NPMAS Parmentier Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NPMAS Parmentier Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	12% 8% 3 7% 5% 4 5% 4 6% 7% 39%	138326
	Night	12% 9% 3 7% 5% 4 4 3 5% 7% 40%	134985
Transparency	Day	43% 4 12% 26% 14% 1	141813
	Night	44% 3 12% 24% 15% 2	139575
Seeing	Day	15% 9% 29% 29% 15% 4	18385
	Night	16% 9% 31% 31% 13% 1	28206

By Month

Percentage Cloud Cover SE (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	11% 11% 4 12% 5% 5% 5% 4 5% 6% 31%	4691
	11th to 20th	Day	10% 12% 4 9% 5% 4 4 4 5% 7% 37%	4710
	21st to end	Day	11% 11% 5% 9% 5% 5% 4 3 6% 6% 35%	5156
February	1st to 10th	Day	9% 11% 5% 10% 5% 5% 4 4 6% 8% 32%	1819
	11th to 20th	Day	12% 10% 4 8% 5% 4 4 4 5% 7% 37%	2039
	21st to end	Day	12% 11% 4 9% 5% 5% 5% 4 6% 6% 33%	1730
March	1st to 10th	Day	13% 8% 3 5% 3 3 4 3 5% 7% 46%	4580
	11th to 20th	Day	11% 8% 3 8% 4 5% 5% 4 6% 8% 38%	4750
	21st to end	Day	22% 12% 4 8% 5% 4 4 3 4 4 30%	6099
April	1st to 10th	Day	14% 12% 4 9% 6% 5% 4 4 6% 6% 30%	2520
	11th to 20th	Day	18% 10% 3 6% 4 4 4 3 6% 5% 35%	2494
	21st to end	Day	16% 10% 3 8% 4 4 5% 4 6% 7% 33%	2721
May	1st to 10th	Day	11% 7% 2 7% 4 5% 4 4 6% 7% 41%	7693
	11th to 20th	Day	11% 7% 2 7% 4 4 5% 3 6% 7% 43%	8222
	21st to end	Day	13% 7% 3 6% 4 4 4 3 5% 7% 45%	9047
June	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 7% 8% 45%	2940
	11th to 20th	Day	12% 6% 2 7% 4 4 5% 4 6% 9% 41%	2940
	21st to end	Day	11% 5% 3 5% 4 5% 5% 5% 6% 9% 42%	2940
July	1st to 10th	Day	12% 6% 2 5% 4 4 5% 4 7% 10% 40%	6500
	11th to 20th	Day	6% 4 2 5% 4 4 5% 5% 7% 9% 49%	6500
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 7% 8% 47%	7065
August	1st to 10th	Day	8% 6% 2 6% 4 5% 6% 4 7% 9% 43%	4563
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 8% 48%	4081
	21st to end	Day	11% 5% 2 7% 5% 5% 4 4 6% 8% 43%	4312
September	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 7% 7% 44%	2400
	11th to 20th	Day	11% 4 2 6% 4 4 4 3 6% 8% 47%	2265
	21st to end	Day	11% 7% 3 7% 6% 4 4 4 6% 8% 39%	2200
October	1st to 10th	Day	15% 7% 2 5% 3 4 4 4 4 6% 45%	2145
	11th to 20th	Day	19% 9% 3 9% 4 5% 4 3 6% 7% 29%	1921
	21st to end	Day	15% 9% 4 8% 6% 5% 4 4 5% 6% 34%	1980
November	1st to 10th	Day	14% 7% 2 7% 5% 4 4 4 6% 7% 40%	1852
	11th to 20th	Day	12% 11% 4 10% 6% 4 6% 3 6% 7% 31%	1890
	21st to end	Day	16% 12% 4 7% 4 4 4 5% 5% 8% 30%	1713
December	1st to 10th	Day	10% 11% 4 8% 5% 6% 5% 5% 8% 8% 30%	2690
	11th to 20th	Day	13% 14% 4 9% 6% 5% 5% 3 6% 7% 29%	3088
	21st to end	Day	19% 19% 6% 12% 5% 4 3 3 4 5% 19%	4070
January	1st to 10th	Night	13% 11% 4 9% 4 4 4 3 4 5% 39%	8232
	11th to 20th	Night	9% 13% 5% 10% 7% 6% 5% 4 5% 6% 31%	8280
	21st to end	Night	8% 11% 5% 10% 5% 6% 5% 4 5% 7% 35%	9058
February	1st to 10th	Night	11% 13% 4 9% 6% 5% 4 4 5% 6% 33%	2798
	11th to 20th	Night	11% 10% 4 9% 5% 4 5% 4 5% 6% 37%	2465
	21st to end	Night	13% 13% 4 8% 4 3 4 3 4 7% 36%	2076
March	1st to 10th	Night	14% 7% 2 6% 4 3 4 3 5% 6% 47%	5493
	11th to 20th	Night	10% 8% 3 7% 4 5% 5% 4 6% 8% 39%	5448
	21st to end	Night	19% 10% 3 8% 5% 4 5% 4 4 5% 32%	5083
April	1st to 10th	Night	16% 12% 3 7% 5% 4 4 4 4 6% 36%	2100
	11th to 20th	Night	19% 9% 3 5% 4 4 4 3 5% 6% 39%	2075
	21st to end	Night	16% 10% 3 7% 5% 5% 3 3 5% 7% 37%	1898
May	1st to 10th	Night	12% 7% 2 6% 4 5% 4 3 6% 8% 42%	5149
	11th to 20th	Night	9% 6% 3 7% 4 4 4 4 7% 9% 41%	4670
	21st to end	Night	16% 7% 3 7% 4 4 3 3 5% 6% 42%	5139
June	1st to 10th	Night	11% 5% 3 5% 4 4 4 3 7% 8% 45%	1680
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 7% 9% 42%	1680
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 5% 8% 46%	1680
July	1st to 10th	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 45%	3698
	11th to 20th	Night	7% 4 2 4 3 3 4 4 5% 8% 57%	3697
	21st to end	Night	5% 4 2 5% 4 4 4 3 6% 8% 54%	4027
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 8% 46%	2597
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 7% 50%	2963
	21st to end	Night	11% 6% 2 5% 4 4 4 3 5% 7% 49%	3586
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 4 5% 7% 54%	2000
	11th to 20th	Night	10% 4 1 5% 3 3 4 3 5% 7% 54%	2115
	21st to end	Night	13% 6% 2 6% 4 4 3 3 5% 7% 46%	2200
October	1st to 10th	Night	13% 6% 2 6% 3 4 4 3 5% 6% 48%	2252
	11th to 20th	Night	15% 8% 4 6% 5% 4 5% 4 5% 8% 38%	2478
	21st to end	Night	18% 9% 3 6% 4 4 4 4 5% 7% 36%	2860
November	1st to 10th	Night	13% 7% 2 6% 5% 4 4 4 4 7% 45%	2666
	11th to 20th	Night	13% 9% 3 8% 6% 4 4 3 6% 7% 36%	2730
	21st to end	Night	15% 11% 2 6% 5% 5% 4 4 5% 7% 35%	2903
December	1st to 10th	Night	12% 10% 3 7% 4 4 4 3 6% 8% 38%	4720
	11th to 20th	Night	14% 15% 5% 9% 6% 5% 4 3 4 5% 28%	5339
	21st to end	Night	21% 16% 6% 9% 4 4 4 3 5% 5% 24%	7150

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	53% 3 15% 19% 9%	4692
	11th to 20th	Day	48% 2 9% 26% 14% 1	4710
	21st to end	Day	50% 3 8% 22% 17%	5156
February	1st to 10th	Day	51% 4 11% 22% 11% 1	1819
	11th to 20th	Day	46% 3 11% 23% 14% 2	2049
	21st to end	Day	50% 4 11% 22% 11% 2	1730
March	1st to 10th	Day	40% 2 14% 21% 18% 6%	4580
	11th to 20th	Day	43% 4 14% 23% 14% 2	4750
	21st to end	Day	59% 3 9% 19% 11%	6101
April	1st to 10th	Day	55% 4 11% 20% 11%	2520
	11th to 20th	Day	50% 4 9% 22% 13% 2	2494
	21st to end	Day	50% 4 12% 20% 13% 2	2721
May	1st to 10th	Day	40% 5% 11% 28% 15% 2	7728
	11th to 20th	Day	40% 4 10% 28% 16% 1	8226
	21st to end	Day	40% 3 9% 24% 19% 5%	9061
June	1st to 10th	Day	36% 5% 12% 29% 16% 2	2940
	11th to 20th	Day	40% 4 14% 25% 15% 1	2940
	21st to end	Day	37% 6% 17% 25% 14% 1	2940
July	1st to 10th	Day	38% 6% 14% 32% 9% 1	6431
	11th to 20th	Day	29% 6% 15% 34% 15% 1	6425
	21st to end	Day	33% 6% 15% 27% 19% 2	6869
August	1st to 10th	Day	38% 5% 14% 28% 14% 1	4548
	11th to 20th	Day	34% 5% 13% 35% 12% 1	4120
	21st to end	Day	38% 5% 16% 25% 15% 1	4311
September	1st to 10th	Day	38% 5% 14% 29% 13% 1	2400
	11th to 20th	Day	35% 4 16% 33% 11% 1	2265
	21st to end	Day	42% 4 13% 29% 11% 1	2200
October	1st to 10th	Day	25% 2 11% 36% 23% 3	3496
	11th to 20th	Day	48% 4 9% 25% 14% 1	3111
	21st to end	Day	43% 4 12% 28% 12%	3180
November	1st to 10th	Day	42% 4 13% 27% 14% 1	1852
	11th to 20th	Day	51% 4 15% 21% 9% 1	1890
	21st to end	Day	51% 3 15% 23% 7%	1713
December	1st to 10th	Day	48% 5% 17% 24% 6%	2690
	11th to 20th	Day	55% 3 12% 17% 12% 2	3085
	21st to end	Day	69% 2 6% 17% 6%	4070
January	1st to 10th	Night	49% 2 11% 26% 12% 1	8233
	11th to 20th	Night	55% 3 9% 17% 15% 1	8280
	21st to end	Night	50% 3 12% 21% 15%	9058
February	1st to 10th	Night	53% 3 8% 22% 12% 2	2798
	11th to 20th	Night	48% 3 10% 24% 13% 2	2466
	21st to end	Night	50% 3 12% 23% 11% 1	2076
March	1st to 10th	Night	39% 2 15% 28% 13% 3	5493
	11th to 20th	Night	43% 3 17% 22% 14% 2	5448
	21st to end	Night	55% 3 9% 19% 12% 1	5083
April	1st to 10th	Night	50% 4 8% 20% 17% 1	2100
	11th to 20th	Night	47% 2 7% 24% 16% 3	2075
	21st to end	Night	48% 2 10% 23% 14% 2	1898
May	1st to 10th	Night	39% 3 12% 25% 19% 2	5176
	11th to 20th	Night	39% 4 12% 25% 17% 2	4671
	21st to end	Night	44% 3 8% 23% 16% 6%	5149
June	1st to 10th	Night	36% 5% 11% 29% 18% 2	1680
	11th to 20th	Night	38% 5% 10% 28% 17% 2	1680
	21st to end	Night	35% 5% 16% 27% 14% 3	1680
July	1st to 10th	Night	37% 4 14% 32% 10% 4	3660
	11th to 20th	Night	26% 4 15% 34% 19% 2	3652
	21st to end	Night	27% 5% 15% 28% 23% 2	3912
August	1st to 10th	Night	35% 5% 13% 28% 18% 1	2588
	11th to 20th	Night	34% 4 12% 32% 17% 1	2990
	21st to end	Night	34% 5% 12% 24% 22% 2	3586
September	1st to 10th	Night	29% 4 13% 31% 20% 2	2000
	11th to 20th	Night	31% 2 13% 36% 16% 1	2115
	21st to end	Night	39% 3 12% 30% 15% 1	2200
October	1st to 10th	Night	29% 2 9% 39% 19% 1	3681
	11th to 20th	Night	37% 3 14% 26% 17% 2	4027
	21st to end	Night	43% 3 12% 25% 16%	4610
November	1st to 10th	Night	39% 3 12% 28% 17% 2	2666
	11th to 20th	Night	47% 4 13% 22% 13% 2	2730
	21st to end	Night	47% 4 15% 26% 8% 1	2903
December	1st to 10th	Night	43% 4 22% 23% 7% 1	4720
	11th to 20th	Night	59% 3 11% 14% 12% 1	5341
	21st to end	Night	64% 3 9% 15% 9%	7150

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	15% 13% 32% 28% 10% 2	330
	11th to 20th	Day	21% 12% 35% 24% 7% 1	330
	21st to end	Day	19% 13% 31% 29% 7% 1	363
February	1st to 10th	Day	13% 13% 42% 23% 7% 2	330
	11th to 20th	Day	13% 16% 45% 20% 7%	330
	21st to end	Day	18% 15% 42% 22% 2 1	273
March	1st to 10th	Day	16% 18% 37% 25% 4	330
	11th to 20th	Day	18% 15% 32% 25% 8% 2	377
	21st to end	Day	23% 11% 32% 25% 8% 2	594
April	1st to 10th	Day	22% 14% 31% 25% 7% 1	540
	11th to 20th	Day	22% 16% 28% 23% 9% 2	532
	21st to end	Day	18% 10% 33% 25% 13% 2	540
May	1st to 10th	Day	16% 11% 34% 26% 11% 2	569
	11th to 20th	Day	17% 9% 30% 31% 10% 3	775
	21st to end	Day	13% 7% 30% 29% 16% 5%	844
June	1st to 10th	Day	10% 7% 29% 34% 16% 4	780
	11th to 20th	Day	15% 9% 27% 32% 15% 2	780
	21st to end	Day	12% 7% 25% 35% 18% 3	780
July	1st to 10th	Day	8% 3 19% 38% 24% 7%	771
	11th to 20th	Day	8% 4 24% 37% 21% 6%	768
	21st to end	Day	6% 3 23% 38% 23% 7%	845
August	1st to 10th	Day	6% 4 20% 37% 25% 7%	726
	11th to 20th	Day	13% 3 17% 30% 27% 10%	524
	21st to end	Day	12% 5% 19% 31% 25% 9%	583
September	1st to 10th	Day	13% 7% 23% 30% 19% 8%	530
	11th to 20th	Day	10% 3 20% 33% 26% 8%	530
	21st to end	Day	14% 7% 27% 26% 20% 5%	530
October	1st to 10th	Day	17% 11% 26% 24% 19% 3	475
	11th to 20th	Day	17% 19% 32% 25% 7% 1	330
	21st to end	Day	19% 14% 36% 25% 6% 1	363
November	1st to 10th	Day	17% 13% 32% 25% 11% 2	330
	11th to 20th	Day	17% 16% 37% 22% 8% 1	330
	21st to end	Day	21% 12% 42% 20% 5%	330
December	1st to 10th	Day	14% 14% 43% 21% 8% 1	330
	11th to 20th	Day	20% 19% 40% 15% 5% 1	330
	21st to end	Day	26% 15% 36% 17% 6% 1	363
January	1st to 10th	Night	15% 13% 40% 26% 6%	1050
	11th to 20th	Night	18% 12% 38% 24% 8%	1050
	21st to end	Night	16% 10% 38% 27% 8%	1155
February	1st to 10th	Night	16% 12% 38% 27% 7% 1	1050
	11th to 20th	Night	14% 12% 40% 27% 7%	830
	21st to end	Night	18% 10% 39% 29% 4	692
March	1st to 10th	Night	17% 9% 33% 32% 8% 1	840
	11th to 20th	Night	15% 10% 37% 30% 7% 1	840
	21st to end	Night	19% 8% 31% 32% 9% 1	704
April	1st to 10th	Night	19% 10% 36% 30% 6%	630
	11th to 20th	Night	24% 7% 29% 29% 10% 1	623
	21st to end	Night	17% 7% 32% 32% 11% 1	630
May	1st to 10th	Night	18% 4 30% 37% 10% 1	630
	11th to 20th	Night	15% 5% 29% 35% 14% 1	621
	21st to end	Night	12% 7% 20% 37% 21% 2	683
June	1st to 10th	Night	11% 4 21% 43% 19% 1	630
	11th to 20th	Night	15% 4 25% 37% 18% 1	630
	21st to end	Night	12% 3 19% 44% 21% 1	630
July	1st to 10th	Night	7% 3 16% 43% 28% 4	615
	11th to 20th	Night	8% 1 19% 40% 28% 3	612
	21st to end	Night	6% 2 18% 48% 24% 2	687
August	1st to 10th	Night	8% 3 16% 43% 27% 4	597
	11th to 20th	Night	9% 1 15% 39% 30% 6%	594
	21st to end	Night	9% 3 20% 38% 28% 3	660
September	1st to 10th	Night	10% 4 22% 34% 25% 6%	600
	11th to 20th	Night	11% 5% 19% 34% 25% 6%	715
	21st to end	Night	13% 8% 23% 30% 24% 3	800
October	1st to 10th	Night	16% 7% 28% 28% 20% 2	800
	11th to 20th	Night	20% 11% 31% 29% 10%	800
	21st to end	Night	22% 11% 30% 27% 10% 1	880
November	1st to 10th	Night	17% 10% 36% 30% 6% 1	820
	11th to 20th	Night	17% 16% 36% 25% 6%	840
	21st to end	Night	19% 13% 37% 24% 6%	1013
December	1st to 10th	Night	18% 13% 40% 23% 6%	1050
	11th to 20th	Night	21% 12% 37% 23% 5% 1	1050
	21st to end	Night	26% 11% 35% 23% 4	1155

Page generated at 2026-07-28 02:25:21. Version ac07

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