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 2024-04-10.

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	8% 11% 5% 10% 9% 5% 7% 7% 7% 8% 23%	81385
	Night	5% 11% 6% 11% 10% 6% 8% 7% 8% 8% 21%	87379
Transparency	Day	58% 7% 15% 15% 5%	81039
	Night	60% 7% 13% 14% 5% 1	87307
Seeing	Day	16% 13% 26% 26% 15% 4	16198
	Night	12% 9% 28% 31% 18% 3	22743

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 9% 14% 10% 14% 11% 12% 8% 8%	1393
	11th to 20th	Day	2 14% 7% 14% 10% 6% 7% 8% 13% 9% 11%	1731
	21st to end	Day	4 16% 8% 12% 12% 7% 8% 7% 7% 7% 13%	2094
February	1st to 10th	Day	1 10% 6% 13% 8% 5% 9% 9% 8% 9% 22%	1340
	11th to 20th	Day	3 12% 7% 11% 9% 5% 6% 8% 7% 9% 24%	1480
	21st to end	Day	2 8% 6% 14% 11% 6% 8% 6% 6% 9% 23%	1384
March	1st to 10th	Day	1 6% 5% 10% 13% 9% 11% 8% 10% 8% 21%	3082
	11th to 20th	Day	1 11% 7% 12% 10% 5% 7% 7% 6% 8% 26%	3289
	21st to end	Day	2 8% 5% 13% 9% 5% 6% 8% 8% 8% 28%	4128
April	1st to 10th	Day	2 12% 7% 13% 9% 6% 7% 6% 7% 8% 23%	2293
	11th to 20th	Day	3 13% 6% 12% 9% 4 6% 6% 7% 9% 25%	2486
	21st to end	Day	3 13% 6% 12% 9% 4 8% 8% 6% 8% 25%	2520
May	1st to 10th	Day	7% 13% 6% 10% 7% 6% 7% 6% 7% 7% 25%	2825
	11th to 20th	Day	8% 13% 5% 8% 8% 5% 7% 5% 6% 7% 29%	2833
	21st to end	Day	6% 9% 5% 9% 8% 5% 6% 7% 7% 8% 29%	3262
June	1st to 10th	Day	13% 9% 4 9% 8% 5% 6% 7% 6% 8% 26%	3240
	11th to 20th	Day	14% 10% 4 9% 9% 5% 6% 7% 5% 8% 21%	3240
	21st to end	Day	9% 8% 5% 10% 9% 6% 8% 8% 8% 9% 21%	3240
July	1st to 10th	Day	11% 8% 4 7% 8% 4 7% 7% 8% 8% 27%	3240
	11th to 20th	Day	15% 10% 4 10% 9% 5% 8% 6% 6% 8% 19%	3074
	21st to end	Day	13% 9% 5% 8% 7% 5% 6% 6% 7% 7% 27%	3135
August	1st to 10th	Day	12% 7% 4 8% 8% 5% 6% 7% 7% 8% 29%	2822
	11th to 20th	Day	17% 10% 4 9% 7% 5% 6% 5% 6% 8% 23%	2510
	21st to end	Day	18% 12% 4 8% 7% 4 5% 6% 7% 8% 21%	2772
September	1st to 10th	Day	16% 12% 4 10% 8% 5% 7% 6% 6% 6% 21%	2204
	11th to 20th	Day	10% 10% 4 8% 6% 5% 6% 7% 7% 7% 29%	2160
	21st to end	Day	11% 14% 5% 11% 8% 4 6% 7% 6% 7% 21%	1918
October	1st to 10th	Day	11% 13% 4 10% 9% 5% 6% 6% 7% 7% 23%	1800
	11th to 20th	Day	9% 15% 4 13% 11% 4 6% 6% 5% 6% 20%	1613
	21st to end	Day	4 13% 7% 12% 12% 6% 6% 8% 7% 7% 19%	1576
November	1st to 10th	Day	4 14% 8% 14% 13% 6% 9% 9% 6% 6% 13%	1302
	11th to 20th	Day	4 14% 10% 14% 13% 6% 7% 9% 6% 8% 11%	1155
	21st to end	Day	3 11% 6% 14% 11% 6% 11% 8% 11% 7% 13%	1022
December	1st to 10th	Day	4 8% 5% 12% 13% 10% 13% 10% 7% 9% 9%	874
	11th to 20th	Day	2 10% 7% 10% 8% 5% 8% 8% 10% 12% 20%	962
	21st to end	Day	3 13% 5% 9% 11% 6% 9% 9% 10% 9% 16%	1386
January	1st to 10th	Night	3 9% 4 10% 15% 9% 12% 10% 7% 8% 11%	5581
	11th to 20th	Night	3 13% 6% 13% 10% 5% 7% 8% 13% 9% 13%	5166
	21st to end	Night	4 14% 6% 13% 12% 8% 9% 7% 6% 7% 13%	5562
February	1st to 10th	Night	3 9% 5% 11% 11% 6% 9% 9% 8% 10% 19%	2840
	11th to 20th	Night	2 10% 6% 12% 12% 7% 8% 8% 7% 8% 21%	2587
	21st to end	Night	2 9% 6% 12% 12% 6% 8% 7% 7% 8% 24%	2069
March	1st to 10th	Night	1 7% 4 9% 12% 8% 11% 9% 8% 7% 24%	3782
	11th to 20th	Night	3 11% 8% 13% 9% 5% 6% 7% 7% 8% 23%	3674
	21st to end	Night	2 8% 6% 13% 9% 5% 7% 6% 8% 9% 27%	3513
April	1st to 10th	Night	1 9% 6% 12% 8% 5% 7% 6% 7% 8% 29%	1876
	11th to 20th	Night	3 8% 5% 9% 8% 5% 7% 7% 7% 10% 30%	1423
	21st to end	Night	4 9% 5% 8% 7% 3 7% 7% 9% 9% 31%	1440
May	1st to 10th	Night	5% 8% 4 7% 6% 5% 6% 6% 9% 10% 33%	1132
	11th to 20th	Night	6% 7% 4 7% 5% 4 8% 6% 9% 8% 35%	1062
	21st to end	Night	5% 6% 3 6% 7% 5% 7% 6% 8% 8% 40%	1011
June	1st to 10th	Night	8% 8% 3 7% 6% 7% 5% 5% 6% 10% 34%	720
	11th to 20th	Night	12% 8% 5% 6% 9% 5% 7% 8% 8% 9% 25%	720
	21st to end	Night	6% 6% 5% 9% 8% 4 8% 9% 8% 10% 28%	720
July	1st to 10th	Night	11% 5% 2 6% 8% 5% 7% 5% 9% 9% 33%	720
	11th to 20th	Night	12% 7% 4 7% 7% 5% 7% 7% 8% 8% 28%	885
	21st to end	Night	11% 6% 3 7% 7% 5% 8% 5% 8% 9% 33%	1182
August	1st to 10th	Night	11% 5% 2 4 7% 6% 6% 6% 8% 9% 35%	1116
	11th to 20th	Night	12% 9% 3 7% 6% 4 6% 6% 8% 9% 29%	1390
	21st to end	Night	17% 11% 4 8% 6% 3 5% 5% 6% 8% 27%	1584
September	1st to 10th	Night	10% 8% 4 7% 8% 6% 8% 6% 7% 9% 28%	1756
	11th to 20th	Night	8% 6% 4 8% 7% 3 6% 6% 6% 9% 37%	1800
	21st to end	Night	11% 14% 5% 10% 8% 4 5% 6% 7% 8% 23%	2041
October	1st to 10th	Night	9% 13% 5% 9% 9% 5% 7% 7% 5% 7% 25%	2160
	11th to 20th	Night	10% 14% 5% 11% 8% 5% 6% 6% 6% 7% 22%	2345
	21st to end	Night	6% 15% 6% 11% 10% 6% 7% 7% 6% 7% 20%	2780
November	1st to 10th	Night	4 12% 7% 16% 11% 8% 9% 7% 7% 7% 13%	2776
	11th to 20th	Night	3 14% 9% 14% 13% 6% 7% 8% 8% 6% 12%	3021
	21st to end	Night	3 12% 6% 13% 13% 7% 8% 8% 8% 8% 13%	3139
December	1st to 10th	Night	3 11% 7% 12% 13% 8% 9% 9% 8% 8% 12%	3306
	11th to 20th	Night	3 10% 6% 13% 12% 7% 9% 8% 8% 9% 17%	4230
	21st to end	Night	3 13% 6% 11% 10% 6% 8% 8% 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%	2293
	11th to 20th	Day	55% 7% 15% 18% 5%	2486
	21st to end	Day	57% 6% 14% 17% 6%	2520
May	1st to 10th	Day	56% 7% 17% 17% 4	2825
	11th to 20th	Day	52% 5% 11% 23% 10%	2836
	21st to end	Day	49% 6% 16% 21% 7%	3263
June	1st to 10th	Day	55% 7% 13% 18% 7%	3240
	11th to 20th	Day	59% 6% 15% 16% 3	3240
	21st to end	Day	55% 8% 16% 17% 3	3240
July	1st to 10th	Day	49% 8% 18% 18% 6% 1	3151
	11th to 20th	Day	62% 8% 17% 11% 1	2979
	21st to end	Day	54% 8% 20% 16% 2	2961
August	1st to 10th	Day	51% 7% 22% 16% 3	2803
	11th to 20th	Day	60% 7% 16% 15% 2	2510
	21st to end	Day	60% 8% 19% 12% 1	2772
September	1st to 10th	Day	63% 7% 12% 15% 3	2204
	11th to 20th	Day	51% 9% 18% 20% 3	2160
	21st to end	Day	62% 8% 14% 14% 3	1918
October	1st to 10th	Day	60% 8% 13% 16% 3	1800
	11th to 20th	Day	66% 5% 15% 12% 2	1613
	21st to end	Day	62% 8% 18% 10% 2	1576
November	1st to 10th	Day	72% 8% 11% 8% 2	1302
	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% 18% 22% 7%	1423
	21st to end	Night	44% 8% 17% 23% 8%	1440
May	1st to 10th	Night	44% 6% 21% 24% 5%	1132
	11th to 20th	Night	42% 8% 13% 22% 13% 2	1062
	21st to end	Night	38% 7% 20% 26% 10%	1011
June	1st to 10th	Night	44% 7% 18% 24% 7%	720
	11th to 20th	Night	52% 8% 16% 20% 4	720
	21st to end	Night	47% 11% 19% 20% 3	720
July	1st to 10th	Night	44% 6% 20% 24% 6% 1	700
	11th to 20th	Night	50% 8% 20% 20% 1	858
	21st to end	Night	47% 8% 23% 19% 4	1116
August	1st to 10th	Night	43% 10% 23% 20% 4	1110
	11th to 20th	Night	49% 8% 20% 19% 4	1390
	21st to end	Night	55% 6% 24% 13% 1	1584
September	1st to 10th	Night	53% 8% 19% 18% 2	1756
	11th to 20th	Night	43% 8% 22% 22% 5%	1800
	21st to end	Night	59% 7% 14% 17% 4	2041
October	1st to 10th	Night	57% 8% 15% 17% 3	2160
	11th to 20th	Night	61% 8% 15% 13% 2	2345
	21st to end	Night	63% 7% 16% 11% 3	2780
November	1st to 10th	Night	70% 8% 12% 7% 2	2776
	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% 25% 12% 2	475
	11th to 20th	Day	13% 15% 26% 28% 15% 3	590
	21st to end	Day	15% 17% 30% 27% 9% 2	600
May	1st to 10th	Day	19% 21% 30% 22% 7% 2	603
	11th to 20th	Day	16% 14% 27% 23% 14% 5%	625
	21st to end	Day	14% 14% 24% 27% 16% 4	782
June	1st to 10th	Day	17% 10% 23% 28% 18% 4	810
	11th to 20th	Day	21% 9% 23% 24% 19% 4	810
	21st to end	Day	13% 8% 18% 30% 24% 7%	810
July	1st to 10th	Day	17% 7% 18% 28% 24% 6%	796
	11th to 20th	Day	19% 10% 18% 27% 19% 6%	652
	21st to end	Day	18% 10% 16% 29% 21% 6%	684
August	1st to 10th	Day	18% 11% 21% 27% 17% 5%	626
	11th to 20th	Day	25% 14% 25% 23% 10% 2	615
	21st to end	Day	25% 11% 24% 26% 12% 2	693
September	1st to 10th	Day	28% 12% 25% 19% 13% 4	476
	11th to 20th	Day	18% 13% 24% 25% 17% 4	450
	21st to end	Day	25% 20% 26% 17% 10% 2	412
October	1st to 10th	Day	24% 19% 27% 19% 10% 2	360
	11th to 20th	Day	22% 17% 26% 23% 7% 4	360
	21st to end	Day	15% 13% 30% 27% 12% 3	388
November	1st to 10th	Day	14% 16% 32% 26% 11% 2	180
	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% 22% 31% 27% 5%	533
	21st to end	Night	11% 7% 20% 31% 28% 4	540
May	1st to 10th	Night	11% 9% 24% 29% 22% 4	364
	11th to 20th	Night	10% 10% 23% 28% 26% 3	354
	21st to end	Night	8% 6% 17% 35% 31% 3	339
June	1st to 10th	Night	13% 3 21% 33% 26% 4	180
	11th to 20th	Night	14% 5% 14% 31% 33% 2	180
	21st to end	Night	9% 3 17% 34% 32% 4	180
July	1st to 10th	Night	13% 2 13% 36% 31% 5%	175
	11th to 20th	Night	18% 7% 12% 29% 30% 5%	196
	21st to end	Night	16% 5% 18% 30% 27% 4	394
August	1st to 10th	Night	16% 6% 19% 31% 23% 6%	400
	11th to 20th	Night	19% 8% 20% 26% 21% 5%	534
	21st to end	Night	25% 5% 18% 30% 18% 4	594
September	1st to 10th	Night	16% 9% 21% 30% 21% 4	540
	11th to 20th	Night	13% 8% 22% 31% 22% 4	540
	21st to end	Night	23% 11% 23% 26% 15% 3	706
October	1st to 10th	Night	20% 11% 27% 24% 16% 2	720
	11th to 20th	Night	22% 10% 22% 29% 14% 3	724
	21st to end	Night	16% 8% 27% 32% 15% 2	891
November	1st to 10th	Night	11% 12% 27% 33% 13% 3	830
	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 2024-04-07 05:28:14. Version ac07

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