Pinchot Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pinchot Creek clear sky chart from 2005-11-06 to 2025-09-19.

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	1 2 1 3 2 3 3 3 5% 6% 70%	134620
	Night	1 3 1 3 3 3 3 3 5% 7% 68%	131797
Transparency	Day	13% 5% 9% 18% 27% 28%	129669
	Night	14% 6% 11% 20% 27% 22%	127735
Seeing	Day	4 10% 25% 32% 22% 8%	16238
	Night	2 4 23% 41% 26% 4	25718

By Month

Percentage Cloud Cover SW (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	2 1 3 3 3 4 4 6% 10% 64%	3639
	11th to 20th	Day	2 1 4 3 4 4 3 5% 8% 66%	3640
	21st to end	Day	1 6% 2 4 3 3 4 4 7% 11% 55%	4445
February	1st to 10th	Day	1 3 2 5% 2 3 2 4 5% 9% 64%	1985
	11th to 20th	Day	1 4 1 4 3 3 4 4 5% 10% 61%	1950
	21st to end	Day	1 4 1 4 2 3 3 4 6% 7% 65%	1650
March	1st to 10th	Day	1 4 2 5% 3 4 4 4 7% 10% 56%	4518
	11th to 20th	Day	1 4 1 4 3 4 4 4 6% 8% 61%	4682
	21st to end	Day	1 4 1 4 3 4 4 3 5% 9% 62%	5969
April	1st to 10th	Day	2 4 1 4 3 3 4 3 6% 8% 64%	2400
	11th to 20th	Day	1 3 1 4 3 3 3 3 5% 8% 67%	2369
	21st to end	Day	2 4 1 3 3 3 4 3 5% 8% 66%	2400
May	1st to 10th	Day	2 2 1 4 2 3 3 3 4 5% 72%	5879
	11th to 20th	Day	1 2 1 3 2 2 3 3 4 6% 73%	5841
	21st to end	Day	2 3 1 3 3 3 3 2 4 5% 71%	6725
June	1st to 10th	Day	3 3 1 4 3 3 3 4 6% 6% 63%	2800
	11th to 20th	Day	2 2 1 2 2 2 3 3 4 5% 75%	2800
	21st to end	Day	2 2 1 3 2 2 3 2 3 4 75%	2800
July	1st to 10th	Day	1 1 1 2 2 2 2 2 2 3 82%	6319
	11th to 20th	Day	1 2 1 3 3 3 4 3 4 5% 70%	6320
	21st to end	Day	2 2 1 3 2 3 4 3 5% 6% 70%	6849
August	1st to 10th	Day	2 2 1 2 2 2 3 2 3 3 80%	5400
	11th to 20th	Day	1 1 1 1 2 2 2 2 3 84%	5364
	21st to end	Day	2 2 1 3 2 3 3 2 4 5% 74%	5984
September	1st to 10th	Day	2 2 1 2 2 2 3 3 3 5% 77%	2400
	11th to 20th	Day	1 1 1 3 2 2 2 2 3 4 79%	2254
	21st to end	Day	1 1 1 1 1 1 2 2 3 5% 82%	2090
October	1st to 10th	Day	1 1 1 2 2 2 2 3 4 6% 77%	3475
	11th to 20th	Day	1 1 1 2 2 2 2 4 5% 80%	3161
	21st to end	Day	1 1 2 1 3 2 2 4 6% 78%	3232
November	1st to 10th	Day	1 1 1 3 3 2 2 2 4 9% 72%	1764
	11th to 20th	Day	1 1 1 2 2 2 2 2 5% 7% 76%	1800
	21st to end	Day	2 2 1 3 2 3 3 3 5% 7% 69%	1800
December	1st to 10th	Day	1 1 1 2 2 2 4 3 5% 9% 71%	2884
	11th to 20th	Day	3 1 4 3 4 4 4 6% 11% 60%	3028
	21st to end	Day	1 3 2 5% 3 5% 4 4 7% 11% 55%	4004
January	1st to 10th	Night	3 2 5% 3 3 4 3 6% 10% 62%	6306
	11th to 20th	Night	2 2 4 3 3 4 3 7% 9% 64%	6320
	21st to end	Night	1 6% 2 5% 3 3 4 4 6% 10% 57%	6516
February	1st to 10th	Night	1 3 2 5% 3 4 3 3 5% 8% 64%	2412
	11th to 20th	Night	2 3 1 3 2 3 4 4 6% 9% 64%	2338
	21st to end	Night	3 2 3 2 3 4 3 6% 8% 65%	1980
March	1st to 10th	Night	1 4 2 5% 4 4 4 3 5% 7% 61%	5376
	11th to 20th	Night	2 4 1 3 3 2 3 3 6% 9% 63%	5301
	21st to end	Night	1 3 2 4 3 3 4 4 5% 8% 63%	5006
April	1st to 10th	Night	2 3 2 3 3 3 4 2 5% 5% 68%	2000
	11th to 20th	Night	1 2 1 3 3 3 2 3 5% 6% 70%	1979
	21st to end	Night	3 5% 1 3 3 3 3 3 4 7% 68%	2000
May	1st to 10th	Night	4 3 1 3 2 3 2 2 4 5% 70%	4100
	11th to 20th	Night	2 3 1 3 2 2 3 3 4 5% 71%	4074
	21st to end	Night	3 3 1 3 3 2 2 2 4 6% 70%	4139
June	1st to 10th	Night	2 2 1 4 3 3 3 4 6% 7% 65%	1600
	11th to 20th	Night	2 2 1 2 2 2 3 2 4 4 76%	1600
	21st to end	Night	1 3 1 3 2 2 2 1 3 3 78%	1600
July	1st to 10th	Night	1 1 1 2 2 2 2 3 3 84%	3640
	11th to 20th	Night	3 3 2 5% 4 4 4 4 6% 7% 61%	3640
	21st to end	Night	1 2 1 3 2 3 3 3 5% 6% 73%	3987
August	1st to 10th	Night	2 2 1 3 2 3 3 2 3 4 75%	4412
	11th to 20th	Night	1 2 1 3 2 2 3 2 3 4 79%	4506
	21st to end	Night	2 2 1 3 2 3 3 2 5% 5% 72%	5015
September	1st to 10th	Night	1 1 1 2 2 2 2 3 4 5% 77%	2000
	11th to 20th	Night	1 2 1 3 3 3 3 2 4 5% 74%	2103
	21st to end	Night	1 1 2 2 2 2 2 3 4 81%	2090
October	1st to 10th	Night	2 2 1 3 2 2 2 2 3 4 77%	3490
	11th to 20th	Night	1 1 1 2 1 1 2 2 3 6% 81%	3776
	21st to end	Night	1 1 1 2 2 2 2 4 5% 81%	4329
November	1st to 10th	Night	1 2 1 2 2 2 2 2 4 6% 77%	2535
	11th to 20th	Night	1 1 2 1 2 3 3 4 8% 75%	2600
	21st to end	Night	2 2 1 3 2 3 3 3 5% 7% 69%	2600
December	1st to 10th	Night	1 2 1 3 2 2 3 3 5% 8% 70%	4299
	11th to 20th	Night	1 2 1 3 2 3 4 4 7% 16% 57%	5176
	21st to end	Night	1 3 1 6% 4 5% 6% 6% 9% 12% 46%	6952

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	12% 10% 25% 30% 21% 2	3639
	11th to 20th	Day	15% 9% 13% 20% 31% 12%	3640
	21st to end	Day	20% 9% 16% 20% 29% 6%	4445
February	1st to 10th	Day	17% 6% 15% 26% 25% 11%	1985
	11th to 20th	Day	19% 6% 13% 26% 29% 8%	1960
	21st to end	Day	16% 6% 15% 29% 25% 8%	1650
March	1st to 10th	Day	20% 7% 10% 23% 30% 10%	4518
	11th to 20th	Day	16% 6% 12% 34% 25% 7%	4682
	21st to end	Day	15% 8% 13% 26% 27% 10%	5969
April	1st to 10th	Day	18% 7% 12% 27% 24% 13%	2400
	11th to 20th	Day	17% 5% 10% 22% 31% 15%	2372
	21st to end	Day	15% 6% 12% 28% 28% 9%	2400
May	1st to 10th	Day	13% 4 8% 21% 38% 16%	5879
	11th to 20th	Day	11% 4 7% 19% 37% 23%	5844
	21st to end	Day	14% 4 7% 15% 34% 26%	6726
June	1st to 10th	Day	18% 7% 9% 17% 29% 20%	2800
	11th to 20th	Day	12% 4 6% 12% 29% 38%	2800
	21st to end	Day	12% 4 3 9% 24% 48%	2800
July	1st to 10th	Day	9% 2 2 5% 10% 72%	6251
	11th to 20th	Day	13% 3 5% 6% 13% 61%	6245
	21st to end	Day	13% 3 5% 11% 23% 46%	6650
August	1st to 10th	Day	14% 3 4 7% 24% 49%	3931
	11th to 20th	Day	7% 2 3 6% 13% 68%	3880
	21st to end	Day	7% 1 3 6% 24% 58%	4311
September	1st to 10th	Day	10% 3 5% 10% 24% 48%	2400
	11th to 20th	Day	10% 3 4 14% 32% 37%	2254
	21st to end	Day	7% 2 5% 14% 35% 37%	2090
October	1st to 10th	Day	9% 3 5% 11% 35% 37%	3475
	11th to 20th	Day	8% 2 4 13% 41% 32%	3161
	21st to end	Day	8% 2 6% 21% 46% 17%	3232
November	1st to 10th	Day	13% 5% 11% 26% 31% 14%	1764
	11th to 20th	Day	9% 5% 10% 29% 37% 10%	1800
	21st to end	Day	14% 6% 12% 26% 30% 11%	1800
December	1st to 10th	Day	10% 5% 12% 34% 30% 9%	2884
	11th to 20th	Day	18% 8% 18% 32% 20% 5%	3028
	21st to end	Day	19% 10% 25% 25% 18% 2	4004
January	1st to 10th	Night	15% 10% 21% 29% 22% 4	6306
	11th to 20th	Night	14% 9% 16% 22% 30% 10%	6320
	21st to end	Night	20% 8% 16% 22% 25% 8%	6516
February	1st to 10th	Night	18% 6% 14% 27% 22% 13%	2412
	11th to 20th	Night	16% 7% 13% 28% 27% 9%	2339
	21st to end	Night	15% 7% 15% 30% 24% 9%	1980
March	1st to 10th	Night	18% 8% 9% 21% 32% 12%	5376
	11th to 20th	Night	15% 7% 12% 30% 28% 7%	5301
	21st to end	Night	14% 8% 15% 29% 27% 6%	5006
April	1st to 10th	Night	16% 7% 12% 27% 27% 10%	2000
	11th to 20th	Night	14% 7% 10% 26% 30% 13%	1979
	21st to end	Night	16% 6% 13% 31% 28% 7%	2000
May	1st to 10th	Night	15% 5% 8% 21% 38% 13%	4097
	11th to 20th	Night	12% 6% 10% 15% 38% 19%	4075
	21st to end	Night	14% 5% 7% 13% 40% 21%	4139
June	1st to 10th	Night	15% 6% 11% 18% 32% 18%	1600
	11th to 20th	Night	11% 4 5% 13% 31% 35%	1600
	21st to end	Night	10% 3 6% 10% 24% 48%	1600
July	1st to 10th	Night	6% 2 4 5% 11% 72%	3600
	11th to 20th	Night	18% 4 6% 7% 12% 53%	3592
	21st to end	Night	11% 4 5% 10% 23% 47%	3874
August	1st to 10th	Night	16% 4 5% 11% 22% 42%	3209
	11th to 20th	Night	8% 3 4 5% 13% 67%	3256
	21st to end	Night	6% 2 5% 8% 21% 58%	3608
September	1st to 10th	Night	9% 4 5% 12% 24% 47%	2000
	11th to 20th	Night	12% 3 7% 13% 29% 36%	2103
	21st to end	Night	8% 3 5% 12% 34% 39%	2090
October	1st to 10th	Night	12% 2 5% 11% 31% 39%	3490
	11th to 20th	Night	7% 3 4 14% 41% 31%	3776
	21st to end	Night	7% 2 5% 18% 45% 23%	4329
November	1st to 10th	Night	10% 4 10% 28% 34% 14%	2535
	11th to 20th	Night	9% 6% 12% 29% 34% 11%	2600
	21st to end	Night	15% 5% 11% 24% 34% 11%	2600
December	1st to 10th	Night	11% 6% 13% 33% 24% 13%	4299
	11th to 20th	Night	14% 9% 22% 29% 23% 3	5176
	21st to end	Night	22% 13% 22% 24% 17% 3	6952

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	2 8% 35% 39% 15% 3	200
	11th to 20th	Day	1 5% 32% 34% 21% 8%	200
	21st to end	Day	2 10% 21% 34% 25% 7%	414
February	1st to 10th	Day	3 13% 33% 29% 15% 6%	493
	11th to 20th	Day	5% 11% 34% 29% 18% 3	495
	21st to end	Day	5% 13% 30% 36% 13% 3	414
March	1st to 10th	Day	5% 17% 31% 32% 13% 3	500
	11th to 20th	Day	5% 17% 30% 28% 16% 3	500
	21st to end	Day	5% 21% 30% 30% 12% 2	550
April	1st to 10th	Day	6% 17% 28% 26% 18% 5%	500
	11th to 20th	Day	8% 18% 28% 28% 15% 3	492
	21st to end	Day	5% 17% 30% 25% 16% 8%	500
May	1st to 10th	Day	7% 19% 28% 27% 14% 5%	503
	11th to 20th	Day	5% 18% 25% 30% 14% 7%	528
	21st to end	Day	8% 12% 22% 28% 22% 8%	573
June	1st to 10th	Day	4 11% 23% 28% 25% 10%	530
	11th to 20th	Day	3 15% 27% 30% 18% 7%	530
	21st to end	Day	2 8% 23% 36% 24% 7%	530
July	1st to 10th	Day	4 5% 21% 37% 24% 10%	526
	11th to 20th	Day	3 3 15% 33% 32% 13%	524
	21st to end	Day	3 3 20% 36% 26% 12%	575
August	1st to 10th	Day	3 4 24% 37% 20% 12%	527
	11th to 20th	Day	2 5% 21% 32% 28% 12%	517
	21st to end	Day	2 4 19% 34% 30% 12%	583
September	1st to 10th	Day	2 4 20% 35% 25% 13%	530
	11th to 20th	Day	2 7% 24% 37% 24% 7%	523
	21st to end	Day	2 7% 20% 34% 30% 8%	490
October	1st to 10th	Day	4 9% 22% 31% 26% 9%	490
	11th to 20th	Day	3 8% 20% 32% 29% 8%	490
	21st to end	Day	3 8% 19% 33% 28% 8%	411
November	1st to 10th	Day	1 5% 22% 34% 26% 11%	300
	11th to 20th	Day	1 7% 19% 38% 22% 12%	300
	21st to end	Day	2 5% 24% 33% 29% 7%	300
December	1st to 10th	Day	2 4 24% 38% 24% 7%	280
	11th to 20th	Day	2 10% 22% 34% 26% 8%	200
	21st to end	Day	3 9% 33% 33% 18% 4	220
January	1st to 10th	Night	2 4 29% 37% 20% 7%	800
	11th to 20th	Night	1 3 29% 39% 22% 6%	800
	21st to end	Night	2 4 25% 45% 20% 5%	880
February	1st to 10th	Night	1 6% 30% 39% 21% 3	800
	11th to 20th	Night	2 4 28% 41% 22% 3	784
	21st to end	Night	2 5% 33% 42% 15% 3	660
March	1st to 10th	Night	3 7% 31% 42% 15% 3	800
	11th to 20th	Night	2 6% 28% 39% 21% 4	800
	21st to end	Night	3 7% 34% 39% 16% 1	880
April	1st to 10th	Night	3 7% 32% 39% 16% 2	800
	11th to 20th	Night	2 11% 27% 41% 17% 3	791
	21st to end	Night	4 8% 27% 39% 19% 4	800
May	1st to 10th	Night	5% 10% 33% 36% 14% 2	600
	11th to 20th	Night	4 9% 27% 38% 21% 1	591
	21st to end	Night	6% 8% 23% 39% 23% 2	510
June	1st to 10th	Night	2 5% 19% 44% 29% 2	400
	11th to 20th	Night	2 3 22% 48% 24% 1	400
	21st to end	Night	1 2 14% 57% 26% 1	400
July	1st to 10th	Night	1 1 9% 51% 37% 1	390
	11th to 20th	Night	3 1 6% 44% 45% 2	388
	21st to end	Night	4 1 5% 47% 42% 1	443
August	1st to 10th	Night	4 2 15% 44% 33% 2	761
	11th to 20th	Night	1 2 14% 41% 39% 3	792
	21st to end	Night	2 1 11% 41% 41% 3	880
September	1st to 10th	Night	2 2 14% 36% 43% 4	800
	11th to 20th	Night	2 3 15% 41% 35% 5%	792
	21st to end	Night	2 3 13% 38% 38% 6%	760
October	1st to 10th	Night	3 3 16% 40% 31% 7%	760
	11th to 20th	Night	2 3 17% 40% 32% 6%	760
	21st to end	Night	1 2 21% 36% 30% 10%	836
November	1st to 10th	Night	1 2 22% 37% 32% 7%	780
	11th to 20th	Night	1 2 21% 46% 25% 5%	800
	21st to end	Night	3 2 24% 41% 26% 5%	800
December	1st to 10th	Night	2 3 24% 45% 21% 5%	800
	11th to 20th	Night	3 4 28% 43% 20% 3	800
	21st to end	Night	2 5% 34% 40% 17% 3	880

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