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 2025-02-21.

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	17% 11% 4 8% 5% 4 4 4 5% 6% 31%	108778
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 31%	109903
Transparency	Day	53% 5% 12% 20% 9% 1	112383
	Night	54% 5% 11% 20% 10% 1	114463
Seeing	Day	26% 19% 32% 16% 5% 1	17268
	Night	26% 16% 31% 21% 5%	24946

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% 22% 5% 10% 6% 5% 4 3 5% 4 23%	3157
	11th to 20th	Day	14% 15% 8% 12% 5% 4 3 3 4 4 27%	3542
	21st to end	Day	10% 10% 4 11% 5% 4 5% 4 5% 6% 36%	4466
February	1st to 10th	Day	16% 13% 4 10% 6% 6% 3 3 5% 6% 29%	1800
	11th to 20th	Day	15% 15% 4 9% 6% 5% 4 4 5% 5% 27%	1753
	21st to end	Day	11% 13% 5% 10% 5% 6% 4 3 5% 7% 32%	1413
March	1st to 10th	Day	22% 16% 4 7% 4 4 3 3 4 5% 26%	3424
	11th to 20th	Day	13% 21% 5% 12% 6% 4 4 3 5% 4 23%	3480
	21st to end	Day	29% 15% 5% 8% 5% 4 3 3 4 4 19%	3816
April	1st to 10th	Day	20% 15% 4 8% 6% 4 4 3 5% 6% 26%	2263
	11th to 20th	Day	19% 14% 3 7% 5% 4 4 3 5% 7% 30%	2368
	21st to end	Day	22% 11% 3 7% 4 5% 4 3 6% 6% 29%	2470
May	1st to 10th	Day	22% 17% 3 8% 5% 4 4 3 5% 6% 24%	4230
	11th to 20th	Day	17% 8% 3 6% 4 5% 5% 4 5% 7% 36%	4398
	21st to end	Day	16% 10% 3 9% 6% 5% 6% 4 6% 9% 26%	4836
June	1st to 10th	Day	26% 10% 3 6% 5% 5% 4 4 6% 6% 26%	2752
	11th to 20th	Day	21% 9% 3 7% 5% 5% 5% 4 6% 6% 32%	2850
	21st to end	Day	26% 9% 3 7% 4 4 4 3 5% 7% 28%	2850
July	1st to 10th	Day	16% 9% 3 7% 5% 5% 5% 4 7% 8% 31%	4760
	11th to 20th	Day	15% 7% 3 8% 5% 5% 5% 4 6% 8% 35%	4601
	21st to end	Day	14% 7% 3 7% 5% 4 5% 4 7% 8% 35%	4722
August	1st to 10th	Day	18% 8% 3 9% 6% 5% 4 4 6% 7% 30%	4105
	11th to 20th	Day	14% 6% 3 7% 5% 5% 5% 4 6% 8% 37%	4045
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 45%	4409
September	1st to 10th	Day	17% 5% 2 5% 4 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	15% 9% 3 7% 4 3 4 3 5% 7% 40%	2190
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 7% 42%	2042
October	1st to 10th	Day	17% 7% 3 7% 4 4 4 4 5% 7% 38%	1900
	11th to 20th	Day	19% 8% 3 7% 4 5% 4 3 5% 6% 36%	1900
	21st to end	Day	17% 11% 3 7% 5% 5% 5% 4 4 6% 33%	2081
November	1st to 10th	Day	19% 12% 2 9% 5% 5% 5% 3 4 6% 31%	1575
	11th to 20th	Day	20% 13% 4 8% 4 4 4 3 5% 5% 30%	1600
	21st to end	Day	19% 13% 5% 9% 5% 4 4 4 4 5% 29%	1600
December	1st to 10th	Day	18% 13% 4 8% 5% 3 3 2 5% 6% 32%	2610
	11th to 20th	Day	19% 15% 4 8% 4 4 3 3 3 4 34%	2996
	21st to end	Day	16% 13% 6% 12% 5% 5% 4 4 4 5% 26%	3494
January	1st to 10th	Night	14% 18% 5% 9% 5% 4 4 3 4 5% 29%	6808
	11th to 20th	Night	15% 17% 6% 12% 6% 4 4 3 4 5% 25%	6341
	21st to end	Night	10% 12% 5% 10% 6% 4 3 2 5% 5% 36%	6490
February	1st to 10th	Night	17% 13% 4 10% 6% 5% 4 3 5% 6% 28%	2600
	11th to 20th	Night	17% 14% 4 10% 5% 5% 4 4 5% 5% 28%	2533
	21st to end	Night	12% 15% 4 9% 5% 4 4 4 5% 5% 32%	2042
March	1st to 10th	Night	23% 14% 4 11% 5% 5% 4 3 3 4 24%	3413
	11th to 20th	Night	19% 20% 6% 10% 5% 5% 3 3 5% 4 20%	3479
	21st to end	Night	28% 12% 5% 9% 4 4 4 3 3 3 25%	3816
April	1st to 10th	Night	22% 14% 4 8% 6% 5% 4 3 4 4 26%	1916
	11th to 20th	Night	21% 12% 3 6% 4 3 4 3 5% 5% 33%	1759
	21st to end	Night	22% 12% 4 8% 4 4 3 4 4 6% 29%	1710
May	1st to 10th	Night	23% 15% 3 6% 5% 5% 5% 4 5% 6% 23%	2712
	11th to 20th	Night	17% 9% 3 6% 4 3 5% 3 5% 8% 38%	2506
	21st to end	Night	15% 10% 3 9% 6% 6% 5% 4 6% 7% 28%	2749
June	1st to 10th	Night	26% 11% 2 8% 5% 5% 4 4 5% 7% 25%	1442
	11th to 20th	Night	21% 6% 3 7% 5% 4 3 4 5% 8% 33%	1330
	21st to end	Night	22% 11% 3 7% 5% 4 5% 4 6% 7% 26%	1330
July	1st to 10th	Night	16% 9% 4 10% 6% 6% 5% 4 6% 8% 27%	2210
	11th to 20th	Night	14% 9% 4 8% 5% 5% 6% 4 6% 9% 30%	2333
	21st to end	Night	14% 7% 3 6% 5% 5% 5% 4 6% 8% 38%	2836
August	1st to 10th	Night	16% 9% 3 9% 6% 5% 6% 4 7% 7% 27%	2825
	11th to 20th	Night	10% 8% 3 8% 5% 5% 6% 4 8% 8% 35%	2782
	21st to end	Night	13% 6% 2 6% 3 4 3 3 6% 8% 46%	3247
September	1st to 10th	Night	16% 6% 2 6% 4 3 4 4 5% 8% 41%	1900
	11th to 20th	Night	16% 7% 3 6% 4 3 4 3 4 6% 45%	1987
	21st to end	Night	17% 7% 2 6% 4 4 3 3 4 6% 42%	2137
October	1st to 10th	Night	19% 7% 3 6% 5% 3 3 3 5% 7% 39%	2280
	11th to 20th	Night	18% 9% 3 7% 4 4 4 3 4 7% 38%	2280
	21st to end	Night	25% 9% 3 7% 4 4 4 3 4 5% 33%	2515
November	1st to 10th	Night	21% 10% 3 7% 5% 5% 4 3 4 6% 32%	2723
	11th to 20th	Night	21% 11% 4 8% 5% 5% 4 3 4 6% 29%	2800
	21st to end	Night	22% 12% 4 8% 5% 4 4 3 5% 5% 30%	2800
December	1st to 10th	Night	16% 11% 4 8% 4 4 3 3 5% 6% 36%	4580
	11th to 20th	Night	20% 15% 4 8% 4 3 3 2 4 5% 33%	5213
	21st to end	Night	20% 14% 5% 11% 4 3 3 3 4 5% 28%	7479

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	66% 3 11% 14% 7% 1	3158
	11th to 20th	Day	63% 4 9% 15% 9% 1	3571
	21st to end	Day	50% 4 9% 17% 16% 4	4466
February	1st to 10th	Day	58% 4 11% 15% 11% 1	1800
	11th to 20th	Day	59% 5% 10% 16% 10% 1	1761
	21st to end	Day	53% 4 11% 19% 11% 3	1413
March	1st to 10th	Day	61% 4 10% 18% 6% 2	3428
	11th to 20th	Day	64% 6% 8% 14% 6% 1	3480
	21st to end	Day	68% 4 7% 13% 7% 1	3816
April	1st to 10th	Day	61% 4 7% 16% 9% 2	2263
	11th to 20th	Day	55% 5% 9% 20% 11% 1	2368
	21st to end	Day	56% 4 11% 17% 11% 2	2470
May	1st to 10th	Day	61% 6% 9% 17% 6% 1	4244
	11th to 20th	Day	47% 9% 13% 23% 7%	4402
	21st to end	Day	51% 10% 15% 17% 7%	4836
June	1st to 10th	Day	59% 6% 11% 19% 5%	2752
	11th to 20th	Day	51% 7% 12% 21% 9% 1	2850
	21st to end	Day	57% 6% 11% 16% 9% 1	2850
July	1st to 10th	Day	50% 5% 16% 18% 11%	4685
	11th to 20th	Day	47% 6% 16% 25% 7%	4520
	21st to end	Day	45% 7% 18% 24% 5%	4572
August	1st to 10th	Day	53% 7% 12% 24% 5%	4092
	11th to 20th	Day	45% 6% 14% 24% 12%	4084
	21st to end	Day	38% 4 14% 27% 17%	4409
September	1st to 10th	Day	41% 6% 15% 25% 13%	2280
	11th to 20th	Day	44% 5% 12% 24% 13% 1	2190
	21st to end	Day	43% 4 10% 28% 13% 1	2042
October	1st to 10th	Day	47% 3 11% 30% 9%	3160
	11th to 20th	Day	47% 3 9% 33% 9%	3140
	21st to end	Day	45% 4 14% 21% 16%	3407
November	1st to 10th	Day	57% 5% 9% 19% 9%	1575
	11th to 20th	Day	56% 5% 13% 16% 9% 1	1600
	21st to end	Day	59% 5% 13% 17% 8%	1600
December	1st to 10th	Day	55% 3 12% 25% 5%	2610
	11th to 20th	Day	57% 3 10% 17% 11% 1	2995
	21st to end	Day	62% 3 11% 16% 7% 1	3494
January	1st to 10th	Night	58% 3 10% 24% 5%	6808
	11th to 20th	Night	62% 4 10% 17% 6% 1	6387
	21st to end	Night	50% 3 9% 21% 15% 3	6490
February	1st to 10th	Night	58% 4 10% 13% 13% 3	2600
	11th to 20th	Night	58% 5% 10% 15% 11% 1	2536
	21st to end	Night	54% 3 10% 18% 13% 2	2042
March	1st to 10th	Night	66% 4 6% 15% 8% 2	3422
	11th to 20th	Night	66% 6% 7% 13% 7% 1	3480
	21st to end	Night	65% 4 6% 15% 9% 1	3816
April	1st to 10th	Night	61% 5% 8% 13% 10% 3	1916
	11th to 20th	Night	53% 4 9% 21% 12% 1	1759
	21st to end	Night	56% 5% 9% 15% 12% 2	1710
May	1st to 10th	Night	59% 7% 13% 14% 6% 1	2718
	11th to 20th	Night	44% 8% 17% 23% 7% 1	2507
	21st to end	Night	51% 10% 18% 15% 6%	2750
June	1st to 10th	Night	58% 6% 11% 17% 8%	1442
	11th to 20th	Night	50% 6% 11% 23% 8% 1	1330
	21st to end	Night	56% 8% 12% 14% 8% 1	1330
July	1st to 10th	Night	54% 5% 13% 17% 10% 1	2175
	11th to 20th	Night	50% 7% 17% 19% 7%	2291
	21st to end	Night	44% 6% 17% 22% 11%	2747
August	1st to 10th	Night	54% 7% 14% 20% 5%	2813
	11th to 20th	Night	44% 7% 18% 19% 12%	2809
	21st to end	Night	38% 4 18% 26% 14%	3246
September	1st to 10th	Night	42% 6% 12% 28% 12%	1900
	11th to 20th	Night	41% 5% 13% 27% 13% 1	1987
	21st to end	Night	44% 5% 11% 27% 12% 1	2137
October	1st to 10th	Night	51% 3 11% 27% 8%	3800
	11th to 20th	Night	39% 4 9% 33% 14%	3779
	21st to end	Night	46% 3 13% 22% 15%	4139
November	1st to 10th	Night	56% 5% 11% 18% 10% 1	2723
	11th to 20th	Night	56% 6% 12% 16% 10% 1	2800
	21st to end	Night	57% 5% 13% 18% 8%	2800
December	1st to 10th	Night	50% 3 11% 26% 9%	4580
	11th to 20th	Night	56% 2 8% 19% 12% 2	5215
	21st to end	Night	61% 2 11% 16% 9% 1	7479

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	34% 24% 30% 11% 1	200
	11th to 20th	Day	31% 23% 26% 14% 6% 1	345
	21st to end	Day	20% 21% 40% 15% 4	440
February	1st to 10th	Day	28% 22% 32% 14% 4 1	400
	11th to 20th	Day	32% 24% 29% 12% 3 1	396
	21st to end	Day	22% 21% 37% 16% 3	307
March	1st to 10th	Day	30% 25% 32% 11% 2 1	460
	11th to 20th	Day	25% 24% 33% 14% 4 1	460
	21st to end	Day	32% 25% 28% 10% 4 1	506
April	1st to 10th	Day	36% 28% 25% 8% 2 1	460
	11th to 20th	Day	33% 27% 26% 11% 3	452
	21st to end	Day	30% 24% 29% 12% 5% 1	460
May	1st to 10th	Day	36% 22% 24% 14% 4 1	535
	11th to 20th	Day	27% 19% 29% 17% 6% 1	674
	21st to end	Day	26% 20% 34% 17% 3	735
June	1st to 10th	Day	34% 17% 31% 14% 4	680
	11th to 20th	Day	25% 17% 34% 19% 5%	680
	21st to end	Day	27% 16% 31% 20% 6% 1	680
July	1st to 10th	Day	24% 15% 37% 18% 6% 1	670
	11th to 20th	Day	18% 11% 41% 22% 7% 1	668
	21st to end	Day	21% 13% 40% 19% 7%	683
August	1st to 10th	Day	16% 14% 40% 25% 6%	486
	11th to 20th	Day	20% 12% 34% 22% 10% 2	479
	21st to end	Day	16% 17% 32% 24% 7% 3	539
September	1st to 10th	Day	17% 16% 41% 17% 8% 1	490
	11th to 20th	Day	21% 17% 32% 21% 7% 2	490
	21st to end	Day	22% 16% 31% 19% 9% 2	464
October	1st to 10th	Day	25% 15% 28% 20% 10% 2	390
	11th to 20th	Day	24% 21% 28% 19% 6% 2	390
	21st to end	Day	27% 22% 30% 15% 6% 1	429
November	1st to 10th	Day	29% 18% 32% 13% 6% 2	395
	11th to 20th	Day	36% 21% 25% 13% 5% 1	400
	21st to end	Day	33% 21% 31% 12% 3	400
December	1st to 10th	Day	33% 18% 31% 15% 3 1	400
	11th to 20th	Day	35% 24% 27% 12% 2	400
	21st to end	Day	28% 22% 34% 13% 4	225
January	1st to 10th	Night	29% 19% 31% 17% 5%	900
	11th to 20th	Night	30% 19% 28% 18% 5%	881
	21st to end	Night	21% 21% 34% 19% 5%	880
February	1st to 10th	Night	28% 18% 34% 18% 3	800
	11th to 20th	Night	29% 24% 30% 14% 2 1	783
	21st to end	Night	22% 19% 36% 18% 3 1	629
March	1st to 10th	Night	26% 20% 35% 17% 2	760
	11th to 20th	Night	26% 19% 29% 20% 5% 1	760
	21st to end	Night	28% 18% 30% 18% 6%	836
April	1st to 10th	Night	32% 19% 29% 17% 3	586
	11th to 20th	Night	29% 18% 29% 18% 5% 1	564
	21st to end	Night	30% 16% 31% 17% 5% 1	570
May	1st to 10th	Night	31% 15% 29% 20% 5%	570
	11th to 20th	Night	26% 15% 29% 24% 6%	562
	21st to end	Night	23% 13% 43% 18% 3	616
June	1st to 10th	Night	32% 12% 32% 20% 5%	492
	11th to 20th	Night	24% 11% 34% 27% 4	380
	21st to end	Night	24% 8% 34% 28% 5% 1	380
July	1st to 10th	Night	19% 9% 42% 23% 7%	370
	11th to 20th	Night	17% 10% 40% 28% 5%	439
	21st to end	Night	19% 9% 38% 29% 5%	623
August	1st to 10th	Night	16% 8% 40% 29% 7%	568
	11th to 20th	Night	17% 10% 35% 28% 9% 1	562
	21st to end	Night	16% 9% 32% 32% 10%	627
September	1st to 10th	Night	21% 9% 37% 26% 7%	570
	11th to 20th	Night	19% 12% 28% 31% 9% 1	657
	21st to end	Night	22% 12% 30% 26% 10%	760
October	1st to 10th	Night	23% 11% 28% 29% 9% 1	760
	11th to 20th	Night	23% 15% 31% 23% 7% 1	760
	21st to end	Night	30% 21% 29% 17% 4	836
November	1st to 10th	Night	30% 17% 28% 19% 6%	875
	11th to 20th	Night	29% 21% 26% 18% 6% 1	900
	21st to end	Night	30% 20% 29% 16% 4	900
December	1st to 10th	Night	32% 18% 27% 18% 4	900
	11th to 20th	Night	31% 22% 31% 12% 3	900
	21st to end	Night	32% 21% 24% 19% 4 1	990

Page generated at 2025-02-18 04:26:28. Version ac07

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