Vermilion
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vermilion clear sky chart from 2005-11-06 to 2025-01-07.

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	10% 9% 4 9% 6% 5% 5% 4 6% 8% 34%	108525
	Night	8% 10% 4 10% 6% 5% 5% 5% 6% 8% 33%	108953
Transparency	Day	45% 9% 17% 22% 7%	108265
	Night	46% 8% 16% 21% 8% 1	108858
Seeing	Day	13% 7% 27% 30% 17% 5%	15731
	Night	12% 6% 29% 36% 15% 2	24931

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	6% 10% 5% 17% 12% 9% 6% 4 5% 5% 21%	2261
	11th to 20th	Day	5% 8% 4 10% 8% 9% 10% 10% 9% 5% 23%	2199
	21st to end	Day	6% 15% 5% 11% 7% 6% 5% 3 6% 6% 29%	2451
February	1st to 10th	Day	8% 16% 5% 14% 8% 5% 6% 4 7% 6% 23%	1571
	11th to 20th	Day	6% 14% 6% 14% 7% 6% 6% 4 5% 7% 25%	1665
	21st to end	Day	6% 13% 4 12% 8% 7% 7% 6% 7% 8% 22%	1413
March	1st to 10th	Day	5% 12% 5% 9% 8% 7% 9% 6% 7% 7% 25%	3176
	11th to 20th	Day	5% 10% 6% 12% 5% 4 3 4 5% 11% 34%	3489
	21st to end	Day	8% 12% 5% 16% 7% 5% 5% 4 5% 6% 27%	3825
April	1st to 10th	Day	8% 14% 4 9% 6% 4 5% 4 6% 7% 32%	2375
	11th to 20th	Day	13% 11% 5% 10% 5% 5% 5% 4 5% 6% 32%	2440
	21st to end	Day	15% 12% 3 7% 4 4 5% 4 7% 8% 32%	2524
May	1st to 10th	Day	16% 11% 4 10% 5% 5% 5% 4 5% 5% 29%	4492
	11th to 20th	Day	14% 11% 3 9% 6% 5% 5% 5% 6% 7% 29%	4694
	21st to end	Day	12% 8% 3 9% 6% 5% 6% 5% 7% 8% 30%	5161
June	1st to 10th	Day	14% 8% 3 8% 6% 6% 5% 5% 6% 8% 31%	2850
	11th to 20th	Day	19% 10% 4 8% 6% 6% 6% 5% 7% 7% 22%	2909
	21st to end	Day	12% 6% 3 6% 5% 5% 6% 5% 8% 11% 34%	2850
July	1st to 10th	Day	8% 5% 2 5% 5% 5% 4 4 6% 9% 47%	4740
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 4 7% 10% 42%	4740
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 10% 46%	5138
August	1st to 10th	Day	13% 5% 2 6% 3 4 5% 4 6% 7% 45%	4656
	11th to 20th	Day	7% 4 2 6% 4 4 4 5% 7% 11% 45%	4028
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 45%	4521
September	1st to 10th	Day	10% 6% 3 6% 5% 5% 5% 4 6% 8% 43%	2375
	11th to 20th	Day	16% 8% 2 6% 4 3 4 4 6% 7% 40%	2161
	21st to end	Day	11% 7% 2 6% 3 4 4 4 6% 7% 45%	2085
October	1st to 10th	Day	8% 10% 3 7% 5% 5% 5% 3 5% 7% 42%	3170
	11th to 20th	Day	11% 8% 3 8% 4 4 5% 4 6% 10% 39%	3067
	21st to end	Day	7% 9% 4 9% 4 5% 5% 4 7% 8% 38%	2895
November	1st to 10th	Day	11% 15% 4 10% 9% 5% 4 4 5% 7% 26%	1568
	11th to 20th	Day	8% 12% 6% 16% 7% 5% 4 4 7% 7% 24%	1560
	21st to end	Day	5% 13% 6% 13% 9% 5% 5% 4 6% 8% 27%	1400
December	1st to 10th	Day	8% 13% 5% 11% 6% 6% 7% 5% 7% 8% 23%	2203
	11th to 20th	Day	8% 17% 5% 12% 7% 6% 6% 4 7% 7% 20%	2375
	21st to end	Day	3 9% 5% 13% 7% 6% 5% 4 5% 7% 37%	3498
January	1st to 10th	Night	4 11% 5% 17% 9% 8% 7% 6% 6% 7% 20%	4817
	11th to 20th	Night	4 8% 4 10% 9% 8% 9% 8% 8% 8% 26%	4699
	21st to end	Night	6% 13% 5% 10% 7% 6% 5% 4 6% 7% 31%	5214
February	1st to 10th	Night	7% 12% 5% 12% 8% 6% 6% 6% 6% 8% 26%	2613
	11th to 20th	Night	6% 10% 4 11% 8% 7% 6% 6% 6% 6% 29%	2402
	21st to end	Night	4 9% 4 12% 8% 6% 6% 5% 7% 9% 29%	2041
March	1st to 10th	Night	6% 13% 4 12% 8% 6% 6% 5% 7% 8% 26%	3692
	11th to 20th	Night	4 9% 4 9% 6% 5% 5% 5% 7% 10% 35%	3490
	21st to end	Night	7% 12% 4 12% 7% 6% 4 4 7% 9% 27%	3828
April	1st to 10th	Night	8% 9% 3 7% 6% 5% 6% 4 7% 8% 37%	1803
	11th to 20th	Night	10% 9% 4 11% 7% 6% 6% 4 7% 8% 29%	1691
	21st to end	Night	13% 11% 4 8% 4 4 4 4 6% 8% 35%	1655
May	1st to 10th	Night	20% 11% 5% 8% 6% 4 5% 4 5% 6% 27%	2461
	11th to 20th	Night	13% 8% 3 8% 6% 4 6% 5% 7% 7% 33%	2199
	21st to end	Night	12% 7% 3 10% 6% 6% 6% 4 8% 8% 29%	2414
June	1st to 10th	Night	13% 7% 3 9% 5% 6% 7% 5% 7% 7% 31%	1330
	11th to 20th	Night	18% 10% 3 7% 5% 5% 4 5% 7% 9% 27%	1223
	21st to end	Night	10% 5% 2 7% 5% 5% 8% 6% 6% 7% 39%	1330
July	1st to 10th	Night	9% 5% 2 6% 5% 4 6% 4 7% 8% 45%	2220
	11th to 20th	Night	7% 4 1 4 3 4 5% 5% 7% 10% 50%	2220
	21st to end	Night	9% 5% 2 5% 3 3 3 4 6% 8% 52%	2414
August	1st to 10th	Night	13% 4 2 5% 4 4 4 4 6% 9% 45%	2272
	11th to 20th	Night	8% 5% 2 6% 4 5% 5% 5% 7% 9% 45%	2811
	21st to end	Night	9% 6% 2 7% 4 4 3 3 6% 8% 48%	3146
September	1st to 10th	Night	11% 6% 2 6% 5% 3 4 2 5% 7% 48%	1805
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 6% 7% 47%	2017
	21st to end	Night	6% 6% 3 6% 4 4 4 5% 6% 9% 48%	2095
October	1st to 10th	Night	8% 8% 3 7% 5% 5% 5% 4 6% 8% 43%	3800
	11th to 20th	Night	8% 9% 3 7% 4 3 4 4 6% 8% 45%	3859
	21st to end	Night	8% 12% 4 8% 4 4 4 4 6% 10% 36%	4632
November	1st to 10th	Night	13% 14% 5% 8% 6% 5% 5% 4 4 6% 28%	2730
	11th to 20th	Night	8% 12% 5% 15% 8% 7% 6% 3 6% 6% 24%	2838
	21st to end	Night	5% 12% 5% 13% 9% 6% 5% 4 6% 7% 28%	3000
December	1st to 10th	Night	9% 14% 5% 14% 8% 6% 6% 5% 6% 7% 19%	4955
	11th to 20th	Night	7% 16% 5% 15% 9% 7% 6% 5% 6% 7% 19%	5779
	21st to end	Night	3 8% 3 12% 8% 6% 5% 4 5% 6% 40%	7458

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	61% 8% 10% 15% 5%	2261
	11th to 20th	Day	53% 10% 13% 15% 8% 1	2220
	21st to end	Day	54% 8% 13% 18% 6%	2451
February	1st to 10th	Day	60% 6% 13% 16% 6%	1571
	11th to 20th	Day	57% 8% 12% 16% 8%	1674
	21st to end	Day	56% 7% 14% 16% 7%	1413
March	1st to 10th	Day	50% 10% 18% 15% 6%	3176
	11th to 20th	Day	43% 9% 24% 18% 7%	3490
	21st to end	Day	52% 10% 14% 18% 6%	3825
April	1st to 10th	Day	50% 8% 15% 19% 9%	2375
	11th to 20th	Day	50% 7% 14% 19% 9% 1	2440
	21st to end	Day	47% 9% 14% 20% 8% 2	2524
May	1st to 10th	Day	54% 8% 11% 20% 6%	4492
	11th to 20th	Day	48% 11% 12% 19% 9% 1	4698
	21st to end	Day	44% 14% 17% 17% 8%	5162
June	1st to 10th	Day	47% 9% 16% 19% 8% 1	2850
	11th to 20th	Day	56% 11% 12% 16% 4 1	2909
	21st to end	Day	39% 13% 21% 20% 7% 1	2850
July	1st to 10th	Day	33% 9% 22% 27% 9% 1	4666
	11th to 20th	Day	35% 9% 19% 26% 11%	4659
	21st to end	Day	33% 8% 23% 29% 7%	4976
August	1st to 10th	Day	36% 9% 19% 32% 4	4638
	11th to 20th	Day	31% 9% 25% 29% 7%	4067
	21st to end	Day	33% 8% 26% 29% 4	4520
September	1st to 10th	Day	38% 8% 19% 24% 9% 2	2375
	11th to 20th	Day	42% 7% 17% 28% 5%	2161
	21st to end	Day	36% 9% 17% 27% 9% 2	2085
October	1st to 10th	Day	41% 5% 23% 25% 5%	3170
	11th to 20th	Day	41% 6% 15% 30% 8%	3067
	21st to end	Day	42% 8% 20% 25% 5%	2895
November	1st to 10th	Day	57% 7% 14% 17% 5%	1568
	11th to 20th	Day	57% 10% 16% 14% 4	1560
	21st to end	Day	55% 8% 16% 18% 4 1	1400
December	1st to 10th	Day	57% 8% 17% 14% 4	2203
	11th to 20th	Day	61% 6% 15% 14% 3	2376
	21st to end	Day	47% 4 10% 27% 10% 1	3498
January	1st to 10th	Night	58% 10% 12% 14% 5%	4817
	11th to 20th	Night	50% 8% 16% 17% 8% 1	4740
	21st to end	Night	50% 9% 16% 19% 6%	5214
February	1st to 10th	Night	54% 8% 13% 17% 8%	2613
	11th to 20th	Night	51% 8% 13% 17% 10%	2403
	21st to end	Night	47% 10% 12% 22% 8% 1	2041
March	1st to 10th	Night	51% 8% 17% 17% 7%	3692
	11th to 20th	Night	39% 10% 21% 21% 8%	3490
	21st to end	Night	47% 11% 15% 19% 7%	3828
April	1st to 10th	Night	42% 8% 15% 20% 14% 1	1803
	11th to 20th	Night	49% 8% 13% 18% 9% 2	1691
	21st to end	Night	45% 8% 14% 20% 11% 2	1655
May	1st to 10th	Night	55% 7% 9% 21% 7% 1	2461
	11th to 20th	Night	41% 13% 13% 22% 11% 1	2199
	21st to end	Night	43% 15% 17% 18% 6% 1	2414
June	1st to 10th	Night	47% 9% 14% 20% 9% 1	1330
	11th to 20th	Night	50% 12% 13% 18% 7%	1223
	21st to end	Night	38% 12% 21% 22% 6% 1	1330
July	1st to 10th	Night	35% 8% 21% 19% 16% 1	2185
	11th to 20th	Night	27% 8% 18% 31% 15%	2178
	21st to end	Night	29% 7% 24% 29% 11%	2337
August	1st to 10th	Night	35% 8% 19% 35% 3	2265
	11th to 20th	Night	33% 8% 22% 28% 8%	2838
	21st to end	Night	34% 6% 21% 32% 7%	3146
September	1st to 10th	Night	35% 8% 18% 25% 11% 3	1805
	11th to 20th	Night	36% 7% 17% 29% 9% 1	2017
	21st to end	Night	32% 8% 15% 30% 12% 3	2095
October	1st to 10th	Night	38% 6% 21% 28% 6%	3800
	11th to 20th	Night	35% 5% 15% 35% 8%	3859
	21st to end	Night	44% 6% 22% 23% 5%	4632
November	1st to 10th	Night	56% 7% 13% 17% 6% 1	2730
	11th to 20th	Night	59% 7% 14% 14% 5%	2838
	21st to end	Night	53% 8% 17% 16% 5%	3000
December	1st to 10th	Night	63% 7% 14% 12% 4 1	4955
	11th to 20th	Night	63% 6% 16% 11% 4	5776
	21st to end	Night	43% 6% 13% 22% 14% 2	7458

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	8% 6% 26% 35% 20% 5%	192
	11th to 20th	Day	13% 10% 21% 30% 24% 2	180
	21st to end	Day	15% 12% 27% 35% 8% 4	198
February	1st to 10th	Day	8% 11% 35% 31% 12% 3	204
	11th to 20th	Day	9% 7% 36% 27% 17% 4	270
	21st to end	Day	9% 5% 30% 32% 18% 6%	225
March	1st to 10th	Day	11% 8% 31% 32% 16% 2	408
	11th to 20th	Day	10% 7% 34% 28% 15% 5%	460
	21st to end	Day	13% 7% 30% 30% 18% 3	506
April	1st to 10th	Day	14% 9% 33% 31% 10% 3	460
	11th to 20th	Day	16% 9% 29% 29% 13% 4	452
	21st to end	Day	18% 9% 29% 30% 12% 2	514
May	1st to 10th	Day	14% 11% 25% 29% 16% 5%	653
	11th to 20th	Day	11% 7% 27% 32% 16% 8%	675
	21st to end	Day	16% 8% 19% 31% 19% 7%	734
June	1st to 10th	Day	17% 7% 26% 34% 13% 4	680
	11th to 20th	Day	19% 8% 26% 25% 15% 6%	680
	21st to end	Day	11% 5% 22% 31% 22% 9%	680
July	1st to 10th	Day	11% 4 17% 32% 27% 8%	671
	11th to 20th	Day	11% 5% 22% 33% 20% 8%	668
	21st to end	Day	11% 4 22% 31% 24% 9%	739
August	1st to 10th	Day	13% 5% 17% 31% 25% 10%	671
	11th to 20th	Day	9% 6% 22% 34% 22% 6%	477
	21st to end	Day	11% 6% 22% 30% 21% 9%	539
September	1st to 10th	Day	12% 7% 34% 27% 16% 5%	490
	11th to 20th	Day	21% 7% 26% 28% 14% 2	490
	21st to end	Day	13% 13% 30% 27% 14% 3	485
October	1st to 10th	Day	14% 7% 33% 26% 16% 3	300
	11th to 20th	Day	17% 6% 32% 31% 11% 3	300
	21st to end	Day	15% 11% 36% 24% 11% 3	330
November	1st to 10th	Day	17% 7% 30% 31% 12% 2	300
	11th to 20th	Day	12% 9% 41% 29% 9% 1	280
	21st to end	Day	6% 7% 43% 29% 11% 5%	200
December	1st to 10th	Day	11% 6% 32% 35% 14% 4	200
	11th to 20th	Day	12% 13% 32% 29% 13% 2	200
	21st to end	Day	8% 3 30% 35% 18% 6%	220
January	1st to 10th	Night	10% 7% 31% 37% 13% 1	981
	11th to 20th	Night	10% 7% 34% 35% 12% 1	950
	21st to end	Night	16% 8% 34% 31% 10% 2	1045
February	1st to 10th	Night	9% 8% 28% 36% 15% 3	765
	11th to 20th	Night	9% 4 33% 35% 16% 2	744
	21st to end	Night	7% 4 25% 39% 21% 5%	628
March	1st to 10th	Night	11% 6% 29% 39% 13% 2	760
	11th to 20th	Night	10% 5% 31% 36% 15% 2	760
	21st to end	Night	12% 7% 27% 36% 16% 3	836
April	1st to 10th	Night	9% 8% 28% 37% 15% 3	582
	11th to 20th	Night	13% 6% 31% 37% 13% 1	563
	21st to end	Night	16% 7% 23% 37% 15%	570
May	1st to 10th	Night	14% 7% 28% 35% 15% 2	530
	11th to 20th	Night	11% 6% 22% 42% 16% 2	374
	21st to end	Night	18% 4 23% 32% 22% 2	411
June	1st to 10th	Night	14% 5% 27% 37% 16% 2	380
	11th to 20th	Night	23% 6% 18% 31% 20% 1	380
	21st to end	Night	11% 4 21% 36% 26% 2	380
July	1st to 10th	Night	11% 5% 16% 41% 27% 1	370
	11th to 20th	Night	11% 4 19% 45% 19% 2	368
	21st to end	Night	8% 4 18% 43% 23% 4	416
August	1st to 10th	Night	11% 1 17% 37% 29% 5%	399
	11th to 20th	Night	11% 4 19% 41% 23% 2	564
	21st to end	Night	10% 4 23% 40% 23% 1	627
September	1st to 10th	Night	15% 4 23% 36% 21% 1	570
	11th to 20th	Night	14% 4 22% 42% 17% 1	687
	21st to end	Night	9% 7% 31% 36% 16% 1	760
October	1st to 10th	Night	13% 5% 30% 36% 13% 2	760
	11th to 20th	Night	12% 5% 33% 36% 13% 2	760
	21st to end	Night	15% 8% 34% 32% 10% 1	936
November	1st to 10th	Night	19% 6% 31% 32% 10% 2	975
	11th to 20th	Night	13% 7% 34% 32% 12% 3	1000
	21st to end	Night	9% 6% 37% 36% 10% 2	1000
December	1st to 10th	Night	12% 7% 35% 27% 14% 4	1000
	11th to 20th	Night	13% 7% 34% 33% 12% 1	1000
	21st to end	Night	10% 5% 29% 37% 16% 4	1100

Page generated at 2025-01-04 01:23:57. Version ac07

Copyright © 2025 Attilla Danko.