Skunk Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skunk Ridge Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	14% 9% 3 7% 5% 5% 5% 4 5% 7% 37%	131712
	Night	15% 10% 3 8% 5% 4 4 3 5% 6% 37%	130836
Transparency	Day	30% 37% 7% 16% 10% 1	135351
	Night	31% 36% 7% 15% 10% 1	135255
Seeing	Day	19% 14% 28% 22% 12% 5%	17291
	Night	19% 11% 26% 27% 14% 2	27086

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	16% 17% 6% 8% 4 4 4 3 4 6% 28%	4691
	11th to 20th	Day	12% 13% 5% 15% 5% 5% 3 3 3 5% 32%	4993
	21st to end	Day	19% 12% 6% 9% 6% 5% 5% 4 5% 5% 24%	5780
February	1st to 10th	Day	19% 13% 4 8% 4 3 3 3 5% 5% 33%	2053
	11th to 20th	Day	18% 11% 5% 8% 4 4 4 3 5% 5% 33%	2048
	21st to end	Day	17% 13% 5% 9% 4 3 4 3 5% 6% 33%	1730
March	1st to 10th	Day	20% 13% 4 7% 4 4 3 2 3 4 35%	4580
	11th to 20th	Day	13% 8% 3 7% 4 4 4 4 6% 8% 40%	5076
	21st to end	Day	17% 9% 3 6% 4 5% 4 4 5% 7% 35%	5586
April	1st to 10th	Day	16% 9% 3 6% 4 4 4 4 6% 8% 36%	2520
	11th to 20th	Day	16% 8% 3 6% 4 4 4 2 5% 7% 40%	2511
	21st to end	Day	17% 7% 3 7% 4 5% 5% 3 5% 7% 37%	2730
May	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 9% 26%	5875
	11th to 20th	Day	21% 8% 2 7% 4 4 4 3 5% 7% 34%	5861
	21st to end	Day	13% 6% 3 8% 5% 5% 6% 5% 7% 9% 31%	6433
June	1st to 10th	Day	11% 6% 2 7% 5% 4 5% 4 5% 7% 42%	2630
	11th to 20th	Day	9% 5% 3 7% 6% 5% 4 5% 6% 9% 43%	2800
	21st to end	Day	9% 5% 3 6% 5% 6% 5% 4 6% 9% 41%	2800
July	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 7% 10% 41%	6360
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 11% 38%	6222
	21st to end	Day	10% 7% 3 9% 7% 7% 7% 5% 8% 8% 30%	6424
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 7% 10% 46%	4234
	11th to 20th	Day	8% 5% 2 6% 4 5% 6% 4 7% 11% 41%	4093
	21st to end	Day	5% 4 1 5% 3 4 5% 3 6% 8% 56%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 7% 48%	2300
	11th to 20th	Day	8% 5% 2 6% 5% 4 4 4 6% 7% 49%	2200
	21st to end	Day	16% 4 2 6% 3 4 3 3 5% 6% 48%	2200
October	1st to 10th	Day	10% 5% 2 5% 4 4 4 3 5% 5% 53%	2200
	11th to 20th	Day	13% 7% 2 5% 4 4 4 3 5% 6% 48%	2066
	21st to end	Day	20% 8% 3 5% 4 4 4 3 4 6% 39%	2017
November	1st to 10th	Day	10% 8% 2 5% 3 4 3 3 4 6% 53%	1852
	11th to 20th	Day	16% 11% 3 6% 4 4 4 3 5% 6% 38%	1890
	21st to end	Day	18% 11% 4 7% 4 3 3 2 4 5% 38%	1890
December	1st to 10th	Day	19% 11% 3 7% 4 3 3 3 4 4 40%	3020
	11th to 20th	Day	18% 14% 5% 8% 5% 5% 5% 4 4 5% 27%	3463
	21st to end	Day	22% 19% 4 9% 6% 4 4 3 4 5% 20%	4272
January	1st to 10th	Night	15% 14% 6% 12% 5% 5% 5% 4 5% 5% 24%	8232
	11th to 20th	Night	13% 15% 6% 14% 6% 4 4 3 3 5% 27%	7948
	21st to end	Night	18% 12% 4 8% 5% 4 4 3 4 5% 33%	8401
February	1st to 10th	Night	20% 14% 5% 8% 4 4 4 4 4 5% 28%	2562
	11th to 20th	Night	18% 11% 4 8% 5% 3 4 3 5% 6% 32%	2458
	21st to end	Night	20% 14% 4 8% 4 3 3 3 4 5% 32%	2076
March	1st to 10th	Night	21% 13% 3 6% 4 3 3 2 4 5% 36%	5493
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 6% 6% 44%	5103
	21st to end	Night	16% 9% 4 8% 6% 4 5% 4 5% 6% 33%	5588
April	1st to 10th	Night	14% 9% 3 6% 4 4 5% 4 7% 7% 37%	2117
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 4 5% 6% 40%	2055
	21st to end	Night	17% 6% 3 6% 5% 4 3 3 7% 7% 37%	1890
May	1st to 10th	Night	20% 10% 3 8% 5% 5% 5% 3 5% 8% 28%	4042
	11th to 20th	Night	17% 7% 2 7% 5% 5% 5% 4 6% 9% 32%	4032
	21st to end	Night	13% 6% 3 7% 4 5% 4 4 6% 9% 38%	4421
June	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 5% 8% 49%	1764
	11th to 20th	Night	8% 5% 2 6% 3 5% 5% 3 7% 11% 46%	1600
	21st to end	Night	6% 4 1 5% 4 4 5% 5% 7% 10% 49%	1600
July	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 8% 48%	3618
	11th to 20th	Night	7% 5% 2 8% 4 5% 6% 5% 6% 9% 43%	3746
	21st to end	Night	9% 6% 2 8% 5% 5% 5% 5% 7% 9% 38%	4427
August	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 4 6% 10% 48%	2915
	11th to 20th	Night	7% 5% 2 7% 4 4 4 4 6% 8% 48%	2938
	21st to end	Night	4 2 1 4 3 3 4 3 5% 9% 61%	3586
September	1st to 10th	Night	11% 4 2 5% 3 3 3 3 6% 7% 52%	2080
	11th to 20th	Night	9% 4 2 4 3 3 4 3 5% 9% 53%	2200
	21st to end	Night	15% 5% 2 6% 4 3 4 2 5% 6% 49%	2200
October	1st to 10th	Night	9% 4 2 5% 3 3 4 4 5% 6% 56%	2200
	11th to 20th	Night	14% 6% 2 5% 3 4 4 4 5% 6% 47%	2333
	21st to end	Night	19% 8% 2 6% 3 4 3 3 4 6% 41%	2820
November	1st to 10th	Night	13% 8% 2 5% 3 3 4 3 5% 5% 49%	2666
	11th to 20th	Night	15% 9% 3 7% 3 3 4 3 5% 7% 41%	2730
	21st to end	Night	20% 12% 4 6% 4 4 3 3 4 6% 35%	2730
December	1st to 10th	Night	17% 11% 4 8% 5% 3 3 2 4 4 38%	4380
	11th to 20th	Night	19% 13% 5% 9% 4 4 4 3 4 6% 29%	4952
	21st to end	Night	23% 19% 6% 10% 5% 4 4 3 4 4 18%	6933

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	47% 21% 9% 16% 6%	4692
	11th to 20th	Day	44% 21% 6% 15% 12% 2	4993
	21st to end	Day	51% 23% 5% 13% 5% 3	5780
February	1st to 10th	Day	22% 58% 4 9% 5%	2053
	11th to 20th	Day	23% 58% 3 10% 6%	2058
	21st to end	Day	19% 59% 5% 10% 5% 1	1730
March	1st to 10th	Day	41% 29% 3 11% 11% 5%	4580
	11th to 20th	Day	29% 29% 6% 23% 12% 1	5076
	21st to end	Day	32% 30% 10% 15% 11% 1	5586
April	1st to 10th	Day	22% 59% 6% 9% 4	2520
	11th to 20th	Day	18% 60% 5% 10% 6% 1	2511
	21st to end	Day	18% 59% 5% 11% 6% 1	2730
May	1st to 10th	Day	38% 32% 10% 12% 8%	5910
	11th to 20th	Day	36% 30% 9% 18% 7%	5865
	21st to end	Day	34% 31% 10% 16% 8% 1	6447
June	1st to 10th	Day	16% 63% 4 8% 8% 1	2630
	11th to 20th	Day	17% 64% 4 8% 8% 1	2800
	21st to end	Day	16% 62% 7% 7% 7% 1	2800
July	1st to 10th	Day	28% 27% 8% 19% 16% 1	6291
	11th to 20th	Day	30% 28% 11% 22% 9%	6147
	21st to end	Day	40% 27% 9% 14% 10% 1	6240
August	1st to 10th	Day	20% 38% 9% 26% 6%	4221
	11th to 20th	Day	23% 37% 7% 24% 9%	4132
	21st to end	Day	14% 37% 10% 25% 14% 1	4311
September	1st to 10th	Day	13% 58% 5% 12% 10% 2	2300
	11th to 20th	Day	14% 57% 6% 11% 10% 1	2200
	21st to end	Day	16% 57% 5% 12% 10%	2200
October	1st to 10th	Day	12% 36% 3 23% 25% 1	3590
	11th to 20th	Day	16% 37% 4 19% 23% 1	3345
	21st to end	Day	20% 35% 6% 18% 20% 1	3229
November	1st to 10th	Day	20% 54% 5% 14% 7% 1	1852
	11th to 20th	Day	21% 54% 2 11% 10% 2	1890
	21st to end	Day	25% 55% 5% 11% 4	1890
December	1st to 10th	Day	30% 34% 5% 18% 12%	3020
	11th to 20th	Day	42% 31% 5% 15% 6% 1	3460
	21st to end	Day	52% 27% 7% 8% 5% 1	4272
January	1st to 10th	Night	50% 22% 7% 13% 7%	8233
	11th to 20th	Night	49% 21% 5% 11% 11% 3	7948
	21st to end	Night	43% 22% 7% 17% 9% 1	8401
February	1st to 10th	Night	24% 59% 4 9% 5%	2562
	11th to 20th	Night	23% 58% 4 9% 5%	2459
	21st to end	Night	22% 58% 4 9% 6% 1	2076
March	1st to 10th	Night	39% 29% 4 18% 7% 3	5493
	11th to 20th	Night	26% 29% 7% 21% 16% 1	5103
	21st to end	Night	38% 30% 4 19% 9% 1	5588
April	1st to 10th	Night	21% 60% 5% 8% 5%	2117
	11th to 20th	Night	19% 59% 5% 9% 6% 1	2055
	21st to end	Night	18% 59% 4 13% 5% 1	1890
May	1st to 10th	Night	39% 32% 8% 14% 6% 1	4069
	11th to 20th	Night	34% 31% 11% 18% 5%	4033
	21st to end	Night	32% 31% 12% 16% 8% 1	4429
June	1st to 10th	Night	14% 62% 4 10% 8% 2	1764
	11th to 20th	Night	15% 62% 5% 8% 9% 2	1600
	21st to end	Night	11% 62% 8% 10% 8% 1	1600
July	1st to 10th	Night	26% 28% 8% 20% 16% 2	3580
	11th to 20th	Night	29% 28% 11% 22% 10%	3701
	21st to end	Night	33% 27% 11% 17% 10% 2	4297
August	1st to 10th	Night	23% 38% 9% 25% 6%	2904
	11th to 20th	Night	23% 37% 7% 22% 10%	2965
	21st to end	Night	11% 36% 11% 26% 16% 1	3586
September	1st to 10th	Night	11% 58% 6% 12% 11% 2	2080
	11th to 20th	Night	11% 58% 4 12% 13% 2	2200
	21st to end	Night	15% 57% 6% 10% 11% 1	2200
October	1st to 10th	Night	12% 36% 3 16% 33% 1	3590
	11th to 20th	Night	13% 36% 6% 15% 29% 2	3793
	21st to end	Night	19% 35% 4 15% 23% 3	4546
November	1st to 10th	Night	22% 53% 5% 11% 8% 1	2666
	11th to 20th	Night	19% 54% 3 11% 10% 2	2730
	21st to end	Night	26% 54% 5% 10% 4	2730
December	1st to 10th	Night	33% 34% 7% 16% 10%	4380
	11th to 20th	Night	39% 32% 9% 13% 7%	4954
	21st to end	Night	55% 27% 6% 9% 3	6933

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% 24% 32% 12% 3 1	330
	11th to 20th	Day	34% 28% 27% 9% 2	330
	21st to end	Day	31% 29% 32% 6% 2	363
February	1st to 10th	Day	29% 24% 35% 10% 2	330
	11th to 20th	Day	33% 29% 28% 7% 1 1	330
	21st to end	Day	32% 21% 36% 8% 2	273
March	1st to 10th	Day	27% 28% 33% 11% 1	330
	11th to 20th	Day	28% 24% 32% 12% 5%	526
	21st to end	Day	31% 20% 30% 13% 5%	594
April	1st to 10th	Day	27% 19% 30% 16% 7% 1	540
	11th to 20th	Day	25% 20% 29% 18% 6% 3	532
	21st to end	Day	22% 19% 35% 15% 7% 2	540
May	1st to 10th	Day	23% 18% 36% 13% 7% 4	507
	11th to 20th	Day	20% 15% 29% 22% 9% 5%	527
	21st to end	Day	16% 10% 29% 24% 13% 7%	573
June	1st to 10th	Day	13% 9% 28% 28% 16% 6%	560
	11th to 20th	Day	11% 7% 25% 33% 17% 6%	730
	21st to end	Day	11% 7% 28% 29% 17% 8%	730
July	1st to 10th	Day	14% 5% 19% 27% 21% 15%	721
	11th to 20th	Day	8% 5% 24% 30% 22% 10%	658
	21st to end	Day	13% 3 19% 34% 20% 11%	576
August	1st to 10th	Day	9% 4 21% 31% 22% 13%	526
	11th to 20th	Day	12% 6% 22% 31% 20% 10%	519
	21st to end	Day	9% 4 18% 31% 28% 11%	583
September	1st to 10th	Day	11% 6% 19% 29% 26% 8%	530
	11th to 20th	Day	10% 4 17% 30% 25% 15%	530
	21st to end	Day	20% 7% 22% 24% 21% 6%	530
October	1st to 10th	Day	11% 6% 24% 32% 20% 6%	530
	11th to 20th	Day	18% 14% 30% 21% 12% 4	530
	21st to end	Day	24% 18% 36% 18% 4 1	400
November	1st to 10th	Day	15% 18% 36% 24% 5% 2	330
	11th to 20th	Day	27% 22% 25% 21% 4 1	330
	21st to end	Day	29% 16% 35% 15% 4	330
December	1st to 10th	Day	26% 23% 36% 11% 4 1	330
	11th to 20th	Day	25% 23% 35% 12% 5%	330
	21st to end	Day	34% 21% 31% 12% 2	363
January	1st to 10th	Night	24% 20% 31% 21% 4	1050
	11th to 20th	Night	30% 20% 32% 16% 2	939
	21st to end	Night	26% 19% 35% 17% 3	924
February	1st to 10th	Night	27% 16% 32% 22% 2	840
	11th to 20th	Night	26% 21% 32% 19% 1	823
	21st to end	Night	29% 16% 36% 18% 1	692
March	1st to 10th	Night	25% 19% 30% 22% 4	840
	11th to 20th	Night	23% 17% 32% 20% 6% 1	840
	21st to end	Night	23% 16% 32% 23% 6%	924
April	1st to 10th	Night	20% 13% 35% 25% 6%	647
	11th to 20th	Night	20% 14% 30% 26% 9% 1	623
	21st to end	Night	19% 11% 36% 25% 8% 1	630
May	1st to 10th	Night	21% 9% 32% 25% 12% 1	603
	11th to 20th	Night	16% 7% 29% 31% 16% 2	591
	21st to end	Night	12% 5% 23% 32% 25% 4	650
June	1st to 10th	Night	12% 3 21% 39% 22% 2	600
	11th to 20th	Night	10% 4 18% 41% 25% 3	600
	21st to end	Night	7% 4 22% 36% 27% 4	600
July	1st to 10th	Night	13% 2 13% 33% 30% 9%	585
	11th to 20th	Night	7% 3 14% 38% 34% 5%	582
	21st to end	Night	13% 2 12% 37% 32% 5%	657
August	1st to 10th	Night	9% 2 11% 37% 36% 6%	597
	11th to 20th	Night	9% 2 12% 37% 34% 6%	594
	21st to end	Night	6% 3 13% 34% 37% 6%	660
September	1st to 10th	Night	13% 2 15% 34% 31% 4	680
	11th to 20th	Night	9% 4 16% 32% 34% 5%	800
	21st to end	Night	16% 7% 21% 30% 24% 3	800
October	1st to 10th	Night	11% 6% 22% 32% 24% 5%	800
	11th to 20th	Night	18% 10% 25% 30% 16% 2	800
	21st to end	Night	23% 13% 30% 23% 10% 1	880
November	1st to 10th	Night	17% 11% 29% 27% 15% 1	820
	11th to 20th	Night	20% 18% 29% 23% 9% 1	840
	21st to end	Night	28% 15% 23% 27% 7%	840
December	1st to 10th	Night	28% 15% 31% 20% 6%	840
	11th to 20th	Night	26% 17% 30% 21% 6% 1	840
	21st to end	Night	31% 16% 32% 19% 3	1055

Page generated at 2026-04-29 02:21:43. Version ac07

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