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 2024-02-15.

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	13% 8% 4 6% 6% 3 5% 5% 6% 8% 37%	78211
	Night	13% 9% 4 6% 6% 3 4 5% 5% 7% 38%	80922
Transparency	Day	31% 37% 9% 15% 7% 1	77912
	Night	32% 35% 9% 15% 7% 1	80742
Seeing	Day	15% 8% 28% 30% 16% 4	14883
	Night	16% 8% 30% 31% 13% 1	24947

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	13% 11% 5% 9% 7% 3 6% 5% 6% 7% 30%	2527
	11th to 20th	Day	14% 12% 5% 9% 8% 4 6% 6% 6% 7% 24%	2530
	21st to end	Day	18% 15% 7% 9% 7% 3 4 4 5% 6% 22%	2783
February	1st to 10th	Day	10% 10% 6% 8% 7% 3 5% 5% 6% 6% 33%	1645
	11th to 20th	Day	12% 10% 4 6% 7% 3 4 4 5% 7% 37%	1779
	21st to end	Day	13% 10% 4 7% 7% 4 5% 5% 6% 6% 32%	1480
March	1st to 10th	Day	13% 10% 5% 6% 4 3 5% 4 5% 7% 38%	1800
	11th to 20th	Day	11% 9% 5% 7% 5% 3 4 5% 5% 7% 39%	1844
	21st to end	Day	16% 10% 4 7% 7% 4 5% 5% 5% 6% 32%	2376
April	1st to 10th	Day	14% 11% 5% 8% 6% 3 5% 5% 6% 6% 30%	2160
	11th to 20th	Day	20% 9% 4 5% 5% 3 4 4 6% 5% 35%	2134
	21st to end	Day	17% 9% 3 7% 5% 3 5% 5% 5% 7% 33%	2331
May	1st to 10th	Day	15% 7% 2 7% 6% 3 5% 5% 5% 7% 37%	2362
	11th to 20th	Day	15% 6% 3 6% 6% 3 4 4 5% 7% 40%	2479
	21st to end	Day	10% 6% 3 5% 6% 3 6% 5% 6% 8% 42%	2725
June	1st to 10th	Day	10% 5% 2 5% 5% 4 4 5% 7% 8% 46%	2520
	11th to 20th	Day	12% 5% 2 6% 5% 3 5% 5% 5% 10% 43%	2520
	21st to end	Day	10% 4 3 4 5% 3 6% 5% 6% 9% 43%	2520
July	1st to 10th	Day	6% 3 2 4 4 3 5% 5% 8% 12% 48%	2520
	11th to 20th	Day	8% 3 2 5% 5% 3 5% 6% 6% 9% 48%	2520
	21st to end	Day	6% 4 2 5% 5% 3 5% 6% 7% 8% 48%	2743
August	1st to 10th	Day	7% 4 2 4 5% 4 6% 6% 7% 10% 45%	2507
	11th to 20th	Day	9% 4 2 5% 5% 3 4 6% 6% 9% 46%	2255
	21st to end	Day	11% 5% 2 5% 5% 4 4 5% 5% 9% 46%	2376
September	1st to 10th	Day	12% 6% 3 5% 4 3 4 5% 6% 8% 43%	2160
	11th to 20th	Day	12% 4 2 5% 4 3 4 4 6% 8% 47%	2039
	21st to end	Day	11% 7% 3 6% 7% 3 4 5% 6% 9% 37%	1980
October	1st to 10th	Day	16% 7% 2 5% 4 4 4 5% 4 6% 43%	1931
	11th to 20th	Day	20% 9% 3 8% 5% 4 4 5% 5% 7% 29%	1729
	21st to end	Day	16% 9% 4 7% 7% 4 5% 5% 5% 6% 31%	1782
November	1st to 10th	Day	14% 6% 2 6% 6% 3 4 5% 6% 8% 41%	1672
	11th to 20th	Day	12% 10% 5% 9% 8% 3 6% 5% 6% 7% 30%	1710
	21st to end	Day	17% 10% 5% 6% 5% 3 4 6% 5% 8% 31%	1551
December	1st to 10th	Day	13% 11% 4 7% 6% 3 5% 6% 8% 9% 29%	1520
	11th to 20th	Day	16% 12% 4 7% 6% 3 5% 5% 7% 7% 27%	1918
	21st to end	Day	18% 17% 7% 11% 8% 4 4 4 4 5% 18%	2783
January	1st to 10th	Night	13% 13% 5% 8% 6% 3 4 3 3 5% 35%	4428
	11th to 20th	Night	11% 13% 5% 9% 8% 4 6% 5% 5% 6% 27%	4440
	21st to end	Night	14% 15% 8% 9% 6% 3 4 4 4 6% 26%	4884
February	1st to 10th	Night	11% 12% 5% 8% 7% 4 4 5% 5% 5% 34%	2532
	11th to 20th	Night	11% 9% 5% 8% 6% 3 5% 5% 5% 6% 37%	2160
	21st to end	Night	15% 13% 5% 7% 5% 2 4 4 4 6% 35%	1776
March	1st to 10th	Night	13% 8% 3 6% 6% 3 4 5% 5% 6% 40%	2160
	11th to 20th	Night	12% 7% 3 5% 6% 4 4 5% 5% 6% 43%	2120
	21st to end	Night	17% 8% 4 6% 5% 3 5% 5% 4 5% 37%	1990
April	1st to 10th	Night	15% 11% 4 6% 7% 4 5% 5% 4 6% 35%	1800
	11th to 20th	Night	19% 8% 3 5% 4 3 4 4 5% 7% 39%	1775
	21st to end	Night	17% 10% 3 6% 6% 3 4 4 5% 7% 36%	1628
May	1st to 10th	Night	16% 6% 2 7% 7% 4 6% 5% 7% 7% 33%	1596
	11th to 20th	Night	16% 7% 3 6% 4 3 4 5% 5% 7% 40%	1416
	21st to end	Night	12% 6% 2 5% 5% 3 4 4 7% 10% 43%	1551
June	1st to 10th	Night	11% 5% 3 4 4 3 5% 4 7% 9% 45%	1440
	11th to 20th	Night	12% 6% 3 4 5% 3 4 4 6% 9% 44%	1440
	21st to end	Night	8% 4 2 5% 5% 3 5% 6% 6% 9% 48%	1440
July	1st to 10th	Night	6% 3 1 5% 6% 2 4 5% 7% 8% 54%	1440
	11th to 20th	Night	7% 4 2 5% 4 2 4 5% 6% 9% 51%	1440
	21st to end	Night	5% 4 2 4 4 4 4 5% 5% 8% 54%	1575
August	1st to 10th	Night	8% 4 2 4 5% 3 5% 5% 6% 9% 48%	1432
	11th to 20th	Night	7% 4 2 4 5% 3 5% 5% 6% 8% 52%	1641
	21st to end	Night	9% 5% 2 5% 4 3 4 4 5% 6% 52%	1980
September	1st to 10th	Night	9% 5% 2 4 4 2 3 5% 5% 7% 53%	1800
	11th to 20th	Night	11% 4 2 4 4 1 4 4 4 7% 55%	1903
	21st to end	Night	13% 6% 2 6% 6% 3 4 4 5% 7% 44%	1980
October	1st to 10th	Night	14% 7% 2 5% 4 3 4 4 5% 7% 46%	2026
	11th to 20th	Night	15% 7% 4 6% 6% 3 5% 5% 5% 7% 37%	2230
	21st to end	Night	19% 9% 3 5% 5% 3 4 5% 5% 8% 34%	2574
November	1st to 10th	Night	12% 7% 2 5% 5% 3 4 5% 4 8% 45%	2406
	11th to 20th	Night	14% 9% 4 7% 7% 3 5% 5% 6% 7% 35%	2470
	21st to end	Night	16% 10% 3 5% 5% 4 4 5% 5% 7% 36%	2626
December	1st to 10th	Night	14% 10% 4 8% 6% 4 5% 5% 6% 8% 31%	2660
	11th to 20th	Night	14% 12% 5% 7% 7% 4 4 5% 5% 6% 32%	3279
	21st to end	Night	21% 18% 6% 7% 5% 3 4 4 4 5% 21%	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	44% 29% 11% 11% 4	2528
	11th to 20th	Day	45% 29% 10% 14% 2	2530
	21st to end	Day	52% 24% 9% 12% 3	2783
February	1st to 10th	Day	34% 36% 8% 15% 6%	1645
	11th to 20th	Day	31% 37% 9% 15% 8% 1	1789
	21st to end	Day	35% 37% 7% 14% 6% 1	1480
March	1st to 10th	Day	32% 38% 10% 14% 5% 1	1800
	11th to 20th	Day	29% 39% 10% 14% 7% 1	1844
	21st to end	Day	36% 38% 8% 14% 4	2376
April	1st to 10th	Day	35% 37% 9% 13% 7%	2160
	11th to 20th	Day	33% 36% 6% 16% 8% 1	2134
	21st to end	Day	34% 38% 8% 12% 7% 1	2331
May	1st to 10th	Day	32% 39% 8% 15% 6% 1	2362
	11th to 20th	Day	27% 38% 7% 16% 10% 2	2483
	21st to end	Day	25% 40% 8% 17% 8% 2	2725
June	1st to 10th	Day	25% 38% 9% 17% 10% 1	2520
	11th to 20th	Day	23% 38% 9% 17% 12% 1	2520
	21st to end	Day	24% 39% 10% 16% 10% 1	2520
July	1st to 10th	Day	19% 40% 9% 21% 9% 1	2451
	11th to 20th	Day	20% 41% 9% 18% 10% 2	2445
	21st to end	Day	23% 40% 9% 17% 9% 2	2591
August	1st to 10th	Day	23% 39% 11% 18% 7% 1	2492
	11th to 20th	Day	19% 37% 11% 20% 11% 1	2255
	21st to end	Day	21% 38% 10% 18% 12% 1	2376
September	1st to 10th	Day	25% 38% 8% 20% 9% 1	2160
	11th to 20th	Day	25% 39% 10% 22% 4	2039
	21st to end	Day	28% 38% 11% 17% 6%	1980
October	1st to 10th	Day	25% 37% 9% 21% 7% 1	1931
	11th to 20th	Day	38% 37% 8% 12% 3 1	1729
	21st to end	Day	34% 39% 8% 12% 7%	1782
November	1st to 10th	Day	25% 41% 9% 15% 9% 1	1672
	11th to 20th	Day	35% 41% 8% 10% 5%	1710
	21st to end	Day	30% 40% 13% 14% 3	1551
December	1st to 10th	Day	33% 43% 9% 13% 3	1520
	11th to 20th	Day	38% 35% 12% 11% 2 2	1915
	21st to end	Day	55% 27% 6% 10% 2	2783
January	1st to 10th	Night	43% 26% 8% 17% 5% 1	4428
	11th to 20th	Night	46% 27% 8% 16% 4	4440
	21st to end	Night	50% 24% 10% 13% 4	4884
February	1st to 10th	Night	34% 35% 7% 15% 8% 1	2532
	11th to 20th	Night	33% 36% 8% 13% 7% 1	2161
	21st to end	Night	36% 36% 8% 13% 5% 1	1776
March	1st to 10th	Night	29% 37% 10% 18% 6%	2160
	11th to 20th	Night	27% 38% 8% 16% 9% 2	2120
	21st to end	Night	34% 38% 7% 15% 6%	1990
April	1st to 10th	Night	33% 37% 6% 14% 10% 1	1800
	11th to 20th	Night	29% 35% 5% 17% 12% 1	1775
	21st to end	Night	32% 37% 7% 15% 8% 1	1628
May	1st to 10th	Night	32% 37% 9% 12% 9% 1	1596
	11th to 20th	Night	29% 38% 6% 14% 11% 2	1417
	21st to end	Night	25% 40% 9% 14% 12% 1	1552
June	1st to 10th	Night	24% 38% 8% 18% 11% 1	1440
	11th to 20th	Night	21% 37% 7% 21% 13% 1	1440
	21st to end	Night	21% 39% 11% 17% 9% 3	1440
July	1st to 10th	Night	18% 39% 10% 20% 11% 1	1400
	11th to 20th	Night	19% 39% 9% 17% 12% 3	1392
	21st to end	Night	18% 40% 12% 18% 10% 1	1487
August	1st to 10th	Night	21% 38% 9% 22% 9% 1	1423
	11th to 20th	Night	18% 37% 10% 21% 13% 1	1641
	21st to end	Night	21% 38% 8% 16% 15% 2	1980
September	1st to 10th	Night	19% 37% 7% 20% 16% 1	1800
	11th to 20th	Night	21% 37% 10% 25% 7%	1903
	21st to end	Night	26% 38% 10% 18% 8% 1	1980
October	1st to 10th	Night	22% 38% 8% 22% 9% 1	2026
	11th to 20th	Night	32% 38% 10% 12% 6% 1	2230
	21st to end	Night	31% 38% 10% 13% 7%	2574
November	1st to 10th	Night	21% 42% 9% 17% 10% 1	2406
	11th to 20th	Night	32% 40% 9% 11% 7% 1	2470
	21st to end	Night	29% 40% 11% 17% 3	2626
December	1st to 10th	Night	33% 42% 10% 12% 4	2660
	11th to 20th	Night	38% 35% 10% 11% 5%	3281
	21st to end	Night	53% 27% 8% 10% 2	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	15% 11% 31% 29% 11% 2	270
	11th to 20th	Day	24% 7% 35% 24% 9% 1	270
	21st to end	Day	21% 8% 29% 32% 9% 1	297
February	1st to 10th	Day	13% 12% 41% 24% 8% 2	270
	11th to 20th	Day	12% 15% 45% 19% 8%	252
	21st to end	Day	19% 14% 42% 22% 2 1	198
March	1st to 10th	Day	15% 17% 38% 26% 4	240
	11th to 20th	Day	18% 10% 31% 29% 10% 3	280
	21st to end	Day	22% 10% 30% 26% 10% 2	462
April	1st to 10th	Day	20% 13% 29% 29% 8% 1	420
	11th to 20th	Day	21% 15% 27% 25% 10% 3	412
	21st to end	Day	18% 9% 31% 26% 14% 2	420
May	1st to 10th	Day	18% 9% 34% 27% 11% 2	445
	11th to 20th	Day	18% 7% 29% 32% 10% 3	625
	21st to end	Day	13% 5% 28% 29% 19% 6%	679
June	1st to 10th	Day	10% 5% 28% 34% 18% 4	630
	11th to 20th	Day	14% 5% 23% 36% 18% 3	630
	21st to end	Day	10% 6% 21% 38% 20% 3	630
July	1st to 10th	Day	7% 2 16% 38% 27% 9%	621
	11th to 20th	Day	8% 3 22% 38% 21% 7%	618
	21st to end	Day	6% 3 21% 38% 25% 7%	684
August	1st to 10th	Day	7% 3 19% 38% 26% 8%	626
	11th to 20th	Day	13% 3 15% 29% 30% 11%	444
	21st to end	Day	13% 4 18% 31% 25% 9%	495
September	1st to 10th	Day	14% 7% 21% 30% 20% 8%	450
	11th to 20th	Day	11% 4 21% 33% 23% 8%	450
	21st to end	Day	14% 8% 27% 25% 21% 6%	450
October	1st to 10th	Day	19% 10% 24% 23% 20% 3	401
	11th to 20th	Day	18% 19% 30% 24% 7% 1	270
	21st to end	Day	22% 13% 36% 22% 5% 1	297
November	1st to 10th	Day	16% 11% 31% 27% 13% 3	270
	11th to 20th	Day	14% 16% 38% 24% 9%	270
	21st to end	Day	21% 11% 40% 22% 6%	270
December	1st to 10th	Day	15% 12% 43% 22% 7% 1	270
	11th to 20th	Day	21% 15% 41% 16% 6% 1	270
	21st to end	Day	25% 14% 37% 18% 6%	297
January	1st to 10th	Night	15% 13% 40% 26% 6%	950
	11th to 20th	Night	18% 12% 36% 25% 8% 1	950
	21st to end	Night	17% 8% 37% 29% 9%	1045
February	1st to 10th	Night	16% 11% 38% 28% 7% 1	950
	11th to 20th	Night	14% 11% 41% 27% 7%	729
	21st to end	Night	20% 10% 39% 28% 4	592
March	1st to 10th	Night	16% 7% 33% 33% 9% 1	720
	11th to 20th	Night	14% 9% 37% 31% 8% 1	720
	21st to end	Night	20% 7% 28% 34% 11% 1	604
April	1st to 10th	Night	18% 8% 37% 30% 6% 1	540
	11th to 20th	Night	23% 6% 28% 30% 11% 2	533
	21st to end	Night	17% 6% 31% 33% 12% 1	540
May	1st to 10th	Night	19% 4 29% 36% 11% 1	540
	11th to 20th	Night	17% 5% 28% 35% 14% 1	531
	21st to end	Night	12% 5% 20% 39% 22% 3	584
June	1st to 10th	Night	12% 4 20% 43% 20% 1	540
	11th to 20th	Night	14% 2 24% 38% 20% 2	540
	21st to end	Night	10% 2 18% 45% 24% 1	540
July	1st to 10th	Night	6% 2 15% 42% 30% 4	525
	11th to 20th	Night	9% 1 19% 38% 29% 4	522
	21st to end	Night	6% 1 17% 47% 26% 2	591
August	1st to 10th	Night	8% 2 16% 43% 27% 4	537
	11th to 20th	Night	8% 1 15% 38% 31% 7%	534
	21st to end	Night	10% 3 19% 37% 28% 3	594
September	1st to 10th	Night	10% 3 21% 34% 25% 6%	540
	11th to 20th	Night	12% 5% 20% 34% 23% 5%	643
	21st to end	Night	14% 9% 23% 28% 23% 3	720
October	1st to 10th	Night	17% 7% 27% 27% 21% 2	720
	11th to 20th	Night	20% 12% 30% 28% 10%	720
	21st to end	Night	23% 10% 31% 26% 9% 1	792
November	1st to 10th	Night	16% 9% 36% 31% 7% 1	740
	11th to 20th	Night	17% 17% 35% 25% 6%	760
	21st to end	Night	19% 12% 37% 25% 7%	916
December	1st to 10th	Night	18% 12% 41% 23% 6%	950
	11th to 20th	Night	21% 11% 37% 24% 5% 1	950
	21st to end	Night	26% 12% 36% 23% 4	1045

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