% 12% 28% 9%	3314
September	1st to 10th	Night	15% 60% 7% 9% 7% 1	2090
	11th to 20th	Night	15% 61% 6% 9% 7% 1	2090
	21st to end	Night	16% 61% 7% 12% 5%	2090
October	1st to 10th	Night	23% 38% 4 11% 19% 4	3594
	11th to 20th	Night	15% 38% 4 14% 18% 11%	3779
	21st to end	Night	13% 36% 3 22% 16% 9%	4120
November	1st to 10th	Night	19% 57% 4 11% 7% 1	2368
	11th to 20th	Night	16% 60% 2 7% 11% 4	2470
	21st to end	Night	18% 60% 4 11% 7%	2470
December	1st to 10th	Night	27% 60% 3 6% 3 2	2470
	11th to 20th	Night	27% 49% 3 10% 9% 1	3044
	21st to end	Night	36% 41% 7% 9% 7%	4532

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	30% 29% 26% 11% 3 1	270
	11th to 20th	Day	41% 23% 24% 11% 1	270
	21st to end	Day	36% 22% 27% 12% 3	297
February	1st to 10th	Day	32% 19% 33% 12% 4	270
	11th to 20th	Day	44% 24% 22% 8% 1	270
	21st to end	Day	41% 22% 29% 7% 1	225
March	1st to 10th	Day	27% 20% 25% 22% 6% 1	422
	11th to 20th	Day	30% 20% 29% 17% 3 1	460
	21st to end	Day	32% 17% 24% 19% 7%	506
April	1st to 10th	Day	28% 18% 23% 21% 9% 2	460
	11th to 20th	Day	23% 17% 28% 18% 12% 2	452
	21st to end	Day	25% 14% 26% 20% 11% 4	460
May	1st to 10th	Day	27% 16% 24% 19% 9% 5%	463
	11th to 20th	Day	20% 9% 25% 24% 16% 7%	487
	21st to end	Day	15% 8% 21% 22% 21% 13%	529
June	1st to 10th	Day	14% 6% 20% 30% 22% 8%	490
	11th to 20th	Day	8% 8% 19% 27% 27% 11%	490
	21st to end	Day	14% 8% 23% 24% 23% 9%	490
July	1st to 10th	Day	15% 3 15% 24% 27% 16%	485
	11th to 20th	Day	15% 3 11% 32% 26% 13%	484
	21st to end	Day	17% 4 14% 28% 26% 10%	532
August	1st to 10th	Day	14% 6% 18% 24% 23% 14%	486
	11th to 20th	Day	15% 3 15% 30% 23% 14%	479
	21st to end	Day	11% 3 11% 28% 27% 21%	539
September	1st to 10th	Day	11% 4 13% 27% 30% 14%	490
	11th to 20th	Day	14% 6% 13% 24% 29% 14%	490
	21st to end	Day	19% 9% 18% 27% 20% 7%	490
October	1st to 10th	Day	18% 4 18% 31% 22% 7%	490
	11th to 20th	Day	17% 15% 20% 26% 18% 4	490
	21st to end	Day	22% 10% 22% 28% 14% 4	539
November	1st to 10th	Day	17% 13% 24% 29% 14% 3	381
	11th to 20th	Day	21% 20% 28% 21% 9% 1	270
	21st to end	Day	19% 19% 34% 19% 7% 1	270
December	1st to 10th	Day	35% 15% 30% 16% 4	270
	11th to 20th	Day	29% 18% 27% 18% 8%	270
	21st to end	Day	31% 18% 30% 14% 6% 1	297
January	1st to 10th	Night	24% 18% 30% 24% 4	760
	11th to 20th	Night	30% 16% 27% 22% 4	760
	21st to end	Night	23% 18% 32% 25% 2	836
February	1st to 10th	Night	24% 15% 29% 29% 3	760
	11th to 20th	Night	31% 19% 30% 19% 1	743
	21st to end	Night	31% 17% 29% 21% 2	628
March	1st to 10th	Night	24% 15% 28% 28% 5%	760
	11th to 20th	Night	24% 16% 27% 25% 7%	760
	21st to end	Night	20% 12% 32% 28% 8%	836
April	1st to 10th	Night	20% 15% 27% 29% 9%	760
	11th to 20th	Night	20% 12% 25% 31% 11% 1	667
	21st to end	Night	17% 7% 26% 39% 11% 1	570
May	1st to 10th	Night	17% 11% 22% 34% 15% 2	570
	11th to 20th	Night	17% 6% 18% 37% 21% 2	561
	21st to end	Night	11% 3 13% 35% 32% 6%	617
June	1st to 10th	Night	12% 2 12% 39% 29% 4	570
	11th to 20th	Night	8% 1 12% 37% 35% 6%	570
	21st to end	Night	12% 2 11% 36% 35% 4	570
July	1st to 10th	Night	15% 3 8% 30% 40% 4	555
	11th to 20th	Night	12% 2 5% 31% 42% 7%	552
	21st to end	Night	13% 2 9% 33% 34% 9%	624
August	1st to 10th	Night	13% 2 7% 32% 43% 4	567
	11th to 20th	Night	14% 2 6% 36% 35% 6%	564
	21st to end	Night	12% 2 6% 31% 42% 7%	684
September	1st to 10th	Night	14% 4 10% 33% 35% 5%	760
	11th to 20th	Night	16% 3 10% 31% 35% 5%	760
	21st to end	Night	16% 4 16% 33% 28% 3	760
October	1st to 10th	Night	16% 5% 16% 30% 27% 5%	760
	11th to 20th	Night	19% 7% 21% 35% 17% 1	760
	21st to end	Night	20% 9% 19% 36% 14% 1	836
November	1st to 10th	Night	18% 8% 16% 41% 16% 2	760
	11th to 20th	Night	20% 11% 23% 36% 10% 1	760
	21st to end	Night	19% 11% 24% 34% 11% 1	760
December	1st to 10th	Night	28% 13% 26% 25% 7%	760
	11th to 20th	Night	25% 13% 26% 31% 5% 1	760
	21st to end	Night	28% 11% 25% 30% 5%	836

Page generated at 2024-11-03 02:11:12. Version ac07

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