Penitentiary Glen Reservation
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Penitentiary Glen Reservation clear sky chart from 2005-11-06 to 2024-08-30.

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	16% 12% 4 9% 5% 4 4 3 5% 7% 31%	95342
	Night	17% 14% 5% 9% 5% 4 4 3 5% 6% 29%	93648
Transparency	Day	51% 8% 12% 18% 10% 1	95115
	Night	55% 7% 11% 16% 9% 1	93479
Seeing	Day	21% 16% 29% 22% 10% 3	14309
	Night	23% 15% 27% 23% 11% 1	24039

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	17% 25% 10% 14% 5% 3 4 2 3 4 14%	2836
	11th to 20th	Day	14% 25% 9% 16% 7% 6% 3 3 3 4 12%	2840
	21st to end	Day	24% 22% 12% 17% 7% 4 3 2 2 2 6%	3124
February	1st to 10th	Day	17% 20% 6% 13% 9% 5% 2 2 3 4 18%	1710
	11th to 20th	Day	15% 17% 7% 16% 9% 3 3 3 3 4 19%	1696
	21st to end	Day	18% 17% 5% 13% 4 4 4 4 5% 5% 21%	1570
March	1st to 10th	Day	20% 14% 7% 8% 4 3 4 2 5% 6% 26%	3367
	11th to 20th	Day	13% 19% 6% 10% 4 3 3 2 4 5% 31%	3480
	21st to end	Day	20% 14% 5% 10% 4 3 4 3 4 5% 29%	3815
April	1st to 10th	Day	16% 15% 4 7% 4 4 4 3 5% 6% 31%	2141
	11th to 20th	Day	19% 13% 3 5% 4 4 4 4 4 6% 33%	2404
	21st to end	Day	20% 12% 3 7% 4 3 3 3 4 5% 35%	2470
May	1st to 10th	Day	20% 9% 3 8% 6% 4 4 3 5% 6% 32%	4082
	11th to 20th	Day	19% 9% 3 6% 4 4 4 3 5% 7% 35%	4081
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 7% 41%	4632
June	1st to 10th	Day	17% 6% 2 6% 4 4 5% 4 7% 8% 38%	2660
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 7% 8% 40%	2660
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 6% 10% 41%	2660
July	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 7% 11% 41%	4217
	11th to 20th	Day	12% 5% 2 5% 3 4 4 4 7% 9% 45%	4120
	21st to end	Day	10% 6% 2 7% 5% 4 5% 5% 7% 8% 42%	4466
August	1st to 10th	Day	10% 6% 2 7% 4 5% 5% 4 7% 9% 41%	2457
	11th to 20th	Day	11% 5% 2 7% 5% 5% 6% 5% 8% 9% 36%	2433
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 6% 10% 41%	2648
September	1st to 10th	Day	16% 7% 2 6% 4 3 5% 4 6% 8% 40%	2085
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 4 6% 9% 42%	1980
	21st to end	Day	19% 9% 2 7% 4 3 4 4 5% 6% 37%	1980
October	1st to 10th	Day	18% 7% 3 7% 4 4 4 4 5% 7% 37%	1850
	11th to 20th	Day	24% 10% 3 6% 5% 4 4 3 5% 6% 30%	1800
	21st to end	Day	27% 13% 3 7% 5% 4 4 4 5% 5% 24%	1980
November	1st to 10th	Day	14% 15% 4 7% 5% 3 4 4 5% 7% 33%	1672
	11th to 20th	Day	18% 22% 4 8% 5% 4 4 2 4 5% 24%	1640
	21st to end	Day	20% 24% 7% 8% 5% 4 3 3 4 6% 16%	1520
December	1st to 10th	Day	17% 28% 8% 12% 6% 4 3 2 3 4 13%	1520
	11th to 20th	Day	18% 22% 10% 15% 4 3 4 4 4 4 13%	1910
	21st to end	Day	23% 25% 9% 13% 5% 4 3 2 4 3 9%	2836
January	1st to 10th	Night	15% 27% 12% 15% 6% 3 3 2 3 4 11%	4109
	11th to 20th	Night	13% 21% 11% 20% 6% 4 5% 3 4 3 10%	4120
	21st to end	Night	24% 22% 8% 17% 6% 3 2 2 2 3 11%	4532
February	1st to 10th	Night	20% 17% 5% 14% 7% 4 4 2 5% 3 18%	2470
	11th to 20th	Night	16% 17% 7% 13% 6% 5% 3 3 4 4 20%	2368
	21st to end	Night	20% 14% 5% 13% 6% 4 4 3 4 4 23%	1884
March	1st to 10th	Night	21% 16% 4 7% 4 3 3 2 4 4 33%	3484
	11th to 20th	Night	16% 15% 6% 8% 4 3 3 3 4 6% 33%	3480
	21st to end	Night	18% 15% 6% 9% 4 3 3 3 3 4 32%	3817
April	1st to 10th	Night	18% 16% 4 7% 5% 4 3 3 5% 5% 30%	2038
	11th to 20th	Night	18% 11% 3 7% 4 4 4 5% 6% 6% 33%	1741
	21st to end	Night	17% 10% 2 6% 5% 4 4 4 6% 6% 35%	1710
May	1st to 10th	Night	24% 9% 3 7% 4 4 4 3 5% 6% 30%	2813
	11th to 20th	Night	15% 10% 3 7% 5% 4 4 4 6% 8% 35%	2812
	21st to end	Night	14% 4 2 4 3 3 5% 4 7% 9% 45%	2920
June	1st to 10th	Night	13% 7% 3 7% 5% 4 4 5% 5% 6% 41%	1520
	11th to 20th	Night	10% 5% 2 7% 6% 5% 5% 5% 6% 7% 43%	1520
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	1520
July	1st to 10th	Night	11% 6% 2 6% 4 3 3 3 6% 9% 47%	2736
	11th to 20th	Night	10% 5% 2 6% 3 4 4 5% 6% 8% 48%	2840
	21st to end	Night	9% 6% 2 7% 4 4 5% 4 6% 8% 45%	3087
August	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 3 6% 9% 46%	1701
	11th to 20th	Night	12% 6% 2 6% 4 4 6% 4 6% 7% 43%	1688
	21st to end	Night	12% 5% 2 6% 4 4 5% 3 6% 9% 45%	1899
September	1st to 10th	Night	13% 6% 2 5% 4 4 6% 4 5% 7% 43%	1872
	11th to 20th	Night	13% 5% 2 5% 4 4 4 3 6% 6% 49%	1980
	21st to end	Night	18% 6% 2 6% 5% 5% 5% 4 5% 6% 38%	1980
October	1st to 10th	Night	16% 7% 3 6% 3 4 4 4 6% 8% 41%	2110
	11th to 20th	Night	22% 9% 3 7% 5% 4 4 4 5% 6% 31%	2160
	21st to end	Night	29% 12% 3 7% 4 4 3 3 4 5% 26%	2376
November	1st to 10th	Night	18% 15% 3 6% 4 3 3 3 5% 7% 34%	2404
	11th to 20th	Night	18% 22% 4 9% 5% 4 4 3 4 5% 22%	2536
	21st to end	Night	20% 22% 5% 8% 5% 4 4 3 5% 5% 19%	2660
December	1st to 10th	Night	20% 27% 8% 9% 5% 3 3 3 3 3 14%	2660
	11th to 20th	Night	17% 24% 7% 13% 5% 4 3 3 4 4 16%	3285
	21st to end	Night	21% 25% 8% 11% 6% 5% 4 3 4 4 9%	4816

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	75% 7% 10% 7% 2	2837
	11th to 20th	Day	77% 4 12% 5% 1	2840
	21st to end	Day	85% 5% 4 4 2	3124
February	1st to 10th	Day	71% 5% 8% 11% 4	1710
	11th to 20th	Day	69% 6% 8% 11% 6%	1705
	21st to end	Day	62% 8% 12% 11% 6% 2	1570
March	1st to 10th	Day	56% 8% 11% 22% 4	3367
	11th to 20th	Day	53% 10% 15% 16% 5% 1	3480
	21st to end	Day	54% 9% 9% 16% 10% 1	3815
April	1st to 10th	Day	51% 6% 13% 17% 12% 1	2141
	11th to 20th	Day	50% 7% 10% 17% 13% 2	2404
	21st to end	Day	51% 6% 11% 20% 10% 3	2470
May	1st to 10th	Day	51% 8% 9% 22% 9% 1	4120
	11th to 20th	Day	46% 9% 14% 20% 9% 2	4085
	21st to end	Day	37% 10% 13% 19% 15% 5%	4646
June	1st to 10th	Day	41% 8% 12% 25% 13% 1	2660
	11th to 20th	Day	38% 9% 15% 21% 15% 2	2660
	21st to end	Day	38% 7% 13% 25% 15% 2	2660
July	1st to 10th	Day	36% 7% 13% 25% 16% 3	4152
	11th to 20th	Day	33% 6% 14% 28% 18% 2	4051
	21st to end	Day	35% 9% 15% 20% 19% 1	4324
August	1st to 10th	Day	36% 9% 16% 26% 13%	2444
	11th to 20th	Day	38% 12% 15% 24% 10% 2	2433
	21st to end	Day	37% 9% 14% 23% 15% 2	2648
September	1st to 10th	Day	40% 8% 14% 21% 14% 2	2085
	11th to 20th	Day	37% 7% 16% 24% 15% 1	1980
	21st to end	Day	45% 7% 11% 23% 13% 1	1980
October	1st to 10th	Day	45% 8% 13% 20% 13% 1	1850
	11th to 20th	Day	54% 7% 12% 19% 8% 1	1800
	21st to end	Day	62% 6% 12% 13% 7% 1	1980
November	1st to 10th	Day	51% 8% 11% 18% 11% 1	1672
	11th to 20th	Day	62% 5% 10% 13% 7% 2	1640
	21st to end	Day	70% 5% 10% 11% 5%	1520
December	1st to 10th	Day	76% 5% 8% 8% 2	1520
	11th to 20th	Day	75% 5% 8% 10% 2	1906
	21st to end	Day	81% 5% 8% 5% 1	2836
January	1st to 10th	Night	78% 6% 6% 7% 2	4109
	11th to 20th	Night	78% 6% 9% 5% 1	4120
	21st to end	Night	80% 4 7% 7% 2	4532
February	1st to 10th	Night	69% 7% 9% 11% 4	2470
	11th to 20th	Night	67% 5% 9% 14% 5%	2370
	21st to end	Night	64% 7% 8% 13% 7% 1	1884
March	1st to 10th	Night	56% 5% 12% 19% 8%	3484
	11th to 20th	Night	50% 9% 15% 16% 9% 1	3480
	21st to end	Night	52% 8% 10% 18% 10% 1	3817
April	1st to 10th	Night	54% 6% 11% 16% 12% 2	2038
	11th to 20th	Night	49% 6% 12% 18% 13% 2	1741
	21st to end	Night	46% 8% 11% 18% 13% 3	1710
May	1st to 10th	Night	52% 8% 9% 18% 10% 3	2840
	11th to 20th	Night	44% 10% 11% 21% 12% 2	2813
	21st to end	Night	30% 9% 15% 25% 18% 3	2927
June	1st to 10th	Night	41% 8% 10% 24% 15% 3	1520
	11th to 20th	Night	38% 8% 12% 21% 18% 2	1520
	21st to end	Night	37% 9% 12% 25% 16% 2	1520
July	1st to 10th	Night	35% 6% 12% 25% 17% 5%	2691
	11th to 20th	Night	32% 7% 13% 27% 19% 3	2786
	21st to end	Night	35% 7% 14% 19% 22% 2	2988
August	1st to 10th	Night	33% 9% 13% 28% 15% 1	1690
	11th to 20th	Night	37% 8% 14% 27% 12% 2	1688
	21st to end	Night	35% 7% 13% 26% 16% 3	1899
September	1st to 10th	Night	37% 8% 14% 24% 14% 3	1872
	11th to 20th	Night	34% 7% 14% 25% 18% 1	1980
	21st to end	Night	45% 7% 11% 20% 17% 1	1980
October	1st to 10th	Night	41% 8% 14% 19% 17% 1	2110
	11th to 20th	Night	52% 6% 12% 20% 9% 1	2160
	21st to end	Night	61% 6% 10% 15% 7% 1	2376
November	1st to 10th	Night	51% 5% 12% 18% 11% 2	2404
	11th to 20th	Night	63% 6% 10% 13% 6% 2	2536
	21st to end	Night	68% 5% 10% 13% 4	2660
December	1st to 10th	Night	74% 7% 8% 8% 3	2660
	11th to 20th	Night	72% 6% 11% 10% 2	3288
	21st to end	Night	78% 7% 9% 5% 1	4816

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% 29% 31% 9% 3	270
	11th to 20th	Day	31% 29% 30% 8% 2	270
	21st to end	Day	27% 30% 31% 10% 1 1	297
February	1st to 10th	Day	33% 23% 35% 9% 1	270
	11th to 20th	Day	30% 34% 27% 9% 1	270
	21st to end	Day	32% 31% 31% 7%	225
March	1st to 10th	Day	27% 24% 32% 13% 3	414
	11th to 20th	Day	26% 23% 34% 14% 2 1	460
	21st to end	Day	33% 21% 28% 14% 4	506
April	1st to 10th	Day	23% 25% 30% 18% 4 1	460
	11th to 20th	Day	27% 19% 30% 15% 7% 1	452
	21st to end	Day	25% 22% 31% 17% 4 1	460
May	1st to 10th	Day	23% 19% 32% 21% 4 2	463
	11th to 20th	Day	18% 11% 33% 27% 9% 2	487
	21st to end	Day	14% 8% 30% 29% 16% 4	529
June	1st to 10th	Day	17% 7% 36% 27% 11% 2	490
	11th to 20th	Day	16% 10% 30% 30% 13% 1	490
	21st to end	Day	15% 9% 34% 29% 11% 2	490
July	1st to 10th	Day	12% 5% 25% 31% 21% 6%	485
	11th to 20th	Day	15% 8% 26% 28% 18% 5%	484
	21st to end	Day	10% 6% 29% 33% 17% 6%	532
August	1st to 10th	Day	11% 6% 24% 33% 19% 7%	486
	11th to 20th	Day	15% 6% 25% 32% 16% 6%	479
	21st to end	Day	13% 7% 22% 31% 19% 7%	532
September	1st to 10th	Day	17% 9% 20% 29% 20% 5%	450
	11th to 20th	Day	13% 4 22% 31% 22% 9%	450
	21st to end	Day	20% 13% 26% 23% 13% 5%	450
October	1st to 10th	Day	16% 14% 25% 25% 16% 4	450
	11th to 20th	Day	27% 16% 33% 19% 4 1	450
	21st to end	Day	34% 19% 28% 17% 3	495
November	1st to 10th	Day	20% 28% 26% 17% 7% 1	270
	11th to 20th	Day	34% 21% 26% 14% 5%	237
	21st to end	Day	33% 26% 32% 9% 1	180
December	1st to 10th	Day	26% 32% 27% 12% 2 1	180
	11th to 20th	Day	24% 37% 31% 8%	180
	21st to end	Day	31% 29% 31% 9%	216
January	1st to 10th	Night	28% 28% 31% 11% 3	760
	11th to 20th	Night	32% 23% 30% 13% 2	760
	21st to end	Night	24% 24% 33% 15% 3	836
February	1st to 10th	Night	29% 23% 28% 18% 2	760
	11th to 20th	Night	27% 23% 32% 16% 2	743
	21st to end	Night	29% 24% 31% 16% 1	628
March	1st to 10th	Night	23% 21% 32% 21% 4	760
	11th to 20th	Night	24% 21% 30% 19% 5% 1	760
	21st to end	Night	26% 17% 29% 21% 7%	836
April	1st to 10th	Night	23% 19% 28% 24% 6%	760
	11th to 20th	Night	22% 14% 37% 18% 8% 1	617
	21st to end	Night	20% 11% 34% 27% 7% 1	570
May	1st to 10th	Night	22% 11% 25% 31% 11% 1	570
	11th to 20th	Night	17% 9% 25% 36% 10% 2	561
	21st to end	Night	13% 3 25% 36% 20% 2	522
June	1st to 10th	Night	12% 5% 32% 34% 15% 1	380
	11th to 20th	Night	13% 4 28% 36% 19% 1	380
	21st to end	Night	11% 5% 27% 39% 17%	380
July	1st to 10th	Night	8% 4 17% 37% 28% 5%	490
	11th to 20th	Night	10% 5% 22% 35% 23% 4	552
	21st to end	Night	10% 6% 17% 38% 26% 2	624
August	1st to 10th	Night	11% 3 18% 37% 26% 5%	567
	11th to 20th	Night	12% 3 15% 38% 28% 4	564
	21st to end	Night	12% 5% 20% 31% 28% 3	651
September	1st to 10th	Night	15% 7% 18% 31% 25% 4	720
	11th to 20th	Night	14% 5% 17% 35% 25% 5%	720
	21st to end	Night	19% 9% 24% 26% 18% 4	720
October	1st to 10th	Night	19% 10% 25% 26% 17% 3	720
	11th to 20th	Night	25% 18% 26% 23% 8%	720
	21st to end	Night	37% 16% 27% 17% 3	792
November	1st to 10th	Night	25% 16% 29% 21% 8% 1	740
	11th to 20th	Night	30% 22% 29% 13% 5% 1	760
	21st to end	Night	34% 23% 28% 12% 4	760
December	1st to 10th	Night	34% 23% 28% 12% 4	760
	11th to 20th	Night	29% 28% 29% 12% 2	760
	21st to end	Night	32% 23% 31% 12% 1	836

Page generated at 2024-08-27 09:49:36. Version ac07

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