Halifax
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halifax clear sky chart from 2005-11-06 to 2025-11-03.

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% 11% 4 9% 5% 4 4 3 5% 7% 29%	127206
	Night	20% 11% 4 9% 5% 4 4 3 5% 6% 29%	123019
Transparency	Day	54% 7% 11% 18% 9% 1	130786
	Night	54% 7% 10% 19% 10% 1	127527
Seeing	Day	27% 19% 31% 16% 5% 1	18757
	Night	27% 16% 30% 21% 6%	26488

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	13% 17% 6% 14% 8% 5% 5% 3 4 4 21%	3616
	11th to 20th	Day	14% 15% 7% 16% 7% 5% 5% 4 5% 6% 17%	3699
	21st to end	Day	14% 10% 4 9% 6% 5% 5% 4 6% 6% 30%	4466
February	1st to 10th	Day	20% 13% 5% 10% 6% 5% 5% 5% 4 5% 22%	1800
	11th to 20th	Day	16% 13% 5% 12% 6% 5% 5% 4 6% 5% 23%	1753
	21st to end	Day	12% 14% 3 8% 7% 5% 5% 4 4 7% 30%	1533
March	1st to 10th	Day	22% 14% 5% 11% 6% 5% 4 3 4 5% 23%	4877
	11th to 20th	Day	17% 16% 4 10% 4 3 3 3 4 6% 29%	4980
	21st to end	Day	27% 14% 4 10% 5% 4 4 3 4 5% 21%	5483
April	1st to 10th	Day	26% 15% 4 7% 5% 3 4 2 4 5% 25%	2400
	11th to 20th	Day	22% 11% 3 6% 4 4 4 3 5% 7% 30%	2416
	21st to end	Day	23% 11% 3 6% 4 4 4 3 4 7% 31%	2600
May	1st to 10th	Day	27% 13% 3 10% 5% 5% 5% 4 5% 5% 18%	6065
	11th to 20th	Day	24% 12% 4 9% 5% 4 3 3 4 5% 28%	6318
	21st to end	Day	21% 12% 3 6% 4 4 4 4 5% 8% 29%	6948
June	1st to 10th	Day	25% 11% 3 7% 5% 4 4 3 5% 7% 25%	2800
	11th to 20th	Day	22% 10% 3 7% 4 4 4 3 5% 7% 33%	2800
	21st to end	Day	30% 10% 2 6% 5% 4 4 4 4 7% 25%	2800
July	1st to 10th	Day	19% 11% 4 8% 4 4 5% 4 6% 8% 26%	6360
	11th to 20th	Day	16% 10% 4 10% 5% 4 4 3 5% 8% 31%	6360
	21st to end	Day	17% 7% 2 6% 4 4 4 4 6% 9% 38%	6755
August	1st to 10th	Day	24% 11% 3 8% 4 3 4 3 5% 7% 28%	4235
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	4175
	21st to end	Day	10% 5% 2 6% 3 4 5% 4 6% 8% 45%	4454
September	1st to 10th	Day	17% 6% 2 7% 5% 4 4 4 4 7% 40%	2400
	11th to 20th	Day	19% 7% 3 5% 3 3 4 3 4 6% 43%	2349
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 6% 41%	2120
October	1st to 10th	Day	19% 6% 3 6% 4 3 4 3 6% 8% 39%	2000
	11th to 20th	Day	19% 9% 3 7% 5% 4 4 4 6% 7% 33%	2000
	21st to end	Day	21% 8% 3 7% 5% 4 4 3 6% 6% 32%	2200
November	1st to 10th	Day	22% 11% 3 8% 5% 4 4 3 5% 6% 29%	1656
	11th to 20th	Day	23% 11% 3 7% 6% 5% 4 3 5% 7% 25%	1600
	21st to end	Day	20% 11% 4 9% 6% 5% 6% 3 5% 6% 25%	1600
December	1st to 10th	Day	21% 12% 4 11% 5% 6% 4 3 5% 7% 22%	2610
	11th to 20th	Day	30% 11% 3 6% 4 4 4 3 4 5% 26%	2996
	21st to end	Day	21% 13% 5% 11% 5% 4 3 2 5% 6% 26%	3982
January	1st to 10th	Night	14% 15% 4 11% 7% 6% 5% 5% 5% 6% 22%	6349
	11th to 20th	Night	17% 12% 6% 17% 7% 5% 5% 4 4 5% 18%	6199
	21st to end	Night	12% 11% 4 12% 7% 5% 5% 4 5% 7% 28%	6490
February	1st to 10th	Night	20% 13% 4 10% 6% 5% 5% 4 5% 5% 23%	2600
	11th to 20th	Night	17% 12% 4 9% 6% 5% 5% 4 7% 7% 24%	2533
	21st to end	Night	13% 12% 4 9% 5% 5% 5% 5% 5% 7% 28%	2096
March	1st to 10th	Night	24% 11% 4 11% 7% 6% 4 3 4 5% 22%	4959
	11th to 20th	Night	20% 14% 6% 8% 5% 4 3 3 4 5% 28%	4979
	21st to end	Night	28% 14% 4 10% 4 3 3 3 3 4 24%	5435
April	1st to 10th	Night	25% 12% 3 7% 4 4 4 3 6% 5% 27%	2000
	11th to 20th	Night	23% 11% 4 7% 4 4 4 3 4 5% 32%	1931
	21st to end	Night	24% 10% 3 7% 4 4 3 3 5% 6% 32%	1800
May	1st to 10th	Night	26% 16% 4 8% 5% 4 4 3 4 6% 22%	3883
	11th to 20th	Night	25% 13% 3 6% 3 3 4 3 4 6% 29%	3596
	21st to end	Night	19% 16% 4 8% 4 3 4 3 4 6% 30%	3948
June	1st to 10th	Night	28% 11% 3 7% 4 3 3 3 4 6% 28%	1600
	11th to 20th	Night	22% 10% 3 6% 3 4 4 3 4 7% 35%	1600
	21st to end	Night	28% 12% 3 7% 4 4 4 4 5% 6% 24%	1600
July	1st to 10th	Night	19% 12% 4 10% 6% 5% 5% 4 6% 7% 22%	3619
	11th to 20th	Night	19% 13% 3 8% 5% 4 5% 3 5% 6% 30%	3620
	21st to end	Night	18% 7% 2 7% 4 4 4 4 6% 7% 37%	4109
August	1st to 10th	Night	21% 13% 3 7% 3 3 3 3 4 6% 34%	2915
	11th to 20th	Night	17% 10% 3 7% 4 4 3 5% 6% 7% 34%	2872
	21st to end	Night	11% 7% 2 5% 3 3 3 3 5% 6% 51%	3444
September	1st to 10th	Night	18% 8% 2 5% 3 3 4 3 5% 6% 43%	2000
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 4 6% 45%	2049
	21st to end	Night	21% 9% 3 6% 3 4 3 2 5% 6% 39%	2280
October	1st to 10th	Night	18% 6% 2 5% 4 4 3 3 4 7% 43%	2400
	11th to 20th	Night	20% 7% 2 6% 4 4 4 3 5% 7% 39%	2400
	21st to end	Night	25% 9% 2 5% 4 3 4 4 4 5% 34%	2640
November	1st to 10th	Night	21% 9% 2 7% 5% 4 4 3 4 7% 34%	2684
	11th to 20th	Night	21% 11% 3 7% 5% 5% 4 4 5% 7% 28%	2800
	21st to end	Night	22% 9% 4 8% 5% 5% 4 3 6% 6% 28%	2800
December	1st to 10th	Night	16% 10% 4 10% 6% 5% 5% 4 6% 7% 27%	4580
	11th to 20th	Night	27% 11% 3 6% 4 4 3 3 4 6% 29%	5213
	21st to end	Night	24% 11% 3 8% 4 3 4 3 5% 5% 30%	6996

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	64% 7% 12% 10% 6%	3617
	11th to 20th	Day	64% 9% 10% 13% 3	3728
	21st to end	Day	51% 8% 9% 13% 16% 3	4466
February	1st to 10th	Day	63% 6% 8% 12% 9% 2	1800
	11th to 20th	Day	62% 7% 9% 15% 7% 1	1761
	21st to end	Day	53% 6% 11% 16% 11% 3	1533
March	1st to 10th	Day	64% 4 8% 12% 8% 3	4881
	11th to 20th	Day	52% 9% 12% 20% 6%	4980
	21st to end	Day	66% 4 6% 15% 9% 1	5483
April	1st to 10th	Day	60% 5% 7% 13% 11% 2	2400
	11th to 20th	Day	53% 5% 9% 20% 12% 1	2416
	21st to end	Day	54% 6% 10% 18% 10% 2	2600
May	1st to 10th	Day	64% 8% 9% 13% 5% 1	6076
	11th to 20th	Day	57% 8% 9% 20% 6%	6322
	21st to end	Day	52% 8% 14% 17% 8% 1	6948
June	1st to 10th	Day	58% 7% 11% 17% 7%	2800
	11th to 20th	Day	51% 7% 11% 20% 10% 1	2800
	21st to end	Day	59% 8% 9% 15% 9% 1	2800
July	1st to 10th	Day	56% 6% 14% 15% 9%	6290
	11th to 20th	Day	51% 6% 12% 23% 8%	6284
	21st to end	Day	43% 7% 16% 24% 9%	6561
August	1st to 10th	Day	56% 7% 12% 17% 8%	4222
	11th to 20th	Day	47% 8% 13% 25% 7%	4214
	21st to end	Day	35% 6% 12% 29% 17% 1	4454
September	1st to 10th	Day	43% 6% 13% 23% 13% 2	2400
	11th to 20th	Day	43% 5% 12% 24% 15% 1	2349
	21st to end	Day	44% 6% 9% 24% 17% 1	2120
October	1st to 10th	Day	45% 6% 10% 25% 13% 1	3260
	11th to 20th	Day	41% 6% 9% 27% 17% 1	3240
	21st to end	Day	45% 5% 14% 23% 13% 2	3538
November	1st to 10th	Day	55% 7% 10% 19% 8% 1	1656
	11th to 20th	Day	56% 8% 13% 16% 6% 1	1600
	21st to end	Day	59% 7% 13% 14% 7%	1600
December	1st to 10th	Day	61% 7% 10% 20% 3	2610
	11th to 20th	Day	59% 7% 8% 14% 11%	2995
	21st to end	Day	59% 5% 13% 15% 8%	3982
January	1st to 10th	Night	58% 10% 10% 18% 4	6349
	11th to 20th	Night	63% 10% 10% 13% 4	6245
	21st to end	Night	53% 8% 9% 16% 12% 2	6490
February	1st to 10th	Night	62% 6% 10% 13% 8% 1	2600
	11th to 20th	Night	57% 7% 12% 15% 7% 1	2536
	21st to end	Night	54% 6% 10% 19% 9% 1	2096
March	1st to 10th	Night	65% 5% 6% 12% 10% 2	4968
	11th to 20th	Night	56% 8% 9% 18% 8% 1	4980
	21st to end	Night	65% 4 6% 16% 8% 1	5435
April	1st to 10th	Night	57% 7% 8% 14% 12% 2	2000
	11th to 20th	Night	53% 6% 8% 19% 13% 2	1931
	21st to end	Night	53% 6% 10% 17% 11% 2	1800
May	1st to 10th	Night	63% 6% 10% 13% 7% 1	3889
	11th to 20th	Night	56% 6% 9% 21% 7% 2	3597
	21st to end	Night	56% 6% 10% 21% 7% 1	3949
June	1st to 10th	Night	58% 5% 9% 19% 8% 1	1600
	11th to 20th	Night	51% 6% 9% 21% 13% 1	1600
	21st to end	Night	62% 7% 9% 14% 8% 1	1600
July	1st to 10th	Night	60% 6% 11% 15% 8% 1	3581
	11th to 20th	Night	54% 6% 10% 18% 11% 1	3572
	21st to end	Night	45% 7% 12% 22% 12% 1	3989
August	1st to 10th	Night	52% 6% 12% 23% 6% 1	2903
	11th to 20th	Night	47% 8% 15% 23% 7%	2899
	21st to end	Night	32% 6% 14% 29% 18%	3443
September	1st to 10th	Night	41% 6% 11% 25% 16% 2	2000
	11th to 20th	Night	40% 5% 11% 28% 15% 1	2049
	21st to end	Night	46% 5% 9% 25% 14% 1	2280
October	1st to 10th	Night	46% 5% 12% 25% 12% 1	3920
	11th to 20th	Night	35% 6% 11% 28% 19%	3899
	21st to end	Night	42% 5% 12% 24% 17%	4252
November	1st to 10th	Night	50% 7% 13% 19% 11% 1	2684
	11th to 20th	Night	54% 9% 12% 17% 9%	2800
	21st to end	Night	55% 9% 14% 16% 6%	2800
December	1st to 10th	Night	53% 7% 10% 24% 5%	4580
	11th to 20th	Night	57% 5% 9% 17% 11% 1	5215
	21st to end	Night	56% 7% 10% 18% 9%	6996

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	31% 25% 30% 13% 2	400
	11th to 20th	Day	32% 20% 30% 13% 4	400
	21st to end	Day	24% 23% 37% 13% 3	440
February	1st to 10th	Day	32% 25% 28% 14% 2	400
	11th to 20th	Day	33% 28% 28% 11% 1	396
	21st to end	Day	25% 24% 35% 12% 5%	331
March	1st to 10th	Day	28% 27% 32% 10% 2	487
	11th to 20th	Day	28% 27% 30% 11% 4	500
	21st to end	Day	31% 27% 28% 10% 3 1	550
April	1st to 10th	Day	36% 29% 27% 6% 2	500
	11th to 20th	Day	30% 28% 29% 11% 2	492
	21st to end	Day	27% 25% 30% 12% 4	500
May	1st to 10th	Day	32% 22% 31% 12% 2 1	578
	11th to 20th	Day	25% 18% 31% 20% 5% 1	724
	21st to end	Day	28% 16% 35% 17% 3 1	790
June	1st to 10th	Day	31% 16% 31% 16% 5%	730
	11th to 20th	Day	24% 17% 33% 18% 6% 1	730
	21st to end	Day	34% 12% 28% 19% 6% 1	730
July	1st to 10th	Day	23% 11% 34% 23% 7% 1	720
	11th to 20th	Day	22% 10% 34% 23% 10% 1	718
	21st to end	Day	27% 10% 32% 23% 7% 1	724
August	1st to 10th	Day	20% 9% 35% 27% 7% 2	526
	11th to 20th	Day	21% 12% 32% 23% 10% 2	519
	21st to end	Day	18% 13% 35% 23% 8% 3	583
September	1st to 10th	Day	18% 12% 38% 23% 7% 2	530
	11th to 20th	Day	24% 16% 30% 18% 9% 3	530
	21st to end	Day	20% 15% 32% 24% 7% 2	486
October	1st to 10th	Day	22% 13% 34% 19% 10% 2	420
	11th to 20th	Day	21% 20% 34% 15% 7% 2	420
	21st to end	Day	26% 23% 32% 13% 5% 1	462
November	1st to 10th	Day	27% 21% 30% 15% 6% 1	401
	11th to 20th	Day	35% 22% 26% 13% 5% 1	400
	21st to end	Day	31% 26% 28% 13% 2 1	400
December	1st to 10th	Day	34% 20% 31% 13% 2 1	400
	11th to 20th	Day	36% 26% 27% 10% 1	400
	21st to end	Day	29% 27% 30% 11% 3 1	440
January	1st to 10th	Night	29% 22% 34% 13% 2	900
	11th to 20th	Night	29% 22% 30% 16% 3	875
	21st to end	Night	23% 25% 34% 16% 2	880
February	1st to 10th	Night	29% 22% 30% 18% 2	800
	11th to 20th	Night	29% 26% 31% 13% 1	783
	21st to end	Night	20% 23% 34% 19% 3	660
March	1st to 10th	Night	25% 24% 33% 16% 2	800
	11th to 20th	Night	24% 20% 30% 20% 5%	800
	21st to end	Night	27% 23% 29% 16% 4	874
April	1st to 10th	Night	34% 19% 29% 16% 3	600
	11th to 20th	Night	28% 20% 32% 16% 3	594
	21st to end	Night	29% 14% 33% 19% 4 1	600
May	1st to 10th	Night	32% 13% 32% 18% 5% 1	600
	11th to 20th	Night	27% 14% 29% 22% 7% 1	592
	21st to end	Night	24% 14% 34% 24% 4	649
June	1st to 10th	Night	33% 10% 29% 23% 5%	600
	11th to 20th	Night	24% 10% 37% 24% 5% 1	600
	21st to end	Night	30% 9% 28% 26% 7%	600
July	1st to 10th	Night	23% 9% 30% 31% 7%	586
	11th to 20th	Night	25% 6% 28% 31% 10%	582
	21st to end	Night	22% 7% 28% 32% 10%	656
August	1st to 10th	Night	20% 4 28% 33% 14% 1	598
	11th to 20th	Night	23% 5% 23% 34% 14% 1	592
	21st to end	Night	19% 7% 27% 31% 14% 1	660
September	1st to 10th	Night	22% 7% 31% 29% 11% 1	600
	11th to 20th	Night	22% 11% 25% 29% 13% 1	649
	21st to end	Night	25% 12% 27% 26% 9% 1	800
October	1st to 10th	Night	21% 13% 29% 27% 10% 1	800
	11th to 20th	Night	23% 16% 30% 22% 9% 1	800
	21st to end	Night	31% 15% 31% 18% 4	880
November	1st to 10th	Night	29% 15% 31% 20% 4 1	888
	11th to 20th	Night	29% 21% 27% 18% 5%	900
	21st to end	Night	31% 22% 27% 16% 4	900
December	1st to 10th	Night	32% 18% 32% 14% 4	900
	11th to 20th	Night	33% 23% 30% 12% 2	900
	21st to end	Night	29% 22% 30% 16% 3	990

Page generated at 2025-10-31 03:02:35. Version ac07

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