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 2024-01-31.

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 7% 6% 4 5% 5% 6% 7% 34%	74812
	Night	16% 10% 4 7% 6% 4 5% 5% 5% 7% 32%	75316
Transparency	Day	33% 37% 9% 14% 7% 1	74529
	Night	35% 37% 8% 13% 6% 1	75133
Seeing	Day	17% 9% 25% 27% 16% 6%	13405
	Night	20% 10% 27% 28% 14% 2	22991

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% 14% 6% 10% 9% 5% 7% 7% 6% 6% 18%	1517
	11th to 20th	Day	14% 16% 5% 11% 10% 4 7% 5% 5% 5% 17%	1691
	21st to end	Day	14% 13% 6% 14% 10% 6% 7% 6% 4 6% 12%	1872
February	1st to 10th	Day	17% 16% 5% 10% 8% 4 5% 5% 5% 5% 18%	1620
	11th to 20th	Day	12% 16% 7% 12% 7% 4 5% 5% 5% 6% 20%	1573
	21st to end	Day	18% 13% 3 10% 9% 4 5% 5% 4 7% 22%	1398
March	1st to 10th	Day	14% 9% 5% 9% 8% 4 4 6% 5% 6% 28%	1977
	11th to 20th	Day	13% 11% 5% 8% 7% 3 5% 5% 5% 5% 33%	1980
	21st to end	Day	18% 9% 3 7% 6% 3 6% 5% 4 6% 33%	2178
April	1st to 10th	Day	17% 9% 4 6% 7% 3 5% 5% 5% 7% 32%	2120
	11th to 20th	Day	17% 7% 3 5% 6% 3 4 5% 5% 7% 36%	2189
	21st to end	Day	19% 8% 3 6% 6% 3 5% 5% 5% 6% 35%	2340
May	1st to 10th	Day	13% 8% 3 7% 7% 3 5% 5% 5% 8% 36%	2340
	11th to 20th	Day	14% 6% 3 6% 6% 4 6% 6% 5% 6% 39%	2436
	21st to end	Day	10% 4 2 5% 5% 2 5% 6% 6% 9% 45%	2725
June	1st to 10th	Day	13% 5% 3 5% 5% 3 5% 5% 6% 8% 42%	2520
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 5% 7% 10% 41%	2520
	21st to end	Day	11% 4 2 5% 5% 3 5% 5% 6% 10% 44%	2520
July	1st to 10th	Day	5% 4 1 4 5% 3 5% 6% 7% 9% 50%	2520
	11th to 20th	Day	11% 5% 2 4 5% 3 6% 6% 8% 9% 41%	2512
	21st to end	Day	9% 4 2 6% 7% 3 7% 6% 7% 10% 41%	2547
August	1st to 10th	Day	7% 4 2 5% 5% 4 5% 5% 8% 11% 43%	2327
	11th to 20th	Day	8% 5% 2 6% 6% 4 6% 7% 7% 10% 40%	2303
	21st to end	Day	10% 5% 2 5% 5% 3 4 5% 6% 9% 47%	2470
September	1st to 10th	Day	13% 6% 2 5% 4 4 5% 5% 6% 8% 41%	2160
	11th to 20th	Day	10% 6% 2 4 5% 3 4 4 5% 7% 49%	2050
	21st to end	Day	14% 6% 2 5% 7% 3 5% 5% 6% 9% 37%	1944
October	1st to 10th	Day	19% 7% 2 6% 5% 3 5% 5% 6% 6% 34%	1800
	11th to 20th	Day	18% 10% 4 8% 6% 3 5% 5% 5% 6% 31%	1800
	21st to end	Day	24% 12% 3 7% 7% 3 5% 4 4 6% 24%	1980
November	1st to 10th	Day	13% 8% 4 8% 6% 4 5% 5% 5% 8% 34%	1645
	11th to 20th	Day	13% 11% 4 8% 7% 3 5% 6% 5% 7% 31%	1520
	21st to end	Day	19% 14% 3 7% 6% 3 5% 5% 6% 8% 25%	1520
December	1st to 10th	Day	17% 13% 6% 10% 8% 4 5% 4 6% 6% 20%	1520
	11th to 20th	Day	17% 14% 6% 9% 7% 5% 6% 5% 6% 6% 20%	1906
	21st to end	Day	27% 18% 6% 10% 7% 4 4 4 4 4 11%	2772
January	1st to 10th	Night	15% 16% 6% 9% 9% 4 5% 4 5% 5% 21%	2649
	11th to 20th	Night	18% 15% 6% 11% 9% 5% 6% 5% 5% 6% 16%	2485
	21st to end	Night	13% 14% 6% 10% 9% 5% 6% 5% 5% 6% 19%	2711
February	1st to 10th	Night	17% 15% 5% 10% 7% 4 6% 5% 5% 6% 21%	2340
	11th to 20th	Night	14% 13% 6% 10% 7% 4 5% 5% 5% 8% 24%	2273
	21st to end	Night	18% 12% 5% 9% 8% 4 6% 4 5% 8% 22%	1855
March	1st to 10th	Night	14% 10% 4 7% 9% 4 5% 5% 5% 6% 31%	1970
	11th to 20th	Night	17% 11% 5% 8% 6% 2 4 5% 4 6% 32%	1979
	21st to end	Night	16% 9% 4 8% 6% 3 4 5% 4 4 37%	2178
April	1st to 10th	Night	17% 9% 4 7% 7% 3 4 4 5% 7% 33%	1838
	11th to 20th	Night	17% 7% 3 5% 5% 4 4 5% 5% 6% 38%	1737
	21st to end	Night	16% 8% 4 6% 5% 3 5% 5% 6% 6% 35%	1620
May	1st to 10th	Night	15% 9% 4 6% 5% 3 4 4 6% 7% 37%	1620
	11th to 20th	Night	13% 5% 3 6% 5% 3 4 6% 6% 7% 42%	1456
	21st to end	Night	11% 5% 3 4 5% 3 3 5% 5% 7% 50%	1550
June	1st to 10th	Night	11% 6% 3 5% 6% 4 5% 6% 7% 9% 38%	1440
	11th to 20th	Night	9% 5% 3 5% 7% 4 5% 5% 5% 8% 44%	1440
	21st to end	Night	11% 5% 2 5% 4 3 5% 5% 6% 9% 45%	1440
July	1st to 10th	Night	5% 4 1 4 5% 3 3 5% 4 8% 56%	1440
	11th to 20th	Night	9% 3 2 6% 4 2 5% 5% 7% 9% 47%	1445
	21st to end	Night	9% 3 2 5% 5% 3 5% 5% 7% 9% 47%	1771
August	1st to 10th	Night	9% 4 2 5% 5% 3 5% 5% 7% 8% 47%	1611
	11th to 20th	Night	7% 4 2 5% 5% 4 5% 5% 7% 9% 48%	1598
	21st to end	Night	9% 4 2 5% 5% 3 4 5% 6% 9% 48%	1867
September	1st to 10th	Night	13% 5% 3 5% 5% 4 4 4 6% 7% 44%	1800
	11th to 20th	Night	11% 5% 2 4 3 4 3 4 5% 6% 52%	1908
	21st to end	Night	15% 6% 3 7% 6% 3 4 5% 5% 7% 39%	2015
October	1st to 10th	Night	18% 7% 3 6% 5% 3 4 4 5% 6% 39%	2160
	11th to 20th	Night	20% 9% 4 6% 6% 4 5% 4 4 7% 32%	2160
	21st to end	Night	24% 9% 3 6% 6% 3 5% 4 5% 7% 27%	2376
November	1st to 10th	Night	16% 8% 3 6% 6% 3 5% 5% 4 6% 39%	2432
	11th to 20th	Night	15% 9% 4 7% 7% 4 5% 5% 5% 7% 31%	2660
	21st to end	Night	19% 11% 5% 7% 6% 4 5% 5% 6% 7% 26%	2660
December	1st to 10th	Night	18% 16% 6% 9% 6% 4 5% 5% 5% 5% 21%	2660
	11th to 20th	Night	15% 17% 6% 10% 7% 4 5% 5% 5% 6% 22%	3288
	21st to end	Night	29% 15% 6% 9% 7% 3 4 4 4 5% 12%	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	45% 40% 7% 6% 1	1518
	11th to 20th	Day	46% 40% 6% 6% 2	1691
	21st to end	Day	51% 36% 7% 6% 1	1872
February	1st to 10th	Day	45% 36% 7% 9% 2	1620
	11th to 20th	Day	44% 37% 7% 8% 3	1582
	21st to end	Day	46% 36% 8% 7% 3	1398
March	1st to 10th	Day	36% 37% 11% 12% 3 1	1980
	11th to 20th	Day	36% 36% 9% 11% 7% 1	1980
	21st to end	Day	34% 36% 8% 16% 6% 1	2178
April	1st to 10th	Day	32% 36% 9% 13% 9% 1	2120
	11th to 20th	Day	31% 36% 8% 14% 10% 1	2189
	21st to end	Day	34% 36% 7% 13% 8% 1	2340
May	1st to 10th	Day	32% 36% 7% 14% 9% 2	2340
	11th to 20th	Day	29% 37% 7% 14% 12% 2	2440
	21st to end	Day	22% 38% 11% 17% 10% 2	2725
June	1st to 10th	Day	26% 37% 9% 16% 11% 1	2520
	11th to 20th	Day	24% 37% 11% 19% 10%	2520
	21st to end	Day	24% 38% 11% 18% 8% 1	2520
July	1st to 10th	Day	20% 39% 9% 19% 12% 1	2450
	11th to 20th	Day	23% 39% 12% 18% 8% 1	2437
	21st to end	Day	25% 39% 11% 16% 8%	2405
August	1st to 10th	Day	24% 37% 11% 20% 8%	2314
	11th to 20th	Day	22% 36% 13% 18% 10% 1	2303
	21st to end	Day	24% 37% 9% 20% 10% 1	2470
September	1st to 10th	Day	27% 37% 9% 17% 8% 1	2160
	11th to 20th	Day	24% 36% 11% 21% 8%	2050
	21st to end	Day	32% 36% 10% 16% 5% 1	1944
October	1st to 10th	Day	32% 38% 8% 14% 8%	1800
	11th to 20th	Day	39% 36% 8% 13% 3	1800
	21st to end	Day	41% 37% 8% 10% 3 1	1980
November	1st to 10th	Day	28% 41% 9% 15% 6% 1	1645
	11th to 20th	Day	34% 41% 10% 9% 6%	1520
	21st to end	Day	37% 40% 9% 12% 2	1520
December	1st to 10th	Day	41% 40% 11% 8% 1	1520
	11th to 20th	Day	45% 34% 11% 8% 3	1906
	21st to end	Day	62% 26% 7% 5%	2772
January	1st to 10th	Night	44% 40% 7% 7% 2	2649
	11th to 20th	Night	46% 40% 7% 5% 1	2485
	21st to end	Night	46% 36% 7% 9% 1	2711
February	1st to 10th	Night	43% 36% 7% 10% 4	2340
	11th to 20th	Night	40% 37% 9% 10% 4	2275
	21st to end	Night	42% 36% 8% 10% 4	1855
March	1st to 10th	Night	36% 36% 10% 13% 4 1	1980
	11th to 20th	Night	37% 37% 6% 13% 6% 1	1980
	21st to end	Night	34% 36% 5% 16% 7% 2	2178
April	1st to 10th	Night	33% 36% 6% 15% 9% 1	1838
	11th to 20th	Night	33% 36% 6% 14% 11% 1	1737
	21st to end	Night	34% 36% 6% 11% 10% 2	1620
May	1st to 10th	Night	30% 36% 6% 16% 10% 3	1620
	11th to 20th	Night	25% 37% 7% 16% 11% 4	1457
	21st to end	Night	22% 37% 9% 17% 13% 3	1551
June	1st to 10th	Night	26% 38% 9% 15% 10% 1	1440
	11th to 20th	Night	25% 37% 8% 16% 13% 2	1440
	21st to end	Night	25% 38% 11% 16% 10%	1440
July	1st to 10th	Night	20% 38% 8% 18% 16% 1	1400
	11th to 20th	Night	22% 38% 10% 18% 11% 2	1397
	21st to end	Night	20% 38% 10% 18% 12% 1	1672
August	1st to 10th	Night	26% 38% 10% 18% 8% 1	1600
	11th to 20th	Night	21% 36% 12% 20% 10% 1	1598
	21st to end	Night	22% 36% 9% 21% 10% 2	1867
September	1st to 10th	Night	28% 36% 8% 17% 10% 2	1800
	11th to 20th	Night	23% 37% 7% 24% 9%	1908
	21st to end	Night	32% 36% 8% 15% 8%	2015
October	1st to 10th	Night	32% 37% 6% 17% 8% 1	2160
	11th to 20th	Night	37% 36% 9% 13% 5%	2160
	21st to end	Night	39% 37% 8% 10% 5%	2376
November	1st to 10th	Night	27% 42% 6% 18% 7% 1	2432
	11th to 20th	Night	33% 41% 9% 11% 6%	2660
	21st to end	Night	36% 41% 10% 12% 2	2660
December	1st to 10th	Night	42% 42% 8% 7% 1	2660
	11th to 20th	Night	45% 34% 10% 9% 2	3288
	21st to end	Night	61% 26% 9% 4 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	20% 16% 36% 18% 9% 2	180
	11th to 20th	Day	20% 19% 38% 15% 5% 2	261
	21st to end	Day	20% 17% 32% 26% 4 1	294
February	1st to 10th	Day	25% 18% 40% 16% 1	240
	11th to 20th	Day	23% 16% 41% 18% 2	240
	21st to end	Day	27% 20% 35% 15% 3	220
March	1st to 10th	Day	20% 14% 33% 27% 6%	420
	11th to 20th	Day	19% 14% 33% 26% 7% 1	420
	21st to end	Day	26% 11% 28% 24% 9% 2	462
April	1st to 10th	Day	15% 11% 31% 30% 11% 1	420
	11th to 20th	Day	24% 10% 26% 24% 11% 5%	412
	21st to end	Day	23% 7% 26% 31% 11% 2	420
May	1st to 10th	Day	20% 6% 27% 27% 15% 4	423
	11th to 20th	Day	17% 5% 17% 32% 21% 7%	447
	21st to end	Day	12% 3 20% 32% 24% 10%	485
June	1st to 10th	Day	12% 5% 22% 38% 20% 4	450
	11th to 20th	Day	12% 5% 23% 30% 25% 5%	450
	21st to end	Day	13% 4 19% 34% 22% 6%	450
July	1st to 10th	Day	7% 2 13% 33% 31% 14%	445
	11th to 20th	Day	16% 3 14% 31% 24% 12%	444
	21st to end	Day	8% 3 17% 40% 23% 9%	488
August	1st to 10th	Day	8% 3 15% 32% 28% 14%	446
	11th to 20th	Day	10% 3 17% 27% 31% 12%	439
	21st to end	Day	12% 4 17% 29% 25% 12%	495
September	1st to 10th	Day	14% 5% 18% 27% 26% 11%	450
	11th to 20th	Day	11% 4 17% 24% 28% 16%	450
	21st to end	Day	15% 7% 26% 25% 16% 10%	450
October	1st to 10th	Day	22% 8% 24% 21% 16% 9%	450
	11th to 20th	Day	21% 14% 29% 24% 10% 2	450
	21st to end	Day	34% 12% 23% 22% 9% 1	495
November	1st to 10th	Day	18% 19% 27% 23% 10% 3	291
	11th to 20th	Day	22% 18% 29% 22% 7% 1	180
	21st to end	Day	22% 16% 38% 18% 6%	180
December	1st to 10th	Day	22% 21% 36% 16% 6% 1	180
	11th to 20th	Day	26% 23% 34% 14% 2	180
	21st to end	Day	26% 15% 37% 19% 3	198
January	1st to 10th	Night	26% 19% 32% 16% 7% 1	760
	11th to 20th	Night	28% 16% 31% 20% 4	760
	21st to end	Night	20% 13% 37% 23% 6%	835
February	1st to 10th	Night	26% 16% 36% 19% 3	720
	11th to 20th	Night	23% 14% 35% 24% 4	703
	21st to end	Night	25% 13% 36% 22% 3	592
March	1st to 10th	Night	20% 12% 35% 24% 9%	720
	11th to 20th	Night	25% 11% 32% 24% 8% 1	720
	21st to end	Night	20% 9% 27% 32% 12% 1	792
April	1st to 10th	Night	21% 11% 29% 31% 7% 1	720
	11th to 20th	Night	22% 7% 31% 27% 12% 2	673
	21st to end	Night	20% 6% 28% 34% 13%	540
May	1st to 10th	Night	19% 5% 22% 31% 20% 3	540
	11th to 20th	Night	16% 4 21% 40% 18% 1	395
	21st to end	Night	12% 4 20% 37% 25% 4	389
June	1st to 10th	Night	12% 2 25% 40% 19% 2	360
	11th to 20th	Night	13% 3 25% 36% 24% 1	360
	21st to end	Night	11% 3 19% 45% 21% 1	360
July	1st to 10th	Night	8% 2 13% 45% 28% 4	350
	11th to 20th	Night	10% 3 18% 40% 24% 5%	353
	21st to end	Night	10% 2 15% 44% 25% 3	591
August	1st to 10th	Night	10% 2 12% 38% 32% 6%	537
	11th to 20th	Night	7% 3 15% 32% 37% 5%	534
	21st to end	Night	11% 2 16% 36% 30% 5%	679
September	1st to 10th	Night	13% 5% 16% 33% 26% 7%	720
	11th to 20th	Night	13% 4 16% 30% 29% 8%	720
	21st to end	Night	17% 5% 20% 29% 23% 6%	720
October	1st to 10th	Night	20% 6% 23% 27% 20% 3	720
	11th to 20th	Night	24% 12% 27% 25% 10% 2	720
	21st to end	Night	30% 9% 28% 26% 6% 1	792
November	1st to 10th	Night	21% 11% 26% 28% 13% 1	740
	11th to 20th	Night	21% 16% 31% 20% 9% 2	760
	21st to end	Night	26% 13% 33% 22% 6%	760
December	1st to 10th	Night	31% 16% 30% 16% 6%	760
	11th to 20th	Night	25% 17% 34% 19% 5%	760
	21st to end	Night	30% 14% 32% 20% 3	836

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