Shades State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shades State Park clear sky chart from 2005-11-06 to 2026-05-17.

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	13% 9% 3 8% 5% 4 4 4 6% 8% 36%	131511
	Night	14% 10% 4 8% 5% 4 4 3 5% 7% 37%	131538
Transparency	Day	46% 5% 11% 23% 13% 2	135089
	Night	47% 5% 10% 22% 14% 2	136035
Seeing	Day	17% 11% 28% 24% 15% 5%	17651
	Night	18% 10% 29% 29% 13% 1	27559

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	13% 14% 7% 13% 6% 4 4 3 5% 7% 24%	4691
	11th to 20th	Day	9% 12% 7% 15% 8% 7% 5% 5% 5% 5% 21%	4710
	21st to end	Day	18% 16% 5% 14% 6% 4 4 5% 3 5% 21%	5318
February	1st to 10th	Day	16% 13% 6% 9% 7% 6% 4 2 5% 5% 27%	2090
	11th to 20th	Day	15% 12% 4 11% 6% 4 4 4 5% 6% 29%	2048
	21st to end	Day	16% 15% 5% 9% 4 4 3 2 4 6% 33%	1730
March	1st to 10th	Day	19% 15% 5% 7% 4 3 3 2 3 4 34%	4580
	11th to 20th	Day	10% 9% 3 6% 4 4 4 3 5% 8% 42%	4805
	21st to end	Day	16% 12% 4 9% 5% 5% 4 3 5% 7% 30%	6000
April	1st to 10th	Day	16% 12% 3 7% 5% 4 4 3 5% 7% 34%	2520
	11th to 20th	Day	16% 9% 3 7% 5% 5% 4 3 6% 7% 36%	2494
	21st to end	Day	20% 8% 3 7% 4 4 4 3 5% 8% 35%	2646
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 8% 28%	5992
	11th to 20th	Day	17% 8% 3 7% 4 5% 5% 4 6% 7% 35%	5939
	21st to end	Day	12% 7% 3 8% 5% 5% 5% 5% 6% 9% 35%	6795
June	1st to 10th	Day	10% 6% 3 6% 5% 4 4 4 7% 8% 43%	2800
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 45%	2800
	21st to end	Day	9% 6% 2 6% 6% 5% 5% 4 6% 10% 41%	2800
July	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 7% 10% 42%	6360
	11th to 20th	Day	8% 6% 3 8% 5% 5% 6% 5% 8% 12% 35%	6360
	21st to end	Day	11% 7% 2 6% 5% 5% 6% 5% 7% 10% 37%	6907
August	1st to 10th	Day	8% 5% 1 6% 3 4 5% 4 6% 9% 49%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 4 7% 11% 40%	3880
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 10% 52%	4312
September	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 7% 47%	2400
	11th to 20th	Day	8% 5% 2 5% 3 3 6% 4 7% 7% 51%	2212
	21st to end	Day	13% 5% 2 6% 4 4 4 4 6% 7% 46%	2200
October	1st to 10th	Day	11% 5% 2 5% 5% 5% 4 2 5% 8% 48%	2200
	11th to 20th	Day	15% 7% 2 6% 4 5% 4 4 5% 6% 42%	2020
	21st to end	Day	17% 10% 3 7% 4 5% 5% 3 4 6% 36%	1980
November	1st to 10th	Day	11% 7% 2 5% 4 3 4 3 5% 7% 49%	1852
	11th to 20th	Day	18% 11% 3 7% 3 4 4 3 5% 4 38%	1890
	21st to end	Day	18% 11% 3 9% 4 3 3 3 5% 5% 35%	1890
December	1st to 10th	Day	11% 12% 4 8% 5% 3 3 3 5% 5% 41%	2898
	11th to 20th	Day	15% 15% 5% 13% 5% 5% 4 4 6% 6% 23%	3088
	21st to end	Day	26% 18% 6% 11% 5% 4 4 3 5% 4 14%	4070
January	1st to 10th	Night	15% 14% 7% 13% 6% 4 4 3 4 4 25%	8232
	11th to 20th	Night	9% 17% 6% 14% 8% 6% 5% 4 4 4 23%	8280
	21st to end	Night	17% 12% 5% 9% 6% 5% 4 4 5% 6% 28%	8878
February	1st to 10th	Night	18% 13% 5% 9% 5% 5% 4 3 4 5% 29%	2527
	11th to 20th	Night	15% 12% 5% 10% 5% 4 4 2 5% 6% 33%	2458
	21st to end	Night	17% 12% 4 9% 5% 4 4 3 4 5% 34%	2076
March	1st to 10th	Night	19% 15% 4 6% 4 3 3 2 4 6% 36%	5493
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	5374
	21st to end	Night	17% 9% 4 9% 5% 4 4 4 5% 7% 31%	5213
April	1st to 10th	Night	14% 9% 3 6% 4 4 3 4 5% 7% 38%	2100
	11th to 20th	Night	17% 8% 2 6% 4 3 4 3 6% 7% 39%	2075
	21st to end	Night	17% 7% 3 6% 6% 4 5% 4 6% 6% 37%	1973
May	1st to 10th	Night	19% 11% 3 8% 5% 4 4 3 5% 7% 31%	4123
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 6% 9% 39%	4086
	21st to end	Night	14% 8% 3 7% 5% 5% 5% 4 5% 8% 36%	4072
June	1st to 10th	Night	10% 5% 3 6% 4 3 4 3 6% 6% 49%	1600
	11th to 20th	Night	9% 5% 2 6% 4 4 4 3 6% 9% 47%	1600
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 8% 11% 43%	1600
July	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 7% 10% 45%	3618
	11th to 20th	Night	7% 5% 2 5% 4 4 6% 5% 7% 10% 45%	3617
	21st to end	Night	8% 7% 3 8% 5% 5% 5% 4 6% 9% 40%	3959
August	1st to 10th	Night	9% 5% 2 4 3 3 4 3 6% 9% 52%	2915
	11th to 20th	Night	7% 5% 2 6% 5% 4 6% 4 6% 8% 47%	3165
	21st to end	Night	5% 5% 2 5% 3 3 3 3 5% 9% 56%	3586
September	1st to 10th	Night	11% 6% 2 5% 4 3 3 2 6% 6% 51%	2000
	11th to 20th	Night	7% 4 2 3 3 3 4 3 5% 9% 57%	2166
	21st to end	Night	13% 5% 3 5% 4 4 5% 3 5% 6% 48%	2200
October	1st to 10th	Night	9% 4 2 5% 4 3 4 3 6% 5% 56%	2200
	11th to 20th	Night	16% 6% 2 5% 3 3 4 3 4 6% 49%	2377
	21st to end	Night	17% 9% 3 7% 4 4 4 4 4 7% 39%	2860
November	1st to 10th	Night	12% 7% 2 5% 4 3 4 3 4 7% 50%	2666
	11th to 20th	Night	13% 10% 4 7% 4 4 4 4 5% 6% 40%	2730
	21st to end	Night	19% 13% 4 8% 4 4 3 3 4 5% 33%	2730
December	1st to 10th	Night	13% 10% 4 8% 6% 3 4 3 4 5% 40%	4500
	11th to 20th	Night	17% 14% 5% 11% 5% 4 4 3 4 5% 29%	5339
	21st to end	Night	26% 19% 6% 10% 5% 4 3 3 4 5% 15%	7150

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	60% 3 12% 18% 6% 1	4692
	11th to 20th	Day	65% 3 9% 12% 9% 2	4710
	21st to end	Day	67% 3 8% 16% 5% 1	5318
February	1st to 10th	Day	60% 3 10% 17% 8% 1	2090
	11th to 20th	Day	57% 4 10% 20% 9% 1	2058
	21st to end	Day	54% 4 10% 22% 8% 2	1730
March	1st to 10th	Day	55% 3 6% 20% 14% 3	4580
	11th to 20th	Day	40% 4 10% 33% 12% 1	4805
	21st to end	Day	53% 5% 12% 20% 8% 1	6002
April	1st to 10th	Day	48% 5% 14% 19% 13% 1	2520
	11th to 20th	Day	47% 5% 11% 24% 10% 3	2494
	21st to end	Day	48% 5% 12% 22% 11% 2	2646
May	1st to 10th	Day	52% 7% 12% 20% 9% 1	6027
	11th to 20th	Day	47% 7% 11% 24% 11% 1	5943
	21st to end	Day	42% 7% 12% 22% 14% 2	6809
June	1st to 10th	Day	37% 7% 13% 25% 16% 3	2800
	11th to 20th	Day	35% 6% 12% 23% 21% 3	2800
	21st to end	Day	37% 7% 16% 19% 17% 3	2800
July	1st to 10th	Day	36% 5% 11% 29% 17% 2	6291
	11th to 20th	Day	39% 8% 16% 25% 13% 1	6285
	21st to end	Day	41% 8% 15% 23% 12% 2	6711
August	1st to 10th	Day	30% 7% 15% 31% 15% 1	4221
	11th to 20th	Day	35% 7% 13% 29% 15% 1	3917
	21st to end	Day	27% 6% 15% 31% 17% 4	4311
September	1st to 10th	Day	35% 6% 12% 25% 18% 4	2400
	11th to 20th	Day	31% 7% 11% 25% 23% 3	2212
	21st to end	Day	36% 5% 10% 24% 22% 3	2200
October	1st to 10th	Day	24% 3 8% 29% 32% 2	3590
	11th to 20th	Day	32% 4 9% 25% 29% 1	3262
	21st to end	Day	42% 3 8% 24% 22% 1	3180
November	1st to 10th	Day	35% 4 14% 26% 17% 4	1852
	11th to 20th	Day	48% 3 10% 21% 13% 4	1890
	21st to end	Day	51% 5% 9% 22% 12% 1	1890
December	1st to 10th	Day	47% 3 11% 27% 12%	2898
	11th to 20th	Day	61% 4 10% 19% 5%	3085
	21st to end	Day	73% 4 9% 10% 4	4070
January	1st to 10th	Night	62% 3 10% 18% 6%	8233
	11th to 20th	Night	64% 3 8% 12% 10% 3	8280
	21st to end	Night	58% 3 10% 20% 8% 1	8878
February	1st to 10th	Night	57% 4 11% 18% 9% 1	2527
	11th to 20th	Night	53% 3 10% 20% 12% 2	2459
	21st to end	Night	54% 4 10% 20% 10% 2	2076
March	1st to 10th	Night	52% 3 6% 23% 11% 4	5493
	11th to 20th	Night	39% 5% 10% 27% 18% 1	5374
	21st to end	Night	51% 4 11% 26% 7% 1	5213
April	1st to 10th	Night	46% 5% 11% 23% 14% 2	2100
	11th to 20th	Night	44% 5% 9% 22% 16% 4	2075
	21st to end	Night	45% 6% 10% 23% 12% 3	1973
May	1st to 10th	Night	53% 7% 10% 18% 11% 2	4150
	11th to 20th	Night	41% 7% 12% 26% 13% 1	4087
	21st to end	Night	44% 8% 13% 19% 14% 3	4080
June	1st to 10th	Night	34% 5% 10% 27% 21% 3	1600
	11th to 20th	Night	34% 6% 11% 24% 20% 4	1600
	21st to end	Night	32% 8% 15% 23% 18% 5%	1600
July	1st to 10th	Night	33% 6% 11% 28% 18% 3	3580
	11th to 20th	Night	31% 8% 15% 28% 17% 1	3572
	21st to end	Night	39% 7% 15% 23% 14% 2	3844
August	1st to 10th	Night	29% 6% 17% 33% 14% 1	2904
	11th to 20th	Night	33% 6% 14% 29% 17% 1	3194
	21st to end	Night	26% 5% 12% 32% 21% 4	3586
September	1st to 10th	Night	33% 5% 11% 26% 19% 6%	2000
	11th to 20th	Night	24% 6% 10% 26% 29% 5%	2166
	21st to end	Night	36% 6% 9% 22% 23% 4	2200
October	1st to 10th	Night	20% 4 7% 27% 40% 2	3590
	11th to 20th	Night	28% 3 9% 24% 33% 2	3874
	21st to end	Night	37% 3 8% 23% 25% 5%	4610
November	1st to 10th	Night	36% 4 9% 26% 21% 4	2666
	11th to 20th	Night	45% 3 10% 23% 16% 3	2730
	21st to end	Night	54% 4 9% 22% 11%	2730
December	1st to 10th	Night	47% 3 12% 26% 12%	4500
	11th to 20th	Night	58% 3 11% 17% 10% 1	5341
	21st to end	Night	72% 4 9% 10% 5%	7150

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	24% 19% 32% 19% 6%	330
	11th to 20th	Day	20% 25% 37% 16% 2 1	330
	21st to end	Day	22% 21% 35% 19% 3	363
February	1st to 10th	Day	25% 16% 37% 20% 3	330
	11th to 20th	Day	25% 21% 36% 12% 5% 1	330
	21st to end	Day	27% 17% 40% 14% 2	273
March	1st to 10th	Day	23% 25% 38% 10% 3	330
	11th to 20th	Day	28% 20% 34% 14% 4	411
	21st to end	Day	30% 16% 31% 16% 6%	594
April	1st to 10th	Day	23% 19% 31% 20% 6% 1	540
	11th to 20th	Day	21% 19% 29% 20% 9% 2	532
	21st to end	Day	25% 16% 30% 19% 8% 2	540
May	1st to 10th	Day	22% 13% 31% 23% 8% 2	543
	11th to 20th	Day	20% 9% 29% 27% 12% 4	551
	21st to end	Day	12% 8% 29% 26% 17% 8%	727
June	1st to 10th	Day	12% 7% 29% 28% 18% 5%	730
	11th to 20th	Day	13% 5% 28% 32% 17% 5%	730
	21st to end	Day	11% 7% 30% 28% 19% 6%	730
July	1st to 10th	Day	12% 3 17% 29% 23% 16%	721
	11th to 20th	Day	7% 5% 20% 31% 25% 11%	718
	21st to end	Day	11% 3 17% 32% 28% 9%	789
August	1st to 10th	Day	8% 2 18% 27% 31% 14%	526
	11th to 20th	Day	12% 4 19% 28% 26% 12%	519
	21st to end	Day	6% 3 14% 33% 31% 12%	583
September	1st to 10th	Day	11% 4 19% 29% 28% 9%	530
	11th to 20th	Day	8% 4 14% 28% 32% 14%	530
	21st to end	Day	14% 9% 22% 23% 21% 10%	530
October	1st to 10th	Day	9% 6% 28% 31% 20% 6%	530
	11th to 20th	Day	15% 15% 32% 23% 13% 2	385
	21st to end	Day	28% 17% 32% 20% 2	363
November	1st to 10th	Day	12% 16% 37% 22% 11% 2	330
	11th to 20th	Day	26% 18% 30% 17% 7% 2	330
	21st to end	Day	27% 13% 36% 22% 2	330
December	1st to 10th	Day	18% 21% 40% 16% 4 1	330
	11th to 20th	Day	20% 18% 40% 17% 4 1	330
	21st to end	Day	29% 17% 36% 17% 2	363
January	1st to 10th	Night	21% 17% 34% 24% 4	1050
	11th to 20th	Night	23% 16% 38% 20% 4	1050
	21st to end	Night	21% 15% 37% 24% 3	1155
February	1st to 10th	Night	24% 12% 37% 24% 3	847
	11th to 20th	Night	19% 16% 40% 21% 4	823
	21st to end	Night	24% 15% 38% 22% 2	692
March	1st to 10th	Night	24% 15% 34% 23% 4	840
	11th to 20th	Night	21% 13% 37% 23% 5%	840
	21st to end	Night	24% 11% 36% 25% 4 1	756
April	1st to 10th	Night	17% 15% 37% 26% 5%	630
	11th to 20th	Night	20% 13% 32% 28% 8%	623
	21st to end	Night	19% 10% 36% 27% 7% 1	630
May	1st to 10th	Night	20% 8% 35% 27% 9%	630
	11th to 20th	Night	17% 8% 26% 33% 15% 1	609
	21st to end	Night	13% 4 24% 37% 21% 1	650
June	1st to 10th	Night	12% 4 22% 44% 18%	600
	11th to 20th	Night	12% 4 20% 46% 18% 1	600
	21st to end	Night	8% 3 23% 40% 26%	600
July	1st to 10th	Night	9% 2 13% 38% 32% 6%	585
	11th to 20th	Night	6% 4 18% 38% 31% 3	582
	21st to end	Night	6% 2 13% 42% 33% 3	657
August	1st to 10th	Night	8% 2 10% 44% 31% 4	597
	11th to 20th	Night	7% 2 13% 42% 32% 4	594
	21st to end	Night	8% 3 13% 33% 39% 4	660
September	1st to 10th	Night	13% 3 15% 37% 29% 4	600
	11th to 20th	Night	7% 3 15% 37% 34% 4	766
	21st to end	Night	15% 5% 20% 31% 27% 2	800
October	1st to 10th	Night	10% 5% 23% 38% 20% 4	800
	11th to 20th	Night	19% 11% 27% 29% 14% 1	800
	21st to end	Night	21% 12% 34% 26% 6%	880
November	1st to 10th	Night	15% 9% 39% 27% 9% 1	820
	11th to 20th	Night	18% 16% 33% 26% 7%	840
	21st to end	Night	25% 14% 29% 25% 6%	840
December	1st to 10th	Night	23% 11% 39% 22% 4	908
	11th to 20th	Night	25% 11% 34% 24% 5% 1	1050
	21st to end	Night	31% 14% 31% 20% 3	1155

Page generated at 2026-05-14 01:59:01. Version ac07

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