FoxStar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the FoxStar Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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 4 4 5% 7% 44%	74622
	Night	12% 6% 3 5% 4 3 4 4 5% 7% 48%	75122
Transparency	Day	40% 3 13% 26% 15% 2	74345
	Night	38% 3 11% 27% 18% 3	74919
Seeing	Day	15% 9% 28% 28% 16% 4	14500
	Night	15% 9% 32% 31% 12% 1	24478

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% 7% 3 5% 5% 3 5% 4 4 6% 44%	1707
	11th to 20th	Day	14% 11% 4 6% 5% 4 4 5% 3 5% 39%	1638
	21st to end	Day	13% 9% 5% 8% 5% 3 4 4 5% 5% 38%	1782
February	1st to 10th	Day	15% 11% 5% 7% 6% 3 3 3 5% 6% 37%	1620
	11th to 20th	Day	14% 9% 5% 7% 4 3 4 4 4 7% 39%	1574
	21st to end	Day	13% 9% 4 6% 5% 2 4 4 5% 6% 42%	1520
March	1st to 10th	Day	11% 9% 4 8% 6% 3 4 4 5% 6% 40%	1980
	11th to 20th	Day	21% 10% 4 5% 4 2 3 4 4 6% 35%	1980
	21st to end	Day	21% 12% 5% 6% 6% 3 4 4 4 5% 31%	2178
April	1st to 10th	Day	14% 7% 3 5% 4 3 4 4 4 8% 44%	2101
	11th to 20th	Day	15% 8% 3 6% 6% 3 5% 4 4 7% 40%	2134
	21st to end	Day	20% 6% 3 7% 6% 3 5% 5% 4 6% 34%	2251
May	1st to 10th	Day	18% 8% 4 5% 6% 3 5% 4 5% 7% 36%	2340
	11th to 20th	Day	17% 6% 3 5% 6% 2 4 4 5% 6% 40%	2302
	21st to end	Day	14% 8% 3 6% 6% 4 5% 6% 6% 7% 36%	2649
June	1st to 10th	Day	8% 4 2 3 4 3 4 6% 7% 11% 49%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 5% 6% 10% 48%	2520
	21st to end	Day	8% 3 1 4 4 3 4 5% 6% 9% 53%	2520
July	1st to 10th	Day	10% 4 2 4 4 3 5% 5% 8% 10% 46%	2404
	11th to 20th	Day	4 3 2 4 4 3 4 6% 7% 8% 54%	2340
	21st to end	Day	8% 4 3 5% 5% 4 5% 5% 7% 8% 45%	2546
August	1st to 10th	Day	8% 4 2 5% 5% 3 5% 5% 7% 11% 46%	2328
	11th to 20th	Day	8% 4 3 4 5% 3 4 4 6% 10% 49%	2301
	21st to end	Day	8% 4 2 4 4 2 3 4 5% 9% 53%	2405
September	1st to 10th	Day	13% 4 2 4 3 2 3 4 6% 7% 53%	2160
	11th to 20th	Day	10% 4 2 4 4 3 4 5% 5% 7% 52%	2035
	21st to end	Day	9% 4 1 4 4 2 5% 5% 4 6% 56%	1946
October	1st to 10th	Day	12% 5% 2 5% 4 2 4 3 5% 7% 52%	1800
	11th to 20th	Day	14% 6% 2 5% 4 2 3 3 4 6% 54%	1800
	21st to end	Day	17% 7% 2 5% 4 2 4 3 4 6% 46%	1980
November	1st to 10th	Day	10% 6% 2 5% 3 2 3 4 4 7% 54%	1858
	11th to 20th	Day	15% 6% 2 4 3 2 4 4 4 5% 50%	1621
	21st to end	Day	15% 8% 4 5% 4 2 3 3 3 4 47%	1520
December	1st to 10th	Day	11% 8% 2 6% 7% 3 3 4 4 7% 45%	1520
	11th to 20th	Day	12% 9% 4 7% 7% 3 4 3 5% 5% 41%	1918
	21st to end	Day	17% 14% 7% 11% 6% 3 4 4 4 4 27%	2824
January	1st to 10th	Night	9% 9% 3 6% 5% 3 4 4 4 6% 48%	2458
	11th to 20th	Night	13% 8% 4 6% 5% 3 5% 4 5% 6% 40%	2367
	21st to end	Night	10% 9% 4 7% 6% 3 4 4 5% 6% 42%	2574
February	1st to 10th	Night	13% 11% 4 6% 6% 4 5% 4 5% 6% 38%	2340
	11th to 20th	Night	13% 8% 3 6% 6% 2 4 4 5% 7% 42%	2273
	21st to end	Night	15% 7% 3 7% 5% 3 4 4 3 5% 45%	1749
March	1st to 10th	Night	12% 7% 3 5% 4 2 4 4 4 6% 49%	1980
	11th to 20th	Night	17% 8% 3 5% 5% 2 4 4 4 7% 40%	1980
	21st to end	Night	21% 9% 3 6% 5% 3 4 4 4 7% 33%	2178
April	1st to 10th	Night	12% 6% 2 5% 3 2 4 4 4 7% 50%	1859
	11th to 20th	Night	15% 6% 3 5% 4 2 3 4 5% 6% 46%	1775
	21st to end	Night	18% 6% 3 5% 4 3 4 3 4 7% 43%	1706
May	1st to 10th	Night	15% 6% 3 5% 5% 4 5% 5% 4 7% 42%	1620
	11th to 20th	Night	15% 5% 2 4 4 2 4 4 5% 6% 48%	1593
	21st to end	Night	11% 5% 2 5% 6% 3 6% 4 6% 8% 45%	1625
June	1st to 10th	Night	6% 2 1 3 4 3 4 5% 6% 12% 54%	1440
	11th to 20th	Night	6% 3 2 4 5% 3 4 4 6% 12% 50%	1440
	21st to end	Night	5% 2 1 3 4 2 4 5% 6% 10% 60%	1440
July	1st to 10th	Night	9% 2 2 3 3 3 4 5% 6% 11% 52%	1550
	11th to 20th	Night	4 2 1 3 4 2 4 5% 5% 9% 62%	1620
	21st to end	Night	7% 3 2 5% 5% 3 4 5% 6% 10% 51%	1772
August	1st to 10th	Night	4 2 1 3 4 3 5% 5% 6% 11% 56%	1611
	11th to 20th	Night	7% 4 2 4 4 3 4 5% 5% 7% 57%	1600
	21st to end	Night	5% 3 2 4 4 2 3 3 5% 7% 62%	1949
September	1st to 10th	Night	12% 4 2 4 4 2 4 4 4 6% 56%	1800
	11th to 20th	Night	10% 3 2 3 3 2 4 5% 5% 8% 55%	1921
	21st to end	Night	7% 4 2 4 4 3 4 3 4 7% 58%	1995
October	1st to 10th	Night	11% 4 2 4 3 3 4 4 4 5% 57%	2160
	11th to 20th	Night	14% 4 2 4 4 2 3 2 3 5% 56%	2160
	21st to end	Night	17% 6% 2 5% 3 2 3 3 4 4 52%	2376
November	1st to 10th	Night	9% 4 2 3 3 3 3 3 3 6% 61%	2220
	11th to 20th	Night	11% 6% 2 4 4 2 3 4 5% 6% 53%	2554
	21st to end	Night	15% 7% 3 5% 3 3 3 3 4 5% 50%	2660
December	1st to 10th	Night	13% 7% 4 5% 5% 2 4 4 5% 6% 46%	2660
	11th to 20th	Night	12% 8% 3 6% 4 3 4 4 5% 7% 45%	3279
	21st to end	Night	18% 16% 5% 10% 5% 3 3 3 3 4 29%	4838

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	43% 3 10% 25% 17% 1	1708
	11th to 20th	Day	49% 2 11% 26% 12% 1	1638
	21st to end	Day	48% 2 15% 23% 10% 1	1782
February	1st to 10th	Day	50% 3 12% 22% 11% 2	1620
	11th to 20th	Day	47% 3 13% 22% 14% 2	1583
	21st to end	Day	44% 2 11% 24% 16% 2	1520
March	1st to 10th	Day	45% 3 11% 25% 13% 3	1980
	11th to 20th	Day	52% 3 8% 23% 11% 2	1980
	21st to end	Day	57% 2 14% 18% 8% 1	2178
April	1st to 10th	Day	41% 3 13% 25% 16% 2	2101
	11th to 20th	Day	45% 3 13% 24% 15% 1	2134
	21st to end	Day	52% 3 10% 25% 10% 1	2251
May	1st to 10th	Day	50% 4 12% 22% 12% 1	2340
	11th to 20th	Day	45% 4 14% 24% 13%	2306
	21st to end	Day	46% 5% 14% 22% 10% 2	2649
June	1st to 10th	Day	30% 4 18% 33% 14% 1	2520
	11th to 20th	Day	33% 3 15% 30% 18% 1	2520
	21st to end	Day	28% 4 17% 32% 15% 4	2520
July	1st to 10th	Day	34% 4 17% 27% 15% 4	2340
	11th to 20th	Day	26% 5% 18% 30% 19% 3	2271
	21st to end	Day	34% 4 12% 33% 16% 1	2405
August	1st to 10th	Day	32% 5% 19% 29% 13% 1	2314
	11th to 20th	Day	31% 4 13% 34% 17% 2	2301
	21st to end	Day	28% 4 13% 28% 20% 6%	2405
September	1st to 10th	Day	32% 3 13% 28% 19% 6%	2160
	11th to 20th	Day	31% 4 11% 26% 25% 2	2035
	21st to end	Day	30% 3 8% 32% 23% 3	1946
October	1st to 10th	Day	34% 2 11% 29% 21% 3	1800
	11th to 20th	Day	34% 2 6% 30% 23% 4	1800
	21st to end	Day	42% 2 10% 21% 19% 5%	1980
November	1st to 10th	Day	32% 2 13% 28% 20% 5%	1858
	11th to 20th	Day	38% 2 10% 26% 22% 3	1621
	21st to end	Day	43% 1 9% 27% 19% 1	1520
December	1st to 10th	Day	41% 2 13% 29% 14% 1	1520
	11th to 20th	Day	46% 2 13% 27% 10% 2	1915
	21st to end	Day	63% 2 10% 16% 8% 1	2824
January	1st to 10th	Night	39% 3 13% 26% 17% 2	2458
	11th to 20th	Night	45% 3 13% 26% 13% 1	2367
	21st to end	Night	44% 2 14% 25% 13% 2	2574
February	1st to 10th	Night	48% 4 10% 22% 13% 3	2340
	11th to 20th	Night	44% 3 12% 22% 18% 3	2274
	21st to end	Night	43% 2 9% 23% 18% 5%	1749
March	1st to 10th	Night	38% 2 10% 26% 20% 4	1980
	11th to 20th	Night	45% 3 10% 24% 14% 4	1980
	21st to end	Night	53% 3 12% 20% 9% 2	2178
April	1st to 10th	Night	36% 3 10% 27% 20% 4	1859
	11th to 20th	Night	40% 2 8% 30% 17% 4	1775
	21st to end	Night	43% 3 10% 26% 17% 1	1706
May	1st to 10th	Night	43% 4 13% 23% 16% 1	1620
	11th to 20th	Night	37% 4 15% 26% 17% 1	1594
	21st to end	Night	38% 5% 15% 28% 12% 2	1626
June	1st to 10th	Night	23% 4 18% 35% 17% 3	1440
	11th to 20th	Night	29% 4 13% 32% 21% 2	1440
	21st to end	Night	20% 4 15% 36% 20% 4	1440
July	1st to 10th	Night	27% 4 16% 32% 17% 4	1505
	11th to 20th	Night	20% 4 14% 36% 22% 3	1566
	21st to end	Night	27% 4 12% 36% 19% 2	1673
August	1st to 10th	Night	23% 4 21% 34% 16% 3	1601
	11th to 20th	Night	27% 3 11% 34% 23% 2	1600
	21st to end	Night	23% 3 10% 30% 26% 7%	1949
September	1st to 10th	Night	30% 3 10% 28% 21% 7%	1800
	11th to 20th	Night	28% 4 10% 28% 26% 5%	1921
	21st to end	Night	28% 3 7% 29% 28% 5%	1995
October	1st to 10th	Night	31% 2 9% 27% 25% 6%	2160
	11th to 20th	Night	33% 1 6% 30% 22% 8%	2160
	21st to end	Night	38% 2 8% 23% 24% 4	2376
November	1st to 10th	Night	28% 2 13% 28% 24% 6%	2220
	11th to 20th	Night	33% 2 8% 28% 24% 5%	2554
	21st to end	Night	39% 2 9% 29% 18% 3	2660
December	1st to 10th	Night	40% 3 13% 28% 16% 1	2660
	11th to 20th	Night	41% 2 10% 30% 15% 1	3281
	21st to end	Night	62% 2 7% 18% 9% 2	4838

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% 17% 37% 20% 5%	270
	11th to 20th	Day	33% 14% 38% 15% 1	246
	21st to end	Day	14% 15% 51% 17% 3	264
February	1st to 10th	Day	26% 16% 40% 16% 2	240
	11th to 20th	Day	22% 23% 36% 14% 5%	240
	21st to end	Day	19% 26% 37% 12% 5% 1	198
March	1st to 10th	Day	18% 16% 48% 15% 3	240
	11th to 20th	Day	33% 9% 35% 20% 4	240
	21st to end	Day	33% 18% 32% 14% 3	264
April	1st to 10th	Day	19% 17% 39% 17% 7% 1	361
	11th to 20th	Day	19% 16% 35% 22% 7% 1	412
	21st to end	Day	23% 14% 35% 17% 9% 2	511
May	1st to 10th	Day	20% 12% 37% 22% 8% 1	603
	11th to 20th	Day	20% 9% 31% 26% 12% 3	625
	21st to end	Day	16% 7% 28% 28% 16% 4	679
June	1st to 10th	Day	6% 5% 19% 35% 28% 7%	630
	11th to 20th	Day	9% 3 26% 39% 20% 4	630
	21st to end	Day	9% 6% 31% 35% 17% 3	630
July	1st to 10th	Day	13% 2 12% 29% 30% 14%	621
	11th to 20th	Day	4 2 20% 37% 27% 10%	618
	21st to end	Day	8% 3 14% 36% 31% 7%	684
August	1st to 10th	Day	6% 3 16% 39% 29% 6%	626
	11th to 20th	Day	7% 4 16% 37% 29% 6%	615
	21st to end	Day	9% 1 15% 34% 30% 11%	524
September	1st to 10th	Day	14% 3 13% 37% 27% 6%	450
	11th to 20th	Day	5% 4 20% 40% 25% 6%	325
	21st to end	Day	11% 5% 29% 32% 17% 6%	270
October	1st to 10th	Day	15% 8% 29% 26% 17% 6%	270
	11th to 20th	Day	14% 20% 38% 21% 7%	270
	21st to end	Day	23% 18% 31% 23% 4 1	297
November	1st to 10th	Day	17% 9% 39% 24% 7% 4	270
	11th to 20th	Day	17% 18% 32% 23% 9% 1	270
	21st to end	Day	23% 13% 34% 24% 6%	270
December	1st to 10th	Day	12% 17% 41% 21% 6% 4	270
	11th to 20th	Day	23% 14% 37% 20% 5% 1	270
	21st to end	Day	20% 25% 38% 16%	297
January	1st to 10th	Night	14% 13% 39% 27% 7%	950
	11th to 20th	Night	17% 14% 38% 24% 6% 1	911
	21st to end	Night	15% 13% 43% 27% 3	990
February	1st to 10th	Night	18% 13% 44% 22% 4	900
	11th to 20th	Night	19% 13% 38% 27% 4	879
	21st to end	Night	20% 14% 42% 19% 5%	565
March	1st to 10th	Night	16% 13% 42% 24% 5%	540
	11th to 20th	Night	21% 11% 33% 28% 6%	540
	21st to end	Night	27% 10% 37% 23% 4	594
April	1st to 10th	Night	14% 10% 42% 27% 6%	540
	11th to 20th	Night	20% 13% 32% 28% 7%	533
	21st to end	Night	21% 9% 35% 27% 7%	540
May	1st to 10th	Night	18% 8% 33% 33% 7% 1	540
	11th to 20th	Night	16% 5% 29% 34% 14% 1	531
	21st to end	Night	12% 5% 28% 36% 16% 3	584
June	1st to 10th	Night	6% 3 18% 45% 24% 4	540
	11th to 20th	Night	6% 3 24% 46% 19% 2	540
	21st to end	Night	5% 2 30% 47% 15% 1	540
July	1st to 10th	Night	8% 2 11% 39% 35% 4	525
	11th to 20th	Night	4 2 14% 44% 33% 3	522
	21st to end	Night	7% 2 13% 44% 32% 2	591
August	1st to 10th	Night	4 2 12% 48% 34% 1	537
	11th to 20th	Night	8% 3 11% 43% 30% 5%	534
	21st to end	Night	6% 1 13% 41% 37% 3	594
September	1st to 10th	Night	11% 2 18% 41% 23% 5%	540
	11th to 20th	Night	11% 1 20% 38% 25% 5%	540
	21st to end	Night	7% 4 24% 41% 20% 4	555
October	1st to 10th	Night	12% 5% 27% 36% 18% 2	720
	11th to 20th	Night	16% 8% 38% 31% 7%	720
	21st to end	Night	20% 10% 34% 26% 10% 1	792
November	1st to 10th	Night	12% 9% 36% 32% 10% 1	740
	11th to 20th	Night	13% 13% 38% 27% 9%	916
	21st to end	Night	20% 9% 38% 28% 5%	950
December	1st to 10th	Night	17% 11% 38% 27% 6% 1	950
	11th to 20th	Night	19% 10% 39% 27% 5%	950
	21st to end	Night	21% 15% 37% 23% 4	1045

Page generated at 2024-01-10 00:25:00. Version ac07

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