Sackville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sackville clear sky chart from 2005-11-06 to 2026-06-16.

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% 11% 4 8% 5% 4 4 4 5% 6% 31%	138168
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 31%	134028
Transparency	Day	54% 4 11% 20% 9% 1	141728
	Night	55% 4 11% 20% 10% 1	138558
Seeing	Day	27% 19% 32% 16% 5% 1	19125
	Night	26% 16% 32% 21% 5%	26653

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	12% 21% 5% 10% 5% 5% 4 3 5% 4 24%	4093
	11th to 20th	Day	17% 16% 7% 13% 5% 4 3 2 4 4 24%	4616
	21st to end	Day	9% 10% 4 11% 5% 4 4 4 5% 6% 37%	5781
February	1st to 10th	Day	15% 14% 5% 10% 6% 6% 3 3 5% 6% 28%	1890
	11th to 20th	Day	15% 15% 4 10% 6% 4 4 4 5% 5% 28%	1843
	21st to end	Day	10% 13% 5% 10% 5% 5% 4 3 5% 7% 32%	1557
March	1st to 10th	Day	19% 15% 5% 12% 5% 4 3 3 4 5% 25%	5034
	11th to 20th	Day	15% 16% 5% 10% 5% 4 5% 4 5% 6% 26%	5090
	21st to end	Day	26% 16% 4 8% 4 5% 4 3 5% 5% 20%	5587
April	1st to 10th	Day	21% 14% 4 8% 5% 4 4 3 5% 6% 26%	2501
	11th to 20th	Day	19% 14% 3 7% 5% 4 4 3 5% 7% 29%	2620
	21st to end	Day	21% 11% 3 7% 4 5% 4 3 5% 6% 29%	2730
May	1st to 10th	Day	27% 14% 3 8% 5% 4 4 3 4 5% 24%	7873
	11th to 20th	Day	20% 9% 3 6% 4 5% 5% 4 5% 6% 33%	8220
	21st to end	Day	22% 12% 3 8% 4 4 5% 3 5% 7% 27%	9059
June	1st to 10th	Day	24% 10% 2 6% 5% 5% 4 4 6% 7% 27%	3042
	11th to 20th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 7% 31%	3075
	21st to end	Day	26% 9% 3 7% 4 4 4 3 5% 7% 28%	3000
July	1st to 10th	Day	16% 10% 3 8% 5% 6% 5% 4 7% 9% 27%	6820
	11th to 20th	Day	14% 6% 3 7% 5% 5% 4 3 6% 8% 40%	6591
	21st to end	Day	12% 6% 2 7% 5% 4 5% 5% 7% 9% 38%	6792
August	1st to 10th	Day	17% 8% 3 9% 5% 5% 4 4 6% 7% 31%	4235
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 37%	4175
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 45%	4548
September	1st to 10th	Day	16% 5% 2 5% 4 4 4 4 5% 7% 42%	2400
	11th to 20th	Day	15% 9% 3 7% 4 4 4 3 4 7% 40%	2305
	21st to end	Day	18% 6% 2 5% 4 4 4 3 5% 7% 42%	2149
October	1st to 10th	Day	17% 7% 3 7% 4 4 4 4 5% 7% 39%	2000
	11th to 20th	Day	18% 8% 3 8% 5% 5% 4 3 5% 6% 35%	2000
	21st to end	Day	18% 11% 3 7% 5% 5% 5% 4 4 6% 32%	2190
November	1st to 10th	Day	20% 12% 3 9% 5% 5% 4 3 4 6% 31%	1655
	11th to 20th	Day	20% 14% 4 7% 4 4 4 3 5% 6% 30%	1680
	21st to end	Day	19% 13% 5% 9% 5% 4 4 4 4 5% 28%	1680
December	1st to 10th	Day	17% 14% 5% 8% 5% 3 3 2 4 6% 32%	2690
	11th to 20th	Day	18% 15% 4 8% 4 4 3 3 3 4 34%	3076
	21st to end	Day	16% 13% 6% 13% 5% 5% 4 4 4 5% 26%	3571
January	1st to 10th	Night	14% 17% 5% 9% 5% 4 4 3 4 5% 29%	8831
	11th to 20th	Night	19% 17% 6% 12% 6% 4 4 2 4 4 23%	8261
	21st to end	Night	9% 13% 5% 9% 6% 5% 4 3 5% 5% 37%	8400
February	1st to 10th	Night	16% 13% 4 11% 5% 5% 4 3 5% 6% 27%	2730
	11th to 20th	Night	16% 14% 4 10% 5% 4 4 4 5% 5% 29%	2663
	21st to end	Night	13% 14% 4 9% 5% 4 4 4 5% 5% 32%	2249
March	1st to 10th	Night	24% 14% 4 12% 5% 5% 3 3 3 4 24%	5023
	11th to 20th	Night	21% 17% 5% 9% 5% 4 3 3 4 5% 25%	5089
	21st to end	Night	28% 13% 4 8% 4 3 4 3 4 3 26%	5587
April	1st to 10th	Night	23% 14% 4 8% 5% 5% 4 3 4 4 25%	2118
	11th to 20th	Night	22% 13% 3 6% 4 3 4 3 5% 5% 32%	1947
	21st to end	Night	22% 12% 4 8% 4 4 3 4 4 6% 29%	1890
May	1st to 10th	Night	27% 13% 3 8% 5% 4 5% 3 5% 6% 20%	5035
	11th to 20th	Night	22% 9% 3 7% 5% 4 5% 4 5% 6% 30%	4670
	21st to end	Night	19% 12% 3 9% 5% 5% 4 4 5% 5% 29%	5147
June	1st to 10th	Night	25% 10% 2 8% 4 4 4 4 5% 7% 27%	1594
	11th to 20th	Night	21% 6% 3 7% 5% 4 3 4 6% 8% 32%	1435
	21st to end	Night	22% 11% 3 7% 4 4 5% 4 6% 7% 26%	1400
July	1st to 10th	Night	15% 10% 4 10% 6% 6% 6% 4 6% 8% 26%	3160
	11th to 20th	Night	11% 8% 4 8% 5% 5% 6% 4 6% 9% 35%	3339
	21st to end	Night	16% 6% 2 6% 4 5% 5% 4 7% 9% 36%	4073
August	1st to 10th	Night	16% 9% 3 9% 6% 5% 6% 4 6% 7% 29%	2915
	11th to 20th	Night	10% 8% 3 8% 5% 5% 6% 4 8% 8% 35%	2872
	21st to end	Night	13% 6% 2 6% 3 4 3 4 6% 8% 46%	3350
September	1st to 10th	Night	16% 6% 2 6% 4 3 4 4 5% 8% 42%	2000
	11th to 20th	Night	15% 7% 3 6% 4 3 4 3 4 6% 45%	2092
	21st to end	Night	17% 7% 2 6% 4 4 4 3 4 6% 42%	2250
October	1st to 10th	Night	18% 7% 3 6% 5% 3 3 4 5% 7% 40%	2400
	11th to 20th	Night	19% 9% 3 7% 4 4 4 3 4 7% 37%	2400
	21st to end	Night	25% 9% 3 7% 4 4 4 3 4 5% 33%	2648
November	1st to 10th	Night	21% 10% 2 7% 5% 5% 4 3 5% 6% 31%	2863
	11th to 20th	Night	21% 12% 4 8% 5% 5% 4 3 4 6% 29%	2940
	21st to end	Night	22% 12% 3 8% 5% 4 4 3 5% 5% 30%	2940
December	1st to 10th	Night	16% 11% 4 8% 4 4 3 3 5% 6% 36%	4720
	11th to 20th	Night	20% 15% 4 8% 4 3 3 2 4 5% 33%	5353
	21st to end	Night	20% 14% 5% 11% 4 3 4 3 4 5% 28%	7644

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% 2 10% 14% 9% 1	4094
	11th to 20th	Day	66% 3 8% 13% 8% 1	4645
	21st to end	Day	48% 3 9% 21% 17% 3	5781
February	1st to 10th	Day	59% 4 11% 15% 10% 1	1890
	11th to 20th	Day	59% 5% 10% 16% 10% 1	1851
	21st to end	Day	53% 4 10% 19% 11% 2	1557
March	1st to 10th	Day	63% 3 8% 14% 10% 2	5038
	11th to 20th	Day	60% 5% 13% 16% 5% 1	5090
	21st to end	Day	67% 3 6% 17% 7% 1	5587
April	1st to 10th	Day	61% 4 7% 15% 10% 2	2501
	11th to 20th	Day	56% 5% 8% 19% 11% 1	2620
	21st to end	Day	55% 4 10% 17% 11% 2	2730
May	1st to 10th	Day	63% 4 9% 15% 8%	7885
	11th to 20th	Day	52% 6% 13% 22% 7%	8224
	21st to end	Day	56% 6% 10% 17% 10% 1	9060
June	1st to 10th	Day	56% 5% 12% 20% 6%	3042
	11th to 20th	Day	51% 6% 12% 21% 9% 1	3075
	21st to end	Day	56% 6% 11% 17% 9% 1	3000
July	1st to 10th	Day	53% 4 16% 18% 9%	6745
	11th to 20th	Day	43% 4 16% 29% 7% 1	6510
	21st to end	Day	43% 5% 18% 28% 6%	6598
August	1st to 10th	Day	51% 6% 11% 25% 6%	4222
	11th to 20th	Day	44% 6% 14% 24% 12%	4214
	21st to end	Day	37% 4 14% 27% 16% 1	4548
September	1st to 10th	Day	41% 6% 15% 26% 13%	2400
	11th to 20th	Day	44% 4 13% 25% 13% 1	2305
	21st to end	Day	43% 4 10% 28% 14% 1	2149
October	1st to 10th	Day	47% 3 11% 30% 9%	3260
	11th to 20th	Day	47% 3 8% 32% 8%	3240
	21st to end	Day	46% 3 13% 22% 15%	3516
November	1st to 10th	Day	57% 5% 9% 19% 9%	1655
	11th to 20th	Day	56% 5% 13% 17% 9%	1680
	21st to end	Day	59% 4 13% 16% 7%	1680
December	1st to 10th	Day	55% 3 12% 25% 5%	2690
	11th to 20th	Day	57% 3 10% 18% 11% 1	3075
	21st to end	Day	62% 3 11% 16% 7% 1	3571
January	1st to 10th	Night	58% 3 9% 23% 7%	8831
	11th to 20th	Night	66% 3 8% 16% 7%	8307
	21st to end	Night	50% 3 8% 20% 16% 3	8400
February	1st to 10th	Night	58% 4 10% 13% 12% 2	2730
	11th to 20th	Night	57% 4 10% 16% 11% 1	2666
	21st to end	Night	54% 3 9% 19% 13% 2	2249
March	1st to 10th	Night	66% 3 4 12% 13% 2	5032
	11th to 20th	Night	63% 4 11% 13% 8% 1	5090
	21st to end	Night	65% 3 5% 16% 11% 1	5587
April	1st to 10th	Night	61% 4 7% 13% 10% 3	2118
	11th to 20th	Night	55% 4 9% 20% 11% 1	1947
	21st to end	Night	57% 4 9% 15% 12% 2	1890
May	1st to 10th	Night	65% 4 10% 14% 7% 1	5041
	11th to 20th	Night	55% 6% 11% 21% 7% 1	4671
	21st to end	Night	56% 5% 14% 15% 9% 1	5148
June	1st to 10th	Night	56% 6% 11% 19% 8%	1594
	11th to 20th	Night	50% 6% 11% 24% 8% 1	1435
	21st to end	Night	56% 8% 12% 14% 9% 1	1400
July	1st to 10th	Night	57% 4 13% 18% 8%	3125
	11th to 20th	Night	46% 5% 17% 24% 8%	3297
	21st to end	Night	45% 5% 18% 21% 10%	3954
August	1st to 10th	Night	53% 7% 13% 21% 6%	2903
	11th to 20th	Night	44% 6% 18% 19% 12%	2899
	21st to end	Night	38% 4 17% 26% 14%	3349
September	1st to 10th	Night	41% 5% 12% 29% 13%	2000
	11th to 20th	Night	41% 5% 13% 27% 14% 1	2092
	21st to end	Night	44% 5% 11% 27% 13% 1	2250
October	1st to 10th	Night	50% 3 11% 27% 9%	3920
	11th to 20th	Night	40% 4 9% 32% 14%	3899
	21st to end	Night	47% 3 12% 23% 15%	4272
November	1st to 10th	Night	56% 5% 11% 19% 10% 1	2863
	11th to 20th	Night	56% 5% 12% 17% 9% 1	2940
	21st to end	Night	57% 4 13% 18% 8%	2940
December	1st to 10th	Night	50% 2 11% 26% 10%	4720
	11th to 20th	Night	56% 2 8% 20% 12% 2	5355
	21st to end	Night	61% 2 10% 17% 9% 1	7644

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	33% 24% 31% 11% 1	220
	11th to 20th	Day	32% 23% 26% 13% 5% 1	372
	21st to end	Day	20% 22% 39% 15% 4	473
February	1st to 10th	Day	27% 22% 31% 15% 5% 1	430
	11th to 20th	Day	30% 23% 29% 14% 3 1	426
	21st to end	Day	22% 21% 37% 18% 3	355
March	1st to 10th	Day	29% 25% 33% 11% 2 1	540
	11th to 20th	Day	26% 24% 33% 14% 4 1	540
	21st to end	Day	32% 24% 28% 10% 3 1	594
April	1st to 10th	Day	36% 28% 26% 8% 1 1	540
	11th to 20th	Day	36% 25% 25% 11% 3	532
	21st to end	Day	30% 22% 29% 13% 6% 1	540
May	1st to 10th	Day	37% 21% 25% 14% 3	623
	11th to 20th	Day	29% 19% 29% 16% 6% 1	774
	21st to end	Day	28% 19% 34% 16% 3	845
June	1st to 10th	Day	31% 17% 31% 15% 5%	780
	11th to 20th	Day	25% 17% 35% 18% 5%	755
	21st to end	Day	27% 15% 31% 20% 6% 1	730
July	1st to 10th	Day	24% 14% 37% 19% 5% 1	720
	11th to 20th	Day	18% 11% 41% 23% 7% 1	718
	21st to end	Day	20% 13% 41% 20% 7%	735
August	1st to 10th	Day	14% 13% 39% 26% 7% 1	526
	11th to 20th	Day	19% 13% 33% 22% 11% 2	519
	21st to end	Day	16% 18% 32% 24% 7% 3	583
September	1st to 10th	Day	16% 16% 40% 19% 8% 2	530
	11th to 20th	Day	20% 17% 32% 22% 7% 2	530
	21st to end	Day	22% 15% 34% 18% 9% 2	501
October	1st to 10th	Day	24% 15% 29% 21% 10% 2	420
	11th to 20th	Day	23% 20% 29% 19% 8% 2	420
	21st to end	Day	27% 21% 29% 15% 6% 1	462
November	1st to 10th	Day	31% 19% 31% 12% 6% 1	425
	11th to 20th	Day	37% 21% 24% 13% 5% 1	430
	21st to end	Day	33% 20% 30% 12% 3 1	430
December	1st to 10th	Day	33% 18% 31% 15% 3	430
	11th to 20th	Day	35% 24% 28% 12% 1	430
	21st to end	Day	27% 23% 33% 13% 4	247
January	1st to 10th	Night	29% 18% 31% 17% 5%	950
	11th to 20th	Night	30% 19% 29% 18% 4	929
	21st to end	Night	21% 21% 34% 19% 5%	924
February	1st to 10th	Night	28% 17% 34% 18% 3 1	840
	11th to 20th	Night	28% 23% 30% 15% 3 1	823
	21st to end	Night	23% 17% 36% 19% 3 1	692
March	1st to 10th	Night	26% 20% 35% 17% 2	840
	11th to 20th	Night	26% 19% 30% 20% 5% 1	840
	21st to end	Night	29% 17% 31% 18% 5%	924
April	1st to 10th	Night	32% 19% 29% 17% 3	648
	11th to 20th	Night	30% 17% 29% 18% 4	624
	21st to end	Night	30% 15% 30% 18% 6% 1	630
May	1st to 10th	Night	32% 14% 29% 19% 5%	630
	11th to 20th	Night	27% 15% 30% 23% 5%	622
	21st to end	Night	24% 13% 42% 17% 3	682
June	1st to 10th	Night	32% 11% 31% 21% 5%	544
	11th to 20th	Night	24% 10% 35% 27% 4	410
	21st to end	Night	25% 8% 34% 27% 5% 1	400
July	1st to 10th	Night	20% 8% 42% 23% 7%	390
	11th to 20th	Night	17% 10% 40% 29% 5%	463
	21st to end	Night	19% 9% 38% 29% 5%	656
August	1st to 10th	Night	16% 8% 39% 30% 8%	598
	11th to 20th	Night	17% 9% 34% 30% 9% 1	592
	21st to end	Night	16% 9% 33% 31% 10%	660
September	1st to 10th	Night	20% 9% 37% 26% 7% 1	600
	11th to 20th	Night	18% 12% 28% 32% 9% 1	692
	21st to end	Night	21% 11% 31% 26% 10%	800
October	1st to 10th	Night	22% 11% 29% 28% 9% 1	800
	11th to 20th	Night	24% 14% 30% 23% 8% 1	800
	21st to end	Night	30% 20% 28% 17% 4	880
November	1st to 10th	Night	30% 17% 28% 18% 6%	925
	11th to 20th	Night	29% 21% 26% 18% 5% 1	950
	21st to end	Night	30% 19% 30% 16% 4 1	950
December	1st to 10th	Night	32% 18% 28% 18% 4	950
	11th to 20th	Night	32% 22% 31% 12% 3	950
	21st to end	Night	31% 21% 25% 19% 3 1	1045

Page generated at 2026-06-13 03:31:40. Version ac07

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