New Glasgow
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New Glasgow clear sky chart from 2005-11-06 to 2025-10-04.

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% 12% 4 9% 5% 5% 4 4 5% 6% 27%	127018
	Night	17% 13% 4 11% 5% 4 4 3 5% 6% 27%	122582
Transparency	Day	55% 7% 12% 17% 7% 1	130551
	Night	57% 6% 12% 17% 7% 1	127141
Seeing	Day	27% 21% 31% 16% 4 1	18812
	Night	26% 19% 31% 20% 4	26339

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% 24% 7% 22% 5% 4 3 2 3 4 13%	3616
	11th to 20th	Day	11% 19% 10% 15% 5% 5% 4 3 4 4 20%	3591
	21st to end	Day	11% 14% 6% 12% 7% 7% 4 3 4 5% 27%	4356
February	1st to 10th	Day	16% 16% 5% 11% 7% 5% 4 3 4 5% 23%	1800
	11th to 20th	Day	16% 16% 6% 12% 6% 5% 4 3 4 4 24%	1753
	21st to end	Day	10% 17% 4 10% 7% 6% 5% 3 5% 6% 27%	1565
March	1st to 10th	Day	19% 14% 4 13% 6% 6% 4 3 4 4 23%	4720
	11th to 20th	Day	12% 18% 7% 10% 6% 4 4 4 5% 6% 24%	4980
	21st to end	Day	19% 21% 7% 12% 5% 4 4 3 3 4 17%	5596
April	1st to 10th	Day	20% 18% 5% 8% 5% 3 4 4 4 5% 25%	2400
	11th to 20th	Day	21% 14% 4 8% 4 4 4 3 5% 5% 28%	2381
	21st to end	Day	23% 16% 3 7% 5% 4 4 3 5% 6% 25%	2600
May	1st to 10th	Day	26% 16% 3 7% 4 3 4 3 5% 6% 22%	6269
	11th to 20th	Day	21% 13% 3 7% 4 4 4 4 5% 6% 29%	6318
	21st to end	Day	17% 10% 3 8% 5% 5% 5% 4 6% 8% 29%	6948
June	1st to 10th	Day	28% 9% 2 6% 5% 4 5% 4 6% 7% 23%	2800
	11th to 20th	Day	22% 8% 3 6% 5% 4 5% 4 5% 6% 33%	2800
	21st to end	Day	24% 9% 3 7% 6% 4 5% 4 6% 6% 27%	2800
July	1st to 10th	Day	19% 8% 3 7% 5% 6% 5% 4 6% 9% 28%	6360
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 4 7% 9% 38%	6360
	21st to end	Day	12% 6% 3 6% 5% 5% 6% 5% 7% 10% 36%	6927
August	1st to 10th	Day	17% 9% 3 9% 5% 5% 5% 5% 6% 8% 28%	4306
	11th to 20th	Day	14% 8% 3 8% 5% 5% 6% 5% 6% 8% 34%	4175
	21st to end	Day	11% 5% 2 7% 5% 5% 5% 4 7% 9% 42%	4412
September	1st to 10th	Day	18% 5% 3 7% 4 4 4 4 5% 7% 39%	2400
	11th to 20th	Day	19% 7% 2 7% 5% 4 4 4 6% 6% 36%	2400
	21st to end	Day	18% 7% 3 6% 5% 4 4 4 6% 6% 37%	2092
October	1st to 10th	Day	20% 7% 3 7% 5% 5% 4 4 6% 7% 32%	1930
	11th to 20th	Day	19% 10% 3 8% 6% 5% 5% 3 6% 8% 28%	1900
	21st to end	Day	20% 15% 3 9% 6% 5% 4 3 4 6% 24%	2020
November	1st to 10th	Day	22% 15% 4 7% 5% 5% 5% 4 5% 5% 24%	1655
	11th to 20th	Day	19% 22% 4 9% 5% 4 4 2 5% 7% 20%	1600
	21st to end	Day	17% 18% 5% 9% 6% 5% 5% 3 5% 6% 21%	1600
December	1st to 10th	Day	14% 16% 6% 12% 6% 5% 4 3 5% 5% 24%	2610
	11th to 20th	Day	20% 15% 5% 12% 6% 5% 4 3 4 5% 21%	2996
	21st to end	Day	17% 12% 11% 15% 5% 4 4 4 5% 5% 18%	3982
January	1st to 10th	Night	15% 20% 8% 18% 7% 4 4 3 4 4 15%	6349
	11th to 20th	Night	11% 18% 8% 17% 7% 5% 4 3 3 4 21%	6314
	21st to end	Night	10% 12% 5% 18% 7% 5% 5% 4 5% 5% 25%	6604
February	1st to 10th	Night	17% 14% 5% 12% 7% 5% 5% 3 5% 3 24%	2600
	11th to 20th	Night	16% 16% 4 11% 8% 5% 4 4 4 5% 22%	2533
	21st to end	Night	11% 17% 5% 10% 6% 5% 4 4 4 4 29%	2065
March	1st to 10th	Night	20% 15% 6% 12% 7% 5% 4 3 4 4 19%	5118
	11th to 20th	Night	16% 17% 5% 9% 5% 4 4 3 4 5% 27%	4979
	21st to end	Night	21% 18% 8% 12% 5% 4 3 3 3 3 20%	5335
April	1st to 10th	Night	20% 15% 4 9% 5% 5% 5% 4 3 5% 25%	2000
	11th to 20th	Night	19% 14% 3 6% 4 4 4 4 4 5% 32%	1966
	21st to end	Night	23% 15% 4 7% 5% 4 4 4 5% 4 26%	1800
May	1st to 10th	Night	27% 20% 3 7% 4 4 4 3 5% 6% 18%	3686
	11th to 20th	Night	19% 13% 3 8% 5% 5% 4 4 5% 6% 29%	3596
	21st to end	Night	15% 11% 3 8% 5% 5% 5% 4 6% 8% 29%	3948
June	1st to 10th	Night	25% 9% 3 8% 5% 4 5% 3 5% 8% 27%	1600
	11th to 20th	Night	20% 7% 2 6% 4 4 4 4 6% 7% 38%	1600
	21st to end	Night	20% 8% 3 7% 5% 6% 5% 4 6% 8% 29%	1600
July	1st to 10th	Night	14% 8% 3 9% 6% 6% 6% 5% 7% 9% 25%	3619
	11th to 20th	Night	11% 7% 2 6% 4 5% 5% 4 6% 9% 40%	3620
	21st to end	Night	14% 7% 3 7% 4 4 5% 4 6% 9% 37%	3948
August	1st to 10th	Night	13% 8% 4 8% 6% 5% 4 4 6% 9% 33%	2842
	11th to 20th	Night	12% 8% 3 7% 5% 5% 5% 4 7% 8% 37%	2872
	21st to end	Night	13% 5% 2 5% 4 4 5% 3 6% 8% 43%	3485
September	1st to 10th	Night	13% 7% 2 6% 5% 4 5% 4 5% 8% 42%	2000
	11th to 20th	Night	17% 8% 2 6% 3 4 3 3 5% 6% 43%	2000
	21st to end	Night	19% 7% 2 7% 4 4 4 3 6% 6% 38%	2303
October	1st to 10th	Night	20% 7% 2 6% 5% 3 5% 3 5% 7% 38%	2317
	11th to 20th	Night	18% 8% 3 7% 5% 4 5% 3 6% 7% 34%	2280
	21st to end	Night	25% 11% 3 7% 4 4 5% 4 5% 5% 27%	2576
November	1st to 10th	Night	18% 16% 4 9% 5% 5% 4 3 4 5% 27%	2638
	11th to 20th	Night	20% 15% 4 8% 6% 4 5% 4 5% 5% 22%	2800
	21st to end	Night	21% 18% 6% 9% 5% 4 4 4 5% 6% 20%	2800
December	1st to 10th	Night	13% 15% 5% 11% 5% 4 4 3 5% 5% 30%	4580
	11th to 20th	Night	18% 14% 5% 15% 6% 4 4 3 3 4 23%	5213
	21st to end	Night	21% 14% 7% 17% 4 3 3 3 3 4 20%	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	77% 5% 10% 5% 3	3617
	11th to 20th	Day	66% 8% 10% 10% 5%	3620
	21st to end	Day	60% 4 9% 14% 10% 3	4356
February	1st to 10th	Day	64% 5% 10% 14% 7% 1	1800
	11th to 20th	Day	64% 6% 9% 15% 6%	1761
	21st to end	Day	56% 7% 11% 16% 9% 2	1565
March	1st to 10th	Day	64% 5% 8% 13% 9% 1	4724
	11th to 20th	Day	60% 7% 15% 13% 4 1	4980
	21st to end	Day	70% 6% 7% 12% 5% 1	5596
April	1st to 10th	Day	61% 6% 8% 13% 10% 2	2400
	11th to 20th	Day	57% 6% 8% 18% 10% 1	2381
	21st to end	Day	59% 7% 10% 15% 9% 1	2600
May	1st to 10th	Day	62% 6% 11% 15% 5%	6281
	11th to 20th	Day	54% 7% 12% 21% 6%	6322
	21st to end	Day	49% 10% 15% 18% 8%	6948
June	1st to 10th	Day	58% 7% 12% 17% 5% 1	2800
	11th to 20th	Day	50% 7% 12% 21% 9% 1	2800
	21st to end	Day	57% 8% 9% 15% 9% 1	2800
July	1st to 10th	Day	52% 7% 15% 17% 9%	6290
	11th to 20th	Day	41% 7% 16% 26% 9%	6284
	21st to end	Day	41% 9% 19% 25% 6%	6730
August	1st to 10th	Day	53% 9% 12% 20% 7%	4292
	11th to 20th	Day	45% 8% 15% 24% 8%	4214
	21st to end	Day	36% 7% 14% 29% 13%	4412
September	1st to 10th	Day	44% 7% 13% 25% 11% 1	2400
	11th to 20th	Day	47% 7% 13% 22% 11% 1	2400
	21st to end	Day	46% 7% 11% 24% 13%	2092
October	1st to 10th	Day	49% 9% 14% 20% 8%	3190
	11th to 20th	Day	50% 7% 12% 22% 9%	3140
	21st to end	Day	52% 5% 15% 19% 8% 1	3314
November	1st to 10th	Day	63% 6% 10% 15% 5%	1655
	11th to 20th	Day	67% 6% 13% 11% 3	1600
	21st to end	Day	66% 7% 15% 10% 2	1600
December	1st to 10th	Day	62% 6% 11% 17% 4	2610
	11th to 20th	Day	68% 5% 11% 8% 8%	2995
	21st to end	Day	69% 5% 13% 10% 2	3982
January	1st to 10th	Night	74% 4 11% 9% 2	6349
	11th to 20th	Night	67% 7% 9% 13% 4	6360
	21st to end	Night	60% 6% 10% 13% 9% 2	6604
February	1st to 10th	Night	65% 4 9% 13% 8% 1	2600
	11th to 20th	Night	65% 5% 10% 14% 5% 1	2536
	21st to end	Night	57% 6% 9% 18% 9% 1	2065
March	1st to 10th	Night	68% 5% 5% 10% 10% 1	5127
	11th to 20th	Night	59% 6% 12% 15% 7% 1	4980
	21st to end	Night	69% 5% 5% 14% 7% 1	5335
April	1st to 10th	Night	62% 6% 9% 13% 9% 2	2000
	11th to 20th	Night	54% 5% 9% 19% 11% 1	1966
	21st to end	Night	59% 7% 9% 14% 11% 1	1800
May	1st to 10th	Night	67% 5% 8% 14% 6%	3691
	11th to 20th	Night	54% 7% 11% 20% 7% 1	3597
	21st to end	Night	50% 8% 19% 19% 4	3949
June	1st to 10th	Night	56% 8% 10% 20% 6%	1600
	11th to 20th	Night	45% 7% 13% 21% 14%	1600
	21st to end	Night	52% 8% 13% 17% 8% 1	1600
July	1st to 10th	Night	52% 8% 16% 17% 6% 1	3581
	11th to 20th	Night	39% 7% 19% 24% 11% 1	3572
	21st to end	Night	43% 8% 17% 25% 7%	3831
August	1st to 10th	Night	47% 8% 16% 23% 4	2831
	11th to 20th	Night	44% 9% 16% 26% 5%	2899
	21st to end	Night	37% 8% 18% 26% 11% 1	3484
September	1st to 10th	Night	40% 8% 13% 29% 11% 1	2000
	11th to 20th	Night	42% 6% 13% 27% 11% 1	2000
	21st to end	Night	45% 7% 12% 26% 10%	2303
October	1st to 10th	Night	50% 8% 13% 20% 9%	3837
	11th to 20th	Night	44% 7% 14% 26% 10%	3779
	21st to end	Night	51% 6% 14% 19% 9% 1	4236
November	1st to 10th	Night	60% 6% 12% 16% 6%	2638
	11th to 20th	Night	64% 7% 13% 12% 4	2800
	21st to end	Night	65% 8% 14% 11% 2	2800
December	1st to 10th	Night	56% 6% 13% 20% 5%	4580
	11th to 20th	Night	66% 6% 9% 12% 6% 2	5215
	21st to end	Night	70% 5% 12% 11% 3	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	32% 26% 30% 11% 2	400
	11th to 20th	Day	30% 28% 26% 13% 4	400
	21st to end	Day	23% 30% 33% 12% 1	440
February	1st to 10th	Day	29% 29% 30% 11% 2	400
	11th to 20th	Day	31% 31% 27% 10% 1	396
	21st to end	Day	24% 24% 36% 12% 4 1	331
March	1st to 10th	Day	26% 28% 32% 12% 1	453
	11th to 20th	Day	24% 31% 30% 11% 3	500
	21st to end	Day	33% 30% 25% 10% 2	550
April	1st to 10th	Day	37% 30% 24% 7% 1	500
	11th to 20th	Day	34% 29% 24% 10% 3	492
	21st to end	Day	30% 23% 31% 13% 3	500
May	1st to 10th	Day	36% 23% 26% 11% 3 2	666
	11th to 20th	Day	25% 20% 32% 17% 5% 1	724
	21st to end	Day	25% 21% 36% 15% 3 1	790
June	1st to 10th	Day	34% 18% 28% 17% 4	730
	11th to 20th	Day	23% 18% 37% 18% 4 1	730
	21st to end	Day	26% 15% 33% 20% 5% 1	730
July	1st to 10th	Day	20% 13% 38% 23% 4 1	720
	11th to 20th	Day	15% 11% 40% 26% 8%	718
	21st to end	Day	20% 10% 36% 26% 7% 1	795
August	1st to 10th	Day	16% 9% 39% 27% 6% 2	571
	11th to 20th	Day	21% 12% 33% 22% 10% 2	519
	21st to end	Day	16% 13% 35% 26% 9% 1	583
September	1st to 10th	Day	19% 16% 37% 20% 6% 1	530
	11th to 20th	Day	25% 15% 31% 21% 7% 1	530
	21st to end	Day	21% 18% 33% 18% 8% 2	461
October	1st to 10th	Day	22% 17% 30% 21% 8% 2	399
	11th to 20th	Day	26% 24% 27% 15% 6% 1	390
	21st to end	Day	28% 27% 28% 12% 4 1	429
November	1st to 10th	Day	31% 27% 27% 11% 3 1	395
	11th to 20th	Day	39% 24% 23% 11% 2 1	400
	21st to end	Day	37% 29% 22% 10% 2 1	400
December	1st to 10th	Day	34% 27% 30% 9% 1	400
	11th to 20th	Day	38% 30% 24% 8% 1	400
	21st to end	Day	26% 30% 29% 12% 2	440
January	1st to 10th	Night	28% 26% 31% 14% 2	900
	11th to 20th	Night	26% 25% 31% 14% 3	900
	21st to end	Night	22% 28% 31% 16% 3	904
February	1st to 10th	Night	28% 23% 31% 17% 2	800
	11th to 20th	Night	30% 29% 27% 13% 2	783
	21st to end	Night	23% 22% 32% 18% 5%	660
March	1st to 10th	Night	26% 25% 30% 18% 1	800
	11th to 20th	Night	22% 24% 28% 21% 5%	800
	21st to end	Night	27% 23% 28% 19% 3	826
April	1st to 10th	Night	31% 23% 27% 17% 3	600
	11th to 20th	Night	27% 21% 30% 18% 4	594
	21st to end	Night	31% 17% 29% 19% 5%	600
May	1st to 10th	Night	34% 16% 26% 18% 6% 1	600
	11th to 20th	Night	26% 14% 31% 24% 5% 1	592
	21st to end	Night	22% 16% 40% 19% 4	649
June	1st to 10th	Night	30% 13% 34% 20% 4	600
	11th to 20th	Night	22% 12% 40% 22% 4	600
	21st to end	Night	22% 11% 36% 27% 5%	600
July	1st to 10th	Night	17% 9% 40% 29% 6%	586
	11th to 20th	Night	14% 8% 39% 32% 6%	582
	21st to end	Night	20% 6% 34% 34% 6%	656
August	1st to 10th	Night	15% 8% 35% 34% 8% 1	598
	11th to 20th	Night	20% 9% 31% 30% 9% 1	592
	21st to end	Night	15% 8% 33% 35% 8%	660
September	1st to 10th	Night	16% 8% 41% 29% 7%	600
	11th to 20th	Night	22% 11% 30% 29% 9%	600
	21st to end	Night	22% 16% 31% 25% 6% 1	781
October	1st to 10th	Night	24% 14% 28% 25% 8%	773
	11th to 20th	Night	22% 19% 32% 21% 6% 1	760
	21st to end	Night	32% 23% 27% 14% 3	873
November	1st to 10th	Night	30% 23% 28% 15% 3 1	880
	11th to 20th	Night	33% 23% 25% 14% 3 1	900
	21st to end	Night	34% 24% 26% 15% 1	900
December	1st to 10th	Night	29% 25% 30% 13% 2	900
	11th to 20th	Night	33% 29% 26% 10% 2	900
	21st to end	Night	31% 28% 25% 13% 2 1	990

Page generated at 2025-10-01 02:39:02. Version ac07

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