St Catharines
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St Catharines clear sky chart from 2005-11-06 to 2026-06-01.

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% 4 9% 6% 5% 5% 4 5% 7% 32%	132393
	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 31%	130750
Transparency	Day	49% 8% 13% 20% 10% 1	135987
	Night	52% 7% 12% 18% 10% 1	135242
Seeing	Day	19% 12% 28% 23% 13% 5%	16429
	Night	20% 11% 28% 27% 12% 1	25929

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	14% 17% 6% 14% 7% 5% 4 4 5% 5% 19%	4661
	11th to 20th	Day	10% 22% 8% 18% 8% 6% 6% 3 4 4 10%	5158
	21st to end	Day	15% 15% 6% 15% 11% 7% 5% 3 4 5% 14%	5780
February	1st to 10th	Day	17% 17% 4 13% 7% 6% 5% 4 5% 6% 17%	1890
	11th to 20th	Day	13% 16% 7% 14% 8% 6% 5% 3 5% 6% 18%	1843
	21st to end	Day	18% 15% 4 11% 8% 4 5% 4 6% 5% 20%	1633
March	1st to 10th	Day	17% 11% 4 11% 5% 5% 4 3 5% 5% 30%	5042
	11th to 20th	Day	10% 15% 4 10% 5% 5% 4 4 5% 7% 32%	5090
	21st to end	Day	18% 10% 4 9% 6% 4 4 3 5% 5% 32%	5586
April	1st to 10th	Day	18% 11% 3 8% 5% 5% 4 3 5% 6% 31%	2485
	11th to 20th	Day	18% 10% 3 7% 4 4 4 3 5% 6% 35%	2543
	21st to end	Day	19% 8% 3 7% 5% 5% 4 3 5% 6% 35%	2730
May	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 3 5% 7% 33%	6018
	11th to 20th	Day	14% 10% 3 9% 5% 5% 5% 4 6% 7% 33%	6400
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 5% 7% 39%	7103
June	1st to 10th	Day	14% 6% 3 6% 5% 5% 4 4 6% 7% 41%	2800
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	2800
	21st to end	Day	12% 5% 2 5% 4 4 4 4 7% 9% 43%	2800
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 11% 43%	6360
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 43%	6360
	21st to end	Day	8% 4 2 6% 4 5% 4 4 6% 8% 49%	6432
August	1st to 10th	Day	15% 7% 2 6% 4 5% 4 4 6% 9% 39%	4234
	11th to 20th	Day	12% 5% 2 7% 5% 4 5% 5% 7% 11% 36%	4174
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 10% 47%	4456
September	1st to 10th	Day	12% 7% 2 6% 5% 4 4 4 6% 8% 42%	2400
	11th to 20th	Day	10% 5% 2 5% 5% 4 4 4 5% 8% 48%	2293
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 8% 9% 34%	2150
October	1st to 10th	Day	18% 7% 3 6% 4 4 5% 3 6% 7% 38%	2000
	11th to 20th	Day	19% 10% 2 9% 5% 5% 5% 3 5% 6% 31%	2000
	21st to end	Day	23% 13% 3 8% 5% 5% 5% 4 5% 5% 25%	2200
November	1st to 10th	Day	14% 11% 3 9% 5% 5% 5% 4 6% 7% 32%	1818
	11th to 20th	Day	14% 12% 4 8% 6% 6% 6% 3 5% 7% 30%	1680
	21st to end	Day	19% 14% 5% 9% 5% 5% 5% 4 4 6% 23%	1680
December	1st to 10th	Day	19% 17% 6% 11% 8% 5% 5% 4 5% 6% 15%	2680
	11th to 20th	Day	19% 16% 5% 9% 5% 5% 5% 3 5% 5% 22%	3066
	21st to end	Day	22% 18% 6% 12% 8% 7% 4 3 4 5% 11%	4048
January	1st to 10th	Night	15% 16% 6% 14% 7% 5% 4 4 5% 5% 20%	8234
	11th to 20th	Night	11% 18% 7% 16% 7% 6% 5% 4 4 5% 17%	7722
	21st to end	Night	16% 14% 5% 14% 8% 7% 5% 4 4 5% 18%	8401
February	1st to 10th	Night	16% 17% 5% 10% 7% 5% 5% 4 5% 5% 22%	2730
	11th to 20th	Night	15% 15% 5% 12% 6% 6% 5% 4 5% 6% 23%	2663
	21st to end	Night	17% 14% 5% 13% 7% 5% 5% 3 5% 6% 21%	2167
March	1st to 10th	Night	17% 10% 4 9% 7% 5% 4 4 5% 5% 29%	5018
	11th to 20th	Night	13% 12% 3 7% 4 4 4 4 5% 8% 37%	5089
	21st to end	Night	18% 9% 3 8% 4 4 4 4 4 5% 36%	5588
April	1st to 10th	Night	18% 12% 3 9% 5% 4 3 3 4 6% 31%	2134
	11th to 20th	Night	19% 8% 2 7% 5% 5% 5% 4 5% 5% 36%	2044
	21st to end	Night	16% 9% 3 7% 4 4 6% 4 5% 7% 35%	1890
May	1st to 10th	Night	21% 11% 4 9% 4 4 4 3 4 6% 31%	4143
	11th to 20th	Night	12% 8% 3 8% 5% 6% 5% 5% 6% 8% 34%	3713
	21st to end	Night	16% 6% 2 7% 4 4 3 4 6% 7% 40%	4014
June	1st to 10th	Night	12% 6% 3 7% 5% 6% 6% 5% 6% 8% 37%	1600
	11th to 20th	Night	9% 5% 3 6% 5% 6% 6% 4 6% 8% 43%	1600
	21st to end	Night	12% 6% 2 6% 4 5% 5% 5% 5% 9% 43%	1600
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 4 4 6% 9% 45%	3600
	11th to 20th	Night	8% 5% 3 7% 4 4 4 4 6% 9% 46%	3600
	21st to end	Night	8% 5% 2 5% 4 4 4 4 6% 7% 51%	4417
August	1st to 10th	Night	10% 5% 3 7% 4 4 5% 4 6% 8% 45%	2915
	11th to 20th	Night	13% 7% 2 6% 4 4 6% 4 6% 7% 42%	2875
	21st to end	Night	8% 4 2 6% 4 4 4 4 7% 10% 46%	3407
September	1st to 10th	Night	13% 5% 2 5% 5% 4 4 3 5% 8% 46%	2000
	11th to 20th	Night	11% 4 2 5% 4 3 4 3 5% 6% 53%	2104
	21st to end	Night	16% 7% 3 8% 5% 4 4 3 5% 7% 37%	2249
October	1st to 10th	Night	16% 8% 2 7% 3 4 4 3 5% 7% 41%	2400
	11th to 20th	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 33%	2400
	21st to end	Night	23% 9% 3 7% 5% 4 4 4 5% 6% 30%	2640
November	1st to 10th	Night	16% 10% 3 8% 4 4 4 3 4 7% 37%	2695
	11th to 20th	Night	15% 12% 3 8% 6% 5% 5% 4 6% 6% 29%	2940
	21st to end	Night	19% 14% 5% 9% 6% 5% 5% 4 5% 6% 23%	2940
December	1st to 10th	Night	15% 19% 5% 13% 7% 5% 5% 4 5% 7% 15%	4720
	11th to 20th	Night	16% 19% 5% 10% 5% 4 4 3 5% 5% 24%	5348
	21st to end	Night	24% 16% 6% 11% 7% 6% 4 3 4 5% 14%	7150

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	67% 8% 12% 9% 4	4662
	11th to 20th	Day	76% 7% 7% 7% 2	5192
	21st to end	Day	72% 7% 11% 7% 3	5780
February	1st to 10th	Day	68% 8% 10% 12% 3	1890
	11th to 20th	Day	67% 7% 10% 13% 3	1852
	21st to end	Day	64% 7% 12% 12% 5%	1633
March	1st to 10th	Day	55% 6% 15% 15% 9%	5045
	11th to 20th	Day	50% 8% 17% 16% 7% 2	5090
	21st to end	Day	51% 8% 8% 23% 10% 1	5586
April	1st to 10th	Day	53% 7% 11% 18% 11% 1	2485
	11th to 20th	Day	49% 6% 10% 19% 13% 1	2543
	21st to end	Day	49% 7% 10% 18% 12% 3	2730
May	1st to 10th	Day	50% 8% 11% 16% 10% 5%	6027
	11th to 20th	Day	49% 9% 11% 19% 12% 1	6404
	21st to end	Day	42% 7% 12% 23% 13% 2	7103
June	1st to 10th	Day	40% 8% 13% 21% 15% 2	2800
	11th to 20th	Day	38% 9% 14% 24% 14% 1	2800
	21st to end	Day	36% 9% 15% 25% 15% 1	2800
July	1st to 10th	Day	32% 8% 14% 27% 17% 1	6290
	11th to 20th	Day	33% 9% 14% 29% 14% 1	6285
	21st to end	Day	31% 8% 14% 28% 17% 1	6247
August	1st to 10th	Day	41% 9% 15% 22% 13% 1	4221
	11th to 20th	Day	40% 9% 16% 25% 10% 1	4213
	21st to end	Day	31% 8% 13% 35% 12% 1	4456
September	1st to 10th	Day	38% 8% 14% 27% 12% 1	2400
	11th to 20th	Day	33% 8% 13% 31% 14% 1	2293
	21st to end	Day	44% 8% 15% 23% 9% 1	2150
October	1st to 10th	Day	34% 7% 17% 27% 15% 1	3260
	11th to 20th	Day	42% 6% 15% 23% 13%	3240
	21st to end	Day	50% 7% 15% 20% 7%	3538
November	1st to 10th	Day	50% 8% 12% 20% 8% 1	1818
	11th to 20th	Day	53% 7% 16% 15% 9% 1	1680
	21st to end	Day	63% 6% 14% 14% 3	1680
December	1st to 10th	Day	69% 8% 15% 7% 1	2680
	11th to 20th	Day	64% 8% 10% 11% 7% 1	3066
	21st to end	Day	75% 7% 9% 7% 2	4048
January	1st to 10th	Night	66% 7% 13% 12% 2	8234
	11th to 20th	Night	68% 7% 10% 10% 4	7763
	21st to end	Night	68% 6% 11% 8% 6%	8401
February	1st to 10th	Night	65% 7% 11% 14% 4	2730
	11th to 20th	Night	62% 6% 12% 14% 4	2665
	21st to end	Night	63% 7% 11% 13% 6%	2167
March	1st to 10th	Night	57% 5% 12% 17% 8% 1	5028
	11th to 20th	Night	44% 7% 18% 20% 9% 2	5090
	21st to end	Night	48% 6% 9% 21% 14% 2	5588
April	1st to 10th	Night	55% 5% 8% 19% 11% 1	2134
	11th to 20th	Night	48% 6% 9% 20% 14% 2	2044
	21st to end	Night	47% 6% 10% 20% 14% 2	1890
May	1st to 10th	Night	55% 6% 8% 14% 12% 5%	4150
	11th to 20th	Night	44% 7% 17% 19% 11% 1	3714
	21st to end	Night	42% 7% 11% 22% 16% 1	4015
June	1st to 10th	Night	42% 8% 10% 22% 17% 2	1600
	11th to 20th	Night	37% 7% 14% 23% 17% 2	1600
	21st to end	Night	39% 6% 14% 22% 17% 2	1600
July	1st to 10th	Night	35% 7% 12% 22% 22% 2	3560
	11th to 20th	Night	33% 7% 14% 28% 16% 2	3552
	21st to end	Night	31% 6% 14% 24% 23% 1	4287
August	1st to 10th	Night	35% 8% 15% 26% 14% 2	2904
	11th to 20th	Night	39% 9% 14% 28% 11%	2902
	21st to end	Night	30% 8% 15% 32% 14% 1	3407
September	1st to 10th	Night	36% 7% 14% 26% 16% 1	2000
	11th to 20th	Night	30% 5% 13% 33% 18% 1	2104
	21st to end	Night	45% 6% 12% 22% 13% 1	2249
October	1st to 10th	Night	36% 6% 10% 26% 21% 1	3920
	11th to 20th	Night	48% 6% 12% 22% 11% 1	3899
	21st to end	Night	42% 5% 17% 25% 10% 1	4252
November	1st to 10th	Night	46% 6% 12% 22% 11% 1	2695
	11th to 20th	Night	52% 6% 15% 17% 9% 1	2940
	21st to end	Night	60% 7% 14% 15% 3	2940
December	1st to 10th	Night	67% 9% 15% 7% 2	4720
	11th to 20th	Night	63% 6% 9% 12% 9% 1	5348
	21st to end	Night	71% 6% 13% 8% 2	7150

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% 19% 35% 15% 7% 1	220
	11th to 20th	Day	26% 23% 35% 11% 4 1	312
	21st to end	Day	25% 21% 33% 17% 4	363
February	1st to 10th	Day	25% 22% 35% 16% 2	330
	11th to 20th	Day	25% 24% 34% 15% 2	330
	21st to end	Day	30% 21% 32% 15% 1	312
March	1st to 10th	Day	24% 16% 33% 21% 6%	540
	11th to 20th	Day	24% 17% 33% 20% 4 1	540
	21st to end	Day	27% 15% 32% 20% 5% 1	594
April	1st to 10th	Day	22% 17% 32% 20% 7% 1	540
	11th to 20th	Day	26% 17% 26% 19% 9% 3	532
	21st to end	Day	25% 10% 30% 23% 10% 2	540
May	1st to 10th	Day	21% 14% 29% 23% 11% 3	543
	11th to 20th	Day	17% 10% 24% 27% 17% 5%	567
	21st to end	Day	13% 9% 25% 29% 18% 6%	617
June	1st to 10th	Day	12% 10% 30% 32% 13% 2	530
	11th to 20th	Day	12% 9% 27% 29% 19% 4	530
	21st to end	Day	14% 6% 29% 29% 18% 4	530
July	1st to 10th	Day	7% 5% 18% 32% 29% 9%	525
	11th to 20th	Day	13% 6% 19% 30% 21% 10%	524
	21st to end	Day	9% 4 26% 34% 20% 7%	576
August	1st to 10th	Day	11% 4 19% 32% 22% 12%	526
	11th to 20th	Day	10% 7% 18% 28% 25% 12%	519
	21st to end	Day	12% 7% 20% 30% 21% 11%	583
September	1st to 10th	Day	13% 6% 22% 25% 22% 11%	530
	11th to 20th	Day	9% 5% 17% 26% 27% 17%	530
	21st to end	Day	14% 10% 26% 24% 18% 8%	530
October	1st to 10th	Day	20% 9% 28% 19% 18% 7%	530
	11th to 20th	Day	22% 17% 30% 21% 8% 2	530
	21st to end	Day	31% 15% 27% 20% 7%	583
November	1st to 10th	Day	21% 19% 30% 21% 7% 3	351
	11th to 20th	Day	22% 21% 30% 20% 5% 2	220
	21st to end	Day	29% 19% 36% 12% 4	220
December	1st to 10th	Day	29% 16% 37% 14% 4	220
	11th to 20th	Day	28% 24% 34% 11% 4	220
	21st to end	Day	28% 22% 33% 12% 2 1	242
January	1st to 10th	Night	26% 20% 34% 14% 6%	840
	11th to 20th	Night	29% 18% 30% 19% 3 1	840
	21st to end	Night	21% 16% 35% 22% 6%	924
February	1st to 10th	Night	25% 20% 32% 21% 3	840
	11th to 20th	Night	23% 18% 35% 21% 4	823
	21st to end	Night	24% 17% 35% 21% 3	692
March	1st to 10th	Night	21% 14% 35% 24% 6%	840
	11th to 20th	Night	22% 15% 35% 21% 6% 1	840
	21st to end	Night	22% 11% 31% 27% 9% 1	924
April	1st to 10th	Night	22% 13% 33% 27% 5%	840
	11th to 20th	Night	22% 11% 32% 26% 9% 1	800
	21st to end	Night	21% 7% 28% 33% 11%	630
May	1st to 10th	Night	19% 7% 26% 32% 14% 2	630
	11th to 20th	Night	15% 5% 29% 37% 13%	446
	21st to end	Night	15% 6% 23% 36% 19% 2	455
June	1st to 10th	Night	13% 2 32% 37% 16% 1	400
	11th to 20th	Night	11% 5% 27% 40% 17% 1	400
	21st to end	Night	10% 6% 24% 43% 17% 1	400
July	1st to 10th	Night	8% 2 18% 47% 22% 2	390
	11th to 20th	Night	10% 4 20% 43% 20% 3	388
	21st to end	Night	10% 3 17% 45% 23% 2	646
August	1st to 10th	Night	10% 3 14% 39% 31% 4	597
	11th to 20th	Night	10% 4 15% 32% 35% 4	594
	21st to end	Night	11% 3 17% 39% 26% 3	766
September	1st to 10th	Night	13% 6% 19% 35% 24% 4	800
	11th to 20th	Night	13% 4 14% 32% 30% 7%	800
	21st to end	Night	17% 8% 19% 31% 20% 5%	800
October	1st to 10th	Night	19% 6% 26% 26% 21% 3	800
	11th to 20th	Night	25% 14% 26% 25% 10% 1	800
	21st to end	Night	29% 10% 29% 27% 5%	880
November	1st to 10th	Night	22% 13% 27% 27% 11% 1	820
	11th to 20th	Night	23% 16% 32% 20% 8% 1	840
	21st to end	Night	25% 15% 35% 19% 7%	840
December	1st to 10th	Night	30% 18% 30% 18% 5%	840
	11th to 20th	Night	24% 21% 31% 19% 4	840
	21st to end	Night	30% 16% 32% 19% 2	924

Page generated at 2026-05-29 01:53:30. Version ac07

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