Blue Mountain Vista Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Mountain Vista Observatory 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	17% 7% 2 7% 4 4 4 4 6% 7% 37%	101633
	Night	17% 7% 2 6% 4 4 4 3 5% 7% 40%	98016
Transparency	Day	44% 6% 12% 23% 14% 2	105195
	Night	42% 5% 12% 23% 15% 2	102542
Seeing	Day	22% 16% 28% 21% 10% 3	14960
	Night	21% 12% 28% 28% 11% 1	24279

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	15% 10% 3 7% 5% 3 4 3 5% 5% 40%	2517
	11th to 20th	Day	14% 12% 6% 12% 6% 6% 5% 3 4 6% 26%	2620
	21st to end	Day	21% 13% 4 8% 4 4 4 3 4 5% 30%	3124
February	1st to 10th	Day	17% 8% 3 9% 6% 5% 4 4 5% 6% 33%	1710
	11th to 20th	Day	14% 9% 2 8% 5% 5% 5% 4 5% 7% 37%	1752
	21st to end	Day	19% 11% 3 9% 4 4 4 4 4 5% 34%	1570
March	1st to 10th	Day	26% 8% 2 5% 4 4 4 3 4 6% 34%	3198
	11th to 20th	Day	9% 6% 2 8% 6% 5% 5% 4 6% 6% 43%	3480
	21st to end	Day	21% 9% 2 5% 3 3 3 3 4 5% 42%	3994
April	1st to 10th	Day	16% 9% 2 7% 5% 5% 5% 4 6% 5% 36%	2280
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 4 5% 5% 39%	2254
	21st to end	Day	17% 6% 2 6% 4 5% 5% 4 5% 7% 38%	2280
May	1st to 10th	Day	28% 8% 2 6% 4 4 4 3 5% 7% 30%	4153
	11th to 20th	Day	24% 10% 3 9% 5% 5% 4 4 5% 6% 25%	4398
	21st to end	Day	14% 5% 2 5% 4 4 4 4 7% 9% 42%	4837
June	1st to 10th	Day	13% 6% 2 7% 5% 6% 5% 4 7% 9% 36%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 6% 5% 4 7% 10% 35%	2660
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 4 7% 9% 40%	2660
July	1st to 10th	Day	8% 5% 2 8% 5% 6% 7% 5% 8% 10% 35%	4440
	11th to 20th	Day	9% 6% 2 6% 4 5% 6% 5% 6% 10% 39%	4440
	21st to end	Day	13% 8% 3 8% 6% 6% 5% 4 6% 7% 34%	4695
August	1st to 10th	Day	22% 6% 2 6% 5% 5% 5% 4 7% 8% 30%	4104
	11th to 20th	Day	15% 6% 2 6% 4 5% 5% 4 7% 8% 39%	3826
	21st to end	Day	16% 5% 2 4 2 4 4 4 6% 8% 45%	4180
September	1st to 10th	Day	17% 5% 2 7% 3 4 4 3 5% 6% 43%	2280
	11th to 20th	Day	13% 5% 1 4 3 3 3 4 5% 6% 51%	2280
	21st to end	Day	23% 8% 2 5% 3 4 3 4 4 6% 37%	2037
October	1st to 10th	Day	19% 7% 2 5% 3 4 4 4 6% 7% 40%	1900
	11th to 20th	Day	18% 5% 2 6% 4 4 4 3 4 6% 44%	1900
	21st to end	Day	21% 6% 2 5% 5% 3 4 4 5% 6% 39%	2047
November	1st to 10th	Day	14% 7% 2 4 3 2 3 2 4 7% 51%	1761
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 7% 6% 42%	1790
	21st to end	Day	18% 7% 2 5% 4 4 4 4 6% 7% 40%	1600
December	1st to 10th	Day	20% 9% 4 6% 5% 4 5% 3 5% 6% 33%	1528
	11th to 20th	Day	22% 8% 2 6% 3 4 3 4 5% 6% 36%	1906
	21st to end	Day	20% 10% 3 10% 5% 5% 5% 4 6% 7% 27%	2772
January	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 6% 7% 40%	4429
	11th to 20th	Night	17% 9% 3 8% 5% 5% 5% 4 5% 6% 34%	4339
	21st to end	Night	24% 9% 3 7% 4 4 4 3 5% 5% 33%	4532
February	1st to 10th	Night	17% 8% 3 6% 4 3 4 3 5% 7% 39%	2470
	11th to 20th	Night	16% 8% 2 7% 5% 4 4 4 6% 6% 38%	2313
	21st to end	Night	18% 8% 2 6% 5% 4 4 3 6% 6% 38%	1884
March	1st to 10th	Night	22% 12% 2 5% 4 3 3 3 4 5% 35%	3639
	11th to 20th	Night	11% 7% 3 6% 4 4 4 4 5% 6% 48%	3479
	21st to end	Night	16% 10% 2 6% 4 3 4 2 4 5% 44%	3636
April	1st to 10th	Night	18% 7% 2 6% 5% 5% 4 5% 5% 7% 37%	1900
	11th to 20th	Night	15% 7% 2 5% 6% 4 4 4 5% 7% 40%	1875
	21st to end	Night	19% 6% 2 5% 3 3 4 3 5% 6% 43%	1900
May	1st to 10th	Night	27% 8% 2 6% 4 4 4 4 4 7% 31%	2815
	11th to 20th	Night	25% 10% 3 6% 4 4 3 3 4 6% 30%	2495
	21st to end	Night	15% 7% 2 7% 5% 4 4 3 6% 9% 40%	2738
June	1st to 10th	Night	17% 6% 2 6% 4 4 4 3 5% 7% 43%	1520
	11th to 20th	Night	14% 6% 2 5% 4 4 5% 4 6% 9% 42%	1520
	21st to end	Night	12% 5% 2 5% 3 4 5% 4 6% 10% 44%	1520
July	1st to 10th	Night	9% 5% 2 7% 5% 6% 6% 5% 6% 9% 41%	2520
	11th to 20th	Night	12% 5% 2 6% 4 4 4 5% 7% 10% 40%	2520
	21st to end	Night	15% 7% 2 5% 5% 4 5% 4 5% 7% 40%	2854
August	1st to 10th	Night	22% 6% 2 7% 4 4 4 3 6% 8% 34%	2825
	11th to 20th	Night	16% 7% 2 6% 4 4 4 3 4 6% 42%	2971
	21st to end	Night	14% 4 2 4 3 3 4 3 6% 7% 49%	3476
September	1st to 10th	Night	16% 6% 2 6% 4 3 3 2 4 6% 48%	1900
	11th to 20th	Night	12% 6% 2 6% 4 3 4 3 4 7% 51%	1900
	21st to end	Night	21% 7% 2 5% 3 4 4 3 4 6% 43%	2138
October	1st to 10th	Night	22% 5% 1 5% 3 3 3 3 5% 6% 43%	2280
	11th to 20th	Night	17% 6% 2 4 4 3 3 3 4 7% 47%	2280
	21st to end	Night	20% 5% 2 5% 4 3 4 3 4 7% 44%	2548
November	1st to 10th	Night	12% 5% 2 5% 4 3 4 3 5% 6% 51%	2537
	11th to 20th	Night	17% 8% 2 6% 3 3 3 4 5% 7% 43%	2605
	21st to end	Night	16% 6% 2 6% 4 4 4 3 5% 8% 40%	2800
December	1st to 10th	Night	20% 7% 2 8% 5% 4 5% 4 5% 6% 34%	2686
	11th to 20th	Night	19% 8% 2 6% 4 4 4 4 6% 6% 37%	3288
	21st to end	Night	19% 10% 3 6% 5% 4 4 3 5% 7% 34%	4884

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	43% 5% 14% 26% 10% 2	2518
	11th to 20th	Day	56% 4 12% 16% 10% 2	2620
	21st to end	Day	56% 5% 11% 20% 8% 1	3124
February	1st to 10th	Day	48% 6% 14% 20% 12% 1	1710
	11th to 20th	Day	46% 5% 11% 24% 12% 2	1761
	21st to end	Day	51% 4 9% 23% 10% 3	1570
March	1st to 10th	Day	50% 4 11% 25% 8% 1	3201
	11th to 20th	Day	38% 5% 14% 27% 13% 3	3480
	21st to end	Day	45% 4 11% 17% 20% 3	3994
April	1st to 10th	Day	47% 5% 9% 20% 14% 5%	2280
	11th to 20th	Day	44% 5% 11% 22% 14% 4	2254
	21st to end	Day	43% 6% 10% 21% 15% 5%	2280
May	1st to 10th	Day	53% 6% 11% 19% 10% 2	4165
	11th to 20th	Day	57% 7% 10% 16% 8% 1	4402
	21st to end	Day	35% 7% 13% 26% 16% 3	4837
June	1st to 10th	Day	42% 8% 13% 22% 13% 2	2660
	11th to 20th	Day	43% 8% 14% 23% 10% 2	2660
	21st to end	Day	38% 8% 14% 25% 14% 1	2660
July	1st to 10th	Day	40% 10% 14% 23% 13% 1	4370
	11th to 20th	Day	37% 8% 16% 25% 13% 1	4365
	21st to end	Day	47% 7% 11% 18% 16% 1	4545
August	1st to 10th	Day	49% 8% 13% 20% 10%	4091
	11th to 20th	Day	41% 7% 12% 29% 12% 1	3865
	21st to end	Day	36% 5% 12% 30% 16% 2	4180
September	1st to 10th	Day	41% 6% 11% 21% 19% 3	2280
	11th to 20th	Day	33% 5% 10% 24% 24% 3	2280
	21st to end	Day	48% 4 9% 18% 19% 2	2037
October	1st to 10th	Day	40% 4 9% 20% 22% 5%	3160
	11th to 20th	Day	31% 4 11% 28% 22% 5%	3140
	21st to end	Day	28% 4 15% 25% 25% 3	3349
November	1st to 10th	Day	35% 3 14% 25% 19% 3	1761
	11th to 20th	Day	40% 4 11% 24% 17% 3	1790
	21st to end	Day	42% 5% 13% 29% 10% 2	1600
December	1st to 10th	Day	52% 5% 14% 19% 9% 1	1528
	11th to 20th	Day	47% 5% 17% 23% 8% 1	1906
	21st to end	Day	54% 6% 13% 19% 7%	2772
January	1st to 10th	Night	42% 5% 14% 27% 10% 2	4429
	11th to 20th	Night	47% 6% 13% 22% 9% 2	4339
	21st to end	Night	52% 5% 10% 23% 9% 1	4532
February	1st to 10th	Night	45% 4 13% 25% 10% 2	2470
	11th to 20th	Night	46% 4 11% 20% 16% 3	2315
	21st to end	Night	45% 3 10% 22% 16% 3	1884
March	1st to 10th	Night	50% 5% 8% 23% 12% 2	3649
	11th to 20th	Night	36% 4 15% 27% 16% 2	3480
	21st to end	Night	43% 4 8% 18% 22% 6%	3636
April	1st to 10th	Night	45% 5% 11% 22% 14% 3	1900
	11th to 20th	Night	42% 6% 11% 20% 20% 1	1875
	21st to end	Night	40% 6% 11% 21% 17% 4	1900
May	1st to 10th	Night	52% 6% 9% 21% 10% 2	2822
	11th to 20th	Night	53% 8% 12% 14% 10% 1	2496
	21st to end	Night	40% 8% 13% 23% 13% 3	2739
June	1st to 10th	Night	41% 6% 10% 24% 19% 1	1520
	11th to 20th	Night	38% 8% 14% 26% 13% 1	1520
	21st to end	Night	34% 9% 14% 28% 13% 1	1520
July	1st to 10th	Night	40% 7% 16% 17% 16% 4	2480
	11th to 20th	Night	38% 7% 16% 24% 14% 1	2472
	21st to end	Night	42% 7% 14% 17% 19% 1	2763
August	1st to 10th	Night	48% 7% 16% 19% 10% 1	2814
	11th to 20th	Night	43% 6% 11% 24% 16% 1	2998
	21st to end	Night	34% 6% 11% 29% 18% 1	3476
September	1st to 10th	Night	38% 6% 9% 25% 20% 3	1900
	11th to 20th	Night	34% 5% 8% 25% 24% 3	1900
	21st to end	Night	44% 3 9% 20% 21% 2	2138
October	1st to 10th	Night	42% 4 10% 22% 21% 1	3800
	11th to 20th	Night	29% 4 8% 30% 24% 5%	3779
	21st to end	Night	28% 3 13% 31% 22% 2	4196
November	1st to 10th	Night	34% 5% 13% 25% 20% 4	2537
	11th to 20th	Night	42% 3 10% 24% 17% 4	2605
	21st to end	Night	41% 5% 13% 27% 13% 2	2800
December	1st to 10th	Night	49% 5% 12% 21% 11% 1	2686
	11th to 20th	Night	45% 4 15% 20% 13% 2	3288
	21st to end	Night	49% 5% 14% 23% 8%	4884

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	29% 28% 28% 11% 3 1	180
	11th to 20th	Day	35% 26% 27% 9% 2	209
	21st to end	Day	24% 28% 31% 13% 3 1	297
February	1st to 10th	Day	25% 29% 33% 11% 2	270
	11th to 20th	Day	28% 26% 35% 9% 1	359
	21st to end	Day	32% 19% 28% 19% 2	382
March	1st to 10th	Day	28% 21% 29% 18% 4	460
	11th to 20th	Day	26% 27% 30% 11% 4 1	460
	21st to end	Day	30% 23% 28% 13% 5% 1	506
April	1st to 10th	Day	27% 23% 27% 17% 5% 1	460
	11th to 20th	Day	23% 25% 29% 14% 8% 2	452
	21st to end	Day	28% 19% 30% 15% 6% 3	460
May	1st to 10th	Day	30% 20% 25% 15% 7% 3	463
	11th to 20th	Day	24% 17% 31% 19% 8% 2	487
	21st to end	Day	20% 9% 29% 22% 16% 4	529
June	1st to 10th	Day	16% 16% 30% 22% 14% 3	490
	11th to 20th	Day	21% 12% 29% 23% 12% 3	490
	21st to end	Day	16% 11% 33% 24% 12% 3	490
July	1st to 10th	Day	14% 7% 25% 29% 20% 6%	485
	11th to 20th	Day	9% 8% 25% 33% 21% 4	484
	21st to end	Day	14% 8% 31% 30% 13% 4	532
August	1st to 10th	Day	14% 7% 24% 29% 17% 9%	486
	11th to 20th	Day	16% 5% 22% 34% 17% 7%	479
	21st to end	Day	15% 6% 26% 28% 14% 9%	539
September	1st to 10th	Day	20% 11% 20% 23% 20% 6%	490
	11th to 20th	Day	13% 5% 24% 29% 18% 10%	490
	21st to end	Day	28% 12% 23% 19% 13% 4	490
October	1st to 10th	Day	24% 10% 24% 21% 15% 5%	490
	11th to 20th	Day	21% 15% 28% 21% 12% 3	490
	21st to end	Day	23% 16% 31% 19% 10% 1	516
November	1st to 10th	Day	19% 17% 27% 24% 10% 3	395
	11th to 20th	Day	24% 20% 30% 20% 6%	390
	21st to end	Day	29% 26% 31% 11% 5%	200
December	1st to 10th	Day	31% 26% 26% 12% 5% 1	182
	11th to 20th	Day	33% 24% 27% 12% 4	180
	21st to end	Day	28% 24% 30% 15% 2 2	198
January	1st to 10th	Night	19% 19% 39% 19% 3	760
	11th to 20th	Night	26% 17% 30% 23% 4	760
	21st to end	Night	18% 20% 36% 23% 2	836
February	1st to 10th	Night	23% 16% 34% 25% 2	760
	11th to 20th	Night	24% 21% 36% 17% 1	743
	21st to end	Night	27% 20% 31% 19% 3	628
March	1st to 10th	Night	23% 19% 32% 22% 4	760
	11th to 20th	Night	24% 18% 32% 20% 5% 1	760
	21st to end	Night	23% 17% 35% 21% 4	836
April	1st to 10th	Night	24% 16% 35% 20% 5%	760
	11th to 20th	Night	19% 14% 36% 24% 6%	751
	21st to end	Night	24% 12% 32% 24% 8%	760
May	1st to 10th	Night	25% 11% 28% 26% 10% 1	565
	11th to 20th	Night	19% 10% 32% 28% 11% 1	374
	21st to end	Night	18% 7% 19% 41% 13% 2	411
June	1st to 10th	Night	18% 7% 24% 33% 18%	380
	11th to 20th	Night	17% 4 26% 39% 13% 1	380
	21st to end	Night	12% 5% 26% 41% 16% 1	380
July	1st to 10th	Night	11% 4 21% 38% 24% 2	370
	11th to 20th	Night	13% 3 17% 41% 24% 2	368
	21st to end	Night	12% 4 18% 44% 20% 1	482
August	1st to 10th	Night	15% 2 16% 40% 26% 2	567
	11th to 20th	Night	16% 5% 13% 38% 26% 2	672
	21st to end	Night	17% 3 16% 35% 26% 2	836
September	1st to 10th	Night	18% 4 21% 34% 20% 2	760
	11th to 20th	Night	15% 6% 17% 34% 24% 5%	760
	21st to end	Night	24% 5% 21% 29% 19% 2	760
October	1st to 10th	Night	25% 7% 22% 26% 17% 3	760
	11th to 20th	Night	20% 10% 25% 33% 11% 1	760
	21st to end	Night	23% 11% 28% 28% 10%	836
November	1st to 10th	Night	16% 13% 32% 27% 11% 1	780
	11th to 20th	Night	20% 17% 28% 27% 7% 1	800
	21st to end	Night	19% 17% 31% 26% 6%	800
December	1st to 10th	Night	26% 17% 30% 21% 5% 1	768
	11th to 20th	Night	22% 16% 32% 26% 5%	760
	21st to end	Night	25% 14% 32% 26% 3	836

Page generated at 2024-11-29 10:43:08. Version ac07

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