Merrickville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Merrickville clear sky chart from 2005-11-06 to 2025-12-03.

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	17% 10% 3 8% 5% 4 4 4 5% 6% 32%	127398
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	123273
Transparency	Day	51% 6% 11% 21% 10% 1	130876
	Night	53% 6% 11% 19% 10% 1	127882
Seeing	Day	23% 17% 30% 19% 8% 2	15844
	Night	23% 14% 30% 24% 8% 1	24956

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% 19% 6% 12% 5% 5% 5% 3 4 5% 22%	3597
	11th to 20th	Day	13% 16% 7% 14% 6% 5% 4 3 5% 4 22%	3570
	21st to end	Day	14% 17% 7% 14% 6% 6% 4 4 4 5% 20%	4172
February	1st to 10th	Day	17% 15% 5% 11% 8% 5% 5% 4 4 4 24%	1800
	11th to 20th	Day	14% 15% 6% 10% 7% 5% 4 3 4 5% 27%	1765
	21st to end	Day	19% 16% 5% 9% 7% 5% 4 3 5% 4 23%	1650
March	1st to 10th	Day	19% 14% 4 10% 5% 4 4 3 4 6% 26%	4492
	11th to 20th	Day	11% 13% 4 8% 6% 5% 5% 4 6% 7% 31%	4980
	21st to end	Day	18% 11% 3 7% 5% 3 3 2 4 5% 37%	5773
April	1st to 10th	Day	20% 13% 3 6% 5% 3 4 3 5% 6% 32%	2400
	11th to 20th	Day	21% 10% 3 6% 5% 4 3 4 4 5% 36%	2374
	21st to end	Day	23% 10% 3 8% 4 5% 4 3 5% 5% 32%	2512
May	1st to 10th	Day	25% 11% 3 9% 5% 5% 5% 3 4 6% 25%	6346
	11th to 20th	Day	18% 9% 3 9% 6% 5% 5% 4 5% 7% 31%	6318
	21st to end	Day	21% 8% 3 6% 4 4 4 4 5% 7% 34%	6949
June	1st to 10th	Day	21% 9% 3 6% 5% 4 5% 4 6% 7% 31%	2800
	11th to 20th	Day	15% 6% 3 7% 5% 4 5% 4 6% 8% 38%	2800
	21st to end	Day	19% 8% 3 7% 5% 4 5% 4 6% 7% 32%	2800
July	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 4 7% 9% 35%	6360
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 4 7% 8% 42%	6360
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 7% 10% 45%	6926
August	1st to 10th	Day	16% 8% 3 7% 5% 4 4 4 5% 7% 37%	4451
	11th to 20th	Day	17% 7% 2 6% 3 4 5% 4 6% 8% 38%	4110
	21st to end	Day	15% 5% 2 5% 4 5% 4 4 6% 9% 39%	4312
September	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 3 6% 7% 43%	2400
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 4 7% 48%	2400
	21st to end	Day	18% 6% 3 6% 4 4 5% 3 5% 7% 40%	2134
October	1st to 10th	Day	20% 7% 3 7% 4 4 4 3 4 6% 38%	2000
	11th to 20th	Day	20% 9% 3 8% 5% 5% 5% 4 5% 6% 31%	2000
	21st to end	Day	25% 10% 4 6% 5% 4 4 4 5% 5% 28%	2050
November	1st to 10th	Day	17% 10% 2 7% 5% 5% 5% 4 6% 6% 32%	1851
	11th to 20th	Day	16% 13% 4 9% 6% 5% 4 3 4 6% 29%	1704
	21st to end	Day	22% 14% 5% 9% 6% 4 5% 3 5% 5% 22%	1680
December	1st to 10th	Day	22% 19% 5% 11% 5% 4 4 3 4 5% 16%	2616
	11th to 20th	Day	19% 17% 5% 12% 6% 5% 4 3 3 3 24%	2986
	21st to end	Day	22% 17% 5% 11% 5% 4 4 3 4 4 22%	3960
January	1st to 10th	Night	15% 19% 8% 13% 6% 4 3 2 4 4 22%	6349
	11th to 20th	Night	12% 17% 7% 15% 8% 6% 5% 3 4 5% 18%	6315
	21st to end	Night	16% 16% 6% 13% 6% 6% 4 3 4 5% 20%	6767
February	1st to 10th	Night	16% 17% 5% 11% 7% 5% 4 3 4 5% 22%	2600
	11th to 20th	Night	14% 15% 4 11% 6% 5% 4 3 4 5% 28%	2520
	21st to end	Night	16% 15% 4 9% 7% 4 4 3 4 4 29%	1980
March	1st to 10th	Night	22% 13% 4 9% 5% 5% 4 2 3 4 29%	5346
	11th to 20th	Night	14% 12% 4 8% 5% 4 5% 4 7% 8% 31%	4979
	21st to end	Night	19% 11% 3 9% 5% 4 4 3 4 5% 34%	5158
April	1st to 10th	Night	20% 12% 4 7% 4 4 4 3 5% 6% 31%	2000
	11th to 20th	Night	22% 9% 3 7% 5% 4 3 3 4 5% 37%	1975
	21st to end	Night	22% 10% 2 8% 4 4 4 5% 4 5% 34%	1905
May	1st to 10th	Night	26% 10% 3 7% 5% 4 5% 4 5% 6% 24%	3594
	11th to 20th	Night	16% 8% 3 7% 4 4 4 3 5% 6% 39%	3575
	21st to end	Night	18% 9% 3 7% 4 4 4 4 6% 7% 33%	3926
June	1st to 10th	Night	17% 6% 4 7% 5% 5% 5% 4 6% 7% 33%	1600
	11th to 20th	Night	15% 6% 2 7% 4 4 5% 3 6% 9% 41%	1600
	21st to end	Night	17% 8% 3 6% 4 5% 5% 4 5% 7% 35%	1600
July	1st to 10th	Night	13% 6% 3 8% 5% 5% 5% 4 6% 9% 36%	3600
	11th to 20th	Night	13% 5% 2 7% 4 3 4 4 5% 8% 44%	3600
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 7% 47%	3926
August	1st to 10th	Night	12% 7% 2 6% 5% 4 5% 3 6% 8% 41%	2682
	11th to 20th	Night	13% 6% 3 7% 4 5% 4 3 6% 7% 42%	2904
	21st to end	Night	11% 5% 2 7% 5% 4 5% 4 6% 8% 43%	3586
September	1st to 10th	Night	12% 6% 2 7% 4 4 3 4 5% 5% 48%	2000
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 5% 7% 51%	2000
	21st to end	Night	16% 7% 3 6% 4 3 4 4 6% 6% 42%	2262
October	1st to 10th	Night	16% 7% 3 7% 4 5% 5% 3 5% 7% 39%	2400
	11th to 20th	Night	20% 8% 2 7% 5% 4 4 3 6% 7% 33%	2400
	21st to end	Night	24% 10% 3 8% 4 4 4 3 5% 6% 30%	2790
November	1st to 10th	Night	19% 11% 3 6% 4 4 4 3 4 6% 36%	2667
	11th to 20th	Night	18% 11% 4 8% 5% 4 4 4 4 5% 32%	2914
	21st to end	Night	21% 14% 4 9% 5% 5% 4 3 4 6% 24%	2940
December	1st to 10th	Night	19% 18% 6% 12% 6% 6% 4 3 4 5% 17%	4609
	11th to 20th	Night	23% 15% 4 9% 5% 4 4 3 4 4 26%	5208
	21st to end	Night	26% 17% 4 11% 5% 3 3 3 5% 4 19%	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	65% 6% 11% 13% 4 1	3598
	11th to 20th	Day	66% 5% 10% 11% 8% 1	3600
	21st to end	Day	67% 6% 9% 10% 8% 1	4172
February	1st to 10th	Day	63% 5% 8% 18% 5% 1	1800
	11th to 20th	Day	60% 5% 10% 16% 8% 1	1774
	21st to end	Day	64% 6% 8% 12% 9% 1	1650
March	1st to 10th	Day	60% 5% 8% 14% 11% 2	4495
	11th to 20th	Day	51% 5% 18% 14% 11% 1	4980
	21st to end	Day	50% 4 6% 18% 18% 3	5773
April	1st to 10th	Day	54% 5% 7% 19% 13% 3	2400
	11th to 20th	Day	52% 4 8% 19% 16% 2	2374
	21st to end	Day	54% 5% 8% 15% 14% 3	2512
May	1st to 10th	Day	60% 5% 8% 17% 8% 2	6357
	11th to 20th	Day	52% 8% 11% 18% 10% 1	6322
	21st to end	Day	49% 7% 11% 22% 10% 1	6949
June	1st to 10th	Day	51% 7% 10% 20% 12% 1	2800
	11th to 20th	Day	43% 7% 10% 26% 12% 2	2800
	21st to end	Day	49% 9% 11% 19% 11% 1	2800
July	1st to 10th	Day	44% 6% 13% 27% 10%	6290
	11th to 20th	Day	37% 7% 13% 29% 14%	6285
	21st to end	Day	34% 8% 13% 37% 9%	6728
August	1st to 10th	Day	46% 6% 14% 23% 10%	4437
	11th to 20th	Day	42% 6% 14% 29% 9% 1	4149
	21st to end	Day	40% 6% 16% 27% 11%	4312
September	1st to 10th	Day	39% 8% 13% 28% 12%	2400
	11th to 20th	Day	35% 7% 12% 32% 14%	2400
	21st to end	Day	43% 7% 14% 25% 11%	2134
October	1st to 10th	Day	46% 4 12% 30% 9%	3260
	11th to 20th	Day	46% 6% 14% 25% 8% 1	3240
	21st to end	Day	48% 5% 16% 23% 8%	3288
November	1st to 10th	Day	51% 7% 13% 21% 7% 1	1851
	11th to 20th	Day	56% 6% 11% 16% 10% 1	1704
	21st to end	Day	65% 7% 11% 11% 6%	1680
December	1st to 10th	Day	70% 6% 12% 10% 1	2616
	11th to 20th	Day	66% 5% 10% 13% 6%	2986
	21st to end	Day	68% 4 8% 15% 6%	3960
January	1st to 10th	Night	67% 5% 11% 12% 4	6349
	11th to 20th	Night	68% 6% 10% 10% 5%	6360
	21st to end	Night	67% 5% 7% 9% 11% 1	6767
February	1st to 10th	Night	64% 5% 10% 15% 6% 1	2600
	11th to 20th	Night	59% 4 10% 19% 7%	2522
	21st to end	Night	60% 5% 8% 17% 9% 1	1980
March	1st to 10th	Night	60% 4 6% 16% 11% 3	5356
	11th to 20th	Night	49% 6% 19% 16% 8% 3	4980
	21st to end	Night	53% 3 7% 21% 13% 2	5158
April	1st to 10th	Night	54% 4 9% 19% 13% 2	2000
	11th to 20th	Night	51% 4 8% 19% 17% 1	1975
	21st to end	Night	52% 5% 8% 16% 15% 3	1905
May	1st to 10th	Night	59% 7% 8% 16% 8% 3	3600
	11th to 20th	Night	44% 7% 14% 20% 14% 1	3576
	21st to end	Night	48% 7% 12% 18% 13% 1	3927
June	1st to 10th	Night	48% 8% 12% 19% 12% 1	1600
	11th to 20th	Night	41% 7% 12% 22% 16% 2	1600
	21st to end	Night	46% 10% 10% 20% 13% 1	1600
July	1st to 10th	Night	43% 7% 15% 19% 14% 1	3560
	11th to 20th	Night	38% 6% 13% 31% 12%	3552
	21st to end	Night	36% 7% 12% 30% 14%	3809
August	1st to 10th	Night	40% 8% 13% 26% 12%	2672
	11th to 20th	Night	41% 6% 15% 29% 8% 1	2931
	21st to end	Night	38% 8% 14% 28% 12% 1	3586
September	1st to 10th	Night	38% 8% 10% 30% 14% 1	2000
	11th to 20th	Night	32% 7% 13% 36% 12% 1	2000
	21st to end	Night	41% 6% 11% 28% 12% 1	2262
October	1st to 10th	Night	41% 6% 11% 29% 12% 1	3920
	11th to 20th	Night	43% 5% 15% 27% 10% 1	3899
	21st to end	Night	48% 6% 16% 22% 8%	4502
November	1st to 10th	Night	50% 6% 13% 21% 9% 1	2667
	11th to 20th	Night	54% 5% 12% 18% 10% 1	2914
	21st to end	Night	62% 6% 11% 14% 5%	2940
December	1st to 10th	Night	70% 5% 11% 11% 2	4609
	11th to 20th	Night	63% 5% 7% 14% 10% 1	5208
	21st to end	Night	69% 4 6% 12% 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	23% 25% 35% 14% 5%	200
	11th to 20th	Day	32% 19% 31% 16% 3 1	200
	21st to end	Day	24% 26% 31% 13% 4	267
February	1st to 10th	Day	32% 27% 28% 11% 1	300
	11th to 20th	Day	30% 27% 34% 8%	312
	21st to end	Day	31% 20% 35% 13% 1	414
March	1st to 10th	Day	27% 22% 31% 16% 3	500
	11th to 20th	Day	27% 22% 33% 13% 4 1	500
	21st to end	Day	31% 22% 27% 13% 6% 1	550
April	1st to 10th	Day	33% 22% 27% 13% 4 1	500
	11th to 20th	Day	33% 21% 24% 12% 8% 2	492
	21st to end	Day	31% 21% 29% 12% 5% 2	500
May	1st to 10th	Day	27% 18% 29% 18% 7% 1	503
	11th to 20th	Day	21% 18% 34% 18% 7% 2	527
	21st to end	Day	22% 17% 28% 23% 9% 1	573
June	1st to 10th	Day	23% 15% 33% 21% 7% 1	530
	11th to 20th	Day	15% 16% 35% 21% 10% 2	530
	21st to end	Day	21% 15% 33% 19% 9% 2	530
July	1st to 10th	Day	13% 9% 32% 32% 12% 2	525
	11th to 20th	Day	12% 12% 31% 28% 14% 3	524
	21st to end	Day	14% 9% 33% 30% 10% 3	576
August	1st to 10th	Day	15% 10% 26% 33% 13% 2	526
	11th to 20th	Day	16% 6% 27% 28% 15% 7%	519
	21st to end	Day	15% 12% 31% 22% 13% 7%	583
September	1st to 10th	Day	15% 12% 29% 23% 13% 7%	530
	11th to 20th	Day	13% 8% 25% 25% 18% 12%	530
	21st to end	Day	19% 12% 29% 23% 13% 4	530
October	1st to 10th	Day	23% 15% 26% 19% 12% 5%	530
	11th to 20th	Day	25% 19% 32% 18% 5% 1	530
	21st to end	Day	32% 16% 27% 21% 4	500
November	1st to 10th	Day	30% 18% 28% 17% 6% 1	425
	11th to 20th	Day	23% 24% 32% 12% 7% 2	244
	21st to end	Day	32% 21% 34% 9% 4	220
December	1st to 10th	Day	33% 20% 31% 13% 3	204
	11th to 20th	Day	32% 30% 28% 8% 3 1	200
	21st to end	Day	34% 19% 29% 15% 3 1	220
January	1st to 10th	Night	27% 20% 34% 17% 4	800
	11th to 20th	Night	31% 18% 28% 20% 3 1	800
	21st to end	Night	21% 17% 34% 24% 4	880
February	1st to 10th	Night	26% 20% 33% 19% 3	800
	11th to 20th	Night	24% 19% 38% 17% 2	783
	21st to end	Night	25% 21% 31% 20% 3	660
March	1st to 10th	Night	26% 16% 33% 21% 4	800
	11th to 20th	Night	26% 21% 30% 19% 4	800
	21st to end	Night	26% 16% 29% 23% 6% 1	880
April	1st to 10th	Night	28% 15% 32% 23% 3	800
	11th to 20th	Night	29% 16% 29% 19% 7%	791
	21st to end	Night	27% 14% 29% 23% 7%	705
May	1st to 10th	Night	26% 10% 28% 27% 8% 2	400
	11th to 20th	Night	19% 10% 37% 27% 7%	394
	21st to end	Night	15% 10% 37% 27% 11%	433
June	1st to 10th	Night	18% 9% 31% 35% 7% 1	400
	11th to 20th	Night	16% 11% 30% 32% 11% 1	400
	21st to end	Night	21% 6% 33% 28% 12%	400
July	1st to 10th	Night	8% 7% 32% 40% 12% 1	390
	11th to 20th	Night	13% 5% 26% 41% 14% 1	388
	21st to end	Night	10% 4 31% 42% 12% 1	438
August	1st to 10th	Night	13% 4 25% 37% 19% 1	455
	11th to 20th	Night	13% 3 25% 34% 23% 2	610
	21st to end	Night	13% 7% 29% 33% 16% 2	880
September	1st to 10th	Night	15% 7% 30% 32% 15% 1	800
	11th to 20th	Night	16% 6% 22% 29% 23% 4	800
	21st to end	Night	18% 11% 25% 25% 20% 1	800
October	1st to 10th	Night	19% 12% 29% 23% 15% 2	800
	11th to 20th	Night	25% 13% 30% 24% 8%	800
	21st to end	Night	29% 14% 26% 25% 5%	880
November	1st to 10th	Night	27% 15% 29% 20% 8%	820
	11th to 20th	Night	25% 17% 32% 18% 9%	840
	21st to end	Night	31% 18% 27% 18% 6%	840
December	1st to 10th	Night	31% 18% 29% 18% 3	809
	11th to 20th	Night	30% 19% 31% 17% 4 1	800
	21st to end	Night	34% 16% 29% 18% 3	880

Page generated at 2025-11-30 01:00:50. Version ac07

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