Sarnia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sarnia clear sky chart from 2005-11-06 to 2024-11-04.

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% 34%	101213
	Night	15% 11% 4 8% 5% 4 4 3 5% 6% 35%	97784
Transparency	Day	47% 6% 13% 21% 11% 1	104829
	Night	48% 5% 13% 21% 11% 1	102307
Seeing	Day	17% 8% 23% 28% 18% 6%	15258
	Night	20% 8% 26% 30% 14% 2	24703

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	15% 20% 8% 12% 6% 3 4 4 5% 5% 18%	2527
	11th to 20th	Day	15% 20% 7% 15% 7% 6% 4 4 4 5% 15%	2601
	21st to end	Day	26% 19% 6% 10% 6% 4 4 3 4 4 14%	3124
February	1st to 10th	Day	15% 17% 4 12% 8% 5% 5% 3 4 5% 20%	1710
	11th to 20th	Day	14% 15% 5% 11% 7% 4 5% 3 5% 6% 25%	1729
	21st to end	Day	14% 14% 5% 13% 6% 5% 4 4 4 5% 26%	1570
March	1st to 10th	Day	17% 16% 5% 9% 6% 4 4 2 4 5% 28%	3269
	11th to 20th	Day	12% 14% 4 10% 5% 5% 5% 3 5% 7% 30%	3480
	21st to end	Day	18% 13% 4 9% 4 5% 4 3 5% 6% 29%	3815
April	1st to 10th	Day	15% 13% 2 8% 5% 5% 4 4 5% 7% 32%	2167
	11th to 20th	Day	17% 11% 3 6% 4 4 4 3 4 7% 36%	2442
	21st to end	Day	19% 9% 3 7% 5% 5% 4 4 5% 6% 34%	2470
May	1st to 10th	Day	17% 7% 3 6% 5% 4 5% 4 6% 7% 37%	4082
	11th to 20th	Day	16% 8% 3 6% 5% 5% 5% 4 6% 8% 35%	4081
	21st to end	Day	10% 6% 3 6% 4 5% 4 3 5% 7% 47%	4630
June	1st to 10th	Day	10% 7% 3 7% 5% 3 5% 4 7% 8% 42%	2774
	11th to 20th	Day	9% 5% 2 6% 4 4 6% 4 7% 9% 43%	2850
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 4 8% 9% 40%	2850
July	1st to 10th	Day	11% 5% 3 6% 4 5% 5% 4 7% 9% 40%	4547
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 5% 7% 9% 47%	4413
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 10% 43%	4466
August	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 5% 7% 9% 40%	4104
	11th to 20th	Day	9% 6% 2 7% 4 5% 6% 5% 7% 9% 39%	4044
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	4532
September	1st to 10th	Day	12% 5% 2 7% 4 5% 4 5% 7% 8% 41%	2164
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 7% 8% 47%	2090
	21st to end	Day	16% 7% 2 7% 4 5% 4 4 6% 9% 35%	2090
October	1st to 10th	Day	13% 7% 2 7% 5% 5% 4 4 5% 7% 40%	1990
	11th to 20th	Day	18% 10% 3 7% 5% 4 5% 4 4 7% 33%	1900
	21st to end	Day	20% 10% 3 9% 6% 5% 4 3 6% 6% 28%	1986
November	1st to 10th	Day	13% 10% 3 8% 5% 4 5% 5% 6% 8% 33%	1699
	11th to 20th	Day	13% 11% 4 9% 6% 5% 5% 4 6% 5% 31%	1656
	21st to end	Day	18% 13% 5% 9% 6% 5% 5% 3 5% 6% 25%	1520
December	1st to 10th	Day	14% 16% 5% 11% 7% 6% 4 3 6% 6% 22%	1520
	11th to 20th	Day	17% 17% 4 10% 5% 4 4 4 5% 6% 23%	1848
	21st to end	Day	27% 20% 6% 9% 5% 5% 4 3 4 5% 12%	2473
January	1st to 10th	Night	16% 17% 5% 11% 6% 4 4 3 4 5% 24%	4428
	11th to 20th	Night	14% 20% 7% 13% 7% 6% 4 4 4 4 18%	4363
	21st to end	Night	23% 18% 8% 10% 5% 4 3 3 4 4 19%	4532
February	1st to 10th	Night	17% 16% 5% 12% 7% 5% 5% 3 4 5% 22%	2470
	11th to 20th	Night	15% 15% 5% 10% 5% 5% 5% 4 5% 6% 26%	2335
	21st to end	Night	17% 12% 4 11% 6% 6% 4 4 5% 5% 26%	1884
March	1st to 10th	Night	15% 15% 4 8% 5% 3 4 3 4 5% 34%	3583
	11th to 20th	Night	10% 10% 3 8% 5% 5% 5% 4 6% 7% 38%	3480
	21st to end	Night	17% 9% 3 8% 6% 4 4 3 4 5% 38%	3817
April	1st to 10th	Night	17% 13% 3 7% 4 4 4 4 5% 6% 34%	2028
	11th to 20th	Night	19% 8% 3 5% 5% 4 4 4 5% 7% 37%	1687
	21st to end	Night	17% 11% 3 5% 4 4 4 4 5% 8% 35%	1710
May	1st to 10th	Night	16% 8% 3 7% 4 4 3 4 6% 8% 37%	2813
	11th to 20th	Night	13% 9% 3 8% 5% 4 5% 4 5% 6% 39%	2812
	21st to end	Night	11% 4 1 5% 5% 4 4 4 5% 8% 49%	2921
June	1st to 10th	Night	12% 6% 2 5% 4 4 4 5% 7% 6% 45%	1401
	11th to 20th	Night	9% 5% 2 5% 5% 5% 4 4 7% 9% 45%	1330
	21st to end	Night	9% 5% 3 6% 4 4 4 4 5% 7% 49%	1330
July	1st to 10th	Night	8% 4 2 5% 4 4 4 3 5% 11% 49%	2418
	11th to 20th	Night	9% 4 1 4 3 3 4 4 6% 8% 52%	2554
	21st to end	Night	5% 4 2 5% 4 5% 5% 4 8% 9% 48%	3087
August	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 8% 46%	2825
	11th to 20th	Night	9% 8% 3 6% 4 4 4 4 6% 7% 45%	2785
	21st to end	Night	9% 6% 2 7% 5% 4 5% 4 6% 7% 47%	3124
September	1st to 10th	Night	10% 5% 3 7% 4 4 5% 4 5% 7% 46%	1994
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 4 6% 54%	2090
	21st to end	Night	16% 7% 3 7% 4 4 3 3 4 6% 42%	2090
October	1st to 10th	Night	14% 7% 2 6% 5% 4 3 3 4 7% 45%	2190
	11th to 20th	Night	19% 9% 3 8% 4 4 4 3 4 5% 35%	2280
	21st to end	Night	21% 9% 4 7% 5% 5% 4 4 5% 6% 30%	2608
November	1st to 10th	Night	15% 10% 3 6% 4 4 4 2 6% 7% 39%	2452
	11th to 20th	Night	15% 13% 4 8% 5% 4 4 4 6% 7% 31%	2522
	21st to end	Night	20% 14% 4 7% 4 4 4 3 5% 6% 29%	2660
December	1st to 10th	Night	17% 16% 6% 10% 5% 5% 5% 4 5% 6% 22%	2660
	11th to 20th	Night	15% 15% 6% 11% 6% 4 5% 3 6% 5% 25%	3331
	21st to end	Night	26% 21% 6% 10% 5% 4 4 3 3 4 14%	5190

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% 5% 15% 11% 3 1	2528
	11th to 20th	Day	73% 4 13% 7% 2	2601
	21st to end	Day	75% 3 11% 7% 3	3124
February	1st to 10th	Day	66% 4 11% 14% 5%	1710
	11th to 20th	Day	60% 4 10% 17% 7% 1	1738
	21st to end	Day	60% 5% 12% 15% 7% 2	1570
March	1st to 10th	Day	59% 4 11% 20% 5%	3269
	11th to 20th	Day	52% 7% 13% 20% 8% 1	3480
	21st to end	Day	55% 5% 12% 16% 11% 2	3815
April	1st to 10th	Day	51% 6% 12% 20% 10% 1	2167
	11th to 20th	Day	48% 5% 11% 20% 14% 2	2442
	21st to end	Day	49% 6% 13% 18% 12% 2	2470
May	1st to 10th	Day	45% 6% 12% 21% 14% 3	4120
	11th to 20th	Day	47% 6% 15% 21% 9% 1	4085
	21st to end	Day	37% 5% 11% 19% 21% 7%	4644
June	1st to 10th	Day	38% 6% 13% 27% 14% 2	2774
	11th to 20th	Day	35% 7% 14% 26% 16% 2	2850
	21st to end	Day	38% 7% 14% 25% 16% 1	2850
July	1st to 10th	Day	39% 6% 14% 24% 16% 2	4478
	11th to 20th	Day	31% 6% 12% 35% 14% 1	4338
	21st to end	Day	34% 8% 16% 19% 21% 2	4324
August	1st to 10th	Day	37% 9% 14% 24% 15% 1	4091
	11th to 20th	Day	37% 8% 15% 31% 9% 1	4083
	21st to end	Day	38% 6% 12% 30% 13% 1	4531
September	1st to 10th	Day	38% 7% 15% 25% 13% 2	2164
	11th to 20th	Day	33% 6% 14% 31% 15% 1	2090
	21st to end	Day	45% 6% 14% 24% 11% 1	2090
October	1st to 10th	Day	33% 5% 12% 31% 17% 2	3302
	11th to 20th	Day	43% 6% 12% 24% 15%	3140
	21st to end	Day	46% 5% 15% 23% 10%	3249
November	1st to 10th	Day	47% 6% 13% 22% 9% 1	1699
	11th to 20th	Day	51% 6% 17% 17% 9% 1	1656
	21st to end	Day	60% 6% 12% 17% 4	1520
December	1st to 10th	Day	62% 5% 14% 14% 4	1520
	11th to 20th	Day	61% 5% 16% 15% 3	1844
	21st to end	Day	76% 4 12% 6% 2	2473
January	1st to 10th	Night	62% 3 15% 15% 4	4428
	11th to 20th	Night	70% 6% 12% 9% 3	4363
	21st to end	Night	71% 3 10% 14% 2	4532
February	1st to 10th	Night	64% 5% 9% 15% 6% 1	2470
	11th to 20th	Night	58% 5% 11% 17% 8% 1	2337
	21st to end	Night	60% 4 10% 18% 7% 1	1884
March	1st to 10th	Night	53% 5% 12% 25% 5%	3583
	11th to 20th	Night	43% 6% 15% 21% 14% 1	3480
	21st to end	Night	47% 4 12% 23% 13% 1	3817
April	1st to 10th	Night	51% 5% 10% 20% 12% 2	2028
	11th to 20th	Night	46% 5% 10% 20% 17% 2	1687
	21st to end	Night	45% 6% 11% 19% 15% 4	1710
May	1st to 10th	Night	45% 5% 11% 20% 14% 5%	2840
	11th to 20th	Night	44% 6% 11% 26% 11% 2	2813
	21st to end	Night	33% 6% 11% 23% 20% 7%	2928
June	1st to 10th	Night	36% 5% 11% 29% 16% 2	1401
	11th to 20th	Night	34% 7% 14% 24% 19% 2	1330
	21st to end	Night	33% 6% 13% 26% 21% 1	1330
July	1st to 10th	Night	31% 5% 11% 30% 17% 6%	2378
	11th to 20th	Night	29% 5% 12% 36% 16% 1	2506
	21st to end	Night	29% 8% 17% 21% 21% 3	2988
August	1st to 10th	Night	36% 6% 14% 27% 16% 2	2814
	11th to 20th	Night	36% 7% 14% 30% 11% 2	2812
	21st to end	Night	36% 6% 12% 29% 16% 1	3124
September	1st to 10th	Night	36% 7% 13% 28% 14% 2	1994
	11th to 20th	Night	32% 5% 12% 30% 19% 2	2090
	21st to end	Night	42% 5% 12% 28% 12% 1	2090
October	1st to 10th	Night	28% 5% 11% 31% 25% 1	3658
	11th to 20th	Night	46% 4 10% 22% 16% 1	3779
	21st to end	Night	44% 3 13% 26% 12% 1	4295
November	1st to 10th	Night	44% 6% 12% 25% 12% 1	2452
	11th to 20th	Night	52% 5% 16% 19% 8% 1	2522
	21st to end	Night	56% 5% 17% 16% 5%	2660
December	1st to 10th	Night	62% 5% 16% 13% 3	2660
	11th to 20th	Night	59% 5% 15% 16% 5%	3334
	21st to end	Night	75% 4 11% 7% 2	5190

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% 11% 37% 20% 9% 1	270
	11th to 20th	Day	24% 13% 38% 21% 4 1	270
	21st to end	Day	27% 8% 32% 25% 6% 1	297
February	1st to 10th	Day	25% 11% 40% 19% 4 1	270
	11th to 20th	Day	20% 11% 36% 28% 4	270
	21st to end	Day	18% 16% 44% 18% 5%	225
March	1st to 10th	Day	23% 13% 32% 25% 6% 1	354
	11th to 20th	Day	16% 13% 28% 33% 8% 1	460
	21st to end	Day	25% 10% 29% 26% 9% 1	506
April	1st to 10th	Day	18% 9% 33% 28% 10% 2	460
	11th to 20th	Day	23% 11% 26% 24% 12% 5%	452
	21st to end	Day	23% 7% 26% 27% 15% 2	460
May	1st to 10th	Day	21% 7% 21% 32% 15% 3	463
	11th to 20th	Day	18% 4 20% 30% 21% 7%	487
	21st to end	Day	13% 2 18% 29% 29% 9%	529
June	1st to 10th	Day	13% 5% 21% 34% 21% 6%	604
	11th to 20th	Day	12% 4 21% 36% 21% 6%	680
	21st to end	Day	14% 4 21% 35% 21% 5%	680
July	1st to 10th	Day	10% 4 17% 31% 26% 13%	671
	11th to 20th	Day	12% 3 17% 34% 23% 11%	654
	21st to end	Day	8% 2 12% 36% 32% 11%	532
August	1st to 10th	Day	11% 3 11% 29% 31% 14%	486
	11th to 20th	Day	12% 3 11% 33% 28% 12%	479
	21st to end	Day	13% 5% 14% 26% 30% 12%	539
September	1st to 10th	Day	14% 4 17% 27% 27% 12%	490
	11th to 20th	Day	10% 3 13% 25% 33% 17%	490
	21st to end	Day	16% 9% 22% 25% 18% 11%	490
October	1st to 10th	Day	16% 7% 22% 27% 18% 9%	490
	11th to 20th	Day	23% 11% 27% 25% 11% 2	490
	21st to end	Day	23% 14% 27% 26% 9% 1	435
November	1st to 10th	Day	19% 11% 31% 25% 10% 4	279
	11th to 20th	Day	21% 14% 29% 27% 7% 2	244
	21st to end	Day	28% 12% 36% 19% 4	180
December	1st to 10th	Day	20% 18% 34% 21% 5% 1	180
	11th to 20th	Day	23% 21% 33% 20% 3 1	180
	21st to end	Day	27% 16% 35% 18% 3	212
January	1st to 10th	Night	24% 12% 37% 20% 7% 1	950
	11th to 20th	Night	27% 12% 31% 24% 4 1	899
	21st to end	Night	22% 8% 33% 29% 8%	836
February	1st to 10th	Night	24% 6% 39% 27% 4	760
	11th to 20th	Night	22% 10% 32% 30% 5% 1	743
	21st to end	Night	22% 11% 38% 25% 4	628
March	1st to 10th	Night	19% 10% 32% 31% 8%	760
	11th to 20th	Night	18% 8% 36% 31% 6% 1	760
	21st to end	Night	22% 7% 27% 33% 9% 1	836
April	1st to 10th	Night	21% 10% 30% 31% 8%	717
	11th to 20th	Night	23% 5% 30% 28% 11% 3	563
	21st to end	Night	24% 6% 22% 36% 10% 2	570
May	1st to 10th	Night	19% 5% 21% 36% 16% 3	570
	11th to 20th	Night	18% 3 21% 38% 18% 1	561
	21st to end	Night	11% 3 17% 39% 24% 6%	523
June	1st to 10th	Night	13% 4 19% 40% 23% 1	380
	11th to 20th	Night	11% 2 18% 40% 27% 2	380
	21st to end	Night	11% 4 17% 41% 25% 2	380
July	1st to 10th	Night	9% 2 10% 40% 34% 5%	482
	11th to 20th	Night	12% 2 12% 39% 30% 5%	552
	21st to end	Night	8% 3 11% 46% 29% 3	624
August	1st to 10th	Night	11% 2 11% 38% 32% 5%	567
	11th to 20th	Night	10% 2 11% 36% 34% 6%	564
	21st to end	Night	11% 3 15% 35% 30% 5%	627
September	1st to 10th	Night	12% 6% 18% 31% 26% 7%	722
	11th to 20th	Night	11% 4 13% 35% 30% 6%	760
	21st to end	Night	20% 6% 16% 33% 19% 6%	760
October	1st to 10th	Night	15% 9% 24% 30% 19% 3	760
	11th to 20th	Night	23% 11% 26% 27% 11% 1	760
	21st to end	Night	26% 11% 30% 27% 6%	836
November	1st to 10th	Night	22% 10% 27% 28% 12% 1	755
	11th to 20th	Night	22% 12% 37% 21% 7% 1	760
	21st to end	Night	27% 12% 31% 23% 6%	760
December	1st to 10th	Night	26% 14% 35% 20% 5%	760
	11th to 20th	Night	23% 14% 36% 22% 4	793
	21st to end	Night	30% 11% 33% 23% 3	1045

Page generated at 2024-11-01 22:47:45. Version ac07

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