Kellogg Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kellogg Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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% 11% 4 8% 5% 5% 4 4 5% 7% 31%	101839
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 29%	98280
Transparency	Day	52% 5% 13% 20% 9% 1	105443
	Night	56% 5% 12% 18% 9% 1	102764
Seeing	Day	23% 17% 28% 19% 9% 3	14640
	Night	23% 15% 27% 24% 10% 1	24116

By Month

Percentage Cloud Cover NE (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	18% 25% 7% 12% 7% 6% 3 2 3 4 13%	2517
	11th to 20th	Day	13% 22% 8% 21% 11% 5% 4 2 2 3 8%	2755
	21st to end	Day	22% 19% 8% 13% 7% 5% 5% 3 4 3 10%	3124
February	1st to 10th	Day	16% 19% 5% 14% 8% 6% 5% 3 4 5% 13%	1710
	11th to 20th	Day	13% 19% 6% 16% 8% 6% 5% 2 4 5% 16%	1663
	21st to end	Day	21% 15% 5% 12% 8% 4 4 4 4 5% 17%	1484
March	1st to 10th	Day	19% 13% 5% 9% 5% 4 4 3 4 5% 29%	3432
	11th to 20th	Day	11% 20% 5% 8% 5% 5% 4 4 5% 6% 28%	3480
	21st to end	Day	17% 12% 4 9% 5% 4 4 3 5% 6% 29%	3815
April	1st to 10th	Day	18% 15% 4 7% 4 4 4 3 4 5% 30%	2265
	11th to 20th	Day	19% 10% 3 7% 4 4 4 4 5% 5% 35%	2266
	21st to end	Day	21% 10% 3 7% 4 4 4 4 4 5% 33%	2470
May	1st to 10th	Day	21% 9% 3 7% 5% 4 4 3 5% 7% 32%	4108
	11th to 20th	Day	15% 10% 3 9% 5% 5% 5% 4 6% 8% 29%	4384
	21st to end	Day	13% 7% 2 6% 3 4 3 4 6% 7% 45%	4837
June	1st to 10th	Day	16% 6% 2 6% 4 5% 5% 4 6% 7% 37%	2660
	11th to 20th	Day	13% 5% 3 6% 5% 5% 4 5% 7% 9% 39%	2660
	21st to end	Day	15% 6% 2 5% 4 4 4 4 6% 8% 42%	2660
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	4440
	11th to 20th	Day	13% 6% 2 6% 4 5% 4 4 7% 9% 40%	4440
	21st to end	Day	7% 6% 2 6% 4 5% 6% 5% 7% 10% 41%	4504
August	1st to 10th	Day	18% 6% 2 5% 4 4 4 4 5% 9% 37%	4104
	11th to 20th	Day	13% 6% 3 7% 5% 5% 6% 5% 8% 10% 33%	4044
	21st to end	Day	12% 5% 2 6% 4 4 4 4 6% 9% 44%	4285
September	1st to 10th	Day	15% 7% 2 6% 4 5% 5% 3 6% 6% 41%	2280
	11th to 20th	Day	12% 5% 2 6% 3 5% 4 4 6% 8% 45%	2205
	21st to end	Day	16% 8% 3 7% 5% 6% 5% 4 6% 7% 32%	2028
October	1st to 10th	Day	21% 7% 3 7% 4 4 5% 3 5% 8% 33%	1900
	11th to 20th	Day	21% 10% 3 8% 5% 4 5% 4 6% 6% 28%	1900
	21st to end	Day	26% 13% 4 9% 5% 5% 4 4 4 5% 22%	2090
November	1st to 10th	Day	15% 11% 4 8% 6% 6% 4 3 4 6% 32%	1747
	11th to 20th	Day	15% 15% 5% 9% 5% 6% 4 4 5% 6% 27%	1600
	21st to end	Day	21% 17% 4 9% 7% 5% 4 3 5% 6% 18%	1600
December	1st to 10th	Day	20% 19% 6% 11% 6% 6% 4 4 5% 6% 13%	1600
	11th to 20th	Day	21% 22% 5% 11% 6% 4 4 4 4 5% 13%	1986
	21st to end	Day	26% 25% 6% 11% 5% 4 3 2 3 3 11%	2796
January	1st to 10th	Night	20% 23% 7% 11% 6% 5% 3 2 3 4 15%	4429
	11th to 20th	Night	14% 21% 7% 18% 10% 7% 4 3 4 3 9%	4202
	21st to end	Night	24% 22% 7% 14% 6% 4 4 2 3 3 10%	4532
February	1st to 10th	Night	19% 19% 6% 13% 6% 5% 4 3 4 4 17%	2470
	11th to 20th	Night	16% 16% 6% 12% 7% 5% 5% 4 5% 5% 19%	2403
	21st to end	Night	19% 16% 5% 13% 7% 4 4 3 5% 5% 19%	1966
March	1st to 10th	Night	21% 13% 4 8% 5% 3 3 3 3 5% 31%	3408
	11th to 20th	Night	20% 17% 3 8% 5% 4 4 3 4 6% 26%	3479
	21st to end	Night	17% 10% 3 7% 4 4 4 3 5% 5% 39%	3817
April	1st to 10th	Night	22% 12% 4 7% 5% 4 4 3 5% 4 30%	1914
	11th to 20th	Night	19% 9% 3 8% 4 4 4 4 4 6% 34%	1875
	21st to end	Night	19% 9% 4 6% 4 4 5% 4 4 7% 35%	1715
May	1st to 10th	Night	24% 10% 3 7% 5% 3 3 3 5% 6% 32%	2833
	11th to 20th	Night	14% 7% 3 7% 6% 6% 5% 4 6% 9% 33%	2506
	21st to end	Night	13% 6% 2 6% 3 3 4 4 6% 8% 45%	2738
June	1st to 10th	Night	13% 7% 3 7% 6% 6% 6% 5% 5% 8% 36%	1520
	11th to 20th	Night	13% 5% 2 5% 5% 5% 6% 4 6% 8% 41%	1520
	21st to end	Night	16% 6% 2 6% 4 4 5% 3 6% 7% 40%	1520
July	1st to 10th	Night	9% 7% 3 7% 5% 4 4 4 6% 9% 42%	2520
	11th to 20th	Night	12% 6% 2 6% 4 4 3 3 6% 8% 44%	2520
	21st to end	Night	10% 5% 2 5% 4 5% 5% 4 7% 7% 46%	3045
August	1st to 10th	Night	11% 8% 2 7% 5% 4 4 3 6% 9% 40%	2825
	11th to 20th	Night	16% 7% 2 7% 4 5% 5% 4 6% 7% 37%	2785
	21st to end	Night	9% 4 2 5% 5% 5% 5% 4 7% 9% 45%	3338
September	1st to 10th	Night	14% 7% 2 5% 4 3 4 3 5% 8% 44%	1900
	11th to 20th	Night	13% 5% 2 5% 4 3 3 3 4 8% 51%	1971
	21st to end	Night	17% 8% 2 6% 5% 4 5% 5% 6% 7% 36%	2152
October	1st to 10th	Night	18% 6% 3 7% 5% 4 4 3 4 7% 38%	2280
	11th to 20th	Night	22% 10% 3 7% 4 5% 5% 3 5% 6% 30%	2280
	21st to end	Night	27% 9% 3 6% 5% 5% 4 4 5% 6% 26%	2508
November	1st to 10th	Night	18% 9% 3 7% 4 4 4 3 5% 6% 37%	2548
	11th to 20th	Night	16% 13% 4 9% 6% 5% 5% 3 5% 6% 28%	2800
	21st to end	Night	19% 16% 4 9% 5% 5% 5% 5% 5% 5% 22%	2800
December	1st to 10th	Night	21% 20% 6% 10% 6% 5% 4 3 5% 5% 15%	2800
	11th to 20th	Night	19% 22% 5% 11% 6% 4 4 3 4 4 18%	3428
	21st to end	Night	30% 17% 6% 10% 5% 5% 5% 3 4 5% 11%	4933

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	78% 5% 7% 7% 3	2518
	11th to 20th	Day	82% 5% 6% 5% 1	2755
	21st to end	Day	80% 4 10% 5% 1	3124
February	1st to 10th	Day	75% 4 11% 9% 1	1710
	11th to 20th	Day	72% 4 8% 12% 3	1672
	21st to end	Day	68% 4 10% 12% 5%	1484
March	1st to 10th	Day	57% 5% 11% 21% 6%	3435
	11th to 20th	Day	56% 5% 18% 15% 6% 1	3480
	21st to end	Day	57% 4 10% 21% 7% 1	3815
April	1st to 10th	Day	57% 3 11% 20% 9% 1	2265
	11th to 20th	Day	51% 4 10% 21% 12% 2	2266
	21st to end	Day	54% 3 10% 18% 13% 2	2470
May	1st to 10th	Day	52% 5% 12% 19% 11% 2	4120
	11th to 20th	Day	52% 6% 14% 20% 7% 1	4388
	21st to end	Day	38% 5% 14% 26% 15% 3	4837
June	1st to 10th	Day	45% 6% 13% 20% 15% 1	2660
	11th to 20th	Day	41% 6% 15% 24% 13% 1	2660
	21st to end	Day	40% 6% 14% 25% 14% 1	2660
July	1st to 10th	Day	36% 5% 13% 29% 16% 2	4370
	11th to 20th	Day	39% 5% 14% 25% 16%	4365
	21st to end	Day	37% 7% 18% 22% 15% 1	4360
August	1st to 10th	Day	44% 6% 14% 23% 13% 1	4091
	11th to 20th	Day	44% 7% 17% 24% 7% 1	4083
	21st to end	Day	37% 4 13% 33% 11% 1	4285
September	1st to 10th	Day	42% 6% 14% 25% 11% 1	2280
	11th to 20th	Day	37% 5% 14% 30% 13% 1	2205
	21st to end	Day	50% 5% 14% 21% 9% 1	2028
October	1st to 10th	Day	42% 5% 15% 25% 12% 1	3160
	11th to 20th	Day	46% 5% 16% 20% 12% 1	3140
	21st to end	Day	52% 4 15% 22% 7%	3428
November	1st to 10th	Day	54% 6% 11% 19% 9% 1	1747
	11th to 20th	Day	58% 5% 15% 16% 5% 1	1600
	21st to end	Day	68% 4 13% 11% 4	1600
December	1st to 10th	Day	73% 5% 13% 9% 1	1600
	11th to 20th	Day	74% 5% 10% 9% 2	1986
	21st to end	Day	81% 4 8% 7% 1	2796
January	1st to 10th	Night	75% 6% 8% 8% 2	4429
	11th to 20th	Night	81% 4 8% 5% 1	4202
	21st to end	Night	80% 4 8% 5% 2	4532
February	1st to 10th	Night	73% 4 10% 11% 3	2470
	11th to 20th	Night	68% 3 11% 14% 4	2405
	21st to end	Night	68% 4 9% 13% 5%	1966
March	1st to 10th	Night	58% 4 11% 22% 6%	3418
	11th to 20th	Night	61% 3 14% 15% 6% 1	3480
	21st to end	Night	47% 4 10% 24% 14% 1	3817
April	1st to 10th	Night	57% 4 9% 19% 10% 1	1914
	11th to 20th	Night	51% 4 11% 19% 14% 2	1875
	21st to end	Night	50% 5% 10% 20% 14% 2	1715
May	1st to 10th	Night	54% 5% 10% 18% 10% 3	2840
	11th to 20th	Night	47% 7% 16% 21% 8% 1	2507
	21st to end	Night	37% 6% 12% 24% 19% 2	2739
June	1st to 10th	Night	45% 6% 11% 21% 16% 1	1520
	11th to 20th	Night	40% 5% 14% 21% 18% 2	1520
	21st to end	Night	42% 6% 14% 23% 14% 2	1520
July	1st to 10th	Night	39% 5% 12% 24% 17% 3	2480
	11th to 20th	Night	38% 5% 15% 26% 15% 1	2472
	21st to end	Night	36% 6% 16% 23% 16% 2	2948
August	1st to 10th	Night	41% 5% 16% 26% 11% 1	2814
	11th to 20th	Night	46% 5% 16% 24% 8%	2812
	21st to end	Night	35% 5% 14% 32% 13% 1	3338
September	1st to 10th	Night	38% 5% 13% 27% 14% 2	1900
	11th to 20th	Night	34% 4 13% 30% 18% 1	1971
	21st to end	Night	46% 6% 14% 22% 12% 1	2152
October	1st to 10th	Night	44% 4 10% 24% 16% 1	3800
	11th to 20th	Night	50% 4 13% 19% 13%	3779
	21st to end	Night	46% 4 17% 24% 7% 1	4120
November	1st to 10th	Night	50% 5% 11% 23% 10% 2	2548
	11th to 20th	Night	59% 4 13% 16% 7% 1	2800
	21st to end	Night	64% 5% 15% 13% 3	2800
December	1st to 10th	Night	73% 5% 12% 9% 1	2800
	11th to 20th	Night	72% 5% 11% 10% 3	3428
	21st to end	Night	78% 4 10% 7% 1	4933

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	28% 30% 23% 12% 5% 2	180
	11th to 20th	Day	27% 30% 26% 12% 4 1	249
	21st to end	Day	26% 24% 27% 19% 4	297
February	1st to 10th	Day	31% 27% 28% 11% 3	270
	11th to 20th	Day	29% 33% 28% 9% 1	270
	21st to end	Day	39% 19% 29% 11% 1	282
March	1st to 10th	Day	26% 21% 31% 16% 5% 1	460
	11th to 20th	Day	31% 17% 33% 15% 4 1	460
	21st to end	Day	31% 20% 25% 17% 5% 2	506
April	1st to 10th	Day	25% 23% 28% 17% 6% 1	460
	11th to 20th	Day	31% 21% 22% 15% 7% 3	452
	21st to end	Day	30% 17% 29% 16% 7% 2	460
May	1st to 10th	Day	27% 15% 29% 17% 8% 4	463
	11th to 20th	Day	20% 14% 31% 21% 11% 3	487
	21st to end	Day	17% 13% 31% 23% 10% 5%	529
June	1st to 10th	Day	23% 14% 32% 22% 8% 1	490
	11th to 20th	Day	15% 16% 30% 25% 10% 3	490
	21st to end	Day	21% 15% 30% 24% 8% 2	490
July	1st to 10th	Day	11% 10% 27% 31% 18% 4	485
	11th to 20th	Day	16% 12% 29% 25% 13% 5%	484
	21st to end	Day	11% 9% 34% 28% 12% 5%	532
August	1st to 10th	Day	16% 9% 24% 28% 15% 8%	486
	11th to 20th	Day	13% 9% 28% 26% 16% 8%	479
	21st to end	Day	14% 8% 31% 24% 15% 7%	539
September	1st to 10th	Day	16% 13% 23% 24% 16% 8%	490
	11th to 20th	Day	12% 7% 21% 24% 23% 13%	490
	21st to end	Day	20% 15% 27% 21% 12% 6%	490
October	1st to 10th	Day	26% 12% 25% 19% 13% 5%	490
	11th to 20th	Day	26% 21% 28% 18% 6% 2	490
	21st to end	Day	35% 19% 24% 15% 6%	539
November	1st to 10th	Day	26% 20% 30% 16% 7% 1	347
	11th to 20th	Day	33% 25% 28% 10% 3 3	200
	21st to end	Day	34% 30% 25% 10% 3	200
December	1st to 10th	Day	33% 24% 30% 9% 4 1	200
	11th to 20th	Day	34% 26% 24% 14% 2	200
	21st to end	Day	34% 30% 24% 10% 2	204
January	1st to 10th	Night	32% 24% 26% 13% 4	760
	11th to 20th	Night	32% 24% 26% 15% 3	760
	21st to end	Night	25% 21% 31% 17% 6%	836
February	1st to 10th	Night	28% 26% 28% 15% 3	760
	11th to 20th	Night	26% 23% 30% 17% 3	743
	21st to end	Night	29% 23% 28% 17% 2	628
March	1st to 10th	Night	24% 18% 30% 22% 6%	760
	11th to 20th	Night	28% 17% 30% 20% 5% 1	760
	21st to end	Night	24% 14% 31% 22% 7% 1	836
April	1st to 10th	Night	26% 16% 32% 22% 3	760
	11th to 20th	Night	24% 16% 29% 23% 7% 1	751
	21st to end	Night	24% 9% 31% 28% 8%	575
May	1st to 10th	Night	22% 11% 22% 31% 12% 2	570
	11th to 20th	Night	16% 8% 30% 37% 9%	385
	21st to end	Night	14% 10% 25% 34% 16% 1	411
June	1st to 10th	Night	14% 8% 32% 32% 13% 1	380
	11th to 20th	Night	14% 9% 27% 36% 12%	380
	21st to end	Night	18% 7% 32% 32% 11%	380
July	1st to 10th	Night	10% 6% 25% 41% 17% 1	370
	11th to 20th	Night	13% 7% 29% 33% 18% 1	368
	21st to end	Night	13% 4 25% 39% 17% 2	595
August	1st to 10th	Night	12% 4 20% 40% 22% 2	567
	11th to 20th	Night	11% 6% 21% 34% 26% 3	564
	21st to end	Night	13% 5% 24% 32% 24% 2	750
September	1st to 10th	Night	17% 8% 21% 33% 18% 3	760
	11th to 20th	Night	14% 5% 22% 29% 26% 5%	760
	21st to end	Night	20% 10% 24% 27% 16% 4	760
October	1st to 10th	Night	20% 11% 27% 25% 16% 2	760
	11th to 20th	Night	28% 16% 24% 23% 8% 1	760
	21st to end	Night	33% 15% 26% 22% 4	836
November	1st to 10th	Night	24% 16% 27% 24% 9% 1	780
	11th to 20th	Night	25% 21% 28% 17% 8% 1	800
	21st to end	Night	28% 22% 28% 16% 5%	800
December	1st to 10th	Night	35% 23% 23% 15% 4	800
	11th to 20th	Night	31% 26% 24% 16% 3	800
	21st to end	Night	35% 20% 28% 16% 2	851

Page generated at 2024-12-21 04:13:53. Version ac07

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