Fox Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fox Observatory clear sky chart from 2005-11-06 to 2026-10-29.

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	7% 5% 2 7% 6% 6% 7% 6% 8% 11% 36%	148083
	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 43%	143968
Transparency	Day	38% 9% 19% 21% 10% 3	151749
	Night	34% 8% 21% 23% 11% 3	148374
Seeing	Day	8% 3 16% 28% 25% 20%	18747
	Night	8% 3 13% 32% 32% 12%	28836

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	6% 5% 2 4 3 3 4 4 6% 10% 54%	5258
	11th to 20th	Day	14% 6% 3 9% 6% 5% 5% 5% 7% 10% 28%	5280
	21st to end	Day	11% 6% 3 8% 5% 5% 5% 4 6% 7% 40%	5882
February	1st to 10th	Day	9% 7% 2 6% 6% 4 5% 4 6% 8% 42%	2100
	11th to 20th	Day	7% 4 1 5% 4 4 5% 4 6% 10% 51%	2170
	21st to end	Day	6% 5% 1 5% 5% 5% 6% 5% 6% 8% 47%	1903
March	1st to 10th	Day	6% 4 2 6% 5% 6% 6% 6% 7% 10% 42%	5045
	11th to 20th	Day	4 3 1 4 3 4 4 4 7% 8% 59%	5090
	21st to end	Day	8% 4 2 6% 5% 5% 5% 5% 7% 9% 43%	5586
April	1st to 10th	Day	5% 3 1 5% 6% 5% 6% 5% 8% 12% 45%	2310
	11th to 20th	Day	7% 4 2 7% 5% 5% 5% 5% 7% 9% 42%	2383
	21st to end	Day	7% 4 2 6% 5% 5% 6% 4 8% 10% 44%	2520
May	1st to 10th	Day	4 3 1 4 4 4 5% 4 7% 10% 53%	7021
	11th to 20th	Day	6% 4 2 6% 5% 6% 7% 6% 9% 10% 40%	7125
	21st to end	Day	5% 4 2 6% 6% 6% 7% 7% 9% 13% 36%	8391
June	1st to 10th	Day	14% 10% 3 12% 9% 7% 8% 5% 8% 7% 17%	2730
	11th to 20th	Day	8% 8% 4 10% 8% 7% 9% 6% 8% 11% 21%	2730
	21st to end	Day	8% 7% 3 10% 9% 8% 9% 7% 9% 9% 21%	2730
July	1st to 10th	Day	5% 6% 3 10% 7% 8% 7% 6% 10% 12% 25%	7680
	11th to 20th	Day	4 5% 2 8% 7% 8% 9% 7% 10% 13% 27%	7680
	21st to end	Day	3 4 2 7% 5% 7% 7% 7% 10% 15% 33%	8340
August	1st to 10th	Day	5% 5% 2 10% 8% 8% 9% 7% 10% 13% 23%	5904
	11th to 20th	Day	4 3 2 6% 6% 7% 8% 6% 9% 13% 36%	5488
	21st to end	Day	4 4 2 7% 7% 8% 10% 8% 12% 16% 22%	5640
September	1st to 10th	Day	8% 6% 4 11% 8% 9% 10% 8% 8% 10% 19%	2310
	11th to 20th	Day	10% 7% 3 10% 9% 8% 8% 5% 9% 11% 20%	2310
	21st to end	Day	12% 8% 4 11% 9% 7% 8% 7% 7% 8% 19%	2310
October	1st to 10th	Day	9% 7% 3 10% 7% 8% 8% 7% 9% 10% 22%	2210
	11th to 20th	Day	10% 5% 3 8% 7% 7% 9% 7% 8% 8% 29%	2100
	21st to end	Day	12% 6% 2 7% 6% 5% 5% 5% 6% 10% 36%	2280
November	1st to 10th	Day	7% 6% 2 7% 6% 5% 7% 5% 7% 9% 39%	2057
	11th to 20th	Day	10% 6% 2 7% 8% 6% 5% 5% 6% 9% 36%	2100
	21st to end	Day	8% 6% 2 6% 5% 6% 7% 5% 7% 9% 41%	2100
December	1st to 10th	Day	6% 4 2 5% 4 3 5% 4 6% 7% 54%	3292
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 4 7% 10% 40%	3463
	21st to end	Day	11% 6% 3 8% 6% 6% 7% 5% 8% 9% 31%	4565
January	1st to 10th	Night	5% 4 2 5% 4 4 4 4 6% 9% 53%	7635
	11th to 20th	Night	13% 8% 4 9% 5% 5% 5% 5% 6% 8% 31%	7680
	21st to end	Night	12% 6% 2 7% 4 4 5% 3 5% 7% 44%	8281
February	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 5% 9% 49%	2520
	11th to 20th	Night	6% 3 1 3 3 4 5% 4 5% 7% 57%	2334
	21st to end	Night	5% 2 2 4 4 4 4 3 5% 8% 60%	1903
March	1st to 10th	Night	5% 4 1 6% 4 4 4 4 7% 9% 52%	5028
	11th to 20th	Night	5% 3 1 5% 3 3 3 3 6% 8% 59%	5090
	21st to end	Night	6% 4 2 5% 4 4 5% 4 6% 8% 50%	5588
April	1st to 10th	Night	4 2 1 4 3 3 4 4 7% 10% 57%	2310
	11th to 20th	Night	6% 3 1 5% 3 4 5% 4 7% 9% 54%	2185
	21st to end	Night	6% 4 2 4 4 4 4 5% 6% 9% 53%	2100
May	1st to 10th	Night	4 3 1 4 3 3 4 4 7% 10% 58%	5833
	11th to 20th	Night	7% 4 2 6% 4 5% 5% 5% 7% 10% 46%	5775
	21st to end	Night	5% 4 2 6% 4 5% 6% 5% 10% 13% 40%	5761
June	1st to 10th	Night	11% 7% 3 9% 7% 7% 6% 7% 7% 10% 26%	1890
	11th to 20th	Night	6% 7% 2 7% 6% 6% 6% 5% 9% 14% 32%	1890
	21st to end	Night	6% 5% 1 7% 6% 5% 7% 6% 10% 14% 32%	1890
July	1st to 10th	Night	5% 5% 2 8% 6% 6% 6% 6% 9% 12% 36%	5278
	11th to 20th	Night	3 4 2 7% 5% 5% 7% 6% 9% 13% 40%	5277
	21st to end	Night	2 3 1 5% 4 4 5% 5% 9% 15% 46%	5736
August	1st to 10th	Night	4 4 2 7% 6% 7% 7% 6% 9% 13% 34%	4182
	11th to 20th	Night	3 3 1 5% 4 5% 6% 5% 8% 13% 47%	4557
	21st to end	Night	3 4 2 6% 6% 7% 8% 7% 12% 16% 29%	5464
September	1st to 10th	Night	7% 6% 2 7% 7% 7% 7% 7% 10% 11% 28%	2310
	11th to 20th	Night	7% 6% 3 9% 6% 6% 6% 5% 9% 12% 29%	2310
	21st to end	Night	9% 6% 3 8% 7% 8% 7% 6% 9% 11% 26%	2310
October	1st to 10th	Night	9% 6% 3 9% 6% 7% 7% 5% 9% 11% 29%	2406
	11th to 20th	Night	8% 6% 3 7% 5% 5% 5% 5% 7% 10% 41%	2520
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 44%	2737
November	1st to 10th	Night	9% 5% 2 5% 4 4 5% 4 6% 8% 48%	2461
	11th to 20th	Night	8% 5% 2 6% 6% 6% 5% 4 6% 8% 43%	2520
	21st to end	Night	7% 5% 2 6% 5% 4 4 5% 6% 9% 48%	2520
December	1st to 10th	Night	6% 4 2 5% 4 3 4 3 5% 8% 57%	4102
	11th to 20th	Night	12% 7% 3 7% 5% 4 4 4 6% 8% 40%	4952
	21st to end	Night	9% 7% 3 9% 7% 6% 5% 5% 7% 9% 32%	6633

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	26% 4 8% 33% 23% 7%	5259
	11th to 20th	Day	49% 6% 13% 19% 8% 3	5280
	21st to end	Day	42% 4 7% 27% 14% 5%	5882
February	1st to 10th	Day	38% 5% 10% 24% 17% 7%	2100
	11th to 20th	Day	28% 4 10% 29% 22% 6%	2180
	21st to end	Day	32% 6% 10% 20% 24% 9%	1903
March	1st to 10th	Day	34% 7% 12% 20% 22% 4	5045
	11th to 20th	Day	22% 4 13% 29% 20% 12%	5090
	21st to end	Day	35% 6% 9% 28% 17% 6%	5586
April	1st to 10th	Day	29% 5% 16% 28% 17% 3	2310
	11th to 20th	Day	35% 6% 15% 20% 17% 6%	2383
	21st to end	Day	33% 6% 10% 26% 22% 4	2520
May	1st to 10th	Day	23% 6% 16% 36% 17% 2	7053
	11th to 20th	Day	34% 8% 20% 30% 7% 1	7129
	21st to end	Day	34% 10% 24% 25% 8%	8405
June	1st to 10th	Day	62% 9% 15% 11% 3	2730
	11th to 20th	Day	53% 12% 19% 13% 2	2730
	21st to end	Day	52% 13% 24% 10% 1	2730
July	1st to 10th	Day	44% 13% 31% 12%	7615
	11th to 20th	Day	42% 12% 31% 14% 1	7611
	21st to end	Day	33% 13% 31% 22% 2	8156
August	1st to 10th	Day	46% 15% 26% 12% 1	5891
	11th to 20th	Day	32% 12% 27% 23% 6%	5524
	21st to end	Day	41% 16% 36% 7%	5640
September	1st to 10th	Day	54% 16% 20% 10% 1	2310
	11th to 20th	Day	53% 14% 21% 10% 2	2310
	21st to end	Day	59% 11% 15% 11% 5% 1	2310
October	1st to 10th	Day	51% 11% 17% 15% 5% 1	3535
	11th to 20th	Day	48% 7% 15% 17% 12% 1	3340
	21st to end	Day	38% 5% 10% 26% 17% 4	3618
November	1st to 10th	Day	38% 6% 12% 20% 18% 7%	2057
	11th to 20th	Day	44% 6% 9% 18% 17% 6%	2100
	21st to end	Day	37% 6% 11% 20% 22% 4	2100
December	1st to 10th	Day	27% 5% 12% 29% 22% 5%	3292
	11th to 20th	Day	37% 6% 12% 21% 19% 4	3460
	21st to end	Day	46% 6% 14% 17% 15% 2	4565
January	1st to 10th	Night	28% 4 12% 32% 19% 5%	7636
	11th to 20th	Night	49% 6% 18% 16% 9% 3	7680
	21st to end	Night	40% 5% 8% 30% 13% 4	8281
February	1st to 10th	Night	31% 5% 12% 28% 18% 6%	2520
	11th to 20th	Night	24% 6% 11% 29% 23% 6%	2335
	21st to end	Night	23% 5% 11% 26% 28% 7%	1903
March	1st to 10th	Night	28% 6% 14% 22% 24% 5%	5028
	11th to 20th	Night	22% 5% 19% 27% 18% 10%	5090
	21st to end	Night	30% 6% 12% 27% 21% 3	5588
April	1st to 10th	Night	21% 5% 18% 35% 17% 3	2310
	11th to 20th	Night	26% 6% 18% 24% 21% 5%	2185
	21st to end	Night	26% 6% 15% 29% 20% 4	2100
May	1st to 10th	Night	20% 5% 23% 37% 13% 2	5863
	11th to 20th	Night	30% 8% 22% 29% 10% 1	5776
	21st to end	Night	30% 11% 31% 24% 5%	5771
June	1st to 10th	Night	50% 11% 22% 15% 2	1890
	11th to 20th	Night	38% 13% 29% 18% 3	1890
	21st to end	Night	38% 15% 34% 12% 1	1890
July	1st to 10th	Night	37% 14% 38% 12%	5235
	11th to 20th	Night	32% 12% 41% 15%	5226
	21st to end	Night	26% 12% 37% 24% 2	5606
August	1st to 10th	Night	39% 14% 32% 13% 1	4171
	11th to 20th	Night	25% 13% 32% 27% 4	4587
	21st to end	Night	36% 19% 39% 6% 1	5464
September	1st to 10th	Night	42% 18% 27% 12% 1	2310
	11th to 20th	Night	44% 16% 26% 12% 2	2310
	21st to end	Night	48% 14% 18% 15% 5%	2310
October	1st to 10th	Night	49% 11% 18% 17% 4 1	3861
	11th to 20th	Night	44% 6% 19% 17% 12% 1	4019
	21st to end	Night	36% 5% 12% 29% 15% 4	4349
November	1st to 10th	Night	33% 5% 14% 23% 18% 7%	2461
	11th to 20th	Night	38% 5% 12% 24% 16% 5%	2520
	21st to end	Night	33% 6% 14% 23% 20% 5%	2520
December	1st to 10th	Night	26% 5% 14% 33% 17% 4	4102
	11th to 20th	Night	40% 6% 11% 22% 16% 5%	4954
	21st to end	Night	46% 8% 15% 16% 14% 2	6633

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	9% 7% 33% 35% 14% 3	330
	11th to 20th	Day	14% 8% 35% 28% 12% 3	330
	21st to end	Day	13% 7% 44% 28% 7% 1	363
February	1st to 10th	Day	9% 7% 28% 38% 14% 4	330
	11th to 20th	Day	7% 4 26% 38% 20% 5%	453
	21st to end	Day	5% 6% 24% 37% 26% 2	446
March	1st to 10th	Day	5% 6% 30% 35% 21% 3	540
	11th to 20th	Day	8% 6% 28% 36% 19% 3	540
	21st to end	Day	5% 3 27% 36% 22% 7%	594
April	1st to 10th	Day	4 5% 31% 32% 21% 6%	540
	11th to 20th	Day	8% 4 27% 33% 21% 7%	532
	21st to end	Day	6% 3 22% 34% 25% 10%	540
May	1st to 10th	Day	4 2 19% 33% 28% 14%	543
	11th to 20th	Day	8% 2 19% 32% 26% 13%	567
	21st to end	Day	10% 3 7% 29% 28% 24%	617
June	1st to 10th	Day	16% 3 7% 24% 28% 22%	570
	11th to 20th	Day	9% 3 5% 22% 28% 33%	570
	21st to end	Day	5% 1 2 18% 26% 47%	570
July	1st to 10th	Day	5% 2 2 13% 29% 48%	565
	11th to 20th	Day	6% 2 1 17% 30% 44%	564
	21st to end	Day	4 3 3 18% 29% 44%	620
August	1st to 10th	Day	7% 2 4 16% 28% 43%	566
	11th to 20th	Day	6% 2 3 16% 29% 45%	559
	21st to end	Day	9% 2 3 19% 30% 36%	627
September	1st to 10th	Day	8% 3 3 14% 28% 44%	570
	11th to 20th	Day	7% 2 5% 16% 28% 42%	570
	21st to end	Day	11% 4 6% 22% 26% 31%	570
October	1st to 10th	Day	11% 3 8% 35% 30% 14%	570
	11th to 20th	Day	11% 1 15% 31% 28% 13%	570
	21st to end	Day	9% 3 19% 36% 24% 8%	615
November	1st to 10th	Day	9% 4 21% 35% 24% 7%	535
	11th to 20th	Day	12% 3 21% 32% 26% 7%	540
	21st to end	Day	6% 3 24% 35% 29% 4	540
December	1st to 10th	Day	10% 4 19% 38% 24% 4	498
	11th to 20th	Day	7% 5% 26% 39% 17% 5%	330
	21st to end	Day	10% 6% 29% 33% 15% 7%	363
January	1st to 10th	Night	8% 4 20% 41% 24% 2	840
	11th to 20th	Night	10% 5% 26% 40% 18% 1	840
	21st to end	Night	9% 6% 27% 43% 14% 1	924
February	1st to 10th	Night	10% 5% 22% 41% 20% 2	840
	11th to 20th	Night	7% 4 23% 43% 22% 1	823
	21st to end	Night	7% 3 21% 48% 21% 1	692
March	1st to 10th	Night	5% 4 27% 44% 19% 1	840
	11th to 20th	Night	8% 4 21% 44% 21% 1	840
	21st to end	Night	7% 3 24% 43% 22% 2	924
April	1st to 10th	Night	5% 3 18% 50% 23% 2	840
	11th to 20th	Night	6% 3 22% 46% 22% 2	831
	21st to end	Night	7% 2 17% 45% 26% 2	840
May	1st to 10th	Night	4 2 15% 45% 32% 2	840
	11th to 20th	Night	9% 2 12% 41% 32% 3	813
	21st to end	Night	8% 2 4 30% 47% 10%	683
June	1st to 10th	Night	11% 2 3 22% 47% 15%	630
	11th to 20th	Night	7% 2 2 13% 47% 30%	630
	21st to end	Night	5% 2 2 9% 44% 38%	630
July	1st to 10th	Night	5% 1 1 8% 42% 43%	615
	11th to 20th	Night	5% 2 8% 46% 38%	612
	21st to end	Night	2 1 6% 46% 44%	690
August	1st to 10th	Night	6% 2 1 8% 47% 36%	648
	11th to 20th	Night	4 2 2 10% 44% 38%	830
	21st to end	Night	8% 2 2 17% 41% 29%	924
September	1st to 10th	Night	8% 2 4 11% 40% 35%	840
	11th to 20th	Night	10% 2 3 15% 43% 28%	840
	21st to end	Night	11% 2 4 19% 42% 22%	840
October	1st to 10th	Night	10% 2 6% 33% 38% 10%	840
	11th to 20th	Night	11% 3 6% 32% 40% 9%	840
	21st to end	Night	12% 2 14% 38% 28% 7%	913
November	1st to 10th	Night	10% 3 19% 36% 29% 4	820
	11th to 20th	Night	9% 2 16% 37% 31% 5%	840
	21st to end	Night	7% 3 17% 43% 28% 3	840
December	1st to 10th	Night	8% 3 14% 40% 33% 3	840
	11th to 20th	Night	10% 4 18% 38% 27% 3	840
	21st to end	Night	8% 2 21% 39% 27% 3	924

Page generated at 2026-10-26 04:37:47. Version ac07

Copyright © 2026 Attilla Danko.