Vanderhoof
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vanderhoof clear sky chart from 2005-11-06 to 2025-03-27.

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	11% 11% 4 9% 6% 5% 5% 4 6% 7% 31%	111836
	Night	12% 14% 4 10% 6% 5% 5% 4 6% 6% 27%	116128
Transparency	Day	49% 9% 15% 19% 7% 1	111575
	Night	54% 9% 14% 16% 6% 1	116035
Seeing	Day	17% 12% 26% 26% 15% 4	16808
	Night	19% 11% 25% 28% 15% 2	24816

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% 19% 7% 16% 8% 7% 5% 3 5% 5% 16%	3115
	11th to 20th	Day	10% 14% 5% 10% 7% 6% 5% 4 6% 6% 28%	3159
	21st to end	Day	10% 25% 5% 10% 6% 5% 3 2 4 6% 24%	3498
February	1st to 10th	Day	13% 15% 4 10% 7% 6% 4 3 7% 5% 25%	1603
	11th to 20th	Day	9% 16% 5% 10% 6% 5% 4 4 6% 7% 26%	1755
	21st to end	Day	7% 17% 6% 12% 8% 4 5% 4 5% 6% 27%	1485
March	1st to 10th	Day	6% 13% 4 11% 8% 6% 6% 5% 7% 7% 26%	3238
	11th to 20th	Day	6% 14% 5% 10% 6% 7% 7% 5% 8% 8% 24%	3600
	21st to end	Day	6% 11% 4 8% 6% 5% 5% 4 6% 7% 38%	3978
April	1st to 10th	Day	9% 14% 5% 12% 8% 6% 6% 4 6% 6% 24%	2323
	11th to 20th	Day	11% 14% 5% 10% 6% 5% 6% 3 5% 6% 28%	2438
	21st to end	Day	13% 14% 4 9% 6% 6% 5% 5% 6% 7% 27%	2608
May	1st to 10th	Day	8% 11% 3 9% 6% 5% 6% 5% 8% 8% 33%	4420
	11th to 20th	Day	12% 11% 4 9% 7% 7% 6% 5% 7% 7% 25%	4682
	21st to end	Day	11% 11% 4 11% 8% 7% 6% 5% 6% 7% 24%	5284
June	1st to 10th	Day	12% 9% 3 9% 7% 7% 6% 5% 6% 8% 29%	3040
	11th to 20th	Day	15% 8% 3 8% 7% 6% 6% 4 7% 7% 29%	3040
	21st to end	Day	11% 7% 4 8% 6% 7% 5% 5% 6% 7% 34%	3040
July	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 6% 7% 52%	4969
	11th to 20th	Day	8% 4 1 4 4 4 4 4 6% 8% 54%	4740
	21st to end	Day	11% 6% 3 8% 6% 6% 7% 5% 7% 8% 34%	5138
August	1st to 10th	Day	4 4 2 4 3 3 4 3 6% 8% 58%	4597
	11th to 20th	Day	11% 7% 2 5% 4 4 5% 4 7% 8% 44%	4180
	21st to end	Day	14% 6% 3 8% 5% 6% 5% 5% 7% 8% 34%	4521
September	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 5% 7% 7% 38%	2323
	11th to 20th	Day	11% 8% 3 7% 6% 5% 5% 4 6% 8% 36%	2243
	21st to end	Day	17% 10% 4 8% 5% 5% 5% 4 7% 7% 27%	2024
October	1st to 10th	Day	17% 14% 5% 10% 6% 6% 5% 4 6% 7% 21%	3180
	11th to 20th	Day	14% 13% 4 9% 5% 5% 5% 4 7% 9% 24%	3161
	21st to end	Day	14% 15% 4 9% 4 5% 4 4 6% 7% 29%	2807
November	1st to 10th	Day	20% 16% 2 10% 5% 5% 4 3 5% 6% 24%	1568
	11th to 20th	Day	13% 17% 6% 13% 6% 6% 6% 4 6% 7% 18%	1600
	21st to end	Day	14% 19% 5% 11% 6% 7% 6% 4 6% 5% 16%	1265
December	1st to 10th	Day	21% 19% 4 9% 6% 4 5% 3 6% 5% 18%	1960
	11th to 20th	Day	13% 19% 7% 16% 7% 6% 5% 3 6% 5% 13%	2262
	21st to end	Day	8% 19% 7% 13% 6% 6% 6% 4 5% 5% 20%	2992
January	1st to 10th	Night	9% 18% 7% 15% 7% 6% 6% 4 6% 6% 16%	6858
	11th to 20th	Night	11% 14% 4 10% 7% 6% 6% 4 5% 6% 27%	6739
	21st to end	Night	15% 20% 5% 9% 5% 5% 5% 3 4 7% 23%	7458
February	1st to 10th	Night	14% 17% 5% 11% 7% 5% 5% 3 5% 4 24%	2794
	11th to 20th	Night	11% 14% 5% 9% 6% 5% 5% 4 5% 8% 27%	2532
	21st to end	Night	9% 15% 5% 10% 7% 5% 5% 4 5% 5% 29%	2145
March	1st to 10th	Night	6% 15% 5% 13% 7% 6% 6% 5% 5% 6% 27%	3850
	11th to 20th	Night	8% 14% 5% 10% 7% 6% 6% 5% 6% 6% 26%	3599
	21st to end	Night	7% 11% 3 8% 4 4 4 4 6% 7% 43%	3812
April	1st to 10th	Night	7% 14% 5% 10% 6% 6% 5% 5% 6% 6% 28%	1856
	11th to 20th	Night	9% 12% 4 11% 6% 7% 6% 5% 7% 8% 27%	1691
	21st to end	Night	10% 13% 3 8% 6% 5% 4 4 6% 6% 34%	1572
May	1st to 10th	Night	11% 10% 4 8% 6% 6% 5% 5% 6% 7% 31%	2540
	11th to 20th	Night	16% 12% 4 10% 6% 5% 6% 5% 8% 6% 22%	2209
	21st to end	Night	17% 13% 4 10% 6% 7% 6% 4 6% 6% 23%	2289
June	1st to 10th	Night	14% 10% 3 8% 6% 6% 7% 5% 7% 5% 28%	1140
	11th to 20th	Night	15% 8% 4 8% 7% 6% 6% 4 7% 6% 27%	1140
	21st to end	Night	11% 7% 3 8% 4 5% 7% 6% 8% 9% 31%	1140
July	1st to 10th	Night	8% 6% 2 6% 5% 4 4 3 5% 7% 50%	1987
	11th to 20th	Night	8% 3 1 5% 4 4 4 4 6% 8% 52%	2220
	21st to end	Night	14% 6% 2 7% 5% 5% 4 4 6% 7% 39%	2414
August	1st to 10th	Night	4 3 1 2 3 2 3 3 5% 6% 67%	2332
	11th to 20th	Night	10% 6% 2 6% 5% 4 5% 4 6% 8% 44%	2650
	21st to end	Night	16% 8% 4 8% 5% 5% 6% 5% 6% 6% 31%	3146
September	1st to 10th	Night	13% 8% 3 8% 5% 4 5% 4 6% 8% 37%	1857
	11th to 20th	Night	11% 9% 3 7% 6% 4 4 4 4 7% 40%	1933
	21st to end	Night	18% 9% 3 8% 5% 6% 5% 4 5% 7% 30%	2156
October	1st to 10th	Night	19% 15% 5% 9% 5% 4 5% 4 5% 6% 23%	3800
	11th to 20th	Night	14% 12% 5% 11% 5% 5% 6% 4 6% 7% 25%	3777
	21st to end	Night	14% 14% 4 9% 5% 5% 5% 4 6% 6% 28%	4740
November	1st to 10th	Night	18% 15% 4 8% 5% 6% 5% 4 6% 6% 22%	2730
	11th to 20th	Night	13% 18% 4 11% 7% 5% 5% 4 5% 6% 21%	2800
	21st to end	Night	10% 21% 6% 12% 6% 6% 5% 4 5% 6% 20%	3108
December	1st to 10th	Night	18% 18% 4 9% 6% 4 5% 4 5% 6% 22%	5220
	11th to 20th	Night	15% 21% 6% 12% 7% 5% 4 4 5% 6% 14%	5930
	21st to end	Night	8% 18% 6% 13% 7% 6% 6% 5% 6% 7% 18%	7964

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	64% 11% 13% 8% 4	3115
	11th to 20th	Day	57% 7% 15% 11% 7% 4	3180
	21st to end	Day	62% 7% 13% 14% 4	3498
February	1st to 10th	Day	58% 7% 13% 11% 9% 2	1603
	11th to 20th	Day	55% 9% 16% 14% 5% 1	1764
	21st to end	Day	57% 7% 12% 15% 7% 2	1485
March	1st to 10th	Day	52% 10% 11% 15% 12%	3238
	11th to 20th	Day	51% 11% 15% 18% 6%	3600
	21st to end	Day	44% 8% 14% 21% 11% 1	3978
April	1st to 10th	Day	58% 9% 11% 16% 5%	2323
	11th to 20th	Day	58% 7% 11% 17% 7%	2438
	21st to end	Day	55% 7% 12% 17% 8%	2608
May	1st to 10th	Day	44% 10% 18% 20% 7% 1	4420
	11th to 20th	Day	53% 9% 13% 16% 8% 1	4685
	21st to end	Day	54% 9% 14% 16% 5% 1	5285
June	1st to 10th	Day	52% 8% 15% 17% 8% 1	3040
	11th to 20th	Day	52% 10% 14% 19% 5%	3040
	21st to end	Day	47% 10% 15% 20% 7%	3040
July	1st to 10th	Day	30% 7% 12% 27% 23% 1	4892
	11th to 20th	Day	28% 6% 23% 34% 8%	4659
	21st to end	Day	43% 10% 16% 20% 10% 1	4976
August	1st to 10th	Day	24% 8% 18% 38% 13%	4579
	11th to 20th	Day	37% 9% 17% 30% 7%	4222
	21st to end	Day	46% 9% 23% 19% 2	4520
September	1st to 10th	Day	42% 11% 22% 20% 5%	2323
	11th to 20th	Day	44% 10% 17% 24% 6%	2243
	21st to end	Day	53% 10% 16% 16% 4 1	2024
October	1st to 10th	Day	60% 9% 15% 12% 4	3180
	11th to 20th	Day	54% 10% 17% 16% 3	3161
	21st to end	Day	52% 8% 19% 16% 5%	2807
November	1st to 10th	Day	61% 9% 13% 12% 5%	1568
	11th to 20th	Day	63% 10% 13% 10% 4	1600
	21st to end	Day	67% 8% 11% 11% 3	1265
December	1st to 10th	Day	64% 11% 13% 10% 2	1960
	11th to 20th	Day	69% 9% 10% 8% 3	2264
	21st to end	Day	60% 9% 12% 14% 5%	2992
January	1st to 10th	Night	63% 10% 13% 11% 3	6858
	11th to 20th	Night	55% 9% 14% 9% 9% 4	6780
	21st to end	Night	61% 9% 16% 11% 3	7458
February	1st to 10th	Night	62% 7% 10% 10% 10% 1	2794
	11th to 20th	Night	56% 6% 16% 15% 7%	2534
	21st to end	Night	54% 7% 12% 18% 7% 2	2145
March	1st to 10th	Night	53% 9% 12% 14% 12% 1	3850
	11th to 20th	Night	53% 9% 13% 18% 7%	3600
	21st to end	Night	38% 8% 12% 26% 16%	3812
April	1st to 10th	Night	52% 9% 14% 17% 7%	1856
	11th to 20th	Night	52% 9% 13% 19% 8%	1691
	21st to end	Night	48% 8% 13% 21% 10%	1572
May	1st to 10th	Night	45% 9% 18% 21% 7%	2540
	11th to 20th	Night	52% 12% 15% 16% 5% 1	2209
	21st to end	Night	56% 10% 10% 20% 4	2289
June	1st to 10th	Night	51% 12% 11% 17% 9% 1	1140
	11th to 20th	Night	53% 8% 15% 18% 7%	1140
	21st to end	Night	45% 12% 18% 20% 6%	1140
July	1st to 10th	Night	32% 7% 10% 27% 23% 1	1955
	11th to 20th	Night	28% 7% 20% 38% 6%	2178
	21st to end	Night	39% 10% 22% 16% 13%	2337
August	1st to 10th	Night	18% 6% 17% 43% 17%	2325
	11th to 20th	Night	35% 10% 18% 31% 7%	2674
	21st to end	Night	50% 10% 22% 15% 2	3146
September	1st to 10th	Night	44% 10% 17% 23% 6% 1	1857
	11th to 20th	Night	41% 8% 15% 26% 8% 1	1933
	21st to end	Night	53% 8% 13% 19% 6%	2156
October	1st to 10th	Night	59% 8% 14% 15% 4	3800
	11th to 20th	Night	55% 8% 15% 18% 4	3777
	21st to end	Night	53% 8% 18% 17% 4	4740
November	1st to 10th	Night	61% 8% 12% 13% 4	2730
	11th to 20th	Night	61% 9% 14% 11% 5%	2800
	21st to end	Night	62% 9% 13% 10% 5%	3108
December	1st to 10th	Night	62% 7% 16% 13% 2	5220
	11th to 20th	Night	68% 10% 10% 9% 4	5927
	21st to end	Night	60% 9% 13% 13% 4	7964

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	20% 10% 30% 23% 15% 4	200
	11th to 20th	Day	20% 16% 26% 24% 14% 2	200
	21st to end	Day	19% 19% 27% 22% 9% 5%	220
February	1st to 10th	Day	23% 15% 28% 18% 12% 4	295
	11th to 20th	Day	16% 12% 31% 30% 9% 2	395
	21st to end	Day	19% 18% 32% 18% 10% 3	331
March	1st to 10th	Day	15% 16% 27% 25% 16% 3	463
	11th to 20th	Day	16% 14% 32% 24% 12% 1	500
	21st to end	Day	20% 17% 24% 23% 11% 6%	531
April	1st to 10th	Day	17% 18% 30% 23% 8% 4	460
	11th to 20th	Day	18% 18% 24% 21% 12% 8%	452
	21st to end	Day	20% 13% 30% 23% 11% 3	460
May	1st to 10th	Day	16% 16% 30% 23% 13% 4	463
	11th to 20th	Day	16% 12% 28% 25% 15% 4	661
	21st to end	Day	16% 13% 24% 29% 15% 3	806
June	1st to 10th	Day	15% 14% 27% 28% 13% 3	870
	11th to 20th	Day	18% 10% 25% 30% 14% 3	870
	21st to end	Day	14% 7% 28% 29% 17% 5%	870
July	1st to 10th	Day	15% 7% 23% 27% 23% 4	806
	11th to 20th	Day	15% 9% 23% 28% 21% 3	668
	21st to end	Day	12% 8% 23% 35% 18% 4	739
August	1st to 10th	Day	8% 7% 20% 33% 25% 8%	606
	11th to 20th	Day	11% 10% 21% 30% 20% 8%	477
	21st to end	Day	16% 11% 27% 26% 15% 5%	539
September	1st to 10th	Day	18% 10% 25% 24% 18% 4	490
	11th to 20th	Day	16% 9% 25% 23% 20% 6%	490
	21st to end	Day	26% 15% 29% 17% 12% 1	490
October	1st to 10th	Day	26% 12% 21% 23% 12% 5%	490
	11th to 20th	Day	25% 13% 29% 21% 12% 1	490
	21st to end	Day	22% 12% 30% 24% 9% 3	256
November	1st to 10th	Day	36% 14% 19% 22% 9% 2	200
	11th to 20th	Day	25% 14% 24% 17% 16% 5%	200
	21st to end	Day	24% 14% 27% 21% 10% 5%	200
December	1st to 10th	Day	20% 10% 23% 29% 17% 4	200
	11th to 20th	Day	14% 13% 22% 33% 16% 3	200
	21st to end	Day	23% 8% 25% 24% 14% 6%	220
January	1st to 10th	Night	21% 16% 26% 26% 9% 2	940
	11th to 20th	Night	21% 14% 28% 25% 11% 1	900
	21st to end	Night	20% 14% 27% 26% 12% 1	990
February	1st to 10th	Night	23% 11% 25% 25% 13% 3	845
	11th to 20th	Night	18% 9% 28% 30% 14% 1	784
	21st to end	Night	15% 12% 28% 28% 14% 3	660
March	1st to 10th	Night	17% 13% 25% 28% 15% 3	800
	11th to 20th	Night	14% 13% 29% 29% 14% 2	800
	21st to end	Night	14% 12% 20% 29% 22% 3	862
April	1st to 10th	Night	15% 10% 24% 30% 19% 3	716
	11th to 20th	Night	13% 9% 27% 30% 18% 3	563
	21st to end	Night	16% 12% 28% 27% 16% 1	432
May	1st to 10th	Night	15% 11% 25% 33% 16% 1	380
	11th to 20th	Night	15% 6% 27% 33% 18% 1	374
	21st to end	Night	19% 8% 27% 25% 20% 2	411
June	1st to 10th	Night	17% 8% 25% 34% 15% 1	380
	11th to 20th	Night	18% 7% 27% 28% 19% 1	380
	21st to end	Night	14% 6% 23% 34% 20% 2	380
July	1st to 10th	Night	15% 6% 22% 35% 21% 1	370
	11th to 20th	Night	15% 6% 23% 29% 24% 2	368
	21st to end	Night	14% 6% 21% 31% 23% 4	416
August	1st to 10th	Night	10% 4 18% 31% 31% 6%	378
	11th to 20th	Night	10% 5% 19% 36% 27% 3	464
	21st to end	Night	18% 4 23% 33% 20% 3	627
September	1st to 10th	Night	16% 5% 21% 32% 24% 2	717
	11th to 20th	Night	14% 7% 18% 30% 26% 5%	760
	21st to end	Night	22% 11% 26% 26% 14% 1	760
October	1st to 10th	Night	22% 9% 20% 29% 16% 3	760
	11th to 20th	Night	27% 9% 21% 28% 13% 2	760
	21st to end	Night	25% 11% 27% 27% 10%	836
November	1st to 10th	Night	27% 15% 24% 24% 8% 2	780
	11th to 20th	Night	24% 15% 29% 22% 10% 1	800
	21st to end	Night	24% 13% 27% 26% 9% 1	1013
December	1st to 10th	Night	20% 11% 23% 32% 12% 2	1100
	11th to 20th	Night	21% 13% 26% 27% 12% 1	1100
	21st to end	Night	20% 13% 27% 27% 13% 1	1210

Page generated at 2025-03-24 06:04:27. Version ac07

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