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 2024-04-10.

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% 5% 8% 7% 4 5% 5% 5% 7% 29%	83622
	Night	15% 11% 5% 8% 6% 3 5% 5% 5% 6% 30%	85129
Transparency	Day	53% 7% 12% 18% 9% 1	83334
	Night	53% 7% 11% 18% 10% 1	84952
Seeing	Day	20% 13% 29% 23% 12% 4	14058
	Night	19% 12% 31% 26% 10% 1	23233

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	16% 18% 9% 13% 8% 2 4 3 3 4 20%	2531
	11th to 20th	Day	12% 20% 11% 15% 10% 6% 7% 4 3 3 9%	2840
	21st to end	Day	19% 19% 8% 14% 8% 4 5% 4 4 4 12%	3124
February	1st to 10th	Day	15% 17% 7% 11% 11% 6% 6% 4 3 4 16%	1710
	11th to 20th	Day	14% 11% 8% 13% 10% 4 6% 6% 5% 6% 18%	1663
	21st to end	Day	17% 15% 7% 10% 7% 3 6% 4 5% 6% 20%	1503
March	1st to 10th	Day	20% 14% 5% 8% 7% 3 4 3 3 5% 27%	3398
	11th to 20th	Day	11% 14% 8% 8% 8% 4 5% 4 5% 6% 27%	3480
	21st to end	Day	16% 11% 4 8% 7% 4 5% 5% 5% 6% 30%	3815
April	1st to 10th	Day	18% 13% 5% 9% 6% 3 4 4 6% 6% 26%	2194
	11th to 20th	Day	19% 10% 3 5% 5% 3 5% 5% 4 7% 34%	2255
	21st to end	Day	21% 10% 4 6% 6% 3 4 3 5% 7% 31%	2340
May	1st to 10th	Day	17% 8% 3 6% 6% 3 5% 4 6% 8% 33%	2340
	11th to 20th	Day	16% 7% 3 7% 6% 3 5% 5% 4 6% 37%	2401
	21st to end	Day	13% 6% 2 5% 5% 3 5% 5% 6% 8% 41%	2725
June	1st to 10th	Day	14% 6% 3 5% 5% 4 5% 6% 7% 8% 36%	2520
	11th to 20th	Day	11% 6% 2 6% 5% 3 6% 6% 7% 9% 39%	2641
	21st to end	Day	14% 6% 2 6% 5% 3 5% 4 6% 9% 39%	2700
July	1st to 10th	Day	9% 5% 3 5% 5% 3 5% 6% 7% 9% 44%	2700
	11th to 20th	Day	11% 6% 3 5% 6% 3 5% 6% 7% 10% 37%	2479
	21st to end	Day	10% 6% 3 6% 6% 4 6% 5% 7% 10% 37%	2547
August	1st to 10th	Day	9% 5% 2 6% 7% 4 6% 6% 8% 10% 37%	2327
	11th to 20th	Day	10% 7% 3 7% 7% 4 6% 7% 7% 9% 35%	2303
	21st to end	Day	12% 7% 3 5% 5% 4 5% 6% 7% 8% 38%	2516
September	1st to 10th	Day	12% 6% 2 5% 7% 4 5% 5% 6% 8% 39%	2160
	11th to 20th	Day	12% 5% 3 6% 5% 3 5% 5% 5% 9% 41%	1996
	21st to end	Day	15% 8% 3 6% 6% 4 5% 5% 6% 8% 34%	1980
October	1st to 10th	Day	18% 10% 3 8% 6% 3 5% 6% 4 6% 31%	1800
	11th to 20th	Day	23% 10% 4 7% 6% 3 4 4 5% 6% 26%	1800
	21st to end	Day	25% 14% 5% 7% 6% 4 5% 5% 5% 7% 18%	1976
November	1st to 10th	Day	15% 13% 5% 8% 6% 3 5% 6% 5% 7% 28%	1620
	11th to 20th	Day	15% 14% 6% 10% 6% 4 5% 6% 6% 7% 23%	1520
	21st to end	Day	19% 16% 8% 11% 6% 4 4 5% 5% 6% 17%	1520
December	1st to 10th	Day	14% 21% 9% 12% 9% 4 5% 4 6% 5% 13%	1520
	11th to 20th	Day	18% 18% 7% 11% 7% 4 5% 4 5% 5% 16%	1906
	21st to end	Day	27% 20% 8% 13% 7% 3 4 3 3 3 8%	2772
January	1st to 10th	Night	17% 17% 9% 14% 7% 4 5% 5% 4 5% 14%	4398
	11th to 20th	Night	14% 14% 9% 14% 13% 6% 8% 5% 4 3 9%	4120
	21st to end	Night	20% 15% 10% 12% 7% 4 4 4 5% 5% 16%	4532
February	1st to 10th	Night	14% 15% 6% 10% 10% 5% 6% 5% 6% 5% 18%	2470
	11th to 20th	Night	14% 12% 7% 11% 8% 4 5% 5% 5% 6% 23%	2403
	21st to end	Night	15% 11% 5% 11% 8% 3 4 4 6% 7% 25%	1948
March	1st to 10th	Night	15% 9% 5% 8% 6% 4 5% 5% 5% 7% 32%	3440
	11th to 20th	Night	10% 10% 4 9% 6% 3 5% 5% 5% 7% 36%	3479
	21st to end	Night	16% 8% 4 6% 6% 3 4 5% 4 5% 39%	3817
April	1st to 10th	Night	19% 10% 4 7% 6% 3 5% 4 6% 6% 30%	1975
	11th to 20th	Night	15% 9% 4 6% 6% 3 4 5% 5% 6% 38%	1669
	21st to end	Night	15% 9% 4 8% 6% 3 5% 4 5% 8% 34%	1620
May	1st to 10th	Night	15% 8% 2 5% 6% 3 4 5% 6% 7% 37%	1620
	11th to 20th	Night	15% 6% 3 5% 5% 2 4 4 5% 7% 43%	1492
	21st to end	Night	9% 4 2 5% 4 3 5% 4 6% 9% 50%	1550
June	1st to 10th	Night	12% 5% 2 4 6% 3 5% 5% 6% 9% 44%	1440
	11th to 20th	Night	11% 4 3 5% 5% 3 5% 5% 7% 10% 43%	1313
	21st to end	Night	12% 5% 2 5% 6% 3 4 5% 4 8% 46%	1260
July	1st to 10th	Night	5% 3 2 4 3 3 3 5% 6% 8% 58%	1260
	11th to 20th	Night	9% 4 2 5% 5% 3 5% 4 4 10% 48%	1473
	21st to end	Night	7% 6% 2 5% 5% 3 5% 4 6% 8% 49%	1771
August	1st to 10th	Night	8% 6% 2 5% 5% 3 5% 5% 6% 9% 48%	1611
	11th to 20th	Night	7% 5% 2 4 5% 2 4 6% 7% 9% 50%	1598
	21st to end	Night	10% 6% 3 5% 5% 3 5% 5% 5% 7% 47%	1822
September	1st to 10th	Night	10% 5% 3 5% 5% 3 4 5% 5% 8% 46%	1800
	11th to 20th	Night	11% 5% 1 5% 4 2 3 4 5% 7% 51%	1962
	21st to end	Night	15% 8% 3 6% 5% 3 4 3 5% 7% 42%	1980
October	1st to 10th	Night	16% 7% 3 7% 5% 3 4 4 6% 6% 37%	2160
	11th to 20th	Night	19% 9% 3 8% 6% 3 5% 3 5% 6% 32%	2160
	21st to end	Night	22% 10% 4 8% 7% 3 5% 5% 6% 8% 24%	2376
November	1st to 10th	Night	15% 10% 4 6% 6% 4 4 5% 5% 7% 34%	2458
	11th to 20th	Night	15% 13% 4 9% 6% 3 5% 6% 5% 8% 25%	2660
	21st to end	Night	18% 13% 5% 7% 8% 3 5% 5% 5% 7% 24%	2660
December	1st to 10th	Night	19% 16% 8% 11% 7% 3 6% 5% 5% 5% 15%	2660
	11th to 20th	Night	15% 17% 7% 12% 6% 4 4 5% 5% 5% 19%	3288
	21st to end	Night	26% 19% 8% 12% 7% 4 4 4 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	57% 6% 10% 17% 10%	2194
	11th to 20th	Day	49% 5% 11% 20% 13% 1	2255
	21st to end	Day	53% 5% 11% 18% 10% 2	2340
May	1st to 10th	Day	49% 6% 11% 22% 12% 1	2340
	11th to 20th	Day	47% 7% 11% 22% 12% 1	2405
	21st to end	Day	40% 7% 16% 23% 14% 2	2725
June	1st to 10th	Day	42% 7% 13% 21% 15% 1	2520
	11th to 20th	Day	39% 8% 14% 24% 14% 1	2641
	21st to end	Day	41% 7% 13% 25% 14%	2700
July	1st to 10th	Day	34% 6% 15% 25% 17% 2	2626
	11th to 20th	Day	39% 8% 15% 27% 10% 1	2403
	21st to end	Day	40% 9% 14% 23% 13% 2	2405
August	1st to 10th	Day	39% 9% 17% 24% 10% 2	2314
	11th to 20th	Day	42% 8% 18% 22% 10%	2303
	21st to end	Day	41% 8% 14% 24% 11% 1	2516
September	1st to 10th	Day	41% 7% 15% 25% 11% 1	2160
	11th to 20th	Day	37% 6% 15% 29% 12% 1	1996
	21st to end	Day	46% 7% 15% 24% 8% 1	1980
October	1st to 10th	Day	52% 6% 13% 17% 11% 2	1800
	11th to 20th	Day	57% 6% 11% 17% 7% 1	1800
	21st to end	Day	63% 6% 12% 12% 6%	1976
November	1st to 10th	Day	53% 8% 12% 19% 7% 1	1620
	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	54% 5% 9% 18% 14% 1	1975
	11th to 20th	Night	47% 5% 8% 22% 16% 2	1669
	21st to end	Night	49% 4 10% 20% 15% 2	1620
May	1st to 10th	Night	45% 6% 9% 22% 15% 2	1620
	11th to 20th	Night	40% 5% 11% 24% 16% 3	1493
	21st to end	Night	31% 7% 15% 26% 17% 4	1551
June	1st to 10th	Night	36% 7% 13% 25% 18% 1	1440
	11th to 20th	Night	35% 7% 13% 26% 18% 2	1313
	21st to end	Night	36% 8% 13% 27% 16% 1	1260
July	1st to 10th	Night	24% 6% 14% 28% 25% 3	1225
	11th to 20th	Night	32% 5% 13% 31% 17% 1	1426
	21st to end	Night	31% 8% 15% 27% 15% 3	1672
August	1st to 10th	Night	32% 7% 17% 31% 12% 2	1600
	11th to 20th	Night	28% 8% 16% 31% 15% 1	1598
	21st to end	Night	35% 8% 12% 29% 15% 1	1822
September	1st to 10th	Night	35% 8% 14% 27% 14% 1	1800
	11th to 20th	Night	31% 6% 13% 31% 18% 1	1962
	21st to end	Night	43% 5% 14% 27% 12%	1980
October	1st to 10th	Night	46% 7% 10% 21% 15% 1	2160
	11th to 20th	Night	51% 6% 12% 22% 8% 1	2160
	21st to end	Night	56% 7% 11% 17% 8%	2376
November	1st to 10th	Night	47% 8% 13% 21% 11% 1	2458
	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	23% 21% 30% 20% 6% 1	457
	11th to 20th	Day	27% 16% 27% 18% 9% 3	412
	21st to end	Day	27% 12% 31% 20% 8% 2	420
May	1st to 10th	Day	23% 12% 28% 24% 10% 4	423
	11th to 20th	Day	18% 12% 29% 23% 13% 5%	447
	21st to end	Day	15% 7% 27% 27% 16% 7%	485
June	1st to 10th	Day	15% 12% 28% 29% 12% 3	450
	11th to 20th	Day	13% 10% 27% 31% 16% 3	571
	21st to end	Day	15% 7% 32% 30% 13% 3	630
July	1st to 10th	Day	9% 6% 25% 29% 23% 8%	621
	11th to 20th	Day	15% 6% 23% 27% 21% 8%	448
	21st to end	Day	11% 3 28% 35% 16% 7%	488
August	1st to 10th	Day	11% 6% 21% 28% 23% 11%	446
	11th to 20th	Day	12% 5% 21% 27% 23% 13%	439
	21st to end	Day	14% 7% 24% 26% 20% 9%	495
September	1st to 10th	Day	13% 9% 24% 24% 20% 10%	450
	11th to 20th	Day	11% 6% 22% 27% 22% 12%	450
	21st to end	Day	17% 13% 25% 22% 16% 7%	450
October	1st to 10th	Day	21% 13% 25% 21% 14% 6%	450
	11th to 20th	Day	24% 17% 33% 19% 6% 1	450
	21st to end	Day	33% 14% 29% 20% 5%	491
November	1st to 10th	Day	26% 17% 30% 19% 7% 1	246
	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% 33% 24% 4	760
	11th to 20th	Night	20% 13% 34% 22% 10% 1	605
	21st to end	Night	19% 10% 34% 29% 7%	540
May	1st to 10th	Night	17% 8% 31% 29% 13% 1	540
	11th to 20th	Night	16% 5% 33% 34% 10% 1	431
	21st to end	Night	12% 5% 30% 35% 19%	389
June	1st to 10th	Night	12% 6% 31% 39% 13% 1	360
	11th to 20th	Night	12% 6% 30% 39% 13%	360
	21st to end	Night	14% 4 29% 36% 16%	360
July	1st to 10th	Night	6% 4 20% 49% 20% 1	350
	11th to 20th	Night	8% 2 30% 37% 22% 1	391
	21st to end	Night	10% 3 21% 44% 21% 1	591
August	1st to 10th	Night	9% 2 23% 38% 26% 3	537
	11th to 20th	Night	9% 4 16% 39% 28% 4	534
	21st to end	Night	14% 3 24% 31% 25% 3	634
September	1st to 10th	Night	12% 6% 22% 35% 21% 5%	720
	11th to 20th	Night	13% 6% 21% 32% 23% 5%	720
	21st to end	Night	18% 8% 23% 29% 18% 4	720
October	1st to 10th	Night	19% 7% 28% 27% 15% 3	720
	11th to 20th	Night	23% 13% 29% 27% 8% 1	720
	21st to end	Night	27% 14% 31% 24% 5%	792
November	1st to 10th	Night	22% 13% 29% 26% 9% 1	740
	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 2024-04-07 09:28:16. Version ac07

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