Niagara
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Niagara clear sky chart from 2005-11-06 to 2024-01-31.

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% 3 5% 5% 6% 7% 33%	74821
	Night	17% 11% 4 8% 6% 4 5% 5% 5% 6% 30%	75303
Transparency	Day	50% 8% 12% 19% 10% 1	74536
	Night	54% 7% 11% 17% 10% 1	75122
Seeing	Day	20% 11% 26% 24% 14% 5%	13414
	Night	22% 11% 27% 27% 12% 2	22964

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	17% 15% 7% 10% 10% 4 7% 5% 5% 6% 15%	1517
	11th to 20th	Day	17% 17% 7% 13% 9% 4 6% 4 5% 5% 12%	1662
	21st to end	Day	15% 16% 7% 13% 12% 7% 5% 4 4 4 12%	1872
February	1st to 10th	Day	19% 16% 5% 13% 9% 4 5% 6% 5% 4 15%	1620
	11th to 20th	Day	13% 15% 8% 13% 11% 4 6% 5% 4 4 17%	1573
	21st to end	Day	19% 14% 4 10% 10% 3 6% 4 5% 5% 21%	1392
March	1st to 10th	Day	16% 10% 5% 10% 9% 4 6% 4 5% 5% 26%	1977
	11th to 20th	Day	13% 13% 4 8% 6% 3 5% 4 4 5% 33%	1980
	21st to end	Day	19% 8% 4 8% 6% 3 4 4 5% 5% 33%	2178
April	1st to 10th	Day	17% 11% 4 6% 6% 3 4 4 5% 6% 34%	2137
	11th to 20th	Day	19% 8% 3 5% 5% 3 3 4 5% 6% 37%	2167
	21st to end	Day	19% 8% 2 7% 5% 4 4 4 5% 7% 35%	2340
May	1st to 10th	Day	15% 9% 3 6% 6% 3 4 5% 6% 8% 36%	2340
	11th to 20th	Day	14% 6% 3 5% 5% 3 5% 5% 6% 7% 40%	2464
	21st to end	Day	10% 5% 2 4 5% 3 5% 5% 7% 8% 45%	2725
June	1st to 10th	Day	13% 5% 3 5% 5% 3 5% 5% 6% 8% 42%	2520
	11th to 20th	Day	11% 5% 2 5% 5% 3 5% 5% 6% 10% 42%	2520
	21st to end	Day	12% 5% 2 4 4 2 5% 5% 6% 9% 45%	2520
July	1st to 10th	Day	7% 4 3 4 4 3 4 5% 7% 9% 52%	2520
	11th to 20th	Day	11% 6% 2 5% 5% 3 5% 6% 8% 11% 41%	2520
	21st to end	Day	10% 4 2 6% 6% 4 5% 6% 7% 10% 40%	2574
August	1st to 10th	Day	8% 4 2 5% 5% 3 4 5% 8% 11% 45%	2327
	11th to 20th	Day	9% 5% 2 5% 6% 4 6% 6% 7% 10% 41%	2303
	21st to end	Day	11% 6% 2 4 4 3 4 5% 6% 9% 46%	2453
September	1st to 10th	Day	14% 6% 3 5% 5% 3 3 5% 7% 9% 42%	2160
	11th to 20th	Day	11% 5% 2 5% 4 3 4 5% 6% 8% 46%	2077
	21st to end	Day	13% 6% 3 6% 6% 4 5% 5% 7% 8% 36%	1929
October	1st to 10th	Day	19% 7% 3 7% 5% 2 5% 4 5% 7% 35%	1800
	11th to 20th	Day	21% 10% 3 7% 6% 3 5% 5% 5% 7% 27%	1800
	21st to end	Day	25% 13% 4 7% 7% 3 4 4 4 5% 23%	1980
November	1st to 10th	Day	12% 11% 4 8% 6% 4 5% 5% 5% 7% 32%	1636
	11th to 20th	Day	15% 12% 4 8% 6% 3 5% 6% 5% 7% 30%	1520
	21st to end	Day	20% 15% 6% 8% 6% 3 5% 4 5% 6% 21%	1520
December	1st to 10th	Day	18% 18% 8% 10% 7% 4 6% 5% 4 4 16%	1520
	11th to 20th	Day	19% 16% 7% 12% 7% 3 5% 5% 5% 6% 15%	1906
	21st to end	Day	27% 20% 6% 10% 7% 4 4 3 3 4 12%	2772
January	1st to 10th	Night	18% 17% 7% 11% 9% 4 5% 5% 4 4 17%	2649
	11th to 20th	Night	19% 18% 8% 12% 10% 4 4 4 4 4 13%	2515
	21st to end	Night	14% 16% 7% 13% 10% 6% 6% 5% 4 5% 14%	2711
February	1st to 10th	Night	17% 17% 6% 11% 9% 4 5% 5% 4 5% 17%	2340
	11th to 20th	Night	16% 14% 6% 11% 9% 4 6% 5% 4 5% 19%	2273
	21st to end	Night	19% 12% 8% 11% 7% 3 4 4 5% 5% 21%	1862
March	1st to 10th	Night	15% 10% 5% 9% 8% 4 5% 6% 5% 5% 28%	1970
	11th to 20th	Night	18% 11% 4 8% 6% 3 5% 4 5% 5% 31%	1979
	21st to end	Night	18% 10% 4 8% 5% 3 5% 4 4 5% 36%	2178
April	1st to 10th	Night	19% 11% 4 7% 6% 3 4 4 4 5% 33%	1822
	11th to 20th	Night	19% 6% 3 6% 6% 3 5% 4 5% 5% 38%	1758
	21st to end	Night	17% 8% 3 6% 4 4 6% 5% 5% 7% 35%	1620
May	1st to 10th	Night	17% 8% 4 5% 5% 3 5% 5% 5% 8% 36%	1620
	11th to 20th	Night	13% 7% 3 5% 5% 4 4 5% 5% 8% 41%	1426
	21st to end	Night	11% 4 2 6% 4 4 4 5% 6% 7% 46%	1550
June	1st to 10th	Night	13% 4 3 5% 7% 3 6% 6% 8% 8% 36%	1440
	11th to 20th	Night	9% 7% 2 5% 6% 3 5% 6% 6% 8% 43%	1440
	21st to end	Night	12% 4 3 5% 5% 3 5% 6% 5% 10% 42%	1440
July	1st to 10th	Night	7% 3 2 5% 4 3 5% 4 5% 7% 56%	1440
	11th to 20th	Night	9% 5% 2 5% 5% 3 4 5% 7% 9% 46%	1440
	21st to end	Night	10% 3 2 5% 5% 3 5% 6% 6% 8% 46%	1741
August	1st to 10th	Night	8% 6% 2 5% 5% 3 4 5% 6% 9% 47%	1611
	11th to 20th	Night	9% 5% 2 5% 6% 3 5% 5% 7% 8% 45%	1598
	21st to end	Night	10% 4 2 5% 5% 4 4 5% 6% 9% 47%	1884
September	1st to 10th	Night	13% 5% 3 7% 4 3 4 5% 6% 7% 44%	1800
	11th to 20th	Night	13% 5% 2 4 5% 2 4 4 6% 6% 50%	1880
	21st to end	Night	17% 6% 3 6% 5% 3 5% 4 6% 8% 38%	2030
October	1st to 10th	Night	17% 7% 3 6% 5% 3 5% 4 5% 8% 37%	2160
	11th to 20th	Night	22% 9% 4 7% 6% 3 5% 4 5% 6% 30%	2160
	21st to end	Night	27% 11% 3 6% 5% 3 4 5% 5% 5% 25%	2376
November	1st to 10th	Night	16% 9% 3 6% 5% 3 5% 4 4 7% 37%	2438
	11th to 20th	Night	17% 10% 4 7% 6% 4 6% 5% 5% 7% 29%	2660
	21st to end	Night	19% 13% 6% 9% 6% 4 5% 6% 5% 5% 22%	2660
December	1st to 10th	Night	21% 19% 7% 10% 6% 4 5% 5% 4 5% 14%	2660
	11th to 20th	Night	16% 19% 6% 11% 7% 3 6% 4 4 5% 18%	3288
	21st to end	Night	31% 16% 5% 9% 7% 4 5% 4 5% 4 11%	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	69% 10% 9% 10% 3	1518
	11th to 20th	Day	74% 7% 10% 8% 1	1662
	21st to end	Day	77% 6% 8% 6% 2	1872
February	1st to 10th	Day	70% 8% 10% 9% 2	1620
	11th to 20th	Day	71% 6% 8% 11% 4	1582
	21st to end	Day	66% 7% 10% 11% 6%	1392
March	1st to 10th	Day	60% 6% 12% 15% 6% 1	1980
	11th to 20th	Day	52% 6% 12% 17% 11% 2	1980
	21st to end	Day	53% 7% 8% 20% 10% 2	2178
April	1st to 10th	Day	53% 5% 12% 18% 11% 1	2137
	11th to 20th	Day	47% 6% 11% 20% 14% 2	2167
	21st to end	Day	50% 6% 11% 18% 12% 3	2340
May	1st to 10th	Day	46% 7% 11% 22% 12% 2	2340
	11th to 20th	Day	43% 8% 11% 23% 13% 2	2468
	21st to end	Day	35% 7% 17% 25% 14% 2	2725
June	1st to 10th	Day	40% 8% 13% 22% 16% 2	2520
	11th to 20th	Day	38% 7% 13% 26% 15% 1	2520
	21st to end	Day	36% 8% 14% 25% 16% 1	2520
July	1st to 10th	Day	28% 9% 14% 26% 20% 3	2450
	11th to 20th	Day	37% 9% 15% 26% 12% 1	2445
	21st to end	Day	38% 10% 15% 22% 14% 1	2430
August	1st to 10th	Day	32% 9% 17% 26% 13% 2	2314
	11th to 20th	Day	36% 11% 16% 26% 11% 1	2303
	21st to end	Day	35% 8% 13% 30% 13% 1	2453
September	1st to 10th	Day	39% 7% 14% 26% 12% 1	2160
	11th to 20th	Day	35% 8% 13% 28% 15% 1	2077
	21st to end	Day	43% 9% 15% 23% 10% 1	1929
October	1st to 10th	Day	49% 7% 12% 19% 13% 1	1800
	11th to 20th	Day	55% 8% 13% 17% 7% 1	1800
	21st to end	Day	64% 6% 11% 13% 6% 1	1980
November	1st to 10th	Day	51% 8% 12% 19% 9% 1	1636
	11th to 20th	Day	54% 7% 17% 13% 8% 1	1520
	21st to end	Day	63% 7% 14% 13% 4	1520
December	1st to 10th	Day	69% 10% 11% 8% 2	1520
	11th to 20th	Day	69% 9% 12% 7% 2	1906
	21st to end	Day	77% 7% 10% 6% 1	2772
January	1st to 10th	Night	70% 7% 10% 9% 4	2649
	11th to 20th	Night	75% 7% 9% 6% 2	2515
	21st to end	Night	71% 8% 9% 8% 3	2711
February	1st to 10th	Night	69% 8% 10% 10% 3	2340
	11th to 20th	Night	65% 7% 11% 11% 5%	2275
	21st to end	Night	65% 7% 11% 12% 6%	1862
March	1st to 10th	Night	57% 6% 13% 17% 6% 1	1980
	11th to 20th	Night	54% 7% 9% 18% 11% 1	1980
	21st to end	Night	52% 5% 7% 21% 13% 2	2178
April	1st to 10th	Night	55% 5% 9% 20% 11% 1	1822
	11th to 20th	Night	47% 6% 9% 20% 15% 2	1758
	21st to end	Night	49% 7% 9% 20% 14% 2	1620
May	1st to 10th	Night	46% 7% 9% 20% 15% 3	1620
	11th to 20th	Night	41% 5% 13% 23% 14% 3	1427
	21st to end	Night	36% 8% 12% 24% 17% 3	1551
June	1st to 10th	Night	43% 8% 9% 21% 18% 1	1440
	11th to 20th	Night	36% 8% 12% 22% 19% 2	1440
	21st to end	Night	38% 7% 13% 23% 18% 1	1440
July	1st to 10th	Night	30% 6% 11% 27% 23% 3	1400
	11th to 20th	Night	33% 7% 13% 27% 17% 2	1392
	21st to end	Night	34% 7% 15% 23% 17% 3	1644
August	1st to 10th	Night	32% 10% 16% 27% 15% 1	1600
	11th to 20th	Night	33% 10% 15% 29% 13%	1598
	21st to end	Night	34% 8% 13% 29% 15% 2	1884
September	1st to 10th	Night	38% 7% 14% 23% 15% 2	1800
	11th to 20th	Night	33% 6% 12% 30% 18% 1	1880
	21st to end	Night	43% 8% 11% 23% 14% 1	2030
October	1st to 10th	Night	46% 8% 11% 21% 14% 1	2160
	11th to 20th	Night	54% 7% 11% 18% 8% 1	2160
	21st to end	Night	60% 7% 11% 13% 9% 1	2376
November	1st to 10th	Night	47% 8% 11% 21% 12% 1	2438
	11th to 20th	Night	54% 7% 13% 16% 9% 1	2660
	21st to end	Night	60% 8% 14% 14% 3	2660
December	1st to 10th	Night	70% 8% 12% 7% 3	2660
	11th to 20th	Night	68% 8% 11% 10% 3	3288
	21st to end	Night	74% 8% 12% 5% 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	24% 17% 34% 16% 6% 2	180
	11th to 20th	Day	26% 25% 31% 13% 3 2	247
	21st to end	Day	23% 20% 34% 17% 5% 1	294
February	1st to 10th	Day	33% 18% 37% 11% 1	240
	11th to 20th	Day	26% 23% 38% 13% 1	240
	21st to end	Day	37% 16% 33% 13% 2	238
March	1st to 10th	Day	24% 15% 35% 19% 6%	420
	11th to 20th	Day	24% 13% 33% 23% 6% 1	420
	21st to end	Day	28% 13% 29% 21% 7% 2	462
April	1st to 10th	Day	20% 15% 34% 23% 8% 1	420
	11th to 20th	Day	28% 11% 27% 19% 10% 4	412
	21st to end	Day	27% 8% 30% 23% 9% 3	420
May	1st to 10th	Day	24% 9% 27% 23% 13% 5%	423
	11th to 20th	Day	18% 6% 24% 28% 18% 6%	447
	21st to end	Day	13% 6% 24% 30% 19% 9%	485
June	1st to 10th	Day	14% 8% 26% 34% 15% 3	450
	11th to 20th	Day	14% 7% 23% 28% 23% 4	450
	21st to end	Day	14% 6% 27% 31% 17% 4	450
July	1st to 10th	Day	9% 3 17% 33% 28% 10%	445
	11th to 20th	Day	14% 6% 18% 29% 22% 11%	444
	21st to end	Day	13% 4 23% 33% 21% 6%	488
August	1st to 10th	Day	11% 2 19% 32% 23% 13%	446
	11th to 20th	Day	10% 6% 16% 31% 25% 11%	439
	21st to end	Day	12% 7% 19% 30% 21% 11%	495
September	1st to 10th	Day	14% 7% 22% 26% 21% 11%	450
	11th to 20th	Day	11% 6% 19% 24% 23% 16%	450
	21st to end	Day	15% 10% 26% 22% 19% 8%	450
October	1st to 10th	Day	23% 12% 21% 18% 16% 9%	450
	11th to 20th	Day	26% 16% 30% 20% 7% 2	450
	21st to end	Day	35% 12% 27% 17% 8%	495
November	1st to 10th	Day	21% 20% 27% 20% 9% 2	296
	11th to 20th	Day	22% 26% 26% 19% 5% 2	180
	21st to end	Day	30% 16% 34% 14% 6%	180
December	1st to 10th	Day	28% 19% 35% 11% 6% 1	180
	11th to 20th	Day	28% 26% 30% 13% 3	180
	21st to end	Day	26% 27% 33% 12% 3	198
January	1st to 10th	Night	29% 20% 32% 14% 6%	760
	11th to 20th	Night	31% 16% 30% 19% 4	760
	21st to end	Night	23% 15% 34% 23% 5%	835
February	1st to 10th	Night	26% 20% 32% 19% 3	720
	11th to 20th	Night	24% 18% 34% 19% 5%	703
	21st to end	Night	28% 15% 33% 22% 3	592
March	1st to 10th	Night	22% 12% 35% 24% 7%	720
	11th to 20th	Night	24% 16% 28% 24% 6% 1	720
	21st to end	Night	21% 9% 31% 28% 11% 1	792
April	1st to 10th	Night	24% 13% 30% 27% 5%	720
	11th to 20th	Night	21% 10% 32% 26% 10% 1	694
	21st to end	Night	22% 7% 27% 32% 11% 1	540
May	1st to 10th	Night	20% 6% 24% 33% 15% 3	540
	11th to 20th	Night	16% 5% 26% 42% 11% 1	365
	21st to end	Night	12% 6% 23% 37% 20% 3	389
June	1st to 10th	Night	15% 3 32% 34% 16% 1	360
	11th to 20th	Night	13% 5% 25% 38% 18% 1	360
	21st to end	Night	12% 6% 23% 43% 15% 1	360
July	1st to 10th	Night	9% 3 19% 41% 26% 2	350
	11th to 20th	Night	11% 3 22% 41% 21% 3	348
	21st to end	Night	12% 3 18% 44% 22% 2	561
August	1st to 10th	Night	11% 4 12% 38% 30% 5%	537
	11th to 20th	Night	10% 3 17% 34% 31% 5%	534
	21st to end	Night	12% 3 19% 37% 25% 4	696
September	1st to 10th	Night	15% 4 18% 34% 25% 4	720
	11th to 20th	Night	15% 4 17% 30% 26% 8%	720
	21st to end	Night	18% 6% 20% 30% 20% 5%	720
October	1st to 10th	Night	20% 8% 23% 27% 19% 3	720
	11th to 20th	Night	28% 13% 26% 24% 8% 1	720
	21st to end	Night	33% 12% 24% 25% 5%	792
November	1st to 10th	Night	23% 11% 28% 25% 11% 1	740
	11th to 20th	Night	24% 16% 32% 18% 9% 1	760
	21st to end	Night	28% 15% 31% 20% 6%	760
December	1st to 10th	Night	34% 18% 27% 17% 4	760
	11th to 20th	Night	26% 20% 32% 18% 5% 1	760
	21st to end	Night	32% 17% 31% 18% 3	836

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