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 2024-01-31.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	75017
	Night	15% 9% 4 7% 6% 3 4 4 5% 7% 36%	75127
Transparency	Day	48% 7% 12% 20% 12% 2	74724
	Night	47% 6% 11% 20% 13% 2	74941
Seeing	Day	19% 9% 27% 24% 15% 6%	14507
	Night	20% 8% 28% 29% 13% 1	24483

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	18% 14% 7% 11% 7% 3 4 5% 5% 6% 20%	1517
	11th to 20th	Day	18% 17% 8% 10% 6% 5% 5% 4 4 5% 19%	1520
	21st to end	Day	17% 18% 8% 11% 6% 4 5% 4 4 6% 18%	1744
February	1st to 10th	Day	18% 15% 7% 11% 8% 3 5% 3 4 5% 21%	1747
	11th to 20th	Day	16% 12% 5% 10% 8% 4 5% 3 5% 5% 26%	1748
	21st to end	Day	17% 14% 7% 8% 6% 3 4 4 4 6% 26%	1480
March	1st to 10th	Day	17% 12% 6% 8% 5% 3 4 4 4 6% 28%	1800
	11th to 20th	Day	17% 11% 4 7% 6% 2 5% 4 7% 7% 30%	1930
	21st to end	Day	21% 12% 5% 9% 5% 2 4 4 5% 6% 27%	2240
April	1st to 10th	Day	15% 11% 4 7% 6% 3 5% 5% 4 6% 33%	2160
	11th to 20th	Day	18% 9% 3 6% 5% 3 5% 4 5% 7% 35%	2147
	21st to end	Day	20% 9% 2 6% 6% 3 4 5% 5% 8% 32%	2340
May	1st to 10th	Day	19% 7% 3 7% 7% 3 5% 5% 5% 7% 31%	2340
	11th to 20th	Day	19% 7% 3 6% 6% 4 4 4 5% 7% 34%	2301
	21st to end	Day	10% 5% 2 6% 7% 4 6% 6% 8% 8% 37%	2587
June	1st to 10th	Day	11% 6% 3 6% 6% 4 5% 5% 6% 7% 41%	2520
	11th to 20th	Day	11% 4 2 5% 6% 3 6% 5% 7% 9% 43%	2520
	21st to end	Day	10% 5% 2 6% 6% 4 6% 6% 7% 10% 39%	2520
July	1st to 10th	Day	10% 6% 2 5% 6% 3 5% 6% 7% 10% 41%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 4 5% 7% 11% 46%	2520
	21st to end	Day	9% 4 3 5% 6% 3 7% 6% 7% 9% 41%	2663
August	1st to 10th	Day	6% 4 2 5% 6% 4 5% 6% 7% 10% 45%	2327
	11th to 20th	Day	9% 4 3 6% 6% 5% 6% 6% 7% 9% 41%	2267
	21st to end	Day	8% 4 2 6% 5% 3 5% 6% 6% 9% 47%	2376
September	1st to 10th	Day	12% 6% 2 5% 4 3 4 4 6% 7% 45%	2116
	11th to 20th	Day	10% 5% 2 4 5% 3 6% 5% 7% 8% 45%	1980
	21st to end	Day	13% 7% 2 4 4 3 5% 4 5% 7% 48%	1980
October	1st to 10th	Day	13% 5% 3 6% 4 3 4 5% 5% 7% 44%	1980
	11th to 20th	Day	15% 6% 3 5% 5% 3 5% 5% 5% 7% 41%	1825
	21st to end	Day	21% 9% 4 6% 6% 3 5% 4 5% 6% 32%	1782
November	1st to 10th	Day	10% 6% 3 5% 4 3 4 5% 5% 6% 50%	1672
	11th to 20th	Day	17% 13% 4 8% 6% 3 4 3 4 6% 33%	1710
	21st to end	Day	19% 11% 5% 8% 5% 3 4 4 4 6% 31%	1710
December	1st to 10th	Day	17% 16% 7% 11% 6% 3 4 4 3 5% 24%	1710
	11th to 20th	Day	15% 16% 5% 12% 6% 3 5% 5% 4 5% 24%	1935
	21st to end	Day	24% 20% 9% 11% 6% 3 4 3 4 3 12%	2783
January	1st to 10th	Night	17% 13% 7% 10% 7% 3 4 3 4 5% 26%	2648
	11th to 20th	Night	17% 16% 7% 9% 8% 3 4 3 3 5% 24%	2660
	21st to end	Night	17% 14% 7% 11% 7% 3 4 4 4 5% 23%	2836
February	1st to 10th	Night	20% 14% 6% 9% 7% 4 3 3 4 5% 25%	2210
	11th to 20th	Night	13% 13% 6% 8% 8% 4 5% 4 3 6% 30%	2098
	21st to end	Night	19% 13% 5% 9% 5% 3 4 3 5% 4 29%	1776
March	1st to 10th	Night	16% 9% 4 7% 7% 4 6% 4 4 5% 34%	2160
	11th to 20th	Night	14% 10% 3 6% 6% 2 4 5% 5% 8% 37%	2029
	21st to end	Night	21% 10% 3 7% 5% 3 3 4 5% 6% 33%	2130
April	1st to 10th	Night	14% 8% 4 6% 6% 4 5% 5% 6% 7% 37%	1800
	11th to 20th	Night	18% 7% 2 5% 6% 3 5% 4 6% 7% 38%	1762
	21st to end	Night	20% 9% 2 5% 5% 3 4 5% 5% 7% 36%	1620
May	1st to 10th	Night	19% 8% 4 6% 6% 4 5% 4 6% 8% 30%	1620
	11th to 20th	Night	19% 8% 2 5% 4 3 4 4 5% 7% 39%	1592
	21st to end	Night	8% 5% 2 5% 5% 3 6% 6% 7% 10% 43%	1684
June	1st to 10th	Night	9% 4 3 6% 4 3 5% 5% 5% 8% 49%	1440
	11th to 20th	Night	7% 5% 3 5% 5% 3 4 4 5% 10% 48%	1440
	21st to end	Night	9% 5% 2 6% 5% 3 5% 6% 6% 10% 45%	1440
July	1st to 10th	Night	8% 6% 1 4 6% 3 5% 6% 6% 9% 47%	1440
	11th to 20th	Night	8% 3 2 4 4 2 3 5% 6% 9% 53%	1440
	21st to end	Night	8% 5% 2 5% 4 3 5% 5% 5% 9% 50%	1651
August	1st to 10th	Night	6% 5% 2 5% 5% 3 4 6% 5% 10% 49%	1611
	11th to 20th	Night	7% 4 3 5% 5% 3 4 5% 5% 8% 51%	1629
	21st to end	Night	7% 3 2 5% 5% 3 4 6% 5% 8% 52%	1980
September	1st to 10th	Night	12% 5% 2 5% 5% 2 4 4 5% 8% 47%	1826
	11th to 20th	Night	9% 4 2 4 5% 2 3 3 4 8% 56%	1980
	21st to end	Night	11% 5% 2 4 4 3 4 4 5% 7% 52%	1980
October	1st to 10th	Night	11% 5% 2 4 4 3 4 4 5% 7% 51%	1980
	11th to 20th	Night	18% 8% 3 5% 5% 3 3 3 4 5% 42%	2132
	21st to end	Night	20% 7% 3 6% 5% 2 5% 4 5% 6% 37%	2574
November	1st to 10th	Night	12% 8% 4 5% 4 2 3 3 5% 7% 46%	2406
	11th to 20th	Night	15% 9% 5% 7% 5% 2 4 4 5% 8% 36%	2470
	21st to end	Night	18% 12% 4 7% 6% 4 5% 4 5% 6% 30%	2470
December	1st to 10th	Night	18% 13% 5% 8% 7% 3 4 3 5% 6% 27%	2470
	11th to 20th	Night	17% 14% 7% 8% 7% 3 4 4 4 5% 25%	3259
	21st to end	Night	24% 19% 8% 9% 6% 3 4 4 4 5% 15%	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	64% 6% 10% 14% 7%	1518
	11th to 20th	Day	69% 4 11% 11% 4	1520
	21st to end	Day	69% 4 10% 12% 5% 1	1744
February	1st to 10th	Day	67% 4 9% 12% 7% 1	1747
	11th to 20th	Day	59% 5% 11% 19% 6% 1	1758
	21st to end	Day	60% 5% 11% 16% 6% 2	1480
March	1st to 10th	Day	56% 6% 11% 19% 8%	1800
	11th to 20th	Day	52% 6% 13% 18% 10% 1	1930
	21st to end	Day	59% 5% 13% 18% 4 1	2240
April	1st to 10th	Day	51% 6% 12% 18% 12%	2160
	11th to 20th	Day	49% 5% 11% 21% 11% 3	2147
	21st to end	Day	50% 6% 13% 19% 9% 3	2340
May	1st to 10th	Day	52% 8% 11% 18% 10% 1	2340
	11th to 20th	Day	50% 8% 11% 18% 12% 1	2305
	21st to end	Day	41% 10% 13% 22% 13% 2	2587
June	1st to 10th	Day	40% 8% 11% 24% 15% 3	2520
	11th to 20th	Day	36% 7% 12% 23% 19% 3	2520
	21st to end	Day	38% 10% 16% 19% 14% 3	2520
July	1st to 10th	Day	37% 9% 14% 22% 15% 3	2451
	11th to 20th	Day	31% 8% 16% 26% 18% 2	2445
	21st to end	Day	35% 10% 15% 23% 14% 3	2515
August	1st to 10th	Day	31% 8% 17% 29% 13% 2	2314
	11th to 20th	Day	36% 10% 14% 24% 16% 1	2267
	21st to end	Day	32% 10% 13% 22% 18% 5%	2376
September	1st to 10th	Day	37% 7% 13% 23% 16% 4	2116
	11th to 20th	Day	35% 6% 12% 26% 19% 2	1980
	21st to end	Day	36% 6% 12% 24% 22% 2	1980
October	1st to 10th	Day	38% 7% 11% 24% 17% 3	1980
	11th to 20th	Day	40% 7% 10% 24% 18% 1	1825
	21st to end	Day	53% 5% 11% 20% 11% 1	1782
November	1st to 10th	Day	35% 6% 15% 25% 17% 2	1672
	11th to 20th	Day	53% 4 10% 19% 11% 2	1710
	21st to end	Day	55% 5% 11% 19% 8% 1	1710
December	1st to 10th	Day	64% 5% 10% 15% 7%	1710
	11th to 20th	Day	62% 5% 11% 20% 2	1932
	21st to end	Day	77% 5% 6% 7% 4	2783
January	1st to 10th	Night	62% 4 9% 15% 10%	2648
	11th to 20th	Night	64% 4 10% 14% 7%	2660
	21st to end	Night	63% 4 10% 14% 8%	2836
February	1st to 10th	Night	63% 4 12% 13% 6% 1	2210
	11th to 20th	Night	56% 5% 11% 17% 10% 1	2099
	21st to end	Night	59% 5% 9% 16% 9% 2	1776
March	1st to 10th	Night	52% 6% 10% 20% 11% 1	2160
	11th to 20th	Night	45% 6% 11% 23% 11% 3	2029
	21st to end	Night	53% 5% 10% 21% 9% 1	2130
April	1st to 10th	Night	44% 8% 12% 23% 12% 1	1800
	11th to 20th	Night	45% 6% 11% 19% 14% 4	1762
	21st to end	Night	46% 7% 10% 22% 11% 4	1620
May	1st to 10th	Night	52% 7% 11% 17% 10% 2	1620
	11th to 20th	Night	44% 7% 12% 23% 13% 2	1593
	21st to end	Night	34% 10% 16% 22% 14% 4	1685
June	1st to 10th	Night	34% 6% 11% 26% 20% 3	1440
	11th to 20th	Night	31% 8% 13% 25% 19% 4	1440
	21st to end	Night	33% 9% 16% 23% 15% 4	1440
July	1st to 10th	Night	34% 10% 12% 22% 17% 6%	1400
	11th to 20th	Night	28% 6% 15% 28% 21% 2	1392
	21st to end	Night	29% 8% 16% 25% 17% 5%	1559
August	1st to 10th	Night	30% 7% 16% 26% 20% 2	1600
	11th to 20th	Night	31% 7% 15% 25% 20% 2	1629
	21st to end	Night	29% 7% 14% 24% 21% 5%	1980
September	1st to 10th	Night	34% 7% 14% 21% 17% 6%	1826
	11th to 20th	Night	28% 5% 11% 28% 26% 2	1980
	21st to end	Night	32% 7% 11% 24% 23% 3	1980
October	1st to 10th	Night	33% 6% 10% 27% 21% 3	1980
	11th to 20th	Night	43% 4 9% 25% 17% 1	2132
	21st to end	Night	47% 5% 9% 23% 14% 2	2574
November	1st to 10th	Night	38% 5% 10% 26% 19% 2	2406
	11th to 20th	Night	46% 5% 11% 20% 15% 2	2470
	21st to end	Night	56% 4 10% 21% 8%	2470
December	1st to 10th	Night	59% 5% 11% 17% 8% 1	2470
	11th to 20th	Night	58% 7% 11% 17% 6% 1	3261
	21st to end	Night	72% 6% 9% 9% 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% 16% 37% 15% 5% 1	270
	11th to 20th	Day	26% 19% 37% 13% 4 1	270
	21st to end	Day	33% 14% 31% 16% 6%	294
February	1st to 10th	Day	31% 14% 38% 15% 3	240
	11th to 20th	Day	27% 18% 37% 14% 4 1	240
	21st to end	Day	29% 19% 39% 11% 2	198
March	1st to 10th	Day	23% 21% 37% 16% 3	240
	11th to 20th	Day	28% 9% 35% 19% 8% 1	370
	21st to end	Day	32% 13% 29% 18% 7% 1	462
April	1st to 10th	Day	23% 12% 35% 18% 10% 3	420
	11th to 20th	Day	23% 16% 29% 18% 11% 3	412
	21st to end	Day	27% 13% 31% 18% 10% 2	420
May	1st to 10th	Day	25% 10% 33% 22% 8% 2	423
	11th to 20th	Day	23% 7% 28% 23% 13% 6%	447
	21st to end	Day	12% 5% 29% 26% 18% 9%	541
June	1st to 10th	Day	13% 5% 28% 27% 22% 5%	630
	11th to 20th	Day	13% 6% 26% 29% 21% 6%	630
	21st to end	Day	13% 7% 27% 27% 20% 7%	630
July	1st to 10th	Day	13% 2 17% 29% 22% 16%	621
	11th to 20th	Day	9% 2 19% 33% 24% 14%	618
	21st to end	Day	13% 2 15% 32% 25% 13%	604
August	1st to 10th	Day	7% 2 13% 31% 30% 17%	446
	11th to 20th	Day	11% 1 20% 29% 26% 14%	439
	21st to end	Day	9% 3 15% 30% 32% 12%	495
September	1st to 10th	Day	16% 5% 13% 29% 26% 10%	450
	11th to 20th	Day	12% 2 16% 25% 29% 16%	450
	21st to end	Day	17% 8% 19% 27% 20% 8%	450
October	1st to 10th	Day	12% 6% 25% 31% 17% 9%	450
	11th to 20th	Day	18% 16% 32% 23% 10%	403
	21st to end	Day	31% 9% 38% 19% 2	297
November	1st to 10th	Day	11% 15% 34% 24% 12% 3	270
	11th to 20th	Day	25% 14% 34% 17% 9% 1	270
	21st to end	Day	29% 12% 35% 21% 3	270
December	1st to 10th	Day	27% 16% 35% 15% 6% 1	270
	11th to 20th	Day	23% 14% 39% 16% 7%	270
	21st to end	Day	31% 16% 36% 16% 1	297
January	1st to 10th	Night	24% 16% 34% 21% 5%	950
	11th to 20th	Night	25% 14% 36% 20% 4	950
	21st to end	Night	24% 13% 34% 24% 4	960
February	1st to 10th	Night	29% 11% 33% 25% 3	720
	11th to 20th	Night	22% 13% 37% 26% 3	703
	21st to end	Night	27% 13% 37% 19% 4	592
March	1st to 10th	Night	21% 13% 34% 26% 6%	720
	11th to 20th	Night	21% 10% 36% 25% 8% 1	720
	21st to end	Night	28% 8% 32% 26% 6% 1	744
April	1st to 10th	Night	17% 9% 37% 29% 8% 1	540
	11th to 20th	Night	22% 10% 31% 27% 9% 1	533
	21st to end	Night	24% 6% 35% 24% 9% 1	540
May	1st to 10th	Night	24% 6% 30% 31% 9%	540
	11th to 20th	Night	22% 3 25% 33% 16% 1	531
	21st to end	Night	10% 4 22% 42% 18% 3	584
June	1st to 10th	Night	10% 2 23% 46% 19% 1	540
	11th to 20th	Night	11% 3 24% 41% 21% 1	540
	21st to end	Night	11% 2 21% 39% 26% 1	540
July	1st to 10th	Night	11% 2 14% 38% 32% 4	525
	11th to 20th	Night	9% 1 13% 42% 30% 5%	522
	21st to end	Night	9% 1 12% 44% 31% 2	591
August	1st to 10th	Night	9% 1 12% 43% 32% 4	537
	11th to 20th	Night	9% 2 12% 38% 35% 4	534
	21st to end	Night	8% 2 15% 35% 36% 5%	594
September	1st to 10th	Night	16% 1 12% 37% 29% 5%	566
	11th to 20th	Night	12% 3 15% 35% 32% 4	720
	21st to end	Night	14% 5% 21% 35% 23% 3	720
October	1st to 10th	Night	14% 5% 24% 34% 18% 4	720
	11th to 20th	Night	22% 9% 29% 29% 10% 1	720
	21st to end	Night	25% 11% 33% 25% 6%	792
November	1st to 10th	Night	17% 10% 35% 26% 11% 1	740
	11th to 20th	Night	20% 15% 33% 24% 8%	760
	21st to end	Night	27% 10% 33% 22% 8%	760
December	1st to 10th	Night	26% 12% 34% 22% 6% 1	760
	11th to 20th	Night	25% 12% 31% 25% 6%	930
	21st to end	Night	32% 13% 31% 20% 3	1045

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