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 2025-02-21.

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% 4 4 4 5% 7% 34%	108493
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 35%	110224
Transparency	Day	47% 6% 12% 21% 13% 1	112121
	Night	48% 5% 11% 21% 14% 2	114723
Seeing	Day	19% 9% 27% 24% 15% 6%	15947
	Night	20% 8% 28% 29% 13% 1	25911

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	13% 15% 9% 17% 6% 4 4 3 4 5% 19%	3617
	11th to 20th	Day	13% 16% 9% 13% 6% 8% 7% 5% 4 3 16%	3620
	21st to end	Day	22% 18% 8% 13% 4 3 2 3 3 4 20%	4176
February	1st to 10th	Day	17% 15% 6% 12% 7% 5% 4 3 4 5% 22%	1942
	11th to 20th	Day	15% 13% 4 11% 7% 5% 4 3 5% 5% 28%	1948
	21st to end	Day	17% 16% 5% 9% 5% 4 4 3 4 5% 28%	1570
March	1st to 10th	Day	20% 19% 6% 8% 4 4 3 3 4 5% 25%	3120
	11th to 20th	Day	14% 9% 4 7% 4 4 4 3 6% 8% 39%	3402
	21st to end	Day	17% 12% 6% 10% 5% 4 5% 3 5% 6% 28%	3931
April	1st to 10th	Day	15% 13% 4 8% 5% 5% 5% 4 5% 6% 32%	2280
	11th to 20th	Day	18% 10% 3 6% 4 4 4 3 5% 7% 36%	2268
	21st to end	Day	19% 9% 2 7% 5% 4 4 4 5% 8% 32%	2470
May	1st to 10th	Day	20% 9% 3 8% 5% 5% 5% 4 6% 7% 28%	4082
	11th to 20th	Day	18% 7% 2 6% 5% 4 4 4 5% 8% 36%	4081
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 8% 9% 40%	4588
June	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 7% 9% 44%	2660
	21st to end	Day	10% 5% 2 7% 6% 5% 5% 5% 7% 9% 39%	2660
July	1st to 10th	Day	13% 7% 2 8% 5% 4 5% 4 7% 10% 35%	4440
	11th to 20th	Day	7% 4 1 5% 4 4 4 5% 7% 12% 46%	4440
	21st to end	Day	9% 7% 3 7% 5% 5% 6% 5% 7% 8% 38%	4666
August	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 44%	4104
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 5% 6% 9% 44%	3980
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 9% 49%	4180
September	1st to 10th	Day	12% 7% 2 5% 4 4 4 3 6% 7% 47%	2233
	11th to 20th	Day	9% 5% 2 5% 4 5% 4 4 7% 8% 47%	2090
	21st to end	Day	14% 7% 1 5% 3 4 5% 3 5% 6% 46%	2090
October	1st to 10th	Day	12% 5% 3 6% 3 4 4 4 5% 7% 46%	2090
	11th to 20th	Day	14% 6% 2 6% 4 4 6% 3 5% 6% 42%	1925
	21st to end	Day	20% 9% 3 8% 4 4 5% 3 6% 6% 32%	1881
November	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 5% 6% 49%	1762
	11th to 20th	Day	16% 13% 3 8% 5% 5% 4 3 4 6% 31%	1800
	21st to end	Day	19% 12% 5% 9% 5% 4 4 3 4 5% 30%	1800
December	1st to 10th	Day	13% 13% 4 10% 4 3 4 3 4 5% 38%	2930
	11th to 20th	Day	16% 17% 5% 12% 5% 5% 5% 4 4 6% 22%	3025
	21st to end	Day	27% 18% 7% 11% 5% 5% 4 3 4 4 11%	3982
January	1st to 10th	Night	16% 15% 8% 14% 5% 4 4 3 4 5% 22%	6348
	11th to 20th	Night	12% 20% 9% 15% 7% 6% 5% 3 3 3 17%	6360
	21st to end	Night	21% 13% 6% 9% 5% 5% 4 4 4 4 26%	6790
February	1st to 10th	Night	18% 15% 5% 10% 6% 5% 3 3 4 5% 26%	2455
	11th to 20th	Night	13% 13% 5% 10% 7% 5% 4 3 4 6% 30%	2338
	21st to end	Night	19% 14% 4 9% 5% 5% 4 3 5% 4 29%	1885
March	1st to 10th	Night	19% 13% 3 6% 4 3 4 2 4 5% 34%	3733
	11th to 20th	Night	11% 7% 3 6% 5% 4 4 4 5% 7% 44%	3557
	21st to end	Night	19% 9% 3 8% 4 4 4 3 5% 6% 35%	3728
April	1st to 10th	Night	14% 10% 3 7% 5% 4 5% 4 6% 7% 36%	1900
	11th to 20th	Night	18% 8% 2 6% 5% 4 4 3 6% 6% 37%	1861
	21st to end	Night	19% 10% 2 6% 4 4 4 3 5% 6% 36%	1710
May	1st to 10th	Night	19% 10% 3 7% 6% 5% 5% 3 7% 7% 29%	2813
	11th to 20th	Night	20% 8% 2 6% 4 3 4 3 5% 7% 39%	2812
	21st to end	Night	9% 6% 2 7% 4 4 5% 4 6% 9% 44%	2967
June	1st to 10th	Night	9% 5% 2 6% 4 5% 4 4 6% 7% 48%	1520
	11th to 20th	Night	7% 6% 3 5% 4 4 4 3 6% 10% 47%	1520
	21st to end	Night	8% 6% 2 6% 5% 4 5% 4 6% 10% 44%	1520
July	1st to 10th	Night	9% 5% 2 5% 4 4 5% 4 6% 10% 45%	2530
	11th to 20th	Night	7% 3 2 4 4 3 4 3 6% 9% 57%	2530
	21st to end	Night	10% 7% 2 7% 4 4 4 4 6% 9% 42%	2889
August	1st to 10th	Night	11% 6% 3 6% 4 4 4 4 5% 9% 46%	2825
	11th to 20th	Night	8% 5% 3 5% 5% 5% 4 4 6% 8% 48%	2844
	21st to end	Night	7% 5% 2 6% 4 4 4 4 5% 8% 52%	3476
September	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 5% 7% 49%	1928
	11th to 20th	Night	8% 4 1 5% 4 3 3 3 4 8% 57%	2090
	21st to end	Night	12% 6% 2 5% 3 4 3 3 5% 6% 50%	2090
October	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 5% 7% 52%	2090
	11th to 20th	Night	17% 8% 3 6% 4 3 3 3 4 5% 44%	2251
	21st to end	Night	19% 7% 3 7% 4 3 4 3 5% 6% 38%	2717
November	1st to 10th	Night	12% 9% 3 6% 4 3 3 3 5% 6% 46%	2536
	11th to 20th	Night	15% 11% 4 8% 5% 3 4 3 5% 7% 36%	2600
	21st to end	Night	18% 14% 4 9% 5% 5% 5% 3 5% 5% 29%	2600
December	1st to 10th	Night	13% 11% 4 7% 5% 5% 4 4 6% 7% 36%	4250
	11th to 20th	Night	18% 16% 7% 11% 5% 4 4 3 4 5% 22%	5165
	21st to end	Night	26% 19% 7% 11% 5% 4 4 3 4 5% 13%	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	68% 4 7% 17% 5%	3618
	11th to 20th	Day	73% 3 9% 7% 7% 2	3620
	21st to end	Day	70% 2 8% 12% 7%	4176
February	1st to 10th	Day	66% 4 9% 12% 9% 1	1942
	11th to 20th	Day	58% 5% 10% 20% 6%	1958
	21st to end	Day	58% 5% 12% 17% 6% 2	1570
March	1st to 10th	Day	62% 5% 8% 17% 8%	3120
	11th to 20th	Day	42% 6% 11% 31% 10% 1	3402
	21st to end	Day	55% 8% 16% 18% 3	3931
April	1st to 10th	Day	52% 6% 12% 18% 12%	2280
	11th to 20th	Day	48% 5% 11% 22% 11% 3	2268
	21st to end	Day	49% 6% 13% 20% 9% 3	2470
May	1st to 10th	Day	51% 9% 12% 19% 8%	4120
	11th to 20th	Day	44% 8% 14% 24% 9% 1	4085
	21st to end	Day	35% 9% 14% 23% 17% 2	4601
June	1st to 10th	Day	40% 7% 11% 24% 15% 3	2660
	11th to 20th	Day	36% 7% 11% 24% 19% 2	2660
	21st to end	Day	37% 10% 16% 19% 14% 4	2660
July	1st to 10th	Day	44% 6% 12% 20% 15% 2	4371
	11th to 20th	Day	29% 7% 15% 27% 20% 1	4365
	21st to end	Day	40% 8% 14% 17% 17% 3	4518
August	1st to 10th	Day	33% 7% 19% 26% 14% 1	4091
	11th to 20th	Day	34% 8% 12% 31% 15% 1	4019
	21st to end	Day	30% 8% 13% 28% 18% 3	4179
September	1st to 10th	Day	36% 7% 12% 24% 18% 4	2233
	11th to 20th	Day	33% 6% 11% 25% 21% 3	2090
	21st to end	Day	38% 6% 11% 23% 21% 1	2090
October	1st to 10th	Day	26% 5% 11% 31% 25% 2	3480
	11th to 20th	Day	33% 6% 11% 25% 25% 1	3167
	21st to end	Day	43% 4 10% 25% 17% 1	3081
November	1st to 10th	Day	35% 5% 14% 26% 17% 2	1762
	11th to 20th	Day	54% 4 10% 19% 11% 2	1800
	21st to end	Day	56% 5% 11% 19% 8% 1	1800
December	1st to 10th	Day	50% 4 13% 23% 10%	2930
	11th to 20th	Day	64% 4 13% 16% 3	3022
	21st to end	Day	77% 4 7% 8% 3	3982
January	1st to 10th	Night	66% 4 8% 16% 7%	6348
	11th to 20th	Night	72% 3 7% 9% 8% 1	6360
	21st to end	Night	63% 3 10% 16% 7% 1	6790
February	1st to 10th	Night	61% 4 12% 15% 7% 1	2455
	11th to 20th	Night	56% 5% 11% 17% 11% 1	2339
	21st to end	Night	58% 5% 9% 16% 9% 2	1885
March	1st to 10th	Night	52% 5% 9% 24% 9% 1	3733
	11th to 20th	Night	37% 7% 12% 28% 14% 2	3557
	21st to end	Night	49% 7% 12% 24% 7% 1	3728
April	1st to 10th	Night	45% 8% 12% 22% 12% 1	1900
	11th to 20th	Night	45% 6% 12% 19% 14% 4	1861
	21st to end	Night	46% 7% 10% 21% 12% 4	1710
May	1st to 10th	Night	51% 9% 10% 19% 9% 2	2840
	11th to 20th	Night	43% 8% 13% 26% 9% 1	2813
	21st to end	Night	33% 11% 15% 22% 16% 3	2975
June	1st to 10th	Night	34% 6% 10% 27% 20% 3	1520
	11th to 20th	Night	31% 8% 13% 25% 20% 4	1520
	21st to end	Night	33% 9% 16% 23% 15% 5%	1520
July	1st to 10th	Night	35% 7% 11% 25% 16% 6%	2490
	11th to 20th	Night	25% 5% 15% 28% 24% 2	2482
	21st to end	Night	37% 7% 15% 18% 18% 5%	2797
August	1st to 10th	Night	35% 6% 15% 27% 15% 1	2814
	11th to 20th	Night	33% 6% 13% 29% 18% 1	2871
	21st to end	Night	31% 6% 12% 28% 21% 3	3476
September	1st to 10th	Night	33% 7% 13% 22% 20% 6%	1928
	11th to 20th	Night	27% 5% 10% 28% 27% 3	2090
	21st to end	Night	34% 7% 11% 23% 22% 3	2090
October	1st to 10th	Night	21% 4 6% 32% 34% 2	3480
	11th to 20th	Night	32% 4 10% 23% 31% 1	3735
	21st to end	Night	34% 4 8% 30% 22% 2	4467
November	1st to 10th	Night	38% 4 10% 26% 19% 2	2536
	11th to 20th	Night	47% 5% 11% 20% 15% 3	2600
	21st to end	Night	57% 4 10% 21% 7%	2600
December	1st to 10th	Night	48% 4 13% 25% 8% 1	4250
	11th to 20th	Night	63% 6% 11% 13% 7% 1	5167
	21st to end	Night	74% 5% 9% 9% 3	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	26% 16% 37% 14% 5% 1	300
	11th to 20th	Day	25% 22% 36% 13% 3 1	300
	21st to end	Day	31% 15% 33% 15% 5%	330
February	1st to 10th	Day	28% 16% 34% 19% 3	300
	11th to 20th	Day	26% 20% 35% 14% 4 1	300
	21st to end	Day	29% 19% 38% 12% 3	225
March	1st to 10th	Day	25% 20% 37% 16% 3	270
	11th to 20th	Day	28% 11% 35% 18% 7% 1	408
	21st to end	Day	31% 13% 31% 18% 7% 1	506
April	1st to 10th	Day	24% 13% 34% 17% 9% 2	460
	11th to 20th	Day	23% 17% 29% 18% 11% 3	452
	21st to end	Day	26% 13% 32% 18% 9% 2	460
May	1st to 10th	Day	25% 10% 33% 22% 9% 2	463
	11th to 20th	Day	23% 7% 28% 24% 12% 7%	487
	21st to end	Day	12% 5% 30% 26% 18% 9%	589
June	1st to 10th	Day	13% 6% 28% 26% 22% 5%	680
	11th to 20th	Day	13% 5% 26% 30% 20% 6%	680
	21st to end	Day	13% 6% 28% 27% 19% 6%	680
July	1st to 10th	Day	14% 2 19% 28% 21% 15%	671
	11th to 20th	Day	8% 2 20% 32% 23% 14%	668
	21st to end	Day	12% 3 15% 33% 25% 12%	654
August	1st to 10th	Day	8% 2 15% 31% 29% 15%	486
	11th to 20th	Day	12% 1 20% 29% 24% 13%	479
	21st to end	Day	9% 2 13% 31% 32% 12%	539
September	1st to 10th	Day	14% 5% 14% 30% 26% 10%	490
	11th to 20th	Day	11% 2 16% 26% 30% 17%	490
	21st to end	Day	20% 8% 19% 27% 19% 7%	490
October	1st to 10th	Day	11% 7% 24% 32% 17% 9%	490
	11th to 20th	Day	17% 16% 31% 23% 11% 2	440
	21st to end	Day	29% 10% 38% 20% 4	330
November	1st to 10th	Day	12% 16% 34% 24% 11% 3	300
	11th to 20th	Day	25% 14% 36% 16% 8% 1	300
	21st to end	Day	29% 13% 35% 21% 3	300
December	1st to 10th	Day	26% 16% 37% 14% 6% 1	300
	11th to 20th	Day	24% 15% 40% 15% 6%	300
	21st to end	Day	33% 14% 35% 16% 2	330
January	1st to 10th	Night	24% 16% 34% 21% 5%	1000
	11th to 20th	Night	25% 15% 37% 20% 4	1000
	21st to end	Night	24% 14% 36% 23% 4	1011
February	1st to 10th	Night	27% 12% 33% 25% 3	800
	11th to 20th	Night	22% 13% 38% 25% 2	783
	21st to end	Night	27% 14% 37% 19% 4	629
March	1st to 10th	Night	22% 12% 35% 25% 6%	760
	11th to 20th	Night	20% 10% 37% 25% 7% 1	760
	21st to end	Night	27% 8% 32% 26% 6% 1	785
April	1st to 10th	Night	19% 9% 36% 28% 7% 1	570
	11th to 20th	Night	23% 10% 32% 26% 8% 1	563
	21st to end	Night	24% 7% 35% 24% 9% 1	570
May	1st to 10th	Night	24% 5% 30% 32% 8%	570
	11th to 20th	Night	22% 3 25% 33% 16% 1	561
	21st to end	Night	10% 4 23% 42% 18% 3	617
June	1st to 10th	Night	10% 2 25% 45% 18% 1	570
	11th to 20th	Night	10% 3 24% 41% 20% 1	570
	21st to end	Night	11% 2 21% 39% 25% 1	570
July	1st to 10th	Night	11% 2 14% 38% 31% 4	555
	11th to 20th	Night	10% 1 13% 41% 30% 5%	552
	21st to end	Night	8% 1 12% 46% 30% 2	624
August	1st to 10th	Night	9% 1 12% 43% 31% 4	567
	11th to 20th	Night	9% 2 13% 38% 34% 4	564
	21st to end	Night	8% 1 14% 35% 37% 5%	627
September	1st to 10th	Night	15% 1 12% 38% 29% 5%	598
	11th to 20th	Night	11% 2 15% 36% 32% 4	760
	21st to end	Night	16% 5% 21% 34% 22% 3	760
October	1st to 10th	Night	14% 5% 24% 35% 19% 4	760
	11th to 20th	Night	21% 9% 29% 28% 12% 1	760
	21st to end	Night	23% 11% 33% 26% 7%	836
November	1st to 10th	Night	18% 10% 34% 26% 11% 1	780
	11th to 20th	Night	20% 15% 34% 23% 7%	800
	21st to end	Night	28% 11% 33% 21% 7%	800
December	1st to 10th	Night	26% 12% 35% 22% 5% 1	800
	11th to 20th	Night	26% 13% 31% 24% 6%	979
	21st to end	Night	33% 13% 31% 20% 3	1100

Page generated at 2025-02-18 03:26:27. Version ac07

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