Fossil
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fossil clear sky chart from 2005-11-06 to 2025-04-26.

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	8% 9% 3 7% 4 4 4 3 5% 6% 46%	117594
	Night	9% 10% 3 7% 5% 4 4 4 5% 6% 43%	119813
Transparency	Day	36% 6% 11% 20% 17% 9%	117337
	Night	39% 8% 13% 21% 14% 6%	119659
Seeing	Day	13% 13% 26% 27% 17% 5%	15047
	Night	14% 7% 20% 37% 20% 2	24275

By Month

Percentage Cloud Cover SW (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	17% 20% 5% 11% 6% 5% 5% 3 5% 5% 17%	3639
	11th to 20th	Day	13% 13% 4 9% 6% 6% 4 3 4 5% 34%	3640
	21st to end	Day	9% 11% 3 9% 5% 4 4 4 6% 7% 37%	4096
February	1st to 10th	Day	11% 18% 5% 9% 6% 5% 4 4 5% 6% 26%	1800
	11th to 20th	Day	12% 16% 5% 10% 5% 5% 3 5% 5% 6% 28%	1800
	21st to end	Day	11% 17% 4 11% 6% 5% 5% 4 5% 7% 25%	1650
March	1st to 10th	Day	8% 12% 4 11% 6% 5% 6% 5% 7% 8% 28%	4518
	11th to 20th	Day	6% 15% 6% 11% 6% 5% 4 4 4 5% 35%	4899
	21st to end	Day	8% 14% 6% 13% 8% 7% 6% 5% 6% 7% 21%	5832
April	1st to 10th	Day	12% 14% 4 9% 7% 5% 5% 5% 5% 7% 27%	2400
	11th to 20th	Day	10% 14% 4 8% 5% 4 5% 4 5% 5% 38%	2369
	21st to end	Day	9% 12% 3 6% 5% 4 4 5% 6% 7% 39%	2431
May	1st to 10th	Day	11% 11% 3 6% 4 4 4 3 5% 6% 42%	4420
	11th to 20th	Day	7% 5% 2 4 3 3 2 3 4 6% 60%	4377
	21st to end	Day	11% 9% 3 7% 4 4 5% 4 6% 7% 40%	4813
June	1st to 10th	Day	13% 8% 3 6% 5% 4 4 4 6% 7% 41%	2660
	11th to 20th	Day	10% 7% 3 5% 4 4 4 3 5% 6% 48%	2660
	21st to end	Day	5% 4 1 3 2 2 4 3 5% 6% 65%	2660
July	1st to 10th	Day	1 1 1 2 1 1 2 2 3 4 83%	4420
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 81%	4420
	21st to end	Day	2 2 1 2 2 2 2 2 3 4 79%	4790
August	1st to 10th	Day	3 4 1 3 2 2 3 2 4 5% 71%	4372
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 5% 74%	3943
	21st to end	Day	3 3 2 5% 2 2 3 2 4 5% 70%	4180
September	1st to 10th	Day	3 2 1 3 2 2 2 3 4 5% 72%	2280
	11th to 20th	Day	6% 5% 2 5% 4 3 4 3 4 7% 56%	2275
	21st to end	Day	9% 6% 2 6% 3 4 3 3 4 5% 55%	2062
October	1st to 10th	Day	7% 5% 2 5% 4 3 3 3 4 5% 59%	3180
	11th to 20th	Day	6% 6% 3 7% 5% 5% 5% 4 7% 9% 44%	3161
	21st to end	Day	10% 11% 4 8% 6% 6% 5% 4 6% 7% 33%	3177
November	1st to 10th	Day	14% 13% 4 9% 6% 5% 5% 5% 5% 7% 28%	1764
	11th to 20th	Day	15% 13% 3 11% 6% 5% 7% 5% 6% 6% 23%	1654
	21st to end	Day	12% 14% 4 9% 5% 6% 4 4 6% 8% 29%	1600
December	1st to 10th	Day	9% 9% 3 7% 4 4 4 3 5% 6% 46%	2620
	11th to 20th	Day	11% 15% 5% 13% 7% 7% 6% 5% 7% 7% 19%	3028
	21st to end	Day	11% 17% 5% 13% 6% 6% 6% 5% 6% 6% 19%	4004
January	1st to 10th	Night	16% 18% 5% 11% 6% 5% 6% 4 6% 6% 16%	6306
	11th to 20th	Night	14% 15% 4 7% 4 3 4 3 4 7% 35%	6320
	21st to end	Night	9% 13% 4 9% 5% 5% 5% 4 5% 6% 38%	6849
February	1st to 10th	Night	14% 14% 5% 10% 6% 4 5% 5% 5% 6% 26%	2600
	11th to 20th	Night	11% 16% 5% 10% 6% 4 4 4 5% 5% 31%	2487
	21st to end	Night	11% 18% 5% 9% 5% 5% 5% 4 5% 6% 27%	1980
March	1st to 10th	Night	6% 10% 3 9% 6% 5% 6% 6% 7% 8% 33%	5376
	11th to 20th	Night	6% 11% 4 10% 6% 5% 5% 4 6% 6% 37%	5098
	21st to end	Night	8% 14% 5% 12% 7% 7% 6% 5% 7% 7% 22%	5142
April	1st to 10th	Night	11% 14% 4 8% 5% 5% 4 4 5% 7% 34%	2000
	11th to 20th	Night	10% 12% 4 6% 4 4 5% 3 5% 6% 41%	1979
	21st to end	Night	9% 11% 3 6% 5% 5% 5% 4 6% 6% 40%	1861
May	1st to 10th	Night	10% 13% 3 7% 5% 3 3 3 3 5% 44%	2540
	11th to 20th	Night	7% 4 1 4 3 3 2 3 4 5% 64%	2516
	21st to end	Night	11% 9% 2 4 3 4 4 3 5% 7% 49%	2762
June	1st to 10th	Night	12% 7% 2 5% 4 4 3 4 5% 8% 45%	1520
	11th to 20th	Night	10% 8% 2 5% 3 3 3 3 4 7% 51%	1520
	21st to end	Night	5% 4 1 3 3 2 4 2 4 5% 66%	1520
July	1st to 10th	Night	2 1 1 1 1 1 2 3 3 84%	2540
	11th to 20th	Night	1 1 1 3 2 2 2 1 3 4 80%	2540
	21st to end	Night	1 1 1 2 3 2 2 2 3 4 81%	2761
August	1st to 10th	Night	2 3 1 3 3 3 3 3 5% 6% 68%	2555
	11th to 20th	Night	1 2 1 3 2 2 3 2 4 6% 74%	2896
	21st to end	Night	2 3 1 4 2 2 3 3 3 4 74%	3498
September	1st to 10th	Night	3 2 1 3 2 2 2 3 3 5% 75%	1900
	11th to 20th	Night	5% 4 1 4 4 3 4 4 5% 6% 60%	1905
	21st to end	Night	8% 5% 2 5% 3 3 3 3 4 7% 59%	2114
October	1st to 10th	Night	6% 5% 2 4 3 2 2 2 3 5% 64%	3800
	11th to 20th	Night	8% 5% 2 7% 4 5% 5% 3 6% 8% 47%	3777
	21st to end	Night	9% 9% 3 9% 5% 6% 5% 4 5% 7% 37%	4383
November	1st to 10th	Night	14% 13% 4 9% 5% 5% 5% 3 4 6% 32%	2535
	11th to 20th	Night	15% 12% 4 10% 5% 5% 5% 4 5% 6% 28%	2745
	21st to end	Night	11% 12% 4 8% 5% 5% 5% 5% 6% 7% 32%	2800
December	1st to 10th	Night	7% 9% 3 6% 4 4 4 3 5% 7% 48%	4560
	11th to 20th	Night	11% 17% 6% 14% 7% 7% 6% 5% 6% 5% 16%	5176
	21st to end	Night	12% 15% 5% 11% 6% 6% 6% 4 6% 7% 23%	6952

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	63% 12% 13% 11% 2	3639
	11th to 20th	Day	49% 8% 11% 19% 13% 1	3640
	21st to end	Day	44% 10% 13% 14% 14% 5%	4096
February	1st to 10th	Day	55% 8% 16% 14% 6%	1800
	11th to 20th	Day	52% 9% 15% 16% 8% 1	1809
	21st to end	Day	55% 8% 16% 14% 7% 1	1650
March	1st to 10th	Day	45% 8% 13% 21% 10% 3	4518
	11th to 20th	Day	46% 8% 12% 24% 10%	4899
	21st to end	Day	54% 11% 14% 16% 4	5832
April	1st to 10th	Day	51% 8% 14% 17% 9% 1	2400
	11th to 20th	Day	45% 6% 14% 19% 13% 2	2372
	21st to end	Day	40% 7% 14% 25% 12% 2	2431
May	1st to 10th	Day	36% 9% 12% 28% 14% 1	4420
	11th to 20th	Day	24% 4 10% 31% 27% 4	4380
	21st to end	Day	36% 10% 19% 25% 9% 1	4814
June	1st to 10th	Day	41% 7% 11% 26% 14% 2	2660
	11th to 20th	Day	33% 6% 12% 28% 19% 3	2660
	21st to end	Day	20% 4 11% 30% 27% 9%	2660
July	1st to 10th	Day	8% 2 5% 12% 24% 48%	4351
	11th to 20th	Day	9% 2 5% 7% 24% 53%	4345
	21st to end	Day	10% 2 5% 17% 36% 29%	4639
August	1st to 10th	Day	16% 3 5% 14% 38% 25%	4356
	11th to 20th	Day	13% 3 5% 34% 33% 12%	3982
	21st to end	Day	18% 3 7% 28% 26% 18%	4179
September	1st to 10th	Day	14% 2 9% 25% 31% 19%	2280
	11th to 20th	Day	26% 6% 9% 24% 24% 11%	2275
	21st to end	Day	29% 5% 12% 25% 21% 7%	2062
October	1st to 10th	Day	27% 3 8% 23% 29% 9%	3180
	11th to 20th	Day	35% 6% 17% 24% 16% 2	3161
	21st to end	Day	47% 6% 11% 23% 12% 1	3177
November	1st to 10th	Day	52% 7% 13% 19% 7% 1	1764
	11th to 20th	Day	57% 10% 15% 14% 4	1654
	21st to end	Day	51% 7% 18% 16% 7% 1	1600
December	1st to 10th	Day	37% 8% 12% 23% 19% 1	2620
	11th to 20th	Day	62% 10% 16% 11% 1	3028
	21st to end	Day	62% 10% 15% 11% 2	4004
January	1st to 10th	Night	64% 12% 11% 10% 2	6306
	11th to 20th	Night	47% 9% 10% 23% 10% 1	6320
	21st to end	Night	47% 12% 9% 13% 15% 5%	6849
February	1st to 10th	Night	54% 9% 16% 14% 7%	2600
	11th to 20th	Night	52% 7% 15% 18% 7% 1	2489
	21st to end	Night	54% 9% 12% 15% 8% 1	1980
March	1st to 10th	Night	40% 8% 12% 24% 13% 3	5376
	11th to 20th	Night	40% 9% 15% 28% 8%	5098
	21st to end	Night	51% 13% 16% 16% 3	5142
April	1st to 10th	Night	46% 9% 16% 22% 7%	2000
	11th to 20th	Night	41% 7% 16% 22% 11% 2	1979
	21st to end	Night	40% 8% 15% 22% 13% 2	1861
May	1st to 10th	Night	36% 7% 15% 25% 16%	2540
	11th to 20th	Night	21% 5% 13% 38% 22% 1	2516
	21st to end	Night	30% 10% 29% 23% 7% 1	2762
June	1st to 10th	Night	36% 7% 14% 27% 14% 2	1520
	11th to 20th	Night	31% 6% 13% 33% 13% 4	1520
	21st to end	Night	20% 4 12% 32% 25% 7%	1520
July	1st to 10th	Night	7% 2 7% 14% 27% 42%	2500
	11th to 20th	Night	10% 2 6% 12% 19% 50%	2492
	21st to end	Night	9% 2 5% 20% 35% 29%	2674
August	1st to 10th	Night	15% 4 6% 15% 37% 23%	2547
	11th to 20th	Night	12% 3 7% 40% 27% 10%	2923
	21st to end	Night	14% 3 12% 29% 26% 16%	3498
September	1st to 10th	Night	13% 3 9% 28% 30% 17%	1900
	11th to 20th	Night	23% 5% 11% 25% 22% 14%	1905
	21st to end	Night	27% 4 10% 27% 25% 7%	2114
October	1st to 10th	Night	23% 3 10% 24% 34% 5%	3800
	11th to 20th	Night	33% 5% 18% 23% 19% 2	3777
	21st to end	Night	42% 8% 11% 26% 12% 1	4383
November	1st to 10th	Night	51% 7% 11% 21% 9% 1	2535
	11th to 20th	Night	53% 9% 16% 18% 5%	2745
	21st to end	Night	46% 9% 16% 19% 9% 1	2800
December	1st to 10th	Night	35% 8% 11% 25% 21% 1	4560
	11th to 20th	Night	66% 9% 12% 12% 2	5176
	21st to end	Night	57% 11% 17% 12% 3	6952

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	28% 14% 21% 22% 13% 3	200
	11th to 20th	Day	16% 14% 28% 27% 13% 4	200
	21st to end	Day	15% 11% 30% 26% 15% 3	260
February	1st to 10th	Day	26% 15% 24% 25% 8% 2	400
	11th to 20th	Day	22% 14% 30% 21% 11%	418
	21st to end	Day	19% 18% 28% 26% 8% 1	414
March	1st to 10th	Day	20% 19% 27% 26% 9% 1	500
	11th to 20th	Day	18% 19% 25% 23% 12% 3	500
	21st to end	Day	20% 20% 28% 24% 8% 1	550
April	1st to 10th	Day	22% 16% 26% 23% 10% 4	500
	11th to 20th	Day	17% 17% 32% 21% 10% 4	492
	21st to end	Day	12% 19% 31% 21% 14% 3	481
May	1st to 10th	Day	14% 16% 29% 25% 13% 4	463
	11th to 20th	Day	19% 13% 23% 28% 13% 5%	488
	21st to end	Day	14% 13% 23% 25% 18% 7%	529
June	1st to 10th	Day	13% 14% 23% 25% 18% 7%	490
	11th to 20th	Day	13% 19% 27% 25% 13% 3	490
	21st to end	Day	6% 10% 27% 32% 19% 6%	490
July	1st to 10th	Day	1 7% 31% 35% 22% 3	486
	11th to 20th	Day	4 9% 29% 31% 22% 5%	484
	21st to end	Day	2 8% 27% 32% 25% 7%	531
August	1st to 10th	Day	3 8% 27% 33% 19% 10%	487
	11th to 20th	Day	4 6% 21% 32% 26% 12%	477
	21st to end	Day	6% 8% 25% 29% 24% 7%	539
September	1st to 10th	Day	3 7% 23% 32% 25% 10%	490
	11th to 20th	Day	9% 8% 21% 34% 22% 6%	490
	21st to end	Day	12% 9% 22% 30% 23% 4	490
October	1st to 10th	Day	14% 9% 25% 24% 20% 7%	490
	11th to 20th	Day	13% 12% 23% 23% 23% 6%	490
	21st to end	Day	17% 14% 24% 24% 15% 6%	382
November	1st to 10th	Day	16% 18% 22% 28% 15% 2	300
	11th to 20th	Day	19% 15% 19% 27% 16% 4	226
	21st to end	Day	18% 13% 23% 24% 21% 2	200
December	1st to 10th	Day	12% 15% 20% 25% 19% 10%	200
	11th to 20th	Day	25% 12% 31% 25% 8% 1	200
	21st to end	Day	21% 15% 24% 26% 12% 2	220
January	1st to 10th	Night	21% 11% 24% 29% 14% 1	800
	11th to 20th	Night	20% 10% 21% 30% 17% 3	800
	21st to end	Night	18% 7% 20% 35% 18% 1	880
February	1st to 10th	Night	21% 8% 23% 33% 14% 1	800
	11th to 20th	Night	17% 10% 23% 34% 15% 1	784
	21st to end	Night	21% 12% 24% 33% 8% 1	660
March	1st to 10th	Night	16% 10% 24% 36% 14% 1	800
	11th to 20th	Night	14% 9% 22% 39% 16% 1	800
	21st to end	Night	15% 12% 27% 33% 12% 1	880
April	1st to 10th	Night	16% 9% 23% 35% 16% 2	800
	11th to 20th	Night	14% 9% 25% 32% 16% 3	791
	21st to end	Night	14% 9% 25% 33% 18% 2	689
May	1st to 10th	Night	10% 8% 20% 39% 21% 2	380
	11th to 20th	Night	13% 5% 15% 38% 28% 2	374
	21st to end	Night	12% 4 18% 38% 24% 3	411
June	1st to 10th	Night	13% 4 19% 40% 23% 1	380
	11th to 20th	Night	12% 7% 21% 41% 17% 1	380
	21st to end	Night	8% 3 12% 48% 28% 1	380
July	1st to 10th	Night	2 2 11% 50% 33% 2	370
	11th to 20th	Night	2 1 13% 56% 27% 2	368
	21st to end	Night	1 10% 52% 34% 2	416
August	1st to 10th	Night	3 7% 49% 38% 3	391
	11th to 20th	Night	3 1 10% 36% 43% 8%	609
	21st to end	Night	3 3 16% 44% 29% 4	836
September	1st to 10th	Night	4 2 14% 41% 36% 4	760
	11th to 20th	Night	6% 3 12% 39% 33% 7%	760
	21st to end	Night	11% 3 13% 37% 31% 5%	760
October	1st to 10th	Night	13% 2 16% 39% 28% 2	760
	11th to 20th	Night	12% 6% 17% 37% 25% 4	760
	21st to end	Night	16% 7% 20% 36% 17% 4	836
November	1st to 10th	Night	18% 8% 21% 37% 15% 1	780
	11th to 20th	Night	21% 9% 22% 32% 14% 2	800
	21st to end	Night	16% 9% 20% 36% 16% 3	800
December	1st to 10th	Night	18% 8% 20% 35% 17% 3	800
	11th to 20th	Night	22% 9% 22% 33% 13% 1	800
	21st to end	Night	24% 12% 26% 28% 9%	880

Page generated at 2025-04-23 06:25:08. Version ac07

Copyright © 2025 Attilla Danko.