Carcross
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carcross clear sky chart from 2005-11-06 to 2025-05-26.

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% 12% 4 12% 8% 7% 6% 5% 7% 8% 24%	116308
	Night	6% 14% 6% 15% 9% 7% 7% 5% 7% 7% 19%	121598
Transparency	Day	55% 10% 17% 14% 4	116007
	Night	59% 9% 14% 12% 5% 1	121546
Seeing	Day	15% 14% 28% 26% 14% 4	17772
	Night	13% 9% 26% 32% 18% 3	24225

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 11% 6% 15% 13% 10% 10% 7% 7% 7% 11%	2098
	11th to 20th	Day	4 17% 6% 15% 9% 6% 5% 6% 6% 9% 15%	2677
	21st to end	Day	4 17% 5% 16% 6% 7% 6% 4 7% 8% 18%	3038
February	1st to 10th	Day	3 12% 5% 15% 9% 10% 8% 5% 7% 6% 20%	1441
	11th to 20th	Day	4 12% 7% 14% 9% 9% 7% 5% 7% 8% 20%	1560
	21st to end	Day	2 11% 6% 16% 10% 8% 7% 5% 6% 9% 19%	1457
March	1st to 10th	Day	2 8% 4 15% 12% 12% 9% 5% 6% 7% 20%	4452
	11th to 20th	Day	2 13% 6% 17% 13% 9% 6% 6% 7% 7% 15%	4689
	21st to end	Day	1 9% 5% 16% 10% 7% 8% 6% 8% 8% 23%	5939
April	1st to 10th	Day	3 12% 5% 13% 8% 7% 7% 5% 7% 8% 23%	2405
	11th to 20th	Day	3 13% 6% 11% 8% 7% 6% 4 7% 8% 25%	2762
	21st to end	Day	4 16% 5% 11% 7% 6% 7% 5% 6% 7% 26%	2800
May	1st to 10th	Day	7% 14% 5% 9% 7% 6% 6% 5% 8% 7% 27%	5063
	11th to 20th	Day	5% 15% 5% 11% 8% 7% 6% 5% 7% 7% 23%	5173
	21st to end	Day	6% 9% 3 10% 7% 6% 6% 4 6% 8% 35%	5717
June	1st to 10th	Day	11% 11% 3 9% 7% 6% 6% 6% 6% 8% 28%	3404
	11th to 20th	Day	12% 10% 3 10% 6% 6% 6% 5% 7% 9% 25%	3420
	21st to end	Day	8% 7% 3 9% 7% 7% 7% 5% 7% 9% 30%	3420
July	1st to 10th	Day	8% 6% 2 7% 6% 6% 6% 6% 8% 9% 36%	5681
	11th to 20th	Day	14% 9% 4 11% 7% 6% 6% 5% 8% 8% 23%	5226
	21st to end	Day	12% 8% 2 8% 5% 6% 5% 4 6% 9% 34%	5486
August	1st to 10th	Day	7% 5% 2 5% 4 3 5% 4 6% 8% 50%	4928
	11th to 20th	Day	14% 9% 3 7% 5% 5% 5% 4 6% 8% 35%	4349
	21st to end	Day	18% 12% 3 8% 6% 6% 6% 5% 6% 7% 24%	4873
September	1st to 10th	Day	17% 13% 5% 9% 7% 7% 5% 5% 5% 6% 21%	2309
	11th to 20th	Day	13% 12% 4 9% 5% 6% 6% 4 7% 7% 28%	2280
	21st to end	Day	16% 17% 5% 13% 6% 5% 6% 4 6% 5% 18%	2027
October	1st to 10th	Day	10% 22% 6% 14% 7% 7% 5% 4 5% 6% 15%	3170
	11th to 20th	Day	9% 19% 6% 11% 7% 6% 6% 5% 8% 7% 17%	2843
	21st to end	Day	12% 17% 6% 13% 9% 7% 6% 4 6% 6% 14%	2768
November	1st to 10th	Day	8% 18% 6% 16% 12% 8% 7% 3 5% 6% 11%	1372
	11th to 20th	Day	5% 21% 9% 22% 11% 6% 5% 3 4 5% 10%	1254
	21st to end	Day	6% 16% 7% 15% 8% 8% 6% 6% 7% 7% 12%	1110
December	1st to 10th	Day	10% 18% 7% 14% 9% 6% 8% 5% 7% 6% 9%	1630
	11th to 20th	Day	2 11% 6% 18% 11% 11% 8% 5% 8% 8% 13%	1507
	21st to end	Day	4 15% 7% 23% 11% 9% 6% 4 5% 6% 9%	1980
January	1st to 10th	Night	4 13% 6% 17% 11% 9% 10% 6% 5% 6% 12%	7889
	11th to 20th	Night	3 14% 7% 14% 9% 7% 6% 6% 9% 11% 15%	7219
	21st to end	Night	6% 15% 5% 16% 8% 8% 8% 5% 7% 8% 15%	7920
February	1st to 10th	Night	3 13% 5% 15% 10% 8% 7% 5% 7% 8% 18%	2959
	11th to 20th	Night	3 13% 5% 13% 9% 7% 8% 5% 8% 8% 20%	2727
	21st to end	Night	2 13% 5% 13% 10% 7% 6% 5% 6% 8% 23%	2170
March	1st to 10th	Night	2 10% 4 17% 9% 9% 10% 8% 7% 7% 18%	5422
	11th to 20th	Night	2 14% 7% 17% 11% 9% 7% 5% 6% 7% 16%	5266
	21st to end	Night	2 11% 6% 16% 8% 7% 8% 6% 9% 8% 20%	5013
April	1st to 10th	Night	3 11% 5% 13% 7% 6% 7% 4 7% 9% 27%	1995
	11th to 20th	Night	4 13% 4 10% 8% 6% 6% 5% 7% 8% 28%	1584
	21st to end	Night	5% 13% 4 10% 6% 6% 6% 5% 6% 8% 31%	1600
May	1st to 10th	Night	4 12% 3 9% 5% 5% 6% 6% 8% 9% 34%	2116
	11th to 20th	Night	5% 12% 5% 13% 8% 7% 7% 5% 7% 7% 25%	1942
	21st to end	Night	6% 8% 4 9% 8% 6% 6% 6% 6% 9% 33%	1973
June	1st to 10th	Night	14% 6% 4 10% 7% 6% 5% 4 6% 7% 31%	774
	11th to 20th	Night	12% 11% 3 10% 8% 5% 6% 5% 8% 9% 24%	760
	21st to end	Night	7% 7% 3 9% 7% 7% 8% 6% 11% 10% 27%	760
July	1st to 10th	Night	7% 4 2 6% 6% 5% 6% 8% 9% 11% 38%	1278
	11th to 20th	Night	14% 8% 4 10% 6% 7% 6% 5% 6% 8% 25%	1733
	21st to end	Night	13% 8% 3 10% 7% 7% 6% 5% 8% 6% 27%	2066
August	1st to 10th	Night	6% 5% 2 6% 4 4 5% 3 7% 8% 50%	2003
	11th to 20th	Night	10% 5% 2 7% 5% 5% 6% 4 8% 10% 38%	2489
	21st to end	Night	18% 14% 4 7% 5% 5% 5% 4 6% 6% 26%	2794
September	1st to 10th	Night	12% 12% 4 10% 6% 6% 6% 5% 8% 6% 25%	1870
	11th to 20th	Night	11% 9% 4 8% 7% 5% 6% 4 6% 8% 32%	1900
	21st to end	Night	15% 15% 5% 10% 6% 7% 6% 5% 5% 6% 20%	2151
October	1st to 10th	Night	10% 17% 5% 11% 8% 8% 7% 4 6% 6% 17%	3800
	11th to 20th	Night	10% 21% 7% 12% 7% 6% 6% 4 5% 5% 17%	4085
	21st to end	Night	9% 15% 6% 13% 7% 6% 7% 5% 7% 6% 17%	4790
November	1st to 10th	Night	6% 18% 7% 16% 11% 7% 6% 4 6% 6% 12%	2926
	11th to 20th	Night	4 20% 8% 21% 11% 8% 5% 4 6% 6% 8%	3145
	21st to end	Night	4 17% 7% 17% 10% 8% 7% 5% 7% 7% 11%	3268
December	1st to 10th	Night	9% 17% 7% 16% 8% 7% 7% 5% 7% 7% 11%	5550
	11th to 20th	Night	3 13% 7% 20% 14% 9% 7% 5% 6% 7% 11%	6685
	21st to end	Night	3 18% 8% 23% 10% 7% 6% 4 5% 5% 11%	8976

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	63% 13% 8% 5% 10% 1	2098
	11th to 20th	Day	63% 7% 12% 7% 10% 1	2695
	21st to end	Day	60% 9% 13% 12% 4 1	3038
February	1st to 10th	Day	61% 8% 10% 10% 10% 2	1441
	11th to 20th	Day	62% 9% 12% 9% 8% 1	1568
	21st to end	Day	60% 9% 12% 13% 5% 1	1457
March	1st to 10th	Day	59% 8% 14% 9% 9% 1	4452
	11th to 20th	Day	64% 8% 16% 8% 4	4689
	21st to end	Day	53% 12% 16% 15% 5%	5939
April	1st to 10th	Day	56% 11% 17% 12% 4	2405
	11th to 20th	Day	56% 8% 16% 14% 6% 1	2762
	21st to end	Day	54% 10% 17% 15% 4	2800
May	1st to 10th	Day	50% 10% 18% 20% 3	5063
	11th to 20th	Day	54% 10% 16% 16% 4	5176
	21st to end	Day	44% 8% 23% 19% 7%	5718
June	1st to 10th	Day	51% 10% 22% 14% 3	3404
	11th to 20th	Day	52% 11% 23% 13% 2	3420
	21st to end	Day	47% 13% 23% 15% 2	3420
July	1st to 10th	Day	39% 10% 30% 18% 3	5592
	11th to 20th	Day	57% 12% 17% 14% 1	5133
	21st to end	Day	45% 10% 24% 19% 3	5313
August	1st to 10th	Day	31% 10% 20% 25% 14% 1	4909
	11th to 20th	Day	46% 8% 19% 19% 7%	4391
	21st to end	Day	58% 10% 14% 16% 2	4872
September	1st to 10th	Day	62% 10% 14% 13% 2	2309
	11th to 20th	Day	53% 11% 17% 16% 3	2280
	21st to end	Day	67% 9% 14% 9% 2	2027
October	1st to 10th	Day	69% 10% 11% 10% 1	3170
	11th to 20th	Day	63% 9% 15% 12% 2	2843
	21st to end	Day	66% 10% 14% 7% 2	2768
November	1st to 10th	Day	69% 11% 12% 7% 1	1372
	11th to 20th	Day	76% 7% 9% 6% 2	1254
	21st to end	Day	66% 10% 12% 8% 3	1110
December	1st to 10th	Day	66% 15% 12% 5% 1	1630
	11th to 20th	Day	62% 8% 12% 13% 4	1509
	21st to end	Day	72% 7% 10% 7% 3	1980
January	1st to 10th	Night	66% 11% 8% 5% 9% 1	7889
	11th to 20th	Night	57% 7% 11% 12% 9% 4	7263
	21st to end	Night	62% 9% 14% 10% 4 1	7920
February	1st to 10th	Night	60% 10% 9% 11% 9% 1	2959
	11th to 20th	Night	58% 10% 12% 11% 8% 1	2730
	21st to end	Night	55% 8% 14% 16% 6% 1	2170
March	1st to 10th	Night	58% 6% 14% 14% 8% 1	5422
	11th to 20th	Night	62% 8% 11% 11% 7%	5268
	21st to end	Night	52% 10% 18% 12% 7%	5013
April	1st to 10th	Night	52% 9% 18% 17% 5%	1995
	11th to 20th	Night	50% 9% 17% 17% 7% 1	1584
	21st to end	Night	50% 10% 16% 19% 6%	1600
May	1st to 10th	Night	39% 10% 24% 23% 4	2116
	11th to 20th	Night	48% 10% 19% 16% 6% 1	1942
	21st to end	Night	40% 8% 22% 23% 7%	1973
June	1st to 10th	Night	48% 9% 22% 17% 3	774
	11th to 20th	Night	50% 10% 28% 10% 2	760
	21st to end	Night	44% 14% 26% 15% 1	760
July	1st to 10th	Night	34% 12% 33% 18% 3	1258
	11th to 20th	Night	54% 12% 17% 15% 2	1703
	21st to end	Night	52% 13% 22% 12% 1	2000
August	1st to 10th	Night	30% 11% 23% 22% 13%	1997
	11th to 20th	Night	39% 10% 28% 17% 6%	2513
	21st to end	Night	57% 9% 16% 16% 1	2794
September	1st to 10th	Night	56% 12% 19% 12% 1	1870
	11th to 20th	Night	48% 11% 20% 18% 3	1900
	21st to end	Night	61% 8% 15% 13% 3	2151
October	1st to 10th	Night	61% 8% 15% 13% 2	3800
	11th to 20th	Night	66% 8% 13% 11% 3	4085
	21st to end	Night	58% 11% 19% 10% 2	4790
November	1st to 10th	Night	69% 9% 13% 7% 2	2926
	11th to 20th	Night	74% 9% 9% 6% 2	3145
	21st to end	Night	69% 9% 12% 8% 2	3268
December	1st to 10th	Night	67% 12% 9% 10% 2	5550
	11th to 20th	Night	69% 7% 11% 10% 3	6682
	21st to end	Night	71% 7% 9% 7% 5% 1	8976

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	5% 10% 30% 26% 18% 11%	100
	11th to 20th	Day	19% 8% 21% 27% 19% 6%	195
	21st to end	Day	16% 15% 29% 22% 14% 3	240
February	1st to 10th	Day	10% 8% 31% 31% 15% 4	400
	11th to 20th	Day	8% 13% 31% 28% 13% 7%	395
	21st to end	Day	7% 13% 36% 27% 13% 4	331
March	1st to 10th	Day	8% 13% 30% 31% 14% 5%	400
	11th to 20th	Day	10% 15% 33% 24% 14% 4	400
	21st to end	Day	7% 17% 28% 24% 19% 4	543
April	1st to 10th	Day	9% 14% 35% 28% 12% 2	500
	11th to 20th	Day	9% 19% 23% 29% 18% 3	686
	21st to end	Day	11% 15% 30% 27% 14% 3	700
May	1st to 10th	Day	17% 15% 29% 27% 11% 2	703
	11th to 20th	Day	12% 12% 29% 26% 15% 6%	725
	21st to end	Day	12% 12% 29% 26% 17% 4	833
June	1st to 10th	Day	16% 10% 26% 29% 16% 4	870
	11th to 20th	Day	16% 10% 27% 27% 16% 3	870
	21st to end	Day	11% 10% 25% 28% 22% 4	870
July	1st to 10th	Day	13% 9% 24% 30% 19% 5%	850
	11th to 20th	Day	19% 13% 24% 27% 14% 3	668
	21st to end	Day	16% 12% 25% 27% 17% 4	739
August	1st to 10th	Day	15% 12% 28% 27% 14% 5%	676
	11th to 20th	Day	26% 20% 24% 20% 8% 2	665
	21st to end	Day	27% 14% 26% 23% 9% 1	748
September	1st to 10th	Day	28% 18% 22% 18% 11% 3	500
	11th to 20th	Day	22% 15% 25% 23% 12% 3	490
	21st to end	Day	25% 21% 27% 17% 7% 2	453
October	1st to 10th	Day	24% 19% 31% 17% 7% 2	390
	11th to 20th	Day	23% 18% 31% 18% 7% 3	390
	21st to end	Day	15% 14% 28% 27% 13% 3	429
November	1st to 10th	Day	17% 19% 28% 25% 9% 4	200
	11th to 20th	Day	16% 9% 29% 28% 14% 5%	200
	21st to end	Day	8% 16% 31% 30% 12% 5%	200
December	1st to 10th	Day	13% 12% 30% 25% 16% 5%	200
	11th to 20th	Day	13% 4 25% 28% 19% 11%	103
	21st to end	Day	5% 13% 29% 25% 21% 7%	110
January	1st to 10th	Night	10% 6% 27% 33% 21% 3	986
	11th to 20th	Night	14% 11% 31% 29% 12% 3	900
	21st to end	Night	12% 13% 30% 28% 15% 2	990
February	1st to 10th	Night	8% 8% 26% 41% 14% 2	900
	11th to 20th	Night	8% 10% 32% 32% 15% 3	884
	21st to end	Night	7% 8% 33% 35% 14% 3	743
March	1st to 10th	Night	6% 10% 28% 32% 20% 4	810
	11th to 20th	Night	8% 8% 26% 34% 19% 4	732
	21st to end	Night	6% 8% 22% 33% 25% 6%	660
April	1st to 10th	Night	6% 7% 23% 37% 23% 3	600
	11th to 20th	Night	9% 7% 24% 31% 26% 4	593
	21st to end	Night	12% 6% 21% 34% 24% 4	600
May	1st to 10th	Night	9% 8% 21% 32% 26% 4	415
	11th to 20th	Night	11% 6% 22% 35% 24% 2	394
	21st to end	Night	10% 6% 20% 33% 28% 2	422
June	1st to 10th	Night	16% 3 22% 31% 27%	204
	11th to 20th	Night	16% 4 16% 36% 28% 1	190
	21st to end	Night	9% 3 21% 36% 31% 1	190
July	1st to 10th	Night	11% 4 21% 39% 23% 1	185
	11th to 20th	Night	15% 7% 19% 38% 21%	272
	21st to end	Night	12% 6% 25% 34% 22% 2	416
August	1st to 10th	Night	13% 6% 23% 33% 24% 1	436
	11th to 20th	Night	17% 7% 28% 29% 16% 3	564
	21st to end	Night	25% 7% 22% 28% 16% 2	627
September	1st to 10th	Night	19% 9% 26% 29% 16% 1	570
	11th to 20th	Night	16% 10% 23% 28% 19% 4	570
	21st to end	Night	23% 12% 25% 25% 12% 3	755
October	1st to 10th	Night	22% 13% 24% 25% 14% 1	760
	11th to 20th	Night	21% 12% 23% 29% 13% 2	760
	21st to end	Night	15% 8% 31% 30% 14% 2	939
November	1st to 10th	Night	14% 10% 25% 35% 14% 2	880
	11th to 20th	Night	13% 10% 25% 31% 17% 4	900
	21st to end	Night	12% 13% 27% 30% 15% 3	968
December	1st to 10th	Night	13% 10% 28% 31% 16% 3	1100
	11th to 20th	Night	14% 6% 23% 35% 17% 5%	1100
	21st to end	Night	12% 9% 27% 31% 16% 4	1210

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