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 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	14% 10% 3 8% 5% 5% 4 4 5% 7% 33%	108628
	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 31%	109612
Transparency	Day	49% 8% 13% 20% 10% 1	112267
	Night	52% 7% 13% 18% 10% 1	114136
Seeing	Day	18% 12% 27% 24% 14% 5%	14712
	Night	20% 11% 28% 28% 12% 1	24271

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	12% 18% 7% 15% 6% 5% 4 4 5% 4 19%	3597
	11th to 20th	Day	11% 21% 7% 16% 8% 6% 6% 4 5% 5% 11%	3952
	21st to end	Day	19% 16% 6% 15% 8% 6% 4 3 3 5% 15%	4466
February	1st to 10th	Day	17% 18% 4 13% 7% 6% 5% 4 5% 6% 17%	1755
	11th to 20th	Day	12% 17% 7% 14% 8% 6% 5% 3 4 6% 19%	1663
	21st to end	Day	18% 14% 4 11% 8% 5% 6% 3 6% 5% 21%	1481
March	1st to 10th	Day	18% 12% 4 10% 6% 4 4 3 5% 5% 29%	3432
	11th to 20th	Day	11% 17% 4 9% 5% 5% 4 4 5% 6% 30%	3480
	21st to end	Day	17% 9% 3 7% 5% 4 4 4 6% 6% 36%	3815
April	1st to 10th	Day	18% 11% 3 8% 5% 5% 4 3 5% 6% 32%	2248
	11th to 20th	Day	18% 9% 3 6% 4 4 4 3 5% 6% 37%	2298
	21st to end	Day	19% 8% 3 7% 5% 5% 4 3 4 6% 35%	2470
May	1st to 10th	Day	17% 9% 3 7% 5% 5% 4 3 5% 8% 34%	4108
	11th to 20th	Day	14% 10% 3 9% 5% 5% 5% 4 6% 7% 33%	4356
	21st to end	Day	9% 6% 3 6% 4 4 4 4 6% 8% 47%	4837
June	1st to 10th	Day	14% 6% 2 6% 5% 5% 4 4 6% 7% 41%	2660
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 3 7% 9% 41%	2660
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 9% 43%	2660
July	1st to 10th	Day	7% 4 2 5% 5% 5% 4 5% 7% 11% 45%	4440
	11th to 20th	Day	10% 5% 2 5% 4 5% 4 5% 7% 9% 44%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 9% 45%	4474
August	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 6% 9% 38%	4104
	11th to 20th	Day	12% 5% 2 7% 5% 4 5% 5% 7% 11% 36%	4044
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 9% 48%	4320
September	1st to 10th	Day	12% 7% 2 5% 5% 4 4 4 6% 8% 42%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 8% 48%	2179
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 7% 9% 34%	2043
October	1st to 10th	Day	19% 7% 3 6% 4 4 5% 4 6% 7% 36%	1900
	11th to 20th	Day	19% 10% 2 9% 5% 5% 5% 3 5% 6% 31%	1900
	21st to end	Day	24% 14% 3 8% 5% 5% 4 4 4 5% 24%	2090
November	1st to 10th	Day	13% 11% 3 10% 5% 5% 4 3 6% 7% 33%	1730
	11th to 20th	Day	14% 12% 3 8% 6% 6% 6% 3 6% 7% 30%	1600
	21st to end	Day	20% 14% 5% 9% 5% 5% 5% 4 4 6% 23%	1600
December	1st to 10th	Day	19% 17% 6% 11% 8% 5% 5% 4 5% 6% 15%	2600
	11th to 20th	Day	19% 16% 5% 9% 5% 5% 4 3 5% 5% 22%	2986
	21st to end	Day	22% 18% 6% 12% 8% 7% 4 3 4 5% 11%	3960
January	1st to 10th	Night	15% 14% 5% 14% 7% 5% 5% 5% 5% 5% 21%	6349
	11th to 20th	Night	11% 17% 7% 17% 8% 6% 5% 4 4 5% 16%	5928
	21st to end	Night	20% 16% 5% 14% 6% 5% 4 3 4 4 19%	6490
February	1st to 10th	Night	16% 18% 6% 10% 6% 4 5% 4 5% 5% 21%	2536
	11th to 20th	Night	15% 15% 5% 12% 6% 6% 5% 4 5% 5% 23%	2403
	21st to end	Night	17% 13% 4 12% 7% 5% 5% 3 5% 6% 22%	1967
March	1st to 10th	Night	21% 11% 3 7% 6% 4 4 3 4 5% 31%	3408
	11th to 20th	Night	16% 14% 3 8% 4 4 4 4 5% 6% 33%	3479
	21st to end	Night	16% 8% 2 7% 4 4 4 3 5% 5% 42%	3817
April	1st to 10th	Night	18% 12% 3 9% 5% 4 3 4 4 6% 33%	1931
	11th to 20th	Night	19% 8% 2 7% 5% 4 4 4 5% 5% 37%	1848
	21st to end	Night	16% 9% 3 7% 5% 4 5% 4 5% 7% 35%	1710
May	1st to 10th	Night	20% 10% 3 8% 4 3 3 3 5% 6% 34%	2833
	11th to 20th	Night	13% 7% 3 9% 5% 6% 5% 5% 7% 9% 32%	2537
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 47%	2738
June	1st to 10th	Night	12% 5% 2 7% 5% 6% 6% 5% 7% 8% 36%	1520
	11th to 20th	Night	9% 5% 3 6% 5% 6% 6% 4 6% 8% 43%	1520
	21st to end	Night	12% 6% 2 6% 3 5% 5% 5% 5% 9% 42%	1520
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 5% 4 5% 9% 47%	2520
	11th to 20th	Night	9% 5% 2 6% 3 3 4 4 6% 9% 47%	2520
	21st to end	Night	8% 5% 2 5% 4 4 4 4 7% 8% 49%	3076
August	1st to 10th	Night	10% 5% 3 7% 4 4 5% 4 6% 8% 44%	2825
	11th to 20th	Night	13% 7% 2 6% 5% 4 6% 4 6% 7% 41%	2785
	21st to end	Night	8% 4 2 6% 4 4 4 4 7% 10% 46%	3302
September	1st to 10th	Night	13% 6% 2 6% 5% 4 4 3 5% 8% 45%	1900
	11th to 20th	Night	12% 4 2 5% 4 3 4 3 5% 6% 52%	1999
	21st to end	Night	16% 7% 3 8% 5% 5% 4 3 6% 7% 37%	2136
October	1st to 10th	Night	17% 8% 3 7% 3 4 4 3 5% 7% 39%	2280
	11th to 20th	Night	20% 10% 3 7% 5% 4 4 3 5% 6% 32%	2280
	21st to end	Night	24% 10% 3 7% 5% 4 4 4 5% 7% 28%	2508
November	1st to 10th	Night	16% 10% 3 8% 4 4 4 3 4 7% 38%	2563
	11th to 20th	Night	15% 12% 3 8% 5% 6% 5% 4 6% 6% 30%	2800
	21st to end	Night	19% 13% 5% 8% 5% 5% 5% 4 5% 6% 24%	2800
December	1st to 10th	Night	15% 18% 5% 13% 7% 5% 5% 4 5% 7% 15%	4580
	11th to 20th	Night	16% 19% 5% 9% 5% 4 4 3 5% 5% 24%	5208
	21st to end	Night	24% 16% 6% 11% 7% 6% 4 3 4 5% 14%	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	68% 8% 11% 8% 5%	3598
	11th to 20th	Day	74% 8% 8% 8% 2 1	3986
	21st to end	Day	71% 7% 11% 7% 4	4466
February	1st to 10th	Day	69% 7% 10% 11% 3	1755
	11th to 20th	Day	67% 7% 9% 13% 4	1672
	21st to end	Day	64% 7% 12% 11% 6%	1481
March	1st to 10th	Day	55% 7% 13% 19% 5% 1	3435
	11th to 20th	Day	52% 9% 14% 16% 7% 1	3480
	21st to end	Day	45% 9% 9% 26% 9% 1	3815
April	1st to 10th	Day	53% 6% 11% 18% 11% 1	2248
	11th to 20th	Day	48% 7% 11% 19% 14% 2	2298
	21st to end	Day	50% 7% 10% 17% 12% 3	2470
May	1st to 10th	Day	47% 8% 12% 19% 12% 2	4120
	11th to 20th	Day	50% 9% 14% 19% 8% 1	4360
	21st to end	Day	34% 7% 14% 27% 16% 3	4837
June	1st to 10th	Day	41% 8% 13% 21% 15% 2	2660
	11th to 20th	Day	37% 8% 14% 25% 15% 1	2660
	21st to end	Day	36% 8% 14% 25% 15% 1	2660
July	1st to 10th	Day	31% 8% 14% 28% 17% 2	4370
	11th to 20th	Day	32% 9% 14% 32% 12% 1	4365
	21st to end	Day	34% 10% 15% 24% 16% 1	4331
August	1st to 10th	Day	42% 9% 14% 22% 13% 1	4091
	11th to 20th	Day	40% 9% 16% 25% 10% 1	4083
	21st to end	Day	31% 8% 13% 34% 12% 1	4320
September	1st to 10th	Day	38% 8% 14% 27% 12% 1	2280
	11th to 20th	Day	34% 8% 13% 30% 15% 1	2179
	21st to end	Day	44% 8% 15% 23% 9% 1	2043
October	1st to 10th	Day	35% 7% 18% 26% 14% 1	3160
	11th to 20th	Day	42% 6% 16% 22% 13%	3140
	21st to end	Day	50% 7% 16% 21% 6%	3428
November	1st to 10th	Day	50% 8% 12% 20% 8% 1	1730
	11th to 20th	Day	53% 7% 17% 15% 8% 1	1600
	21st to end	Day	63% 6% 14% 13% 4	1600
December	1st to 10th	Day	69% 8% 16% 6% 1	2600
	11th to 20th	Day	64% 8% 10% 10% 7% 1	2986
	21st to end	Day	75% 8% 9% 7% 2	3960
January	1st to 10th	Night	65% 7% 13% 12% 3	6349
	11th to 20th	Night	69% 8% 11% 10% 2	5969
	21st to end	Night	68% 5% 11% 7% 8% 1	6490
February	1st to 10th	Night	65% 7% 11% 14% 3	2536
	11th to 20th	Night	62% 6% 12% 14% 5%	2405
	21st to end	Night	62% 7% 11% 13% 6%	1967
March	1st to 10th	Night	56% 5% 12% 21% 6%	3418
	11th to 20th	Night	49% 8% 16% 17% 8% 1	3480
	21st to end	Night	41% 6% 10% 26% 15% 1	3817
April	1st to 10th	Night	54% 6% 8% 20% 11% 1	1931
	11th to 20th	Night	48% 6% 9% 20% 15% 2	1848
	21st to end	Night	47% 7% 10% 19% 14% 2	1710
May	1st to 10th	Night	50% 7% 10% 18% 13% 2	2840
	11th to 20th	Night	45% 7% 20% 18% 8% 2	2538
	21st to end	Night	33% 8% 11% 25% 21% 2	2739
June	1st to 10th	Night	42% 8% 10% 22% 17% 1	1520
	11th to 20th	Night	37% 7% 13% 23% 18% 3	1520
	21st to end	Night	39% 6% 14% 23% 16% 1	1520
July	1st to 10th	Night	35% 7% 12% 23% 22% 2	2480
	11th to 20th	Night	32% 7% 15% 31% 14% 1	2472
	21st to end	Night	32% 7% 17% 24% 18% 2	2978
August	1st to 10th	Night	36% 7% 14% 26% 14% 2	2814
	11th to 20th	Night	40% 9% 14% 27% 10%	2812
	21st to end	Night	30% 8% 14% 32% 14% 1	3302
September	1st to 10th	Night	37% 7% 14% 24% 16% 1	1900
	11th to 20th	Night	31% 6% 13% 31% 18% 1	1999
	21st to end	Night	45% 6% 13% 22% 13% 1	2136
October	1st to 10th	Night	37% 6% 10% 26% 20% 1	3800
	11th to 20th	Night	48% 6% 12% 23% 10%	3779
	21st to end	Night	43% 5% 17% 25% 9% 1	4120
November	1st to 10th	Night	46% 6% 12% 22% 11% 2	2563
	11th to 20th	Night	52% 6% 15% 17% 9% 1	2800
	21st to end	Night	59% 7% 15% 16% 3	2800
December	1st to 10th	Night	68% 9% 15% 7% 2	4580
	11th to 20th	Night	64% 6% 9% 12% 9% 1	5208
	21st to end	Night	71% 6% 13% 8% 2	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	24% 17% 34% 17% 8% 2	200
	11th to 20th	Day	24% 23% 36% 11% 4 1	283
	21st to end	Day	23% 20% 34% 18% 5%	330
February	1st to 10th	Day	24% 22% 38% 14% 2	285
	11th to 20th	Day	23% 24% 37% 15% 2	270
	21st to end	Day	29% 22% 33% 15% 1	260
March	1st to 10th	Day	21% 15% 35% 23% 6%	460
	11th to 20th	Day	21% 16% 35% 22% 5% 1	460
	21st to end	Day	27% 11% 32% 22% 6% 2	506
April	1st to 10th	Day	20% 14% 34% 23% 8% 1	460
	11th to 20th	Day	25% 15% 26% 19% 10% 4	452
	21st to end	Day	25% 10% 30% 22% 10% 2	460
May	1st to 10th	Day	20% 12% 26% 25% 13% 4	463
	11th to 20th	Day	16% 8% 23% 29% 19% 5%	487
	21st to end	Day	11% 7% 23% 31% 20% 7%	529
June	1st to 10th	Day	12% 9% 29% 34% 14% 2	490
	11th to 20th	Day	13% 7% 24% 31% 20% 4	490
	21st to end	Day	15% 6% 28% 30% 18% 3	490
July	1st to 10th	Day	7% 5% 18% 32% 29% 9%	485
	11th to 20th	Day	14% 5% 19% 31% 21% 11%	484
	21st to end	Day	9% 4 24% 35% 21% 7%	532
August	1st to 10th	Day	12% 4 20% 30% 23% 12%	486
	11th to 20th	Day	10% 8% 18% 27% 26% 12%	479
	21st to end	Day	12% 6% 20% 29% 22% 11%	539
September	1st to 10th	Day	13% 7% 22% 25% 22% 11%	490
	11th to 20th	Day	9% 5% 17% 25% 27% 17%	490
	21st to end	Day	14% 10% 27% 23% 18% 8%	490
October	1st to 10th	Day	20% 9% 28% 18% 18% 7%	490
	11th to 20th	Day	22% 17% 29% 21% 9% 3	490
	21st to end	Day	32% 14% 26% 20% 8%	539
November	1st to 10th	Day	19% 20% 29% 22% 7% 3	323
	11th to 20th	Day	22% 20% 31% 22% 6% 1	200
	21st to end	Day	28% 19% 37% 13% 4	200
December	1st to 10th	Day	27% 16% 38% 14% 5% 1	200
	11th to 20th	Day	27% 25% 33% 12% 4	200
	21st to end	Day	25% 23% 35% 14% 3 1	220
January	1st to 10th	Night	26% 20% 34% 14% 7%	800
	11th to 20th	Night	28% 18% 31% 20% 3 1	800
	21st to end	Night	21% 15% 35% 23% 6%	880
February	1st to 10th	Night	26% 19% 31% 21% 3	781
	11th to 20th	Night	22% 16% 36% 22% 4	743
	21st to end	Night	24% 16% 34% 23% 3	628
March	1st to 10th	Night	21% 12% 36% 24% 7%	760
	11th to 20th	Night	22% 15% 34% 22% 7% 1	760
	21st to end	Night	21% 10% 31% 28% 10% 1	836
April	1st to 10th	Night	21% 12% 33% 29% 5%	760
	11th to 20th	Night	21% 10% 32% 27% 9% 1	724
	21st to end	Night	22% 6% 28% 32% 12%	570
May	1st to 10th	Night	18% 6% 25% 33% 15% 3	570
	11th to 20th	Night	15% 4 28% 39% 14%	403
	21st to end	Night	13% 5% 21% 37% 21% 2	411
June	1st to 10th	Night	13% 2 32% 36% 16% 1	380
	11th to 20th	Night	11% 4 26% 41% 18% 1	380
	21st to end	Night	11% 5% 23% 43% 17% 1	380
July	1st to 10th	Night	9% 2 18% 45% 23% 2	370
	11th to 20th	Night	11% 4 20% 43% 20% 3	368
	21st to end	Night	11% 3 16% 45% 23% 2	613
August	1st to 10th	Night	10% 3 14% 38% 31% 4	567
	11th to 20th	Night	10% 4 16% 32% 36% 4	564
	21st to end	Night	12% 3 17% 39% 26% 3	727
September	1st to 10th	Night	13% 6% 18% 35% 24% 4	760
	11th to 20th	Night	14% 4 14% 32% 29% 7%	760
	21st to end	Night	18% 7% 19% 31% 20% 5%	760
October	1st to 10th	Night	20% 6% 26% 25% 20% 3	760
	11th to 20th	Night	25% 14% 24% 26% 10% 1	760
	21st to end	Night	30% 10% 28% 27% 5%	836
November	1st to 10th	Night	21% 12% 27% 27% 11% 1	780
	11th to 20th	Night	22% 15% 33% 20% 8% 2	800
	21st to end	Night	25% 14% 34% 19% 7%	800
December	1st to 10th	Night	29% 18% 30% 18% 5%	800
	11th to 20th	Night	24% 20% 32% 20% 5%	800
	21st to end	Night	30% 15% 33% 20% 2	880

Page generated at 2025-02-03 03:05:50. Version ac07

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