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 2024-11-12.

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 8% 5% 5% 5% 4 6% 7% 37%	105501
	Night	10% 9% 4 9% 6% 5% 5% 4 5% 6% 37%	102334
Transparency	Day	45% 5% 14% 26% 9% 1	105232
	Night	47% 5% 13% 24% 10% 1	102192
Seeing	Day	15% 9% 31% 29% 14% 3	16137
	Night	15% 8% 33% 33% 10% 1	26033

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	7% 15% 6% 15% 10% 7% 6% 5% 6% 5% 18%	2218
	11th to 20th	Day	5% 8% 5% 14% 9% 11% 13% 7% 9% 6% 14%	2389
	21st to end	Day	7% 12% 8% 20% 8% 5% 5% 4 5% 5% 20%	2924
February	1st to 10th	Day	7% 14% 6% 10% 6% 7% 6% 6% 7% 6% 24%	1710
	11th to 20th	Day	5% 12% 4 11% 9% 8% 8% 5% 7% 7% 25%	1664
	21st to end	Day	9% 12% 4 12% 7% 8% 6% 4 7% 8% 22%	1507
March	1st to 10th	Day	11% 11% 3 10% 7% 6% 5% 3 5% 6% 34%	3283
	11th to 20th	Day	10% 9% 5% 10% 8% 4 5% 4 6% 9% 31%	3480
	21st to end	Day	17% 14% 5% 12% 8% 4 4 4 5% 6% 22%	3814
April	1st to 10th	Day	13% 10% 4 9% 5% 5% 5% 4 5% 6% 33%	2235
	11th to 20th	Day	16% 12% 4 8% 5% 5% 4 4 5% 6% 31%	2439
	21st to end	Day	21% 9% 3 7% 4 5% 4 4 5% 6% 33%	2470
May	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 6% 7% 37%	4120
	11th to 20th	Day	13% 7% 2 7% 4 4 5% 4 6% 7% 40%	4394
	21st to end	Day	19% 7% 3 6% 5% 5% 4 3 5% 7% 37%	5064
June	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 6% 8% 43%	2850
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 6% 7% 42%	2850
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	2850
July	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 8% 10% 44%	4750
	11th to 20th	Day	6% 3 1 4 3 4 4 4 6% 9% 56%	4750
	21st to end	Day	5% 4 1 5% 5% 4 5% 5% 7% 10% 48%	4795
August	1st to 10th	Day	11% 3 2 5% 4 4 4 4 7% 10% 45%	4103
	11th to 20th	Day	13% 7% 2 5% 4 4 4 3 5% 8% 44%	4041
	21st to end	Day	11% 4 2 5% 4 4 5% 3 6% 7% 50%	4532
September	1st to 10th	Day	11% 5% 1 5% 4 4 4 3 5% 8% 50%	2304
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 6% 7% 47%	2090
	21st to end	Day	15% 5% 2 5% 4 4 4 4 6% 7% 45%	2090
October	1st to 10th	Day	11% 6% 2 6% 2 3 4 4 5% 7% 52%	3200
	11th to 20th	Day	14% 9% 3 7% 4 4 3 2 4 6% 46%	3140
	21st to end	Day	17% 10% 3 8% 5% 4 5% 3 4 7% 34%	3188
November	1st to 10th	Day	14% 13% 6% 10% 5% 4 4 2 5% 5% 33%	1654
	11th to 20th	Day	10% 15% 7% 14% 7% 6% 4 3 3 5% 26%	1528
	21st to end	Day	10% 13% 5% 12% 8% 5% 4 4 4 5% 29%	1520
December	1st to 10th	Day	7% 15% 5% 14% 9% 8% 5% 6% 5% 5% 21%	1430
	11th to 20th	Day	8% 13% 6% 13% 7% 6% 5% 5% 6% 7% 24%	1683
	21st to end	Day	20% 14% 5% 12% 8% 6% 4 2 4 4 21%	2442
January	1st to 10th	Night	6% 11% 6% 15% 9% 10% 8% 6% 5% 5% 19%	4737
	11th to 20th	Night	5% 10% 5% 15% 10% 11% 14% 7% 6% 5% 13%	4578
	21st to end	Night	7% 15% 9% 15% 6% 6% 6% 5% 6% 5% 20%	4741
February	1st to 10th	Night	6% 12% 4 11% 6% 8% 5% 5% 7% 5% 29%	2470
	11th to 20th	Night	6% 11% 4 11% 7% 7% 7% 5% 7% 7% 29%	2403
	21st to end	Night	10% 12% 4 9% 7% 5% 5% 4 6% 6% 30%	1965
March	1st to 10th	Night	8% 8% 3 9% 6% 5% 5% 4 6% 9% 37%	3575
	11th to 20th	Night	10% 11% 3 10% 7% 5% 4 3 5% 6% 35%	3480
	21st to end	Night	16% 17% 4 12% 5% 4 3 3 4 5% 29%	3817
April	1st to 10th	Night	13% 8% 3 7% 4 5% 4 4 5% 8% 39%	1943
	11th to 20th	Night	18% 10% 5% 6% 4 4 4 3 5% 5% 36%	1689
	21st to end	Night	18% 10% 3 6% 5% 3 3 3 5% 6% 37%	1710
May	1st to 10th	Night	16% 9% 3 7% 4 3 4 3 6% 6% 38%	2850
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 6% 6% 45%	2510
	21st to end	Night	15% 7% 3 6% 4 4 4 3 5% 7% 42%	2519
June	1st to 10th	Night	10% 5% 2 6% 3 3 4 4 6% 9% 47%	1330
	11th to 20th	Night	10% 7% 2 5% 5% 3 4 5% 5% 8% 47%	1330
	21st to end	Night	6% 5% 1 5% 4 4 5% 5% 7% 11% 48%	1330
July	1st to 10th	Night	8% 4 2 6% 5% 6% 5% 5% 6% 11% 42%	2220
	11th to 20th	Night	4 3 1 3 2 3 3 3 5% 7% 66%	2220
	21st to end	Night	5% 3 2 5% 4 4 4 4 7% 9% 52%	2764
August	1st to 10th	Night	8% 4 1 5% 4 3 4 4 6% 8% 53%	2836
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 6% 10% 50%	2798
	21st to end	Night	10% 6% 2 5% 3 3 4 3 5% 7% 51%	3135
September	1st to 10th	Night	9% 4 1 3 3 3 4 3 6% 9% 55%	1872
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 4 7% 54%	2090
	21st to end	Night	12% 6% 2 4 4 4 3 3 4 6% 53%	2090
October	1st to 10th	Night	8% 5% 1 4 3 3 4 3 5% 5% 58%	3727
	11th to 20th	Night	13% 8% 2 5% 4 4 4 4 5% 6% 46%	3779
	21st to end	Night	16% 9% 3 8% 4 4 4 3 5% 6% 38%	4363
November	1st to 10th	Night	12% 14% 4 8% 5% 4 4 4 5% 6% 34%	2643
	11th to 20th	Night	11% 13% 6% 12% 6% 5% 4 4 5% 6% 28%	2675
	21st to end	Night	11% 11% 3 9% 7% 5% 4 4 6% 6% 34%	2660
December	1st to 10th	Night	8% 14% 5% 12% 10% 6% 6% 4 5% 6% 24%	2746
	11th to 20th	Night	10% 14% 5% 14% 8% 6% 5% 3 5% 5% 24%	3514
	21st to end	Night	19% 14% 5% 12% 7% 5% 5% 4 5% 4 21%	5225

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	66% 5% 10% 16% 4	2219
	11th to 20th	Day	66% 5% 11% 14% 3	2389
	21st to end	Day	66% 5% 9% 15% 5%	2924
February	1st to 10th	Day	58% 5% 12% 18% 7%	1710
	11th to 20th	Day	55% 5% 14% 19% 6% 1	1673
	21st to end	Day	58% 6% 13% 15% 7%	1507
March	1st to 10th	Day	52% 5% 12% 25% 6%	3283
	11th to 20th	Day	50% 4 14% 26% 5%	3480
	21st to end	Day	63% 5% 12% 17% 4	3814
April	1st to 10th	Day	51% 5% 11% 21% 11% 1	2235
	11th to 20th	Day	54% 4 12% 19% 11% 1	2442
	21st to end	Day	52% 5% 12% 22% 8% 1	2470
May	1st to 10th	Day	44% 6% 12% 25% 12% 1	4120
	11th to 20th	Day	41% 6% 13% 27% 11% 3	4398
	21st to end	Day	46% 6% 13% 26% 8% 1	5064
June	1st to 10th	Day	39% 5% 18% 28% 9% 1	2850
	11th to 20th	Day	40% 7% 16% 25% 12% 1	2850
	21st to end	Day	35% 8% 20% 26% 11%	2850
July	1st to 10th	Day	33% 8% 21% 28% 10% 1	4676
	11th to 20th	Day	24% 6% 18% 38% 12% 1	4669
	21st to end	Day	28% 8% 19% 35% 10% 1	4642
August	1st to 10th	Day	33% 6% 16% 32% 13% 1	4090
	11th to 20th	Day	38% 6% 16% 32% 8% 1	4080
	21st to end	Day	33% 4 19% 33% 9% 1	4531
September	1st to 10th	Day	33% 5% 15% 35% 11% 1	2304
	11th to 20th	Day	36% 6% 18% 30% 10%	2090
	21st to end	Day	37% 6% 16% 31% 10% 1	2090
October	1st to 10th	Day	33% 3 10% 36% 16% 1	3200
	11th to 20th	Day	43% 3 9% 28% 17%	3140
	21st to end	Day	52% 4 13% 24% 7%	3188
November	1st to 10th	Day	55% 5% 13% 17% 10% 1	1654
	11th to 20th	Day	61% 4 12% 15% 7%	1528
	21st to end	Day	57% 5% 16% 16% 6% 1	1520
December	1st to 10th	Day	63% 6% 12% 16% 3	1430
	11th to 20th	Day	59% 5% 16% 16% 3	1680
	21st to end	Day	68% 5% 7% 17% 3	2442
January	1st to 10th	Night	65% 6% 11% 14% 4	4737
	11th to 20th	Night	70% 5% 11% 9% 4	4578
	21st to end	Night	64% 5% 11% 17% 4	4741
February	1st to 10th	Night	53% 5% 15% 19% 8% 1	2470
	11th to 20th	Night	52% 6% 11% 20% 11% 1	2404
	21st to end	Night	53% 5% 13% 20% 9% 1	1965
March	1st to 10th	Night	44% 5% 15% 24% 11% 1	3575
	11th to 20th	Night	49% 5% 11% 25% 10%	3480
	21st to end	Night	59% 4 10% 20% 6% 1	3817
April	1st to 10th	Night	43% 6% 12% 24% 13% 2	1943
	11th to 20th	Night	49% 3 9% 22% 14% 2	1689
	21st to end	Night	49% 4 11% 24% 11% 1	1710
May	1st to 10th	Night	44% 6% 13% 23% 11% 2	2850
	11th to 20th	Night	38% 6% 10% 26% 17% 3	2511
	21st to end	Night	41% 5% 12% 28% 12% 1	2520
June	1st to 10th	Night	31% 6% 17% 33% 10% 2	1330
	11th to 20th	Night	35% 6% 17% 23% 15% 5%	1330
	21st to end	Night	28% 8% 20% 31% 11% 2	1330
July	1st to 10th	Night	35% 8% 20% 24% 12% 1	2185
	11th to 20th	Night	18% 5% 14% 46% 15% 2	2178
	21st to end	Night	27% 7% 20% 34% 10% 1	2677
August	1st to 10th	Night	29% 6% 14% 33% 17% 2	2826
	11th to 20th	Night	31% 5% 17% 35% 12% 1	2825
	21st to end	Night	32% 5% 16% 32% 15% 1	3135
September	1st to 10th	Night	27% 6% 14% 37% 15% 1	1872
	11th to 20th	Night	31% 5% 17% 32% 14%	2090
	21st to end	Night	33% 5% 12% 32% 16% 1	2090
October	1st to 10th	Night	28% 3 8% 36% 19% 5%	3727
	11th to 20th	Night	40% 3 9% 28% 18% 2	3779
	21st to end	Night	47% 4 11% 26% 12%	4363
November	1st to 10th	Night	50% 5% 11% 23% 10% 2	2643
	11th to 20th	Night	57% 5% 13% 15% 8% 1	2675
	21st to end	Night	49% 6% 19% 19% 6%	2660
December	1st to 10th	Night	60% 5% 16% 15% 4	2746
	11th to 20th	Night	62% 4 15% 15% 3	3516
	21st to end	Night	67% 4 11% 13% 5%	5225

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	13% 11% 34% 28% 11% 2	270
	11th to 20th	Day	13% 9% 36% 34% 9%	270
	21st to end	Day	16% 8% 36% 26% 12% 2	297
February	1st to 10th	Day	16% 11% 35% 32% 5% 1	270
	11th to 20th	Day	11% 16% 37% 25% 9%	270
	21st to end	Day	10% 8% 41% 34% 7%	225
March	1st to 10th	Day	16% 13% 37% 28% 7%	270
	11th to 20th	Day	16% 9% 35% 24% 12% 4	270
	21st to end	Day	18% 12% 25% 32% 11% 2	297
April	1st to 10th	Day	21% 14% 34% 22% 8%	415
	11th to 20th	Day	24% 13% 27% 26% 9% 1	640
	21st to end	Day	22% 10% 32% 24% 10% 2	650
May	1st to 10th	Day	20% 11% 31% 25% 12% 2	653
	11th to 20th	Day	18% 9% 29% 28% 13% 3	675
	21st to end	Day	18% 8% 30% 27% 15% 3	734
June	1st to 10th	Day	11% 9% 29% 30% 17% 4	680
	11th to 20th	Day	14% 10% 35% 25% 14% 2	680
	21st to end	Day	12% 8% 30% 31% 16% 4	680
July	1st to 10th	Day	8% 4 21% 34% 25% 7%	671
	11th to 20th	Day	10% 6% 27% 33% 18% 6%	668
	21st to end	Day	6% 5% 25% 37% 23% 6%	739
August	1st to 10th	Day	8% 4 24% 38% 22% 4	676
	11th to 20th	Day	15% 5% 19% 34% 18% 9%	665
	21st to end	Day	11% 6% 27% 32% 21% 3	748
September	1st to 10th	Day	10% 5% 35% 30% 18% 3	514
	11th to 20th	Day	13% 9% 35% 30% 10% 4	300
	21st to end	Day	17% 14% 32% 26% 11% 1	300
October	1st to 10th	Day	18% 9% 30% 29% 11% 2	300
	11th to 20th	Day	18% 13% 36% 25% 8%	300
	21st to end	Day	23% 18% 34% 18% 5% 2	330
November	1st to 10th	Day	21% 8% 28% 36% 6% 1	300
	11th to 20th	Day	18% 14% 41% 21% 5%	273
	21st to end	Day	15% 15% 37% 30% 4	270
December	1st to 10th	Day	12% 8% 40% 28% 11% 1	270
	11th to 20th	Day	14% 11% 43% 26% 4 1	270
	21st to end	Day	21% 11% 35% 25% 7% 2	297
January	1st to 10th	Night	10% 10% 38% 29% 11% 2	950
	11th to 20th	Night	14% 8% 39% 32% 7%	950
	21st to end	Night	14% 9% 38% 30% 8% 1	1045
February	1st to 10th	Night	11% 11% 33% 35% 9% 1	950
	11th to 20th	Night	12% 10% 39% 29% 8% 2	929
	21st to end	Night	15% 9% 32% 31% 12% 2	709
March	1st to 10th	Night	14% 10% 36% 30% 9% 1	666
	11th to 20th	Night	13% 10% 41% 27% 8% 1	570
	21st to end	Night	19% 7% 31% 30% 11% 3	627
April	1st to 10th	Night	18% 10% 35% 29% 8% 1	570
	11th to 20th	Night	23% 10% 31% 26% 9% 1	563
	21st to end	Night	23% 9% 31% 25% 12%	570
May	1st to 10th	Night	21% 7% 30% 32% 8% 1	570
	11th to 20th	Night	17% 6% 36% 32% 10%	561
	21st to end	Night	14% 8% 37% 30% 11% 1	617
June	1st to 10th	Night	12% 7% 29% 37% 14% 1	570
	11th to 20th	Night	13% 6% 32% 40% 8%	570
	21st to end	Night	7% 5% 28% 46% 13% 1	570
July	1st to 10th	Night	6% 2 24% 45% 21% 2	555
	11th to 20th	Night	6% 3 26% 47% 17% 1	552
	21st to end	Night	6% 3 22% 47% 20% 2	624
August	1st to 10th	Night	6% 2 21% 53% 16% 2	567
	11th to 20th	Night	10% 2 25% 39% 22% 2	564
	21st to end	Night	9% 6% 28% 39% 17% 1	627
September	1st to 10th	Night	11% 5% 30% 38% 15% 2	570
	11th to 20th	Night	9% 6% 31% 40% 12% 1	570
	21st to end	Night	14% 6% 35% 34% 11% 1	570
October	1st to 10th	Night	18% 10% 33% 31% 8%	713
	11th to 20th	Night	20% 10% 33% 29% 8%	760
	21st to end	Night	24% 10% 35% 25% 5%	978
November	1st to 10th	Night	17% 10% 34% 31% 7%	975
	11th to 20th	Night	17% 11% 36% 27% 7% 1	956
	21st to end	Night	17% 11% 42% 25% 6%	950
December	1st to 10th	Night	14% 10% 37% 29% 9% 1	950
	11th to 20th	Night	18% 10% 37% 27% 7% 1	950
	21st to end	Night	22% 9% 34% 27% 6% 1	1045

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