Just a Camp Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Just a Camp Observatory 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% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	108404
	Night	17% 14% 5% 10% 5% 5% 4 3 4 5% 27%	109843
Transparency	Day	54% 7% 11% 19% 9% 1	111921
	Night	60% 6% 10% 16% 8% 1	114490
Seeing	Day	25% 17% 28% 19% 8% 2	14880
	Night	26% 14% 26% 24% 9% 1	23993

By Month

Percentage Cloud Cover NE (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	14% 19% 9% 18% 6% 5% 4 2 3 4 16%	3597
	11th to 20th	Day	11% 17% 9% 18% 6% 4 5% 3 4 5% 18%	3570
	21st to end	Day	13% 17% 7% 11% 6% 7% 5% 4 5% 5% 20%	3960
February	1st to 10th	Day	15% 15% 4 11% 8% 7% 5% 4 4 5% 21%	1719
	11th to 20th	Day	12% 17% 6% 13% 7% 5% 5% 4 4 6% 23%	1799
	21st to end	Day	16% 15% 5% 11% 7% 5% 4 3 5% 5% 25%	1570
March	1st to 10th	Day	22% 13% 4 10% 5% 4 4 3 5% 5% 24%	3116
	11th to 20th	Day	13% 21% 5% 10% 6% 5% 5% 3 4 5% 23%	3271
	21st to end	Day	16% 11% 4 10% 4 4 3 3 4 5% 36%	4166
April	1st to 10th	Day	20% 13% 3 7% 5% 5% 4 3 5% 6% 29%	2280
	11th to 20th	Day	18% 8% 3 7% 6% 5% 4 3 3 5% 36%	2254
	21st to end	Day	22% 10% 4 6% 4 4 4 3 4 5% 33%	2433
May	1st to 10th	Day	22% 9% 3 8% 5% 5% 4 3 5% 7% 29%	4264
	11th to 20th	Day	17% 8% 3 8% 6% 5% 5% 4 6% 7% 32%	4398
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 5% 7% 9% 37%	4837
June	1st to 10th	Day	22% 7% 2 6% 5% 5% 5% 4 7% 7% 30%	2660
	11th to 20th	Day	15% 6% 2 7% 4 4 4 4 6% 9% 37%	2660
	21st to end	Day	19% 7% 3 8% 5% 5% 4 4 6% 8% 30%	2660
July	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 5% 8% 10% 37%	4440
	11th to 20th	Day	11% 6% 3 7% 4 5% 6% 5% 8% 10% 35%	4440
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 6% 8% 40%	4814
August	1st to 10th	Day	15% 8% 3 7% 5% 5% 6% 4 7% 8% 32%	4423
	11th to 20th	Day	13% 7% 3 8% 5% 5% 5% 4 6% 7% 36%	3925
	21st to end	Day	13% 5% 2 6% 4 4 4 4 6% 9% 41%	4180
September	1st to 10th	Day	13% 7% 2 5% 4 5% 3 4 6% 7% 45%	2280
	11th to 20th	Day	14% 6% 1 5% 4 4 4 3 4 6% 49%	2180
	21st to end	Day	14% 5% 3 6% 5% 5% 5% 3 6% 9% 40%	2090
October	1st to 10th	Day	20% 8% 3 8% 5% 5% 5% 3 5% 6% 32%	1995
	11th to 20th	Day	19% 9% 3 6% 6% 4 5% 4 6% 6% 32%	1853
	21st to end	Day	23% 13% 4 8% 4 5% 4 3 4 4 27%	1881
November	1st to 10th	Day	19% 13% 3 9% 5% 4 3 4 5% 6% 30%	1761
	11th to 20th	Day	18% 15% 3 9% 6% 5% 4 4 4 5% 27%	1782
	21st to end	Day	19% 16% 5% 9% 6% 4 5% 4 5% 4 22%	1600
December	1st to 10th	Day	17% 19% 7% 15% 7% 6% 5% 3 5% 4 11%	2600
	11th to 20th	Day	18% 14% 4 11% 6% 5% 5% 4 5% 5% 23%	2986
	21st to end	Day	20% 15% 5% 11% 7% 4 5% 5% 5% 5% 16%	3960
January	1st to 10th	Night	14% 23% 11% 16% 6% 4 3 2 3 3 15%	6349
	11th to 20th	Night	11% 20% 9% 18% 7% 5% 4 3 4 4 14%	6315
	21st to end	Night	14% 18% 5% 14% 8% 6% 5% 3 4 4 18%	6996
February	1st to 10th	Night	15% 16% 6% 14% 7% 6% 5% 3 5% 4 20%	2571
	11th to 20th	Night	13% 15% 6% 14% 7% 6% 4 4 5% 4 23%	2267
	21st to end	Night	17% 15% 5% 11% 6% 4 3 3 4 5% 27%	1884
March	1st to 10th	Night	22% 14% 4 8% 6% 4 3 3 4 5% 27%	3724
	11th to 20th	Night	18% 20% 4 9% 5% 4 4 2 3 4 26%	3686
	21st to end	Night	16% 16% 5% 10% 4 4 3 3 3 3 33%	3466
April	1st to 10th	Night	20% 12% 5% 8% 5% 4 4 4 4 5% 28%	1900
	11th to 20th	Night	23% 12% 3 8% 5% 4 4 3 4 5% 30%	1875
	21st to end	Night	21% 13% 3 7% 4 4 4 3 4 5% 33%	1745
May	1st to 10th	Night	23% 11% 4 8% 5% 4 5% 4 4 6% 26%	2692
	11th to 20th	Night	20% 11% 3 10% 4 4 3 3 4 6% 34%	2495
	21st to end	Night	16% 5% 3 7% 4 5% 5% 3 7% 8% 37%	2738
June	1st to 10th	Night	24% 7% 2 7% 4 4 4 4 6% 8% 31%	1520
	11th to 20th	Night	15% 7% 3 7% 4 4 4 3 6% 10% 36%	1520
	21st to end	Night	19% 8% 2 7% 4 4 6% 4 6% 7% 34%	1520
July	1st to 10th	Night	13% 7% 3 8% 5% 6% 5% 4 6% 9% 35%	2520
	11th to 20th	Night	13% 6% 2 6% 5% 6% 5% 4 5% 8% 40%	2520
	21st to end	Night	13% 8% 2 8% 5% 4 6% 4 6% 5% 38%	2739
August	1st to 10th	Night	18% 8% 3 7% 5% 5% 3 3 6% 7% 35%	2506
	11th to 20th	Night	13% 8% 4 9% 6% 5% 5% 4 4 6% 36%	2868
	21st to end	Night	15% 6% 2 5% 4 4 5% 4 5% 8% 42%	3476
September	1st to 10th	Night	13% 6% 3 6% 5% 4 5% 4 6% 6% 43%	1900
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 49%	2000
	21st to end	Night	17% 6% 2 5% 4 3 5% 4 5% 6% 43%	2090
October	1st to 10th	Night	21% 8% 2 7% 5% 5% 4 3 5% 7% 33%	2183
	11th to 20th	Night	22% 9% 3 7% 4 4 4 4 5% 6% 32%	2325
	21st to end	Night	24% 12% 3 8% 5% 4 5% 4 4 4 27%	2717
November	1st to 10th	Night	21% 9% 4 9% 4 4 5% 3 4 6% 32%	2537
	11th to 20th	Night	19% 13% 4 9% 6% 4 4 4 3 6% 30%	2615
	21st to end	Night	21% 17% 5% 11% 5% 4 4 3 4 5% 21%	2800
December	1st to 10th	Night	18% 28% 8% 13% 5% 5% 3 3 3 3 11%	4580
	11th to 20th	Night	23% 18% 5% 11% 5% 5% 4 3 3 4 20%	5208
	21st to end	Night	21% 17% 7% 11% 6% 5% 5% 4 4 6% 16%	6996

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	73% 6% 8% 11% 2	3598
	11th to 20th	Day	69% 5% 8% 11% 5% 1	3600
	21st to end	Day	67% 7% 8% 10% 7% 1	3960
February	1st to 10th	Day	65% 7% 7% 14% 5% 2	1719
	11th to 20th	Day	65% 7% 9% 14% 5%	1808
	21st to end	Day	63% 6% 9% 12% 8% 2	1570
March	1st to 10th	Day	63% 10% 8% 11% 6% 1	3119
	11th to 20th	Day	63% 7% 11% 10% 9% 1	3271
	21st to end	Day	53% 6% 8% 15% 16% 2	4166
April	1st to 10th	Day	57% 6% 7% 19% 9% 2	2280
	11th to 20th	Day	53% 6% 7% 19% 14% 1	2254
	21st to end	Day	56% 5% 8% 17% 11% 2	2433
May	1st to 10th	Day	55% 9% 9% 18% 8% 1	4278
	11th to 20th	Day	48% 11% 12% 18% 9% 1	4402
	21st to end	Day	41% 11% 13% 25% 10% 1	4837
June	1st to 10th	Day	52% 9% 10% 17% 10% 1	2660
	11th to 20th	Day	44% 9% 11% 22% 12% 2	2660
	21st to end	Day	52% 8% 10% 19% 9% 1	2660
July	1st to 10th	Day	42% 6% 14% 27% 11%	4370
	11th to 20th	Day	43% 6% 13% 31% 6%	4365
	21st to end	Day	43% 7% 11% 30% 9%	4661
August	1st to 10th	Day	49% 6% 14% 22% 8%	4409
	11th to 20th	Day	48% 7% 16% 24% 6%	3965
	21st to end	Day	40% 6% 17% 23% 14% 1	4180
September	1st to 10th	Day	38% 9% 10% 29% 13% 1	2280
	11th to 20th	Day	38% 6% 10% 32% 14% 1	2180
	21st to end	Day	43% 9% 14% 23% 10% 2	2090
October	1st to 10th	Day	48% 4 11% 29% 9%	3320
	11th to 20th	Day	50% 5% 14% 21% 10%	3056
	21st to end	Day	50% 5% 14% 25% 6% 1	3081
November	1st to 10th	Day	56% 8% 11% 17% 7%	1761
	11th to 20th	Day	60% 7% 10% 13% 8% 1	1782
	21st to end	Day	65% 7% 12% 12% 4	1600
December	1st to 10th	Day	79% 5% 7% 7% 2	2600
	11th to 20th	Day	68% 5% 7% 15% 5%	2986
	21st to end	Day	69% 6% 7% 11% 6%	3960
January	1st to 10th	Night	77% 5% 9% 7% 2	6349
	11th to 20th	Night	74% 6% 9% 7% 3 1	6360
	21st to end	Night	72% 5% 7% 7% 8% 1	6996
February	1st to 10th	Night	69% 6% 8% 11% 5% 1	2571
	11th to 20th	Night	65% 6% 9% 13% 7%	2269
	21st to end	Night	62% 5% 9% 14% 8% 1	1884
March	1st to 10th	Night	61% 6% 10% 14% 9% 1	3734
	11th to 20th	Night	61% 6% 9% 14% 9% 1	3687
	21st to end	Night	57% 5% 7% 14% 15% 2	3466
April	1st to 10th	Night	60% 5% 7% 16% 11% 1	1900
	11th to 20th	Night	58% 5% 9% 17% 12% 1	1875
	21st to end	Night	55% 5% 8% 15% 13% 3	1745
May	1st to 10th	Night	57% 8% 8% 16% 9% 2	2698
	11th to 20th	Night	52% 8% 10% 19% 9% 1	2496
	21st to end	Night	41% 10% 14% 20% 14% 1	2739
June	1st to 10th	Night	53% 9% 9% 19% 9% 1	1520
	11th to 20th	Night	46% 7% 13% 22% 11% 2	1520
	21st to end	Night	50% 9% 12% 20% 9% 1	1520
July	1st to 10th	Night	46% 6% 14% 22% 12%	2480
	11th to 20th	Night	44% 6% 13% 27% 9%	2472
	21st to end	Night	47% 7% 12% 23% 11%	2651
August	1st to 10th	Night	50% 6% 13% 23% 8%	2496
	11th to 20th	Night	49% 6% 15% 21% 9% 1	2894
	21st to end	Night	41% 5% 15% 24% 14% 1	3476
September	1st to 10th	Night	40% 9% 12% 27% 12% 1	1900
	11th to 20th	Night	37% 6% 13% 30% 13% 1	2000
	21st to end	Night	41% 8% 12% 24% 13% 2	2090
October	1st to 10th	Night	57% 4 8% 23% 9%	3638
	11th to 20th	Night	52% 4 10% 22% 11%	3861
	21st to end	Night	54% 4 12% 22% 8% 1	4467
November	1st to 10th	Night	55% 6% 12% 18% 8% 1	2537
	11th to 20th	Night	58% 6% 10% 15% 8% 2	2615
	21st to end	Night	66% 7% 11% 13% 3	2800
December	1st to 10th	Night	83% 4 6% 6% 1	4580
	11th to 20th	Night	71% 6% 7% 10% 7%	5208
	21st to end	Night	72% 5% 6% 11% 6%	6996

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% 25% 27% 18% 4	200
	11th to 20th	Day	32% 26% 31% 7% 4 1	200
	21st to end	Day	25% 24% 35% 11% 4	220
February	1st to 10th	Day	33% 32% 25% 8% 2	268
	11th to 20th	Day	27% 29% 34% 8% 2	407
	21st to end	Day	31% 21% 34% 12% 2	382
March	1st to 10th	Day	32% 19% 28% 18% 3	460
	11th to 20th	Day	26% 27% 28% 15% 4 1	460
	21st to end	Day	32% 22% 26% 12% 6% 2	506
April	1st to 10th	Day	35% 18% 25% 15% 6% 1	460
	11th to 20th	Day	31% 25% 20% 15% 7% 2	452
	21st to end	Day	31% 20% 28% 13% 6% 2	460
May	1st to 10th	Day	30% 19% 26% 17% 8% 2	463
	11th to 20th	Day	21% 15% 32% 23% 8% 2	487
	21st to end	Day	19% 18% 33% 21% 8% 1	529
June	1st to 10th	Day	28% 13% 31% 20% 7% 1	490
	11th to 20th	Day	19% 15% 32% 22% 10% 2	490
	21st to end	Day	23% 16% 31% 20% 8% 1	490
July	1st to 10th	Day	17% 10% 29% 30% 12% 3	485
	11th to 20th	Day	14% 9% 34% 28% 12% 2	484
	21st to end	Day	19% 7% 34% 30% 10% 1	532
August	1st to 10th	Day	16% 9% 29% 26% 17% 2	486
	11th to 20th	Day	18% 10% 23% 30% 14% 5%	479
	21st to end	Day	15% 14% 28% 26% 11% 6%	539
September	1st to 10th	Day	17% 14% 29% 22% 12% 5%	490
	11th to 20th	Day	17% 14% 19% 22% 19% 8%	490
	21st to end	Day	15% 14% 30% 22% 14% 5%	490
October	1st to 10th	Day	27% 13% 26% 16% 15% 3	490
	11th to 20th	Day	29% 17% 26% 20% 8% 1	465
	21st to end	Day	38% 16% 25% 17% 4	429
November	1st to 10th	Day	32% 18% 27% 17% 5% 1	395
	11th to 20th	Day	31% 27% 21% 14% 7% 1	382
	21st to end	Day	38% 20% 28% 14% 1	200
December	1st to 10th	Day	28% 25% 29% 17% 3	200
	11th to 20th	Day	32% 27% 30% 10% 2	200
	21st to end	Day	28% 27% 29% 12% 3	220
January	1st to 10th	Night	29% 21% 32% 17% 3	800
	11th to 20th	Night	30% 18% 30% 18% 4	800
	21st to end	Night	23% 18% 31% 24% 4	880
February	1st to 10th	Night	25% 17% 34% 22% 2	781
	11th to 20th	Night	26% 20% 33% 19% 3	743
	21st to end	Night	27% 19% 29% 20% 5%	628
March	1st to 10th	Night	30% 16% 27% 25% 3 1	760
	11th to 20th	Night	28% 21% 25% 20% 5% 1	760
	21st to end	Night	31% 17% 25% 20% 7% 1	836
April	1st to 10th	Night	29% 16% 26% 25% 4	760
	11th to 20th	Night	31% 18% 21% 22% 8%	751
	21st to end	Night	28% 18% 26% 21% 7%	605
May	1st to 10th	Night	30% 12% 25% 24% 8% 1	493
	11th to 20th	Night	24% 9% 32% 26% 8% 1	374
	21st to end	Night	17% 10% 27% 34% 11% 1	411
June	1st to 10th	Night	27% 8% 25% 31% 9% 1	380
	11th to 20th	Night	19% 7% 27% 34% 13% 1	380
	21st to end	Night	22% 5% 26% 36% 10% 1	380
July	1st to 10th	Night	16% 3 23% 42% 16% 1	370
	11th to 20th	Night	11% 4 23% 41% 18% 2	368
	21st to end	Night	17% 5% 20% 42% 15%	416
August	1st to 10th	Night	16% 4 17% 40% 22% 1	378
	11th to 20th	Night	18% 4 20% 32% 22% 3	607
	21st to end	Night	16% 6% 23% 31% 21% 1	836
September	1st to 10th	Night	17% 8% 25% 33% 16% 2	760
	11th to 20th	Night	18% 8% 18% 29% 23% 4	760
	21st to end	Night	20% 9% 27% 25% 18% 2	760
October	1st to 10th	Night	28% 12% 20% 24% 15% 1	760
	11th to 20th	Night	31% 11% 23% 26% 9% 1	760
	21st to end	Night	32% 15% 27% 21% 5%	836
November	1st to 10th	Night	29% 18% 25% 21% 6% 1	780
	11th to 20th	Night	30% 17% 26% 18% 8% 1	800
	21st to end	Night	33% 20% 25% 17% 5% 1	800
December	1st to 10th	Night	34% 20% 28% 14% 4	800
	11th to 20th	Night	29% 22% 28% 17% 4	800
	21st to end	Night	33% 17% 30% 17% 3	880

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

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