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 2024-01-27.

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	17% 12% 5% 7% 6% 3 4 4 5% 7% 31%	74729
	Night	17% 13% 5% 8% 6% 3 4 4 5% 6% 29%	75320
Transparency	Day	52% 7% 12% 18% 10% 1	74450
	Night	55% 7% 11% 16% 10% 1	75118
Seeing	Day	21% 16% 28% 22% 10% 3	13480
	Night	23% 15% 27% 23% 11% 1	23352

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% 20% 9% 13% 8% 3 4 4 3 4 15%	1706
	11th to 20th	Day	17% 22% 10% 13% 8% 4 3 4 3 4 13%	1710
	21st to end	Day	18% 20% 11% 15% 10% 3 3 3 4 3 10%	1836
February	1st to 10th	Day	18% 19% 8% 13% 10% 4 3 2 3 4 17%	1620
	11th to 20th	Day	16% 16% 9% 14% 11% 4 3 4 3 4 18%	1605
	21st to end	Day	19% 16% 6% 13% 5% 2 5% 5% 4 5% 21%	1480
March	1st to 10th	Day	18% 14% 7% 9% 6% 2 3 3 5% 7% 26%	1936
	11th to 20th	Day	16% 16% 6% 9% 6% 3 4 3 3 6% 29%	1980
	21st to end	Day	21% 14% 5% 7% 5% 3 4 3 4 5% 29%	2178
April	1st to 10th	Day	16% 14% 5% 6% 5% 3 4 4 5% 6% 32%	2028
	11th to 20th	Day	19% 12% 4 5% 4 3 4 5% 4 6% 33%	2276
	21st to end	Day	21% 12% 4 6% 4 3 4 3 4 5% 35%	2340
May	1st to 10th	Day	18% 9% 3 7% 6% 4 5% 4 5% 6% 32%	2340
	11th to 20th	Day	19% 7% 3 5% 5% 4 5% 4 6% 6% 35%	2301
	21st to end	Day	12% 5% 3 6% 6% 4 6% 6% 5% 9% 40%	2618
June	1st to 10th	Day	17% 5% 2 5% 5% 3 5% 5% 7% 7% 39%	2520
	11th to 20th	Day	14% 6% 3 6% 5% 3 4 5% 6% 8% 40%	2520
	21st to end	Day	13% 5% 2 4 5% 3 5% 5% 6% 10% 42%	2520
July	1st to 10th	Day	11% 4 2 5% 4 3 5% 5% 6% 9% 45%	2395
	11th to 20th	Day	13% 5% 3 4 3 3 4 5% 7% 10% 41%	2340
	21st to end	Day	11% 5% 2 4 5% 3 4 6% 7% 10% 43%	2547
August	1st to 10th	Day	9% 5% 2 6% 5% 3 5% 5% 7% 9% 43%	2327
	11th to 20th	Day	11% 5% 2 6% 6% 4 5% 7% 8% 9% 36%	2303
	21st to end	Day	13% 6% 3 5% 5% 3 5% 6% 6% 9% 40%	2530
September	1st to 10th	Day	16% 6% 3 5% 4 2 4 5% 6% 8% 40%	2085
	11th to 20th	Day	14% 5% 2 5% 4 3 5% 5% 6% 9% 42%	1980
	21st to end	Day	19% 9% 2 6% 5% 2 4 5% 5% 6% 38%	1980
October	1st to 10th	Day	18% 6% 3 7% 5% 3 4 5% 5% 7% 37%	1850
	11th to 20th	Day	24% 10% 3 5% 6% 3 4 4 5% 6% 30%	1800
	21st to end	Day	27% 12% 3 7% 5% 3 4 4 4 6% 24%	1980
November	1st to 10th	Day	14% 15% 4 6% 5% 3 4 4 4 7% 33%	1672
	11th to 20th	Day	19% 21% 5% 7% 5% 2 4 4 3 5% 24%	1640
	21st to end	Day	20% 23% 7% 8% 5% 3 4 4 4 6% 16%	1520
December	1st to 10th	Day	17% 25% 11% 10% 6% 3 4 3 3 4 13%	1520
	11th to 20th	Day	18% 20% 10% 14% 5% 2 4 5% 4 4 13%	1910
	21st to end	Day	23% 24% 9% 11% 6% 3 4 3 4 3 9%	2836
January	1st to 10th	Night	19% 20% 10% 13% 7% 2 3 3 3 4 15%	2459
	11th to 20th	Night	18% 21% 10% 14% 7% 3 3 3 3 3 15%	2470
	21st to end	Night	17% 20% 9% 14% 10% 3 4 3 3 4 15%	2664
February	1st to 10th	Night	21% 16% 6% 13% 7% 3 5% 3 4 4 17%	2340
	11th to 20th	Night	18% 16% 7% 12% 7% 4 4 4 4 4 19%	2240
	21st to end	Night	20% 13% 6% 12% 6% 3 4 4 4 4 24%	1776
March	1st to 10th	Night	16% 14% 6% 8% 6% 3 5% 4 5% 5% 29%	2022
	11th to 20th	Night	17% 12% 5% 7% 5% 3 3 4 4 6% 32%	1980
	21st to end	Night	19% 15% 6% 8% 5% 3 3 3 4 5% 30%	2178
April	1st to 10th	Night	18% 14% 6% 6% 5% 3 3 4 5% 6% 31%	1931
	11th to 20th	Night	17% 11% 3 6% 4 3 5% 6% 6% 7% 34%	1649
	21st to end	Night	17% 9% 3 6% 6% 3 4 5% 6% 7% 35%	1620
May	1st to 10th	Night	20% 8% 3 7% 6% 3 5% 4 5% 6% 31%	1620
	11th to 20th	Night	15% 9% 4 6% 6% 3 4 5% 6% 7% 35%	1592
	21st to end	Night	12% 4 2 4 4 3 4 5% 7% 10% 43%	1654
June	1st to 10th	Night	12% 6% 3 7% 5% 3 4 6% 5% 7% 42%	1440
	11th to 20th	Night	11% 5% 2 6% 6% 4 5% 6% 5% 8% 43%	1440
	21st to end	Night	10% 5% 2 6% 5% 3 6% 5% 6% 10% 42%	1440
July	1st to 10th	Night	10% 4 2 5% 4 2 3 4 6% 8% 50%	1558
	11th to 20th	Night	9% 5% 2 5% 4 3 4 7% 6% 10% 46%	1620
	21st to end	Night	10% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	1771
August	1st to 10th	Night	8% 4 2 5% 6% 4 5% 5% 6% 9% 47%	1611
	11th to 20th	Night	11% 5% 3 5% 5% 3 6% 5% 6% 8% 44%	1598
	21st to end	Night	12% 5% 2 5% 5% 3 5% 4 5% 9% 45%	1808
September	1st to 10th	Night	13% 6% 2 5% 4 3 5% 6% 5% 7% 43%	1872
	11th to 20th	Night	13% 4 2 4 5% 3 4 4 5% 6% 50%	1980
	21st to end	Night	18% 6% 2 6% 6% 4 5% 5% 5% 6% 38%	1980
October	1st to 10th	Night	16% 7% 3 5% 4 3 3 5% 6% 8% 41%	2110
	11th to 20th	Night	22% 8% 3 6% 6% 3 4 4 5% 6% 31%	2160
	21st to end	Night	30% 11% 3 6% 5% 3 4 4 4 5% 26%	2376
November	1st to 10th	Night	18% 14% 4 5% 5% 2 3 3 5% 7% 34%	2404
	11th to 20th	Night	18% 21% 4 9% 5% 3 4 4 4 5% 23%	2536
	21st to end	Night	21% 21% 6% 7% 6% 3 5% 3 4 5% 20%	2660
December	1st to 10th	Night	21% 25% 10% 8% 5% 3 4 4 3 3 15%	2660
	11th to 20th	Night	17% 23% 8% 12% 6% 3 4 3 4 4 16%	3285
	21st to end	Night	22% 24% 8% 10% 7% 4 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% 5% 9% 8% 3	1707
	11th to 20th	Day	77% 5% 11% 6% 2	1710
	21st to end	Day	79% 5% 7% 6% 3	1836
February	1st to 10th	Day	73% 5% 7% 11% 3	1620
	11th to 20th	Day	71% 5% 7% 11% 5%	1614
	21st to end	Day	64% 7% 11% 10% 6% 2	1480
March	1st to 10th	Day	58% 6% 13% 18% 5%	1936
	11th to 20th	Day	57% 7% 9% 16% 9% 2	1980
	21st to end	Day	58% 6% 8% 19% 8% 1	2178
April	1st to 10th	Day	51% 6% 12% 18% 13% 1	2028
	11th to 20th	Day	51% 7% 10% 17% 13% 2	2276
	21st to end	Day	52% 6% 11% 20% 9% 3	2340
May	1st to 10th	Day	51% 8% 9% 20% 10% 2	2340
	11th to 20th	Day	48% 7% 11% 17% 14% 3	2305
	21st to end	Day	39% 9% 15% 23% 13% 1	2618
June	1st to 10th	Day	41% 8% 12% 25% 13% 1	2520
	11th to 20th	Day	39% 10% 15% 21% 14% 2	2520
	21st to end	Day	37% 7% 12% 26% 15% 2	2520
July	1st to 10th	Day	35% 8% 12% 26% 17% 2	2330
	11th to 20th	Day	36% 7% 15% 25% 15% 1	2271
	21st to end	Day	33% 10% 15% 24% 16% 2	2405
August	1st to 10th	Day	34% 9% 16% 27% 13%	2314
	11th to 20th	Day	38% 12% 16% 22% 10% 2	2303
	21st to end	Day	38% 9% 14% 22% 16% 2	2530
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	74% 5% 7% 10% 4	2459
	11th to 20th	Night	76% 4 9% 9% 2 1	2470
	21st to end	Night	76% 4 7% 9% 3	2664
February	1st to 10th	Night	71% 6% 9% 10% 3	2340
	11th to 20th	Night	68% 5% 8% 13% 5%	2242
	21st to end	Night	64% 7% 8% 13% 7% 1	1776
March	1st to 10th	Night	58% 6% 9% 19% 8%	2022
	11th to 20th	Night	52% 6% 11% 17% 11% 2	1980
	21st to end	Night	58% 5% 6% 18% 11% 2	2178
April	1st to 10th	Night	53% 5% 12% 16% 12% 2	1931
	11th to 20th	Night	49% 6% 12% 18% 13% 3	1649
	21st to end	Night	46% 8% 11% 18% 13% 3	1620
May	1st to 10th	Night	52% 6% 10% 17% 11% 3	1620
	11th to 20th	Night	46% 8% 10% 17% 15% 4	1593
	21st to end	Night	34% 9% 17% 25% 14% 2	1655
June	1st to 10th	Night	41% 8% 10% 24% 15% 3	1440
	11th to 20th	Night	38% 8% 12% 21% 18% 2	1440
	21st to end	Night	36% 9% 12% 25% 16% 2	1440
July	1st to 10th	Night	32% 7% 11% 26% 19% 5%	1513
	11th to 20th	Night	32% 8% 14% 24% 19% 3	1566
	21st to end	Night	35% 9% 15% 21% 17% 2	1672
August	1st to 10th	Night	32% 9% 14% 29% 15% 1	1600
	11th to 20th	Night	36% 9% 14% 27% 12% 2	1598
	21st to end	Night	35% 7% 13% 25% 16% 3	1808
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	28% 31% 29% 10% 1 1	282
February	1st to 10th	Day	35% 23% 34% 7%	240
	11th to 20th	Day	31% 33% 28% 7%	240
	21st to end	Day	31% 32% 31% 6%	198
March	1st to 10th	Day	27% 24% 32% 13% 3 1	376
	11th to 20th	Day	25% 23% 34% 15% 2 1	420
	21st to end	Day	33% 20% 28% 15% 4	462
April	1st to 10th	Day	23% 24% 29% 19% 4 1	420
	11th to 20th	Day	26% 17% 31% 16% 8% 1	412
	21st to end	Day	26% 21% 30% 17% 4 1	420
May	1st to 10th	Day	23% 18% 32% 21% 4 2	423
	11th to 20th	Day	19% 10% 33% 27% 9% 2	447
	21st to end	Day	13% 7% 30% 28% 18% 4	485
June	1st to 10th	Day	17% 6% 36% 28% 11% 2	450
	11th to 20th	Day	17% 10% 29% 29% 14% 2	450
	21st to end	Day	13% 9% 34% 30% 12% 2	450
July	1st to 10th	Day	11% 4 23% 32% 23% 7%	445
	11th to 20th	Day	15% 7% 25% 29% 19% 5%	444
	21st to end	Day	9% 6% 30% 33% 17% 5%	488
August	1st to 10th	Day	9% 5% 23% 34% 20% 8%	446
	11th to 20th	Day	14% 6% 23% 33% 17% 7%	439
	21st to end	Day	13% 7% 22% 31% 19% 7%	495
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	25% 25% 33% 15% 3	820
February	1st to 10th	Night	30% 23% 28% 17% 2	720
	11th to 20th	Night	28% 23% 32% 16% 2	703
	21st to end	Night	29% 24% 31% 15% 1	592
March	1st to 10th	Night	23% 21% 33% 20% 3	720
	11th to 20th	Night	23% 21% 30% 19% 5% 1	720
	21st to end	Night	26% 16% 29% 22% 7% 1	792
April	1st to 10th	Night	23% 19% 28% 25% 6%	720
	11th to 20th	Night	22% 14% 36% 19% 8% 1	585
	21st to end	Night	20% 11% 34% 27% 7% 1	540
May	1st to 10th	Night	23% 9% 25% 30% 11% 1	540
	11th to 20th	Night	18% 9% 25% 36% 10% 2	531
	21st to end	Night	14% 3 25% 36% 20% 3	494
June	1st to 10th	Night	12% 4 33% 35% 16% 1	360
	11th to 20th	Night	14% 4 27% 36% 20% 1	360
	21st to end	Night	12% 4 27% 40% 17%	360
July	1st to 10th	Night	8% 4 16% 37% 30% 5%	463
	11th to 20th	Night	10% 5% 22% 35% 23% 5%	522
	21st to end	Night	11% 6% 17% 38% 25% 2	591
August	1st to 10th	Night	10% 3 18% 37% 27% 5%	537
	11th to 20th	Night	11% 3 14% 39% 29% 4	534
	21st to end	Night	13% 5% 20% 31% 28% 4	620
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 2024-01-24 09:37:28. Version ac07

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