Teslin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Teslin clear sky chart from 2005-11-06 to 2024-11-12.

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	10% 12% 5% 11% 8% 6% 6% 5% 6% 7% 24%	106534
	Night	9% 15% 5% 13% 8% 7% 6% 4 6% 7% 20%	101160
Transparency	Day	55% 10% 15% 15% 5%	106233
	Night	59% 9% 13% 13% 5%	101108
Seeing	Day	15% 11% 22% 26% 18% 7%	17306
	Night	14% 7% 21% 33% 21% 4	23684

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	5% 13% 6% 21% 17% 11% 6% 3 3 4 11%	1547
	11th to 20th	Day	7% 16% 8% 16% 7% 7% 6% 3 5% 8% 17%	1882
	21st to end	Day	11% 22% 7% 16% 8% 6% 5% 4 4 5% 11%	2090
February	1st to 10th	Day	6% 15% 4 13% 8% 6% 6% 5% 7% 7% 21%	1389
	11th to 20th	Day	5% 18% 7% 13% 7% 7% 5% 5% 9% 8% 15%	1480
	21st to end	Day	3 11% 7% 11% 10% 7% 6% 6% 8% 7% 23%	1360
March	1st to 10th	Day	1 10% 4 14% 13% 11% 9% 6% 6% 6% 20%	3126
	11th to 20th	Day	4 15% 8% 15% 8% 6% 5% 4 5% 8% 21%	3229
	21st to end	Day	2 9% 6% 16% 10% 7% 7% 5% 6% 7% 26%	4165
April	1st to 10th	Day	4 13% 6% 16% 9% 8% 6% 5% 6% 7% 20%	2337
	11th to 20th	Day	4 15% 5% 12% 8% 6% 6% 4 6% 7% 27%	2559
	21st to end	Day	6% 14% 5% 11% 7% 7% 6% 5% 6% 7% 26%	2703
May	1st to 10th	Day	13% 16% 5% 10% 6% 5% 5% 4 5% 7% 25%	4821
	11th to 20th	Day	9% 16% 6% 12% 8% 6% 6% 5% 6% 6% 22%	5013
	21st to end	Day	10% 11% 3 9% 6% 6% 6% 5% 7% 8% 29%	5781
June	1st to 10th	Day	13% 10% 4 10% 8% 6% 6% 5% 6% 7% 25%	3306
	11th to 20th	Day	13% 10% 4 11% 7% 6% 6% 5% 7% 8% 24%	3420
	21st to end	Day	10% 9% 4 10% 8% 7% 6% 6% 8% 9% 24%	3420
July	1st to 10th	Day	9% 6% 3 8% 6% 6% 6% 5% 8% 10% 33%	5700
	11th to 20th	Day	18% 11% 4 10% 8% 7% 6% 5% 6% 6% 19%	5196
	21st to end	Day	12% 7% 4 9% 6% 6% 6% 6% 7% 8% 28%	5486
August	1st to 10th	Day	6% 5% 2 7% 5% 5% 4 4 5% 7% 49%	4952
	11th to 20th	Day	14% 7% 2 7% 5% 5% 6% 4 6% 9% 34%	4343
	21st to end	Day	21% 10% 3 9% 5% 5% 5% 4 7% 8% 23%	4791
September	1st to 10th	Day	17% 13% 5% 10% 7% 6% 5% 4 6% 7% 21%	2363
	11th to 20th	Day	14% 9% 4 9% 5% 7% 5% 4 6% 6% 29%	2234
	21st to end	Day	17% 14% 4 14% 7% 6% 4 4 5% 5% 19%	2085
October	1st to 10th	Day	12% 13% 5% 12% 9% 8% 8% 5% 6% 6% 17%	3083
	11th to 20th	Day	13% 17% 7% 10% 5% 5% 5% 4 6% 6% 20%	2843
	21st to end	Day	7% 18% 8% 17% 9% 9% 5% 4 5% 5% 13%	2772
November	1st to 10th	Day	8% 18% 8% 17% 10% 8% 6% 5% 6% 6% 10%	1372
	11th to 20th	Day	9% 19% 8% 18% 7% 9% 7% 5% 6% 4 8%	1257
	21st to end	Day	6% 18% 9% 15% 8% 9% 7% 6% 7% 6% 9%	969
December	1st to 10th	Day	7% 17% 7% 17% 9% 9% 7% 6% 6% 7% 9%	950
	11th to 20th	Day	3 16% 6% 14% 11% 10% 7% 5% 8% 9% 11%	1124
	21st to end	Day	10% 16% 6% 13% 10% 9% 8% 6% 8% 7% 8%	1386
January	1st to 10th	Night	6% 16% 6% 21% 16% 12% 6% 3 3 3 8%	5425
	11th to 20th	Night	7% 18% 7% 15% 7% 5% 4 3 6% 9% 20%	5016
	21st to end	Night	13% 24% 8% 16% 7% 5% 5% 4 4 4 11%	5566
February	1st to 10th	Night	6% 16% 6% 15% 8% 7% 6% 6% 6% 6% 20%	2790
	11th to 20th	Night	4 15% 6% 14% 11% 8% 7% 5% 6% 7% 17%	2587
	21st to end	Night	3 12% 5% 13% 9% 6% 5% 4 6% 8% 29%	2091
March	1st to 10th	Night	2 10% 5% 13% 10% 8% 5% 4 6% 7% 29%	3738
	11th to 20th	Night	6% 15% 7% 16% 8% 7% 6% 5% 5% 7% 20%	3726
	21st to end	Night	4 15% 7% 16% 9% 7% 6% 5% 6% 7% 20%	3477
April	1st to 10th	Night	4 12% 6% 12% 8% 7% 6% 6% 7% 7% 25%	1843
	11th to 20th	Night	4 13% 4 9% 7% 5% 6% 6% 7% 8% 30%	1567
	21st to end	Night	7% 14% 5% 10% 6% 5% 7% 4 7% 8% 27%	1477
May	1st to 10th	Night	8% 12% 4 10% 5% 5% 5% 5% 6% 7% 32%	2138
	11th to 20th	Night	6% 10% 5% 10% 7% 6% 6% 4 8% 8% 28%	1882
	21st to end	Night	6% 8% 4 8% 6% 6% 6% 6% 7% 9% 35%	1794
June	1st to 10th	Night	11% 7% 3 9% 6% 8% 5% 5% 8% 8% 29%	871
	11th to 20th	Night	13% 8% 2 9% 5% 6% 5% 4 5% 9% 34%	760
	21st to end	Night	9% 8% 3 9% 7% 6% 6% 6% 10% 10% 29%	760
July	1st to 10th	Night	7% 6% 2 6% 6% 6% 5% 5% 9% 11% 35%	1260
	11th to 20th	Night	17% 9% 3 11% 7% 6% 6% 5% 7% 7% 21%	1761
	21st to end	Night	16% 10% 3 9% 6% 6% 5% 4 6% 6% 28%	2066
August	1st to 10th	Night	7% 5% 3 5% 3 4 4 4 7% 8% 50%	1978
	11th to 20th	Night	11% 6% 3 7% 5% 4 4 4 7% 10% 39%	2493
	21st to end	Night	19% 13% 4 11% 6% 5% 6% 5% 6% 5% 21%	2876
September	1st to 10th	Night	15% 11% 4 10% 7% 5% 6% 5% 6% 7% 25%	1814
	11th to 20th	Night	11% 9% 3 9% 7% 5% 6% 4 6% 7% 33%	1946
	21st to end	Night	18% 14% 4 12% 7% 6% 5% 3 5% 6% 20%	2094
October	1st to 10th	Night	13% 13% 4 9% 6% 6% 7% 5% 7% 7% 22%	3887
	11th to 20th	Night	14% 19% 8% 12% 6% 4 5% 4 5% 6% 17%	4085
	21st to end	Night	9% 17% 4 13% 7% 8% 7% 5% 5% 6% 20%	4768
November	1st to 10th	Night	8% 17% 6% 15% 9% 8% 6% 4 6% 6% 12%	2926
	11th to 20th	Night	8% 19% 7% 18% 8% 8% 6% 5% 7% 6% 8%	2943
	21st to end	Night	8% 19% 7% 17% 10% 9% 7% 5% 6% 5% 8%	3192
December	1st to 10th	Night	7% 18% 7% 18% 11% 9% 6% 5% 6% 5% 6%	3230
	11th to 20th	Night	5% 17% 7% 17% 11% 8% 5% 4 6% 7% 12%	4063
	21st to end	Night	9% 17% 6% 12% 9% 9% 9% 5% 7% 6% 12%	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	76% 4 6% 4 7% 2	1547
	11th to 20th	Day	63% 6% 6% 10% 14% 1	1900
	21st to end	Day	71% 8% 10% 7% 3	2090
February	1st to 10th	Day	56% 9% 8% 15% 10% 2	1389
	11th to 20th	Day	58% 10% 14% 10% 7%	1488
	21st to end	Day	52% 9% 17% 15% 6%	1360
March	1st to 10th	Day	59% 7% 13% 12% 8% 1	3126
	11th to 20th	Day	58% 10% 14% 12% 6% 1	3229
	21st to end	Day	50% 15% 18% 11% 5% 1	4165
April	1st to 10th	Day	60% 10% 14% 11% 4	2337
	11th to 20th	Day	55% 11% 13% 16% 6%	2559
	21st to end	Day	55% 11% 16% 14% 5%	2703
May	1st to 10th	Day	54% 8% 12% 21% 4	4821
	11th to 20th	Day	56% 9% 14% 14% 6%	5016
	21st to end	Day	48% 9% 16% 20% 7%	5782
June	1st to 10th	Day	56% 11% 12% 16% 4	3306
	11th to 20th	Day	54% 11% 14% 17% 4	3420
	21st to end	Day	53% 13% 17% 13% 3	3420
July	1st to 10th	Day	41% 10% 23% 22% 3	5611
	11th to 20th	Day	61% 12% 16% 11% 1	5103
	21st to end	Day	47% 13% 21% 16% 3	5313
August	1st to 10th	Day	33% 9% 18% 25% 12% 3	4933
	11th to 20th	Day	43% 11% 21% 20% 5%	4385
	21st to end	Day	56% 11% 16% 15% 1	4790
September	1st to 10th	Day	60% 13% 11% 13% 3	2363
	11th to 20th	Day	52% 11% 15% 19% 3	2234
	21st to end	Day	65% 10% 11% 11% 2	2085
October	1st to 10th	Day	61% 10% 14% 14% 1	3083
	11th to 20th	Day	58% 10% 16% 15% 1	2843
	21st to end	Day	66% 13% 12% 7% 1	2772
November	1st to 10th	Day	71% 8% 11% 8% 2	1372
	11th to 20th	Day	72% 8% 10% 9% 1	1257
	21st to end	Day	68% 8% 13% 7% 4	969
December	1st to 10th	Day	70% 9% 11% 6% 3	950
	11th to 20th	Day	62% 6% 14% 10% 7%	1126
	21st to end	Day	66% 7% 9% 12% 7%	1386
January	1st to 10th	Night	78% 6% 8% 4 4	5425
	11th to 20th	Night	60% 5% 8% 10% 16% 1	5060
	21st to end	Night	73% 8% 8% 8% 3	5566
February	1st to 10th	Night	60% 8% 8% 14% 8% 1	2790
	11th to 20th	Night	61% 10% 12% 11% 6%	2590
	21st to end	Night	50% 8% 19% 15% 7% 1	2091
March	1st to 10th	Night	51% 5% 14% 20% 8% 1	3738
	11th to 20th	Night	57% 10% 14% 11% 6% 1	3728
	21st to end	Night	52% 15% 18% 11% 4	3477
April	1st to 10th	Night	52% 10% 15% 18% 5%	1843
	11th to 20th	Night	46% 11% 16% 20% 7%	1567
	21st to end	Night	52% 10% 18% 16% 5%	1477
May	1st to 10th	Night	44% 10% 15% 28% 3	2138
	11th to 20th	Night	46% 12% 16% 18% 7%	1882
	21st to end	Night	39% 10% 14% 29% 7%	1794
June	1st to 10th	Night	49% 10% 15% 21% 4 1	871
	11th to 20th	Night	44% 12% 17% 22% 4	760
	21st to end	Night	46% 12% 22% 19% 2	760
July	1st to 10th	Night	38% 10% 27% 22% 3	1240
	11th to 20th	Night	56% 12% 16% 14% 2	1731
	21st to end	Night	53% 12% 17% 17% 1	2000
August	1st to 10th	Night	30% 11% 17% 27% 12% 3	1972
	11th to 20th	Night	39% 11% 19% 23% 9%	2517
	21st to end	Night	63% 10% 12% 13% 2	2876
September	1st to 10th	Night	55% 13% 17% 14% 1	1814
	11th to 20th	Night	47% 12% 16% 21% 3	1946
	21st to end	Night	64% 10% 11% 13% 3	2094
October	1st to 10th	Night	54% 11% 16% 16% 3	3887
	11th to 20th	Night	64% 10% 12% 12% 1	4085
	21st to end	Night	56% 14% 17% 11% 2	4768
November	1st to 10th	Night	66% 10% 12% 10% 2	2926
	11th to 20th	Night	70% 10% 10% 9% 1	2943
	21st to end	Night	70% 8% 10% 9% 3	3192
December	1st to 10th	Night	75% 7% 8% 8% 2	3230
	11th to 20th	Night	68% 7% 10% 10% 5%	4060
	21st to end	Night	62% 8% 9% 10% 9% 1	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	6% 4 16% 34% 32% 8%	151
	11th to 20th	Day	13% 9% 13% 30% 26% 8%	180
	21st to end	Day	17% 16% 16% 21% 23% 7%	198
February	1st to 10th	Day	12% 6% 20% 36% 20% 5%	332
	11th to 20th	Day	11% 12% 23% 28% 18% 8%	365
	21st to end	Day	8% 8% 26% 29% 20% 8%	307
March	1st to 10th	Day	7% 10% 24% 31% 19% 9%	370
	11th to 20th	Day	8% 12% 31% 25% 20% 4	386
	21st to end	Day	8% 12% 24% 27% 22% 8%	506
April	1st to 10th	Day	11% 15% 28% 25% 17% 3	460
	11th to 20th	Day	9% 13% 26% 25% 21% 6%	573
	21st to end	Day	13% 14% 29% 25% 15% 4	650
May	1st to 10th	Day	20% 18% 24% 24% 12% 4	653
	11th to 20th	Day	16% 13% 25% 27% 11% 8%	675
	21st to end	Day	13% 12% 23% 25% 21% 6%	890
June	1st to 10th	Day	17% 10% 22% 25% 20% 6%	870
	11th to 20th	Day	16% 7% 21% 28% 21% 6%	870
	21st to end	Day	12% 9% 19% 28% 24% 9%	870
July	1st to 10th	Day	14% 9% 19% 29% 23% 7%	856
	11th to 20th	Day	19% 9% 19% 25% 19% 8%	743
	21st to end	Day	17% 8% 21% 22% 22% 10%	739
August	1st to 10th	Day	13% 7% 20% 28% 20% 12%	676
	11th to 20th	Day	23% 17% 19% 23% 12% 6%	665
	21st to end	Day	25% 11% 21% 23% 16% 4	705
September	1st to 10th	Day	20% 14% 25% 21% 16% 4	490
	11th to 20th	Day	15% 13% 22% 21% 21% 8%	490
	21st to end	Day	23% 18% 22% 21% 11% 5%	487
October	1st to 10th	Day	22% 15% 27% 24% 9% 3	390
	11th to 20th	Day	21% 16% 28% 22% 10% 3	390
	21st to end	Day	14% 10% 23% 35% 15% 3	372
November	1st to 10th	Day	15% 10% 26% 29% 17% 4	200
	11th to 20th	Day	16% 7% 22% 30% 18% 8%	182
	21st to end	Day	13% 11% 26% 32% 11% 8%	180
December	1st to 10th	Day	11% 7% 21% 33% 19% 8%	180
	11th to 20th	Day	17% 8% 19% 24% 23% 10%	156
	21st to end	Day	7% 8% 18% 34% 20% 12%	99
January	1st to 10th	Night	13% 4 19% 35% 25% 5%	1015
	11th to 20th	Night	16% 7% 22% 31% 19% 4	850
	21st to end	Night	16% 11% 21% 29% 20% 3	935
February	1st to 10th	Night	12% 7% 19% 40% 19% 4	850
	11th to 20th	Night	9% 7% 24% 38% 19% 3	834
	21st to end	Night	7% 5% 24% 38% 22% 4	687
March	1st to 10th	Night	6% 6% 23% 37% 21% 6%	760
	11th to 20th	Night	7% 8% 24% 34% 24% 3	758
	21st to end	Night	5% 8% 19% 31% 28% 8%	627
April	1st to 10th	Night	8% 7% 19% 31% 30% 5%	570
	11th to 20th	Night	8% 6% 18% 35% 27% 6%	563
	21st to end	Night	11% 8% 18% 31% 27% 6%	527
May	1st to 10th	Night	11% 6% 20% 33% 26% 5%	380
	11th to 20th	Night	11% 7% 20% 30% 29% 2	374
	21st to end	Night	10% 7% 19% 32% 30% 2	411
June	1st to 10th	Night	13% 4 23% 35% 23% 3	301
	11th to 20th	Night	16% 4 16% 34% 26% 4	190
	21st to end	Night	9% 6% 17% 33% 32% 3	190
July	1st to 10th	Night	12% 4 17% 36% 30% 2	185
	11th to 20th	Night	15% 8% 19% 33% 23% 2	364
	21st to end	Night	15% 4 20% 29% 26% 6%	416
August	1st to 10th	Night	13% 2 22% 34% 25% 4	378
	11th to 20th	Night	19% 9% 20% 31% 18% 3	559
	21st to end	Night	24% 6% 20% 25% 22% 3	627
September	1st to 10th	Night	18% 9% 22% 30% 19% 2	570
	11th to 20th	Night	16% 7% 17% 31% 25% 3	616
	21st to end	Night	23% 12% 21% 27% 14% 3	760
October	1st to 10th	Night	22% 8% 23% 29% 15% 3	760
	11th to 20th	Night	26% 9% 23% 28% 12% 2	760
	21st to end	Night	17% 10% 24% 32% 15% 3	906
November	1st to 10th	Night	15% 5% 23% 35% 20% 3	880
	11th to 20th	Night	14% 8% 20% 32% 23% 4	855
	21st to end	Night	14% 8% 25% 32% 17% 4	1002
December	1st to 10th	Night	16% 7% 21% 34% 20% 2	1040
	11th to 20th	Night	13% 6% 19% 37% 19% 6%	1040
	21st to end	Night	14% 7% 18% 34% 21% 7%	1144

Page generated at 2024-11-08 19:45:40. Version ac07

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