Strathroy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strathroy clear sky chart from 2005-11-06 to 2024-09-29.

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 8% 5% 5% 5% 4 5% 7% 32%	101166
	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 33%	96982
Transparency	Day	50% 7% 13% 19% 10% 1	100965
	Night	50% 7% 13% 18% 10% 1	96854
Seeing	Day	18% 11% 28% 24% 13% 5%	14965
	Night	20% 10% 28% 29% 12% 1	24226

By Month

Percentage Cloud Cover SE (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	18% 21% 6% 13% 5% 5% 4 3 4 4 17%	2463
	11th to 20th	Day	14% 20% 9% 17% 9% 7% 6% 3 3 3 9%	2810
	21st to end	Day	26% 20% 9% 11% 5% 4 3 3 2 4 13%	3124
February	1st to 10th	Day	17% 16% 4 14% 7% 5% 4 4 4 5% 19%	1710
	11th to 20th	Day	15% 15% 6% 13% 7% 6% 4 3 4 6% 20%	1683
	21st to end	Day	18% 15% 6% 11% 6% 4 5% 3 5% 4 23%	1570
March	1st to 10th	Day	20% 14% 5% 10% 5% 4 3 3 3 4 28%	3330
	11th to 20th	Day	13% 14% 6% 9% 4 4 3 4 5% 7% 31%	3480
	21st to end	Day	18% 12% 4 9% 5% 4 4 4 4 5% 32%	3815
April	1st to 10th	Day	15% 14% 4 7% 6% 4 4 3 6% 6% 31%	2149
	11th to 20th	Day	19% 11% 3 6% 4 4 4 3 6% 7% 33%	2442
	21st to end	Day	20% 10% 4 6% 5% 4 4 3 5% 6% 33%	2470
May	1st to 10th	Day	18% 8% 3 7% 4 4 5% 4 6% 7% 36%	4082
	11th to 20th	Day	17% 9% 2 8% 5% 4 4 4 6% 8% 32%	4081
	21st to end	Day	13% 4 2 5% 4 4 4 4 5% 8% 47%	4761
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 4 5% 7% 7% 40%	2683
	11th to 20th	Day	10% 6% 3 6% 5% 4 6% 5% 6% 9% 41%	2850
	21st to end	Day	13% 5% 3 6% 5% 4 5% 4 7% 9% 40%	2850
July	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 10% 39%	4700
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 10% 44%	4262
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	4466
August	1st to 10th	Day	15% 5% 2 5% 5% 5% 5% 5% 7% 9% 38%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 8% 10% 36%	4044
	21st to end	Day	9% 6% 2 7% 4 5% 4 4 6% 9% 42%	4503
September	1st to 10th	Day	11% 6% 3 7% 4 5% 5% 5% 5% 8% 41%	2199
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 46%	2090
	21st to end	Day	17% 7% 2 7% 5% 4 5% 4 6% 9% 35%	2069
October	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 7% 36%	1854
	11th to 20th	Day	20% 10% 4 7% 5% 4 4 4 6% 8% 28%	1800
	21st to end	Day	25% 12% 4 9% 5% 5% 4 4 5% 5% 23%	1926
November	1st to 10th	Day	15% 12% 3 8% 6% 5% 4 4 5% 6% 33%	1672
	11th to 20th	Day	15% 15% 4 7% 6% 6% 5% 5% 5% 7% 25%	1592
	21st to end	Day	21% 17% 5% 9% 6% 5% 4 5% 5% 6% 18%	1520
December	1st to 10th	Day	16% 18% 6% 12% 5% 4 4 4 6% 7% 17%	1520
	11th to 20th	Day	19% 18% 8% 11% 6% 5% 4 4 5% 5% 16%	1910
	21st to end	Day	29% 21% 7% 10% 5% 4 3 3 4 4 10%	2582
January	1st to 10th	Night	17% 19% 7% 12% 5% 5% 4 3 4 5% 19%	4488
	11th to 20th	Night	15% 20% 8% 14% 7% 7% 6% 5% 4 4 11%	4145
	21st to end	Night	24% 17% 7% 12% 5% 4 4 3 5% 5% 14%	4532
February	1st to 10th	Night	17% 16% 5% 11% 7% 5% 5% 4 5% 5% 20%	2470
	11th to 20th	Night	16% 14% 5% 9% 6% 5% 6% 4 6% 7% 23%	2380
	21st to end	Night	18% 13% 4 11% 6% 5% 5% 4 5% 5% 24%	1884
March	1st to 10th	Night	17% 14% 4 8% 5% 4 4 3 4 5% 32%	3523
	11th to 20th	Night	11% 9% 4 7% 5% 5% 5% 4 5% 8% 36%	3480
	21st to end	Night	17% 10% 3 8% 5% 5% 4 3 4 4 37%	3817
April	1st to 10th	Night	18% 12% 3 5% 5% 4 4 3 6% 6% 33%	2038
	11th to 20th	Night	18% 9% 2 6% 4 4 4 3 5% 8% 36%	1697
	21st to end	Night	16% 10% 3 8% 4 5% 4 3 5% 8% 34%	1710
May	1st to 10th	Night	19% 8% 3 7% 4 4 4 3 5% 8% 37%	2813
	11th to 20th	Night	12% 9% 3 7% 5% 5% 5% 4 7% 8% 36%	2812
	21st to end	Night	12% 4 1 4 4 4 5% 4 5% 7% 50%	2780
June	1st to 10th	Night	13% 5% 2 6% 4 4 5% 4 6% 9% 43%	1492
	11th to 20th	Night	10% 4 2 6% 5% 3 6% 5% 7% 10% 43%	1330
	21st to end	Night	10% 5% 2 6% 5% 5% 4 4 6% 8% 47%	1330
July	1st to 10th	Night	8% 4 2 4 4 3 4 3 5% 10% 51%	2264
	11th to 20th	Night	9% 4 2 5% 3 3 3 3 5% 9% 53%	2685
	21st to end	Night	6% 5% 1 5% 4 5% 6% 5% 7% 9% 48%	3087
August	1st to 10th	Night	12% 5% 3 6% 4 4 4 4 5% 7% 46%	2825
	11th to 20th	Night	10% 7% 2 6% 4 4 5% 3 5% 7% 49%	2785
	21st to end	Night	9% 5% 2 5% 4 4 5% 3 6% 8% 49%	3124
September	1st to 10th	Night	9% 6% 3 6% 4 4 4 4 5% 8% 47%	1973
	11th to 20th	Night	10% 5% 1 4 3 3 4 4 4 8% 52%	2090
	21st to end	Night	17% 7% 2 7% 4 5% 4 3 5% 6% 40%	2079
October	1st to 10th	Night	14% 7% 3 7% 5% 4 4 3 5% 6% 41%	2106
	11th to 20th	Night	21% 9% 3 8% 4 3 3 4 5% 6% 34%	2160
	21st to end	Night	24% 11% 3 8% 4 5% 4 3 5% 6% 26%	2426
November	1st to 10th	Night	15% 10% 3 6% 4 4 4 3 6% 7% 39%	2406
	11th to 20th	Night	16% 12% 4 8% 5% 5% 5% 5% 7% 7% 27%	2588
	21st to end	Night	20% 17% 4 8% 5% 4 4 4 5% 5% 23%	2660
December	1st to 10th	Night	19% 18% 6% 9% 5% 4 4 4 5% 6% 19%	2660
	11th to 20th	Night	16% 18% 7% 10% 7% 5% 4 4 4 5% 21%	3285
	21st to end	Night	28% 21% 7% 10% 5% 4 4 3 4 4 13%	5058

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	70% 9% 9% 10% 2	2464
	11th to 20th	Day	79% 7% 7% 4 2	2810
	21st to end	Day	78% 5% 9% 5% 3	3124
February	1st to 10th	Day	67% 7% 10% 10% 5% 1	1710
	11th to 20th	Day	65% 5% 10% 13% 6%	1692
	21st to end	Day	63% 7% 11% 12% 6% 1	1570
March	1st to 10th	Day	61% 5% 10% 20% 4	3330
	11th to 20th	Day	53% 7% 15% 17% 7% 1	3480
	21st to end	Day	54% 6% 11% 16% 11% 1	3815
April	1st to 10th	Day	54% 6% 12% 19% 10% 1	2149
	11th to 20th	Day	49% 6% 12% 19% 13% 1	2442
	21st to end	Day	50% 6% 13% 17% 12% 2	2470
May	1st to 10th	Day	45% 7% 13% 21% 12% 3	4120
	11th to 20th	Day	47% 9% 15% 20% 8% 1	4085
	21st to end	Day	35% 7% 12% 20% 20% 6%	4775
June	1st to 10th	Day	40% 8% 13% 25% 13% 2	2683
	11th to 20th	Day	38% 9% 13% 22% 17% 2	2850
	21st to end	Day	40% 8% 12% 24% 15% 1	2850
July	1st to 10th	Day	39% 7% 14% 23% 15% 2	4627
	11th to 20th	Day	33% 7% 14% 32% 14% 1	4188
	21st to end	Day	36% 8% 15% 19% 20% 1	4324
August	1st to 10th	Day	40% 8% 15% 23% 15% 1	4091
	11th to 20th	Day	39% 9% 16% 27% 9% 1	4083
	21st to end	Day	37% 6% 14% 30% 13% 1	4503
September	1st to 10th	Day	40% 8% 15% 23% 13% 1	2199
	11th to 20th	Day	34% 7% 13% 30% 16%	2090
	21st to end	Day	45% 7% 13% 23% 11% 1	2069
October	1st to 10th	Day	45% 7% 13% 20% 13% 1	1854
	11th to 20th	Day	54% 8% 14% 17% 7% 1	1800
	21st to end	Day	62% 6% 12% 13% 6%	1926
November	1st to 10th	Day	51% 6% 13% 20% 8% 1	1672
	11th to 20th	Day	56% 8% 16% 12% 7% 1	1592
	21st to end	Day	66% 6% 14% 12% 2	1520
December	1st to 10th	Day	65% 10% 12% 10% 3	1520
	11th to 20th	Day	70% 7% 12% 9% 2	1906
	21st to end	Day	79% 7% 10% 4	2582
January	1st to 10th	Night	67% 8% 13% 9% 3	4488
	11th to 20th	Night	74% 9% 9% 5% 2	4145
	21st to end	Night	71% 7% 11% 8% 2	4532
February	1st to 10th	Night	65% 8% 10% 12% 5%	2470
	11th to 20th	Night	59% 6% 14% 15% 6%	2382
	21st to end	Night	60% 7% 12% 15% 6%	1884
March	1st to 10th	Night	53% 6% 13% 22% 5%	3523
	11th to 20th	Night	43% 8% 18% 19% 11% 1	3480
	21st to end	Night	49% 6% 11% 20% 13% 1	3817
April	1st to 10th	Night	50% 7% 10% 19% 12% 1	2038
	11th to 20th	Night	47% 5% 10% 20% 16% 2	1697
	21st to end	Night	48% 6% 11% 17% 15% 3	1710
May	1st to 10th	Night	45% 6% 11% 18% 16% 5%	2840
	11th to 20th	Night	43% 9% 13% 22% 11% 2	2813
	21st to end	Night	32% 8% 11% 23% 22% 4	2787
June	1st to 10th	Night	37% 6% 12% 26% 16% 2	1492
	11th to 20th	Night	34% 9% 14% 22% 19% 2	1330
	21st to end	Night	34% 7% 13% 26% 18% 1	1330
July	1st to 10th	Night	29% 6% 13% 28% 18% 7%	2228
	11th to 20th	Night	29% 6% 14% 31% 19% 2	2636
	21st to end	Night	29% 8% 18% 21% 21% 3	2988
August	1st to 10th	Night	36% 7% 14% 25% 17% 1	2814
	11th to 20th	Night	35% 6% 13% 32% 12% 1	2812
	21st to end	Night	32% 6% 12% 31% 17% 1	3124
September	1st to 10th	Night	35% 6% 15% 26% 16% 2	1973
	11th to 20th	Night	29% 6% 14% 31% 19% 1	2090
	21st to end	Night	44% 6% 13% 23% 13%	2079
October	1st to 10th	Night	42% 6% 12% 22% 17% 1	2106
	11th to 20th	Night	51% 5% 13% 20% 9% 1	2160
	21st to end	Night	58% 7% 11% 14% 9% 1	2426
November	1st to 10th	Night	44% 6% 13% 24% 11% 1	2406
	11th to 20th	Night	54% 7% 15% 16% 7% 1	2588
	21st to end	Night	61% 7% 17% 12% 3	2660
December	1st to 10th	Night	65% 8% 14% 10% 3	2660
	11th to 20th	Night	65% 7% 13% 12% 3	3288
	21st to end	Night	76% 7% 11% 5% 1	5058

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% 23% 29% 19% 5% 1	252
	11th to 20th	Day	22% 19% 43% 11% 4 1	270
	21st to end	Day	29% 15% 33% 20% 2 1	297
February	1st to 10th	Day	24% 21% 39% 11% 4	270
	11th to 20th	Day	26% 21% 38% 14% 1	270
	21st to end	Day	27% 26% 35% 11% 1	225
March	1st to 10th	Day	26% 15% 37% 16% 5% 1	389
	11th to 20th	Day	21% 16% 32% 24% 5% 1	460
	21st to end	Day	28% 14% 32% 21% 5% 1	506
April	1st to 10th	Day	18% 19% 35% 20% 8% 1	460
	11th to 20th	Day	27% 13% 27% 20% 7% 4	452
	21st to end	Day	23% 12% 32% 22% 9% 2	460
May	1st to 10th	Day	21% 12% 27% 27% 10% 3	463
	11th to 20th	Day	18% 8% 27% 25% 17% 6%	487
	21st to end	Day	12% 8% 22% 31% 19% 8%	529
June	1st to 10th	Day	12% 8% 31% 30% 15% 4	513
	11th to 20th	Day	12% 9% 29% 33% 15% 4	680
	21st to end	Day	13% 8% 29% 30% 16% 4	680
July	1st to 10th	Day	10% 7% 21% 30% 24% 9%	671
	11th to 20th	Day	15% 4 27% 26% 20% 8%	569
	21st to end	Day	9% 5% 20% 31% 25% 11%	532
August	1st to 10th	Day	10% 4 19% 29% 22% 16%	486
	11th to 20th	Day	10% 5% 19% 28% 22% 16%	479
	21st to end	Day	10% 6% 19% 27% 27% 10%	539
September	1st to 10th	Day	12% 5% 23% 27% 22% 11%	490
	11th to 20th	Day	8% 4 20% 23% 29% 15%	490
	21st to end	Day	17% 11% 23% 26% 14% 8%	483
October	1st to 10th	Day	20% 9% 25% 23% 17% 6%	450
	11th to 20th	Day	20% 16% 33% 22% 7% 1	450
	21st to end	Day	28% 15% 33% 20% 4	441
November	1st to 10th	Day	19% 18% 33% 19% 9% 3	270
	11th to 20th	Day	23% 22% 30% 16% 6% 2	214
	21st to end	Day	29% 16% 35% 17% 3	180
December	1st to 10th	Day	28% 19% 31% 16% 6% 1	180
	11th to 20th	Day	28% 22% 27% 19% 3	180
	21st to end	Day	29% 23% 31% 15% 2	198
January	1st to 10th	Night	24% 16% 37% 16% 5% 1	950
	11th to 20th	Night	29% 15% 31% 21% 4	772
	21st to end	Night	23% 11% 35% 25% 6%	836
February	1st to 10th	Night	25% 12% 37% 23% 2	760
	11th to 20th	Night	24% 14% 30% 26% 6%	743
	21st to end	Night	25% 15% 37% 20% 3	628
March	1st to 10th	Night	19% 13% 35% 27% 6%	760
	11th to 20th	Night	18% 15% 35% 24% 7% 1	760
	21st to end	Night	24% 12% 30% 27% 8%	836
April	1st to 10th	Night	23% 14% 31% 27% 5%	760
	11th to 20th	Night	21% 12% 32% 24% 10% 1	573
	21st to end	Night	20% 9% 33% 30% 7% 1	570
May	1st to 10th	Night	19% 7% 29% 32% 11% 1	570
	11th to 20th	Night	14% 4 28% 40% 12% 2	561
	21st to end	Night	13% 3 26% 41% 17% 1	447
June	1st to 10th	Night	14% 4 28% 40% 14%	380
	11th to 20th	Night	12% 3 26% 44% 14%	380
	21st to end	Night	10% 6% 22% 46% 16% 1	380
July	1st to 10th	Night	7% 1 18% 47% 25% 2	397
	11th to 20th	Night	12% 3 17% 41% 25% 2	552
	21st to end	Night	9% 2 16% 48% 23% 2	624
August	1st to 10th	Night	8% 2 13% 44% 29% 3	567
	11th to 20th	Night	10% 2 14% 38% 32% 4	564
	21st to end	Night	12% 2 16% 37% 30% 3	627
September	1st to 10th	Night	10% 5% 22% 35% 24% 5%	756
	11th to 20th	Night	11% 4 16% 37% 28% 4	760
	21st to end	Night	19% 7% 21% 33% 16% 5%	756
October	1st to 10th	Night	18% 6% 26% 31% 17% 3	720
	11th to 20th	Night	24% 12% 27% 27% 10% 1	720
	21st to end	Night	28% 11% 31% 25% 4	792
November	1st to 10th	Night	20% 11% 29% 30% 9% 1	740
	11th to 20th	Night	22% 13% 36% 21% 6% 1	760
	21st to end	Night	28% 13% 29% 24% 6%	760
December	1st to 10th	Night	29% 15% 33% 18% 5%	760
	11th to 20th	Night	24% 17% 36% 19% 4	760
	21st to end	Night	29% 12% 35% 21% 3	945

Page generated at 2024-09-26 09:52:25. Version ac07

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