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 2026-01-02.

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	9% 11% 5% 12% 8% 7% 6% 5% 6% 7% 24%	131941
	Night	8% 14% 5% 14% 8% 7% 6% 5% 6% 7% 20%	128032
Transparency	Day	54% 10% 15% 15% 5%	131592
	Night	58% 10% 13% 13% 5%	127959
Seeing	Day	15% 11% 22% 26% 19% 7%	18760
	Night	13% 7% 21% 33% 22% 4	25293

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 13% 6% 20% 15% 11% 5% 3 4 6% 11%	2231
	11th to 20th	Day	5% 14% 7% 16% 9% 8% 8% 5% 5% 8% 17%	2702
	21st to end	Day	8% 16% 5% 14% 9% 9% 8% 6% 7% 6% 13%	2992
February	1st to 10th	Day	5% 14% 4 13% 8% 7% 7% 5% 8% 7% 22%	1463
	11th to 20th	Day	5% 18% 7% 13% 7% 6% 5% 5% 9% 8% 16%	1560
	21st to end	Day	3 11% 6% 12% 10% 7% 6% 7% 8% 7% 23%	1430
March	1st to 10th	Day	2 10% 4 16% 12% 10% 8% 5% 5% 6% 23%	4496
	11th to 20th	Day	3 12% 7% 15% 9% 8% 7% 5% 6% 8% 21%	4627
	21st to end	Day	1 8% 5% 14% 9% 6% 6% 5% 7% 8% 30%	5969
April	1st to 10th	Day	4 13% 5% 15% 9% 8% 6% 5% 6% 7% 21%	2460
	11th to 20th	Day	4 14% 5% 12% 8% 6% 7% 5% 6% 7% 26%	2696
	21st to end	Day	6% 13% 5% 11% 7% 7% 6% 5% 6% 7% 26%	2845
May	1st to 10th	Day	12% 15% 4 11% 7% 6% 5% 4 5% 7% 25%	6889
	11th to 20th	Day	7% 15% 5% 12% 8% 7% 7% 5% 6% 7% 21%	7193
	21st to end	Day	9% 10% 4 11% 7% 7% 7% 5% 7% 7% 27%	8291
June	1st to 10th	Day	13% 10% 4 10% 8% 6% 6% 5% 6% 7% 25%	3480
	11th to 20th	Day	13% 10% 4 11% 6% 6% 6% 5% 7% 9% 24%	3600
	21st to end	Day	10% 8% 3 10% 8% 7% 7% 6% 8% 9% 23%	3600
July	1st to 10th	Day	11% 8% 3 9% 6% 6% 6% 5% 8% 9% 28%	8160
	11th to 20th	Day	15% 9% 3 9% 8% 7% 7% 6% 7% 8% 22%	7432
	21st to end	Day	11% 6% 3 9% 7% 6% 7% 6% 8% 9% 29%	7876
August	1st to 10th	Day	7% 5% 2 7% 5% 5% 4 4 6% 7% 48%	5109
	11th to 20th	Day	15% 8% 2 7% 5% 5% 6% 4 6% 9% 33%	4483
	21st to end	Day	20% 10% 3 8% 5% 5% 5% 4 7% 8% 24%	4943
September	1st to 10th	Day	16% 12% 4 10% 6% 6% 5% 4 6% 7% 24%	2487
	11th to 20th	Day	14% 9% 4 9% 6% 6% 5% 4 6% 6% 29%	2351
	21st to end	Day	17% 14% 4 14% 7% 6% 4 4 5% 5% 19%	2195
October	1st to 10th	Day	11% 13% 5% 12% 9% 8% 8% 5% 7% 6% 17%	3180
	11th to 20th	Day	13% 17% 7% 10% 5% 5% 5% 5% 6% 6% 20%	2933
	21st to end	Day	8% 18% 7% 17% 9% 9% 6% 4 5% 5% 14%	2861
November	1st to 10th	Day	8% 18% 8% 16% 10% 8% 6% 5% 6% 6% 10%	1442
	11th to 20th	Day	8% 19% 8% 18% 8% 9% 7% 5% 6% 4 8%	1381
	21st to end	Day	6% 17% 9% 16% 9% 9% 6% 5% 8% 6% 9%	1071
December	1st to 10th	Day	8% 19% 7% 17% 10% 12% 7% 6% 4 4 5%	1680
	11th to 20th	Day	3 13% 6% 19% 13% 9% 7% 3 7% 7% 11%	1809
	21st to end	Day	8% 18% 8% 16% 10% 7% 7% 5% 6% 6% 8%	2024
January	1st to 10th	Night	6% 14% 7% 21% 14% 10% 6% 3 4 7% 9%	7778
	11th to 20th	Night	5% 16% 6% 13% 8% 6% 5% 4 6% 9% 21%	7196
	21st to end	Night	9% 17% 6% 16% 9% 8% 7% 5% 6% 5% 11%	7964
February	1st to 10th	Night	5% 15% 5% 14% 7% 7% 6% 6% 6% 6% 21%	2936
	11th to 20th	Night	4 14% 6% 14% 11% 8% 7% 5% 6% 8% 17%	2727
	21st to end	Night	3 13% 5% 13% 9% 6% 5% 4 6% 8% 28%	2197
March	1st to 10th	Night	2 10% 6% 15% 9% 9% 6% 4 6% 7% 25%	5378
	11th to 20th	Night	5% 13% 6% 16% 9% 7% 7% 6% 6% 7% 19%	5340
	21st to end	Night	3 12% 5% 14% 8% 7% 7% 5% 7% 8% 23%	4984
April	1st to 10th	Night	4 11% 6% 12% 8% 7% 7% 6% 7% 7% 25%	1940
	11th to 20th	Night	4 13% 4 9% 7% 6% 5% 6% 7% 8% 30%	1650
	21st to end	Night	7% 15% 5% 10% 6% 5% 7% 4 8% 8% 27%	1555
May	1st to 10th	Night	7% 11% 4 10% 6% 5% 6% 5% 6% 7% 33%	3070
	11th to 20th	Night	6% 10% 4 11% 8% 7% 7% 5% 8% 8% 26%	2702
	21st to end	Night	7% 7% 4 8% 6% 6% 7% 6% 7% 8% 34%	2584
June	1st to 10th	Night	11% 7% 3 9% 6% 8% 5% 5% 8% 8% 29%	917
	11th to 20th	Night	12% 7% 2 9% 5% 6% 6% 4 5% 9% 34%	800
	21st to end	Night	8% 8% 3 8% 7% 6% 6% 6% 10% 10% 29%	800
July	1st to 10th	Night	7% 6% 3 8% 7% 7% 6% 5% 9% 10% 31%	1800
	11th to 20th	Night	14% 8% 3 10% 7% 6% 6% 5% 7% 8% 27%	2525
	21st to end	Night	16% 9% 3 8% 6% 6% 6% 4 6% 7% 28%	2967
August	1st to 10th	Night	7% 5% 3 5% 4 4 4 4 7% 8% 48%	2041
	11th to 20th	Night	11% 6% 3 7% 5% 4 4 4 7% 10% 38%	2573
	21st to end	Night	18% 13% 4 10% 6% 5% 6% 4 5% 5% 23%	2966
September	1st to 10th	Night	14% 11% 4 9% 7% 5% 6% 5% 6% 7% 26%	1910
	11th to 20th	Night	11% 9% 3 9% 7% 5% 6% 4 6% 7% 32%	2049
	21st to end	Night	18% 14% 4 12% 7% 6% 5% 3 5% 7% 19%	2204
October	1st to 10th	Night	13% 13% 4 9% 5% 6% 7% 5% 7% 7% 23%	4010
	11th to 20th	Night	14% 19% 7% 12% 6% 4 5% 4 5% 6% 17%	4215
	21st to end	Night	9% 17% 4 13% 7% 8% 7% 5% 5% 5% 20%	4921
November	1st to 10th	Night	8% 18% 6% 15% 9% 8% 6% 5% 6% 6% 12%	3076
	11th to 20th	Night	7% 20% 7% 18% 9% 8% 6% 5% 7% 6% 8%	3237
	21st to end	Night	7% 18% 6% 17% 10% 8% 7% 5% 7% 6% 8%	3528
December	1st to 10th	Night	10% 21% 7% 16% 11% 8% 6% 5% 4 6% 5%	5720
	11th to 20th	Night	4 13% 7% 22% 12% 7% 5% 4 5% 6% 14%	6598
	21st to end	Night	7% 17% 7% 16% 9% 9% 8% 5% 6% 5% 12%	9174

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	69% 8% 8% 6% 8% 1	2231
	11th to 20th	Day	60% 8% 8% 10% 13% 1	2720
	21st to end	Day	58% 13% 14% 10% 5%	2992
February	1st to 10th	Day	54% 10% 9% 16% 10% 2	1463
	11th to 20th	Day	58% 10% 14% 11% 7%	1568
	21st to end	Day	52% 10% 17% 15% 6%	1430
March	1st to 10th	Day	55% 8% 13% 14% 9% 1	4496
	11th to 20th	Day	55% 9% 12% 12% 11% 1	4627
	21st to end	Day	44% 13% 17% 19% 7%	5969
April	1st to 10th	Day	58% 10% 14% 13% 4	2460
	11th to 20th	Day	54% 11% 13% 16% 6%	2696
	21st to end	Day	54% 11% 17% 14% 5%	2845
May	1st to 10th	Day	54% 8% 11% 20% 7%	6889
	11th to 20th	Day	56% 9% 13% 16% 5%	7196
	21st to end	Day	50% 9% 14% 20% 8%	8292
June	1st to 10th	Day	55% 11% 13% 16% 5%	3480
	11th to 20th	Day	54% 10% 14% 17% 4	3600
	21st to end	Day	52% 13% 17% 14% 3	3600
July	1st to 10th	Day	47% 10% 21% 19% 2	8071
	11th to 20th	Day	53% 12% 21% 13% 1	7339
	21st to end	Day	45% 13% 26% 14% 2	7655
August	1st to 10th	Day	34% 9% 18% 25% 12% 3	5090
	11th to 20th	Day	43% 11% 21% 20% 5%	4525
	21st to end	Day	55% 11% 17% 16% 1	4942
September	1st to 10th	Day	58% 13% 12% 14% 3	2487
	11th to 20th	Day	52% 11% 15% 19% 4	2351
	21st to end	Day	65% 10% 12% 11% 2	2195
October	1st to 10th	Day	60% 10% 14% 14% 2	3180
	11th to 20th	Day	58% 10% 16% 15% 1	2933
	21st to end	Day	66% 14% 12% 7% 1	2861
November	1st to 10th	Day	70% 8% 11% 9% 2	1442
	11th to 20th	Day	72% 8% 10% 8% 2	1381
	21st to end	Day	67% 7% 14% 8% 4	1071
December	1st to 10th	Day	74% 11% 8% 5% 3	1680
	11th to 20th	Day	66% 6% 16% 8% 5%	1811
	21st to end	Day	68% 7% 8% 11% 5%	2024
January	1st to 10th	Night	71% 7% 8% 6% 8%	7778
	11th to 20th	Night	56% 8% 10% 11% 13% 1	7240
	21st to end	Night	65% 12% 10% 9% 4	7964
February	1st to 10th	Night	58% 9% 9% 15% 9% 1	2936
	11th to 20th	Night	60% 10% 12% 12% 6%	2730
	21st to end	Night	51% 9% 18% 15% 6% 1	2197
March	1st to 10th	Night	51% 9% 14% 17% 8% 1	5378
	11th to 20th	Night	53% 12% 13% 13% 8%	5342
	21st to end	Night	46% 14% 18% 16% 7%	4984
April	1st to 10th	Night	51% 11% 15% 18% 4	1940
	11th to 20th	Night	46% 11% 16% 20% 7%	1650
	21st to end	Night	51% 10% 18% 16% 5%	1555
May	1st to 10th	Night	43% 9% 13% 27% 8%	3067
	11th to 20th	Night	48% 12% 15% 18% 7%	2702
	21st to end	Night	40% 10% 13% 29% 8%	2584
June	1st to 10th	Night	49% 10% 15% 22% 4 1	917
	11th to 20th	Night	45% 12% 18% 22% 4	800
	21st to end	Night	45% 13% 22% 19% 2	800
July	1st to 10th	Night	42% 11% 25% 20% 2	1780
	11th to 20th	Night	48% 13% 22% 16% 2	2495
	21st to end	Night	51% 12% 24% 13% 1	2883
August	1st to 10th	Night	31% 11% 17% 27% 12% 3	2035
	11th to 20th	Night	39% 11% 19% 23% 8%	2597
	21st to end	Night	61% 10% 13% 14% 3	2966
September	1st to 10th	Night	54% 13% 17% 15% 2	1910
	11th to 20th	Night	47% 12% 16% 21% 3	2049
	21st to end	Night	63% 10% 11% 13% 3	2204
October	1st to 10th	Night	53% 11% 16% 16% 3	4010
	11th to 20th	Night	63% 10% 12% 12% 2	4215
	21st to end	Night	56% 14% 17% 11% 2	4921
November	1st to 10th	Night	66% 9% 12% 11% 2	3076
	11th to 20th	Night	70% 11% 10% 9% 1	3237
	21st to end	Night	68% 8% 11% 9% 3	3528
December	1st to 10th	Night	75% 9% 7% 8% 2	5720
	11th to 20th	Night	68% 7% 12% 9% 4	6595
	21st to end	Night	66% 8% 8% 9% 7% 1	9174

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% 5% 15% 36% 31% 7%	169
	11th to 20th	Day	12% 10% 16% 32% 25% 8%	200
	21st to end	Day	15% 15% 15% 25% 23% 6%	220
February	1st to 10th	Day	11% 6% 19% 37% 21% 6%	360
	11th to 20th	Day	10% 12% 21% 28% 19% 10%	395
	21st to end	Day	8% 9% 26% 29% 21% 8%	331
March	1st to 10th	Day	7% 11% 23% 30% 21% 10%	400
	11th to 20th	Day	8% 11% 29% 24% 21% 7%	418
	21st to end	Day	7% 11% 23% 26% 23% 10%	550
April	1st to 10th	Day	11% 14% 29% 26% 17% 3	500
	11th to 20th	Day	8% 14% 27% 25% 20% 6%	620
	21st to end	Day	13% 15% 29% 25% 15% 4	700
May	1st to 10th	Day	20% 18% 24% 23% 11% 3	703
	11th to 20th	Day	15% 14% 25% 27% 11% 8%	725
	21st to end	Day	12% 12% 24% 25% 20% 6%	953
June	1st to 10th	Day	16% 12% 22% 25% 19% 6%	930
	11th to 20th	Day	16% 7% 21% 28% 22% 7%	930
	21st to end	Day	11% 8% 18% 28% 25% 10%	930
July	1st to 10th	Day	14% 9% 18% 29% 23% 7%	916
	11th to 20th	Day	18% 9% 19% 25% 19% 9%	797
	21st to end	Day	15% 8% 20% 22% 23% 11%	794
August	1st to 10th	Day	13% 7% 21% 28% 20% 11%	726
	11th to 20th	Day	23% 17% 19% 23% 12% 6%	715
	21st to end	Day	23% 11% 20% 24% 18% 5%	758
September	1st to 10th	Day	19% 13% 24% 22% 18% 5%	530
	11th to 20th	Day	15% 14% 22% 21% 21% 7%	530
	21st to end	Day	21% 19% 23% 21% 11% 5%	527
October	1st to 10th	Day	21% 15% 27% 24% 10% 3	420
	11th to 20th	Day	20% 16% 30% 22% 10% 3	420
	21st to end	Day	13% 11% 22% 34% 16% 4	402
November	1st to 10th	Day	15% 10% 25% 29% 17% 4	220
	11th to 20th	Day	14% 8% 21% 29% 20% 7%	220
	21st to end	Day	11% 9% 24% 32% 15% 9%	220
December	1st to 10th	Day	12% 8% 21% 33% 19% 7%	220
	11th to 20th	Day	14% 6% 16% 27% 24% 13%	190
	21st to end	Day	7% 8% 17% 34% 23% 11%	121
January	1st to 10th	Night	12% 4 19% 34% 26% 5%	1080
	11th to 20th	Night	15% 8% 23% 32% 19% 4	900
	21st to end	Night	15% 10% 22% 31% 19% 3	990
February	1st to 10th	Night	11% 7% 18% 40% 20% 4	900
	11th to 20th	Night	9% 7% 23% 38% 20% 4	884
	21st to end	Night	7% 6% 24% 38% 21% 4	725
March	1st to 10th	Night	6% 6% 23% 37% 22% 6%	800
	11th to 20th	Night	6% 8% 23% 33% 24% 5%	798
	21st to end	Night	5% 8% 19% 31% 30% 8%	660
April	1st to 10th	Night	8% 6% 19% 33% 30% 5%	600
	11th to 20th	Night	8% 7% 19% 35% 27% 5%	593
	21st to end	Night	10% 8% 18% 32% 26% 5%	555
May	1st to 10th	Night	10% 6% 21% 34% 25% 5%	400
	11th to 20th	Night	11% 7% 20% 31% 29% 2	394
	21st to end	Night	10% 7% 19% 33% 30% 2	433
June	1st to 10th	Night	13% 5% 23% 34% 22% 3	317
	11th to 20th	Night	15% 4 16% 35% 27% 4	200
	21st to end	Night	9% 6% 16% 33% 34% 3	200
July	1st to 10th	Night	11% 4 18% 35% 30% 2	195
	11th to 20th	Night	15% 8% 19% 34% 23% 2	384
	21st to end	Night	15% 5% 19% 29% 27% 5%	438
August	1st to 10th	Night	13% 4 21% 34% 24% 4	398
	11th to 20th	Night	19% 9% 20% 31% 18% 4	589
	21st to end	Night	23% 6% 20% 26% 23% 3	660
September	1st to 10th	Night	17% 9% 22% 30% 20% 2	600
	11th to 20th	Night	16% 8% 17% 31% 25% 3	649
	21st to end	Night	23% 13% 22% 26% 14% 2	800
October	1st to 10th	Night	21% 8% 24% 29% 15% 3	800
	11th to 20th	Night	26% 9% 23% 28% 12% 2	800
	21st to end	Night	17% 10% 24% 31% 16% 3	957
November	1st to 10th	Night	15% 6% 23% 35% 19% 2	930
	11th to 20th	Night	13% 8% 20% 32% 23% 4	950
	21st to end	Night	13% 7% 23% 33% 20% 4	1118
December	1st to 10th	Night	16% 8% 22% 33% 19% 2	1160
	11th to 20th	Night	12% 5% 17% 37% 22% 6%	1160
	21st to end	Night	13% 6% 18% 34% 21% 7%	1276

Page generated at 2025-12-29 22:14:10. Version ac07

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