Niverville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Niverville clear sky chart from 2005-11-06 to 2026-04-02.

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	10% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	135117
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	135513
Transparency	Day	47% 5% 15% 24% 9% 1	134815
	Night	50% 4 13% 22% 9% 1	135397
Seeing	Day	15% 9% 30% 29% 13% 4	18091
	Night	15% 7% 31% 33% 12% 1	28205

By Month

Percentage Cloud Cover NW (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	6% 16% 6% 13% 7% 6% 7% 5% 6% 6% 21%	4125
	11th to 20th	Day	4 11% 5% 14% 10% 9% 10% 10% 8% 8% 11%	4137
	21st to end	Day	5% 12% 6% 13% 8% 8% 8% 5% 7% 8% 20%	5188
February	1st to 10th	Day	7% 12% 7% 13% 8% 7% 8% 6% 8% 6% 17%	1817
	11th to 20th	Day	7% 9% 4 10% 7% 8% 8% 6% 9% 8% 25%	1844
	21st to end	Day	6% 9% 4 14% 8% 8% 7% 7% 7% 6% 24%	1639
March	1st to 10th	Day	9% 11% 4 9% 8% 6% 5% 4 6% 9% 29%	4727
	11th to 20th	Day	8% 11% 5% 15% 10% 7% 5% 5% 5% 7% 23%	5088
	21st to end	Day	10% 12% 6% 11% 7% 6% 5% 4 6% 7% 27%	5585
April	1st to 10th	Day	10% 13% 4 8% 6% 5% 5% 4 5% 7% 34%	2441
	11th to 20th	Day	12% 11% 4 9% 6% 5% 5% 3 5% 6% 34%	2572
	21st to end	Day	17% 10% 3 8% 5% 5% 4 3 5% 7% 33%	2600
May	1st to 10th	Day	12% 8% 2 6% 4 4 4 3 5% 6% 45%	6081
	11th to 20th	Day	18% 9% 2 7% 5% 5% 4 4 6% 8% 33%	6579
	21st to end	Day	14% 7% 2 6% 4 4 3 3 5% 5% 46%	7428
June	1st to 10th	Day	14% 7% 2 7% 5% 4 5% 4 7% 9% 36%	3000
	11th to 20th	Day	14% 7% 2 6% 5% 5% 5% 4 6% 9% 36%	3000
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 6% 8% 8% 36%	3000
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 7% 10% 45%	6800
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 44%	6800
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 6% 10% 46%	7312
August	1st to 10th	Day	8% 5% 2 5% 4 4 5% 4 7% 10% 46%	4371
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 45%	4171
	21st to end	Day	12% 5% 2 6% 3 4 4 3 6% 8% 47%	4675
September	1st to 10th	Day	9% 5% 2 6% 4 4 4 3 6% 8% 49%	2479
	11th to 20th	Day	14% 7% 2 6% 4 5% 4 4 6% 9% 39%	2200
	21st to end	Day	15% 6% 2 6% 4 4 3 3 6% 8% 43%	2200
October	1st to 10th	Day	12% 7% 2 5% 4 5% 4 4 5% 6% 47%	3308
	11th to 20th	Day	12% 9% 3 7% 4 3 4 4 6% 8% 40%	3189
	21st to end	Day	14% 11% 4 8% 4 5% 5% 4 5% 8% 33%	3190
November	1st to 10th	Day	15% 14% 4 10% 5% 4 4 4 5% 6% 28%	1677
	11th to 20th	Day	11% 15% 5% 13% 6% 5% 4 3 6% 6% 26%	1680
	21st to end	Day	12% 15% 5% 12% 8% 6% 4 3 5% 5% 24%	1570
December	1st to 10th	Day	10% 17% 6% 13% 10% 8% 6% 4 5% 6% 15%	2360
	11th to 20th	Day	9% 14% 5% 13% 7% 4 5% 5% 8% 10% 19%	2709
	21st to end	Day	8% 16% 7% 18% 9% 7% 7% 4 6% 5% 15%	3575
January	1st to 10th	Night	5% 14% 7% 14% 8% 8% 7% 5% 6% 7% 18%	8799
	11th to 20th	Night	4 13% 6% 14% 9% 8% 10% 8% 7% 5% 14%	8775
	21st to end	Night	6% 14% 6% 12% 6% 5% 7% 6% 7% 8% 23%	9026
February	1st to 10th	Night	8% 13% 5% 11% 8% 7% 8% 5% 5% 5% 24%	2803
	11th to 20th	Night	7% 10% 3 8% 6% 7% 6% 6% 6% 7% 33%	2663
	21st to end	Night	6% 12% 5% 13% 8% 5% 6% 4 5% 6% 30%	2186
March	1st to 10th	Night	9% 11% 4 10% 7% 5% 5% 4 6% 7% 33%	5360
	11th to 20th	Night	7% 10% 5% 9% 6% 6% 5% 4 6% 8% 36%	5090
	21st to end	Night	12% 12% 4 12% 5% 4 4 3 4 6% 34%	5588
April	1st to 10th	Night	11% 8% 3 6% 5% 4 5% 4 6% 7% 40%	1978
	11th to 20th	Night	14% 11% 4 8% 5% 4 4 4 5% 6% 36%	1779
	21st to end	Night	13% 8% 3 7% 5% 5% 5% 5% 5% 6% 38%	1800
May	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 5% 7% 44%	3897
	11th to 20th	Night	16% 8% 3 7% 5% 5% 4 4 5% 8% 36%	3323
	21st to end	Night	13% 6% 3 5% 3 3 3 4 5% 7% 50%	3470
June	1st to 10th	Night	11% 7% 2 5% 4 4 4 5% 6% 9% 43%	1400
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 3 6% 9% 43%	1400
	21st to end	Night	10% 5% 2 7% 5% 5% 5% 3 7% 10% 42%	1400
July	1st to 10th	Night	7% 4 2 5% 3 4 5% 4 7% 10% 49%	3180
	11th to 20th	Night	6% 4 1 5% 4 4 4 4 7% 9% 52%	3180
	21st to end	Night	5% 4 2 6% 5% 5% 5% 5% 8% 9% 48%	3551
August	1st to 10th	Night	6% 4 2 5% 4 4 5% 5% 7% 9% 49%	2788
	11th to 20th	Night	10% 3 2 5% 3 4 4 4 5% 8% 50%	2888
	21st to end	Night	10% 5% 2 5% 4 3 4 4 6% 9% 48%	3234
September	1st to 10th	Night	8% 4 1 4 4 3 4 4 6% 8% 54%	1919
	11th to 20th	Night	14% 6% 2 5% 3 5% 5% 3 5% 8% 45%	2200
	21st to end	Night	14% 6% 3 6% 5% 4 4 3 5% 7% 44%	2200
October	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 4 7% 47%	3839
	11th to 20th	Night	11% 9% 3 7% 4 4 4 4 5% 7% 42%	3948
	21st to end	Night	10% 10% 3 9% 5% 4 5% 4 5% 7% 39%	4610
November	1st to 10th	Night	13% 14% 5% 10% 6% 5% 4 4 4 5% 31%	2841
	11th to 20th	Night	11% 16% 5% 12% 6% 5% 4 4 4 6% 27%	2940
	21st to end	Night	11% 14% 6% 14% 7% 5% 5% 4 4 6% 25%	3045
December	1st to 10th	Night	8% 15% 7% 17% 11% 8% 5% 4 5% 5% 14%	5050
	11th to 20th	Night	8% 14% 6% 14% 8% 5% 5% 4 7% 7% 22%	5718
	21st to end	Night	7% 13% 5% 18% 10% 8% 5% 4 6% 5% 19%	7645

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	63% 4 10% 17% 6%	4125
	11th to 20th	Day	66% 3 10% 14% 6%	4158
	21st to end	Day	61% 3 9% 22% 5%	5188
February	1st to 10th	Day	63% 6% 11% 13% 7% 1	1817
	11th to 20th	Day	52% 5% 14% 22% 7%	1853
	21st to end	Day	56% 5% 14% 16% 8%	1639
March	1st to 10th	Day	51% 4 18% 16% 10%	4727
	11th to 20th	Day	59% 6% 13% 16% 6%	5090
	21st to end	Day	56% 5% 11% 21% 7%	5585
April	1st to 10th	Day	49% 5% 10% 25% 10% 1	2441
	11th to 20th	Day	49% 5% 11% 22% 11% 1	2572
	21st to end	Day	49% 5% 15% 21% 8% 2	2600
May	1st to 10th	Day	39% 4 11% 27% 19% 1	6081
	11th to 20th	Day	48% 5% 10% 26% 11%	6583
	21st to end	Day	39% 5% 8% 24% 21% 3	7428
June	1st to 10th	Day	43% 7% 15% 25% 10% 1	3000
	11th to 20th	Day	44% 6% 16% 25% 9%	3000
	21st to end	Day	41% 9% 20% 23% 8%	3000
July	1st to 10th	Day	34% 4 27% 28% 6%	6726
	11th to 20th	Day	37% 4 20% 34% 5%	6719
	21st to end	Day	35% 4 23% 31% 7%	7106
August	1st to 10th	Day	33% 5% 20% 31% 11%	4355
	11th to 20th	Day	36% 4 20% 35% 5%	4210
	21st to end	Day	36% 4 23% 32% 6%	4674
September	1st to 10th	Day	33% 5% 18% 33% 10% 1	2479
	11th to 20th	Day	42% 6% 20% 26% 5% 1	2200
	21st to end	Day	40% 5% 16% 32% 7%	2200
October	1st to 10th	Day	39% 4 15% 31% 11%	3308
	11th to 20th	Day	42% 4 12% 28% 14%	3189
	21st to end	Day	51% 4 15% 24% 6%	3190
November	1st to 10th	Day	57% 6% 15% 18% 4 1	1677
	11th to 20th	Day	58% 5% 17% 14% 5% 1	1680
	21st to end	Day	62% 5% 16% 14% 3	1570
December	1st to 10th	Day	69% 6% 12% 8% 5%	2360
	11th to 20th	Day	59% 4 14% 15% 8%	2710
	21st to end	Day	69% 4 9% 14% 4	3575
January	1st to 10th	Night	64% 4 12% 13% 7%	8800
	11th to 20th	Night	69% 3 6% 16% 5%	8816
	21st to end	Night	57% 4 11% 22% 6%	9026
February	1st to 10th	Night	58% 6% 12% 15% 8%	2803
	11th to 20th	Night	47% 6% 16% 22% 9%	2664
	21st to end	Night	55% 5% 11% 19% 10%	2186
March	1st to 10th	Night	50% 5% 16% 16% 11% 3	5360
	11th to 20th	Night	44% 5% 15% 23% 12%	5090
	21st to end	Night	52% 4 9% 24% 11% 1	5588
April	1st to 10th	Night	42% 4 12% 25% 15% 3	1978
	11th to 20th	Night	48% 5% 8% 22% 16% 2	1779
	21st to end	Night	46% 5% 12% 25% 10% 2	1800
May	1st to 10th	Night	39% 4 11% 27% 19%	3897
	11th to 20th	Night	46% 5% 9% 24% 13% 3	3323
	21st to end	Night	35% 4 8% 23% 25% 5%	3470
June	1st to 10th	Night	36% 7% 16% 25% 14% 1	1400
	11th to 20th	Night	38% 6% 18% 24% 12% 2	1400
	21st to end	Night	37% 7% 20% 27% 8% 1	1400
July	1st to 10th	Night	31% 4 25% 30% 9% 1	3145
	11th to 20th	Night	29% 4 20% 40% 7%	3138
	21st to end	Night	31% 3 27% 32% 6% 1	3452
August	1st to 10th	Night	30% 4 16% 35% 14% 1	2780
	11th to 20th	Night	32% 3 24% 31% 9%	2915
	21st to end	Night	34% 3 19% 34% 9%	3234
September	1st to 10th	Night	27% 5% 18% 35% 14% 1	1919
	11th to 20th	Night	38% 6% 18% 26% 10% 1	2200
	21st to end	Night	40% 5% 13% 30% 11% 1	2200
October	1st to 10th	Night	39% 4 10% 33% 13% 1	3839
	11th to 20th	Night	43% 3 12% 30% 11%	3948
	21st to end	Night	46% 3 14% 30% 6%	4610
November	1st to 10th	Night	56% 5% 14% 17% 7% 1	2841
	11th to 20th	Night	58% 6% 15% 14% 6% 1	2940
	21st to end	Night	62% 5% 14% 13% 5%	3045
December	1st to 10th	Night	71% 4 12% 9% 3	5050
	11th to 20th	Night	61% 4 12% 11% 11%	5716
	21st to end	Night	65% 4 9% 17% 4	7645

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	11% 8% 33% 31% 14% 2	330
	11th to 20th	Day	12% 8% 30% 35% 14% 1	330
	21st to end	Day	13% 10% 31% 30% 13% 3	363
February	1st to 10th	Day	12% 14% 35% 28% 9% 2	330
	11th to 20th	Day	9% 12% 33% 32% 12% 2	330
	21st to end	Day	10% 7% 42% 30% 11%	273
March	1st to 10th	Day	14% 8% 36% 30% 11% 1	330
	11th to 20th	Day	14% 13% 33% 26% 12% 3	330
	21st to end	Day	15% 11% 34% 28% 10% 2	363
April	1st to 10th	Day	14% 12% 29% 32% 9% 3	533
	11th to 20th	Day	18% 12% 31% 25% 12% 1	690
	21st to end	Day	19% 10% 30% 27% 11% 2	700
May	1st to 10th	Day	16% 12% 32% 26% 12% 2	703
	11th to 20th	Day	21% 9% 29% 26% 12% 3	725
	21st to end	Day	19% 8% 24% 28% 16% 5%	789
June	1st to 10th	Day	14% 11% 28% 26% 14% 6%	730
	11th to 20th	Day	15% 12% 31% 29% 11% 3	730
	21st to end	Day	12% 9% 27% 32% 15% 5%	730
July	1st to 10th	Day	10% 3 27% 31% 18% 10%	721
	11th to 20th	Day	11% 7% 28% 28% 20% 6%	718
	21st to end	Day	6% 5% 28% 34% 20% 8%	794
August	1st to 10th	Day	8% 5% 27% 32% 21% 7%	726
	11th to 20th	Day	11% 6% 23% 31% 19% 9%	715
	21st to end	Day	13% 6% 28% 30% 18% 5%	803
September	1st to 10th	Day	10% 8% 33% 32% 14% 3	609
	11th to 20th	Day	18% 10% 37% 24% 8% 3	330
	21st to end	Day	20% 8% 34% 27% 8% 2	330
October	1st to 10th	Day	20% 13% 25% 28% 10% 4	330
	11th to 20th	Day	17% 14% 34% 27% 7% 2	330
	21st to end	Day	26% 9% 32% 24% 9% 1	363
November	1st to 10th	Day	25% 11% 28% 25% 10% 1	330
	11th to 20th	Day	19% 11% 36% 24% 9%	330
	21st to end	Day	17% 11% 39% 26% 6%	330
December	1st to 10th	Day	16% 6% 37% 27% 12% 2	330
	11th to 20th	Day	16% 11% 37% 28% 7% 1	330
	21st to end	Day	15% 9% 29% 28% 14% 5%	363
January	1st to 10th	Night	12% 8% 34% 31% 14% 2	1050
	11th to 20th	Night	14% 8% 32% 35% 10%	1050
	21st to end	Night	13% 8% 34% 32% 11% 1	1155
February	1st to 10th	Night	14% 8% 29% 33% 14% 1	1050
	11th to 20th	Night	11% 7% 30% 36% 13% 3	1029
	21st to end	Night	10% 7% 36% 32% 14% 1	802
March	1st to 10th	Night	15% 7% 32% 32% 12% 2	784
	11th to 20th	Night	10% 8% 40% 30% 11% 1	630
	21st to end	Night	19% 8% 29% 28% 13% 2	693
April	1st to 10th	Night	15% 8% 28% 38% 10% 1	603
	11th to 20th	Night	17% 8% 30% 34% 11%	593
	21st to end	Night	17% 7% 30% 35% 12%	600
May	1st to 10th	Night	17% 6% 35% 32% 9% 1	600
	11th to 20th	Night	17% 8% 29% 33% 12% 1	591
	21st to end	Night	18% 6% 32% 33% 12%	650
June	1st to 10th	Night	13% 6% 32% 35% 14% 1	600
	11th to 20th	Night	16% 5% 32% 34% 14% 1	600
	21st to end	Night	12% 4 24% 40% 19% 1	600
July	1st to 10th	Night	6% 2 26% 44% 21% 2	585
	11th to 20th	Night	7% 4 25% 44% 17% 2	582
	21st to end	Night	7% 3 23% 44% 20% 3	657
August	1st to 10th	Night	9% 2 22% 47% 18% 2	597
	11th to 20th	Night	10% 4 21% 40% 23% 3	594
	21st to end	Night	12% 6% 25% 38% 19% 1	660
September	1st to 10th	Night	9% 4 30% 38% 17% 2	600
	11th to 20th	Night	17% 6% 27% 37% 14%	600
	21st to end	Night	17% 6% 32% 32% 12% 1	600
October	1st to 10th	Night	22% 8% 32% 29% 8%	745
	11th to 20th	Night	20% 9% 33% 30% 8%	825
	21st to end	Night	21% 9% 31% 30% 8% 1	1100
November	1st to 10th	Night	19% 10% 34% 26% 10%	1025
	11th to 20th	Night	19% 8% 34% 29% 8% 2	1050
	21st to end	Night	17% 9% 39% 26% 8% 1	1050
December	1st to 10th	Night	14% 6% 34% 32% 12% 2	1050
	11th to 20th	Night	17% 7% 35% 31% 8% 1	1050
	21st to end	Night	19% 8% 31% 29% 11% 2	1155

Page generated at 2026-03-30 01:18:39. Version ac07

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