Elentirmo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elentirmo Observatory 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	21% 10% 3 8% 5% 5% 4 3 5% 6% 29%	109487
	Night	20% 10% 3 8% 5% 4 4 3 5% 6% 29%	109609
Transparency	Day	32% 44% 7% 11% 6% 1	113117
	Night	33% 42% 6% 12% 6%	114143
Seeing	Day	29% 19% 31% 16% 5% 1	17722
	Night	27% 16% 30% 20% 6%	25360

By Month

Percentage Cloud Cover NE (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	14% 13% 6% 14% 10% 6% 5% 3 5% 4 20%	3616
	11th to 20th	Day	14% 15% 6% 16% 7% 7% 6% 3 5% 6% 14%	3778
	21st to end	Day	16% 11% 5% 10% 6% 5% 5% 4 5% 6% 29%	4466
February	1st to 10th	Day	20% 13% 4 10% 8% 5% 4 5% 4 6% 21%	1800
	11th to 20th	Day	17% 11% 4 14% 6% 6% 5% 4 5% 6% 23%	1753
	21st to end	Day	13% 13% 4 8% 7% 5% 5% 3 5% 6% 31%	1513
March	1st to 10th	Day	24% 14% 3 7% 6% 5% 4 3 4 5% 25%	3540
	11th to 20th	Day	16% 16% 4 9% 5% 5% 4 4 5% 6% 25%	3491
	21st to end	Day	31% 12% 4 10% 5% 4 3 2 3 4 21%	3816
April	1st to 10th	Day	25% 14% 4 8% 5% 4 3 3 4 4 26%	2265
	11th to 20th	Day	21% 10% 3 7% 5% 4 3 3 6% 6% 33%	2323
	21st to end	Day	23% 9% 3 7% 5% 4 4 3 4 8% 31%	2470
May	1st to 10th	Day	24% 12% 4 8% 5% 5% 5% 3 6% 6% 22%	4170
	11th to 20th	Day	23% 10% 4 8% 4 4 4 3 5% 6% 29%	4398
	21st to end	Day	19% 8% 3 6% 4 4 5% 4 7% 9% 30%	4836
June	1st to 10th	Day	24% 11% 3 8% 5% 4 4 3 5% 6% 26%	2660
	11th to 20th	Day	21% 9% 3 6% 5% 4 4 4 4 6% 34%	2733
	21st to end	Day	27% 10% 3 8% 6% 4 5% 4 4 7% 24%	2850
July	1st to 10th	Day	22% 9% 3 7% 5% 5% 4 4 6% 7% 29%	4604
	11th to 20th	Day	19% 11% 3 8% 4 4 4 4 6% 8% 30%	4440
	21st to end	Day	21% 8% 3 7% 5% 4 4 4 6% 8% 31%	4634
August	1st to 10th	Day	24% 9% 3 7% 5% 4 5% 4 5% 7% 27%	4105
	11th to 20th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 9% 33%	4045
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 45%	4351
September	1st to 10th	Day	17% 6% 2 6% 4 3 4 4 5% 8% 41%	2280
	11th to 20th	Day	19% 6% 2 6% 4 4 4 3 5% 6% 43%	2198
	21st to end	Day	20% 6% 2 6% 4 4 3 3 4 6% 41%	2034
October	1st to 10th	Day	19% 5% 3 6% 4 4 4 4 5% 7% 38%	1900
	11th to 20th	Day	20% 7% 3 6% 4 3 4 3 6% 7% 35%	1900
	21st to end	Day	20% 11% 3 6% 6% 4 5% 4 4 6% 33%	2090
November	1st to 10th	Day	21% 10% 3 8% 5% 5% 4 3 4 6% 31%	1640
	11th to 20th	Day	23% 10% 4 8% 6% 4 4 4 5% 7% 25%	1600
	21st to end	Day	21% 11% 4 9% 7% 5% 5% 3 5% 6% 25%	1600
December	1st to 10th	Day	23% 10% 4 10% 6% 5% 5% 4 6% 7% 21%	2610
	11th to 20th	Day	30% 10% 2 6% 5% 4 5% 4 5% 5% 25%	2996
	21st to end	Day	21% 12% 4 9% 4 4 4 3 5% 6% 26%	3982
January	1st to 10th	Night	14% 13% 4 15% 8% 6% 6% 4 5% 6% 20%	6349
	11th to 20th	Night	17% 13% 6% 16% 7% 6% 5% 4 5% 5% 17%	6114
	21st to end	Night	13% 11% 4 10% 7% 6% 6% 4 6% 7% 25%	6490
February	1st to 10th	Night	20% 13% 4 9% 6% 6% 5% 5% 6% 5% 22%	2600
	11th to 20th	Night	17% 11% 3 10% 6% 5% 6% 6% 6% 7% 24%	2533
	21st to end	Night	14% 11% 4 9% 6% 5% 5% 5% 6% 6% 30%	2114
March	1st to 10th	Night	24% 11% 3 8% 6% 6% 5% 3 4 6% 24%	3520
	11th to 20th	Night	18% 13% 5% 10% 5% 5% 5% 4 5% 6% 23%	3497
	21st to end	Night	32% 11% 4 10% 4 3 3 2 3 3 25%	3816
April	1st to 10th	Night	25% 12% 3 6% 4 4 4 4 5% 4 29%	1914
	11th to 20th	Night	23% 9% 2 7% 4 4 4 3 5% 6% 33%	1803
	21st to end	Night	25% 9% 3 7% 4 4 3 3 4 7% 31%	1710
May	1st to 10th	Night	21% 14% 4 8% 4 4 4 3 5% 6% 27%	2758
	11th to 20th	Night	25% 10% 3 7% 5% 4 4 3 5% 5% 29%	2506
	21st to end	Night	21% 12% 4 7% 5% 4 4 3 5% 7% 29%	2749
June	1st to 10th	Night	29% 10% 2 6% 3 4 4 3 5% 6% 28%	1520
	11th to 20th	Night	21% 10% 3 7% 4 4 4 3 5% 6% 34%	1457
	21st to end	Night	31% 9% 3 7% 5% 5% 4 3 4 5% 25%	1330
July	1st to 10th	Night	20% 10% 4 10% 6% 5% 5% 4 6% 6% 25%	2328
	11th to 20th	Night	20% 11% 3 8% 5% 4 4 4 6% 7% 28%	2530
	21st to end	Night	20% 8% 2 5% 4 4 4 3 5% 7% 37%	2923
August	1st to 10th	Night	21% 10% 4 7% 4 4 4 3 5% 6% 33%	2825
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 6% 7% 35%	2782
	21st to end	Night	11% 6% 2 5% 3 3 4 3 5% 7% 50%	3303
September	1st to 10th	Night	16% 6% 2 5% 3 3 4 3 5% 7% 45%	1900
	11th to 20th	Night	19% 6% 2 4 3 3 4 3 5% 6% 45%	1980
	21st to end	Night	20% 9% 3 5% 4 3 3 3 5% 7% 38%	2145
October	1st to 10th	Night	18% 6% 2 6% 4 3 3 3 5% 7% 42%	2280
	11th to 20th	Night	20% 6% 2 5% 4 4 4 3 6% 7% 39%	2280
	21st to end	Night	24% 8% 2 5% 4 4 5% 3 5% 6% 35%	2508
November	1st to 10th	Night	21% 9% 2 6% 5% 4 5% 3 5% 6% 35%	2656
	11th to 20th	Night	21% 10% 3 7% 5% 5% 4 3 5% 7% 29%	2800
	21st to end	Night	21% 9% 3 8% 6% 4 5% 4 5% 7% 27%	2800
December	1st to 10th	Night	17% 10% 3 10% 6% 6% 5% 4 6% 8% 26%	4580
	11th to 20th	Night	27% 10% 3 6% 5% 3 4 4 4 6% 28%	5213
	21st to end	Night	25% 10% 4 8% 4 4 4 3 4 5% 29%	6996

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	50% 27% 9% 8% 5%	3617
	11th to 20th	Day	50% 29% 7% 11% 3	3809
	21st to end	Day	40% 29% 6% 10% 13% 3	4466
February	1st to 10th	Day	26% 62% 3 5% 4 1	1800
	11th to 20th	Day	23% 61% 3 7% 5% 1	1761
	21st to end	Day	20% 61% 3 8% 6% 2	1513
March	1st to 10th	Day	39% 38% 6% 11% 4 2	3544
	11th to 20th	Day	38% 39% 7% 11% 4	3491
	21st to end	Day	48% 39% 2 5% 5% 1	3816
April	1st to 10th	Day	22% 64% 3 4 5% 2	2265
	11th to 20th	Day	18% 66% 4 9% 3	2323
	21st to end	Day	19% 65% 4 6% 5% 1	2470
May	1st to 10th	Day	38% 39% 11% 9% 2	4184
	11th to 20th	Day	37% 39% 7% 12% 3	4402
	21st to end	Day	32% 39% 11% 11% 6%	4836
June	1st to 10th	Day	19% 65% 4 8% 4	2660
	11th to 20th	Day	16% 65% 6% 8% 5% 1	2733
	21st to end	Day	21% 64% 3 7% 6%	2850
July	1st to 10th	Day	38% 38% 5% 8% 9% 1	4533
	11th to 20th	Day	36% 38% 7% 14% 5%	4364
	21st to end	Day	34% 38% 8% 12% 8% 1	4486
August	1st to 10th	Day	39% 40% 6% 11% 5%	4092
	11th to 20th	Day	30% 40% 11% 15% 3	4084
	21st to end	Day	19% 39% 8% 20% 14% 1	4351
September	1st to 10th	Day	16% 60% 6% 11% 5% 1	2280
	11th to 20th	Day	19% 61% 5% 9% 6%	2198
	21st to end	Day	15% 60% 4 13% 7%	2034
October	1st to 10th	Day	28% 39% 7% 17% 9%	3160
	11th to 20th	Day	21% 38% 6% 18% 16% 1	3140
	21st to end	Day	26% 38% 11% 14% 9% 2	3428
November	1st to 10th	Day	26% 57% 4 8% 4	1640
	11th to 20th	Day	28% 57% 4 7% 3 1	1600
	21st to end	Day	29% 57% 5% 6% 3	1600
December	1st to 10th	Day	38% 38% 9% 14% 2	2610
	11th to 20th	Day	41% 32% 7% 11% 9%	2995
	21st to end	Day	43% 26% 12% 11% 7% 1	3982
January	1st to 10th	Night	47% 27% 8% 15% 3	6349
	11th to 20th	Night	51% 28% 8% 9% 4	6158
	21st to end	Night	40% 29% 8% 13% 9% 1	6490
February	1st to 10th	Night	26% 62% 3 4 4	2600
	11th to 20th	Night	23% 61% 3 8% 5%	2536
	21st to end	Night	20% 62% 4 8% 6% 1	2114
March	1st to 10th	Night	40% 38% 4 11% 7% 1	3529
	11th to 20th	Night	41% 39% 5% 8% 6%	3498
	21st to end	Night	48% 39% 3 6% 4 1	3816
April	1st to 10th	Night	22% 64% 2 5% 5% 2	1914
	11th to 20th	Night	19% 65% 3 8% 4	1803
	21st to end	Night	20% 64% 2 7% 5% 2	1710
May	1st to 10th	Night	39% 39% 10% 8% 4	2764
	11th to 20th	Night	38% 39% 6% 13% 3	2507
	21st to end	Night	39% 39% 7% 12% 4	2750
June	1st to 10th	Night	20% 65% 3 8% 4	1520
	11th to 20th	Night	17% 65% 4 10% 4	1457
	21st to end	Night	21% 63% 3 7% 5%	1330
July	1st to 10th	Night	44% 37% 5% 7% 6% 1	2290
	11th to 20th	Night	40% 40% 6% 8% 6%	2482
	21st to end	Night	33% 36% 7% 13% 9% 1	2831
August	1st to 10th	Night	36% 39% 8% 14% 4	2813
	11th to 20th	Night	30% 41% 12% 15% 3	2809
	21st to end	Night	17% 39% 11% 19% 15%	3302
September	1st to 10th	Night	14% 60% 5% 13% 7% 1	1900
	11th to 20th	Night	18% 60% 3 12% 6%	1980
	21st to end	Night	17% 60% 3 14% 5%	2145
October	1st to 10th	Night	30% 38% 8% 15% 8%	3800
	11th to 20th	Night	19% 38% 7% 19% 17%	3779
	21st to end	Night	23% 38% 9% 17% 12%	4120
November	1st to 10th	Night	24% 56% 7% 8% 4	2656
	11th to 20th	Night	26% 57% 5% 8% 4	2800
	21st to end	Night	27% 57% 5% 7% 4 1	2800
December	1st to 10th	Night	33% 39% 9% 16% 3	4580
	11th to 20th	Night	38% 33% 7% 14% 8% 1	5215
	21st to end	Night	43% 26% 8% 15% 8% 1	6996

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	35% 23% 29% 12% 2	400
	11th to 20th	Day	35% 22% 27% 14% 3	400
	21st to end	Day	24% 24% 36% 13% 3	440
February	1st to 10th	Day	34% 23% 28% 13% 2 1	400
	11th to 20th	Day	34% 28% 26% 11% 1	396
	21st to end	Day	28% 23% 32% 13% 4 1	334
March	1st to 10th	Day	30% 28% 30% 10% 2	500
	11th to 20th	Day	30% 30% 26% 9% 4	464
	21st to end	Day	33% 26% 28% 10% 3 1	506
April	1st to 10th	Day	41% 24% 26% 7% 2	460
	11th to 20th	Day	32% 27% 28% 10% 3	452
	21st to end	Day	32% 20% 30% 13% 3 1	460
May	1st to 10th	Day	34% 24% 28% 10% 2 1	501
	11th to 20th	Day	24% 21% 30% 20% 5% 1	674
	21st to end	Day	30% 17% 32% 17% 3 1	735
June	1st to 10th	Day	30% 17% 32% 16% 5%	680
	11th to 20th	Day	25% 17% 33% 19% 6% 1	680
	21st to end	Day	34% 12% 29% 17% 7% 1	680
July	1st to 10th	Day	26% 8% 35% 23% 8% 1	670
	11th to 20th	Day	25% 9% 33% 23% 9% 1	668
	21st to end	Day	26% 12% 33% 21% 7%	634
August	1st to 10th	Day	22% 9% 34% 25% 8% 1	486
	11th to 20th	Day	23% 10% 34% 22% 9% 2	479
	21st to end	Day	20% 15% 29% 24% 8% 4	539
September	1st to 10th	Day	19% 13% 37% 23% 7% 1	490
	11th to 20th	Day	25% 17% 31% 14% 10% 3	490
	21st to end	Day	24% 15% 31% 20% 8% 2	460
October	1st to 10th	Day	24% 14% 33% 17% 11% 1	390
	11th to 20th	Day	26% 19% 31% 14% 7% 2	390
	21st to end	Day	27% 25% 29% 13% 4 2	429
November	1st to 10th	Day	27% 21% 30% 15% 6% 1	395
	11th to 20th	Day	34% 21% 27% 13% 5% 1	400
	21st to end	Day	34% 24% 29% 11% 2 1	400
December	1st to 10th	Day	36% 20% 30% 12% 2	400
	11th to 20th	Day	41% 24% 25% 8% 2	400
	21st to end	Day	33% 23% 31% 10% 3 1	440
January	1st to 10th	Night	29% 21% 33% 14% 2	900
	11th to 20th	Night	31% 19% 31% 16% 3	857
	21st to end	Night	25% 25% 32% 16% 2	880
February	1st to 10th	Night	30% 22% 30% 17% 2	800
	11th to 20th	Night	30% 26% 30% 12% 2	783
	21st to end	Night	22% 22% 33% 20% 4	660
March	1st to 10th	Night	27% 23% 32% 16% 2	800
	11th to 20th	Night	24% 21% 30% 19% 5%	767
	21st to end	Night	27% 21% 31% 15% 5%	836
April	1st to 10th	Night	33% 17% 31% 16% 3	584
	11th to 20th	Night	27% 20% 35% 15% 3	564
	21st to end	Night	30% 16% 31% 18% 4 1	570
May	1st to 10th	Night	31% 12% 33% 18% 5% 1	570
	11th to 20th	Night	28% 11% 30% 23% 6% 1	562
	21st to end	Night	22% 14% 35% 24% 5%	616
June	1st to 10th	Night	34% 8% 31% 24% 4	570
	11th to 20th	Night	24% 11% 34% 25% 6%	507
	21st to end	Night	33% 5% 23% 29% 9%	380
July	1st to 10th	Night	21% 8% 30% 32% 9%	433
	11th to 20th	Night	23% 8% 31% 30% 9%	552
	21st to end	Night	22% 5% 28% 34% 11%	623
August	1st to 10th	Night	21% 5% 25% 35% 14% 1	568
	11th to 20th	Night	22% 6% 25% 32% 14% 2	562
	21st to end	Night	19% 8% 26% 32% 15% 1	627
September	1st to 10th	Night	21% 7% 31% 30% 11% 1	570
	11th to 20th	Night	22% 10% 27% 26% 14% 1	650
	21st to end	Night	26% 11% 28% 24% 9% 2	760
October	1st to 10th	Night	23% 11% 30% 26% 10% 1	760
	11th to 20th	Night	23% 16% 30% 21% 9% 1	760
	21st to end	Night	30% 18% 28% 18% 5%	836
November	1st to 10th	Night	27% 16% 31% 20% 5% 1	863
	11th to 20th	Night	29% 21% 27% 18% 5%	900
	21st to end	Night	30% 25% 26% 16% 4	900
December	1st to 10th	Night	31% 20% 31% 15% 3	900
	11th to 20th	Night	34% 23% 28% 12% 3	900
	21st to end	Night	32% 19% 30% 16% 2 1	990

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

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