Vulcan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vulcan clear sky chart from 2005-11-06 to 2024-11-08.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 41%	105582
	Night	6% 9% 3 8% 5% 5% 5% 4 6% 8% 39%	102105
Transparency	Day	38% 7% 15% 26% 12% 2	105327
	Night	40% 8% 14% 23% 12% 2	102006
Seeing	Day	12% 9% 27% 29% 18% 5%	15407
	Night	11% 7% 30% 35% 15% 2	24493

By Month

Percentage Cloud Cover NW (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	2 12% 7% 10% 5% 5% 6% 5% 8% 8% 32%	2219
	11th to 20th	Day	4 8% 5% 14% 6% 5% 6% 6% 7% 7% 32%	2237
	21st to end	Day	3 7% 3 11% 7% 5% 5% 4 6% 9% 39%	2794
February	1st to 10th	Day	6% 11% 4 11% 7% 8% 7% 5% 6% 6% 29%	1560
	11th to 20th	Day	5% 13% 5% 10% 8% 6% 6% 5% 6% 8% 29%	1665
	21st to end	Day	4 13% 6% 12% 7% 7% 5% 4 5% 8% 29%	1508
March	1st to 10th	Day	2 11% 4 13% 8% 7% 6% 4 5% 7% 32%	3153
	11th to 20th	Day	6% 8% 3 7% 4 5% 4 3 5% 9% 45%	3489
	21st to end	Day	8% 20% 6% 13% 6% 5% 4 4 4 6% 24%	3825
April	1st to 10th	Day	9% 13% 5% 9% 6% 5% 5% 5% 5% 8% 30%	2342
	11th to 20th	Day	9% 12% 3 9% 5% 5% 6% 5% 6% 8% 31%	2440
	21st to end	Day	10% 10% 3 9% 6% 5% 5% 4 7% 7% 33%	2470
May	1st to 10th	Day	17% 14% 4 7% 4 4 4 4 5% 5% 31%	4244
	11th to 20th	Day	9% 7% 3 9% 6% 7% 7% 5% 8% 10% 31%	4694
	21st to end	Day	13% 9% 4 10% 7% 6% 6% 5% 6% 8% 25%	5161
June	1st to 10th	Day	13% 8% 3 7% 5% 6% 5% 5% 8% 9% 33%	2850
	11th to 20th	Day	17% 9% 3 7% 5% 5% 6% 5% 6% 8% 30%	2850
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 7% 10% 44%	2850
July	1st to 10th	Day	5% 4 1 5% 3 4 4 4 7% 8% 54%	4740
	11th to 20th	Day	4 4 1 4 3 4 4 4 6% 9% 56%	4740
	21st to end	Day	3 3 1 3 2 3 3 3 6% 8% 65%	5025
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 7% 10% 45%	4356
	11th to 20th	Day	6% 5% 2 5% 4 3 5% 4 6% 9% 50%	4028
	21st to end	Day	8% 3 2 4 3 3 3 3 6% 8% 56%	4521
September	1st to 10th	Day	9% 5% 2 5% 3 3 4 4 5% 7% 52%	2352
	11th to 20th	Day	13% 7% 3 5% 4 3 4 3 5% 7% 46%	2090
	21st to end	Day	9% 7% 2 6% 3 3 4 4 6% 8% 47%	2090
October	1st to 10th	Day	8% 7% 2 6% 5% 5% 5% 5% 7% 8% 43%	3312
	11th to 20th	Day	6% 6% 2 5% 4 3 5% 4 6% 9% 48%	2980
	21st to end	Day	6% 8% 3 6% 5% 4 5% 4 7% 7% 45%	3101
November	1st to 10th	Day	10% 13% 5% 9% 4 4 4 5% 6% 7% 32%	1601
	11th to 20th	Day	6% 10% 4 9% 5% 4 5% 3 7% 9% 39%	1511
	21st to end	Day	3 10% 5% 10% 5% 4 4 5% 8% 10% 36%	1330
December	1st to 10th	Day	4 12% 5% 11% 6% 6% 6% 4 5% 6% 35%	1330
	11th to 20th	Day	3 10% 5% 12% 9% 6% 6% 5% 6% 7% 31%	1682
	21st to end	Day	4 7% 3 8% 4 5% 5% 5% 6% 10% 43%	2442
January	1st to 10th	Night	3 12% 5% 11% 7% 6% 7% 5% 7% 10% 27%	4726
	11th to 20th	Night	3 9% 6% 13% 6% 6% 6% 5% 6% 8% 33%	4690
	21st to end	Night	4 10% 4 10% 6% 5% 5% 4 6% 8% 40%	4862
February	1st to 10th	Night	5% 12% 5% 11% 7% 7% 5% 5% 6% 8% 30%	2618
	11th to 20th	Night	5% 13% 5% 11% 7% 6% 5% 5% 7% 8% 28%	2402
	21st to end	Night	4 11% 5% 11% 8% 6% 6% 4 6% 7% 33%	1941
March	1st to 10th	Night	2 9% 5% 14% 7% 6% 7% 5% 7% 7% 30%	3720
	11th to 20th	Night	5% 9% 3 7% 4 5% 5% 4 6% 8% 44%	3490
	21st to end	Night	10% 21% 6% 12% 6% 4 5% 4 5% 7% 20%	3828
April	1st to 10th	Night	8% 12% 4 10% 6% 5% 6% 4 6% 9% 30%	1834
	11th to 20th	Night	9% 10% 4 10% 7% 5% 4 5% 6% 8% 32%	1691
	21st to end	Night	10% 10% 3 9% 6% 5% 5% 4 7% 8% 33%	1710
May	1st to 10th	Night	17% 14% 4 8% 5% 5% 4 3 5% 6% 29%	2720
	11th to 20th	Night	8% 7% 4 7% 5% 6% 6% 5% 7% 9% 36%	2199
	21st to end	Night	12% 8% 3 10% 6% 7% 7% 5% 7% 9% 27%	2414
June	1st to 10th	Night	13% 9% 2 7% 5% 5% 4 5% 8% 7% 36%	1330
	11th to 20th	Night	16% 8% 2 7% 5% 5% 5% 4 7% 8% 32%	1330
	21st to end	Night	5% 4 2 6% 3 5% 5% 5% 8% 10% 46%	1330
July	1st to 10th	Night	4 4 1 6% 5% 5% 5% 4 8% 8% 49%	2220
	11th to 20th	Night	4 4 1 6% 4 4 6% 4 8% 10% 49%	2220
	21st to end	Night	4 3 1 4 3 3 3 4 7% 8% 60%	2525
August	1st to 10th	Night	6% 6% 2 7% 5% 5% 5% 4 5% 8% 47%	2575
	11th to 20th	Night	5% 5% 2 7% 4 5% 5% 5% 7% 12% 44%	2811
	21st to end	Night	6% 3 1 4 3 3 3 3 5% 10% 59%	3146
September	1st to 10th	Night	9% 4 2 6% 4 4 4 4 5% 7% 51%	1825
	11th to 20th	Night	12% 6% 2 5% 3 4 3 2 5% 8% 51%	2090
	21st to end	Night	7% 6% 2 6% 4 4 5% 4 6% 8% 47%	2090
October	1st to 10th	Night	7% 6% 2 5% 4 3 4 4 6% 7% 52%	3662
	11th to 20th	Night	7% 7% 2 6% 4 4 4 3 6% 8% 49%	3944
	21st to end	Night	5% 6% 3 7% 5% 5% 5% 4 6% 8% 46%	4457
November	1st to 10th	Night	9% 12% 4 9% 5% 5% 5% 4 6% 8% 34%	2617
	11th to 20th	Night	4 9% 4 8% 5% 5% 5% 5% 7% 9% 39%	2664
	21st to end	Night	5% 11% 3 7% 5% 5% 4 4 7% 10% 39%	2850
December	1st to 10th	Night	4 11% 4 9% 7% 6% 5% 4 7% 8% 35%	2850
	11th to 20th	Night	3 9% 3 11% 6% 6% 5% 5% 8% 9% 34%	3510
	21st to end	Night	4 8% 3 8% 6% 4 5% 4 6% 8% 43%	5214

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	44% 8% 16% 23% 7% 1	2219
	11th to 20th	Day	46% 8% 11% 15% 16% 3	2258
	21st to end	Day	39% 8% 15% 30% 7% 1	2794
February	1st to 10th	Day	54% 8% 13% 16% 8% 2	1560
	11th to 20th	Day	50% 7% 15% 18% 8% 2	1674
	21st to end	Day	52% 7% 11% 18% 11% 1	1508
March	1st to 10th	Day	47% 7% 15% 19% 11% 1	3153
	11th to 20th	Day	35% 7% 20% 25% 12% 1	3490
	21st to end	Day	59% 8% 12% 16% 4	3825
April	1st to 10th	Day	50% 7% 14% 21% 8%	2342
	11th to 20th	Day	47% 8% 13% 20% 9% 2	2440
	21st to end	Day	45% 9% 14% 21% 10% 1	2470
May	1st to 10th	Day	53% 7% 10% 24% 5%	4244
	11th to 20th	Day	40% 11% 16% 23% 9%	4698
	21st to end	Day	49% 10% 15% 18% 7% 1	5162
June	1st to 10th	Day	43% 9% 17% 20% 10% 1	2850
	11th to 20th	Day	48% 8% 14% 19% 9% 2	2850
	21st to end	Day	31% 8% 18% 28% 12% 2	2850
July	1st to 10th	Day	25% 7% 15% 30% 18% 5%	4666
	11th to 20th	Day	22% 7% 18% 34% 17% 3	4659
	21st to end	Day	17% 4 11% 29% 26% 14%	4866
August	1st to 10th	Day	31% 8% 14% 35% 11% 2	4339
	11th to 20th	Day	28% 7% 20% 33% 9% 2	4067
	21st to end	Day	26% 4 15% 39% 14% 2	4520
September	1st to 10th	Day	30% 6% 13% 26% 17% 7%	2352
	11th to 20th	Day	37% 6% 12% 29% 13% 3	2090
	21st to end	Day	33% 7% 14% 30% 12% 4	2090
October	1st to 10th	Day	37% 6% 11% 34% 11% 1	3312
	11th to 20th	Day	32% 5% 19% 26% 15% 2	2980
	21st to end	Day	36% 6% 11% 31% 12% 3	3101
November	1st to 10th	Day	49% 8% 12% 20% 9% 1	1601
	11th to 20th	Day	40% 7% 18% 24% 10% 1	1511
	21st to end	Day	39% 8% 17% 23% 10% 3	1330
December	1st to 10th	Day	48% 9% 11% 18% 11% 3	1330
	11th to 20th	Day	49% 7% 15% 23% 5% 1	1684
	21st to end	Day	34% 8% 13% 24% 19% 3	2442
January	1st to 10th	Night	47% 10% 15% 20% 6% 1	4726
	11th to 20th	Night	48% 7% 12% 14% 16% 3	4731
	21st to end	Night	40% 8% 15% 24% 12% 1	4862
February	1st to 10th	Night	50% 8% 12% 17% 11% 2	2618
	11th to 20th	Night	50% 8% 12% 19% 10% 1	2403
	21st to end	Night	48% 7% 12% 20% 10% 2	1941
March	1st to 10th	Night	47% 10% 13% 21% 9% 1	3720
	11th to 20th	Night	35% 8% 20% 23% 13% 1	3490
	21st to end	Night	62% 8% 12% 14% 4	3828
April	1st to 10th	Night	49% 9% 12% 19% 11%	1834
	11th to 20th	Night	48% 7% 13% 21% 10% 1	1691
	21st to end	Night	45% 9% 13% 22% 8% 2	1710
May	1st to 10th	Night	54% 8% 10% 22% 6% 1	2720
	11th to 20th	Night	36% 12% 16% 29% 6% 1	2199
	21st to end	Night	47% 13% 16% 17% 6% 1	2414
June	1st to 10th	Night	43% 9% 14% 22% 11% 1	1330
	11th to 20th	Night	46% 8% 15% 19% 9% 2	1330
	21st to end	Night	29% 9% 20% 25% 15% 2	1330
July	1st to 10th	Night	27% 8% 18% 24% 20% 3	2185
	11th to 20th	Night	26% 9% 17% 29% 15% 4	2178
	21st to end	Night	20% 5% 12% 28% 23% 13%	2445
August	1st to 10th	Night	34% 7% 14% 28% 15% 2	2567
	11th to 20th	Night	32% 7% 19% 29% 11% 2	2838
	21st to end	Night	22% 5% 14% 39% 16% 4	3146
September	1st to 10th	Night	31% 7% 13% 25% 17% 7%	1825
	11th to 20th	Night	32% 6% 14% 27% 16% 5%	2090
	21st to end	Night	32% 6% 16% 28% 15% 4	2090
October	1st to 10th	Night	29% 5% 13% 32% 19% 3	3662
	11th to 20th	Night	34% 5% 16% 25% 17% 3	3944
	21st to end	Night	35% 5% 12% 32% 16%	4457
November	1st to 10th	Night	47% 7% 11% 22% 11% 1	2617
	11th to 20th	Night	39% 8% 16% 20% 15% 1	2664
	21st to end	Night	38% 9% 19% 20% 11% 3	2850
December	1st to 10th	Night	45% 7% 15% 20% 10% 3	2850
	11th to 20th	Night	42% 10% 21% 21% 6% 1	3507
	21st to end	Night	37% 6% 13% 25% 14% 5%	5214

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	4 9% 33% 29% 13% 12%	180
	11th to 20th	Day	7% 9% 34% 29% 14% 7%	180
	21st to end	Day	6% 8% 32% 34% 17% 3	198
February	1st to 10th	Day	11% 11% 34% 32% 11% 3	200
	11th to 20th	Day	8% 9% 33% 31% 15% 4	270
	21st to end	Day	12% 12% 26% 29% 17% 3	320
March	1st to 10th	Day	8% 13% 36% 26% 13% 4	460
	11th to 20th	Day	10% 10% 31% 33% 13% 3	460
	21st to end	Day	13% 15% 29% 26% 13% 5%	506
April	1st to 10th	Day	14% 15% 31% 27% 12% 2	460
	11th to 20th	Day	13% 13% 28% 28% 16% 3	452
	21st to end	Day	16% 12% 28% 27% 13% 3	460
May	1st to 10th	Day	17% 11% 24% 26% 16% 6%	510
	11th to 20th	Day	17% 6% 21% 30% 22% 4	675
	21st to end	Day	19% 8% 19% 29% 18% 8%	734
June	1st to 10th	Day	13% 9% 28% 31% 16% 3	680
	11th to 20th	Day	19% 10% 27% 27% 15% 2	680
	21st to end	Day	10% 4 25% 33% 22% 6%	680
July	1st to 10th	Day	7% 4 20% 36% 27% 5%	671
	11th to 20th	Day	10% 4 23% 35% 22% 6%	668
	21st to end	Day	5% 4 25% 35% 24% 7%	675
August	1st to 10th	Day	9% 5% 23% 32% 24% 7%	487
	11th to 20th	Day	9% 5% 19% 32% 25% 10%	477
	21st to end	Day	8% 9% 24% 31% 18% 10%	539
September	1st to 10th	Day	12% 7% 28% 26% 20% 7%	490
	11th to 20th	Day	19% 6% 24% 29% 16% 6%	490
	21st to end	Day	16% 14% 29% 24% 13% 4	490
October	1st to 10th	Day	16% 8% 23% 26% 22% 6%	390
	11th to 20th	Day	10% 15% 30% 22% 18% 6%	300
	21st to end	Day	14% 15% 30% 26% 13% 3	330
November	1st to 10th	Day	18% 10% 28% 29% 12% 3	291
	11th to 20th	Day	11% 15% 33% 26% 14% 1	266
	21st to end	Day	4 17% 31% 24% 15% 9%	180
December	1st to 10th	Day	8% 11% 29% 32% 16% 4	180
	11th to 20th	Day	11% 9% 41% 24% 12% 3	180
	21st to end	Day	10% 7% 25% 30% 23% 6%	198
January	1st to 10th	Night	8% 12% 34% 31% 13% 1	950
	11th to 20th	Night	8% 8% 35% 35% 12% 1	941
	21st to end	Night	10% 8% 35% 33% 12% 1	836
February	1st to 10th	Night	10% 10% 29% 33% 15% 3	760
	11th to 20th	Night	9% 7% 32% 38% 13% 2	744
	21st to end	Night	9% 7% 25% 36% 20% 3	628
March	1st to 10th	Night	10% 8% 32% 34% 14% 2	760
	11th to 20th	Night	11% 7% 36% 32% 12% 2	760
	21st to end	Night	13% 8% 30% 33% 12% 4	836
April	1st to 10th	Night	13% 8% 34% 30% 13% 2	689
	11th to 20th	Night	15% 6% 33% 33% 12% 1	563
	21st to end	Night	15% 9% 30% 34% 12% 1	570
May	1st to 10th	Night	18% 8% 22% 34% 17% 1	542
	11th to 20th	Night	13% 6% 22% 36% 22% 1	374
	21st to end	Night	18% 6% 23% 30% 21% 2	411
June	1st to 10th	Night	16% 6% 28% 34% 16% 1	380
	11th to 20th	Night	19% 9% 27% 31% 14%	380
	21st to end	Night	9% 3 23% 41% 22% 2	380
July	1st to 10th	Night	7% 2 18% 46% 26% 1	370
	11th to 20th	Night	8% 2 22% 46% 21% 1	368
	21st to end	Night	6% 2 24% 43% 24% 2	416
August	1st to 10th	Night	8% 4 18% 42% 27% 2	398
	11th to 20th	Night	7% 3 20% 45% 23% 2	564
	21st to end	Night	11% 4 22% 42% 19% 1	627
September	1st to 10th	Night	13% 3 23% 39% 22% 2	640
	11th to 20th	Night	15% 5% 20% 38% 20% 2	760
	21st to end	Night	12% 6% 29% 36% 14% 3	760
October	1st to 10th	Night	14% 6% 26% 35% 18% 2	760
	11th to 20th	Night	12% 8% 31% 33% 15% 3	760
	21st to end	Night	10% 8% 36% 32% 13% 1	836
November	1st to 10th	Night	14% 8% 38% 30% 8% 1	885
	11th to 20th	Night	10% 12% 39% 28% 10% 1	950
	21st to end	Night	10% 9% 36% 33% 10% 2	950
December	1st to 10th	Night	9% 8% 32% 34% 14% 2	950
	11th to 20th	Night	8% 9% 34% 36% 11% 1	950
	21st to end	Night	11% 8% 33% 34% 12% 2	1045

Page generated at 2024-11-05 06:15:54. Version ac07

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