Blue Mountain Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Mountain Star Party clear sky chart from 2005-11-06 to 2024-12-02.

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	8% 11% 3 7% 4 4 4 3 5% 6% 46%	105501
	Night	9% 12% 4 7% 4 4 4 3 5% 6% 43%	102815
Transparency	Day	42% 2 8% 21% 17% 10%	105247
	Night	44% 2 10% 22% 16% 6%	102658
Seeing	Day	16% 16% 27% 24% 13% 4	14536
	Night	16% 10% 16% 34% 20% 3	23685

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	12% 24% 9% 12% 6% 5% 4 4 4 4 16%	2539
	11th to 20th	Day	13% 19% 9% 11% 5% 4 4 2 4 5% 24%	2540
	21st to end	Day	11% 18% 6% 12% 7% 6% 6% 4 4 5% 23%	2794
February	1st to 10th	Day	13% 18% 6% 11% 6% 5% 3 4 5% 6% 25%	1676
	11th to 20th	Day	11% 21% 7% 9% 6% 4 4 3 4 5% 25%	1768
	21st to end	Day	9% 19% 8% 12% 6% 4 4 3 6% 5% 23%	1570
March	1st to 10th	Day	6% 12% 5% 12% 8% 6% 5% 5% 7% 8% 25%	3138
	11th to 20th	Day	5% 12% 4 7% 5% 5% 4 3 4 4 46%	3290
	21st to end	Day	8% 22% 7% 13% 8% 6% 5% 4 4 4 19%	4157
April	1st to 10th	Day	12% 19% 6% 10% 6% 4 4 4 5% 5% 25%	2280
	11th to 20th	Day	10% 16% 5% 10% 6% 4 4 3 5% 6% 32%	2249
	21st to end	Day	13% 17% 4 7% 5% 5% 4 3 4 5% 32%	2418
May	1st to 10th	Day	10% 16% 3 9% 5% 5% 4 3 4 6% 37%	4322
	11th to 20th	Day	8% 7% 2 5% 4 3 3 3 5% 6% 55%	4377
	21st to end	Day	11% 13% 3 7% 5% 4 4 3 6% 8% 35%	4813
June	1st to 10th	Day	16% 10% 2 6% 5% 4 4 4 5% 7% 38%	2660
	11th to 20th	Day	13% 9% 2 5% 4 4 3 3 6% 7% 43%	2660
	21st to end	Day	6% 4 2 4 2 3 4 2 5% 6% 62%	2660
July	1st to 10th	Day	1 2 1 2 2 2 2 2 3 4 80%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 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 4 3 2 3 3 4 6% 68%	4400
	11th to 20th	Day	2 3 1 3 2 3 3 2 3 6% 74%	3951
	21st to end	Day	3 3 1 3 2 3 3 2 4 6% 70%	4180
September	1st to 10th	Day	4 2 1 3 3 3 3 2 3 7% 69%	2280
	11th to 20th	Day	8% 5% 2 5% 4 3 3 3 5% 5% 56%	2222
	21st to end	Day	9% 9% 2 6% 4 3 3 3 4 5% 53%	2090
October	1st to 10th	Day	9% 8% 2 4 2 2 2 2 3 5% 61%	3256
	11th to 20th	Day	7% 9% 3 7% 4 3 4 3 7% 9% 45%	3140
	21st to end	Day	12% 13% 4 9% 5% 5% 5% 3 5% 6% 32%	3101
November	1st to 10th	Day	16% 16% 3 8% 5% 4 4 4 5% 7% 27%	1764
	11th to 20th	Day	13% 18% 4 11% 6% 5% 4 4 6% 6% 23%	1726
	21st to end	Day	10% 19% 4 9% 5% 4 4 3 5% 5% 31%	1600
December	1st to 10th	Day	11% 17% 4 8% 4 4 4 3 6% 7% 32%	1528
	11th to 20th	Day	10% 20% 5% 9% 6% 5% 6% 3 6% 5% 25%	1928
	21st to end	Day	10% 17% 5% 10% 6% 6% 5% 4 4 6% 26%	2794
January	1st to 10th	Night	13% 23% 8% 12% 5% 5% 5% 3 4 4 18%	4406
	11th to 20th	Night	15% 22% 7% 9% 5% 4 3 2 4 6% 23%	4420
	21st to end	Night	11% 15% 5% 10% 6% 6% 6% 4 6% 7% 24%	4862
February	1st to 10th	Night	12% 18% 6% 10% 5% 5% 4 4 5% 5% 26%	2504
	11th to 20th	Night	11% 21% 6% 9% 4 4 3 3 4 6% 29%	2300
	21st to end	Night	9% 20% 6% 11% 6% 5% 5% 3 4 6% 24%	1884
March	1st to 10th	Night	6% 12% 5% 11% 6% 5% 5% 4 6% 7% 32%	3736
	11th to 20th	Night	6% 11% 4 8% 5% 4 3 3 4 5% 47%	3687
	21st to end	Night	9% 20% 5% 11% 7% 6% 6% 5% 7% 7% 19%	3495
April	1st to 10th	Night	12% 15% 6% 9% 5% 5% 5% 3 4 6% 32%	1900
	11th to 20th	Night	12% 13% 3 7% 4 4 3 3 5% 7% 39%	1879
	21st to end	Night	10% 12% 3 7% 6% 4 4 4 5% 7% 38%	1762
May	1st to 10th	Night	12% 15% 4 7% 5% 4 3 3 4 4 40%	2637
	11th to 20th	Night	8% 5% 1 3 3 3 3 3 4 5% 62%	2516
	21st to end	Night	14% 11% 2 4 3 3 3 3 5% 6% 45%	2762
June	1st to 10th	Night	13% 8% 3 6% 4 4 3 4 5% 8% 44%	1520
	11th to 20th	Night	14% 9% 2 5% 3 3 3 3 4 6% 48%	1520
	21st to end	Night	4 3 1 4 3 3 4 3 5% 6% 63%	1520
July	1st to 10th	Night	1 1 1 1 1 2 2 2 3 84%	2540
	11th to 20th	Night	1 1 1 2 1 2 2 2 4 4 81%	2540
	21st to end	Night	2 1 1 2 1 2 2 3 4 4 78%	2761
August	1st to 10th	Night	3 2 1 2 2 2 3 3 6% 8% 67%	2529
	11th to 20th	Night	1 2 1 3 2 2 3 2 3 5% 76%	2887
	21st to end	Night	2 2 1 3 2 2 3 3 4 5% 72%	3498
September	1st to 10th	Night	4 3 1 3 2 2 2 2 3 5% 73%	1900
	11th to 20th	Night	6% 3 2 5% 3 4 3 3 5% 7% 59%	1957
	21st to end	Night	9% 6% 2 4 3 3 3 3 4 6% 56%	2090
October	1st to 10th	Night	7% 7% 2 4 2 2 2 2 2 4 66%	3720
	11th to 20th	Night	9% 7% 2 6% 4 3 5% 4 5% 8% 49%	3797
	21st to end	Night	9% 13% 4 8% 4 4 5% 3 5% 7% 38%	4457
November	1st to 10th	Night	14% 14% 3 7% 5% 5% 5% 3 5% 7% 31%	2535
	11th to 20th	Night	16% 15% 4 9% 5% 5% 5% 4 5% 5% 28%	2670
	21st to end	Night	10% 16% 5% 8% 4 4 5% 5% 5% 6% 32%	2800
December	1st to 10th	Night	13% 14% 4 7% 5% 4 5% 4 6% 6% 31%	2686
	11th to 20th	Night	9% 18% 5% 10% 6% 6% 6% 5% 6% 7% 23%	3276
	21st to end	Night	11% 17% 5% 8% 5% 5% 5% 4 5% 6% 30%	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	74% 3 7% 13% 2	2539
	11th to 20th	Day	65% 2 9% 16% 6% 2	2540
	21st to end	Day	65% 2 11% 15% 5% 1	2794
February	1st to 10th	Day	62% 4 12% 15% 7%	1676
	11th to 20th	Day	62% 4 10% 14% 8% 2	1777
	21st to end	Day	64% 3 10% 14% 8% 1	1570
March	1st to 10th	Day	59% 1 8% 17% 15%	3138
	11th to 20th	Day	44% 2 8% 35% 12%	3290
	21st to end	Day	69% 2 8% 16% 4	4157
April	1st to 10th	Day	62% 3 12% 16% 7% 1	2280
	11th to 20th	Day	55% 2 12% 18% 12% 2	2252
	21st to end	Day	56% 3 8% 21% 12%	2418
May	1st to 10th	Day	52% 1 8% 26% 12% 1	4322
	11th to 20th	Day	33% 1 8% 33% 19% 5%	4380
	21st to end	Day	49% 2 17% 26% 6%	4814
June	1st to 10th	Day	47% 4 11% 27% 10% 1	2660
	11th to 20th	Day	43% 2 10% 27% 15% 3	2660
	21st to end	Day	25% 2 9% 34% 24% 6%	2660
July	1st to 10th	Day	11% 2 5% 14% 23% 45%	4351
	11th to 20th	Day	12% 2 4 8% 22% 52%	4345
	21st to end	Day	13% 1 2 17% 38% 28%	4639
August	1st to 10th	Day	20% 2 3 13% 35% 26%	4384
	11th to 20th	Day	16% 1 3 29% 37% 15%	3993
	21st to end	Day	18% 1 6% 32% 23% 20%	4179
September	1st to 10th	Day	19% 1 5% 26% 30% 19%	2280
	11th to 20th	Day	30% 2 7% 25% 25% 11%	2222
	21st to end	Day	35% 2 8% 26% 23% 7%	2090
October	1st to 10th	Day	30% 1 8% 20% 31% 9%	3256
	11th to 20th	Day	38% 1 14% 28% 18% 2	3140
	21st to end	Day	56% 1 6% 24% 12% 1	3101
November	1st to 10th	Day	57% 3 10% 20% 9% 1	1764
	11th to 20th	Day	62% 3 12% 18% 5%	1726
	21st to end	Day	56% 3 10% 18% 12% 2	1600
December	1st to 10th	Day	53% 5% 16% 16% 9% 1	1528
	11th to 20th	Day	59% 3 17% 13% 7%	1928
	21st to end	Day	62% 1 11% 21% 4	2794
January	1st to 10th	Night	72% 2 8% 14% 4	4406
	11th to 20th	Night	66% 2 7% 16% 6% 2	4420
	21st to end	Night	60% 2 18% 14% 6% 1	4862
February	1st to 10th	Night	62% 3 13% 14% 8%	2504
	11th to 20th	Night	60% 3 11% 17% 6% 3	2302
	21st to end	Night	64% 2 8% 17% 7% 2	1884
March	1st to 10th	Night	53% 2 7% 23% 14% 1	3736
	11th to 20th	Night	43% 2 10% 37% 8%	3687
	21st to end	Night	65% 3 12% 15% 4 1	3495
April	1st to 10th	Night	57% 3 12% 21% 6% 1	1900
	11th to 20th	Night	48% 4 14% 22% 10% 2	1879
	21st to end	Night	48% 5% 13% 19% 14% 1	1762
May	1st to 10th	Night	50% 2 11% 23% 13% 1	2637
	11th to 20th	Night	27% 2 11% 37% 23% 1	2516
	21st to end	Night	42% 2 23% 26% 7%	2762
June	1st to 10th	Night	41% 5% 11% 28% 13% 2	1520
	11th to 20th	Night	39% 3 11% 30% 13% 4	1520
	21st to end	Night	23% 2 11% 33% 23% 8%	1520
July	1st to 10th	Night	9% 1 6% 15% 27% 43%	2500
	11th to 20th	Night	9% 2 5% 12% 24% 48%	2492
	21st to end	Night	12% 1 2 19% 37% 28%	2674
August	1st to 10th	Night	16% 2 4 16% 44% 18%	2521
	11th to 20th	Night	14% 1 4 35% 36% 9%	2911
	21st to end	Night	17% 1 7% 33% 24% 18%	3498
September	1st to 10th	Night	17% 1 7% 27% 32% 16%	1900
	11th to 20th	Night	27% 2 8% 27% 24% 12%	1957
	21st to end	Night	31% 2 8% 29% 21% 9%	2090
October	1st to 10th	Night	26% 2 7% 24% 34% 7%	3720
	11th to 20th	Night	37% 2 15% 20% 24% 3	3797
	21st to end	Night	47% 2 7% 26% 16% 2	4457
November	1st to 10th	Night	54% 4 9% 19% 12% 2	2535
	11th to 20th	Night	58% 3 11% 18% 9%	2670
	21st to end	Night	53% 3 9% 16% 17% 1	2800
December	1st to 10th	Night	54% 4 15% 16% 9% 2	2686
	11th to 20th	Night	60% 3 15% 14% 8% 1	3276
	21st to end	Night	57% 2 10% 21% 7% 1	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	31% 19% 20% 13% 13% 4	180
	11th to 20th	Day	19% 20% 28% 17% 11% 5%	180
	21st to end	Day	19% 18% 28% 22% 11% 3	198
February	1st to 10th	Day	25% 23% 28% 16% 5% 2	336
	11th to 20th	Day	24% 22% 28% 18% 7% 2	414
	21st to end	Day	27% 19% 28% 20% 6% 1	382
March	1st to 10th	Day	25% 21% 30% 19% 4	460
	11th to 20th	Day	18% 23% 27% 21% 9% 2	460
	21st to end	Day	25% 20% 32% 17% 5%	506
April	1st to 10th	Day	26% 19% 28% 17% 7% 3	460
	11th to 20th	Day	22% 24% 27% 17% 8% 3	452
	21st to end	Day	22% 20% 30% 17% 10% 1	460
May	1st to 10th	Day	17% 20% 28% 24% 9% 3	463
	11th to 20th	Day	22% 14% 29% 20% 12% 4	488
	21st to end	Day	16% 13% 23% 27% 15% 5%	529
June	1st to 10th	Day	17% 14% 22% 26% 17% 4	490
	11th to 20th	Day	17% 18% 29% 24% 10% 2	490
	21st to end	Day	6% 12% 33% 27% 17% 5%	490
July	1st to 10th	Day	2 11% 31% 34% 17% 3	486
	11th to 20th	Day	3 14% 31% 35% 14% 3	484
	21st to end	Day	1 10% 35% 31% 17% 6%	531
August	1st to 10th	Day	5% 9% 29% 33% 18% 6%	487
	11th to 20th	Day	3 7% 26% 36% 18% 10%	477
	21st to end	Day	6% 13% 29% 29% 17% 7%	539
September	1st to 10th	Day	6% 9% 26% 30% 21% 8%	490
	11th to 20th	Day	10% 11% 27% 29% 19% 4	490
	21st to end	Day	12% 13% 24% 30% 16% 5%	490
October	1st to 10th	Day	14% 13% 22% 26% 19% 4	490
	11th to 20th	Day	14% 16% 25% 23% 16% 6%	481
	21st to end	Day	20% 18% 22% 22% 13% 5%	330
November	1st to 10th	Day	24% 20% 20% 21% 13% 1	300
	11th to 20th	Day	23% 22% 21% 19% 11% 3	263
	21st to end	Day	19% 16% 26% 24% 14% 3	200
December	1st to 10th	Day	20% 17% 23% 20% 10% 9%	182
	11th to 20th	Day	28% 21% 31% 13% 7% 1	180
	21st to end	Day	23% 20% 25% 22% 9% 2	198
January	1st to 10th	Night	25% 15% 19% 24% 16% 2	760
	11th to 20th	Night	25% 13% 17% 25% 17% 3	760
	21st to end	Night	22% 10% 18% 31% 17% 2	836
February	1st to 10th	Night	21% 15% 21% 29% 13% 2	760
	11th to 20th	Night	21% 13% 20% 29% 17% 1	744
	21st to end	Night	23% 16% 20% 29% 11% 2	628
March	1st to 10th	Night	19% 15% 22% 30% 12% 2	760
	11th to 20th	Night	16% 15% 20% 30% 18% 2	760
	21st to end	Night	21% 15% 21% 29% 12% 1	836
April	1st to 10th	Night	21% 13% 16% 31% 16% 3	760
	11th to 20th	Night	16% 13% 22% 30% 15% 3	751
	21st to end	Night	15% 11% 21% 34% 17% 2	622
May	1st to 10th	Night	13% 10% 18% 37% 20% 2	438
	11th to 20th	Night	16% 6% 9% 34% 32% 3	374
	21st to end	Night	18% 7% 11% 36% 26% 3	411
June	1st to 10th	Night	14% 7% 15% 38% 23% 3	380
	11th to 20th	Night	17% 7% 13% 40% 21% 2	380
	21st to end	Night	5% 2 11% 52% 28% 2	380
July	1st to 10th	Night	2 2 10% 50% 34% 2	370
	11th to 20th	Night	1 1 10% 61% 25% 2	368
	21st to end	Night	2 1 7% 48% 39% 3	416
August	1st to 10th	Night	4 1 6% 45% 41% 2	378
	11th to 20th	Night	2 2 9% 39% 40% 8%	597
	21st to end	Night	5% 3 12% 44% 32% 4	836
September	1st to 10th	Night	5% 3 11% 43% 33% 5%	760
	11th to 20th	Night	7% 3 11% 38% 33% 8%	760
	21st to end	Night	13% 5% 11% 38% 25% 8%	760
October	1st to 10th	Night	14% 5% 13% 42% 23% 4	760
	11th to 20th	Night	15% 8% 14% 34% 22% 6%	760
	21st to end	Night	18% 11% 15% 33% 18% 5%	836
November	1st to 10th	Night	21% 12% 17% 34% 15% 1	780
	11th to 20th	Night	23% 11% 21% 28% 14% 2	800
	21st to end	Night	18% 14% 18% 28% 16% 5%	800
December	1st to 10th	Night	21% 11% 19% 29% 19% 2	768
	11th to 20th	Night	23% 12% 20% 29% 13% 2	760
	21st to end	Night	28% 16% 21% 24% 10% 1	836

Page generated at 2024-11-29 07:43:07. Version ac07

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