Teterville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Teterville clear sky chart from 2005-11-06 to 2025-03-27.

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	10% 6% 2 6% 4 4 4 3 5% 7% 48%	109722
	Night	10% 6% 2 5% 4 4 4 3 5% 6% 52%	109847
Transparency	Day	34% 4 11% 27% 20% 4	113425
	Night	31% 4 11% 27% 22% 5%	114271
Seeing	Day	14% 9% 29% 29% 15% 3	16021
	Night	13% 10% 33% 32% 11% 1	26076

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	13% 8% 2 7% 5% 5% 5% 4 5% 6% 41%	4077
	11th to 20th	Day	7% 9% 3 9% 5% 7% 5% 3 4 6% 43%	4080
	21st to end	Day	9% 10% 3 8% 5% 3 3 3 4 5% 47%	4488
February	1st to 10th	Day	12% 11% 3 7% 5% 3 3 3 5% 7% 42%	1800
	11th to 20th	Day	9% 8% 3 9% 5% 4 4 3 5% 6% 45%	1881
	21st to end	Day	10% 7% 3 5% 4 4 4 4 6% 6% 46%	1650
March	1st to 10th	Day	11% 8% 2 5% 3 3 2 3 4 6% 53%	3534
	11th to 20th	Day	10% 5% 2 3 3 2 3 2 5% 7% 58%	3590
	21st to end	Day	14% 9% 4 7% 4 3 4 3 5% 5% 41%	3880
April	1st to 10th	Day	12% 6% 3 5% 3 3 4 3 5% 6% 49%	2095
	11th to 20th	Day	14% 7% 3 6% 5% 4 4 3 4 6% 44%	2309
	21st to end	Day	18% 8% 2 5% 5% 4 3 3 5% 6% 41%	2470
May	1st to 10th	Day	20% 11% 3 6% 4 3 4 3 4 5% 37%	4082
	11th to 20th	Day	13% 7% 3 6% 4 4 3 3 5% 7% 45%	4082
	21st to end	Day	13% 6% 2 7% 5% 5% 4 4 5% 7% 42%	4477
June	1st to 10th	Day	5% 3 1 6% 4 5% 4 4 7% 9% 51%	2470
	11th to 20th	Day	8% 4 1 5% 5% 4 5% 3 5% 9% 51%	2470
	21st to end	Day	6% 3 2 4 3 4 4 3 6% 10% 55%	2470
July	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 41%	4120
	11th to 20th	Day	7% 4 1 4 3 4 4 4 7% 9% 52%	4120
	21st to end	Day	6% 4 2 6% 5% 5% 6% 6% 8% 10% 41%	4465
August	1st to 10th	Day	6% 4 2 6% 4 4 4 4 6% 8% 53%	4104
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 5% 8% 49%	4041
	21st to end	Day	4 3 1 4 3 3 4 4 6% 9% 59%	4404
September	1st to 10th	Day	12% 5% 2 4 3 3 4 3 5% 6% 54%	2132
	11th to 20th	Day	10% 4 2 4 4 3 3 3 5% 7% 53%	2090
	21st to end	Day	9% 4 2 5% 4 4 3 3 5% 6% 55%	2090
October	1st to 10th	Day	9% 5% 2 5% 3 3 4 3 5% 7% 54%	1976
	11th to 20th	Day	10% 4 1 4 2 2 3 2 4 5% 63%	1900
	21st to end	Day	13% 6% 2 4 3 3 3 2 3 5% 54%	2090
November	1st to 10th	Day	10% 4 2 5% 3 3 3 2 4 7% 58%	1866
	11th to 20th	Day	9% 5% 2 6% 3 3 2 3 4 6% 57%	1800
	21st to end	Day	13% 5% 2 4 3 2 2 2 4 6% 56%	1800
December	1st to 10th	Day	6% 4 2 4 3 3 3 3 4 6% 61%	2940
	11th to 20th	Day	8% 5% 2 6% 4 4 4 3 4 5% 55%	3391
	21st to end	Day	16% 10% 5% 14% 4 4 3 3 4 5% 30%	4488
January	1st to 10th	Night	11% 7% 3 9% 4 4 4 3 5% 6% 43%	5888
	11th to 20th	Night	5% 6% 2 6% 5% 5% 5% 4 6% 6% 50%	5900
	21st to end	Night	12% 9% 3 6% 3 3 3 2 3 5% 51%	6490
February	1st to 10th	Night	10% 9% 3 7% 4 5% 4 3 6% 6% 44%	2600
	11th to 20th	Night	12% 8% 3 5% 5% 3 4 3 5% 6% 47%	2424
	21st to end	Night	9% 6% 2 5% 4 3 4 3 5% 6% 52%	1980
March	1st to 10th	Night	11% 7% 2 4 3 2 3 2 4 5% 55%	3539
	11th to 20th	Night	9% 4 1 4 3 3 5% 3 5% 6% 58%	3590
	21st to end	Night	13% 8% 2 7% 4 4 4 3 5% 5% 46%	3889
April	1st to 10th	Night	11% 5% 2 6% 4 3 3 2 4 7% 54%	2083
	11th to 20th	Night	13% 6% 2 5% 4 4 3 3 4 8% 49%	1816
	21st to end	Night	14% 6% 2 5% 4 3 3 3 6% 7% 47%	1710
May	1st to 10th	Night	17% 9% 2 5% 3 4 4 3 4 6% 42%	2823
	11th to 20th	Night	15% 6% 2 6% 3 3 3 3 5% 7% 47%	2823
	21st to end	Night	10% 5% 2 4 3 3 4 3 5% 8% 54%	3090
June	1st to 10th	Night	5% 3 2 4 3 4 5% 4 6% 10% 53%	1710
	11th to 20th	Night	4 4 2 4 5% 5% 5% 5% 7% 9% 52%	1710
	21st to end	Night	6% 2 1 4 3 4 4 3 5% 7% 59%	1710
July	1st to 10th	Night	7% 5% 2 6% 3 4 4 4 6% 8% 51%	2850
	11th to 20th	Night	2 3 2 4 3 4 4 3 5% 11% 59%	2850
	21st to end	Night	7% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	3098
August	1st to 10th	Night	3 3 2 5% 3 5% 4 4 7% 8% 55%	2836
	11th to 20th	Night	7% 4 2 5% 5% 4 4 4 6% 7% 52%	2798
	21st to end	Night	4 3 1 4 3 3 3 2 4 7% 65%	3259
September	1st to 10th	Night	10% 4 1 4 3 2 3 3 4 5% 61%	2044
	11th to 20th	Night	9% 4 2 5% 4 4 4 3 4 7% 54%	2090
	21st to end	Night	7% 4 2 4 3 3 3 3 5% 6% 61%	2090
October	1st to 10th	Night	11% 5% 2 5% 3 3 3 2 5% 5% 56%	2183
	11th to 20th	Night	12% 4 1 3 2 3 3 2 4 5% 61%	2280
	21st to end	Night	12% 6% 2 4 2 3 3 3 3 5% 56%	2508
November	1st to 10th	Night	9% 4 2 4 3 3 2 2 4 5% 62%	2430
	11th to 20th	Night	9% 5% 1 4 3 3 3 3 5% 6% 58%	2600
	21st to end	Night	12% 7% 2 4 2 2 2 3 4 5% 56%	2600
December	1st to 10th	Night	5% 5% 1 4 3 3 3 3 4 6% 63%	4250
	11th to 20th	Night	10% 4 2 5% 3 4 3 3 5% 6% 55%	4816
	21st to end	Night	16% 8% 3 9% 4 4 4 3 4 5% 38%	6490

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	42% 4 11% 24% 16% 3	4078
	11th to 20th	Day	44% 2 9% 22% 19% 4	4080
	21st to end	Day	41% 2 9% 23% 20% 5%	4488
February	1st to 10th	Day	43% 4 10% 26% 13% 4	1800
	11th to 20th	Day	40% 3 11% 27% 14% 4	1890
	21st to end	Day	37% 3 9% 23% 22% 6%	1650
March	1st to 10th	Day	35% 2 6% 23% 26% 8%	3534
	11th to 20th	Day	27% 3 12% 28% 27% 4	3590
	21st to end	Day	43% 5% 12% 29% 9% 2	3880
April	1st to 10th	Day	36% 4 11% 25% 20% 5%	2095
	11th to 20th	Day	42% 3 9% 25% 17% 3	2309
	21st to end	Day	45% 3 10% 29% 12% 1	2470
May	1st to 10th	Day	50% 3 9% 21% 14% 3	4120
	11th to 20th	Day	38% 4 11% 27% 18% 1	4086
	21st to end	Day	40% 6% 11% 23% 16% 3	4489
June	1st to 10th	Day	29% 5% 17% 31% 16% 3	2470
	11th to 20th	Day	31% 4 13% 29% 20% 3	2470
	21st to end	Day	24% 5% 16% 29% 22% 5%	2470
July	1st to 10th	Day	37% 6% 11% 24% 18% 4	4056
	11th to 20th	Day	26% 6% 12% 33% 20% 3	4051
	21st to end	Day	31% 8% 16% 28% 16%	4325
August	1st to 10th	Day	28% 5% 13% 26% 22% 5%	4090
	11th to 20th	Day	34% 6% 15% 26% 17% 2	4080
	21st to end	Day	22% 5% 15% 36% 16% 5%	4403
September	1st to 10th	Day	32% 3 12% 25% 21% 8%	2132
	11th to 20th	Day	30% 4 9% 31% 23% 3	2090
	21st to end	Day	30% 3 9% 25% 28% 5%	2090
October	1st to 10th	Day	20% 2 7% 18% 43% 9%	3288
	11th to 20th	Day	15% 2 5% 34% 32% 11%	3140
	21st to end	Day	27% 2 8% 28% 28% 7%	3428
November	1st to 10th	Day	29% 2 10% 29% 23% 7%	1866
	11th to 20th	Day	30% 2 8% 27% 26% 6%	1800
	21st to end	Day	31% 3 9% 30% 23% 4	1800
December	1st to 10th	Day	25% 3 10% 39% 22% 1	2940
	11th to 20th	Day	32% 4 7% 34% 21% 2	3389
	21st to end	Day	55% 3 7% 24% 8% 1	4488
January	1st to 10th	Night	42% 3 10% 27% 16% 2	5888
	11th to 20th	Night	33% 4 11% 26% 22% 5%	5900
	21st to end	Night	39% 2 9% 22% 24% 6%	6490
February	1st to 10th	Night	41% 3 11% 25% 15% 5%	2600
	11th to 20th	Night	39% 3 12% 26% 17% 4	2425
	21st to end	Night	32% 3 9% 24% 24% 9%	1980
March	1st to 10th	Night	32% 3 8% 26% 24% 7%	3539
	11th to 20th	Night	27% 4 10% 23% 31% 4	3590
	21st to end	Night	39% 5% 14% 29% 12% 1	3889
April	1st to 10th	Night	32% 3 11% 23% 24% 7%	2083
	11th to 20th	Night	35% 3 12% 25% 21% 4	1816
	21st to end	Night	37% 3 14% 24% 18% 4	1710
May	1st to 10th	Night	44% 5% 12% 21% 14% 4	2850
	11th to 20th	Night	38% 4 15% 29% 14%	2824
	21st to end	Night	28% 6% 16% 29% 19% 1	3099
June	1st to 10th	Night	25% 6% 21% 30% 15% 3	1710
	11th to 20th	Night	26% 5% 16% 31% 19% 3	1710
	21st to end	Night	24% 5% 13% 33% 20% 6%	1710
July	1st to 10th	Night	29% 5% 13% 26% 20% 6%	2805
	11th to 20th	Night	20% 5% 13% 35% 24% 3	2796
	21st to end	Night	31% 7% 18% 31% 13% 1	2999
August	1st to 10th	Night	24% 5% 15% 28% 20% 9%	2826
	11th to 20th	Night	30% 6% 15% 27% 19% 3	2825
	21st to end	Night	20% 3 15% 39% 18% 4	3259
September	1st to 10th	Night	27% 3 11% 27% 23% 10%	2044
	11th to 20th	Night	31% 4 11% 24% 26% 5%	2090
	21st to end	Night	25% 3 8% 27% 31% 6%	2090
October	1st to 10th	Night	20% 2 6% 15% 46% 11%	3638
	11th to 20th	Night	18% 3 4 27% 34% 14%	3779
	21st to end	Night	26% 3 8% 24% 34% 5%	4120
November	1st to 10th	Night	26% 2 9% 30% 24% 9%	2430
	11th to 20th	Night	28% 3 9% 27% 28% 6%	2600
	21st to end	Night	31% 2 10% 27% 23% 7%	2600
December	1st to 10th	Night	23% 3 12% 40% 21% 1	4250
	11th to 20th	Night	30% 3 8% 32% 23% 4	4817
	21st to end	Night	47% 4 8% 26% 13% 3	6490

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	20% 15% 33% 25% 6% 1	300
	11th to 20th	Day	20% 19% 38% 19% 3	300
	21st to end	Day	13% 14% 50% 20% 3 1	330
February	1st to 10th	Day	23% 19% 39% 16% 2 1	300
	11th to 20th	Day	18% 20% 41% 18% 3	300
	21st to end	Day	18% 24% 38% 20% 1	249
March	1st to 10th	Day	19% 18% 42% 18% 2	300
	11th to 20th	Day	25% 14% 37% 20% 4	300
	21st to end	Day	28% 20% 38% 11% 2 1	315
April	1st to 10th	Day	23% 21% 38% 14% 4	275
	11th to 20th	Day	20% 18% 38% 20% 4	507
	21st to end	Day	24% 12% 36% 20% 6% 2	650
May	1st to 10th	Day	21% 12% 39% 19% 8% 1	653
	11th to 20th	Day	20% 10% 27% 29% 12% 2	675
	21st to end	Day	19% 7% 31% 25% 15% 3	734
June	1st to 10th	Day	6% 4 24% 37% 23% 6%	680
	11th to 20th	Day	8% 4 32% 37% 16% 3	680
	21st to end	Day	7% 5% 32% 39% 15% 2	680
July	1st to 10th	Day	11% 3 15% 35% 28% 8%	671
	11th to 20th	Day	6% 3 16% 41% 29% 6%	668
	21st to end	Day	9% 1 13% 37% 31% 9%	739
August	1st to 10th	Day	9% 1 18% 40% 27% 4	676
	11th to 20th	Day	8% 2 16% 41% 28% 4	665
	21st to end	Day	7% 2 13% 39% 33% 7%	672
September	1st to 10th	Day	11% 1 13% 42% 30% 4	342
	11th to 20th	Day	6% 2 21% 43% 20% 7%	300
	21st to end	Day	16% 3 27% 35% 15% 4	300
October	1st to 10th	Day	12% 7% 31% 27% 17% 6%	300
	11th to 20th	Day	9% 13% 47% 24% 7%	300
	21st to end	Day	23% 12% 38% 21% 5% 2	330
November	1st to 10th	Day	17% 13% 34% 25% 10% 1	300
	11th to 20th	Day	18% 22% 33% 17% 10% 1	300
	21st to end	Day	19% 14% 39% 20% 7% 1	300
December	1st to 10th	Day	11% 12% 46% 21% 7% 3	300
	11th to 20th	Day	15% 17% 36% 24% 7%	300
	21st to end	Day	18% 22% 39% 18% 2	330
January	1st to 10th	Night	13% 13% 40% 27% 6%	1000
	11th to 20th	Night	14% 15% 39% 27% 5% 1	1000
	21st to end	Night	14% 14% 41% 28% 4	1100
February	1st to 10th	Night	16% 15% 42% 24% 4	1000
	11th to 20th	Night	17% 17% 38% 25% 3	870
	21st to end	Night	15% 13% 41% 27% 4	660
March	1st to 10th	Night	15% 13% 39% 28% 5%	610
	11th to 20th	Night	19% 13% 36% 26% 6%	600
	21st to end	Night	23% 15% 36% 22% 4	647
April	1st to 10th	Night	15% 15% 42% 21% 7% 1	570
	11th to 20th	Night	17% 16% 38% 25% 4	563
	21st to end	Night	18% 13% 38% 25% 6% 1	570
May	1st to 10th	Night	19% 8% 36% 30% 5% 1	570
	11th to 20th	Night	18% 7% 28% 33% 14% 1	561
	21st to end	Night	12% 7% 31% 35% 13% 2	617
June	1st to 10th	Night	6% 4 28% 39% 22% 2	570
	11th to 20th	Night	6% 4 33% 41% 16%	570
	21st to end	Night	7% 1 34% 44% 13%	570
July	1st to 10th	Night	8% 2 16% 43% 29% 2	555
	11th to 20th	Night	3 1 16% 51% 26% 2	552
	21st to end	Night	7% 1 14% 43% 32% 3	624
August	1st to 10th	Night	7% 1 15% 46% 29% 2	567
	11th to 20th	Night	8% 2 15% 46% 29% 1	564
	21st to end	Night	6% 1 15% 43% 33% 3	627
September	1st to 10th	Night	10% 2 19% 43% 22% 3	570
	11th to 20th	Night	10% 3 24% 38% 23% 3	570
	21st to end	Night	10% 5% 24% 41% 18% 2	570
October	1st to 10th	Night	14% 4 28% 32% 20% 2	663
	11th to 20th	Night	14% 9% 39% 30% 8%	760
	21st to end	Night	17% 13% 32% 28% 9% 1	836
November	1st to 10th	Night	11% 9% 38% 30% 11% 1	870
	11th to 20th	Night	13% 15% 36% 28% 7% 1	1000
	21st to end	Night	17% 12% 33% 31% 7%	1000
December	1st to 10th	Night	13% 12% 36% 32% 6% 1	1000
	11th to 20th	Night	16% 12% 38% 30% 5%	1000
	21st to end	Night	17% 16% 35% 29% 3	1100

Page generated at 2025-03-24 08:04:32. Version ac07

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