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 2025-03-12.

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	7% 10% 3 7% 5% 4 4 4 5% 6% 44%	112677
	Night	8% 10% 3 8% 5% 5% 5% 4 5% 6% 42%	115048
Transparency	Day	39% 8% 12% 19% 14% 8%	112422
	Night	41% 9% 14% 19% 12% 5%	114892
Seeing	Day	15% 14% 26% 26% 14% 5%	14700
	Night	15% 8% 19% 34% 20% 3	24012

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% 23% 8% 14% 9% 8% 6% 4 4 5% 14%	3639
	11th to 20th	Day	6% 14% 7% 12% 5% 5% 4 3 5% 7% 31%	3640
	21st to end	Day	8% 12% 4 10% 5% 5% 4 4 5% 6% 36%	4004
February	1st to 10th	Day	10% 19% 6% 11% 7% 6% 5% 4 7% 5% 21%	1685
	11th to 20th	Day	9% 21% 6% 9% 7% 5% 5% 4 5% 5% 23%	1900
	21st to end	Day	8% 20% 6% 11% 7% 6% 5% 4 5% 6% 23%	1650
March	1st to 10th	Day	6% 15% 5% 9% 7% 6% 6% 5% 8% 8% 26%	3238
	11th to 20th	Day	6% 11% 4 7% 5% 5% 4 4 5% 7% 42%	3250
	21st to end	Day	10% 19% 5% 11% 7% 7% 7% 5% 6% 6% 16%	4165
April	1st to 10th	Day	10% 16% 5% 9% 7% 6% 4 4 6% 7% 24%	2280
	11th to 20th	Day	9% 13% 4 9% 6% 5% 5% 4 6% 6% 33%	2258
	21st to end	Day	11% 13% 3 9% 6% 5% 5% 4 5% 6% 32%	2470
May	1st to 10th	Day	10% 13% 2 8% 5% 4 4 3 5% 6% 39%	4257
	11th to 20th	Day	7% 7% 2 5% 4 4 4 3 5% 6% 54%	4377
	21st to end	Day	10% 11% 2 7% 5% 5% 5% 4 7% 9% 34%	4813
June	1st to 10th	Day	14% 9% 2 7% 5% 5% 5% 4 5% 7% 37%	2660
	11th to 20th	Day	12% 8% 2 6% 4 4 4 4 6% 6% 43%	2660
	21st to end	Day	5% 4 1 4 3 3 3 3 4 6% 63%	2660
July	1st to 10th	Day	2 1 2 2 2 2 2 3 4 80%	4420
	11th to 20th	Day	1 2 1 2 2 2 2 2 4 4 78%	4420
	21st to end	Day	1 1 1 2 2 2 3 2 4 5% 76%	4790
August	1st to 10th	Day	3 3 1 3 3 3 3 3 4 7% 67%	4400
	11th to 20th	Day	2 2 1 4 2 3 3 2 4 5% 71%	4039
	21st to end	Day	3 2 1 4 3 3 4 3 4 6% 67%	4180
September	1st to 10th	Day	3 2 1 4 2 2 2 2 4 6% 70%	2280
	11th to 20th	Day	7% 5% 2 5% 3 4 5% 3 5% 7% 54%	2182
	21st to end	Day	8% 5% 2 6% 3 4 4 4 4 6% 55%	2090
October	1st to 10th	Day	8% 5% 2 4 3 2 3 2 4 6% 62%	3349
	11th to 20th	Day	7% 8% 3 6% 4 4 4 4 7% 9% 45%	3044
	21st to end	Day	11% 13% 4 9% 7% 5% 6% 4 5% 6% 30%	3101
November	1st to 10th	Day	14% 14% 4 11% 5% 5% 6% 5% 5% 7% 27%	1764
	11th to 20th	Day	11% 17% 5% 11% 7% 6% 6% 5% 6% 8% 18%	1760
	21st to end	Day	8% 17% 4 9% 6% 5% 5% 5% 8% 7% 26%	1600
December	1st to 10th	Day	5% 11% 4 8% 4 6% 5% 4 5% 7% 39%	2620
	11th to 20th	Day	10% 15% 6% 14% 7% 6% 6% 5% 6% 7% 18%	3028
	21st to end	Day	9% 16% 8% 14% 6% 6% 5% 4 5% 6% 22%	4004
January	1st to 10th	Night	11% 21% 7% 12% 7% 6% 6% 4 5% 6% 15%	6306
	11th to 20th	Night	8% 15% 6% 11% 5% 5% 4 3 4 6% 33%	6320
	21st to end	Night	7% 11% 4 10% 6% 5% 5% 5% 9% 7% 31%	6952
February	1st to 10th	Night	10% 19% 5% 11% 6% 5% 4 4 5% 6% 23%	2713
	11th to 20th	Night	8% 16% 4 11% 6% 5% 4 4 6% 6% 30%	2388
	21st to end	Night	7% 17% 6% 9% 7% 6% 6% 4 6% 7% 25%	1980
March	1st to 10th	Night	6% 12% 4 8% 7% 6% 6% 4 6% 8% 33%	3856
	11th to 20th	Night	6% 9% 4 6% 4 4 4 3 5% 6% 47%	3741
	21st to end	Night	8% 16% 4 11% 7% 6% 6% 5% 7% 7% 23%	3488
April	1st to 10th	Night	10% 12% 2 8% 6% 5% 6% 4 6% 8% 33%	1900
	11th to 20th	Night	11% 11% 2 7% 6% 4 4 4 5% 5% 41%	1870
	21st to end	Night	7% 8% 2 7% 5% 4 5% 5% 5% 7% 43%	1710
May	1st to 10th	Night	11% 9% 2 4 4 4 4 4 5% 7% 47%	2705
	11th to 20th	Night	7% 6% 2 4 3 2 3 3 5% 7% 58%	2516
	21st to end	Night	12% 9% 2 5% 4 4 4 3 5% 7% 44%	2762
June	1st to 10th	Night	12% 7% 1 6% 5% 3 4 4 7% 8% 42%	1520
	11th to 20th	Night	10% 6% 1 5% 4 4 5% 4 5% 7% 49%	1520
	21st to end	Night	4 5% 2 5% 3 3 4 4 5% 6% 61%	1520
July	1st to 10th	Night	2 1 1 1 2 2 2 2 3 3 83%	2540
	11th to 20th	Night	1 1 2 1 2 2 2 3 5% 83%	2540
	21st to end	Night	2 2 2 2 2 2 2 4 5% 77%	2761
August	1st to 10th	Night	3 2 1 2 2 2 3 3 6% 7% 70%	2529
	11th to 20th	Night	1 2 1 4 3 3 3 2 4 5% 71%	2794
	21st to end	Night	2 2 1 3 2 2 3 2 4 5% 74%	3498
September	1st to 10th	Night	4 2 1 3 2 2 3 2 4 5% 73%	1900
	11th to 20th	Night	5% 4 1 5% 3 5% 4 3 5% 6% 58%	1997
	21st to end	Night	7% 4 2 5% 4 3 3 3 4 7% 58%	2090
October	1st to 10th	Night	5% 5% 2 5% 3 3 3 2 3 5% 64%	3627
	11th to 20th	Night	8% 6% 2 5% 4 4 5% 4 6% 8% 48%	3890
	21st to end	Night	9% 10% 5% 7% 5% 5% 5% 4 6% 7% 38%	4457
November	1st to 10th	Night	14% 12% 4 8% 6% 6% 5% 4 5% 5% 31%	2535
	11th to 20th	Night	12% 14% 4 8% 6% 6% 6% 5% 6% 6% 26%	2635
	21st to end	Night	8% 14% 4 8% 6% 6% 5% 5% 6% 7% 32%	2800
December	1st to 10th	Night	6% 9% 4 8% 4 7% 5% 4 5% 10% 38%	4560
	11th to 20th	Night	10% 15% 5% 11% 8% 8% 7% 5% 7% 7% 16%	5176
	21st to end	Night	10% 16% 6% 14% 7% 6% 5% 4 5% 6% 21%	6952

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	66% 14% 8% 10% 1	3639
	11th to 20th	Day	52% 7% 14% 20% 5% 1	3640
	21st to end	Day	48% 8% 10% 19% 14%	4004
February	1st to 10th	Day	63% 10% 12% 11% 4	1685
	11th to 20th	Day	62% 10% 11% 11% 7%	1910
	21st to end	Day	60% 11% 11% 11% 5% 1	1650
March	1st to 10th	Day	50% 11% 15% 18% 6%	3238
	11th to 20th	Day	41% 9% 14% 31% 6%	3250
	21st to end	Day	64% 13% 12% 9% 2	4165
April	1st to 10th	Day	58% 9% 15% 14% 3	2280
	11th to 20th	Day	50% 9% 15% 16% 10% 1	2261
	21st to end	Day	51% 10% 11% 19% 9%	2470
May	1st to 10th	Day	44% 8% 13% 24% 10% 1	4257
	11th to 20th	Day	30% 7% 15% 30% 15% 3	4380
	21st to end	Day	44% 10% 22% 19% 5%	4814
June	1st to 10th	Day	46% 9% 14% 23% 8% 1	2660
	11th to 20th	Day	39% 8% 15% 22% 14% 2	2660
	21st to end	Day	22% 6% 12% 32% 22% 6%	2660
July	1st to 10th	Day	10% 4 6% 14% 24% 42%	4351
	11th to 20th	Day	10% 3 6% 9% 23% 49%	4345
	21st to end	Day	10% 3 5% 18% 34% 30%	4639
August	1st to 10th	Day	17% 4 6% 14% 37% 22%	4384
	11th to 20th	Day	15% 4 7% 30% 33% 11%	4079
	21st to end	Day	17% 4 12% 26% 28% 13%	4179
September	1st to 10th	Day	16% 4 10% 25% 28% 16%	2280
	11th to 20th	Day	28% 7% 12% 21% 21% 11%	2182
	21st to end	Day	29% 8% 13% 26% 19% 5%	2090
October	1st to 10th	Day	26% 5% 10% 27% 26% 6%	3349
	11th to 20th	Day	33% 8% 19% 25% 14% 1	3044
	21st to end	Day	52% 8% 10% 22% 8%	3101
November	1st to 10th	Day	57% 9% 13% 16% 6%	1764
	11th to 20th	Day	62% 10% 14% 10% 2	1760
	21st to end	Day	53% 12% 14% 13% 7% 1	1600
December	1st to 10th	Day	42% 10% 19% 25% 3	2620
	11th to 20th	Day	61% 13% 16% 8% 1	3028
	21st to end	Day	58% 12% 18% 10% 2	4004
January	1st to 10th	Night	65% 13% 10% 10% 1	6306
	11th to 20th	Night	51% 8% 18% 16% 7%	6320
	21st to end	Night	45% 11% 14% 19% 10%	6952
February	1st to 10th	Night	62% 10% 14% 11% 3	2713
	11th to 20th	Night	55% 9% 15% 14% 6% 1	2389
	21st to end	Night	59% 8% 11% 15% 5% 1	1980
March	1st to 10th	Night	44% 11% 16% 21% 8%	3856
	11th to 20th	Night	39% 8% 13% 34% 5%	3741
	21st to end	Night	57% 14% 15% 11% 3	3488
April	1st to 10th	Night	51% 10% 17% 18% 4	1900
	11th to 20th	Night	45% 9% 16% 18% 12% 1	1870
	21st to end	Night	41% 10% 17% 19% 12% 1	1710
May	1st to 10th	Night	37% 8% 18% 24% 12% 1	2705
	11th to 20th	Night	25% 7% 14% 36% 16% 1	2516
	21st to end	Night	39% 12% 20% 23% 6%	2762
June	1st to 10th	Night	38% 12% 12% 27% 10% 1	1520
	11th to 20th	Night	34% 9% 16% 27% 12% 3	1520
	21st to end	Night	23% 7% 13% 30% 21% 6%	1520
July	1st to 10th	Night	8% 3 6% 15% 29% 39%	2500
	11th to 20th	Night	7% 3 6% 14% 20% 50%	2492
	21st to end	Night	11% 2 4 20% 31% 32%	2674
August	1st to 10th	Night	13% 4 6% 18% 44% 16%	2521
	11th to 20th	Night	15% 5% 7% 30% 34% 10%	2820
	21st to end	Night	13% 4 10% 32% 29% 12%	3498
September	1st to 10th	Night	16% 3 9% 27% 28% 16%	1900
	11th to 20th	Night	26% 7% 11% 23% 23% 10%	1997
	21st to end	Night	27% 6% 12% 29% 18% 7%	2090
October	1st to 10th	Night	25% 5% 9% 26% 30% 4	3627
	11th to 20th	Night	33% 8% 18% 22% 19% 1	3890
	21st to end	Night	43% 9% 12% 25% 11% 1	4457
November	1st to 10th	Night	52% 10% 13% 18% 6% 1	2535
	11th to 20th	Night	56% 11% 15% 15% 3	2635
	21st to end	Night	51% 9% 14% 18% 8% 1	2800
December	1st to 10th	Night	40% 11% 24% 20% 4 1	4560
	11th to 20th	Night	63% 12% 14% 10% 1	5176
	21st to end	Night	60% 11% 17% 9% 3	6952

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	16% 18% 29% 25% 11% 3	200
	11th to 20th	Day	19% 13% 37% 17% 12% 4	200
	21st to end	Day	17% 10% 32% 25% 13% 1	220
February	1st to 10th	Day	26% 21% 28% 19% 6% 1	285
	11th to 20th	Day	24% 19% 29% 19% 8%	470
	21st to end	Day	21% 21% 28% 22% 7% 1	414
March	1st to 10th	Day	20% 23% 30% 20% 7% 1	500
	11th to 20th	Day	19% 21% 22% 23% 12% 3	465
	21st to end	Day	24% 24% 27% 19% 6% 1	506
April	1st to 10th	Day	24% 21% 25% 18% 9% 4	460
	11th to 20th	Day	20% 23% 28% 16% 10% 4	452
	21st to end	Day	19% 19% 26% 21% 13% 2	460
May	1st to 10th	Day	16% 13% 29% 27% 10% 4	463
	11th to 20th	Day	20% 14% 24% 22% 14% 7%	488
	21st to end	Day	16% 11% 24% 28% 15% 6%	529
June	1st to 10th	Day	16% 13% 23% 23% 18% 7%	490
	11th to 20th	Day	16% 18% 29% 23% 10% 3	490
	21st to end	Day	7% 11% 28% 32% 15% 7%	490
July	1st to 10th	Day	4 9% 28% 34% 22% 3	486
	11th to 20th	Day	4 10% 30% 34% 18% 4	484
	21st to end	Day	2 9% 28% 31% 23% 8%	531
August	1st to 10th	Day	6% 7% 27% 33% 19% 9%	487
	11th to 20th	Day	3 7% 19% 37% 21% 12%	477
	21st to end	Day	8% 11% 26% 29% 17% 9%	539
September	1st to 10th	Day	6% 10% 24% 28% 23% 9%	490
	11th to 20th	Day	11% 11% 27% 28% 19% 6%	490
	21st to end	Day	12% 10% 28% 28% 16% 6%	490
October	1st to 10th	Day	16% 13% 21% 24% 22% 5%	490
	11th to 20th	Day	18% 12% 21% 25% 18% 7%	424
	21st to end	Day	17% 17% 22% 28% 11% 4	330
November	1st to 10th	Day	24% 14% 22% 31% 9%	300
	11th to 20th	Day	24% 13% 21% 26% 15% 2	280
	21st to end	Day	18% 16% 23% 32% 12% 1	200
December	1st to 10th	Day	17% 14% 26% 23% 16% 6%	200
	11th to 20th	Day	26% 20% 29% 22% 4 1	200
	21st to end	Day	19% 18% 28% 27% 5% 3	220
January	1st to 10th	Night	21% 10% 26% 29% 12% 2	800
	11th to 20th	Night	21% 10% 22% 32% 14% 2	800
	21st to end	Night	16% 9% 23% 35% 16% 2	880
February	1st to 10th	Night	23% 11% 24% 32% 9% 2	800
	11th to 20th	Night	17% 13% 21% 32% 15% 2	784
	21st to end	Night	19% 17% 22% 28% 12% 2	660
March	1st to 10th	Night	18% 10% 23% 33% 15% 1	800
	11th to 20th	Night	15% 13% 22% 31% 18% 2	766
	21st to end	Night	19% 11% 24% 32% 13%	836
April	1st to 10th	Night	18% 10% 21% 32% 17% 2	760
	11th to 20th	Night	17% 12% 22% 30% 16% 3	742
	21st to end	Night	12% 11% 23% 33% 20% 2	570
May	1st to 10th	Night	12% 8% 21% 36% 21% 2	480
	11th to 20th	Night	14% 6% 13% 29% 32% 6%	374
	21st to end	Night	14% 7% 14% 30% 33% 3	411
June	1st to 10th	Night	15% 7% 14% 32% 28% 4	380
	11th to 20th	Night	12% 9% 21% 34% 22% 2	380
	21st to end	Night	7% 4 16% 40% 31% 2	380
July	1st to 10th	Night	4 3 13% 40% 37% 2	370
	11th to 20th	Night	1 3 13% 51% 30% 2	368
	21st to end	Night	2 4 8% 45% 37% 3	416
August	1st to 10th	Night	3 3 9% 41% 40% 4	378
	11th to 20th	Night	3 2 12% 38% 39% 6%	545
	21st to end	Night	5% 5% 16% 37% 33% 4	836
September	1st to 10th	Night	5% 3 13% 41% 34% 5%	760
	11th to 20th	Night	6% 4 12% 33% 38% 7%	760
	21st to end	Night	11% 5% 14% 38% 29% 5%	760
October	1st to 10th	Night	11% 5% 14% 41% 25% 4	760
	11th to 20th	Night	16% 6% 15% 35% 23% 5%	760
	21st to end	Night	17% 8% 18% 37% 17% 4	836
November	1st to 10th	Night	21% 9% 23% 35% 11% 1	780
	11th to 20th	Night	24% 9% 24% 30% 12% 2	800
	21st to end	Night	16% 10% 21% 33% 16% 3	800
December	1st to 10th	Night	17% 7% 24% 36% 15% 2	800
	11th to 20th	Night	21% 11% 25% 32% 11% 1	800
	21st to end	Night	22% 14% 26% 30% 7% 1	880

Page generated at 2025-03-09 05:08:48. Version ac07

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