Fennell Auxiliary Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fennell Auxiliary Observatory clear sky chart from 2005-11-06 to 2024-11-12.

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	12% 7% 2 6% 4 4 4 4 5% 7% 43%	100860
	Night	13% 6% 2 5% 4 4 4 3 5% 7% 48%	98374
Transparency	Day	37% 6% 11% 22% 19% 5%	104537
	Night	34% 6% 10% 22% 21% 7%	102838
Seeing	Day	14% 9% 22% 25% 21% 10%	15335
	Night	15% 7% 24% 31% 19% 3	25090

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	15% 14% 4 7% 3 2 2 2 3 4 43%	2687
	11th to 20th	Day	20% 8% 2 6% 4 4 3 3 3 4 42%	2850
	21st to end	Day	22% 10% 3 6% 3 3 3 2 4 4 40%	3135
February	1st to 10th	Day	21% 9% 3 6% 4 3 3 3 4 4 40%	1839
	11th to 20th	Day	21% 8% 3 6% 3 4 4 3 4 5% 39%	1848
	21st to end	Day	23% 9% 3 7% 4 3 4 3 4 4 37%	1570
March	1st to 10th	Day	17% 12% 4 9% 5% 4 4 3 3 5% 34%	3176
	11th to 20th	Day	14% 6% 3 6% 5% 4 5% 4 5% 6% 43%	3480
	21st to end	Day	12% 7% 3 8% 5% 5% 4 3 5% 5% 41%	4032
April	1st to 10th	Day	12% 6% 3 6% 4 5% 4 4 6% 6% 44%	2280
	11th to 20th	Day	16% 6% 2 6% 4 4 3 3 5% 7% 45%	2254
	21st to end	Day	13% 7% 3 7% 5% 4 4 3 6% 7% 42%	2280
May	1st to 10th	Day	13% 6% 3 8% 5% 4 4 4 5% 9% 39%	3765
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	3944
	21st to end	Day	11% 6% 3 7% 6% 6% 5% 5% 7% 9% 35%	4713
June	1st to 10th	Day	7% 5% 2 7% 4 6% 5% 5% 8% 10% 42%	2660
	11th to 20th	Day	4 4 2 6% 5% 5% 5% 5% 7% 10% 48%	2660
	21st to end	Day	4 4 2 5% 4 5% 5% 6% 7% 10% 48%	2660
July	1st to 10th	Day	6% 5% 2 7% 5% 5% 6% 6% 8% 10% 39%	4440
	11th to 20th	Day	8% 5% 2 7% 6% 6% 5% 5% 8% 11% 39%	4197
	21st to end	Day	14% 8% 3 8% 6% 5% 6% 4 6% 8% 31%	4465
August	1st to 10th	Day	3 3 1 4 3 4 4 4 6% 9% 60%	3821
	11th to 20th	Day	5% 4 2 6% 4 5% 6% 4 7% 10% 47%	3729
	21st to end	Day	6% 4 2 6% 4 4 5% 3 6% 7% 52%	4180
September	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 9% 44%	2280
	11th to 20th	Day	13% 5% 2 6% 5% 4 4 3 6% 8% 45%	2230
	21st to end	Day	11% 5% 2 4 3 3 4 3 5% 6% 55%	2090
October	1st to 10th	Day	7% 5% 1 4 4 4 3 3 4 6% 58%	1958
	11th to 20th	Day	12% 4 1 4 3 3 3 3 5% 6% 56%	1900
	21st to end	Day	19% 6% 1 4 2 2 3 3 4 4 53%	2090
November	1st to 10th	Day	12% 6% 2 4 2 2 3 3 3 4 58%	1830
	11th to 20th	Day	13% 6% 2 4 3 3 3 3 4 6% 52%	1719
	21st to end	Day	19% 7% 3 6% 3 3 3 3 4 6% 43%	1710
December	1st to 10th	Day	20% 8% 2 6% 4 4 4 3 5% 5% 39%	1687
	11th to 20th	Day	14% 8% 3 7% 5% 4 4 3 4 4 44%	1918
	21st to end	Day	14% 11% 3 8% 4 5% 4 4 5% 6% 36%	2783
January	1st to 10th	Night	19% 8% 2 5% 4 4 3 2 4 4 45%	4264
	11th to 20th	Night	18% 8% 2 6% 3 3 4 2 3 4 47%	4120
	21st to end	Night	23% 8% 2 5% 3 2 2 2 4 5% 45%	4532
February	1st to 10th	Night	20% 8% 3 7% 4 3 3 2 3 5% 41%	2338
	11th to 20th	Night	19% 9% 3 6% 4 3 3 2 4 4 44%	2218
	21st to end	Night	20% 8% 3 6% 4 3 3 3 4 5% 42%	1884
March	1st to 10th	Night	18% 10% 3 6% 4 4 3 3 4 6% 39%	3705
	11th to 20th	Night	15% 7% 2 5% 4 3 3 3 4 6% 49%	3480
	21st to end	Night	13% 6% 2 6% 5% 4 4 3 6% 7% 44%	3599
April	1st to 10th	Night	11% 6% 2 6% 4 4 4 5% 5% 7% 48%	1900
	11th to 20th	Night	14% 6% 2 5% 3 3 4 4 4 6% 50%	1875
	21st to end	Night	12% 6% 2 6% 4 3 5% 3 4 6% 49%	1900
May	1st to 10th	Night	18% 7% 2 6% 3 3 4 3 5% 8% 40%	3130
	11th to 20th	Night	13% 7% 2 6% 4 4 3 4 5% 7% 46%	2945
	21st to end	Night	10% 5% 3 6% 5% 4 5% 4 7% 10% 40%	2847
June	1st to 10th	Night	7% 5% 2 5% 4 3 5% 5% 8% 10% 46%	1520
	11th to 20th	Night	2 3 1 4 3 3 4 3 8% 9% 60%	1520
	21st to end	Night	3 3 1 4 4 3 4 4 7% 12% 55%	1520
July	1st to 10th	Night	5% 3 2 5% 5% 4 5% 5% 6% 13% 48%	2530
	11th to 20th	Night	6% 4 2 4 4 4 4 4 6% 12% 50%	2768
	21st to end	Night	11% 8% 3 7% 5% 5% 5% 4 6% 8% 39%	3098
August	1st to 10th	Night	2 2 1 2 2 3 3 3 5% 8% 70%	3109
	11th to 20th	Night	3 3 1 5% 3 5% 5% 4 6% 12% 53%	3100
	21st to end	Night	4 3 1 4 3 4 4 3 6% 9% 57%	3476
September	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 6% 6% 52%	1900
	11th to 20th	Night	10% 5% 2 5% 2 4 5% 4 5% 6% 51%	1929
	21st to end	Night	10% 5% 2 4 3 3 3 3 4 6% 58%	2090
October	1st to 10th	Night	6% 3 1 4 2 3 3 3 5% 7% 63%	2218
	11th to 20th	Night	11% 4 2 3 2 2 3 2 4 6% 60%	2280
	21st to end	Night	16% 5% 2 5% 3 3 4 2 3 4 54%	2508
November	1st to 10th	Night	11% 5% 1 4 3 3 4 2 5% 5% 56%	2465
	11th to 20th	Night	11% 5% 2 4 3 4 4 3 4 7% 54%	2484
	21st to end	Night	14% 6% 2 4 4 4 4 3 4 6% 49%	2470
December	1st to 10th	Night	18% 8% 3 6% 4 2 2 3 4 6% 44%	2489
	11th to 20th	Night	16% 7% 2 6% 3 3 3 3 4 5% 48%	3279
	21st to end	Night	15% 8% 2 7% 5% 5% 5% 4 6% 6% 36%	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	46% 3 6% 21% 21% 3	2688
	11th to 20th	Day	44% 6% 8% 22% 19% 1	2850
	21st to end	Day	47% 4 7% 18% 21% 3	3135
February	1st to 10th	Day	48% 5% 8% 21% 16% 3	1839
	11th to 20th	Day	48% 4 7% 18% 18% 5%	1858
	21st to end	Day	50% 4 9% 15% 15% 6%	1570
March	1st to 10th	Day	53% 5% 7% 11% 15% 9%	3176
	11th to 20th	Day	41% 6% 9% 22% 18% 4	3480
	21st to end	Day	44% 5% 8% 22% 20% 1	4032
April	1st to 10th	Day	39% 7% 9% 22% 20% 3	2280
	11th to 20th	Day	39% 5% 8% 21% 20% 6%	2254
	21st to end	Day	40% 7% 9% 23% 19% 2	2280
May	1st to 10th	Day	39% 9% 12% 24% 13% 2	3800
	11th to 20th	Day	37% 10% 17% 21% 13% 1	3948
	21st to end	Day	40% 11% 14% 25% 9% 1	4726
June	1st to 10th	Day	34% 9% 14% 23% 19% 2	2660
	11th to 20th	Day	28% 8% 13% 29% 18% 4	2660
	21st to end	Day	28% 9% 14% 26% 18% 4	2660
July	1st to 10th	Day	36% 8% 17% 26% 12% 2	4371
	11th to 20th	Day	36% 8% 14% 30% 9% 2	4125
	21st to end	Day	50% 7% 13% 23% 6% 1	4325
August	1st to 10th	Day	20% 6% 17% 30% 23% 3	3807
	11th to 20th	Day	30% 7% 17% 27% 16% 2	3765
	21st to end	Day	29% 6% 12% 25% 24% 3	4179
September	1st to 10th	Day	34% 10% 11% 22% 17% 6%	2280
	11th to 20th	Day	37% 7% 11% 15% 24% 6%	2230
	21st to end	Day	30% 5% 9% 23% 24% 8%	2090
October	1st to 10th	Day	17% 4 6% 14% 31% 29%	3257
	11th to 20th	Day	17% 3 4 21% 38% 16%	3140
	21st to end	Day	27% 3 4 26% 31% 10%	3428
November	1st to 10th	Day	31% 3 8% 24% 25% 9%	1830
	11th to 20th	Day	33% 4 9% 20% 26% 8%	1719
	21st to end	Day	42% 4 8% 18% 23% 5%	1710
December	1st to 10th	Day	47% 5% 8% 18% 17% 5%	1687
	11th to 20th	Day	43% 5% 7% 19% 23% 4	1915
	21st to end	Day	45% 7% 11% 20% 14% 2	2783
January	1st to 10th	Night	42% 5% 6% 19% 25% 3	4264
	11th to 20th	Night	42% 5% 7% 20% 21% 5%	4120
	21st to end	Night	44% 3 6% 22% 21% 4	4532
February	1st to 10th	Night	47% 3 8% 18% 20% 4	2338
	11th to 20th	Night	44% 5% 6% 21% 17% 6%	2219
	21st to end	Night	46% 4 8% 15% 21% 7%	1884
March	1st to 10th	Night	46% 6% 10% 13% 16% 10%	3705
	11th to 20th	Night	37% 6% 9% 21% 20% 8%	3480
	21st to end	Night	38% 6% 11% 20% 23% 2	3599
April	1st to 10th	Night	35% 6% 11% 22% 20% 6%	1900
	11th to 20th	Night	35% 4 7% 22% 24% 7%	1875
	21st to end	Night	35% 6% 10% 24% 22% 3	1900
May	1st to 10th	Night	42% 7% 12% 21% 16% 3	3160
	11th to 20th	Night	37% 7% 16% 25% 14% 1	2946
	21st to end	Night	34% 11% 14% 25% 14% 2	2855
June	1st to 10th	Night	29% 11% 13% 23% 23% 2	1520
	11th to 20th	Night	18% 8% 15% 29% 26% 5%	1520
	21st to end	Night	21% 8% 16% 28% 22% 5%	1520
July	1st to 10th	Night	28% 8% 22% 26% 15% 2	2490
	11th to 20th	Night	26% 6% 15% 38% 12% 3	2717
	21st to end	Night	43% 8% 13% 24% 11% 1	2999
August	1st to 10th	Night	13% 6% 12% 41% 25% 3	3099
	11th to 20th	Night	24% 6% 21% 28% 19% 2	3130
	21st to end	Night	24% 6% 13% 24% 29% 4	3476
September	1st to 10th	Night	29% 7% 11% 23% 21% 9%	1900
	11th to 20th	Night	32% 6% 10% 19% 26% 6%	1929
	21st to end	Night	28% 3 10% 24% 25% 9%	2090
October	1st to 10th	Night	15% 3 6% 18% 28% 29%	3699
	11th to 20th	Night	17% 3 4 16% 34% 27%	3779
	21st to end	Night	25% 3 5% 26% 26% 15%	4120
November	1st to 10th	Night	31% 4 7% 22% 28% 9%	2465
	11th to 20th	Night	30% 5% 7% 21% 27% 10%	2484
	21st to end	Night	36% 5% 8% 20% 25% 6%	2470
December	1st to 10th	Night	42% 5% 8% 22% 18% 6%	2489
	11th to 20th	Night	39% 4 8% 21% 24% 5%	3281
	21st to end	Night	42% 7% 12% 19% 15% 4	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	26% 17% 37% 14% 5% 1	270
	11th to 20th	Day	29% 19% 33% 13% 5% 1	270
	21st to end	Day	21% 21% 40% 14% 3	297
February	1st to 10th	Day	27% 17% 34% 14% 7% 1	270
	11th to 20th	Day	35% 18% 31% 13% 3	270
	21st to end	Day	40% 23% 25% 8% 4	225
March	1st to 10th	Day	24% 19% 33% 17% 6% 1	270
	11th to 20th	Day	24% 23% 27% 23% 2	270
	21st to end	Day	21% 16% 34% 19% 9%	425
April	1st to 10th	Day	17% 18% 33% 22% 10%	460
	11th to 20th	Day	21% 15% 32% 21% 9% 3	452
	21st to end	Day	16% 16% 30% 24% 12% 3	460
May	1st to 10th	Day	16% 13% 29% 25% 15% 3	463
	11th to 20th	Day	10% 7% 25% 29% 21% 8%	487
	21st to end	Day	10% 5% 23% 30% 22% 10%	662
June	1st to 10th	Day	9% 5% 15% 27% 28% 15%	680
	11th to 20th	Day	5% 3 13% 34% 33% 13%	680
	21st to end	Day	6% 1 17% 33% 28% 16%	680
July	1st to 10th	Day	7% 2 10% 27% 34% 20%	671
	11th to 20th	Day	7% 1 11% 24% 36% 20%	668
	21st to end	Day	8% 2 8% 29% 32% 21%	739
August	1st to 10th	Day	7% 2 9% 28% 35% 19%	510
	11th to 20th	Day	10% 3 12% 30% 33% 13%	479
	21st to end	Day	11% 2 8% 18% 33% 27%	539
September	1st to 10th	Day	9% 1 12% 28% 33% 16%	490
	11th to 20th	Day	11% 2 13% 20% 36% 19%	490
	21st to end	Day	15% 3 14% 32% 24% 11%	490
October	1st to 10th	Day	7% 5% 21% 33% 27% 8%	358
	11th to 20th	Day	9% 7% 41% 27% 13% 4	300
	21st to end	Day	23% 11% 28% 25% 10% 3	330
November	1st to 10th	Day	19% 10% 26% 28% 15% 2	300
	11th to 20th	Day	11% 14% 38% 28% 9% 1	273
	21st to end	Day	26% 13% 31% 16% 13% 1	270
December	1st to 10th	Day	26% 19% 28% 19% 7% 1	270
	11th to 20th	Day	23% 16% 31% 20% 9% 1	270
	21st to end	Day	22% 23% 32% 18% 5%	297
January	1st to 10th	Night	23% 11% 35% 26% 5%	950
	11th to 20th	Night	25% 14% 32% 25% 3	950
	21st to end	Night	21% 11% 38% 27% 2	1045
February	1st to 10th	Night	25% 12% 33% 26% 4	818
	11th to 20th	Night	24% 14% 32% 26% 3	743
	21st to end	Night	28% 13% 33% 23% 3	628
March	1st to 10th	Night	20% 12% 31% 31% 6%	745
	11th to 20th	Night	22% 10% 35% 27% 6% 1	570
	21st to end	Night	18% 11% 32% 28% 11%	627
April	1st to 10th	Night	14% 10% 37% 29% 9% 1	570
	11th to 20th	Night	18% 9% 32% 28% 12% 1	563
	21st to end	Night	14% 9% 32% 32% 10% 2	570
May	1st to 10th	Night	16% 5% 27% 35% 16% 2	570
	11th to 20th	Night	13% 6% 22% 37% 19% 3	561
	21st to end	Night	7% 2 19% 39% 27% 6%	617
June	1st to 10th	Night	9% 2 11% 38% 34% 6%	570
	11th to 20th	Night	3 1 9% 37% 47% 3	570
	21st to end	Night	4 2 10% 38% 39% 8%	570
July	1st to 10th	Night	4 1 8% 34% 45% 10%	555
	11th to 20th	Night	8% 1 9% 26% 42% 14%	552
	21st to end	Night	6% 1 6% 30% 45% 11%	624
August	1st to 10th	Night	5% 5% 30% 49% 11%	567
	11th to 20th	Night	6% 1 7% 38% 41% 7%	564
	21st to end	Night	7% 2 5% 26% 50% 10%	627
September	1st to 10th	Night	8% 2 7% 34% 44% 5%	570
	11th to 20th	Night	13% 2 11% 30% 38% 8%	599
	21st to end	Night	11% 3 14% 37% 30% 5%	760
October	1st to 10th	Night	8% 3 18% 35% 32% 5%	760
	11th to 20th	Night	13% 5% 23% 39% 18% 2	760
	21st to end	Night	19% 6% 23% 35% 16% 1	836
November	1st to 10th	Night	15% 5% 25% 36% 17% 2	780
	11th to 20th	Night	12% 8% 32% 36% 12%	765
	21st to end	Night	17% 10% 30% 29% 13% 1	760
December	1st to 10th	Night	21% 10% 31% 31% 7%	779
	11th to 20th	Night	23% 9% 29% 32% 8%	950
	21st to end	Night	25% 13% 29% 29% 4	1045

Page generated at 2024-11-08 21:45:38. Version ac07

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