Greater Napanee
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greater Napanee clear sky chart from 2005-11-06 to 2024-01-22.

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% 8% 3 6% 6% 3 5% 5% 5% 7% 35%	74788
	Night	17% 9% 3 6% 5% 3 5% 5% 5% 7% 35%	75149
Transparency	Day	31% 39% 9% 13% 7% 1	74493
	Night	33% 39% 8% 13% 7% 1	74978
Seeing	Day	20% 13% 30% 23% 11% 3	13407
	Night	21% 11% 31% 26% 11% 1	22759

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% 15% 4 7% 7% 3 4 5% 5% 7% 27%	1517
	11th to 20th	Day	19% 17% 5% 8% 7% 3 5% 5% 4 4 24%	1520
	21st to end	Day	13% 14% 5% 9% 8% 4 6% 5% 6% 6% 24%	1763
February	1st to 10th	Day	16% 14% 5% 10% 8% 4 6% 5% 5% 6% 21%	1620
	11th to 20th	Day	15% 12% 5% 11% 7% 4 6% 4 4 5% 27%	1573
	21st to end	Day	20% 13% 5% 6% 7% 4 5% 5% 4 5% 26%	1452
March	1st to 10th	Day	16% 10% 4 9% 8% 5% 5% 3 4 5% 30%	1868
	11th to 20th	Day	16% 12% 4 8% 6% 4 5% 4 5% 4 32%	1980
	21st to end	Day	20% 10% 3 6% 6% 3 4 3 4 5% 37%	2245
April	1st to 10th	Day	20% 11% 3 7% 6% 3 4 4 4 6% 33%	2160
	11th to 20th	Day	19% 8% 3 5% 4 3 3 4 5% 6% 40%	2134
	21st to end	Day	21% 9% 4 7% 5% 4 4 5% 5% 6% 32%	2272
May	1st to 10th	Day	16% 8% 3 7% 6% 4 5% 5% 5% 7% 34%	2479
	11th to 20th	Day	14% 7% 3 4 5% 3 5% 4 6% 9% 41%	2478
	21st to end	Day	12% 5% 3 5% 6% 4 6% 5% 6% 8% 41%	2725
June	1st to 10th	Day	18% 5% 2 6% 7% 3 5% 5% 6% 8% 36%	2520
	11th to 20th	Day	14% 5% 3 5% 4 3 5% 5% 6% 9% 40%	2520
	21st to end	Day	14% 8% 2 5% 5% 3 5% 5% 5% 8% 39%	2520
July	1st to 10th	Day	10% 4 3 5% 5% 3 5% 5% 6% 9% 46%	2520
	11th to 20th	Day	11% 6% 2 5% 5% 3 6% 5% 7% 9% 42%	2520
	21st to end	Day	10% 4 2 5% 6% 4 6% 6% 7% 10% 40%	2744
August	1st to 10th	Day	10% 5% 2 5% 6% 3 4 6% 7% 9% 42%	2351
	11th to 20th	Day	10% 5% 2 5% 5% 4 6% 6% 8% 9% 40%	2303
	21st to end	Day	12% 6% 2 5% 5% 3 5% 5% 7% 8% 44%	2378
September	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 5% 5% 8% 44%	2160
	11th to 20th	Day	11% 6% 2 5% 4 2 3 4 4 7% 51%	2160
	21st to end	Day	15% 6% 2 6% 5% 3 5% 5% 6% 8% 39%	1900
October	1st to 10th	Day	20% 7% 3 5% 5% 3 5% 5% 5% 7% 36%	1800
	11th to 20th	Day	21% 7% 3 6% 5% 3 6% 6% 5% 7% 32%	1800
	21st to end	Day	26% 10% 3 6% 6% 3 5% 5% 5% 6% 26%	1913
November	1st to 10th	Day	16% 8% 3 6% 5% 4 5% 6% 6% 6% 36%	1655
	11th to 20th	Day	16% 10% 3 6% 7% 4 5% 4 6% 7% 31%	1520
	21st to end	Day	21% 11% 4 8% 7% 3 4 5% 5% 6% 26%	1520
December	1st to 10th	Day	21% 14% 4 9% 7% 4 5% 5% 4 6% 22%	1520
	11th to 20th	Day	19% 14% 5% 7% 6% 3 4 5% 4 6% 27%	1906
	21st to end	Day	30% 13% 5% 8% 6% 3 4 3 4 4 21%	2772
January	1st to 10th	Night	20% 13% 5% 8% 8% 3 5% 4 4 6% 24%	2649
	11th to 20th	Night	19% 13% 6% 9% 8% 4 6% 5% 4 5% 22%	2660
	21st to end	Night	14% 14% 5% 8% 7% 3 5% 5% 5% 6% 28%	2624
February	1st to 10th	Night	17% 13% 5% 10% 7% 4 6% 5% 5% 4 25%	2340
	11th to 20th	Night	16% 12% 4 9% 6% 3 4 4 6% 6% 30%	2273
	21st to end	Night	18% 10% 4 7% 6% 4 4 5% 5% 7% 30%	1803
March	1st to 10th	Night	15% 10% 4 7% 7% 4 5% 4 4 6% 33%	2078
	11th to 20th	Night	19% 9% 4 7% 6% 2 4 4 5% 5% 35%	1979
	21st to end	Night	17% 8% 4 6% 4 3 3 5% 4 6% 40%	2111
April	1st to 10th	Night	21% 7% 4 6% 4 3 4 4 5% 7% 34%	1800
	11th to 20th	Night	18% 8% 3 7% 5% 3 5% 5% 4 5% 38%	1775
	21st to end	Night	19% 8% 3 6% 5% 3 4 5% 6% 6% 34%	1705
May	1st to 10th	Night	20% 7% 4 5% 4 3 3 5% 6% 6% 37%	1479
	11th to 20th	Night	12% 5% 3 5% 5% 4 4 5% 6% 7% 45%	1415
	21st to end	Night	10% 5% 2 5% 5% 3 5% 5% 6% 8% 46%	1550
June	1st to 10th	Night	14% 6% 3 6% 5% 4 5% 6% 6% 9% 36%	1440
	11th to 20th	Night	11% 5% 2 5% 5% 3 4 5% 6% 9% 44%	1440
	21st to end	Night	14% 6% 3 6% 5% 3 4 4 6% 7% 42%	1440
July	1st to 10th	Night	8% 3 2 5% 5% 2 6% 5% 6% 8% 50%	1440
	11th to 20th	Night	10% 5% 2 4 5% 3 4 6% 7% 9% 45%	1440
	21st to end	Night	10% 5% 2 4 4 3 4 5% 7% 8% 48%	1574
August	1st to 10th	Night	9% 5% 3 5% 5% 3 5% 5% 5% 9% 47%	1583
	11th to 20th	Night	10% 6% 3 5% 5% 3 4 5% 7% 9% 45%	1598
	21st to end	Night	9% 5% 2 6% 4 3 5% 4 7% 9% 46%	1959
September	1st to 10th	Night	12% 6% 2 5% 5% 3 4 4 6% 8% 46%	1800
	11th to 20th	Night	12% 4 2 4 4 2 4 4 5% 7% 52%	1800
	21st to end	Night	17% 5% 2 5% 5% 3 4 5% 5% 7% 44%	2058
October	1st to 10th	Night	17% 7% 3 6% 6% 4 4 5% 5% 5% 37%	2160
	11th to 20th	Night	21% 7% 3 6% 6% 3 5% 4 5% 6% 34%	2160
	21st to end	Night	23% 8% 4 7% 6% 3 4 5% 5% 6% 30%	2443
November	1st to 10th	Night	19% 8% 3 5% 4 2 5% 4 5% 8% 38%	2421
	11th to 20th	Night	19% 8% 3 5% 5% 3 5% 5% 6% 7% 33%	2660
	21st to end	Night	22% 10% 3 6% 5% 3 5% 5% 6% 7% 28%	2660
December	1st to 10th	Night	21% 14% 4 7% 5% 3 4 4 5% 7% 24%	2660
	11th to 20th	Night	20% 14% 4 7% 5% 3 4 4 5% 4 29%	3288
	21st to end	Night	31% 13% 4 8% 5% 3 4 4 4 5% 18%	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	38% 42% 6% 11% 2	1518
	11th to 20th	Day	41% 42% 5% 6% 5% 1	1520
	21st to end	Day	39% 40% 6% 8% 6% 1	1763
February	1st to 10th	Day	40% 38% 8% 11% 3	1620
	11th to 20th	Day	41% 39% 6% 8% 5% 1	1582
	21st to end	Day	39% 38% 8% 8% 6%	1452
March	1st to 10th	Day	35% 38% 11% 11% 5%	1871
	11th to 20th	Day	36% 38% 9% 11% 6% 1	1980
	21st to end	Day	31% 38% 7% 13% 9% 2	2245
April	1st to 10th	Day	33% 37% 7% 14% 8% 2	2160
	11th to 20th	Day	30% 37% 8% 14% 10% 1	2134
	21st to end	Day	35% 37% 7% 10% 8% 2	2272
May	1st to 10th	Day	30% 38% 7% 11% 11% 3	2479
	11th to 20th	Day	26% 40% 7% 15% 10% 2	2482
	21st to end	Day	24% 40% 11% 14% 9% 3	2725
June	1st to 10th	Day	31% 39% 10% 12% 7% 1	2520
	11th to 20th	Day	25% 38% 9% 18% 9% 1	2520
	21st to end	Day	28% 40% 12% 13% 7%	2520
July	1st to 10th	Day	23% 40% 9% 19% 8%	2450
	11th to 20th	Day	23% 40% 14% 17% 7%	2445
	21st to end	Day	24% 42% 12% 15% 6%	2591
August	1st to 10th	Day	26% 38% 11% 18% 7%	2337
	11th to 20th	Day	21% 39% 14% 17% 9% 1	2303
	21st to end	Day	24% 39% 9% 19% 7% 1	2378
September	1st to 10th	Day	25% 39% 10% 18% 8%	2160
	11th to 20th	Day	24% 38% 9% 19% 8% 1	2160
	21st to end	Day	30% 40% 8% 18% 5%	1900
October	1st to 10th	Day	31% 38% 9% 14% 8%	1800
	11th to 20th	Day	34% 40% 11% 11% 4	1800
	21st to end	Day	39% 39% 7% 10% 5%	1913
November	1st to 10th	Day	25% 43% 10% 15% 6%	1655
	11th to 20th	Day	33% 42% 9% 10% 6% 1	1520
	21st to end	Day	37% 42% 9% 8% 4	1520
December	1st to 10th	Day	39% 43% 9% 7% 2	1520
	11th to 20th	Day	41% 36% 11% 8% 3	1906
	21st to end	Day	51% 29% 7% 11% 2	2772
January	1st to 10th	Night	41% 41% 7% 8% 3	2649
	11th to 20th	Night	42% 43% 6% 6% 3	2660
	21st to end	Night	38% 38% 6% 10% 6% 1	2624
February	1st to 10th	Night	40% 38% 8% 10% 3	2340
	11th to 20th	Night	37% 39% 7% 13% 5%	2275
	21st to end	Night	36% 38% 8% 13% 4 1	1803
March	1st to 10th	Night	34% 38% 8% 14% 6% 1	2088
	11th to 20th	Night	34% 38% 8% 13% 6% 1	1980
	21st to end	Night	30% 37% 6% 13% 12% 2	2111
April	1st to 10th	Night	32% 37% 6% 15% 9% 2	1800
	11th to 20th	Night	34% 37% 6% 12% 10% 1	1775
	21st to end	Night	31% 38% 7% 11% 10% 3	1705
May	1st to 10th	Night	30% 37% 6% 12% 13% 3	1479
	11th to 20th	Night	24% 38% 9% 15% 12% 3	1416
	21st to end	Night	23% 39% 9% 14% 12% 3	1551
June	1st to 10th	Night	30% 40% 10% 13% 7%	1440
	11th to 20th	Night	22% 40% 11% 14% 12% 1	1440
	21st to end	Night	27% 40% 13% 14% 7%	1440
July	1st to 10th	Night	23% 40% 7% 16% 13% 1	1400
	11th to 20th	Night	24% 39% 9% 18% 9%	1392
	21st to end	Night	21% 40% 10% 20% 8% 1	1486
August	1st to 10th	Night	25% 38% 10% 19% 7%	1573
	11th to 20th	Night	23% 38% 10% 18% 11% 1	1598
	21st to end	Night	23% 40% 9% 18% 9% 1	1959
September	1st to 10th	Night	26% 38% 9% 17% 9% 1	1800
	11th to 20th	Night	21% 39% 10% 21% 8%	1800
	21st to end	Night	27% 39% 8% 19% 7% 1	2058
October	1st to 10th	Night	32% 39% 8% 13% 7%	2160
	11th to 20th	Night	36% 38% 10% 12% 4	2160
	21st to end	Night	36% 40% 9% 8% 6%	2443
November	1st to 10th	Night	25% 43% 8% 15% 8% 1	2421
	11th to 20th	Night	30% 42% 9% 12% 6% 1	2660
	21st to end	Night	35% 44% 9% 10% 2	2660
December	1st to 10th	Night	40% 43% 8% 8% 2	2660
	11th to 20th	Night	41% 35% 8% 12% 4	3288
	21st to end	Night	54% 28% 8% 8% 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	26% 18% 32% 16% 8% 1	180
	11th to 20th	Day	28% 19% 33% 16% 4 1	180
	21st to end	Day	21% 19% 35% 19% 6%	254
February	1st to 10th	Day	30% 22% 36% 10% 1	240
	11th to 20th	Day	23% 24% 38% 14% 1	240
	21st to end	Day	35% 18% 33% 12% 3	318
March	1st to 10th	Day	22% 16% 36% 20% 5%	420
	11th to 20th	Day	24% 20% 32% 19% 5%	420
	21st to end	Day	32% 14% 30% 16% 8% 1	462
April	1st to 10th	Day	25% 20% 32% 16% 7%	420
	11th to 20th	Day	25% 16% 28% 17% 10% 3	412
	21st to end	Day	25% 11% 40% 15% 8% 1	420
May	1st to 10th	Day	23% 10% 32% 23% 9% 3	423
	11th to 20th	Day	16% 8% 36% 26% 10% 3	447
	21st to end	Day	16% 7% 33% 25% 16% 3	485
June	1st to 10th	Day	17% 10% 34% 28% 10% 2	450
	11th to 20th	Day	12% 11% 32% 28% 14% 3	450
	21st to end	Day	16% 8% 30% 29% 14% 3	450
July	1st to 10th	Day	10% 6% 23% 36% 21% 4	445
	11th to 20th	Day	13% 6% 26% 31% 19% 5%	444
	21st to end	Day	10% 6% 29% 38% 12% 4	488
August	1st to 10th	Day	12% 4 25% 32% 21% 6%	446
	11th to 20th	Day	12% 5% 22% 35% 21% 6%	439
	21st to end	Day	12% 9% 27% 30% 15% 7%	495
September	1st to 10th	Day	12% 8% 31% 27% 14% 8%	450
	11th to 20th	Day	11% 8% 24% 26% 21% 11%	450
	21st to end	Day	16% 9% 28% 26% 16% 4	450
October	1st to 10th	Day	23% 12% 27% 18% 15% 5%	450
	11th to 20th	Day	22% 19% 30% 20% 8% 1	450
	21st to end	Day	30% 16% 28% 21% 5%	462
November	1st to 10th	Day	23% 17% 27% 23% 10% 1	349
	11th to 20th	Day	22% 23% 33% 14% 6% 2	180
	21st to end	Day	22% 19% 38% 14% 6% 1	180
December	1st to 10th	Day	26% 22% 33% 12% 7% 1	180
	11th to 20th	Day	26% 24% 34% 12% 4	180
	21st to end	Day	33% 17% 33% 13% 3	198
January	1st to 10th	Night	27% 16% 34% 19% 4	760
	11th to 20th	Night	29% 16% 29% 20% 6%	760
	21st to end	Night	21% 12% 36% 25% 6%	800
February	1st to 10th	Night	23% 16% 37% 20% 3	720
	11th to 20th	Night	22% 14% 38% 21% 5%	703
	21st to end	Night	23% 16% 36% 21% 4	592
March	1st to 10th	Night	21% 13% 36% 26% 4	720
	11th to 20th	Night	24% 13% 33% 23% 5% 1	720
	21st to end	Night	21% 11% 35% 23% 8% 1	792
April	1st to 10th	Night	23% 11% 36% 24% 5%	720
	11th to 20th	Night	20% 12% 35% 22% 9% 1	711
	21st to end	Night	23% 9% 30% 26% 11% 1	625
May	1st to 10th	Night	24% 6% 27% 29% 13% 1	399
	11th to 20th	Night	13% 7% 34% 35% 10% 1	354
	21st to end	Night	11% 6% 33% 33% 16% 2	389
June	1st to 10th	Night	16% 4 30% 33% 16% 1	360
	11th to 20th	Night	11% 5% 30% 36% 16% 1	360
	21st to end	Night	16% 5% 25% 38% 16%	360
July	1st to 10th	Night	7% 5% 26% 39% 23% 1	350
	11th to 20th	Night	11% 4 22% 38% 24% 2	348
	21st to end	Night	12% 2 23% 47% 15% 1	394
August	1st to 10th	Night	11% 3 20% 38% 26% 3	509
	11th to 20th	Night	12% 4 19% 35% 26% 4	534
	21st to end	Night	10% 4 26% 37% 20% 2	771
September	1st to 10th	Night	13% 6% 26% 32% 20% 3	720
	11th to 20th	Night	13% 4 22% 29% 25% 6%	720
	21st to end	Night	19% 7% 23% 28% 19% 3	720
October	1st to 10th	Night	20% 11% 29% 22% 17% 2	720
	11th to 20th	Night	24% 13% 29% 24% 9% 1	720
	21st to end	Night	27% 13% 30% 25% 5%	792
November	1st to 10th	Night	25% 10% 29% 25% 10% 1	740
	11th to 20th	Night	24% 16% 33% 19% 8% 1	760
	21st to end	Night	28% 15% 30% 20% 7%	760
December	1st to 10th	Night	29% 20% 29% 19% 4	760
	11th to 20th	Night	26% 16% 37% 18% 3	760
	21st to end	Night	33% 15% 33% 16% 3	836

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