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 2025-03-27.

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%	109350
	Night	19% 14% 5% 11% 6% 4 4 3 4 5% 24%	110052
Transparency	Day	56% 6% 11% 17% 9% 1	112961
	Night	60% 6% 11% 16% 7% 1	114594
Seeing	Day	25% 19% 31% 19% 6% 1	17472
	Night	25% 18% 30% 21% 5%	25165

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% 23% 8% 17% 9% 5% 3 2 3 3 13%	3183
	11th to 20th	Day	13% 20% 11% 23% 6% 5% 4 2 3 3 9%	3781
	21st to end	Day	13% 15% 5% 14% 10% 9% 6% 3 4 4 17%	4466
February	1st to 10th	Day	19% 15% 5% 14% 10% 6% 4 4 5% 5% 13%	1800
	11th to 20th	Day	16% 17% 4 14% 10% 6% 4 3 4 4 18%	1753
	21st to end	Day	11% 14% 6% 10% 9% 5% 4 4 4 6% 28%	1509
March	1st to 10th	Day	22% 17% 5% 9% 6% 7% 3 2 3 4 20%	3534
	11th to 20th	Day	14% 19% 5% 11% 5% 4 4 3 4 6% 25%	3590
	21st to end	Day	27% 16% 5% 10% 4 4 3 2 3 4 21%	3882
April	1st to 10th	Day	22% 14% 3 7% 4 4 4 3 4 5% 28%	2247
	11th to 20th	Day	19% 12% 3 6% 4 3 4 3 6% 6% 35%	2366
	21st to end	Day	20% 11% 2 6% 5% 4 4 3 5% 7% 32%	2470
May	1st to 10th	Day	23% 17% 3 7% 4 4 4 4 5% 6% 23%	4165
	11th to 20th	Day	17% 9% 2 8% 5% 4 5% 4 5% 7% 35%	4398
	21st to end	Day	15% 9% 3 8% 5% 5% 4 4 6% 9% 32%	4836
June	1st to 10th	Day	24% 9% 3 7% 5% 4 5% 4 6% 7% 27%	2703
	11th to 20th	Day	21% 8% 2 7% 5% 4 4 3 6% 7% 33%	2850
	21st to end	Day	23% 11% 3 6% 5% 5% 4 4 6% 5% 28%	2850
July	1st to 10th	Day	21% 9% 3 7% 4 4 4 4 6% 8% 31%	4760
	11th to 20th	Day	20% 9% 3 7% 4 4 4 4 6% 8% 32%	4536
	21st to end	Day	13% 8% 3 8% 5% 5% 5% 4 7% 9% 33%	4630
August	1st to 10th	Day	19% 11% 4 8% 5% 4 5% 3 4 7% 29%	4105
	11th to 20th	Day	13% 7% 3 7% 4 5% 5% 4 6% 8% 37%	4045
	21st to end	Day	10% 5% 2 5% 3 4 4 4 5% 8% 49%	4409
September	1st to 10th	Day	16% 7% 2 4 4 3 4 3 5% 6% 45%	2280
	11th to 20th	Day	17% 7% 3 6% 4 4 3 3 4 5% 45%	2171
	21st to end	Day	16% 7% 3 5% 4 3 4 3 5% 7% 43%	2052
October	1st to 10th	Day	17% 9% 3 6% 4 3 4 3 5% 6% 39%	1900
	11th to 20th	Day	18% 11% 3 6% 4 3 4 3 5% 7% 34%	1900
	21st to end	Day	19% 13% 3 7% 6% 4 4 3 4 6% 30%	2086
November	1st to 10th	Day	22% 13% 3 7% 5% 4 4 3 4 6% 29%	1608
	11th to 20th	Day	19% 19% 6% 9% 6% 5% 3 3 5% 4 22%	1600
	21st to end	Day	20% 20% 6% 12% 6% 4 5% 3 3 4 18%	1600
December	1st to 10th	Day	19% 17% 9% 20% 5% 5% 4 3 4 3 12%	2610
	11th to 20th	Day	23% 19% 6% 15% 7% 4 3 2 2 2 16%	2996
	21st to end	Day	19% 18% 9% 15% 6% 5% 3 3 4 4 15%	3679
January	1st to 10th	Night	13% 21% 10% 19% 8% 3 3 3 3 4 12%	6747
	11th to 20th	Night	15% 20% 9% 22% 6% 4 4 2 3 3 12%	6114
	21st to end	Night	12% 13% 6% 16% 13% 8% 5% 3 4 5% 14%	6490
February	1st to 10th	Night	18% 17% 6% 14% 10% 6% 4 3 4 4 14%	2600
	11th to 20th	Night	18% 15% 5% 13% 10% 6% 3 3 5% 5% 17%	2533
	21st to end	Night	13% 15% 6% 11% 8% 4 4 4 5% 5% 26%	2120
March	1st to 10th	Night	23% 16% 5% 13% 7% 5% 3 2 2 4 21%	3525
	11th to 20th	Night	18% 20% 7% 10% 6% 4 4 3 4 5% 19%	3589
	21st to end	Night	27% 13% 7% 10% 5% 4 3 2 3 3 24%	3889
April	1st to 10th	Night	23% 15% 4 8% 5% 4 4 3 4 4 27%	1932
	11th to 20th	Night	21% 11% 4 6% 5% 4 4 3 4 6% 31%	1759
	21st to end	Night	23% 12% 3 6% 5% 3 4 3 5% 4 31%	1710
May	1st to 10th	Night	23% 19% 3 6% 4 4 4 3 5% 5% 25%	2777
	11th to 20th	Night	19% 10% 3 6% 5% 5% 5% 4 6% 8% 31%	2506
	21st to end	Night	16% 12% 4 8% 5% 4 5% 4 6% 7% 28%	2749
June	1st to 10th	Night	25% 8% 4 8% 6% 4 5% 4 5% 6% 24%	1491
	11th to 20th	Night	23% 8% 3 7% 4 3 3 4 5% 5% 34%	1330
	21st to end	Night	22% 11% 3 6% 6% 5% 4 4 5% 7% 26%	1330
July	1st to 10th	Night	20% 13% 3 8% 6% 4 5% 5% 5% 7% 24%	2210
	11th to 20th	Night	21% 10% 3 8% 4 4 5% 4 6% 8% 26%	2398
	21st to end	Night	14% 9% 3 7% 5% 5% 5% 5% 6% 8% 35%	2925
August	1st to 10th	Night	21% 12% 3 8% 5% 3 4 4 6% 7% 27%	2825
	11th to 20th	Night	15% 9% 3 7% 4 5% 5% 4 7% 7% 32%	2782
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 7% 44%	3247
September	1st to 10th	Night	14% 7% 3 6% 5% 4 4 3 6% 6% 42%	1900
	11th to 20th	Night	18% 8% 2 6% 3 4 3 3 4 6% 43%	2007
	21st to end	Night	18% 8% 2 7% 4 4 4 3 6% 7% 37%	2127
October	1st to 10th	Night	18% 7% 2 6% 4 4 5% 3 5% 7% 39%	2280
	11th to 20th	Night	18% 10% 3 6% 5% 4 4 4 5% 7% 35%	2280
	21st to end	Night	25% 13% 3 7% 4 4 3 3 4 6% 28%	2508
November	1st to 10th	Night	23% 12% 3 6% 5% 4 4 3 4 5% 30%	2689
	11th to 20th	Night	20% 20% 5% 10% 5% 5% 4 3 4 5% 20%	2800
	21st to end	Night	23% 19% 6% 9% 4 3 4 4 4 5% 19%	2800
December	1st to 10th	Night	16% 18% 9% 19% 7% 5% 4 3 4 4 11%	4580
	11th to 20th	Night	20% 18% 5% 14% 7% 4 4 2 4 4 19%	5213
	21st to end	Night	23% 18% 6% 13% 6% 4 3 2 3 3 18%	7290

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	77% 5% 11% 5% 1	3184
	11th to 20th	Day	77% 8% 6% 7% 1	3812
	21st to end	Day	69% 5% 9% 8% 7% 1	4466
February	1st to 10th	Day	73% 5% 8% 8% 5% 1	1800
	11th to 20th	Day	71% 6% 9% 9% 4	1761
	21st to end	Day	58% 6% 11% 16% 8% 1	1509
March	1st to 10th	Day	68% 4 7% 14% 6% 1	3538
	11th to 20th	Day	61% 7% 11% 13% 7% 1	3590
	21st to end	Day	70% 5% 5% 12% 8% 1	3882
April	1st to 10th	Day	60% 5% 7% 14% 11% 2	2247
	11th to 20th	Day	50% 6% 8% 22% 13% 1	2366
	21st to end	Day	54% 6% 9% 17% 11% 2	2470
May	1st to 10th	Day	61% 7% 10% 15% 7% 1	4179
	11th to 20th	Day	49% 9% 13% 20% 9%	4402
	21st to end	Day	45% 9% 17% 17% 11% 1	4836
June	1st to 10th	Day	56% 7% 10% 19% 7%	2703
	11th to 20th	Day	49% 7% 14% 19% 10% 1	2850
	21st to end	Day	57% 8% 9% 16% 10% 1	2850
July	1st to 10th	Day	49% 5% 14% 19% 12% 1	4685
	11th to 20th	Day	47% 7% 14% 23% 8%	4457
	21st to end	Day	46% 9% 14% 21% 9%	4482
August	1st to 10th	Day	55% 7% 11% 18% 9%	4092
	11th to 20th	Day	43% 8% 14% 24% 11%	4084
	21st to end	Day	34% 6% 13% 29% 17% 1	4409
September	1st to 10th	Day	40% 6% 13% 25% 14% 2	2280
	11th to 20th	Day	43% 5% 12% 24% 15% 1	2171
	21st to end	Day	42% 5% 10% 27% 15% 1	2052
October	1st to 10th	Day	45% 7% 11% 26% 11%	3160
	11th to 20th	Day	46% 4 10% 26% 13%	3140
	21st to end	Day	47% 4 14% 22% 13% 1	3412
November	1st to 10th	Day	59% 6% 10% 16% 8% 1	1608
	11th to 20th	Day	65% 6% 13% 12% 4	1600
	21st to end	Day	70% 7% 10% 10% 3	1600
December	1st to 10th	Day	76% 4 8% 9% 2	2610
	11th to 20th	Day	76% 4 6% 9% 4 1	2995
	21st to end	Day	74% 5% 9% 8% 4	3679
January	1st to 10th	Night	75% 7% 9% 9% 1	6747
	11th to 20th	Night	76% 8% 6% 8% 2	6158
	21st to end	Night	69% 7% 10% 10% 3	6490
February	1st to 10th	Night	73% 5% 8% 7% 6% 1	2600
	11th to 20th	Night	69% 6% 10% 10% 4 1	2536
	21st to end	Night	59% 6% 10% 17% 7% 1	2120
March	1st to 10th	Night	70% 4 6% 12% 7% 1	3534
	11th to 20th	Night	67% 6% 9% 11% 6% 1	3590
	21st to end	Night	67% 4 7% 13% 7% 1	3889
April	1st to 10th	Night	61% 5% 9% 12% 11% 3	1932
	11th to 20th	Night	53% 6% 9% 18% 13% 1	1759
	21st to end	Night	55% 6% 9% 16% 12% 2	1710
May	1st to 10th	Night	60% 6% 13% 15% 5% 1	2783
	11th to 20th	Night	49% 9% 15% 21% 5% 1	2507
	21st to end	Night	50% 9% 19% 17% 5% 1	2750
June	1st to 10th	Night	54% 8% 14% 18% 5%	1491
	11th to 20th	Night	51% 5% 12% 23% 8% 1	1330
	21st to end	Night	55% 8% 12% 16% 7% 1	1330
July	1st to 10th	Night	54% 7% 14% 15% 9% 1	2175
	11th to 20th	Night	48% 8% 19% 16% 9%	2355
	21st to end	Night	40% 9% 16% 23% 11% 1	2833
August	1st to 10th	Night	52% 7% 15% 21% 6%	2813
	11th to 20th	Night	44% 8% 18% 22% 8%	2809
	21st to end	Night	35% 6% 16% 27% 16%	3246
September	1st to 10th	Night	39% 6% 12% 27% 14% 1	1900
	11th to 20th	Night	41% 4 12% 27% 15% 1	2007
	21st to end	Night	44% 7% 11% 24% 13% 1	2127
October	1st to 10th	Night	47% 5% 11% 25% 10% 1	3800
	11th to 20th	Night	42% 5% 13% 26% 14%	3779
	21st to end	Night	47% 4 12% 22% 13%	4120
November	1st to 10th	Night	56% 7% 11% 18% 8% 1	2689
	11th to 20th	Night	66% 6% 9% 13% 5%	2800
	21st to end	Night	66% 6% 14% 11% 3	2800
December	1st to 10th	Night	74% 5% 9% 10% 1	4580
	11th to 20th	Night	70% 5% 9% 13% 3	5215
	21st to end	Night	70% 5% 8% 12% 5%	7290

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% 31% 33% 10% 1	213
	11th to 20th	Day	29% 26% 29% 13% 3 1	400
	21st to end	Day	22% 27% 37% 12% 2	440
February	1st to 10th	Day	28% 27% 31% 11% 3 1	400
	11th to 20th	Day	28% 33% 27% 11% 1	396
	21st to end	Day	22% 25% 36% 14% 3	344
March	1st to 10th	Day	29% 24% 34% 11% 2	500
	11th to 20th	Day	23% 28% 34% 11% 3 1	500
	21st to end	Day	28% 26% 29% 11% 4	530
April	1st to 10th	Day	35% 26% 27% 9% 3	460
	11th to 20th	Day	24% 28% 31% 13% 4	452
	21st to end	Day	23% 22% 29% 16% 9%	460
May	1st to 10th	Day	30% 23% 26% 16% 4 1	496
	11th to 20th	Day	23% 17% 27% 24% 8% 1	674
	21st to end	Day	24% 16% 36% 19% 4 1	735
June	1st to 10th	Day	30% 12% 30% 21% 6% 1	680
	11th to 20th	Day	22% 14% 34% 23% 7% 1	680
	21st to end	Day	28% 11% 29% 24% 7% 2	680
July	1st to 10th	Day	21% 7% 37% 25% 10% 1	670
	11th to 20th	Day	19% 6% 33% 29% 12% 1	668
	21st to end	Day	21% 7% 34% 28% 10% 1	630
August	1st to 10th	Day	15% 7% 35% 31% 11% 1	486
	11th to 20th	Day	18% 11% 31% 25% 12% 3	479
	21st to end	Day	16% 13% 29% 27% 13% 3	539
September	1st to 10th	Day	20% 10% 32% 26% 10% 1	490
	11th to 20th	Day	21% 14% 28% 25% 11% 2	490
	21st to end	Day	19% 14% 32% 21% 12% 2	470
October	1st to 10th	Day	20% 16% 29% 23% 9% 3	390
	11th to 20th	Day	24% 23% 26% 18% 7% 1	390
	21st to end	Day	24% 23% 31% 16% 5% 1	429
November	1st to 10th	Day	27% 24% 31% 15% 3 1	395
	11th to 20th	Day	34% 27% 23% 12% 5%	400
	21st to end	Day	29% 28% 32% 10% 2 1	400
December	1st to 10th	Day	32% 25% 29% 13% 2	400
	11th to 20th	Day	36% 32% 20% 11% 1	400
	21st to end	Day	29% 27% 34% 6% 4 1	306
January	1st to 10th	Night	27% 27% 31% 13% 2	900
	11th to 20th	Night	26% 27% 28% 15% 4	857
	21st to end	Night	21% 28% 33% 14% 3	880
February	1st to 10th	Night	28% 27% 28% 14% 2	800
	11th to 20th	Night	29% 29% 28% 12% 2	783
	21st to end	Night	20% 24% 33% 19% 2	660
March	1st to 10th	Night	26% 25% 31% 15% 3	800
	11th to 20th	Night	22% 23% 32% 19% 5%	800
	21st to end	Night	26% 21% 33% 15% 4	863
April	1st to 10th	Night	32% 21% 29% 16% 3	602
	11th to 20th	Night	26% 20% 33% 18% 4	564
	21st to end	Night	28% 15% 30% 22% 4 1	570
May	1st to 10th	Night	29% 12% 32% 21% 6% 1	570
	11th to 20th	Night	25% 11% 31% 27% 6%	562
	21st to end	Night	21% 12% 38% 23% 6%	616
June	1st to 10th	Night	26% 11% 31% 26% 6%	541
	11th to 20th	Night	25% 7% 31% 31% 6% 1	380
	21st to end	Night	25% 8% 29% 31% 7%	380
July	1st to 10th	Night	19% 6% 33% 36% 7%	370
	11th to 20th	Night	15% 7% 35% 33% 10%	477
	21st to end	Night	18% 5% 28% 38% 9%	623
August	1st to 10th	Night	18% 6% 27% 40% 9%	568
	11th to 20th	Night	17% 8% 29% 31% 15% 1	562
	21st to end	Night	16% 7% 28% 34% 15%	627
September	1st to 10th	Night	16% 9% 32% 33% 10% 1	570
	11th to 20th	Night	18% 10% 29% 30% 11% 1	677
	21st to end	Night	20% 11% 33% 23% 11% 1	760
October	1st to 10th	Night	21% 11% 34% 24% 10% 1	760
	11th to 20th	Night	24% 16% 32% 20% 8% 1	760
	21st to end	Night	31% 23% 24% 18% 4	836
November	1st to 10th	Night	29% 20% 30% 17% 4 1	857
	11th to 20th	Night	30% 24% 27% 15% 4 1	900
	21st to end	Night	32% 23% 27% 16% 2	900
December	1st to 10th	Night	30% 23% 31% 13% 2	900
	11th to 20th	Night	31% 28% 28% 11% 2	900
	21st to end	Night	31% 25% 27% 15% 3	990

Page generated at 2025-03-24 10:04:32. Version ac07

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