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 2026-07-16.

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	20% 10% 3 8% 5% 5% 4 3 5% 6% 28%	139080
	Night	21% 11% 3 8% 5% 5% 4 3 5% 6% 28%	133768
Transparency	Day	37% 36% 7% 12% 7% 1	142667
	Night	38% 35% 7% 13% 7% 1	138270
Seeing	Day	29% 20% 30% 15% 5% 1	19678
	Night	27% 16% 30% 20% 6%	27084

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% 9% 6% 5% 3 5% 5% 20%	4690
	11th to 20th	Day	18% 16% 7% 16% 7% 7% 5% 3 4 5% 13%	4920
	21st to end	Day	15% 9% 4 10% 8% 6% 6% 4 6% 6% 26%	5781
February	1st to 10th	Day	19% 13% 4 11% 8% 5% 5% 5% 4 6% 21%	1890
	11th to 20th	Day	16% 10% 4 13% 6% 6% 5% 4 5% 6% 24%	1843
	21st to end	Day	13% 12% 4 8% 7% 5% 5% 3 6% 6% 32%	1586
March	1st to 10th	Day	23% 13% 4 10% 6% 5% 4 3 3 5% 23%	5040
	11th to 20th	Day	17% 16% 4 8% 4 4 3 3 5% 6% 29%	5090
	21st to end	Day	27% 13% 4 10% 6% 4 4 3 4 5% 21%	5587
April	1st to 10th	Day	25% 14% 4 8% 5% 4 3 3 4 4 27%	2503
	11th to 20th	Day	21% 10% 3 7% 5% 4 3 3 5% 6% 32%	2571
	21st to end	Day	22% 10% 3 7% 5% 4 4 3 4 8% 30%	2730
May	1st to 10th	Day	29% 11% 3 7% 4 5% 4 3 5% 5% 23%	7757
	11th to 20th	Day	22% 10% 3 7% 4 4 4 3 5% 6% 31%	8220
	21st to end	Day	22% 11% 3 7% 4 4 4 4 5% 7% 28%	9059
June	1st to 10th	Day	23% 10% 3 8% 5% 4 5% 3 5% 6% 27%	2940
	11th to 20th	Day	21% 9% 3 6% 5% 4 4 4 4 6% 34%	3021
	21st to end	Day	26% 10% 3 8% 6% 4 5% 4 4 7% 24%	3150
July	1st to 10th	Day	21% 10% 3 8% 5% 5% 5% 4 6% 8% 26%	6739
	11th to 20th	Day	18% 11% 3 8% 5% 4 4 4 5% 8% 31%	6430
	21st to end	Day	16% 7% 2 7% 5% 4 4 4 7% 8% 37%	6662
August	1st to 10th	Day	24% 9% 3 7% 5% 4 5% 4 5% 7% 28%	4235
	11th to 20th	Day	17% 8% 3 7% 5% 4 5% 4 6% 8% 34%	4175
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 45%	4488
September	1st to 10th	Day	16% 6% 3 6% 4 3 4 4 5% 8% 41%	2400
	11th to 20th	Day	18% 6% 2 6% 4 4 4 3 5% 6% 44%	2313
	21st to end	Day	19% 6% 2 6% 4 4 4 3 4 6% 42%	2141
October	1st to 10th	Day	18% 5% 3 6% 4 4 4 4 5% 7% 39%	2000
	11th to 20th	Day	20% 8% 3 7% 5% 4 5% 3 6% 7% 34%	2000
	21st to end	Day	20% 10% 3 6% 5% 4 5% 4 5% 6% 33%	2200
November	1st to 10th	Day	21% 11% 3 7% 5% 5% 4 3 4 6% 31%	1723
	11th to 20th	Day	22% 11% 5% 8% 6% 4 4 4 5% 7% 25%	1680
	21st to end	Day	21% 11% 4 9% 7% 5% 5% 3 5% 6% 24%	1680
December	1st to 10th	Day	23% 11% 4 10% 6% 5% 5% 4 6% 7% 21%	2690
	11th to 20th	Day	30% 10% 2 6% 5% 4 5% 3 5% 5% 25%	3076
	21st to end	Day	21% 12% 5% 10% 4 4 4 3 5% 6% 26%	4070
January	1st to 10th	Night	15% 13% 4 14% 8% 7% 6% 4 5% 6% 18%	8234
	11th to 20th	Night	22% 13% 6% 15% 6% 6% 4 4 4 5% 15%	7978
	21st to end	Night	13% 11% 4 11% 9% 7% 7% 5% 7% 7% 22%	8400
February	1st to 10th	Night	19% 12% 4 10% 6% 6% 5% 5% 6% 6% 21%	2730
	11th to 20th	Night	17% 10% 3 9% 6% 5% 6% 6% 6% 7% 25%	2663
	21st to end	Night	14% 11% 4 9% 6% 5% 5% 5% 6% 6% 29%	2217
March	1st to 10th	Night	25% 11% 4 9% 6% 5% 5% 3 4 5% 23%	5020
	11th to 20th	Night	20% 13% 6% 8% 4 4 4 3 4 5% 27%	5089
	21st to end	Night	31% 11% 4 9% 4 3 3 2 4 4 25%	5587
April	1st to 10th	Night	25% 12% 3 6% 4 4 4 3 5% 4 29%	2116
	11th to 20th	Night	24% 9% 2 7% 4 4 4 3 5% 6% 32%	1995
	21st to end	Night	24% 9% 3 7% 4 4 3 3 4 7% 32%	1890
May	1st to 10th	Night	27% 13% 4 8% 5% 4 4 3 4 5% 24%	5133
	11th to 20th	Night	27% 11% 3 6% 4 4 4 3 5% 5% 29%	4670
	21st to end	Night	18% 14% 4 8% 5% 4 4 3 4 5% 29%	5147
June	1st to 10th	Night	27% 9% 2 6% 3 3 4 3 5% 6% 30%	1680
	11th to 20th	Night	22% 11% 3 7% 4 4 3 3 5% 5% 34%	1610
	21st to end	Night	29% 9% 4 7% 4 5% 4 3 4 5% 26%	1470
July	1st to 10th	Night	19% 11% 4 9% 6% 5% 5% 4 6% 6% 25%	3407
	11th to 20th	Night	20% 11% 3 7% 5% 4 4 3 6% 7% 31%	3661
	21st to end	Night	18% 7% 2 6% 4 4 5% 3 5% 7% 39%	4199
August	1st to 10th	Night	21% 10% 3 7% 4 4 4 3 5% 6% 34%	2915
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 6% 7% 36%	2872
	21st to end	Night	11% 6% 2 5% 3 3 5% 3 5% 7% 50%	3408
September	1st to 10th	Night	17% 7% 2 5% 3 3 4 3 5% 7% 45%	2000
	11th to 20th	Night	19% 6% 2 4 3 3 4 3 5% 6% 46%	2084
	21st to end	Night	20% 9% 3 5% 4 3 3 3 5% 7% 39%	2258
October	1st to 10th	Night	18% 6% 2 6% 4 3 3 3 5% 7% 44%	2400
	11th to 20th	Night	20% 8% 3 5% 4 4 4 3 6% 7% 38%	2400
	21st to end	Night	25% 7% 2 5% 4 4 5% 3 5% 6% 34%	2640
November	1st to 10th	Night	21% 9% 2 6% 5% 4 4 3 5% 6% 35%	2792
	11th to 20th	Night	21% 11% 3 8% 5% 5% 4 3 5% 7% 28%	2940
	21st to end	Night	20% 10% 3 8% 6% 4 5% 4 5% 6% 28%	2940
December	1st to 10th	Night	17% 10% 3 10% 6% 6% 5% 4 6% 8% 26%	4720
	11th to 20th	Night	27% 11% 3 6% 5% 3 4 4 4 6% 28%	5353
	21st to end	Night	24% 10% 4 9% 5% 4 4 3 4 5% 29%	7150

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	52% 23% 10% 10% 5%	4691
	11th to 20th	Day	56% 23% 7% 10% 3	4951
	21st to end	Day	44% 23% 7% 11% 12% 2	5781
February	1st to 10th	Day	27% 60% 3 6% 4 1	1890
	11th to 20th	Day	24% 59% 4 8% 5% 1	1851
	21st to end	Day	21% 58% 4 9% 7% 2	1586
March	1st to 10th	Day	47% 29% 6% 9% 6% 3	5044
	11th to 20th	Day	41% 28% 9% 16% 5%	5090
	21st to end	Day	51% 28% 3 10% 7% 1	5587
April	1st to 10th	Day	24% 58% 4 5% 6% 2	2503
	11th to 20th	Day	22% 60% 4 9% 4	2571
	21st to end	Day	22% 59% 5% 8% 5% 1	2730
May	1st to 10th	Day	50% 23% 10% 11% 6%	7769
	11th to 20th	Day	44% 24% 8% 18% 5% 1	8224
	21st to end	Day	45% 24% 9% 12% 10% 1	9060
June	1st to 10th	Day	21% 59% 5% 9% 5%	2940
	11th to 20th	Day	19% 60% 6% 9% 6% 1	3021
	21st to end	Day	23% 59% 3 8% 6% 1	3150
July	1st to 10th	Day	45% 29% 9% 9% 7% 1	6668
	11th to 20th	Day	40% 29% 8% 17% 7%	6354
	21st to end	Day	31% 30% 12% 17% 9%	6472
August	1st to 10th	Day	38% 38% 6% 11% 7%	4222
	11th to 20th	Day	30% 39% 11% 16% 3	4214
	21st to end	Day	20% 38% 8% 20% 13% 1	4488
September	1st to 10th	Day	17% 57% 7% 12% 6% 1	2400
	11th to 20th	Day	19% 58% 5% 11% 7%	2313
	21st to end	Day	16% 57% 4 13% 9% 1	2141
October	1st to 10th	Day	28% 38% 7% 18% 9% 1	3260
	11th to 20th	Day	23% 37% 6% 18% 15%	3240
	21st to end	Day	26% 37% 10% 15% 9% 2	3538
November	1st to 10th	Day	27% 55% 4 9% 4	1723
	11th to 20th	Day	30% 55% 4 8% 3 1	1680
	21st to end	Day	30% 54% 5% 7% 4	1680
December	1st to 10th	Day	38% 37% 9% 14% 2	2690
	11th to 20th	Day	41% 31% 7% 11% 9%	3075
	21st to end	Day	44% 26% 12% 11% 7% 1	4070
January	1st to 10th	Night	52% 23% 8% 14% 3	8234
	11th to 20th	Night	57% 23% 7% 9% 4	8022
	21st to end	Night	45% 25% 8% 13% 8% 1	8400
February	1st to 10th	Night	28% 60% 4 4 4	2730
	11th to 20th	Night	23% 58% 4 10% 5%	2666
	21st to end	Night	22% 59% 4 9% 6% 1	2217
March	1st to 10th	Night	48% 28% 4 9% 10% 1	5029
	11th to 20th	Night	45% 28% 7% 13% 6%	5090
	21st to end	Night	51% 28% 4 11% 6%	5587
April	1st to 10th	Night	26% 58% 3 6% 6% 2	2116
	11th to 20th	Night	23% 59% 4 9% 5%	1995
	21st to end	Night	21% 59% 4 9% 6% 1	1890
May	1st to 10th	Night	53% 23% 8% 11% 5%	5139
	11th to 20th	Night	47% 23% 7% 16% 6% 2	4671
	21st to end	Night	48% 23% 7% 14% 8% 1	5148
June	1st to 10th	Night	21% 59% 4 11% 5%	1680
	11th to 20th	Night	20% 59% 4 12% 5%	1610
	21st to end	Night	24% 58% 4 8% 6%	1470
July	1st to 10th	Night	50% 27% 7% 10% 6% 1	3369
	11th to 20th	Night	43% 29% 6% 12% 10% 1	3613
	21st to end	Night	35% 27% 8% 18% 11% 1	4075
August	1st to 10th	Night	36% 38% 8% 14% 4	2903
	11th to 20th	Night	30% 40% 12% 15% 3	2899
	21st to end	Night	17% 38% 11% 20% 15%	3407
September	1st to 10th	Night	15% 57% 5% 14% 8% 1	2000
	11th to 20th	Night	18% 57% 4 13% 7%	2084
	21st to end	Night	17% 57% 4 16% 6%	2258
October	1st to 10th	Night	30% 37% 9% 16% 8% 1	3920
	11th to 20th	Night	21% 37% 7% 19% 16%	3899
	21st to end	Night	24% 37% 9% 18% 12%	4252
November	1st to 10th	Night	26% 54% 7% 8% 5%	2792
	11th to 20th	Night	28% 54% 5% 8% 4	2940
	21st to end	Night	28% 54% 6% 7% 4 1	2940
December	1st to 10th	Night	33% 38% 9% 17% 3	4720
	11th to 20th	Night	39% 32% 7% 14% 8% 1	5355
	21st to end	Night	43% 26% 8% 15% 8% 1	7150

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	430
	11th to 20th	Day	37% 22% 26% 13% 3	430
	21st to end	Day	26% 23% 36% 12% 3	473
February	1st to 10th	Day	31% 23% 29% 14% 2	430
	11th to 20th	Day	32% 27% 27% 12% 1	426
	21st to end	Day	29% 23% 31% 13% 4 1	358
March	1st to 10th	Day	29% 29% 30% 9% 2	540
	11th to 20th	Day	31% 31% 25% 9% 4	540
	21st to end	Day	34% 27% 27% 9% 3 1	594
April	1st to 10th	Day	42% 25% 25% 6% 2	540
	11th to 20th	Day	35% 27% 26% 9% 2	532
	21st to end	Day	32% 21% 30% 12% 3 1	540
May	1st to 10th	Day	35% 24% 28% 10% 2 1	585
	11th to 20th	Day	25% 22% 29% 18% 5% 1	774
	21st to end	Day	31% 18% 31% 16% 3 1	845
June	1st to 10th	Day	29% 17% 32% 16% 6%	780
	11th to 20th	Day	25% 18% 32% 18% 5% 1	780
	21st to end	Day	33% 14% 30% 17% 6% 1	780
July	1st to 10th	Day	24% 10% 36% 22% 8% 1	770
	11th to 20th	Day	24% 10% 33% 23% 9% 1	743
	21st to end	Day	24% 12% 35% 21% 6%	683
August	1st to 10th	Day	21% 9% 36% 24% 8% 2	526
	11th to 20th	Day	22% 10% 34% 22% 9% 2	519
	21st to end	Day	20% 16% 30% 23% 8% 3	583
September	1st to 10th	Day	19% 14% 36% 23% 7% 1	530
	11th to 20th	Day	23% 17% 31% 15% 10% 3	530
	21st to end	Day	23% 15% 32% 20% 7% 2	497
October	1st to 10th	Day	23% 15% 33% 17% 11% 1	420
	11th to 20th	Day	26% 20% 32% 13% 7% 2	420
	21st to end	Day	27% 25% 29% 13% 4 2	462
November	1st to 10th	Day	29% 21% 29% 14% 6% 1	425
	11th to 20th	Day	34% 21% 26% 13% 5%	430
	21st to end	Day	33% 24% 28% 12% 2	430
December	1st to 10th	Day	36% 21% 29% 12% 2	430
	11th to 20th	Day	41% 24% 25% 8% 2	430
	21st to end	Day	33% 24% 30% 10% 3 1	473
January	1st to 10th	Night	29% 22% 33% 14% 2	950
	11th to 20th	Night	32% 19% 30% 15% 3	903
	21st to end	Night	26% 24% 31% 16% 2	924
February	1st to 10th	Night	29% 21% 31% 16% 2	840
	11th to 20th	Night	29% 25% 31% 12% 2	823
	21st to end	Night	22% 22% 32% 20% 4	692
March	1st to 10th	Night	27% 24% 32% 16% 2	840
	11th to 20th	Night	25% 21% 30% 19% 5%	840
	21st to end	Night	28% 21% 32% 15% 4	924
April	1st to 10th	Night	34% 17% 30% 15% 3	646
	11th to 20th	Night	28% 20% 34% 15% 3	624
	21st to end	Night	30% 15% 31% 19% 5% 1	630
May	1st to 10th	Night	33% 13% 32% 17% 4	630
	11th to 20th	Night	29% 12% 29% 23% 6% 1	622
	21st to end	Night	23% 14% 35% 23% 5%	682
June	1st to 10th	Night	32% 8% 31% 25% 4	630
	11th to 20th	Night	25% 11% 33% 25% 5% 1	560
	21st to end	Night	33% 6% 23% 30% 9%	420
July	1st to 10th	Night	21% 8% 30% 31% 10%	480
	11th to 20th	Night	23% 8% 30% 31% 8%	598
	21st to end	Night	22% 6% 27% 34% 11%	656
August	1st to 10th	Night	20% 5% 24% 36% 14% 1	598
	11th to 20th	Night	21% 6% 24% 33% 14% 2	592
	21st to end	Night	19% 8% 27% 32% 14% 1	660
September	1st to 10th	Night	21% 7% 30% 30% 11% 1	600
	11th to 20th	Night	21% 10% 26% 27% 14% 1	684
	21st to end	Night	25% 11% 29% 24% 9% 2	800
October	1st to 10th	Night	22% 11% 30% 26% 10% 1	800
	11th to 20th	Night	24% 16% 30% 21% 9% 1	800
	21st to end	Night	31% 18% 28% 19% 4	880
November	1st to 10th	Night	29% 16% 30% 19% 4 1	911
	11th to 20th	Night	30% 20% 27% 18% 5%	950
	21st to end	Night	29% 25% 26% 16% 5%	950
December	1st to 10th	Night	32% 19% 31% 15% 3	950
	11th to 20th	Night	35% 23% 27% 12% 2	950
	21st to end	Night	31% 20% 30% 15% 2 1	1045

Page generated at 2026-07-13 04:14:53. Version ac07

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