Whitehorse
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitehorse clear sky chart from 2005-11-06 to 2024-11-05.

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% 11% 5% 12% 8% 7% 7% 5% 7% 8% 24%	106423
	Night	5% 11% 5% 13% 8% 8% 7% 6% 8% 8% 22%	101154
Transparency	Day	55% 8% 15% 16% 5%	106120
	Night	58% 8% 13% 15% 6% 1	101105
Seeing	Day	16% 13% 26% 26% 15% 4	17179
	Night	12% 9% 28% 31% 18% 3	23282

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	2 7% 4 11% 13% 14% 12% 8% 12% 8% 8%	1393
	11th to 20th	Day	2 15% 6% 16% 8% 8% 6% 7% 12% 9% 11%	1731
	21st to end	Day	4 17% 7% 14% 11% 9% 7% 5% 7% 7% 13%	2094
February	1st to 10th	Day	1 11% 5% 14% 8% 7% 8% 7% 7% 9% 22%	1340
	11th to 20th	Day	3 13% 6% 13% 7% 7% 6% 6% 7% 8% 24%	1480
	21st to end	Day	2 9% 6% 15% 10% 9% 7% 5% 6% 9% 23%	1384
March	1st to 10th	Day	1 6% 4 11% 12% 11% 10% 7% 10% 8% 21%	3082
	11th to 20th	Day	1 12% 7% 14% 8% 7% 6% 6% 6% 8% 26%	3289
	21st to end	Day	1 9% 5% 15% 8% 6% 6% 6% 8% 8% 28%	4128
April	1st to 10th	Day	1 13% 6% 14% 8% 7% 7% 5% 7% 8% 23%	2303
	11th to 20th	Day	2 14% 5% 14% 7% 5% 5% 5% 7% 9% 27%	2626
	21st to end	Day	3 14% 5% 13% 8% 6% 7% 6% 7% 7% 25%	2660
May	1st to 10th	Day	6% 16% 5% 11% 6% 6% 6% 3 6% 7% 28%	4977
	11th to 20th	Day	6% 13% 5% 11% 8% 8% 7% 5% 7% 7% 23%	5013
	21st to end	Day	6% 10% 5% 10% 7% 6% 6% 5% 7% 8% 29%	5786
June	1st to 10th	Day	12% 10% 3 11% 7% 6% 6% 5% 6% 7% 25%	3420
	11th to 20th	Day	14% 11% 4 10% 8% 6% 6% 6% 6% 8% 22%	3420
	21st to end	Day	8% 9% 4 11% 8% 7% 7% 6% 8% 9% 22%	3420
July	1st to 10th	Day	8% 8% 3 8% 7% 7% 7% 6% 8% 10% 28%	5700
	11th to 20th	Day	12% 11% 4 12% 8% 8% 7% 5% 7% 7% 19%	5380
	21st to end	Day	11% 9% 4 10% 7% 6% 6% 5% 7% 7% 26%	5486
August	1st to 10th	Day	8% 6% 2 7% 5% 5% 5% 4 6% 8% 44%	4955
	11th to 20th	Day	15% 10% 4 8% 5% 5% 4 4 6% 8% 32%	4400
	21st to end	Day	15% 11% 4 9% 7% 6% 6% 5% 8% 8% 21%	4873
September	1st to 10th	Day	15% 13% 3 11% 6% 7% 6% 5% 6% 6% 21%	2325
	11th to 20th	Day	10% 10% 4 9% 5% 6% 7% 6% 7% 7% 28%	2280
	21st to end	Day	11% 14% 5% 12% 7% 6% 6% 5% 6% 7% 21%	2023
October	1st to 10th	Day	8% 13% 5% 14% 9% 7% 8% 5% 8% 7% 17%	3170
	11th to 20th	Day	5% 13% 6% 16% 8% 6% 7% 4 6% 8% 22%	2823
	21st to end	Day	8% 15% 5% 13% 9% 8% 7% 6% 8% 7% 14%	2733
November	1st to 10th	Day	4 15% 8% 15% 11% 8% 8% 7% 6% 5% 13%	1330
	11th to 20th	Day	4 15% 9% 16% 11% 7% 7% 7% 6% 8% 11%	1155
	21st to end	Day	2 12% 6% 16% 9% 10% 9% 6% 12% 6% 13%	1022
December	1st to 10th	Day	4 9% 5% 14% 12% 12% 12% 8% 7% 10% 8%	874
	11th to 20th	Day	2 11% 6% 11% 7% 8% 6% 7% 10% 12% 20%	962
	21st to end	Day	3 13% 5% 12% 8% 8% 9% 8% 10% 9% 16%	1386
January	1st to 10th	Night	3 10% 4 12% 13% 12% 12% 8% 8% 7% 11%	5581
	11th to 20th	Night	3 14% 6% 15% 8% 7% 6% 7% 13% 9% 13%	5166
	21st to end	Night	4 14% 6% 15% 10% 10% 8% 5% 6% 7% 13%	5562
February	1st to 10th	Night	3 10% 5% 12% 10% 8% 9% 6% 8% 9% 19%	2840
	11th to 20th	Night	1 11% 5% 15% 10% 9% 7% 6% 7% 8% 21%	2587
	21st to end	Night	2 10% 5% 13% 11% 7% 7% 6% 7% 8% 24%	2069
March	1st to 10th	Night	1 8% 3 11% 10% 12% 10% 6% 9% 7% 24%	3782
	11th to 20th	Night	3 12% 7% 15% 8% 7% 6% 6% 7% 7% 23%	3674
	21st to end	Night	2 9% 5% 15% 7% 7% 7% 5% 8% 9% 27%	3513
April	1st to 10th	Night	1 10% 6% 13% 8% 7% 6% 5% 8% 8% 29%	1876
	11th to 20th	Night	2 8% 5% 11% 7% 7% 6% 6% 7% 10% 31%	1503
	21st to end	Night	4 10% 5% 9% 5% 5% 6% 6% 9% 9% 32%	1520
May	1st to 10th	Night	3 11% 4 8% 5% 6% 5% 4 7% 9% 37%	1980
	11th to 20th	Night	5% 11% 5% 11% 5% 7% 7% 5% 7% 7% 29%	1882
	21st to end	Night	5% 6% 2 8% 6% 7% 7% 5% 7% 9% 37%	1787
June	1st to 10th	Night	9% 9% 3 8% 6% 7% 5% 4 7% 10% 33%	760
	11th to 20th	Night	11% 9% 5% 7% 8% 7% 6% 6% 9% 9% 25%	760
	21st to end	Night	6% 7% 4 10% 6% 7% 6% 8% 7% 11% 28%	760
July	1st to 10th	Night	6% 5% 2 8% 6% 6% 6% 4 7% 12% 38%	1260
	11th to 20th	Night	8% 7% 4 10% 7% 6% 6% 5% 8% 8% 29%	1565
	21st to end	Night	10% 8% 3 9% 7% 8% 8% 5% 9% 7% 26%	2066
August	1st to 10th	Night	7% 4 1 4 5% 5% 4 3 7% 8% 51%	1977
	11th to 20th	Night	12% 8% 3 7% 4 4 5% 4 7% 9% 36%	2438
	21st to end	Night	13% 11% 4 10% 7% 6% 6% 5% 7% 7% 25%	2794
September	1st to 10th	Night	10% 9% 3 8% 7% 8% 6% 5% 7% 9% 27%	1854
	11th to 20th	Night	7% 7% 3 9% 6% 5% 7% 4 6% 10% 36%	1900
	21st to end	Night	11% 14% 5% 12% 7% 5% 5% 4 7% 8% 23%	2156
October	1st to 10th	Night	8% 14% 4 10% 6% 6% 7% 6% 8% 8% 24%	3800
	11th to 20th	Night	6% 13% 6% 16% 7% 6% 6% 5% 6% 7% 22%	4103
	21st to end	Night	5% 17% 6% 15% 8% 7% 6% 5% 6% 7% 18%	4825
November	1st to 10th	Night	4 13% 7% 17% 10% 10% 8% 5% 7% 7% 13%	2848
	11th to 20th	Night	3 17% 7% 16% 11% 9% 7% 6% 8% 5% 12%	3021
	21st to end	Night	3 13% 6% 15% 11% 9% 8% 7% 9% 7% 13%	3139
December	1st to 10th	Night	3 12% 6% 15% 11% 10% 8% 7% 9% 8% 12%	3306
	11th to 20th	Night	2 11% 5% 15% 10% 9% 8% 6% 8% 8% 17%	4230
	21st to end	Night	3 14% 6% 12% 8% 8% 8% 6% 8% 8% 18%	6270

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	72% 8% 6% 7% 6% 2	1393
	11th to 20th	Day	63% 7% 9% 12% 9% 1	1748
	21st to end	Day	68% 6% 11% 11% 4	2094
February	1st to 10th	Day	56% 7% 12% 14% 11% 1	1340
	11th to 20th	Day	57% 7% 13% 12% 11%	1488
	21st to end	Day	55% 8% 16% 15% 5%	1384
March	1st to 10th	Day	58% 8% 8% 17% 8% 1	3082
	11th to 20th	Day	55% 7% 14% 14% 7% 3	3289
	21st to end	Day	53% 8% 19% 13% 6% 1	4128
April	1st to 10th	Day	57% 8% 17% 13% 6%	2303
	11th to 20th	Day	53% 6% 15% 18% 7% 1	2626
	21st to end	Day	56% 7% 14% 18% 6%	2660
May	1st to 10th	Day	53% 6% 12% 20% 8%	4977
	11th to 20th	Day	54% 7% 11% 21% 7%	5016
	21st to end	Day	47% 7% 12% 22% 11%	5787
June	1st to 10th	Day	55% 7% 13% 18% 7% 1	3420
	11th to 20th	Day	58% 6% 15% 17% 3	3420
	21st to end	Day	54% 8% 16% 18% 4	3420
July	1st to 10th	Day	44% 9% 24% 18% 4 1	5611
	11th to 20th	Day	60% 9% 15% 14% 1	5285
	21st to end	Day	51% 10% 21% 16% 2	5313
August	1st to 10th	Day	37% 7% 19% 23% 14% 1	4936
	11th to 20th	Day	50% 6% 18% 20% 6%	4443
	21st to end	Day	55% 9% 18% 16% 1	4872
September	1st to 10th	Day	62% 8% 12% 15% 3	2325
	11th to 20th	Day	51% 9% 18% 20% 3	2280
	21st to end	Day	61% 8% 13% 15% 3	2023
October	1st to 10th	Day	62% 9% 10% 17% 2	3170
	11th to 20th	Day	59% 6% 18% 16% 2	2823
	21st to end	Day	62% 14% 15% 7% 2	2733
November	1st to 10th	Day	71% 8% 11% 8% 2	1330
	11th to 20th	Day	72% 7% 11% 10% 1	1155
	21st to end	Day	68% 8% 12% 7% 6%	1022
December	1st to 10th	Day	71% 7% 12% 8% 1	874
	11th to 20th	Day	59% 7% 8% 15% 11%	964
	21st to end	Day	68% 7% 7% 12% 7%	1386
January	1st to 10th	Night	75% 7% 7% 6% 4	5581
	11th to 20th	Night	61% 5% 8% 10% 10% 5%	5211
	21st to end	Night	69% 8% 8% 10% 4 1	5562
February	1st to 10th	Night	59% 7% 11% 14% 8% 2	2840
	11th to 20th	Night	59% 7% 12% 13% 7% 1	2590
	21st to end	Night	57% 8% 13% 15% 8%	2069
March	1st to 10th	Night	57% 6% 8% 20% 8% 1	3782
	11th to 20th	Night	56% 7% 12% 15% 8% 2	3676
	21st to end	Night	55% 7% 20% 13% 5%	3513
April	1st to 10th	Night	49% 7% 19% 19% 6%	1876
	11th to 20th	Night	48% 5% 17% 22% 8% 1	1503
	21st to end	Night	43% 8% 16% 24% 8%	1520
May	1st to 10th	Night	40% 6% 16% 30% 7% 1	1980
	11th to 20th	Night	46% 10% 14% 18% 11% 1	1882
	21st to end	Night	37% 9% 14% 29% 11%	1787
June	1st to 10th	Night	45% 7% 17% 24% 7%	760
	11th to 20th	Night	50% 8% 16% 21% 4	760
	21st to end	Night	47% 10% 18% 22% 3	760
July	1st to 10th	Night	37% 6% 29% 24% 3	1240
	11th to 20th	Night	49% 7% 18% 23% 3	1538
	21st to end	Night	50% 11% 19% 17% 2	2000
August	1st to 10th	Night	31% 7% 22% 26% 14% 1	1971
	11th to 20th	Night	42% 7% 20% 24% 7% 1	2461
	21st to end	Night	53% 10% 19% 17% 2	2794
September	1st to 10th	Night	52% 8% 19% 18% 2	1854
	11th to 20th	Night	43% 8% 22% 22% 5%	1900
	21st to end	Night	58% 7% 13% 18% 4	2156
October	1st to 10th	Night	54% 9% 14% 20% 3	3800
	11th to 20th	Night	59% 8% 13% 18% 2	4103
	21st to end	Night	62% 11% 15% 10% 2	4825
November	1st to 10th	Night	69% 8% 12% 8% 2	2848
	11th to 20th	Night	70% 9% 10% 9% 2	3021
	21st to end	Night	66% 8% 11% 11% 3	3139
December	1st to 10th	Night	67% 9% 12% 9% 2	3306
	11th to 20th	Night	64% 7% 10% 11% 7% 1	4227
	21st to end	Night	65% 6% 6% 11% 9% 2	6270

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	4 11% 24% 34% 24% 1	90
	11th to 20th	Day	11% 9% 25% 29% 19% 7%	139
	21st to end	Day	11% 13% 36% 22% 15% 3	202
February	1st to 10th	Day	8% 11% 33% 30% 14% 4	370
	11th to 20th	Day	7% 16% 32% 31% 12% 2	365
	21st to end	Day	10% 12% 35% 28% 11% 3	307
March	1st to 10th	Day	7% 14% 33% 28% 14% 4	370
	11th to 20th	Day	9% 16% 34% 26% 14% 1	370
	21st to end	Day	9% 14% 29% 27% 16% 5%	495
April	1st to 10th	Day	12% 15% 34% 26% 12% 2	478
	11th to 20th	Day	12% 14% 27% 29% 15% 3	640
	21st to end	Day	14% 17% 28% 27% 10% 4	650
May	1st to 10th	Day	20% 21% 29% 22% 7% 2	653
	11th to 20th	Day	16% 15% 27% 24% 14% 5%	675
	21st to end	Day	14% 15% 24% 27% 16% 4	843
June	1st to 10th	Day	16% 11% 24% 28% 17% 4	870
	11th to 20th	Day	20% 8% 23% 24% 20% 5%	870
	21st to end	Day	13% 8% 17% 30% 25% 7%	870
July	1st to 10th	Day	16% 7% 19% 29% 24% 6%	856
	11th to 20th	Day	18% 12% 19% 27% 18% 6%	703
	21st to end	Day	18% 11% 17% 29% 20% 6%	739
August	1st to 10th	Day	17% 11% 21% 28% 17% 5%	676
	11th to 20th	Day	25% 15% 25% 22% 10% 3	665
	21st to end	Day	25% 13% 24% 24% 12% 2	748
September	1st to 10th	Day	27% 12% 25% 18% 13% 5%	517
	11th to 20th	Day	18% 14% 23% 25% 16% 4	490
	21st to end	Day	24% 20% 25% 17% 11% 3	447
October	1st to 10th	Day	24% 20% 27% 19% 9% 2	390
	11th to 20th	Day	21% 18% 27% 23% 7% 4	390
	21st to end	Day	16% 13% 30% 27% 11% 3	420
November	1st to 10th	Day	14% 17% 31% 24% 11% 2	188
	11th to 20th	Day	13% 9% 28% 33% 12% 4	180
	21st to end	Day	6% 13% 36% 25% 11% 10%	180
December	1st to 10th	Day	7% 14% 27% 31% 15% 6%	144
	11th to 20th	Day	9% 8% 26% 38% 18% 2	90
	21st to end	Day	7% 10% 31% 28% 15% 8%	99
January	1st to 10th	Night	7% 7% 30% 37% 16% 3	974
	11th to 20th	Night	11% 9% 38% 27% 14% 2	850
	21st to end	Night	9% 12% 37% 28% 13% 1	935
February	1st to 10th	Night	9% 9% 30% 37% 14% 2	850
	11th to 20th	Night	6% 11% 37% 32% 12% 2	834
	21st to end	Night	8% 9% 36% 32% 14% 3	703
March	1st to 10th	Night	5% 11% 29% 33% 20% 1	775
	11th to 20th	Night	7% 10% 27% 34% 19% 3	688
	21st to end	Night	5% 9% 24% 27% 31% 5%	627
April	1st to 10th	Night	6% 7% 26% 33% 24% 4	570
	11th to 20th	Night	6% 8% 23% 32% 27% 5%	563
	21st to end	Night	10% 7% 19% 30% 29% 4	570
May	1st to 10th	Night	11% 10% 24% 28% 22% 4	384
	11th to 20th	Night	10% 11% 23% 28% 25% 3	374
	21st to end	Night	7% 7% 19% 35% 30% 3	358
June	1st to 10th	Night	13% 5% 21% 33% 25% 4	190
	11th to 20th	Night	13% 5% 15% 31% 34% 2	190
	21st to end	Night	9% 4 17% 33% 33% 4	190
July	1st to 10th	Night	12% 2 14% 36% 31% 5%	185
	11th to 20th	Night	17% 8% 14% 28% 29% 5%	208
	21st to end	Night	15% 5% 19% 31% 26% 4	416
August	1st to 10th	Night	15% 5% 19% 32% 22% 5%	423
	11th to 20th	Night	20% 8% 21% 27% 20% 5%	564
	21st to end	Night	24% 6% 20% 29% 17% 4	627
September	1st to 10th	Night	16% 9% 21% 29% 21% 4	570
	11th to 20th	Night	12% 9% 22% 31% 21% 4	570
	21st to end	Night	22% 11% 22% 27% 15% 3	746
October	1st to 10th	Night	20% 11% 27% 24% 16% 1	760
	11th to 20th	Night	21% 12% 22% 28% 14% 3	765
	21st to end	Night	15% 9% 28% 32% 14% 2	946
November	1st to 10th	Night	11% 13% 28% 32% 13% 3	854
	11th to 20th	Night	12% 8% 30% 30% 18% 2	850
	21st to end	Night	11% 10% 34% 28% 14% 3	949
December	1st to 10th	Night	9% 12% 33% 30% 14% 2	1040
	11th to 20th	Night	11% 8% 32% 32% 14% 3	1040
	21st to end	Night	10% 10% 33% 29% 15% 3	1144

Page generated at 2024-11-02 22:11:14. Version ac07

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