Vincennes
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vincennes clear sky chart from 2005-11-06 to 2026-04-17.

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	13% 8% 3 7% 5% 4 4 4 6% 8% 39%	131202
	Night	15% 8% 3 7% 4 4 4 3 5% 7% 40%	131136
Transparency	Day	42% 6% 12% 24% 15% 2	134804
	Night	42% 5% 11% 23% 17% 2	135609
Seeing	Day	16% 9% 25% 24% 18% 8%	17432
	Night	17% 7% 27% 31% 16% 2	27352

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% 11% 6% 10% 5% 5% 5% 4 4 6% 31%	4691
	11th to 20th	Day	10% 10% 5% 12% 7% 6% 4 4 4 6% 33%	4710
	21st to end	Day	19% 14% 4 9% 6% 4 4 3 5% 5% 27%	5590
February	1st to 10th	Day	17% 12% 4 9% 5% 4 4 3 5% 6% 33%	2100
	11th to 20th	Day	16% 12% 4 9% 5% 4 4 3 5% 6% 34%	2048
	21st to end	Day	15% 10% 4 10% 5% 4 4 3 4 6% 35%	1730
March	1st to 10th	Day	19% 11% 4 7% 4 3 3 2 3 4 41%	4580
	11th to 20th	Day	12% 10% 2 6% 4 3 3 3 5% 8% 44%	4756
	21st to end	Day	15% 10% 3 7% 5% 4 4 4 5% 8% 34%	6088
April	1st to 10th	Day	15% 8% 3 7% 5% 4 4 3 5% 8% 39%	2520
	11th to 20th	Day	16% 8% 2 7% 4 4 4 3 6% 6% 39%	2446
	21st to end	Day	19% 6% 3 6% 5% 4 4 3 5% 7% 39%	2460
May	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 5% 7% 10% 27%	5862
	11th to 20th	Day	17% 7% 2 7% 5% 5% 4 4 6% 7% 36%	5861
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 9% 34%	6704
June	1st to 10th	Day	10% 6% 3 5% 4 4 4 4 7% 7% 46%	2800
	11th to 20th	Day	8% 5% 2 5% 5% 5% 5% 5% 7% 8% 46%	2800
	21st to end	Day	8% 5% 2 6% 5% 6% 5% 4 7% 9% 44%	2800
July	1st to 10th	Day	10% 5% 2 6% 5% 4 4 3 6% 10% 45%	6360
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 6% 7% 12% 39%	6360
	21st to end	Day	9% 6% 3 8% 5% 6% 6% 5% 8% 11% 33%	6847
August	1st to 10th	Day	8% 4 1 4 3 4 4 4 6% 11% 51%	4109
	11th to 20th	Day	8% 5% 2 6% 4 4 6% 5% 7% 10% 42%	3849
	21st to end	Day	4 4 2 5% 3 4 5% 4 6% 9% 54%	4312
September	1st to 10th	Day	10% 5% 2 5% 4 3 4 3 5% 8% 49%	2400
	11th to 20th	Day	9% 4 2 6% 4 4 4 3 6% 8% 51%	2227
	21st to end	Day	12% 5% 2 4 3 3 3 3 5% 7% 53%	2200
October	1st to 10th	Day	11% 5% 2 4 3 3 4 3 5% 6% 56%	2200
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 4 6% 50%	2040
	21st to end	Day	19% 7% 3 5% 3 4 3 2 4 4 44%	1992
November	1st to 10th	Day	9% 6% 2 6% 4 3 3 3 5% 6% 52%	1852
	11th to 20th	Day	16% 9% 2 7% 4 3 3 2 4 7% 43%	1890
	21st to end	Day	19% 11% 3 7% 4 3 3 2 4 6% 38%	1890
December	1st to 10th	Day	12% 10% 3 6% 4 4 3 2 4 5% 46%	2970
	11th to 20th	Day	15% 12% 6% 10% 5% 5% 5% 4 5% 5% 30%	3088
	21st to end	Day	27% 16% 6% 9% 5% 4 3 2 4 5% 19%	4070
January	1st to 10th	Night	16% 12% 6% 8% 4 4 4 4 5% 6% 33%	8232
	11th to 20th	Night	12% 12% 4 10% 4 6% 6% 3 4 5% 33%	8280
	21st to end	Night	18% 11% 4 7% 4 4 4 3 5% 6% 34%	8602
February	1st to 10th	Night	19% 11% 4 8% 5% 4 4 4 5% 5% 30%	2520
	11th to 20th	Night	16% 10% 3 7% 5% 5% 4 3 4 7% 36%	2458
	21st to end	Night	19% 10% 3 7% 5% 4 3 3 5% 5% 36%	2076
March	1st to 10th	Night	21% 11% 4 7% 4 3 3 3 4 5% 35%	5493
	11th to 20th	Night	12% 6% 2 6% 4 3 4 3 4 6% 49%	5422
	21st to end	Night	18% 8% 3 8% 6% 5% 5% 4 5% 5% 35%	5126
April	1st to 10th	Night	13% 6% 2 7% 5% 4 4 4 5% 7% 43%	2100
	11th to 20th	Night	16% 7% 2 6% 4 3 4 3 6% 7% 43%	2035
	21st to end	Night	18% 7% 2 5% 5% 4 4 4 6% 7% 37%	1939
May	1st to 10th	Night	17% 9% 3 7% 5% 5% 4 4 6% 9% 31%	4033
	11th to 20th	Night	15% 7% 2 7% 5% 4 5% 4 6% 7% 37%	4032
	21st to end	Night	14% 6% 2 7% 4 5% 5% 4 7% 10% 37%	4145
June	1st to 10th	Night	10% 7% 2 5% 3 3 4 3 7% 9% 48%	1600
	11th to 20th	Night	8% 5% 1 4 4 4 5% 4 6% 9% 49%	1600
	21st to end	Night	6% 3 1 4 3 5% 6% 4 7% 9% 52%	1600
July	1st to 10th	Night	9% 6% 3 6% 4 4 4 4 5% 8% 47%	3618
	11th to 20th	Night	7% 5% 2 6% 4 5% 5% 5% 8% 9% 46%	3617
	21st to end	Night	7% 6% 2 7% 6% 6% 5% 5% 7% 11% 37%	4006
August	1st to 10th	Night	5% 4 1 5% 4 4 3 3 6% 8% 57%	3036
	11th to 20th	Night	6% 4 2 5% 4 4 5% 4 7% 8% 51%	3200
	21st to end	Night	3 3 2 5% 3 4 4 4 6% 8% 59%	3586
September	1st to 10th	Night	10% 6% 2 5% 3 4 3 3 5% 6% 53%	2000
	11th to 20th	Night	7% 4 2 5% 4 4 3 4 5% 7% 55%	2151
	21st to end	Night	12% 5% 2 5% 3 3 3 3 5% 7% 50%	2200
October	1st to 10th	Night	9% 4 1 5% 2 3 3 3 5% 6% 60%	2200
	11th to 20th	Night	15% 5% 2 5% 3 4 3 2 4 5% 53%	2355
	21st to end	Night	19% 7% 2 6% 3 3 4 2 4 5% 44%	2845
November	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 52%	2666
	11th to 20th	Night	14% 7% 2 5% 4 3 4 3 4 6% 48%	2730
	21st to end	Night	20% 9% 3 6% 4 3 3 3 4 6% 41%	2730
December	1st to 10th	Night	19% 9% 2 7% 4 3 3 2 4 6% 42%	4414
	11th to 20th	Night	19% 9% 3 7% 3 4 4 3 5% 6% 38%	5339
	21st to end	Night	28% 15% 4 8% 5% 4 3 3 3 4 23%	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	54% 4 12% 23% 7%	4692
	11th to 20th	Day	52% 5% 10% 21% 10% 2	4710
	21st to end	Day	60% 4 9% 16% 7% 4	5590
February	1st to 10th	Day	53% 4 11% 21% 9% 2	2100
	11th to 20th	Day	52% 4 9% 21% 12% 2	2058
	21st to end	Day	51% 5% 8% 22% 11% 3	1730
March	1st to 10th	Day	49% 3 5% 19% 20% 4	4580
	11th to 20th	Day	38% 4 10% 31% 15% 2	4756
	21st to end	Day	47% 7% 12% 23% 10% 1	6090
April	1st to 10th	Day	43% 6% 13% 22% 14% 1	2520
	11th to 20th	Day	44% 6% 11% 24% 13% 2	2446
	21st to end	Day	45% 5% 11% 25% 11% 3	2460
May	1st to 10th	Day	49% 9% 13% 19% 10%	5897
	11th to 20th	Day	45% 8% 11% 24% 11%	5865
	21st to end	Day	42% 8% 13% 20% 15% 2	6718
June	1st to 10th	Day	33% 8% 12% 25% 18% 3	2800
	11th to 20th	Day	32% 9% 12% 24% 20% 4	2800
	21st to end	Day	35% 8% 15% 21% 16% 5%	2800
July	1st to 10th	Day	35% 6% 10% 29% 18% 2	6291
	11th to 20th	Day	35% 10% 15% 26% 12% 1	6285
	21st to end	Day	41% 10% 17% 24% 8% 1	6652
August	1st to 10th	Day	26% 7% 15% 36% 16% 1	4096
	11th to 20th	Day	34% 8% 16% 25% 16% 1	3885
	21st to end	Day	25% 6% 17% 32% 16% 4	4311
September	1st to 10th	Day	34% 6% 11% 25% 20% 4	2400
	11th to 20th	Day	31% 5% 12% 26% 23% 3	2227
	21st to end	Day	32% 5% 8% 25% 27% 3	2200
October	1st to 10th	Day	19% 3 6% 27% 41% 3	3590
	11th to 20th	Day	25% 4 8% 25% 34% 3	3306
	21st to end	Day	35% 3 7% 24% 28% 2	3192
November	1st to 10th	Day	33% 5% 10% 30% 17% 5%	1852
	11th to 20th	Day	43% 3 9% 23% 17% 5%	1890
	21st to end	Day	49% 3 9% 22% 15% 1	1890
December	1st to 10th	Day	42% 3 14% 27% 13%	2970
	11th to 20th	Day	56% 5% 9% 20% 9% 1	3085
	21st to end	Day	69% 5% 11% 11% 4	4070
January	1st to 10th	Night	52% 5% 12% 23% 7%	8233
	11th to 20th	Night	53% 4 8% 16% 15% 3	8280
	21st to end	Night	51% 3 12% 21% 12% 1	8602
February	1st to 10th	Night	55% 5% 11% 19% 9% 1	2520
	11th to 20th	Night	48% 5% 10% 22% 14% 1	2459
	21st to end	Night	50% 4 10% 22% 12% 2	2076
March	1st to 10th	Night	51% 3 7% 21% 15% 3	5493
	11th to 20th	Night	36% 5% 10% 26% 21% 2	5422
	21st to end	Night	50% 6% 9% 25% 8% 1	5126
April	1st to 10th	Night	40% 6% 10% 27% 15% 2	2100
	11th to 20th	Night	39% 5% 12% 22% 18% 4	2035
	21st to end	Night	44% 6% 11% 22% 14% 3	1939
May	1st to 10th	Night	47% 10% 14% 21% 8% 1	4060
	11th to 20th	Night	44% 8% 11% 24% 12%	4033
	21st to end	Night	40% 8% 15% 21% 14% 3	4153
June	1st to 10th	Night	33% 6% 10% 26% 22% 4	1600
	11th to 20th	Night	31% 7% 12% 22% 23% 7%	1600
	21st to end	Night	26% 10% 14% 22% 21% 7%	1600
July	1st to 10th	Night	35% 6% 10% 24% 22% 3	3580
	11th to 20th	Night	32% 9% 16% 27% 15% 2	3572
	21st to end	Night	38% 8% 20% 22% 11% 1	3890
August	1st to 10th	Night	24% 7% 15% 39% 14% 2	3025
	11th to 20th	Night	29% 7% 14% 30% 19% 2	3230
	21st to end	Night	22% 6% 14% 29% 25% 4	3586
September	1st to 10th	Night	32% 6% 9% 26% 22% 6%	2000
	11th to 20th	Night	28% 4 11% 24% 28% 4	2151
	21st to end	Night	33% 5% 10% 21% 24% 6%	2200
October	1st to 10th	Night	17% 4 7% 19% 49% 5%	3590
	11th to 20th	Night	25% 2 6% 27% 36% 4	3828
	21st to end	Night	33% 4 7% 24% 27% 6%	4595
November	1st to 10th	Night	34% 5% 9% 26% 22% 5%	2666
	11th to 20th	Night	38% 4 9% 23% 22% 4	2730
	21st to end	Night	46% 3 11% 23% 15% 2	2730
December	1st to 10th	Night	45% 4 10% 25% 15%	4414
	11th to 20th	Night	47% 5% 13% 22% 13% 1	5341
	21st to end	Night	66% 5% 9% 14% 6% 1	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	22% 15% 33% 23% 7% 1	330
	11th to 20th	Day	23% 19% 34% 19% 4	330
	21st to end	Day	22% 16% 40% 16% 6%	363
February	1st to 10th	Day	24% 15% 37% 20% 4	330
	11th to 20th	Day	23% 21% 37% 14% 4 1	330
	21st to end	Day	24% 12% 41% 19% 4	273
March	1st to 10th	Day	21% 19% 37% 18% 5% 1	330
	11th to 20th	Day	27% 17% 35% 15% 6% 1	388
	21st to end	Day	27% 15% 34% 17% 6% 1	594
April	1st to 10th	Day	18% 16% 33% 24% 8% 1	540
	11th to 20th	Day	20% 15% 28% 22% 13% 2	516
	21st to end	Day	21% 13% 32% 21% 9% 3	500
May	1st to 10th	Day	19% 11% 28% 29% 10% 3	503
	11th to 20th	Day	19% 6% 27% 24% 15% 8%	527
	21st to end	Day	11% 5% 27% 26% 19% 12%	688
June	1st to 10th	Day	12% 5% 21% 26% 27% 8%	730
	11th to 20th	Day	10% 4 19% 32% 25% 11%	730
	21st to end	Day	8% 4 23% 30% 23% 11%	730
July	1st to 10th	Day	11% 3 12% 25% 26% 24%	721
	11th to 20th	Day	8% 2 14% 33% 27% 17%	718
	21st to end	Day	9% 2 12% 28% 36% 13%	767
August	1st to 10th	Day	9% 3 12% 25% 33% 19%	526
	11th to 20th	Day	12% 3 11% 29% 32% 13%	519
	21st to end	Day	7% 1 9% 24% 37% 22%	583
September	1st to 10th	Day	9% 3 15% 25% 33% 15%	530
	11th to 20th	Day	8% 2 9% 26% 37% 18%	530
	21st to end	Day	15% 5% 19% 23% 25% 14%	530
October	1st to 10th	Day	11% 4 18% 34% 24% 9%	530
	11th to 20th	Day	12% 11% 31% 26% 15% 5%	370
	21st to end	Day	24% 13% 32% 24% 7% 1	363
November	1st to 10th	Day	13% 10% 34% 24% 13% 6%	330
	11th to 20th	Day	18% 16% 32% 22% 10% 2	330
	21st to end	Day	27% 10% 25% 26% 10% 2	330
December	1st to 10th	Day	15% 18% 37% 18% 7% 3	330
	11th to 20th	Day	23% 14% 36% 19% 8% 1	330
	21st to end	Day	29% 15% 34% 17% 5% 1	363
January	1st to 10th	Night	20% 12% 35% 28% 4	1050
	11th to 20th	Night	24% 14% 37% 22% 4	1050
	21st to end	Night	22% 10% 38% 28% 2	1142
February	1st to 10th	Night	25% 11% 37% 25% 3	840
	11th to 20th	Night	23% 13% 36% 26% 2	823
	21st to end	Night	24% 13% 38% 23% 2	692
March	1st to 10th	Night	23% 12% 35% 27% 4	840
	11th to 20th	Night	21% 11% 36% 25% 6% 1	840
	21st to end	Night	24% 9% 30% 31% 5% 1	721
April	1st to 10th	Night	17% 10% 33% 33% 7%	630
	11th to 20th	Night	18% 9% 33% 28% 12% 1	611
	21st to end	Night	21% 6% 32% 32% 9% 1	600
May	1st to 10th	Night	16% 7% 29% 38% 10% 1	600
	11th to 20th	Night	15% 5% 23% 37% 18% 2	591
	21st to end	Night	10% 4 20% 39% 25% 2	650
June	1st to 10th	Night	13% 2 19% 40% 25% 1	600
	11th to 20th	Night	9% 2 17% 43% 27% 2	600
	21st to end	Night	7% 1 19% 41% 31% 2	600
July	1st to 10th	Night	10% 1 10% 34% 36% 8%	585
	11th to 20th	Night	5% 2 10% 42% 37% 4	582
	21st to end	Night	8% 1 10% 37% 38% 5%	657
August	1st to 10th	Night	7% 1 9% 40% 38% 5%	597
	11th to 20th	Night	7% 1 9% 38% 40% 5%	594
	21st to end	Night	6% 2 7% 35% 41% 8%	660
September	1st to 10th	Night	12% 2 10% 34% 38% 5%	600
	11th to 20th	Night	7% 1 13% 35% 37% 7%	751
	21st to end	Night	13% 4 19% 30% 30% 4	800
October	1st to 10th	Night	10% 4 19% 38% 25% 5%	800
	11th to 20th	Night	17% 6% 29% 31% 16% 2	800
	21st to end	Night	22% 9% 31% 30% 8%	880
November	1st to 10th	Night	13% 7% 31% 35% 13% 1	820
	11th to 20th	Night	17% 11% 33% 30% 9%	840
	21st to end	Night	24% 10% 28% 29% 9%	840
December	1st to 10th	Night	24% 8% 34% 27% 6%	861
	11th to 20th	Night	25% 8% 31% 30% 6% 1	1050
	21st to end	Night	29% 13% 32% 22% 4	1155

Page generated at 2026-04-14 02:44:29. Version ac07

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