Palmer Junction
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Palmer Junction clear sky chart from 2005-11-05 to 2024-10-14.

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% 45%	101291
	Night	8% 10% 3 7% 5% 5% 4 4 5% 6% 42%	97412
Transparency	Day	39% 8% 12% 18% 14% 9%	101036
	Night	42% 9% 13% 19% 12% 6%	97256
Seeing	Day	15% 14% 26% 26% 14% 5%	14302
	Night	15% 8% 19% 34% 21% 3	23416

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	6% 24% 8% 14% 9% 7% 6% 4 4 5% 12%	2539
	11th to 20th	Day	9% 19% 7% 13% 6% 6% 5% 4 5% 6% 22%	2540
	21st to end	Day	11% 16% 5% 13% 7% 8% 6% 5% 5% 5% 19%	2794
February	1st to 10th	Day	10% 20% 6% 11% 6% 6% 5% 4 7% 5% 22%	1600
	11th to 20th	Day	10% 20% 5% 10% 7% 6% 6% 4 5% 5% 23%	1802
	21st to end	Day	8% 20% 6% 11% 7% 6% 5% 4 5% 6% 22%	1570
March	1st to 10th	Day	6% 15% 5% 9% 6% 5% 6% 5% 8% 8% 26%	3138
	11th to 20th	Day	6% 11% 4 7% 5% 5% 4 4 5% 7% 42%	3239
	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	11% 7% 3 6% 4 3 4 3 4 6% 50%	2009
	11th to 20th	Day	10% 8% 2 6% 4 4 4 4 7% 8% 42%	1769
	21st to end	Day	11% 13% 3 9% 7% 5% 5% 3 4 5% 35%	1782
November	1st to 10th	Day	14% 14% 3 11% 5% 5% 6% 4 5% 7% 27%	1674
	11th to 20th	Day	10% 17% 5% 11% 7% 6% 6% 5% 6% 8% 19%	1672
	21st to end	Day	8% 17% 3 9% 6% 5% 5% 6% 8% 7% 27%	1520
December	1st to 10th	Day	9% 16% 5% 10% 5% 7% 6% 5% 6% 7% 23%	1520
	11th to 20th	Day	8% 13% 5% 12% 7% 6% 6% 5% 7% 7% 23%	1928
	21st to end	Day	7% 14% 6% 12% 6% 6% 5% 5% 6% 7% 26%	2794
January	1st to 10th	Night	9% 21% 8% 14% 7% 6% 5% 4 5% 6% 16%	4406
	11th to 20th	Night	11% 20% 7% 10% 6% 5% 5% 3 4 6% 24%	4420
	21st to end	Night	10% 15% 5% 13% 8% 6% 5% 5% 6% 7% 20%	4862
February	1st to 10th	Night	10% 19% 5% 10% 6% 6% 4 4 5% 6% 24%	2578
	11th to 20th	Night	8% 16% 4 10% 6% 5% 4 4 6% 6% 31%	2266
	21st to end	Night	7% 17% 6% 9% 7% 6% 6% 4 6% 7% 24%	1884
March	1st to 10th	Night	6% 12% 4 8% 7% 6% 6% 4 6% 7% 33%	3736
	11th to 20th	Night	6% 9% 4 6% 4 4 4 3 5% 6% 48%	3724
	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	8% 5% 2 7% 4 5% 4 3 4 6% 51%	2167
	11th to 20th	Night	10% 7% 2 6% 6% 4 5% 4 4 6% 44%	2269
	21st to end	Night	11% 9% 3 6% 6% 6% 5% 4 6% 5% 40%	2574
November	1st to 10th	Night	14% 11% 3 8% 6% 6% 5% 3 5% 5% 31%	2405
	11th to 20th	Night	12% 15% 4 8% 6% 6% 6% 5% 6% 6% 27%	2503
	21st to end	Night	7% 14% 4 8% 6% 6% 5% 4 6% 6% 33%	2660
December	1st to 10th	Night	9% 13% 5% 10% 6% 7% 6% 5% 6% 6% 27%	2660
	11th to 20th	Night	8% 14% 5% 12% 8% 7% 6% 4 7% 7% 20%	3276
	21st to end	Night	8% 14% 5% 11% 7% 6% 6% 5% 5% 6% 26%	4862

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	72% 12% 8% 7% 1	2539
	11th to 20th	Day	64% 8% 12% 13% 3 1	2540
	21st to end	Day	66% 11% 13% 8% 2	2794
February	1st to 10th	Day	63% 10% 12% 11% 3	1600
	11th to 20th	Day	61% 10% 11% 11% 6%	1812
	21st to end	Day	61% 11% 11% 12% 4 1	1570
March	1st to 10th	Day	50% 11% 15% 18% 6%	3138
	11th to 20th	Day	40% 9% 14% 31% 6%	3239
	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	38% 7% 11% 24% 18% 4	2009
	11th to 20th	Day	38% 8% 14% 24% 14% 1	1769
	21st to end	Day	51% 8% 11% 20% 10%	1782
November	1st to 10th	Day	57% 9% 12% 16% 6%	1674
	11th to 20th	Day	62% 10% 14% 11% 3	1672
	21st to end	Day	54% 12% 14% 13% 7% 1	1520
December	1st to 10th	Day	57% 12% 13% 13% 4 1	1520
	11th to 20th	Day	58% 14% 17% 10% 2	1928
	21st to end	Day	54% 12% 21% 11% 3	2794
January	1st to 10th	Night	66% 14% 10% 8% 1	4406
	11th to 20th	Night	63% 7% 14% 13% 3	4420
	21st to end	Night	60% 13% 15% 9% 2	4862
February	1st to 10th	Night	61% 10% 15% 11% 3	2578
	11th to 20th	Night	54% 9% 15% 15% 6%	2267
	21st to end	Night	60% 9% 12% 14% 5% 1	1884
March	1st to 10th	Night	44% 11% 16% 21% 7%	3736
	11th to 20th	Night	39% 8% 13% 35% 5%	3724
	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	35% 7% 12% 25% 19% 3	2167
	11th to 20th	Night	40% 9% 11% 21% 18% 2	2269
	21st to end	Night	45% 9% 13% 18% 13% 1	2574
November	1st to 10th	Night	53% 10% 12% 18% 6% 1	2405
	11th to 20th	Night	56% 10% 15% 15% 3	2503
	21st to end	Night	51% 8% 14% 18% 8% 1	2660
December	1st to 10th	Night	56% 12% 15% 13% 3 1	2660
	11th to 20th	Night	61% 12% 14% 12% 1	3276
	21st to end	Night	55% 10% 20% 10% 4	4862

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	14% 18% 28% 24% 12% 3	180
	11th to 20th	Day	21% 11% 37% 14% 12% 4	180
	21st to end	Day	18% 11% 33% 25% 13% 1	198
February	1st to 10th	Day	26% 21% 27% 18% 7% 1	260
	11th to 20th	Day	25% 17% 30% 19% 9%	432
	21st to end	Day	20% 22% 27% 23% 7% 1	382
March	1st to 10th	Day	21% 23% 29% 19% 7% 1	460
	11th to 20th	Day	19% 21% 22% 23% 12% 3	460
	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% 11% 20% 25% 17% 7%	401
	21st to end	Day	16% 18% 23% 26% 11% 5%	297
November	1st to 10th	Day	22% 14% 24% 32% 8%	270
	11th to 20th	Day	21% 13% 20% 28% 16% 2	252
	21st to end	Day	18% 14% 22% 34% 12% 1	180
December	1st to 10th	Day	17% 14% 28% 23% 13% 4	180
	11th to 20th	Day	24% 19% 29% 22% 4 1	180
	21st to end	Day	16% 18% 28% 29% 6% 3	198
January	1st to 10th	Night	21% 9% 26% 29% 13% 2	760
	11th to 20th	Night	22% 10% 22% 31% 14% 2	760
	21st to end	Night	17% 9% 22% 36% 15% 2	836
February	1st to 10th	Night	23% 10% 24% 32% 9% 2	760
	11th to 20th	Night	18% 13% 20% 32% 16% 1	744
	21st to end	Night	19% 17% 22% 28% 12% 2	628
March	1st to 10th	Night	19% 10% 23% 33% 15% 1	760
	11th to 20th	Night	15% 13% 21% 31% 18% 2	760
	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% 7% 15% 34% 24% 6%	734
	21st to end	Night	17% 8% 17% 36% 17% 4	792
November	1st to 10th	Night	21% 9% 23% 35% 11% 1	740
	11th to 20th	Night	24% 9% 23% 30% 13% 2	760
	21st to end	Night	16% 10% 21% 33% 16% 3	760
December	1st to 10th	Night	17% 7% 25% 35% 15% 1	760
	11th to 20th	Night	20% 11% 25% 32% 11% 1	760
	21st to end	Night	22% 13% 26% 31% 8% 1	836

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