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 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	16% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	137683
	Night	15% 8% 3 7% 4 4 4 4 5% 6% 38%	135028
Transparency	Day	44% 6% 12% 22% 14% 2	141192
	Night	43% 6% 12% 22% 15% 2	139608
Seeing	Day	24% 20% 30% 17% 6% 2	17073
	Night	22% 18% 31% 22% 6% 1	25976

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	9% 7% 3 13% 7% 6% 5% 4 6% 6% 33%	4661
	11th to 20th	Day	12% 10% 4 8% 4 4 4 4 6% 6% 39%	4650
	21st to end	Day	11% 11% 3 7% 4 3 4 4 5% 6% 42%	5124
February	1st to 10th	Day	15% 8% 3 7% 6% 6% 6% 4 6% 6% 33%	1917
	11th to 20th	Day	11% 7% 2 9% 6% 5% 5% 4 6% 8% 36%	2048
	21st to end	Day	16% 12% 3 8% 4 4 4 4 4 4 35%	1730
March	1st to 10th	Day	17% 13% 3 9% 4 4 4 3 5% 5% 33%	4576
	11th to 20th	Day	14% 9% 2 7% 5% 5% 5% 4 5% 7% 37%	4804
	21st to end	Day	22% 9% 3 6% 4 4 4 3 6% 6% 33%	6003
April	1st to 10th	Day	17% 11% 3 6% 6% 5% 4 3 5% 6% 34%	2520
	11th to 20th	Day	16% 7% 2 7% 4 5% 5% 4 6% 6% 37%	2494
	21st to end	Day	19% 8% 3 7% 5% 4 4 4 4 6% 35%	2723
May	1st to 10th	Day	27% 9% 3 7% 4 4 5% 3 5% 6% 26%	7639
	11th to 20th	Day	18% 8% 3 8% 5% 4 4 4 5% 7% 33%	7979
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 4 6% 8% 31%	9060
June	1st to 10th	Day	18% 6% 2 7% 5% 5% 5% 4 6% 9% 33%	2940
	11th to 20th	Day	16% 6% 2 7% 5% 5% 5% 4 6% 9% 36%	2940
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 6% 8% 33%	2940
July	1st to 10th	Day	14% 6% 2 7% 5% 6% 6% 4 7% 9% 33%	6500
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 5% 8% 11% 38%	6430
	21st to end	Day	15% 6% 2 6% 4 4 4 3 6% 8% 42%	6926
August	1st to 10th	Day	14% 6% 3 8% 5% 5% 5% 4 6% 8% 35%	4377
	11th to 20th	Day	13% 7% 3 8% 5% 5% 5% 4 7% 8% 36%	4076
	21st to end	Day	8% 4 2 6% 5% 5% 6% 4 7% 10% 43%	4312
September	1st to 10th	Day	12% 6% 2 7% 4 5% 4 4 6% 7% 45%	2400
	11th to 20th	Day	13% 6% 2 5% 3 4 3 3 4 7% 50%	2226
	21st to end	Day	16% 6% 2 6% 4 4 4 4 5% 7% 42%	2200
October	1st to 10th	Day	20% 7% 2 6% 5% 4 4 3 4 4 39%	2200
	11th to 20th	Day	13% 8% 3 6% 3 4 4 3 5% 7% 43%	1925
	21st to end	Day	20% 7% 3 7% 4 4 5% 3 4 6% 37%	1980
November	1st to 10th	Day	12% 7% 3 7% 4 4 3 3 4 6% 47%	1851
	11th to 20th	Day	16% 7% 2 5% 4 5% 3 3 5% 6% 45%	1890
	21st to end	Day	18% 9% 2 6% 4 4 4 4 4 7% 38%	1848
December	1st to 10th	Day	13% 9% 3 8% 5% 4 4 4 4 8% 39%	2680
	11th to 20th	Day	18% 8% 3 6% 4 4 5% 3 4 4 41%	3066
	21st to end	Day	16% 11% 3 9% 5% 3 4 3 5% 6% 35%	4048
January	1st to 10th	Night	11% 7% 3 10% 5% 5% 5% 4 7% 7% 37%	8234
	11th to 20th	Night	12% 9% 3 10% 5% 5% 4 4 6% 7% 33%	8235
	21st to end	Night	12% 8% 3 7% 5% 5% 5% 4 5% 6% 39%	9057
February	1st to 10th	Night	13% 9% 3 7% 4 4 5% 4 6% 7% 38%	2700
	11th to 20th	Night	11% 8% 2 6% 6% 5% 6% 5% 7% 7% 37%	2458
	21st to end	Night	13% 10% 3 7% 5% 4 5% 4 5% 5% 38%	2076
March	1st to 10th	Night	19% 10% 2 6% 4 4 4 4 5% 7% 35%	5484
	11th to 20th	Night	14% 9% 3 7% 5% 5% 5% 4 5% 7% 37%	5374
	21st to end	Night	22% 9% 3 6% 4 3 4 4 6% 6% 33%	5167
April	1st to 10th	Night	18% 8% 3 8% 5% 4 4 3 6% 5% 35%	2100
	11th to 20th	Night	17% 9% 2 6% 5% 4 5% 3 5% 6% 39%	2075
	21st to end	Night	18% 8% 3 8% 3 3 3 3 5% 5% 40%	1895
May	1st to 10th	Night	27% 10% 3 7% 4 4 4 3 5% 7% 26%	5259
	11th to 20th	Night	15% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	4937
	21st to end	Night	21% 8% 3 7% 5% 4 4 4 6% 7% 31%	5114
June	1st to 10th	Night	17% 9% 3 6% 5% 3 4 3 4 6% 40%	1680
	11th to 20th	Night	18% 6% 3 5% 5% 5% 5% 4 5% 7% 37%	1680
	21st to end	Night	15% 7% 2 7% 3 4 4 4 6% 8% 39%	1680
July	1st to 10th	Night	11% 7% 2 6% 5% 5% 4 4 6% 8% 41%	3680
	11th to 20th	Night	11% 7% 2 7% 4 4 5% 4 6% 9% 41%	3640
	21st to end	Night	12% 5% 2 6% 3 4 4 4 5% 6% 50%	3926
August	1st to 10th	Night	19% 8% 2 7% 4 4 5% 4 5% 7% 36%	2738
	11th to 20th	Night	12% 9% 3 7% 5% 5% 5% 3 6% 6% 39%	2967
	21st to end	Night	9% 3 2 4 3 3 3 3 5% 8% 58%	3586
September	1st to 10th	Night	12% 5% 2 6% 3 3 4 3 5% 6% 50%	2000
	11th to 20th	Night	12% 6% 2 5% 2 3 4 3 4 6% 53%	2173
	21st to end	Night	14% 5% 3 7% 4 4 4 3 5% 6% 46%	2200
October	1st to 10th	Night	19% 6% 2 7% 4 3 4 3 4 6% 42%	2200
	11th to 20th	Night	15% 6% 2 5% 4 3 4 4 6% 7% 44%	2471
	21st to end	Night	21% 8% 2 6% 4 4 5% 3 5% 5% 37%	2860
November	1st to 10th	Night	13% 7% 3 7% 4 4 4 3 4 6% 46%	2667
	11th to 20th	Night	15% 6% 3 5% 5% 4 4 4 5% 6% 44%	2730
	21st to end	Night	14% 8% 3 6% 4 4 5% 4 5% 7% 42%	2767
December	1st to 10th	Night	14% 10% 4 9% 4 4 4 3 5% 6% 37%	4720
	11th to 20th	Night	21% 8% 3 6% 4 3 4 3 4 5% 38%	5348
	21st to end	Night	16% 11% 4 7% 4 4 4 3 5% 5% 36%	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	46% 6% 10% 25% 12% 1	4662
	11th to 20th	Day	43% 5% 11% 20% 17% 3	4680
	21st to end	Day	40% 5% 9% 25% 19% 3	5124
February	1st to 10th	Day	47% 7% 13% 18% 13% 2	1917
	11th to 20th	Day	44% 7% 11% 21% 14% 3	2057
	21st to end	Day	49% 5% 11% 19% 13% 2	1730
March	1st to 10th	Day	51% 5% 10% 14% 11% 8%	4579
	11th to 20th	Day	42% 7% 15% 22% 11% 2	4804
	21st to end	Day	49% 5% 6% 16% 18% 5%	6003
April	1st to 10th	Day	49% 5% 9% 18% 15% 3	2520
	11th to 20th	Day	44% 7% 12% 19% 16% 2	2494
	21st to end	Day	49% 6% 9% 18% 16% 3	2723
May	1st to 10th	Day	56% 7% 11% 14% 11% 1	7651
	11th to 20th	Day	50% 6% 14% 18% 11% 1	7983
	21st to end	Day	49% 7% 10% 22% 11% 1	9061
June	1st to 10th	Day	46% 8% 13% 21% 12% 1	2940
	11th to 20th	Day	43% 7% 13% 20% 14% 2	2940
	21st to end	Day	47% 8% 13% 19% 12% 1	2940
July	1st to 10th	Day	45% 7% 13% 20% 15% 1	6430
	11th to 20th	Day	38% 8% 16% 24% 13% 1	6355
	21st to end	Day	39% 6% 12% 27% 16% 1	6728
August	1st to 10th	Day	44% 8% 15% 21% 11% 1	4363
	11th to 20th	Day	43% 8% 15% 25% 8% 1	4115
	21st to end	Day	34% 8% 13% 28% 16% 1	4312
September	1st to 10th	Day	36% 6% 12% 26% 18% 1	2400
	11th to 20th	Day	34% 5% 9% 26% 23% 2	2226
	21st to end	Day	40% 7% 10% 23% 19% 3	2200
October	1st to 10th	Day	44% 5% 8% 22% 18% 2	3590
	11th to 20th	Day	34% 5% 9% 27% 20% 4	3102
	21st to end	Day	35% 5% 10% 30% 17% 4	3180
November	1st to 10th	Day	39% 5% 13% 24% 16% 2	1851
	11th to 20th	Day	39% 6% 11% 22% 20% 3	1890
	21st to end	Day	45% 5% 16% 23% 10% 2	1848
December	1st to 10th	Day	43% 5% 14% 28% 9% 1	2680
	11th to 20th	Day	43% 5% 12% 20% 18% 3	3066
	21st to end	Day	49% 5% 9% 18% 13% 6%	4048
January	1st to 10th	Night	42% 5% 14% 25% 12% 2	8234
	11th to 20th	Night	48% 6% 12% 17% 13% 4	8280
	21st to end	Night	44% 5% 10% 19% 19% 4	9057
February	1st to 10th	Night	43% 7% 13% 21% 13% 2	2700
	11th to 20th	Night	42% 7% 13% 21% 14% 3	2460
	21st to end	Night	45% 5% 11% 24% 12% 4	2076
March	1st to 10th	Night	47% 5% 11% 17% 15% 6%	5494
	11th to 20th	Night	45% 8% 16% 19% 11% 2	5375
	21st to end	Night	48% 5% 6% 15% 22% 4	5167
April	1st to 10th	Night	47% 7% 11% 18% 16% 2	2100
	11th to 20th	Night	45% 6% 11% 20% 17% 2	2075
	21st to end	Night	45% 6% 10% 18% 17% 4	1895
May	1st to 10th	Night	56% 6% 13% 14% 10% 1	5265
	11th to 20th	Night	48% 8% 13% 20% 9% 1	4938
	21st to end	Night	51% 6% 12% 21% 9% 1	5115
June	1st to 10th	Night	44% 7% 13% 24% 12% 1	1680
	11th to 20th	Night	44% 9% 13% 19% 13% 2	1680
	21st to end	Night	41% 8% 15% 22% 13% 1	1680
July	1st to 10th	Night	40% 6% 15% 25% 14%	3640
	11th to 20th	Night	38% 8% 17% 20% 16% 1	3592
	21st to end	Night	34% 6% 12% 32% 15% 1	3809
August	1st to 10th	Night	48% 8% 13% 20% 11% 1	2728
	11th to 20th	Night	43% 8% 15% 23% 10%	2994
	21st to end	Night	25% 6% 15% 35% 18% 1	3586
September	1st to 10th	Night	34% 6% 12% 27% 19% 1	2000
	11th to 20th	Night	31% 6% 11% 27% 24% 2	2173
	21st to end	Night	38% 7% 10% 26% 17% 2	2200
October	1st to 10th	Night	39% 5% 15% 24% 15% 2	3590
	11th to 20th	Night	29% 5% 12% 26% 24% 4	4033
	21st to end	Night	36% 5% 11% 32% 13% 2	4610
November	1st to 10th	Night	38% 6% 11% 23% 19% 3	2667
	11th to 20th	Night	40% 5% 11% 23% 18% 3	2730
	21st to end	Night	40% 6% 16% 25% 12% 1	2767
December	1st to 10th	Night	46% 5% 12% 28% 9%	4720
	11th to 20th	Night	47% 5% 14% 14% 19% 2	5348
	21st to end	Night	46% 5% 9% 20% 15% 4	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	31% 25% 29% 12% 3	220
	11th to 20th	Day	35% 25% 31% 8% 1 1	220
	21st to end	Day	30% 30% 29% 8% 2	242
February	1st to 10th	Day	31% 31% 29% 8% 1	386
	11th to 20th	Day	35% 25% 29% 11% 1	536
	21st to end	Day	30% 28% 29% 11% 2	446
March	1st to 10th	Day	33% 22% 33% 9% 3	540
	11th to 20th	Day	31% 28% 27% 10% 3 1	540
	21st to end	Day	32% 26% 28% 8% 4 2	594
April	1st to 10th	Day	34% 26% 24% 10% 5% 1	540
	11th to 20th	Day	31% 27% 27% 9% 5% 1	532
	21st to end	Day	29% 22% 30% 12% 6% 1	540
May	1st to 10th	Day	34% 23% 27% 12% 4 1	543
	11th to 20th	Day	20% 22% 38% 14% 5% 2	567
	21st to end	Day	20% 18% 33% 23% 5% 1	617
June	1st to 10th	Day	19% 16% 37% 19% 8% 1	570
	11th to 20th	Day	18% 18% 35% 21% 7% 1	570
	21st to end	Day	20% 18% 35% 18% 7% 2	570
July	1st to 10th	Day	16% 11% 34% 27% 10% 2	565
	11th to 20th	Day	14% 11% 33% 29% 10% 2	544
	21st to end	Day	14% 14% 36% 26% 8% 2	576
August	1st to 10th	Day	11% 10% 33% 31% 11% 3	526
	11th to 20th	Day	15% 10% 30% 28% 13% 4	519
	21st to end	Day	12% 13% 33% 26% 10% 4	583
September	1st to 10th	Day	17% 13% 30% 21% 15% 5%	530
	11th to 20th	Day	16% 15% 26% 21% 14% 8%	530
	21st to end	Day	18% 15% 32% 21% 9% 5%	530
October	1st to 10th	Day	26% 16% 24% 20% 10% 4	530
	11th to 20th	Day	23% 20% 29% 21% 6% 2	480
	21st to end	Day	30% 18% 28% 19% 4 1	462
November	1st to 10th	Day	24% 24% 26% 17% 8% 1	425
	11th to 20th	Day	30% 22% 26% 17% 3 1	430
	21st to end	Day	35% 21% 27% 12% 4 1	388
December	1st to 10th	Day	25% 34% 27% 11% 4	220
	11th to 20th	Day	39% 24% 30% 6% 2	220
	21st to end	Day	33% 24% 29% 11% 3	242
January	1st to 10th	Night	23% 27% 34% 14% 2	840
	11th to 20th	Night	27% 26% 30% 15% 3	840
	21st to end	Night	21% 25% 36% 16% 3	924
February	1st to 10th	Night	24% 23% 35% 16% 2	840
	11th to 20th	Night	23% 26% 36% 14% 1	823
	21st to end	Night	26% 26% 32% 14% 1	692
March	1st to 10th	Night	28% 22% 33% 16% 2	840
	11th to 20th	Night	26% 24% 29% 18% 3	840
	21st to end	Night	26% 21% 32% 16% 4	924
April	1st to 10th	Night	28% 21% 31% 17% 3	840
	11th to 20th	Night	23% 23% 31% 17% 5%	831
	21st to end	Night	25% 19% 33% 20% 3	635
May	1st to 10th	Night	27% 17% 33% 20% 3	630
	11th to 20th	Night	21% 15% 35% 24% 4	519
	21st to end	Night	20% 8% 35% 30% 6%	455
June	1st to 10th	Night	18% 11% 34% 29% 8%	420
	11th to 20th	Night	19% 12% 33% 30% 7%	420
	21st to end	Night	16% 9% 32% 37% 6%	420
July	1st to 10th	Night	15% 7% 33% 37% 7%	410
	11th to 20th	Night	14% 6% 29% 38% 12% 2	398
	21st to end	Night	12% 5% 35% 37% 11%	438
August	1st to 10th	Night	13% 7% 27% 39% 14%	485
	11th to 20th	Night	14% 9% 30% 32% 13% 1	648
	21st to end	Night	13% 9% 27% 35% 15% 1	880
September	1st to 10th	Night	16% 8% 31% 30% 14% 1	800
	11th to 20th	Night	15% 9% 27% 29% 17% 3	800
	21st to end	Night	16% 12% 29% 29% 13% 2	800
October	1st to 10th	Night	23% 14% 25% 26% 12% 2	800
	11th to 20th	Night	20% 15% 32% 22% 10% 1	800
	21st to end	Night	27% 19% 28% 22% 5%	880
November	1st to 10th	Night	20% 19% 32% 22% 6% 1	820
	11th to 20th	Night	22% 25% 28% 18% 5% 1	840
	21st to end	Night	24% 22% 32% 18% 4	840
December	1st to 10th	Night	25% 23% 33% 15% 3	840
	11th to 20th	Night	27% 23% 32% 15% 3	840
	21st to end	Night	26% 25% 31% 15% 3	924

Page generated at 2026-07-13 03:14:54. Version ac07

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