Pettigrew State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pettigrew State Park clear sky chart from 2005-11-06 to 2025-10-19.

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	12% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	125911
	Night	13% 7% 2 6% 4 4 4 4 6% 7% 43%	123778
Transparency	Day	41% 6% 12% 21% 16% 4	129508
	Night	39% 6% 12% 20% 18% 5%	128250
Seeing	Day	18% 13% 26% 25% 14% 4	16682
	Night	17% 11% 27% 30% 13% 2	26342

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% 6% 2 4 3 3 3 3 3 4 57%	3992
	11th to 20th	Day	12% 6% 2 5% 4 3 3 3 3 5% 54%	4060
	21st to end	Day	12% 13% 3 7% 5% 4 3 3 4 6% 41%	4466
February	1st to 10th	Day	15% 8% 2 7% 4 4 3 4 5% 7% 42%	1800
	11th to 20th	Day	20% 6% 2 5% 5% 4 3 3 4 5% 43%	1939
	21st to end	Day	14% 8% 2 5% 4 4 5% 4 6% 7% 42%	1650
March	1st to 10th	Day	21% 8% 2 6% 4 4 4 3 4 5% 39%	4801
	11th to 20th	Day	11% 5% 2 5% 4 3 4 3 5% 5% 53%	4980
	21st to end	Day	13% 5% 2 6% 4 4 3 3 5% 5% 50%	5617
April	1st to 10th	Day	12% 6% 1 4 3 4 4 3 4 6% 51%	2400
	11th to 20th	Day	9% 5% 1 6% 4 4 5% 3 5% 7% 50%	2374
	21st to end	Day	11% 5% 2 5% 5% 4 4 4 5% 8% 47%	2400
May	1st to 10th	Day	10% 6% 3 9% 5% 6% 6% 5% 7% 9% 35%	5405
	11th to 20th	Day	18% 8% 3 8% 6% 5% 5% 4 7% 8% 29%	5754
	21st to end	Day	13% 6% 3 7% 4 5% 5% 4 6% 8% 40%	6934
June	1st to 10th	Day	10% 5% 2 7% 6% 5% 6% 5% 7% 10% 36%	2800
	11th to 20th	Day	9% 5% 1 7% 6% 5% 7% 6% 8% 10% 38%	2800
	21st to end	Day	6% 6% 2 7% 6% 6% 6% 7% 9% 12% 34%	2800
July	1st to 10th	Day	8% 6% 3 8% 7% 7% 7% 6% 10% 11% 26%	6232
	11th to 20th	Day	8% 7% 3 10% 7% 7% 8% 7% 9% 12% 22%	5900
	21st to end	Day	9% 7% 3 9% 7% 7% 7% 6% 8% 11% 27%	6424
August	1st to 10th	Day	18% 12% 4 10% 7% 6% 6% 5% 6% 8% 19%	4143
	11th to 20th	Day	9% 8% 2 8% 6% 6% 6% 5% 7% 9% 35%	3850
	21st to end	Day	8% 5% 2 7% 7% 6% 7% 5% 7% 9% 37%	4312
September	1st to 10th	Day	12% 7% 3 7% 6% 5% 6% 5% 7% 8% 34%	2400
	11th to 20th	Day	16% 7% 2 7% 5% 5% 5% 5% 5% 7% 36%	2400
	21st to end	Day	20% 8% 3 8% 2 4 4 4 6% 7% 35%	2141
October	1st to 10th	Day	16% 6% 2 6% 5% 4 4 3 5% 7% 43%	2000
	11th to 20th	Day	15% 7% 2 5% 3 4 4 3 3 5% 50%	1980
	21st to end	Day	12% 6% 2 7% 3 4 3 3 4 5% 51%	2090
November	1st to 10th	Day	16% 6% 1 5% 3 4 3 2 4 7% 47%	1917
	11th to 20th	Day	16% 5% 2 4 4 3 3 3 5% 6% 50%	1800
	21st to end	Day	14% 5% 2 4 3 2 4 4 5% 6% 50%	1800
December	1st to 10th	Day	12% 5% 2 5% 4 4 3 3 4 5% 53%	2600
	11th to 20th	Day	14% 8% 2 7% 4 3 4 3 5% 5% 44%	2990
	21st to end	Day	13% 6% 2 5% 3 3 4 3 5% 7% 49%	3960
January	1st to 10th	Night	12% 8% 3 5% 3 3 3 2 4 5% 53%	5935
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 5% 5% 51%	5900
	21st to end	Night	13% 8% 3 6% 4 4 4 3 4 7% 44%	6490
February	1st to 10th	Night	19% 7% 2 5% 3 3 3 4 6% 6% 42%	2600
	11th to 20th	Night	20% 9% 2 6% 3 3 4 3 4 6% 41%	2345
	21st to end	Night	15% 7% 2 5% 3 3 4 3 5% 6% 47%	1980
March	1st to 10th	Night	21% 8% 2 6% 4 4 3 3 4 5% 40%	5035
	11th to 20th	Night	15% 5% 2 5% 3 3 3 4 5% 6% 50%	4980
	21st to end	Night	15% 6% 2 5% 4 4 4 3 4 5% 49%	5313
April	1st to 10th	Night	13% 6% 2 6% 4 4 3 4 5% 6% 47%	2000
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 6% 7% 47%	1975
	21st to end	Night	10% 6% 2 5% 4 4 5% 4 6% 7% 48%	2000
May	1st to 10th	Night	10% 6% 3 9% 6% 6% 6% 5% 7% 10% 34%	4490
	11th to 20th	Night	19% 8% 3 7% 5% 5% 4 4 6% 8% 32%	4177
	21st to end	Night	12% 7% 4 7% 4 5% 5% 4 6% 9% 38%	3920
June	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 5% 6% 10% 41%	1600
	11th to 20th	Night	8% 4 3 6% 5% 5% 5% 6% 8% 11% 39%	1600
	21st to end	Night	7% 5% 2 6% 5% 4 6% 5% 8% 10% 42%	1600
July	1st to 10th	Night	6% 4 2 6% 5% 5% 7% 6% 9% 14% 36%	3707
	11th to 20th	Night	7% 7% 3 9% 7% 6% 7% 5% 10% 13% 26%	4057
	21st to end	Night	11% 6% 2 8% 6% 6% 6% 5% 7% 10% 32%	4427
August	1st to 10th	Night	16% 10% 3 9% 5% 5% 5% 4 6% 10% 27%	2971
	11th to 20th	Night	8% 6% 3 10% 6% 6% 5% 5% 7% 8% 36%	3197
	21st to end	Night	6% 5% 2 7% 5% 4 7% 5% 8% 10% 40%	3586
September	1st to 10th	Night	10% 6% 2 6% 5% 6% 5% 4 6% 8% 42%	2000
	11th to 20th	Night	14% 7% 3 7% 4 4 5% 4 6% 9% 38%	2000
	21st to end	Night	18% 7% 2 7% 5% 5% 4 4 6% 7% 35%	2252
October	1st to 10th	Night	13% 6% 2 5% 4 4 4 3 5% 6% 49%	2400
	11th to 20th	Night	16% 6% 2 4 3 2 3 3 4 5% 52%	2377
	21st to end	Night	11% 5% 2 5% 2 3 3 3 5% 6% 55%	2508
November	1st to 10th	Night	15% 5% 2 6% 3 4 4 3 4 6% 49%	2380
	11th to 20th	Night	17% 7% 2 5% 4 3 3 4 4 6% 46%	2600
	21st to end	Night	12% 6% 2 5% 3 4 4 3 5% 7% 50%	2600
December	1st to 10th	Night	10% 7% 2 5% 3 3 3 3 4 5% 55%	4575
	11th to 20th	Night	15% 7% 3 7% 5% 5% 5% 4 5% 6% 39%	5205
	21st to end	Night	13% 6% 2 5% 3 3 3 3 5% 7% 51%	6996

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	32% 3 5% 25% 25% 11%	3993
	11th to 20th	Day	34% 3 5% 17% 34% 7%	4060
	21st to end	Day	47% 4 6% 18% 19% 7%	4466
February	1st to 10th	Day	42% 4 10% 24% 17% 3	1800
	11th to 20th	Day	46% 3 8% 18% 20% 5%	1948
	21st to end	Day	41% 4 10% 21% 19% 5%	1650
March	1st to 10th	Day	48% 3 8% 16% 16% 8%	4801
	11th to 20th	Day	33% 4 6% 18% 25% 13%	4980
	21st to end	Day	36% 4 11% 22% 21% 6%	5617
April	1st to 10th	Day	34% 4 11% 22% 24% 5%	2400
	11th to 20th	Day	33% 4 10% 25% 20% 7%	2374
	21st to end	Day	34% 6% 12% 25% 19% 4	2400
May	1st to 10th	Day	43% 7% 18% 21% 10% 1	5437
	11th to 20th	Day	50% 7% 13% 20% 9% 1	5758
	21st to end	Day	40% 6% 11% 27% 14% 1	6949
June	1st to 10th	Day	41% 8% 14% 21% 15% 1	2800
	11th to 20th	Day	38% 8% 19% 22% 13% 1	2800
	21st to end	Day	38% 9% 19% 23% 11% 1	2800
July	1st to 10th	Day	44% 12% 20% 17% 7% 1	6164
	11th to 20th	Day	48% 15% 22% 11% 3	5831
	21st to end	Day	46% 12% 14% 21% 7%	6240
August	1st to 10th	Day	60% 8% 17% 11% 4	4130
	11th to 20th	Day	42% 10% 14% 22% 13%	3886
	21st to end	Day	40% 8% 15% 25% 11% 2	4312
September	1st to 10th	Day	46% 7% 13% 16% 14% 3	2400
	11th to 20th	Day	47% 6% 9% 20% 16% 2	2400
	21st to end	Day	49% 4 11% 19% 14% 3	2141
October	1st to 10th	Day	35% 5% 9% 22% 24% 5%	3260
	11th to 20th	Day	28% 3 6% 20% 26% 16%	3220
	21st to end	Day	24% 4 6% 29% 31% 6%	3428
November	1st to 10th	Day	38% 3 10% 21% 24% 4	1917
	11th to 20th	Day	37% 3 9% 22% 23% 6%	1800
	21st to end	Day	34% 4 9% 26% 23% 4	1800
December	1st to 10th	Day	34% 4 8% 23% 26% 5%	2600
	11th to 20th	Day	42% 4 11% 21% 16% 6%	2986
	21st to end	Day	35% 5% 12% 28% 20% 1	3960
January	1st to 10th	Night	34% 3 5% 20% 29% 9%	5935
	11th to 20th	Night	37% 3 6% 16% 31% 7%	5900
	21st to end	Night	42% 4 8% 18% 23% 6%	6490
February	1st to 10th	Night	42% 4 10% 24% 16% 5%	2600
	11th to 20th	Night	46% 4 9% 17% 19% 6%	2347
	21st to end	Night	39% 3 9% 21% 21% 7%	1980
March	1st to 10th	Night	47% 3 8% 17% 17% 8%	5035
	11th to 20th	Night	36% 4 9% 13% 24% 14%	4980
	21st to end	Night	38% 4 10% 26% 17% 6%	5313
April	1st to 10th	Night	38% 4 12% 18% 23% 5%	2000
	11th to 20th	Night	35% 5% 12% 25% 19% 4	1975
	21st to end	Night	35% 6% 12% 27% 17% 3	2000
May	1st to 10th	Night	43% 8% 18% 21% 8% 1	4520
	11th to 20th	Night	49% 7% 12% 21% 10% 1	4178
	21st to end	Night	42% 7% 16% 23% 12% 1	3927
June	1st to 10th	Night	38% 7% 16% 24% 14% 1	1600
	11th to 20th	Night	35% 9% 20% 23% 11% 1	1600
	21st to end	Night	34% 8% 20% 27% 11%	1600
July	1st to 10th	Night	35% 11% 29% 18% 6% 1	3667
	11th to 20th	Night	44% 14% 26% 13% 3	4006
	21st to end	Night	42% 12% 17% 20% 9%	4297
August	1st to 10th	Night	52% 8% 21% 16% 3	2960
	11th to 20th	Night	42% 9% 18% 20% 11%	3227
	21st to end	Night	35% 8% 17% 27% 12% 1	3586
September	1st to 10th	Night	38% 9% 18% 19% 14% 2	2000
	11th to 20th	Night	43% 7% 12% 21% 15% 3	2000
	21st to end	Night	47% 6% 12% 21% 12% 1	2252
October	1st to 10th	Night	38% 4 7% 21% 26% 3	3920
	11th to 20th	Night	27% 3 6% 18% 27% 19%	3876
	21st to end	Night	22% 3 7% 29% 29% 10%	4120
November	1st to 10th	Night	38% 4 7% 23% 23% 4	2380
	11th to 20th	Night	40% 4 8% 17% 23% 7%	2600
	21st to end	Night	34% 3 10% 25% 23% 5%	2600
December	1st to 10th	Night	33% 3 8% 15% 33% 8%	4575
	11th to 20th	Night	45% 5% 12% 15% 18% 6%	5208
	21st to end	Night	33% 4 14% 28% 18% 2	6996

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	27% 27% 33% 11% 1	287
	11th to 20th	Day	23% 28% 34% 13% 1	300
	21st to end	Day	27% 25% 34% 11% 3	330
February	1st to 10th	Day	25% 22% 37% 12% 4	300
	11th to 20th	Day	33% 24% 30% 11% 2	487
	21st to end	Day	25% 22% 31% 17% 4 1	414
March	1st to 10th	Day	25% 19% 34% 16% 5% 1	500
	11th to 20th	Day	24% 24% 32% 15% 4 1	500
	21st to end	Day	22% 22% 37% 15% 5%	550
April	1st to 10th	Day	24% 23% 31% 15% 5% 2	500
	11th to 20th	Day	16% 19% 33% 21% 8% 3	492
	21st to end	Day	14% 15% 34% 25% 11% 2	500
May	1st to 10th	Day	17% 15% 35% 24% 7% 2	503
	11th to 20th	Day	20% 6% 31% 29% 11% 2	527
	21st to end	Day	18% 6% 25% 27% 18% 5%	573
June	1st to 10th	Day	13% 7% 28% 31% 16% 5%	530
	11th to 20th	Day	10% 7% 20% 36% 20% 7%	530
	21st to end	Day	8% 4 21% 36% 24% 7%	530
July	1st to 10th	Day	10% 5% 17% 34% 26% 9%	525
	11th to 20th	Day	10% 4 12% 37% 29% 9%	524
	21st to end	Day	10% 3 18% 38% 23% 7%	576
August	1st to 10th	Day	17% 6% 20% 30% 20% 7%	526
	11th to 20th	Day	13% 4 14% 28% 28% 12%	519
	21st to end	Day	13% 4 18% 33% 23% 10%	583
September	1st to 10th	Day	16% 5% 23% 25% 19% 12%	530
	11th to 20th	Day	20% 6% 20% 28% 17% 8%	530
	21st to end	Day	26% 6% 20% 25% 17% 7%	530
October	1st to 10th	Day	19% 6% 24% 26% 17% 7%	530
	11th to 20th	Day	20% 11% 25% 27% 14% 4	522
	21st to end	Day	15% 12% 25% 26% 17% 4	539
November	1st to 10th	Day	20% 11% 30% 23% 12% 4	475
	11th to 20th	Day	20% 17% 30% 24% 9% 2	400
	21st to end	Day	20% 17% 24% 22% 16% 2	400
December	1st to 10th	Day	24% 26% 32% 14% 6% 1	200
	11th to 20th	Day	23% 22% 30% 17% 9%	200
	21st to end	Day	20% 21% 30% 19% 9% 1	220
January	1st to 10th	Night	21% 23% 29% 22% 5%	800
	11th to 20th	Night	20% 18% 32% 24% 6%	800
	21st to end	Night	21% 19% 35% 22% 4	880
February	1st to 10th	Night	22% 18% 33% 25% 2	800
	11th to 20th	Night	29% 22% 31% 16% 2	783
	21st to end	Night	22% 20% 33% 22% 3	660
March	1st to 10th	Night	21% 15% 37% 22% 5%	800
	11th to 20th	Night	22% 14% 39% 21% 4	800
	21st to end	Night	19% 20% 34% 22% 5%	880
April	1st to 10th	Night	18% 19% 37% 22% 4	800
	11th to 20th	Night	14% 15% 41% 22% 7%	791
	21st to end	Night	14% 11% 38% 30% 6% 1	800
May	1st to 10th	Night	15% 13% 38% 27% 6% 1	800
	11th to 20th	Night	19% 9% 29% 33% 10%	658
	21st to end	Night	11% 4 23% 43% 17% 1	433
June	1st to 10th	Night	12% 4 24% 45% 15% 1	400
	11th to 20th	Night	9% 3 22% 42% 21% 3	400
	21st to end	Night	8% 2 20% 50% 20%	400
July	1st to 10th	Night	8% 3 14% 47% 25% 3	432
	11th to 20th	Night	7% 1 12% 44% 29% 7%	582
	21st to end	Night	10% 4 16% 40% 26% 4	657
August	1st to 10th	Night	15% 3 12% 39% 27% 4	627
	11th to 20th	Night	10% 2 14% 41% 28% 6%	790
	21st to end	Night	13% 4 13% 36% 30% 5%	880
September	1st to 10th	Night	12% 3 18% 34% 26% 7%	800
	11th to 20th	Night	18% 5% 17% 34% 23% 4	800
	21st to end	Night	22% 4 17% 34% 20% 3	800
October	1st to 10th	Night	15% 5% 22% 29% 25% 4	800
	11th to 20th	Night	20% 8% 26% 29% 15% 2	793
	21st to end	Night	15% 9% 26% 29% 18% 3	836
November	1st to 10th	Night	18% 9% 26% 31% 14% 3	780
	11th to 20th	Night	22% 13% 27% 27% 11% 1	800
	21st to end	Night	17% 14% 28% 26% 15% 1	800
December	1st to 10th	Night	22% 15% 30% 27% 7%	800
	11th to 20th	Night	19% 14% 30% 28% 8%	800
	21st to end	Night	18% 16% 29% 29% 8%	880

Page generated at 2025-10-16 01:50:27. Version ac07

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