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 2025-02-06.

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 10% 5% 4 4 3 5% 6% 30%	108504
	Night	16% 15% 5% 10% 5% 4 4 3 5% 5% 28%	109740
Transparency	Day	52% 7% 11% 18% 10% 1	112180
	Night	56% 6% 10% 17% 10% 1	114203
Seeing	Day	22% 16% 29% 21% 10% 3	14808
	Night	23% 16% 27% 23% 11% 1	24676

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% 22% 10% 27% 4 2 3 1 2 3 12%	4056
	11th to 20th	Day	12% 23% 9% 21% 9% 6% 3 2 3 3 10%	4060
	21st to end	Day	20% 20% 10% 16% 8% 5% 3 2 3 2 11%	4466
February	1st to 10th	Day	17% 20% 6% 13% 8% 5% 2 2 3 4 18%	1755
	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	13% 7% 2 7% 4 4 5% 4 7% 9% 38%	4104
	11th to 20th	Day	13% 7% 2 7% 4 4 6% 5% 8% 9% 35%	4044
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 6% 9% 42%	4446
September	1st to 10th	Day	16% 7% 2 6% 3 3 4 4 6% 8% 41%	2200
	11th to 20th	Day	13% 6% 2 5% 3 4 5% 4 6% 9% 44%	2090
	21st to end	Day	19% 10% 2 7% 4 3 4 4 4 6% 36%	2090
October	1st to 10th	Day	17% 6% 3 7% 4 4 4 4 5% 7% 38%	1952
	11th to 20th	Day	24% 10% 3 6% 5% 4 4 3 5% 6% 32%	1900
	21st to end	Day	26% 12% 3 7% 5% 4 4 4 5% 6% 25%	2090
November	1st to 10th	Day	14% 15% 4 7% 5% 4 4 4 5% 7% 33%	1762
	11th to 20th	Day	18% 22% 4 8% 5% 4 4 2 4 5% 24%	1726
	21st to end	Day	20% 25% 7% 9% 5% 4 3 3 4 6% 15%	1600
December	1st to 10th	Day	17% 23% 11% 14% 6% 4 4 3 3 4 12%	2600
	11th to 20th	Day	21% 24% 8% 13% 7% 3 3 3 4 4 10%	2990
	21st to end	Day	23% 24% 7% 15% 5% 4 4 2 4 3 8%	4052
January	1st to 10th	Night	13% 23% 12% 25% 5% 2 2 2 2 3 10%	5889
	11th to 20th	Night	10% 21% 13% 21% 9% 5% 5% 3 3 2 9%	5900
	21st to end	Night	20% 20% 8% 17% 6% 3 4 2 3 3 13%	6490
February	1st to 10th	Night	20% 17% 5% 14% 7% 4 4 2 5% 3 18%	2536
	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	11% 6% 3 7% 5% 5% 5% 4 6% 9% 40%	2825
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 6% 40%	2785
	21st to end	Night	9% 5% 2 7% 5% 4 5% 4 6% 8% 43%	3178
September	1st to 10th	Night	13% 6% 2 5% 4 4 6% 4 5% 7% 44%	1976
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 6% 6% 51%	2090
	21st to end	Night	19% 7% 2 6% 6% 5% 5% 3 5% 6% 37%	2090
October	1st to 10th	Night	15% 7% 3 6% 4 4 4 4 6% 7% 42%	2228
	11th to 20th	Night	22% 9% 3 7% 5% 4 4 4 5% 6% 32%	2280
	21st to end	Night	27% 12% 3 7% 4 4 3 4 5% 5% 27%	2508
November	1st to 10th	Night	17% 14% 3 6% 4 3 3 3 5% 7% 34%	2534
	11th to 20th	Night	18% 22% 4 10% 5% 4 4 3 4 5% 22%	2670
	21st to end	Night	20% 23% 5% 8% 4 4 4 3 5% 5% 19%	2800
December	1st to 10th	Night	16% 23% 12% 13% 5% 4 3 3 4 4 13%	4580
	11th to 20th	Night	18% 26% 8% 12% 5% 4 3 3 4 4 14%	5205
	21st to end	Night	20% 24% 7% 12% 5% 5% 4 3 5% 5% 10%	6886

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	79% 5% 7% 5% 3 1	4057
	11th to 20th	Day	81% 4 10% 4 2	4060
	21st to end	Day	80% 4 5% 8% 2	4466
February	1st to 10th	Day	71% 5% 8% 11% 4	1755
	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	40% 8% 15% 25% 12%	4091
	11th to 20th	Day	40% 9% 12% 30% 7% 1	4083
	21st to end	Day	36% 8% 15% 28% 12% 1	4446
September	1st to 10th	Day	39% 8% 14% 22% 15% 2	2200
	11th to 20th	Day	36% 8% 15% 24% 17% 1	2090
	21st to end	Day	47% 7% 10% 22% 13% 1	2090
October	1st to 10th	Day	36% 6% 14% 25% 18% 1	3238
	11th to 20th	Day	48% 5% 10% 19% 16% 1	3140
	21st to end	Day	45% 5% 14% 24% 11% 1	3428
November	1st to 10th	Day	51% 7% 10% 19% 11% 1	1762
	11th to 20th	Day	63% 6% 10% 13% 7% 2	1726
	21st to end	Day	71% 5% 9% 11% 4	1600
December	1st to 10th	Day	76% 7% 10% 6% 1	2600
	11th to 20th	Day	78% 5% 7% 8% 1	2986
	21st to end	Day	81% 5% 7% 6% 1	4052
January	1st to 10th	Night	80% 5% 5% 7% 3	5889
	11th to 20th	Night	81% 4 7% 5% 1	5900
	21st to end	Night	77% 4 8% 8% 4	6490
February	1st to 10th	Night	70% 7% 9% 11% 4	2536
	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	38% 8% 12% 27% 13% 1	2814
	11th to 20th	Night	44% 6% 11% 27% 11% 1	2812
	21st to end	Night	36% 7% 12% 28% 15% 2	3178
September	1st to 10th	Night	36% 7% 14% 25% 15% 3	1976
	11th to 20th	Night	33% 7% 13% 26% 19% 2	2090
	21st to end	Night	47% 7% 10% 19% 16% 1	2090
October	1st to 10th	Night	33% 6% 10% 28% 21% 1	3722
	11th to 20th	Night	49% 5% 10% 19% 16% 2	3779
	21st to end	Night	46% 5% 13% 22% 14% 1	4120
November	1st to 10th	Night	51% 5% 11% 19% 11% 2	2534
	11th to 20th	Night	63% 6% 9% 13% 6% 3	2670
	21st to end	Night	69% 5% 9% 13% 4	2800
December	1st to 10th	Night	75% 6% 10% 7% 2	4580
	11th to 20th	Night	75% 5% 9% 10% 1	5208
	21st to end	Night	75% 7% 8% 8% 1	6886

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% 31% 31% 8% 3	300
	11th to 20th	Day	33% 30% 28% 7% 2	300
	21st to end	Day	29% 30% 31% 9% 1 1	330
February	1st to 10th	Day	34% 22% 34% 8% 1	285
	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%	539
September	1st to 10th	Day	17% 9% 20% 28% 20% 5%	490
	11th to 20th	Day	12% 4 22% 32% 21% 9%	490
	21st to end	Day	22% 13% 26% 22% 12% 5%	490
October	1st to 10th	Day	15% 15% 26% 25% 16% 3	490
	11th to 20th	Day	27% 16% 32% 18% 6% 1	490
	21st to end	Day	33% 19% 28% 18% 2	539
November	1st to 10th	Day	22% 27% 28% 15% 7% 1	300
	11th to 20th	Day	35% 22% 26% 13% 4	263
	21st to end	Day	35% 26% 31% 8% 1	200
December	1st to 10th	Day	27% 31% 29% 11% 2 1	200
	11th to 20th	Day	25% 36% 31% 9% 1	200
	21st to end	Day	31% 29% 32% 8%	240
January	1st to 10th	Night	28% 28% 31% 10% 3	800
	11th to 20th	Night	32% 24% 29% 13% 2	800
	21st to end	Night	26% 25% 32% 15% 3	880
February	1st to 10th	Night	30% 23% 27% 17% 2	781
	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	655
September	1st to 10th	Night	15% 7% 19% 31% 25% 4	760
	11th to 20th	Night	14% 5% 17% 36% 25% 4	760
	21st to end	Night	20% 10% 24% 25% 17% 4	760
October	1st to 10th	Night	19% 10% 26% 26% 17% 3	760
	11th to 20th	Night	26% 17% 26% 23% 9%	760
	21st to end	Night	35% 16% 27% 18% 3	836
November	1st to 10th	Night	26% 17% 29% 21% 7% 1	780
	11th to 20th	Night	31% 22% 29% 13% 5% 1	800
	21st to end	Night	35% 23% 27% 12% 4	800
December	1st to 10th	Night	34% 24% 27% 12% 4	800
	11th to 20th	Night	30% 28% 29% 12% 2	800
	21st to end	Night	32% 23% 32% 13% 1	880

Page generated at 2025-02-03 03:05:51. Version ac07

Copyright © 2025 Attilla Danko.