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 2024-07-31.

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	15% 9% 3 7% 4 4 4 3 5% 7% 37%	89968
	Night	16% 10% 3 7% 4 4 4 3 5% 6% 38%	89821
Transparency	Day	22% 55% 5% 10% 7% 1	89732
	Night	23% 53% 5% 11% 7% 1	89662
Seeing	Day	19% 14% 28% 22% 12% 5%	14973
	Night	19% 11% 26% 27% 14% 2	24714

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	15% 18% 6% 8% 4 4 4 4 4 5% 29%	2527
	11th to 20th	Day	17% 14% 5% 12% 5% 6% 4 3 3 4 27%	2683
	21st to end	Day	29% 15% 8% 7% 4 3 3 3 3 4 22%	3124
February	1st to 10th	Day	19% 13% 4 9% 4 3 3 3 5% 5% 32%	1857
	11th to 20th	Day	17% 11% 5% 8% 4 4 4 2 5% 5% 34%	1848
	21st to end	Day	19% 13% 5% 8% 4 3 4 3 5% 6% 31%	1570
March	1st to 10th	Day	24% 14% 4 7% 4 3 3 2 3 4 32%	3120
	11th to 20th	Day	14% 8% 3 6% 4 4 3 3 5% 7% 42%	3467
	21st to end	Day	17% 9% 3 6% 4 5% 4 4 5% 7% 36%	3815
April	1st to 10th	Day	16% 9% 3 6% 4 4 4 4 6% 8% 36%	2280
	11th to 20th	Day	17% 8% 3 6% 4 4 4 2 5% 7% 40%	2269
	21st to end	Day	18% 7% 3 7% 4 5% 5% 3 5% 8% 36%	2470
May	1st to 10th	Day	21% 9% 3 7% 5% 5% 4 4 5% 8% 29%	4082
	11th to 20th	Day	21% 7% 2 6% 4 4 4 3 5% 6% 39%	4081
	21st to end	Day	11% 6% 3 8% 6% 5% 6% 5% 7% 9% 34%	4476
June	1st to 10th	Day	11% 6% 2 7% 6% 4 5% 4 5% 7% 42%	2498
	11th to 20th	Day	9% 4 2 7% 6% 5% 4 5% 6% 9% 44%	2660
	21st to end	Day	9% 6% 3 6% 5% 6% 5% 4 6% 9% 41%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 5% 6% 5% 6% 9% 38%	2660
	11th to 20th	Day	8% 6% 2 6% 5% 5% 6% 4 8% 10% 41%	2603
	21st to end	Day	10% 6% 2 6% 6% 5% 6% 4 6% 8% 41%	2679
August	1st to 10th	Day	8% 5% 2 6% 5% 4 6% 5% 7% 9% 43%	2327
	11th to 20th	Day	10% 6% 2 7% 4 5% 6% 4 7% 9% 40%	2266
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 6% 8% 46%	2376
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 5% 6% 46%	2070
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 6% 7% 47%	1980
	21st to end	Day	15% 4 2 5% 3 4 3 2 4 6% 51%	1980
October	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 4 5% 51%	1980
	11th to 20th	Day	14% 7% 2 6% 4 4 3 3 5% 6% 46%	1860
	21st to end	Day	20% 8% 3 5% 4 4 3 4 4 6% 38%	1816
November	1st to 10th	Day	9% 7% 2 5% 3 3 3 3 3 5% 55%	1672
	11th to 20th	Day	15% 11% 4 5% 5% 4 4 3 5% 6% 39%	1710
	21st to end	Day	18% 10% 3 7% 4 3 3 2 4 6% 40%	1710
December	1st to 10th	Day	22% 14% 3 9% 6% 3 4 2 4 4 28%	1710
	11th to 20th	Day	16% 14% 5% 8% 4 5% 4 3 4 5% 31%	2153
	21st to end	Day	21% 21% 4 8% 5% 4 4 3 4 5% 20%	2929
January	1st to 10th	Night	17% 16% 6% 9% 5% 4 5% 4 5% 5% 24%	4428
	11th to 20th	Night	17% 16% 6% 15% 5% 4 3 2 3 4 25%	4276
	21st to end	Night	26% 18% 5% 6% 4 3 3 2 3 4 25%	4532
February	1st to 10th	Night	21% 14% 5% 7% 4 4 3 4 4 5% 29%	2318
	11th to 20th	Night	18% 11% 4 8% 5% 3 4 3 5% 6% 33%	2218
	21st to end	Night	21% 14% 4 8% 4 3 3 3 4 5% 30%	1884
March	1st to 10th	Night	23% 13% 3 6% 4 3 3 3 4 5% 32%	3733
	11th to 20th	Night	14% 8% 2 6% 3 3 4 3 5% 6% 47%	3492
	21st to end	Night	16% 8% 3 7% 5% 4 4 3 5% 6% 39%	3817
April	1st to 10th	Night	13% 8% 3 6% 5% 4 5% 4 7% 7% 38%	1915
	11th to 20th	Night	15% 8% 2 6% 5% 4 3 4 5% 6% 41%	1857
	21st to end	Night	18% 6% 2 6% 6% 4 3 3 7% 7% 37%	1710
May	1st to 10th	Night	21% 11% 3 9% 5% 5% 4 3 5% 7% 27%	2813
	11th to 20th	Night	19% 6% 1 5% 4 4 5% 4 6% 8% 39%	2812
	21st to end	Night	10% 5% 2 6% 4 5% 4 4 7% 9% 45%	3079
June	1st to 10th	Night	9% 5% 2 5% 5% 4 4 4 5% 9% 49%	1676
	11th to 20th	Night	7% 5% 2 5% 3 5% 5% 3 7% 11% 47%	1520
	21st to end	Night	6% 4 1 5% 4 5% 5% 5% 7% 10% 48%	1520
July	1st to 10th	Night	11% 5% 2 6% 5% 4 4 4 6% 8% 44%	1520
	11th to 20th	Night	6% 4 1 5% 4 4 4 4 6% 10% 51%	1574
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 5% 8% 48%	1870
August	1st to 10th	Night	8% 5% 1 5% 4 4 5% 4 6% 10% 47%	1611
	11th to 20th	Night	7% 3 2 6% 5% 4 5% 5% 6% 9% 47%	1631
	21st to end	Night	7% 3 2 5% 3 4 4 4 5% 10% 54%	1980
September	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 6% 7% 50%	1872
	11th to 20th	Night	10% 4 1 4 3 3 4 3 5% 9% 53%	1980
	21st to end	Night	13% 4 2 6% 4 3 4 2 6% 5% 52%	1980
October	1st to 10th	Night	9% 4 2 5% 3 3 4 4 5% 6% 55%	1980
	11th to 20th	Night	15% 6% 2 5% 3 4 4 4 6% 7% 45%	2099
	21st to end	Night	19% 8% 2 7% 3 4 3 3 4 6% 40%	2538
November	1st to 10th	Night	13% 8% 2 5% 4 3 4 3 5% 5% 50%	2406
	11th to 20th	Night	16% 8% 3 7% 4 3 4 3 5% 6% 41%	2470
	21st to end	Night	19% 11% 4 5% 4 4 3 3 4 6% 36%	2470
December	1st to 10th	Night	21% 12% 4 8% 5% 3 3 3 5% 5% 31%	2470
	11th to 20th	Night	18% 13% 5% 8% 4 3 4 3 4 6% 33%	3042
	21st to end	Night	20% 20% 5% 10% 6% 4 4 3 4 5% 19%	4728

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	37% 38% 7% 10% 7%	2528
	11th to 20th	Day	40% 38% 6% 12% 5%	2683
	21st to end	Day	46% 40% 3 9% 2	3124
February	1st to 10th	Day	20% 64% 4 7% 5%	1857
	11th to 20th	Day	18% 64% 3 9% 5%	1858
	21st to end	Day	17% 65% 4 8% 5% 1	1570
March	1st to 10th	Day	39% 41% 3 8% 5% 3	3120
	11th to 20th	Day	20% 41% 7% 20% 12% 1	3467
	21st to end	Day	23% 43% 9% 14% 10%	3815
April	1st to 10th	Day	19% 65% 4 8% 3	2280
	11th to 20th	Day	15% 66% 4 8% 6% 1	2269
	21st to end	Day	15% 65% 5% 9% 5% 1	2470
May	1st to 10th	Day	31% 44% 9% 11% 5%	4120
	11th to 20th	Day	27% 42% 9% 16% 7%	4085
	21st to end	Day	26% 44% 8% 11% 10% 1	4489
June	1st to 10th	Day	15% 66% 4 8% 7% 1	2498
	11th to 20th	Day	14% 66% 3 8% 7% 1	2660
	21st to end	Day	15% 65% 6% 7% 6% 1	2660
July	1st to 10th	Day	18% 61% 5% 7% 7% 1	2591
	11th to 20th	Day	14% 61% 6% 12% 7% 1	2528
	21st to end	Day	16% 60% 5% 10% 8% 1	2537
August	1st to 10th	Day	13% 66% 6% 11% 4	2314
	11th to 20th	Day	16% 65% 5% 10% 4	2266
	21st to end	Day	12% 65% 7% 9% 5% 1	2376
September	1st to 10th	Day	13% 64% 4 10% 7% 2	2070
	11th to 20th	Day	13% 64% 6% 9% 8%	1980
	21st to end	Day	12% 63% 4 12% 9%	1980
October	1st to 10th	Day	16% 63% 3 10% 6% 1	1980
	11th to 20th	Day	14% 63% 3 8% 10% 2	1860
	21st to end	Day	18% 62% 4 9% 7% 1	1816
November	1st to 10th	Day	17% 59% 5% 12% 6% 1	1672
	11th to 20th	Day	17% 59% 2 9% 10% 1	1710
	21st to end	Day	20% 60% 5% 10% 4	1710
December	1st to 10th	Day	26% 59% 4 6% 5%	1710
	11th to 20th	Day	27% 49% 4 12% 9% 1	2150
	21st to end	Day	45% 39% 4 6% 5% 1	2929
January	1st to 10th	Night	39% 41% 5% 8% 7%	4428
	11th to 20th	Night	43% 37% 6% 9% 5%	4276
	21st to end	Night	41% 40% 4 9% 5%	4532
February	1st to 10th	Night	20% 65% 3 7% 4	2318
	11th to 20th	Night	18% 64% 4 8% 5%	2219
	21st to end	Night	20% 64% 3 6% 5% 1	1884
March	1st to 10th	Night	36% 42% 5% 12% 4 1	3733
	11th to 20th	Night	17% 42% 8% 18% 14% 1	3492
	21st to end	Night	25% 42% 4 19% 9% 1	3817
April	1st to 10th	Night	18% 66% 4 7% 4	1915
	11th to 20th	Night	16% 65% 4 8% 6% 1	1857
	21st to end	Night	16% 65% 4 10% 4 1	1710
May	1st to 10th	Night	35% 44% 5% 11% 4 1	2840
	11th to 20th	Night	23% 43% 12% 19% 3	2813
	21st to end	Night	19% 44% 9% 17% 10% 2	3087
June	1st to 10th	Night	13% 65% 3 10% 7% 2	1676
	11th to 20th	Night	12% 65% 5% 7% 9% 2	1520
	21st to end	Night	11% 65% 7% 10% 7% 1	1520
July	1st to 10th	Night	16% 61% 5% 10% 6% 2	1480
	11th to 20th	Night	11% 60% 7% 13% 9% 1	1526
	21st to end	Night	13% 59% 6% 12% 8% 2	1771
August	1st to 10th	Night	14% 65% 7% 10% 4 1	1600
	11th to 20th	Night	13% 66% 6% 11% 4	1631
	21st to end	Night	8% 64% 9% 11% 8% 1	1980
September	1st to 10th	Night	10% 64% 6% 10% 7% 2	1872
	11th to 20th	Night	10% 64% 4 11% 10% 1	1980
	21st to end	Night	11% 63% 5% 10% 10% 1	1980
October	1st to 10th	Night	11% 64% 4 12% 8% 1	1980
	11th to 20th	Night	13% 64% 3 8% 11% 1	2099
	21st to end	Night	18% 62% 4 9% 7% 1	2538
November	1st to 10th	Night	19% 58% 4 9% 8% 1	2406
	11th to 20th	Night	17% 60% 3 9% 9% 2	2470
	21st to end	Night	22% 60% 5% 10% 4	2470
December	1st to 10th	Night	23% 60% 4 6% 6% 1	2470
	11th to 20th	Night	25% 50% 5% 12% 8% 1	3044
	21st to end	Night	45% 39% 5% 7% 3	4728

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	26% 25% 32% 13% 3 1	270
	11th to 20th	Day	31% 29% 28% 10% 1	270
	21st to end	Day	31% 28% 32% 6% 3	297
February	1st to 10th	Day	30% 26% 32% 10% 1	270
	11th to 20th	Day	32% 28% 30% 7% 1 1	270
	21st to end	Day	34% 21% 36% 7% 2	225
March	1st to 10th	Day	27% 28% 34% 10% 1	270
	11th to 20th	Day	27% 24% 32% 12% 5%	447
	21st to end	Day	31% 21% 29% 13% 5%	506
April	1st to 10th	Day	26% 19% 29% 16% 8% 1	460
	11th to 20th	Day	26% 19% 28% 19% 6% 3	452
	21st to end	Day	23% 20% 36% 14% 6% 2	460
May	1st to 10th	Day	23% 18% 35% 14% 6% 4	463
	11th to 20th	Day	20% 14% 30% 22% 9% 5%	487
	21st to end	Day	14% 10% 29% 24% 14% 8%	529
June	1st to 10th	Day	13% 9% 26% 29% 17% 7%	518
	11th to 20th	Day	11% 7% 26% 34% 16% 6%	680
	21st to end	Day	11% 7% 30% 28% 16% 8%	680
July	1st to 10th	Day	15% 5% 20% 26% 20% 15%	671
	11th to 20th	Day	8% 5% 25% 30% 22% 10%	611
	21st to end	Day	14% 3 21% 32% 19% 11%	529
August	1st to 10th	Day	9% 4 20% 31% 22% 13%	446
	11th to 20th	Day	13% 5% 21% 32% 19% 10%	439
	21st to end	Day	10% 4 18% 31% 26% 10%	495
September	1st to 10th	Day	13% 6% 19% 29% 25% 8%	450
	11th to 20th	Day	11% 4 17% 32% 23% 13%	450
	21st to end	Day	18% 8% 23% 24% 20% 7%	450
October	1st to 10th	Day	12% 6% 26% 33% 17% 5%	450
	11th to 20th	Day	20% 15% 32% 20% 11% 2	450
	21st to end	Day	24% 18% 37% 18% 3	331
November	1st to 10th	Day	13% 19% 34% 26% 6% 3	270
	11th to 20th	Day	26% 21% 26% 22% 4 1	270
	21st to end	Day	27% 16% 35% 17% 4	270
December	1st to 10th	Day	26% 23% 34% 12% 5% 1	270
	11th to 20th	Day	22% 25% 33% 14% 6%	270
	21st to end	Day	33% 23% 30% 10% 3	297
January	1st to 10th	Night	24% 20% 31% 20% 5%	950
	11th to 20th	Night	31% 19% 32% 16% 3	851
	21st to end	Night	27% 19% 34% 18% 3	836
February	1st to 10th	Night	28% 16% 31% 22% 2	760
	11th to 20th	Night	26% 22% 32% 19% 1	743
	21st to end	Night	30% 17% 35% 17% 1	628
March	1st to 10th	Night	24% 20% 30% 22% 4	760
	11th to 20th	Night	24% 17% 33% 20% 6% 1	760
	21st to end	Night	24% 16% 32% 23% 6%	836
April	1st to 10th	Night	19% 14% 36% 25% 7%	585
	11th to 20th	Night	20% 14% 30% 25% 10% 1	563
	21st to end	Night	20% 11% 36% 24% 7% 1	570
May	1st to 10th	Night	21% 9% 32% 24% 13% 1	570
	11th to 20th	Night	17% 6% 29% 31% 16% 2	561
	21st to end	Night	11% 4 22% 33% 26% 4	617
June	1st to 10th	Night	12% 3 21% 39% 22% 2	570
	11th to 20th	Night	9% 4 18% 42% 24% 3	570
	21st to end	Night	6% 4 24% 36% 27% 3	570
July	1st to 10th	Night	13% 2 14% 33% 29% 9%	555
	11th to 20th	Night	6% 3 15% 38% 34% 4	552
	21st to end	Night	13% 2 13% 38% 30% 4	624
August	1st to 10th	Night	10% 2 10% 37% 36% 5%	537
	11th to 20th	Night	9% 2 13% 37% 34% 6%	534
	21st to end	Night	7% 3 14% 33% 38% 6%	594
September	1st to 10th	Night	14% 2 15% 33% 31% 5%	612
	11th to 20th	Night	9% 4 17% 30% 34% 5%	720
	21st to end	Night	14% 7% 22% 31% 24% 3	720
October	1st to 10th	Night	11% 6% 24% 33% 22% 5%	720
	11th to 20th	Night	19% 10% 26% 28% 15% 1	720
	21st to end	Night	23% 13% 30% 23% 10% 1	792
November	1st to 10th	Night	16% 11% 29% 26% 16% 1	740
	11th to 20th	Night	20% 18% 29% 23% 10% 1	760
	21st to end	Night	26% 14% 23% 28% 7% 1	760
December	1st to 10th	Night	28% 16% 30% 20% 6%	760
	11th to 20th	Night	25% 17% 29% 21% 6% 1	760
	21st to end	Night	30% 16% 32% 19% 3	954

Page generated at 2024-07-28 09:52:11. Version ac07

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