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 2024-01-16.

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	17% 9% 4 7% 6% 3 5% 5% 5% 6% 33%	74746
	Night	17% 10% 4 7% 6% 3 4 4 5% 6% 32%	75039
Transparency	Day	51% 6% 11% 20% 11% 1	74451
	Night	52% 6% 11% 20% 10% 1	74868
Seeing	Day	23% 16% 30% 20% 9% 3	13349
	Night	23% 13% 30% 24% 9% 1	22603

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	14% 16% 7% 11% 8% 4 4 4 5% 5% 22%	1517
	11th to 20th	Day	18% 14% 7% 10% 7% 5% 4 4 3 3 24%	1480
	21st to end	Day	13% 13% 5% 10% 9% 5% 6% 5% 5% 5% 24%	1678
February	1st to 10th	Day	15% 14% 6% 13% 8% 4 5% 5% 4 5% 22%	1620
	11th to 20th	Day	12% 15% 5% 10% 7% 4 5% 4 4 5% 29%	1573
	21st to end	Day	19% 13% 4 9% 8% 4 5% 5% 5% 5% 24%	1466
March	1st to 10th	Day	15% 12% 5% 10% 7% 4 5% 4 4 5% 29%	1819
	11th to 20th	Day	15% 12% 5% 7% 7% 4 5% 5% 4 4 31%	1980
	21st to end	Day	18% 11% 4 6% 5% 3 3 4 4 5% 37%	2276
April	1st to 10th	Day	22% 11% 4 6% 6% 2 4 4 4 6% 31%	2160
	11th to 20th	Day	21% 9% 3 6% 4 3 4 4 4 5% 37%	2134
	21st to end	Day	22% 10% 4 6% 6% 3 4 4 4 6% 32%	2280
May	1st to 10th	Day	20% 8% 3 6% 6% 3 5% 4 5% 6% 34%	2520
	11th to 20th	Day	16% 8% 3 6% 5% 2 4 4 5% 6% 39%	2478
	21st to end	Day	15% 6% 3 6% 5% 4 5% 5% 5% 7% 38%	2725
June	1st to 10th	Day	21% 7% 3 7% 6% 4 6% 5% 5% 6% 31%	2520
	11th to 20th	Day	15% 5% 3 5% 5% 3 5% 6% 6% 8% 38%	2520
	21st to end	Day	17% 7% 3 7% 7% 4 6% 5% 5% 8% 32%	2520
July	1st to 10th	Day	10% 6% 3 5% 6% 3 6% 6% 6% 9% 40%	2520
	11th to 20th	Day	11% 5% 3 5% 5% 3 5% 5% 7% 10% 39%	2520
	21st to end	Day	12% 5% 2 5% 5% 3 6% 6% 8% 9% 38%	2744
August	1st to 10th	Day	11% 6% 3 6% 7% 4 5% 5% 6% 8% 40%	2439
	11th to 20th	Day	12% 5% 2 7% 6% 4 6% 6% 6% 8% 39%	2295
	21st to end	Day	14% 6% 3 5% 5% 4 5% 5% 6% 9% 39%	2376
September	1st to 10th	Day	14% 5% 3 6% 6% 4 5% 4 6% 8% 41%	2160
	11th to 20th	Day	13% 4 2 5% 5% 3 4 6% 6% 7% 44%	2160
	21st to end	Day	17% 6% 2 6% 6% 3 4 5% 4 7% 39%	1913
October	1st to 10th	Day	21% 7% 3 6% 6% 3 4 4 5% 6% 36%	1800
	11th to 20th	Day	22% 9% 3 7% 7% 3 5% 5% 5% 7% 27%	1800
	21st to end	Day	26% 11% 3 7% 6% 3 4 4 4 5% 27%	1858
November	1st to 10th	Day	14% 9% 4 7% 5% 3 6% 6% 5% 7% 34%	1657
	11th to 20th	Day	18% 11% 5% 7% 6% 4 5% 5% 5% 5% 28%	1520
	21st to end	Day	20% 14% 5% 9% 8% 4 5% 3 5% 6% 21%	1520
December	1st to 10th	Day	21% 17% 6% 10% 7% 4 5% 5% 5% 5% 16%	1520
	11th to 20th	Day	20% 14% 4 8% 6% 3 5% 4 4 6% 25%	1906
	21st to end	Day	27% 17% 5% 13% 6% 2 3 3 3 3 19%	2772
January	1st to 10th	Night	17% 14% 7% 10% 8% 4 6% 4 5% 5% 19%	2649
	11th to 20th	Night	16% 16% 6% 11% 8% 3 5% 4 4 4 22%	2591
	21st to end	Night	12% 14% 6% 9% 8% 3 4 5% 5% 6% 29%	2673
February	1st to 10th	Night	14% 15% 6% 10% 9% 3 5% 5% 5% 6% 22%	2340
	11th to 20th	Night	14% 12% 6% 9% 8% 4 4 4 5% 5% 30%	2273
	21st to end	Night	16% 12% 4 8% 8% 3 4 5% 5% 6% 29%	1790
March	1st to 10th	Night	16% 12% 5% 9% 7% 3 5% 3 5% 5% 29%	2125
	11th to 20th	Night	14% 13% 5% 7% 5% 3 5% 4 4 5% 34%	1979
	21st to end	Night	16% 8% 3 7% 6% 3 4 4 5% 5% 38%	2080
April	1st to 10th	Night	20% 11% 4 6% 6% 2 3 4 4 6% 35%	1800
	11th to 20th	Night	19% 9% 3 6% 6% 3 4 3 4 6% 36%	1775
	21st to end	Night	20% 11% 4 5% 7% 3 4 4 5% 6% 31%	1691
May	1st to 10th	Night	20% 8% 2 6% 4 3 4 4 5% 6% 37%	1440
	11th to 20th	Night	17% 7% 3 6% 5% 2 4 4 5% 6% 41%	1415
	21st to end	Night	13% 5% 3 5% 5% 3 5% 4 6% 7% 45%	1550
June	1st to 10th	Night	16% 6% 3 6% 6% 3 6% 5% 7% 8% 34%	1440
	11th to 20th	Night	13% 6% 3 6% 6% 3 5% 4 5% 7% 43%	1440
	21st to end	Night	15% 7% 3 6% 5% 4 5% 4 6% 8% 37%	1440
July	1st to 10th	Night	9% 5% 3 5% 6% 3 5% 5% 6% 7% 45%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 3 5% 5% 7% 9% 43%	1440
	21st to end	Night	9% 4 2 5% 6% 4 5% 6% 6% 9% 45%	1574
August	1st to 10th	Night	8% 5% 3 6% 7% 3 5% 5% 6% 9% 43%	1496
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 5% 6% 7% 47%	1598
	21st to end	Night	11% 5% 3 5% 5% 3 4 5% 6% 8% 45%	1970
September	1st to 10th	Night	11% 6% 2 5% 5% 4 5% 4 5% 7% 46%	1800
	11th to 20th	Night	14% 5% 2 3 4 3 4 4 5% 6% 49%	1800
	21st to end	Night	15% 7% 3 5% 5% 3 4 4 5% 7% 43%	2044
October	1st to 10th	Night	18% 8% 3 6% 6% 3 4 5% 5% 6% 37%	2160
	11th to 20th	Night	20% 9% 3 7% 6% 4 4 4 6% 6% 31%	2160
	21st to end	Night	22% 11% 4 6% 6% 3 4 5% 5% 6% 28%	2497
November	1st to 10th	Night	18% 10% 4 7% 5% 2 4 4 5% 5% 36%	2417
	11th to 20th	Night	18% 10% 3 7% 7% 4 5% 5% 5% 6% 30%	2660
	21st to end	Night	20% 13% 4 9% 7% 3 4 4 5% 6% 23%	2660
December	1st to 10th	Night	19% 18% 5% 10% 7% 3 5% 5% 5% 5% 18%	2660
	11th to 20th	Night	21% 14% 5% 10% 6% 3 4 4 4 4 26%	3288
	21st to end	Night	29% 16% 5% 11% 6% 3 3 3 3 4 17%	4884

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% 6% 11% 13% 6%	1518
	11th to 20th	Day	66% 5% 7% 11% 10% 1	1480
	21st to end	Day	62% 5% 10% 13% 9% 1	1678
February	1st to 10th	Day	64% 5% 9% 16% 5% 1	1620
	11th to 20th	Day	57% 4 12% 16% 10% 1	1582
	21st to end	Day	61% 5% 10% 13% 10% 1	1466
March	1st to 10th	Day	57% 5% 10% 16% 10% 1	1822
	11th to 20th	Day	56% 4 10% 15% 12% 3	1980
	21st to end	Day	50% 4 8% 18% 14% 6%	2276
April	1st to 10th	Day	54% 5% 6% 19% 13% 3	2160
	11th to 20th	Day	50% 5% 7% 21% 16% 2	2134
	21st to end	Day	55% 4 8% 15% 15% 4	2280
May	1st to 10th	Day	50% 5% 8% 18% 15% 3	2520
	11th to 20th	Day	45% 6% 7% 22% 17% 2	2482
	21st to end	Day	44% 7% 12% 21% 13% 3	2725
June	1st to 10th	Day	53% 7% 9% 18% 12% 1	2520
	11th to 20th	Day	42% 8% 10% 25% 13% 3	2520
	21st to end	Day	50% 8% 11% 20% 11% 1	2520
July	1st to 10th	Day	37% 8% 13% 27% 15% 1	2450
	11th to 20th	Day	37% 10% 15% 26% 11% 1	2445
	21st to end	Day	39% 8% 14% 27% 11%	2591
August	1st to 10th	Day	41% 8% 14% 26% 10%	2425
	11th to 20th	Day	41% 8% 14% 26% 10% 1	2295
	21st to end	Day	40% 7% 14% 26% 12% 1	2376
September	1st to 10th	Day	40% 7% 12% 29% 11%	2160
	11th to 20th	Day	36% 8% 12% 31% 13%	2160
	21st to end	Day	44% 7% 13% 27% 9%	1913
October	1st to 10th	Day	49% 6% 11% 23% 10% 1	1800
	11th to 20th	Day	56% 8% 13% 17% 6% 1	1800
	21st to end	Day	60% 5% 11% 15% 8% 1	1858
November	1st to 10th	Day	48% 7% 14% 23% 7% 1	1657
	11th to 20th	Day	56% 7% 12% 14% 10% 1	1520
	21st to end	Day	64% 7% 12% 10% 7% 1	1520
December	1st to 10th	Day	68% 7% 11% 10% 3 1	1520
	11th to 20th	Day	62% 7% 12% 12% 6%	1906
	21st to end	Day	73% 4 6% 14% 3	2772
January	1st to 10th	Night	66% 6% 10% 12% 6%	2649
	11th to 20th	Night	66% 5% 9% 12% 8% 1	2591
	21st to end	Night	56% 6% 8% 18% 11% 1	2673
February	1st to 10th	Night	63% 4 11% 15% 6% 1	2340
	11th to 20th	Night	56% 5% 11% 19% 8% 1	2275
	21st to end	Night	55% 6% 9% 19% 10%	1790
March	1st to 10th	Night	56% 6% 10% 17% 10% 1	2135
	11th to 20th	Night	52% 4 11% 19% 12% 2	1980
	21st to end	Night	48% 5% 8% 20% 15% 4	2080
April	1st to 10th	Night	53% 4 9% 18% 15% 2	1800
	11th to 20th	Night	51% 4 7% 22% 16% 2	1775
	21st to end	Night	53% 6% 7% 15% 16% 3	1691
May	1st to 10th	Night	48% 6% 7% 19% 15% 5%	1440
	11th to 20th	Night	44% 6% 7% 23% 17% 3	1416
	21st to end	Night	37% 7% 15% 19% 19% 2	1551
June	1st to 10th	Night	46% 8% 12% 23% 11% 2	1440
	11th to 20th	Night	40% 7% 10% 23% 17% 2	1440
	21st to end	Night	44% 9% 12% 21% 13% 1	1440
July	1st to 10th	Night	34% 8% 12% 26% 17% 3	1400
	11th to 20th	Night	37% 8% 11% 31% 13%	1392
	21st to end	Night	34% 10% 15% 26% 14%	1486
August	1st to 10th	Night	38% 8% 17% 23% 13% 1	1486
	11th to 20th	Night	35% 7% 16% 30% 11% 1	1598
	21st to end	Night	37% 7% 14% 29% 12%	1970
September	1st to 10th	Night	38% 7% 12% 28% 15% 1	1800
	11th to 20th	Night	34% 7% 13% 34% 10% 2	1800
	21st to end	Night	41% 6% 12% 31% 9% 1	2044
October	1st to 10th	Night	46% 6% 10% 22% 14% 1	2160
	11th to 20th	Night	52% 7% 12% 20% 8%	2160
	21st to end	Night	57% 6% 13% 15% 9%	2497
November	1st to 10th	Night	50% 5% 14% 21% 9% 1	2417
	11th to 20th	Night	54% 6% 12% 18% 9% 1	2660
	21st to end	Night	60% 7% 13% 15% 5%	2660
December	1st to 10th	Night	68% 6% 10% 13% 4	2660
	11th to 20th	Night	62% 5% 10% 15% 8% 1	3288
	21st to end	Night	73% 5% 6% 12% 3	4884

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% 35% 14% 4	180
	11th to 20th	Day	32% 16% 34% 13% 4	170
	21st to end	Day	22% 22% 38% 15% 4	218
February	1st to 10th	Day	33% 28% 29% 10%	240
	11th to 20th	Day	29% 27% 38% 6% 1	240
	21st to end	Day	32% 22% 33% 12% 2	332
March	1st to 10th	Day	25% 21% 33% 17% 3	420
	11th to 20th	Day	28% 17% 37% 14% 3 1	420
	21st to end	Day	32% 21% 26% 14% 6% 1	462
April	1st to 10th	Day	30% 21% 29% 12% 6% 1	420
	11th to 20th	Day	32% 20% 21% 16% 9% 2	412
	21st to end	Day	30% 20% 29% 13% 7% 1	420
May	1st to 10th	Day	26% 14% 32% 19% 5% 2	423
	11th to 20th	Day	21% 17% 33% 20% 6% 3	447
	21st to end	Day	19% 14% 36% 19% 10% 3	485
June	1st to 10th	Day	25% 13% 32% 20% 8% 2	450
	11th to 20th	Day	18% 12% 33% 24% 11% 3	450
	21st to end	Day	20% 12% 31% 24% 11% 2	450
July	1st to 10th	Day	12% 7% 29% 35% 14% 4	445
	11th to 20th	Day	12% 11% 30% 28% 15% 5%	444
	21st to end	Day	16% 8% 31% 30% 12% 3	488
August	1st to 10th	Day	14% 7% 29% 30% 16% 4	446
	11th to 20th	Day	11% 7% 29% 29% 18% 7%	439
	21st to end	Day	14% 11% 30% 25% 12% 8%	495
September	1st to 10th	Day	15% 12% 28% 23% 13% 8%	450
	11th to 20th	Day	12% 11% 27% 24% 18% 8%	450
	21st to end	Day	18% 14% 29% 20% 13% 6%	450
October	1st to 10th	Day	24% 14% 26% 20% 11% 4	450
	11th to 20th	Day	26% 21% 27% 19% 6% 1	450
	21st to end	Day	32% 17% 26% 20% 4 1	434
November	1st to 10th	Day	26% 17% 30% 19% 7% 1	351
	11th to 20th	Day	29% 24% 29% 13% 4 2	180
	21st to end	Day	29% 23% 36% 9% 3	180
December	1st to 10th	Day	29% 17% 39% 13% 2	180
	11th to 20th	Day	33% 25% 30% 10% 2	180
	21st to end	Day	32% 22% 29% 13% 4 1	198
January	1st to 10th	Night	26% 18% 35% 18% 3	760
	11th to 20th	Night	29% 18% 29% 18% 5% 1	741
	21st to end	Night	19% 15% 35% 26% 5%	792
February	1st to 10th	Night	23% 18% 36% 19% 3	720
	11th to 20th	Night	21% 19% 39% 18% 3	703
	21st to end	Night	24% 21% 30% 20% 4	592
March	1st to 10th	Night	23% 17% 34% 22% 4	720
	11th to 20th	Night	24% 19% 31% 20% 6%	720
	21st to end	Night	23% 16% 29% 24% 8% 1	792
April	1st to 10th	Night	26% 16% 30% 25% 3	720
	11th to 20th	Night	25% 18% 29% 19% 8%	711
	21st to end	Night	25% 14% 29% 24% 8%	611
May	1st to 10th	Night	25% 8% 27% 29% 10% 1	360
	11th to 20th	Night	20% 11% 32% 27% 8% 1	354
	21st to end	Night	15% 8% 37% 25% 14% 1	389
June	1st to 10th	Night	19% 6% 33% 33% 9%	360
	11th to 20th	Night	16% 9% 28% 34% 12% 1	360
	21st to end	Night	19% 6% 31% 32% 13% 1	360
July	1st to 10th	Night	8% 6% 27% 43% 15% 1	350
	11th to 20th	Night	14% 4 26% 43% 12% 1	348
	21st to end	Night	10% 4 30% 43% 13% 1	394
August	1st to 10th	Night	10% 5% 27% 38% 20%	422
	11th to 20th	Night	12% 3 22% 37% 23% 3	534
	21st to end	Night	13% 7% 28% 32% 18% 2	782
September	1st to 10th	Night	15% 6% 30% 29% 17% 2	720
	11th to 20th	Night	18% 7% 23% 30% 20% 3	720
	21st to end	Night	19% 10% 26% 24% 20% 2	720
October	1st to 10th	Night	22% 11% 28% 24% 15% 1	720
	11th to 20th	Night	25% 13% 30% 22% 8% 1	720
	21st to end	Night	29% 15% 28% 23% 5%	792
November	1st to 10th	Night	27% 14% 29% 23% 7% 1	740
	11th to 20th	Night	26% 16% 32% 17% 8% 1	760
	21st to end	Night	31% 17% 26% 20% 5%	760
December	1st to 10th	Night	30% 17% 32% 18% 3	760
	11th to 20th	Night	29% 18% 29% 19% 4 1	760
	21st to end	Night	35% 16% 28% 18% 3	836

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