Hall's Harbour Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hall's Harbour Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	18% 13% 4 9% 5% 5% 4 3 5% 6% 28%	138993
	Night	19% 14% 5% 11% 6% 5% 4 3 4 5% 23%	134163
Transparency	Day	57% 6% 11% 17% 9% 1	142561
	Night	61% 6% 10% 16% 7% 1	138673
Seeing	Day	25% 19% 31% 18% 6% 1	19424
	Night	25% 18% 30% 21% 5%	26845

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	14% 21% 8% 16% 10% 7% 3 2 4 3 12%	4133
	11th to 20th	Day	17% 21% 11% 22% 6% 5% 3 2 3 3 8%	4923
	21st to end	Day	12% 14% 5% 16% 14% 9% 7% 2 3 3 14%	5781
February	1st to 10th	Day	18% 15% 5% 15% 10% 6% 4 4 4 5% 13%	1890
	11th to 20th	Day	16% 17% 4 14% 10% 6% 4 3 3 4 19%	1843
	21st to end	Day	11% 14% 6% 11% 9% 5% 4 3 4 6% 27%	1582
March	1st to 10th	Day	21% 16% 5% 13% 6% 7% 3 2 3 4 19%	5034
	11th to 20th	Day	15% 15% 4 10% 5% 4 4 4 5% 6% 28%	5090
	21st to end	Day	25% 17% 5% 9% 5% 4 4 3 4 5% 21%	5587
April	1st to 10th	Day	22% 14% 4 7% 4 4 4 3 4 5% 29%	2484
	11th to 20th	Day	20% 12% 3 6% 4 3 4 3 5% 6% 34%	2618
	21st to end	Day	20% 10% 2 6% 5% 4 4 3 5% 7% 33%	2730
May	1st to 10th	Day	27% 14% 3 6% 4 4 5% 3 5% 5% 24%	7752
	11th to 20th	Day	17% 10% 3 8% 4 4 4 3 5% 7% 33%	8220
	21st to end	Day	20% 12% 3 7% 5% 4 4 3 5% 7% 30%	9059
June	1st to 10th	Day	22% 9% 3 7% 5% 4 5% 4 6% 7% 27%	2988
	11th to 20th	Day	19% 8% 2 7% 4 4 4 3 6% 8% 34%	3150
	21st to end	Day	23% 11% 3 7% 5% 5% 4 4 6% 6% 28%	3150
July	1st to 10th	Day	20% 9% 3 7% 5% 4 4 4 7% 9% 28%	6970
	11th to 20th	Day	17% 10% 3 7% 4 4 4 3 6% 10% 33%	6641
	21st to end	Day	11% 8% 3 7% 5% 4 5% 4 7% 10% 37%	6793
August	1st to 10th	Day	18% 11% 4 8% 5% 4 5% 3 4 7% 31%	4235
	11th to 20th	Day	13% 7% 3 7% 4 5% 5% 4 6% 9% 38%	4175
	21st to end	Day	10% 5% 2 5% 3 4 4 4 5% 8% 49%	4548
September	1st to 10th	Day	16% 7% 2 5% 4 3 4 3 5% 6% 45%	2400
	11th to 20th	Day	16% 7% 2 6% 4 3 3 3 4 6% 46%	2285
	21st to end	Day	16% 7% 3 5% 4 3 4 3 5% 7% 44%	2160
October	1st to 10th	Day	17% 9% 3 6% 4 3 4 3 5% 6% 41%	2000
	11th to 20th	Day	18% 12% 3 6% 4 4 5% 3 5% 7% 34%	2000
	21st to end	Day	19% 13% 3 8% 5% 4 4 3 5% 6% 30%	2196
November	1st to 10th	Day	22% 13% 4 7% 5% 4 3 3 4 6% 28%	1690
	11th to 20th	Day	19% 20% 6% 9% 6% 5% 3 3 5% 4 21%	1680
	21st to end	Day	19% 19% 6% 12% 6% 4 5% 3 3 4 18%	1680
December	1st to 10th	Day	19% 17% 9% 20% 6% 5% 4 3 3 3 11%	2690
	11th to 20th	Day	23% 19% 6% 16% 7% 4 3 2 2 2 16%	3076
	21st to end	Day	19% 18% 9% 16% 6% 4 3 2 3 4 15%	3760
January	1st to 10th	Night	13% 21% 9% 19% 10% 5% 3 3 3 3 11%	8756
	11th to 20th	Night	20% 20% 8% 20% 5% 4 3 2 3 3 12%	7978
	21st to end	Night	11% 13% 6% 18% 16% 9% 5% 3 4 4 12%	8400
February	1st to 10th	Night	18% 17% 6% 15% 10% 6% 4 2 4 4 14%	2730
	11th to 20th	Night	17% 15% 5% 13% 10% 6% 3 3 5% 5% 19%	2663
	21st to end	Night	13% 15% 6% 11% 8% 4 4 4 5% 5% 26%	2223
March	1st to 10th	Night	23% 16% 5% 13% 8% 5% 3 2 2 4 19%	5025
	11th to 20th	Night	18% 16% 6% 9% 5% 4 4 3 4 5% 25%	5089
	21st to end	Night	27% 13% 6% 9% 5% 4 3 2 3 3 24%	5587
April	1st to 10th	Night	23% 16% 4 7% 5% 4 4 3 4 4 27%	2135
	11th to 20th	Night	22% 11% 4 6% 5% 4 4 3 4 6% 30%	1947
	21st to end	Night	22% 12% 3 7% 5% 3 4 3 5% 4 31%	1890
May	1st to 10th	Night	27% 17% 3 7% 4 4 3 3 4 5% 22%	5152
	11th to 20th	Night	22% 11% 3 7% 5% 4 5% 4 5% 6% 27%	4670
	21st to end	Night	17% 15% 4 8% 5% 4 4 3 5% 6% 29%	5147
June	1st to 10th	Night	24% 9% 4 7% 6% 4 4 4 5% 7% 25%	1647
	11th to 20th	Night	22% 8% 3 8% 4 3 3 4 6% 5% 34%	1470
	21st to end	Night	22% 11% 3 6% 6% 5% 4 4 5% 7% 26%	1470
July	1st to 10th	Night	20% 12% 4 9% 5% 5% 5% 5% 6% 8% 21%	3230
	11th to 20th	Night	17% 9% 3 8% 4 5% 6% 4 6% 8% 29%	3508
	21st to end	Night	15% 8% 3 7% 4 4 5% 4 6% 8% 36%	4287
August	1st to 10th	Night	21% 11% 3 8% 4 3 4 4 6% 7% 29%	2915
	11th to 20th	Night	15% 9% 3 7% 4 5% 5% 4 7% 7% 33%	2872
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	3350
September	1st to 10th	Night	14% 7% 3 6% 5% 4 4 3 6% 6% 43%	2000
	11th to 20th	Night	17% 8% 2 6% 3 4 3 3 4 6% 44%	2113
	21st to end	Night	17% 8% 2 7% 4 4 4 3 6% 7% 38%	2239
October	1st to 10th	Night	17% 6% 2 6% 4 4 5% 3 5% 7% 40%	2400
	11th to 20th	Night	19% 11% 3 6% 4 4 4 4 5% 6% 34%	2400
	21st to end	Night	26% 13% 3 7% 4 4 3 3 4 6% 28%	2640
November	1st to 10th	Night	23% 13% 3 7% 5% 4 4 3 4 5% 29%	2827
	11th to 20th	Night	20% 20% 5% 10% 5% 5% 4 3 4 5% 19%	2940
	21st to end	Night	23% 19% 6% 9% 4 3 4 4 4 5% 19%	2940
December	1st to 10th	Night	16% 18% 9% 18% 7% 5% 5% 3 4 4 11%	4720
	11th to 20th	Night	20% 18% 5% 14% 7% 4 4 2 4 4 19%	5353
	21st to end	Night	23% 18% 6% 13% 6% 4 3 2 3 3 18%	7450

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	78% 5% 10% 6% 1	4134
	11th to 20th	Day	81% 7% 5% 6% 1	4954
	21st to end	Day	74% 5% 7% 7% 6% 1	5781
February	1st to 10th	Day	74% 5% 7% 8% 5% 1	1890
	11th to 20th	Day	70% 6% 8% 10% 5%	1851
	21st to end	Day	58% 6% 11% 16% 8% 1	1582
March	1st to 10th	Day	70% 4 7% 11% 8% 1	5038
	11th to 20th	Day	56% 6% 13% 17% 7% 1	5090
	21st to end	Day	69% 4 4 14% 8% 1	5587
April	1st to 10th	Day	60% 5% 7% 13% 12% 2	2484
	11th to 20th	Day	52% 5% 8% 21% 13% 1	2618
	21st to end	Day	53% 6% 9% 18% 12% 2	2730
May	1st to 10th	Day	61% 6% 9% 15% 8%	7764
	11th to 20th	Day	50% 7% 12% 21% 9% 1	8224
	21st to end	Day	53% 7% 12% 16% 13% 1	9060
June	1st to 10th	Day	55% 7% 11% 19% 7% 1	2988
	11th to 20th	Day	48% 7% 14% 20% 11% 1	3150
	21st to end	Day	57% 7% 10% 16% 10% 1	3150
July	1st to 10th	Day	50% 6% 15% 18% 10% 1	6895
	11th to 20th	Day	45% 5% 14% 25% 10%	6562
	21st to end	Day	41% 7% 15% 25% 10%	6603
August	1st to 10th	Day	53% 7% 10% 19% 11%	4222
	11th to 20th	Day	43% 8% 14% 24% 11%	4214
	21st to end	Day	34% 6% 13% 30% 17% 1	4548
September	1st to 10th	Day	40% 6% 13% 26% 14% 2	2400
	11th to 20th	Day	42% 5% 12% 24% 16% 1	2285
	21st to end	Day	41% 5% 9% 27% 17% 1	2160
October	1st to 10th	Day	44% 7% 11% 27% 12%	3260
	11th to 20th	Day	47% 4 10% 26% 13%	3240
	21st to end	Day	47% 4 14% 22% 13% 1	3522
November	1st to 10th	Day	59% 6% 10% 17% 8% 1	1690
	11th to 20th	Day	66% 6% 13% 11% 4	1680
	21st to end	Day	70% 7% 10% 10% 3	1680
December	1st to 10th	Day	76% 4 8% 10% 2	2690
	11th to 20th	Day	76% 4 6% 9% 4 1	3075
	21st to end	Day	74% 5% 8% 8% 4	3760
January	1st to 10th	Night	77% 6% 8% 8% 1	8756
	11th to 20th	Night	77% 7% 6% 8% 2	8022
	21st to end	Night	74% 6% 8% 9% 3 1	8400
February	1st to 10th	Night	73% 5% 8% 8% 5% 1	2730
	11th to 20th	Night	68% 6% 10% 12% 4 1	2666
	21st to end	Night	59% 6% 10% 17% 7% 1	2223
March	1st to 10th	Night	72% 3 5% 11% 8% 1	5034
	11th to 20th	Night	60% 6% 13% 15% 6% 1	5090
	21st to end	Night	66% 4 6% 15% 8% 1	5587
April	1st to 10th	Night	62% 5% 8% 11% 12% 3	2135
	11th to 20th	Night	54% 6% 9% 18% 13% 1	1947
	21st to end	Night	56% 6% 9% 16% 11% 2	1890
May	1st to 10th	Night	64% 5% 10% 15% 6%	5158
	11th to 20th	Night	55% 7% 11% 20% 6% 2	4671
	21st to end	Night	53% 7% 14% 15% 10% 1	5148
June	1st to 10th	Night	54% 7% 13% 19% 6%	1647
	11th to 20th	Night	49% 6% 12% 23% 8% 1	1470
	21st to end	Night	54% 8% 13% 16% 8% 1	1470
July	1st to 10th	Night	56% 7% 13% 17% 8%	3195
	11th to 20th	Night	44% 7% 17% 20% 11% 1	3465
	21st to end	Night	39% 8% 16% 24% 13%	4163
August	1st to 10th	Night	50% 7% 14% 21% 7%	2903
	11th to 20th	Night	43% 8% 18% 21% 8%	2899
	21st to end	Night	35% 6% 16% 27% 15%	3349
September	1st to 10th	Night	39% 6% 12% 27% 14% 1	2000
	11th to 20th	Night	41% 4 12% 28% 15% 1	2113
	21st to end	Night	44% 7% 10% 24% 13% 1	2239
October	1st to 10th	Night	47% 5% 12% 26% 11% 1	3920
	11th to 20th	Night	43% 5% 13% 26% 14%	3899
	21st to end	Night	48% 4 12% 22% 13%	4252
November	1st to 10th	Night	57% 6% 11% 18% 8%	2827
	11th to 20th	Night	67% 6% 9% 13% 5%	2940
	21st to end	Night	66% 6% 14% 11% 3	2940
December	1st to 10th	Night	74% 5% 10% 10% 1	4720
	11th to 20th	Night	70% 5% 8% 13% 3	5355
	21st to end	Night	70% 5% 8% 12% 5%	7450

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	26% 32% 32% 9% 1	234
	11th to 20th	Day	31% 26% 28% 12% 3	430
	21st to end	Day	24% 26% 37% 11% 2	473
February	1st to 10th	Day	26% 26% 31% 13% 3	430
	11th to 20th	Day	27% 32% 27% 12% 1	426
	21st to end	Day	22% 26% 35% 14% 3	369
March	1st to 10th	Day	29% 25% 33% 10% 2	540
	11th to 20th	Day	25% 29% 32% 11% 3 1	540
	21st to end	Day	32% 26% 27% 10% 4	594
April	1st to 10th	Day	38% 25% 26% 8% 3	540
	11th to 20th	Day	29% 28% 28% 11% 4	532
	21st to end	Day	24% 22% 29% 16% 8%	540
May	1st to 10th	Day	30% 24% 27% 15% 3 1	580
	11th to 20th	Day	25% 18% 28% 22% 7% 1	774
	21st to end	Day	27% 16% 33% 18% 4 1	845
June	1st to 10th	Day	29% 13% 30% 21% 7% 1	780
	11th to 20th	Day	22% 15% 33% 22% 7% 1	780
	21st to end	Day	27% 12% 30% 22% 7% 1	780
July	1st to 10th	Day	20% 8% 38% 24% 9% 1	770
	11th to 20th	Day	19% 9% 32% 28% 11% 1	768
	21st to end	Day	20% 8% 35% 27% 10% 1	724
August	1st to 10th	Day	14% 7% 35% 32% 11% 1	526
	11th to 20th	Day	17% 11% 31% 27% 12% 3	519
	21st to end	Day	16% 14% 30% 25% 12% 3	583
September	1st to 10th	Day	19% 10% 32% 27% 10% 1	530
	11th to 20th	Day	20% 13% 29% 24% 11% 2	530
	21st to end	Day	19% 15% 31% 21% 12% 2	508
October	1st to 10th	Day	20% 15% 29% 25% 8% 3	420
	11th to 20th	Day	25% 22% 26% 18% 7% 1	420
	21st to end	Day	24% 23% 31% 16% 5% 1	462
November	1st to 10th	Day	29% 23% 29% 14% 3 1	425
	11th to 20th	Day	33% 27% 24% 11% 5%	430
	21st to end	Day	29% 29% 30% 9% 2	430
December	1st to 10th	Day	32% 25% 28% 13% 2	430
	11th to 20th	Day	38% 32% 20% 10% 1	430
	21st to end	Day	30% 27% 33% 6% 3 1	332
January	1st to 10th	Night	27% 27% 31% 13% 2	950
	11th to 20th	Night	28% 27% 28% 15% 3	903
	21st to end	Night	22% 28% 32% 14% 3	924
February	1st to 10th	Night	28% 27% 29% 15% 2	840
	11th to 20th	Night	28% 28% 28% 13% 2	823
	21st to end	Night	21% 24% 34% 19% 2	692
March	1st to 10th	Night	26% 26% 31% 15% 3	840
	11th to 20th	Night	23% 22% 31% 19% 5%	840
	21st to end	Night	27% 22% 32% 15% 4	924
April	1st to 10th	Night	33% 21% 28% 15% 2	665
	11th to 20th	Night	28% 19% 33% 17% 4	624
	21st to end	Night	28% 15% 30% 22% 4 1	630
May	1st to 10th	Night	31% 13% 31% 19% 5% 1	630
	11th to 20th	Night	25% 13% 31% 26% 5%	622
	21st to end	Night	22% 13% 37% 22% 6%	682
June	1st to 10th	Night	27% 10% 30% 26% 7%	597
	11th to 20th	Night	24% 7% 32% 31% 5%	420
	21st to end	Night	25% 8% 30% 30% 7%	420
July	1st to 10th	Night	18% 6% 33% 34% 8%	410
	11th to 20th	Night	15% 7% 34% 32% 11%	529
	21st to end	Night	18% 6% 28% 38% 9%	687
August	1st to 10th	Night	18% 5% 27% 41% 9%	598
	11th to 20th	Night	16% 8% 28% 32% 15% 1	592
	21st to end	Night	16% 7% 28% 34% 14%	660
September	1st to 10th	Night	16% 9% 32% 33% 11% 1	600
	11th to 20th	Night	18% 10% 29% 30% 11% 1	713
	21st to end	Night	20% 11% 33% 24% 11% 1	800
October	1st to 10th	Night	20% 11% 34% 24% 10% 1	800
	11th to 20th	Night	25% 15% 31% 20% 8% 1	800
	21st to end	Night	31% 22% 24% 18% 4	880
November	1st to 10th	Night	30% 20% 29% 17% 4 1	905
	11th to 20th	Night	31% 23% 27% 15% 4 1	950
	21st to end	Night	31% 23% 27% 16% 2	950
December	1st to 10th	Night	31% 23% 31% 13% 2	950
	11th to 20th	Night	33% 28% 27% 11% 2	950
	21st to end	Night	31% 25% 27% 15% 3	1045

Page generated at 2026-07-28 04:25:24. Version ac07

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