Teulon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Teulon clear sky chart from 2005-11-06 to 2025-08-05.

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% 8% 3 9% 5% 5% 5% 4 6% 8% 36%	130054
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 34%	126777
Transparency	Day	45% 8% 16% 23% 8% 1	129751
	Night	47% 7% 14% 21% 9% 1	126661
Seeing	Day	13% 9% 30% 29% 14% 4	17336
	Night	14% 7% 30% 33% 14% 1	27237

By Month

Percentage Cloud Cover NW (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	6% 14% 7% 14% 7% 8% 8% 5% 7% 6% 20%	3179
	11th to 20th	Day	5% 11% 5% 15% 10% 7% 7% 9% 10% 9% 12%	3159
	21st to end	Day	5% 15% 7% 14% 8% 7% 7% 4 6% 8% 19%	3958
February	1st to 10th	Day	9% 12% 5% 11% 9% 8% 9% 5% 8% 5% 19%	1690
	11th to 20th	Day	7% 9% 4 10% 6% 7% 8% 6% 7% 9% 27%	1754
	21st to end	Day	6% 13% 4 11% 7% 6% 7% 6% 6% 7% 27%	1560
March	1st to 10th	Day	9% 10% 4 12% 7% 5% 5% 5% 7% 8% 28%	4587
	11th to 20th	Day	9% 10% 6% 13% 9% 6% 6% 4 6% 8% 25%	4978
	21st to end	Day	8% 11% 5% 11% 6% 5% 5% 4 5% 6% 34%	5464
April	1st to 10th	Day	10% 11% 3 8% 6% 4 5% 4 6% 7% 37%	2451
	11th to 20th	Day	12% 10% 3 9% 5% 5% 5% 4 5% 5% 36%	2572
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	2600
May	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 5% 7% 46%	6126
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 5% 7% 32%	6701
	21st to end	Day	14% 6% 2 6% 4 3 4 3 4 6% 48%	7428
June	1st to 10th	Day	15% 8% 3 6% 5% 4 6% 4 6% 8% 36%	3000
	11th to 20th	Day	15% 7% 3 6% 5% 5% 6% 5% 6% 7% 36%	3000
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 9% 36%	3000
July	1st to 10th	Day	8% 4 2 5% 4 6% 6% 5% 7% 9% 43%	6800
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 7% 9% 44%	6800
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 10% 47%	7365
August	1st to 10th	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 9% 46%	4357
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 3 5% 8% 46%	4041
	21st to end	Day	13% 5% 2 6% 4 3 4 3 5% 8% 46%	4532
September	1st to 10th	Day	10% 5% 2 6% 3 4 4 3 5% 8% 50%	2366
	11th to 20th	Day	12% 8% 3 9% 5% 5% 4 3 6% 8% 37%	2090
	21st to end	Day	15% 7% 2 6% 4 4 4 4 6% 8% 41%	2090
October	1st to 10th	Day	13% 7% 2 7% 4 5% 5% 3 4 7% 43%	3210
	11th to 20th	Day	9% 10% 4 7% 5% 4 5% 4 6% 9% 37%	3054
	21st to end	Day	14% 12% 3 9% 4 4 4 4 6% 8% 33%	3091
November	1st to 10th	Day	16% 15% 4 10% 6% 5% 5% 4 5% 5% 27%	1581
	11th to 20th	Day	9% 16% 5% 13% 6% 5% 5% 4 5% 7% 25%	1600
	21st to end	Day	13% 15% 6% 11% 7% 5% 5% 3 3 7% 25%	1443
December	1st to 10th	Day	11% 15% 6% 14% 9% 6% 5% 5% 7% 8% 16%	2290
	11th to 20th	Day	10% 12% 5% 13% 7% 4 5% 5% 7% 8% 24%	2639
	21st to end	Day	7% 12% 7% 17% 8% 6% 5% 3 5% 6% 24%	3498
January	1st to 10th	Night	4 14% 7% 14% 8% 9% 7% 5% 6% 7% 21%	6787
	11th to 20th	Night	4 13% 6% 14% 9% 9% 10% 8% 7% 5% 15%	6759
	21st to end	Night	7% 16% 7% 15% 6% 6% 6% 4 7% 6% 19%	7006
February	1st to 10th	Night	8% 13% 4 12% 7% 7% 6% 5% 5% 8% 26%	2710
	11th to 20th	Night	7% 9% 3 9% 6% 6% 8% 6% 6% 7% 34%	2533
	21st to end	Night	6% 12% 4 10% 6% 6% 6% 5% 6% 7% 33%	2088
March	1st to 10th	Night	8% 11% 4 11% 6% 5% 5% 5% 6% 8% 31%	5282
	11th to 20th	Night	6% 9% 4 8% 6% 5% 5% 5% 6% 8% 38%	4980
	21st to end	Night	10% 11% 4 8% 5% 4 4 3 5% 6% 37%	5467
April	1st to 10th	Night	10% 7% 2 6% 5% 4 5% 5% 7% 8% 41%	1945
	11th to 20th	Night	13% 9% 3 8% 6% 4 5% 5% 5% 6% 35%	1779
	21st to end	Night	11% 9% 2 7% 6% 5% 5% 4 5% 6% 39%	1800
May	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 6% 6% 42%	3853
	11th to 20th	Night	18% 5% 2 6% 4 5% 5% 5% 6% 9% 35%	3211
	21st to end	Night	12% 4 2 6% 4 3 3 3 4 6% 52%	3470
June	1st to 10th	Night	10% 8% 2 6% 5% 5% 4 5% 6% 10% 39%	1400
	11th to 20th	Night	14% 6% 2 5% 5% 4 5% 5% 6% 7% 42%	1400
	21st to end	Night	10% 5% 1 6% 5% 4 5% 4 8% 10% 43%	1400
July	1st to 10th	Night	7% 3 2 5% 4 4 5% 4 5% 9% 53%	3180
	11th to 20th	Night	7% 4 3 6% 3 5% 5% 4 7% 10% 48%	3180
	21st to end	Night	6% 4 2 5% 4 4 4 4 7% 9% 52%	3500
August	1st to 10th	Night	6% 3 2 5% 4 5% 4 4 7% 9% 52%	2671
	11th to 20th	Night	7% 4 1 4 4 4 4 4 7% 10% 51%	2798
	21st to end	Night	10% 6% 3 6% 3 4 4 4 5% 8% 47%	3135
September	1st to 10th	Night	9% 5% 2 6% 4 3 4 3 5% 8% 51%	1809
	11th to 20th	Night	12% 6% 2 7% 5% 4 5% 2 6% 8% 45%	2090
	21st to end	Night	15% 6% 2 7% 4 4 3 3 4 8% 42%	2090
October	1st to 10th	Night	13% 7% 2 5% 3 3 4 3 5% 8% 47%	3704
	11th to 20th	Night	9% 8% 2 7% 5% 5% 5% 4 7% 8% 40%	3865
	21st to end	Night	9% 9% 3 8% 5% 5% 5% 4 5% 7% 39%	4467
November	1st to 10th	Night	13% 13% 4 9% 6% 5% 5% 4 6% 6% 29%	2715
	11th to 20th	Night	10% 16% 6% 12% 6% 5% 4 4 5% 6% 26%	2800
	21st to end	Night	12% 14% 5% 14% 6% 6% 5% 4 5% 5% 24%	2955
December	1st to 10th	Night	8% 17% 6% 14% 11% 7% 5% 4 5% 6% 15%	4900
	11th to 20th	Night	8% 13% 6% 14% 6% 5% 5% 5% 6% 7% 25%	5568
	21st to end	Night	7% 11% 5% 16% 9% 7% 6% 4 5% 6% 23%	7480

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	63% 5% 11% 15% 5%	3179
	11th to 20th	Day	63% 6% 9% 16% 6%	3180
	21st to end	Day	62% 7% 13% 14% 3	3958
February	1st to 10th	Day	61% 7% 12% 11% 8% 1	1690
	11th to 20th	Day	49% 8% 15% 21% 7%	1763
	21st to end	Day	53% 9% 13% 17% 8%	1560
March	1st to 10th	Day	50% 7% 17% 16% 9%	4587
	11th to 20th	Day	55% 8% 14% 16% 6%	4980
	21st to end	Day	49% 7% 13% 21% 9%	5464
April	1st to 10th	Day	45% 7% 13% 24% 10% 1	2451
	11th to 20th	Day	47% 7% 11% 21% 12% 1	2572
	21st to end	Day	45% 7% 16% 24% 7% 2	2600
May	1st to 10th	Day	36% 6% 13% 27% 18%	6126
	11th to 20th	Day	49% 7% 9% 24% 10% 1	6705
	21st to end	Day	36% 7% 9% 22% 22% 5%	7428
June	1st to 10th	Day	44% 8% 15% 22% 11% 1	3000
	11th to 20th	Day	43% 10% 16% 21% 10% 1	3000
	21st to end	Day	41% 11% 18% 22% 8%	3000
July	1st to 10th	Day	33% 10% 24% 27% 6%	6726
	11th to 20th	Day	33% 8% 20% 34% 5%	6719
	21st to end	Day	31% 9% 23% 32% 6%	7158
August	1st to 10th	Day	31% 8% 20% 31% 10%	4341
	11th to 20th	Day	34% 8% 22% 30% 5%	4080
	21st to end	Day	36% 7% 24% 27% 5%	4531
September	1st to 10th	Day	32% 8% 19% 32% 8% 1	2366
	11th to 20th	Day	44% 9% 18% 25% 4	2090
	21st to end	Day	41% 7% 17% 28% 7%	2090
October	1st to 10th	Day	41% 6% 16% 30% 8%	3210
	11th to 20th	Day	42% 7% 13% 27% 10%	3054
	21st to end	Day	49% 7% 19% 20% 5%	3091
November	1st to 10th	Day	58% 8% 13% 16% 4 1	1581
	11th to 20th	Day	57% 10% 14% 14% 4	1600
	21st to end	Day	60% 6% 18% 12% 3	1443
December	1st to 10th	Day	64% 10% 13% 7% 6%	2290
	11th to 20th	Day	56% 6% 15% 15% 8%	2640
	21st to end	Day	62% 6% 9% 17% 6%	3498
January	1st to 10th	Night	61% 7% 10% 13% 9%	6787
	11th to 20th	Night	66% 6% 8% 16% 4	6800
	21st to end	Night	63% 6% 11% 15% 5%	7006
February	1st to 10th	Night	56% 7% 12% 15% 9%	2710
	11th to 20th	Night	44% 8% 17% 22% 8%	2534
	21st to end	Night	49% 8% 12% 22% 10%	2088
March	1st to 10th	Night	49% 7% 14% 17% 9% 4	5282
	11th to 20th	Night	40% 8% 16% 23% 13% 1	4980
	21st to end	Night	46% 6% 9% 25% 13% 1	5467
April	1st to 10th	Night	39% 6% 12% 24% 16% 3	1945
	11th to 20th	Night	47% 5% 10% 21% 15% 2	1779
	21st to end	Night	44% 7% 12% 23% 12% 2	1800
May	1st to 10th	Night	40% 7% 11% 24% 19%	3853
	11th to 20th	Night	43% 7% 13% 25% 10% 2	3211
	21st to end	Night	33% 6% 8% 24% 23% 6%	3470
June	1st to 10th	Night	39% 9% 16% 22% 13% 1	1400
	11th to 20th	Night	38% 8% 17% 22% 14% 2	1400
	21st to end	Night	34% 8% 25% 24% 9% 1	1400
July	1st to 10th	Night	28% 10% 20% 34% 9% 1	3145
	11th to 20th	Night	31% 7% 20% 35% 6% 1	3138
	21st to end	Night	27% 8% 25% 32% 8%	3402
August	1st to 10th	Night	27% 7% 18% 33% 14%	2663
	11th to 20th	Night	26% 7% 27% 31% 9%	2825
	21st to end	Night	33% 7% 18% 33% 9%	3135
September	1st to 10th	Night	32% 7% 17% 32% 12%	1809
	11th to 20th	Night	37% 8% 19% 25% 10% 1	2090
	21st to end	Night	41% 6% 16% 27% 9% 1	2090
October	1st to 10th	Night	38% 7% 12% 31% 12%	3704
	11th to 20th	Night	41% 6% 14% 28% 10%	3865
	21st to end	Night	44% 7% 16% 29% 4	4467
November	1st to 10th	Night	54% 8% 16% 16% 5% 1	2715
	11th to 20th	Night	59% 8% 14% 13% 5%	2800
	21st to end	Night	62% 7% 14% 12% 4	2955
December	1st to 10th	Night	69% 8% 12% 8% 3	4900
	11th to 20th	Night	56% 6% 14% 12% 12%	5566
	21st to end	Night	61% 6% 10% 16% 7%	7480

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	9% 6% 33% 33% 14% 4	300
	11th to 20th	Day	10% 8% 32% 34% 14% 2	300
	21st to end	Day	15% 8% 31% 28% 14% 4	330
February	1st to 10th	Day	13% 8% 34% 34% 9% 3	300
	11th to 20th	Day	9% 10% 31% 31% 14% 5%	300
	21st to end	Day	6% 10% 38% 31% 14% 1	249
March	1st to 10th	Day	14% 8% 31% 30% 16% 1	300
	11th to 20th	Day	10% 9% 37% 27% 14% 3	300
	21st to end	Day	11% 7% 35% 30% 13% 3	330
April	1st to 10th	Day	12% 8% 33% 34% 9% 3	551
	11th to 20th	Day	16% 13% 29% 29% 11% 2	690
	21st to end	Day	15% 11% 34% 27% 12% 2	700
May	1st to 10th	Day	15% 12% 32% 28% 11% 2	703
	11th to 20th	Day	19% 10% 28% 24% 15% 3	725
	21st to end	Day	18% 10% 23% 28% 17% 4	789
June	1st to 10th	Day	16% 12% 28% 25% 13% 6%	730
	11th to 20th	Day	15% 11% 31% 28% 11% 3	730
	21st to end	Day	11% 8% 26% 32% 18% 5%	730
July	1st to 10th	Day	9% 6% 29% 28% 19% 9%	721
	11th to 20th	Day	13% 8% 26% 31% 17% 6%	718
	21st to end	Day	5% 5% 29% 33% 20% 8%	794
August	1st to 10th	Day	7% 6% 28% 31% 21% 7%	697
	11th to 20th	Day	10% 6% 22% 31% 22% 8%	665
	21st to end	Day	12% 8% 27% 30% 20% 3	748
September	1st to 10th	Day	9% 9% 31% 34% 14% 2	576
	11th to 20th	Day	15% 10% 38% 25% 9% 3	300
	21st to end	Day	21% 5% 32% 31% 10% 1	300
October	1st to 10th	Day	20% 11% 27% 28% 10% 3	300
	11th to 20th	Day	13% 15% 33% 26% 11% 2	300
	21st to end	Day	22% 10% 32% 22% 12% 2	330
November	1st to 10th	Day	24% 11% 25% 28% 11% 2	300
	11th to 20th	Day	15% 12% 37% 26% 9% 1	300
	21st to end	Day	16% 14% 37% 28% 5%	300
December	1st to 10th	Day	14% 8% 35% 25% 15% 2	300
	11th to 20th	Day	13% 9% 40% 29% 8% 1	300
	21st to end	Day	10% 9% 30% 29% 16% 5%	330
January	1st to 10th	Night	11% 7% 36% 31% 13% 2	1000
	11th to 20th	Night	14% 8% 32% 35% 11% 1	1000
	21st to end	Night	14% 7% 32% 33% 13% 1	1100
February	1st to 10th	Night	14% 6% 28% 36% 14% 1	1000
	11th to 20th	Night	10% 6% 29% 36% 16% 3	979
	21st to end	Night	10% 7% 35% 29% 16% 2	768
March	1st to 10th	Night	14% 7% 31% 30% 16% 2	760
	11th to 20th	Night	10% 6% 42% 30% 11% 2	600
	21st to end	Night	17% 5% 30% 31% 13% 3	660
April	1st to 10th	Night	14% 6% 30% 38% 11% 2	600
	11th to 20th	Night	18% 6% 27% 36% 13% 1	593
	21st to end	Night	15% 8% 31% 34% 11% 1	600
May	1st to 10th	Night	18% 9% 29% 34% 10% 1	600
	11th to 20th	Night	16% 8% 31% 29% 14% 1	591
	21st to end	Night	17% 8% 28% 34% 13%	650
June	1st to 10th	Night	15% 7% 30% 31% 18% 1	600
	11th to 20th	Night	15% 7% 28% 36% 13% 1	600
	21st to end	Night	11% 6% 23% 40% 20% 1	600
July	1st to 10th	Night	7% 4 23% 42% 23% 1	585
	11th to 20th	Night	8% 4 26% 40% 20% 2	582
	21st to end	Night	8% 3 20% 43% 23% 3	657
August	1st to 10th	Night	7% 4 19% 46% 22% 2	579
	11th to 20th	Night	8% 4 21% 40% 23% 4	564
	21st to end	Night	12% 5% 22% 40% 20% 1	627
September	1st to 10th	Night	10% 5% 30% 34% 19% 2	570
	11th to 20th	Night	14% 7% 26% 39% 13%	570
	21st to end	Night	17% 5% 33% 32% 12% 1	570
October	1st to 10th	Night	21% 6% 33% 31% 8%	703
	11th to 20th	Night	18% 8% 32% 30% 11% 1	809
	21st to end	Night	20% 9% 30% 30% 10% 1	1045
November	1st to 10th	Night	18% 8% 35% 27% 11% 1	975
	11th to 20th	Night	18% 9% 36% 26% 9% 3	1000
	21st to end	Night	17% 10% 40% 26% 7% 1	1000
December	1st to 10th	Night	12% 8% 31% 36% 13% 2	1000
	11th to 20th	Night	15% 9% 37% 30% 9% 1	1000
	21st to end	Night	18% 7% 30% 30% 14% 2	1100

Page generated at 2025-08-02 00:32:24. Version ac07

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