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 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	15% 10% 4 9% 5% 5% 5% 4 6% 7% 31%	109068
	Night	15% 10% 4 9% 5% 4 4 4 5% 7% 33%	109152
Transparency	Day	50% 7% 13% 19% 10% 1	112723
	Night	49% 6% 12% 20% 12% 1	113662
Seeing	Day	18% 12% 28% 24% 13% 5%	15070
	Night	19% 10% 29% 29% 12% 1	24385

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	13% 15% 6% 17% 6% 6% 5% 3 4 5% 20%	3809
	11th to 20th	Day	11% 20% 9% 21% 7% 6% 4 3 4 4 11%	4026
	21st to end	Day	18% 18% 6% 15% 7% 5% 4 3 4 4 16%	4466
February	1st to 10th	Day	16% 18% 5% 11% 7% 6% 5% 4 5% 4 19%	1755
	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	16% 6% 2 5% 4 5% 5% 5% 6% 9% 37%	4104
	11th to 20th	Day	10% 7% 3 7% 5% 5% 6% 5% 7% 10% 35%	4044
	21st to end	Day	8% 6% 3 7% 5% 5% 5% 5% 6% 9% 41%	4436
September	1st to 10th	Day	11% 6% 2 7% 4 5% 6% 5% 6% 8% 40%	2261
	11th to 20th	Day	9% 6% 2 5% 4 4 5% 3 6% 9% 46%	2090
	21st to end	Day	14% 8% 2 6% 5% 4 6% 4 6% 9% 35%	2090
October	1st to 10th	Day	15% 8% 4 7% 5% 5% 5% 3 6% 5% 37%	1919
	11th to 20th	Day	18% 10% 3 8% 5% 5% 6% 4 5% 7% 31%	1900
	21st to end	Day	22% 10% 3 10% 6% 4 4 4 6% 6% 24%	2090
November	1st to 10th	Day	14% 9% 3 8% 5% 5% 5% 4 5% 8% 34%	1762
	11th to 20th	Day	15% 12% 4 9% 5% 4 4 3 6% 8% 30%	1606
	21st to end	Day	21% 14% 5% 9% 6% 5% 6% 4 5% 5% 20%	1600
December	1st to 10th	Day	18% 17% 5% 13% 6% 5% 5% 4 6% 6% 16%	2600
	11th to 20th	Day	22% 17% 5% 10% 4 4 4 3 5% 5% 20%	2986
	21st to end	Day	27% 19% 6% 11% 6% 5% 4 3 5% 5% 11%	3960
January	1st to 10th	Night	14% 12% 5% 15% 7% 6% 5% 4 5% 6% 21%	6122
	11th to 20th	Night	12% 16% 6% 16% 10% 7% 6% 3 6% 6% 14%	5859
	21st to end	Night	19% 15% 7% 14% 5% 4 4 3 4 5% 19%	6490
February	1st to 10th	Night	16% 16% 4 11% 7% 5% 4 5% 5% 5% 22%	2536
	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	11% 6% 2 6% 4 5% 5% 4 6% 9% 44%	2825
	11th to 20th	Night	10% 6% 2 6% 4 3 4 3 6% 9% 47%	2785
	21st to end	Night	7% 4 2 6% 5% 4 5% 3 6% 9% 48%	3188
September	1st to 10th	Night	11% 7% 2 7% 5% 5% 4 4 4 6% 46%	1914
	11th to 20th	Night	9% 4 2 4 3 3 3 3 6% 6% 55%	2090
	21st to end	Night	17% 5% 2 7% 5% 5% 4 4 6% 7% 40%	2090
October	1st to 10th	Night	14% 6% 3 6% 4 4 4 3 5% 6% 44%	2261
	11th to 20th	Night	16% 8% 3 8% 4 4 4 3 5% 7% 37%	2280
	21st to end	Night	21% 9% 3 8% 5% 5% 4 4 5% 6% 31%	2508
November	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 6% 7% 41%	2534
	11th to 20th	Night	15% 11% 3 8% 5% 5% 5% 5% 5% 8% 30%	2791
	21st to end	Night	21% 12% 4 8% 5% 5% 5% 4 5% 7% 25%	2800
December	1st to 10th	Night	14% 15% 5% 12% 6% 5% 5% 5% 6% 7% 19%	4580
	11th to 20th	Night	16% 19% 5% 10% 6% 4 4 4 4 5% 23%	5208
	21st to end	Night	24% 18% 5% 10% 5% 4 4 3 5% 5% 17%	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	65% 6% 11% 12% 7%	3810
	11th to 20th	Day	76% 7% 8% 5% 4	4060
	21st to end	Day	71% 5% 10% 7% 6% 1	4466
February	1st to 10th	Day	67% 6% 10% 12% 5%	1755
	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	42% 7% 14% 22% 13% 1	4091
	11th to 20th	Day	40% 8% 16% 26% 9% 1	4083
	21st to end	Day	37% 7% 13% 30% 12% 1	4436
September	1st to 10th	Day	39% 8% 15% 25% 12% 1	2261
	11th to 20th	Day	34% 7% 15% 29% 15%	2090
	21st to end	Day	43% 8% 13% 23% 11% 1	2090
October	1st to 10th	Day	39% 6% 15% 22% 17% 1	3192
	11th to 20th	Day	39% 5% 15% 23% 18%	3140
	21st to end	Day	48% 5% 16% 24% 6%	3428
November	1st to 10th	Day	48% 6% 12% 24% 8% 2	1762
	11th to 20th	Day	51% 6% 17% 15% 9% 1	1606
	21st to end	Day	63% 6% 14% 13% 4	1600
December	1st to 10th	Day	68% 6% 15% 9% 2	2600
	11th to 20th	Day	67% 6% 12% 8% 8%	2986
	21st to end	Day	75% 6% 8% 8% 3	3960
January	1st to 10th	Night	60% 7% 11% 16% 5%	6122
	11th to 20th	Night	69% 7% 10% 10% 4	5900
	21st to end	Night	67% 6% 8% 11% 9% 1	6490
February	1st to 10th	Night	63% 6% 10% 15% 5%	2536
	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	36% 5% 14% 25% 17% 2	2814
	11th to 20th	Night	34% 6% 17% 31% 11% 1	2812
	21st to end	Night	30% 7% 13% 32% 17% 1	3188
September	1st to 10th	Night	38% 5% 13% 25% 17% 2	1914
	11th to 20th	Night	29% 6% 11% 34% 19% 1	2090
	21st to end	Night	43% 7% 12% 25% 13% 1	2090
October	1st to 10th	Night	31% 5% 8% 29% 25% 2	3768
	11th to 20th	Night	41% 4 14% 24% 17%	3779
	21st to end	Night	41% 5% 15% 26% 13% 1	4120
November	1st to 10th	Night	41% 5% 13% 26% 13% 1	2534
	11th to 20th	Night	51% 7% 13% 19% 9% 1	2791
	21st to end	Night	58% 6% 16% 14% 5% 1	2800
December	1st to 10th	Night	62% 7% 15% 12% 3	4580
	11th to 20th	Night	63% 6% 10% 12% 8% 1	5208
	21st to end	Night	69% 6% 10% 10% 5%	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	21% 21% 32% 16% 7% 2	247
	11th to 20th	Day	23% 20% 40% 12% 5% 1	300
	21st to end	Day	25% 20% 33% 16% 4 1	330
February	1st to 10th	Day	25% 18% 41% 12% 4 1	285
	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	10% 5% 22% 29% 23% 10%	539
September	1st to 10th	Day	12% 5% 25% 27% 19% 12%	490
	11th to 20th	Day	7% 6% 16% 27% 28% 16%	490
	21st to end	Day	17% 10% 25% 26% 16% 7%	490
October	1st to 10th	Day	19% 8% 26% 23% 17% 6%	490
	11th to 20th	Day	19% 15% 31% 24% 8% 3	490
	21st to end	Day	27% 14% 31% 22% 6% 1	539
November	1st to 10th	Day	16% 24% 34% 17% 6% 3	300
	11th to 20th	Day	24% 22% 29% 17% 6% 2	203
	21st to end	Day	28% 21% 32% 18% 3	200
December	1st to 10th	Day	28% 22% 29% 15% 6% 1	200
	11th to 20th	Day	30% 22% 31% 14% 4	200
	21st to end	Day	31% 20% 31% 13% 5%	220
January	1st to 10th	Night	22% 19% 37% 16% 6% 1	800
	11th to 20th	Night	27% 18% 32% 21% 3	800
	21st to end	Night	20% 14% 37% 24% 5%	880
February	1st to 10th	Night	24% 16% 36% 22% 2	781
	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 20% 37% 28% 3	665
September	1st to 10th	Night	13% 5% 19% 35% 24% 4	760
	11th to 20th	Night	10% 3 15% 37% 31% 4	760
	21st to end	Night	18% 6% 21% 32% 18% 5%	760
October	1st to 10th	Night	17% 6% 25% 32% 18% 3	760
	11th to 20th	Night	20% 12% 29% 27% 11% 1	760
	21st to end	Night	25% 10% 31% 29% 6%	836
November	1st to 10th	Night	19% 11% 30% 28% 11% 1	780
	11th to 20th	Night	22% 16% 33% 21% 7% 1	800
	21st to end	Night	28% 11% 32% 22% 7%	800
December	1st to 10th	Night	28% 17% 34% 17% 5% 1	800
	11th to 20th	Night	23% 17% 38% 18% 4	800
	21st to end	Night	29% 13% 33% 23% 2	880

Page generated at 2025-02-03 03:05:51. Version ac07

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