Twillingate Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twillingate Astronomical Observatory clear sky chart from 2005-11-06 to 2025-07-06.

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	20% 14% 5% 11% 6% 5% 4 3 4 5% 23%	120035
	Night	20% 15% 5% 13% 7% 5% 4 3 4 5% 19%	118972
Transparency	Day	64% 3 11% 16% 6% 1	123505
	Night	69% 3 10% 13% 5%	123674
Seeing	Day	30% 10% 26% 23% 10% 2	19078
	Night	31% 11% 27% 22% 8% 1	25810

By Month

Percentage Cloud Cover NE (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	20% 23% 7% 17% 8% 4 3 2 3 3 10%	3176
	11th to 20th	Day	15% 22% 9% 21% 10% 5% 3 2 2 2 9%	3476
	21st to end	Day	9% 13% 6% 19% 17% 10% 4 3 3 4 12%	3982
February	1st to 10th	Day	18% 14% 5% 17% 15% 6% 5% 3 5% 4 10%	1600
	11th to 20th	Day	18% 19% 5% 12% 11% 5% 4 4 3 4 14%	1785
	21st to end	Day	14% 13% 5% 12% 9% 9% 7% 5% 4 5% 19%	1650
March	1st to 10th	Day	15% 13% 4 15% 14% 7% 5% 4 4 4 16%	4474
	11th to 20th	Day	20% 15% 6% 11% 9% 6% 4 3 4 4 16%	4875
	21st to end	Day	26% 16% 6% 11% 5% 3 3 2 4 4 20%	5649
April	1st to 10th	Day	18% 17% 5% 9% 6% 4 4 4 5% 6% 21%	2404
	11th to 20th	Day	22% 15% 5% 7% 4 3 4 3 5% 6% 27%	2571
	21st to end	Day	20% 18% 5% 9% 5% 4 3 3 4 5% 24%	2600
May	1st to 10th	Day	25% 17% 6% 9% 5% 5% 4 3 4 4 19%	6105
	11th to 20th	Day	20% 14% 6% 10% 5% 5% 4 3 5% 5% 23%	6613
	21st to end	Day	25% 15% 4 7% 3 4 3 3 4 6% 26%	7428
June	1st to 10th	Day	29% 14% 3 7% 5% 4 4 3 4 5% 21%	3000
	11th to 20th	Day	25% 11% 3 7% 5% 5% 4 3 5% 6% 26%	3000
	21st to end	Day	21% 11% 3 8% 5% 4 5% 4 5% 7% 27%	3000
July	1st to 10th	Day	19% 11% 3 8% 5% 6% 4 4 5% 7% 28%	4825
	11th to 20th	Day	16% 8% 3 8% 6% 5% 5% 4 6% 8% 33%	4750
	21st to end	Day	14% 7% 2 6% 4 4 4 4 7% 9% 39%	4829
August	1st to 10th	Day	20% 10% 3 7% 5% 4 4 4 5% 7% 29%	4424
	11th to 20th	Day	18% 7% 3 6% 3 3 4 3 4 6% 43%	4050
	21st to end	Day	19% 8% 2 6% 4 4 4 3 6% 8% 37%	4532
September	1st to 10th	Day	20% 8% 3 7% 4 4 4 3 5% 7% 35%	2297
	11th to 20th	Day	26% 9% 3 7% 4 4 4 3 4 7% 29%	2090
	21st to end	Day	20% 10% 3 7% 4 4 5% 3 5% 8% 30%	2090
October	1st to 10th	Day	22% 13% 3 7% 5% 4 4 3 3 5% 31%	2033
	11th to 20th	Day	22% 17% 4 8% 5% 3 4 3 5% 7% 22%	1745
	21st to end	Day	27% 17% 4 7% 4 4 4 2 5% 6% 19%	1881
November	1st to 10th	Day	24% 20% 5% 8% 4 4 4 3 4 5% 18%	1730
	11th to 20th	Day	23% 18% 7% 9% 6% 3 3 3 4 5% 19%	1555
	21st to end	Day	25% 19% 7% 13% 3 3 3 4 4 3 16%	1400
December	1st to 10th	Day	15% 13% 6% 18% 6% 4 4 4 4 5% 20%	2290
	11th to 20th	Day	19% 17% 7% 20% 7% 4 3 2 3 4 12%	2628
	21st to end	Day	20% 16% 8% 26% 8% 4 4 2 3 2 8%	3498
January	1st to 10th	Night	19% 22% 8% 18% 9% 4 4 2 3 3 7%	6789
	11th to 20th	Night	14% 20% 7% 21% 10% 5% 4 3 3 4 10%	6425
	21st to end	Night	8% 11% 5% 19% 14% 10% 6% 3 4 5% 15%	6996
February	1st to 10th	Night	18% 14% 5% 20% 15% 6% 4 2 3 2 11%	2800
	11th to 20th	Night	20% 18% 6% 12% 10% 5% 4 4 4 5% 14%	2497
	21st to end	Night	14% 13% 5% 13% 10% 6% 5% 4 5% 5% 21%	1980
March	1st to 10th	Night	18% 14% 4 17% 8% 5% 4 3 4 5% 18%	5366
	11th to 20th	Night	19% 15% 5% 14% 7% 7% 5% 4 5% 5% 16%	5084
	21st to end	Night	24% 15% 5% 11% 5% 4 4 3 4 5% 19%	5269
April	1st to 10th	Night	23% 18% 7% 10% 5% 4 3 3 3 5% 19%	1995
	11th to 20th	Night	24% 15% 6% 8% 4 3 3 2 4 5% 26%	1778
	21st to end	Night	25% 17% 5% 6% 5% 4 3 3 4 5% 24%	1800
May	1st to 10th	Night	33% 18% 5% 8% 4 3 3 2 3 4 17%	3852
	11th to 20th	Night	24% 17% 8% 11% 4 4 3 3 2 4 20%	3301
	21st to end	Night	29% 15% 5% 7% 4 4 4 2 4 5% 22%	3468
June	1st to 10th	Night	31% 14% 4 9% 4 4 4 3 4 5% 18%	1400
	11th to 20th	Night	28% 11% 3 8% 4 4 4 3 5% 5% 24%	1400
	21st to end	Night	24% 13% 4 8% 3 4 4 3 5% 6% 25%	1400
July	1st to 10th	Night	23% 13% 4 9% 4 4 4 3 4 7% 26%	2256
	11th to 20th	Night	14% 12% 4 10% 6% 5% 6% 4 6% 6% 28%	2220
	21st to end	Night	17% 10% 3 7% 5% 4 4 3 5% 7% 36%	2732
August	1st to 10th	Night	16% 9% 3 9% 6% 4 4 4 7% 7% 32%	2516
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 5% 6% 38%	2786
	21st to end	Night	21% 7% 3 6% 4 5% 4 3 5% 8% 35%	3135
September	1st to 10th	Night	22% 8% 3 7% 4 3 4 3 5% 7% 34%	1881
	11th to 20th	Night	25% 11% 2 7% 4 4 4 3 4 5% 30%	2090
	21st to end	Night	22% 13% 3 9% 4 4 3 3 5% 6% 29%	2090
October	1st to 10th	Night	25% 12% 2 8% 4 4 4 3 5% 6% 27%	2147
	11th to 20th	Night	24% 16% 3 7% 4 5% 4 3 6% 6% 22%	2432
	21st to end	Night	30% 19% 3 7% 3 3 3 2 4 5% 21%	2717
November	1st to 10th	Night	25% 21% 4 9% 6% 4 4 3 5% 5% 15%	2567
	11th to 20th	Night	26% 19% 7% 8% 5% 4 3 3 5% 5% 14%	2842
	21st to end	Night	24% 20% 9% 11% 6% 4 3 3 4 5% 13%	3000
December	1st to 10th	Night	15% 15% 6% 15% 6% 5% 5% 3 4 4 21%	4900
	11th to 20th	Night	24% 17% 8% 18% 6% 4 3 2 2 4 11%	5581
	21st to end	Night	18% 16% 9% 25% 7% 4 3 2 3 3 11%	7480

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	82% 2 5% 9% 1	3177
	11th to 20th	Day	82% 4 6% 5% 3	3505
	21st to end	Day	77% 3 5% 8% 5% 2	3982
February	1st to 10th	Day	77% 4 8% 6% 5% 1	1600
	11th to 20th	Day	75% 3 8% 9% 5%	1792
	21st to end	Day	67% 4 7% 13% 7%	1650
March	1st to 10th	Day	72% 4 6% 12% 6% 1	4478
	11th to 20th	Day	73% 3 8% 10% 5% 2	4875
	21st to end	Day	70% 2 7% 13% 7%	5649
April	1st to 10th	Day	65% 3 9% 15% 7% 1	2404
	11th to 20th	Day	60% 2 10% 19% 9% 1	2571
	21st to end	Day	65% 3 7% 15% 9% 1	2600
May	1st to 10th	Day	71% 2 10% 13% 4 1	6117
	11th to 20th	Day	66% 2 10% 16% 6%	6617
	21st to end	Day	62% 2 12% 19% 5%	7428
June	1st to 10th	Day	66% 3 10% 16% 4	3000
	11th to 20th	Day	59% 4 12% 20% 5% 1	3000
	21st to end	Day	57% 5% 12% 18% 7% 1	3000
July	1st to 10th	Day	57% 3 14% 20% 6%	4750
	11th to 20th	Day	51% 3 18% 23% 5%	4668
	21st to end	Day	42% 4 20% 29% 5%	4675
August	1st to 10th	Day	55% 5% 17% 21% 3	4410
	11th to 20th	Day	45% 3 16% 24% 11% 2	4089
	21st to end	Day	47% 3 17% 25% 7%	4532
September	1st to 10th	Day	49% 4 12% 25% 8% 1	2297
	11th to 20th	Day	56% 4 15% 18% 6%	2090
	21st to end	Day	53% 4 19% 18% 6%	2090
October	1st to 10th	Day	62% 3 11% 18% 6%	3387
	11th to 20th	Day	67% 3 9% 16% 5%	2880
	21st to end	Day	65% 3 10% 13% 8% 1	3092
November	1st to 10th	Day	70% 5% 11% 10% 4	1730
	11th to 20th	Day	69% 4 11% 10% 5% 1	1555
	21st to end	Day	73% 5% 8% 9% 5%	1400
December	1st to 10th	Day	66% 3 9% 14% 8%	2290
	11th to 20th	Day	79% 3 13% 4 1	2627
	21st to end	Day	85% 2 6% 6% 1	3498
January	1st to 10th	Night	84% 2 6% 5% 2	6789
	11th to 20th	Night	78% 5% 5% 8% 4	6471
	21st to end	Night	72% 3 11% 7% 6% 1	6996
February	1st to 10th	Night	80% 3 6% 7% 4	2800
	11th to 20th	Night	75% 3 8% 10% 3	2501
	21st to end	Night	65% 5% 7% 16% 7% 1	1980
March	1st to 10th	Night	69% 3 9% 12% 5% 2	5375
	11th to 20th	Night	71% 3 9% 10% 6% 1	5085
	21st to end	Night	69% 2 9% 14% 6%	5269
April	1st to 10th	Night	69% 3 5% 13% 9%	1995
	11th to 20th	Night	62% 2 9% 19% 7% 1	1778
	21st to end	Night	64% 3 7% 15% 9% 1	1800
May	1st to 10th	Night	73% 2 9% 13% 3	3857
	11th to 20th	Night	71% 1 7% 15% 5%	3302
	21st to end	Night	67% 2 9% 17% 4	3469
June	1st to 10th	Night	68% 4 10% 12% 6%	1400
	11th to 20th	Night	62% 3 12% 17% 5%	1400
	21st to end	Night	61% 4 11% 17% 6% 1	1400
July	1st to 10th	Night	60% 3 14% 20% 3	2222
	11th to 20th	Night	57% 4 13% 18% 7%	2178
	21st to end	Night	49% 3 17% 27% 4	2646
August	1st to 10th	Night	50% 5% 16% 25% 4	2505
	11th to 20th	Night	47% 4 16% 22% 11% 1	2813
	21st to end	Night	49% 2 15% 28% 6%	3134
September	1st to 10th	Night	51% 4 13% 22% 9% 1	1881
	11th to 20th	Night	57% 4 12% 18% 8%	2090
	21st to end	Night	56% 5% 14% 18% 7%	2090
October	1st to 10th	Night	64% 3 13% 14% 5%	3576
	11th to 20th	Night	65% 3 14% 13% 5%	4033
	21st to end	Night	65% 3 13% 13% 7% 1	4467
November	1st to 10th	Night	72% 4 9% 11% 5%	2567
	11th to 20th	Night	72% 5% 9% 11% 2	2842
	21st to end	Night	75% 5% 8% 8% 4	3000
December	1st to 10th	Night	66% 3 6% 15% 9%	4900
	11th to 20th	Night	80% 3 10% 4 3	5583
	21st to end	Night	81% 3 6% 9% 2	7480

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	29% 14% 34% 18% 4 1	400
	11th to 20th	Day	27% 17% 35% 18% 4	400
	21st to end	Day	29% 21% 31% 17% 2	440
February	1st to 10th	Day	26% 21% 34% 15% 5%	400
	11th to 20th	Day	27% 22% 33% 15% 3 1	396
	21st to end	Day	19% 18% 38% 17% 5% 2	331
March	1st to 10th	Day	26% 13% 38% 18% 6% 1	400
	11th to 20th	Day	28% 16% 24% 20% 11% 2	400
	21st to end	Day	34% 12% 27% 19% 6% 2	480
April	1st to 10th	Day	29% 13% 33% 19% 5% 1	504
	11th to 20th	Day	31% 8% 27% 24% 7% 2	689
	21st to end	Day	32% 8% 27% 24% 8% 1	700
May	1st to 10th	Day	35% 7% 23% 21% 11% 3	703
	11th to 20th	Day	28% 5% 27% 24% 13% 3	724
	21st to end	Day	34% 6% 23% 26% 9% 1	790
June	1st to 10th	Day	37% 7% 21% 22% 9% 3	730
	11th to 20th	Day	30% 6% 22% 26% 14% 2	730
	21st to end	Day	26% 3 24% 28% 14% 3	730
July	1st to 10th	Day	27% 3 24% 31% 11% 4	695
	11th to 20th	Day	24% 3 22% 28% 21% 2	668
	21st to end	Day	24% 4 22% 33% 15% 1	740
August	1st to 10th	Day	27% 6% 19% 30% 14% 4	675
	11th to 20th	Day	23% 4 21% 29% 20% 3	667
	21st to end	Day	27% 5% 21% 26% 17% 5%	748
September	1st to 10th	Day	26% 8% 25% 26% 11% 3	514
	11th to 20th	Day	35% 9% 23% 25% 7% 1	390
	21st to end	Day	27% 9% 35% 21% 7% 2	390
October	1st to 10th	Day	27% 12% 34% 19% 7% 1	390
	11th to 20th	Day	37% 10% 24% 16% 11% 2	390
	21st to end	Day	34% 16% 26% 17% 6% 2	429
November	1st to 10th	Day	39% 14% 31% 13% 3	395
	11th to 20th	Day	37% 17% 23% 17% 5% 1	400
	21st to end	Day	38% 16% 31% 13% 2	400
December	1st to 10th	Day	29% 15% 32% 18% 6%	400
	11th to 20th	Day	31% 24% 27% 16% 2	400
	21st to end	Day	27% 18% 30% 18% 7% 1	440
January	1st to 10th	Night	30% 18% 29% 18% 5% 1	900
	11th to 20th	Night	27% 17% 36% 14% 6%	900
	21st to end	Night	25% 19% 36% 16% 4	990
February	1st to 10th	Night	27% 21% 31% 17% 3 1	900
	11th to 20th	Night	32% 17% 33% 15% 3 1	860
	21st to end	Night	23% 12% 37% 19% 7% 2	660
March	1st to 10th	Night	27% 16% 32% 19% 5% 1	800
	11th to 20th	Night	25% 10% 30% 24% 10% 1	653
	21st to end	Night	34% 13% 26% 21% 6% 1	660
April	1st to 10th	Night	32% 12% 30% 19% 6% 1	600
	11th to 20th	Night	32% 8% 29% 20% 9% 1	594
	21st to end	Night	35% 5% 26% 28% 6% 1	600
May	1st to 10th	Night	38% 5% 19% 26% 11% 2	600
	11th to 20th	Night	38% 5% 19% 23% 12% 2	592
	21st to end	Night	36% 5% 24% 26% 8% 1	649
June	1st to 10th	Night	38% 6% 18% 28% 10% 1	600
	11th to 20th	Night	35% 4 19% 27% 14% 2	600
	21st to end	Night	32% 6% 21% 26% 14% 1	600
July	1st to 10th	Night	28% 3 23% 33% 11% 2	572
	11th to 20th	Night	24% 3 26% 36% 11% 1	552
	21st to end	Night	26% 4 23% 33% 13% 1	623
August	1st to 10th	Night	26% 4 20% 35% 15% 1	568
	11th to 20th	Night	24% 3 23% 32% 17% 1	562
	21st to end	Night	27% 4 19% 31% 17% 2	627
September	1st to 10th	Night	27% 5% 26% 31% 11% 1	570
	11th to 20th	Night	32% 9% 24% 29% 6%	570
	21st to end	Night	32% 7% 31% 23% 6% 1	570
October	1st to 10th	Night	36% 8% 28% 22% 7% 1	600
	11th to 20th	Night	35% 9% 23% 23% 9% 1	822
	21st to end	Night	40% 13% 21% 19% 6% 1	946
November	1st to 10th	Night	36% 16% 28% 17% 3	880
	11th to 20th	Night	38% 12% 27% 17% 6% 1	900
	21st to end	Night	36% 16% 29% 15% 3	900
December	1st to 10th	Night	31% 15% 29% 19% 5% 1	900
	11th to 20th	Night	35% 17% 30% 14% 4	900
	21st to end	Night	26% 18% 29% 19% 7% 1	990

Page generated at 2025-07-03 02:30:14. Version ac07

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