Donnacona
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Donnacona 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	19% 9% 4 7% 6% 3 5% 5% 5% 7% 31%	74577
	Night	20% 11% 4 7% 6% 3 4 4 5% 6% 30%	75221
Transparency	Day	36% 37% 9% 13% 5% 1	74282
	Night	38% 37% 8% 12% 5% 1	75051
Seeing	Day	24% 14% 29% 22% 9% 2	13942
	Night	25% 10% 29% 27% 8% 1	22712

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	20% 16% 6% 9% 8% 4 5% 5% 4 5% 20%	1517
	11th to 20th	Day	18% 17% 6% 10% 6% 4 4 4 4 4 23%	1480
	21st to end	Day	11% 12% 5% 9% 7% 3 6% 6% 6% 6% 28%	1584
February	1st to 10th	Day	11% 15% 7% 11% 8% 4 5% 5% 4 6% 24%	1454
	11th to 20th	Day	15% 15% 5% 9% 6% 4 6% 5% 5% 6% 24%	1729
	21st to end	Day	13% 13% 6% 10% 7% 3 5% 4 5% 7% 27%	1480
March	1st to 10th	Day	16% 12% 4 8% 6% 3 4 5% 5% 6% 31%	1797
	11th to 20th	Day	18% 11% 5% 7% 6% 4 5% 4 4 6% 31%	1872
	21st to end	Day	15% 10% 4 6% 6% 4 6% 5% 5% 6% 32%	2334
April	1st to 10th	Day	22% 10% 4 8% 7% 4 4 4 4 5% 28%	2160
	11th to 20th	Day	20% 7% 3 6% 6% 3 4 3 4 5% 39%	2199
	21st to end	Day	23% 9% 3 7% 6% 3 4 4 4 6% 31%	2340
May	1st to 10th	Day	21% 7% 3 6% 5% 3 4 5% 5% 6% 34%	2412
	11th to 20th	Day	18% 7% 3 6% 6% 4 5% 5% 6% 7% 34%	2478
	21st to end	Day	21% 7% 3 6% 6% 4 5% 5% 4 7% 32%	2725
June	1st to 10th	Day	20% 7% 2 7% 7% 5% 6% 6% 6% 8% 28%	2654
	11th to 20th	Day	19% 7% 3 5% 5% 3 5% 6% 6% 7% 35%	2700
	21st to end	Day	22% 8% 4 6% 6% 3 6% 4 6% 7% 28%	2659
July	1st to 10th	Day	14% 7% 3 5% 6% 4 6% 6% 7% 8% 33%	2520
	11th to 20th	Day	14% 6% 3 6% 6% 4 6% 7% 7% 9% 31%	2520
	21st to end	Day	15% 6% 3 6% 6% 3 6% 7% 7% 9% 32%	2744
August	1st to 10th	Day	17% 6% 3 6% 7% 3 6% 6% 7% 10% 29%	2506
	11th to 20th	Day	15% 6% 2 6% 5% 3 5% 5% 7% 9% 36%	2310
	21st to end	Day	16% 6% 3 6% 5% 3 5% 5% 6% 8% 38%	2439
September	1st to 10th	Day	17% 6% 3 6% 5% 3 4 4 5% 8% 37%	2160
	11th to 20th	Day	19% 4 2 4 3 3 4 4 4 7% 45%	2016
	21st to end	Day	21% 6% 3 5% 4 2 4 4 4 7% 38%	1980
October	1st to 10th	Day	22% 7% 3 6% 5% 3 6% 6% 5% 6% 32%	1955
	11th to 20th	Day	25% 8% 3 8% 6% 4 5% 4 6% 5% 24%	1666
	21st to end	Day	29% 10% 3 7% 6% 3 5% 4 4 5% 24%	1782
November	1st to 10th	Day	20% 10% 3 7% 6% 3 5% 4 5% 5% 31%	1671
	11th to 20th	Day	22% 12% 4 9% 6% 3 4 4 5% 5% 24%	1696
	21st to end	Day	23% 15% 5% 7% 5% 3 4 6% 4 6% 22%	1421
December	1st to 10th	Day	25% 15% 5% 8% 6% 3 4 3 4 4 22%	1330
	11th to 20th	Day	22% 12% 4 9% 8% 3 4 3 4 5% 26%	1668
	21st to end	Day	23% 17% 5% 8% 5% 3 3 4 4 5% 23%	2619
January	1st to 10th	Night	18% 20% 7% 9% 7% 3 5% 4 4 4 19%	2649
	11th to 20th	Night	18% 17% 6% 9% 6% 3 4 4 4 5% 23%	2602
	21st to end	Night	10% 14% 6% 9% 8% 4 5% 6% 5% 6% 28%	2772
February	1st to 10th	Night	12% 13% 7% 10% 9% 3 6% 4 5% 4 26%	2505
	11th to 20th	Night	14% 15% 6% 10% 8% 4 5% 4 4 5% 25%	2116
	21st to end	Night	16% 13% 5% 8% 6% 3 4 4 5% 6% 29%	1776
March	1st to 10th	Night	15% 12% 5% 8% 8% 3 5% 4 5% 6% 29%	2150
	11th to 20th	Night	18% 11% 4 8% 6% 5% 5% 4 4 5% 28%	2087
	21st to end	Night	18% 11% 4 6% 5% 2 3 5% 5% 5% 35%	2020
April	1st to 10th	Night	23% 13% 5% 7% 5% 2 4 4 5% 5% 27%	1800
	11th to 20th	Night	21% 8% 3 5% 6% 3 4 5% 4 6% 34%	1709
	21st to end	Night	23% 10% 3 6% 5% 2 3 4 5% 6% 33%	1620
May	1st to 10th	Night	23% 8% 4 6% 4 4 5% 4 4 6% 32%	1562
	11th to 20th	Night	22% 7% 3 5% 5% 3 4 5% 5% 5% 37%	1415
	21st to end	Night	22% 6% 3 5% 5% 3 4 4 5% 7% 36%	1550
June	1st to 10th	Night	22% 8% 3 5% 6% 3 5% 5% 6% 9% 28%	1302
	11th to 20th	Night	21% 6% 2 5% 4 2 5% 5% 6% 7% 36%	1260
	21st to end	Night	20% 9% 4 6% 5% 3 5% 4 6% 8% 30%	1295
July	1st to 10th	Night	15% 6% 3 7% 4 4 5% 5% 7% 9% 35%	1440
	11th to 20th	Night	16% 6% 3 6% 6% 3 5% 6% 6% 8% 37%	1440
	21st to end	Night	15% 7% 3 6% 5% 3 6% 6% 6% 8% 34%	1574
August	1st to 10th	Night	15% 5% 2 6% 6% 4 5% 5% 7% 10% 37%	1432
	11th to 20th	Night	15% 6% 3 7% 7% 4 5% 5% 5% 8% 34%	1572
	21st to end	Night	16% 7% 3 6% 6% 3 4 4 5% 7% 40%	1915
September	1st to 10th	Night	19% 5% 2 6% 6% 3 4 4 5% 6% 41%	1800
	11th to 20th	Night	19% 5% 2 5% 4 3 4 4 4 6% 43%	1944
	21st to end	Night	19% 6% 3 5% 5% 3 4 4 4 6% 41%	1980
October	1st to 10th	Night	19% 7% 3 6% 5% 3 4 4 6% 6% 38%	2002
	11th to 20th	Night	24% 9% 3 7% 5% 4 4 4 5% 5% 30%	2294
	21st to end	Night	28% 10% 3 6% 5% 3 3 4 5% 6% 27%	2574
November	1st to 10th	Night	20% 11% 3 6% 6% 3 5% 4 4 8% 30%	2407
	11th to 20th	Night	21% 11% 4 7% 5% 3 5% 4 5% 5% 30%	2483
	21st to end	Night	24% 14% 4 8% 6% 3 5% 4 4 4 25%	2755
December	1st to 10th	Night	24% 15% 5% 9% 7% 4 5% 4 4 4 19%	2850
	11th to 20th	Night	21% 15% 5% 9% 7% 3 4 4 3 5% 23%	3531
	21st to end	Night	25% 19% 4 8% 5% 2 3 3 3 3 24%	5038

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	44% 39% 5% 9% 3	1518
	11th to 20th	Day	41% 39% 6% 9% 3 1	1480
	21st to end	Day	35% 38% 8% 11% 8%	1584
February	1st to 10th	Day	43% 36% 6% 10% 4 1	1454
	11th to 20th	Day	42% 37% 9% 7% 4 1	1738
	21st to end	Day	39% 36% 7% 14% 4	1480
March	1st to 10th	Day	37% 36% 9% 12% 5% 1	1800
	11th to 20th	Day	38% 36% 8% 13% 4	1872
	21st to end	Day	35% 37% 8% 13% 7% 1	2334
April	1st to 10th	Day	41% 36% 7% 9% 6% 2	2160
	11th to 20th	Day	32% 35% 7% 15% 8% 2	2199
	21st to end	Day	35% 36% 7% 12% 7% 2	2340
May	1st to 10th	Day	31% 36% 7% 12% 11% 2	2412
	11th to 20th	Day	31% 38% 8% 13% 8% 1	2482
	21st to end	Day	33% 37% 6% 13% 10% 1	2725
June	1st to 10th	Day	36% 39% 8% 12% 4 1	2654
	11th to 20th	Day	31% 37% 11% 14% 6% 1	2700
	21st to end	Day	40% 38% 8% 9% 5%	2659
July	1st to 10th	Day	29% 40% 12% 15% 3	2450
	11th to 20th	Day	32% 38% 12% 14% 5%	2445
	21st to end	Day	33% 40% 11% 12% 4	2591
August	1st to 10th	Day	35% 38% 12% 13% 2	2492
	11th to 20th	Day	29% 37% 12% 16% 6%	2310
	21st to end	Day	30% 36% 9% 17% 7%	2439
September	1st to 10th	Day	30% 37% 10% 17% 6%	2160
	11th to 20th	Day	26% 36% 10% 21% 7%	2016
	21st to end	Day	33% 36% 11% 14% 6%	1980
October	1st to 10th	Day	33% 37% 9% 16% 4	1955
	11th to 20th	Day	41% 37% 12% 9% 1	1666
	21st to end	Day	40% 38% 5% 13% 3 1	1782
November	1st to 10th	Day	31% 41% 8% 14% 6%	1671
	11th to 20th	Day	40% 39% 7% 9% 5%	1696
	21st to end	Day	40% 40% 8% 9% 2	1421
December	1st to 10th	Day	44% 40% 6% 8% 2	1330
	11th to 20th	Day	45% 32% 5% 14% 4	1668
	21st to end	Day	52% 26% 9% 7% 4 1	2619
January	1st to 10th	Night	45% 39% 6% 8% 2	2649
	11th to 20th	Night	40% 41% 7% 9% 3	2602
	21st to end	Night	39% 37% 7% 10% 6%	2772
February	1st to 10th	Night	41% 36% 6% 10% 6%	2505
	11th to 20th	Night	42% 38% 8% 8% 5% 1	2118
	21st to end	Night	42% 35% 6% 11% 6%	1776
March	1st to 10th	Night	40% 36% 6% 13% 5%	2160
	11th to 20th	Night	40% 36% 8% 9% 7%	2088
	21st to end	Night	35% 36% 7% 14% 7% 2	2020
April	1st to 10th	Night	40% 36% 8% 10% 5% 1	1800
	11th to 20th	Night	32% 36% 7% 15% 9% 1	1709
	21st to end	Night	36% 35% 5% 12% 9% 2	1620
May	1st to 10th	Night	35% 37% 6% 10% 10% 2	1562
	11th to 20th	Night	33% 36% 7% 11% 11% 2	1416
	21st to end	Night	32% 36% 7% 14% 11% 1	1551
June	1st to 10th	Night	36% 37% 7% 14% 5%	1302
	11th to 20th	Night	32% 38% 9% 13% 7% 2	1260
	21st to end	Night	38% 37% 8% 10% 6%	1295
July	1st to 10th	Night	31% 39% 12% 13% 5%	1400
	11th to 20th	Night	31% 40% 10% 13% 5% 1	1392
	21st to end	Night	34% 41% 9% 10% 5%	1486
August	1st to 10th	Night	29% 38% 11% 18% 3	1422
	11th to 20th	Night	30% 37% 13% 14% 5%	1572
	21st to end	Night	31% 37% 9% 18% 6%	1915
September	1st to 10th	Night	30% 36% 10% 17% 7% 1	1800
	11th to 20th	Night	29% 36% 10% 19% 6%	1944
	21st to end	Night	32% 37% 8% 15% 8%	1980
October	1st to 10th	Night	33% 37% 7% 16% 6%	2002
	11th to 20th	Night	38% 37% 10% 12% 2	2294
	21st to end	Night	37% 37% 9% 11% 5%	2574
November	1st to 10th	Night	33% 42% 8% 15% 3	2407
	11th to 20th	Night	36% 40% 10% 9% 5%	2483
	21st to end	Night	41% 39% 6% 10% 3	2755
December	1st to 10th	Night	45% 39% 7% 7% 2	2850
	11th to 20th	Night	44% 33% 5% 12% 5%	3532
	21st to end	Night	51% 25% 7% 13% 4 1	5038

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	30% 18% 33% 16% 3 1	180
	11th to 20th	Day	29% 16% 35% 14% 5%	170
	21st to end	Day	18% 19% 39% 16% 8%	176
February	1st to 10th	Day	25% 32% 29% 11% 2 1	166
	11th to 20th	Day	24% 19% 37% 16% 4	397
	21st to end	Day	25% 23% 30% 19% 3	346
March	1st to 10th	Day	25% 20% 30% 19% 5%	420
	11th to 20th	Day	25% 20% 29% 18% 5% 1	420
	21st to end	Day	25% 17% 27% 20% 9% 2	462
April	1st to 10th	Day	27% 18% 28% 21% 5%	420
	11th to 20th	Day	27% 17% 27% 20% 6% 2	412
	21st to end	Day	30% 17% 28% 17% 5% 2	420
May	1st to 10th	Day	26% 16% 33% 18% 6% 1	423
	11th to 20th	Day	20% 13% 32% 23% 9% 2	447
	21st to end	Day	23% 18% 33% 15% 10% 1	485
June	1st to 10th	Day	22% 12% 34% 22% 9% 1	584
	11th to 20th	Day	23% 10% 28% 27% 12% 1	630
	21st to end	Day	25% 8% 26% 26% 14% 1	589
July	1st to 10th	Day	16% 11% 31% 27% 14% 1	445
	11th to 20th	Day	16% 9% 33% 28% 12% 2	444
	21st to end	Day	17% 8% 29% 32% 12% 2	488
August	1st to 10th	Day	16% 9% 26% 32% 14% 4	446
	11th to 20th	Day	18% 6% 26% 28% 18% 4	439
	21st to end	Day	22% 11% 27% 17% 16% 8%	495
September	1st to 10th	Day	18% 10% 29% 24% 14% 4	450
	11th to 20th	Day	18% 12% 23% 24% 16% 5%	450
	21st to end	Day	21% 12% 25% 23% 14% 5%	450
October	1st to 10th	Day	24% 11% 27% 25% 12% 2	450
	11th to 20th	Day	28% 13% 28% 21% 9% 1	383
	21st to end	Day	34% 15% 27% 19% 6%	396
November	1st to 10th	Day	32% 13% 26% 22% 6% 1	365
	11th to 20th	Day	30% 17% 28% 17% 8% 1	356
	21st to end	Day	31% 20% 30% 16% 3 1	180
December	1st to 10th	Day	34% 14% 26% 21% 4 1	180
	11th to 20th	Day	29% 22% 26% 16% 6% 2	180
	21st to end	Day	37% 18% 29% 11% 5% 1	198
January	1st to 10th	Night	28% 13% 34% 21% 4	760
	11th to 20th	Night	27% 13% 34% 21% 5%	744
	21st to end	Night	18% 11% 35% 29% 6% 1	792
February	1st to 10th	Night	20% 11% 37% 26% 5%	720
	11th to 20th	Night	22% 15% 38% 20% 5%	703
	21st to end	Night	24% 13% 32% 27% 4	592
March	1st to 10th	Night	24% 12% 35% 25% 5%	720
	11th to 20th	Night	25% 13% 34% 21% 6% 1	720
	21st to end	Night	24% 10% 31% 28% 7% 1	792
April	1st to 10th	Night	30% 12% 29% 23% 5%	720
	11th to 20th	Night	27% 10% 32% 25% 6%	645
	21st to end	Night	29% 12% 31% 23% 5%	540
May	1st to 10th	Night	27% 10% 31% 27% 5%	482
	11th to 20th	Night	26% 7% 29% 31% 6% 1	354
	21st to end	Night	25% 9% 31% 28% 7%	389
June	1st to 10th	Night	25% 6% 28% 34% 7%	360
	11th to 20th	Night	23% 4 26% 33% 14%	360
	21st to end	Night	22% 6% 25% 34% 12% 1	360
July	1st to 10th	Night	16% 5% 29% 38% 11%	350
	11th to 20th	Night	17% 4 24% 41% 14% 1	348
	21st to end	Night	16% 5% 23% 43% 14%	394
August	1st to 10th	Night	17% 4 15% 43% 20% 1	358
	11th to 20th	Night	17% 5% 21% 38% 17% 1	508
	21st to end	Night	18% 6% 27% 32% 17% 1	727
September	1st to 10th	Night	21% 4 26% 34% 13% 1	720
	11th to 20th	Night	21% 6% 22% 32% 18% 1	720
	21st to end	Night	22% 6% 28% 30% 14% 1	720
October	1st to 10th	Night	22% 10% 26% 34% 9%	720
	11th to 20th	Night	28% 10% 26% 25% 9% 1	720
	21st to end	Night	31% 11% 31% 22% 4	792
November	1st to 10th	Night	28% 11% 27% 26% 8% 1	740
	11th to 20th	Night	27% 14% 28% 21% 9% 1	760
	21st to end	Night	33% 14% 25% 22% 7%	805
December	1st to 10th	Night	32% 13% 26% 21% 7%	850
	11th to 20th	Night	27% 17% 29% 20% 6%	850
	21st to end	Night	36% 14% 28% 18% 4	877

Page generated at 2024-01-13 09:37:57. Version ac07

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