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 2025-03-27.

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% 9% 3 7% 5% 4 4 4 6% 7% 38%	108999
	Night	13% 9% 3 7% 5% 4 4 4 5% 7% 39%	110548
Transparency	Day	44% 4 12% 25% 13% 1	112531
	Night	45% 3 12% 24% 14% 2	115157
Seeing	Day	15% 9% 28% 29% 15% 4	16407
	Night	16% 8% 30% 31% 13% 1	26467

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	9% 9% 3 13% 6% 5% 6% 4 5% 6% 34%	3617
	11th to 20th	Day	12% 12% 4 8% 5% 4 4 4 5% 6% 36%	3620
	21st to end	Day	15% 14% 6% 9% 5% 4 3 3 5% 6% 31%	3982
February	1st to 10th	Day	9% 11% 5% 10% 6% 5% 4 4 6% 8% 32%	1732
	11th to 20th	Day	12% 11% 4 8% 5% 4 4 3 5% 7% 36%	1939
	21st to end	Day	12% 11% 4 8% 5% 5% 5% 4 6% 7% 33%	1650
March	1st to 10th	Day	12% 10% 3 5% 4 3 4 3 5% 6% 45%	3220
	11th to 20th	Day	10% 9% 3 8% 4 5% 5% 4 5% 7% 40%	3362
	21st to end	Day	20% 13% 4 10% 5% 4 4 3 4 4 30%	4237
April	1st to 10th	Day	14% 12% 4 9% 6% 5% 4 4 6% 6% 30%	2280
	11th to 20th	Day	19% 10% 3 6% 4 4 4 3 6% 5% 36%	2254
	21st to end	Day	16% 10% 3 8% 4 4 5% 4 5% 7% 34%	2461
May	1st to 10th	Day	14% 7% 2 7% 5% 5% 4 4 5% 6% 41%	4132
	11th to 20th	Day	11% 6% 3 7% 4 4 4 3 6% 7% 45%	4399
	21st to end	Day	11% 7% 3 7% 5% 5% 4 4 6% 8% 41%	4824
June	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 7% 7% 46%	2660
	11th to 20th	Day	12% 6% 2 7% 5% 4 5% 4 6% 9% 42%	2660
	21st to end	Day	11% 5% 3 5% 4 4 5% 5% 7% 9% 42%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 7% 10% 38%	4440
	11th to 20th	Day	5% 3 1 5% 4 5% 6% 5% 8% 10% 49%	4440
	21st to end	Day	7% 6% 2 6% 4 4 5% 4 6% 8% 48%	4813
August	1st to 10th	Day	8% 6% 3 6% 4 5% 6% 4 7% 9% 43%	4423
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 5% 8% 48%	3954
	21st to end	Day	11% 5% 2 7% 5% 5% 4 4 6% 8% 43%	4180
September	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 6% 7% 44%	2280
	11th to 20th	Day	11% 4 2 6% 4 4 4 3 6% 8% 47%	2152
	21st to end	Day	11% 7% 3 7% 6% 4 4 4 6% 8% 39%	2090
October	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 4 6% 45%	2038
	11th to 20th	Day	19% 10% 2 9% 4 6% 4 3 6% 7% 29%	1825
	21st to end	Day	16% 9% 4 8% 6% 5% 5% 4 6% 6% 32%	1881
November	1st to 10th	Day	15% 7% 2 7% 4 4 3 4 6% 7% 41%	1762
	11th to 20th	Day	12% 11% 4 10% 6% 4 6% 4 6% 7% 30%	1800
	21st to end	Day	17% 11% 4 7% 5% 4 4 5% 5% 8% 31%	1632
December	1st to 10th	Day	10% 11% 4 8% 5% 6% 5% 5% 8% 8% 30%	2610
	11th to 20th	Day	13% 15% 4 9% 6% 5% 5% 3 6% 6% 28%	3008
	21st to end	Day	19% 19% 6% 12% 5% 4 3 3 4 5% 19%	3982
January	1st to 10th	Night	9% 11% 4 9% 5% 4 4 3 4 5% 42%	6348
	11th to 20th	Night	10% 13% 4 9% 6% 6% 4 4 5% 6% 33%	6360
	21st to end	Night	10% 13% 6% 8% 4 5% 5% 4 5% 7% 34%	6996
February	1st to 10th	Night	11% 13% 4 9% 6% 5% 4 4 5% 6% 33%	2665
	11th to 20th	Night	11% 10% 4 9% 5% 5% 5% 4 5% 6% 36%	2345
	21st to end	Night	14% 13% 4 8% 4 3 4 3 4 7% 36%	1980
March	1st to 10th	Night	14% 8% 2 6% 4 3 4 3 5% 6% 44%	3853
	11th to 20th	Night	9% 8% 3 8% 5% 6% 5% 4 5% 7% 40%	3836
	21st to end	Night	17% 10% 3 9% 5% 4 4 4 4 5% 33%	3542
April	1st to 10th	Night	15% 12% 3 7% 5% 4 4 4 4 6% 35%	1900
	11th to 20th	Night	18% 9% 2 5% 4 4 4 3 5% 6% 40%	1875
	21st to end	Night	16% 10% 3 7% 5% 5% 3 3 5% 6% 36%	1718
May	1st to 10th	Night	14% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	2763
	11th to 20th	Night	11% 6% 2 7% 4 5% 5% 5% 6% 8% 41%	2506
	21st to end	Night	16% 6% 2 7% 5% 5% 4 3 6% 7% 39%	2743
June	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 7% 8% 45%	1520
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 7% 9% 44%	1520
	21st to end	Night	9% 5% 2 5% 4 4 5% 4 6% 9% 47%	1520
July	1st to 10th	Night	12% 7% 2 7% 5% 4 5% 3 6% 7% 43%	2530
	11th to 20th	Night	5% 3 1 4 3 3 4 4 6% 8% 58%	2530
	21st to end	Night	5% 5% 2 6% 5% 5% 5% 3 6% 8% 51%	2750
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 9% 45%	2517
	11th to 20th	Night	10% 5% 2 6% 4 3 4 3 5% 7% 50%	2870
	21st to end	Night	11% 6% 2 6% 4 5% 4 3 5% 7% 48%	3476
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 5% 7% 54%	1900
	11th to 20th	Night	10% 4 1 5% 3 3 4 3 5% 7% 54%	2009
	21st to end	Night	13% 6% 2 7% 5% 4 3 3 5% 7% 45%	2090
October	1st to 10th	Night	13% 6% 2 6% 3 4 4 3 5% 6% 47%	2139
	11th to 20th	Night	15% 8% 4 6% 5% 4 5% 4 5% 8% 38%	2354
	21st to end	Night	19% 9% 3 6% 4 4 4 4 5% 7% 34%	2717
November	1st to 10th	Night	13% 7% 2 6% 5% 4 4 4 5% 7% 45%	2536
	11th to 20th	Night	14% 10% 4 8% 6% 4 4 4 6% 7% 35%	2600
	21st to end	Night	15% 11% 2 6% 5% 5% 4 4 5% 7% 35%	2765
December	1st to 10th	Night	12% 9% 3 7% 4 4 4 3 6% 8% 39%	4580
	11th to 20th	Night	14% 15% 5% 10% 6% 5% 4 3 4 5% 28%	5199
	21st to end	Night	21% 16% 6% 9% 4 4 4 3 5% 5% 23%	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	50% 3 15% 21% 11% 1	3618
	11th to 20th	Day	49% 2 10% 24% 14% 2	3620
	21st to end	Day	55% 2 9% 20% 13%	3982
February	1st to 10th	Day	51% 4 11% 22% 11% 1	1732
	11th to 20th	Day	48% 3 11% 23% 14% 2	1949
	21st to end	Day	50% 4 12% 22% 10% 2	1650
March	1st to 10th	Day	41% 3 12% 24% 17% 3	3220
	11th to 20th	Day	44% 3 11% 24% 15% 2	3362
	21st to end	Day	59% 2 9% 21% 8% 1	4237
April	1st to 10th	Day	55% 4 11% 19% 12%	2280
	11th to 20th	Day	50% 4 8% 22% 13% 2	2254
	21st to end	Day	49% 3 11% 21% 13% 2	2461
May	1st to 10th	Day	44% 3 9% 27% 15% 1	4170
	11th to 20th	Day	39% 2 10% 32% 15% 2	4403
	21st to end	Day	43% 3 11% 23% 16% 4	4837
June	1st to 10th	Day	36% 4 12% 30% 16% 2	2660
	11th to 20th	Day	39% 4 15% 25% 16% 2	2660
	21st to end	Day	37% 5% 16% 25% 15% 1	2660
July	1st to 10th	Day	41% 5% 14% 27% 11% 2	4371
	11th to 20th	Day	27% 6% 16% 34% 15% 2	4365
	21st to end	Day	33% 5% 13% 26% 21% 2	4662
August	1st to 10th	Day	38% 5% 14% 29% 14% 1	4408
	11th to 20th	Day	34% 5% 14% 34% 12% 1	3993
	21st to end	Day	39% 5% 16% 24% 16% 1	4179
September	1st to 10th	Day	39% 5% 13% 29% 14% 1	2280
	11th to 20th	Day	35% 4 15% 34% 11% 1	2152
	21st to end	Day	42% 4 14% 30% 10% 1	2090
October	1st to 10th	Day	25% 2 11% 36% 23% 3	3389
	11th to 20th	Day	48% 4 8% 25% 14% 1	3015
	21st to end	Day	44% 4 12% 28% 12%	3081
November	1st to 10th	Day	42% 4 12% 27% 14% 1	1762
	11th to 20th	Day	52% 4 15% 20% 9% 1	1800
	21st to end	Day	51% 4 16% 23% 6%	1632
December	1st to 10th	Day	48% 5% 17% 24% 5%	2610
	11th to 20th	Day	56% 3 12% 17% 11% 2	3005
	21st to end	Day	69% 2 6% 17% 6%	3982
January	1st to 10th	Night	46% 2 10% 28% 14% 1	6348
	11th to 20th	Night	53% 2 9% 18% 16% 2	6360
	21st to end	Night	51% 3 14% 20% 12%	6996
February	1st to 10th	Night	53% 3 8% 21% 12% 2	2665
	11th to 20th	Night	49% 3 11% 23% 12% 2	2346
	21st to end	Night	50% 3 12% 23% 12% 1	1980
March	1st to 10th	Night	42% 2 15% 30% 10% 2	3853
	11th to 20th	Night	44% 2 10% 26% 17% 2	3836
	21st to end	Night	55% 2 9% 21% 10% 2	3542
April	1st to 10th	Night	50% 4 7% 20% 17% 1	1900
	11th to 20th	Night	46% 2 8% 24% 17% 3	1875
	21st to end	Night	49% 2 9% 23% 14% 2	1718
May	1st to 10th	Night	45% 3 13% 20% 19% 2	2790
	11th to 20th	Night	42% 2 11% 29% 14% 2	2507
	21st to end	Night	45% 3 11% 20% 14% 7%	2751
June	1st to 10th	Night	36% 5% 11% 30% 17% 1	1520
	11th to 20th	Night	36% 5% 10% 29% 18% 2	1520
	21st to end	Night	34% 5% 16% 28% 15% 3	1520
July	1st to 10th	Night	42% 4 14% 25% 11% 5%	2490
	11th to 20th	Night	23% 4 17% 35% 18% 2	2482
	21st to end	Night	30% 5% 12% 25% 24% 3	2662
August	1st to 10th	Night	35% 5% 13% 28% 18% 1	2508
	11th to 20th	Night	34% 4 12% 32% 17% 1	2897
	21st to end	Night	35% 5% 12% 23% 22% 2	3476
September	1st to 10th	Night	29% 4 13% 31% 21% 2	1900
	11th to 20th	Night	31% 2 13% 37% 16% 1	2009
	21st to end	Night	39% 3 12% 29% 15% 1	2090
October	1st to 10th	Night	29% 2 9% 38% 19% 1	3568
	11th to 20th	Night	37% 3 15% 26% 17% 2	3903
	21st to end	Night	44% 4 12% 25% 16%	4467
November	1st to 10th	Night	39% 3 12% 28% 17% 1	2536
	11th to 20th	Night	48% 3 13% 21% 13% 1	2600
	21st to end	Night	47% 4 15% 26% 7% 1	2765
December	1st to 10th	Night	43% 4 23% 23% 6% 1	4580
	11th to 20th	Night	59% 3 11% 14% 12% 1	5201
	21st to end	Night	64% 3 9% 15% 9%	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	14% 12% 33% 29% 10% 2	300
	11th to 20th	Day	23% 10% 35% 24% 8% 1	300
	21st to end	Day	21% 12% 29% 30% 8% 1	330
February	1st to 10th	Day	14% 13% 41% 23% 7% 2	300
	11th to 20th	Day	13% 16% 45% 19% 7%	300
	21st to end	Day	18% 14% 41% 23% 2 1	249
March	1st to 10th	Day	15% 18% 38% 25% 4	300
	11th to 20th	Day	17% 15% 32% 26% 9% 2	345
	21st to end	Day	23% 10% 29% 27% 9% 2	530
April	1st to 10th	Day	21% 13% 30% 28% 7% 1	460
	11th to 20th	Day	21% 15% 28% 25% 9% 2	452
	21st to end	Day	18% 9% 32% 26% 13% 2	460
May	1st to 10th	Day	17% 9% 34% 26% 11% 1	487
	11th to 20th	Day	17% 7% 29% 33% 11% 3	675
	21st to end	Day	12% 6% 29% 29% 18% 6%	734
June	1st to 10th	Day	10% 6% 29% 34% 17% 4	680
	11th to 20th	Day	14% 7% 24% 35% 17% 3	680
	21st to end	Day	11% 7% 23% 36% 19% 3	680
July	1st to 10th	Day	8% 3 17% 37% 26% 8%	671
	11th to 20th	Day	8% 4 23% 38% 22% 7%	668
	21st to end	Day	6% 3 20% 38% 25% 7%	739
August	1st to 10th	Day	6% 4 20% 37% 25% 7%	676
	11th to 20th	Day	12% 2 15% 30% 29% 11%	484
	21st to end	Day	12% 5% 19% 30% 26% 9%	539
September	1st to 10th	Day	13% 7% 23% 30% 20% 7%	490
	11th to 20th	Day	10% 3 21% 33% 24% 8%	490
	21st to end	Day	14% 7% 27% 26% 20% 5%	490
October	1st to 10th	Day	18% 11% 26% 23% 19% 3	438
	11th to 20th	Day	17% 19% 30% 25% 7% 1	300
	21st to end	Day	21% 15% 37% 22% 5% 1	330
November	1st to 10th	Day	17% 12% 32% 25% 11% 2	300
	11th to 20th	Day	16% 15% 37% 23% 8%	300
	21st to end	Day	22% 11% 41% 21% 5%	300
December	1st to 10th	Day	15% 13% 43% 21% 7% 1	300
	11th to 20th	Day	21% 17% 40% 16% 5% 1	300
	21st to end	Day	25% 14% 36% 18% 6% 1	330
January	1st to 10th	Night	15% 13% 40% 26% 6%	1000
	11th to 20th	Night	18% 12% 37% 25% 8% 1	1000
	21st to end	Night	17% 9% 37% 28% 8%	1100
February	1st to 10th	Night	16% 12% 38% 27% 7% 1	1000
	11th to 20th	Night	14% 12% 40% 27% 7%	790
	21st to end	Night	18% 10% 39% 29% 4	660
March	1st to 10th	Night	17% 8% 34% 32% 9% 1	800
	11th to 20th	Night	14% 10% 37% 31% 8% 1	800
	21st to end	Night	20% 7% 29% 34% 10% 1	657
April	1st to 10th	Night	18% 9% 37% 31% 6% 1	570
	11th to 20th	Night	23% 7% 29% 30% 10% 1	563
	21st to end	Night	17% 7% 31% 32% 12% 1	570
May	1st to 10th	Night	19% 4 29% 37% 11% 1	570
	11th to 20th	Night	16% 4 28% 36% 14% 1	561
	21st to end	Night	12% 6% 19% 38% 22% 3	617
June	1st to 10th	Night	12% 4 21% 43% 20% 1	570
	11th to 20th	Night	14% 3 24% 38% 20% 2	570
	21st to end	Night	11% 3 18% 44% 23% 1	570
July	1st to 10th	Night	6% 2 16% 42% 29% 4	555
	11th to 20th	Night	9% 1 19% 39% 29% 4	552
	21st to end	Night	6% 2 17% 47% 26% 2	624
August	1st to 10th	Night	8% 3 16% 43% 27% 4	567
	11th to 20th	Night	8% 1 15% 39% 30% 6%	564
	21st to end	Night	10% 3 20% 37% 27% 3	627
September	1st to 10th	Night	10% 4 22% 35% 24% 6%	570
	11th to 20th	Night	11% 5% 20% 34% 24% 5%	679
	21st to end	Night	13% 8% 23% 29% 23% 3	760
October	1st to 10th	Night	16% 8% 27% 27% 20% 2	760
	11th to 20th	Night	20% 11% 30% 29% 10%	760
	21st to end	Night	23% 11% 31% 27% 9% 1	836
November	1st to 10th	Night	17% 9% 36% 31% 6% 1	780
	11th to 20th	Night	18% 16% 35% 25% 6%	800
	21st to end	Night	19% 12% 38% 24% 7%	965
December	1st to 10th	Night	18% 13% 40% 23% 6%	1000
	11th to 20th	Night	22% 11% 37% 23% 6% 1	1000
	21st to end	Night	26% 11% 35% 23% 4	1100

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