Paul P. Feder Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Paul P. Feder Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	11% 8% 3 8% 5% 5% 5% 4 6% 7% 38%	136288
	Night	10% 9% 4 9% 6% 5% 5% 4 6% 7% 36%	132413
Transparency	Day	45% 5% 14% 25% 9% 1	130942
	Night	48% 5% 13% 23% 10% 1	128766
Seeing	Day	15% 9% 31% 29% 13% 3	17690
	Night	15% 8% 34% 32% 10% 1	27661

By Month

Percentage Cloud Cover SW (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	5% 12% 5% 14% 11% 9% 8% 7% 6% 7% 15%	3185
	11th to 20th	Day	5% 7% 5% 13% 8% 9% 13% 9% 10% 8% 13%	3433
	21st to end	Day	5% 11% 8% 19% 9% 6% 5% 5% 6% 6% 22%	4199
February	1st to 10th	Day	7% 15% 6% 10% 7% 7% 6% 6% 7% 6% 24%	1800
	11th to 20th	Day	5% 11% 4 10% 8% 8% 8% 5% 7% 8% 25%	1754
	21st to end	Day	9% 12% 3 11% 7% 9% 6% 4 7% 9% 22%	1584
March	1st to 10th	Day	10% 8% 3 8% 6% 5% 5% 4 5% 7% 39%	4718
	11th to 20th	Day	10% 9% 4 9% 7% 4 6% 5% 6% 9% 31%	4980
	21st to end	Day	16% 14% 5% 11% 6% 4 4 4 5% 7% 25%	5464
April	1st to 10th	Day	14% 10% 4 9% 5% 5% 5% 4 5% 6% 33%	2353
	11th to 20th	Day	16% 12% 4 8% 5% 5% 3 3 5% 7% 31%	2569
	21st to end	Day	21% 9% 3 7% 4 5% 4 4 5% 6% 32%	2600
May	1st to 10th	Day	13% 6% 2 5% 3 3 4 3 5% 6% 49%	5900
	11th to 20th	Day	16% 8% 2 6% 4 4 4 4 5% 6% 42%	6314
	21st to end	Day	16% 6% 2 5% 4 4 4 3 5% 7% 43%	7266
June	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	3000
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 4 7% 8% 41%	3000
	21st to end	Day	11% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	3000
July	1st to 10th	Day	6% 4 2 6% 4 4 5% 5% 7% 10% 47%	6799
	11th to 20th	Day	10% 5% 2 5% 3 4 4 3 6% 8% 50%	6800
	21st to end	Day	8% 5% 2 6% 5% 4 5% 4 7% 10% 44%	6886
August	1st to 10th	Day	13% 4 2 5% 4 4 4 4 7% 10% 42%	5801
	11th to 20th	Day	13% 7% 2 6% 4 3 4 3 5% 8% 44%	5821
	21st to end	Day	8% 3 2 4 3 4 4 3 6% 8% 54%	6490
September	1st to 10th	Day	10% 5% 1 5% 4 4 4 3 5% 8% 50%	2425
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 6% 7% 45%	2200
	21st to end	Day	14% 5% 2 5% 4 4 4 4 6% 7% 47%	2200
October	1st to 10th	Day	11% 6% 2 5% 2 3 4 3 5% 7% 52%	3301
	11th to 20th	Day	15% 9% 3 7% 4 4 3 2 4 6% 45%	3240
	21st to end	Day	17% 10% 3 8% 5% 4 5% 3 4 7% 34%	3290
November	1st to 10th	Day	13% 14% 6% 11% 5% 4 4 2 5% 5% 32%	1738
	11th to 20th	Day	10% 14% 6% 13% 6% 6% 4 3 3 5% 28%	1680
	21st to end	Day	10% 13% 5% 13% 9% 6% 4 4 4 5% 29%	1680
December	1st to 10th	Day	8% 12% 5% 16% 13% 10% 6% 5% 5% 5% 15%	2530
	11th to 20th	Day	8% 16% 7% 12% 5% 6% 5% 6% 7% 7% 21%	2713
	21st to end	Day	15% 15% 6% 17% 9% 6% 4 2 4 4 18%	3575
January	1st to 10th	Night	5% 9% 6% 16% 11% 10% 9% 6% 7% 7% 15%	6803
	11th to 20th	Night	4 10% 5% 12% 9% 9% 13% 10% 8% 6% 14%	6544
	21st to end	Night	5% 15% 9% 13% 6% 5% 6% 4 6% 6% 24%	6777
February	1st to 10th	Night	7% 12% 4 11% 6% 8% 5% 5% 7% 5% 29%	2600
	11th to 20th	Night	6% 11% 4 11% 7% 7% 7% 5% 7% 7% 30%	2533
	21st to end	Night	10% 11% 4 9% 7% 5% 5% 4 6% 6% 31%	2065
March	1st to 10th	Night	8% 7% 2 7% 5% 5% 4 4 6% 9% 42%	5145
	11th to 20th	Night	10% 10% 3 11% 8% 5% 5% 4 5% 6% 32%	4980
	21st to end	Night	16% 15% 4 11% 5% 4 4 3 4 5% 30%	5467
April	1st to 10th	Night	13% 8% 3 7% 4 5% 4 4 5% 8% 39%	2045
	11th to 20th	Night	17% 10% 5% 6% 4 4 4 3 5% 5% 37%	1779
	21st to end	Night	19% 10% 3 6% 5% 3 3 3 5% 6% 37%	1800
May	1st to 10th	Night	14% 7% 2 5% 3 3 3 3 5% 5% 50%	4080
	11th to 20th	Night	16% 7% 2 5% 3 3 4 4 5% 6% 45%	3600
	21st to end	Night	14% 6% 2 6% 4 4 4 3 6% 7% 43%	3627
June	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 6% 9% 47%	1400
	11th to 20th	Night	11% 7% 2 5% 5% 3 4 5% 6% 9% 46%	1400
	21st to end	Night	6% 5% 1 5% 3 4 5% 5% 7% 10% 48%	1400
July	1st to 10th	Night	8% 4 2 5% 4 5% 4 4 6% 10% 48%	3180
	11th to 20th	Night	5% 4 1 4 3 3 4 4 6% 9% 58%	3180
	21st to end	Night	8% 4 2 6% 5% 4 5% 4 7% 9% 46%	3970
August	1st to 10th	Night	12% 5% 2 5% 4 3 4 4 6% 8% 48%	4011
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 6% 9% 48%	4028
	21st to end	Night	7% 5% 2 5% 3 3 4 3 6% 8% 55%	4487
September	1st to 10th	Night	9% 4 1 4 3 4 4 3 6% 8% 55%	1971
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 4 7% 53%	2200
	21st to end	Night	11% 6% 2 4 4 4 3 3 4 6% 54%	2200
October	1st to 10th	Night	8% 5% 1 4 3 3 4 3 5% 6% 58%	3845
	11th to 20th	Night	14% 8% 2 5% 4 4 4 4 5% 6% 45%	3899
	21st to end	Night	16% 9% 3 8% 4 4 4 3 5% 6% 38%	4503
November	1st to 10th	Night	11% 13% 4 9% 5% 4 4 4 5% 6% 33%	2779
	11th to 20th	Night	11% 13% 6% 12% 5% 5% 4 4 6% 6% 29%	2940
	21st to end	Night	11% 11% 4 10% 7% 5% 4 4 6% 6% 33%	2940
December	1st to 10th	Night	5% 12% 5% 15% 12% 8% 6% 4 5% 7% 20%	4876
	11th to 20th	Night	9% 15% 5% 15% 9% 6% 5% 4 5% 5% 21%	5714
	21st to end	Night	15% 15% 6% 16% 9% 6% 5% 4 4 4 17%	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	67% 4 8% 15% 6%	3186
	11th to 20th	Day	64% 4 10% 18% 4	3433
	21st to end	Day	62% 5% 12% 16% 5%	4199
February	1st to 10th	Day	59% 5% 12% 17% 8%	1800
	11th to 20th	Day	54% 5% 14% 20% 6% 1	1763
	21st to end	Day	57% 7% 14% 15% 7%	1584
March	1st to 10th	Day	44% 5% 17% 24% 9% 1	4718
	11th to 20th	Day	49% 4 15% 26% 6%	4980
	21st to end	Day	60% 5% 12% 19% 4	5464
April	1st to 10th	Day	51% 5% 11% 22% 11% 1	2353
	11th to 20th	Day	53% 4 13% 18% 11% 1	2572
	21st to end	Day	53% 5% 12% 22% 8% 1	2600
May	1st to 10th	Day	35% 5% 12% 30% 17% 1	5900
	11th to 20th	Day	43% 5% 11% 22% 15% 5%	6318
	21st to end	Day	40% 5% 11% 31% 13% 1	7267
June	1st to 10th	Day	39% 5% 18% 28% 9% 1	3000
	11th to 20th	Day	40% 7% 17% 24% 11% 1	3000
	21st to end	Day	35% 8% 20% 26% 11%	3000
July	1st to 10th	Day	31% 7% 23% 30% 10%	6726
	11th to 20th	Day	32% 5% 17% 35% 10% 1	6719
	21st to end	Day	33% 7% 19% 31% 9% 1	6687
August	1st to 10th	Day	33% 6% 16% 31% 13% 1	4220
	11th to 20th	Day	37% 6% 16% 32% 8% 1	4210
	21st to end	Day	33% 4 20% 33% 9% 1	4674
September	1st to 10th	Day	33% 5% 15% 35% 11% 1	2425
	11th to 20th	Day	38% 6% 18% 29% 10%	2200
	21st to end	Day	36% 6% 15% 32% 10% 1	2200
October	1st to 10th	Day	32% 3 11% 36% 16% 1	3301
	11th to 20th	Day	43% 3 8% 28% 17%	3240
	21st to end	Day	52% 4 13% 24% 7%	3290
November	1st to 10th	Day	55% 5% 12% 17% 10% 1	1738
	11th to 20th	Day	60% 4 13% 17% 7%	1680
	21st to end	Day	58% 4 15% 16% 6% 1	1680
December	1st to 10th	Day	71% 5% 12% 9% 2	2530
	11th to 20th	Day	61% 4 14% 15% 6%	2710
	21st to end	Day	71% 4 8% 14% 3	3575
January	1st to 10th	Night	66% 5% 9% 14% 6%	6803
	11th to 20th	Night	66% 5% 11% 11% 7% 1	6544
	21st to end	Night	59% 5% 14% 18% 4	6777
February	1st to 10th	Night	54% 5% 14% 19% 8% 1	2600
	11th to 20th	Night	50% 6% 11% 21% 11% 1	2534
	21st to end	Night	52% 5% 13% 21% 9% 1	2065
March	1st to 10th	Night	39% 4 18% 26% 12% 1	5145
	11th to 20th	Night	53% 4 10% 23% 10%	4980
	21st to end	Night	58% 3 11% 20% 7%	5467
April	1st to 10th	Night	43% 5% 12% 24% 13% 2	2045
	11th to 20th	Night	49% 3 9% 23% 14% 2	1779
	21st to end	Night	49% 4 11% 24% 11% 2	1800
May	1st to 10th	Night	36% 5% 14% 23% 21% 1	4080
	11th to 20th	Night	39% 5% 9% 23% 19% 5%	3601
	21st to end	Night	40% 5% 10% 27% 17% 1	3628
June	1st to 10th	Night	31% 6% 18% 33% 10% 2	1400
	11th to 20th	Night	35% 6% 17% 23% 14% 5%	1400
	21st to end	Night	29% 8% 20% 30% 12% 2	1400
July	1st to 10th	Night	31% 6% 19% 31% 12%	3145
	11th to 20th	Night	23% 6% 18% 40% 12% 1	3138
	21st to end	Night	33% 6% 20% 30% 9% 1	3856
August	1st to 10th	Night	29% 6% 15% 32% 17% 2	2916
	11th to 20th	Night	31% 5% 17% 35% 12% 1	2915
	21st to end	Night	32% 5% 16% 32% 14% 1	3234
September	1st to 10th	Night	27% 6% 14% 38% 15% 1	1971
	11th to 20th	Night	32% 5% 18% 31% 14%	2200
	21st to end	Night	33% 5% 12% 33% 17% 1	2200
October	1st to 10th	Night	28% 3 9% 36% 19% 5%	3845
	11th to 20th	Night	41% 3 9% 27% 18% 2	3899
	21st to end	Night	47% 4 12% 26% 11%	4503
November	1st to 10th	Night	50% 4 11% 23% 10% 2	2779
	11th to 20th	Night	56% 5% 13% 17% 8% 1	2940
	21st to end	Night	51% 5% 18% 19% 6%	2940
December	1st to 10th	Night	63% 5% 16% 12% 3	4876
	11th to 20th	Night	65% 4 11% 17% 3	5716
	21st to end	Night	71% 4 9% 12% 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	12% 12% 35% 28% 11% 3	303
	11th to 20th	Day	13% 9% 35% 34% 9%	300
	21st to end	Day	15% 9% 38% 25% 11% 2	330
February	1st to 10th	Day	17% 12% 34% 31% 5% 1	300
	11th to 20th	Day	11% 15% 39% 25% 9% 1	300
	21st to end	Day	10% 8% 43% 33% 6%	249
March	1st to 10th	Day	15% 12% 36% 29% 7%	300
	11th to 20th	Day	16% 10% 35% 24% 12% 3	300
	21st to end	Day	18% 12% 26% 30% 11% 2	330
April	1st to 10th	Day	21% 13% 34% 23% 8%	453
	11th to 20th	Day	23% 14% 28% 25% 8% 1	690
	21st to end	Day	22% 9% 33% 24% 10% 2	700
May	1st to 10th	Day	19% 11% 30% 25% 13% 2	703
	11th to 20th	Day	19% 9% 29% 27% 13% 3	725
	21st to end	Day	17% 7% 28% 29% 16% 3	789
June	1st to 10th	Day	12% 9% 28% 30% 18% 4	730
	11th to 20th	Day	15% 9% 35% 26% 14% 2	730
	21st to end	Day	12% 8% 30% 30% 15% 4	730
July	1st to 10th	Day	8% 4 22% 34% 25% 7%	721
	11th to 20th	Day	11% 6% 27% 32% 18% 6%	718
	21st to end	Day	7% 5% 26% 36% 22% 5%	794
August	1st to 10th	Day	9% 4 24% 37% 22% 4	726
	11th to 20th	Day	14% 5% 20% 34% 18% 9%	715
	21st to end	Day	10% 6% 27% 32% 22% 3	803
September	1st to 10th	Day	9% 6% 34% 29% 19% 3	555
	11th to 20th	Day	14% 9% 34% 30% 10% 4	330
	21st to end	Day	16% 12% 31% 26% 13% 2	330
October	1st to 10th	Day	17% 9% 32% 30% 11% 2	330
	11th to 20th	Day	18% 14% 37% 23% 7%	330
	21st to end	Day	23% 18% 33% 19% 5% 2	363
November	1st to 10th	Day	21% 11% 29% 33% 6% 1	330
	11th to 20th	Day	20% 14% 40% 20% 5%	330
	21st to end	Day	15% 14% 38% 28% 5%	330
December	1st to 10th	Day	14% 9% 40% 26% 10% 1	330
	11th to 20th	Day	15% 15% 42% 24% 4 1	330
	21st to end	Day	21% 11% 36% 25% 7% 1	363
January	1st to 10th	Night	9% 10% 39% 29% 11% 2	1006
	11th to 20th	Night	13% 8% 39% 33% 7%	1000
	21st to end	Night	14% 9% 40% 30% 7% 1	1100
February	1st to 10th	Night	11% 12% 33% 34% 8% 1	1000
	11th to 20th	Night	11% 10% 40% 28% 8% 2	979
	21st to end	Night	14% 10% 32% 31% 11% 1	745
March	1st to 10th	Night	14% 10% 37% 30% 9% 1	701
	11th to 20th	Night	13% 11% 42% 26% 8% 1	600
	21st to end	Night	19% 7% 31% 30% 10% 3	660
April	1st to 10th	Night	18% 10% 36% 29% 8% 1	600
	11th to 20th	Night	22% 10% 32% 26% 9% 1	593
	21st to end	Night	23% 10% 31% 25% 11%	600
May	1st to 10th	Night	21% 7% 30% 33% 9% 1	600
	11th to 20th	Night	17% 6% 36% 31% 9%	591
	21st to end	Night	14% 7% 35% 31% 12% 1	650
June	1st to 10th	Night	13% 7% 29% 38% 14% 1	600
	11th to 20th	Night	13% 6% 32% 41% 8%	600
	21st to end	Night	8% 5% 28% 45% 13% 1	600
July	1st to 10th	Night	6% 2 23% 45% 22% 2	585
	11th to 20th	Night	6% 3 27% 47% 17% 1	582
	21st to end	Night	6% 3 23% 47% 19% 2	657
August	1st to 10th	Night	7% 3 21% 52% 16% 2	597
	11th to 20th	Night	11% 2 25% 39% 22% 2	594
	21st to end	Night	9% 6% 28% 40% 17% 1	660
September	1st to 10th	Night	11% 5% 29% 39% 16% 2	600
	11th to 20th	Night	9% 7% 32% 39% 12% 1	600
	21st to end	Night	14% 6% 34% 34% 12% 1	600
October	1st to 10th	Night	18% 10% 32% 32% 8%	751
	11th to 20th	Night	21% 11% 33% 28% 7%	800
	21st to end	Night	24% 10% 35% 25% 5%	1030
November	1st to 10th	Night	17% 10% 34% 32% 7%	1025
	11th to 20th	Night	17% 12% 37% 26% 7% 1	1050
	21st to end	Night	17% 11% 42% 25% 6%	1050
December	1st to 10th	Night	14% 10% 38% 29% 9% 1	1050
	11th to 20th	Night	18% 11% 38% 26% 6% 1	1050
	21st to end	Night	22% 10% 35% 26% 6% 1	1155

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