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 2026-07-31.

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% 11% 4 9% 6% 5% 5% 4 6% 7% 31%	142134
	Night	12% 14% 4 10% 6% 5% 5% 4 6% 7% 28%	139572
Transparency	Day	49% 8% 15% 20% 7% 1	141829
	Night	53% 8% 14% 17% 7%	139460
Seeing	Day	17% 12% 26% 26% 15% 4	18780
	Night	19% 11% 25% 29% 15% 2	26420

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	11% 20% 7% 14% 7% 6% 5% 4 5% 5% 15%	4048
	11th to 20th	Day	9% 12% 4 8% 6% 6% 6% 4 6% 8% 31%	4119
	21st to end	Day	9% 22% 4 10% 7% 5% 4 3 4 7% 23%	4529
February	1st to 10th	Day	13% 15% 4 11% 7% 7% 4 3 7% 5% 25%	1684
	11th to 20th	Day	9% 16% 6% 11% 7% 5% 4 4 6% 7% 26%	1845
	21st to end	Day	7% 17% 6% 12% 7% 4 5% 4 5% 6% 27%	1557
March	1st to 10th	Day	6% 14% 5% 12% 8% 7% 6% 5% 7% 6% 23%	4601
	11th to 20th	Day	5% 14% 5% 10% 6% 7% 7% 6% 8% 8% 22%	5110
	21st to end	Day	7% 13% 4 8% 6% 5% 5% 4 6% 6% 34%	5734
April	1st to 10th	Day	8% 14% 5% 11% 8% 6% 6% 4 6% 7% 24%	2567
	11th to 20th	Day	11% 14% 5% 10% 6% 5% 6% 3 5% 7% 28%	2698
	21st to end	Day	12% 13% 4 8% 6% 5% 5% 5% 6% 7% 30%	2882
May	1st to 10th	Day	7% 9% 3 8% 5% 5% 5% 4 6% 7% 41%	8195
	11th to 20th	Day	9% 10% 4 11% 7% 7% 6% 5% 8% 8% 25%	8730
	21st to end	Day	12% 10% 4 10% 7% 7% 6% 5% 7% 7% 24%	9884
June	1st to 10th	Day	11% 8% 3 9% 7% 6% 6% 5% 7% 8% 31%	3360
	11th to 20th	Day	14% 8% 3 8% 7% 6% 6% 4 7% 7% 29%	3360
	21st to end	Day	11% 7% 3 8% 6% 7% 5% 5% 6% 7% 33%	3360
July	1st to 10th	Day	10% 6% 2 5% 4 4 5% 4 6% 8% 45%	7264
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 6% 8% 45%	6930
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 10% 40%	7526
August	1st to 10th	Day	4 4 2 4 3 3 4 3 6% 8% 57%	4743
	11th to 20th	Day	11% 7% 2 6% 4 4 5% 4 6% 8% 43%	4315
	21st to end	Day	13% 6% 3 8% 5% 5% 5% 5% 7% 8% 35%	4664
September	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 5% 7% 8% 39%	2445
	11th to 20th	Day	12% 7% 3 7% 6% 5% 5% 4 6% 8% 36%	2361
	21st to end	Day	17% 11% 3 9% 5% 5% 5% 4 7% 7% 26%	2130
October	1st to 10th	Day	17% 14% 5% 10% 6% 6% 5% 4 6% 7% 21%	3280
	11th to 20th	Day	14% 13% 4 9% 5% 5% 5% 4 7% 9% 25%	3261
	21st to end	Day	14% 15% 4 9% 5% 5% 4 4 6% 7% 28%	2896
November	1st to 10th	Day	19% 17% 3 10% 5% 5% 4 3 5% 6% 23%	1648
	11th to 20th	Day	12% 16% 5% 13% 5% 6% 6% 4 6% 7% 19%	1680
	21st to end	Day	13% 18% 5% 12% 6% 7% 6% 4 6% 5% 17%	1328
December	1st to 10th	Day	20% 19% 4 9% 6% 4 5% 3 6% 6% 18%	2020
	11th to 20th	Day	13% 20% 7% 16% 7% 6% 5% 3 6% 5% 13%	2322
	21st to end	Day	8% 19% 7% 13% 6% 6% 6% 4 5% 5% 20%	3058
January	1st to 10th	Night	11% 20% 7% 14% 7% 6% 5% 4 6% 5% 14%	8887
	11th to 20th	Night	10% 12% 4 9% 6% 5% 6% 4 6% 8% 31%	8779
	21st to end	Night	13% 19% 5% 9% 5% 5% 5% 4 5% 8% 24%	9651
February	1st to 10th	Night	14% 17% 5% 11% 7% 6% 5% 3 5% 4 23%	2933
	11th to 20th	Night	11% 14% 5% 10% 6% 5% 5% 4 5% 8% 27%	2662
	21st to end	Night	9% 16% 5% 10% 7% 5% 5% 4 5% 5% 28%	2249
March	1st to 10th	Night	7% 16% 5% 13% 6% 6% 6% 4 5% 6% 26%	5503
	11th to 20th	Night	6% 14% 6% 11% 7% 7% 6% 5% 7% 7% 24%	5109
	21st to end	Night	9% 12% 3 8% 4 4 4 3 5% 7% 38%	5482
April	1st to 10th	Night	7% 14% 5% 10% 6% 6% 6% 5% 6% 6% 28%	2051
	11th to 20th	Night	8% 11% 4 10% 6% 7% 6% 5% 7% 8% 27%	1871
	21st to end	Night	9% 12% 3 8% 6% 5% 5% 4 7% 7% 34%	1738
May	1st to 10th	Night	10% 8% 3 7% 6% 6% 6% 5% 7% 8% 35%	4724
	11th to 20th	Night	12% 10% 3 9% 7% 6% 7% 5% 8% 8% 23%	4128
	21st to end	Night	15% 12% 4 11% 7% 6% 5% 3 5% 6% 25%	4285
June	1st to 10th	Night	13% 10% 3 8% 6% 6% 6% 5% 7% 5% 30%	1260
	11th to 20th	Night	15% 8% 4 9% 7% 6% 6% 4 7% 6% 28%	1260
	21st to end	Night	12% 7% 3 9% 5% 5% 7% 6% 8% 9% 30%	1260
July	1st to 10th	Night	10% 7% 2 7% 5% 4 4 4 5% 7% 45%	2912
	11th to 20th	Night	12% 5% 2 6% 5% 4 4 4 6% 8% 45%	3250
	21st to end	Night	11% 6% 2 6% 4 5% 5% 4 7% 8% 42%	3538
August	1st to 10th	Night	4 3 1 2 3 2 3 3 5% 7% 66%	2406
	11th to 20th	Night	10% 6% 2 6% 5% 4 5% 4 6% 8% 44%	2735
	21st to end	Night	15% 7% 4 8% 5% 4 5% 5% 6% 6% 33%	3245
September	1st to 10th	Night	13% 7% 3 7% 5% 4 5% 4 6% 8% 39%	1955
	11th to 20th	Night	11% 8% 3 7% 5% 4 5% 5% 4 7% 40%	2035
	21st to end	Night	18% 10% 3 8% 5% 5% 5% 4 5% 7% 30%	2270
October	1st to 10th	Night	19% 14% 5% 9% 5% 4 5% 4 5% 6% 24%	3920
	11th to 20th	Night	13% 11% 5% 10% 5% 5% 6% 4 6% 8% 26%	3897
	21st to end	Night	14% 14% 4 9% 5% 5% 5% 4 6% 6% 28%	4893
November	1st to 10th	Night	18% 15% 4 8% 5% 6% 5% 4 6% 7% 22%	2870
	11th to 20th	Night	13% 19% 4 11% 7% 5% 5% 4 5% 6% 21%	2940
	21st to end	Night	10% 21% 6% 12% 6% 6% 5% 4 5% 6% 20%	3264
December	1st to 10th	Night	17% 18% 4 10% 6% 4 4 4 5% 6% 21%	5380
	11th to 20th	Night	15% 21% 6% 12% 7% 5% 4 4 5% 6% 14%	6090
	21st to end	Night	8% 18% 6% 13% 7% 6% 6% 5% 6% 7% 18%	8140

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	65% 10% 12% 10% 3	4048
	11th to 20th	Day	49% 8% 19% 14% 7% 3	4140
	21st to end	Day	60% 7% 14% 16% 3	4530
February	1st to 10th	Day	58% 7% 12% 11% 9% 2	1684
	11th to 20th	Day	55% 9% 16% 14% 5% 1	1854
	21st to end	Day	57% 7% 12% 15% 6% 2	1557
March	1st to 10th	Day	56% 9% 11% 14% 10%	4601
	11th to 20th	Day	52% 10% 13% 16% 9%	5110
	21st to end	Day	48% 7% 12% 22% 10% 1	5734
April	1st to 10th	Day	57% 8% 12% 18% 5%	2567
	11th to 20th	Day	56% 7% 12% 18% 7%	2698
	21st to end	Day	52% 7% 13% 20% 8%	2882
May	1st to 10th	Day	39% 7% 17% 27% 9% 1	8195
	11th to 20th	Day	50% 9% 13% 20% 8%	8733
	21st to end	Day	54% 8% 14% 16% 7% 1	9885
June	1st to 10th	Day	50% 7% 15% 18% 9% 1	3360
	11th to 20th	Day	50% 10% 15% 19% 5%	3360
	21st to end	Day	47% 10% 16% 20% 7%	3360
July	1st to 10th	Day	35% 7% 14% 24% 19% 1	7187
	11th to 20th	Day	35% 7% 22% 30% 6%	6849
	21st to end	Day	36% 9% 21% 26% 8% 1	7319
August	1st to 10th	Day	25% 7% 18% 37% 12%	4725
	11th to 20th	Day	37% 9% 17% 30% 7%	4357
	21st to end	Day	45% 9% 23% 20% 4	4663
September	1st to 10th	Day	41% 10% 22% 21% 6%	2445
	11th to 20th	Day	44% 9% 18% 23% 6%	2361
	21st to end	Day	54% 10% 16% 16% 4 1	2130
October	1st to 10th	Day	59% 9% 15% 13% 4	3280
	11th to 20th	Day	54% 10% 17% 16% 3	3261
	21st to end	Day	52% 8% 18% 17% 5%	2896
November	1st to 10th	Day	61% 9% 13% 12% 5%	1648
	11th to 20th	Day	62% 10% 13% 10% 4	1680
	21st to end	Day	67% 7% 11% 11% 3	1328
December	1st to 10th	Day	64% 10% 13% 10% 2	2020
	11th to 20th	Day	69% 9% 10% 8% 3	2324
	21st to end	Day	60% 9% 12% 14% 5%	3058
January	1st to 10th	Night	66% 9% 11% 10% 4	8888
	11th to 20th	Night	48% 9% 17% 15% 8% 3	8820
	21st to end	Night	59% 8% 15% 14% 2	9651
February	1st to 10th	Night	63% 6% 10% 11% 10% 1	2933
	11th to 20th	Night	55% 6% 16% 15% 7%	2664
	21st to end	Night	55% 7% 12% 17% 7% 1	2249
March	1st to 10th	Night	55% 8% 10% 15% 11% 1	5503
	11th to 20th	Night	53% 9% 12% 18% 8%	5110
	21st to end	Night	44% 7% 10% 25% 14%	5482
April	1st to 10th	Night	53% 9% 14% 17% 7%	2051
	11th to 20th	Night	51% 9% 14% 18% 8%	1871
	21st to end	Night	46% 8% 13% 22% 10%	1738
May	1st to 10th	Night	42% 7% 19% 24% 8%	4721
	11th to 20th	Night	49% 10% 13% 22% 4	4128
	21st to end	Night	57% 7% 9% 19% 8%	4289
June	1st to 10th	Night	49% 12% 10% 18% 10% 1	1260
	11th to 20th	Night	52% 8% 15% 18% 7%	1260
	21st to end	Night	47% 11% 17% 20% 5%	1260
July	1st to 10th	Night	35% 8% 13% 24% 19% 1	2880
	11th to 20th	Night	37% 7% 19% 32% 5%	3208
	21st to end	Night	34% 10% 25% 21% 10%	3440
August	1st to 10th	Night	18% 6% 17% 42% 17%	2399
	11th to 20th	Night	35% 10% 18% 30% 7%	2759
	21st to end	Night	49% 10% 21% 16% 4	3245
September	1st to 10th	Night	42% 9% 17% 25% 6% 1	1955
	11th to 20th	Night	41% 9% 15% 26% 8% 1	2035
	21st to end	Night	54% 8% 13% 18% 6%	2270
October	1st to 10th	Night	58% 8% 14% 15% 4	3920
	11th to 20th	Night	54% 8% 15% 18% 4	3897
	21st to end	Night	53% 8% 18% 17% 4	4893
November	1st to 10th	Night	61% 9% 13% 13% 5%	2870
	11th to 20th	Night	62% 8% 14% 11% 6%	2940
	21st to end	Night	62% 9% 13% 11% 5%	3264
December	1st to 10th	Night	62% 7% 15% 13% 3	5380
	11th to 20th	Night	68% 10% 10% 9% 4	6087
	21st to end	Night	60% 9% 13% 13% 4	8140

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	21% 11% 29% 22% 14% 4	220
	11th to 20th	Day	20% 15% 24% 24% 15% 2	220
	21st to end	Day	19% 18% 26% 21% 12% 4	242
February	1st to 10th	Day	23% 16% 27% 19% 11% 3	320
	11th to 20th	Day	16% 12% 32% 29% 9% 2	425
	21st to end	Day	20% 17% 31% 19% 10% 3	355
March	1st to 10th	Day	16% 16% 27% 24% 15% 2	499
	11th to 20th	Day	17% 16% 31% 24% 11% 1	540
	21st to end	Day	18% 17% 25% 23% 12% 6%	594
April	1st to 10th	Day	17% 17% 29% 24% 9% 4	540
	11th to 20th	Day	18% 18% 25% 21% 11% 7%	532
	21st to end	Day	18% 13% 30% 23% 12% 3	540
May	1st to 10th	Day	15% 15% 31% 24% 12% 3	543
	11th to 20th	Day	16% 13% 27% 25% 15% 4	760
	21st to end	Day	16% 14% 25% 28% 14% 3	924
June	1st to 10th	Day	14% 14% 27% 28% 14% 3	990
	11th to 20th	Day	18% 10% 25% 30% 14% 3	990
	21st to end	Day	14% 7% 26% 29% 18% 5%	990
July	1st to 10th	Day	15% 8% 23% 27% 22% 4	920
	11th to 20th	Day	14% 9% 24% 29% 20% 3	768
	21st to end	Day	11% 9% 22% 35% 19% 5%	845
August	1st to 10th	Day	8% 7% 19% 34% 25% 7%	652
	11th to 20th	Day	11% 11% 22% 29% 19% 8%	517
	21st to end	Day	15% 10% 25% 25% 16% 8%	583
September	1st to 10th	Day	17% 9% 23% 24% 20% 7%	530
	11th to 20th	Day	17% 9% 24% 24% 20% 6%	530
	21st to end	Day	26% 15% 28% 18% 12% 1	530
October	1st to 10th	Day	26% 12% 22% 23% 13% 4	530
	11th to 20th	Day	25% 13% 28% 20% 12% 2	530
	21st to end	Day	24% 12% 29% 24% 8% 3	279
November	1st to 10th	Day	35% 14% 20% 21% 8% 1	220
	11th to 20th	Day	24% 14% 25% 19% 15% 5%	220
	21st to end	Day	22% 13% 26% 24% 10% 5%	220
December	1st to 10th	Day	21% 11% 22% 27% 15% 3	220
	11th to 20th	Day	14% 13% 25% 31% 15% 3	220
	21st to end	Day	24% 8% 24% 26% 13% 6%	242
January	1st to 10th	Night	22% 16% 26% 26% 9% 2	992
	11th to 20th	Night	20% 14% 27% 26% 11% 1	950
	21st to end	Night	20% 14% 26% 26% 13% 1	1045
February	1st to 10th	Night	23% 12% 26% 25% 13% 3	889
	11th to 20th	Night	18% 9% 29% 30% 14% 1	824
	21st to end	Night	16% 12% 28% 27% 14% 2	692
March	1st to 10th	Night	17% 13% 26% 27% 14% 3	840
	11th to 20th	Night	15% 13% 29% 28% 13% 2	840
	21st to end	Night	14% 12% 19% 30% 22% 3	924
April	1st to 10th	Night	14% 10% 24% 31% 18% 3	791
	11th to 20th	Night	12% 9% 28% 30% 18% 3	623
	21st to end	Night	14% 11% 29% 29% 15% 1	478
May	1st to 10th	Night	15% 10% 24% 36% 15% 1	420
	11th to 20th	Night	14% 6% 26% 33% 19% 1	414
	21st to end	Night	18% 8% 27% 27% 18% 2	455
June	1st to 10th	Night	17% 8% 25% 35% 15% 1	420
	11th to 20th	Night	18% 6% 26% 28% 20% 1	420
	21st to end	Night	15% 5% 22% 35% 21% 2	420
July	1st to 10th	Night	14% 7% 22% 36% 20% 1	410
	11th to 20th	Night	15% 7% 22% 30% 24% 2	408
	21st to end	Night	14% 6% 22% 31% 24% 4	458
August	1st to 10th	Night	10% 4 17% 33% 30% 5%	398
	11th to 20th	Night	10% 5% 19% 37% 26% 3	489
	21st to end	Night	17% 4 22% 32% 22% 3	660
September	1st to 10th	Night	15% 5% 21% 32% 26% 2	755
	11th to 20th	Night	14% 7% 18% 31% 26% 5%	800
	21st to end	Night	22% 11% 27% 26% 13% 1	800
October	1st to 10th	Night	21% 10% 21% 30% 16% 3	800
	11th to 20th	Night	26% 9% 22% 29% 13% 2	800
	21st to end	Night	25% 11% 27% 26% 9%	880
November	1st to 10th	Night	27% 15% 25% 23% 8% 2	820
	11th to 20th	Night	24% 14% 29% 23% 10% 1	840
	21st to end	Night	24% 12% 26% 27% 9% 1	1069
December	1st to 10th	Night	21% 11% 23% 31% 12% 2	1160
	11th to 20th	Night	22% 13% 26% 26% 11% 1	1160
	21st to end	Night	20% 13% 26% 27% 13% 1	1276

Page generated at 2026-07-28 00:25:25. Version ac07

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