Sherman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sherman clear sky chart from 2005-11-06 to 2024-10-20.

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% 5% 2 5% 4 4 4 3 5% 7% 51%	101030
	Night	10% 5% 2 4 3 3 3 3 5% 6% 56%	97753
Transparency	Day	33% 5% 10% 24% 22% 6%	100844
	Night	29% 5% 9% 24% 24% 9%	97610
Seeing	Day	11% 7% 23% 29% 22% 7%	15182
	Night	12% 9% 29% 34% 15% 1	25000

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% 7% 2 5% 3 4 3 3 4 6% 52%	2847
	11th to 20th	Day	10% 6% 1 3 2 2 2 2 4 5% 63%	2850
	21st to end	Day	19% 9% 3 7% 3 3 2 2 2 3 46%	3135
February	1st to 10th	Day	16% 8% 2 8% 4 3 3 2 4 4 45%	1781
	11th to 20th	Day	16% 6% 3 6% 4 3 3 3 4 6% 47%	1849
	21st to end	Day	20% 9% 2 5% 2 2 2 1 3 4 50%	1599
March	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 4 6% 51%	3436
	11th to 20th	Day	14% 8% 2 6% 4 3 5% 4 6% 5% 44%	3480
	21st to end	Day	15% 9% 2 6% 5% 4 4 4 5% 7% 41%	3814
April	1st to 10th	Day	12% 6% 2 5% 4 3 4 3 5% 6% 50%	2090
	11th to 20th	Day	12% 7% 2 5% 5% 4 3 3 5% 6% 46%	2188
	21st to end	Day	13% 6% 2 6% 4 4 4 4 5% 7% 46%	2418
May	1st to 10th	Day	16% 7% 3 7% 4 4 3 3 5% 6% 41%	4082
	11th to 20th	Day	14% 6% 2 5% 4 4 4 4 6% 6% 47%	4082
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 4 5% 7% 37%	4477
June	1st to 10th	Day	6% 4 2 6% 5% 6% 5% 5% 7% 9% 47%	2470
	11th to 20th	Day	6% 4 2 5% 5% 5% 5% 4 7% 9% 50%	2470
	21st to end	Day	4 4 1 4 4 3 5% 4 7% 8% 56%	2470
July	1st to 10th	Day	7% 4 2 5% 5% 4 5% 4 6% 8% 51%	4120
	11th to 20th	Day	2 3 1 4 4 4 4 4 7% 9% 58%	4120
	21st to end	Day	5% 5% 2 6% 5% 5% 6% 5% 7% 10% 44%	4465
August	1st to 10th	Day	2 2 1 3 3 3 3 3 6% 8% 65%	4104
	11th to 20th	Day	5% 2 1 4 3 3 4 4 6% 10% 57%	4041
	21st to end	Day	3 3 1 4 4 5% 5% 4 7% 10% 54%	4142
September	1st to 10th	Day	9% 4 2 5% 4 4 4 4 5% 6% 53%	2090
	11th to 20th	Day	9% 5% 2 7% 5% 5% 4 3 5% 7% 47%	2090
	21st to end	Day	7% 4 2 4 3 4 4 3 6% 7% 59%	2090
October	1st to 10th	Day	6% 3 1 4 3 4 3 3 5% 5% 61%	2019
	11th to 20th	Day	11% 4 1 3 2 3 3 2 3 5% 62%	1890
	21st to end	Day	15% 5% 1 4 3 3 3 2 3 4 57%	1980
November	1st to 10th	Day	12% 5% 1 4 3 3 3 2 4 5% 58%	1858
	11th to 20th	Day	7% 3 2 4 3 3 3 3 4 6% 61%	1767
	21st to end	Day	14% 6% 2 4 3 2 3 2 4 5% 55%	1710
December	1st to 10th	Day	13% 7% 3 5% 3 3 3 3 4 6% 50%	1710
	11th to 20th	Day	15% 9% 2 6% 4 3 3 3 4 4 47%	2161
	21st to end	Day	17% 7% 2 5% 3 3 4 3 4 6% 47%	3135
January	1st to 10th	Night	13% 6% 1 4 3 3 3 3 4 5% 54%	4108
	11th to 20th	Night	9% 5% 2 4 3 2 3 2 3 4 63%	4120
	21st to end	Night	19% 7% 3 5% 2 2 3 2 3 4 48%	4532
February	1st to 10th	Night	13% 8% 2 7% 4 3 4 2 3 5% 49%	2413
	11th to 20th	Night	14% 7% 2 5% 3 3 4 3 4 5% 49%	2218
	21st to end	Night	16% 7% 1 4 4 3 3 3 2 4 53%	1853
March	1st to 10th	Night	14% 9% 2 6% 4 4 4 4 5% 6% 44%	3419
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 4 7% 51%	3480
	21st to end	Night	14% 6% 2 5% 3 4 4 3 5% 6% 47%	3817
April	1st to 10th	Night	9% 6% 2 4 4 3 4 3 6% 7% 53%	2090
	11th to 20th	Night	11% 6% 2 5% 3 3 4 4 5% 6% 51%	1938
	21st to end	Night	10% 6% 2 5% 3 3 3 3 6% 7% 53%	1758
May	1st to 10th	Night	18% 8% 2 6% 4 4 3 4 5% 5% 41%	2823
	11th to 20th	Night	12% 6% 2 6% 3 3 3 3 5% 8% 49%	2823
	21st to end	Night	10% 6% 2 5% 3 4 5% 4 6% 8% 46%	3090
June	1st to 10th	Night	4 3 2 3 3 3 5% 3 6% 10% 59%	1710
	11th to 20th	Night	3 3 1 3 3 3 3 3 6% 10% 62%	1710
	21st to end	Night	3 2 1 2 3 3 4 3 6% 9% 64%	1710
July	1st to 10th	Night	5% 3 1 3 3 4 4 4 6% 9% 57%	2850
	11th to 20th	Night	2 2 1 3 2 2 3 3 6% 9% 67%	2850
	21st to end	Night	4 3 1 4 3 4 4 4 6% 9% 58%	3098
August	1st to 10th	Night	2 1 1 3 2 2 2 3 4 8% 73%	2836
	11th to 20th	Night	3 2 1 2 2 2 3 3 5% 10% 67%	2798
	21st to end	Night	3 2 1 3 3 2 4 4 6% 10% 62%	3512
September	1st to 10th	Night	8% 5% 1 4 3 3 3 3 5% 7% 59%	2090
	11th to 20th	Night	9% 5% 2 5% 4 3 4 3 5% 6% 54%	2090
	21st to end	Night	6% 3 2 3 2 2 3 3 5% 7% 63%	2090
October	1st to 10th	Night	6% 3 1 4 2 3 3 2 4 6% 64%	2140
	11th to 20th	Night	10% 4 1 3 2 2 3 3 4 5% 64%	2275
	21st to end	Night	15% 5% 2 3 2 2 2 2 2 5% 60%	2376
November	1st to 10th	Night	10% 4 2 4 3 3 3 2 4 5% 61%	2220
	11th to 20th	Night	7% 4 2 4 3 3 4 3 5% 5% 61%	2408
	21st to end	Night	13% 7% 2 4 3 2 3 3 4 5% 53%	2470
December	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 3 5% 56%	2470
	11th to 20th	Night	12% 6% 3 6% 3 3 3 3 4 4 52%	3036
	21st to end	Night	15% 7% 2 6% 3 2 3 2 4 5% 51%	4532

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	34% 3 7% 22% 30% 4	2848
	11th to 20th	Day	26% 3 9% 24% 33% 5%	2850
	21st to end	Day	46% 2 4 18% 22% 8%	3135
February	1st to 10th	Day	44% 4 7% 17% 22% 7%	1781
	11th to 20th	Day	40% 3 7% 22% 19% 8%	1859
	21st to end	Day	42% 2 4 15% 26% 11%	1599
March	1st to 10th	Day	36% 4 7% 16% 26% 11%	3436
	11th to 20th	Day	40% 7% 10% 22% 18% 4	3480
	21st to end	Day	43% 5% 8% 21% 18% 4	3814
April	1st to 10th	Day	36% 5% 9% 22% 19% 10%	2090
	11th to 20th	Day	38% 6% 9% 19% 20% 9%	2188
	21st to end	Day	37% 7% 8% 22% 22% 4	2418
May	1st to 10th	Day	43% 6% 8% 22% 16% 4	4120
	11th to 20th	Day	37% 6% 10% 26% 20% 1	4086
	21st to end	Day	45% 8% 10% 19% 12% 5%	4489
June	1st to 10th	Day	32% 8% 14% 26% 17% 3	2470
	11th to 20th	Day	28% 7% 13% 27% 20% 4	2470
	21st to end	Day	24% 7% 13% 28% 25% 3	2470
July	1st to 10th	Day	29% 7% 13% 36% 13% 1	4056
	11th to 20th	Day	19% 6% 12% 37% 23% 2	4051
	21st to end	Day	31% 8% 14% 32% 15%	4325
August	1st to 10th	Day	16% 5% 12% 26% 31% 10%	4090
	11th to 20th	Day	22% 5% 14% 38% 18% 2	4080
	21st to end	Day	24% 8% 17% 34% 14% 3	4141
September	1st to 10th	Day	31% 6% 9% 23% 19% 12%	2090
	11th to 20th	Day	35% 6% 10% 20% 21% 8%	2090
	21st to end	Day	25% 4 8% 22% 30% 11%	2090
October	1st to 10th	Day	24% 5% 10% 21% 25% 15%	2019
	11th to 20th	Day	27% 3 6% 17% 31% 16%	1890
	21st to end	Day	32% 4 7% 19% 25% 13%	1980
November	1st to 10th	Day	30% 4 9% 23% 26% 9%	1858
	11th to 20th	Day	25% 4 9% 22% 29% 11%	1767
	21st to end	Day	35% 3 5% 20% 27% 10%	1710
December	1st to 10th	Day	36% 4 7% 24% 24% 5%	1710
	11th to 20th	Day	42% 3 6% 16% 25% 9%	2159
	21st to end	Day	39% 3 6% 22% 23% 7%	3135
January	1st to 10th	Night	32% 4 6% 18% 32% 7%	4108
	11th to 20th	Night	26% 3 8% 22% 31% 9%	4120
	21st to end	Night	41% 3 5% 17% 26% 8%	4532
February	1st to 10th	Night	40% 3 8% 18% 21% 9%	2413
	11th to 20th	Night	38% 4 7% 19% 23% 9%	2218
	21st to end	Night	37% 4 6% 16% 23% 15%	1853
March	1st to 10th	Night	40% 5% 6% 16% 20% 13%	3419
	11th to 20th	Night	34% 5% 8% 25% 19% 8%	3480
	21st to end	Night	37% 5% 10% 17% 27% 3	3817
April	1st to 10th	Night	30% 5% 10% 21% 20% 14%	2090
	11th to 20th	Night	34% 5% 8% 20% 20% 12%	1938
	21st to end	Night	31% 5% 11% 23% 25% 5%	1758
May	1st to 10th	Night	44% 7% 9% 18% 16% 7%	2850
	11th to 20th	Night	34% 6% 13% 24% 21% 2	2824
	21st to end	Night	33% 8% 15% 23% 14% 6%	3099
June	1st to 10th	Night	21% 7% 15% 32% 21% 4	1710
	11th to 20th	Night	18% 6% 14% 32% 23% 7%	1710
	21st to end	Night	17% 6% 14% 31% 26% 6%	1710
July	1st to 10th	Night	22% 6% 16% 38% 15% 3	2805
	11th to 20th	Night	14% 5% 9% 42% 27% 3	2796
	21st to end	Night	22% 6% 15% 35% 21% 1	2999
August	1st to 10th	Night	12% 4 8% 31% 39% 6%	2826
	11th to 20th	Night	14% 4 13% 40% 23% 6%	2825
	21st to end	Night	17% 5% 19% 37% 19% 3	3512
September	1st to 10th	Night	26% 4 11% 21% 27% 11%	2090
	11th to 20th	Night	31% 6% 10% 21% 22% 11%	2090
	21st to end	Night	21% 5% 8% 24% 28% 15%	2090
October	1st to 10th	Night	21% 5% 8% 22% 24% 19%	2140
	11th to 20th	Night	24% 3 7% 15% 30% 20%	2275
	21st to end	Night	30% 3 5% 19% 26% 17%	2376
November	1st to 10th	Night	27% 4 7% 21% 26% 15%	2220
	11th to 20th	Night	25% 4 8% 21% 28% 13%	2408
	21st to end	Night	34% 4 7% 16% 30% 9%	2470
December	1st to 10th	Night	32% 4 8% 24% 23% 10%	2470
	11th to 20th	Night	36% 3 5% 17% 28% 11%	3037
	21st to end	Night	36% 4 6% 20% 25% 10%	4532

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	19% 17% 34% 23% 8%	270
	11th to 20th	Day	18% 18% 40% 18% 4 2	270
	21st to end	Day	17% 12% 39% 22% 7% 2	297
February	1st to 10th	Day	23% 13% 39% 17% 9%	270
	11th to 20th	Day	21% 17% 43% 16% 3	270
	21st to end	Day	26% 17% 41% 12% 3	225
March	1st to 10th	Day	19% 19% 36% 21% 4 1	270
	11th to 20th	Day	19% 19% 42% 14% 6%	270
	21st to end	Day	18% 13% 46% 18% 5% 1	297
April	1st to 10th	Day	17% 16% 35% 26% 5% 1	270
	11th to 20th	Day	17% 18% 37% 21% 8%	386
	21st to end	Day	16% 14% 38% 23% 7% 2	598
May	1st to 10th	Day	13% 11% 34% 32% 8%	653
	11th to 20th	Day	17% 7% 30% 32% 12% 3	675
	21st to end	Day	14% 8% 26% 33% 15% 4	734
June	1st to 10th	Day	6% 3 16% 38% 29% 9%	680
	11th to 20th	Day	7% 3 17% 39% 27% 7%	680
	21st to end	Day	4 3 11% 39% 33% 10%	680
July	1st to 10th	Day	7% 1 8% 35% 35% 13%	671
	11th to 20th	Day	2 1 8% 34% 44% 12%	668
	21st to end	Day	3 1 6% 32% 43% 15%	739
August	1st to 10th	Day	4 1 5% 34% 43% 14%	676
	11th to 20th	Day	8% 1 8% 33% 38% 12%	665
	21st to end	Day	5% 1 4 30% 40% 20%	527
September	1st to 10th	Day	8% 5% 19% 42% 25%	300
	11th to 20th	Day	4 1 8% 25% 45% 17%	300
	21st to end	Day	10% 2 10% 34% 28% 16%	300
October	1st to 10th	Day	2 2 21% 31% 33% 11%	300
	11th to 20th	Day	11% 8% 24% 35% 20% 1	297
	21st to end	Day	24% 11% 25% 23% 16% 2	297
November	1st to 10th	Day	17% 5% 35% 27% 12% 4	270
	11th to 20th	Day	11% 11% 32% 31% 10% 4	270
	21st to end	Day	19% 13% 37% 21% 7% 2	270
December	1st to 10th	Day	14% 17% 31% 27% 10% 1	270
	11th to 20th	Day	19% 11% 42% 20% 7%	270
	21st to end	Day	20% 14% 36% 24% 5%	297
January	1st to 10th	Night	13% 12% 37% 30% 7%	950
	11th to 20th	Night	17% 16% 33% 28% 6% 1	950
	21st to end	Night	15% 12% 36% 32% 6%	1045
February	1st to 10th	Night	17% 13% 40% 25% 4	893
	11th to 20th	Night	18% 15% 41% 23% 3	744
	21st to end	Night	22% 16% 41% 19% 2	597
March	1st to 10th	Night	16% 15% 37% 28% 5%	570
	11th to 20th	Night	15% 12% 43% 26% 4	570
	21st to end	Night	13% 15% 40% 27% 5%	627
April	1st to 10th	Night	11% 16% 42% 27% 4	570
	11th to 20th	Night	13% 14% 40% 29% 4	563
	21st to end	Night	12% 11% 42% 26% 9%	570
May	1st to 10th	Night	10% 10% 39% 33% 7% 1	570
	11th to 20th	Night	11% 6% 36% 32% 15% 1	561
	21st to end	Night	8% 4 32% 38% 16% 2	617
June	1st to 10th	Night	4 3 19% 44% 27% 2	570
	11th to 20th	Night	4 2 24% 54% 17% 1	570
	21st to end	Night	2 2 18% 48% 25% 5%	570
July	1st to 10th	Night	4 1 10% 45% 36% 5%	555
	11th to 20th	Night	2 1 10% 48% 36% 3	552
	21st to end	Night	2 8% 45% 39% 5%	624
August	1st to 10th	Night	2 1 7% 49% 38% 4	567
	11th to 20th	Night	6% 1 6% 46% 37% 3	564
	21st to end	Night	3 5% 46% 37% 8%	627
September	1st to 10th	Night	10% 1 7% 40% 37% 4	570
	11th to 20th	Night	12% 1 10% 37% 36% 3	570
	21st to end	Night	8% 1 15% 41% 32% 3	570
October	1st to 10th	Night	8% 2 22% 39% 26% 3	620
	11th to 20th	Night	12% 6% 28% 39% 14% 1	759
	21st to end	Night	17% 11% 27% 31% 13% 1	792
November	1st to 10th	Night	11% 6% 33% 37% 12% 1	740
	11th to 20th	Night	9% 12% 32% 35% 11%	888
	21st to end	Night	18% 11% 35% 25% 10%	950
December	1st to 10th	Night	15% 12% 35% 32% 6%	950
	11th to 20th	Night	18% 11% 34% 31% 5%	950
	21st to end	Night	18% 13% 37% 26% 6%	1045

Page generated at 2024-10-17 12:09:38. Version ac07

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