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 2024-03-28.

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 7% 6% 3 5% 5% 5% 7% 33%	78690
	Night	16% 11% 4 7% 6% 3 4 4 5% 6% 33%	81312
Transparency	Day	49% 6% 13% 20% 10% 1	78401
	Night	52% 5% 12% 20% 10% 1	81121
Seeing	Day	17% 8% 23% 28% 18% 6%	14338
	Night	20% 8% 26% 30% 14% 2	24003

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	16% 19% 8% 10% 7% 3 4 5% 5% 5% 18%	2527
	11th to 20th	Day	15% 19% 7% 13% 9% 4 4 4 4 5% 15%	2601
	21st to end	Day	26% 18% 7% 9% 7% 3 5% 3 4 4 14%	3124
February	1st to 10th	Day	16% 15% 5% 11% 10% 4 6% 4 4 5% 20%	1710
	11th to 20th	Day	14% 13% 6% 10% 8% 3 5% 4 5% 6% 25%	1729
	21st to end	Day	15% 13% 5% 12% 7% 4 5% 5% 4 5% 26%	1570
March	1st to 10th	Day	15% 13% 5% 8% 8% 4 5% 4 4 6% 30%	1984
	11th to 20th	Day	12% 12% 4 7% 7% 4 5% 4 6% 8% 31%	2090
	21st to end	Day	19% 12% 5% 8% 6% 3 5% 5% 5% 6% 27%	2255
April	1st to 10th	Day	16% 12% 3 7% 6% 3 4 5% 5% 7% 32%	2052
	11th to 20th	Day	17% 11% 3 5% 5% 3 5% 4 4 7% 36%	2312
	21st to end	Day	19% 8% 3 6% 5% 3 5% 5% 5% 6% 34%	2340
May	1st to 10th	Day	17% 7% 3 6% 6% 3 5% 6% 6% 7% 35%	2340
	11th to 20th	Day	18% 7% 4 5% 5% 4 5% 4 5% 6% 38%	2301
	21st to end	Day	12% 5% 3 5% 5% 4 5% 5% 5% 7% 43%	2616
June	1st to 10th	Day	10% 5% 4 5% 6% 2 4 5% 6% 9% 43%	2628
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 6% 6% 10% 43%	2700
	21st to end	Day	11% 5% 3 5% 5% 4 5% 5% 7% 9% 42%	2700
July	1st to 10th	Day	9% 4 3 4 4 3 4 4 8% 8% 49%	2585
	11th to 20th	Day	9% 5% 3 5% 5% 4 5% 6% 6% 9% 44%	2507
	21st to end	Day	10% 4 2 5% 5% 3 5% 6% 8% 10% 43%	2547
August	1st to 10th	Day	9% 5% 2 5% 4 4 5% 7% 8% 9% 43%	2327
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 7% 6% 9% 42%	2303
	21st to end	Day	10% 6% 2 6% 6% 3 5% 5% 5% 8% 44%	2574
September	1st to 10th	Day	12% 5% 2 7% 5% 4 5% 6% 7% 8% 40%	2051
	11th to 20th	Day	11% 4 2 5% 4 3 6% 5% 7% 9% 45%	1980
	21st to end	Day	16% 7% 2 6% 5% 3 5% 5% 6% 9% 37%	1980
October	1st to 10th	Day	14% 7% 2 7% 5% 4 4 5% 5% 7% 39%	1886
	11th to 20th	Day	18% 9% 3 7% 7% 3 5% 5% 4 7% 32%	1800
	21st to end	Day	22% 9% 3 8% 7% 3 5% 4 6% 6% 28%	1882
November	1st to 10th	Day	13% 10% 4 7% 6% 3 5% 6% 6% 8% 33%	1672
	11th to 20th	Day	13% 11% 4 8% 7% 4 6% 5% 6% 6% 31%	1656
	21st to end	Day	18% 12% 6% 8% 7% 4 4 5% 5% 6% 26%	1520
December	1st to 10th	Day	14% 16% 5% 9% 8% 4 5% 4 5% 6% 23%	1520
	11th to 20th	Day	17% 16% 6% 9% 6% 3 5% 4 5% 6% 23%	1848
	21st to end	Day	28% 19% 7% 8% 6% 3 4 4 4 5% 12%	2473
January	1st to 10th	Night	17% 17% 5% 9% 7% 3 4 4 4 6% 24%	4428
	11th to 20th	Night	14% 19% 7% 11% 8% 5% 5% 5% 4 4 18%	4363
	21st to end	Night	24% 17% 9% 9% 6% 3 3 3 4 4 19%	4532
February	1st to 10th	Night	17% 15% 6% 11% 7% 4 5% 4 4 6% 22%	2470
	11th to 20th	Night	15% 14% 5% 9% 6% 4 5% 5% 5% 6% 26%	2335
	21st to end	Night	18% 11% 4 10% 6% 5% 5% 4 4 5% 26%	1884
March	1st to 10th	Night	15% 11% 5% 8% 7% 4 5% 4 5% 5% 32%	2195
	11th to 20th	Night	13% 9% 3 7% 6% 4 5% 5% 6% 7% 36%	2090
	21st to end	Night	20% 8% 4 7% 7% 3 4 4 5% 5% 33%	2256
April	1st to 10th	Night	17% 11% 4 7% 5% 3 5% 4 5% 6% 35%	1922
	11th to 20th	Night	18% 8% 3 4 6% 3 4 4 5% 7% 38%	1597
	21st to end	Night	18% 10% 4 5% 4 3 4 4 5% 7% 36%	1620
May	1st to 10th	Night	14% 8% 4 7% 6% 3 5% 5% 6% 8% 33%	1620
	11th to 20th	Night	15% 7% 3 5% 5% 3 5% 5% 5% 7% 40%	1592
	21st to end	Night	11% 3 2 5% 5% 3 5% 6% 6% 8% 48%	1655
June	1st to 10th	Night	12% 5% 3 4 4 3 4 6% 7% 7% 46%	1328
	11th to 20th	Night	10% 5% 2 4 5% 4 5% 5% 6% 9% 46%	1260
	21st to end	Night	8% 4 3 5% 5% 3 4 6% 5% 7% 49%	1260
July	1st to 10th	Night	7% 4 2 5% 5% 2 4 4 3 9% 55%	1370
	11th to 20th	Night	8% 5% 2 4 4 2 5% 5% 6% 9% 49%	1451
	21st to end	Night	7% 4 2 5% 4 3 5% 5% 7% 9% 49%	1771
August	1st to 10th	Night	8% 4 2 5% 4 3 4 6% 6% 10% 48%	1611
	11th to 20th	Night	6% 4 2 5% 4 4 5% 6% 6% 8% 49%	1598
	21st to end	Night	9% 5% 3 5% 4 2 4 5% 5% 7% 52%	1782
September	1st to 10th	Night	11% 5% 3 7% 5% 3 4 5% 5% 7% 44%	1889
	11th to 20th	Night	10% 5% 2 5% 5% 3 4 4 4 6% 53%	1980
	21st to end	Night	16% 6% 3 5% 5% 3 4 4 4 6% 43%	1980
October	1st to 10th	Night	15% 7% 2 6% 5% 3 4 4 4 7% 44%	2074
	11th to 20th	Night	20% 9% 3 7% 6% 4 4 5% 4 5% 34%	2160
	21st to end	Night	23% 9% 4 6% 6% 4 4 4 5% 6% 29%	2470
November	1st to 10th	Night	15% 9% 3 6% 4 3 4 3 6% 8% 39%	2406
	11th to 20th	Night	15% 12% 4 7% 6% 3 5% 5% 6% 6% 31%	2522
	21st to end	Night	20% 13% 4 7% 5% 4 4 4 4 6% 29%	2660
December	1st to 10th	Night	17% 15% 6% 9% 6% 3 5% 5% 5% 6% 23%	2660
	11th to 20th	Night	15% 14% 7% 10% 6% 3 4 4 6% 5% 25%	3331
	21st to end	Night	26% 19% 7% 9% 6% 3 4 4 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	57% 6% 12% 17% 8% 1	1984
	11th to 20th	Day	51% 6% 11% 19% 11% 2	2090
	21st to end	Day	58% 5% 9% 19% 8% 1	2255
April	1st to 10th	Day	52% 6% 12% 20% 10% 1	2052
	11th to 20th	Day	48% 5% 12% 19% 14% 2	2312
	21st to end	Day	49% 6% 14% 18% 12% 2	2340
May	1st to 10th	Day	47% 7% 10% 22% 11% 2	2340
	11th to 20th	Day	47% 6% 10% 21% 14% 2	2305
	21st to end	Day	40% 6% 12% 24% 16% 2	2616
June	1st to 10th	Day	38% 6% 14% 27% 14% 2	2628
	11th to 20th	Day	35% 7% 14% 26% 15% 2	2700
	21st to end	Day	37% 7% 14% 25% 16% 1	2700
July	1st to 10th	Day	32% 6% 11% 29% 19% 3	2516
	11th to 20th	Day	34% 7% 13% 28% 16% 2	2432
	21st to end	Day	35% 8% 15% 24% 16% 3	2405
August	1st to 10th	Day	33% 10% 17% 26% 13% 1	2314
	11th to 20th	Day	36% 9% 15% 27% 12% 1	2303
	21st to end	Day	38% 6% 12% 28% 15% 1	2574
September	1st to 10th	Day	39% 7% 16% 23% 13% 2	2051
	11th to 20th	Day	34% 7% 14% 32% 13%	1980
	21st to end	Day	43% 6% 14% 25% 11% 1	1980
October	1st to 10th	Day	44% 5% 12% 24% 13% 1	1886
	11th to 20th	Day	52% 5% 14% 20% 9% 1	1800
	21st to end	Day	55% 6% 14% 18% 7%	1882
November	1st to 10th	Day	47% 6% 13% 22% 9% 1	1672
	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	55% 5% 11% 21% 8% 1	2195
	11th to 20th	Night	47% 5% 13% 22% 12% 2	2090
	21st to end	Night	53% 4 10% 22% 11% 1	2256
April	1st to 10th	Night	50% 5% 10% 20% 12% 2	1922
	11th to 20th	Night	45% 6% 10% 20% 18% 2	1597
	21st to end	Night	45% 6% 11% 19% 14% 4	1620
May	1st to 10th	Night	48% 6% 11% 20% 11% 4	1620
	11th to 20th	Night	43% 5% 9% 21% 18% 3	1593
	21st to end	Night	33% 7% 13% 26% 17% 3	1656
June	1st to 10th	Night	35% 6% 12% 29% 16% 2	1328
	11th to 20th	Night	33% 7% 15% 24% 19% 2	1260
	21st to end	Night	33% 6% 13% 26% 21% 1	1260
July	1st to 10th	Night	29% 5% 10% 29% 23% 4	1330
	11th to 20th	Night	31% 6% 11% 33% 17% 2	1403
	21st to end	Night	29% 8% 18% 23% 18% 3	1672
August	1st to 10th	Night	30% 7% 16% 31% 14% 2	1600
	11th to 20th	Night	30% 9% 15% 32% 12% 3	1598
	21st to end	Night	32% 5% 13% 30% 17% 1	1782
September	1st to 10th	Night	37% 7% 13% 27% 14% 2	1889
	11th to 20th	Night	33% 5% 12% 31% 17% 1	1980
	21st to end	Night	40% 5% 13% 28% 12% 1	1980
October	1st to 10th	Night	41% 6% 11% 24% 17% 1	2074
	11th to 20th	Night	52% 5% 12% 20% 11% 1	2160
	21st to end	Night	56% 5% 11% 19% 9% 1	2470
November	1st to 10th	Night	44% 6% 12% 25% 12% 1	2406
	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% 11% 29% 25% 9% 1	490
April	1st to 10th	Day	19% 9% 32% 27% 11% 2	420
	11th to 20th	Day	23% 10% 26% 24% 13% 5%	412
	21st to end	Day	24% 7% 26% 26% 15% 2	420
May	1st to 10th	Day	22% 7% 22% 31% 15% 3	423
	11th to 20th	Day	19% 4 21% 28% 21% 7%	447
	21st to end	Day	14% 2 18% 27% 29% 9%	485
June	1st to 10th	Day	13% 4 20% 36% 21% 6%	558
	11th to 20th	Day	13% 3 19% 36% 22% 7%	630
	21st to end	Day	13% 4 19% 36% 22% 6%	630
July	1st to 10th	Day	9% 3 16% 30% 28% 14%	621
	11th to 20th	Day	12% 3 16% 35% 24% 10%	605
	21st to end	Day	8% 3 12% 36% 31% 10%	488
August	1st to 10th	Day	11% 3 10% 30% 32% 15%	446
	11th to 20th	Day	12% 3 10% 34% 28% 13%	439
	21st to end	Day	14% 5% 14% 25% 29% 13%	495
September	1st to 10th	Day	15% 3 16% 27% 28% 11%	450
	11th to 20th	Day	11% 3 14% 25% 32% 16%	450
	21st to end	Day	15% 9% 21% 26% 18% 12%	450
October	1st to 10th	Day	17% 7% 21% 27% 19% 10%	450
	11th to 20th	Day	24% 11% 28% 25% 11% 1	450
	21st to end	Day	25% 13% 27% 26% 8% 1	397
November	1st to 10th	Day	19% 11% 31% 25% 10% 4	270
	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	23% 7% 28% 32% 9% 1	821
April	1st to 10th	Night	21% 10% 30% 30% 8%	680
	11th to 20th	Night	22% 5% 30% 29% 12% 3	533
	21st to end	Night	24% 6% 22% 36% 10% 2	540
May	1st to 10th	Night	19% 6% 21% 36% 16% 2	540
	11th to 20th	Night	19% 2 21% 39% 18% 2	531
	21st to end	Night	10% 4 18% 38% 24% 6%	495
June	1st to 10th	Night	13% 4 20% 40% 22% 1	360
	11th to 20th	Night	12% 2 16% 41% 27% 2	360
	21st to end	Night	11% 4 15% 42% 26% 3	360
July	1st to 10th	Night	9% 2 9% 38% 36% 5%	455
	11th to 20th	Night	12% 2 11% 40% 30% 5%	522
	21st to end	Night	8% 3 12% 46% 28% 3	591
August	1st to 10th	Night	11% 2 10% 38% 34% 6%	537
	11th to 20th	Night	9% 2 11% 36% 35% 7%	534
	21st to end	Night	12% 3 14% 35% 31% 5%	594
September	1st to 10th	Night	13% 5% 17% 32% 26% 7%	684
	11th to 20th	Night	12% 5% 14% 36% 28% 6%	720
	21st to end	Night	19% 6% 15% 33% 20% 7%	720
October	1st to 10th	Night	16% 8% 23% 30% 19% 3	720
	11th to 20th	Night	23% 11% 26% 27% 11% 1	720
	21st to end	Night	28% 11% 29% 27% 6%	792
November	1st to 10th	Night	22% 10% 27% 28% 13% 1	740
	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 2024-03-24 23:36:58. Version ac07

Copyright © 2024 Attilla Danko.