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 2025-02-21.

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% 5% 5% 5% 4 5% 7% 32%	108771
	Night	16% 12% 4 10% 5% 5% 5% 4 5% 6% 29%	109802
Transparency	Day	50% 7% 13% 20% 10% 1	112409
	Night	53% 7% 12% 17% 10% 1	114327
Seeing	Day	20% 12% 27% 23% 13% 5%	14757
	Night	22% 11% 27% 27% 12% 2	24309

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	13% 19% 6% 18% 8% 5% 4 3 4 4 16%	3597
	11th to 20th	Day	11% 21% 8% 17% 8% 7% 6% 4 5% 4 9%	3911
	21st to end	Day	18% 17% 7% 14% 9% 7% 4 3 4 4 14%	4466
February	1st to 10th	Day	17% 17% 4 14% 8% 6% 4 5% 5% 4 16%	1800
	11th to 20th	Day	13% 16% 7% 15% 10% 5% 5% 4 4 4 17%	1753
	21st to end	Day	18% 15% 4 11% 8% 5% 5% 4 5% 5% 21%	1478
March	1st to 10th	Day	18% 12% 4 9% 6% 4 4 3 5% 5% 30%	3432
	11th to 20th	Day	10% 17% 4 9% 6% 5% 5% 3 5% 5% 30%	3480
	21st to end	Day	16% 8% 3 8% 4 5% 4 4 5% 6% 36%	3815
April	1st to 10th	Day	17% 12% 3 7% 5% 4 4 3 5% 6% 33%	2256
	11th to 20th	Day	19% 9% 3 6% 4 4 3 3 5% 6% 36%	2289
	21st to end	Day	19% 9% 2 8% 4 5% 4 4 5% 6% 35%	2470
May	1st to 10th	Day	17% 8% 3 8% 5% 4 4 4 5% 7% 34%	4108
	11th to 20th	Day	14% 10% 4 9% 5% 5% 4 4 5% 7% 33%	4384
	21st to end	Day	9% 6% 2 6% 4 3 4 4 6% 8% 47%	4837
June	1st to 10th	Day	13% 6% 3 6% 4 4 5% 4 6% 8% 41%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	2660
	21st to end	Day	12% 6% 2 5% 4 4 5% 4 7% 9% 44%	2660
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 4 7% 10% 46%	4440
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 7% 10% 45%	4440
	21st to end	Day	8% 4 2 6% 5% 5% 5% 5% 7% 9% 44%	4507
August	1st to 10th	Day	16% 6% 2 6% 4 4 3 4 6% 8% 39%	4104
	11th to 20th	Day	13% 5% 2 7% 5% 5% 5% 4 7% 10% 37%	4044
	21st to end	Day	10% 5% 2 5% 4 4 4 4 7% 9% 47%	4313
September	1st to 10th	Day	13% 6% 2 6% 4 3 4 4 7% 9% 42%	2280
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 6% 8% 47%	2192
	21st to end	Day	13% 7% 3 8% 5% 6% 5% 4 7% 7% 35%	2036
October	1st to 10th	Day	18% 8% 3 8% 4 3 5% 3 5% 7% 36%	1900
	11th to 20th	Day	21% 9% 3 8% 5% 5% 5% 4 5% 7% 29%	1900
	21st to end	Day	24% 13% 4 9% 5% 4 4 3 4 5% 24%	2090
November	1st to 10th	Day	12% 12% 4 9% 6% 5% 5% 4 5% 7% 32%	1723
	11th to 20th	Day	15% 13% 4 9% 5% 5% 5% 4 5% 7% 30%	1600
	21st to end	Day	20% 17% 5% 9% 6% 5% 5% 3 5% 5% 21%	1600
December	1st to 10th	Day	19% 18% 6% 11% 7% 6% 5% 4 5% 5% 13%	2600
	11th to 20th	Day	20% 16% 5% 10% 5% 5% 6% 4 4 5% 20%	2986
	21st to end	Day	23% 19% 7% 12% 8% 6% 4 3 4 4 12%	3960
January	1st to 10th	Night	15% 15% 6% 18% 7% 5% 4 4 4 4 16%	6349
	11th to 20th	Night	11% 18% 9% 17% 8% 6% 5% 3 4 4 14%	5971
	21st to end	Night	19% 17% 6% 15% 7% 5% 4 3 3 4 16%	6490
February	1st to 10th	Night	17% 18% 5% 12% 7% 5% 5% 4 5% 5% 19%	2600
	11th to 20th	Night	15% 15% 5% 13% 7% 5% 5% 4 5% 6% 19%	2533
	21st to end	Night	18% 14% 6% 13% 6% 5% 4 3 6% 6% 21%	1975
March	1st to 10th	Night	21% 12% 4 9% 5% 4 4 3 4 5% 30%	3408
	11th to 20th	Night	16% 15% 4 8% 5% 4 4 3 5% 6% 30%	3479
	21st to end	Night	16% 8% 3 7% 4 4 4 3 5% 6% 41%	3817
April	1st to 10th	Night	19% 12% 4 8% 5% 4 4 3 4 5% 32%	1923
	11th to 20th	Night	19% 7% 3 7% 5% 5% 4 3 5% 5% 37%	1856
	21st to end	Night	17% 9% 3 6% 4 5% 6% 4 5% 7% 35%	1710
May	1st to 10th	Night	21% 10% 4 7% 4 4 4 3 5% 7% 33%	2833
	11th to 20th	Night	12% 9% 3 8% 7% 5% 5% 4 7% 7% 33%	2506
	21st to end	Night	11% 4 2 6% 3 4 5% 4 6% 8% 46%	2738
June	1st to 10th	Night	13% 5% 3 6% 7% 5% 6% 5% 8% 8% 36%	1520
	11th to 20th	Night	8% 7% 1 7% 5% 4 5% 5% 7% 8% 43%	1520
	21st to end	Night	12% 5% 2 6% 4 5% 5% 4 6% 9% 41%	1520
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 5% 4 5% 7% 47%	2520
	11th to 20th	Night	10% 5% 2 6% 4 4 3 4 6% 9% 47%	2520
	21st to end	Night	9% 3 2 6% 4 4 4 4 6% 8% 48%	3043
August	1st to 10th	Night	10% 6% 3 7% 4 5% 4 4 6% 8% 44%	2825
	11th to 20th	Night	14% 7% 3 6% 5% 4 5% 3 7% 7% 40%	2785
	21st to end	Night	9% 4 2 6% 4 4 5% 4 6% 10% 46%	3310
September	1st to 10th	Night	13% 6% 2 7% 3 4 4 4 6% 7% 45%	1900
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 6% 6% 50%	1985
	21st to end	Night	17% 6% 3 7% 5% 4 5% 3 6% 7% 36%	2143
October	1st to 10th	Night	17% 7% 3 7% 4 5% 4 3 5% 7% 38%	2280
	11th to 20th	Night	21% 10% 3 8% 5% 5% 5% 3 5% 6% 31%	2280
	21st to end	Night	26% 11% 3 6% 5% 4 4 4 5% 5% 27%	2508
November	1st to 10th	Night	16% 10% 3 7% 5% 4 5% 3 4 7% 37%	2571
	11th to 20th	Night	16% 12% 4 8% 5% 6% 5% 4 5% 6% 28%	2800
	21st to end	Night	19% 14% 5% 10% 5% 5% 6% 4 5% 5% 22%	2800
December	1st to 10th	Night	16% 20% 7% 14% 6% 6% 5% 4 5% 5% 12%	4580
	11th to 20th	Night	17% 20% 5% 10% 5% 5% 5% 3 4 4 21%	5208
	21st to end	Night	26% 16% 6% 10% 6% 6% 4 3 5% 4 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	71% 8% 9% 7% 4	3598
	11th to 20th	Day	77% 6% 9% 5% 2 1	3945
	21st to end	Day	73% 6% 11% 5% 4	4466
February	1st to 10th	Day	70% 8% 9% 11% 3	1800
	11th to 20th	Day	70% 6% 8% 11% 4	1762
	21st to end	Day	65% 7% 11% 11% 6%	1478
March	1st to 10th	Day	56% 6% 11% 21% 5% 1	3435
	11th to 20th	Day	53% 8% 15% 16% 7% 1	3480
	21st to end	Day	47% 8% 11% 24% 10% 1	3815
April	1st to 10th	Day	53% 5% 13% 18% 11% 1	2256
	11th to 20th	Day	48% 6% 11% 19% 14% 2	2289
	21st to end	Day	50% 6% 11% 18% 13% 3	2470
May	1st to 10th	Day	47% 7% 12% 19% 12% 2	4120
	11th to 20th	Day	48% 11% 13% 20% 8% 1	4388
	21st to end	Day	34% 7% 13% 27% 16% 3	4837
June	1st to 10th	Day	40% 8% 13% 21% 15% 2	2660
	11th to 20th	Day	38% 8% 13% 25% 15% 1	2660
	21st to end	Day	36% 8% 14% 25% 16% 1	2660
July	1st to 10th	Day	32% 7% 13% 29% 17% 2	4370
	11th to 20th	Day	33% 8% 14% 32% 12% 1	4365
	21st to end	Day	35% 8% 16% 24% 15% 1	4363
August	1st to 10th	Day	42% 8% 15% 22% 13% 1	4091
	11th to 20th	Day	41% 8% 16% 25% 10% 1	4083
	21st to end	Day	33% 7% 13% 34% 13% 1	4313
September	1st to 10th	Day	39% 7% 14% 27% 13% 1	2280
	11th to 20th	Day	34% 8% 13% 29% 15% 1	2192
	21st to end	Day	45% 9% 14% 22% 9% 1	2036
October	1st to 10th	Day	36% 7% 16% 25% 15% 1	3160
	11th to 20th	Day	45% 6% 15% 20% 13% 1	3140
	21st to end	Day	51% 7% 15% 21% 6%	3428
November	1st to 10th	Day	52% 8% 12% 19% 8% 1	1723
	11th to 20th	Day	54% 7% 16% 13% 8% 1	1600
	21st to end	Day	64% 7% 13% 12% 4	1600
December	1st to 10th	Day	71% 8% 13% 6% 1	2600
	11th to 20th	Day	66% 7% 9% 9% 7% 1	2986
	21st to end	Day	75% 6% 10% 6% 2	3960
January	1st to 10th	Night	69% 8% 12% 8% 3	6349
	11th to 20th	Night	72% 7% 10% 8% 3	6012
	21st to end	Night	70% 7% 9% 6% 8%	6490
February	1st to 10th	Night	67% 8% 10% 12% 3	2600
	11th to 20th	Night	64% 7% 12% 12% 5%	2535
	21st to end	Night	64% 7% 11% 12% 6%	1975
March	1st to 10th	Night	56% 5% 11% 22% 6%	3418
	11th to 20th	Night	52% 7% 16% 15% 9% 1	3480
	21st to end	Night	42% 5% 12% 24% 16% 1	3817
April	1st to 10th	Night	55% 5% 9% 19% 11% 1	1923
	11th to 20th	Night	48% 6% 10% 20% 15% 2	1856
	21st to end	Night	48% 6% 9% 19% 14% 3	1710
May	1st to 10th	Night	51% 6% 10% 18% 13% 2	2840
	11th to 20th	Night	45% 8% 18% 20% 9% 2	2507
	21st to end	Night	33% 9% 11% 24% 21% 2	2739
June	1st to 10th	Night	43% 8% 10% 21% 17% 1	1520
	11th to 20th	Night	36% 8% 12% 22% 19% 2	1520
	21st to end	Night	39% 7% 13% 22% 17% 1	1520
July	1st to 10th	Night	36% 5% 12% 23% 21% 2	2480
	11th to 20th	Night	33% 6% 14% 32% 14% 1	2472
	21st to end	Night	33% 7% 17% 24% 18% 2	2946
August	1st to 10th	Night	36% 7% 13% 27% 14% 2	2814
	11th to 20th	Night	41% 7% 15% 27% 10%	2812
	21st to end	Night	32% 7% 13% 32% 14% 1	3310
September	1st to 10th	Night	37% 7% 14% 24% 17% 2	1900
	11th to 20th	Night	32% 6% 12% 30% 18% 1	1985
	21st to end	Night	45% 8% 11% 22% 13% 1	2143
October	1st to 10th	Night	38% 7% 10% 25% 20% 1	3800
	11th to 20th	Night	49% 6% 12% 22% 11%	3779
	21st to end	Night	44% 5% 16% 25% 8% 1	4120
November	1st to 10th	Night	47% 7% 11% 22% 12% 1	2571
	11th to 20th	Night	54% 7% 13% 16% 9% 1	2800
	21st to end	Night	60% 8% 14% 14% 3	2800
December	1st to 10th	Night	71% 8% 13% 5% 2	4580
	11th to 20th	Night	66% 7% 8% 10% 8% 1	5208
	21st to end	Night	72% 7% 11% 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	26% 17% 36% 15% 6% 2	200
	11th to 20th	Day	27% 27% 30% 12% 3 1	275
	21st to end	Day	25% 21% 34% 15% 5% 1	330
February	1st to 10th	Day	31% 20% 34% 12% 3	300
	11th to 20th	Day	27% 23% 36% 12% 1	300
	21st to end	Day	36% 16% 33% 13% 2	268
March	1st to 10th	Day	24% 15% 34% 19% 7%	460
	11th to 20th	Day	23% 15% 32% 23% 5% 1	460
	21st to end	Day	27% 14% 29% 21% 7% 2	506
April	1st to 10th	Day	21% 14% 33% 23% 7% 1	460
	11th to 20th	Day	28% 13% 27% 19% 10% 4	452
	21st to end	Day	27% 9% 31% 22% 8% 3	460
May	1st to 10th	Day	23% 9% 25% 25% 13% 5%	463
	11th to 20th	Day	17% 6% 25% 28% 19% 6%	487
	21st to end	Day	12% 6% 25% 30% 19% 8%	529
June	1st to 10th	Day	15% 9% 25% 33% 14% 3	490
	11th to 20th	Day	13% 8% 25% 28% 23% 4	490
	21st to end	Day	15% 7% 28% 30% 16% 4	490
July	1st to 10th	Day	9% 4 19% 33% 26% 9%	485
	11th to 20th	Day	14% 6% 19% 29% 21% 10%	484
	21st to end	Day	12% 4 23% 33% 22% 7%	532
August	1st to 10th	Day	14% 2 20% 30% 22% 12%	486
	11th to 20th	Day	11% 7% 17% 30% 24% 11%	479
	21st to end	Day	12% 6% 20% 30% 21% 11%	539
September	1st to 10th	Day	14% 8% 22% 24% 21% 11%	490
	11th to 20th	Day	11% 6% 18% 23% 24% 18%	490
	21st to end	Day	16% 10% 27% 22% 18% 7%	490
October	1st to 10th	Day	22% 12% 23% 19% 15% 9%	490
	11th to 20th	Day	24% 15% 31% 20% 8% 2	490
	21st to end	Day	34% 14% 27% 18% 8%	539
November	1st to 10th	Day	22% 20% 28% 20% 8% 2	323
	11th to 20th	Day	22% 25% 29% 18% 5% 2	200
	21st to end	Day	31% 17% 34% 13% 5%	200
December	1st to 10th	Day	30% 19% 35% 12% 5% 1	200
	11th to 20th	Day	29% 25% 32% 12% 3	200
	21st to end	Day	26% 27% 31% 12% 3 1	220
January	1st to 10th	Night	28% 21% 32% 13% 6%	800
	11th to 20th	Night	31% 17% 31% 18% 3	800
	21st to end	Night	24% 15% 34% 22% 5%	880
February	1st to 10th	Night	26% 20% 31% 20% 3	800
	11th to 20th	Night	24% 19% 33% 19% 4	783
	21st to end	Night	27% 15% 33% 22% 3	629
March	1st to 10th	Night	22% 12% 35% 24% 6%	760
	11th to 20th	Night	24% 17% 28% 24% 6% 1	760
	21st to end	Night	21% 11% 30% 27% 10% 1	836
April	1st to 10th	Night	25% 13% 30% 27% 5%	760
	11th to 20th	Night	21% 10% 32% 26% 9% 1	732
	21st to end	Night	22% 7% 28% 31% 11% 1	570
May	1st to 10th	Night	20% 7% 23% 33% 15% 3	570
	11th to 20th	Night	15% 5% 25% 42% 12% 1	385
	21st to end	Night	12% 6% 23% 36% 20% 3	411
June	1st to 10th	Night	15% 3 32% 34% 15% 1	380
	11th to 20th	Night	12% 5% 26% 38% 18% 1	380
	21st to end	Night	13% 6% 23% 42% 14% 1	380
July	1st to 10th	Night	9% 4 19% 42% 24% 2	370
	11th to 20th	Night	11% 2 23% 40% 21% 3	368
	21st to end	Night	11% 3 18% 43% 23% 2	593
August	1st to 10th	Night	11% 4 14% 38% 29% 4	567
	11th to 20th	Night	10% 4 17% 33% 30% 5%	564
	21st to end	Night	12% 3 18% 37% 26% 4	735
September	1st to 10th	Night	15% 5% 18% 34% 24% 4	760
	11th to 20th	Night	14% 4 16% 30% 28% 7%	760
	21st to end	Night	19% 6% 21% 30% 19% 5%	760
October	1st to 10th	Night	19% 8% 24% 28% 19% 3	760
	11th to 20th	Night	27% 13% 25% 25% 9% 1	760
	21st to end	Night	32% 13% 25% 25% 6%	836
November	1st to 10th	Night	24% 12% 28% 24% 11% 1	780
	11th to 20th	Night	25% 16% 31% 18% 9% 1	800
	21st to end	Night	28% 15% 31% 19% 6%	800
December	1st to 10th	Night	33% 19% 27% 17% 4 1	800
	11th to 20th	Night	27% 20% 31% 18% 4 1	800
	21st to end	Night	31% 16% 31% 19% 3	880

Page generated at 2025-02-18 03:26:32. Version ac07

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