Atwood Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Atwood Observing Site clear sky chart from 2005-11-06 to 2024-12-06.

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	11% 7% 3 6% 4 4 4 4 5% 7% 44%	100927
	Night	10% 7% 3 6% 4 4 4 3 5% 7% 48%	98817
Transparency	Day	37% 6% 11% 23% 18% 5%	104574
	Night	34% 6% 11% 24% 20% 6%	103309
Seeing	Day	16% 14% 29% 24% 14% 3	15544
	Night	16% 14% 28% 27% 14% 2	25384

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	12% 12% 4 6% 3 3 3 3 4 5% 46%	2847
	11th to 20th	Day	8% 8% 2 7% 5% 3 4 3 5% 5% 50%	2850
	21st to end	Day	20% 8% 3 5% 3 2 3 3 4 5% 45%	3135
February	1st to 10th	Day	14% 11% 3 7% 5% 4 3 3 4 5% 41%	1710
	11th to 20th	Day	11% 10% 3 8% 5% 4 3 3 5% 5% 42%	1701
	21st to end	Day	14% 12% 4 6% 4 4 4 3 4 6% 39%	1675
March	1st to 10th	Day	14% 9% 3 7% 4 4 4 3 4 5% 43%	3436
	11th to 20th	Day	11% 7% 2 5% 4 3 4 4 4 7% 48%	3480
	21st to end	Day	14% 10% 3 8% 4 4 4 3 5% 6% 38%	3814
April	1st to 10th	Day	10% 7% 3 7% 5% 4 5% 4 5% 7% 42%	2232
	11th to 20th	Day	14% 8% 3 6% 4 4 5% 3 6% 6% 40%	2254
	21st to end	Day	17% 9% 3 7% 5% 5% 4 3 4 4 38%	2280
May	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 4 6% 6% 34%	3957
	11th to 20th	Day	11% 6% 3 8% 5% 5% 5% 4 6% 7% 38%	4082
	21st to end	Day	13% 7% 3 9% 6% 5% 6% 4 5% 7% 35%	4477
June	1st to 10th	Day	9% 6% 3 6% 5% 5% 5% 4 7% 9% 42%	2513
	11th to 20th	Day	5% 5% 2 7% 6% 5% 5% 6% 7% 9% 43%	2593
	21st to end	Day	4 5% 1 5% 5% 5% 6% 4 7% 9% 49%	2470
July	1st to 10th	Day	10% 5% 2 6% 4 5% 6% 5% 7% 9% 41%	4120
	11th to 20th	Day	5% 4 2 5% 5% 4 5% 4 6% 9% 50%	4120
	21st to end	Day	8% 5% 3 7% 5% 6% 6% 6% 9% 9% 36%	4465
August	1st to 10th	Day	5% 4 1 4 4 4 5% 4 6% 9% 55%	4104
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 7% 8% 44%	3896
	21st to end	Day	5% 4 2 5% 5% 5% 5% 4 6% 8% 53%	4180
September	1st to 10th	Day	11% 6% 2 6% 3 4 4 4 5% 6% 48%	2280
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 6% 8% 44%	2195
	21st to end	Day	8% 4 2 5% 4 4 4 5% 5% 7% 52%	2024
October	1st to 10th	Day	8% 5% 2 5% 4 4 4 3 5% 6% 56%	1900
	11th to 20th	Day	12% 6% 2 5% 3 2 3 2 4 5% 57%	1900
	21st to end	Day	17% 7% 1 5% 3 3 3 3 3 4 50%	2090
November	1st to 10th	Day	10% 7% 2 5% 4 3 2 2 5% 5% 55%	1958
	11th to 20th	Day	9% 8% 2 5% 3 3 4 4 5% 6% 52%	1985
	21st to end	Day	13% 7% 4 6% 4 4 3 3 5% 5% 45%	1619
December	1st to 10th	Day	11% 8% 2 6% 4 4 4 4 4 6% 47%	1560
	11th to 20th	Day	10% 10% 3 8% 5% 4 4 3 4 5% 44%	1918
	21st to end	Day	11% 14% 8% 8% 4 4 4 3 5% 4 33%	3107
January	1st to 10th	Night	10% 8% 5% 9% 5% 5% 5% 3 5% 5% 40%	4108
	11th to 20th	Night	9% 7% 3 6% 4 4 4 3 4 6% 50%	4120
	21st to end	Night	16% 11% 4 6% 3 3 3 3 3 4 43%	4532
February	1st to 10th	Night	14% 10% 3 7% 5% 4 3 3 5% 6% 40%	2470
	11th to 20th	Night	13% 8% 3 6% 4 3 4 4 4 6% 45%	2365
	21st to end	Night	11% 9% 3 7% 4 4 3 3 4 5% 45%	1794
March	1st to 10th	Night	18% 10% 3 6% 3 4 3 3 5% 5% 41%	3419
	11th to 20th	Night	12% 9% 3 5% 3 3 3 3 4 6% 48%	3480
	21st to end	Night	11% 10% 3 8% 5% 4 4 4 5% 6% 40%	3817
April	1st to 10th	Night	9% 8% 3 5% 4 4 4 3 5% 7% 48%	1947
	11th to 20th	Night	12% 9% 2 5% 4 4 3 3 4 6% 49%	1875
	21st to end	Night	16% 7% 3 6% 4 4 3 3 5% 7% 42%	1900
May	1st to 10th	Night	14% 8% 2 7% 4 3 4 4 5% 7% 43%	2929
	11th to 20th	Night	11% 8% 2 8% 4 4 5% 4 7% 8% 39%	2823
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 8% 40%	3090
June	1st to 10th	Night	7% 4 1 4 3 4 3 4 5% 10% 54%	1647
	11th to 20th	Night	4 3 1 3 3 3 3 3 7% 12% 57%	1565
	21st to end	Night	3 3 1 4 3 3 4 3 6% 8% 61%	1710
July	1st to 10th	Night	9% 5% 2 6% 5% 4 4 3 6% 8% 49%	2850
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 7% 65%	2850
	21st to end	Night	7% 7% 3 6% 5% 4 4 5% 6% 8% 44%	3098
August	1st to 10th	Night	3 2 1 3 3 3 4 4 7% 9% 61%	2836
	11th to 20th	Night	5% 4 2 5% 4 4 4 3 6% 9% 53%	2935
	21st to end	Night	4 3 1 3 4 3 3 3 5% 9% 62%	3476
September	1st to 10th	Night	8% 4 2 4 2 3 3 3 5% 8% 58%	1900
	11th to 20th	Night	11% 6% 2 6% 4 3 4 4 5% 6% 50%	1981
	21st to end	Night	7% 6% 2 5% 3 3 4 3 5% 6% 57%	2136
October	1st to 10th	Night	5% 4 2 5% 2 3 3 3 5% 8% 60%	2280
	11th to 20th	Night	11% 5% 2 4 3 3 3 2 4 5% 59%	2280
	21st to end	Night	14% 8% 2 4 2 3 3 3 3 5% 52%	2508
November	1st to 10th	Night	11% 7% 2 4 3 3 2 3 4 4 57%	2340
	11th to 20th	Night	10% 6% 2 4 3 2 4 3 5% 6% 55%	2410
	21st to end	Night	12% 8% 2 4 3 3 3 3 5% 6% 49%	2778
December	1st to 10th	Night	12% 9% 3 6% 3 3 3 3 4 6% 48%	2737
	11th to 20th	Night	10% 11% 3 8% 5% 4 5% 3 5% 4 43%	3279
	21st to end	Night	13% 12% 8% 8% 5% 4 4 3 4 5% 33%	4552

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	40% 4 7% 23% 22% 3	2848
	11th to 20th	Day	34% 5% 12% 24% 20% 4	2850
	21st to end	Day	42% 4 8% 20% 19% 7%	3135
February	1st to 10th	Day	46% 6% 8% 21% 15% 4	1710
	11th to 20th	Day	45% 5% 8% 21% 17% 5%	1710
	21st to end	Day	47% 4 8% 16% 16% 9%	1675
March	1st to 10th	Day	43% 5% 7% 17% 17% 11%	3436
	11th to 20th	Day	36% 6% 10% 24% 20% 5%	3480
	21st to end	Day	47% 5% 10% 22% 15% 1	3814
April	1st to 10th	Day	40% 7% 11% 20% 19% 3	2232
	11th to 20th	Day	44% 7% 9% 19% 17% 4	2254
	21st to end	Day	48% 6% 8% 22% 14% 2	2280
May	1st to 10th	Day	49% 7% 9% 20% 14% 1	3992
	11th to 20th	Day	41% 10% 11% 25% 12% 1	4086
	21st to end	Day	46% 8% 12% 19% 14% 1	4489
June	1st to 10th	Day	37% 9% 15% 26% 12% 1	2513
	11th to 20th	Day	33% 9% 14% 27% 15% 2	2593
	21st to end	Day	29% 8% 15% 27% 16% 4	2470
July	1st to 10th	Day	37% 7% 17% 25% 12% 2	4056
	11th to 20th	Day	28% 7% 13% 34% 17% 2	4051
	21st to end	Day	39% 8% 19% 25% 8%	4325
August	1st to 10th	Day	25% 7% 16% 29% 18% 5%	4090
	11th to 20th	Day	37% 6% 16% 28% 12% 1	3935
	21st to end	Day	29% 7% 14% 33% 13% 3	4179
September	1st to 10th	Day	35% 6% 11% 22% 17% 8%	2280
	11th to 20th	Day	37% 7% 10% 20% 23% 3	2195
	21st to end	Day	31% 5% 11% 24% 25% 4	2024
October	1st to 10th	Day	18% 3 6% 14% 38% 20%	3160
	11th to 20th	Day	20% 3 4 20% 36% 18%	3140
	21st to end	Day	29% 4 9% 30% 22% 5%	3428
November	1st to 10th	Day	33% 4 8% 25% 22% 9%	1958
	11th to 20th	Day	33% 5% 8% 21% 23% 10%	1985
	21st to end	Day	40% 4 8% 18% 24% 5%	1619
December	1st to 10th	Day	38% 6% 9% 25% 19% 5%	1560
	11th to 20th	Day	42% 5% 7% 15% 27% 4	1915
	21st to end	Day	50% 6% 9% 16% 14% 4	3107
January	1st to 10th	Night	44% 5% 8% 18% 23% 3	4108
	11th to 20th	Night	33% 7% 13% 23% 21% 4	4120
	21st to end	Night	45% 3 9% 19% 18% 5%	4532
February	1st to 10th	Night	44% 5% 9% 21% 16% 4	2470
	11th to 20th	Night	41% 5% 9% 22% 18% 5%	2366
	21st to end	Night	41% 5% 8% 18% 20% 8%	1794
March	1st to 10th	Night	44% 6% 8% 15% 17% 10%	3419
	11th to 20th	Night	36% 6% 9% 27% 18% 4	3480
	21st to end	Night	43% 6% 11% 25% 14% 1	3817
April	1st to 10th	Night	35% 6% 10% 23% 20% 6%	1947
	11th to 20th	Night	37% 5% 8% 24% 20% 5%	1875
	21st to end	Night	41% 7% 11% 25% 15% 2	1900
May	1st to 10th	Night	41% 6% 13% 22% 15% 3	2958
	11th to 20th	Night	39% 9% 16% 24% 12% 1	2824
	21st to end	Night	40% 9% 15% 23% 12% 1	3099
June	1st to 10th	Night	25% 7% 16% 33% 17% 2	1647
	11th to 20th	Night	18% 9% 15% 36% 19% 2	1565
	21st to end	Night	21% 7% 16% 29% 22% 6%	1710
July	1st to 10th	Night	32% 7% 21% 21% 15% 3	2805
	11th to 20th	Night	19% 5% 13% 40% 22% 2	2796
	21st to end	Night	34% 8% 16% 31% 10%	2999
August	1st to 10th	Night	19% 6% 18% 34% 22% 1	2826
	11th to 20th	Night	27% 7% 21% 28% 16% 1	2962
	21st to end	Night	21% 5% 15% 37% 19% 3	3476
September	1st to 10th	Night	26% 6% 13% 29% 18% 8%	1900
	11th to 20th	Night	34% 6% 11% 21% 24% 4	1981
	21st to end	Night	28% 5% 11% 22% 29% 5%	2136
October	1st to 10th	Night	14% 4 7% 14% 35% 27%	3800
	11th to 20th	Night	19% 2 5% 17% 34% 22%	3779
	21st to end	Night	28% 3 6% 30% 23% 9%	4120
November	1st to 10th	Night	32% 4 8% 23% 24% 9%	2340
	11th to 20th	Night	29% 5% 8% 22% 26% 9%	2410
	21st to end	Night	36% 5% 9% 21% 24% 5%	2778
December	1st to 10th	Night	38% 5% 9% 22% 21% 5%	2737
	11th to 20th	Night	44% 5% 7% 20% 20% 5%	3281
	21st to end	Night	52% 5% 9% 17% 14% 3	4552

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% 26% 31% 16% 2	270
	11th to 20th	Day	25% 31% 34% 9% 1	270
	21st to end	Day	24% 31% 32% 10% 3	297
February	1st to 10th	Day	30% 26% 33% 9% 1	270
	11th to 20th	Day	32% 29% 29% 9% 1	270
	21st to end	Day	40% 29% 25% 5% 1	225
March	1st to 10th	Day	26% 23% 36% 14% 1	270
	11th to 20th	Day	34% 23% 31% 11% 1	270
	21st to end	Day	29% 33% 27% 9% 2	297
April	1st to 10th	Day	23% 27% 31% 14% 4 1	412
	11th to 20th	Day	26% 24% 31% 14% 5%	452
	21st to end	Day	27% 23% 31% 14% 5% 1	460
May	1st to 10th	Day	21% 21% 37% 16% 4	577
	11th to 20th	Day	15% 16% 35% 24% 8% 2	675
	21st to end	Day	13% 14% 38% 21% 12% 3	734
June	1st to 10th	Day	10% 8% 25% 33% 21% 3	680
	11th to 20th	Day	5% 5% 32% 35% 20% 3	680
	21st to end	Day	4 5% 36% 34% 18% 3	680
July	1st to 10th	Day	9% 3 22% 32% 27% 6%	671
	11th to 20th	Day	5% 3 23% 36% 27% 7%	668
	21st to end	Day	8% 2 17% 35% 31% 9%	739
August	1st to 10th	Day	8% 3 19% 40% 25% 4	676
	11th to 20th	Day	13% 3 16% 37% 27% 5%	585
	21st to end	Day	7% 3 16% 32% 31% 12%	539
September	1st to 10th	Day	10% 4 18% 33% 27% 7%	490
	11th to 20th	Day	10% 5% 21% 38% 20% 7%	405
	21st to end	Day	12% 9% 30% 29% 18% 3	300
October	1st to 10th	Day	11% 10% 33% 31% 13% 3	300
	11th to 20th	Day	15% 18% 43% 17% 6% 1	300
	21st to end	Day	31% 12% 36% 16% 4 1	330
November	1st to 10th	Day	17% 22% 36% 16% 7% 2	300
	11th to 20th	Day	20% 24% 35% 16% 4 1	300
	21st to end	Day	27% 21% 31% 16% 4 1	300
December	1st to 10th	Day	20% 32% 29% 13% 5% 1	285
	11th to 20th	Day	24% 25% 34% 12% 5%	270
	21st to end	Day	26% 29% 34% 10% 2	297
January	1st to 10th	Night	20% 21% 34% 20% 4	950
	11th to 20th	Night	21% 26% 33% 17% 3	950
	21st to end	Night	18% 24% 34% 21% 3	1045
February	1st to 10th	Night	23% 20% 36% 19% 2	950
	11th to 20th	Night	23% 24% 36% 15% 2	891
	21st to end	Night	25% 25% 33% 15% 1	538
March	1st to 10th	Night	22% 19% 33% 23% 4	570
	11th to 20th	Night	26% 16% 32% 24% 3	570
	21st to end	Night	20% 20% 34% 19% 5%	627
April	1st to 10th	Night	16% 24% 32% 24% 4	570
	11th to 20th	Night	19% 21% 30% 24% 6%	563
	21st to end	Night	16% 22% 34% 20% 7% 1	570
May	1st to 10th	Night	16% 11% 35% 30% 8%	570
	11th to 20th	Night	16% 11% 28% 30% 13% 2	561
	21st to end	Night	12% 10% 28% 29% 16% 4	617
June	1st to 10th	Night	8% 5% 18% 38% 29% 2	570
	11th to 20th	Night	5% 2 28% 39% 23% 3	570
	21st to end	Night	4 3 24% 39% 28% 2	570
July	1st to 10th	Night	6% 2 16% 32% 37% 7%	555
	11th to 20th	Night	5% 1 16% 36% 36% 7%	552
	21st to end	Night	7% 2 10% 38% 35% 8%	624
August	1st to 10th	Night	6% 2 13% 40% 35% 5%	567
	11th to 20th	Night	7% 2 16% 37% 34% 4	564
	21st to end	Night	6% 1 14% 35% 39% 5%	627
September	1st to 10th	Night	10% 2 15% 35% 36% 3	570
	11th to 20th	Night	15% 1 14% 37% 28% 5%	570
	21st to end	Night	11% 5% 21% 32% 27% 3	616
October	1st to 10th	Night	8% 5% 27% 33% 23% 3	760
	11th to 20th	Night	14% 15% 32% 28% 11%	760
	21st to end	Night	21% 17% 29% 24% 9% 1	836
November	1st to 10th	Night	16% 16% 33% 25% 10%	780
	11th to 20th	Night	19% 15% 30% 29% 7%	800
	21st to end	Night	21% 18% 31% 21% 8%	978
December	1st to 10th	Night	20% 17% 38% 21% 5%	978
	11th to 20th	Night	21% 17% 32% 25% 4	950
	21st to end	Night	23% 23% 31% 21% 4	1045

Page generated at 2024-12-03 05:45:15. Version ac07

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