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 2024-01-13.

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% 4 7% 6% 4 5% 5% 6% 7% 36%	74675
	Night	11% 9% 4 8% 6% 3 5% 5% 5% 7% 36%	75084
Transparency	Day	46% 6% 15% 24% 9% 1	74367
	Night	47% 5% 14% 23% 10% 1	74915
Seeing	Day	15% 9% 30% 29% 14% 3	14921
	Night	15% 8% 33% 33% 10% 1	24969

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	6% 13% 6% 11% 11% 5% 6% 6% 7% 7% 23%	1328
	11th to 20th	Day	9% 12% 7% 12% 9% 5% 7% 6% 7% 6% 20%	1377
	21st to end	Day	9% 14% 6% 15% 11% 5% 7% 7% 5% 6% 15%	1662
February	1st to 10th	Day	7% 13% 6% 9% 7% 5% 7% 7% 8% 6% 25%	1620
	11th to 20th	Day	6% 11% 5% 9% 9% 6% 8% 7% 7% 7% 25%	1574
	21st to end	Day	10% 11% 5% 10% 9% 7% 7% 5% 7% 8% 20%	1421
March	1st to 10th	Day	13% 11% 5% 9% 10% 5% 6% 4 4 6% 27%	1888
	11th to 20th	Day	11% 10% 5% 10% 7% 3 5% 6% 5% 7% 30%	1980
	21st to end	Day	13% 11% 6% 9% 8% 3 4 5% 5% 7% 27%	2178
April	1st to 10th	Day	14% 10% 5% 8% 7% 3 6% 5% 5% 7% 32%	2116
	11th to 20th	Day	17% 11% 4 7% 6% 4 4 4 5% 7% 31%	2309
	21st to end	Day	21% 9% 3 6% 5% 3 4 5% 5% 6% 33%	2340
May	1st to 10th	Day	18% 8% 3 6% 5% 3 4 5% 5% 7% 35%	2340
	11th to 20th	Day	14% 7% 3 6% 5% 4 5% 5% 6% 7% 39%	2474
	21st to end	Day	16% 6% 3 5% 5% 3 5% 4 5% 7% 39%	2848
June	1st to 10th	Day	13% 5% 2 6% 5% 3 5% 5% 6% 8% 42%	2700
	11th to 20th	Day	14% 5% 3 4 5% 3 5% 6% 7% 8% 42%	2700
	21st to end	Day	10% 4 3 5% 5% 3 5% 5% 7% 9% 43%	2700
July	1st to 10th	Day	7% 4 2 4 3 2 4 6% 7% 10% 53%	2700
	11th to 20th	Day	9% 4 2 5% 4 3 5% 5% 7% 9% 48%	2700
	21st to end	Day	5% 4 1 4 5% 3 4 5% 6% 10% 53%	2742
August	1st to 10th	Day	8% 3 2 5% 6% 3 5% 5% 8% 10% 45%	2328
	11th to 20th	Day	13% 6% 2 4 4 3 4 5% 6% 8% 45%	2301
	21st to end	Day	9% 4 2 4 4 3 4 4 5% 7% 53%	2574
September	1st to 10th	Day	11% 5% 2 4 4 3 4 4 5% 8% 50%	2183
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 4 6% 7% 46%	1980
	21st to end	Day	16% 5% 2 5% 5% 3 4 5% 5% 7% 44%	1980
October	1st to 10th	Day	17% 9% 3 6% 4 3 4 4 4 7% 39%	1826
	11th to 20th	Day	18% 10% 3 6% 5% 3 4 3 4 5% 39%	1800
	21st to end	Day	18% 11% 4 7% 6% 3 4 4 4 6% 32%	1841
November	1st to 10th	Day	14% 12% 6% 10% 6% 3 4 3 4 5% 34%	1570
	11th to 20th	Day	10% 14% 7% 13% 7% 4 5% 4 3 5% 26%	1520
	21st to end	Day	10% 12% 6% 10% 10% 4 4 5% 4 5% 30%	1520
December	1st to 10th	Day	8% 14% 6% 12% 10% 5% 7% 7% 5% 5% 21%	1430
	11th to 20th	Day	9% 13% 6% 12% 8% 5% 5% 6% 5% 7% 24%	1683
	21st to end	Day	20% 13% 5% 11% 9% 5% 4 4 4 4 21%	2442
January	1st to 10th	Night	7% 9% 7% 10% 10% 5% 8% 7% 6% 6% 25%	2837
	11th to 20th	Night	8% 12% 7% 12% 9% 4 8% 7% 6% 6% 20%	2642
	21st to end	Night	9% 13% 6% 11% 9% 5% 7% 7% 8% 6% 20%	2692
February	1st to 10th	Night	6% 11% 4 11% 8% 5% 7% 7% 7% 6% 29%	2340
	11th to 20th	Night	6% 11% 4 10% 8% 5% 8% 6% 7% 7% 28%	2273
	21st to end	Night	11% 11% 6% 8% 8% 4 5% 5% 5% 7% 30%	1852
March	1st to 10th	Night	12% 10% 5% 10% 7% 3 5% 4 5% 9% 30%	2071
	11th to 20th	Night	10% 10% 4 9% 6% 3 5% 4 5% 6% 38%	1980
	21st to end	Night	13% 9% 3 10% 6% 3 4 4 5% 7% 35%	2178
April	1st to 10th	Night	13% 8% 3 6% 5% 4 5% 5% 5% 9% 39%	1842
	11th to 20th	Night	18% 10% 5% 6% 5% 3 4 3 5% 5% 36%	1599
	21st to end	Night	18% 10% 3 6% 6% 3 3 4 4 6% 37%	1620
May	1st to 10th	Night	16% 9% 4 7% 5% 2 5% 4 5% 5% 39%	1620
	11th to 20th	Night	14% 6% 2 4 5% 3 4 5% 5% 7% 45%	1420
	21st to end	Night	12% 5% 3 5% 5% 3 5% 4 6% 9% 44%	1424
June	1st to 10th	Night	10% 4 2 5% 5% 2 4 6% 6% 9% 47%	1260
	11th to 20th	Night	10% 6% 2 4 5% 3 4 5% 5% 9% 48%	1260
	21st to end	Night	5% 4 2 4 4 3 4 6% 6% 11% 48%	1260
July	1st to 10th	Night	4 3 2 3 4 2 3 4 4 11% 58%	1260
	11th to 20th	Night	5% 3 1 3 3 2 5% 4 6% 7% 60%	1260
	21st to end	Night	5% 2 2 3 5% 2 4 4 6% 7% 60%	1571
August	1st to 10th	Night	6% 4 1 4 5% 3 4 5% 7% 9% 53%	1611
	11th to 20th	Night	8% 5% 2 4 3 2 4 3 6% 9% 54%	1600
	21st to end	Night	8% 5% 1 3 3 2 4 4 5% 7% 58%	1782
September	1st to 10th	Night	10% 4 1 3 4 3 4 3 6% 8% 55%	1773
	11th to 20th	Night	8% 5% 2 4 4 3 4 4 4 7% 54%	1980
	21st to end	Night	12% 6% 2 4 5% 2 3 3 4 6% 52%	1980
October	1st to 10th	Night	14% 7% 2 6% 4 3 5% 5% 5% 7% 42%	2115
	11th to 20th	Night	16% 9% 3 5% 5% 3 4 5% 4 5% 41%	2160
	21st to end	Night	18% 10% 3 6% 5% 3 4 4 5% 6% 36%	2510
November	1st to 10th	Night	12% 12% 5% 7% 5% 3 5% 5% 5% 7% 34%	2507
	11th to 20th	Night	11% 12% 7% 11% 7% 4 4 5% 5% 5% 29%	2660
	21st to end	Night	11% 10% 4 7% 8% 4 5% 5% 6% 6% 34%	2660
December	1st to 10th	Night	8% 12% 7% 10% 11% 5% 6% 6% 5% 6% 24%	2746
	11th to 20th	Night	10% 13% 6% 13% 9% 4 5% 5% 5% 6% 24%	3514
	21st to end	Night	19% 13% 6% 10% 9% 4 5% 5% 4 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	58% 5% 15% 16% 5%	1329
	11th to 20th	Day	62% 6% 10% 16% 6%	1377
	21st to end	Day	68% 5% 11% 11% 5%	1662
February	1st to 10th	Day	57% 5% 12% 18% 8%	1620
	11th to 20th	Day	56% 6% 14% 18% 6% 1	1583
	21st to end	Day	60% 6% 11% 15% 7%	1421
March	1st to 10th	Day	58% 6% 15% 16% 5%	1888
	11th to 20th	Day	53% 5% 14% 19% 8% 1	1980
	21st to end	Day	56% 6% 14% 19% 5%	2178
April	1st to 10th	Day	52% 5% 11% 21% 10% 1	2116
	11th to 20th	Day	53% 4 13% 18% 11% 1	2312
	21st to end	Day	52% 5% 12% 22% 8% 1	2340
May	1st to 10th	Day	49% 5% 12% 24% 9% 1	2340
	11th to 20th	Day	43% 6% 14% 26% 10% 1	2478
	21st to end	Day	44% 7% 14% 24% 10% 1	2848
June	1st to 10th	Day	40% 5% 18% 28% 9%	2700
	11th to 20th	Day	39% 7% 17% 24% 12% 1	2700
	21st to end	Day	35% 8% 20% 26% 11%	2700
July	1st to 10th	Day	25% 7% 18% 34% 14% 1	2626
	11th to 20th	Day	32% 7% 19% 28% 13% 2	2619
	21st to end	Day	26% 7% 17% 34% 14% 1	2589
August	1st to 10th	Day	31% 7% 18% 31% 10% 2	2314
	11th to 20th	Day	35% 7% 18% 28% 10% 1	2301
	21st to end	Day	31% 4 15% 34% 15% 1	2574
September	1st to 10th	Day	33% 5% 16% 34% 12% 1	2183
	11th to 20th	Day	37% 6% 17% 30% 10%	1980
	21st to end	Day	39% 6% 16% 31% 8% 1	1980
October	1st to 10th	Day	46% 4 14% 25% 10%	1826
	11th to 20th	Day	49% 4 12% 25% 11% 1	1800
	21st to end	Day	53% 5% 14% 21% 7%	1841
November	1st to 10th	Day	54% 5% 13% 17% 11% 1	1570
	11th to 20th	Day	62% 4 12% 15% 7%	1520
	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	58% 6% 12% 19% 6%	2837
	11th to 20th	Night	62% 7% 12% 12% 7%	2642
	21st to end	Night	62% 5% 11% 16% 6%	2692
February	1st to 10th	Night	53% 5% 15% 19% 7% 1	2340
	11th to 20th	Night	53% 6% 11% 19% 11% 1	2274
	21st to end	Night	53% 5% 12% 20% 9% 1	1852
March	1st to 10th	Night	52% 5% 15% 20% 7%	2071
	11th to 20th	Night	46% 4 13% 25% 11%	1980
	21st to end	Night	50% 5% 15% 22% 7% 1	2178
April	1st to 10th	Night	44% 5% 13% 24% 12% 2	1842
	11th to 20th	Night	50% 3 9% 22% 13% 2	1599
	21st to end	Night	50% 4 11% 24% 10% 1	1620
May	1st to 10th	Night	46% 6% 11% 21% 14% 2	1620
	11th to 20th	Night	38% 7% 11% 24% 16% 3	1421
	21st to end	Night	38% 6% 14% 26% 14% 2	1425
June	1st to 10th	Night	32% 6% 17% 34% 9% 2	1260
	11th to 20th	Night	34% 6% 17% 24% 14% 5%	1260
	21st to end	Night	28% 8% 20% 31% 11% 2	1260
July	1st to 10th	Night	23% 5% 17% 33% 20% 1	1225
	11th to 20th	Night	22% 6% 16% 34% 18% 3	1218
	21st to end	Night	23% 6% 15% 37% 17% 3	1484
August	1st to 10th	Night	26% 7% 15% 34% 16% 3	1601
	11th to 20th	Night	28% 5% 19% 32% 16% 1	1600
	21st to end	Night	26% 5% 14% 32% 22% 1	1782
September	1st to 10th	Night	27% 6% 14% 35% 16% 1	1773
	11th to 20th	Night	31% 5% 17% 31% 15%	1980
	21st to end	Night	34% 5% 13% 33% 15% 1	1980
October	1st to 10th	Night	41% 5% 13% 27% 12% 2	2115
	11th to 20th	Night	45% 4 11% 26% 12% 1	2160
	21st to end	Night	49% 5% 13% 24% 9%	2510
November	1st to 10th	Night	49% 5% 11% 23% 10% 2	2507
	11th to 20th	Night	57% 5% 13% 15% 8% 1	2660
	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	14% 8% 32% 36% 9%	248
	21st to end	Day	19% 8% 38% 25% 9% 2	264
February	1st to 10th	Day	16% 12% 38% 30% 4	240
	11th to 20th	Day	13% 18% 36% 25% 8%	240
	21st to end	Day	10% 8% 42% 32% 8%	198
March	1st to 10th	Day	16% 13% 35% 28% 8%	240
	11th to 20th	Day	16% 9% 32% 26% 13% 4	240
	21st to end	Day	17% 13% 24% 31% 12% 2	264
April	1st to 10th	Day	20% 15% 35% 20% 9% 1	376
	11th to 20th	Day	24% 13% 26% 26% 9% 1	590
	21st to end	Day	21% 10% 32% 25% 11% 2	600
May	1st to 10th	Day	20% 10% 31% 25% 12% 2	603
	11th to 20th	Day	18% 9% 30% 26% 14% 3	625
	21st to end	Day	17% 8% 30% 28% 15% 3	679
June	1st to 10th	Day	12% 7% 28% 31% 18% 4	630
	11th to 20th	Day	14% 9% 35% 25% 15% 2	630
	21st to end	Day	11% 7% 29% 32% 17% 5%	630
July	1st to 10th	Day	8% 4 21% 36% 25% 7%	621
	11th to 20th	Day	10% 7% 27% 33% 18% 5%	618
	21st to end	Day	6% 5% 25% 37% 23% 5%	684
August	1st to 10th	Day	7% 3 24% 38% 23% 5%	626
	11th to 20th	Day	14% 5% 20% 34% 17% 9%	615
	21st to end	Day	11% 5% 26% 32% 22% 3	693
September	1st to 10th	Day	10% 5% 35% 29% 18% 3	473
	11th to 20th	Day	14% 9% 34% 29% 11% 3	270
	21st to end	Day	18% 14% 32% 25% 10% 1	270
October	1st to 10th	Day	20% 9% 29% 29% 12% 2	270
	11th to 20th	Day	18% 13% 35% 26% 9%	270
	21st to end	Day	23% 18% 34% 18% 5% 2	297
November	1st to 10th	Day	21% 9% 27% 36% 7% 1	270
	11th to 20th	Day	19% 14% 41% 21% 6%	270
	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% 38% 32% 7%	915
	21st to end	Night	15% 9% 39% 29% 8% 1	990
February	1st to 10th	Night	11% 11% 34% 34% 9% 1	900
	11th to 20th	Night	12% 11% 38% 29% 8% 2	879
	21st to end	Night	15% 9% 31% 31% 12% 2	668
March	1st to 10th	Night	14% 9% 36% 30% 10% 1	631
	11th to 20th	Night	13% 9% 41% 28% 9% 1	540
	21st to end	Night	19% 7% 30% 29% 11% 3	594
April	1st to 10th	Night	18% 9% 36% 28% 8% 1	540
	11th to 20th	Night	24% 9% 30% 27% 10% 1	533
	21st to end	Night	23% 9% 31% 25% 12%	540
May	1st to 10th	Night	21% 7% 30% 33% 9% 1	540
	11th to 20th	Night	17% 6% 36% 31% 10%	531
	21st to end	Night	14% 8% 36% 30% 11% 1	584
June	1st to 10th	Night	12% 6% 28% 38% 15% 1	540
	11th to 20th	Night	12% 6% 32% 41% 9%	540
	21st to end	Night	7% 5% 27% 46% 14% 1	540
July	1st to 10th	Night	6% 2 24% 46% 21% 1	525
	11th to 20th	Night	7% 3 26% 48% 16% 1	522
	21st to end	Night	6% 3 21% 48% 20% 2	591
August	1st to 10th	Night	6% 2 20% 54% 16% 2	537
	11th to 20th	Night	10% 2 26% 39% 22% 2	534
	21st to end	Night	9% 6% 27% 39% 17% 1	594
September	1st to 10th	Night	11% 5% 29% 39% 15% 2	540
	11th to 20th	Night	9% 6% 30% 41% 12% 1	540
	21st to end	Night	14% 6% 34% 33% 11% 1	540
October	1st to 10th	Night	19% 10% 32% 30% 8%	675
	11th to 20th	Night	20% 10% 33% 29% 8%	720
	21st to end	Night	24% 11% 34% 26% 6%	926
November	1st to 10th	Night	17% 9% 34% 32% 7%	925
	11th to 20th	Night	17% 11% 36% 27% 7% 1	950
	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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