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 2024-01-27.

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% 9% 4 7% 6% 4 5% 5% 5% 7% 33%	74778
	Night	16% 10% 4 7% 6% 3 5% 5% 5% 6% 32%	75259
Transparency	Day	49% 8% 13% 19% 10% 1	74494
	Night	53% 6% 12% 18% 10% 1	75077
Seeing	Day	18% 11% 27% 25% 14% 5%	13401
	Night	20% 11% 28% 28% 12% 1	22969

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	15% 16% 6% 12% 9% 5% 5% 5% 6% 5% 17%	1517
	11th to 20th	Day	16% 17% 6% 12% 10% 4 6% 4 5% 5% 15%	1676
	21st to end	Day	15% 15% 6% 13% 13% 6% 5% 5% 4 5% 12%	1836
February	1st to 10th	Day	18% 17% 5% 11% 8% 5% 5% 4 5% 6% 16%	1620
	11th to 20th	Day	13% 15% 8% 12% 9% 4 6% 4 4 6% 18%	1573
	21st to end	Day	19% 13% 5% 10% 9% 4 6% 4 5% 6% 20%	1396
March	1st to 10th	Day	15% 10% 5% 11% 8% 4 6% 4 5% 5% 27%	1977
	11th to 20th	Day	14% 13% 5% 7% 6% 3 4 5% 5% 5% 34%	1980
	21st to end	Day	18% 10% 4 6% 6% 3 4 5% 4 6% 33%	2178
April	1st to 10th	Day	18% 9% 4 7% 6% 3 5% 4 5% 6% 32%	2129
	11th to 20th	Day	18% 8% 4 6% 5% 3 4 4 5% 6% 37%	2175
	21st to end	Day	20% 8% 3 6% 6% 3 5% 4 4 7% 35%	2340
May	1st to 10th	Day	15% 9% 3 6% 7% 4 5% 5% 5% 7% 36%	2340
	11th to 20th	Day	14% 6% 2 6% 6% 4 5% 5% 6% 6% 39%	2450
	21st to end	Day	10% 4 3 5% 5% 3 5% 5% 7% 8% 46%	2725
June	1st to 10th	Day	13% 5% 3 5% 5% 3 5% 4 6% 7% 43%	2520
	11th to 20th	Day	12% 5% 3 5% 5% 3 5% 4 6% 10% 42%	2520
	21st to end	Day	12% 5% 2 4 4 3 4 5% 6% 10% 44%	2520
July	1st to 10th	Day	6% 3 2 4 4 4 4 5% 7% 10% 50%	2520
	11th to 20th	Day	12% 5% 3 5% 5% 3 5% 6% 8% 9% 40%	2520
	21st to end	Day	10% 4 2 6% 6% 4 6% 6% 6% 9% 41%	2555
August	1st to 10th	Day	8% 5% 2 4 5% 3 4 6% 7% 11% 44%	2327
	11th to 20th	Day	9% 4 2 5% 6% 3 6% 7% 7% 11% 40%	2303
	21st to end	Day	11% 5% 2 4 5% 3 4 4 5% 9% 47%	2460
September	1st to 10th	Day	13% 7% 2 5% 5% 3 4 5% 6% 8% 41%	2160
	11th to 20th	Day	11% 5% 3 4 5% 3 4 5% 5% 8% 47%	2065
	21st to end	Day	14% 6% 2 6% 6% 4 6% 5% 7% 9% 36%	1936
October	1st to 10th	Day	20% 7% 4 5% 5% 3 6% 5% 6% 6% 35%	1800
	11th to 20th	Day	20% 10% 3 7% 7% 3 6% 5% 5% 5% 30%	1800
	21st to end	Day	25% 14% 3 7% 6% 4 4 4 4 5% 24%	1980
November	1st to 10th	Day	13% 10% 4 9% 6% 3 5% 4 6% 7% 33%	1642
	11th to 20th	Day	15% 10% 5% 7% 7% 4 6% 5% 5% 8% 30%	1520
	21st to end	Day	20% 13% 5% 9% 6% 4 5% 4 4 6% 24%	1520
December	1st to 10th	Day	18% 16% 7% 9% 8% 3 5% 5% 4 6% 19%	1520
	11th to 20th	Day	18% 15% 6% 10% 7% 4 5% 5% 6% 6% 17%	1906
	21st to end	Day	26% 20% 6% 10% 7% 4 4 4 3 4 11%	2772
January	1st to 10th	Night	17% 15% 7% 11% 9% 4 5% 4 4 4 19%	2649
	11th to 20th	Night	19% 16% 6% 12% 9% 4 5% 5% 4 5% 14%	2499
	21st to end	Night	15% 14% 6% 12% 10% 5% 6% 5% 5% 5% 18%	2664
February	1st to 10th	Night	17% 16% 6% 10% 7% 4 5% 4 4 5% 21%	2340
	11th to 20th	Night	16% 13% 6% 10% 7% 4 6% 5% 5% 5% 22%	2273
	21st to end	Night	19% 13% 5% 11% 8% 4 5% 4 5% 5% 22%	1854
March	1st to 10th	Night	15% 10% 5% 8% 8% 4 5% 5% 5% 6% 30%	1970
	11th to 20th	Night	18% 12% 4 8% 5% 3 4 5% 4 6% 32%	1979
	21st to end	Night	17% 10% 3 8% 6% 3 4 4 4 4 37%	2178
April	1st to 10th	Night	18% 10% 4 8% 6% 3 4 4 4 6% 33%	1830
	11th to 20th	Night	19% 7% 3 5% 6% 3 5% 5% 5% 5% 38%	1750
	21st to end	Night	17% 8% 4 6% 5% 3 6% 5% 5% 7% 35%	1620
May	1st to 10th	Night	16% 8% 3 6% 6% 3 4 4 6% 8% 36%	1620
	11th to 20th	Night	14% 5% 2 6% 5% 3 5% 6% 5% 8% 41%	1443
	21st to end	Night	10% 6% 2 5% 5% 4 4 5% 6% 7% 48%	1550
June	1st to 10th	Night	12% 5% 2 6% 6% 4 7% 6% 7% 8% 37%	1440
	11th to 20th	Night	10% 5% 3 6% 5% 4 6% 5% 5% 8% 44%	1440
	21st to end	Night	12% 5% 2 5% 4 3 5% 5% 5% 9% 44%	1440
July	1st to 10th	Night	6% 4 2 4 4 3 4 5% 4 8% 56%	1440
	11th to 20th	Night	9% 5% 3 5% 5% 2 3 6% 6% 9% 47%	1440
	21st to end	Night	9% 5% 2 5% 4 3 5% 5% 7% 9% 47%	1760
August	1st to 10th	Night	8% 4 2 5% 5% 3 5% 5% 7% 8% 47%	1611
	11th to 20th	Night	8% 5% 2 5% 5% 2 6% 6% 6% 8% 47%	1598
	21st to end	Night	9% 4 2 5% 5% 3 5% 5% 5% 9% 48%	1876
September	1st to 10th	Night	13% 5% 2 6% 5% 3 4 4 5% 8% 44%	1800
	11th to 20th	Night	13% 4 2 4 4 2 4 4 5% 6% 52%	1893
	21st to end	Night	16% 7% 3 7% 6% 3 5% 4 5% 7% 39%	2023
October	1st to 10th	Night	17% 8% 3 6% 5% 3 5% 4 4 8% 38%	2160
	11th to 20th	Night	21% 9% 4 6% 6% 3 4 4 5% 6% 31%	2160
	21st to end	Night	25% 9% 4 6% 7% 3 4 5% 5% 6% 27%	2376
November	1st to 10th	Night	16% 9% 3 6% 5% 3 4 4 4 7% 38%	2431
	11th to 20th	Night	15% 11% 4 7% 6% 4 6% 5% 6% 6% 30%	2660
	21st to end	Night	19% 12% 6% 7% 6% 4 5% 5% 6% 6% 24%	2660
December	1st to 10th	Night	20% 16% 6% 9% 8% 3 5% 4 5% 6% 18%	2660
	11th to 20th	Night	16% 18% 7% 9% 7% 3 5% 4 5% 5% 21%	3288
	21st to end	Night	29% 16% 6% 9% 6% 4 4 4 4 5% 12%	4884

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% 10% 3	1518
	11th to 20th	Day	71% 7% 10% 10% 1	1676
	21st to end	Day	75% 6% 9% 8% 2	1836
February	1st to 10th	Day	69% 7% 10% 10% 2	1620
	11th to 20th	Day	68% 6% 9% 12% 4	1582
	21st to end	Day	65% 7% 11% 11% 6%	1396
March	1st to 10th	Day	58% 8% 12% 16% 5% 1	1980
	11th to 20th	Day	52% 7% 11% 18% 11% 2	1980
	21st to end	Day	52% 7% 8% 21% 10% 2	2178
April	1st to 10th	Day	53% 7% 11% 18% 11% 1	2129
	11th to 20th	Day	47% 7% 11% 19% 14% 2	2175
	21st to end	Day	50% 7% 11% 18% 12% 3	2340
May	1st to 10th	Day	46% 8% 10% 22% 12% 2	2340
	11th to 20th	Day	44% 8% 11% 23% 13% 2	2454
	21st to end	Day	35% 8% 17% 25% 14% 2	2725
June	1st to 10th	Day	40% 7% 14% 22% 15% 2	2520
	11th to 20th	Day	37% 8% 14% 25% 15% 1	2520
	21st to end	Day	35% 8% 15% 25% 16% 1	2520
July	1st to 10th	Day	29% 8% 14% 26% 20% 3	2450
	11th to 20th	Day	36% 10% 16% 26% 12% 1	2445
	21st to end	Day	38% 9% 15% 23% 13% 1	2412
August	1st to 10th	Day	32% 10% 17% 26% 13% 2	2314
	11th to 20th	Day	35% 10% 17% 26% 11% 1	2303
	21st to end	Day	34% 9% 12% 30% 13% 1	2460
September	1st to 10th	Day	39% 8% 14% 26% 11% 1	2160
	11th to 20th	Day	34% 8% 14% 29% 15% 1	2065
	21st to end	Day	42% 8% 16% 24% 9% 1	1936
October	1st to 10th	Day	48% 7% 14% 18% 12% 1	1800
	11th to 20th	Day	54% 7% 13% 19% 7% 1	1800
	21st to end	Day	62% 7% 11% 14% 6% 1	1980
November	1st to 10th	Day	50% 8% 12% 20% 9% 1	1642
	11th to 20th	Day	53% 7% 17% 15% 8% 1	1520
	21st to end	Day	62% 6% 15% 14% 4	1520
December	1st to 10th	Day	67% 6% 16% 9% 2	1520
	11th to 20th	Day	67% 9% 13% 9% 2	1906
	21st to end	Day	77% 6% 9% 7% 1	2772
January	1st to 10th	Night	68% 6% 10% 12% 3	2649
	11th to 20th	Night	73% 6% 11% 8% 2	2499
	21st to end	Night	69% 6% 12% 10% 3	2664
February	1st to 10th	Night	66% 6% 11% 13% 3	2340
	11th to 20th	Night	64% 6% 12% 13% 5%	2275
	21st to end	Night	64% 7% 11% 13% 6%	1854
March	1st to 10th	Night	56% 6% 11% 19% 6% 1	1980
	11th to 20th	Night	53% 5% 11% 19% 10% 1	1980
	21st to end	Night	51% 5% 7% 21% 13% 2	2178
April	1st to 10th	Night	53% 6% 8% 21% 11% 1	1830
	11th to 20th	Night	47% 6% 9% 20% 15% 2	1750
	21st to end	Night	47% 7% 10% 20% 14% 2	1620
May	1st to 10th	Night	46% 7% 9% 20% 15% 3	1620
	11th to 20th	Night	40% 7% 12% 23% 14% 3	1444
	21st to end	Night	35% 9% 12% 24% 17% 3	1551
June	1st to 10th	Night	42% 8% 10% 22% 17% 1	1440
	11th to 20th	Night	37% 7% 12% 23% 18% 3	1440
	21st to end	Night	38% 6% 14% 24% 17% 2	1440
July	1st to 10th	Night	29% 7% 12% 26% 24% 3	1400
	11th to 20th	Night	33% 7% 13% 27% 18% 2	1392
	21st to end	Night	33% 8% 16% 24% 17% 3	1662
August	1st to 10th	Night	31% 9% 18% 27% 14% 1	1600
	11th to 20th	Night	32% 10% 15% 30% 13%	1598
	21st to end	Night	33% 8% 13% 29% 15% 2	1876
September	1st to 10th	Night	38% 7% 15% 24% 15% 2	1800
	11th to 20th	Night	32% 5% 13% 31% 18% 1	1893
	21st to end	Night	44% 6% 13% 23% 13% 1	2023
October	1st to 10th	Night	46% 6% 12% 22% 14% 1	2160
	11th to 20th	Night	53% 6% 13% 19% 8% 1	2160
	21st to end	Night	59% 5% 12% 14% 9% 1	2376
November	1st to 10th	Night	46% 6% 13% 22% 11% 2	2431
	11th to 20th	Night	52% 6% 15% 18% 9% 1	2660
	21st to end	Night	59% 7% 15% 16% 3	2660
December	1st to 10th	Night	67% 6% 14% 9% 3	2660
	11th to 20th	Night	65% 7% 13% 12% 3	3288
	21st to end	Night	75% 5% 14% 6% 1	4884

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% 17% 33% 17% 8% 2	180
	11th to 20th	Day	24% 20% 37% 12% 5% 1	254
	21st to end	Day	22% 19% 34% 20% 5%	282
February	1st to 10th	Day	27% 21% 38% 13% 1	240
	11th to 20th	Day	24% 23% 38% 15%	240
	21st to end	Day	30% 20% 33% 16% 1	231
March	1st to 10th	Day	21% 15% 35% 23% 6%	420
	11th to 20th	Day	21% 14% 35% 23% 5% 1	420
	21st to end	Day	27% 11% 31% 22% 7% 2	462
April	1st to 10th	Day	19% 14% 34% 23% 9% 1	420
	11th to 20th	Day	24% 14% 26% 20% 11% 4	412
	21st to end	Day	25% 9% 31% 22% 11% 3	420
May	1st to 10th	Day	21% 11% 28% 25% 12% 4	423
	11th to 20th	Day	17% 8% 23% 28% 19% 5%	447
	21st to end	Day	12% 6% 22% 32% 20% 8%	485
June	1st to 10th	Day	12% 8% 29% 35% 14% 2	450
	11th to 20th	Day	14% 7% 23% 30% 20% 5%	450
	21st to end	Day	14% 5% 26% 32% 19% 4	450
July	1st to 10th	Day	7% 4 16% 32% 31% 10%	445
	11th to 20th	Day	14% 5% 19% 30% 21% 11%	444
	21st to end	Day	9% 3 24% 36% 20% 7%	488
August	1st to 10th	Day	9% 3 19% 32% 24% 13%	446
	11th to 20th	Day	9% 7% 16% 28% 27% 13%	439
	21st to end	Day	12% 6% 19% 30% 21% 12%	495
September	1st to 10th	Day	13% 5% 22% 27% 22% 11%	450
	11th to 20th	Day	10% 6% 18% 26% 26% 15%	450
	21st to end	Day	14% 10% 26% 22% 19% 9%	450
October	1st to 10th	Day	21% 9% 26% 18% 18% 7%	450
	11th to 20th	Day	22% 17% 29% 21% 9% 2	450
	21st to end	Day	33% 14% 25% 20% 8%	495
November	1st to 10th	Day	19% 19% 28% 23% 8% 3	295
	11th to 20th	Day	22% 20% 28% 24% 6% 1	180
	21st to end	Day	26% 19% 37% 13% 4	180
December	1st to 10th	Day	26% 16% 39% 14% 5% 1	180
	11th to 20th	Day	26% 25% 32% 13% 4	180
	21st to end	Day	25% 23% 37% 13% 2 1	198
January	1st to 10th	Night	26% 19% 34% 14% 7%	760
	11th to 20th	Night	28% 17% 30% 20% 3 1	760
	21st to end	Night	21% 15% 35% 24% 6%	820
February	1st to 10th	Night	26% 19% 32% 20% 3	720
	11th to 20th	Night	23% 16% 35% 21% 4	703
	21st to end	Night	25% 15% 35% 22% 3	592
March	1st to 10th	Night	20% 13% 36% 24% 7%	720
	11th to 20th	Night	22% 14% 34% 22% 7% 1	720
	21st to end	Night	21% 9% 30% 29% 10% 1	792
April	1st to 10th	Night	21% 12% 32% 30% 5%	720
	11th to 20th	Night	20% 10% 32% 27% 10% 1	686
	21st to end	Night	22% 6% 27% 33% 12%	540
May	1st to 10th	Night	18% 6% 24% 33% 16% 3	540
	11th to 20th	Night	15% 4 27% 40% 13% 1	382
	21st to end	Night	13% 6% 21% 37% 21% 2	389
June	1st to 10th	Night	13% 2 32% 36% 17% 1	360
	11th to 20th	Night	11% 5% 26% 40% 18% 1	360
	21st to end	Night	9% 5% 24% 44% 18% 1	360
July	1st to 10th	Night	9% 2 17% 45% 25% 2	350
	11th to 20th	Night	10% 4 19% 43% 20% 3	348
	21st to end	Night	11% 3 16% 46% 21% 2	580
August	1st to 10th	Night	10% 3 13% 38% 32% 4	537
	11th to 20th	Night	9% 3 15% 33% 37% 4	534
	21st to end	Night	12% 3 17% 39% 26% 3	688
September	1st to 10th	Night	13% 5% 18% 35% 25% 4	720
	11th to 20th	Night	15% 4 15% 33% 27% 7%	720
	21st to end	Night	17% 7% 19% 32% 20% 5%	720
October	1st to 10th	Night	20% 5% 26% 25% 20% 3	720
	11th to 20th	Night	25% 14% 25% 25% 9% 1	720
	21st to end	Night	31% 9% 28% 26% 5%	792
November	1st to 10th	Night	21% 11% 27% 28% 12% 1	740
	11th to 20th	Night	21% 15% 34% 20% 8% 2	760
	21st to end	Night	25% 14% 35% 20% 7%	760
December	1st to 10th	Night	30% 17% 30% 19% 4	760
	11th to 20th	Night	23% 20% 32% 20% 5%	760
	21st to end	Night	30% 16% 33% 19% 2	836

Page generated at 2024-01-24 09:37:27. Version ac07

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