Long Point Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Point Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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	15% 9% 4 7% 6% 3 5% 5% 6% 8% 33%	74753
	Night	16% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	75285
Transparency	Day	32% 38% 9% 13% 7% 1	74472
	Night	34% 37% 7% 13% 7% 1	75100
Seeing	Day	18% 7% 25% 28% 16% 6%	13404
	Night	21% 8% 27% 29% 14% 2	23084

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	17% 13% 5% 10% 8% 4 6% 5% 5% 7% 21%	1588
	11th to 20th	Day	17% 15% 5% 12% 7% 4 5% 4 6% 6% 17%	1710
	21st to end	Day	15% 15% 6% 13% 10% 4 6% 5% 5% 5% 17%	1836
February	1st to 10th	Day	18% 14% 5% 11% 10% 4 6% 4 4 6% 18%	1620
	11th to 20th	Day	15% 12% 7% 11% 8% 4 5% 6% 5% 5% 21%	1573
	21st to end	Day	19% 12% 6% 10% 8% 3 4 4 5% 6% 23%	1433
March	1st to 10th	Day	16% 11% 5% 8% 8% 4 5% 4 5% 8% 27%	1967
	11th to 20th	Day	13% 12% 7% 8% 7% 3 4 4 4 7% 31%	1980
	21st to end	Day	19% 10% 4 7% 7% 4 5% 4 3 5% 31%	2178
April	1st to 10th	Day	15% 10% 5% 7% 6% 4 4 4 5% 7% 31%	2079
	11th to 20th	Day	16% 10% 4 7% 5% 3 4 4 5% 7% 35%	2232
	21st to end	Day	18% 8% 3 6% 6% 3 5% 5% 5% 6% 34%	2340
May	1st to 10th	Day	16% 7% 3 6% 7% 4 6% 5% 5% 8% 35%	2340
	11th to 20th	Day	15% 7% 3 6% 6% 3 5% 5% 5% 7% 37%	2353
	21st to end	Day	10% 5% 2 4 5% 3 5% 5% 6% 10% 44%	2725
June	1st to 10th	Day	11% 6% 3 6% 5% 3 5% 5% 6% 8% 43%	2520
	11th to 20th	Day	11% 6% 2 6% 6% 3 5% 6% 7% 8% 40%	2520
	21st to end	Day	10% 4 2 5% 5% 3 4 5% 6% 10% 44%	2520
July	1st to 10th	Day	7% 4 2 4 5% 3 5% 5% 6% 10% 47%	2520
	11th to 20th	Day	11% 5% 3 4 5% 3 6% 5% 7% 11% 40%	2408
	21st to end	Day	8% 4 2 5% 6% 4 5% 6% 8% 10% 41%	2547
August	1st to 10th	Day	8% 4 2 4 5% 4 5% 6% 8% 10% 44%	2327
	11th to 20th	Day	8% 4 3 5% 5% 3 7% 7% 8% 10% 39%	2303
	21st to end	Day	10% 6% 2 6% 5% 4 5% 5% 6% 8% 44%	2501
September	1st to 10th	Day	12% 6% 2 5% 5% 4 5% 5% 6% 8% 42%	2160
	11th to 20th	Day	9% 5% 2 4 5% 3 5% 5% 7% 9% 46%	1987
	21st to end	Day	15% 5% 3 6% 5% 3 5% 6% 6% 7% 39%	1980
October	1st to 10th	Day	16% 7% 3 6% 6% 4 5% 6% 5% 7% 37%	1802
	11th to 20th	Day	19% 8% 4 7% 7% 4 5% 5% 6% 7% 29%	1800
	21st to end	Day	22% 11% 4 7% 8% 4 4 4 6% 7% 24%	1980
November	1st to 10th	Day	14% 7% 2 7% 7% 4 4 4 5% 8% 37%	1686
	11th to 20th	Day	16% 9% 4 7% 7% 4 5% 4 5% 8% 30%	1520
	21st to end	Day	21% 14% 4 7% 6% 4 5% 5% 7% 7% 22%	1520
December	1st to 10th	Day	18% 13% 5% 9% 8% 4 5% 5% 5% 7% 20%	1520
	11th to 20th	Day	19% 13% 7% 9% 8% 4 5% 5% 7% 5% 18%	1906
	21st to end	Day	28% 18% 6% 9% 6% 3 4 4 4 5% 12%	2772
January	1st to 10th	Night	18% 13% 6% 9% 8% 3 5% 4 5% 7% 23%	2573
	11th to 20th	Night	19% 15% 6% 9% 7% 3 5% 6% 5% 6% 19%	2470
	21st to end	Night	14% 13% 8% 12% 9% 4 5% 4 4 6% 22%	2664
February	1st to 10th	Night	17% 15% 5% 8% 8% 4 5% 5% 5% 5% 22%	2340
	11th to 20th	Night	16% 12% 5% 10% 7% 3 6% 5% 5% 7% 24%	2273
	21st to end	Night	18% 12% 5% 9% 6% 4 5% 4 5% 8% 24%	1821
March	1st to 10th	Night	14% 8% 4 7% 7% 4 5% 6% 5% 7% 33%	1980
	11th to 20th	Night	16% 10% 5% 7% 5% 3 4 4 4 7% 36%	1979
	21st to end	Night	18% 10% 4 7% 5% 3 4 5% 5% 5% 34%	2178
April	1st to 10th	Night	19% 8% 4 5% 5% 4 6% 4 4 7% 33%	1879
	11th to 20th	Night	17% 7% 3 5% 5% 4 4 6% 5% 7% 37%	1692
	21st to end	Night	15% 6% 3 6% 6% 4 6% 5% 5% 8% 36%	1620
May	1st to 10th	Night	16% 8% 4 6% 5% 3 5% 5% 6% 8% 35%	1620
	11th to 20th	Night	12% 7% 3 6% 5% 3 6% 4 6% 7% 40%	1539
	21st to end	Night	10% 5% 2 5% 5% 2 3 4 6% 9% 48%	1550
June	1st to 10th	Night	11% 6% 2 6% 5% 4 5% 4 6% 9% 43%	1440
	11th to 20th	Night	9% 5% 2 6% 7% 4 4 6% 6% 10% 41%	1440
	21st to end	Night	11% 4 3 5% 5% 3 6% 4 6% 8% 46%	1440
July	1st to 10th	Night	6% 4 2 4 5% 3 4 3 4 9% 55%	1440
	11th to 20th	Night	9% 4 1 4 6% 4 5% 5% 6% 9% 47%	1548
	21st to end	Night	6% 4 3 5% 4 3 5% 6% 7% 8% 49%	1771
August	1st to 10th	Night	6% 4 2 5% 5% 3 5% 6% 6% 10% 47%	1611
	11th to 20th	Night	9% 4 2 4 4 3 4 5% 7% 10% 48%	1598
	21st to end	Night	9% 4 2 4 6% 3 4 4 6% 9% 49%	1836
September	1st to 10th	Night	12% 7% 3 5% 4 3 4 4 5% 8% 45%	1800
	11th to 20th	Night	10% 4 2 4 4 2 3 4 6% 6% 54%	1970
	21st to end	Night	15% 6% 2 6% 6% 3 4 5% 5% 6% 41%	1980
October	1st to 10th	Night	15% 7% 3 6% 5% 2 4 5% 5% 7% 42%	2156
	11th to 20th	Night	18% 8% 4 7% 5% 4 4 4 5% 6% 34%	2160
	21st to end	Night	22% 9% 4 6% 5% 4 4 5% 5% 6% 31%	2376
November	1st to 10th	Night	15% 7% 2 5% 5% 3 5% 5% 5% 7% 41%	2389
	11th to 20th	Night	16% 10% 4 6% 6% 4 5% 6% 6% 8% 30%	2660
	21st to end	Night	19% 13% 4 6% 6% 4 5% 5% 5% 7% 26%	2660
December	1st to 10th	Night	20% 15% 5% 9% 6% 3 4 5% 4 6% 22%	2660
	11th to 20th	Night	17% 15% 6% 9% 7% 4 5% 4 5% 6% 21%	3288
	21st to end	Night	28% 16% 6% 9% 7% 4 4 4 4 5% 14%	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	41% 42% 8% 7% 2	1589
	11th to 20th	Day	45% 42% 6% 6% 2	1710
	21st to end	Day	47% 37% 6% 7% 3	1836
February	1st to 10th	Day	45% 36% 8% 9% 2	1620
	11th to 20th	Day	42% 38% 6% 9% 4 1	1582
	21st to end	Day	45% 37% 7% 9% 3	1433
March	1st to 10th	Day	36% 37% 10% 13% 3	1970
	11th to 20th	Day	37% 37% 7% 12% 5% 2	1980
	21st to end	Day	38% 36% 6% 13% 6% 1	2178
April	1st to 10th	Day	30% 37% 10% 13% 10% 1	2079
	11th to 20th	Day	32% 36% 9% 13% 9% 1	2232
	21st to end	Day	32% 37% 7% 14% 9% 1	2340
May	1st to 10th	Day	30% 37% 7% 15% 10% 2	2340
	11th to 20th	Day	29% 38% 7% 14% 11% 2	2357
	21st to end	Day	23% 38% 11% 15% 10% 2	2725
June	1st to 10th	Day	25% 38% 10% 17% 8% 1	2520
	11th to 20th	Day	24% 38% 11% 17% 9% 1	2520
	21st to end	Day	24% 38% 10% 18% 9% 1	2520
July	1st to 10th	Day	21% 39% 10% 17% 11% 1	2450
	11th to 20th	Day	24% 39% 12% 16% 8% 1	2335
	21st to end	Day	23% 40% 11% 16% 9% 1	2405
August	1st to 10th	Day	23% 38% 11% 20% 8%	2314
	11th to 20th	Day	22% 38% 13% 17% 9% 1	2303
	21st to end	Day	25% 38% 9% 17% 9% 2	2501
September	1st to 10th	Day	25% 38% 10% 17% 8% 1	2160
	11th to 20th	Day	23% 37% 11% 20% 8%	1987
	21st to end	Day	31% 38% 10% 14% 7% 1	1980
October	1st to 10th	Day	31% 37% 10% 13% 8% 1	1802
	11th to 20th	Day	38% 39% 8% 11% 4 1	1800
	21st to end	Day	38% 38% 9% 10% 4 1	1980
November	1st to 10th	Day	26% 42% 8% 16% 6% 1	1686
	11th to 20th	Day	32% 41% 10% 10% 6%	1520
	21st to end	Day	38% 41% 8% 11% 2	1520
December	1st to 10th	Day	40% 41% 9% 8% 1	1520
	11th to 20th	Day	45% 37% 8% 7% 3	1906
	21st to end	Day	60% 27% 7% 5% 1	2772
January	1st to 10th	Night	43% 41% 5% 8% 3	2573
	11th to 20th	Night	43% 42% 6% 6% 3	2470
	21st to end	Night	44% 37% 6% 9% 4	2664
February	1st to 10th	Night	43% 37% 7% 9% 4 1	2340
	11th to 20th	Night	40% 38% 7% 10% 3	2275
	21st to end	Night	41% 35% 8% 11% 5%	1821
March	1st to 10th	Night	33% 37% 8% 15% 5% 1	1990
	11th to 20th	Night	34% 36% 7% 14% 8% 1	1980
	21st to end	Night	35% 36% 5% 14% 8% 1	2178
April	1st to 10th	Night	33% 36% 7% 13% 10% 2	1879
	11th to 20th	Night	31% 36% 6% 14% 11% 1	1692
	21st to end	Night	33% 36% 6% 12% 11% 2	1620
May	1st to 10th	Night	30% 36% 5% 16% 9% 2	1620
	11th to 20th	Night	26% 37% 6% 14% 11% 4	1540
	21st to end	Night	21% 37% 9% 17% 14% 2	1551
June	1st to 10th	Night	26% 38% 8% 16% 11% 2	1440
	11th to 20th	Night	24% 38% 9% 15% 12% 1	1440
	21st to end	Night	24% 38% 8% 17% 11% 1	1440
July	1st to 10th	Night	20% 38% 6% 18% 15% 3	1400
	11th to 20th	Night	23% 38% 9% 18% 10% 2	1498
	21st to end	Night	19% 40% 11% 17% 12% 2	1672
August	1st to 10th	Night	24% 39% 8% 19% 10% 1	1600
	11th to 20th	Night	20% 36% 10% 21% 11% 1	1598
	21st to end	Night	21% 38% 8% 20% 11% 2	1836
September	1st to 10th	Night	27% 37% 8% 17% 10% 2	1800
	11th to 20th	Night	21% 37% 7% 23% 11%	1970
	21st to end	Night	32% 37% 8% 15% 8% 1	1980
October	1st to 10th	Night	28% 38% 6% 18% 9% 1	2156
	11th to 20th	Night	35% 37% 8% 13% 6%	2160
	21st to end	Night	36% 38% 7% 12% 6% 1	2376
November	1st to 10th	Night	24% 41% 7% 19% 8% 1	2389
	11th to 20th	Night	33% 42% 7% 11% 6% 1	2660
	21st to end	Night	36% 41% 10% 10% 3	2660
December	1st to 10th	Night	42% 41% 7% 8% 2	2660
	11th to 20th	Night	45% 37% 8% 9% 2	3288
	21st to end	Night	60% 28% 8% 3 1	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	24% 16% 31% 16% 9% 2	213
	11th to 20th	Day	27% 12% 37% 18% 5% 2	270
	21st to end	Day	25% 14% 32% 23% 6%	282
February	1st to 10th	Day	23% 13% 44% 18% 1	240
	11th to 20th	Day	25% 19% 35% 20% 2	240
	21st to end	Day	24% 22% 34% 17% 3	198
March	1st to 10th	Day	21% 10% 30% 30% 8%	410
	11th to 20th	Day	20% 12% 32% 28% 7% 1	420
	21st to end	Day	27% 9% 32% 22% 9%	462
April	1st to 10th	Day	16% 11% 34% 29% 9% 2	420
	11th to 20th	Day	20% 9% 32% 23% 11% 5%	412
	21st to end	Day	21% 5% 34% 29% 9% 2	420
May	1st to 10th	Day	26% 5% 26% 27% 11% 5%	423
	11th to 20th	Day	18% 4 23% 29% 20% 6%	447
	21st to end	Day	13% 3 21% 32% 22% 9%	485
June	1st to 10th	Day	13% 2 24% 40% 17% 4	450
	11th to 20th	Day	15% 4 20% 34% 22% 5%	450
	21st to end	Day	14% 3 23% 37% 18% 5%	450
July	1st to 10th	Day	9% 2 15% 31% 30% 13%	445
	11th to 20th	Day	16% 2 17% 33% 20% 12%	444
	21st to end	Day	8% 2 20% 38% 26% 7%	488
August	1st to 10th	Day	10% 1 14% 35% 29% 12%	446
	11th to 20th	Day	11% 4 13% 33% 28% 11%	439
	21st to end	Day	13% 3 18% 30% 25% 11%	495
September	1st to 10th	Day	13% 4 17% 30% 24% 12%	450
	11th to 20th	Day	9% 1 16% 27% 31% 16%	450
	21st to end	Day	16% 6% 22% 29% 19% 8%	450
October	1st to 10th	Day	19% 6% 24% 24% 18% 9%	450
	11th to 20th	Day	21% 13% 29% 26% 8% 3	450
	21st to end	Day	30% 10% 28% 22% 9%	495
November	1st to 10th	Day	18% 14% 31% 23% 10% 3	292
	11th to 20th	Day	23% 22% 26% 19% 8% 2	180
	21st to end	Day	28% 12% 36% 20% 3	180
December	1st to 10th	Day	27% 18% 27% 20% 7% 2	180
	11th to 20th	Day	26% 20% 32% 16% 6%	180
	21st to end	Day	28% 18% 30% 19% 6%	198
January	1st to 10th	Night	26% 16% 34% 18% 6%	760
	11th to 20th	Night	30% 13% 33% 19% 5%	760
	21st to end	Night	22% 11% 34% 26% 7%	820
February	1st to 10th	Night	27% 12% 36% 23% 3	720
	11th to 20th	Night	23% 11% 35% 26% 5%	703
	21st to end	Night	24% 11% 36% 24% 4	592
March	1st to 10th	Night	19% 8% 34% 31% 7%	720
	11th to 20th	Night	22% 6% 34% 28% 9% 1	720
	21st to end	Night	23% 7% 29% 29% 10% 2	792
April	1st to 10th	Night	22% 8% 33% 28% 8% 1	720
	11th to 20th	Night	21% 7% 32% 28% 10% 2	628
	21st to end	Night	19% 5% 29% 36% 11% 1	540
May	1st to 10th	Night	20% 4 25% 32% 16% 2	540
	11th to 20th	Night	18% 4 21% 38% 17% 2	478
	21st to end	Night	14% 1 22% 33% 25% 5%	389
June	1st to 10th	Night	14% 1 22% 42% 20% 1	360
	11th to 20th	Night	12% 2 22% 39% 24% 1	360
	21st to end	Night	12% 4 18% 42% 23% 2	360
July	1st to 10th	Night	9% 1 15% 41% 26% 8%	350
	11th to 20th	Night	13% 1 16% 38% 26% 6%	454
	21st to end	Night	11% 1 15% 42% 27% 4	591
August	1st to 10th	Night	9% 2 11% 39% 33% 7%	537
	11th to 20th	Night	11% 2 14% 33% 34% 6%	534
	21st to end	Night	12% 2 17% 35% 28% 7%	648
September	1st to 10th	Night	16% 4 16% 32% 26% 7%	720
	11th to 20th	Night	13% 2 15% 32% 31% 7%	720
	21st to end	Night	18% 5% 19% 31% 21% 6%	720
October	1st to 10th	Night	19% 6% 21% 29% 21% 5%	720
	11th to 20th	Night	22% 10% 29% 27% 11% 1	720
	21st to end	Night	28% 9% 32% 24% 6% 1	792
November	1st to 10th	Night	21% 10% 27% 28% 12% 2	740
	11th to 20th	Night	22% 17% 32% 20% 8% 2	760
	21st to end	Night	28% 14% 29% 22% 7%	760
December	1st to 10th	Night	32% 15% 30% 17% 5% 1	760
	11th to 20th	Night	27% 15% 34% 20% 5%	760
	21st to end	Night	31% 11% 32% 23% 3	836

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