Fergus
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fergus clear sky chart from 2005-11-06 to 2025-08-05.

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	15% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	126618
	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 31%	121431
Transparency	Day	52% 5% 12% 19% 11% 1	130197
	Night	52% 5% 11% 19% 11% 1	125928
Seeing	Day	20% 13% 29% 22% 12% 4	15854
	Night	19% 12% 31% 26% 10% 1	24781

By Month

Percentage Cloud Cover NE (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% 16% 8% 18% 8% 4 4 3 3 4 21%	3625
	11th to 20th	Day	10% 21% 10% 21% 9% 9% 5% 3 3 2 7%	4026
	21st to end	Day	15% 17% 7% 20% 8% 5% 5% 3 4 4 12%	4466
February	1st to 10th	Day	14% 18% 7% 14% 9% 7% 5% 3 3 4 15%	1800
	11th to 20th	Day	14% 12% 7% 15% 9% 6% 5% 4 5% 5% 17%	1753
	21st to end	Day	16% 17% 6% 11% 8% 4 5% 3 5% 6% 19%	1580
March	1st to 10th	Day	19% 12% 5% 11% 7% 4 4 3 4 5% 27%	4884
	11th to 20th	Day	12% 12% 6% 9% 6% 5% 4 4 6% 8% 29%	4980
	21st to end	Day	18% 13% 4 9% 5% 5% 4 3 5% 5% 29%	5465
April	1st to 10th	Day	17% 14% 5% 10% 5% 4 4 3 6% 6% 27%	2320
	11th to 20th	Day	18% 11% 3 6% 4 4 4 4 4 6% 34%	2509
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 5% 6% 32%	2600
May	1st to 10th	Day	18% 10% 3 7% 4 4 4 3 5% 7% 34%	5888
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	6129
	21st to end	Day	19% 7% 2 6% 4 4 4 4 5% 6% 37%	6949
June	1st to 10th	Day	14% 6% 3 6% 5% 5% 5% 5% 7% 8% 35%	2800
	11th to 20th	Day	11% 6% 2 7% 5% 4 6% 5% 7% 9% 38%	2935
	21st to end	Day	15% 6% 2 6% 5% 4 5% 4 6% 9% 37%	3000
July	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 5% 7% 9% 40%	6819
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 7% 9% 45%	6235
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 7% 8% 47%	6424
August	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 4 7% 9% 36%	4156
	11th to 20th	Day	11% 8% 3 8% 5% 5% 6% 5% 8% 9% 32%	4044
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 5% 6% 9% 41%	4418
September	1st to 10th	Day	12% 6% 2 6% 6% 5% 5% 4 6% 8% 40%	2280
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 5% 9% 43%	2106
	21st to end	Day	15% 8% 3 8% 5% 6% 4 4 7% 8% 34%	2089
October	1st to 10th	Day	17% 10% 3 9% 5% 4 5% 4 5% 7% 32%	1900
	11th to 20th	Day	22% 11% 4 8% 6% 4 4 3 5% 6% 28%	1900
	21st to end	Day	24% 14% 4 8% 5% 5% 5% 4 5% 7% 19%	2085
November	1st to 10th	Day	15% 13% 4 9% 5% 4 4 5% 5% 6% 28%	1707
	11th to 20th	Day	14% 15% 5% 11% 5% 4 5% 4 6% 7% 23%	1600
	21st to end	Day	18% 18% 7% 12% 6% 5% 3 4 5% 6% 16%	1600
December	1st to 10th	Day	16% 26% 8% 12% 6% 4 4 3 5% 5% 12%	2600
	11th to 20th	Day	20% 21% 6% 11% 6% 4 4 3 4 4 16%	2986
	21st to end	Day	26% 19% 7% 13% 6% 4 4 3 4 3 11%	3960
January	1st to 10th	Night	13% 14% 6% 15% 7% 5% 5% 3 5% 6% 20%	6304
	11th to 20th	Night	12% 15% 8% 18% 12% 8% 6% 4 4 4 9%	5859
	21st to end	Night	15% 14% 9% 16% 6% 6% 6% 4 5% 5% 15%	6490
February	1st to 10th	Night	13% 16% 6% 12% 8% 6% 5% 4 6% 5% 18%	2600
	11th to 20th	Night	13% 13% 6% 12% 8% 6% 5% 4 5% 6% 22%	2533
	21st to end	Night	14% 12% 5% 13% 7% 4 5% 4 6% 7% 24%	2047
March	1st to 10th	Night	14% 10% 4 11% 6% 5% 5% 4 5% 7% 30%	4954
	11th to 20th	Night	9% 9% 3 9% 5% 5% 6% 5% 7% 9% 35%	4979
	21st to end	Night	20% 9% 3 7% 4 5% 4 3 4 5% 35%	5467
April	1st to 10th	Night	19% 11% 3 8% 5% 5% 3 4 6% 5% 30%	2079
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 5% 5% 37%	1857
	21st to end	Night	15% 9% 3 9% 4 4 5% 4 5% 8% 34%	1800
May	1st to 10th	Night	18% 9% 2 6% 4 5% 4 3 5% 7% 38%	4053
	11th to 20th	Night	14% 9% 2 7% 5% 4 5% 3 5% 6% 38%	3764
	21st to end	Night	17% 6% 3 5% 3 3 4 3 5% 7% 45%	3926
June	1st to 10th	Night	12% 6% 2 5% 5% 4 5% 4 6% 8% 44%	1600
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 4 8% 10% 41%	1458
	21st to end	Night	12% 5% 2 6% 5% 4 4 4 5% 8% 45%	1400
July	1st to 10th	Night	7% 5% 2 5% 4 4 5% 4 6% 8% 50%	3160
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 4 9% 51%	3717
	21st to end	Night	8% 5% 2 5% 4 4 4 3 5% 8% 52%	4428
August	1st to 10th	Night	11% 6% 2 6% 4 3 4 3 5% 7% 47%	2861
	11th to 20th	Night	11% 6% 2 5% 4 4 5% 4 6% 8% 45%	2785
	21st to end	Night	11% 5% 2 6% 3 4 4 3 5% 7% 48%	3206
September	1st to 10th	Night	9% 6% 3 6% 4 5% 4 4 5% 8% 47%	1900
	11th to 20th	Night	10% 5% 1 5% 3 3 4 3 5% 7% 53%	2071
	21st to end	Night	15% 8% 3 7% 4 4 3 3 5% 7% 41%	2090
October	1st to 10th	Night	16% 7% 3 8% 4 5% 4 3 6% 6% 38%	2280
	11th to 20th	Night	18% 9% 3 9% 5% 5% 5% 3 5% 6% 33%	2280
	21st to end	Night	21% 10% 3 8% 6% 4 5% 4 6% 8% 25%	2508
November	1st to 10th	Night	14% 10% 3 7% 5% 5% 5% 4 5% 7% 34%	2591
	11th to 20th	Night	15% 14% 4 10% 5% 4 5% 5% 6% 8% 24%	2800
	21st to end	Night	18% 14% 4 9% 7% 4 4 4 6% 7% 22%	2800
December	1st to 10th	Night	15% 20% 8% 13% 6% 5% 5% 4 5% 5% 14%	4580
	11th to 20th	Night	15% 22% 7% 14% 6% 5% 4 3 4 4 17%	5208
	21st to end	Night	23% 19% 8% 13% 6% 5% 4 3 4 4 12%	6996

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	66% 6% 8% 9% 9% 1	3626
	11th to 20th	Day	80% 7% 5% 5% 3	4060
	21st to end	Day	75% 5% 8% 7% 5%	4466
February	1st to 10th	Day	72% 5% 7% 11% 4 1	1800
	11th to 20th	Day	66% 6% 9% 12% 6% 2	1762
	21st to end	Day	65% 5% 10% 13% 7% 1	1580
March	1st to 10th	Day	60% 4 13% 13% 10% 1	4887
	11th to 20th	Day	53% 4 16% 18% 7% 2	4980
	21st to end	Day	56% 6% 9% 18% 10% 2	5465
April	1st to 10th	Day	56% 6% 10% 18% 10% 1	2320
	11th to 20th	Day	50% 5% 11% 20% 13% 1	2509
	21st to end	Day	52% 5% 11% 19% 11% 2	2600
May	1st to 10th	Day	49% 5% 13% 18% 9% 6%	5897
	11th to 20th	Day	50% 6% 11% 16% 15% 1	6133
	21st to end	Day	46% 5% 12% 19% 14% 4	6949
June	1st to 10th	Day	43% 7% 12% 21% 15% 1	2800
	11th to 20th	Day	39% 8% 14% 24% 14% 1	2935
	21st to end	Day	42% 7% 13% 25% 13%	3000
July	1st to 10th	Day	39% 4 16% 24% 16% 2	6746
	11th to 20th	Day	34% 4 13% 32% 15% 1	6159
	21st to end	Day	33% 5% 14% 29% 18% 1	6240
August	1st to 10th	Day	43% 6% 13% 24% 12% 1	4143
	11th to 20th	Day	45% 6% 16% 24% 9%	4083
	21st to end	Day	38% 6% 13% 31% 10% 1	4418
September	1st to 10th	Day	40% 7% 15% 26% 11% 1	2280
	11th to 20th	Day	36% 6% 15% 29% 13% 1	2106
	21st to end	Day	46% 7% 14% 23% 9%	2089
October	1st to 10th	Day	45% 6% 12% 23% 14% 1	3160
	11th to 20th	Day	45% 5% 13% 21% 16%	3140
	21st to end	Day	55% 4 15% 18% 7%	3411
November	1st to 10th	Day	53% 7% 12% 19% 8% 1	1707
	11th to 20th	Day	58% 8% 12% 14% 7% 1	1600
	21st to end	Day	68% 6% 11% 11% 4	1600
December	1st to 10th	Day	75% 5% 10% 8% 3	2600
	11th to 20th	Day	72% 5% 9% 9% 5%	2986
	21st to end	Day	79% 5% 5% 6% 6%	3960
January	1st to 10th	Night	63% 7% 7% 15% 7%	6304
	11th to 20th	Night	77% 6% 6% 8% 3	5900
	21st to end	Night	70% 5% 9% 10% 5% 1	6490
February	1st to 10th	Night	65% 6% 10% 15% 4 1	2600
	11th to 20th	Night	61% 5% 10% 15% 8% 1	2535
	21st to end	Night	59% 5% 12% 16% 8%	2047
March	1st to 10th	Night	52% 5% 15% 15% 11% 2	4964
	11th to 20th	Night	43% 6% 17% 21% 11% 2	4980
	21st to end	Night	50% 6% 8% 18% 16% 2	5467
April	1st to 10th	Night	54% 5% 9% 18% 13% 1	2079
	11th to 20th	Night	48% 5% 8% 21% 16% 2	1857
	21st to end	Night	48% 5% 10% 20% 15% 2	1800
May	1st to 10th	Night	47% 4 13% 15% 13% 8%	4060
	11th to 20th	Night	45% 7% 14% 19% 14% 2	3765
	21st to end	Night	39% 5% 14% 24% 16% 2	3927
June	1st to 10th	Night	37% 6% 13% 25% 17% 2	1600
	11th to 20th	Night	35% 6% 14% 26% 17% 2	1458
	21st to end	Night	37% 7% 12% 26% 16% 1	1400
July	1st to 10th	Night	32% 3 16% 24% 21% 3	3125
	11th to 20th	Night	33% 4 11% 30% 20% 2	3670
	21st to end	Night	32% 5% 11% 30% 19% 2	4297
August	1st to 10th	Night	36% 5% 13% 28% 16% 2	2850
	11th to 20th	Night	36% 6% 17% 28% 12% 1	2812
	21st to end	Night	35% 6% 11% 32% 15% 1	3206
September	1st to 10th	Night	34% 8% 14% 28% 15% 1	1900
	11th to 20th	Night	29% 6% 13% 31% 20% 1	2071
	21st to end	Night	43% 5% 14% 26% 12%	2090
October	1st to 10th	Night	35% 6% 8% 27% 23% 1	3800
	11th to 20th	Night	45% 4 12% 24% 14%	3779
	21st to end	Night	43% 5% 17% 26% 9%	4120
November	1st to 10th	Night	47% 7% 13% 21% 11% 1	2591
	11th to 20th	Night	57% 7% 13% 15% 7% 1	2800
	21st to end	Night	59% 6% 16% 13% 5% 1	2800
December	1st to 10th	Night	72% 5% 11% 11% 2	4580
	11th to 20th	Night	71% 4 9% 11% 5%	5208
	21st to end	Night	77% 4 7% 7% 5%	6996

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	24% 22% 32% 15% 6% 1	207
	11th to 20th	Day	23% 23% 36% 15% 3 1	300
	21st to end	Day	26% 21% 34% 15% 4	330
February	1st to 10th	Day	28% 22% 35% 12% 3	300
	11th to 20th	Day	25% 24% 38% 12% 1	300
	21st to end	Day	34% 20% 34% 11% 1	249
March	1st to 10th	Day	25% 16% 36% 18% 5%	476
	11th to 20th	Day	22% 17% 37% 18% 5% 1	500
	21st to end	Day	31% 11% 33% 19% 5% 1	550
April	1st to 10th	Day	24% 21% 30% 20% 5% 1	500
	11th to 20th	Day	28% 18% 25% 17% 9% 2	492
	21st to end	Day	27% 14% 31% 19% 8% 1	500
May	1st to 10th	Day	22% 13% 29% 23% 10% 3	503
	11th to 20th	Day	18% 11% 29% 23% 14% 5%	527
	21st to end	Day	17% 8% 29% 26% 15% 6%	573
June	1st to 10th	Day	15% 14% 29% 28% 12% 2	530
	11th to 20th	Day	13% 10% 28% 30% 15% 3	665
	21st to end	Day	16% 8% 31% 30% 12% 3	730
July	1st to 10th	Day	10% 6% 26% 30% 21% 7%	721
	11th to 20th	Day	14% 5% 25% 27% 21% 7%	528
	21st to end	Day	10% 3 28% 33% 17% 8%	576
August	1st to 10th	Day	12% 6% 22% 27% 22% 11%	502
	11th to 20th	Day	13% 6% 20% 27% 21% 13%	479
	21st to end	Day	14% 6% 24% 27% 20% 9%	539
September	1st to 10th	Day	13% 10% 23% 23% 20% 11%	490
	11th to 20th	Day	11% 6% 20% 26% 22% 15%	490
	21st to end	Day	17% 12% 26% 22% 16% 7%	490
October	1st to 10th	Day	21% 13% 27% 22% 13% 6%	490
	11th to 20th	Day	23% 17% 32% 20% 7% 1	490
	21st to end	Day	32% 14% 29% 20% 5%	534
November	1st to 10th	Day	29% 16% 31% 18% 6% 1	273
	11th to 20th	Day	27% 18% 36% 14% 4 3	200
	21st to end	Day	28% 23% 34% 13% 4	200
December	1st to 10th	Day	31% 21% 32% 14% 3	200
	11th to 20th	Day	29% 26% 29% 15% 1 1	200
	21st to end	Day	30% 22% 33% 10% 4	220
January	1st to 10th	Night	23% 20% 36% 16% 5% 1	800
	11th to 20th	Night	28% 17% 33% 19% 3	800
	21st to end	Night	21% 15% 38% 20% 6%	880
February	1st to 10th	Night	23% 20% 35% 20% 2	800
	11th to 20th	Night	22% 17% 35% 21% 4	783
	21st to end	Night	20% 20% 38% 18% 3	660
March	1st to 10th	Night	19% 16% 40% 21% 5%	800
	11th to 20th	Night	18% 18% 38% 20% 6%	800
	21st to end	Night	23% 13% 33% 22% 9% 1	880
April	1st to 10th	Night	23% 16% 34% 24% 3	800
	11th to 20th	Night	22% 14% 33% 21% 9% 1	673
	21st to end	Night	19% 12% 34% 29% 7%	600
May	1st to 10th	Night	17% 8% 32% 29% 13% 1	600
	11th to 20th	Night	16% 6% 33% 34% 11% 1	479
	21st to end	Night	13% 6% 29% 34% 18%	433
June	1st to 10th	Night	13% 6% 31% 38% 12% 1	400
	11th to 20th	Night	12% 7% 30% 39% 12%	400
	21st to end	Night	14% 5% 29% 37% 15%	400
July	1st to 10th	Night	6% 4 21% 50% 18% 1	390
	11th to 20th	Night	8% 3 29% 37% 22% 1	437
	21st to end	Night	10% 3 21% 44% 21% 1	657
August	1st to 10th	Night	9% 2 22% 38% 26% 3	579
	11th to 20th	Night	9% 4 17% 38% 28% 4	564
	21st to end	Night	14% 3 24% 31% 25% 2	670
September	1st to 10th	Night	12% 7% 22% 34% 21% 5%	760
	11th to 20th	Night	12% 6% 20% 32% 26% 5%	760
	21st to end	Night	19% 8% 22% 30% 17% 4	760
October	1st to 10th	Night	19% 7% 28% 28% 15% 3	760
	11th to 20th	Night	22% 13% 28% 27% 9% 1	760
	21st to end	Night	26% 14% 31% 24% 5%	836
November	1st to 10th	Night	22% 13% 29% 26% 8% 1	780
	11th to 20th	Night	22% 17% 34% 20% 6% 1	800
	21st to end	Night	26% 16% 34% 20% 4	800
December	1st to 10th	Night	28% 18% 32% 18% 4	800
	11th to 20th	Night	24% 19% 38% 15% 4	800
	21st to end	Night	30% 17% 33% 18% 2	880

Page generated at 2025-08-02 01:32:23. Version ac07

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