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 2024-11-04.

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 6% 7% 30%	102022
	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 32%	96982
Transparency	Day	51% 6% 12% 20% 10% 1	105611
	Night	50% 6% 12% 20% 11% 1	101470
Seeing	Day	20% 13% 29% 23% 12% 4	14912
	Night	19% 12% 31% 26% 11% 1	23864

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	15% 19% 9% 14% 6% 4 4 3 3 4 20%	2531
	11th to 20th	Day	11% 21% 10% 18% 8% 8% 6% 3 3 3 9%	2840
	21st to end	Day	19% 20% 7% 15% 7% 5% 4 3 4 4 12%	3124
February	1st to 10th	Day	14% 18% 7% 13% 9% 7% 5% 3 3 4 15%	1710
	11th to 20th	Day	13% 12% 7% 15% 8% 6% 5% 4 5% 6% 18%	1663
	21st to end	Day	16% 17% 6% 10% 7% 4 5% 3 5% 6% 20%	1503
March	1st to 10th	Day	20% 15% 5% 9% 6% 4 4 2 4 5% 27%	3398
	11th to 20th	Day	11% 15% 7% 9% 7% 5% 5% 3 5% 6% 27%	3480
	21st to end	Day	16% 12% 3 9% 5% 5% 5% 4 5% 5% 30%	3815
April	1st to 10th	Day	17% 14% 5% 9% 5% 4 4 3 6% 6% 26%	2204
	11th to 20th	Day	19% 11% 3 6% 4 4 4 4 4 6% 34%	2382
	21st to end	Day	21% 10% 3 7% 5% 4 4 3 5% 6% 32%	2470
May	1st to 10th	Day	18% 8% 3 6% 5% 5% 4 4 6% 7% 34%	4108
	11th to 20th	Day	16% 8% 3 9% 5% 5% 5% 5% 5% 8% 31%	4265
	21st to end	Day	14% 6% 2 5% 4 4 4 3 5% 7% 46%	4837
June	1st to 10th	Day	14% 7% 3 6% 5% 5% 5% 5% 7% 8% 35%	2660
	11th to 20th	Day	11% 6% 2 7% 5% 4 6% 5% 7% 9% 39%	2788
	21st to end	Day	15% 6% 2 6% 5% 4 5% 4 6% 9% 37%	2850
July	1st to 10th	Day	11% 5% 3 6% 5% 4 5% 5% 8% 10% 38%	4760
	11th to 20th	Day	10% 5% 2 5% 5% 4 5% 5% 8% 9% 42%	4357
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	4466
August	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 4 7% 9% 35%	4104
	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% 5% 9% 5% 4 4 5% 5% 7% 28%	1647
	11th to 20th	Day	14% 15% 5% 11% 5% 4 6% 4 7% 7% 23%	1520
	21st to end	Day	19% 17% 7% 11% 5% 5% 3 4 5% 6% 17%	1520
December	1st to 10th	Day	14% 23% 8% 13% 7% 5% 4 3 6% 5% 13%	1520
	11th to 20th	Day	18% 19% 6% 13% 6% 5% 5% 3 5% 5% 16%	1906
	21st to end	Day	27% 20% 7% 15% 6% 4 4 2 3 3 8%	2772
January	1st to 10th	Night	16% 18% 8% 15% 6% 5% 5% 4 4 5% 14%	4398
	11th to 20th	Night	14% 15% 9% 16% 11% 9% 7% 4 4 3 9%	4120
	21st to end	Night	20% 15% 9% 13% 6% 5% 4 3 5% 5% 16%	4532
February	1st to 10th	Night	14% 16% 6% 12% 8% 6% 5% 4 6% 5% 18%	2470
	11th to 20th	Night	13% 13% 6% 12% 8% 5% 5% 4 6% 6% 23%	2403
	21st to end	Night	15% 12% 5% 12% 6% 4 4 3 6% 7% 24%	1948
March	1st to 10th	Night	15% 10% 4 9% 5% 5% 4 4 5% 7% 32%	3440
	11th to 20th	Night	10% 10% 4 10% 5% 4 5% 4 5% 7% 36%	3479
	21st to end	Night	16% 9% 3 7% 5% 4 4 4 5% 5% 39%	3817
April	1st to 10th	Night	19% 11% 3 7% 5% 5% 4 3 6% 5% 31%	1975
	11th to 20th	Night	15% 10% 4 7% 5% 4 3 4 5% 6% 37%	1763
	21st to end	Night	15% 9% 3 9% 5% 4 5% 4 5% 8% 34%	1710
May	1st to 10th	Night	16% 8% 2 6% 5% 4 4 3 5% 7% 41%	2833
	11th to 20th	Night	14% 9% 2 7% 5% 4 5% 4 6% 7% 37%	2628
	21st to end	Night	10% 5% 2 6% 3 4 4 3 5% 8% 50%	2738
June	1st to 10th	Night	12% 6% 2 5% 5% 4 5% 4 6% 8% 43%	1520
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 4 8% 9% 42%	1385
	21st to end	Night	12% 6% 2 6% 5% 4 4 4 5% 8% 45%	1330
July	1st to 10th	Night	6% 5% 2 5% 4 4 4 4 6% 9% 53%	2210
	11th to 20th	Night	10% 5% 2 5% 3 3 4 2 4 9% 52%	2595
	21st to end	Night	6% 6% 2 6% 4 5% 5% 4 5% 8% 50%	3087
August	1st to 10th	Night	11% 6% 2 6% 4 3 4 4 6% 7% 46%	2825
	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%	2504
	11th to 20th	Night	15% 14% 4 10% 5% 4 5% 5% 6% 8% 24%	2660
	21st to end	Night	18% 14% 4 8% 7% 4 4 4 6% 7% 23%	2660
December	1st to 10th	Night	19% 18% 7% 12% 6% 5% 5% 4 5% 4 15%	2660
	11th to 20th	Night	15% 18% 7% 13% 5% 5% 4 4 5% 5% 19%	3288
	21st to end	Night	26% 20% 7% 13% 6% 5% 4 3 4 4 9%	4884

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	67% 6% 10% 10% 7%	2532
	11th to 20th	Day	75% 10% 5% 6% 4	2840
	21st to end	Day	76% 6% 7% 7% 4	3124
February	1st to 10th	Day	72% 5% 8% 11% 4 1	1710
	11th to 20th	Day	64% 6% 9% 12% 7% 2	1672
	21st to end	Day	64% 5% 10% 13% 7% 1	1503
March	1st to 10th	Day	60% 5% 10% 16% 8% 1	3401
	11th to 20th	Day	57% 5% 12% 18% 7% 1	3480
	21st to end	Day	51% 8% 11% 18% 10% 2	3815
April	1st to 10th	Day	56% 6% 10% 18% 10%	2204
	11th to 20th	Day	50% 5% 11% 20% 13% 1	2382
	21st to end	Day	53% 5% 11% 18% 11% 2	2470
May	1st to 10th	Day	47% 6% 14% 20% 12% 2	4120
	11th to 20th	Day	50% 8% 15% 20% 7% 1	4269
	21st to end	Day	37% 6% 14% 21% 18% 4	4837
June	1st to 10th	Day	43% 8% 12% 21% 14% 1	2660
	11th to 20th	Day	39% 8% 14% 24% 15% 1	2788
	21st to end	Day	42% 7% 13% 25% 13%	2850
July	1st to 10th	Day	39% 4 17% 23% 15% 2	4686
	11th to 20th	Day	35% 5% 14% 34% 11% 1	4281
	21st to end	Day	37% 7% 15% 23% 18% 1	4324
August	1st to 10th	Day	44% 6% 14% 23% 12% 1	4091
	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% 8% 13% 19% 7% 1	1647
	11th to 20th	Day	58% 9% 12% 13% 7% 1	1520
	21st to end	Day	67% 6% 11% 11% 4	1520
December	1st to 10th	Day	72% 7% 9% 9% 4	1520
	11th to 20th	Day	69% 7% 10% 9% 5%	1906
	21st to end	Day	82% 5% 6% 6% 1	2772
January	1st to 10th	Night	68% 9% 8% 11% 4	4398
	11th to 20th	Night	76% 7% 8% 6% 3	4120
	21st to end	Night	69% 6% 10% 11% 4 1	4532
February	1st to 10th	Night	65% 6% 10% 15% 4 1	2470
	11th to 20th	Night	60% 6% 10% 15% 8% 1	2405
	21st to end	Night	58% 6% 12% 16% 8%	1948
March	1st to 10th	Night	51% 6% 16% 19% 7% 1	3450
	11th to 20th	Night	44% 7% 14% 20% 12% 2	3480
	21st to end	Night	45% 7% 9% 22% 16% 2	3817
April	1st to 10th	Night	53% 5% 9% 19% 14% 1	1975
	11th to 20th	Night	48% 5% 8% 22% 15% 2	1763
	21st to end	Night	49% 5% 10% 20% 15% 2	1710
May	1st to 10th	Night	43% 5% 13% 19% 15% 5%	2840
	11th to 20th	Night	44% 8% 16% 20% 10% 2	2629
	21st to end	Night	31% 6% 14% 23% 22% 3	2739
June	1st to 10th	Night	37% 7% 13% 25% 17% 1	1520
	11th to 20th	Night	35% 7% 14% 26% 18% 2	1385
	21st to end	Night	37% 7% 12% 27% 16% 1	1330
July	1st to 10th	Night	29% 4 15% 26% 21% 5%	2175
	11th to 20th	Night	32% 4 12% 34% 18% 1	2548
	21st to end	Night	32% 7% 15% 29% 16% 2	2988
August	1st to 10th	Night	37% 5% 14% 27% 16% 2	2814
	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	2504
	11th to 20th	Night	56% 7% 13% 15% 7% 1	2660
	21st to end	Night	58% 7% 17% 13% 5% 1	2660
December	1st to 10th	Night	70% 7% 10% 10% 3	2660
	11th to 20th	Night	66% 6% 13% 12% 3	3288
	21st to end	Night	80% 5% 7% 6% 2	4884

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% 31% 16% 6% 1	186
	11th to 20th	Day	22% 23% 38% 14% 3 1	270
	21st to end	Day	26% 20% 34% 16% 4	297
February	1st to 10th	Day	27% 21% 37% 12% 3	270
	11th to 20th	Day	21% 24% 40% 13% 1	270
	21st to end	Day	35% 22% 32% 11% 1	225
March	1st to 10th	Day	25% 15% 36% 18% 6%	437
	11th to 20th	Day	22% 16% 38% 18% 5% 1	460
	21st to end	Day	29% 11% 33% 19% 6% 1	506
April	1st to 10th	Day	22% 20% 31% 20% 6% 1	460
	11th to 20th	Day	29% 17% 25% 17% 9% 3	452
	21st to end	Day	27% 13% 31% 20% 8% 2	460
May	1st to 10th	Day	22% 13% 27% 24% 11% 3	463
	11th to 20th	Day	18% 11% 29% 24% 14% 5%	487
	21st to end	Day	15% 7% 29% 27% 16% 6%	529
June	1st to 10th	Day	15% 13% 28% 29% 12% 3	490
	11th to 20th	Day	13% 10% 28% 31% 16% 3	618
	21st to end	Day	16% 8% 31% 29% 13% 3	680
July	1st to 10th	Day	10% 6% 26% 30% 21% 7%	671
	11th to 20th	Day	15% 5% 24% 27% 21% 8%	488
	21st to end	Day	11% 3 27% 33% 17% 8%	532
August	1st to 10th	Day	13% 6% 22% 27% 22% 11%	486
	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	25% 17% 31% 19% 7% 1	255
	11th to 20th	Day	26% 17% 36% 15% 4 3	180
	21st to end	Day	27% 22% 36% 12% 4	180
December	1st to 10th	Day	30% 21% 33% 14% 3	180
	11th to 20th	Day	27% 28% 29% 14% 1 1	180
	21st to end	Day	29% 24% 34% 11% 2	198
January	1st to 10th	Night	23% 20% 35% 16% 5% 1	760
	11th to 20th	Night	28% 17% 32% 19% 3	760
	21st to end	Night	21% 14% 38% 21% 6%	836
February	1st to 10th	Night	23% 20% 35% 21% 2	760
	11th to 20th	Night	21% 17% 35% 22% 4	743
	21st to end	Night	21% 19% 38% 18% 3	628
March	1st to 10th	Night	18% 15% 39% 22% 5%	760
	11th to 20th	Night	19% 18% 37% 20% 6%	760
	21st to end	Night	21% 13% 34% 22% 9% 1	836
April	1st to 10th	Night	23% 16% 34% 24% 4	760
	11th to 20th	Night	21% 14% 33% 21% 9% 1	639
	21st to end	Night	19% 11% 34% 29% 7%	570
May	1st to 10th	Night	17% 8% 32% 30% 13% 1	570
	11th to 20th	Night	16% 5% 33% 34% 11% 1	455
	21st to end	Night	11% 5% 29% 35% 19%	411
June	1st to 10th	Night	13% 6% 30% 38% 12% 1	380
	11th to 20th	Night	12% 7% 29% 39% 13%	380
	21st to end	Night	14% 5% 28% 37% 16%	380
July	1st to 10th	Night	6% 4 21% 49% 19% 1	370
	11th to 20th	Night	8% 2 30% 36% 23% 1	414
	21st to end	Night	10% 3 20% 44% 22% 1	624
August	1st to 10th	Night	9% 2 23% 38% 26% 2	567
	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	755
	11th to 20th	Night	22% 17% 34% 20% 6% 1	760
	21st to end	Night	25% 15% 35% 20% 4	760
December	1st to 10th	Night	28% 18% 32% 18% 4	760
	11th to 20th	Night	24% 19% 38% 15% 4	760
	21st to end	Night	30% 17% 33% 17% 2	836

Page generated at 2024-11-01 22:47:44. Version ac07

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