Batavia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Batavia clear sky chart from 2005-11-06 to 2025-05-26.

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% 3 8% 5% 4 4 4 5% 7% 36%	115054
	Night	15% 10% 4 8% 5% 4 4 3 5% 7% 37%	114255
Transparency	Day	45% 6% 11% 23% 14% 2	118740
	Night	45% 6% 10% 22% 15% 2	118696
Seeing	Day	20% 13% 27% 22% 13% 5%	15933
	Night	19% 11% 26% 27% 14% 2	25520

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	14% 17% 8% 13% 5% 4 3 3 4 4 25%	4056
	11th to 20th	Day	13% 15% 5% 15% 6% 5% 4 3 3 5% 26%	4060
	21st to end	Day	21% 12% 7% 8% 6% 5% 4 3 5% 5% 24%	4466
February	1st to 10th	Day	20% 13% 5% 8% 5% 4 4 3 5% 5% 30%	1891
	11th to 20th	Day	17% 11% 5% 11% 5% 4 4 3 3 5% 30%	1948
	21st to end	Day	18% 14% 6% 8% 4 4 3 3 4 6% 31%	1650
March	1st to 10th	Day	17% 15% 6% 9% 4 4 3 3 4 5% 31%	4561
	11th to 20th	Day	14% 8% 3 7% 4 4 4 3 5% 8% 39%	4980
	21st to end	Day	17% 10% 3 8% 4 4 4 3 5% 7% 35%	5465
April	1st to 10th	Day	16% 10% 3 7% 5% 4 5% 3 5% 7% 35%	2335
	11th to 20th	Day	17% 8% 3 8% 5% 3 4 3 5% 7% 38%	2442
	21st to end	Day	17% 8% 3 8% 5% 4 4 3 5% 7% 35%	2600
May	1st to 10th	Day	21% 10% 3 7% 5% 4 5% 4 5% 7% 29%	4212
	11th to 20th	Day	20% 8% 3 6% 4 3 5% 3 5% 7% 35%	4211
	21st to end	Day	9% 7% 3 7% 6% 5% 6% 5% 8% 9% 34%	4541
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 8% 40%	2470
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 8% 10% 43%	2589
	21st to end	Day	9% 6% 2 7% 6% 5% 5% 5% 6% 9% 40%	2660
July	1st to 10th	Day	12% 7% 2 8% 5% 4 5% 5% 6% 9% 38%	4440
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 4 7% 11% 46%	4184
	21st to end	Day	11% 7% 3 9% 6% 6% 6% 5% 8% 8% 31%	4466
August	1st to 10th	Day	9% 5% 2 7% 3 5% 4 5% 7% 11% 43%	4104
	11th to 20th	Day	7% 6% 3 6% 5% 5% 5% 5% 8% 10% 41%	4044
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 8% 55%	4244
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 5% 6% 49%	2147
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 9% 48%	2090
	21st to end	Day	16% 6% 2 6% 5% 4 3 3 4 6% 46%	2090
October	1st to 10th	Day	11% 5% 1 5% 4 4 5% 4 4 6% 50%	2090
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 7% 46%	1918
	21st to end	Day	19% 9% 2 6% 3 4 3 3 5% 6% 40%	1969
November	1st to 10th	Day	10% 7% 2 5% 4 3 3 3 4 6% 52%	1762
	11th to 20th	Day	14% 12% 3 8% 5% 4 4 3 4 6% 36%	1800
	21st to end	Day	17% 12% 3 8% 4 4 4 3 4 5% 37%	1800
December	1st to 10th	Day	19% 10% 4 7% 4 4 4 3 4 4 37%	2930
	11th to 20th	Day	18% 15% 5% 10% 5% 5% 4 4 4 4 27%	3373
	21st to end	Day	21% 20% 5% 10% 5% 4 4 3 4 5% 19%	4466
January	1st to 10th	Night	15% 16% 6% 15% 7% 5% 5% 3 4 5% 19%	5889
	11th to 20th	Night	14% 16% 7% 14% 7% 5% 5% 3 4 4 22%	5900
	21st to end	Night	21% 12% 4 8% 5% 4 4 3 4 4 31%	6490
February	1st to 10th	Night	21% 12% 5% 8% 5% 4 4 3 4 6% 28%	2505
	11th to 20th	Night	19% 12% 4 9% 5% 4 5% 3 4 6% 30%	2338
	21st to end	Night	19% 15% 4 7% 4 4 3 2 4 6% 31%	1980
March	1st to 10th	Night	17% 15% 3 6% 4 4 3 2 4 5% 37%	5292
	11th to 20th	Night	12% 7% 3 6% 4 4 4 4 5% 7% 43%	4980
	21st to end	Night	16% 11% 4 8% 5% 5% 4 3 5% 6% 34%	5467
April	1st to 10th	Night	15% 10% 3 6% 6% 4 4 4 6% 7% 36%	2081
	11th to 20th	Night	15% 7% 2 5% 5% 4 4 5% 6% 7% 41%	1907
	21st to end	Night	16% 8% 3 7% 5% 4 3 3 6% 9% 36%	1800
May	1st to 10th	Night	22% 11% 3 8% 6% 4 4 3 6% 6% 27%	2903
	11th to 20th	Night	18% 7% 2 5% 4 4 4 4 6% 9% 37%	2902
	21st to end	Night	9% 5% 2 6% 4 4 4 4 7% 9% 45%	3130
June	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 6% 9% 48%	1710
	11th to 20th	Night	8% 4 2 5% 4 4 4 3 7% 11% 48%	1584
	21st to end	Night	6% 4 2 4 5% 5% 5% 5% 8% 10% 46%	1520
July	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 8% 49%	2530
	11th to 20th	Night	5% 5% 2 5% 4 5% 4 4 6% 9% 50%	2773
	21st to end	Night	11% 7% 3 8% 6% 5% 4 4 6% 9% 37%	3087
August	1st to 10th	Night	8% 5% 3 7% 5% 4 5% 4 7% 8% 46%	2825
	11th to 20th	Night	8% 7% 3 7% 5% 4 5% 3 6% 8% 44%	2785
	21st to end	Night	4 3 1 4 3 4 4 3 6% 10% 60%	3408
September	1st to 10th	Night	11% 5% 2 4 3 4 3 4 5% 7% 51%	2013
	11th to 20th	Night	8% 4 2 6% 3 4 5% 4 5% 7% 53%	2090
	21st to end	Night	14% 5% 3 6% 4 3 4 3 5% 6% 48%	2090
October	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 5% 7% 55%	2090
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 5% 7% 45%	2261
	21st to end	Night	18% 8% 2 5% 4 4 4 3 4 5% 42%	2627
November	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 5% 7% 46%	2536
	11th to 20th	Night	15% 9% 3 7% 4 4 4 3 5% 6% 39%	2600
	21st to end	Night	17% 14% 3 7% 5% 4 4 3 4 6% 33%	2600
December	1st to 10th	Night	17% 12% 4 8% 4 4 3 2 4 5% 37%	4250
	11th to 20th	Night	19% 15% 6% 9% 5% 4 4 3 4 5% 26%	4822
	21st to end	Night	21% 19% 6% 11% 6% 4 4 3 4 5% 17%	6490

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	63% 4 10% 16% 7%	4057
	11th to 20th	Day	61% 4 9% 14% 11% 2	4060
	21st to end	Day	62% 3 8% 18% 6% 2	4466
February	1st to 10th	Day	56% 4 10% 18% 9% 1	1891
	11th to 20th	Day	57% 4 10% 17% 11% 1	1958
	21st to end	Day	56% 4 9% 19% 10% 2	1650
March	1st to 10th	Day	53% 6% 7% 19% 12% 3	4561
	11th to 20th	Day	42% 6% 9% 28% 14% 1	4980
	21st to end	Day	48% 5% 11% 21% 12% 2	5465
April	1st to 10th	Day	47% 6% 10% 23% 13% 1	2335
	11th to 20th	Day	45% 6% 10% 22% 14% 3	2442
	21st to end	Day	47% 7% 12% 21% 11% 2	2600
May	1st to 10th	Day	51% 8% 12% 20% 8% 1	4250
	11th to 20th	Day	47% 8% 12% 21% 11% 1	4215
	21st to end	Day	39% 11% 14% 19% 15% 2	4554
June	1st to 10th	Day	39% 9% 11% 23% 16% 2	2470
	11th to 20th	Day	34% 9% 14% 24% 17% 1	2589
	21st to end	Day	39% 9% 13% 22% 14% 4	2660
July	1st to 10th	Day	41% 7% 11% 21% 18% 1	4371
	11th to 20th	Day	31% 7% 11% 32% 18% 1	4113
	21st to end	Day	47% 9% 12% 18% 12% 2	4324
August	1st to 10th	Day	33% 8% 14% 34% 11% 1	4091
	11th to 20th	Day	35% 7% 11% 31% 15%	4083
	21st to end	Day	26% 7% 15% 28% 21% 3	4243
September	1st to 10th	Day	35% 6% 12% 22% 20% 5%	2147
	11th to 20th	Day	32% 7% 12% 24% 23% 3	2090
	21st to end	Day	40% 5% 9% 23% 21% 2	2090
October	1st to 10th	Day	22% 5% 8% 32% 32% 2	3480
	11th to 20th	Day	29% 4 10% 29% 27% 2	3158
	21st to end	Day	35% 4 10% 25% 23% 3	3219
November	1st to 10th	Day	34% 4 10% 28% 21% 3	1762
	11th to 20th	Day	48% 5% 7% 21% 16% 3	1800
	21st to end	Day	50% 4 9% 22% 14% 1	1800
December	1st to 10th	Day	50% 4 9% 26% 11%	2930
	11th to 20th	Day	60% 6% 8% 18% 8%	3370
	21st to end	Day	67% 5% 9% 13% 5% 1	4466
January	1st to 10th	Night	65% 6% 7% 13% 7%	5889
	11th to 20th	Night	66% 4 8% 12% 7% 3	5900
	21st to end	Night	56% 4 8% 21% 10% 1	6490
February	1st to 10th	Night	57% 4 11% 19% 8% 1	2505
	11th to 20th	Night	56% 5% 9% 18% 11% 1	2339
	21st to end	Night	56% 4 10% 17% 11% 2	1980
March	1st to 10th	Night	50% 4 6% 27% 11% 2	5292
	11th to 20th	Night	38% 6% 10% 28% 17% 1	4980
	21st to end	Night	51% 5% 7% 24% 11% 2	5467
April	1st to 10th	Night	45% 7% 10% 22% 13% 2	2081
	11th to 20th	Night	40% 7% 10% 20% 17% 6%	1907
	21st to end	Night	45% 5% 11% 22% 14% 3	1800
May	1st to 10th	Night	55% 8% 9% 18% 8% 2	2930
	11th to 20th	Night	42% 9% 14% 25% 9% 1	2903
	21st to end	Night	31% 8% 16% 26% 14% 4	3138
June	1st to 10th	Night	31% 7% 13% 26% 20% 3	1710
	11th to 20th	Night	30% 7% 16% 22% 21% 4	1584
	21st to end	Night	29% 11% 17% 22% 17% 5%	1520
July	1st to 10th	Night	33% 8% 11% 24% 19% 5%	2490
	11th to 20th	Night	29% 6% 13% 30% 20% 2	2722
	21st to end	Night	42% 6% 13% 22% 13% 4	2988
August	1st to 10th	Night	34% 7% 14% 32% 12% 1	2814
	11th to 20th	Night	36% 8% 10% 27% 18% 1	2812
	21st to end	Night	20% 6% 16% 32% 23% 3	3408
September	1st to 10th	Night	31% 7% 12% 25% 20% 6%	2013
	11th to 20th	Night	30% 6% 11% 23% 27% 3	2090
	21st to end	Night	37% 6% 9% 21% 25% 2	2090
October	1st to 10th	Night	22% 4 8% 25% 39% 2	3480
	11th to 20th	Night	27% 4 9% 26% 31% 3	3747
	21st to end	Night	33% 3 8% 22% 27% 6%	4327
November	1st to 10th	Night	38% 5% 10% 21% 22% 4	2536
	11th to 20th	Night	46% 4 9% 20% 18% 4	2600
	21st to end	Night	53% 4 10% 20% 12% 2	2600
December	1st to 10th	Night	50% 4 10% 24% 11%	4250
	11th to 20th	Night	58% 5% 11% 18% 7% 1	4824
	21st to end	Night	69% 5% 8% 13% 4	6490

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	29% 25% 30% 14% 3	300
	11th to 20th	Day	32% 27% 33% 7% 1	300
	21st to end	Day	33% 24% 30% 12% 1	330
February	1st to 10th	Day	30% 25% 33% 11% 2	300
	11th to 20th	Day	35% 29% 28% 6% 1	300
	21st to end	Day	35% 21% 39% 6%	249
March	1st to 10th	Day	27% 30% 28% 13% 1	329
	11th to 20th	Day	26% 23% 32% 15% 4	500
	21st to end	Day	34% 19% 29% 14% 5%	550
April	1st to 10th	Day	26% 18% 31% 17% 7% 1	500
	11th to 20th	Day	25% 21% 28% 15% 9% 3	492
	21st to end	Day	25% 19% 32% 14% 9% 2	500
May	1st to 10th	Day	27% 17% 30% 16% 7% 3	503
	11th to 20th	Day	24% 9% 28% 23% 10% 5%	527
	21st to end	Day	15% 8% 27% 28% 15% 8%	549
June	1st to 10th	Day	16% 7% 24% 29% 16% 8%	490
	11th to 20th	Day	12% 6% 24% 33% 17% 7%	609
	21st to end	Day	10% 7% 29% 30% 18% 6%	680
July	1st to 10th	Day	15% 4 18% 26% 20% 17%	671
	11th to 20th	Day	10% 4 23% 30% 23% 10%	520
	21st to end	Day	12% 3 21% 31% 22% 11%	532
August	1st to 10th	Day	12% 4 14% 32% 24% 14%	486
	11th to 20th	Day	11% 5% 21% 32% 21% 9%	479
	21st to end	Day	9% 4 16% 32% 26% 13%	539
September	1st to 10th	Day	14% 3 19% 29% 26% 9%	490
	11th to 20th	Day	11% 3 18% 27% 30% 12%	490
	21st to end	Day	21% 9% 21% 23% 20% 7%	490
October	1st to 10th	Day	12% 6% 27% 31% 19% 6%	490
	11th to 20th	Day	17% 13% 32% 22% 12% 3	490
	21st to end	Day	23% 11% 40% 19% 6%	418
November	1st to 10th	Day	16% 17% 35% 20% 8% 3	300
	11th to 20th	Day	22% 24% 30% 17% 5% 2	300
	21st to end	Day	27% 20% 35% 14% 3	300
December	1st to 10th	Day	27% 20% 34% 14% 5%	300
	11th to 20th	Day	22% 25% 38% 10% 4	300
	21st to end	Day	33% 18% 37% 11% 2 1	330
January	1st to 10th	Night	23% 22% 32% 19% 4	800
	11th to 20th	Night	29% 20% 32% 17% 3	800
	21st to end	Night	25% 18% 34% 20% 3	880
February	1st to 10th	Night	29% 14% 36% 20% 2	800
	11th to 20th	Night	27% 21% 31% 20% 1	783
	21st to end	Night	28% 17% 35% 18% 2	660
March	1st to 10th	Night	24% 20% 30% 21% 5%	800
	11th to 20th	Night	25% 16% 32% 21% 6% 1	800
	21st to end	Night	24% 13% 33% 23% 7%	880
April	1st to 10th	Night	22% 13% 34% 24% 7%	681
	11th to 20th	Night	20% 11% 33% 24% 11% 1	593
	21st to end	Night	18% 11% 38% 24% 9% 1	600
May	1st to 10th	Night	22% 9% 30% 27% 11% 1	600
	11th to 20th	Night	18% 6% 24% 31% 18% 2	591
	21st to end	Night	10% 3 24% 35% 22% 6%	634
June	1st to 10th	Night	11% 3 22% 39% 24% 2	570
	11th to 20th	Night	10% 3 16% 44% 25% 3	570
	21st to end	Night	7% 3 25% 38% 24% 3	570
July	1st to 10th	Night	15% 1 11% 32% 33% 9%	555
	11th to 20th	Night	8% 1 16% 34% 37% 3	552
	21st to end	Night	13% 2 11% 39% 31% 4	624
August	1st to 10th	Night	9% 2 10% 40% 36% 4	567
	11th to 20th	Night	10% 2 12% 41% 31% 5%	564
	21st to end	Night	7% 1 14% 34% 38% 7%	627
September	1st to 10th	Night	14% 3 13% 33% 31% 5%	683
	11th to 20th	Night	10% 3 15% 33% 33% 6%	760
	21st to end	Night	16% 6% 21% 32% 22% 3	760
October	1st to 10th	Night	11% 5% 23% 34% 23% 3	760
	11th to 20th	Night	18% 9% 28% 30% 14% 1	760
	21st to end	Night	23% 9% 34% 23% 11%	836
November	1st to 10th	Night	17% 12% 28% 26% 15% 2	780
	11th to 20th	Night	20% 17% 30% 23% 9% 1	800
	21st to end	Night	25% 13% 27% 27% 6% 1	800
December	1st to 10th	Night	27% 14% 32% 22% 5%	800
	11th to 20th	Night	26% 14% 32% 22% 5% 1	800
	21st to end	Night	31% 16% 30% 20% 3	880

Page generated at 2025-05-23 09:21:01. Version ac07

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