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 2024-11-06.

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	21% 11% 3 8% 5% 4 4 3 5% 7% 29%	101582
	Night	21% 11% 3 8% 5% 4 4 3 5% 6% 29%	97592
Transparency	Day	53% 7% 11% 18% 9% 1	105180
	Night	53% 7% 11% 18% 9% 1	102083
Seeing	Day	27% 19% 31% 16% 5% 1	17381
	Night	27% 16% 30% 21% 6%	25139

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	15% 12% 5% 10% 6% 5% 6% 3 5% 5% 27%	2526
	11th to 20th	Day	16% 13% 5% 15% 7% 6% 5% 4 5% 6% 19%	2599
	21st to end	Day	18% 9% 4 9% 6% 5% 5% 5% 6% 7% 26%	3124
February	1st to 10th	Day	20% 13% 4 9% 6% 5% 5% 5% 4 5% 22%	1710
	11th to 20th	Day	17% 14% 5% 11% 6% 5% 5% 4 6% 5% 23%	1663
	21st to end	Day	13% 14% 4 8% 7% 5% 5% 4 4 7% 31%	1458
March	1st to 10th	Day	24% 14% 5% 8% 5% 5% 4 2 3 5% 26%	3391
	11th to 20th	Day	15% 18% 5% 11% 5% 4 4 3 4 5% 25%	3480
	21st to end	Day	31% 13% 4 10% 5% 4 3 2 3 4 21%	3833
April	1st to 10th	Day	25% 15% 4 7% 5% 3 4 2 4 5% 25%	2280
	11th to 20th	Day	22% 11% 3 6% 4 4 4 3 5% 7% 31%	2294
	21st to end	Day	23% 11% 3 6% 4 4 4 3 4 7% 30%	2470
May	1st to 10th	Day	24% 14% 3 9% 5% 5% 4 4 5% 6% 20%	4229
	11th to 20th	Day	23% 11% 3 8% 5% 4 4 2 4 6% 30%	4398
	21st to end	Day	20% 9% 4 7% 4 4 5% 4 6% 9% 29%	4836
June	1st to 10th	Day	26% 11% 3 7% 5% 4 4 3 5% 7% 24%	2660
	11th to 20th	Day	22% 10% 3 6% 4 4 4 3 4 6% 33%	2660
	21st to end	Day	30% 10% 2 6% 5% 4 4 4 4 7% 25%	2660
July	1st to 10th	Day	20% 10% 4 7% 4 4 4 4 6% 7% 29%	4440
	11th to 20th	Day	16% 11% 4 10% 5% 4 4 3 6% 8% 29%	4440
	21st to end	Day	23% 9% 3 6% 4 4 4 3 5% 8% 31%	4699
August	1st to 10th	Day	24% 11% 3 8% 4 3 4 3 5% 7% 26%	4105
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 9% 31%	4045
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 45%	4318
September	1st to 10th	Day	17% 6% 2 6% 5% 4 4 4 4 7% 40%	2280
	11th to 20th	Day	19% 7% 3 5% 3 3 4 2 4 6% 42%	2232
	21st to end	Day	20% 7% 2 6% 4 4 4 3 5% 6% 40%	2014
October	1st to 10th	Day	19% 6% 3 6% 4 3 4 3 6% 8% 37%	1900
	11th to 20th	Day	20% 8% 3 6% 4 4 4 4 6% 7% 34%	1900
	21st to end	Day	21% 8% 3 7% 5% 4 4 3 6% 6% 33%	2090
November	1st to 10th	Day	22% 11% 3 8% 5% 4 4 3 5% 6% 30%	1599
	11th to 20th	Day	23% 9% 3 7% 6% 5% 4 3 5% 7% 26%	1520
	21st to end	Day	20% 10% 4 8% 6% 5% 6% 3 5% 6% 26%	1520
December	1st to 10th	Day	25% 14% 4 8% 5% 6% 4 3 4 6% 21%	1520
	11th to 20th	Day	32% 12% 3 8% 4 4 4 4 5% 6% 19%	1906
	21st to end	Day	23% 11% 5% 10% 6% 4 4 2 5% 6% 23%	2783
January	1st to 10th	Night	15% 11% 4 9% 7% 6% 5% 5% 5% 6% 27%	4429
	11th to 20th	Night	19% 10% 5% 15% 8% 5% 5% 4 4 5% 19%	4367
	21st to end	Night	17% 12% 5% 12% 6% 4 5% 4 5% 7% 23%	4532
February	1st to 10th	Night	20% 13% 4 9% 6% 5% 5% 4 5% 5% 23%	2470
	11th to 20th	Night	18% 12% 4 9% 6% 5% 5% 4 7% 7% 23%	2403
	21st to end	Night	13% 12% 4 9% 5% 5% 5% 5% 5% 7% 28%	1995
March	1st to 10th	Night	23% 11% 3 10% 7% 6% 4 3 4 5% 24%	3445
	11th to 20th	Night	20% 14% 5% 9% 6% 4 4 4 5% 6% 24%	3479
	21st to end	Night	30% 13% 4 11% 4 3 2 2 3 3 24%	3799
April	1st to 10th	Night	25% 12% 3 7% 4 4 4 3 6% 5% 28%	1900
	11th to 20th	Night	23% 10% 4 7% 5% 4 4 3 4 5% 32%	1834
	21st to end	Night	24% 11% 3 7% 4 4 3 3 5% 5% 32%	1710
May	1st to 10th	Night	22% 15% 4 8% 5% 4 4 3 5% 7% 24%	2715
	11th to 20th	Night	25% 10% 3 7% 4 4 5% 3 5% 6% 29%	2506
	21st to end	Night	22% 12% 4 8% 5% 4 4 3 5% 7% 28%	2749
June	1st to 10th	Night	28% 12% 3 7% 4 3 3 3 4 6% 27%	1520
	11th to 20th	Night	22% 10% 3 6% 3 4 4 3 4 7% 34%	1520
	21st to end	Night	29% 12% 3 7% 4 4 4 3 5% 6% 24%	1520
July	1st to 10th	Night	20% 12% 4 10% 6% 5% 5% 3 6% 6% 24%	2530
	11th to 20th	Night	18% 14% 4 9% 5% 4 5% 4 5% 6% 27%	2530
	21st to end	Night	21% 8% 3 7% 5% 4 4 3 5% 7% 35%	2859
August	1st to 10th	Night	22% 13% 3 7% 3 3 3 3 4 5% 33%	2825
	11th to 20th	Night	18% 10% 3 7% 5% 4 3 5% 6% 8% 33%	2782
	21st to end	Night	11% 7% 2 5% 3 3 3 3 5% 6% 52%	3338
September	1st to 10th	Night	17% 8% 2 5% 3 3 4 3 5% 6% 43%	1900
	11th to 20th	Night	18% 7% 2 5% 3 3 3 3 4 6% 44%	1946
	21st to end	Night	21% 9% 3 6% 3 4 3 2 5% 6% 38%	2166
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 4 7% 41%	2280
	11th to 20th	Night	19% 6% 2 6% 4 4 4 3 5% 7% 40%	2280
	21st to end	Night	25% 9% 2 5% 4 4 4 4 4 5% 35%	2508
November	1st to 10th	Night	22% 9% 3 7% 5% 4 4 3 4 7% 34%	2598
	11th to 20th	Night	21% 10% 3 7% 5% 5% 4 4 5% 7% 30%	2660
	21st to end	Night	21% 8% 4 8% 5% 5% 4 3 6% 6% 30%	2660
December	1st to 10th	Night	24% 12% 3 9% 6% 5% 5% 4 4 6% 21%	2660
	11th to 20th	Night	32% 11% 3 8% 4 4 4 4 4 5% 22%	3293
	21st to end	Night	25% 10% 4 9% 4 4 4 3 5% 6% 25%	4884

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	54% 9% 17% 14% 5% 1	2527
	11th to 20th	Day	60% 11% 10% 14% 4	2599
	21st to end	Day	53% 10% 10% 15% 12%	3124
February	1st to 10th	Day	63% 6% 9% 12% 8% 1	1710
	11th to 20th	Day	62% 7% 9% 14% 7% 1	1671
	21st to end	Day	53% 6% 11% 16% 11% 3	1458
March	1st to 10th	Day	61% 5% 9% 16% 8% 2	3395
	11th to 20th	Day	54% 12% 10% 17% 7% 1	3480
	21st to end	Day	67% 5% 7% 12% 8% 1	3833
April	1st to 10th	Day	60% 5% 7% 13% 11% 2	2280
	11th to 20th	Day	52% 5% 9% 20% 12% 1	2294
	21st to end	Day	54% 6% 10% 18% 11% 2	2470
May	1st to 10th	Day	60% 9% 11% 14% 4 1	4243
	11th to 20th	Day	55% 9% 11% 18% 7%	4402
	21st to end	Day	49% 10% 17% 16% 8% 1	4836
June	1st to 10th	Day	59% 7% 11% 17% 6%	2660
	11th to 20th	Day	51% 7% 12% 20% 10% 1	2660
	21st to end	Day	60% 8% 9% 14% 8% 1	2660
July	1st to 10th	Day	54% 7% 11% 16% 11% 1	4370
	11th to 20th	Day	51% 7% 13% 21% 7%	4364
	21st to end	Day	51% 7% 13% 20% 9%	4549
August	1st to 10th	Day	57% 7% 12% 17% 7%	4092
	11th to 20th	Day	47% 8% 14% 24% 6%	4084
	21st to end	Day	35% 7% 12% 29% 17% 1	4318
September	1st to 10th	Day	42% 6% 14% 23% 13% 2	2280
	11th to 20th	Day	44% 5% 12% 24% 15% 1	2232
	21st to end	Day	45% 6% 9% 25% 16%	2014
October	1st to 10th	Day	46% 6% 10% 24% 13% 1	3160
	11th to 20th	Day	40% 6% 9% 27% 17% 1	3140
	21st to end	Day	44% 5% 14% 23% 13% 2	3428
November	1st to 10th	Day	55% 7% 9% 20% 8% 1	1599
	11th to 20th	Day	54% 8% 14% 16% 7% 1	1520
	21st to end	Day	57% 7% 14% 15% 7%	1520
December	1st to 10th	Day	64% 7% 9% 16% 4	1520
	11th to 20th	Day	65% 8% 7% 14% 5% 1	1905
	21st to end	Day	60% 6% 16% 13% 5%	2783
January	1st to 10th	Night	52% 11% 13% 21% 4	4429
	11th to 20th	Night	62% 12% 10% 11% 5%	4367
	21st to end	Night	58% 9% 10% 14% 7% 1	4532
February	1st to 10th	Night	62% 6% 10% 13% 8% 1	2470
	11th to 20th	Night	58% 7% 12% 15% 7% 1	2406
	21st to end	Night	54% 7% 10% 19% 9% 1	1995
March	1st to 10th	Night	62% 6% 8% 15% 8% 1	3454
	11th to 20th	Night	58% 10% 9% 15% 9% 1	3480
	21st to end	Night	66% 5% 7% 14% 8% 1	3799
April	1st to 10th	Night	57% 7% 8% 14% 11% 3	1900
	11th to 20th	Night	53% 6% 9% 18% 13% 2	1834
	21st to end	Night	54% 6% 10% 17% 12% 3	1710
May	1st to 10th	Night	57% 9% 13% 13% 7% 1	2721
	11th to 20th	Night	54% 7% 11% 20% 7% 1	2507
	21st to end	Night	56% 8% 12% 18% 5% 1	2750
June	1st to 10th	Night	59% 5% 10% 18% 7%	1520
	11th to 20th	Night	52% 6% 10% 20% 12% 1	1520
	21st to end	Night	63% 6% 9% 13% 7% 1	1520
July	1st to 10th	Night	59% 7% 11% 13% 8% 1	2491
	11th to 20th	Night	55% 8% 13% 16% 9% 1	2482
	21st to end	Night	48% 7% 11% 20% 12% 1	2769
August	1st to 10th	Night	53% 6% 13% 23% 5%	2813
	11th to 20th	Night	48% 8% 15% 23% 6%	2809
	21st to end	Night	32% 7% 14% 28% 19%	3337
September	1st to 10th	Night	41% 6% 11% 24% 15% 2	1900
	11th to 20th	Night	41% 5% 11% 28% 15% 1	1946
	21st to end	Night	47% 5% 9% 24% 13% 1	2166
October	1st to 10th	Night	47% 5% 12% 25% 11%	3800
	11th to 20th	Night	34% 6% 11% 29% 20%	3779
	21st to end	Night	42% 5% 12% 23% 18%	4120
November	1st to 10th	Night	51% 6% 13% 18% 11% 1	2598
	11th to 20th	Night	52% 9% 12% 17% 9%	2660
	21st to end	Night	53% 9% 15% 16% 7%	2660
December	1st to 10th	Night	62% 7% 11% 15% 4	2660
	11th to 20th	Night	64% 6% 9% 14% 6%	3295
	21st to end	Night	58% 9% 11% 17% 5%	4884

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% 25% 31% 13% 2	370
	11th to 20th	Day	33% 21% 31% 12% 3	370
	21st to end	Day	24% 22% 37% 13% 3	407
February	1st to 10th	Day	32% 23% 28% 14% 2	370
	11th to 20th	Day	32% 29% 28% 10% 1	366
	21st to end	Day	24% 25% 35% 12% 4	307
March	1st to 10th	Day	27% 28% 32% 10% 2	448
	11th to 20th	Day	29% 27% 29% 11% 3	460
	21st to end	Day	32% 26% 28% 11% 3 1	506
April	1st to 10th	Day	36% 28% 27% 7% 2	460
	11th to 20th	Day	29% 29% 30% 10% 2	452
	21st to end	Day	27% 24% 31% 13% 5%	460
May	1st to 10th	Day	31% 24% 31% 11% 2 1	534
	11th to 20th	Day	25% 18% 32% 20% 5% 1	674
	21st to end	Day	28% 17% 35% 17% 3 1	735
June	1st to 10th	Day	31% 16% 31% 17% 5%	680
	11th to 20th	Day	25% 16% 33% 19% 6% 1	680
	21st to end	Day	35% 11% 28% 19% 6% 1	680
July	1st to 10th	Day	23% 11% 34% 24% 8% 1	670
	11th to 20th	Day	22% 10% 35% 22% 10% 1	668
	21st to end	Day	28% 10% 30% 24% 7% 1	673
August	1st to 10th	Day	21% 9% 34% 28% 7% 1	486
	11th to 20th	Day	22% 12% 31% 23% 10% 2	479
	21st to end	Day	18% 11% 35% 24% 9% 4	539
September	1st to 10th	Day	18% 13% 37% 23% 7% 1	490
	11th to 20th	Day	26% 16% 30% 17% 9% 3	490
	21st to end	Day	22% 15% 31% 23% 8% 2	450
October	1st to 10th	Day	22% 13% 34% 19% 10% 2	390
	11th to 20th	Day	21% 21% 32% 16% 7% 2	390
	21st to end	Day	26% 23% 32% 13% 5% 1	429
November	1st to 10th	Day	27% 19% 30% 16% 7% 1	381
	11th to 20th	Day	32% 22% 26% 14% 5% 1	370
	21st to end	Day	30% 26% 29% 13% 2 1	370
December	1st to 10th	Day	35% 21% 31% 12% 2 1	370
	11th to 20th	Day	36% 27% 26% 9% 1	370
	21st to end	Day	29% 27% 28% 12% 3 1	407
January	1st to 10th	Night	28% 21% 34% 14% 2	850
	11th to 20th	Night	30% 23% 29% 15% 2	828
	21st to end	Night	24% 24% 34% 16% 2	836
February	1st to 10th	Night	29% 22% 30% 18% 2	760
	11th to 20th	Night	28% 26% 31% 12% 1	743
	21st to end	Night	20% 24% 34% 19% 4	628
March	1st to 10th	Night	24% 24% 34% 15% 2	760
	11th to 20th	Night	24% 20% 30% 20% 5%	760
	21st to end	Night	27% 23% 29% 17% 4	831
April	1st to 10th	Night	32% 19% 29% 17% 3	570
	11th to 20th	Night	27% 20% 33% 16% 3	564
	21st to end	Night	29% 15% 33% 19% 4 1	570
May	1st to 10th	Night	31% 13% 33% 18% 5% 1	570
	11th to 20th	Night	27% 13% 29% 22% 7% 1	562
	21st to end	Night	25% 14% 35% 23% 4	616
June	1st to 10th	Night	34% 11% 29% 23% 4	570
	11th to 20th	Night	24% 10% 37% 23% 5% 1	570
	21st to end	Night	30% 8% 28% 25% 8%	570
July	1st to 10th	Night	23% 8% 30% 31% 7%	556
	11th to 20th	Night	25% 6% 29% 31% 10%	552
	21st to end	Night	22% 7% 28% 33% 10%	623
August	1st to 10th	Night	21% 4 29% 32% 14% 1	568
	11th to 20th	Night	24% 5% 24% 33% 13% 1	562
	21st to end	Night	19% 7% 26% 31% 14% 1	627
September	1st to 10th	Night	21% 8% 32% 29% 11% 1	570
	11th to 20th	Night	22% 11% 26% 28% 12% 1	616
	21st to end	Night	25% 13% 27% 25% 9% 1	760
October	1st to 10th	Night	22% 13% 29% 27% 9% 1	760
	11th to 20th	Night	21% 17% 31% 21% 9% 1	760
	21st to end	Night	31% 16% 31% 18% 4	836
November	1st to 10th	Night	29% 14% 31% 21% 4 1	856
	11th to 20th	Night	27% 22% 27% 19% 5%	850
	21st to end	Night	28% 23% 28% 16% 4	850
December	1st to 10th	Night	34% 18% 32% 13% 4	850
	11th to 20th	Night	33% 23% 31% 11% 2	850
	21st to end	Night	29% 23% 31% 15% 3	935

Page generated at 2024-11-03 14:19:01. Version ac07

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