Vernon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vernon clear sky chart from 2005-11-06 to 2025-11-18.

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	7% 8% 3 8% 5% 5% 5% 4 6% 8% 39%	131035
	Night	8% 10% 4 9% 6% 5% 5% 4 6% 7% 35%	127976
Transparency	Day	40% 11% 17% 21% 9% 2	130751
	Night	45% 11% 17% 18% 8% 1	127837
Seeing	Day	13% 13% 27% 28% 16% 4	16860
	Night	14% 9% 24% 32% 18% 2	25231

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	9% 16% 7% 13% 8% 8% 6% 4 6% 6% 17%	3321
	11th to 20th	Day	7% 11% 3 9% 6% 6% 6% 5% 7% 10% 32%	3616
	21st to end	Day	6% 12% 4 11% 8% 6% 7% 5% 7% 8% 26%	4004
February	1st to 10th	Day	8% 14% 4 13% 8% 7% 6% 4 6% 5% 24%	1615
	11th to 20th	Day	7% 13% 4 12% 7% 6% 5% 4 6% 6% 30%	1755
	21st to end	Day	7% 14% 5% 9% 8% 7% 7% 4 8% 8% 23%	1635
March	1st to 10th	Day	3 8% 4 10% 7% 7% 7% 6% 9% 10% 29%	4518
	11th to 20th	Day	4 9% 3 7% 6% 6% 7% 5% 7% 9% 38%	4728
	21st to end	Day	8% 13% 4 9% 6% 6% 6% 5% 7% 8% 28%	5940
April	1st to 10th	Day	8% 13% 5% 9% 7% 6% 6% 4 7% 8% 27%	2400
	11th to 20th	Day	7% 11% 3 9% 7% 6% 5% 5% 7% 7% 33%	2411
	21st to end	Day	8% 10% 3 9% 5% 6% 6% 4 7% 9% 32%	2735
May	1st to 10th	Day	6% 7% 3 8% 5% 4 5% 4 6% 7% 45%	6320
	11th to 20th	Day	8% 9% 3 8% 6% 6% 6% 6% 8% 10% 30%	6277
	21st to end	Day	11% 9% 3 8% 6% 5% 5% 4 6% 8% 35%	7119
June	1st to 10th	Day	13% 7% 3 8% 6% 5% 5% 4 6% 7% 34%	3041
	11th to 20th	Day	14% 8% 3 8% 6% 6% 7% 6% 6% 7% 29%	3200
	21st to end	Day	9% 6% 2 6% 6% 6% 5% 4 7% 8% 42%	3200
July	1st to 10th	Day	4 3 1 4 3 3 4 3 5% 7% 62%	7062
	11th to 20th	Day	4 2 1 3 3 3 3 3 5% 7% 67%	6418
	21st to end	Day	3 3 1 3 3 3 4 3 6% 9% 61%	6874
August	1st to 10th	Day	2 2 1 3 3 4 4 5% 7% 8% 61%	4541
	11th to 20th	Day	3 3 1 4 4 4 5% 4 7% 9% 56%	4470
	21st to end	Day	7% 4 2 5% 4 5% 4 4 7% 8% 51%	4386
September	1st to 10th	Day	6% 4 1 5% 5% 4 4 3 5% 9% 54%	2400
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	2370
	21st to end	Day	10% 8% 3 7% 5% 6% 5% 4 6% 8% 39%	2195
October	1st to 10th	Day	7% 8% 3 8% 6% 5% 5% 3 5% 8% 41%	3280
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 3 5% 7% 35%	3131
	21st to end	Day	10% 9% 3 9% 6% 5% 5% 4 7% 7% 35%	3200
November	1st to 10th	Day	13% 13% 4 11% 7% 6% 6% 5% 7% 6% 23%	1755
	11th to 20th	Day	9% 12% 5% 11% 8% 6% 7% 6% 6% 6% 25%	1656
	21st to end	Day	9% 14% 4 13% 8% 7% 7% 5% 7% 7% 18%	1418
December	1st to 10th	Day	6% 9% 4 10% 8% 7% 7% 6% 7% 8% 29%	2290
	11th to 20th	Day	8% 16% 7% 13% 9% 7% 6% 4 7% 7% 17%	2642
	21st to end	Day	8% 14% 4 13% 8% 8% 6% 5% 6% 7% 18%	3112
January	1st to 10th	Night	10% 20% 6% 14% 8% 7% 6% 5% 5% 6% 12%	6631
	11th to 20th	Night	6% 11% 4 12% 7% 6% 6% 5% 6% 8% 30%	6282
	21st to end	Night	7% 13% 5% 12% 8% 6% 6% 4 6% 8% 26%	6952
February	1st to 10th	Night	11% 16% 5% 11% 8% 6% 6% 5% 6% 6% 20%	2783
	11th to 20th	Night	9% 14% 4 11% 6% 5% 5% 4 5% 7% 31%	2532
	21st to end	Night	8% 16% 5% 11% 7% 5% 5% 5% 5% 7% 27%	1995
March	1st to 10th	Night	4 9% 4 9% 6% 6% 6% 5% 7% 10% 35%	5376
	11th to 20th	Night	4 10% 4 8% 6% 5% 5% 5% 6% 8% 39%	5268
	21st to end	Night	6% 10% 4 11% 6% 7% 6% 5% 7% 8% 29%	5034
April	1st to 10th	Night	7% 9% 4 7% 6% 7% 5% 6% 6% 9% 35%	2000
	11th to 20th	Night	9% 9% 4 9% 7% 7% 6% 5% 7% 6% 33%	1940
	21st to end	Night	9% 8% 4 7% 5% 6% 6% 4 6% 7% 39%	1662
May	1st to 10th	Night	5% 7% 3 9% 6% 6% 6% 4 5% 6% 42%	3640
	11th to 20th	Night	7% 8% 3 8% 5% 6% 6% 4 7% 9% 37%	3616
	21st to end	Night	8% 6% 2 7% 4 5% 6% 4 6% 8% 43%	3752
June	1st to 10th	Night	10% 8% 3 6% 6% 5% 6% 5% 6% 9% 37%	1355
	11th to 20th	Night	13% 6% 3 8% 6% 4 5% 5% 8% 8% 34%	1200
	21st to end	Night	5% 6% 2 7% 5% 4 6% 6% 7% 9% 43%	1200
July	1st to 10th	Night	5% 3 1 4 3 5% 4 4 6% 7% 57%	2894
	11th to 20th	Night	3 3 1 4 3 3 3 3 4 6% 66%	3538
	21st to end	Night	4 3 1 4 3 3 4 3 5% 8% 62%	3969
August	1st to 10th	Night	2 1 1 3 2 4 4 3 8% 11% 60%	2609
	11th to 20th	Night	3 2 1 6% 4 4 5% 4 6% 10% 55%	2577
	21st to end	Night	6% 4 2 6% 3 4 4 4 6% 8% 52%	3530
September	1st to 10th	Night	5% 3 2 4 4 4 4 3 6% 7% 57%	2000
	11th to 20th	Night	8% 5% 3 4 4 4 4 4 5% 7% 52%	2030
	21st to end	Night	9% 6% 3 8% 4 4 5% 3 5% 7% 46%	2203
October	1st to 10th	Night	7% 7% 3 7% 5% 5% 5% 4 6% 7% 44%	3920
	11th to 20th	Night	16% 8% 2 6% 4 4 3 3 5% 7% 41%	4022
	21st to end	Night	9% 10% 3 9% 6% 5% 5% 3 5% 6% 38%	4600
November	1st to 10th	Night	14% 13% 4 10% 6% 5% 5% 4 6% 7% 24%	2760
	11th to 20th	Night	12% 13% 3 11% 8% 8% 6% 5% 5% 6% 24%	2898
	21st to end	Night	10% 16% 5% 12% 7% 6% 6% 5% 7% 7% 20%	2960
December	1st to 10th	Night	8% 10% 3 9% 6% 5% 5% 4 7% 9% 33%	4890
	11th to 20th	Night	10% 19% 6% 14% 9% 7% 5% 4 5% 5% 15%	5550
	21st to end	Night	10% 15% 5% 14% 9% 8% 6% 4 5% 5% 18%	7808

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% 19% 13% 6% 1	3321
	11th to 20th	Day	43% 12% 26% 14% 3 2	3640
	21st to end	Day	55% 14% 17% 11% 3	4004
February	1st to 10th	Day	60% 11% 13% 9% 5% 1	1615
	11th to 20th	Day	53% 14% 16% 12% 5% 1	1764
	21st to end	Day	55% 15% 16% 11% 3	1635
March	1st to 10th	Day	45% 14% 17% 18% 7%	4518
	11th to 20th	Day	39% 11% 18% 26% 5%	4728
	21st to end	Day	51% 11% 15% 16% 6%	5940
April	1st to 10th	Day	52% 14% 16% 15% 3	2400
	11th to 20th	Day	49% 10% 15% 17% 7% 1	2411
	21st to end	Day	48% 11% 16% 17% 7%	2735
May	1st to 10th	Day	35% 10% 12% 27% 15% 1	6320
	11th to 20th	Day	42% 14% 18% 21% 5%	6280
	21st to end	Day	42% 13% 20% 22% 4	7120
June	1st to 10th	Day	47% 12% 13% 15% 10% 2	3041
	11th to 20th	Day	52% 12% 12% 17% 7% 1	3200
	21st to end	Day	38% 12% 18% 19% 12% 2	3200
July	1st to 10th	Day	21% 7% 13% 26% 23% 10%	6986
	11th to 20th	Day	19% 6% 17% 27% 22% 10%	6340
	21st to end	Day	20% 6% 22% 32% 17% 5%	6681
August	1st to 10th	Day	18% 8% 12% 37% 21% 3	4524
	11th to 20th	Day	24% 8% 26% 30% 11% 2	4512
	21st to end	Day	30% 9% 22% 29% 9% 1	4385
September	1st to 10th	Day	27% 10% 17% 31% 13% 3	2400
	11th to 20th	Day	34% 11% 15% 26% 13% 1	2370
	21st to end	Day	42% 10% 22% 18% 8% 1	2195
October	1st to 10th	Day	41% 8% 25% 22% 4	3280
	11th to 20th	Day	49% 8% 15% 25% 3	3131
	21st to end	Day	45% 11% 25% 16% 3	3200
November	1st to 10th	Day	59% 13% 13% 12% 3	1755
	11th to 20th	Day	59% 14% 15% 8% 3 1	1656
	21st to end	Day	61% 15% 16% 7% 1	1418
December	1st to 10th	Day	50% 16% 24% 11%	2290
	11th to 20th	Day	62% 14% 15% 8% 2	2644
	21st to end	Day	59% 13% 18% 10% 1	3112
January	1st to 10th	Night	64% 16% 13% 6% 1	6631
	11th to 20th	Night	49% 12% 21% 12% 5% 1	6320
	21st to end	Night	54% 14% 18% 13% 1	6952
February	1st to 10th	Night	61% 11% 13% 10% 5% 1	2783
	11th to 20th	Night	52% 10% 16% 16% 5% 1	2534
	21st to end	Night	55% 11% 16% 12% 6%	1995
March	1st to 10th	Night	40% 12% 19% 22% 6%	5376
	11th to 20th	Night	40% 10% 20% 21% 9%	5269
	21st to end	Night	49% 13% 15% 17% 6%	5034
April	1st to 10th	Night	42% 16% 21% 16% 5%	2000
	11th to 20th	Night	49% 11% 14% 18% 7% 1	1940
	21st to end	Night	43% 12% 14% 22% 9%	1662
May	1st to 10th	Night	38% 10% 10% 23% 18% 1	3637
	11th to 20th	Night	37% 14% 19% 25% 5%	3616
	21st to end	Night	34% 13% 20% 26% 6% 1	3752
June	1st to 10th	Night	43% 12% 13% 19% 10% 4	1355
	11th to 20th	Night	46% 10% 13% 20% 11%	1200
	21st to end	Night	33% 13% 19% 22% 11% 2	1200
July	1st to 10th	Night	24% 7% 13% 23% 20% 13%	2861
	11th to 20th	Night	20% 6% 16% 24% 25% 9%	3493
	21st to end	Night	21% 5% 16% 34% 17% 7%	3857
August	1st to 10th	Night	17% 6% 12% 37% 25% 3	2601
	11th to 20th	Night	25% 7% 23% 29% 15% 2	2601
	21st to end	Night	29% 8% 23% 25% 13% 2	3530
September	1st to 10th	Night	25% 10% 16% 29% 17% 3	2000
	11th to 20th	Night	30% 10% 14% 25% 18% 3	2030
	21st to end	Night	38% 9% 18% 24% 10% 2	2203
October	1st to 10th	Night	38% 10% 21% 23% 8%	3920
	11th to 20th	Night	43% 8% 18% 24% 7%	4022
	21st to end	Night	47% 8% 18% 24% 3	4600
November	1st to 10th	Night	57% 13% 14% 12% 4	2760
	11th to 20th	Night	59% 14% 12% 10% 5%	2898
	21st to end	Night	60% 14% 15% 8% 2	2960
December	1st to 10th	Night	46% 13% 26% 13% 2	4890
	11th to 20th	Night	67% 12% 14% 7% 1	5547
	21st to end	Night	60% 13% 16% 10% 1	7808

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	17% 12% 26% 25% 13% 8%	200
	11th to 20th	Day	14% 8% 33% 24% 19% 4	200
	21st to end	Day	16% 8% 29% 31% 14% 3	220
February	1st to 10th	Day	15% 19% 34% 22% 7% 2	215
	11th to 20th	Day	12% 17% 32% 27% 9% 2	395
	21st to end	Day	14% 17% 28% 28% 11% 2	407
March	1st to 10th	Day	13% 21% 28% 25% 10% 2	500
	11th to 20th	Day	13% 19% 26% 25% 13% 3	500
	21st to end	Day	17% 20% 27% 18% 16% 2	550
April	1st to 10th	Day	19% 21% 27% 21% 10% 1	500
	11th to 20th	Day	18% 20% 25% 21% 11% 4	492
	21st to end	Day	13% 19% 29% 24% 10% 5%	500
May	1st to 10th	Day	10% 17% 33% 25% 11% 3	503
	11th to 20th	Day	13% 12% 24% 28% 19% 5%	528
	21st to end	Day	15% 12% 23% 28% 18% 5%	659
June	1st to 10th	Day	16% 12% 28% 29% 13% 1	771
	11th to 20th	Day	15% 13% 28% 28% 14% 2	930
	21st to end	Day	11% 11% 25% 30% 20% 4	930
July	1st to 10th	Day	9% 9% 22% 35% 22% 2	845
	11th to 20th	Day	5% 10% 26% 32% 22% 4	567
	21st to end	Day	5% 7% 25% 33% 24% 7%	575
August	1st to 10th	Day	4 7% 21% 35% 23% 9%	527
	11th to 20th	Day	7% 7% 25% 33% 21% 8%	517
	21st to end	Day	9% 9% 23% 31% 21% 7%	583
September	1st to 10th	Day	9% 11% 22% 31% 22% 6%	530
	11th to 20th	Day	10% 11% 24% 30% 21% 4	530
	21st to end	Day	18% 14% 28% 25% 13% 3	530
October	1st to 10th	Day	15% 12% 26% 27% 16% 4	530
	11th to 20th	Day	17% 14% 28% 23% 14% 3	451
	21st to end	Day	21% 11% 32% 24% 10% 1	363
November	1st to 10th	Day	19% 14% 31% 24% 10% 1	278
	11th to 20th	Day	15% 20% 29% 22% 12% 3	214
	21st to end	Day	15% 13% 29% 24% 15% 6%	200
December	1st to 10th	Day	16% 9% 21% 26% 23% 6%	200
	11th to 20th	Day	19% 10% 32% 24% 12% 5%	200
	21st to end	Day	16% 7% 26% 35% 10% 5%	220
January	1st to 10th	Night	22% 12% 27% 26% 11% 2	883
	11th to 20th	Night	17% 9% 28% 31% 14% 1	800
	21st to end	Night	15% 9% 28% 30% 15% 3	880
February	1st to 10th	Night	20% 11% 25% 31% 11% 2	800
	11th to 20th	Night	16% 9% 27% 34% 13% 1	784
	21st to end	Night	16% 10% 25% 28% 18% 3	660
March	1st to 10th	Night	15% 12% 25% 30% 17% 2	800
	11th to 20th	Night	13% 11% 28% 32% 15% 1	800
	21st to end	Night	13% 10% 27% 32% 16% 3	880
April	1st to 10th	Night	12% 12% 26% 30% 18% 2	800
	11th to 20th	Night	15% 10% 28% 30% 16% 1	752
	21st to end	Night	12% 10% 28% 32% 15% 2	462
May	1st to 10th	Night	13% 10% 20% 36% 20% 1	400
	11th to 20th	Night	12% 5% 20% 39% 22% 2	394
	21st to end	Night	14% 7% 20% 30% 25% 3	433
June	1st to 10th	Night	15% 6% 29% 35% 15% 1	400
	11th to 20th	Night	14% 7% 26% 32% 19% 2	400
	21st to end	Night	8% 6% 22% 39% 22% 3	400
July	1st to 10th	Night	8% 6% 15% 37% 31% 2	390
	11th to 20th	Night	4 6% 22% 35% 31% 2	388
	21st to end	Night	6% 2 16% 41% 33% 3	438
August	1st to 10th	Night	5% 2 14% 36% 35% 8%	398
	11th to 20th	Night	5% 2 13% 40% 34% 6%	396
	21st to end	Night	6% 4 18% 40% 29% 2	828
September	1st to 10th	Night	7% 5% 17% 40% 27% 5%	800
	11th to 20th	Night	11% 5% 17% 30% 31% 7%	800
	21st to end	Night	15% 8% 22% 33% 19% 4	800
October	1st to 10th	Night	12% 5% 22% 36% 22% 3	800
	11th to 20th	Night	17% 9% 22% 29% 20% 2	800
	21st to end	Night	18% 10% 27% 30% 13% 3	880
November	1st to 10th	Night	22% 11% 24% 33% 8% 1	820
	11th to 20th	Night	20% 14% 26% 26% 12% 2	828
	21st to end	Night	17% 10% 27% 30% 13% 3	960
December	1st to 10th	Night	14% 9% 28% 32% 14% 2	1000
	11th to 20th	Night	18% 10% 30% 31% 11% 1	1000
	21st to end	Night	20% 10% 29% 31% 9% 1	1177

Page generated at 2025-11-14 21:55:54. Version ac07

Copyright © 2025 Attilla Danko.