Beamsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beamsville clear sky chart from 2005-11-06 to 2026-06-01.

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	14% 9% 3 9% 6% 5% 5% 4 6% 7% 33%	132379
	Night	14% 10% 4 9% 6% 5% 5% 4 5% 7% 32%	130771
Transparency	Day	32% 38% 8% 14% 8% 1	135974
	Night	35% 37% 8% 13% 7% 1	135262
Seeing	Day	17% 9% 24% 27% 17% 6%	16421
	Night	20% 10% 27% 28% 14% 2	25936

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% 15% 5% 12% 6% 5% 5% 4 5% 6% 24%	4661
	11th to 20th	Day	9% 20% 7% 17% 8% 7% 6% 4 5% 5% 13%	5200
	21st to end	Day	14% 14% 5% 14% 9% 8% 6% 4 4 5% 17%	5780
February	1st to 10th	Day	16% 17% 4 11% 7% 5% 6% 4 5% 5% 19%	1890
	11th to 20th	Day	12% 16% 6% 13% 7% 5% 5% 4 5% 6% 21%	1843
	21st to end	Day	17% 14% 3 11% 8% 5% 5% 4 5% 7% 21%	1636
March	1st to 10th	Day	17% 9% 4 10% 7% 5% 4 4 4 6% 30%	5042
	11th to 20th	Day	10% 12% 5% 9% 6% 5% 5% 4 6% 7% 31%	5090
	21st to end	Day	16% 10% 3 8% 6% 5% 5% 4 5% 5% 33%	5586
April	1st to 10th	Day	17% 11% 3 7% 5% 5% 4 4 5% 7% 32%	2474
	11th to 20th	Day	17% 9% 3 7% 5% 5% 4 4 5% 7% 35%	2559
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 5% 6% 35%	2730
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 5% 6% 34%	6018
	11th to 20th	Day	14% 10% 4 9% 5% 5% 4 4 5% 7% 33%	6358
	21st to end	Day	15% 7% 2 7% 4 4 5% 4 5% 7% 39%	7103
June	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 4 7% 8% 41%	2800
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 5% 8% 9% 40%	2800
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 4 6% 10% 43%	2800
July	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	6360
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 4 7% 9% 44%	6324
	21st to end	Day	7% 4 2 6% 5% 4 5% 4 6% 9% 49%	6424
August	1st to 10th	Day	16% 6% 2 5% 4 5% 5% 3 6% 8% 39%	4234
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 10% 36%	4174
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 9% 47%	4481
September	1st to 10th	Day	12% 6% 2 6% 4 5% 6% 4 5% 8% 43%	2400
	11th to 20th	Day	9% 6% 2 5% 5% 4 4 4 5% 7% 50%	2277
	21st to end	Day	14% 7% 2 7% 6% 5% 5% 4 7% 9% 35%	2160
October	1st to 10th	Day	18% 7% 2 7% 4 5% 5% 4 6% 6% 37%	2000
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 3 6% 6% 33%	2000
	21st to end	Day	23% 11% 3 9% 6% 5% 5% 4 4 6% 25%	2200
November	1st to 10th	Day	13% 9% 3 9% 5% 5% 4 4 5% 7% 33%	1821
	11th to 20th	Day	12% 12% 3 9% 7% 5% 5% 5% 5% 7% 31%	1680
	21st to end	Day	18% 14% 3 9% 6% 4 5% 4 6% 7% 23%	1680
December	1st to 10th	Day	18% 14% 5% 12% 7% 6% 5% 4 6% 6% 17%	2680
	11th to 20th	Day	17% 16% 5% 9% 6% 5% 4 4 5% 5% 24%	3066
	21st to end	Day	23% 16% 6% 13% 7% 6% 4 4 5% 5% 11%	4048
January	1st to 10th	Night	14% 15% 5% 11% 6% 5% 5% 4 5% 6% 25%	8234
	11th to 20th	Night	9% 15% 6% 15% 8% 6% 6% 4 5% 6% 19%	7681
	21st to end	Night	15% 14% 5% 12% 7% 6% 6% 3 5% 6% 21%	8401
February	1st to 10th	Night	15% 15% 5% 11% 6% 5% 6% 4 5% 6% 23%	2730
	11th to 20th	Night	13% 14% 5% 11% 6% 5% 5% 4 5% 7% 24%	2663
	21st to end	Night	16% 13% 4 11% 7% 6% 5% 4 5% 7% 21%	2166
March	1st to 10th	Night	16% 8% 4 8% 7% 5% 5% 4 5% 6% 32%	5018
	11th to 20th	Night	13% 10% 3 7% 5% 4 5% 4 5% 8% 38%	5089
	21st to end	Night	17% 9% 3 8% 5% 4 4 4 5% 5% 38%	5588
April	1st to 10th	Night	17% 11% 4 8% 7% 4 4 3 4 6% 32%	2144
	11th to 20th	Night	17% 8% 3 6% 4 5% 5% 4 5% 6% 36%	2029
	21st to end	Night	16% 8% 3 7% 4 4 5% 4 5% 7% 36%	1890
May	1st to 10th	Night	21% 11% 3 8% 5% 4 4 3 4 5% 32%	4143
	11th to 20th	Night	13% 8% 3 9% 6% 6% 5% 5% 6% 6% 34%	3754
	21st to end	Night	16% 6% 3 6% 4 4 4 4 5% 7% 43%	4014
June	1st to 10th	Night	11% 6% 3 6% 6% 5% 6% 4 7% 9% 38%	1600
	11th to 20th	Night	9% 5% 3 7% 6% 6% 4 4 6% 8% 43%	1600
	21st to end	Night	11% 5% 2 6% 4 5% 5% 4 6% 9% 44%	1600
July	1st to 10th	Night	6% 5% 2 6% 5% 4 5% 5% 6% 9% 47%	3600
	11th to 20th	Night	9% 4 2 7% 4 4 4 4 7% 9% 46%	3633
	21st to end	Night	8% 4 2 6% 4 4 4 4 6% 8% 51%	4428
August	1st to 10th	Night	10% 4 2 6% 5% 4 5% 4 6% 8% 45%	2915
	11th to 20th	Night	11% 5% 2 6% 5% 4 5% 4 6% 8% 43%	2875
	21st to end	Night	8% 4 2 6% 4 4 4 4 7% 10% 48%	3383
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 6% 7% 47%	2000
	11th to 20th	Night	10% 5% 2 4 3 4 3 4 5% 7% 53%	2120
	21st to end	Night	16% 6% 3 8% 5% 4 4 4 5% 6% 38%	2239
October	1st to 10th	Night	17% 6% 3 7% 4 3 4 3 5% 6% 42%	2400
	11th to 20th	Night	19% 9% 3 7% 4 5% 4 3 4 7% 33%	2400
	21st to end	Night	22% 9% 3 7% 5% 4 5% 3 6% 7% 30%	2640
November	1st to 10th	Night	15% 9% 3 6% 5% 4 4 4 4 6% 39%	2696
	11th to 20th	Night	15% 11% 3 8% 6% 5% 5% 4 6% 7% 30%	2940
	21st to end	Night	18% 12% 4 8% 6% 5% 5% 4 7% 6% 25%	2940
December	1st to 10th	Night	14% 16% 5% 12% 7% 5% 5% 4 6% 7% 19%	4720
	11th to 20th	Night	15% 16% 5% 10% 6% 5% 5% 4 5% 6% 25%	5348
	21st to end	Night	24% 16% 6% 11% 7% 5% 4 3 4 5% 14%	7150

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	53% 24% 10% 8% 5%	4662
	11th to 20th	Day	62% 23% 6% 6% 3	5234
	21st to end	Day	58% 24% 8% 7% 4	5780
February	1st to 10th	Day	28% 60% 5% 5% 2	1890
	11th to 20th	Day	27% 58% 5% 8% 2	1852
	21st to end	Day	24% 59% 5% 8% 3	1636
March	1st to 10th	Day	39% 30% 9% 12% 9%	5045
	11th to 20th	Day	37% 30% 14% 13% 5% 1	5090
	21st to end	Day	38% 29% 6% 17% 9% 1	5586
April	1st to 10th	Day	24% 60% 4 8% 4	2474
	11th to 20th	Day	21% 60% 4 8% 5% 1	2559
	21st to end	Day	20% 60% 6% 8% 5% 1	2730
May	1st to 10th	Day	37% 30% 9% 12% 7% 5%	6027
	11th to 20th	Day	38% 31% 9% 13% 8% 1	6362
	21st to end	Day	34% 29% 8% 16% 12% 2	7103
June	1st to 10th	Day	16% 63% 5% 9% 6% 1	2800
	11th to 20th	Day	16% 63% 5% 9% 6% 1	2800
	21st to end	Day	14% 62% 5% 11% 8%	2800
July	1st to 10th	Day	26% 28% 10% 22% 13% 1	6290
	11th to 20th	Day	23% 28% 10% 25% 12% 1	6249
	21st to end	Day	22% 28% 10% 23% 17% 1	6240
August	1st to 10th	Day	28% 38% 9% 14% 10% 1	4221
	11th to 20th	Day	28% 39% 10% 18% 5%	4213
	21st to end	Day	18% 38% 8% 26% 9%	4481
September	1st to 10th	Day	15% 59% 7% 13% 6%	2400
	11th to 20th	Day	12% 58% 5% 16% 9%	2277
	21st to end	Day	18% 58% 8% 11% 5%	2160
October	1st to 10th	Day	19% 37% 12% 20% 11% 1	3260
	11th to 20th	Day	22% 37% 11% 17% 13%	3240
	21st to end	Day	29% 38% 11% 16% 6%	3538
November	1st to 10th	Day	27% 54% 7% 9% 3	1821
	11th to 20th	Day	23% 55% 7% 10% 4	1680
	21st to end	Day	29% 56% 7% 6% 2	1680
December	1st to 10th	Day	46% 36% 11% 6% 1	2680
	11th to 20th	Day	45% 32% 7% 9% 7% 1	3066
	21st to end	Day	57% 28% 7% 5% 3	4048
January	1st to 10th	Night	52% 24% 10% 11% 2	8234
	11th to 20th	Night	56% 23% 7% 9% 5% 1	7722
	21st to end	Night	55% 24% 7% 9% 6%	8401
February	1st to 10th	Night	28% 60% 5% 6% 1	2730
	11th to 20th	Night	26% 58% 5% 8% 3	2665
	21st to end	Night	26% 60% 5% 5% 4	2166
March	1st to 10th	Night	41% 30% 9% 12% 8% 1	5028
	11th to 20th	Night	31% 29% 16% 16% 7% 1	5090
	21st to end	Night	35% 30% 5% 16% 13% 1	5588
April	1st to 10th	Night	26% 59% 4 6% 4 1	2144
	11th to 20th	Night	21% 60% 4 9% 5% 1	2029
	21st to end	Night	18% 59% 5% 11% 6% 1	1890
May	1st to 10th	Night	44% 29% 6% 9% 8% 4	4150
	11th to 20th	Night	36% 34% 8% 14% 8%	3755
	21st to end	Night	33% 29% 9% 17% 11% 1	4015
June	1st to 10th	Night	16% 63% 3 9% 8% 1	1600
	11th to 20th	Night	16% 62% 5% 9% 7% 1	1600
	21st to end	Night	16% 61% 4 9% 10% 2	1600
July	1st to 10th	Night	27% 28% 11% 16% 17% 1	3560
	11th to 20th	Night	25% 27% 10% 23% 12% 2	3585
	21st to end	Night	24% 27% 10% 19% 19% 1	4297
August	1st to 10th	Night	24% 37% 9% 18% 11% 2	2904
	11th to 20th	Night	28% 39% 8% 19% 6%	2902
	21st to end	Night	20% 38% 9% 23% 9%	3383
September	1st to 10th	Night	14% 57% 7% 14% 8%	2000
	11th to 20th	Night	12% 58% 5% 15% 10%	2120
	21st to end	Night	20% 57% 5% 12% 6% 1	2239
October	1st to 10th	Night	21% 36% 6% 18% 18%	3920
	11th to 20th	Night	29% 37% 8% 18% 8%	3899
	21st to end	Night	22% 37% 13% 21% 7%	4252
November	1st to 10th	Night	25% 54% 5% 10% 5%	2696
	11th to 20th	Night	24% 55% 5% 11% 4	2940
	21st to end	Night	29% 56% 7% 6% 2	2940
December	1st to 10th	Night	45% 38% 11% 5% 2	4720
	11th to 20th	Night	44% 32% 6% 10% 7% 1	5348
	21st to end	Night	55% 27% 8% 7% 2	7150

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	19% 16% 38% 18% 8% 1	220
	11th to 20th	Day	22% 19% 37% 15% 5% 2	320
	21st to end	Day	19% 19% 33% 24% 4 1	363
February	1st to 10th	Day	21% 17% 38% 19% 5%	330
	11th to 20th	Day	22% 16% 36% 22% 4	330
	21st to end	Day	23% 21% 33% 19% 4	300
March	1st to 10th	Day	20% 13% 33% 26% 7%	540
	11th to 20th	Day	19% 15% 32% 25% 7% 1	540
	21st to end	Day	25% 11% 28% 27% 8% 2	594
April	1st to 10th	Day	17% 13% 31% 29% 9% 1	540
	11th to 20th	Day	24% 10% 28% 23% 12% 4	532
	21st to end	Day	21% 8% 25% 32% 12% 2	540
May	1st to 10th	Day	20% 6% 23% 32% 15% 3	543
	11th to 20th	Day	17% 5% 17% 33% 22% 6%	567
	21st to end	Day	13% 3 20% 33% 22% 8%	617
June	1st to 10th	Day	12% 5% 22% 38% 19% 3	530
	11th to 20th	Day	11% 4 22% 32% 26% 5%	530
	21st to end	Day	13% 4 18% 36% 23% 6%	530
July	1st to 10th	Day	7% 1 13% 34% 33% 12%	525
	11th to 20th	Day	16% 3 13% 31% 26% 12%	524
	21st to end	Day	8% 3 15% 39% 26% 10%	576
August	1st to 10th	Day	10% 2 14% 30% 29% 13%	526
	11th to 20th	Day	11% 3 17% 26% 30% 12%	519
	21st to end	Day	11% 4 16% 28% 29% 12%	583
September	1st to 10th	Day	14% 5% 18% 26% 25% 13%	530
	11th to 20th	Day	9% 4 15% 22% 30% 20%	530
	21st to end	Day	16% 6% 23% 25% 20% 9%	530
October	1st to 10th	Day	20% 7% 23% 22% 18% 10%	530
	11th to 20th	Day	20% 13% 28% 25% 11% 3	530
	21st to end	Day	30% 11% 24% 23% 10% 1	583
November	1st to 10th	Day	19% 17% 27% 25% 10% 2	347
	11th to 20th	Day	21% 16% 30% 23% 8% 1	220
	21st to end	Day	22% 15% 38% 19% 5%	220
December	1st to 10th	Day	23% 20% 32% 17% 6% 1	220
	11th to 20th	Day	25% 22% 33% 18% 2	220
	21st to end	Day	26% 15% 35% 18% 5%	242
January	1st to 10th	Night	25% 19% 33% 17% 6%	840
	11th to 20th	Night	27% 18% 32% 19% 4	840
	21st to end	Night	19% 15% 38% 23% 6%	924
February	1st to 10th	Night	24% 16% 35% 21% 4	840
	11th to 20th	Night	22% 14% 35% 24% 4	823
	21st to end	Night	24% 14% 36% 23% 4	692
March	1st to 10th	Night	19% 13% 35% 25% 8%	840
	11th to 20th	Night	25% 12% 32% 24% 7% 1	840
	21st to end	Night	20% 9% 28% 31% 10% 1	924
April	1st to 10th	Night	22% 11% 28% 31% 7% 1	840
	11th to 20th	Night	22% 7% 29% 29% 11% 2	785
	21st to end	Night	18% 6% 28% 34% 14%	630
May	1st to 10th	Night	19% 5% 22% 32% 19% 3	630
	11th to 20th	Night	15% 4 22% 39% 19% 1	461
	21st to end	Night	13% 4 19% 38% 23% 3	455
June	1st to 10th	Night	12% 2 25% 41% 19% 2	400
	11th to 20th	Night	12% 3 24% 38% 24% 1	400
	21st to end	Night	12% 4 18% 43% 23% 1	400
July	1st to 10th	Night	8% 2 13% 47% 27% 3	390
	11th to 20th	Night	10% 2 18% 39% 26% 4	395
	21st to end	Night	10% 2 14% 43% 27% 4	657
August	1st to 10th	Night	10% 2 12% 37% 34% 5%	597
	11th to 20th	Night	8% 3 14% 32% 37% 6%	594
	21st to end	Night	12% 2 15% 36% 30% 5%	755
September	1st to 10th	Night	13% 5% 16% 33% 27% 7%	800
	11th to 20th	Night	12% 4 15% 27% 31% 11%	800
	21st to end	Night	18% 5% 20% 29% 24% 6%	800
October	1st to 10th	Night	19% 6% 23% 27% 22% 4	800
	11th to 20th	Night	24% 12% 27% 25% 11% 2	800
	21st to end	Night	28% 9% 29% 27% 7%	880
November	1st to 10th	Night	20% 12% 27% 28% 12% 1	820
	11th to 20th	Night	22% 17% 30% 21% 9% 2	840
	21st to end	Night	26% 14% 33% 22% 6%	840
December	1st to 10th	Night	30% 16% 31% 17% 7%	840
	11th to 20th	Night	23% 19% 34% 19% 5%	840
	21st to end	Night	29% 15% 32% 20% 3	924

Page generated at 2026-05-29 01:53:28. Version ac07

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