Kilbourne Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kilbourne Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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	16% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	75402
	Night	16% 10% 4 7% 6% 3 4 4 5% 7% 35%	74650
Transparency	Day	50% 7% 12% 19% 11% 1	75122
	Night	49% 6% 11% 20% 12% 2	74450
Seeing	Day	19% 9% 25% 23% 16% 7%	14131
	Night	19% 8% 27% 30% 14% 2	23907

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	19% 15% 8% 11% 7% 5% 5% 4 4 4 18%	1706
	11th to 20th	Day	19% 18% 8% 10% 8% 4 4 4 3 5% 17%	1710
	21st to end	Day	17% 18% 8% 11% 8% 4 4 3 5% 5% 16%	1836
February	1st to 10th	Day	21% 16% 6% 10% 9% 4 3 3 4 4 21%	1620
	11th to 20th	Day	16% 13% 7% 12% 9% 3 4 4 5% 6% 21%	1720
	21st to end	Day	18% 15% 6% 9% 7% 3 4 3 4 6% 27%	1480
March	1st to 10th	Day	18% 11% 6% 7% 6% 3 4 5% 5% 6% 29%	1876
	11th to 20th	Day	19% 12% 6% 7% 5% 3 4 4 6% 6% 29%	1980
	21st to end	Day	23% 10% 4 8% 6% 4 4 3 4 6% 27%	2178
April	1st to 10th	Day	16% 11% 4 8% 6% 3 4 4 4 7% 33%	2026
	11th to 20th	Day	18% 9% 3 6% 6% 3 5% 4 5% 7% 34%	2274
	21st to end	Day	19% 8% 4 7% 6% 4 4 4 4 6% 33%	2340
May	1st to 10th	Day	19% 8% 4 6% 6% 4 5% 5% 5% 6% 32%	2340
	11th to 20th	Day	21% 8% 3 6% 6% 3 5% 5% 6% 7% 31%	2301
	21st to end	Day	10% 6% 2 5% 6% 4 6% 7% 8% 9% 37%	2531
June	1st to 10th	Day	12% 6% 3 6% 7% 4 5% 5% 5% 9% 37%	2340
	11th to 20th	Day	12% 7% 2 5% 6% 4 6% 6% 5% 10% 38%	2398
	21st to end	Day	12% 5% 2 5% 6% 4 6% 5% 7% 10% 37%	2520
July	1st to 10th	Day	10% 7% 2 6% 6% 4 5% 5% 7% 10% 38%	2494
	11th to 20th	Day	10% 5% 2 4 5% 3 6% 6% 7% 9% 42%	2340
	21st to end	Day	10% 5% 3 5% 6% 3 5% 6% 8% 11% 39%	2547
August	1st to 10th	Day	8% 4 3 6% 6% 4 5% 6% 7% 11% 41%	2327
	11th to 20th	Day	10% 5% 2 5% 7% 4 6% 7% 7% 10% 36%	2303
	21st to end	Day	9% 5% 3 5% 5% 3 5% 6% 6% 10% 43%	2542
September	1st to 10th	Day	13% 5% 2 5% 4 3 5% 5% 5% 7% 46%	1990
	11th to 20th	Day	10% 5% 3 4 6% 3 4 5% 6% 9% 46%	1980
	21st to end	Day	17% 6% 2 5% 4 3 4 4 5% 7% 43%	1980
October	1st to 10th	Day	15% 6% 3 5% 4 3 5% 4 6% 7% 41%	1926
	11th to 20th	Day	16% 8% 2 5% 5% 3 4 4 5% 6% 40%	1800
	21st to end	Day	22% 11% 3 6% 5% 4 4 5% 5% 6% 31%	1918
November	1st to 10th	Day	11% 7% 3 5% 5% 3 5% 4 4 6% 45%	1672
	11th to 20th	Day	17% 12% 4 5% 7% 2 4 3 4 6% 35%	1710
	21st to end	Day	20% 13% 6% 8% 5% 3 4 3 4 5% 30%	1710
December	1st to 10th	Day	20% 16% 8% 11% 6% 3 5% 3 4 6% 18%	1710
	11th to 20th	Day	19% 16% 6% 9% 7% 3 5% 4 4 5% 22%	2153
	21st to end	Day	25% 22% 7% 9% 8% 3 4 3 3 5% 10%	3124
January	1st to 10th	Night	19% 13% 8% 11% 8% 5% 5% 4 4 4 21%	2459
	11th to 20th	Night	20% 16% 6% 10% 8% 4 4 3 4 5% 20%	2470
	21st to end	Night	18% 17% 6% 10% 7% 4 5% 4 3 5% 21%	2664
February	1st to 10th	Night	22% 13% 5% 9% 7% 3 4 4 4 4 24%	2340
	11th to 20th	Night	18% 12% 6% 7% 8% 5% 5% 4 4 6% 25%	2125
	21st to end	Night	21% 13% 6% 9% 5% 3 4 3 4 5% 26%	1776
March	1st to 10th	Night	17% 10% 3 7% 7% 3 5% 4 5% 5% 32%	2084
	11th to 20th	Night	16% 10% 4 5% 5% 3 4 4 5% 7% 37%	1980
	21st to end	Night	20% 10% 4 6% 6% 3 5% 4 4 6% 33%	2178
April	1st to 10th	Night	16% 8% 3 6% 5% 3 4 5% 5% 8% 37%	1949
	11th to 20th	Night	15% 8% 2 6% 5% 3 5% 6% 5% 8% 37%	1633
	21st to end	Night	16% 8% 3 6% 6% 2 4 4 6% 8% 37%	1620
May	1st to 10th	Night	18% 9% 3 6% 6% 3 5% 5% 6% 7% 32%	1620
	11th to 20th	Night	19% 7% 3 6% 5% 3 4 4 4 8% 37%	1592
	21st to end	Night	7% 5% 2 5% 6% 4 5% 6% 7% 11% 42%	1744
June	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 5% 6% 8% 45%	1620
	11th to 20th	Night	8% 6% 2 4 5% 4 5% 5% 7% 11% 43%	1554
	21st to end	Night	10% 4 2 4 5% 4 5% 5% 7% 10% 45%	1440
July	1st to 10th	Night	9% 4 3 5% 5% 3 5% 5% 6% 8% 47%	1462
	11th to 20th	Night	7% 3 2 5% 5% 3 5% 5% 7% 10% 48%	1620
	21st to end	Night	8% 6% 3 5% 6% 3 4 5% 6% 7% 46%	1771
August	1st to 10th	Night	6% 4 2 5% 5% 3 5% 7% 7% 11% 44%	1611
	11th to 20th	Night	9% 6% 2 6% 6% 3 5% 5% 5% 9% 45%	1598
	21st to end	Night	6% 4 1 4 4 3 5% 6% 7% 8% 51%	1810
September	1st to 10th	Night	13% 5% 2 3 4 3 4 4 4 7% 50%	1952
	11th to 20th	Night	10% 4 2 3 4 2 3 4 4 7% 56%	1980
	21st to end	Night	13% 6% 2 4 5% 3 4 5% 5% 6% 48%	1980
October	1st to 10th	Night	11% 6% 2 4 5% 3 4 4 6% 7% 49%	2034
	11th to 20th	Night	18% 7% 2 6% 5% 2 4 5% 5% 6% 40%	2160
	21st to end	Night	22% 8% 3 6% 5% 2 4 5% 4 5% 36%	2434
November	1st to 10th	Night	15% 6% 3 5% 4 2 4 4 4 6% 45%	2406
	11th to 20th	Night	17% 11% 4 6% 5% 3 4 4 5% 6% 35%	2470
	21st to end	Night	20% 11% 5% 7% 5% 3 4 5% 5% 7% 28%	2470
December	1st to 10th	Night	21% 14% 8% 9% 6% 3 5% 3 4 5% 23%	2470
	11th to 20th	Night	18% 14% 7% 9% 6% 3 4 3 5% 6% 25%	3042
	21st to end	Night	24% 21% 8% 8% 6% 3 4 4 3 5% 15%	4532

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	69% 6% 7% 13% 5%	1707
	11th to 20th	Day	71% 5% 12% 9% 3	1710
	21st to end	Day	71% 5% 9% 11% 4 1	1836
February	1st to 10th	Day	67% 5% 10% 12% 6%	1620
	11th to 20th	Day	64% 6% 8% 15% 6% 1	1730
	21st to end	Day	60% 5% 10% 17% 7% 2	1480
March	1st to 10th	Day	56% 6% 11% 20% 6%	1876
	11th to 20th	Day	55% 6% 10% 18% 8% 1	1980
	21st to end	Day	59% 5% 9% 21% 6% 1	2178
April	1st to 10th	Day	52% 6% 12% 18% 11% 1	2026
	11th to 20th	Day	50% 6% 12% 18% 13% 2	2274
	21st to end	Day	52% 6% 10% 19% 11% 2	2340
May	1st to 10th	Day	52% 7% 13% 18% 9% 2	2340
	11th to 20th	Day	51% 8% 13% 16% 11% 1	2305
	21st to end	Day	39% 10% 15% 23% 11% 1	2531
June	1st to 10th	Day	43% 8% 11% 24% 14% 1	2340
	11th to 20th	Day	41% 8% 15% 21% 13% 1	2398
	21st to end	Day	39% 9% 14% 21% 14% 3	2520
July	1st to 10th	Day	40% 10% 13% 21% 14% 2	2426
	11th to 20th	Day	35% 7% 16% 26% 15% 1	2271
	21st to end	Day	35% 9% 16% 26% 11% 2	2405
August	1st to 10th	Day	36% 10% 14% 26% 14% 1	2314
	11th to 20th	Day	38% 9% 14% 26% 10% 1	2303
	21st to end	Day	35% 9% 14% 23% 15% 5%	2542
September	1st to 10th	Day	36% 7% 12% 22% 18% 4	1990
	11th to 20th	Day	36% 6% 14% 24% 17% 3	1980
	21st to end	Day	41% 6% 10% 22% 20% 1	1980
October	1st to 10th	Day	41% 8% 11% 23% 17% 1	1926
	11th to 20th	Day	44% 6% 11% 23% 15% 2	1800
	21st to end	Day	54% 6% 12% 19% 8% 1	1918
November	1st to 10th	Day	39% 5% 11% 25% 16% 2	1672
	11th to 20th	Day	52% 4 10% 21% 11% 2	1710
	21st to end	Day	58% 4 11% 17% 10% 1	1710
December	1st to 10th	Day	68% 5% 10% 14% 3	1710
	11th to 20th	Day	63% 6% 10% 16% 5%	2150
	21st to end	Day	77% 7% 7% 6% 3	3124
January	1st to 10th	Night	67% 5% 6% 15% 6%	2459
	11th to 20th	Night	67% 5% 11% 12% 4	2470
	21st to end	Night	66% 5% 9% 15% 5% 1	2664
February	1st to 10th	Night	64% 5% 10% 15% 6% 1	2340
	11th to 20th	Night	59% 6% 10% 15% 8% 1	2126
	21st to end	Night	62% 5% 9% 14% 8% 2	1776
March	1st to 10th	Night	53% 5% 10% 19% 11% 1	2084
	11th to 20th	Night	47% 5% 11% 24% 10% 3	1980
	21st to end	Night	52% 5% 10% 21% 11% 1	2178
April	1st to 10th	Night	46% 7% 12% 20% 14% 2	1949
	11th to 20th	Night	44% 7% 12% 16% 18% 3	1633
	21st to end	Night	45% 7% 12% 19% 15% 2	1620
May	1st to 10th	Night	50% 8% 12% 17% 10% 3	1620
	11th to 20th	Night	47% 7% 10% 20% 14% 3	1593
	21st to end	Night	34% 10% 15% 26% 13% 2	1745
June	1st to 10th	Night	36% 7% 14% 22% 19% 2	1620
	11th to 20th	Night	33% 9% 15% 25% 15% 3	1554
	21st to end	Night	33% 9% 14% 24% 17% 3	1440
July	1st to 10th	Night	34% 8% 14% 20% 19% 5%	1421
	11th to 20th	Night	30% 9% 14% 28% 17% 2	1566
	21st to end	Night	34% 7% 14% 26% 14% 4	1672
August	1st to 10th	Night	31% 10% 17% 26% 15% 1	1600
	11th to 20th	Night	36% 8% 14% 25% 17% 1	1598
	21st to end	Night	27% 9% 16% 24% 20% 4	1810
September	1st to 10th	Night	34% 7% 12% 24% 18% 6%	1952
	11th to 20th	Night	29% 5% 11% 28% 24% 3	1980
	21st to end	Night	37% 6% 11% 20% 24% 2	1980
October	1st to 10th	Night	34% 6% 12% 25% 20% 2	2034
	11th to 20th	Night	44% 7% 8% 25% 15% 1	2160
	21st to end	Night	50% 5% 9% 21% 12% 2	2434
November	1st to 10th	Night	39% 5% 12% 23% 18% 3	2406
	11th to 20th	Night	50% 5% 8% 21% 13% 2	2470
	21st to end	Night	56% 6% 11% 19% 7% 1	2470
December	1st to 10th	Night	65% 4 9% 16% 6%	2470
	11th to 20th	Night	60% 6% 12% 17% 5%	3044
	21st to end	Night	73% 5% 9% 10% 3	4532

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	29% 15% 33% 16% 6% 1	270
	11th to 20th	Day	25% 17% 42% 11% 4	270
	21st to end	Day	32% 14% 31% 17% 5% 1	282
February	1st to 10th	Day	33% 17% 35% 15% 1	240
	11th to 20th	Day	28% 20% 38% 12% 2	240
	21st to end	Day	25% 21% 41% 11% 2	198
March	1st to 10th	Day	22% 17% 35% 21% 5%	316
	11th to 20th	Day	25% 15% 36% 18% 6% 1	420
	21st to end	Day	30% 12% 32% 19% 6%	462
April	1st to 10th	Day	24% 12% 31% 20% 11% 2	420
	11th to 20th	Day	22% 15% 27% 21% 10% 5%	412
	21st to end	Day	23% 13% 32% 21% 9% 3	420
May	1st to 10th	Day	26% 9% 30% 20% 10% 4	423
	11th to 20th	Day	24% 6% 23% 25% 15% 5%	447
	21st to end	Day	15% 5% 22% 24% 23% 11%	485
June	1st to 10th	Day	14% 4 20% 33% 23% 7%	450
	11th to 20th	Day	16% 6% 22% 26% 24% 7%	508
	21st to end	Day	13% 6% 25% 28% 21% 7%	630
July	1st to 10th	Day	12% 3 14% 27% 24% 20%	596
	11th to 20th	Day	14% 3 17% 25% 25% 17%	444
	21st to end	Day	11% 2 17% 24% 30% 16%	488
August	1st to 10th	Day	11% 3 11% 24% 32% 19%	446
	11th to 20th	Day	15% 4 14% 27% 25% 15%	439
	21st to end	Day	9% 4 16% 24% 32% 16%	495
September	1st to 10th	Day	14% 3 16% 25% 28% 14%	450
	11th to 20th	Day	10% 3 13% 25% 32% 17%	450
	21st to end	Day	20% 8% 19% 26% 18% 10%	450
October	1st to 10th	Day	13% 8% 22% 28% 20% 9%	450
	11th to 20th	Day	15% 15% 31% 24% 13% 2	450
	21st to end	Day	27% 12% 32% 21% 8%	433
November	1st to 10th	Day	14% 13% 33% 25% 11% 5%	270
	11th to 20th	Day	23% 16% 30% 18% 12% 1	270
	21st to end	Day	27% 14% 37% 18% 4	270
December	1st to 10th	Day	25% 15% 35% 17% 6% 2	270
	11th to 20th	Day	23% 16% 40% 18% 3	270
	21st to end	Day	34% 15% 29% 19% 4	297
January	1st to 10th	Night	24% 14% 36% 22% 3	760
	11th to 20th	Night	29% 14% 34% 19% 4 1	760
	21st to end	Night	26% 12% 33% 25% 3	820
February	1st to 10th	Night	28% 10% 34% 25% 3	720
	11th to 20th	Night	25% 13% 35% 25% 2	703
	21st to end	Night	27% 11% 40% 19% 3	592
March	1st to 10th	Night	23% 12% 32% 26% 6%	720
	11th to 20th	Night	21% 10% 35% 27% 7% 1	720
	21st to end	Night	23% 10% 33% 26% 7%	792
April	1st to 10th	Night	20% 10% 36% 26% 7%	689
	11th to 20th	Night	19% 10% 35% 24% 11% 2	533
	21st to end	Night	20% 7% 38% 25% 9% 1	540
May	1st to 10th	Night	23% 6% 29% 31% 11% 1	540
	11th to 20th	Night	22% 6% 25% 34% 13% 1	531
	21st to end	Night	11% 3 20% 38% 26% 2	584
June	1st to 10th	Night	9% 2 24% 42% 22% 1	540
	11th to 20th	Night	12% 2 18% 45% 22% 2	540
	21st to end	Night	11% 1 20% 42% 24% 2	540
July	1st to 10th	Night	11% 3 11% 38% 30% 6%	525
	11th to 20th	Night	8% 4 13% 37% 34% 5%	522
	21st to end	Night	9% 4 11% 40% 34% 2	591
August	1st to 10th	Night	7% 2 11% 44% 32% 5%	537
	11th to 20th	Night	11% 2 10% 40% 32% 5%	534
	21st to end	Night	7% 2 13% 38% 33% 7%	594
September	1st to 10th	Night	15% 2 14% 33% 31% 5%	692
	11th to 20th	Night	12% 3 12% 34% 34% 5%	720
	21st to end	Night	14% 5% 21% 32% 24% 3	720
October	1st to 10th	Night	13% 4 23% 35% 21% 4	720
	11th to 20th	Night	20% 7% 30% 30% 12% 1	720
	21st to end	Night	25% 12% 27% 27% 9%	792
November	1st to 10th	Night	19% 7% 26% 32% 15% 1	740
	11th to 20th	Night	22% 12% 30% 27% 8% 1	760
	21st to end	Night	24% 10% 30% 29% 6%	760
December	1st to 10th	Night	27% 11% 32% 25% 5%	760
	11th to 20th	Night	25% 10% 35% 25% 5%	760
	21st to end	Night	31% 12% 31% 23% 4	836

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