Eagle Bluff Environmental Learning Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Bluff Environmental Learning Center clear sky chart from 2005-11-06 to 2024-12-09.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 37%	101846
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 39%	98043
Transparency	Day	45% 6% 12% 25% 12% 1	105428
	Night	44% 5% 11% 24% 14% 2	102602
Seeing	Day	17% 12% 31% 24% 12% 3	16060
	Night	17% 11% 32% 29% 10% 1	25970

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	9% 13% 7% 19% 7% 5% 5% 3 4 5% 23%	2527
	11th to 20th	Day	8% 12% 5% 14% 9% 7% 5% 8% 8% 6% 19%	2530
	21st to end	Day	13% 19% 9% 14% 6% 4 3 3 4 5% 21%	3115
February	1st to 10th	Day	8% 13% 4 13% 6% 5% 4 5% 5% 6% 29%	1710
	11th to 20th	Day	11% 11% 4 9% 6% 5% 5% 5% 6% 6% 32%	1664
	21st to end	Day	14% 10% 5% 10% 5% 6% 4 3 4 7% 32%	1548
March	1st to 10th	Day	14% 9% 3 7% 4 3 3 2 5% 5% 46%	3266
	11th to 20th	Day	11% 8% 3 7% 4 3 5% 3 5% 8% 42%	3480
	21st to end	Day	23% 13% 5% 11% 5% 4 4 3 4 5% 23%	3934
April	1st to 10th	Day	18% 13% 3 8% 5% 4 3 3 5% 6% 31%	2280
	11th to 20th	Day	20% 12% 4 7% 4 4 4 3 3 5% 32%	2254
	21st to end	Day	21% 12% 3 7% 5% 4 4 3 5% 6% 30%	2365
May	1st to 10th	Day	18% 8% 2 7% 4 5% 4 4 6% 7% 35%	4305
	11th to 20th	Day	14% 7% 3 6% 4 4 5% 3 6% 7% 41%	4399
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 6% 38%	4824
June	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 6% 7% 46%	2660
	11th to 20th	Day	13% 6% 3 7% 4 5% 5% 4 6% 8% 40%	2660
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 7% 7% 40%	2660
July	1st to 10th	Day	10% 6% 2 6% 5% 6% 6% 6% 8% 9% 37%	4440
	11th to 20th	Day	5% 3 2 4 4 4 5% 4 5% 10% 54%	4440
	21st to end	Day	7% 6% 3 6% 5% 5% 5% 5% 7% 9% 42%	4813
August	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	4104
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 9% 43%	4041
	21st to end	Day	9% 5% 2 5% 5% 5% 5% 4 6% 8% 46%	4191
September	1st to 10th	Day	13% 6% 2 5% 3 3 4 3 6% 7% 47%	2280
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 6% 8% 46%	2280
	21st to end	Day	14% 7% 2 7% 4 4 3 3 5% 7% 43%	2001
October	1st to 10th	Day	16% 7% 2 6% 3 4 4 3 5% 5% 45%	1900
	11th to 20th	Day	15% 10% 3 7% 3 3 3 4 6% 6% 40%	1900
	21st to end	Day	16% 13% 3 7% 4 3 4 2 4 6% 38%	2029
November	1st to 10th	Day	12% 8% 4 6% 4 4 4 3 6% 7% 41%	1761
	11th to 20th	Day	14% 13% 5% 10% 6% 4 3 3 5% 5% 31%	1600
	21st to end	Day	11% 13% 4 6% 5% 3 3 3 5% 7% 39%	1600
December	1st to 10th	Day	13% 10% 5% 11% 7% 6% 5% 3 6% 5% 29%	1584
	11th to 20th	Day	11% 13% 5% 9% 6% 5% 4 5% 7% 6% 28%	1918
	21st to end	Day	20% 18% 8% 14% 5% 4 3 3 3 4 18%	2783
January	1st to 10th	Night	10% 13% 8% 17% 6% 5% 4 3 3 4 27%	4428
	11th to 20th	Night	9% 13% 6% 13% 7% 6% 5% 6% 10% 5% 22%	4440
	21st to end	Night	15% 18% 6% 11% 5% 4 4 3 5% 5% 23%	4550
February	1st to 10th	Night	7% 14% 5% 11% 6% 5% 4 4 5% 5% 33%	2470
	11th to 20th	Night	8% 10% 3 10% 6% 5% 6% 3 4 7% 38%	2403
	21st to end	Night	14% 9% 3 10% 5% 5% 4 3 5% 6% 36%	1904
March	1st to 10th	Night	11% 9% 3 7% 4 3 4 4 5% 6% 44%	3615
	11th to 20th	Night	10% 8% 3 8% 5% 5% 5% 4 5% 7% 42%	3480
	21st to end	Night	25% 12% 3 10% 4 3 3 2 3 5% 28%	3695
April	1st to 10th	Night	16% 12% 4 7% 3 4 4 3 4 6% 38%	1900
	11th to 20th	Night	19% 10% 2 7% 3 3 4 4 5% 6% 36%	1875
	21st to end	Night	18% 10% 3 7% 4 4 5% 3 4 6% 36%	1811
May	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 5% 5% 41%	2600
	11th to 20th	Night	12% 5% 3 5% 3 3 4 3 5% 7% 49%	2506
	21st to end	Night	12% 6% 2 7% 5% 4 4 3 5% 7% 44%	2743
June	1st to 10th	Night	10% 5% 1 5% 4 4 5% 3 7% 9% 48%	1520
	11th to 20th	Night	12% 6% 2 6% 4 6% 5% 4 5% 8% 43%	1520
	21st to end	Night	9% 7% 2 4 3 3 3 4 6% 9% 50%	1520
July	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 9% 47%	2530
	11th to 20th	Night	4 3 2 5% 3 4 5% 3 6% 9% 56%	2530
	21st to end	Night	5% 3 1 5% 4 4 4 4 6% 9% 54%	2750
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 5% 6% 49%	2831
	11th to 20th	Night	12% 4 2 4 3 3 4 3 5% 7% 53%	2798
	21st to end	Night	9% 6% 2 6% 4 4 4 3 4 7% 50%	3463
September	1st to 10th	Night	10% 5% 1 4 3 3 4 4 5% 5% 56%	1900
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 6% 54%	1900
	21st to end	Night	12% 6% 1 5% 4 4 3 3 4 6% 53%	2156
October	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 5% 6% 51%	2280
	11th to 20th	Night	13% 7% 2 6% 3 4 3 3 6% 7% 44%	2280
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 6% 39%	2567
November	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 5% 5% 46%	2536
	11th to 20th	Night	12% 13% 5% 9% 5% 4 4 3 4 6% 35%	2800
	21st to end	Night	13% 12% 4 9% 5% 4 3 3 4 5% 37%	2800
December	1st to 10th	Night	11% 12% 5% 10% 6% 5% 5% 3 5% 7% 31%	2779
	11th to 20th	Night	12% 12% 4 12% 6% 5% 5% 4 5% 6% 28%	3279
	21st to end	Night	20% 15% 6% 13% 6% 4 4 3 4 4 21%	4884

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	65% 5% 11% 14% 5%	2528
	11th to 20th	Day	61% 6% 10% 16% 7%	2530
	21st to end	Day	66% 4 12% 13% 4	3115
February	1st to 10th	Day	53% 5% 12% 17% 11% 1	1710
	11th to 20th	Day	51% 5% 11% 24% 8% 1	1673
	21st to end	Day	53% 4 11% 20% 10% 2	1548
March	1st to 10th	Day	42% 4 11% 25% 16% 2	3266
	11th to 20th	Day	41% 4 9% 33% 11% 2	3480
	21st to end	Day	64% 4 9% 15% 6% 1	3934
April	1st to 10th	Day	54% 5% 10% 20% 10% 1	2280
	11th to 20th	Day	54% 4 9% 19% 11% 2	2254
	21st to end	Day	54% 5% 10% 18% 11% 1	2365
May	1st to 10th	Day	46% 7% 9% 22% 15% 1	4344
	11th to 20th	Day	40% 8% 9% 32% 11% 1	4403
	21st to end	Day	45% 6% 9% 23% 14% 1	4837
June	1st to 10th	Day	36% 7% 12% 29% 14% 2	2660
	11th to 20th	Day	41% 7% 12% 23% 17% 1	2660
	21st to end	Day	41% 8% 13% 24% 13% 2	2660
July	1st to 10th	Day	40% 9% 18% 24% 8% 1	4371
	11th to 20th	Day	26% 7% 13% 34% 19% 1	4365
	21st to end	Day	35% 10% 13% 24% 17% 1	4662
August	1st to 10th	Day	39% 7% 12% 28% 13% 2	4090
	11th to 20th	Day	37% 6% 12% 33% 11% 1	4080
	21st to end	Day	34% 7% 15% 29% 14% 1	4190
September	1st to 10th	Day	36% 6% 13% 27% 18% 1	2280
	11th to 20th	Day	35% 8% 13% 31% 12% 1	2280
	21st to end	Day	40% 5% 11% 30% 13% 1	2001
October	1st to 10th	Day	26% 4 7% 40% 23% 1	3160
	11th to 20th	Day	36% 4 13% 25% 20% 2	3140
	21st to end	Day	41% 3 12% 32% 11%	3319
November	1st to 10th	Day	42% 6% 14% 22% 14% 2	1761
	11th to 20th	Day	56% 5% 10% 19% 9% 1	1600
	21st to end	Day	47% 5% 17% 22% 7% 1	1600
December	1st to 10th	Day	56% 5% 14% 16% 8% 1	1584
	11th to 20th	Day	55% 5% 17% 15% 7% 1	1915
	21st to end	Day	72% 4 7% 13% 3	2783
January	1st to 10th	Night	61% 4 9% 19% 7%	4428
	11th to 20th	Night	58% 5% 10% 16% 10%	4440
	21st to end	Night	63% 5% 9% 16% 7% 1	4550
February	1st to 10th	Night	53% 3 12% 20% 11% 1	2470
	11th to 20th	Night	48% 4 12% 23% 11% 2	2404
	21st to end	Night	50% 3 11% 22% 12% 2	1904
March	1st to 10th	Night	40% 5% 10% 30% 13% 2	3615
	11th to 20th	Night	41% 6% 8% 27% 17% 2	3480
	21st to end	Night	60% 4 8% 19% 7% 2	3695
April	1st to 10th	Night	48% 5% 9% 21% 15% 2	1900
	11th to 20th	Night	48% 5% 10% 19% 16% 3	1875
	21st to end	Night	49% 5% 9% 21% 14% 2	1811
May	1st to 10th	Night	43% 6% 9% 19% 22% 1	2626
	11th to 20th	Night	35% 6% 10% 27% 18% 5%	2507
	21st to end	Night	38% 8% 9% 28% 17% 1	2751
June	1st to 10th	Night	32% 8% 13% 29% 16% 2	1520
	11th to 20th	Night	37% 7% 12% 22% 19% 3	1520
	21st to end	Night	31% 6% 16% 28% 16% 4	1520
July	1st to 10th	Night	34% 6% 19% 27% 12% 1	2490
	11th to 20th	Night	24% 6% 16% 35% 16% 2	2482
	21st to end	Night	26% 7% 17% 27% 20% 3	2662
August	1st to 10th	Night	35% 5% 12% 29% 17% 2	2822
	11th to 20th	Night	31% 6% 15% 31% 16% 1	2825
	21st to end	Night	35% 5% 14% 27% 16% 3	3463
September	1st to 10th	Night	29% 7% 9% 32% 22% 1	1900
	11th to 20th	Night	31% 5% 14% 32% 17% 1	1900
	21st to end	Night	33% 5% 11% 29% 21% 1	2156
October	1st to 10th	Night	24% 4 6% 36% 28% 3	3800
	11th to 20th	Night	28% 5% 12% 28% 25% 2	3779
	21st to end	Night	45% 5% 10% 25% 15% 1	4227
November	1st to 10th	Night	40% 4 12% 25% 16% 2	2536
	11th to 20th	Night	51% 5% 12% 20% 11% 2	2800
	21st to end	Night	51% 3 14% 23% 8% 1	2800
December	1st to 10th	Night	54% 4 14% 20% 8% 1	2779
	11th to 20th	Night	55% 6% 13% 18% 7% 1	3281
	21st to end	Night	67% 4 9% 14% 6%	4884

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	14% 20% 36% 20% 9% 2	270
	11th to 20th	Day	21% 17% 38% 18% 4 1	270
	21st to end	Day	19% 15% 40% 21% 5%	297
February	1st to 10th	Day	16% 21% 43% 14% 6% 1	270
	11th to 20th	Day	21% 24% 33% 18% 3 1	270
	21st to end	Day	21% 20% 42% 16% 1	225
March	1st to 10th	Day	19% 20% 40% 17% 4	270
	11th to 20th	Day	22% 16% 39% 16% 6% 1	270
	21st to end	Day	28% 16% 30% 18% 7% 1	366
April	1st to 10th	Day	28% 16% 35% 15% 5%	460
	11th to 20th	Day	26% 19% 25% 20% 8% 1	452
	21st to end	Day	26% 17% 30% 19% 6% 2	545
May	1st to 10th	Day	22% 15% 33% 22% 7% 2	653
	11th to 20th	Day	22% 12% 28% 25% 10% 3	675
	21st to end	Day	20% 12% 29% 24% 13% 3	734
June	1st to 10th	Day	11% 9% 31% 29% 17% 3	680
	11th to 20th	Day	15% 10% 34% 29% 10% 3	680
	21st to end	Day	14% 10% 32% 26% 13% 5%	680
July	1st to 10th	Day	10% 5% 22% 32% 23% 9%	671
	11th to 20th	Day	8% 7% 29% 31% 18% 7%	668
	21st to end	Day	7% 5% 28% 36% 18% 6%	739
August	1st to 10th	Day	8% 4 26% 32% 22% 7%	676
	11th to 20th	Day	14% 4 23% 29% 22% 8%	665
	21st to end	Day	13% 7% 25% 30% 19% 7%	550
September	1st to 10th	Day	16% 8% 24% 30% 17% 5%	490
	11th to 20th	Day	14% 5% 28% 31% 17% 4	490
	21st to end	Day	15% 16% 30% 24% 13% 2	353
October	1st to 10th	Day	18% 13% 28% 27% 12% 2	300
	11th to 20th	Day	23% 22% 33% 14% 7%	300
	21st to end	Day	27% 17% 34% 15% 5% 2	330
November	1st to 10th	Day	18% 18% 36% 22% 5% 1	300
	11th to 20th	Day	23% 24% 33% 16% 4	300
	21st to end	Day	23% 17% 40% 16% 4	300
December	1st to 10th	Day	13% 18% 43% 18% 7% 1	294
	11th to 20th	Day	18% 17% 42% 17% 6%	270
	21st to end	Day	30% 17% 39% 13% 1	297
January	1st to 10th	Night	14% 18% 37% 24% 7% 1	950
	11th to 20th	Night	19% 13% 38% 24% 5% 1	950
	21st to end	Night	21% 14% 34% 25% 6%	1045
February	1st to 10th	Night	15% 16% 39% 25% 5% 1	950
	11th to 20th	Night	14% 18% 40% 22% 6% 1	929
	21st to end	Night	20% 15% 35% 25% 5%	648
March	1st to 10th	Night	20% 14% 38% 22% 6% 1	694
	11th to 20th	Night	18% 13% 35% 27% 6% 1	570
	21st to end	Night	22% 12% 30% 25% 9% 1	627
April	1st to 10th	Night	21% 15% 35% 25% 4	570
	11th to 20th	Night	24% 11% 34% 24% 7% 1	563
	21st to end	Night	22% 11% 35% 26% 7% 1	570
May	1st to 10th	Night	21% 10% 32% 30% 6% 1	570
	11th to 20th	Night	19% 7% 32% 32% 8% 1	561
	21st to end	Night	18% 6% 27% 35% 13% 1	617
June	1st to 10th	Night	12% 4 28% 42% 12% 1	570
	11th to 20th	Night	14% 5% 30% 41% 10%	570
	21st to end	Night	13% 4 27% 39% 16% 1	570
July	1st to 10th	Night	9% 2 19% 40% 29% 2	555
	11th to 20th	Night	6% 4 27% 37% 24% 3	552
	21st to end	Night	6% 2 17% 51% 21% 3	624
August	1st to 10th	Night	7% 2 20% 46% 23% 2	567
	11th to 20th	Night	12% 4 17% 37% 26% 4	564
	21st to end	Night	12% 2 23% 37% 23% 3	627
September	1st to 10th	Night	12% 4 23% 38% 17% 5%	570
	11th to 20th	Night	13% 4 27% 37% 17% 3	570
	21st to end	Night	12% 10% 29% 33% 16% 1	693
October	1st to 10th	Night	16% 8% 30% 30% 15% 1	760
	11th to 20th	Night	18% 14% 32% 29% 8%	760
	21st to end	Night	22% 12% 32% 28% 6%	836
November	1st to 10th	Night	18% 12% 36% 27% 7% 1	780
	11th to 20th	Night	19% 17% 38% 21% 5%	1000
	21st to end	Night	20% 16% 36% 22% 6%	1000
December	1st to 10th	Night	19% 12% 40% 23% 6% 1	993
	11th to 20th	Night	21% 13% 37% 23% 6% 1	950
	21st to end	Night	26% 15% 33% 22% 4	1045

Page generated at 2024-12-06 02:54:50. Version ac07

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