Epiphany
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Epiphany clear sky chart from 2005-11-06 to 2025-03-12.

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% 7% 3 7% 5% 4 4 4 6% 7% 43%	112380
	Night	9% 7% 3 7% 5% 4 4 4 5% 7% 45%	115378
Transparency	Day	40% 5% 15% 25% 14% 2	112128
	Night	38% 5% 15% 25% 16% 2	115220
Seeing	Day	14% 9% 31% 31% 13% 2	16336
	Night	12% 9% 35% 34% 9% 1	26438

By Month

Percentage Cloud Cover SW (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% 12% 4 18% 8% 7% 8% 5% 5% 5% 20%	3610
	11th to 20th	Day	4 10% 5% 12% 7% 7% 7% 4 9% 7% 28%	3640
	21st to end	Day	4 9% 7% 12% 6% 6% 6% 4 5% 6% 35%	4378
February	1st to 10th	Day	9% 12% 4 11% 7% 6% 6% 4 6% 6% 30%	1800
	11th to 20th	Day	7% 9% 5% 10% 6% 7% 5% 5% 5% 6% 35%	1819
	21st to end	Day	8% 10% 4 10% 6% 5% 5% 4 6% 6% 37%	1650
March	1st to 10th	Day	11% 9% 3 8% 4 4 3 3 5% 7% 44%	3348
	11th to 20th	Day	9% 7% 3 7% 4 4 4 3 5% 8% 46%	3491
	21st to end	Day	23% 11% 4 10% 5% 4 3 3 5% 5% 25%	3814
April	1st to 10th	Day	15% 8% 2 7% 4 3 4 4 6% 7% 38%	2179
	11th to 20th	Day	18% 10% 2 6% 5% 4 4 3 5% 7% 36%	2439
	21st to end	Day	18% 10% 3 6% 5% 3 4 3 4 7% 39%	2470
May	1st to 10th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 6% 39%	4120
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 5% 6% 50%	4082
	21st to end	Day	18% 5% 2 5% 4 4 4 3 5% 8% 42%	4776
June	1st to 10th	Day	12% 5% 2 5% 5% 4 4 4 6% 8% 47%	2850
	11th to 20th	Day	14% 5% 2 4 4 4 4 4 6% 7% 46%	2850
	21st to end	Day	9% 5% 1 5% 4 4 4 5% 6% 8% 50%	2850
July	1st to 10th	Day	11% 4 2 5% 4 4 5% 4 6% 9% 46%	4635
	11th to 20th	Day	5% 3 2 4 3 4 4 3 5% 7% 59%	4430
	21st to end	Day	5% 3 1 4 4 4 5% 4 7% 10% 54%	4567
August	1st to 10th	Day	8% 5% 2 6% 5% 4 4 4 7% 8% 47%	4103
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 4 6% 8% 36%	4041
	21st to end	Day	7% 4 2 5% 3 3 4 3 6% 7% 55%	4532
September	1st to 10th	Day	12% 5% 2 4 3 3 3 3 4 6% 54%	2199
	11th to 20th	Day	9% 4 2 4 3 4 4 3 5% 7% 56%	2090
	21st to end	Day	12% 5% 2 5% 3 3 3 3 4 5% 56%	2090
October	1st to 10th	Day	9% 4 1 3 2 3 3 2 3 5% 64%	3306
	11th to 20th	Day	9% 5% 1 5% 4 4 4 3 4 6% 55%	3140
	21st to end	Day	12% 7% 2 6% 4 5% 5% 4 5% 7% 44%	3193
November	1st to 10th	Day	10% 8% 2 7% 4 4 4 4 6% 7% 45%	1763
	11th to 20th	Day	7% 9% 2 10% 5% 4 4 3 5% 7% 44%	1710
	21st to end	Day	9% 9% 2 8% 4 5% 4 4 6% 7% 43%	1600
December	1st to 10th	Day	5% 9% 5% 11% 8% 7% 6% 4 5% 7% 35%	2610
	11th to 20th	Day	8% 12% 4 12% 6% 5% 6% 5% 6% 7% 29%	2707
	21st to end	Day	15% 8% 3 15% 7% 4 5% 4 5% 7% 27%	3498
January	1st to 10th	Night	6% 12% 5% 13% 10% 7% 7% 5% 5% 6% 24%	6350
	11th to 20th	Night	3 7% 4 11% 7% 5% 7% 4 8% 8% 35%	6340
	21st to end	Night	5% 7% 5% 10% 5% 5% 6% 3 6% 6% 42%	6597
February	1st to 10th	Night	8% 11% 4 10% 6% 5% 5% 4 5% 7% 37%	2600
	11th to 20th	Night	7% 10% 4 9% 5% 5% 5% 4 6% 6% 41%	2485
	21st to end	Night	7% 9% 3 8% 4 4 5% 4 6% 7% 42%	1980
March	1st to 10th	Night	9% 9% 3 6% 4 4 4 4 5% 6% 47%	3732
	11th to 20th	Night	9% 6% 3 6% 4 3 4 4 5% 8% 49%	3497
	21st to end	Night	20% 11% 4 8% 6% 4 4 3 4 5% 30%	3817
April	1st to 10th	Night	15% 8% 3 6% 5% 3 4 3 5% 7% 41%	1996
	11th to 20th	Night	17% 9% 2 7% 4 3 3 3 4 6% 43%	1689
	21st to end	Night	15% 8% 2 5% 3 4 4 4 5% 8% 41%	1710
May	1st to 10th	Night	16% 5% 2 4 4 3 4 3 5% 7% 47%	2850
	11th to 20th	Night	9% 4 2 4 4 3 3 3 6% 8% 54%	2823
	21st to end	Night	15% 5% 2 5% 4 4 5% 4 5% 8% 43%	2807
June	1st to 10th	Night	6% 5% 2 5% 4 4 4 4 4 7% 55%	1330
	11th to 20th	Night	9% 5% 2 5% 4 3 4 3 7% 9% 50%	1330
	21st to end	Night	6% 3 1 3 3 3 4 3 7% 8% 58%	1330
July	1st to 10th	Night	10% 5% 1 4 3 3 3 4 7% 8% 51%	2331
	11th to 20th	Night	4 2 1 3 3 3 4 3 6% 7% 65%	2540
	21st to end	Night	2 2 1 3 3 3 4 5% 7% 10% 59%	2996
August	1st to 10th	Night	6% 6% 2 5% 4 5% 4 4 7% 9% 49%	2836
	11th to 20th	Night	10% 5% 2 6% 3 4 4 3 5% 7% 50%	2798
	21st to end	Night	8% 3 2 4 3 3 3 4 5% 8% 56%	3135
September	1st to 10th	Night	9% 3 1 4 3 3 3 3 5% 6% 61%	1977
	11th to 20th	Night	7% 4 2 4 3 3 3 4 6% 6% 59%	2090
	21st to end	Night	9% 5% 1 4 2 2 3 2 5% 6% 58%	2090
October	1st to 10th	Night	9% 3 1 3 2 2 2 2 3 6% 68%	3608
	11th to 20th	Night	8% 5% 2 4 2 2 3 2 5% 8% 59%	3779
	21st to end	Night	11% 6% 2 6% 4 4 4 3 6% 8% 46%	4359
November	1st to 10th	Night	8% 6% 2 6% 3 4 4 4 5% 7% 51%	2535
	11th to 20th	Night	7% 8% 3 8% 5% 4 4 4 6% 7% 46%	2686
	21st to end	Night	8% 8% 3 7% 3 4 4 4 5% 7% 48%	2800
December	1st to 10th	Night	4 7% 3 10% 6% 6% 5% 4 5% 6% 44%	4580
	11th to 20th	Night	8% 10% 4 9% 6% 7% 5% 4 5% 7% 35%	5495
	21st to end	Night	15% 11% 4 12% 6% 5% 4 4 5% 5% 29%	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	64% 6% 14% 12% 4	3611
	11th to 20th	Day	52% 3 13% 17% 14%	3640
	21st to end	Day	48% 6% 17% 18% 11%	4378
February	1st to 10th	Day	52% 8% 15% 16% 9%	1800
	11th to 20th	Day	49% 6% 14% 19% 10% 1	1828
	21st to end	Day	46% 7% 16% 18% 11% 1	1650
March	1st to 10th	Day	41% 5% 12% 28% 12% 1	3348
	11th to 20th	Day	37% 5% 10% 30% 15% 3	3491
	21st to end	Day	61% 5% 16% 14% 3 1	3814
April	1st to 10th	Day	42% 7% 14% 25% 11% 1	2179
	11th to 20th	Day	48% 6% 11% 22% 11% 3	2442
	21st to end	Day	45% 6% 14% 24% 11%	2470
May	1st to 10th	Day	42% 6% 11% 24% 16%	4120
	11th to 20th	Day	35% 6% 12% 28% 17% 3	4086
	21st to end	Day	40% 7% 13% 26% 13% 1	4776
June	1st to 10th	Day	34% 7% 16% 29% 12% 2	2850
	11th to 20th	Day	36% 7% 16% 25% 14% 2	2850
	21st to end	Day	30% 8% 16% 29% 14% 3	2850
July	1st to 10th	Day	34% 6% 20% 27% 12% 1	4564
	11th to 20th	Day	24% 5% 14% 35% 19% 3	4355
	21st to end	Day	25% 7% 17% 29% 20% 2	4422
August	1st to 10th	Day	33% 6% 15% 29% 15% 2	4090
	11th to 20th	Day	46% 6% 15% 24% 9% 1	4080
	21st to end	Day	28% 6% 19% 28% 16% 2	4531
September	1st to 10th	Day	31% 5% 12% 31% 19% 2	2199
	11th to 20th	Day	28% 6% 17% 32% 16% 1	2090
	21st to end	Day	30% 5% 11% 32% 20% 2	2090
October	1st to 10th	Day	25% 3 9% 27% 33% 4	3306
	11th to 20th	Day	31% 3 14% 29% 20% 3	3140
	21st to end	Day	41% 3 14% 21% 19% 1	3193
November	1st to 10th	Day	37% 6% 17% 24% 13% 3	1763
	11th to 20th	Day	41% 5% 14% 25% 13% 2	1710
	21st to end	Day	40% 5% 17% 24% 13% 1	1600
December	1st to 10th	Day	49% 4 17% 22% 7% 1	2610
	11th to 20th	Day	54% 4 19% 18% 5%	2704
	21st to end	Day	56% 3 15% 19% 5%	3498
January	1st to 10th	Night	60% 5% 11% 16% 8%	6350
	11th to 20th	Night	45% 4 16% 17% 16% 1	6340
	21st to end	Night	42% 6% 16% 24% 13%	6597
February	1st to 10th	Night	47% 5% 14% 22% 11% 1	2600
	11th to 20th	Night	43% 6% 12% 23% 13% 3	2486
	21st to end	Night	39% 5% 16% 24% 13% 3	1980
March	1st to 10th	Night	36% 4 14% 25% 20% 2	3732
	11th to 20th	Night	33% 4 12% 30% 18% 2	3497
	21st to end	Night	56% 5% 16% 17% 6% 1	3817
April	1st to 10th	Night	41% 6% 14% 25% 13% 1	1996
	11th to 20th	Night	44% 4 9% 22% 18% 2	1689
	21st to end	Night	41% 6% 13% 26% 12% 2	1710
May	1st to 10th	Night	36% 6% 14% 23% 16% 4	2850
	11th to 20th	Night	28% 7% 13% 27% 23% 3	2824
	21st to end	Night	39% 7% 13% 26% 15% 1	2808
June	1st to 10th	Night	28% 5% 17% 28% 17% 4	1330
	11th to 20th	Night	29% 6% 18% 24% 19% 4	1330
	21st to end	Night	22% 6% 17% 32% 20% 3	1330
July	1st to 10th	Night	31% 5% 23% 25% 15% 2	2293
	11th to 20th	Night	19% 4 14% 38% 21% 4	2492
	21st to end	Night	18% 7% 18% 32% 21% 3	2902
August	1st to 10th	Night	31% 5% 17% 29% 15% 3	2826
	11th to 20th	Night	35% 5% 17% 28% 13% 1	2825
	21st to end	Night	26% 5% 19% 25% 21% 4	3135
September	1st to 10th	Night	25% 6% 14% 29% 23% 4	1977
	11th to 20th	Night	25% 6% 16% 32% 19% 2	2090
	21st to end	Night	27% 4 10% 31% 25% 3	2090
October	1st to 10th	Night	21% 2 7% 22% 43% 5%	3608
	11th to 20th	Night	25% 3 12% 31% 25% 4	3779
	21st to end	Night	37% 4 13% 27% 18% 1	4359
November	1st to 10th	Night	33% 4 14% 25% 19% 4	2535
	11th to 20th	Night	37% 5% 15% 24% 17% 2	2686
	21st to end	Night	36% 4 17% 27% 15% 1	2800
December	1st to 10th	Night	40% 4 17% 30% 9%	4580
	11th to 20th	Night	48% 5% 18% 22% 6%	5497
	21st to end	Night	56% 4 13% 21% 6%	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	15% 10% 29% 35% 10% 1	300
	11th to 20th	Day	13% 13% 32% 34% 7% 1	300
	21st to end	Day	12% 11% 38% 25% 12% 1	330
February	1st to 10th	Day	12% 17% 40% 27% 4	300
	11th to 20th	Day	14% 14% 37% 26% 7% 2	300
	21st to end	Day	13% 15% 38% 29% 5%	249
March	1st to 10th	Day	14% 14% 41% 28% 3	300
	11th to 20th	Day	17% 8% 36% 27% 10% 2	273
	21st to end	Day	24% 12% 30% 26% 7% 1	297
April	1st to 10th	Day	23% 18% 36% 19% 4	359
	11th to 20th	Day	23% 16% 32% 21% 7%	640
	21st to end	Day	24% 14% 28% 23% 10% 2	650
May	1st to 10th	Day	19% 11% 33% 26% 9% 1	653
	11th to 20th	Day	18% 12% 28% 25% 16% 2	675
	21st to end	Day	18% 7% 31% 30% 12% 2	734
June	1st to 10th	Day	10% 8% 25% 33% 20% 5%	680
	11th to 20th	Day	14% 6% 34% 30% 14% 2	680
	21st to end	Day	11% 6% 28% 38% 15% 2	680
July	1st to 10th	Day	7% 3 23% 38% 25% 4	671
	11th to 20th	Day	5% 3 31% 40% 18% 2	668
	21st to end	Day	5% 3 27% 42% 20% 3	739
August	1st to 10th	Day	9% 4 23% 41% 22% 2	676
	11th to 20th	Day	10% 5% 25% 37% 20% 3	665
	21st to end	Day	7% 5% 28% 36% 20% 3	748
September	1st to 10th	Day	12% 7% 29% 32% 17% 3	409
	11th to 20th	Day	8% 6% 36% 31% 16% 3	300
	21st to end	Day	13% 15% 31% 26% 12% 4	300
October	1st to 10th	Day	18% 9% 30% 26% 14% 3	300
	11th to 20th	Day	15% 14% 35% 24% 11% 1	300
	21st to end	Day	18% 16% 34% 24% 8% 1	330
November	1st to 10th	Day	19% 13% 31% 26% 9% 1	300
	11th to 20th	Day	14% 17% 38% 24% 7%	300
	21st to end	Day	16% 16% 32% 27% 8%	300
December	1st to 10th	Day	11% 9% 39% 29% 11% 1	300
	11th to 20th	Day	16% 11% 42% 26% 5%	300
	21st to end	Day	20% 12% 37% 26% 5% 1	330
January	1st to 10th	Night	10% 10% 36% 35% 8% 1	1000
	11th to 20th	Night	10% 11% 37% 33% 7% 1	1000
	21st to end	Night	13% 9% 39% 31% 8%	1100
February	1st to 10th	Night	13% 11% 39% 32% 5%	1000
	11th to 20th	Night	11% 13% 37% 32% 7% 1	931
	21st to end	Night	13% 8% 40% 30% 8% 1	660
March	1st to 10th	Night	13% 11% 41% 31% 4 1	730
	11th to 20th	Night	15% 10% 39% 31% 5%	575
	21st to end	Night	19% 11% 36% 27% 7% 1	627
April	1st to 10th	Night	17% 14% 39% 28% 3	570
	11th to 20th	Night	20% 13% 32% 27% 7%	563
	21st to end	Night	17% 11% 37% 28% 6% 1	570
May	1st to 10th	Night	16% 8% 37% 29% 10%	570
	11th to 20th	Night	14% 6% 39% 29% 12% 1	561
	21st to end	Night	15% 7% 34% 36% 9%	617
June	1st to 10th	Night	7% 7% 31% 38% 16% 1	570
	11th to 20th	Night	11% 5% 34% 40% 9% 1	570
	21st to end	Night	7% 4 30% 45% 14%	570
July	1st to 10th	Night	6% 3 24% 46% 21% 1	555
	11th to 20th	Night	4 1 29% 51% 14%	552
	21st to end	Night	3 2 28% 52% 15% 1	624
August	1st to 10th	Night	7% 3 23% 51% 16%	567
	11th to 20th	Night	8% 1 28% 42% 20% 1	564
	21st to end	Night	7% 2 30% 43% 17% 1	627
September	1st to 10th	Night	10% 4 30% 40% 15% 1	570
	11th to 20th	Night	7% 5% 35% 38% 13% 2	570
	21st to end	Night	9% 6% 35% 35% 13% 1	570
October	1st to 10th	Night	17% 10% 33% 30% 10%	646
	11th to 20th	Night	16% 10% 36% 30% 8%	760
	21st to end	Night	16% 11% 35% 30% 7%	974
November	1st to 10th	Night	11% 9% 37% 33% 8% 1	975
	11th to 20th	Night	11% 12% 40% 29% 8% 1	1000
	21st to end	Night	11% 10% 37% 36% 7%	1000
December	1st to 10th	Night	12% 12% 39% 30% 7%	1000
	11th to 20th	Night	14% 10% 35% 33% 7%	1000
	21st to end	Night	19% 11% 34% 29% 7%	1100

Page generated at 2025-03-09 07:08:45. Version ac07

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