Mark Ice Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mark Ice Station 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	15% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	108564
	Night	15% 8% 3 7% 4 4 4 4 5% 6% 39%	110440
Transparency	Day	43% 7% 12% 21% 14% 2	112119
	Night	42% 6% 13% 22% 14% 2	115049
Seeing	Day	24% 20% 30% 18% 7% 2	15290
	Night	22% 18% 31% 22% 6% 1	24363

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	10% 7% 3 13% 6% 5% 5% 4 6% 7% 34%	3597
	11th to 20th	Day	12% 8% 4 8% 4 4 4 4 6% 6% 40%	3570
	21st to end	Day	13% 11% 4 7% 4 3 3 4 5% 5% 39%	3960
February	1st to 10th	Day	15% 8% 3 7% 6% 6% 6% 5% 6% 6% 32%	1826
	11th to 20th	Day	12% 7% 2 9% 6% 5% 4 4 6% 8% 36%	1948
	21st to end	Day	16% 11% 3 8% 4 4 4 4 5% 4 35%	1650
March	1st to 10th	Day	19% 15% 3 9% 5% 4 4 3 4 5% 29%	3216
	11th to 20th	Day	12% 9% 2 6% 5% 5% 6% 4 6% 7% 37%	3294
	21st to end	Day	19% 10% 4 7% 4 4 4 3 5% 7% 34%	4097
April	1st to 10th	Day	17% 11% 3 6% 5% 5% 4 3 5% 6% 35%	2280
	11th to 20th	Day	15% 7% 2 7% 4 5% 5% 4 7% 6% 37%	2254
	21st to end	Day	20% 8% 3 8% 5% 4 4 4 5% 6% 33%	2463
May	1st to 10th	Day	22% 11% 4 8% 5% 5% 5% 3 5% 6% 27%	4106
	11th to 20th	Day	21% 9% 3 8% 6% 4 4 3 5% 7% 31%	4267
	21st to end	Day	13% 5% 2 6% 5% 4 5% 3 6% 9% 42%	4837
June	1st to 10th	Day	18% 6% 2 7% 5% 5% 5% 4 6% 9% 33%	2660
	11th to 20th	Day	16% 6% 2 7% 5% 5% 5% 3 6% 9% 36%	2660
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 6% 6% 4 7% 9% 36%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 5% 8% 11% 37%	4440
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	4814
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 5% 4 6% 8% 35%	4243
	11th to 20th	Day	13% 7% 3 8% 5% 5% 5% 4 7% 8% 35%	3949
	21st to end	Day	8% 4 2 6% 5% 5% 6% 4 7% 10% 43%	4180
September	1st to 10th	Day	12% 6% 2 7% 4 5% 4 4 6% 7% 45%	2280
	11th to 20th	Day	14% 6% 2 5% 3 4 3 3 5% 6% 49%	2115
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 7% 42%	2090
October	1st to 10th	Day	21% 8% 2 7% 5% 4 4 3 4 4 37%	2090
	11th to 20th	Day	12% 8% 3 6% 3 4 5% 3 5% 7% 43%	1830
	21st to end	Day	21% 7% 3 7% 4 4 5% 3 4 6% 36%	1881
November	1st to 10th	Day	11% 7% 3 7% 4 4 3 3 4 6% 47%	1761
	11th to 20th	Day	17% 7% 2 4 4 4 3 3 5% 6% 45%	1800
	21st to end	Day	18% 9% 2 6% 5% 4 4 4 4 7% 39%	1760
December	1st to 10th	Day	13% 9% 3 8% 5% 4 4 4 4 8% 39%	2600
	11th to 20th	Day	19% 8% 3 6% 4 4 5% 3 4 4 40%	2986
	21st to end	Day	16% 11% 3 8% 5% 3 4 3 5% 6% 35%	3960
January	1st to 10th	Night	12% 6% 3 9% 5% 4 5% 4 6% 7% 38%	6349
	11th to 20th	Night	11% 9% 3 10% 5% 5% 5% 4 6% 7% 35%	6315
	21st to end	Night	14% 9% 4 7% 5% 4 5% 4 5% 6% 37%	6996
February	1st to 10th	Night	14% 9% 3 7% 5% 4 5% 4 6% 6% 36%	2571
	11th to 20th	Night	11% 8% 2 7% 6% 5% 6% 5% 7% 6% 38%	2338
	21st to end	Night	13% 9% 3 7% 5% 5% 5% 4 5% 5% 38%	1980
March	1st to 10th	Night	22% 12% 2 6% 4 4 3 4 4 6% 32%	3844
	11th to 20th	Night	11% 9% 3 8% 5% 5% 5% 5% 6% 7% 37%	3693
	21st to end	Night	21% 9% 3 6% 4 3 5% 4 6% 7% 33%	3531
April	1st to 10th	Night	16% 9% 3 8% 5% 4 4 3 6% 5% 36%	1900
	11th to 20th	Night	17% 9% 2 5% 5% 4 5% 4 5% 6% 39%	1875
	21st to end	Night	19% 9% 3 8% 4 4 3 3 5% 5% 38%	1715
May	1st to 10th	Night	22% 12% 3 8% 4 5% 4 4 6% 6% 26%	2834
	11th to 20th	Night	16% 10% 4 10% 6% 5% 5% 4 6% 7% 27%	2655
	21st to end	Night	15% 6% 3 6% 4 4 4 4 6% 8% 41%	2738
June	1st to 10th	Night	17% 9% 3 6% 5% 3 4 3 4 7% 38%	1520
	11th to 20th	Night	18% 6% 3 6% 4 4 5% 4 5% 7% 37%	1520
	21st to end	Night	15% 7% 2 7% 4 4 4 4 6% 8% 38%	1520
July	1st to 10th	Night	10% 7% 2 6% 6% 6% 5% 4 7% 8% 39%	2520
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 4 5% 8% 43%	2520
	21st to end	Night	16% 6% 2 7% 4 4 4 4 5% 6% 42%	2739
August	1st to 10th	Night	19% 8% 2 7% 4 4 5% 4 5% 7% 35%	2653
	11th to 20th	Night	12% 9% 3 7% 5% 5% 4 3 6% 6% 39%	2874
	21st to end	Night	9% 3 2 4 3 3 3 3 6% 7% 58%	3476
September	1st to 10th	Night	12% 5% 2 6% 3 3 3 3 6% 6% 50%	1900
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	2064
	21st to end	Night	13% 5% 2 7% 4 4 4 4 5% 6% 46%	2090
October	1st to 10th	Night	20% 6% 2 7% 4 4 4 3 4 6% 40%	2090
	11th to 20th	Night	14% 6% 3 5% 4 3 4 4 6% 7% 44%	2347
	21st to end	Night	21% 8% 2 6% 4 4 5% 3 5% 5% 36%	2717
November	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 4 6% 46%	2537
	11th to 20th	Night	15% 6% 3 5% 5% 4 4 3 5% 6% 44%	2600
	21st to end	Night	14% 7% 3 6% 4 4 5% 4 5% 7% 42%	2635
December	1st to 10th	Night	15% 10% 4 9% 4 4 4 3 5% 6% 37%	4580
	11th to 20th	Night	21% 8% 3 6% 4 3 4 3 4 5% 38%	5208
	21st to end	Night	17% 11% 4 7% 4 4 4 3 5% 5% 36%	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	45% 6% 9% 26% 13% 1	3598
	11th to 20th	Day	41% 6% 13% 21% 16% 3	3600
	21st to end	Day	43% 6% 9% 21% 18% 3	3960
February	1st to 10th	Day	48% 7% 13% 18% 12% 2	1826
	11th to 20th	Day	44% 7% 11% 20% 15% 3	1957
	21st to end	Day	49% 5% 11% 19% 13% 2	1650
March	1st to 10th	Day	57% 5% 11% 13% 11% 3	3219
	11th to 20th	Day	38% 10% 17% 21% 13% 2	3294
	21st to end	Day	48% 6% 6% 18% 18% 5%	4097
April	1st to 10th	Day	49% 5% 9% 19% 14% 3	2280
	11th to 20th	Day	44% 7% 12% 19% 16% 2	2254
	21st to end	Day	50% 6% 9% 17% 15% 3	2463
May	1st to 10th	Day	56% 8% 11% 14% 10% 1	4120
	11th to 20th	Day	51% 8% 14% 16% 10% 1	4271
	21st to end	Day	35% 9% 14% 24% 17% 1	4837
June	1st to 10th	Day	46% 8% 13% 21% 11% 1	2660
	11th to 20th	Day	43% 8% 13% 19% 14% 2	2660
	21st to end	Day	48% 9% 13% 19% 11% 1	2660
July	1st to 10th	Day	41% 8% 13% 20% 17% 1	4370
	11th to 20th	Day	38% 8% 17% 24% 12% 1	4365
	21st to end	Day	46% 7% 13% 20% 13% 1	4661
August	1st to 10th	Day	45% 8% 15% 21% 10%	4229
	11th to 20th	Day	44% 8% 15% 24% 8% 1	3988
	21st to end	Day	34% 8% 13% 29% 16% 1	4180
September	1st to 10th	Day	37% 6% 12% 25% 18% 1	2280
	11th to 20th	Day	35% 5% 9% 26% 23% 2	2115
	21st to end	Day	40% 7% 10% 22% 19% 3	2090
October	1st to 10th	Day	45% 5% 9% 22% 17% 2	3480
	11th to 20th	Day	34% 5% 9% 27% 21% 4	3007
	21st to end	Day	35% 5% 10% 30% 17% 4	3081
November	1st to 10th	Day	39% 4 14% 25% 16% 2	1761
	11th to 20th	Day	38% 6% 11% 21% 20% 3	1800
	21st to end	Day	44% 5% 16% 23% 10% 2	1760
December	1st to 10th	Day	43% 5% 14% 28% 9% 1	2600
	11th to 20th	Day	43% 5% 12% 19% 18% 3	2986
	21st to end	Day	49% 5% 10% 18% 13% 6%	3960
January	1st to 10th	Night	41% 5% 14% 26% 12% 2	6349
	11th to 20th	Night	45% 7% 14% 19% 12% 3	6360
	21st to end	Night	46% 5% 11% 16% 17% 5%	6996
February	1st to 10th	Night	44% 8% 14% 20% 12% 2	2571
	11th to 20th	Night	42% 7% 14% 20% 14% 3	2340
	21st to end	Night	44% 5% 11% 23% 12% 4	1980
March	1st to 10th	Night	52% 6% 10% 19% 10% 3	3854
	11th to 20th	Night	42% 10% 13% 21% 12% 2	3694
	21st to end	Night	46% 6% 8% 15% 20% 5%	3531
April	1st to 10th	Night	46% 7% 11% 18% 15% 2	1900
	11th to 20th	Night	44% 6% 12% 20% 17% 1	1875
	21st to end	Night	46% 7% 11% 17% 16% 4	1715
May	1st to 10th	Night	54% 9% 13% 16% 7% 1	2840
	11th to 20th	Night	52% 11% 14% 13% 8% 2	2656
	21st to end	Night	40% 8% 15% 22% 14% 1	2739
June	1st to 10th	Night	45% 7% 13% 23% 11% 1	1520
	11th to 20th	Night	44% 8% 13% 19% 13% 2	1520
	21st to end	Night	42% 9% 16% 20% 13% 1	1520
July	1st to 10th	Night	39% 8% 15% 22% 14% 1	2480
	11th to 20th	Night	38% 8% 15% 23% 15%	2472
	21st to end	Night	42% 7% 12% 23% 15% 1	2651
August	1st to 10th	Night	48% 8% 13% 20% 11% 1	2643
	11th to 20th	Night	44% 8% 15% 23% 9%	2901
	21st to end	Night	25% 6% 16% 34% 18% 1	3476
September	1st to 10th	Night	34% 7% 13% 27% 19% 1	1900
	11th to 20th	Night	32% 6% 11% 26% 23% 2	2064
	21st to end	Night	37% 7% 10% 26% 17% 2	2090
October	1st to 10th	Night	40% 6% 15% 24% 14% 2	3480
	11th to 20th	Night	29% 5% 12% 25% 24% 4	3909
	21st to end	Night	36% 5% 11% 32% 13% 2	4467
November	1st to 10th	Night	38% 6% 11% 23% 19% 3	2537
	11th to 20th	Night	40% 5% 11% 22% 19% 3	2600
	21st to end	Night	40% 6% 16% 24% 12% 1	2635
December	1st to 10th	Night	46% 5% 12% 28% 9%	4580
	11th to 20th	Night	47% 5% 14% 14% 19% 1	5208
	21st to end	Night	46% 5% 9% 20% 15% 4	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	33% 24% 29% 12% 3	200
	11th to 20th	Day	33% 26% 32% 9% 1 1	200
	21st to end	Day	28% 29% 32% 9% 3	220
February	1st to 10th	Day	33% 31% 26% 8% 1	355
	11th to 20th	Day	36% 26% 27% 11% 1	496
	21st to end	Day	30% 28% 29% 12% 2	414
March	1st to 10th	Day	32% 23% 33% 9% 3	500
	11th to 20th	Day	30% 28% 28% 9% 3 1	464
	21st to end	Day	30% 25% 29% 9% 4 2	506
April	1st to 10th	Day	32% 25% 25% 10% 6% 1	460
	11th to 20th	Day	29% 27% 28% 10% 6% 1	452
	21st to end	Day	30% 21% 30% 13% 5% 1	460
May	1st to 10th	Day	31% 23% 28% 12% 5% 1	463
	11th to 20th	Day	20% 20% 38% 15% 5% 1	487
	21st to end	Day	18% 18% 33% 25% 5% 1	529
June	1st to 10th	Day	19% 17% 37% 17% 9% 1	490
	11th to 20th	Day	17% 17% 35% 23% 8% 1	490
	21st to end	Day	20% 19% 34% 17% 8% 2	490
July	1st to 10th	Day	16% 10% 33% 28% 11% 2	485
	11th to 20th	Day	14% 11% 35% 29% 10% 2	484
	21st to end	Day	14% 14% 36% 26% 9% 2	532
August	1st to 10th	Day	12% 11% 32% 32% 10% 3	486
	11th to 20th	Day	15% 10% 32% 27% 13% 4	479
	21st to end	Day	12% 13% 32% 27% 11% 5%	539
September	1st to 10th	Day	17% 14% 28% 21% 15% 5%	490
	11th to 20th	Day	17% 16% 26% 19% 14% 9%	490
	21st to end	Day	17% 16% 32% 21% 9% 6%	490
October	1st to 10th	Day	27% 17% 24% 19% 10% 4	490
	11th to 20th	Day	21% 20% 29% 22% 7% 2	445
	21st to end	Day	31% 17% 28% 19% 4 1	429
November	1st to 10th	Day	23% 23% 27% 18% 9% 1	395
	11th to 20th	Day	31% 22% 25% 18% 3 1	400
	21st to end	Day	34% 20% 28% 13% 5% 1	360
December	1st to 10th	Day	24% 34% 28% 12% 4	200
	11th to 20th	Day	39% 21% 32% 6% 2	200
	21st to end	Day	30% 25% 30% 12% 3	220
January	1st to 10th	Night	23% 27% 34% 15% 2	800
	11th to 20th	Night	26% 26% 30% 15% 3	800
	21st to end	Night	19% 25% 36% 17% 2	880
February	1st to 10th	Night	25% 23% 35% 16% 2	800
	11th to 20th	Night	24% 26% 35% 13% 1	783
	21st to end	Night	26% 26% 32% 14% 1	660
March	1st to 10th	Night	27% 22% 32% 16% 2	800
	11th to 20th	Night	24% 25% 31% 17% 3	767
	21st to end	Night	26% 21% 32% 17% 5%	836
April	1st to 10th	Night	26% 20% 32% 19% 3	760
	11th to 20th	Night	22% 23% 31% 18% 5%	751
	21st to end	Night	26% 19% 31% 20% 3	575
May	1st to 10th	Night	26% 18% 33% 20% 4	570
	11th to 20th	Night	22% 14% 35% 24% 5%	469
	21st to end	Night	19% 9% 34% 31% 7%	411
June	1st to 10th	Night	18% 11% 35% 27% 8%	380
	11th to 20th	Night	19% 11% 33% 29% 7% 1	380
	21st to end	Night	16% 9% 33% 36% 6%	380
July	1st to 10th	Night	16% 7% 32% 37% 8%	370
	11th to 20th	Night	14% 5% 28% 39% 12% 2	368
	21st to end	Night	13% 6% 33% 37% 12%	416
August	1st to 10th	Night	13% 8% 27% 38% 14%	460
	11th to 20th	Night	14% 9% 30% 32% 13% 1	615
	21st to end	Night	14% 8% 26% 35% 15% 1	836
September	1st to 10th	Night	16% 8% 32% 29% 14% 1	760
	11th to 20th	Night	16% 10% 28% 28% 17% 2	760
	21st to end	Night	16% 12% 29% 29% 13% 2	760
October	1st to 10th	Night	23% 14% 24% 25% 11% 1	760
	11th to 20th	Night	19% 15% 32% 22% 10% 1	760
	21st to end	Night	27% 20% 28% 21% 5%	836
November	1st to 10th	Night	19% 19% 32% 23% 7% 1	780
	11th to 20th	Night	22% 25% 28% 18% 6% 1	800
	21st to end	Night	24% 22% 32% 17% 4	800
December	1st to 10th	Night	25% 24% 33% 15% 4	800
	11th to 20th	Night	26% 23% 32% 16% 3	800
	21st to end	Night	26% 25% 32% 15% 3	880

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