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 2024-01-17.

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	17% 9% 3 6% 6% 3 5% 5% 5% 7% 34%	74733
	Night	17% 10% 4 7% 6% 3 4 4 5% 6% 34%	75088
Transparency	Day	49% 6% 11% 20% 11% 1	74439
	Night	50% 6% 11% 20% 11% 1	74916
Seeing	Day	23% 16% 31% 19% 8% 3	13337
	Night	22% 13% 31% 24% 9% 1	22717

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	17% 17% 5% 8% 6% 3 4 5% 4 6% 26%	1517
	11th to 20th	Day	18% 19% 5% 7% 6% 4 5% 3 4 4 24%	1488
	21st to end	Day	14% 14% 7% 10% 8% 4 5% 5% 5% 4 24%	1782
February	1st to 10th	Day	15% 15% 5% 11% 7% 4 5% 5% 4 5% 22%	1620
	11th to 20th	Day	13% 16% 5% 11% 8% 4 3 4 4 6% 28%	1573
	21st to end	Day	18% 16% 4 9% 8% 4 4 4 3 4 26%	1417
March	1st to 10th	Day	15% 11% 5% 9% 6% 4 6% 5% 4 6% 30%	1905
	11th to 20th	Day	15% 14% 4 7% 6% 4 5% 4 5% 5% 32%	1980
	21st to end	Day	20% 11% 3 6% 5% 2 4 4 4 5% 38%	2218
April	1st to 10th	Day	21% 12% 4 6% 4 3 4 4 4 6% 32%	2160
	11th to 20th	Day	22% 8% 2 5% 4 2 4 3 4 7% 39%	2134
	21st to end	Day	22% 9% 3 7% 6% 3 4 4 4 6% 32%	2322
May	1st to 10th	Day	19% 7% 3 6% 6% 3 5% 5% 5% 6% 35%	2451
	11th to 20th	Day	15% 7% 3 6% 6% 3 4 5% 4 8% 39%	2478
	21st to end	Day	14% 5% 3 5% 6% 4 5% 5% 5% 8% 41%	2725
June	1st to 10th	Day	18% 7% 3 6% 6% 4 5% 5% 6% 7% 33%	2520
	11th to 20th	Day	15% 5% 3 5% 5% 3 5% 6% 6% 9% 38%	2520
	21st to end	Day	16% 6% 4 5% 6% 3 5% 5% 5% 8% 36%	2520
July	1st to 10th	Day	12% 4 3 4 6% 4 5% 6% 6% 9% 42%	2520
	11th to 20th	Day	12% 6% 2 5% 6% 4 5% 5% 6% 9% 39%	2520
	21st to end	Day	11% 6% 2 6% 6% 4 6% 6% 7% 9% 36%	2733
August	1st to 10th	Day	11% 6% 2 6% 6% 4 6% 6% 7% 9% 39%	2327
	11th to 20th	Day	13% 6% 3 6% 6% 4 5% 5% 7% 9% 37%	2303
	21st to end	Day	14% 6% 2 5% 6% 4 5% 5% 6% 8% 39%	2414
September	1st to 10th	Day	14% 5% 3 6% 5% 4 4 5% 5% 8% 42%	2160
	11th to 20th	Day	11% 5% 2 5% 5% 3 4 5% 5% 7% 49%	2160
	21st to end	Day	17% 6% 3 5% 5% 3 4 5% 5% 7% 39%	1882
October	1st to 10th	Day	21% 7% 3 6% 7% 3 5% 3 5% 6% 34%	1800
	11th to 20th	Day	23% 8% 3 6% 7% 3 5% 4 6% 7% 28%	1800
	21st to end	Day	27% 11% 3 6% 5% 3 4 5% 5% 5% 26%	1941
November	1st to 10th	Day	16% 8% 3 8% 4 3 5% 6% 5% 7% 34%	1605
	11th to 20th	Day	17% 12% 4 7% 7% 3 5% 5% 5% 6% 29%	1520
	21st to end	Day	21% 15% 5% 6% 7% 3 4 5% 5% 6% 24%	1520
December	1st to 10th	Day	19% 19% 5% 9% 7% 4 5% 5% 4 5% 20%	1520
	11th to 20th	Day	17% 16% 6% 8% 6% 3 4 4 4 5% 28%	1906
	21st to end	Day	29% 16% 5% 9% 6% 2 3 3 4 4 20%	2772
January	1st to 10th	Night	20% 14% 6% 10% 7% 3 5% 4 5% 5% 22%	2649
	11th to 20th	Night	19% 15% 4 10% 7% 4 4 4 4 5% 23%	2612
	21st to end	Night	13% 13% 6% 10% 7% 3 6% 5% 4 6% 27%	2574
February	1st to 10th	Night	14% 15% 5% 9% 8% 5% 5% 5% 4 6% 24%	2340
	11th to 20th	Night	14% 13% 7% 8% 7% 3 4 5% 5% 5% 29%	2273
	21st to end	Night	16% 12% 4 9% 6% 3 4 4 5% 6% 31%	1839
March	1st to 10th	Night	16% 10% 5% 7% 6% 4 5% 4 4 6% 33%	2040
	11th to 20th	Night	17% 11% 4 7% 6% 3 4 3 4 6% 34%	1979
	21st to end	Night	16% 8% 4 6% 5% 3 4 4 5% 6% 39%	2138
April	1st to 10th	Night	20% 9% 4 6% 5% 3 4 4 5% 5% 35%	1800
	11th to 20th	Night	19% 8% 3 6% 4 3 5% 4 5% 6% 37%	1775
	21st to end	Night	19% 7% 3 5% 6% 3 5% 4 6% 8% 33%	1654
May	1st to 10th	Night	19% 6% 3 5% 6% 3 4 4 5% 7% 37%	1508
	11th to 20th	Night	13% 7% 2 5% 4 2 5% 5% 6% 7% 45%	1415
	21st to end	Night	11% 4 2 5% 4 3 6% 4 4 8% 48%	1550
June	1st to 10th	Night	15% 5% 2 6% 6% 4 5% 6% 5% 8% 38%	1440
	11th to 20th	Night	11% 6% 3 5% 5% 3 4 5% 5% 8% 45%	1440
	21st to end	Night	13% 6% 3 6% 5% 3 4 5% 6% 8% 41%	1440
July	1st to 10th	Night	7% 4 2 5% 6% 3 4 4 5% 8% 51%	1440
	11th to 20th	Night	11% 4 2 5% 5% 3 4 5% 6% 9% 46%	1440
	21st to end	Night	10% 4 2 5% 4 3 5% 4 7% 8% 49%	1582
August	1st to 10th	Night	10% 5% 2 5% 5% 3 4 4 7% 7% 48%	1611
	11th to 20th	Night	10% 5% 2 5% 5% 3 5% 4 6% 9% 45%	1598
	21st to end	Night	10% 6% 3 5% 5% 2 4 5% 5% 8% 47%	1923
September	1st to 10th	Night	11% 6% 3 5% 5% 2 4 4 6% 8% 46%	1800
	11th to 20th	Night	13% 4 2 3 4 3 5% 5% 5% 6% 52%	1800
	21st to end	Night	17% 6% 2 5% 4 3 4 4 4 7% 43%	2075
October	1st to 10th	Night	18% 7% 2 6% 5% 3 5% 5% 4 6% 38%	2160
	11th to 20th	Night	22% 9% 3 7% 6% 4 4 4 4 6% 31%	2160
	21st to end	Night	24% 11% 3 6% 6% 3 5% 5% 5% 5% 28%	2413
November	1st to 10th	Night	20% 8% 3 5% 5% 3 4 4 5% 6% 37%	2468
	11th to 20th	Night	19% 10% 4 5% 6% 4 5% 5% 5% 7% 30%	2660
	21st to end	Night	22% 10% 3 7% 6% 3 6% 5% 6% 7% 26%	2660
December	1st to 10th	Night	22% 15% 5% 7% 7% 4 5% 5% 5% 6% 20%	2660
	11th to 20th	Night	19% 16% 5% 8% 6% 3 4 4 4 5% 26%	3288
	21st to end	Night	29% 17% 4 9% 6% 3 4 4 4 4 16%	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	59% 6% 11% 17% 7%	1518
	11th to 20th	Day	65% 4 9% 11% 10% 1	1488
	21st to end	Day	62% 6% 8% 13% 9% 2	1782
February	1st to 10th	Day	63% 6% 9% 15% 5% 1	1620
	11th to 20th	Day	60% 4 9% 14% 11% 2	1582
	21st to end	Day	62% 5% 8% 13% 10% 1	1417
March	1st to 10th	Day	54% 5% 14% 14% 10% 2	1908
	11th to 20th	Day	55% 4 10% 17% 11% 2	1980
	21st to end	Day	50% 5% 6% 20% 15% 5%	2218
April	1st to 10th	Day	54% 4 8% 20% 12% 3	2160
	11th to 20th	Day	47% 4 9% 22% 17% 1	2134
	21st to end	Day	54% 4 8% 18% 14% 2	2322
May	1st to 10th	Day	48% 6% 9% 18% 15% 3	2451
	11th to 20th	Day	43% 6% 9% 24% 15% 2	2482
	21st to end	Day	41% 7% 14% 21% 15% 2	2725
June	1st to 10th	Day	48% 8% 11% 18% 14% 1	2520
	11th to 20th	Day	41% 7% 11% 24% 14% 2	2520
	21st to end	Day	44% 8% 13% 21% 13% 1	2520
July	1st to 10th	Day	35% 8% 12% 27% 17% 1	2450
	11th to 20th	Day	38% 9% 15% 27% 11%	2445
	21st to end	Day	41% 10% 13% 24% 11% 1	2580
August	1st to 10th	Day	38% 9% 16% 25% 11% 1	2314
	11th to 20th	Day	42% 9% 14% 24% 11% 1	2303
	21st to end	Day	41% 8% 12% 27% 12% 1	2414
September	1st to 10th	Day	38% 8% 13% 27% 12% 1	2160
	11th to 20th	Day	34% 6% 13% 30% 15% 1	2160
	21st to end	Day	42% 7% 13% 28% 9%	1882
October	1st to 10th	Day	51% 6% 11% 20% 12% 1	1800
	11th to 20th	Day	54% 7% 13% 18% 7% 1	1800
	21st to end	Day	60% 5% 10% 16% 8%	1941
November	1st to 10th	Day	48% 7% 15% 20% 9% 1	1605
	11th to 20th	Day	53% 7% 13% 16% 10% 1	1520
	21st to end	Day	60% 7% 12% 13% 7%	1520
December	1st to 10th	Day	66% 6% 11% 12% 5%	1520
	11th to 20th	Day	60% 6% 13% 13% 8%	1906
	21st to end	Day	68% 5% 8% 13% 6%	2772
January	1st to 10th	Night	64% 4 9% 15% 7%	2649
	11th to 20th	Night	64% 6% 9% 13% 8% 1	2612
	21st to end	Night	57% 6% 8% 17% 11% 1	2574
February	1st to 10th	Night	61% 6% 11% 16% 6% 1	2340
	11th to 20th	Night	57% 4 9% 20% 9% 1	2275
	21st to end	Night	53% 6% 11% 20% 10% 1	1839
March	1st to 10th	Night	52% 5% 12% 18% 12% 2	2050
	11th to 20th	Night	52% 5% 10% 21% 11% 1	1980
	21st to end	Night	46% 5% 8% 22% 16% 3	2138
April	1st to 10th	Night	51% 4 8% 21% 14% 3	1800
	11th to 20th	Night	47% 5% 9% 20% 17% 2	1775
	21st to end	Night	47% 7% 11% 16% 16% 3	1654
May	1st to 10th	Night	47% 5% 9% 19% 16% 4	1508
	11th to 20th	Night	38% 6% 10% 26% 17% 3	1416
	21st to end	Night	35% 6% 14% 21% 19% 4	1551
June	1st to 10th	Night	43% 6% 12% 23% 15% 1	1440
	11th to 20th	Night	38% 6% 11% 21% 21% 3	1440
	21st to end	Night	41% 6% 14% 23% 14% 2	1440
July	1st to 10th	Night	29% 8% 11% 27% 22% 3	1400
	11th to 20th	Night	34% 8% 11% 31% 15%	1392
	21st to end	Night	31% 7% 15% 33% 13% 1	1494
August	1st to 10th	Night	33% 7% 17% 29% 13% 1	1600
	11th to 20th	Night	34% 7% 17% 26% 14% 2	1598
	21st to end	Night	34% 8% 12% 31% 14% 1	1923
September	1st to 10th	Night	36% 7% 15% 26% 14% 1	1800
	11th to 20th	Night	31% 7% 13% 32% 16% 1	1800
	21st to end	Night	41% 7% 11% 29% 12% 1	2075
October	1st to 10th	Night	46% 7% 11% 22% 14% 1	2160
	11th to 20th	Night	54% 5% 12% 21% 8%	2160
	21st to end	Night	57% 6% 12% 14% 10%	2413
November	1st to 10th	Night	47% 5% 13% 23% 11% 1	2468
	11th to 20th	Night	52% 5% 13% 18% 10% 2	2660
	21st to end	Night	56% 7% 15% 16% 5%	2660
December	1st to 10th	Night	62% 7% 12% 15% 4	2660
	11th to 20th	Night	60% 5% 12% 16% 7% 1	3288
	21st to end	Night	71% 5% 9% 11% 4	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	26% 21% 33% 17% 2 1	180
	11th to 20th	Day	28% 26% 30% 13% 3	172
	21st to end	Day	28% 20% 34% 13% 5%	264
February	1st to 10th	Day	35% 26% 30% 8%	240
	11th to 20th	Day	31% 25% 40% 4 1	240
	21st to end	Day	37% 22% 31% 9% 1	283
March	1st to 10th	Day	25% 20% 35% 16% 3	420
	11th to 20th	Day	27% 19% 35% 15% 4 1	420
	21st to end	Day	34% 18% 28% 13% 6% 1	462
April	1st to 10th	Day	28% 21% 34% 10% 6%	420
	11th to 20th	Day	31% 22% 21% 17% 8% 3	412
	21st to end	Day	31% 18% 34% 10% 6% 2	420
May	1st to 10th	Day	26% 16% 29% 19% 6% 4	423
	11th to 20th	Day	20% 14% 34% 20% 8% 3	447
	21st to end	Day	18% 14% 35% 18% 11% 4	485
June	1st to 10th	Day	21% 14% 35% 21% 7% 2	450
	11th to 20th	Day	16% 15% 31% 24% 11% 3	450
	21st to end	Day	20% 13% 33% 21% 11% 3	450
July	1st to 10th	Day	11% 9% 32% 30% 15% 3	445
	11th to 20th	Day	15% 10% 29% 27% 16% 4	444
	21st to end	Day	11% 10% 39% 26% 10% 4	488
August	1st to 10th	Day	10% 9% 32% 30% 13% 6%	446
	11th to 20th	Day	12% 8% 29% 28% 17% 7%	439
	21st to end	Day	15% 10% 31% 24% 13% 7%	495
September	1st to 10th	Day	12% 13% 34% 22% 12% 8%	450
	11th to 20th	Day	12% 10% 29% 23% 18% 10%	450
	21st to end	Day	18% 14% 27% 24% 11% 6%	450
October	1st to 10th	Day	26% 17% 25% 16% 12% 5%	450
	11th to 20th	Day	27% 19% 31% 15% 6% 1	450
	21st to end	Day	33% 18% 28% 18% 4	475
November	1st to 10th	Day	27% 19% 27% 18% 9% 1	299
	11th to 20th	Day	31% 23% 30% 11% 4 1	180
	21st to end	Day	28% 23% 32% 13% 3 1	180
December	1st to 10th	Day	31% 18% 33% 16% 3	180
	11th to 20th	Day	34% 23% 30% 11% 2 1	180
	21st to end	Day	37% 16% 35% 10% 2	198
January	1st to 10th	Night	27% 20% 29% 20% 4 1	760
	11th to 20th	Night	28% 17% 31% 19% 4	748
	21st to end	Night	21% 16% 35% 22% 5% 1	792
February	1st to 10th	Night	24% 21% 36% 18% 1	720
	11th to 20th	Night	22% 20% 37% 17% 4	703
	21st to end	Night	24% 20% 35% 18% 3	592
March	1st to 10th	Night	23% 16% 36% 21% 3	720
	11th to 20th	Night	26% 19% 32% 19% 4 1	720
	21st to end	Night	22% 16% 31% 24% 7% 1	792
April	1st to 10th	Night	24% 18% 33% 21% 4	720
	11th to 20th	Night	23% 20% 29% 20% 8%	711
	21st to end	Night	22% 13% 31% 24% 10%	574
May	1st to 10th	Night	23% 9% 28% 26% 12% 2	428
	11th to 20th	Night	16% 10% 35% 31% 9%	354
	21st to end	Night	12% 7% 38% 29% 14% 1	389
June	1st to 10th	Night	16% 7% 37% 29% 11%	360
	11th to 20th	Night	14% 9% 31% 32% 12% 1	360
	21st to end	Night	15% 8% 28% 35% 14% 1	360
July	1st to 10th	Night	6% 8% 27% 43% 15% 1	350
	11th to 20th	Night	12% 2 30% 35% 21%	348
	21st to end	Night	10% 4 31% 38% 15% 1	402
August	1st to 10th	Night	12% 4 23% 35% 24% 2	537
	11th to 20th	Night	9% 6% 22% 37% 24% 2	534
	21st to end	Night	11% 6% 31% 31% 19% 2	735
September	1st to 10th	Night	12% 7% 31% 30% 17% 3	720
	11th to 20th	Night	13% 5% 25% 28% 24% 4	720
	21st to end	Night	19% 9% 24% 26% 19% 3	720
October	1st to 10th	Night	21% 12% 26% 23% 15% 2	720
	11th to 20th	Night	26% 13% 31% 21% 9%	720
	21st to end	Night	30% 14% 29% 22% 5%	792
November	1st to 10th	Night	25% 12% 26% 27% 9% 1	740
	11th to 20th	Night	25% 16% 32% 19% 7% 1	760
	21st to end	Night	27% 18% 28% 22% 5%	760
December	1st to 10th	Night	31% 18% 31% 18% 3	760
	11th to 20th	Night	27% 17% 35% 17% 3	760
	21st to end	Night	36% 15% 32% 15% 3	836

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