Vernonia
Clear Sky Chart
History

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

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 8% 5% 5% 4 3 5% 6% 33%	106034
	Night	16% 12% 4 8% 5% 5% 4 3 5% 6% 33%	101745
Transparency	Day	50% 7% 12% 16% 12% 4	105796
	Night	50% 7% 13% 17% 10% 3	101629
Seeing	Day	23% 12% 26% 24% 11% 3	15095
	Night	23% 8% 21% 30% 16% 2	23541

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	26% 21% 5% 12% 7% 6% 5% 3 4 3 8%	2539
	11th to 20th	Day	27% 18% 4 9% 5% 4 3 2 4 4 20%	2516
	21st to end	Day	26% 18% 6% 12% 7% 5% 4 3 4 3 13%	3060
February	1st to 10th	Day	23% 18% 4 11% 6% 5% 5% 3 5% 5% 15%	1710
	11th to 20th	Day	22% 20% 6% 11% 6% 4 3 3 3 4 17%	1665
	21st to end	Day	21% 20% 5% 12% 6% 6% 4 3 3 5% 14%	1462
March	1st to 10th	Day	15% 20% 5% 13% 6% 6% 5% 4 6% 4 15%	3319
	11th to 20th	Day	19% 15% 4 7% 5% 4 3 2 3 4 34%	3490
	21st to end	Day	21% 19% 6% 10% 7% 6% 5% 3 4 5% 13%	3881
April	1st to 10th	Day	23% 19% 5% 9% 6% 5% 4 3 5% 5% 15%	2280
	11th to 20th	Day	23% 16% 5% 10% 5% 5% 5% 3 3 4 21%	2280
	21st to end	Day	22% 15% 4 10% 6% 5% 4 4 5% 5% 20%	2470
May	1st to 10th	Day	20% 11% 4 8% 5% 4 4 3 5% 5% 31%	4344
	11th to 20th	Day	11% 8% 2 8% 5% 5% 5% 4 7% 8% 37%	4377
	21st to end	Day	20% 11% 4 10% 6% 6% 6% 5% 6% 6% 20%	4813
June	1st to 10th	Day	22% 11% 3 7% 6% 5% 4 4 5% 6% 28%	2660
	11th to 20th	Day	17% 12% 4 9% 6% 6% 6% 4 7% 7% 22%	2772
	21st to end	Day	10% 8% 2 6% 5% 4 4 4 6% 8% 43%	2850
July	1st to 10th	Day	4 4 2 5% 3 3 3 3 4 5% 65%	4681
	11th to 20th	Day	5% 3 1 3 3 2 3 2 3 6% 68%	4420
	21st to end	Day	7% 4 2 4 3 3 3 3 4 6% 61%	4790
August	1st to 10th	Day	4 3 2 4 3 3 3 3 4 8% 63%	4107
	11th to 20th	Day	6% 5% 2 8% 5% 5% 5% 4 7% 8% 43%	4026
	21st to end	Day	9% 8% 3 6% 5% 4 4 4 5% 6% 47%	4344
September	1st to 10th	Day	6% 6% 2 5% 3 4 5% 4 6% 7% 53%	2280
	11th to 20th	Day	11% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	2257
	21st to end	Day	14% 9% 3 7% 4 4 4 4 4 7% 40%	2010
October	1st to 10th	Day	14% 7% 2 5% 4 4 4 3 6% 7% 45%	3180
	11th to 20th	Day	18% 9% 3 9% 5% 5% 5% 4 6% 7% 27%	3161
	21st to end	Day	19% 12% 4 9% 6% 5% 6% 4 5% 6% 24%	3391
November	1st to 10th	Day	24% 16% 5% 9% 6% 5% 5% 4 5% 5% 15%	1620
	11th to 20th	Day	26% 15% 4 9% 6% 5% 4 2 4 5% 19%	1520
	21st to end	Day	21% 14% 5% 10% 6% 5% 5% 4 4 3 23%	1520
December	1st to 10th	Day	21% 15% 4 9% 6% 6% 6% 3 4 4 22%	1520
	11th to 20th	Day	22% 16% 5% 11% 6% 7% 5% 3 5% 5% 16%	1925
	21st to end	Day	24% 19% 5% 13% 6% 6% 5% 3 4 4 11%	2794
January	1st to 10th	Night	27% 18% 4 11% 8% 6% 5% 4 4 3 10%	4406
	11th to 20th	Night	24% 18% 5% 11% 6% 4 4 3 4 4 18%	4382
	21st to end	Night	30% 18% 5% 9% 6% 4 3 3 4 4 13%	4600
February	1st to 10th	Night	19% 18% 5% 10% 8% 6% 5% 4 4 4 18%	2470
	11th to 20th	Night	19% 15% 5% 9% 6% 5% 5% 4 4 5% 23%	2402
	21st to end	Night	18% 18% 5% 10% 7% 5% 6% 3 4 5% 19%	1990
March	1st to 10th	Night	12% 16% 5% 13% 7% 7% 6% 4 4 5% 21%	3551
	11th to 20th	Night	14% 14% 3 8% 4 3 3 3 4 4 39%	3489
	21st to end	Night	20% 21% 5% 11% 5% 5% 5% 4 4 4 15%	3772
April	1st to 10th	Night	19% 16% 5% 10% 6% 5% 5% 3 4 5% 21%	1900
	11th to 20th	Night	16% 15% 3 9% 6% 5% 4 3 4 7% 27%	1847
	21st to end	Night	18% 12% 4 7% 4 4 4 4 5% 8% 29%	1710
May	1st to 10th	Night	18% 10% 3 6% 3 3 4 3 5% 6% 39%	2618
	11th to 20th	Night	8% 7% 2 5% 4 4 5% 4 7% 8% 44%	2516
	21st to end	Night	10% 11% 2 8% 6% 6% 6% 5% 7% 8% 32%	2762
June	1st to 10th	Night	15% 8% 4 7% 6% 4 4 4 5% 6% 37%	1520
	11th to 20th	Night	11% 11% 4 7% 4 4 5% 3 6% 9% 36%	1401
	21st to end	Night	6% 6% 2 5% 4 4 3 2 5% 7% 56%	1330
July	1st to 10th	Night	2 2 1 5% 2 3 2 3 4 5% 70%	2274
	11th to 20th	Night	3 3 1 3 3 2 2 2 4 5% 71%	2540
	21st to end	Night	2 2 2 5% 3 3 3 3 4 6% 68%	2762
August	1st to 10th	Night	2 2 1 3 2 2 3 2 5% 6% 73%	2816
	11th to 20th	Night	5% 5% 2 8% 3 4 3 3 5% 7% 55%	2812
	21st to end	Night	10% 5% 2 5% 3 3 2 3 5% 6% 56%	3328
September	1st to 10th	Night	5% 3 2 5% 3 3 3 3 5% 7% 61%	1900
	11th to 20th	Night	9% 5% 3 7% 5% 5% 4 3 5% 7% 48%	1919
	21st to end	Night	9% 6% 2 6% 5% 4 4 4 5% 8% 47%	2169
October	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 5% 7% 49%	3800
	11th to 20th	Night	15% 8% 3 7% 5% 5% 5% 4 6% 9% 34%	3777
	21st to end	Night	18% 9% 4 10% 5% 6% 5% 3 5% 5% 29%	4176
November	1st to 10th	Night	23% 12% 4 10% 6% 5% 5% 4 5% 5% 21%	2678
	11th to 20th	Night	25% 13% 4 9% 6% 6% 5% 3 4 5% 19%	2666
	21st to end	Night	20% 14% 4 9% 6% 5% 5% 4 4 4 26%	2660
December	1st to 10th	Night	19% 14% 5% 10% 6% 5% 5% 4 5% 5% 23%	2660
	11th to 20th	Night	21% 16% 5% 12% 7% 6% 4 3 4 5% 17%	3280
	21st to end	Night	23% 17% 6% 12% 6% 5% 5% 3 4 4 16%	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	80% 7% 7% 4 2	2539
	11th to 20th	Day	71% 5% 8% 11% 4 2	2540
	21st to end	Day	76% 6% 6% 7% 5%	3060
February	1st to 10th	Day	71% 6% 10% 10% 3	1710
	11th to 20th	Day	71% 7% 8% 9% 5%	1674
	21st to end	Day	73% 5% 9% 7% 5% 1	1462
March	1st to 10th	Day	68% 7% 12% 9% 4	3319
	11th to 20th	Day	55% 4 8% 26% 6%	3490
	21st to end	Day	71% 8% 11% 8% 3	3881
April	1st to 10th	Day	69% 6% 12% 10% 2	2280
	11th to 20th	Day	65% 6% 9% 11% 8% 2	2280
	21st to end	Day	63% 7% 11% 12% 6% 1	2470
May	1st to 10th	Day	51% 7% 13% 18% 12%	4344
	11th to 20th	Day	36% 9% 24% 22% 8% 1	4380
	21st to end	Day	60% 10% 17% 11% 2	4814
June	1st to 10th	Day	56% 6% 16% 14% 8%	2660
	11th to 20th	Day	57% 8% 16% 13% 5%	2772
	21st to end	Day	36% 8% 18% 25% 10% 3	2850
July	1st to 10th	Day	22% 5% 8% 16% 21% 29%	4608
	11th to 20th	Day	16% 3 7% 21% 36% 15%	4345
	21st to end	Day	20% 6% 11% 29% 30% 4	4639
August	1st to 10th	Day	19% 5% 10% 25% 29% 12%	4090
	11th to 20th	Day	32% 12% 16% 24% 12% 4	4065
	21st to end	Day	36% 7% 11% 22% 18% 6%	4343
September	1st to 10th	Day	28% 6% 13% 25% 19% 10%	2280
	11th to 20th	Day	41% 8% 14% 17% 15% 5%	2257
	21st to end	Day	42% 6% 14% 18% 15% 4	2010
October	1st to 10th	Day	36% 6% 9% 27% 20% 2	3180
	11th to 20th	Day	54% 7% 13% 14% 11% 1	3161
	21st to end	Day	59% 7% 9% 15% 9%	3391
November	1st to 10th	Day	71% 6% 10% 10% 3	1620
	11th to 20th	Day	69% 4 10% 8% 6% 2	1520
	21st to end	Day	65% 6% 7% 9% 12% 1	1520
December	1st to 10th	Day	66% 6% 7% 11% 9% 1	1520
	11th to 20th	Day	70% 5% 11% 11% 2	1928
	21st to end	Day	76% 6% 10% 5% 3	2794
January	1st to 10th	Night	75% 6% 10% 5% 3 1	4406
	11th to 20th	Night	69% 6% 8% 11% 4 2	4420
	21st to end	Night	75% 4 7% 7% 5% 1	4600
February	1st to 10th	Night	68% 8% 8% 11% 4	2470
	11th to 20th	Night	63% 7% 11% 11% 6% 2	2404
	21st to end	Night	65% 8% 10% 10% 6% 1	1990
March	1st to 10th	Night	63% 7% 13% 14% 3	3551
	11th to 20th	Night	46% 7% 14% 24% 8% 1	3490
	21st to end	Night	70% 7% 13% 9% 1	3772
April	1st to 10th	Night	65% 5% 14% 12% 4	1900
	11th to 20th	Night	56% 7% 13% 14% 8% 3	1847
	21st to end	Night	53% 7% 15% 17% 6% 1	1710
May	1st to 10th	Night	44% 5% 16% 25% 9% 1	2618
	11th to 20th	Night	28% 7% 25% 26% 12% 2	2516
	21st to end	Night	45% 12% 27% 13% 3	2762
June	1st to 10th	Night	46% 6% 18% 22% 7% 1	1520
	11th to 20th	Night	42% 8% 21% 23% 6%	1401
	21st to end	Night	27% 7% 21% 31% 11% 5%	1330
July	1st to 10th	Night	13% 7% 11% 19% 21% 30%	2238
	11th to 20th	Night	15% 3 9% 21% 31% 21%	2492
	21st to end	Night	12% 6% 13% 31% 30% 8%	2674
August	1st to 10th	Night	11% 4 12% 28% 31% 14%	2808
	11th to 20th	Night	22% 11% 24% 29% 10% 5%	2839
	21st to end	Night	28% 6% 17% 23% 21% 4	3328
September	1st to 10th	Night	22% 5% 14% 28% 21% 11%	1900
	11th to 20th	Night	35% 8% 15% 20% 15% 7%	1919
	21st to end	Night	33% 6% 16% 20% 18% 6%	2169
October	1st to 10th	Night	31% 6% 10% 31% 20% 2	3800
	11th to 20th	Night	46% 7% 16% 19% 10% 1	3777
	21st to end	Night	55% 7% 9% 17% 9% 1	4176
November	1st to 10th	Night	64% 7% 10% 13% 6%	2678
	11th to 20th	Night	66% 6% 10% 10% 7% 2	2666
	21st to end	Night	60% 6% 9% 10% 13% 2	2660
December	1st to 10th	Night	62% 7% 10% 12% 9% 1	2660
	11th to 20th	Night	69% 7% 9% 9% 6%	3276
	21st to end	Night	70% 7% 13% 8% 2	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	38% 16% 27% 10% 7% 2	180
	11th to 20th	Day	34% 17% 28% 11% 7% 3	180
	21st to end	Day	33% 12% 22% 22% 9% 2	360
February	1st to 10th	Day	39% 14% 20% 16% 10% 1	370
	11th to 20th	Day	39% 16% 26% 15% 4 1	365
	21st to end	Day	38% 19% 21% 17% 5% 1	332
March	1st to 10th	Day	35% 15% 29% 15% 7%	460
	11th to 20th	Day	31% 15% 26% 17% 8% 3	460
	21st to end	Day	36% 18% 19% 19% 7% 1	506
April	1st to 10th	Day	35% 14% 23% 15% 10% 3	460
	11th to 20th	Day	31% 16% 26% 17% 7% 3	452
	21st to end	Day	30% 15% 28% 17% 7% 2	460
May	1st to 10th	Day	20% 16% 27% 23% 10% 3	463
	11th to 20th	Day	25% 11% 27% 22% 11% 3	488
	21st to end	Day	22% 11% 27% 23% 13% 3	529
June	1st to 10th	Day	24% 11% 25% 27% 12% 2	490
	11th to 20th	Day	20% 18% 34% 21% 6% 1	602
	21st to end	Day	10% 11% 34% 32% 11% 2	680
July	1st to 10th	Day	9% 8% 33% 36% 11% 3	639
	11th to 20th	Day	7% 9% 30% 37% 13% 4	484
	21st to end	Day	6% 5% 26% 41% 17% 4	531
August	1st to 10th	Day	8% 6% 23% 39% 18% 6%	487
	11th to 20th	Day	5% 4 23% 38% 22% 7%	477
	21st to end	Day	11% 8% 29% 32% 16% 5%	539
September	1st to 10th	Day	9% 9% 26% 36% 16% 4	490
	11th to 20th	Day	15% 9% 25% 30% 17% 4	490
	21st to end	Day	18% 13% 24% 28% 14% 3	490
October	1st to 10th	Day	21% 13% 22% 23% 19% 3	490
	11th to 20th	Day	25% 11% 24% 20% 17% 3	490
	21st to end	Day	32% 12% 25% 19% 9% 4	506
November	1st to 10th	Day	33% 18% 24% 15% 9% 1	227
	11th to 20th	Day	31% 14% 28% 17% 9% 2	180
	21st to end	Day	24% 18% 28% 21% 8% 1	180
December	1st to 10th	Day	32% 17% 24% 16% 9% 3	180
	11th to 20th	Day	37% 12% 26% 21% 4	180
	21st to end	Day	36% 17% 23% 16% 7% 1	198
January	1st to 10th	Night	37% 12% 21% 17% 11% 2	760
	11th to 20th	Night	35% 11% 20% 18% 15% 1	760
	21st to end	Night	31% 7% 18% 28% 14% 2	836
February	1st to 10th	Night	28% 11% 23% 25% 12% 1	760
	11th to 20th	Night	28% 9% 21% 27% 15%	744
	21st to end	Night	28% 12% 23% 27% 10%	628
March	1st to 10th	Night	27% 10% 23% 25% 13% 1	760
	11th to 20th	Night	28% 10% 19% 29% 13% 1	760
	21st to end	Night	31% 11% 21% 26% 10% 1	836
April	1st to 10th	Night	28% 13% 19% 26% 13% 1	760
	11th to 20th	Night	25% 9% 24% 29% 11% 2	719
	21st to end	Night	24% 8% 22% 31% 14% 1	570
May	1st to 10th	Night	17% 8% 27% 32% 15% 1	432
	11th to 20th	Night	17% 6% 22% 34% 20% 1	374
	21st to end	Night	16% 7% 25% 34% 18%	411
June	1st to 10th	Night	19% 3 27% 39% 11%	380
	11th to 20th	Night	15% 8% 28% 36% 12% 1	380
	21st to end	Night	10% 6% 24% 44% 15% 1	380
July	1st to 10th	Night	4 3 28% 49% 16%	370
	11th to 20th	Night	5% 5% 33% 41% 15% 1	368
	21st to end	Night	3 2 29% 47% 18%	416
August	1st to 10th	Night	5% 3 16% 45% 27% 3	548
	11th to 20th	Night	6% 3 14% 43% 31% 4	564
	21st to end	Night	10% 5% 23% 39% 22% 2	731
September	1st to 10th	Night	7% 5% 19% 45% 22% 1	760
	11th to 20th	Night	11% 3 17% 35% 28% 6%	760
	21st to end	Night	13% 6% 19% 37% 22% 2	760
October	1st to 10th	Night	18% 4 18% 36% 21% 3	760
	11th to 20th	Night	21% 7% 17% 29% 23% 4	760
	21st to end	Night	27% 9% 19% 25% 17% 2	836
November	1st to 10th	Night	28% 10% 21% 27% 13% 1	780
	11th to 20th	Night	32% 12% 20% 24% 11% 1	762
	21st to end	Night	26% 11% 22% 27% 13% 1	760
December	1st to 10th	Night	27% 9% 23% 25% 14% 2	760
	11th to 20th	Night	34% 12% 22% 21% 11% 1	760
	21st to end	Night	37% 14% 23% 17% 8% 1	836

Page generated at 2024-11-08 03:44:45. Version ac07

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