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 2025-02-06.

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% 10% 3 8% 5% 5% 5% 4 6% 7% 33%	108640
	Night	15% 10% 4 9% 5% 5% 4 4 5% 7% 32%	109607
Transparency	Day	28% 44% 8% 12% 6% 1	112280
	Night	31% 43% 7% 12% 6%	114130
Seeing	Day	17% 9% 25% 27% 16% 6%	14705
	Night	20% 10% 27% 28% 14% 2	24278

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	12% 16% 6% 12% 6% 5% 5% 4 5% 5% 25%	3597
	11th to 20th	Day	10% 20% 7% 15% 7% 6% 6% 4 5% 5% 13%	3994
	21st to end	Day	18% 15% 5% 14% 7% 6% 5% 4 4 5% 17%	4466
February	1st to 10th	Day	16% 17% 5% 12% 8% 5% 5% 4 5% 5% 19%	1755
	11th to 20th	Day	11% 17% 6% 13% 7% 6% 5% 4 6% 6% 21%	1663
	21st to end	Day	17% 14% 3 11% 8% 5% 5% 4 5% 6% 22%	1484
March	1st to 10th	Day	18% 10% 4 10% 7% 5% 4 4 5% 6% 28%	3432
	11th to 20th	Day	10% 15% 4 9% 6% 5% 5% 4 6% 6% 31%	3480
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 5% 6% 36%	3815
April	1st to 10th	Day	17% 11% 3 7% 5% 5% 4 4 5% 6% 32%	2238
	11th to 20th	Day	17% 8% 3 7% 5% 4 4 4 5% 7% 36%	2313
	21st to end	Day	18% 8% 3 7% 5% 4 5% 4 5% 6% 35%	2470
May	1st to 10th	Day	15% 8% 3 8% 5% 5% 5% 4 5% 7% 35%	4108
	11th to 20th	Day	14% 10% 4 9% 6% 5% 5% 4 5% 7% 32%	4328
	21st to end	Day	9% 6% 2 6% 4 3 5% 4 5% 8% 47%	4837
June	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 4 7% 8% 40%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 4 8% 9% 41%	2660
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 6% 10% 43%	2660
July	1st to 10th	Day	7% 4 1 5% 5% 5% 5% 5% 7% 11% 45%	4440
	11th to 20th	Day	10% 5% 2 4 4 4 5% 4 8% 10% 45%	4418
	21st to end	Day	7% 4 2 6% 6% 4 6% 5% 6% 10% 44%	4466
August	1st to 10th	Day	16% 6% 2 6% 4 4 5% 4 7% 8% 39%	4104
	11th to 20th	Day	11% 6% 2 8% 5% 5% 6% 5% 7% 10% 36%	4044
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 10% 47%	4344
September	1st to 10th	Day	13% 6% 2 6% 4 5% 6% 4 5% 8% 42%	2280
	11th to 20th	Day	9% 6% 2 4 5% 4 4 4 5% 7% 50%	2163
	21st to end	Day	14% 7% 2 7% 6% 5% 5% 4 6% 9% 35%	2052
October	1st to 10th	Day	18% 7% 2 7% 4 5% 5% 4 6% 6% 35%	1900
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 3 6% 5% 32%	1900
	21st to end	Day	23% 12% 3 9% 6% 4 5% 4 4 7% 24%	2090
November	1st to 10th	Day	13% 9% 3 9% 5% 5% 4 4 5% 8% 34%	1733
	11th to 20th	Day	13% 12% 3 9% 7% 5% 5% 5% 5% 7% 31%	1600
	21st to end	Day	19% 14% 3 9% 5% 4 5% 4 6% 7% 23%	1600
December	1st to 10th	Day	18% 14% 5% 12% 7% 6% 5% 4 6% 6% 17%	2600
	11th to 20th	Day	18% 16% 5% 9% 6% 5% 4 4 5% 5% 24%	2986
	21st to end	Day	23% 16% 6% 12% 7% 6% 4 4 5% 5% 11%	3960
January	1st to 10th	Night	14% 13% 4 11% 7% 5% 5% 4 5% 6% 26%	6349
	11th to 20th	Night	10% 15% 6% 15% 8% 6% 6% 4 5% 6% 18%	5887
	21st to end	Night	19% 15% 5% 12% 5% 5% 5% 3 5% 5% 21%	6490
February	1st to 10th	Night	16% 15% 5% 12% 6% 4 5% 4 5% 6% 21%	2536
	11th to 20th	Night	13% 14% 4 11% 6% 5% 5% 4 5% 8% 24%	2403
	21st to end	Night	17% 12% 4 11% 7% 6% 4 4 5% 8% 22%	1967
March	1st to 10th	Night	21% 9% 3 7% 6% 5% 4 3 4 5% 32%	3408
	11th to 20th	Night	16% 13% 3 7% 4 3 4 4 4 7% 35%	3479
	21st to end	Night	15% 8% 3 7% 4 3 4 4 5% 6% 41%	3817
April	1st to 10th	Night	18% 11% 3 8% 7% 4 3 3 5% 6% 32%	1940
	11th to 20th	Night	18% 8% 3 6% 4 5% 4 4 5% 5% 37%	1834
	21st to end	Night	16% 9% 3 7% 4 4 5% 4 6% 6% 36%	1710
May	1st to 10th	Night	19% 10% 3 8% 4 4 3 3 5% 6% 35%	2833
	11th to 20th	Night	14% 9% 4 10% 6% 6% 5% 5% 6% 6% 31%	2564
	21st to end	Night	10% 5% 3 5% 4 3 4 4 5% 8% 49%	2738
June	1st to 10th	Night	11% 6% 3 6% 6% 5% 6% 4 7% 9% 37%	1520
	11th to 20th	Night	8% 5% 3 6% 6% 6% 4 4 6% 8% 43%	1520
	21st to end	Night	11% 6% 2 6% 4 5% 5% 4 6% 9% 43%	1520
July	1st to 10th	Night	6% 5% 2 6% 5% 4 4 4 6% 9% 49%	2520
	11th to 20th	Night	9% 4 2 6% 4 4 4 4 6% 9% 48%	2539
	21st to end	Night	8% 4 2 6% 4 4 4 5% 6% 9% 49%	3087
August	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 4 6% 8% 44%	2825
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 4 6% 8% 42%	2785
	21st to end	Night	8% 4 2 6% 4 4 4 4 7% 10% 48%	3279
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 6% 7% 46%	1900
	11th to 20th	Night	11% 5% 2 5% 3 5% 3 4 5% 7% 52%	2014
	21st to end	Night	16% 7% 3 8% 5% 4 4 4 6% 6% 37%	2127
October	1st to 10th	Night	18% 7% 3 7% 5% 4 4 3 5% 6% 40%	2280
	11th to 20th	Night	19% 9% 3 7% 4 5% 4 3 4 7% 33%	2280
	21st to end	Night	23% 9% 3 7% 5% 4 5% 3 6% 7% 28%	2508
November	1st to 10th	Night	16% 8% 3 7% 5% 4 4 4 4 6% 39%	2564
	11th to 20th	Night	15% 11% 3 8% 6% 5% 5% 4 6% 7% 31%	2800
	21st to end	Night	19% 12% 4 8% 6% 5% 5% 4 6% 6% 25%	2800
December	1st to 10th	Night	15% 16% 5% 11% 7% 5% 5% 4 6% 7% 18%	4580
	11th to 20th	Night	15% 17% 5% 9% 6% 5% 5% 4 5% 6% 25%	5208
	21st to end	Night	25% 16% 6% 11% 7% 5% 4 3 4 5% 14%	6996

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	50% 29% 9% 7% 6%	3598
	11th to 20th	Day	56% 28% 8% 5% 2	4028
	21st to end	Day	51% 29% 9% 6% 4	4466
February	1st to 10th	Day	26% 64% 4 4 1	1755
	11th to 20th	Day	23% 65% 4 7% 2	1672
	21st to end	Day	20% 65% 5% 7% 3	1484
March	1st to 10th	Day	35% 43% 5% 14% 3	3435
	11th to 20th	Day	32% 41% 10% 12% 4 1	3480
	21st to end	Day	27% 41% 7% 17% 8% 1	3815
April	1st to 10th	Day	20% 66% 4 7% 3	2238
	11th to 20th	Day	17% 66% 4 7% 5% 1	2313
	21st to end	Day	17% 66% 5% 6% 5% 1	2470
May	1st to 10th	Day	30% 41% 8% 13% 7% 2	4120
	11th to 20th	Day	33% 43% 10% 12% 1	4332
	21st to end	Day	21% 40% 8% 16% 13% 2	4837
June	1st to 10th	Day	15% 66% 4 9% 5% 1	2660
	11th to 20th	Day	14% 66% 5% 8% 6% 1	2660
	21st to end	Day	13% 64% 4 10% 8%	2660
July	1st to 10th	Day	22% 37% 9% 20% 11% 1	4370
	11th to 20th	Day	18% 38% 8% 26% 9%	4343
	21st to end	Day	21% 38% 10% 15% 15% 1	4324
August	1st to 10th	Day	29% 39% 9% 14% 9% 1	4091
	11th to 20th	Day	28% 40% 10% 17% 5%	4083
	21st to end	Day	18% 39% 8% 25% 9%	4344
September	1st to 10th	Day	14% 62% 6% 12% 6%	2280
	11th to 20th	Day	11% 60% 5% 14% 9%	2163
	21st to end	Day	17% 61% 7% 11% 4	2052
October	1st to 10th	Day	19% 38% 12% 19% 10%	3160
	11th to 20th	Day	21% 38% 12% 16% 12%	3140
	21st to end	Day	28% 39% 11% 16% 5%	3428
November	1st to 10th	Day	25% 56% 7% 8% 3	1733
	11th to 20th	Day	22% 58% 7% 10% 4	1600
	21st to end	Day	28% 58% 7% 5% 2	1600
December	1st to 10th	Day	45% 37% 11% 5% 1	2600
	11th to 20th	Day	45% 33% 7% 8% 7% 1	2986
	21st to end	Day	56% 29% 7% 5% 3	3960
January	1st to 10th	Night	47% 30% 9% 12% 2	6349
	11th to 20th	Night	52% 28% 8% 10% 2	5928
	21st to end	Night	49% 29% 7% 7% 7%	6490
February	1st to 10th	Night	26% 63% 5% 5% 1	2536
	11th to 20th	Night	22% 64% 4 7% 3	2405
	21st to end	Night	21% 65% 5% 5% 3	1967
March	1st to 10th	Night	34% 41% 7% 14% 4	3418
	11th to 20th	Night	29% 40% 13% 11% 6% 1	3480
	21st to end	Night	23% 42% 5% 17% 12% 1	3817
April	1st to 10th	Night	22% 65% 3 6% 3	1940
	11th to 20th	Night	17% 66% 3 8% 5% 1	1834
	21st to end	Night	15% 65% 5% 9% 5% 1	1710
May	1st to 10th	Night	34% 41% 7% 10% 8% 1	2840
	11th to 20th	Night	32% 47% 9% 10% 2	2565
	21st to end	Night	20% 41% 7% 16% 14% 1	2739
June	1st to 10th	Night	15% 66% 3 8% 8% 1	1520
	11th to 20th	Night	14% 65% 4 9% 7% 1	1520
	21st to end	Night	15% 64% 3 9% 8% 1	1520
July	1st to 10th	Night	22% 38% 9% 15% 15% 2	2480
	11th to 20th	Night	21% 36% 10% 24% 9%	2491
	21st to end	Night	21% 38% 12% 17% 12% 1	2988
August	1st to 10th	Night	24% 38% 8% 18% 11% 2	2814
	11th to 20th	Night	28% 40% 8% 18% 5%	2812
	21st to end	Night	20% 39% 9% 23% 9%	3279
September	1st to 10th	Night	14% 60% 7% 11% 8%	1900
	11th to 20th	Night	11% 60% 5% 13% 10%	2014
	21st to end	Night	18% 60% 5% 11% 5%	2127
October	1st to 10th	Night	21% 37% 6% 17% 18%	3800
	11th to 20th	Night	28% 38% 8% 18% 7%	3779
	21st to end	Night	21% 38% 13% 21% 7%	4120
November	1st to 10th	Night	24% 57% 5% 9% 5%	2564
	11th to 20th	Night	23% 57% 5% 11% 4	2800
	21st to end	Night	27% 58% 7% 6% 2	2800
December	1st to 10th	Night	44% 39% 11% 5% 2	4580
	11th to 20th	Night	44% 33% 6% 10% 7% 1	5208
	21st to end	Night	55% 28% 8% 7% 2	6996

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	20% 17% 36% 19% 8% 2	200
	11th to 20th	Day	21% 19% 38% 16% 5% 2	291
	21st to end	Day	19% 18% 33% 25% 4 1	330
February	1st to 10th	Day	22% 17% 39% 19% 2	285
	11th to 20th	Day	21% 17% 39% 20% 3	270
	21st to end	Day	25% 22% 33% 17% 3	249
March	1st to 10th	Day	20% 14% 32% 27% 7%	460
	11th to 20th	Day	19% 15% 33% 25% 7% 1	460
	21st to end	Day	25% 11% 28% 25% 8% 2	506
April	1st to 10th	Day	16% 12% 31% 29% 10% 1	460
	11th to 20th	Day	24% 10% 28% 23% 10% 4	452
	21st to end	Day	22% 9% 26% 30% 11% 2	460
May	1st to 10th	Day	19% 6% 26% 28% 16% 4	463
	11th to 20th	Day	17% 5% 17% 32% 22% 6%	487
	21st to end	Day	11% 4 21% 32% 23% 9%	529
June	1st to 10th	Day	12% 6% 22% 37% 19% 4	490
	11th to 20th	Day	12% 4 22% 30% 27% 5%	490
	21st to end	Day	14% 4 19% 36% 22% 6%	490
July	1st to 10th	Day	8% 1 13% 33% 32% 13%	485
	11th to 20th	Day	16% 3 13% 31% 24% 12%	484
	21st to end	Day	8% 3 16% 38% 25% 10%	532
August	1st to 10th	Day	10% 2 16% 31% 28% 13%	486
	11th to 20th	Day	10% 3 18% 27% 30% 12%	479
	21st to end	Day	12% 4 17% 28% 28% 12%	539
September	1st to 10th	Day	14% 5% 18% 27% 24% 12%	490
	11th to 20th	Day	10% 4 16% 22% 29% 19%	490
	21st to end	Day	17% 7% 25% 26% 17% 10%	490
October	1st to 10th	Day	21% 8% 24% 22% 16% 9%	490
	11th to 20th	Day	20% 13% 27% 24% 11% 3	490
	21st to end	Day	31% 11% 24% 22% 10% 1	539
November	1st to 10th	Day	18% 18% 28% 24% 10% 3	319
	11th to 20th	Day	22% 17% 30% 24% 8% 1	200
	21st to end	Day	22% 16% 39% 19% 6%	200
December	1st to 10th	Day	23% 20% 34% 16% 7% 1	200
	11th to 20th	Day	27% 23% 33% 16% 3	200
	21st to end	Day	26% 14% 36% 19% 5%	220
January	1st to 10th	Night	25% 19% 33% 17% 6% 1	800
	11th to 20th	Night	27% 17% 33% 20% 4	800
	21st to end	Night	19% 14% 37% 23% 6%	880
February	1st to 10th	Night	25% 17% 35% 20% 3	781
	11th to 20th	Night	22% 14% 36% 24% 4	743
	21st to end	Night	24% 14% 35% 22% 4	628
March	1st to 10th	Night	20% 12% 34% 25% 9%	760
	11th to 20th	Night	25% 13% 31% 23% 7% 1	760
	21st to end	Night	20% 9% 28% 31% 11% 1	836
April	1st to 10th	Night	21% 11% 29% 31% 7% 1	760
	11th to 20th	Night	22% 7% 30% 27% 11% 2	710
	21st to end	Night	19% 6% 28% 33% 13%	570
May	1st to 10th	Night	19% 5% 21% 32% 20% 3	570
	11th to 20th	Night	16% 4 21% 40% 19% 1	417
	21st to end	Night	11% 4 20% 37% 25% 4	411
June	1st to 10th	Night	13% 2 26% 39% 18% 2	380
	11th to 20th	Night	12% 3 24% 36% 24% 1	380
	21st to end	Night	12% 4 18% 44% 21% 1	380
July	1st to 10th	Night	8% 2 14% 45% 27% 4	370
	11th to 20th	Night	10% 2 18% 40% 25% 5%	374
	21st to end	Night	10% 2 14% 44% 26% 4	624
August	1st to 10th	Night	10% 2 13% 37% 32% 5%	567
	11th to 20th	Night	8% 3 15% 32% 37% 5%	564
	21st to end	Night	12% 2 15% 35% 31% 5%	717
September	1st to 10th	Night	13% 5% 16% 33% 26% 7%	760
	11th to 20th	Night	13% 4 15% 28% 30% 10%	760
	21st to end	Night	18% 5% 20% 28% 23% 6%	760
October	1st to 10th	Night	20% 6% 24% 27% 21% 4	760
	11th to 20th	Night	24% 12% 27% 24% 11% 2	760
	21st to end	Night	29% 9% 28% 26% 7%	836
November	1st to 10th	Night	20% 11% 27% 28% 12% 1	780
	11th to 20th	Night	22% 17% 30% 21% 9% 2	800
	21st to end	Night	26% 13% 33% 22% 6%	800
December	1st to 10th	Night	30% 16% 31% 16% 6%	800
	11th to 20th	Night	24% 18% 34% 19% 5%	800
	21st to end	Night	30% 14% 32% 21% 3	880

Page generated at 2025-02-03 03:05:55. Version ac07

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