Marmora
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marmora clear sky chart from 2005-11-06 to 2026-05-02.

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	16% 10% 3 8% 5% 5% 4 4 5% 7% 33%	132082
	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 32%	130364
Transparency	Day	49% 6% 12% 21% 11% 1	135624
	Night	50% 6% 12% 20% 11% 1	134908
Seeing	Day	23% 16% 31% 18% 8% 3	16253
	Night	22% 14% 31% 24% 9% 1	25626

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	16% 13% 5% 10% 5% 4 5% 4 6% 7% 27%	4661
	11th to 20th	Day	11% 22% 8% 14% 7% 6% 5% 3 4 3 17%	4650
	21st to end	Day	12% 16% 7% 14% 8% 8% 5% 4 4 4 20%	5780
February	1st to 10th	Day	14% 15% 4 12% 7% 5% 5% 4 5% 4 24%	1890
	11th to 20th	Day	12% 16% 5% 12% 8% 5% 3 4 4 5% 27%	1843
	21st to end	Day	17% 17% 4 10% 7% 4 4 3 4 4 26%	1657
March	1st to 10th	Day	20% 13% 5% 9% 4 4 4 3 4 6% 29%	4858
	11th to 20th	Day	13% 13% 4 8% 5% 6% 5% 4 6% 7% 30%	5090
	21st to end	Day	20% 11% 3 6% 4 3 3 3 4 4 39%	5697
April	1st to 10th	Day	21% 13% 4 7% 4 4 3 3 4 6% 31%	2520
	11th to 20th	Day	23% 9% 2 5% 4 3 3 3 4 6% 37%	2494
	21st to end	Day	22% 9% 2 8% 5% 4 4 3 4 5% 33%	2709
May	1st to 10th	Day	23% 8% 3 8% 4 4 4 3 5% 6% 32%	6193
	11th to 20th	Day	18% 10% 3 8% 5% 4 4 3 5% 7% 34%	6318
	21st to end	Day	20% 7% 2 6% 5% 4 4 3 5% 7% 35%	6949
June	1st to 10th	Day	18% 8% 2 7% 5% 5% 5% 5% 6% 7% 32%	2800
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 5% 7% 9% 37%	2800
	21st to end	Day	17% 7% 3 6% 5% 4 4 4 6% 7% 36%	2800
July	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 9% 40%	6360
	11th to 20th	Day	11% 4 2 6% 4 5% 4 3 6% 8% 47%	6360
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 6% 9% 47%	6888
August	1st to 10th	Day	16% 8% 2 7% 4 4 5% 4 6% 7% 38%	4234
	11th to 20th	Day	16% 6% 2 7% 5% 5% 4 3 6% 9% 36%	4174
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	4380
September	1st to 10th	Day	14% 5% 2 6% 4 5% 5% 4 5% 7% 43%	2400
	11th to 20th	Day	10% 5% 2 5% 4 3 4 4 5% 6% 51%	2400
	21st to end	Day	18% 6% 3 6% 4 4 4 4 5% 7% 39%	2090
October	1st to 10th	Day	20% 7% 2 7% 5% 4 4 3 5% 7% 36%	2000
	11th to 20th	Day	21% 9% 3 8% 5% 4 5% 4 6% 7% 29%	2000
	21st to end	Day	25% 11% 3 7% 4 5% 4 4 4 5% 27%	2156
November	1st to 10th	Day	17% 9% 3 8% 4 5% 5% 5% 5% 7% 34%	1777
	11th to 20th	Day	15% 13% 4 8% 6% 4 4 5% 5% 6% 30%	1680
	21st to end	Day	21% 17% 4 7% 6% 4 4 4 5% 6% 23%	1680
December	1st to 10th	Day	18% 21% 4 11% 5% 5% 4 3 4 5% 19%	2680
	11th to 20th	Day	16% 20% 6% 11% 5% 4 3 3 3 4 25%	3066
	21st to end	Day	24% 16% 4 10% 5% 4 3 3 4 4 23%	4048
January	1st to 10th	Night	14% 15% 7% 12% 6% 5% 5% 3 4 5% 22%	8234
	11th to 20th	Night	12% 18% 6% 15% 8% 6% 5% 4 4 5% 17%	8217
	21st to end	Night	12% 14% 7% 12% 6% 5% 5% 3 5% 5% 26%	8401
February	1st to 10th	Night	13% 15% 5% 10% 7% 6% 5% 4 4 6% 26%	2730
	11th to 20th	Night	13% 14% 6% 10% 6% 4 4 4 5% 5% 28%	2663
	21st to end	Night	16% 12% 3 10% 5% 4 5% 3 6% 6% 30%	2149
March	1st to 10th	Night	19% 12% 4 9% 5% 5% 4 3 4 5% 29%	5186
	11th to 20th	Night	12% 11% 4 8% 5% 5% 6% 4 6% 7% 32%	5089
	21st to end	Night	20% 9% 3 7% 4 4 4 3 5% 6% 36%	5463
April	1st to 10th	Night	20% 10% 3 8% 4 4 4 3 5% 5% 34%	2100
	11th to 20th	Night	20% 8% 3 7% 4 4 4 3 5% 7% 36%	2075
	21st to end	Night	18% 7% 3 6% 5% 5% 5% 3 6% 7% 34%	1929
May	1st to 10th	Night	24% 9% 3 7% 4 4 4 3 5% 6% 31%	3769
	11th to 20th	Night	15% 8% 2 6% 4 4 4 4 5% 6% 42%	3575
	21st to end	Night	18% 6% 3 7% 5% 5% 4 3 4 6% 38%	3926
June	1st to 10th	Night	15% 5% 2 7% 5% 5% 4 4 6% 8% 38%	1600
	11th to 20th	Night	11% 6% 3 5% 5% 5% 4 4 5% 8% 44%	1600
	21st to end	Night	14% 6% 3 8% 4 4 4 4 6% 7% 40%	1600
July	1st to 10th	Night	10% 5% 2 7% 5% 4 5% 4 6% 8% 42%	3600
	11th to 20th	Night	12% 4 2 6% 3 4 3 3 5% 7% 50%	3600
	21st to end	Night	10% 4 2 5% 4 4 4 3 6% 8% 51%	3961
August	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 6% 7% 47%	2915
	11th to 20th	Night	15% 5% 2 5% 3 3 4 3 6% 7% 46%	2875
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 9% 48%	3484
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 8% 47%	2000
	11th to 20th	Night	12% 4 1 3 4 4 4 4 5% 6% 54%	2000
	21st to end	Night	18% 6% 2 6% 3 4 4 3 5% 7% 42%	2307
October	1st to 10th	Night	17% 7% 2 6% 4 4 4 4 4 6% 41%	2400
	11th to 20th	Night	21% 9% 3 8% 5% 5% 4 3 4 6% 33%	2400
	21st to end	Night	22% 11% 3 6% 4 4 5% 4 5% 5% 30%	2682
November	1st to 10th	Night	19% 10% 2 6% 4 5% 4 3 5% 6% 37%	2736
	11th to 20th	Night	18% 12% 3 7% 5% 5% 4 4 5% 7% 31%	2940
	21st to end	Night	21% 12% 3 8% 5% 6% 5% 4 6% 6% 25%	2940
December	1st to 10th	Night	19% 17% 4 8% 6% 5% 5% 5% 6% 7% 19%	4720
	11th to 20th	Night	18% 16% 5% 10% 5% 4 4 4 5% 5% 23%	5348
	21st to end	Night	26% 17% 3 10% 5% 4 3 3 4 4 20%	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	53% 7% 14% 18% 8% 1	4662
	11th to 20th	Day	71% 5% 8% 9% 7%	4680
	21st to end	Day	66% 6% 9% 11% 8% 1	5780
February	1st to 10th	Day	61% 6% 10% 17% 6% 1	1890
	11th to 20th	Day	60% 5% 9% 15% 10% 1	1852
	21st to end	Day	62% 6% 8% 14% 10% 1	1657
March	1st to 10th	Day	55% 5% 12% 13% 15% 1	4861
	11th to 20th	Day	52% 5% 17% 14% 9% 2	5090
	21st to end	Day	48% 5% 6% 22% 16% 3	5697
April	1st to 10th	Day	55% 4 8% 19% 12% 2	2520
	11th to 20th	Day	50% 4 8% 21% 16% 1	2494
	21st to end	Day	54% 4 8% 18% 14% 2	2709
May	1st to 10th	Day	53% 7% 8% 18% 11% 3	6203
	11th to 20th	Day	49% 7% 10% 17% 16% 1	6322
	21st to end	Day	47% 6% 11% 22% 11% 2	6949
June	1st to 10th	Day	49% 7% 11% 18% 14% 1	2800
	11th to 20th	Day	41% 7% 12% 25% 14% 2	2800
	21st to end	Day	44% 7% 12% 22% 13% 1	2800
July	1st to 10th	Day	38% 7% 14% 26% 14% 1	6290
	11th to 20th	Day	32% 8% 13% 29% 16%	6285
	21st to end	Day	31% 8% 14% 34% 12%	6690
August	1st to 10th	Day	43% 7% 15% 23% 12% 1	4221
	11th to 20th	Day	42% 8% 14% 27% 9% 1	4213
	21st to end	Day	36% 8% 13% 32% 10% 1	4380
September	1st to 10th	Day	38% 8% 13% 29% 12% 1	2400
	11th to 20th	Day	32% 6% 13% 33% 16% 1	2400
	21st to end	Day	43% 7% 13% 27% 10%	2090
October	1st to 10th	Day	40% 7% 13% 29% 11% 1	3260
	11th to 20th	Day	44% 7% 15% 22% 11% 1	3240
	21st to end	Day	51% 7% 13% 20% 8%	3458
November	1st to 10th	Day	48% 6% 14% 21% 9% 1	1777
	11th to 20th	Day	53% 7% 13% 16% 11% 1	1680
	21st to end	Day	61% 7% 12% 13% 7%	1680
December	1st to 10th	Day	66% 5% 14% 10% 4	2680
	11th to 20th	Day	63% 5% 10% 13% 8%	3066
	21st to end	Day	63% 5% 9% 15% 8%	4048
January	1st to 10th	Night	62% 6% 11% 14% 7%	8234
	11th to 20th	Night	68% 6% 10% 10% 6% 1	8262
	21st to end	Night	58% 6% 10% 12% 14% 1	8401
February	1st to 10th	Night	58% 6% 11% 17% 7% 1	2730
	11th to 20th	Night	58% 5% 9% 19% 8% 1	2665
	21st to end	Night	53% 6% 11% 20% 9% 1	2149
March	1st to 10th	Night	56% 5% 7% 17% 12% 4	5196
	11th to 20th	Night	48% 6% 17% 19% 9% 2	5090
	21st to end	Night	47% 4 9% 21% 16% 2	5463
April	1st to 10th	Night	52% 4 8% 20% 13% 2	2100
	11th to 20th	Night	48% 5% 9% 20% 16% 1	2075
	21st to end	Night	47% 7% 10% 18% 15% 3	1929
May	1st to 10th	Night	54% 5% 10% 15% 12% 4	3775
	11th to 20th	Night	40% 7% 14% 22% 15% 2	3576
	21st to end	Night	45% 7% 13% 19% 15% 2	3927
June	1st to 10th	Night	43% 6% 11% 23% 15% 1	1600
	11th to 20th	Night	38% 6% 11% 22% 20% 2	1600
	21st to end	Night	41% 6% 14% 22% 14% 2	1600
July	1st to 10th	Night	37% 8% 14% 22% 17% 1	3560
	11th to 20th	Night	33% 7% 13% 31% 15% 1	3552
	21st to end	Night	30% 7% 14% 34% 14% 1	3844
August	1st to 10th	Night	35% 6% 14% 28% 15% 1	2904
	11th to 20th	Night	35% 7% 17% 26% 12% 1	2902
	21st to end	Night	30% 8% 14% 35% 11% 1	3484
September	1st to 10th	Night	35% 7% 15% 29% 14% 1	2000
	11th to 20th	Night	30% 7% 13% 33% 17% 1	2000
	21st to end	Night	43% 7% 10% 27% 13% 1	2307
October	1st to 10th	Night	34% 6% 11% 29% 20% 1	3920
	11th to 20th	Night	44% 5% 14% 28% 9%	3899
	21st to end	Night	45% 7% 14% 25% 9%	4330
November	1st to 10th	Night	47% 6% 13% 23% 11% 1	2736
	11th to 20th	Night	52% 5% 13% 19% 9% 2	2940
	21st to end	Night	57% 7% 14% 16% 5%	2940
December	1st to 10th	Night	60% 7% 14% 15% 3	4720
	11th to 20th	Night	61% 6% 12% 13% 7%	5348
	21st to end	Night	67% 5% 9% 11% 8%	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	24% 21% 37% 15% 2 1	220
	11th to 20th	Day	29% 24% 30% 14% 4	220
	21st to end	Day	29% 21% 33% 12% 4	363
February	1st to 10th	Day	30% 25% 29% 12% 3	330
	11th to 20th	Day	32% 25% 37% 5% 1	330
	21st to end	Day	35% 23% 32% 9% 1	373
March	1st to 10th	Day	27% 21% 34% 15% 3	540
	11th to 20th	Day	30% 20% 31% 14% 3 1	540
	21st to end	Day	35% 19% 28% 12% 5% 1	594
April	1st to 10th	Day	31% 21% 33% 9% 5%	540
	11th to 20th	Day	34% 21% 21% 16% 6% 2	532
	21st to end	Day	31% 19% 33% 11% 5% 1	540
May	1st to 10th	Day	24% 17% 31% 18% 6% 3	507
	11th to 20th	Day	20% 15% 35% 21% 8% 3	527
	21st to end	Day	20% 14% 35% 17% 11% 3	573
June	1st to 10th	Day	21% 15% 33% 23% 6% 2	530
	11th to 20th	Day	15% 15% 34% 23% 10% 2	530
	21st to end	Day	21% 15% 32% 20% 10% 2	530
July	1st to 10th	Day	12% 10% 33% 29% 13% 3	525
	11th to 20th	Day	15% 10% 30% 26% 16% 3	524
	21st to end	Day	11% 10% 39% 26% 11% 3	576
August	1st to 10th	Day	11% 9% 30% 30% 14% 6%	526
	11th to 20th	Day	13% 8% 29% 27% 16% 6%	519
	21st to end	Day	15% 10% 31% 25% 12% 7%	583
September	1st to 10th	Day	13% 13% 32% 23% 12% 8%	530
	11th to 20th	Day	10% 8% 27% 23% 19% 13%	530
	21st to end	Day	19% 14% 27% 25% 10% 5%	530
October	1st to 10th	Day	24% 16% 25% 18% 12% 5%	530
	11th to 20th	Day	25% 20% 32% 15% 7% 2	530
	21st to end	Day	30% 18% 30% 17% 4 1	558
November	1st to 10th	Day	29% 19% 27% 16% 8% 1	351
	11th to 20th	Day	30% 25% 30% 10% 4	220
	21st to end	Day	32% 23% 30% 12% 2 1	220
December	1st to 10th	Day	31% 17% 35% 14% 3	220
	11th to 20th	Day	34% 23% 32% 9% 1 1	220
	21st to end	Day	37% 16% 34% 10% 3	242
January	1st to 10th	Night	27% 21% 31% 18% 3	840
	11th to 20th	Night	29% 17% 31% 19% 4	840
	21st to end	Night	21% 17% 35% 22% 4 1	924
February	1st to 10th	Night	23% 22% 35% 19% 2	840
	11th to 20th	Night	23% 20% 37% 17% 4	823
	21st to end	Night	25% 20% 34% 18% 2	692
March	1st to 10th	Night	25% 16% 35% 20% 3	840
	11th to 20th	Night	26% 20% 32% 18% 3 1	840
	21st to end	Night	23% 18% 31% 22% 6%	924
April	1st to 10th	Night	25% 18% 33% 20% 4	840
	11th to 20th	Night	24% 20% 29% 20% 7%	831
	21st to end	Night	21% 14% 32% 24% 9%	669
May	1st to 10th	Night	23% 11% 28% 26% 10% 1	478
	11th to 20th	Night	15% 11% 34% 31% 9%	394
	21st to end	Night	13% 8% 36% 29% 13%	433
June	1st to 10th	Night	16% 7% 36% 30% 11%	400
	11th to 20th	Night	14% 11% 32% 32% 12% 1	400
	21st to end	Night	16% 9% 30% 33% 13% 1	400
July	1st to 10th	Night	6% 8% 29% 43% 13% 1	390
	11th to 20th	Night	11% 3 29% 36% 21%	388
	21st to end	Night	11% 4 31% 38% 15% 1	448
August	1st to 10th	Night	11% 4 24% 36% 24% 2	597
	11th to 20th	Night	10% 6% 22% 38% 22% 2	594
	21st to end	Night	11% 6% 31% 33% 18% 2	817
September	1st to 10th	Night	12% 7% 31% 30% 17% 2	800
	11th to 20th	Night	12% 5% 24% 29% 26% 5%	800
	21st to end	Night	19% 9% 25% 26% 18% 3	800
October	1st to 10th	Night	20% 12% 27% 25% 16% 2	800
	11th to 20th	Night	25% 13% 32% 21% 9% 1	800
	21st to end	Night	28% 14% 31% 22% 5%	880
November	1st to 10th	Night	26% 13% 26% 26% 8%	820
	11th to 20th	Night	24% 17% 33% 18% 7% 1	840
	21st to end	Night	28% 18% 28% 21% 4	840
December	1st to 10th	Night	30% 18% 30% 19% 3	840
	11th to 20th	Night	27% 18% 35% 16% 3	840
	21st to end	Night	35% 15% 31% 16% 3	924

Page generated at 2026-04-29 02:21:43. Version ac07

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