N5PA Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the N5PA Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	11% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	101017
	Night	12% 6% 2 6% 4 4 4 4 6% 7% 44%	98413
Transparency	Day	39% 5% 11% 19% 18% 7%	104804
	Night	37% 5% 11% 19% 19% 9%	102765
Seeing	Day	15% 8% 20% 24% 22% 11%	14834
	Night	14% 7% 22% 29% 22% 5%	24403

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	16% 8% 3 6% 3 3 4 4 5% 5% 42%	2909
	11th to 20th	Day	13% 7% 2 5% 3 3 3 3 4 6% 52%	3016
	21st to end	Day	23% 8% 3 6% 3 3 2 2 4 6% 41%	3476
February	1st to 10th	Day	18% 8% 2 7% 5% 4 5% 3 5% 5% 38%	1900
	11th to 20th	Day	19% 7% 2 5% 4 3 3 3 4 6% 43%	1848
	21st to end	Day	16% 9% 3 7% 5% 4 3 3 4 6% 39%	1570
March	1st to 10th	Day	23% 10% 3 7% 5% 4 4 4 5% 6% 31%	3120
	11th to 20th	Day	15% 7% 2 8% 5% 5% 5% 4 6% 8% 36%	3442
	21st to end	Day	16% 7% 3 7% 5% 5% 4 4 4 5% 40%	4098
April	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 5% 6% 7% 42%	2280
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 4 5% 6% 42%	2254
	21st to end	Day	8% 5% 2 5% 4 5% 4 4 6% 7% 49%	2280
May	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 9% 39%	3765
	11th to 20th	Day	14% 6% 2 7% 4 5% 4 4 6% 7% 41%	3764
	21st to end	Day	6% 5% 2 7% 5% 5% 5% 5% 7% 10% 42%	4476
June	1st to 10th	Day	9% 6% 2 7% 5% 6% 6% 6% 8% 10% 34%	2470
	11th to 20th	Day	4 5% 2 6% 6% 7% 7% 6% 8% 9% 41%	2574
	21st to end	Day	6% 6% 3 7% 7% 8% 9% 6% 9% 9% 31%	2660
July	1st to 10th	Day	6% 6% 3 8% 8% 8% 8% 7% 10% 11% 26%	4230
	11th to 20th	Day	7% 5% 2 8% 7% 7% 8% 7% 10% 10% 29%	3969
	21st to end	Day	9% 7% 3 10% 8% 8% 8% 6% 8% 11% 21%	4118
August	1st to 10th	Day	2 3 2 5% 4 4 4 4 7% 9% 56%	3785
	11th to 20th	Day	5% 4 2 7% 5% 5% 6% 5% 7% 9% 45%	3729
	21st to end	Day	7% 5% 2 8% 6% 6% 6% 5% 7% 9% 40%	4180
September	1st to 10th	Day	9% 7% 2 7% 6% 6% 6% 4 7% 8% 37%	2280
	11th to 20th	Day	12% 7% 3 5% 4 5% 5% 5% 6% 7% 41%	2171
	21st to end	Day	9% 4 2 5% 4 4 3 3 6% 7% 52%	2090
October	1st to 10th	Day	6% 5% 2 5% 3 4 4 4 5% 7% 56%	2090
	11th to 20th	Day	9% 5% 2 5% 4 3 3 3 5% 5% 55%	1905
	21st to end	Day	11% 4 2 6% 3 3 3 2 4 6% 56%	2090
November	1st to 10th	Day	11% 6% 2 5% 3 4 3 3 4 6% 53%	1880
	11th to 20th	Day	13% 6% 2 4 4 3 3 4 4 5% 54%	1800
	21st to end	Day	13% 6% 2 5% 3 5% 3 3 4 6% 48%	1773
December	1st to 10th	Day	14% 8% 2 7% 3 4 3 3 5% 6% 44%	1710
	11th to 20th	Day	14% 11% 3 6% 5% 4 4 2 4 4 42%	2153
	21st to end	Day	15% 8% 2 6% 4 4 4 4 5% 7% 40%	3162
January	1st to 10th	Night	17% 8% 2 5% 3 4 3 3 4 6% 46%	4013
	11th to 20th	Night	16% 7% 2 5% 2 3 3 3 3 5% 51%	3921
	21st to end	Night	26% 10% 2 4 3 2 2 2 3 4 43%	4180
February	1st to 10th	Night	16% 8% 2 6% 4 4 3 4 6% 6% 40%	2280
	11th to 20th	Night	19% 9% 3 6% 4 2 3 2 4 6% 42%	2218
	21st to end	Night	19% 9% 3 6% 5% 3 4 3 4 5% 40%	1884
March	1st to 10th	Night	22% 12% 3 7% 4 3 3 3 4 5% 33%	3733
	11th to 20th	Night	13% 7% 3 7% 5% 4 4 4 6% 8% 40%	3544
	21st to end	Night	15% 6% 3 6% 4 4 3 4 5% 7% 44%	3530
April	1st to 10th	Night	13% 7% 2 5% 4 4 4 4 6% 6% 46%	1900
	11th to 20th	Night	13% 5% 2 6% 5% 4 4 3 5% 7% 46%	1875
	21st to end	Night	7% 5% 2 5% 3 3 4 3 6% 7% 56%	1900
May	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 5% 9% 46%	3130
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	3111
	21st to end	Night	5% 4 1 6% 5% 5% 6% 5% 8% 12% 42%	3079
June	1st to 10th	Night	8% 6% 3 7% 5% 5% 5% 5% 7% 10% 40%	1710
	11th to 20th	Night	4 4 2 5% 6% 5% 6% 5% 8% 11% 45%	1596
	21st to end	Night	6% 5% 3 6% 4 5% 4 5% 9% 12% 41%	1520
July	1st to 10th	Night	4 6% 3 9% 7% 6% 7% 5% 9% 12% 31%	2720
	11th to 20th	Night	7% 5% 3 6% 6% 6% 8% 6% 10% 11% 30%	2991
	21st to end	Night	6% 8% 3 10% 7% 7% 7% 6% 9% 10% 26%	3435
August	1st to 10th	Night	2 3 1 3 3 4 5% 4 7% 12% 56%	3144
	11th to 20th	Night	5% 3 1 6% 5% 4 6% 5% 10% 12% 43%	3100
	21st to end	Night	5% 5% 2 8% 6% 6% 5% 5% 7% 9% 42%	3476
September	1st to 10th	Night	10% 6% 2 6% 5% 5% 7% 5% 7% 7% 39%	1900
	11th to 20th	Night	9% 6% 2 8% 5% 4 4 4 6% 7% 44%	1987
	21st to end	Night	8% 5% 2 5% 4 3 4 3 4 7% 54%	2090
October	1st to 10th	Night	8% 4 2 5% 4 3 4 3 5% 6% 56%	2090
	11th to 20th	Night	9% 4 2 4 4 4 3 3 5% 6% 58%	2270
	21st to end	Night	13% 5% 3 4 3 2 3 3 3 4 58%	2508
November	1st to 10th	Night	11% 5% 2 5% 3 3 3 2 4 5% 58%	2415
	11th to 20th	Night	13% 6% 2 4 2 3 3 3 4 5% 56%	2600
	21st to end	Night	13% 6% 2 5% 4 4 4 3 5% 5% 49%	2562
December	1st to 10th	Night	16% 7% 2 5% 3 4 3 2 6% 6% 46%	2470
	11th to 20th	Night	15% 9% 3 6% 4 3 4 4 4 5% 44%	3042
	21st to end	Night	18% 9% 2 6% 3 3 3 3 5% 6% 43%	4489

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	43% 4 3 20% 24% 6%	2910
	11th to 20th	Day	34% 4 4 20% 29% 8%	3016
	21st to end	Day	47% 2 5% 15% 23% 8%	3476
February	1st to 10th	Day	48% 3 6% 15% 18% 10%	1900
	11th to 20th	Day	43% 4 5% 16% 24% 8%	1858
	21st to end	Day	46% 3 7% 17% 17% 10%	1570
March	1st to 10th	Day	54% 4 9% 15% 13% 5%	3120
	11th to 20th	Day	45% 4 7% 20% 18% 5%	3442
	21st to end	Day	46% 4 8% 14% 21% 8%	4098
April	1st to 10th	Day	40% 5% 8% 18% 20% 9%	2280
	11th to 20th	Day	42% 5% 6% 18% 21% 8%	2254
	21st to end	Day	32% 5% 10% 23% 25% 5%	2280
May	1st to 10th	Day	39% 6% 12% 25% 16% 3	3800
	11th to 20th	Day	41% 5% 12% 20% 20% 2	3768
	21st to end	Day	36% 5% 15% 31% 12% 1	4489
June	1st to 10th	Day	41% 7% 15% 23% 12% 2	2470
	11th to 20th	Day	35% 8% 17% 23% 14% 3	2574
	21st to end	Day	43% 10% 16% 20% 10% 1	2660
July	1st to 10th	Day	46% 10% 22% 17% 5% 1	4166
	11th to 20th	Day	43% 10% 28% 16% 3 1	3900
	21st to end	Day	52% 11% 16% 15% 5% 1	3987
August	1st to 10th	Day	23% 6% 14% 30% 26% 2	3773
	11th to 20th	Day	34% 7% 16% 28% 14% 1	3765
	21st to end	Day	39% 8% 16% 18% 16% 3	4179
September	1st to 10th	Day	42% 7% 16% 15% 14% 6%	2280
	11th to 20th	Day	41% 7% 11% 17% 17% 8%	2171
	21st to end	Day	30% 6% 10% 24% 20% 10%	2090
October	1st to 10th	Day	24% 3 6% 13% 25% 29%	3480
	11th to 20th	Day	19% 3 4 14% 29% 30%	3145
	21st to end	Day	22% 3 3 16% 36% 20%	3428
November	1st to 10th	Day	33% 3 8% 18% 27% 12%	1880
	11th to 20th	Day	34% 3 6% 15% 28% 15%	1800
	21st to end	Day	38% 4 7% 18% 22% 12%	1773
December	1st to 10th	Day	41% 4 9% 21% 17% 8%	1710
	11th to 20th	Day	46% 3 6% 13% 24% 8%	2150
	21st to end	Day	43% 4 6% 23% 20% 4	3162
January	1st to 10th	Night	40% 3 5% 15% 28% 8%	4013
	11th to 20th	Night	37% 3 5% 21% 23% 12%	3921
	21st to end	Night	48% 2 3 16% 25% 7%	4180
February	1st to 10th	Night	44% 3 7% 17% 20% 9%	2280
	11th to 20th	Night	45% 3 5% 13% 22% 11%	2219
	21st to end	Night	46% 3 8% 15% 14% 13%	1884
March	1st to 10th	Night	54% 3 8% 15% 13% 7%	3733
	11th to 20th	Night	43% 4 9% 19% 19% 7%	3544
	21st to end	Night	41% 4 11% 19% 20% 6%	3530
April	1st to 10th	Night	39% 5% 9% 16% 19% 11%	1900
	11th to 20th	Night	38% 4 9% 19% 20% 9%	1875
	21st to end	Night	28% 4 10% 23% 28% 7%	1900
May	1st to 10th	Night	35% 5% 14% 23% 18% 4	3160
	11th to 20th	Night	40% 6% 11% 25% 17% 1	3112
	21st to end	Night	31% 7% 18% 27% 15% 3	3087
June	1st to 10th	Night	37% 8% 15% 25% 11% 3	1710
	11th to 20th	Night	30% 7% 18% 28% 13% 3	1596
	21st to end	Night	34% 7% 19% 26% 11% 3	1520
July	1st to 10th	Night	42% 11% 25% 16% 5% 1	2675
	11th to 20th	Night	41% 11% 31% 13% 3 1	2937
	21st to end	Night	49% 13% 16% 18% 3 1	3325
August	1st to 10th	Night	19% 8% 19% 29% 23% 1	3132
	11th to 20th	Night	29% 10% 19% 27% 13% 1	3130
	21st to end	Night	37% 9% 16% 20% 14% 4	3476
September	1st to 10th	Night	40% 8% 17% 14% 14% 6%	1900
	11th to 20th	Night	37% 6% 15% 18% 15% 9%	1987
	21st to end	Night	30% 5% 9% 25% 20% 10%	2090
October	1st to 10th	Night	26% 4 7% 11% 24% 28%	3480
	11th to 20th	Night	19% 3 4 19% 22% 34%	3769
	21st to end	Night	21% 2 3 14% 36% 23%	4120
November	1st to 10th	Night	30% 3 7% 19% 26% 15%	2415
	11th to 20th	Night	32% 3 5% 16% 28% 16%	2600
	21st to end	Night	36% 4 6% 21% 19% 14%	2562
December	1st to 10th	Night	38% 4 9% 22% 20% 7%	2470
	11th to 20th	Night	43% 3 6% 14% 26% 8%	3044
	21st to end	Night	43% 3 6% 19% 25% 4	4489

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	27% 22% 31% 16% 3 1	270
	11th to 20th	Day	24% 18% 30% 19% 7% 1	270
	21st to end	Day	26% 24% 33% 15% 3	297
February	1st to 10th	Day	28% 20% 31% 14% 7%	270
	11th to 20th	Day	33% 18% 29% 16% 5%	270
	21st to end	Day	23% 22% 43% 12% 1	225
March	1st to 10th	Day	24% 17% 36% 18% 5%	270
	11th to 20th	Day	25% 19% 32% 20% 4 1	270
	21st to end	Day	22% 15% 33% 22% 8%	465
April	1st to 10th	Day	16% 17% 33% 22% 11% 1	460
	11th to 20th	Day	22% 15% 28% 21% 11% 2	452
	21st to end	Day	14% 10% 27% 29% 17% 2	460
May	1st to 10th	Day	14% 10% 25% 24% 22% 5%	463
	11th to 20th	Day	10% 5% 25% 30% 20% 10%	487
	21st to end	Day	8% 4 18% 33% 25% 13%	529
June	1st to 10th	Day	13% 3 16% 31% 26% 12%	490
	11th to 20th	Day	6% 3 12% 31% 32% 15%	594
	21st to end	Day	8% 2 13% 30% 31% 16%	680
July	1st to 10th	Day	7% 1 8% 27% 35% 21%	671
	11th to 20th	Day	9% 1 4 20% 37% 29%	582
	21st to end	Day	9% 1 7% 23% 36% 24%	532
August	1st to 10th	Day	6% 1 9% 22% 33% 29%	486
	11th to 20th	Day	10% 1 7% 18% 38% 26%	479
	21st to end	Day	15% 2 7% 21% 30% 25%	539
September	1st to 10th	Day	11% 1 11% 26% 33% 17%	490
	11th to 20th	Day	15% 4 10% 24% 33% 14%	490
	21st to end	Day	12% 4 13% 28% 31% 12%	490
October	1st to 10th	Day	7% 6% 21% 35% 24% 8%	490
	11th to 20th	Day	11% 5% 23% 31% 25% 5%	305
	21st to end	Day	18% 11% 17% 31% 18% 6%	330
November	1st to 10th	Day	17% 8% 28% 34% 10% 4	300
	11th to 20th	Day	20% 12% 31% 24% 12% 1	300
	21st to end	Day	16% 16% 33% 19% 11% 3	291
December	1st to 10th	Day	23% 13% 34% 21% 9% 1	270
	11th to 20th	Day	27% 15% 34% 18% 5% 1	270
	21st to end	Day	29% 15% 29% 21% 5% 1	297
January	1st to 10th	Night	22% 13% 31% 29% 5%	894
	11th to 20th	Night	22% 12% 32% 26% 7%	829
	21st to end	Night	25% 14% 32% 25% 4	836
February	1st to 10th	Night	20% 13% 32% 30% 5%	760
	11th to 20th	Night	24% 16% 29% 26% 6%	743
	21st to end	Night	22% 18% 38% 19% 3	628
March	1st to 10th	Night	18% 16% 30% 29% 7%	760
	11th to 20th	Night	16% 11% 34% 29% 9%	608
	21st to end	Night	16% 11% 34% 27% 11%	627
April	1st to 10th	Night	18% 9% 32% 29% 12% 1	570
	11th to 20th	Night	15% 8% 33% 28% 14% 1	563
	21st to end	Night	8% 7% 30% 39% 15% 1	570
May	1st to 10th	Night	9% 5% 27% 38% 19% 2	570
	11th to 20th	Night	11% 4 19% 41% 21% 5%	561
	21st to end	Night	7% 2 16% 34% 34% 7%	617
June	1st to 10th	Night	10% 2 12% 34% 36% 6%	570
	11th to 20th	Night	4 1 10% 31% 43% 11%	570
	21st to end	Night	7% 2 10% 26% 43% 12%	570
July	1st to 10th	Night	5% 1 5% 23% 49% 16%	555
	11th to 20th	Night	7% 1 5% 19% 46% 21%	552
	21st to end	Night	6% 4 23% 49% 18%	624
August	1st to 10th	Night	4 4 21% 49% 22%	567
	11th to 20th	Night	9% 5% 20% 45% 21%	564
	21st to end	Night	9% 1 7% 19% 44% 20%	627
September	1st to 10th	Night	11% 2 8% 26% 41% 12%	570
	11th to 20th	Night	11% 2 10% 29% 40% 8%	657
	21st to end	Night	11% 2 14% 29% 38% 6%	760
October	1st to 10th	Night	10% 3 18% 31% 35% 4	760
	11th to 20th	Night	11% 5% 20% 33% 27% 3	760
	21st to end	Night	16% 6% 18% 33% 24% 2	836
November	1st to 10th	Night	13% 7% 20% 39% 19% 3	780
	11th to 20th	Night	16% 8% 26% 33% 15% 1	800
	21st to end	Night	15% 9% 26% 31% 16% 2	789
December	1st to 10th	Night	21% 11% 27% 29% 12%	760
	11th to 20th	Night	22% 8% 33% 27% 10%	760
	21st to end	Night	27% 11% 28% 28% 6%	836

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