Palmer Junction
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Palmer Junction clear sky chart from 2005-11-06 to 2026-07-16.

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	6% 9% 3 7% 4 4 4 4 5% 7% 46%	146942
	Night	7% 10% 3 7% 5% 4 5% 4 5% 7% 43%	143048
Transparency	Day	37% 8% 12% 21% 16% 7%	141660
	Night	39% 9% 13% 21% 13% 4	139335
Seeing	Day	15% 15% 26% 26% 14% 4	16465
	Night	15% 8% 20% 35% 20% 3	25597

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	7% 21% 7% 14% 8% 8% 7% 5% 5% 6% 13%	4722
	11th to 20th	Day	5% 11% 5% 9% 4 4 4 4 6% 8% 39%	4740
	21st to end	Day	6% 10% 4 9% 5% 6% 6% 5% 7% 7% 36%	5187
February	1st to 10th	Day	9% 19% 6% 11% 7% 6% 5% 4 7% 5% 21%	1769
	11th to 20th	Day	9% 20% 6% 10% 7% 5% 5% 4 5% 5% 23%	1998
	21st to end	Day	8% 19% 6% 11% 6% 6% 5% 4 5% 6% 24%	1730
March	1st to 10th	Day	5% 14% 5% 9% 7% 6% 6% 5% 8% 9% 27%	4618
	11th to 20th	Day	6% 12% 5% 10% 6% 5% 6% 4 6% 8% 32%	4747
	21st to end	Day	9% 18% 5% 11% 7% 7% 7% 5% 7% 7% 17%	6101
April	1st to 10th	Day	10% 15% 5% 9% 6% 6% 4 4 7% 7% 26%	2520
	11th to 20th	Day	9% 13% 4 9% 6% 5% 5% 4 6% 7% 33%	2499
	21st to end	Day	10% 12% 3 9% 5% 5% 5% 4 5% 6% 34%	2730
May	1st to 10th	Day	6% 8% 2 6% 4 4 4 3 5% 6% 53%	7902
	11th to 20th	Day	7% 11% 4 7% 5% 5% 5% 4 5% 7% 41%	8160
	21st to end	Day	8% 6% 2 5% 4 4 4 4 7% 8% 48%	8992
June	1st to 10th	Day	13% 8% 2 7% 5% 5% 5% 4 5% 7% 39%	2940
	11th to 20th	Day	11% 7% 2 5% 4 4 4 4 5% 7% 45%	2940
	21st to end	Day	5% 4 1 4 4 3 3 3 4 7% 62%	2940
July	1st to 10th	Day	2 2 1 2 2 2 2 2 4 4 76%	6459
	11th to 20th	Day	1 2 1 2 2 2 2 1 3 4 81%	6391
	21st to end	Day	2 1 2 2 2 3 3 5% 8% 72%	6880
August	1st to 10th	Day	4 4 1 4 3 3 4 3 5% 7% 61%	6210
	11th to 20th	Day	3 2 1 3 2 2 3 2 4 5% 73%	5809
	21st to end	Day	4 3 1 5% 3 4 4 3 5% 7% 62%	5984
September	1st to 10th	Day	3 2 1 4 2 2 3 2 4 7% 69%	2400
	11th to 20th	Day	7% 5% 2 5% 3 4 5% 3 5% 7% 55%	2297
	21st to end	Day	7% 5% 2 6% 3 4 4 3 4 6% 55%	2200
October	1st to 10th	Day	7% 5% 2 4 3 2 3 2 4 6% 62%	3455
	11th to 20th	Day	7% 8% 3 6% 4 4 4 4 7% 10% 44%	3140
	21st to end	Day	11% 12% 4 10% 7% 5% 6% 4 5% 6% 30%	3200
November	1st to 10th	Day	13% 14% 3 11% 5% 5% 6% 5% 5% 7% 26%	1854
	11th to 20th	Day	11% 17% 5% 11% 7% 6% 6% 5% 6% 8% 18%	1848
	21st to end	Day	8% 16% 4 10% 6% 5% 5% 6% 8% 7% 26%	1680
December	1st to 10th	Day	6% 11% 5% 9% 4 6% 5% 5% 5% 7% 38%	2700
	11th to 20th	Day	10% 15% 6% 14% 7% 6% 6% 5% 6% 7% 18%	3108
	21st to end	Day	9% 16% 8% 14% 6% 6% 5% 4 5% 6% 22%	4092
January	1st to 10th	Night	10% 19% 7% 13% 6% 6% 6% 4 5% 7% 15%	8172
	11th to 20th	Night	6% 11% 5% 9% 4 4 4 4 5% 8% 40%	8220
	21st to end	Night	6% 9% 3 9% 6% 5% 6% 6% 10% 8% 32%	8994
February	1st to 10th	Night	10% 19% 5% 11% 6% 5% 4 4 6% 6% 24%	2848
	11th to 20th	Night	8% 16% 5% 11% 6% 5% 4 4 6% 6% 30%	2510
	21st to end	Night	7% 16% 6% 9% 7% 6% 6% 4 5% 7% 26%	2076
March	1st to 10th	Night	5% 11% 4 9% 6% 6% 6% 4 7% 8% 35%	5496
	11th to 20th	Night	7% 15% 5% 9% 5% 4 4 3 4 5% 38%	5456
	21st to end	Night	8% 14% 4 11% 7% 6% 6% 5% 7% 7% 25%	5116
April	1st to 10th	Night	9% 11% 3 8% 6% 5% 6% 4 6% 9% 34%	2100
	11th to 20th	Night	10% 11% 2 7% 6% 4 4 4 5% 5% 41%	2069
	21st to end	Night	7% 9% 2 7% 5% 4 5% 4 5% 7% 44%	1890
May	1st to 10th	Night	7% 6% 1 3 3 3 3 3 5% 7% 59%	5028
	11th to 20th	Night	8% 9% 4 6% 3 3 3 3 5% 6% 49%	4700
	21st to end	Night	8% 7% 2 5% 3 4 4 3 6% 7% 52%	5181
June	1st to 10th	Night	11% 7% 2 6% 5% 3 4 4 7% 8% 44%	1680
	11th to 20th	Night	9% 5% 1 5% 4 4 5% 4 5% 7% 50%	1680
	21st to end	Night	4 5% 2 5% 3 3 4 4 5% 6% 59%	1680
July	1st to 10th	Night	2 2 1 2 2 2 3 2 3 5% 77%	3720
	11th to 20th	Night	1 1 1 1 1 2 2 3 4 84%	3680
	21st to end	Night	3 2 1 2 1 2 2 2 4 7% 75%	3970
August	1st to 10th	Night	2 2 1 3 2 4 4 4 6% 7% 66%	3582
	11th to 20th	Night	2 3 1 4 2 3 3 2 4 5% 72%	4034
	21st to end	Night	4 3 1 4 3 3 3 3 4 6% 67%	5015
September	1st to 10th	Night	4 2 1 3 2 2 3 2 4 5% 72%	2000
	11th to 20th	Night	5% 4 1 5% 3 5% 4 3 5% 6% 58%	2102
	21st to end	Night	7% 4 2 5% 4 3 3 3 5% 7% 58%	2200
October	1st to 10th	Night	5% 5% 2 5% 3 3 3 2 3 5% 63%	3741
	11th to 20th	Night	8% 6% 2 5% 5% 4 5% 4 6% 8% 47%	4014
	21st to end	Night	9% 10% 5% 8% 5% 5% 5% 4 6% 7% 38%	4600
November	1st to 10th	Night	14% 12% 4 9% 6% 6% 5% 4 5% 6% 31%	2665
	11th to 20th	Night	12% 15% 4 9% 6% 6% 6% 5% 6% 6% 25%	2767
	21st to end	Night	8% 14% 4 8% 6% 6% 6% 5% 6% 7% 31%	2940
December	1st to 10th	Night	6% 9% 4 8% 5% 7% 5% 4 5% 10% 37%	4700
	11th to 20th	Night	10% 15% 5% 11% 7% 8% 7% 5% 7% 7% 16%	5316
	21st to end	Night	10% 16% 6% 14% 6% 6% 5% 4 5% 6% 21%	7106

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	64% 15% 9% 10% 1	4723
	11th to 20th	Day	41% 8% 15% 27% 8% 1	4740
	21st to end	Day	45% 9% 12% 22% 12%	5187
February	1st to 10th	Day	62% 11% 13% 11% 4	1769
	11th to 20th	Day	61% 10% 11% 11% 7%	2008
	21st to end	Day	59% 11% 11% 12% 6% 1	1730
March	1st to 10th	Day	48% 10% 14% 18% 9% 1	4618
	11th to 20th	Day	46% 10% 13% 24% 6%	4747
	21st to end	Day	60% 13% 13% 12% 2	6101
April	1st to 10th	Day	55% 9% 15% 16% 4	2520
	11th to 20th	Day	49% 9% 14% 17% 10% 1	2502
	21st to end	Day	48% 9% 11% 21% 10% 1	2730
May	1st to 10th	Day	31% 6% 9% 30% 22% 1	7902
	11th to 20th	Day	36% 10% 15% 26% 12% 1	8163
	21st to end	Day	30% 8% 18% 28% 14% 1	8994
June	1st to 10th	Day	44% 9% 13% 23% 11% 1	2940
	11th to 20th	Day	37% 7% 14% 23% 16% 3	2940
	21st to end	Day	22% 6% 12% 32% 22% 6%	2940
July	1st to 10th	Day	12% 3 6% 19% 29% 31%	6391
	11th to 20th	Day	9% 2 5% 12% 31% 40%	6316
	21st to end	Day	11% 4 5% 27% 32% 21%	6681
August	1st to 10th	Day	17% 4 6% 15% 36% 22%	4524
	11th to 20th	Day	15% 4 7% 30% 33% 12%	4209
	21st to end	Day	17% 4 11% 26% 27% 13%	4311
September	1st to 10th	Day	17% 4 11% 25% 28% 15%	2400
	11th to 20th	Day	28% 6% 12% 21% 22% 11%	2297
	21st to end	Day	29% 8% 13% 25% 20% 5%	2200
October	1st to 10th	Day	25% 5% 11% 28% 26% 6%	3455
	11th to 20th	Day	33% 8% 19% 25% 14% 1	3140
	21st to end	Day	51% 9% 10% 22% 8%	3200
November	1st to 10th	Day	55% 10% 13% 16% 5%	1854
	11th to 20th	Day	62% 10% 14% 11% 2	1848
	21st to end	Day	53% 12% 15% 13% 6% 1	1680
December	1st to 10th	Day	43% 10% 19% 24% 3	2700
	11th to 20th	Day	61% 13% 16% 8% 1	3108
	21st to end	Day	58% 12% 18% 10% 2	4092
January	1st to 10th	Night	64% 14% 11% 10% 1	8172
	11th to 20th	Night	40% 8% 19% 25% 8% 1	8220
	21st to end	Night	43% 11% 15% 21% 10%	8994
February	1st to 10th	Night	60% 10% 15% 12% 3	2848
	11th to 20th	Night	55% 9% 14% 15% 6%	2511
	21st to end	Night	58% 8% 11% 15% 6% 1	2076
March	1st to 10th	Night	41% 10% 15% 20% 13%	5496
	11th to 20th	Night	48% 8% 11% 29% 5%	5456
	21st to end	Night	55% 12% 14% 16% 3	5116
April	1st to 10th	Night	49% 10% 17% 19% 5%	2100
	11th to 20th	Night	44% 9% 15% 20% 11% 1	2069
	21st to end	Night	41% 10% 16% 21% 12% 1	1890
May	1st to 10th	Night	24% 5% 12% 35% 22% 2	5026
	11th to 20th	Night	34% 7% 13% 33% 13% 1	4700
	21st to end	Night	30% 9% 17% 33% 11%	5182
June	1st to 10th	Night	36% 11% 11% 28% 12% 1	1680
	11th to 20th	Night	33% 8% 15% 27% 14% 3	1680
	21st to end	Night	24% 7% 13% 29% 21% 6%	1680
July	1st to 10th	Night	12% 3 6% 20% 30% 29%	3680
	11th to 20th	Night	7% 3 5% 15% 29% 41%	3632
	21st to end	Night	11% 2 4 31% 30% 22%	3857
August	1st to 10th	Night	13% 4 6% 19% 43% 16%	2601
	11th to 20th	Night	15% 5% 7% 30% 33% 10%	2910
	21st to end	Night	14% 4 10% 31% 29% 12%	3608
September	1st to 10th	Night	16% 3 10% 27% 28% 16%	2000
	11th to 20th	Night	26% 7% 11% 23% 23% 10%	2102
	21st to end	Night	27% 6% 12% 29% 19% 8%	2200
October	1st to 10th	Night	25% 5% 9% 27% 29% 4	3741
	11th to 20th	Night	33% 8% 17% 22% 18% 1	4014
	21st to end	Night	42% 9% 12% 25% 11% 1	4600
November	1st to 10th	Night	52% 10% 14% 17% 5% 1	2665
	11th to 20th	Night	57% 10% 15% 14% 3	2767
	21st to end	Night	52% 9% 14% 17% 7% 1	2940
December	1st to 10th	Night	41% 11% 24% 20% 4 1	4700
	11th to 20th	Night	63% 12% 14% 10% 1	5316
	21st to end	Night	60% 11% 17% 9% 3	7106

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	19% 18% 28% 23% 10% 2	220
	11th to 20th	Day	18% 12% 35% 18% 13% 4	220
	21st to end	Day	16% 10% 34% 26% 13% 1	242
February	1st to 10th	Day	25% 21% 27% 19% 7% 2	309
	11th to 20th	Day	23% 19% 30% 19% 8%	508
	21st to end	Day	22% 22% 27% 22% 6% 1	446
March	1st to 10th	Day	22% 22% 29% 19% 7% 1	540
	11th to 20th	Day	23% 21% 21% 21% 11% 3	540
	21st to end	Day	25% 23% 28% 18% 6% 1	594
April	1st to 10th	Day	23% 19% 25% 18% 10% 4	540
	11th to 20th	Day	20% 22% 29% 15% 10% 3	532
	21st to end	Day	19% 17% 27% 22% 14% 2	540
May	1st to 10th	Day	15% 14% 29% 28% 11% 4	543
	11th to 20th	Day	21% 15% 24% 21% 13% 6%	568
	21st to end	Day	15% 11% 24% 28% 16% 6%	617
June	1st to 10th	Day	16% 13% 24% 23% 17% 7%	570
	11th to 20th	Day	16% 19% 29% 24% 10% 2	570
	21st to end	Day	7% 12% 29% 31% 15% 6%	570
July	1st to 10th	Day	4 8% 29% 34% 21% 4	566
	11th to 20th	Day	4 11% 29% 34% 17% 4	545
	21st to end	Day	2 8% 27% 31% 23% 8%	575
August	1st to 10th	Day	6% 7% 26% 34% 19% 8%	527
	11th to 20th	Day	3 8% 21% 36% 21% 11%	517
	21st to end	Day	8% 11% 26% 29% 17% 9%	583
September	1st to 10th	Day	5% 10% 24% 28% 23% 10%	530
	11th to 20th	Day	11% 10% 25% 28% 19% 6%	530
	21st to end	Day	12% 10% 27% 29% 16% 7%	530
October	1st to 10th	Day	15% 13% 22% 24% 21% 5%	530
	11th to 20th	Day	18% 13% 22% 25% 17% 7%	460
	21st to end	Day	17% 17% 23% 28% 11% 4	363
November	1st to 10th	Day	24% 14% 23% 30% 9%	330
	11th to 20th	Day	23% 14% 21% 26% 14% 2	308
	21st to end	Day	18% 15% 24% 32% 11%	220
December	1st to 10th	Day	20% 15% 24% 22% 15% 5%	220
	11th to 20th	Day	28% 19% 28% 21% 4 1	220
	21st to end	Day	21% 17% 27% 27% 6% 2	242
January	1st to 10th	Night	22% 10% 25% 29% 11% 2	840
	11th to 20th	Night	20% 9% 23% 32% 14% 2	840
	21st to end	Night	15% 8% 23% 36% 15% 2	924
February	1st to 10th	Night	22% 11% 23% 33% 10% 2	840
	11th to 20th	Night	17% 13% 21% 33% 15% 1	824
	21st to end	Night	20% 16% 22% 29% 11% 2	692
March	1st to 10th	Night	18% 10% 23% 33% 14% 1	840
	11th to 20th	Night	17% 12% 22% 30% 17% 2	840
	21st to end	Night	18% 12% 25% 32% 12%	924
April	1st to 10th	Night	17% 10% 22% 33% 17% 2	840
	11th to 20th	Night	16% 12% 22% 31% 16% 3	821
	21st to end	Night	12% 10% 22% 35% 19% 1	630
May	1st to 10th	Night	11% 8% 22% 37% 21% 2	530
	11th to 20th	Night	14% 8% 14% 28% 30% 5%	414
	21st to end	Night	14% 7% 14% 32% 31% 3	455
June	1st to 10th	Night	15% 7% 14% 33% 27% 4	420
	11th to 20th	Night	11% 8% 22% 37% 20% 2	420
	21st to end	Night	7% 4 16% 41% 30% 2	420
July	1st to 10th	Night	4 3 13% 41% 36% 2	410
	11th to 20th	Night	2 3 14% 51% 29% 2	398
	21st to end	Night	2 4 8% 45% 38% 3	438
August	1st to 10th	Night	3 3 9% 42% 39% 4	398
	11th to 20th	Night	3 2 12% 39% 39% 6%	575
	21st to end	Night	5% 4 16% 38% 33% 4	880
September	1st to 10th	Night	5% 3 12% 42% 34% 5%	800
	11th to 20th	Night	6% 4 12% 33% 38% 7%	800
	21st to end	Night	11% 5% 14% 38% 29% 4	800
October	1st to 10th	Night	11% 5% 15% 41% 24% 4	800
	11th to 20th	Night	16% 7% 16% 35% 22% 5%	800
	21st to end	Night	16% 8% 18% 38% 16% 4	880
November	1st to 10th	Night	21% 9% 23% 35% 10%	820
	11th to 20th	Night	24% 10% 23% 31% 12% 2	840
	21st to end	Night	16% 10% 22% 33% 16% 3	840
December	1st to 10th	Night	17% 8% 24% 35% 15% 2	840
	11th to 20th	Night	22% 11% 26% 31% 10% 1	840
	21st to end	Night	22% 14% 26% 30% 7% 1	924

Page generated at 2026-07-13 00:14:47. Version ac07

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