Atlin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Atlin clear sky chart from 2005-11-06 to 2024-01-31.

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	8% 10% 5% 10% 9% 5% 7% 7% 7% 8% 24%	74709
	Night	6% 12% 6% 12% 10% 6% 8% 7% 7% 8% 20%	75407
Transparency	Day	58% 12% 13% 12% 4	74356
	Night	60% 11% 13% 11% 5% 1	75280
Seeing	Day	16% 15% 27% 23% 15% 5%	16050
	Night	13% 11% 24% 29% 19% 4	22730

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	4 11% 7% 10% 14% 8% 10% 8% 7% 10% 12%	1074
	11th to 20th	Day	5% 15% 7% 14% 11% 6% 7% 8% 8% 7% 12%	1140
	21st to end	Day	5% 13% 7% 12% 11% 7% 9% 6% 8% 9% 15%	1262
February	1st to 10th	Day	3 10% 7% 14% 9% 5% 7% 8% 8% 11% 19%	1346
	11th to 20th	Day	3 10% 7% 11% 11% 6% 6% 7% 8% 9% 22%	1400
	21st to end	Day	1 10% 7% 10% 11% 5% 9% 7% 8% 9% 24%	1307
March	1st to 10th	Day	2 9% 5% 10% 11% 7% 10% 8% 9% 9% 20%	1800
	11th to 20th	Day	2 8% 7% 13% 11% 7% 8% 9% 7% 9% 20%	1837
	21st to end	Day	3 10% 8% 11% 11% 5% 7% 8% 8% 7% 22%	2376
April	1st to 10th	Day	2 8% 7% 12% 11% 6% 8% 7% 8% 9% 24%	2182
	11th to 20th	Day	3 12% 6% 10% 9% 5% 7% 7% 7% 8% 25%	2440
	21st to end	Day	5% 13% 5% 10% 8% 5% 7% 7% 6% 8% 27%	2520
May	1st to 10th	Day	6% 11% 5% 9% 7% 5% 7% 7% 9% 8% 26%	2737
	11th to 20th	Day	6% 11% 4 8% 8% 4 7% 7% 7% 9% 30%	2833
	21st to end	Day	7% 8% 4 8% 8% 3 6% 6% 6% 9% 35%	3167
June	1st to 10th	Day	11% 8% 4 7% 7% 4 7% 6% 7% 8% 31%	3104
	11th to 20th	Day	11% 10% 4 7% 7% 4 7% 8% 7% 8% 27%	3240
	21st to end	Day	8% 8% 4 8% 8% 4 7% 7% 7% 10% 29%	3240
July	1st to 10th	Day	9% 6% 3 7% 7% 4 6% 7% 8% 11% 31%	3200
	11th to 20th	Day	13% 9% 4 8% 7% 5% 6% 6% 8% 9% 25%	2880
	21st to end	Day	12% 8% 4 8% 6% 4 7% 5% 6% 8% 32%	3135
August	1st to 10th	Day	10% 6% 3 7% 7% 4 6% 5% 7% 8% 36%	2777
	11th to 20th	Day	16% 11% 4 9% 7% 5% 5% 5% 7% 7% 24%	2476
	21st to end	Day	20% 11% 5% 8% 7% 3 5% 6% 6% 7% 21%	2746
September	1st to 10th	Day	16% 12% 4 8% 9% 6% 6% 6% 5% 7% 21%	2199
	11th to 20th	Day	12% 11% 4 8% 7% 5% 6% 6% 6% 7% 28%	2138
	21st to end	Day	17% 16% 5% 10% 9% 5% 6% 6% 5% 5% 18%	1949
October	1st to 10th	Day	10% 14% 6% 10% 9% 5% 6% 7% 6% 7% 21%	1782
	11th to 20th	Day	8% 14% 6% 13% 10% 5% 7% 5% 6% 7% 19%	1620
	21st to end	Day	7% 13% 6% 12% 10% 8% 8% 6% 6% 7% 16%	1630
November	1st to 10th	Day	5% 15% 6% 12% 11% 8% 8% 8% 7% 7% 11%	1302
	11th to 20th	Day	5% 19% 8% 15% 12% 8% 8% 5% 6% 6% 9%	1250
	21st to end	Day	4 15% 8% 14% 15% 5% 7% 8% 7% 6% 10%	1064
December	1st to 10th	Day	5% 12% 5% 13% 15% 8% 12% 8% 6% 6% 9%	950
	11th to 20th	Day	2 10% 5% 11% 11% 5% 11% 11% 10% 11% 13%	1202
	21st to end	Day	3 13% 8% 14% 12% 6% 9% 7% 8% 8% 13%	1404
January	1st to 10th	Night	4 12% 6% 13% 13% 8% 11% 7% 6% 8% 13%	3103
	11th to 20th	Night	6% 12% 7% 13% 12% 6% 8% 8% 8% 7% 13%	3040
	21st to end	Night	5% 13% 7% 14% 11% 6% 9% 8% 7% 7% 14%	3320
February	1st to 10th	Night	3 13% 5% 11% 12% 5% 7% 7% 7% 8% 21%	2614
	11th to 20th	Night	3 11% 7% 13% 11% 7% 7% 7% 8% 8% 19%	2447
	21st to end	Night	2 11% 6% 11% 10% 5% 6% 6% 7% 9% 26%	1949
March	1st to 10th	Night	2 11% 7% 11% 9% 7% 9% 6% 7% 8% 24%	2160
	11th to 20th	Night	2 10% 8% 13% 12% 6% 8% 7% 6% 8% 20%	2119
	21st to end	Night	3 11% 7% 12% 8% 5% 7% 6% 7% 8% 27%	1980
April	1st to 10th	Night	2 9% 6% 10% 10% 5% 7% 7% 7% 9% 29%	1778
	11th to 20th	Night	4 10% 5% 9% 9% 4 7% 6% 7% 10% 29%	1467
	21st to end	Night	4 12% 4 9% 8% 5% 6% 8% 7% 7% 29%	1440
May	1st to 10th	Night	4 8% 4 7% 9% 5% 8% 8% 9% 9% 31%	1221
	11th to 20th	Night	5% 8% 3 9% 8% 4 7% 8% 6% 9% 33%	1062
	21st to end	Night	5% 7% 3 6% 8% 5% 7% 7% 9% 8% 36%	1106
June	1st to 10th	Night	12% 7% 5% 8% 7% 4 4 5% 6% 11% 31%	851
	11th to 20th	Night	9% 8% 4 7% 7% 4 6% 6% 7% 10% 32%	720
	21st to end	Night	5% 5% 4 8% 6% 3 8% 8% 10% 11% 32%	720
July	1st to 10th	Night	10% 5% 4 7% 8% 4 6% 8% 7% 6% 37%	756
	11th to 20th	Night	12% 7% 4 8% 6% 4 9% 6% 8% 10% 27%	1080
	21st to end	Night	8% 7% 4 7% 8% 4 8% 7% 7% 7% 34%	1182
August	1st to 10th	Night	11% 6% 3 6% 5% 3 6% 6% 7% 11% 35%	1160
	11th to 20th	Night	14% 9% 3 8% 6% 5% 6% 6% 8% 8% 29%	1424
	21st to end	Night	18% 12% 5% 7% 6% 3 6% 5% 4 6% 27%	1610
September	1st to 10th	Night	12% 12% 5% 10% 8% 6% 6% 6% 6% 6% 24%	1759
	11th to 20th	Night	10% 11% 4 7% 8% 4 6% 5% 5% 7% 34%	1822
	21st to end	Night	14% 12% 5% 11% 8% 5% 6% 6% 7% 7% 20%	2009
October	1st to 10th	Night	10% 10% 5% 10% 8% 5% 7% 7% 7% 8% 25%	2178
	11th to 20th	Night	10% 15% 6% 13% 9% 4 6% 6% 6% 6% 20%	2340
	21st to end	Night	7% 14% 6% 11% 11% 6% 7% 6% 7% 8% 17%	2722
November	1st to 10th	Night	7% 14% 6% 14% 12% 8% 8% 7% 8% 7% 11%	2776
	11th to 20th	Night	6% 17% 10% 16% 11% 7% 9% 6% 5% 6% 7%	2928
	21st to end	Night	4 13% 8% 15% 13% 8% 10% 8% 7% 6% 10%	3097
December	1st to 10th	Night	5% 13% 7% 15% 14% 8% 11% 8% 6% 6% 7%	3230
	11th to 20th	Night	3 13% 7% 13% 12% 7% 9% 8% 8% 9% 11%	3990
	21st to end	Night	3 14% 6% 13% 11% 6% 9% 8% 7% 8% 15%	6247

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	61% 10% 11% 10% 5% 2	1074
	11th to 20th	Day	67% 11% 9% 4 9%	1140
	21st to end	Day	65% 9% 12% 10% 4	1262
February	1st to 10th	Day	56% 10% 11% 11% 11% 1	1346
	11th to 20th	Day	57% 11% 13% 9% 8% 1	1408
	21st to end	Day	54% 10% 13% 15% 7% 1	1307
March	1st to 10th	Day	59% 10% 13% 10% 7% 2	1800
	11th to 20th	Day	64% 9% 12% 10% 5%	1837
	21st to end	Day	60% 12% 14% 8% 5% 1	2376
April	1st to 10th	Day	60% 15% 11% 11% 3	2182
	11th to 20th	Day	58% 12% 11% 14% 5%	2440
	21st to end	Day	59% 11% 14% 12% 4	2520
May	1st to 10th	Day	55% 15% 15% 12% 3	2737
	11th to 20th	Day	51% 9% 13% 20% 7%	2836
	21st to end	Day	47% 10% 18% 20% 5%	3168
June	1st to 10th	Day	54% 12% 15% 14% 4 1	3104
	11th to 20th	Day	57% 13% 14% 14% 3	3240
	21st to end	Day	52% 15% 15% 15% 2	3240
July	1st to 10th	Day	48% 16% 16% 16% 4	3113
	11th to 20th	Day	59% 16% 15% 9%	2793
	21st to end	Day	52% 15% 15% 16% 2	2961
August	1st to 10th	Day	49% 13% 20% 15% 2	2758
	11th to 20th	Day	62% 13% 13% 11% 1	2476
	21st to end	Day	66% 13% 13% 7% 1	2746
September	1st to 10th	Day	67% 11% 10% 11% 2	2199
	11th to 20th	Day	57% 11% 11% 18% 3	2138
	21st to end	Day	71% 10% 9% 8% 2	1949
October	1st to 10th	Day	63% 12% 12% 11% 3	1782
	11th to 20th	Day	66% 12% 11% 8% 3	1620
	21st to end	Day	65% 12% 13% 7% 3	1630
November	1st to 10th	Day	62% 15% 13% 7% 3	1302
	11th to 20th	Day	71% 11% 11% 4 2	1250
	21st to end	Day	65% 13% 13% 7% 2	1064
December	1st to 10th	Day	68% 10% 12% 8% 1	950
	11th to 20th	Day	53% 10% 18% 13% 6%	1204
	21st to end	Day	63% 6% 13% 8% 9% 1	1404
January	1st to 10th	Night	65% 10% 11% 7% 6% 1	3103
	11th to 20th	Night	67% 10% 10% 6% 6% 1	3040
	21st to end	Night	66% 11% 9% 8% 5%	3320
February	1st to 10th	Night	58% 9% 12% 9% 9% 2	2614
	11th to 20th	Night	60% 11% 10% 10% 7% 1	2450
	21st to end	Night	53% 9% 12% 18% 7% 1	1949
March	1st to 10th	Night	54% 7% 14% 15% 7% 3	2160
	11th to 20th	Night	61% 10% 11% 12% 6%	2121
	21st to end	Night	53% 11% 15% 14% 6%	1980
April	1st to 10th	Night	53% 10% 16% 18% 3	1778
	11th to 20th	Night	50% 11% 16% 16% 7% 1	1467
	21st to end	Night	54% 10% 15% 14% 6%	1440
May	1st to 10th	Night	50% 11% 18% 17% 4	1221
	11th to 20th	Night	48% 9% 12% 21% 8% 1	1062
	21st to end	Night	45% 11% 19% 20% 5%	1106
June	1st to 10th	Night	49% 11% 18% 17% 4 1	851
	11th to 20th	Night	50% 15% 17% 15% 3	720
	21st to end	Night	44% 17% 22% 17% 1	720
July	1st to 10th	Night	45% 14% 16% 19% 5%	735
	11th to 20th	Night	53% 16% 21% 11%	1044
	21st to end	Night	47% 16% 21% 15% 2	1116
August	1st to 10th	Night	43% 14% 22% 19% 2	1154
	11th to 20th	Night	54% 13% 17% 14% 2	1424
	21st to end	Night	61% 12% 15% 11% 1	1610
September	1st to 10th	Night	62% 13% 13% 11% 2	1759
	11th to 20th	Night	53% 10% 13% 19% 4	1822
	21st to end	Night	66% 11% 10% 10% 3	2009
October	1st to 10th	Night	59% 12% 14% 12% 4	2178
	11th to 20th	Night	66% 11% 12% 8% 3	2340
	21st to end	Night	60% 11% 16% 10% 2	2722
November	1st to 10th	Night	65% 13% 12% 7% 3	2776
	11th to 20th	Night	72% 10% 10% 5% 3	2928
	21st to end	Night	67% 12% 11% 8% 2	3097
December	1st to 10th	Night	67% 10% 12% 9% 2	3230
	11th to 20th	Night	61% 7% 13% 13% 5%	3987
	21st to end	Night	62% 8% 11% 7% 10% 2	6247

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	7% 6% 28% 33% 19% 7%	173
	11th to 20th	Day	10% 14% 24% 23% 23% 5%	180
	21st to end	Day	19% 18% 18% 24% 14% 6%	210
February	1st to 10th	Day	11% 9% 29% 35% 12% 4	340
	11th to 20th	Day	11% 17% 30% 24% 13% 6%	335
	21st to end	Day	5% 16% 36% 24% 13% 5%	280
March	1st to 10th	Day	8% 16% 30% 24% 16% 6%	340
	11th to 20th	Day	8% 17% 38% 23% 12% 2	344
	21st to end	Day	10% 18% 28% 26% 14% 4	462
April	1st to 10th	Day	8% 21% 32% 25% 12% 3	420
	11th to 20th	Day	10% 16% 25% 27% 18% 3	544
	21st to end	Day	12% 18% 32% 22% 15% 2	600
May	1st to 10th	Day	13% 16% 30% 23% 16% 3	603
	11th to 20th	Day	10% 10% 21% 26% 21% 12%	625
	21st to end	Day	11% 10% 26% 24% 22% 7%	736
June	1st to 10th	Day	17% 11% 23% 23% 20% 6%	810
	11th to 20th	Day	17% 12% 24% 24% 16% 6%	810
	21st to end	Day	12% 12% 27% 23% 20% 7%	810
July	1st to 10th	Day	13% 10% 24% 26% 20% 7%	775
	11th to 20th	Day	20% 12% 28% 24% 12% 4	618
	21st to end	Day	19% 15% 24% 20% 15% 6%	684
August	1st to 10th	Day	17% 13% 29% 23% 13% 6%	626
	11th to 20th	Day	28% 21% 26% 17% 7% 1	615
	21st to end	Day	31% 14% 27% 18% 8% 2	667
September	1st to 10th	Day	27% 19% 21% 22% 10% 1	450
	11th to 20th	Day	22% 16% 24% 21% 14% 3	450
	21st to end	Day	35% 20% 24% 13% 6% 1	435
October	1st to 10th	Day	28% 15% 31% 18% 7% 1	360
	11th to 20th	Day	25% 20% 31% 14% 6% 3	360
	21st to end	Day	19% 15% 26% 25% 13% 3	386
November	1st to 10th	Day	16% 14% 29% 23% 14% 3	180
	11th to 20th	Day	14% 12% 30% 22% 16% 6%	180
	21st to end	Day	9% 22% 32% 22% 10% 5%	180
December	1st to 10th	Day	8% 18% 24% 29% 15% 6%	180
	11th to 20th	Day	9% 12% 22% 28% 22% 7%	180
	21st to end	Day	6% 18% 22% 25% 22% 8%	102
January	1st to 10th	Night	9% 11% 26% 31% 19% 4	917
	11th to 20th	Night	12% 16% 28% 25% 15% 4	850
	21st to end	Night	12% 19% 25% 25% 15% 4	932
February	1st to 10th	Night	10% 10% 27% 36% 14% 3	800
	11th to 20th	Night	8% 15% 30% 28% 15% 4	784
	21st to end	Night	6% 11% 28% 32% 18% 4	650
March	1st to 10th	Night	6% 13% 28% 28% 21% 5%	720
	11th to 20th	Night	7% 10% 28% 33% 19% 3	689
	21st to end	Night	7% 8% 23% 29% 23% 10%	594
April	1st to 10th	Night	5% 8% 21% 33% 28% 5%	540
	11th to 20th	Night	7% 8% 25% 28% 27% 5%	533
	21st to end	Night	9% 8% 23% 30% 24% 6%	540
May	1st to 10th	Night	9% 8% 21% 28% 29% 5%	365
	11th to 20th	Night	8% 8% 17% 31% 27% 9%	354
	21st to end	Night	6% 7% 16% 31% 32% 8%	389
June	1st to 10th	Night	16% 5% 19% 29% 30% 1	311
	11th to 20th	Night	14% 3 23% 26% 32% 3	180
	21st to end	Night	9% 3 19% 31% 35% 3	180
July	1st to 10th	Night	14% 4 18% 33% 31% 1	192
	11th to 20th	Night	18% 7% 16% 30% 26% 3	348
	21st to end	Night	11% 8% 19% 28% 30% 4	394
August	1st to 10th	Night	14% 5% 14% 34% 29% 3	406
	11th to 20th	Night	21% 11% 20% 25% 19% 4	534
	21st to end	Night	26% 8% 17% 26% 19% 3	594
September	1st to 10th	Night	22% 11% 22% 27% 16% 2	540
	11th to 20th	Night	19% 12% 17% 27% 19% 5%	562
	21st to end	Night	27% 17% 21% 20% 11% 5%	720
October	1st to 10th	Night	19% 14% 23% 24% 16% 4	720
	11th to 20th	Night	23% 16% 22% 25% 12% 3	720
	21st to end	Night	16% 11% 28% 28% 13% 3	861
November	1st to 10th	Night	13% 11% 28% 30% 15% 2	830
	11th to 20th	Night	15% 12% 24% 28% 17% 4	850
	21st to end	Night	12% 15% 27% 27% 15% 4	907
December	1st to 10th	Night	12% 13% 24% 29% 20% 2	1040
	11th to 20th	Night	12% 10% 25% 32% 17% 4	1040
	21st to end	Night	12% 11% 25% 29% 19% 5%	1144

Page generated at 2024-01-28 02:26:33. Version ac07

Copyright 2024 Attilla Danko