CoolHaven Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CoolHaven Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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% 7% 3 5% 5% 3 5% 5% 5% 7% 44%	74649
	Night	11% 6% 3 5% 4 3 4 4 5% 7% 49%	75168
Transparency	Day	38% 6% 11% 24% 17% 4	74372
	Night	35% 5% 11% 25% 20% 4	74965
Seeing	Day	15% 12% 25% 25% 18% 5%	14333
	Night	15% 11% 28% 30% 15% 2	24285

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	12% 8% 3 5% 5% 2 3 3 4 6% 48%	1707
	11th to 20th	Day	14% 7% 4 5% 4 3 4 4 5% 6% 43%	1674
	21st to end	Day	15% 8% 3 5% 4 2 3 3 5% 5% 47%	1782
February	1st to 10th	Day	15% 10% 3 6% 5% 4 4 4 3 5% 41%	1620
	11th to 20th	Day	13% 9% 4 7% 5% 3 4 4 5% 5% 42%	1616
	21st to end	Day	16% 11% 3 6% 5% 3 4 4 4 6% 39%	1556
March	1st to 10th	Day	14% 10% 3 5% 4 3 3 4 4 6% 45%	1980
	11th to 20th	Day	19% 8% 3 5% 4 3 4 4 3 5% 41%	1980
	21st to end	Day	17% 9% 4 6% 6% 3 5% 4 5% 5% 35%	2178
April	1st to 10th	Day	10% 6% 2 5% 4 3 6% 5% 6% 7% 45%	2130
	11th to 20th	Day	16% 7% 2 7% 5% 3 4 4 5% 6% 40%	2134
	21st to end	Day	18% 8% 2 6% 6% 3 4 4 4 5% 40%	2160
May	1st to 10th	Day	16% 7% 3 6% 6% 3 5% 5% 5% 7% 38%	2261
	11th to 20th	Day	13% 6% 2 5% 5% 3 5% 4 6% 8% 41%	2302
	21st to end	Day	10% 5% 3 7% 7% 4 7% 6% 6% 9% 38%	2544
June	1st to 10th	Day	8% 5% 2 4 6% 3 6% 5% 7% 11% 43%	2520
	11th to 20th	Day	6% 4 2 5% 5% 4 6% 6% 7% 10% 46%	2520
	21st to end	Day	4 3 2 4 4 4 6% 5% 8% 9% 52%	2439
July	1st to 10th	Day	9% 5% 2 6% 6% 4 6% 7% 7% 11% 37%	2340
	11th to 20th	Day	4 3 2 4 5% 3 6% 7% 8% 11% 47%	2340
	21st to end	Day	7% 4 3 5% 5% 3 6% 7% 7% 9% 43%	2546
August	1st to 10th	Day	8% 4 2 6% 6% 4 6% 5% 8% 9% 41%	2328
	11th to 20th	Day	10% 4 3 5% 5% 4 5% 6% 6% 8% 44%	2222
	21st to end	Day	6% 5% 2 5% 5% 4 5% 5% 7% 9% 48%	2376
September	1st to 10th	Day	12% 5% 2 4 5% 3 4 5% 5% 7% 49%	2160
	11th to 20th	Day	12% 6% 2 4 5% 3 5% 4 5% 8% 47%	2105
	21st to end	Day	8% 4 2 4 4 3 5% 4 5% 7% 54%	1905
October	1st to 10th	Day	9% 4 2 4 4 3 4 4 5% 6% 54%	1800
	11th to 20th	Day	14% 7% 1 3 3 2 3 3 2 5% 56%	1800
	21st to end	Day	18% 7% 2 4 4 2 3 3 3 6% 48%	1980
November	1st to 10th	Day	12% 5% 2 4 3 2 3 3 4 5% 57%	1858
	11th to 20th	Day	12% 5% 2 5% 4 2 4 4 5% 6% 52%	1824
	21st to end	Day	14% 7% 3 5% 5% 2 4 3 5% 5% 48%	1539
December	1st to 10th	Day	13% 9% 2 5% 4 2 3 4 4 6% 47%	1520
	11th to 20th	Day	13% 9% 3 6% 6% 3 4 4 4 5% 43%	1918
	21st to end	Day	11% 18% 5% 7% 5% 4 4 4 4 5% 33%	2985
January	1st to 10th	Night	14% 5% 3 5% 5% 3 3 4 5% 6% 47%	2458
	11th to 20th	Night	13% 8% 3 5% 4 3 4 3 4 6% 48%	2431
	21st to end	Night	14% 7% 4 5% 3 2 3 3 4 5% 50%	2574
February	1st to 10th	Night	14% 10% 4 6% 4 2 3 4 5% 6% 42%	2340
	11th to 20th	Night	15% 7% 4 6% 4 3 4 3 4 5% 46%	2229
	21st to end	Night	15% 9% 3 5% 4 3 3 3 4 5% 46%	1716
March	1st to 10th	Night	15% 8% 3 5% 4 2 4 4 5% 5% 45%	1980
	11th to 20th	Night	17% 10% 3 5% 4 2 4 3 4 5% 42%	1980
	21st to end	Night	16% 8% 4 7% 5% 3 4 4 4 6% 38%	2178
April	1st to 10th	Night	10% 6% 2 4 3 3 4 4 5% 7% 51%	1828
	11th to 20th	Night	12% 7% 3 4 4 2 5% 4 5% 7% 48%	1775
	21st to end	Night	17% 6% 2 5% 5% 3 4 5% 5% 6% 43%	1800
May	1st to 10th	Night	13% 5% 3 5% 3 3 5% 4 5% 7% 48%	1695
	11th to 20th	Night	14% 5% 2 4 4 3 4 4 5% 7% 48%	1593
	21st to end	Night	8% 6% 2 5% 5% 3 6% 5% 7% 11% 42%	1727
June	1st to 10th	Night	7% 4 1 3 3 2 4 4 7% 10% 54%	1440
	11th to 20th	Night	4 3 1 4 3 2 4 4 7% 11% 59%	1440
	21st to end	Night	3 2 1 3 3 3 4 5% 5% 9% 62%	1513
July	1st to 10th	Night	5% 3 2 5% 5% 3 6% 6% 6% 9% 50%	1620
	11th to 20th	Night	4 2 1 2 4 2 4 5% 6% 10% 61%	1620
	21st to end	Night	6% 4 2 5% 5% 3 4 4 7% 8% 52%	1772
August	1st to 10th	Night	5% 3 2 5% 5% 3 4 6% 7% 12% 48%	1611
	11th to 20th	Night	5% 3 2 4 4 3 5% 6% 5% 9% 53%	1678
	21st to end	Night	5% 3 2 4 5% 2 3 5% 6% 8% 56%	1980
September	1st to 10th	Night	9% 3 1 4 3 3 3 4 6% 8% 56%	1800
	11th to 20th	Night	10% 5% 2 5% 5% 3 4 4 4 6% 52%	1852
	21st to end	Night	7% 4 2 4 4 2 3 4 4 7% 59%	2035
October	1st to 10th	Night	6% 4 1 3 4 3 4 4 5% 6% 60%	2160
	11th to 20th	Night	14% 5% 1 4 3 2 3 3 4 6% 55%	2160
	21st to end	Night	15% 7% 3 4 4 2 3 3 4 4 52%	2376
November	1st to 10th	Night	10% 5% 2 3 4 2 3 3 4 5% 59%	2220
	11th to 20th	Night	11% 5% 2 4 3 2 3 4 4 5% 56%	2351
	21st to end	Night	14% 7% 3 3 3 2 4 4 4 6% 50%	2636
December	1st to 10th	Night	14% 8% 3 5% 4 3 3 3 4 7% 47%	2660
	11th to 20th	Night	13% 10% 4 7% 5% 3 4 3 3 5% 44%	3279
	21st to end	Night	14% 12% 6% 7% 6% 3 4 4 4 5% 35%	4661

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	39% 4 9% 26% 19% 4	1708
	11th to 20th	Day	41% 4 9% 25% 19% 2	1674
	21st to end	Day	39% 4 10% 28% 15% 4	1782
February	1st to 10th	Day	47% 4 10% 22% 14% 3	1620
	11th to 20th	Day	44% 4 9% 23% 16% 4	1625
	21st to end	Day	47% 4 8% 19% 14% 8%	1556
March	1st to 10th	Day	41% 4 9% 19% 20% 8%	1980
	11th to 20th	Day	47% 5% 7% 22% 15% 5%	1980
	21st to end	Day	49% 6% 10% 21% 12% 2	2178
April	1st to 10th	Day	38% 6% 12% 24% 19% 2	2130
	11th to 20th	Day	44% 5% 11% 20% 16% 4	2134
	21st to end	Day	48% 6% 8% 22% 15% 2	2160
May	1st to 10th	Day	46% 6% 11% 22% 14% 1	2261
	11th to 20th	Day	39% 9% 14% 25% 13% 1	2306
	21st to end	Day	41% 9% 14% 24% 12% 1	2544
June	1st to 10th	Day	34% 8% 16% 27% 14% 1	2520
	11th to 20th	Day	31% 8% 15% 29% 15% 2	2520
	21st to end	Day	26% 8% 15% 30% 17% 4	2439
July	1st to 10th	Day	36% 10% 17% 22% 13% 2	2276
	11th to 20th	Day	27% 9% 15% 27% 19% 3	2271
	21st to end	Day	34% 9% 16% 29% 11% 1	2405
August	1st to 10th	Day	34% 10% 17% 26% 13% 1	2314
	11th to 20th	Day	35% 8% 13% 28% 15% 1	2222
	21st to end	Day	31% 8% 14% 24% 18% 5%	2376
September	1st to 10th	Day	34% 6% 12% 25% 17% 7%	2160
	11th to 20th	Day	35% 6% 10% 21% 24% 3	2105
	21st to end	Day	29% 5% 8% 27% 26% 4	1905
October	1st to 10th	Day	30% 6% 10% 25% 23% 6%	1800
	11th to 20th	Day	33% 4 6% 24% 26% 8%	1800
	21st to end	Day	39% 3 7% 26% 17% 7%	1980
November	1st to 10th	Day	30% 4 8% 28% 23% 8%	1858
	11th to 20th	Day	33% 4 7% 23% 24% 9%	1824
	21st to end	Day	39% 6% 8% 17% 26% 4	1539
December	1st to 10th	Day	38% 5% 9% 27% 17% 3	1520
	11th to 20th	Day	42% 5% 6% 18% 25% 3	1915
	21st to end	Day	50% 7% 9% 17% 13% 3	2985
January	1st to 10th	Night	37% 5% 9% 24% 21% 4	2458
	11th to 20th	Night	39% 3 10% 26% 19% 3	2431
	21st to end	Night	38% 3 9% 27% 19% 4	2574
February	1st to 10th	Night	44% 4 10% 23% 15% 4	2340
	11th to 20th	Night	42% 4 9% 24% 18% 4	2230
	21st to end	Night	42% 3 8% 21% 18% 8%	1716
March	1st to 10th	Night	40% 4 8% 19% 20% 9%	1980
	11th to 20th	Night	46% 6% 9% 18% 18% 3	1980
	21st to end	Night	46% 7% 9% 23% 14% 2	2178
April	1st to 10th	Night	33% 5% 11% 25% 21% 5%	1828
	11th to 20th	Night	36% 5% 9% 26% 19% 5%	1775
	21st to end	Night	41% 5% 10% 26% 15% 2	1800
May	1st to 10th	Night	37% 6% 12% 25% 17% 3	1695
	11th to 20th	Night	35% 7% 14% 24% 18% 2	1594
	21st to end	Night	36% 9% 17% 24% 13% 1	1728
June	1st to 10th	Night	24% 8% 14% 33% 18% 3	1440
	11th to 20th	Night	19% 7% 16% 35% 20% 3	1440
	21st to end	Night	18% 6% 16% 31% 21% 8%	1513
July	1st to 10th	Night	28% 9% 17% 26% 18% 1	1575
	11th to 20th	Night	19% 7% 14% 33% 25% 3	1566
	21st to end	Night	27% 7% 14% 35% 16% 1	1673
August	1st to 10th	Night	27% 9% 16% 34% 14% 1	1601
	11th to 20th	Night	27% 8% 14% 28% 20% 3	1678
	21st to end	Night	24% 8% 15% 26% 22% 5%	1980
September	1st to 10th	Night	24% 7% 12% 31% 18% 7%	1800
	11th to 20th	Night	34% 5% 10% 20% 25% 5%	1852
	21st to end	Night	27% 4 10% 24% 31% 5%	2035
October	1st to 10th	Night	24% 5% 13% 26% 25% 8%	2160
	11th to 20th	Night	32% 4 7% 21% 29% 7%	2160
	21st to end	Night	37% 4 7% 23% 20% 8%	2376
November	1st to 10th	Night	29% 4 8% 25% 26% 8%	2220
	11th to 20th	Night	31% 3 7% 25% 27% 7%	2351
	21st to end	Night	36% 4 9% 22% 24% 5%	2636
December	1st to 10th	Night	39% 5% 9% 24% 20% 3	2660
	11th to 20th	Night	43% 4 6% 22% 21% 3	3281
	21st to end	Night	49% 7% 9% 20% 12% 3	4661

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% 21% 35% 16% 5%	270
	11th to 20th	Day	29% 24% 35% 11% 2	258
	21st to end	Day	23% 31% 31% 10% 4	264
February	1st to 10th	Day	23% 28% 36% 10% 2	240
	11th to 20th	Day	25% 33% 26% 13% 3	240
	21st to end	Day	36% 24% 31% 8% 2	198
March	1st to 10th	Day	25% 23% 36% 14% 2	240
	11th to 20th	Day	30% 27% 28% 13% 1	240
	21st to end	Day	28% 25% 38% 6% 3	264
April	1st to 10th	Day	19% 22% 34% 17% 7% 1	390
	11th to 20th	Day	24% 18% 33% 17% 8% 1	412
	21st to end	Day	26% 16% 35% 16% 5% 2	420
May	1st to 10th	Day	19% 16% 35% 22% 8%	524
	11th to 20th	Day	16% 11% 32% 26% 14% 2	625
	21st to end	Day	10% 8% 34% 27% 16% 5%	679
June	1st to 10th	Day	10% 4 18% 34% 27% 7%	630
	11th to 20th	Day	6% 3 20% 41% 24% 7%	630
	21st to end	Day	4 4 28% 32% 27% 5%	630
July	1st to 10th	Day	9% 2 15% 30% 34% 10%	621
	11th to 20th	Day	5% 2 16% 30% 34% 12%	618
	21st to end	Day	8% 2 9% 32% 35% 14%	684
August	1st to 10th	Day	9% 3 11% 40% 30% 7%	626
	11th to 20th	Day	13% 2 11% 34% 32% 8%	536
	21st to end	Day	9% 2 11% 30% 32% 16%	495
September	1st to 10th	Day	10% 3 12% 34% 30% 10%	450
	11th to 20th	Day	10% 2 14% 37% 27% 10%	395
	21st to end	Day	9% 7% 25% 29% 23% 6%	270
October	1st to 10th	Day	13% 7% 29% 29% 19% 3	270
	11th to 20th	Day	18% 16% 37% 20% 8% 1	270
	21st to end	Day	30% 16% 30% 17% 6% 1	297
November	1st to 10th	Day	15% 14% 35% 24% 10% 3	270
	11th to 20th	Day	19% 20% 36% 17% 7% 1	270
	21st to end	Day	24% 20% 31% 18% 6% 1	270
December	1st to 10th	Day	20% 27% 30% 15% 6% 3	270
	11th to 20th	Day	26% 20% 30% 19% 6%	270
	21st to end	Day	24% 27% 34% 12% 3	297
January	1st to 10th	Night	19% 21% 33% 23% 4	950
	11th to 20th	Night	20% 21% 34% 21% 3 1	935
	21st to end	Night	18% 21% 36% 22% 3	990
February	1st to 10th	Night	20% 18% 38% 20% 4	900
	11th to 20th	Night	22% 19% 39% 19% 2	835
	21st to end	Night	23% 20% 39% 17% 2	532
March	1st to 10th	Night	21% 14% 36% 25% 3	540
	11th to 20th	Night	22% 15% 31% 29% 3	540
	21st to end	Night	20% 14% 37% 23% 5%	594
April	1st to 10th	Night	14% 18% 37% 26% 5%	540
	11th to 20th	Night	16% 17% 34% 26% 7%	533
	21st to end	Night	20% 12% 36% 25% 7% 1	540
May	1st to 10th	Night	14% 9% 32% 36% 9%	540
	11th to 20th	Night	17% 7% 27% 30% 18% 2	531
	21st to end	Night	11% 4 25% 35% 20% 4	584
June	1st to 10th	Night	9% 4 14% 39% 32% 3	540
	11th to 20th	Night	5% 2 18% 46% 27% 2	540
	21st to end	Night	2 2 21% 44% 29% 3	540
July	1st to 10th	Night	5% 2 10% 37% 40% 6%	525
	11th to 20th	Night	4 1 10% 41% 36% 8%	522
	21st to end	Night	6% 2 6% 42% 36% 8%	591
August	1st to 10th	Night	6% 2 8% 40% 39% 5%	537
	11th to 20th	Night	7% 1 11% 42% 36% 3	534
	21st to end	Night	6% 2 10% 38% 38% 6%	594
September	1st to 10th	Night	9% 2 11% 39% 37% 2	540
	11th to 20th	Night	12% 1 9% 39% 34% 5%	540
	21st to end	Night	9% 4 19% 33% 31% 4	595
October	1st to 10th	Night	8% 4 23% 37% 24% 4	720
	11th to 20th	Night	16% 11% 30% 31% 11%	720
	21st to end	Night	21% 12% 28% 29% 10% 1	792
November	1st to 10th	Night	12% 11% 35% 30% 12% 1	740
	11th to 20th	Night	14% 14% 34% 29% 9%	760
	21st to end	Night	19% 14% 33% 25% 9%	926
December	1st to 10th	Night	19% 13% 36% 26% 6%	950
	11th to 20th	Night	21% 14% 34% 26% 4	950
	21st to end	Night	22% 18% 34% 23% 3	1045

Page generated at 2024-01-14 08:55:01. Version ac07

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