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 2024-10-20.

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% 32%	101856
	Night	12% 13% 4 10% 6% 5% 5% 4 6% 6% 29%	96874
Transparency	Day	48% 9% 15% 19% 7% 1	101595
	Night	52% 9% 14% 17% 7% 1	96781
Seeing	Day	17% 12% 26% 26% 15% 4	16418
	Night	19% 11% 25% 28% 15% 2	24069

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% 18% 5% 14% 10% 8% 6% 4 5% 6% 14%	2169
	11th to 20th	Day	11% 17% 5% 9% 6% 5% 4 4 7% 7% 26%	2199
	21st to end	Day	12% 24% 5% 12% 8% 6% 4 3 4 6% 15%	2442
February	1st to 10th	Day	14% 15% 5% 10% 7% 7% 4 3 6% 5% 25%	1522
	11th to 20th	Day	9% 16% 6% 11% 6% 5% 4 4 6% 7% 27%	1665
	21st to end	Day	6% 17% 6% 12% 7% 4 5% 4 4 6% 28%	1413
March	1st to 10th	Day	6% 13% 4 11% 8% 6% 6% 5% 7% 7% 27%	3139
	11th to 20th	Day	7% 14% 5% 10% 5% 7% 7% 5% 8% 8% 25%	3490
	21st to end	Day	5% 11% 4 8% 6% 5% 5% 4 6% 7% 38%	3910
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	16% 11% 4 9% 5% 6% 6% 4 6% 8% 28%	1900
	11th to 20th	Day	14% 13% 4 8% 5% 5% 5% 5% 6% 8% 27%	1891
	21st to end	Day	15% 15% 5% 9% 5% 5% 4 4 4 7% 28%	1624
November	1st to 10th	Day	20% 16% 2 9% 5% 4 4 3 5% 6% 24%	1488
	11th to 20th	Day	13% 16% 6% 13% 5% 6% 6% 4 6% 7% 18%	1520
	21st to end	Day	14% 19% 5% 11% 6% 8% 6% 4 6% 5% 16%	1202
December	1st to 10th	Day	12% 14% 4 10% 9% 6% 7% 4 8% 7% 20%	1140
	11th to 20th	Day	16% 18% 5% 12% 7% 6% 5% 3 5% 5% 18%	1442
	21st to end	Day	9% 17% 5% 11% 6% 6% 6% 5% 6% 5% 23%	2090
January	1st to 10th	Night	9% 18% 7% 13% 7% 7% 6% 5% 6% 6% 15%	4790
	11th to 20th	Night	11% 15% 5% 11% 8% 5% 5% 4 4 5% 27%	4699
	21st to end	Night	17% 20% 5% 11% 7% 6% 6% 4 5% 6% 14%	5214
February	1st to 10th	Night	15% 18% 5% 11% 7% 5% 4 3 5% 4 24%	2655
	11th to 20th	Night	11% 15% 5% 9% 6% 5% 5% 4 6% 7% 26%	2402
	21st to end	Night	9% 15% 5% 11% 7% 5% 5% 4 5% 5% 30%	2041
March	1st to 10th	Night	5% 15% 5% 13% 7% 6% 6% 5% 5% 6% 27%	3729
	11th to 20th	Night	9% 14% 5% 10% 7% 6% 6% 5% 6% 6% 26%	3489
	21st to end	Night	6% 11% 3 8% 4 4 4 4 6% 7% 44%	3742
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	16% 11% 4 9% 5% 4 5% 4 6% 6% 30%	2280
	11th to 20th	Night	18% 12% 4 9% 5% 5% 5% 3 5% 6% 27%	2273
	21st to end	Night	16% 13% 4 8% 5% 5% 5% 4 6% 6% 28%	2730
November	1st to 10th	Night	18% 15% 5% 8% 5% 6% 5% 4 6% 6% 22%	2590
	11th to 20th	Night	13% 18% 4 12% 7% 5% 5% 4 5% 6% 21%	2660
	21st to end	Night	11% 20% 6% 12% 6% 6% 5% 4 5% 5% 21%	2952
December	1st to 10th	Night	12% 15% 4 11% 7% 5% 5% 4 6% 5% 26%	3040
	11th to 20th	Night	18% 18% 5% 10% 7% 5% 4 4 5% 5% 18%	3750
	21st to end	Night	9% 17% 6% 12% 8% 6% 6% 5% 5% 6% 20%	5566

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	62% 14% 12% 10% 2	2169
	11th to 20th	Day	57% 8% 13% 7% 10% 5%	2220
	21st to end	Day	70% 8% 8% 9% 4	2442
February	1st to 10th	Day	59% 7% 13% 10% 9% 2	1522
	11th to 20th	Day	55% 9% 16% 14% 5% 1	1674
	21st to end	Day	56% 7% 12% 15% 7% 2	1413
March	1st to 10th	Day	51% 10% 11% 15% 12%	3139
	11th to 20th	Day	50% 11% 15% 18% 5%	3490
	21st to end	Day	44% 8% 14% 22% 10% 1	3910
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	54% 10% 16% 16% 4	1900
	11th to 20th	Day	53% 12% 16% 17% 2	1891
	21st to end	Day	55% 9% 15% 17% 4	1624
November	1st to 10th	Day	60% 9% 13% 12% 5%	1488
	11th to 20th	Day	63% 11% 13% 9% 4	1520
	21st to end	Day	67% 8% 11% 11% 3	1202
December	1st to 10th	Day	55% 14% 14% 13% 4	1140
	11th to 20th	Day	68% 9% 10% 10% 4	1444
	21st to end	Day	55% 11% 14% 14% 7%	2090
January	1st to 10th	Night	62% 12% 12% 11% 2	4790
	11th to 20th	Night	58% 8% 11% 6% 11% 6%	4740
	21st to end	Night	69% 12% 8% 7% 4	5214
February	1st to 10th	Night	63% 7% 10% 11% 9% 1	2655
	11th to 20th	Night	57% 6% 16% 14% 7%	2404
	21st to end	Night	53% 7% 13% 18% 7% 2	2041
March	1st to 10th	Night	52% 9% 12% 14% 12% 1	3729
	11th to 20th	Night	53% 10% 13% 18% 6%	3490
	21st to end	Night	38% 8% 12% 26% 16%	3742
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	51% 10% 17% 17% 5%	2280
	11th to 20th	Night	57% 8% 16% 15% 4	2273
	21st to end	Night	54% 9% 15% 17% 5%	2730
November	1st to 10th	Night	61% 9% 12% 13% 5%	2590
	11th to 20th	Night	61% 9% 14% 10% 5%	2660
	21st to end	Night	62% 9% 13% 10% 5%	2952
December	1st to 10th	Night	57% 9% 14% 16% 4	3040
	11th to 20th	Night	65% 11% 11% 9% 4	3747
	21st to end	Night	59% 10% 12% 13% 6%	5566

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	18% 9% 32% 22% 15% 4	180
	11th to 20th	Day	21% 16% 26% 21% 15% 2	180
	21st to end	Day	20% 19% 27% 22% 8% 5%	198
February	1st to 10th	Day	25% 16% 29% 17% 9% 3	270
	11th to 20th	Day	17% 13% 32% 29% 8% 2	365
	21st to end	Day	17% 17% 33% 20% 10% 3	307
March	1st to 10th	Day	15% 17% 26% 24% 16% 3	427
	11th to 20th	Day	17% 15% 32% 24% 12% 1	460
	21st to end	Day	19% 17% 24% 23% 12% 6%	506
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% 28% 21% 12% 1	487
	21st to end	Day	22% 12% 30% 24% 8% 3	233
November	1st to 10th	Day	35% 13% 18% 22% 9% 2	180
	11th to 20th	Day	25% 14% 24% 16% 16% 4	180
	21st to end	Day	24% 14% 26% 21% 10% 5%	180
December	1st to 10th	Day	18% 9% 22% 32% 16% 4	180
	11th to 20th	Day	15% 12% 24% 32% 14% 3	180
	21st to end	Day	23% 8% 25% 24% 14% 6%	198
January	1st to 10th	Night	22% 16% 27% 26% 8% 2	888
	11th to 20th	Night	21% 14% 28% 25% 12% 1	850
	21st to end	Night	20% 15% 27% 26% 12% 1	935
February	1st to 10th	Night	24% 12% 24% 25% 12% 2	801
	11th to 20th	Night	19% 9% 29% 28% 14% 1	744
	21st to end	Night	15% 12% 28% 28% 15% 2	628
March	1st to 10th	Night	17% 13% 25% 27% 15% 3	760
	11th to 20th	Night	14% 13% 28% 29% 13% 1	760
	21st to end	Night	14% 12% 20% 29% 22% 3	836
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	758
	21st to end	Night	26% 11% 27% 26% 10% 1	792
November	1st to 10th	Night	26% 15% 24% 24% 8% 2	740
	11th to 20th	Night	23% 15% 29% 23% 10% 1	760
	21st to end	Night	24% 13% 27% 25% 9% 1	957
December	1st to 10th	Night	19% 10% 23% 32% 13% 2	1040
	11th to 20th	Night	21% 13% 26% 27% 11% 1	1040
	21st to end	Night	20% 13% 27% 27% 13% 1	1144

Page generated at 2024-10-17 10:09:39. Version ac07

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