Tillsonburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tillsonburg clear sky chart from 2005-11-06 to 2024-08-30.

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	15% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	96041
	Night	15% 10% 4 8% 5% 4 4 4 5% 7% 33%	92985
Transparency	Day	50% 7% 13% 19% 10% 1	95772
	Night	50% 6% 12% 19% 11% 1	92809
Seeing	Day	18% 12% 28% 24% 13% 5%	14584
	Night	19% 10% 29% 29% 12% 1	23748

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	16% 17% 6% 12% 5% 6% 5% 3 4 4 21%	2659
	11th to 20th	Day	12% 20% 9% 18% 6% 4 4 3 4 5% 14%	2840
	21st to end	Day	22% 22% 6% 12% 7% 5% 5% 3 3 3 12%	3124
February	1st to 10th	Day	16% 18% 5% 11% 8% 6% 5% 4 5% 4 19%	1710
	11th to 20th	Day	13% 16% 8% 14% 7% 5% 5% 4 4 6% 19%	1663
	21st to end	Day	18% 15% 4 11% 6% 5% 5% 3 4 7% 22%	1540
March	1st to 10th	Day	20% 13% 4 10% 6% 5% 4 3 4 5% 26%	3391
	11th to 20th	Day	12% 15% 5% 11% 6% 5% 3 3 6% 7% 29%	3480
	21st to end	Day	18% 10% 3 10% 6% 5% 4 3 5% 5% 31%	3815
April	1st to 10th	Day	17% 12% 4 8% 5% 4 5% 4 5% 8% 28%	2180
	11th to 20th	Day	17% 10% 3 9% 5% 5% 4 3 5% 8% 33%	2390
	21st to end	Day	20% 10% 3 7% 4 4 4 3 5% 6% 33%	2470
May	1st to 10th	Day	19% 7% 3 8% 6% 5% 5% 4 6% 7% 32%	4108
	11th to 20th	Day	16% 9% 3 8% 5% 4 5% 4 6% 9% 31%	4139
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 7% 8% 39%	2660
	11th to 20th	Day	11% 7% 2 6% 5% 5% 5% 5% 6% 9% 39%	2717
	21st to end	Day	12% 6% 2 5% 4 4 5% 4 7% 10% 40%	2850
July	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 7% 10% 41%	4664
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 11% 40%	4194
	21st to end	Day	8% 5% 2 6% 6% 5% 5% 5% 7% 9% 41%	4466
August	1st to 10th	Day	9% 6% 2 5% 5% 5% 6% 5% 8% 10% 40%	2457
	11th to 20th	Day	10% 6% 2 7% 6% 6% 6% 5% 7% 10% 36%	2433
	21st to end	Day	10% 6% 3 6% 5% 4 5% 4 6% 9% 42%	2638
September	1st to 10th	Day	11% 6% 2 7% 4 5% 6% 5% 6% 8% 39%	2142
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 4 6% 9% 45%	1980
	21st to end	Day	14% 7% 2 6% 5% 4 5% 4 6% 9% 36%	1980
October	1st to 10th	Day	16% 8% 4 7% 5% 5% 5% 3 6% 5% 36%	1818
	11th to 20th	Day	18% 10% 3 8% 6% 5% 6% 4 5% 7% 29%	1800
	21st to end	Day	23% 11% 3 10% 6% 5% 4 4 6% 6% 23%	1980
November	1st to 10th	Day	14% 10% 3 8% 5% 5% 5% 4 5% 8% 34%	1672
	11th to 20th	Day	16% 12% 3 8% 6% 4 4 3 6% 8% 30%	1526
	21st to end	Day	21% 13% 5% 9% 6% 5% 5% 4 5% 5% 21%	1520
December	1st to 10th	Day	17% 16% 4 13% 4 5% 5% 3 5% 6% 21%	1520
	11th to 20th	Day	19% 16% 6% 11% 5% 6% 6% 4 5% 5% 18%	1906
	21st to end	Day	28% 19% 6% 11% 5% 4 4 3 5% 4 10%	2772
January	1st to 10th	Night	17% 15% 5% 11% 7% 6% 4 4 5% 6% 21%	4272
	11th to 20th	Night	15% 15% 6% 14% 8% 7% 5% 3 6% 6% 15%	4120
	21st to end	Night	24% 16% 8% 13% 5% 4 4 3 4 4 15%	4532
February	1st to 10th	Night	16% 16% 4 11% 7% 5% 4 5% 5% 5% 22%	2470
	11th to 20th	Night	15% 13% 4 11% 6% 6% 6% 4 6% 5% 25%	2403
	21st to end	Night	17% 13% 6% 10% 7% 4 5% 4 6% 6% 23%	1912
March	1st to 10th	Night	17% 11% 4 7% 5% 4 4 3 5% 6% 33%	3448
	11th to 20th	Night	12% 9% 4 8% 4 4 5% 4 5% 8% 37%	3479
	21st to end	Night	16% 10% 3 7% 5% 4 3 3 5% 5% 38%	3817
April	1st to 10th	Night	18% 10% 3 6% 5% 5% 5% 4 5% 6% 32%	1999
	11th to 20th	Night	18% 8% 3 7% 4 4 5% 4 5% 6% 36%	1757
	21st to end	Night	15% 7% 2 8% 6% 5% 5% 5% 7% 7% 34%	1710
May	1st to 10th	Night	19% 9% 3 6% 4 3 4 3 5% 7% 37%	2833
	11th to 20th	Night	10% 8% 3 9% 5% 5% 5% 5% 6% 7% 37%	2749
	21st to end	Night	10% 4 2 5% 4 3 4 4 6% 8% 50%	2738
June	1st to 10th	Night	12% 5% 2 6% 5% 4 5% 3 7% 8% 43%	1520
	11th to 20th	Night	8% 5% 2 5% 5% 5% 5% 5% 7% 11% 42%	1455
	21st to end	Night	11% 5% 2 6% 4 3 4 4 6% 9% 46%	1330
July	1st to 10th	Night	7% 5% 2 5% 4 3 4 3 6% 11% 51%	2296
	11th to 20th	Night	9% 5% 1 5% 4 4 4 4 6% 8% 51%	2762
	21st to end	Night	6% 5% 2 5% 4 5% 5% 4 6% 8% 49%	3087
August	1st to 10th	Night	6% 6% 2 6% 4 6% 5% 4 6% 10% 46%	1701
	11th to 20th	Night	8% 5% 2 6% 4 3 4 3 7% 10% 48%	1688
	21st to end	Night	8% 5% 2 6% 4 4 5% 3 6% 9% 49%	1909
September	1st to 10th	Night	12% 7% 3 7% 5% 5% 4 4 4 6% 44%	1813
	11th to 20th	Night	10% 4 2 5% 4 3 3 3 6% 6% 54%	1980
	21st to end	Night	16% 5% 2 6% 5% 4 4 4 6% 7% 41%	1980
October	1st to 10th	Night	15% 6% 3 6% 5% 4 4 3 4 6% 43%	2142
	11th to 20th	Night	17% 8% 4 9% 4 4 4 3 5% 7% 35%	2160
	21st to end	Night	22% 10% 3 8% 5% 5% 4 4 5% 6% 30%	2376
November	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 6% 8% 41%	2404
	11th to 20th	Night	15% 11% 3 8% 5% 5% 5% 5% 5% 8% 30%	2651
	21st to end	Night	21% 12% 4 8% 5% 5% 5% 3 5% 7% 25%	2660
December	1st to 10th	Night	19% 15% 5% 10% 5% 4 4 4 5% 7% 22%	2660
	11th to 20th	Night	15% 17% 5% 10% 6% 4 4 4 5% 6% 24%	3288
	21st to end	Night	27% 19% 5% 10% 5% 4 4 3 4 5% 13%	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	66% 6% 11% 11% 6%	2660
	11th to 20th	Day	73% 8% 9% 7% 3	2840
	21st to end	Day	76% 6% 8% 7% 3	3124
February	1st to 10th	Day	67% 6% 10% 12% 5%	1710
	11th to 20th	Day	65% 6% 9% 13% 7%	1672
	21st to end	Day	63% 7% 11% 13% 6% 1	1540
March	1st to 10th	Day	60% 5% 9% 21% 4	3394
	11th to 20th	Day	54% 6% 16% 17% 7% 1	3480
	21st to end	Day	52% 5% 12% 18% 11% 1	3815
April	1st to 10th	Day	53% 6% 12% 18% 11% 1	2180
	11th to 20th	Day	51% 4 12% 20% 12% 1	2390
	21st to end	Day	51% 6% 12% 18% 12% 2	2470
May	1st to 10th	Day	49% 7% 13% 18% 10% 2	4120
	11th to 20th	Day	48% 8% 16% 20% 8% 1	4143
	21st to end	Day	36% 7% 13% 21% 18% 4	4837
June	1st to 10th	Day	40% 7% 14% 25% 13% 2	2660
	11th to 20th	Day	40% 7% 14% 21% 15% 2	2717
	21st to end	Day	37% 7% 15% 25% 15% 1	2850
July	1st to 10th	Day	36% 6% 14% 26% 14% 3	4593
	11th to 20th	Day	35% 7% 15% 30% 12% 1	4122
	21st to end	Day	36% 9% 15% 21% 19% 1	4324
August	1st to 10th	Day	37% 8% 16% 26% 12% 1	2444
	11th to 20th	Day	40% 9% 17% 23% 10% 1	2433
	21st to end	Day	37% 8% 14% 27% 13% 2	2638
September	1st to 10th	Day	40% 9% 15% 23% 12% 1	2142
	11th to 20th	Day	34% 7% 15% 29% 14%	1980
	21st to end	Day	42% 8% 14% 24% 11% 1	1980
October	1st to 10th	Day	49% 5% 14% 19% 12% 1	1818
	11th to 20th	Day	53% 7% 14% 17% 9% 1	1800
	21st to end	Day	59% 6% 13% 15% 6% 1	1980
November	1st to 10th	Day	48% 6% 11% 24% 7% 2	1672
	11th to 20th	Day	51% 6% 18% 15% 9% 1	1526
	21st to end	Day	62% 6% 14% 13% 3	1520
December	1st to 10th	Day	63% 7% 15% 12% 3	1520
	11th to 20th	Day	67% 7% 11% 9% 5%	1906
	21st to end	Day	76% 7% 10% 6% 1	2772
January	1st to 10th	Night	63% 8% 13% 11% 5%	4272
	11th to 20th	Night	69% 7% 11% 10% 3	4120
	21st to end	Night	73% 7% 7% 9% 3 1	4532
February	1st to 10th	Night	62% 6% 10% 15% 5%	2470
	11th to 20th	Night	58% 6% 12% 16% 7%	2405
	21st to end	Night	60% 6% 12% 15% 7% 1	1912
March	1st to 10th	Night	51% 5% 14% 22% 7% 1	3458
	11th to 20th	Night	44% 7% 16% 19% 13% 1	3480
	21st to end	Night	47% 6% 10% 20% 16% 2	3817
April	1st to 10th	Night	51% 6% 9% 19% 13% 1	1999
	11th to 20th	Night	48% 5% 9% 20% 16% 2	1757
	21st to end	Night	45% 7% 10% 20% 14% 3	1710
May	1st to 10th	Night	46% 6% 10% 19% 14% 5%	2840
	11th to 20th	Night	45% 7% 15% 23% 9% 2	2750
	21st to end	Night	32% 6% 13% 22% 24% 3	2739
June	1st to 10th	Night	37% 7% 12% 26% 16% 3	1520
	11th to 20th	Night	34% 8% 14% 24% 18% 2	1455
	21st to end	Night	34% 8% 13% 25% 19% 1	1330
July	1st to 10th	Night	29% 5% 14% 27% 20% 6%	2259
	11th to 20th	Night	31% 5% 14% 31% 17% 2	2711
	21st to end	Night	31% 8% 16% 23% 19% 3	2988
August	1st to 10th	Night	33% 6% 15% 30% 15% 1	1690
	11th to 20th	Night	31% 6% 18% 30% 13% 2	1688
	21st to end	Night	30% 8% 13% 31% 16% 2	1909
September	1st to 10th	Night	39% 5% 13% 24% 16% 3	1813
	11th to 20th	Night	30% 7% 11% 33% 18% 1	1980
	21st to end	Night	41% 7% 12% 26% 14% 1	1980
October	1st to 10th	Night	42% 6% 10% 24% 16% 1	2142
	11th to 20th	Night	48% 6% 13% 21% 11%	2160
	21st to end	Night	55% 5% 10% 19% 10% 1	2376
November	1st to 10th	Night	41% 6% 13% 26% 13% 1	2404
	11th to 20th	Night	51% 7% 14% 19% 9% 1	2651
	21st to end	Night	58% 7% 16% 14% 5% 1	2660
December	1st to 10th	Night	62% 7% 14% 14% 4	2660
	11th to 20th	Night	60% 7% 14% 14% 5%	3288
	21st to end	Night	74% 6% 11% 7% 2	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	23% 21% 32% 16% 8% 2	222
	11th to 20th	Day	24% 18% 40% 12% 5% 1	270
	21st to end	Day	25% 19% 34% 17% 4 1	297
February	1st to 10th	Day	25% 18% 40% 12% 4 1	270
	11th to 20th	Day	25% 23% 36% 15% 1	270
	21st to end	Day	28% 26% 34% 11% 1	225
March	1st to 10th	Day	23% 15% 35% 20% 5% 1	430
	11th to 20th	Day	23% 15% 37% 18% 6% 1	460
	21st to end	Day	29% 15% 30% 19% 7%	506
April	1st to 10th	Day	21% 18% 31% 22% 7% 1	460
	11th to 20th	Day	25% 17% 28% 17% 10% 4	452
	21st to end	Day	24% 13% 32% 21% 8% 2	460
May	1st to 10th	Day	23% 12% 29% 21% 12% 3	463
	11th to 20th	Day	18% 10% 28% 25% 16% 4	487
	21st to end	Day	12% 8% 24% 30% 18% 8%	529
June	1st to 10th	Day	13% 7% 33% 30% 14% 3	490
	11th to 20th	Day	14% 8% 25% 32% 16% 5%	547
	21st to end	Day	13% 8% 30% 31% 14% 3	680
July	1st to 10th	Day	9% 5% 22% 30% 25% 9%	617
	11th to 20th	Day	12% 5% 25% 29% 19% 11%	484
	21st to end	Day	9% 4 22% 34% 22% 9%	532
August	1st to 10th	Day	10% 3 21% 32% 20% 14%	486
	11th to 20th	Day	11% 5% 21% 28% 22% 13%	479
	21st to end	Day	11% 4 22% 29% 23% 11%	532
September	1st to 10th	Day	12% 5% 23% 29% 20% 11%	450
	11th to 20th	Day	7% 6% 17% 29% 27% 13%	450
	21st to end	Day	16% 9% 25% 26% 16% 8%	450
October	1st to 10th	Day	20% 8% 26% 22% 18% 6%	450
	11th to 20th	Day	20% 16% 31% 23% 7% 2	450
	21st to end	Day	28% 12% 32% 21% 6% 1	495
November	1st to 10th	Day	16% 23% 34% 17% 6% 3	270
	11th to 20th	Day	23% 23% 28% 16% 7% 2	183
	21st to end	Day	26% 21% 31% 19% 3	180
December	1st to 10th	Day	26% 24% 29% 14% 5% 1	180
	11th to 20th	Day	27% 24% 32% 14% 4	180
	21st to end	Day	31% 21% 31% 13% 5%	198
January	1st to 10th	Night	22% 18% 36% 16% 7% 1	760
	11th to 20th	Night	28% 17% 31% 22% 3	760
	21st to end	Night	21% 13% 36% 25% 5%	836
February	1st to 10th	Night	24% 16% 36% 22% 2	760
	11th to 20th	Night	22% 14% 35% 24% 4	743
	21st to end	Night	24% 17% 34% 22% 3	628
March	1st to 10th	Night	19% 14% 35% 27% 6%	760
	11th to 20th	Night	21% 12% 37% 24% 6%	760
	21st to end	Night	22% 12% 30% 26% 9% 1	836
April	1st to 10th	Night	23% 13% 33% 26% 5%	760
	11th to 20th	Night	21% 11% 32% 26% 9% 1	633
	21st to end	Night	18% 8% 34% 31% 8%	570
May	1st to 10th	Night	20% 9% 26% 31% 14% 1	570
	11th to 20th	Night	15% 4 28% 39% 13% 2	524
	21st to end	Night	11% 5% 27% 37% 18% 1	411
June	1st to 10th	Night	14% 4 28% 40% 14% 1	380
	11th to 20th	Night	9% 5% 30% 42% 13%	380
	21st to end	Night	12% 5% 25% 43% 14% 1	380
July	1st to 10th	Night	6% 2 22% 44% 24% 3	370
	11th to 20th	Night	10% 4 18% 39% 25% 3	503
	21st to end	Night	8% 2 17% 47% 24% 1	624
August	1st to 10th	Night	7% 4 14% 44% 29% 3	567
	11th to 20th	Night	10% 2 15% 35% 34% 4	564
	21st to end	Night	8% 3 21% 38% 28% 3	661
September	1st to 10th	Night	13% 5% 18% 35% 24% 4	720
	11th to 20th	Night	11% 3 16% 38% 29% 4	720
	21st to end	Night	17% 6% 21% 32% 19% 6%	720
October	1st to 10th	Night	17% 6% 24% 32% 17% 3	720
	11th to 20th	Night	20% 13% 30% 27% 10% 1	720
	21st to end	Night	26% 10% 31% 28% 5%	792
November	1st to 10th	Night	19% 10% 29% 29% 11% 1	740
	11th to 20th	Night	21% 16% 33% 21% 8% 1	760
	21st to end	Night	27% 11% 32% 22% 7%	760
December	1st to 10th	Night	28% 16% 33% 17% 5% 1	760
	11th to 20th	Night	23% 17% 38% 19% 4	760
	21st to end	Night	29% 13% 33% 22% 2	836

Page generated at 2024-08-27 09:49:38. Version ac07

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