Fleischmanns Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fleischmanns Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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% 12% 4 11% 6% 5% 5% 4 5% 6% 28%	131411
	Night	13% 13% 5% 12% 6% 5% 4 3 4 6% 28%	130409
Transparency	Day	53% 5% 10% 20% 11% 2	134900
	Night	55% 4 11% 18% 11% 2	134994
Seeing	Day	27% 21% 28% 15% 6% 2	16543
	Night	26% 21% 24% 19% 8% 1	25796

By Month

Percentage Cloud Cover NE (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	9% 15% 9% 24% 10% 4 3 2 3 4 16%	4661
	11th to 20th	Day	8% 15% 7% 19% 9% 7% 5% 3 4 4 17%	4650
	21st to end	Day	13% 13% 7% 10% 8% 6% 5% 4 5% 5% 25%	5500
February	1st to 10th	Day	11% 13% 6% 15% 9% 6% 5% 4 4 5% 22%	1890
	11th to 20th	Day	9% 12% 7% 14% 8% 5% 5% 4 5% 6% 24%	1991
	21st to end	Day	14% 16% 3 12% 8% 5% 4 3 5% 5% 26%	1730
March	1st to 10th	Day	16% 17% 6% 11% 5% 4 4 3 3 4 27%	4576
	11th to 20th	Day	11% 14% 7% 10% 5% 4 4 3 3 5% 34%	4942
	21st to end	Day	16% 11% 4 11% 5% 5% 4 3 5% 6% 30%	6008
April	1st to 10th	Day	15% 18% 4 9% 5% 4 4 3 4 5% 28%	2412
	11th to 20th	Day	13% 14% 4 8% 5% 4 5% 4 5% 6% 32%	2374
	21st to end	Day	17% 15% 4 8% 4 4 4 2 4 6% 32%	2435
May	1st to 10th	Day	26% 14% 4 8% 5% 4 4 3 5% 6% 23%	6065
	11th to 20th	Day	16% 11% 4 9% 5% 5% 6% 4 6% 6% 28%	6318
	21st to end	Day	20% 10% 3 8% 5% 5% 5% 5% 6% 7% 27%	6949
June	1st to 10th	Day	16% 9% 3 8% 6% 5% 6% 4 7% 7% 29%	2800
	11th to 20th	Day	15% 9% 3 7% 6% 5% 6% 6% 6% 10% 28%	2800
	21st to end	Day	16% 9% 3 9% 5% 5% 5% 5% 6% 8% 30%	2800
July	1st to 10th	Day	9% 7% 3 10% 6% 6% 6% 5% 7% 8% 32%	6360
	11th to 20th	Day	8% 6% 3 9% 6% 7% 7% 6% 9% 10% 30%	6360
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 5% 6% 7% 37%	6926
August	1st to 10th	Day	17% 8% 4 10% 6% 5% 5% 4 6% 8% 28%	4415
	11th to 20th	Day	12% 8% 3 9% 6% 6% 7% 6% 8% 8% 28%	3883
	21st to end	Day	12% 8% 3 8% 4 5% 5% 5% 7% 8% 34%	4312
September	1st to 10th	Day	14% 7% 2 8% 5% 4 5% 4 6% 7% 39%	2400
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 5% 8% 43%	2339
	21st to end	Day	15% 8% 3 7% 5% 4 5% 5% 5% 7% 36%	2200
October	1st to 10th	Day	16% 11% 4 8% 6% 4 4 3 5% 6% 33%	2041
	11th to 20th	Day	13% 13% 3 7% 4 5% 5% 3 6% 5% 35%	2000
	21st to end	Day	18% 17% 4 9% 4 4 4 3 5% 5% 27%	2038
November	1st to 10th	Day	12% 14% 4 8% 4 5% 3 3 6% 6% 37%	1851
	11th to 20th	Day	12% 17% 5% 11% 6% 5% 4 3 4 4 30%	1890
	21st to end	Day	14% 18% 6% 11% 6% 3 4 3 4 6% 25%	1701
December	1st to 10th	Day	9% 16% 7% 23% 8% 6% 4 3 4 5% 15%	2680
	11th to 20th	Day	13% 16% 8% 14% 6% 4 4 3 4 4 25%	3066
	21st to end	Day	11% 15% 6% 16% 8% 5% 4 3 6% 6% 21%	4048
January	1st to 10th	Night	10% 15% 7% 24% 9% 5% 4 3 3 4 16%	8234
	11th to 20th	Night	7% 16% 10% 24% 10% 6% 5% 3 4 3 13%	8235
	21st to end	Night	10% 11% 5% 12% 9% 11% 8% 4 4 5% 22%	8663
February	1st to 10th	Night	11% 14% 5% 13% 8% 7% 6% 4 5% 6% 22%	2730
	11th to 20th	Night	9% 12% 7% 15% 9% 7% 5% 5% 5% 5% 22%	2515
	21st to end	Night	15% 13% 5% 12% 7% 4 4 4 5% 6% 25%	2076
March	1st to 10th	Night	13% 12% 5% 13% 8% 5% 4 3 5% 5% 27%	5484
	11th to 20th	Night	11% 14% 8% 10% 6% 4 4 3 4 6% 31%	5234
	21st to end	Night	15% 13% 6% 11% 5% 4 4 3 4 5% 30%	5166
April	1st to 10th	Night	13% 16% 5% 11% 6% 5% 5% 4 5% 6% 25%	2011
	11th to 20th	Night	16% 14% 4 6% 5% 4 4 3 5% 6% 34%	1975
	21st to end	Night	18% 13% 5% 7% 4 4 5% 3 4 5% 34%	1965
May	1st to 10th	Night	29% 14% 3 7% 4 4 3 2 4 6% 24%	3916
	11th to 20th	Night	17% 15% 4 8% 5% 4 4 3 5% 6% 29%	3575
	21st to end	Night	21% 13% 3 7% 4 4 4 4 5% 7% 28%	3926
June	1st to 10th	Night	15% 9% 3 7% 5% 4 5% 3 6% 6% 38%	1600
	11th to 20th	Night	16% 9% 2 6% 4 4 3 3 7% 8% 37%	1600
	21st to end	Night	12% 7% 2 6% 5% 4 5% 5% 6% 8% 40%	1600
July	1st to 10th	Night	10% 8% 3 9% 5% 5% 5% 4 6% 8% 38%	3600
	11th to 20th	Night	12% 7% 4 8% 5% 5% 5% 4 6% 9% 36%	3600
	21st to end	Night	12% 8% 3 6% 5% 4 4 4 5% 6% 43%	3926
August	1st to 10th	Night	21% 10% 3 8% 4 4 5% 3 5% 6% 31%	2717
	11th to 20th	Night	15% 8% 3 9% 5% 4 4 4 5% 6% 38%	3131
	21st to end	Night	11% 11% 3 7% 4 4 3 3 5% 7% 43%	3586
September	1st to 10th	Night	14% 8% 2 7% 4 4 4 4 5% 7% 43%	2000
	11th to 20th	Night	13% 7% 2 5% 3 3 4 2 5% 7% 50%	2060
	21st to end	Night	15% 9% 3 8% 5% 5% 4 3 5% 5% 39%	2200
October	1st to 10th	Night	16% 11% 3 8% 5% 4 4 3 5% 5% 36%	2355
	11th to 20th	Night	15% 11% 3 7% 4 4 4 3 4 7% 37%	2400
	21st to end	Night	18% 15% 4 8% 5% 4 5% 3 5% 6% 28%	2800
November	1st to 10th	Night	11% 14% 4 8% 4 4 5% 3 5% 5% 37%	2667
	11th to 20th	Night	14% 17% 5% 10% 5% 4 4 3 5% 6% 28%	2730
	21st to end	Night	11% 16% 6% 10% 6% 5% 5% 3 5% 6% 27%	2914
December	1st to 10th	Night	10% 16% 8% 19% 7% 5% 5% 4 5% 5% 16%	4720
	11th to 20th	Night	17% 16% 7% 12% 6% 4 3 3 3 3 27%	5348
	21st to end	Night	13% 17% 7% 17% 7% 5% 3 3 3 4 21%	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	66% 3 8% 16% 5% 1	4662
	11th to 20th	Day	65% 3 8% 12% 9% 2	4680
	21st to end	Day	55% 3 9% 21% 10% 1	5500
February	1st to 10th	Day	60% 3 9% 17% 10% 1	1890
	11th to 20th	Day	55% 4 7% 20% 12% 2	2000
	21st to end	Day	57% 3 10% 19% 10% 1	1730
March	1st to 10th	Day	59% 2 11% 14% 10% 4	4579
	11th to 20th	Day	53% 2 11% 23% 7% 4	4942
	21st to end	Day	55% 4 6% 12% 19% 4	6008
April	1st to 10th	Day	58% 3 7% 19% 11% 2	2412
	11th to 20th	Day	53% 3 10% 20% 13% 2	2374
	21st to end	Day	56% 3 8% 18% 12% 3	2435
May	1st to 10th	Day	63% 4 8% 14% 9% 1	6076
	11th to 20th	Day	56% 5% 10% 20% 9% 1	6322
	21st to end	Day	56% 5% 10% 20% 9% 1	6949
June	1st to 10th	Day	53% 4 12% 20% 11%	2800
	11th to 20th	Day	52% 5% 14% 20% 9% 1	2800
	21st to end	Day	51% 5% 12% 22% 10%	2800
July	1st to 10th	Day	47% 7% 14% 21% 10% 1	6290
	11th to 20th	Day	43% 9% 14% 23% 10%	6285
	21st to end	Day	44% 5% 12% 25% 13%	6728
August	1st to 10th	Day	53% 5% 13% 19% 9% 1	4401
	11th to 20th	Day	48% 7% 15% 24% 5%	3920
	21st to end	Day	44% 5% 13% 29% 9% 1	4312
September	1st to 10th	Day	45% 4 10% 26% 14% 1	2400
	11th to 20th	Day	40% 4 10% 24% 21% 1	2339
	21st to end	Day	47% 4 10% 20% 15% 2	2200
October	1st to 10th	Day	49% 3 9% 20% 16% 2	3327
	11th to 20th	Day	43% 3 9% 22% 17% 6%	3240
	21st to end	Day	41% 4 14% 23% 14% 3	3263
November	1st to 10th	Day	46% 4 12% 22% 15% 3	1851
	11th to 20th	Day	57% 2 8% 17% 14% 3	1890
	21st to end	Day	59% 3 11% 19% 6% 1	1701
December	1st to 10th	Day	64% 8% 8% 13% 5% 1	2680
	11th to 20th	Day	58% 5% 10% 15% 11% 1	3066
	21st to end	Day	60% 5% 7% 13% 12% 3	4048
January	1st to 10th	Night	67% 3 7% 15% 7% 1	8234
	11th to 20th	Night	71% 4 9% 9% 6% 2	8280
	21st to end	Night	60% 3 11% 13% 11% 1	8663
February	1st to 10th	Night	57% 4 11% 17% 10% 1	2730
	11th to 20th	Night	58% 4 10% 15% 12% 1	2517
	21st to end	Night	56% 3 9% 20% 9% 2	2076
March	1st to 10th	Night	57% 2 12% 16% 11% 2	5494
	11th to 20th	Night	53% 3 16% 18% 8% 3	5235
	21st to end	Night	56% 4 5% 14% 19% 2	5166
April	1st to 10th	Night	59% 4 9% 17% 10% 1	2011
	11th to 20th	Night	52% 4 11% 20% 14%	1975
	21st to end	Night	52% 4 8% 21% 13% 2	1965
May	1st to 10th	Night	62% 4 9% 14% 8% 3	3922
	11th to 20th	Night	57% 5% 9% 20% 8% 1	3576
	21st to end	Night	55% 5% 11% 19% 10%	3927
June	1st to 10th	Night	47% 4 11% 25% 13% 1	1600
	11th to 20th	Night	46% 5% 16% 24% 9%	1600
	21st to end	Night	40% 7% 17% 25% 12% 1	1600
July	1st to 10th	Night	43% 6% 16% 21% 13% 1	3560
	11th to 20th	Night	43% 8% 14% 23% 10% 1	3552
	21st to end	Night	41% 4 13% 28% 12% 1	3809
August	1st to 10th	Night	54% 5% 14% 21% 7% 1	2707
	11th to 20th	Night	44% 6% 16% 25% 9%	3160
	21st to end	Night	40% 5% 12% 32% 10% 1	3586
September	1st to 10th	Night	41% 5% 12% 27% 14% 1	2000
	11th to 20th	Night	36% 3 10% 27% 23% 1	2060
	21st to end	Night	48% 3 9% 23% 16% 2	2200
October	1st to 10th	Night	51% 5% 10% 21% 12% 1	3849
	11th to 20th	Night	42% 4 12% 19% 18% 6%	3899
	21st to end	Night	43% 5% 15% 24% 11% 2	4512
November	1st to 10th	Night	48% 4 9% 20% 16% 3	2667
	11th to 20th	Night	54% 3 9% 18% 12% 3	2730
	21st to end	Night	54% 4 12% 22% 7% 1	2914
December	1st to 10th	Night	63% 7% 9% 17% 4	4720
	11th to 20th	Night	60% 3 10% 12% 13% 1	5348
	21st to end	Night	64% 2 7% 12% 11% 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	37% 29% 25% 7% 1	220
	11th to 20th	Day	42% 27% 23% 7% 1	220
	21st to end	Day	37% 32% 22% 8% 2	311
February	1st to 10th	Day	42% 32% 22% 4	330
	11th to 20th	Day	43% 31% 19% 7% 1	479
	21st to end	Day	39% 31% 22% 7% 2	446
March	1st to 10th	Day	35% 26% 29% 9% 2	540
	11th to 20th	Day	37% 27% 24% 9% 3 1	540
	21st to end	Day	39% 28% 20% 7% 3 2	594
April	1st to 10th	Day	40% 26% 18% 11% 4 1	504
	11th to 20th	Day	36% 25% 22% 10% 5% 2	492
	21st to end	Day	33% 26% 27% 8% 4 2	500
May	1st to 10th	Day	36% 22% 27% 7% 5% 2	503
	11th to 20th	Day	24% 21% 33% 15% 5% 2	527
	21st to end	Day	20% 15% 35% 18% 10% 3	573
June	1st to 10th	Day	23% 19% 31% 19% 7% 2	530
	11th to 20th	Day	18% 20% 32% 20% 8% 2	530
	21st to end	Day	22% 18% 34% 18% 7% 1	530
July	1st to 10th	Day	15% 12% 38% 22% 11% 3	525
	11th to 20th	Day	11% 11% 38% 27% 9% 3	524
	21st to end	Day	16% 16% 39% 19% 8% 2	576
August	1st to 10th	Day	9% 17% 32% 25% 12% 6%	526
	11th to 20th	Day	16% 12% 32% 22% 10% 7%	519
	21st to end	Day	15% 16% 30% 21% 11% 6%	583
September	1st to 10th	Day	21% 13% 26% 22% 12% 6%	530
	11th to 20th	Day	13% 15% 27% 20% 14% 11%	530
	21st to end	Day	22% 16% 28% 20% 8% 5%	530
October	1st to 10th	Day	24% 17% 25% 20% 10% 4	530
	11th to 20th	Day	29% 20% 26% 16% 7% 1	530
	21st to end	Day	28% 25% 28% 13% 4 1	493
November	1st to 10th	Day	29% 22% 26% 15% 7% 1	425
	11th to 20th	Day	36% 23% 24% 11% 5% 1	430
	21st to end	Day	41% 26% 24% 10%	241
December	1st to 10th	Day	38% 31% 20% 7% 3	220
	11th to 20th	Day	44% 26% 23% 5% 2	220
	21st to end	Day	38% 26% 27% 7% 3	242
January	1st to 10th	Night	30% 32% 26% 10% 2	840
	11th to 20th	Night	32% 26% 25% 15% 2	840
	21st to end	Night	27% 31% 26% 14% 2	924
February	1st to 10th	Night	32% 28% 28% 12% 1	840
	11th to 20th	Night	31% 31% 26% 11% 1	823
	21st to end	Night	35% 26% 25% 13% 2	692
March	1st to 10th	Night	33% 26% 26% 12% 3	840
	11th to 20th	Night	32% 27% 23% 15% 3	840
	21st to end	Night	29% 27% 24% 15% 4 1	924
April	1st to 10th	Night	29% 27% 25% 16% 4	805
	11th to 20th	Night	29% 24% 25% 16% 6% 1	791
	21st to end	Night	28% 21% 24% 19% 8%	765
May	1st to 10th	Night	32% 17% 24% 19% 8% 1	540
	11th to 20th	Night	21% 20% 25% 29% 5% 1	394
	21st to end	Night	18% 12% 27% 27% 14% 1	433
June	1st to 10th	Night	19% 14% 25% 29% 13%	400
	11th to 20th	Night	21% 11% 22% 32% 13% 1	400
	21st to end	Night	17% 10% 26% 35% 12% 1	400
July	1st to 10th	Night	14% 10% 24% 36% 15% 2	390
	11th to 20th	Night	14% 8% 24% 35% 18% 1	388
	21st to end	Night	13% 9% 25% 36% 16% 1	438
August	1st to 10th	Night	12% 5% 27% 31% 23% 1	477
	11th to 20th	Night	17% 7% 20% 32% 21% 3	748
	21st to end	Night	17% 11% 20% 30% 20% 1	880
September	1st to 10th	Night	17% 10% 27% 26% 18% 3	800
	11th to 20th	Night	17% 11% 21% 24% 20% 7%	800
	21st to end	Night	20% 12% 24% 25% 16% 2	800
October	1st to 10th	Night	25% 16% 19% 22% 16% 2	800
	11th to 20th	Night	26% 18% 25% 22% 9% 1	800
	21st to end	Night	29% 25% 23% 18% 4	880
November	1st to 10th	Night	24% 24% 25% 19% 7%	820
	11th to 20th	Night	31% 25% 21% 14% 7% 2	840
	21st to end	Night	28% 27% 24% 16% 4 1	840
December	1st to 10th	Night	33% 28% 23% 12% 4	840
	11th to 20th	Night	34% 25% 26% 13% 2	840
	21st to end	Night	32% 31% 21% 13% 3	924

Page generated at 2026-03-30 02:18:45. Version ac07

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