Marion
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Marion clear sky chart from 2005-11-06 to 2026-06-16.

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	14% 10% 4 8% 5% 5% 5% 4 6% 7% 34%	137004
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 35%	135193
Transparency	Day	47% 6% 12% 21% 13% 1	140588
	Night	48% 5% 11% 21% 14% 2	139671
Seeing	Day	19% 10% 27% 23% 15% 6%	17777
	Night	20% 9% 28% 29% 13% 1	27633

By Month

Percentage Cloud Cover SE (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	15% 15% 8% 16% 6% 5% 4 4 4 5% 19%	4691
	11th to 20th	Day	10% 15% 8% 15% 7% 9% 7% 5% 4 4 17%	4710
	21st to end	Day	18% 17% 7% 14% 5% 5% 4 4 4 4 18%	5414
February	1st to 10th	Day	17% 15% 6% 13% 6% 5% 4 3 4 5% 22%	2039
	11th to 20th	Day	15% 14% 4 11% 7% 5% 4 3 5% 5% 28%	2048
	21st to end	Day	15% 15% 5% 10% 5% 4 4 3 4 5% 29%	1730
March	1st to 10th	Day	19% 16% 7% 9% 4 4 3 2 3 4 29%	4580
	11th to 20th	Day	11% 11% 3 6% 4 3 3 3 5% 8% 41%	4967
	21st to end	Day	17% 13% 5% 11% 5% 4 5% 3 5% 7% 26%	5759
April	1st to 10th	Day	16% 12% 3 8% 5% 5% 4 4 5% 6% 31%	2520
	11th to 20th	Day	17% 10% 3 7% 5% 4 5% 3 5% 7% 35%	2510
	21st to end	Day	18% 9% 2 7% 5% 3 4 4 5% 8% 34%	2730
May	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 4 6% 7% 31%	7616
	11th to 20th	Day	16% 6% 2 7% 5% 4 4 4 5% 8% 38%	7626
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 7% 8% 35%	8587
June	1st to 10th	Day	11% 6% 2 7% 6% 5% 5% 4 6% 7% 41%	2940
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 7% 9% 43%	2871
	21st to end	Day	10% 5% 2 6% 6% 5% 5% 4 7% 10% 40%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 4 7% 10% 40%	6360
	11th to 20th	Day	8% 5% 2 7% 5% 5% 5% 5% 7% 12% 39%	6360
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 7% 8% 37%	6708
August	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 44%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 7% 9% 44%	4108
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 6% 9% 49%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 3 5% 7% 48%	2350
	11th to 20th	Day	9% 5% 2 5% 4 5% 4 4 6% 8% 48%	2200
	21st to end	Day	14% 7% 1 5% 3 4 5% 3 5% 6% 46%	2200
October	1st to 10th	Day	12% 5% 2 6% 3 4 4 4 5% 7% 46%	2200
	11th to 20th	Day	14% 6% 2 6% 4 4 6% 3 5% 6% 43%	2026
	21st to end	Day	19% 9% 3 8% 4 4 5% 3 6% 6% 33%	1980
November	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 5% 6% 49%	1852
	11th to 20th	Day	16% 13% 3 8% 5% 5% 4 3 4 6% 32%	1890
	21st to end	Day	19% 12% 5% 9% 5% 3 4 3 4 5% 30%	1890
December	1st to 10th	Day	12% 13% 4 10% 4 3 4 3 4 5% 37%	3020
	11th to 20th	Day	16% 16% 5% 12% 5% 5% 5% 3 5% 6% 22%	3106
	21st to end	Day	27% 18% 7% 12% 5% 5% 4 3 4 4 11%	4070
January	1st to 10th	Night	14% 15% 8% 14% 6% 5% 4 3 4 5% 22%	8232
	11th to 20th	Night	10% 17% 8% 16% 7% 6% 5% 3 4 4 19%	8280
	21st to end	Night	18% 12% 5% 9% 5% 6% 5% 5% 5% 5% 26%	8783
February	1st to 10th	Night	18% 14% 5% 11% 6% 5% 3 3 4 5% 26%	2578
	11th to 20th	Night	13% 13% 5% 10% 7% 5% 5% 3 4 6% 31%	2458
	21st to end	Night	17% 13% 5% 10% 5% 4 4 3 5% 5% 30%	2076
March	1st to 10th	Night	18% 12% 4 7% 4 3 4 2 4 5% 37%	5493
	11th to 20th	Night	12% 7% 3 6% 4 4 4 4 5% 7% 42%	5198
	21st to end	Night	18% 9% 3 8% 4 4 4 4 5% 6% 34%	5454
April	1st to 10th	Night	15% 10% 3 7% 5% 5% 4 4 6% 7% 36%	2100
	11th to 20th	Night	17% 8% 2 7% 5% 4 4 3 6% 7% 38%	2059
	21st to end	Night	18% 9% 2 6% 4 3 4 3 6% 7% 36%	1890
May	1st to 10th	Night	22% 10% 3 8% 5% 4 5% 3 5% 6% 30%	5237
	11th to 20th	Night	15% 7% 2 6% 4 3 4 3 5% 8% 42%	5234
	21st to end	Night	13% 7% 3 7% 4 4 5% 4 6% 9% 38%	5558
June	1st to 10th	Night	10% 5% 2 6% 4 5% 4 4 5% 7% 48%	1680
	11th to 20th	Night	8% 6% 3 6% 4 5% 4 3 6% 10% 46%	1640
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 10% 45%	1600
July	1st to 10th	Night	8% 4 2 5% 4 5% 4 4 6% 10% 46%	3618
	11th to 20th	Night	8% 5% 2 5% 4 3 4 3 6% 10% 48%	3617
	21st to end	Night	10% 7% 2 8% 5% 4 4 4 6% 9% 41%	4151
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 9% 47%	2915
	11th to 20th	Night	7% 5% 3 5% 5% 5% 4 4 5% 8% 48%	2936
	21st to end	Night	7% 5% 2 6% 4 4 4 4 5% 8% 52%	3586
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 3 5% 7% 50%	2030
	11th to 20th	Night	8% 4 1 4 4 3 3 3 4 8% 57%	2200
	21st to end	Night	12% 6% 2 5% 3 4 4 3 5% 6% 50%	2200
October	1st to 10th	Night	10% 4 2 4 3 4 3 3 5% 7% 53%	2200
	11th to 20th	Night	16% 8% 2 6% 4 4 3 3 4 5% 44%	2370
	21st to end	Night	19% 7% 3 7% 4 4 5% 3 5% 6% 37%	2860
November	1st to 10th	Night	12% 9% 3 6% 4 3 3 3 5% 6% 47%	2666
	11th to 20th	Night	14% 10% 4 8% 4 3 4 3 5% 7% 37%	2730
	21st to end	Night	18% 14% 4 9% 5% 5% 4 3 5% 5% 29%	2730
December	1st to 10th	Night	14% 11% 4 8% 5% 5% 4 4 6% 7% 35%	4380
	11th to 20th	Night	18% 16% 7% 11% 5% 4 4 3 4 5% 22%	5304
	21st to end	Night	26% 19% 7% 11% 5% 4 4 3 4 5% 13%	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	67% 4 11% 14% 4	4692
	11th to 20th	Day	72% 3 8% 8% 7% 2	4710
	21st to end	Day	71% 2 9% 12% 6%	5414
February	1st to 10th	Day	65% 4 9% 13% 8% 1	2039
	11th to 20th	Day	57% 5% 10% 20% 7%	2058
	21st to end	Day	57% 5% 13% 17% 7% 2	1730
March	1st to 10th	Day	59% 4 7% 20% 10%	4580
	11th to 20th	Day	41% 5% 10% 33% 9% 1	4967
	21st to end	Day	56% 6% 14% 16% 6% 1	5761
April	1st to 10th	Day	53% 6% 11% 18% 12%	2520
	11th to 20th	Day	48% 6% 11% 22% 11% 3	2510
	21st to end	Day	47% 6% 13% 22% 9% 3	2730
May	1st to 10th	Day	51% 7% 12% 18% 12%	7651
	11th to 20th	Day	44% 7% 13% 21% 15% 1	7630
	21st to end	Day	43% 7% 11% 23% 12% 4	8601
June	1st to 10th	Day	40% 7% 11% 23% 17% 3	2940
	11th to 20th	Day	37% 7% 12% 24% 19% 2	2871
	21st to end	Day	37% 10% 16% 20% 15% 3	2800
July	1st to 10th	Day	39% 6% 10% 26% 18% 2	6291
	11th to 20th	Day	35% 8% 16% 25% 15% 1	6285
	21st to end	Day	42% 7% 13% 20% 16% 2	6516
August	1st to 10th	Day	32% 7% 19% 26% 14% 1	4221
	11th to 20th	Day	34% 8% 12% 30% 15% 1	4147
	21st to end	Day	30% 7% 13% 28% 18% 3	4311
September	1st to 10th	Day	35% 6% 12% 25% 18% 3	2350
	11th to 20th	Day	32% 6% 11% 26% 22% 3	2200
	21st to end	Day	38% 5% 11% 22% 22% 1	2200
October	1st to 10th	Day	26% 5% 10% 31% 26% 2	3590
	11th to 20th	Day	33% 6% 10% 25% 24% 1	3268
	21st to end	Day	43% 4 10% 26% 17% 1	3180
November	1st to 10th	Day	35% 5% 14% 26% 17% 2	1852
	11th to 20th	Day	53% 4 10% 19% 11% 2	1890
	21st to end	Day	57% 5% 11% 20% 7% 1	1890
December	1st to 10th	Day	50% 3 13% 23% 10%	3020
	11th to 20th	Day	64% 4 13% 16% 3	3103
	21st to end	Day	77% 4 7% 8% 3	4070
January	1st to 10th	Night	65% 4 9% 16% 6%	8233
	11th to 20th	Night	69% 3 7% 10% 9% 1	8280
	21st to end	Night	60% 3 12% 18% 7% 1	8783
February	1st to 10th	Night	61% 4 12% 15% 7% 1	2578
	11th to 20th	Night	55% 4 11% 18% 10% 1	2459
	21st to end	Night	56% 5% 10% 16% 10% 2	2076
March	1st to 10th	Night	50% 4 8% 26% 10% 2	5493
	11th to 20th	Night	40% 6% 12% 28% 13% 2	5198
	21st to end	Night	49% 5% 10% 25% 9% 1	5454
April	1st to 10th	Night	46% 7% 11% 22% 12% 1	2100
	11th to 20th	Night	44% 6% 12% 20% 14% 4	2059
	21st to end	Night	45% 7% 10% 23% 11% 3	1890
May	1st to 10th	Night	55% 6% 7% 17% 13% 2	5264
	11th to 20th	Night	40% 6% 11% 25% 16% 1	5235
	21st to end	Night	41% 7% 13% 21% 14% 4	5568
June	1st to 10th	Night	36% 6% 9% 26% 21% 3	1680
	11th to 20th	Night	33% 7% 12% 25% 19% 3	1640
	21st to end	Night	33% 9% 16% 22% 16% 5%	1600
July	1st to 10th	Night	33% 7% 11% 28% 18% 5%	3580
	11th to 20th	Night	32% 6% 16% 26% 18% 2	3572
	21st to end	Night	39% 7% 15% 21% 16% 3	4030
August	1st to 10th	Night	35% 6% 15% 28% 15% 1	2904
	11th to 20th	Night	33% 6% 13% 29% 18% 1	2963
	21st to end	Night	30% 6% 12% 28% 21% 3	3586
September	1st to 10th	Night	32% 7% 12% 23% 20% 6%	2030
	11th to 20th	Night	27% 4 10% 28% 28% 3	2200
	21st to end	Night	34% 6% 10% 23% 23% 3	2200
October	1st to 10th	Night	21% 4 6% 31% 35% 2	3590
	11th to 20th	Night	32% 3 10% 23% 31% 1	3854
	21st to end	Night	35% 4 8% 30% 22% 2	4610
November	1st to 10th	Night	38% 4 10% 27% 19% 2	2666
	11th to 20th	Night	46% 5% 11% 21% 15% 3	2730
	21st to end	Night	58% 4 10% 20% 7%	2730
December	1st to 10th	Night	49% 4 13% 25% 8% 1	4380
	11th to 20th	Night	63% 6% 11% 13% 7% 1	5306
	21st to end	Night	74% 5% 8% 9% 3	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	26% 16% 37% 15% 5% 1	330
	11th to 20th	Day	25% 24% 35% 12% 3 1	330
	21st to end	Day	30% 18% 31% 16% 5%	363
February	1st to 10th	Day	27% 15% 34% 20% 4	330
	11th to 20th	Day	26% 18% 36% 15% 4 1	330
	21st to end	Day	27% 19% 40% 11% 2	273
March	1st to 10th	Day	25% 20% 39% 13% 2	330
	11th to 20th	Day	30% 12% 34% 17% 6% 1	482
	21st to end	Day	29% 15% 32% 17% 6% 1	594
April	1st to 10th	Day	26% 15% 34% 15% 8% 2	540
	11th to 20th	Day	23% 18% 28% 19% 9% 2	532
	21st to end	Day	25% 12% 32% 20% 9% 2	540
May	1st to 10th	Day	25% 11% 32% 21% 8% 2	543
	11th to 20th	Day	23% 8% 29% 23% 12% 6%	567
	21st to end	Day	14% 6% 30% 25% 17% 8%	683
June	1st to 10th	Day	14% 6% 29% 26% 21% 5%	780
	11th to 20th	Day	14% 6% 26% 30% 19% 5%	756
	21st to end	Day	12% 6% 28% 28% 20% 6%	730
July	1st to 10th	Day	14% 2 19% 29% 22% 14%	721
	11th to 20th	Day	9% 2 20% 33% 23% 14%	718
	21st to end	Day	13% 2 15% 33% 25% 12%	704
August	1st to 10th	Day	8% 2 15% 31% 29% 15%	526
	11th to 20th	Day	13% 1 19% 29% 25% 13%	519
	21st to end	Day	9% 3 14% 31% 31% 12%	583
September	1st to 10th	Day	14% 6% 14% 29% 26% 11%	530
	11th to 20th	Day	10% 2 14% 25% 30% 18%	530
	21st to end	Day	20% 7% 18% 28% 18% 9%	530
October	1st to 10th	Day	11% 6% 23% 33% 18% 9%	530
	11th to 20th	Day	17% 15% 31% 24% 12% 1	477
	21st to end	Day	29% 10% 37% 20% 3	363
November	1st to 10th	Day	14% 17% 33% 23% 10% 3	330
	11th to 20th	Day	26% 15% 35% 15% 8% 1	330
	21st to end	Day	30% 12% 35% 19% 3	330
December	1st to 10th	Day	25% 15% 39% 15% 6% 1	330
	11th to 20th	Day	25% 15% 39% 15% 6%	330
	21st to end	Day	33% 14% 37% 15% 1	363
January	1st to 10th	Night	24% 15% 35% 21% 5%	1050
	11th to 20th	Night	24% 16% 37% 19% 4	1050
	21st to end	Night	24% 15% 35% 23% 4	1061
February	1st to 10th	Night	26% 11% 33% 26% 3	840
	11th to 20th	Night	22% 13% 38% 25% 2	823
	21st to end	Night	25% 15% 37% 20% 3	692
March	1st to 10th	Night	23% 12% 35% 24% 6%	840
	11th to 20th	Night	21% 12% 36% 24% 7% 1	840
	21st to end	Night	27% 9% 33% 25% 5% 1	867
April	1st to 10th	Night	20% 10% 36% 26% 7%	630
	11th to 20th	Night	23% 11% 32% 26% 8% 1	623
	21st to end	Night	23% 7% 35% 26% 9% 1	630
May	1st to 10th	Night	25% 6% 30% 31% 8%	630
	11th to 20th	Night	22% 4 27% 31% 15% 1	621
	21st to end	Night	11% 4 24% 42% 17% 3	683
June	1st to 10th	Night	11% 2 24% 44% 17%	630
	11th to 20th	Night	11% 3 24% 42% 19% 1	615
	21st to end	Night	11% 2 21% 39% 26% 1	600
July	1st to 10th	Night	11% 2 14% 38% 32% 4	585
	11th to 20th	Night	10% 1 13% 41% 30% 4	582
	21st to end	Night	9% 1 12% 45% 31% 2	657
August	1st to 10th	Night	9% 1 11% 43% 32% 4	597
	11th to 20th	Night	9% 2 12% 39% 34% 4	594
	21st to end	Night	8% 1 14% 36% 36% 5%	660
September	1st to 10th	Night	15% 1 12% 38% 29% 5%	630
	11th to 20th	Night	11% 2 14% 37% 32% 5%	800
	21st to end	Night	16% 4 20% 34% 22% 3	800
October	1st to 10th	Night	14% 5% 23% 36% 19% 4	800
	11th to 20th	Night	21% 9% 29% 30% 12% 1	800
	21st to end	Night	23% 11% 33% 26% 6%	880
November	1st to 10th	Night	17% 10% 35% 26% 10% 1	820
	11th to 20th	Night	20% 15% 35% 23% 7%	840
	21st to end	Night	29% 11% 32% 21% 7%	840
December	1st to 10th	Night	26% 12% 35% 22% 5% 1	840
	11th to 20th	Night	25% 13% 32% 24% 5%	1028
	21st to end	Night	33% 13% 31% 20% 3	1155

Page generated at 2026-06-13 02:31:38. Version ac07

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