Elachee Nature Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elachee Nature Science Center clear sky chart from 2005-11-06 to 2024-11-05.

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	14% 6% 2 6% 4 4 5% 4 6% 7% 42%	101006
	Night	15% 6% 2 6% 4 4 4 4 6% 7% 43%	97976
Transparency	Day	38% 7% 12% 19% 18% 6%	104813
	Night	37% 7% 11% 19% 19% 7%	102295
Seeing	Day	18% 10% 23% 23% 18% 8%	14936
	Night	17% 9% 23% 28% 19% 3	24950

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	17% 9% 3 6% 4 4 4 3 5% 5% 39%	2836
	11th to 20th	Day	14% 5% 2 5% 3 4 4 4 4 4 51%	2840
	21st to end	Day	27% 7% 2 5% 3 3 2 2 3 4 43%	3169
February	1st to 10th	Day	18% 6% 2 6% 4 4 5% 4 4 6% 40%	1900
	11th to 20th	Day	23% 6% 2 5% 3 3 3 3 4 6% 42%	1848
	21st to end	Day	21% 7% 3 6% 5% 4 3 3 3 6% 40%	1570
March	1st to 10th	Day	26% 8% 2 6% 3 3 3 3 5% 6% 36%	3264
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 5% 5% 50%	3480
	21st to end	Day	19% 5% 2 7% 5% 4 4 3 4 6% 41%	3815
April	1st to 10th	Day	12% 5% 2 5% 4 4 5% 5% 6% 6% 45%	2104
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 2 5% 6% 46%	2254
	21st to end	Day	11% 4 2 5% 3 4 4 4 6% 7% 51%	2465
May	1st to 10th	Day	12% 7% 2 7% 4 4 4 3 6% 9% 42%	4082
	11th to 20th	Day	18% 7% 2 6% 4 5% 5% 4 6% 7% 36%	4081
	21st to end	Day	8% 5% 2 6% 5% 6% 6% 5% 7% 10% 41%	4476
June	1st to 10th	Day	10% 6% 2 7% 7% 5% 6% 5% 9% 9% 34%	2470
	11th to 20th	Day	6% 4 2 5% 5% 6% 6% 6% 8% 12% 41%	2470
	21st to end	Day	8% 4 2 6% 5% 6% 6% 5% 8% 9% 40%	2470
July	1st to 10th	Day	9% 6% 2 7% 6% 6% 7% 6% 8% 12% 31%	4120
	11th to 20th	Day	10% 4 2 7% 6% 6% 6% 5% 8% 10% 34%	4120
	21st to end	Day	14% 8% 3 10% 8% 8% 8% 6% 8% 9% 19%	4466
August	1st to 10th	Day	10% 5% 2 6% 4 5% 6% 5% 8% 11% 37%	4104
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 4 7% 10% 43%	3886
	21st to end	Day	8% 4 2 5% 4 5% 5% 4 6% 8% 49%	4152
September	1st to 10th	Day	11% 7% 2 7% 6% 4 5% 5% 6% 8% 40%	2090
	11th to 20th	Day	16% 7% 3 6% 4 5% 5% 4 6% 7% 38%	2090
	21st to end	Day	14% 6% 2 5% 3 4 4 4 4 5% 48%	2090
October	1st to 10th	Day	14% 5% 2 4 2 3 3 3 3 5% 56%	2090
	11th to 20th	Day	12% 5% 2 4 2 3 3 3 4 6% 57%	1954
	21st to end	Day	14% 5% 2 4 3 3 3 3 4 5% 55%	2090
November	1st to 10th	Day	12% 5% 1 5% 3 2 3 3 4 4 57%	1753
	11th to 20th	Day	15% 5% 2 3 4 3 4 3 4 6% 52%	1710
	21st to end	Day	15% 5% 2 5% 4 3 4 3 5% 6% 47%	1710
December	1st to 10th	Day	23% 7% 2 5% 4 3 3 4 5% 5% 38%	1710
	11th to 20th	Day	17% 6% 2 6% 4 3 4 2 5% 5% 46%	2153
	21st to end	Day	23% 6% 2 5% 3 3 4 4 6% 7% 37%	3124
January	1st to 10th	Night	19% 6% 2 5% 3 3 3 3 5% 6% 44%	4109
	11th to 20th	Night	14% 7% 3 6% 5% 3 4 3 5% 6% 45%	4120
	21st to end	Night	25% 9% 2 4 4 3 3 2 4 4 41%	4471
February	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 6% 44%	2280
	11th to 20th	Night	21% 7% 2 6% 4 3 3 3 5% 5% 42%	2218
	21st to end	Night	21% 7% 2 5% 4 4 4 4 5% 6% 40%	1884
March	1st to 10th	Night	25% 7% 3 5% 3 3 4 3 4 6% 37%	3587
	11th to 20th	Night	12% 4 2 4 3 3 4 4 6% 8% 50%	3480
	21st to end	Night	18% 7% 3 6% 4 4 4 3 5% 6% 42%	3817
April	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 6% 7% 50%	2090
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 5% 7% 49%	1875
	21st to end	Night	10% 5% 1 5% 4 4 4 4 5% 7% 51%	1713
May	1st to 10th	Night	12% 5% 3 7% 5% 5% 5% 4 6% 8% 40%	2813
	11th to 20th	Night	16% 7% 2 7% 4 4 4 4 6% 7% 40%	2812
	21st to end	Night	8% 4 2 5% 4 5% 5% 4 7% 11% 45%	3079
June	1st to 10th	Night	9% 6% 3 7% 6% 5% 6% 5% 8% 11% 35%	1710
	11th to 20th	Night	5% 5% 1 6% 4 5% 5% 5% 8% 12% 43%	1710
	21st to end	Night	8% 4 2 6% 6% 4 6% 4 8% 10% 42%	1710
July	1st to 10th	Night	13% 6% 3 9% 5% 6% 5% 5% 8% 9% 31%	2840
	11th to 20th	Night	7% 5% 2 7% 6% 6% 7% 6% 9% 12% 32%	2840
	21st to end	Night	15% 8% 4 8% 7% 6% 7% 5% 9% 10% 21%	3087
August	1st to 10th	Night	11% 5% 2 6% 4 5% 5% 5% 8% 13% 35%	2825
	11th to 20th	Night	12% 5% 2 7% 5% 5% 4 4 5% 8% 44%	2938
	21st to end	Night	9% 5% 2 5% 4 3 4 4 6% 7% 52%	3476
September	1st to 10th	Night	10% 6% 2 7% 5% 4 5% 4 6% 8% 42%	2085
	11th to 20th	Night	15% 6% 2 5% 5% 4 4 3 6% 8% 41%	2090
	21st to end	Night	14% 5% 2 6% 4 4 4 3 5% 5% 48%	2090
October	1st to 10th	Night	13% 4 2 4 3 3 4 3 3 6% 55%	2090
	11th to 20th	Night	11% 5% 2 5% 4 3 3 2 4 4 58%	2223
	21st to end	Night	13% 4 1 4 3 3 3 3 3 5% 57%	2508
November	1st to 10th	Night	13% 5% 2 4 2 3 3 3 4 6% 55%	2422
	11th to 20th	Night	15% 4 2 3 4 2 4 3 4 6% 53%	2470
	21st to end	Night	17% 5% 1 4 4 4 4 3 5% 6% 46%	2470
December	1st to 10th	Night	20% 6% 2 6% 4 3 4 3 4 6% 41%	2470
	11th to 20th	Night	18% 6% 2 4 3 3 3 3 4 6% 50%	3042
	21st to end	Night	22% 7% 2 7% 4 4 4 4 5% 6% 35%	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	44% 6% 7% 16% 20% 6%	2837
	11th to 20th	Day	35% 6% 8% 19% 25% 7%	2840
	21st to end	Day	47% 3 5% 17% 21% 8%	3169
February	1st to 10th	Day	45% 4 8% 17% 20% 5%	1900
	11th to 20th	Day	43% 5% 7% 19% 20% 7%	1858
	21st to end	Day	47% 5% 7% 14% 19% 9%	1570
March	1st to 10th	Day	48% 6% 9% 13% 13% 11%	3264
	11th to 20th	Day	35% 5% 7% 17% 24% 11%	3480
	21st to end	Day	44% 5% 8% 19% 20% 3	3815
April	1st to 10th	Day	36% 7% 11% 19% 22% 6%	2104
	11th to 20th	Day	37% 6% 8% 17% 23% 9%	2254
	21st to end	Day	31% 7% 11% 27% 20% 4	2465
May	1st to 10th	Day	38% 8% 14% 20% 18% 2	4120
	11th to 20th	Day	44% 9% 11% 23% 12% 1	4085
	21st to end	Day	33% 10% 14% 21% 20% 1	4489
June	1st to 10th	Day	41% 12% 17% 18% 9% 3	2470
	11th to 20th	Day	32% 11% 21% 23% 12% 1	2470
	21st to end	Day	36% 11% 18% 19% 13% 3	2470
July	1st to 10th	Day	42% 13% 20% 20% 4 1	4055
	11th to 20th	Day	40% 12% 23% 18% 5% 2	4051
	21st to end	Day	56% 14% 15% 12% 4	4324
August	1st to 10th	Day	37% 10% 15% 30% 7%	4091
	11th to 20th	Day	34% 10% 20% 20% 14% 3	3925
	21st to end	Day	32% 9% 13% 22% 21% 3	4152
September	1st to 10th	Day	40% 9% 14% 16% 18% 4	2090
	11th to 20th	Day	43% 9% 11% 16% 20% 2	2090
	21st to end	Day	37% 6% 12% 18% 20% 7%	2090
October	1st to 10th	Day	25% 4 7% 14% 38% 12%	3480
	11th to 20th	Day	21% 3 6% 14% 28% 29%	3220
	21st to end	Day	28% 3 5% 21% 29% 13%	3428
November	1st to 10th	Day	31% 4 8% 15% 30% 12%	1753
	11th to 20th	Day	33% 5% 6% 19% 26% 10%	1710
	21st to end	Day	37% 5% 8% 18% 26% 7%	1710
December	1st to 10th	Day	47% 5% 7% 18% 16% 6%	1710
	11th to 20th	Day	40% 4 7% 16% 25% 8%	2150
	21st to end	Day	42% 6% 12% 17% 19% 3	3124
January	1st to 10th	Night	40% 6% 7% 16% 26% 6%	4109
	11th to 20th	Night	39% 5% 7% 20% 20% 9%	4120
	21st to end	Night	48% 4 5% 13% 24% 6%	4471
February	1st to 10th	Night	40% 5% 9% 18% 21% 7%	2280
	11th to 20th	Night	45% 4 6% 17% 21% 8%	2219
	21st to end	Night	45% 4 8% 16% 18% 9%	1884
March	1st to 10th	Night	47% 6% 9% 17% 14% 7%	3587
	11th to 20th	Night	30% 6% 9% 17% 27% 11%	3480
	21st to end	Night	42% 5% 8% 19% 18% 8%	3817
April	1st to 10th	Night	33% 6% 11% 19% 24% 7%	2090
	11th to 20th	Night	34% 5% 8% 20% 23% 10%	1875
	21st to end	Night	32% 7% 11% 26% 20% 4	1713
May	1st to 10th	Night	38% 11% 14% 20% 15% 2	2840
	11th to 20th	Night	42% 8% 14% 23% 13% 1	2813
	21st to end	Night	29% 10% 16% 26% 17% 2	3087
June	1st to 10th	Night	39% 11% 17% 20% 11% 2	1710
	11th to 20th	Night	30% 11% 20% 24% 13% 1	1710
	21st to end	Night	34% 12% 17% 20% 14% 4	1710
July	1st to 10th	Night	46% 11% 19% 17% 5% 1	2795
	11th to 20th	Night	38% 15% 23% 18% 5% 1	2786
	21st to end	Night	54% 14% 16% 12% 4 1	2988
August	1st to 10th	Night	37% 10% 20% 26% 6%	2814
	11th to 20th	Night	38% 9% 19% 19% 14% 1	2965
	21st to end	Night	30% 9% 13% 23% 22% 2	3476
September	1st to 10th	Night	38% 9% 15% 17% 16% 4	2085
	11th to 20th	Night	40% 9% 12% 19% 18% 2	2090
	21st to end	Night	37% 7% 11% 19% 19% 7%	2090
October	1st to 10th	Night	25% 5% 10% 14% 35% 11%	3480
	11th to 20th	Night	19% 3 5% 17% 31% 25%	3683
	21st to end	Night	25% 3 5% 22% 27% 17%	4120
November	1st to 10th	Night	31% 5% 7% 19% 26% 12%	2422
	11th to 20th	Night	32% 4 7% 17% 27% 12%	2470
	21st to end	Night	37% 5% 7% 19% 24% 7%	2470
December	1st to 10th	Night	45% 5% 8% 19% 18% 6%	2470
	11th to 20th	Night	36% 4 9% 18% 26% 7%	3044
	21st to end	Night	46% 6% 9% 20% 16% 3	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	25% 22% 37% 14% 1	270
	11th to 20th	Day	29% 21% 26% 19% 4	270
	21st to end	Day	28% 24% 34% 11% 2 1	297
February	1st to 10th	Day	26% 19% 35% 18% 2	270
	11th to 20th	Day	37% 21% 30% 10% 1	270
	21st to end	Day	35% 20% 35% 9% 1	225
March	1st to 10th	Day	24% 16% 30% 20% 9%	349
	11th to 20th	Day	23% 19% 32% 19% 6% 1	460
	21st to end	Day	22% 17% 33% 20% 7% 1	506
April	1st to 10th	Day	22% 15% 32% 20% 10% 1	460
	11th to 20th	Day	14% 17% 36% 19% 14% 1	452
	21st to end	Day	17% 11% 27% 27% 14% 4	460
May	1st to 10th	Day	14% 13% 31% 20% 15% 6%	463
	11th to 20th	Day	17% 9% 21% 27% 17% 10%	487
	21st to end	Day	15% 7% 18% 28% 21% 11%	529
June	1st to 10th	Day	13% 4 20% 29% 23% 11%	490
	11th to 20th	Day	8% 3 18% 29% 25% 16%	490
	21st to end	Day	11% 3 19% 30% 23% 13%	490
July	1st to 10th	Day	11% 2 11% 25% 29% 22%	485
	11th to 20th	Day	11% 2 10% 23% 34% 20%	484
	21st to end	Day	9% 1 9% 27% 35% 19%	532
August	1st to 10th	Day	15% 5% 14% 22% 25% 19%	486
	11th to 20th	Day	12% 4 11% 27% 33% 14%	479
	21st to end	Day	16% 3 10% 23% 30% 18%	539
September	1st to 10th	Day	10% 4 16% 28% 29% 14%	490
	11th to 20th	Day	19% 5% 12% 24% 30% 10%	490
	21st to end	Day	17% 5% 17% 26% 26% 10%	490
October	1st to 10th	Day	17% 6% 18% 31% 19% 9%	490
	11th to 20th	Day	14% 10% 24% 27% 22% 4	490
	21st to end	Day	18% 9% 25% 27% 19% 3	539
November	1st to 10th	Day	21% 9% 26% 27% 16% 2	327
	11th to 20th	Day	18% 19% 33% 23% 6% 1	270
	21st to end	Day	16% 13% 36% 23% 10% 1	270
December	1st to 10th	Day	32% 18% 29% 17% 4	270
	11th to 20th	Day	26% 14% 33% 23% 4	270
	21st to end	Day	33% 17% 27% 16% 5% 1	297
January	1st to 10th	Night	26% 18% 29% 21% 5%	760
	11th to 20th	Night	22% 16% 32% 23% 7%	760
	21st to end	Night	22% 18% 35% 22% 3	836
February	1st to 10th	Night	21% 14% 31% 29% 5%	760
	11th to 20th	Night	24% 17% 33% 23% 3	743
	21st to end	Night	24% 16% 35% 22% 3	628
March	1st to 10th	Night	20% 15% 33% 28% 4	760
	11th to 20th	Night	19% 12% 36% 25% 8% 1	760
	21st to end	Night	19% 15% 28% 29% 9%	836
April	1st to 10th	Night	16% 15% 31% 29% 9% 1	760
	11th to 20th	Night	16% 11% 28% 31% 14% 1	563
	21st to end	Night	13% 7% 26% 31% 20% 1	570
May	1st to 10th	Night	13% 8% 26% 30% 23% 1	570
	11th to 20th	Night	14% 6% 22% 30% 24% 4	561
	21st to end	Night	15% 2 14% 33% 32% 5%	617
June	1st to 10th	Night	11% 3 16% 35% 31% 5%	570
	11th to 20th	Night	6% 3 15% 32% 31% 13%	570
	21st to end	Night	8% 2 13% 39% 31% 8%	570
July	1st to 10th	Night	11% 1 9% 26% 41% 11%	555
	11th to 20th	Night	11% 2 6% 24% 47% 10%	552
	21st to end	Night	8% 2 9% 29% 42% 10%	624
August	1st to 10th	Night	15% 2 7% 29% 36% 12%	567
	11th to 20th	Night	13% 2 10% 26% 40% 8%	564
	21st to end	Night	14% 4 9% 26% 36% 11%	627
September	1st to 10th	Night	10% 4 12% 28% 37% 8%	755
	11th to 20th	Night	17% 3 13% 29% 34% 4	760
	21st to end	Night	17% 4 14% 33% 30% 2	760
October	1st to 10th	Night	14% 5% 18% 31% 26% 6%	760
	11th to 20th	Night	13% 8% 24% 32% 21% 2	760
	21st to end	Night	15% 8% 22% 32% 21% 2	836
November	1st to 10th	Night	15% 9% 22% 33% 20% 1	760
	11th to 20th	Night	17% 12% 29% 28% 12% 1	760
	21st to end	Night	18% 11% 29% 29% 12% 1	760
December	1st to 10th	Night	21% 16% 28% 28% 7%	760
	11th to 20th	Night	21% 13% 29% 27% 10%	760
	21st to end	Night	29% 14% 24% 28% 5%	836

Page generated at 2024-11-03 02:11:26. Version ac07

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