Bush Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bush Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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% 8% 3 6% 5% 3 5% 4 5% 7% 41%	78391
	Night	12% 8% 3 6% 5% 3 4 4 5% 7% 45%	80626
Transparency	Day	42% 7% 13% 23% 13% 2	78109
	Night	39% 6% 12% 25% 15% 3	80428
Seeing	Day	15% 10% 28% 28% 16% 4	14663
	Night	14% 9% 32% 32% 12% 1	24711

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	13% 11% 5% 9% 6% 3 5% 5% 5% 7% 31%	2760
	11th to 20th	Day	10% 12% 5% 7% 7% 4 8% 4 4 5% 33%	2850
	21st to end	Day	14% 15% 8% 12% 7% 4 5% 4 4 5% 24%	3135
February	1st to 10th	Day	12% 11% 4 7% 7% 4 5% 4 5% 8% 33%	1701
	11th to 20th	Day	12% 9% 5% 7% 5% 2 3 5% 6% 8% 37%	1574
	21st to end	Day	13% 10% 4 6% 5% 3 5% 4 4 6% 40%	1482
March	1st to 10th	Day	14% 10% 4 7% 4 3 4 4 5% 6% 40%	1980
	11th to 20th	Day	16% 12% 4 7% 5% 2 4 4 4 7% 36%	1980
	21st to end	Day	22% 12% 4 6% 6% 3 5% 4 4 5% 29%	2178
April	1st to 10th	Day	16% 7% 3 6% 5% 3 4 4 5% 7% 41%	2106
	11th to 20th	Day	15% 9% 3 6% 5% 3 4 5% 5% 7% 38%	2134
	21st to end	Day	22% 7% 2 5% 5% 3 4 4 5% 6% 36%	2295
May	1st to 10th	Day	16% 8% 3 6% 7% 3 5% 5% 6% 7% 34%	2340
	11th to 20th	Day	16% 6% 3 6% 6% 3 4 5% 5% 7% 39%	2302
	21st to end	Day	16% 7% 3 6% 6% 3 5% 4 5% 7% 36%	2725
June	1st to 10th	Day	7% 5% 2 5% 6% 3 5% 5% 6% 9% 47%	2520
	11th to 20th	Day	7% 5% 3 5% 5% 3 4 6% 7% 10% 47%	2520
	21st to end	Day	8% 5% 2 5% 5% 3 5% 5% 6% 8% 47%	2520
July	1st to 10th	Day	8% 4 2 4 4 3 5% 5% 7% 9% 47%	2504
	11th to 20th	Day	6% 5% 2 4 4 3 5% 5% 6% 9% 51%	2340
	21st to end	Day	6% 4 2 4 4 3 4 5% 6% 10% 50%	2546
August	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 6% 7% 11% 42%	2328
	11th to 20th	Day	9% 5% 2 4 6% 3 4 5% 6% 8% 48%	2301
	21st to end	Day	8% 4 2 5% 5% 3 5% 4 5% 7% 53%	2433
September	1st to 10th	Day	12% 4 2 4 4 3 4 4 5% 7% 52%	2160
	11th to 20th	Day	10% 4 2 3 5% 3 5% 4 5% 9% 51%	2037
	21st to end	Day	10% 3 2 4 4 2 3 4 5% 7% 55%	1947
October	1st to 10th	Day	14% 7% 3 5% 4 2 4 3 4 6% 48%	1800
	11th to 20th	Day	14% 7% 3 4 2 2 2 3 4 5% 53%	1800
	21st to end	Day	14% 9% 3 5% 4 2 3 4 5% 7% 45%	1980
November	1st to 10th	Day	9% 7% 2 5% 3 2 3 3 4 7% 54%	1837
	11th to 20th	Day	13% 7% 3 4 5% 3 4 2 5% 6% 48%	1535
	21st to end	Day	17% 8% 4 5% 4 2 3 5% 4 6% 42%	1520
December	1st to 10th	Day	10% 8% 3 8% 5% 3 5% 5% 5% 7% 43%	1520
	11th to 20th	Day	11% 11% 4 8% 6% 3 4 4 4 7% 38%	1918
	21st to end	Day	19% 14% 7% 11% 6% 2 4 3 4 6% 23%	2783
January	1st to 10th	Night	9% 8% 5% 14% 9% 4 5% 4 5% 5% 32%	4190
	11th to 20th	Night	10% 10% 5% 8% 5% 3 8% 5% 6% 6% 33%	4120
	21st to end	Night	14% 14% 5% 11% 6% 3 4 3 4 5% 30%	4532
February	1st to 10th	Night	12% 11% 4 7% 6% 3 5% 4 5% 6% 38%	2464
	11th to 20th	Night	12% 8% 4 6% 6% 3 5% 4 5% 7% 42%	2273
	21st to end	Night	11% 10% 4 5% 5% 4 4 3 4 5% 45%	1789
March	1st to 10th	Night	11% 7% 3 6% 5% 2 4 3 4 6% 49%	1980
	11th to 20th	Night	17% 7% 3 6% 4 3 4 5% 5% 6% 41%	1980
	21st to end	Night	23% 10% 4 6% 5% 3 4 5% 6% 7% 28%	2178
April	1st to 10th	Night	11% 7% 2 5% 4 3 4 4 5% 8% 48%	1854
	11th to 20th	Night	14% 7% 3 5% 5% 3 4 5% 4 5% 46%	1775
	21st to end	Night	17% 8% 3 5% 5% 3 3 4 4 6% 42%	1661
May	1st to 10th	Night	14% 7% 3 6% 6% 3 5% 5% 5% 8% 39%	1620
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 5% 8% 45%	1590
	21st to end	Night	10% 6% 3 6% 6% 3 5% 3 4 9% 46%	1551
June	1st to 10th	Night	5% 3 2 3 4 2 5% 6% 6% 10% 54%	1440
	11th to 20th	Night	5% 3 2 4 4 3 4 5% 8% 11% 52%	1440
	21st to end	Night	5% 3 2 3 4 3 4 5% 5% 10% 56%	1440
July	1st to 10th	Night	7% 4 2 4 3 3 3 5% 7% 9% 53%	1451
	11th to 20th	Night	5% 3 1 3 4 2 3 4 5% 8% 62%	1620
	21st to end	Night	5% 3 2 4 4 3 5% 5% 6% 10% 52%	1772
August	1st to 10th	Night	4 3 2 4 4 3 5% 6% 6% 10% 52%	1611
	11th to 20th	Night	7% 3 3 4 4 3 3 5% 5% 8% 56%	1600
	21st to end	Night	5% 4 2 4 3 2 4 3 5% 7% 60%	1921
September	1st to 10th	Night	9% 4 2 3 4 3 3 4 4 8% 56%	1800
	11th to 20th	Night	10% 4 2 4 3 2 4 5% 4 8% 54%	1919
	21st to end	Night	8% 4 2 4 4 2 3 5% 4 7% 57%	1993
October	1st to 10th	Night	13% 6% 2 4 4 2 3 3 5% 7% 52%	2160
	11th to 20th	Night	14% 6% 2 4 4 2 3 3 3 5% 53%	2160
	21st to end	Night	15% 7% 2 4 4 2 4 3 4 5% 50%	2376
November	1st to 10th	Night	8% 4 2 3 3 2 3 3 5% 7% 60%	2239
	11th to 20th	Night	11% 6% 2 5% 5% 2 4 4 4 7% 50%	2644
	21st to end	Night	16% 7% 3 5% 3 2 3 3 4 6% 47%	2660
December	1st to 10th	Night	11% 8% 4 5% 6% 3 5% 4 5% 6% 43%	2660
	11th to 20th	Night	12% 9% 4 7% 5% 2 4 4 4 5% 45%	3279
	21st to end	Night	20% 17% 7% 11% 5% 2 3 3 3 4 26%	4884

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	51% 7% 16% 18% 8% 1	2761
	11th to 20th	Day	53% 5% 14% 19% 9%	2850
	21st to end	Day	63% 5% 11% 15% 6% 1	3135
February	1st to 10th	Day	50% 6% 14% 17% 11% 2	1701
	11th to 20th	Day	44% 6% 14% 22% 12% 2	1583
	21st to end	Day	45% 5% 13% 23% 12% 2	1482
March	1st to 10th	Day	46% 5% 12% 23% 12% 2	1980
	11th to 20th	Day	50% 6% 9% 22% 11% 2	1980
	21st to end	Day	58% 7% 11% 16% 7% 1	2178
April	1st to 10th	Day	43% 7% 12% 24% 12% 2	2106
	11th to 20th	Day	45% 6% 12% 23% 13% 1	2134
	21st to end	Day	48% 6% 11% 23% 10% 1	2295
May	1st to 10th	Day	48% 8% 14% 19% 11% 1	2340
	11th to 20th	Day	44% 9% 12% 22% 11% 1	2306
	21st to end	Day	47% 8% 14% 19% 10% 2	2725
June	1st to 10th	Day	33% 9% 16% 27% 13% 2	2520
	11th to 20th	Day	31% 8% 15% 25% 19% 1	2520
	21st to end	Day	32% 8% 17% 25% 15% 3	2520
July	1st to 10th	Day	31% 7% 17% 28% 13% 3	2435
	11th to 20th	Day	29% 9% 14% 28% 17% 3	2271
	21st to end	Day	28% 8% 17% 31% 15% 1	2405
August	1st to 10th	Day	34% 10% 17% 24% 13% 1	2314
	11th to 20th	Day	33% 7% 15% 28% 17% 1	2301
	21st to end	Day	31% 7% 11% 26% 18% 6%	2433
September	1st to 10th	Day	32% 6% 12% 27% 18% 5%	2160
	11th to 20th	Day	31% 6% 12% 28% 21% 1	2037
	21st to end	Day	29% 5% 11% 31% 21% 2	1947
October	1st to 10th	Day	38% 5% 11% 26% 20% 2	1800
	11th to 20th	Day	35% 4 8% 27% 21% 5%	1800
	21st to end	Day	39% 5% 11% 24% 17% 4	1980
November	1st to 10th	Day	31% 5% 15% 25% 20% 4	1837
	11th to 20th	Day	39% 3 12% 27% 16% 2	1535
	21st to end	Day	42% 6% 12% 25% 14%	1520
December	1st to 10th	Day	41% 6% 16% 24% 12% 1	1520
	11th to 20th	Day	46% 5% 16% 26% 5% 1	1915
	21st to end	Day	63% 5% 11% 14% 6% 1	2783
January	1st to 10th	Night	50% 9% 10% 20% 10% 1	4190
	11th to 20th	Night	49% 6% 13% 21% 11% 1	4120
	21st to end	Night	56% 5% 14% 15% 8% 1	4532
February	1st to 10th	Night	48% 6% 12% 19% 14% 3	2464
	11th to 20th	Night	42% 5% 13% 23% 16% 2	2274
	21st to end	Night	42% 5% 10% 22% 16% 5%	1789
March	1st to 10th	Night	38% 4 12% 28% 16% 2	1980
	11th to 20th	Night	44% 6% 11% 23% 14% 3	1980
	21st to end	Night	55% 6% 13% 17% 8% 1	2178
April	1st to 10th	Night	35% 7% 12% 25% 17% 4	1854
	11th to 20th	Night	40% 5% 11% 27% 14% 3	1775
	21st to end	Night	43% 7% 10% 23% 16% 2	1661
May	1st to 10th	Night	43% 8% 13% 21% 13% 2	1620
	11th to 20th	Night	38% 8% 13% 24% 16% 1	1591
	21st to end	Night	37% 9% 13% 26% 12% 3	1552
June	1st to 10th	Night	23% 9% 20% 29% 16% 3	1440
	11th to 20th	Night	25% 9% 15% 28% 20% 4	1440
	21st to end	Night	24% 7% 18% 29% 18% 4	1440
July	1st to 10th	Night	25% 7% 17% 31% 16% 4	1411
	11th to 20th	Night	21% 6% 18% 32% 19% 4	1566
	21st to end	Night	24% 7% 15% 34% 18% 2	1673
August	1st to 10th	Night	26% 8% 18% 30% 16% 1	1601
	11th to 20th	Night	26% 7% 13% 34% 18% 2	1600
	21st to end	Night	23% 6% 13% 26% 23% 8%	1921
September	1st to 10th	Night	28% 6% 11% 26% 22% 7%	1800
	11th to 20th	Night	29% 6% 11% 30% 22% 3	1919
	21st to end	Night	26% 5% 10% 29% 25% 3	1993
October	1st to 10th	Night	32% 5% 10% 25% 24% 4	2160
	11th to 20th	Night	34% 4 9% 23% 22% 7%	2160
	21st to end	Night	38% 5% 9% 23% 22% 3	2376
November	1st to 10th	Night	25% 5% 16% 26% 22% 5%	2239
	11th to 20th	Night	34% 5% 9% 31% 17% 3	2644
	21st to end	Night	39% 5% 10% 27% 17% 2	2660
December	1st to 10th	Night	42% 5% 12% 27% 12% 1	2660
	11th to 20th	Night	41% 5% 12% 31% 10% 1	3281
	21st to end	Night	63% 5% 8% 16% 7% 1	4884

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	22% 16% 31% 24% 8%	270
	11th to 20th	Day	21% 16% 40% 18% 4	270
	21st to end	Day	17% 12% 40% 27% 4	297
February	1st to 10th	Day	17% 20% 40% 19% 3 1	267
	11th to 20th	Day	19% 20% 38% 18% 5% 1	240
	21st to end	Day	18% 22% 44% 14% 2 1	198
March	1st to 10th	Day	17% 15% 43% 21% 3	240
	11th to 20th	Day	28% 13% 33% 22% 4 1	240
	21st to end	Day	37% 20% 27% 14% 3	264
April	1st to 10th	Day	21% 16% 38% 18% 7% 1	366
	11th to 20th	Day	18% 13% 37% 26% 7%	412
	21st to end	Day	24% 15% 33% 18% 9% 1	555
May	1st to 10th	Day	20% 13% 31% 27% 8% 1	603
	11th to 20th	Day	20% 10% 31% 25% 12% 2	625
	21st to end	Day	18% 9% 27% 27% 17% 3	679
June	1st to 10th	Day	8% 4 21% 33% 26% 8%	630
	11th to 20th	Day	8% 4 25% 40% 19% 4	630
	21st to end	Day	7% 8% 34% 33% 15% 2	630
July	1st to 10th	Day	10% 3 12% 32% 31% 12%	621
	11th to 20th	Day	7% 4 19% 39% 24% 8%	618
	21st to end	Day	7% 2 15% 42% 29% 5%	684
August	1st to 10th	Day	8% 2 19% 38% 27% 6%	626
	11th to 20th	Day	9% 5% 16% 35% 29% 6%	615
	21st to end	Day	9% 2 17% 33% 28% 11%	552
September	1st to 10th	Day	14% 2 21% 28% 29% 5%	450
	11th to 20th	Day	9% 1 20% 37% 28% 6%	327
	21st to end	Day	12% 9% 27% 30% 16% 5%	270
October	1st to 10th	Day	18% 7% 32% 24% 12% 7%	270
	11th to 20th	Day	14% 19% 41% 19% 6% 1	270
	21st to end	Day	17% 17% 34% 23% 6% 3	297
November	1st to 10th	Day	14% 10% 42% 21% 11% 2	270
	11th to 20th	Day	19% 14% 37% 22% 7% 1	270
	21st to end	Day	22% 11% 35% 22% 9%	270
December	1st to 10th	Day	11% 16% 37% 24% 9% 2	270
	11th to 20th	Day	17% 17% 34% 26% 6% 1	270
	21st to end	Day	23% 19% 39% 18% 2	297
January	1st to 10th	Night	12% 13% 39% 29% 7%	950
	11th to 20th	Night	15% 13% 38% 27% 6% 1	950
	21st to end	Night	14% 12% 41% 28% 5%	1045
February	1st to 10th	Night	18% 11% 40% 26% 4	948
	11th to 20th	Night	17% 12% 39% 27% 5%	879
	21st to end	Night	17% 16% 42% 19% 5% 1	605
March	1st to 10th	Night	15% 14% 39% 27% 6%	540
	11th to 20th	Night	21% 9% 34% 30% 6%	540
	21st to end	Night	27% 11% 38% 20% 5%	594
April	1st to 10th	Night	15% 12% 42% 27% 5%	540
	11th to 20th	Night	17% 11% 36% 29% 6%	533
	21st to end	Night	21% 9% 35% 28% 6% 1	540
May	1st to 10th	Night	14% 11% 34% 34% 6% 1	540
	11th to 20th	Night	16% 6% 31% 35% 11% 1	531
	21st to end	Night	14% 6% 28% 35% 17%	584
June	1st to 10th	Night	5% 4 23% 44% 23% 2	540
	11th to 20th	Night	7% 2 26% 44% 19% 1	540
	21st to end	Night	6% 3 30% 47% 15%	540
July	1st to 10th	Night	7% 3 14% 40% 34% 3	525
	11th to 20th	Night	5% 2 16% 46% 29% 1	522
	21st to end	Night	5% 2 15% 49% 28% 1	591
August	1st to 10th	Night	5% 1 19% 46% 28% 1	537
	11th to 20th	Night	7% 2 15% 43% 31% 2	534
	21st to end	Night	7% 2 15% 43% 30% 3	594
September	1st to 10th	Night	11% 2 20% 38% 26% 3	540
	11th to 20th	Night	13% 3 19% 41% 23% 2	540
	21st to end	Night	10% 4 26% 40% 19% 1	553
October	1st to 10th	Night	16% 7% 28% 31% 17% 2	720
	11th to 20th	Night	18% 9% 36% 29% 8%	720
	21st to end	Night	20% 10% 34% 27% 8%	792
November	1st to 10th	Night	10% 10% 35% 35% 10%	759
	11th to 20th	Night	13% 13% 39% 27% 8%	950
	21st to end	Night	19% 11% 34% 29% 8%	950
December	1st to 10th	Night	16% 11% 38% 27% 7% 1	950
	11th to 20th	Night	19% 9% 35% 31% 6%	950
	21st to end	Night	21% 14% 35% 26% 3	1045

Page generated at 2024-02-07 05:11:53. Version ac07

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