Fred Lossing Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fred Lossing Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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	16% 10% 3 9% 5% 5% 5% 4 5% 6% 32%	127180
	Night	16% 11% 4 9% 5% 5% 4 3 5% 6% 31%	122839
Transparency	Day	51% 5% 11% 21% 10% 1	130671
	Night	53% 5% 11% 19% 10% 1	127435
Seeing	Day	23% 16% 31% 20% 9% 3	15724
	Night	22% 13% 30% 25% 9% 1	24797

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	13% 15% 6% 13% 9% 6% 5% 3 5% 5% 21%	3597
	11th to 20th	Day	12% 15% 7% 14% 8% 5% 4 4 5% 5% 22%	3570
	21st to end	Day	11% 17% 8% 15% 7% 6% 4 3 4 4 20%	4208
February	1st to 10th	Day	14% 16% 5% 13% 8% 5% 4 4 4 5% 23%	1800
	11th to 20th	Day	11% 16% 5% 11% 7% 5% 4 4 5% 5% 28%	1753
	21st to end	Day	19% 13% 3 10% 6% 6% 5% 3 5% 4 25%	1635
March	1st to 10th	Day	18% 14% 5% 11% 6% 4 4 3 4 5% 26%	4540
	11th to 20th	Day	10% 13% 4 9% 6% 6% 5% 4 6% 6% 30%	4980
	21st to end	Day	16% 12% 4 8% 5% 4 3 3 4 5% 38%	5730
April	1st to 10th	Day	21% 12% 3 7% 5% 4 4 3 4 6% 31%	2400
	11th to 20th	Day	21% 11% 3 7% 4 4 4 3 4 5% 36%	2374
	21st to end	Day	22% 11% 3 7% 5% 5% 4 3 4 5% 33%	2536
May	1st to 10th	Day	23% 10% 3 8% 5% 4 5% 4 5% 6% 28%	6346
	11th to 20th	Day	15% 10% 3 9% 5% 5% 5% 4 5% 7% 31%	6318
	21st to end	Day	19% 8% 3 7% 4 5% 4 4 5% 6% 34%	6949
June	1st to 10th	Day	20% 9% 2 8% 5% 5% 5% 4 5% 6% 31%	2800
	11th to 20th	Day	14% 5% 3 6% 5% 5% 5% 4 7% 8% 39%	2800
	21st to end	Day	17% 8% 2 7% 6% 5% 5% 4 6% 8% 32%	2800
July	1st to 10th	Day	13% 6% 3 8% 5% 5% 5% 4 7% 9% 35%	6360
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 7% 8% 43%	6360
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 46%	6926
August	1st to 10th	Day	14% 7% 3 8% 5% 5% 4 4 6% 7% 37%	4436
	11th to 20th	Day	16% 6% 2 7% 4 4 5% 4 6% 8% 38%	4151
	21st to end	Day	12% 5% 2 6% 4 5% 5% 4 7% 9% 40%	4312
September	1st to 10th	Day	13% 5% 2 7% 5% 5% 4 3 6% 9% 41%	2400
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 6% 7% 47%	2400
	21st to end	Day	17% 6% 2 7% 5% 4 5% 4 4 7% 39%	2125
October	1st to 10th	Day	20% 7% 3 7% 5% 4 4 3 5% 6% 37%	2000
	11th to 20th	Day	20% 10% 3 8% 5% 4 5% 4 5% 7% 30%	2000
	21st to end	Day	24% 11% 2 8% 5% 5% 4 3 5% 5% 28%	2064
November	1st to 10th	Day	14% 10% 3 7% 5% 5% 5% 4 5% 7% 34%	1764
	11th to 20th	Day	17% 12% 4 8% 5% 6% 5% 4 5% 5% 29%	1600
	21st to end	Day	20% 15% 4 11% 7% 5% 5% 3 5% 6% 20%	1600
December	1st to 10th	Day	21% 19% 5% 13% 6% 5% 5% 3 5% 5% 13%	2600
	11th to 20th	Day	16% 17% 5% 12% 6% 4 5% 3 4 4 24%	2986
	21st to end	Day	22% 17% 5% 14% 5% 4 4 3 3 4 20%	3960
January	1st to 10th	Night	13% 18% 8% 14% 6% 5% 4 3 5% 5% 20%	6349
	11th to 20th	Night	11% 13% 6% 15% 9% 6% 5% 3 5% 5% 21%	6315
	21st to end	Night	13% 17% 6% 12% 7% 6% 5% 4 4 5% 20%	6743
February	1st to 10th	Night	12% 16% 6% 11% 8% 5% 4 4 4 6% 24%	2600
	11th to 20th	Night	13% 13% 5% 11% 8% 5% 4 3 5% 5% 28%	2533
	21st to end	Night	15% 13% 4 9% 7% 4 5% 4 5% 6% 28%	1995
March	1st to 10th	Night	21% 14% 5% 9% 5% 4 4 2 4 4 28%	5283
	11th to 20th	Night	10% 12% 4 8% 5% 5% 5% 5% 6% 8% 30%	4979
	21st to end	Night	17% 10% 4 9% 6% 4 4 3 5% 6% 33%	5202
April	1st to 10th	Night	20% 12% 3 7% 5% 4 3 3 4 6% 33%	2000
	11th to 20th	Night	19% 10% 3 8% 5% 4 3 3 4 5% 36%	1975
	21st to end	Night	20% 11% 4 5% 6% 4 4 3 4 6% 33%	1877
May	1st to 10th	Night	22% 10% 3 8% 5% 5% 5% 4 6% 7% 26%	3594
	11th to 20th	Night	14% 7% 3 6% 4 4 4 4 6% 7% 41%	3575
	21st to end	Night	17% 8% 3 7% 5% 4 5% 4 5% 7% 34%	3926
June	1st to 10th	Night	15% 7% 3 7% 5% 5% 5% 4 7% 7% 34%	1600
	11th to 20th	Night	12% 6% 3 7% 5% 3 4 4 5% 8% 43%	1600
	21st to end	Night	17% 7% 3 7% 5% 5% 5% 3 6% 7% 36%	1600
July	1st to 10th	Night	12% 6% 3 8% 6% 6% 5% 4 7% 8% 35%	3600
	11th to 20th	Night	12% 5% 2 6% 4 4 5% 3 6% 8% 44%	3600
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 4 5% 7% 47%	3926
August	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 4 6% 8% 42%	2710
	11th to 20th	Night	13% 6% 3 6% 4 5% 4 4 6% 7% 43%	2875
	21st to end	Night	12% 5% 3 6% 5% 4 5% 4 6% 8% 42%	3576
September	1st to 10th	Night	10% 6% 2 6% 4 5% 5% 3 5% 7% 48%	2000
	11th to 20th	Night	13% 5% 1 4 4 4 3 3 6% 6% 51%	2000
	21st to end	Night	15% 7% 2 6% 4 4 3 3 5% 6% 43%	2272
October	1st to 10th	Night	16% 8% 3 6% 4 4 4 4 5% 6% 40%	2400
	11th to 20th	Night	19% 9% 3 8% 5% 5% 5% 3 6% 6% 32%	2400
	21st to end	Night	21% 11% 3 7% 5% 4 5% 4 5% 7% 29%	2775
November	1st to 10th	Night	18% 11% 3 7% 5% 3 4 3 5% 5% 35%	2575
	11th to 20th	Night	17% 11% 3 9% 5% 4 5% 4 5% 6% 31%	2800
	21st to end	Night	19% 15% 4 10% 5% 5% 4 3 6% 6% 23%	2800
December	1st to 10th	Night	19% 17% 5% 12% 6% 5% 5% 4 5% 5% 15%	4580
	11th to 20th	Night	21% 15% 5% 11% 5% 5% 4 3 4 4 25%	5208
	21st to end	Night	26% 17% 4 11% 5% 4 3 2 4 4 20%	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	64% 7% 10% 13% 5% 1	3598
	11th to 20th	Day	65% 5% 10% 12% 8% 1	3600
	21st to end	Day	67% 5% 8% 11% 8% 1	4208
February	1st to 10th	Day	62% 5% 8% 17% 6% 1	1800
	11th to 20th	Day	58% 4 11% 16% 9% 1	1762
	21st to end	Day	60% 5% 10% 13% 10% 1	1635
March	1st to 10th	Day	61% 4 8% 12% 12% 2	4543
	11th to 20th	Day	53% 5% 15% 16% 10% 1	4980
	21st to end	Day	49% 4 5% 19% 19% 3	5730
April	1st to 10th	Day	54% 5% 6% 19% 14% 3	2400
	11th to 20th	Day	51% 4 6% 20% 16% 2	2374
	21st to end	Day	54% 4 7% 15% 15% 4	2536
May	1st to 10th	Day	57% 5% 8% 19% 10% 2	6357
	11th to 20th	Day	51% 7% 11% 19% 12% 1	6322
	21st to end	Day	50% 5% 12% 21% 11% 1	6949
June	1st to 10th	Day	53% 6% 9% 19% 13% 1	2800
	11th to 20th	Day	42% 7% 11% 25% 13% 2	2800
	21st to end	Day	49% 7% 11% 21% 11% 1	2800
July	1st to 10th	Day	45% 4 15% 26% 10%	6290
	11th to 20th	Day	37% 6% 13% 30% 14%	6285
	21st to end	Day	34% 5% 14% 36% 11%	6728
August	1st to 10th	Day	46% 5% 15% 24% 10%	4422
	11th to 20th	Day	43% 5% 13% 28% 9% 1	4190
	21st to end	Day	40% 5% 15% 28% 11% 1	4312
September	1st to 10th	Day	40% 7% 12% 30% 11%	2400
	11th to 20th	Day	34% 7% 12% 33% 14%	2400
	21st to end	Day	44% 6% 14% 25% 11%	2125
October	1st to 10th	Day	46% 4 10% 31% 8%	3260
	11th to 20th	Day	46% 5% 14% 24% 11% 1	3240
	21st to end	Day	49% 4 18% 21% 7%	3315
November	1st to 10th	Day	48% 7% 14% 23% 7% 1	1764
	11th to 20th	Day	55% 7% 11% 15% 10% 1	1600
	21st to end	Day	65% 6% 12% 10% 7% 1	1600
December	1st to 10th	Day	73% 5% 12% 9% 2	2600
	11th to 20th	Day	64% 6% 9% 14% 7%	2986
	21st to end	Day	70% 3 7% 15% 5%	3960
January	1st to 10th	Night	67% 5% 11% 13% 5%	6349
	11th to 20th	Night	64% 6% 10% 13% 6%	6360
	21st to end	Night	66% 5% 7% 10% 11% 1	6743
February	1st to 10th	Night	61% 5% 11% 16% 6% 1	2600
	11th to 20th	Night	57% 5% 11% 18% 8% 1	2535
	21st to end	Night	55% 6% 9% 19% 10% 1	1995
March	1st to 10th	Night	60% 5% 6% 15% 11% 3	5293
	11th to 20th	Night	50% 5% 17% 17% 8% 3	4980
	21st to end	Night	51% 4 7% 22% 13% 3	5202
April	1st to 10th	Night	54% 4 8% 18% 14% 2	2000
	11th to 20th	Night	51% 4 6% 22% 16% 1	1975
	21st to end	Night	52% 5% 7% 17% 16% 3	1877
May	1st to 10th	Night	56% 7% 8% 18% 8% 3	3600
	11th to 20th	Night	42% 7% 14% 21% 15% 1	3576
	21st to end	Night	48% 6% 13% 17% 14% 1	3927
June	1st to 10th	Night	46% 7% 11% 23% 11% 2	1600
	11th to 20th	Night	40% 6% 10% 25% 17% 2	1600
	21st to end	Night	46% 9% 11% 21% 13% 1	1600
July	1st to 10th	Night	46% 5% 16% 19% 13% 1	3560
	11th to 20th	Night	38% 5% 13% 32% 13%	3552
	21st to end	Night	35% 6% 12% 32% 15%	3809
August	1st to 10th	Night	40% 6% 14% 26% 13% 1	2700
	11th to 20th	Night	40% 5% 16% 30% 9% 1	2902
	21st to end	Night	39% 6% 15% 27% 12% 2	3576
September	1st to 10th	Night	37% 6% 12% 30% 15% 1	2000
	11th to 20th	Night	32% 7% 12% 36% 11% 1	2000
	21st to end	Night	41% 6% 12% 29% 12%	2272
October	1st to 10th	Night	39% 5% 12% 31% 13%	3920
	11th to 20th	Night	44% 6% 15% 25% 10%	3899
	21st to end	Night	49% 5% 17% 20% 8%	4474
November	1st to 10th	Night	51% 5% 13% 21% 9% 1	2575
	11th to 20th	Night	54% 6% 11% 18% 9% 1	2800
	21st to end	Night	61% 6% 12% 15% 5%	2800
December	1st to 10th	Night	69% 4 13% 11% 2	4580
	11th to 20th	Night	64% 4 8% 13% 10% 1	5208
	21st to end	Night	69% 4 5% 12% 9%	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	23% 23% 38% 13% 4	200
	11th to 20th	Day	29% 17% 37% 14% 4 1	200
	21st to end	Day	22% 22% 37% 15% 4	273
February	1st to 10th	Day	32% 24% 30% 12% 2	300
	11th to 20th	Day	28% 28% 36% 7% 1	300
	21st to end	Day	31% 22% 35% 11% 1	399
March	1st to 10th	Day	26% 22% 32% 16% 3	500
	11th to 20th	Day	28% 18% 37% 14% 3 1	500
	21st to end	Day	31% 22% 27% 13% 5% 1	550
April	1st to 10th	Day	32% 22% 28% 12% 5% 1	500
	11th to 20th	Day	34% 21% 21% 14% 9% 2	492
	21st to end	Day	29% 20% 31% 12% 6% 1	500
May	1st to 10th	Day	25% 15% 34% 19% 5% 2	503
	11th to 20th	Day	20% 16% 33% 21% 7% 2	527
	21st to end	Day	21% 13% 33% 20% 9% 2	573
June	1st to 10th	Day	23% 14% 33% 21% 8% 2	530
	11th to 20th	Day	17% 13% 34% 24% 11% 2	530
	21st to end	Day	21% 13% 32% 22% 10% 2	530
July	1st to 10th	Day	13% 7% 32% 32% 14% 3	525
	11th to 20th	Day	12% 11% 31% 29% 14% 4	524
	21st to end	Day	14% 9% 32% 30% 12% 3	576
August	1st to 10th	Day	14% 7% 28% 32% 15% 4	526
	11th to 20th	Day	13% 7% 28% 29% 17% 6%	519
	21st to end	Day	14% 11% 31% 25% 12% 7%	583
September	1st to 10th	Day	15% 13% 28% 23% 13% 8%	530
	11th to 20th	Day	10% 9% 25% 25% 21% 10%	530
	21st to end	Day	19% 13% 29% 21% 13% 5%	530
October	1st to 10th	Day	23% 15% 26% 22% 11% 4	530
	11th to 20th	Day	25% 20% 30% 18% 6% 1	530
	21st to end	Day	31% 18% 28% 19% 4 1	508
November	1st to 10th	Day	27% 18% 30% 18% 7% 1	386
	11th to 20th	Day	28% 25% 28% 14% 5% 2	200
	21st to end	Day	32% 23% 35% 8% 3	200
December	1st to 10th	Day	29% 17% 38% 14% 3	200
	11th to 20th	Day	34% 25% 30% 9% 3	200
	21st to end	Day	31% 20% 29% 15% 4 1	220
January	1st to 10th	Night	26% 18% 36% 17% 3	800
	11th to 20th	Night	28% 19% 29% 19% 5% 1	800
	21st to end	Night	20% 15% 35% 25% 5%	880
February	1st to 10th	Night	22% 19% 36% 21% 4	800
	11th to 20th	Night	20% 20% 39% 18% 3	783
	21st to end	Night	24% 21% 30% 21% 4	660
March	1st to 10th	Night	25% 17% 34% 20% 4	800
	11th to 20th	Night	24% 20% 31% 20% 5%	800
	21st to end	Night	24% 17% 29% 23% 7% 1	880
April	1st to 10th	Night	27% 16% 30% 24% 3	800
	11th to 20th	Night	25% 18% 29% 19% 8%	791
	21st to end	Night	25% 14% 29% 24% 7% 1	677
May	1st to 10th	Night	25% 8% 28% 29% 9% 1	400
	11th to 20th	Night	20% 11% 33% 27% 9% 1	394
	21st to end	Night	15% 9% 36% 27% 12%	433
June	1st to 10th	Night	18% 7% 33% 34% 9%	400
	11th to 20th	Night	16% 9% 30% 34% 11% 1	400
	21st to end	Night	20% 6% 31% 31% 12% 1	400
July	1st to 10th	Night	9% 6% 28% 42% 14% 1	390
	11th to 20th	Night	13% 4 27% 44% 11% 1	388
	21st to end	Night	10% 4 29% 44% 12% 1	438
August	1st to 10th	Night	10% 5% 26% 39% 20%	470
	11th to 20th	Night	12% 3 23% 36% 23% 3	594
	21st to end	Night	13% 7% 28% 32% 18% 2	870
September	1st to 10th	Night	15% 6% 31% 29% 17% 2	800
	11th to 20th	Night	16% 6% 21% 30% 23% 4	800
	21st to end	Night	19% 9% 26% 25% 20% 2	800
October	1st to 10th	Night	20% 10% 28% 25% 16% 1	800
	11th to 20th	Night	25% 13% 32% 22% 8% 1	800
	21st to end	Night	27% 15% 28% 24% 5%	880
November	1st to 10th	Night	27% 15% 28% 22% 7% 1	789
	11th to 20th	Night	25% 16% 33% 17% 8% 1	800
	21st to end	Night	31% 18% 26% 20% 5%	800
December	1st to 10th	Night	30% 16% 33% 17% 4	800
	11th to 20th	Night	29% 18% 29% 20% 4 1	800
	21st to end	Night	35% 15% 28% 18% 4	880

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