North Glengarry
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Glengarry clear sky chart from 2005-11-06 to 2026-07-01.

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% 4 8% 5% 5% 4 4 5% 6% 31%	138138
	Night	17% 12% 4 9% 5% 5% 4 3 5% 6% 30%	134194
Transparency	Day	53% 3 11% 22% 10% 1	141581
	Night	56% 3 10% 20% 10% 1	138840
Seeing	Day	23% 17% 29% 20% 9% 2	16570
	Night	23% 12% 30% 25% 9% 1	25607

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% 19% 6% 14% 5% 5% 4 3 4 5% 21%	4661
	11th to 20th	Day	12% 17% 8% 14% 7% 6% 5% 3 5% 5% 20%	4650
	21st to end	Day	10% 16% 7% 14% 9% 7% 5% 3 4 5% 20%	5166
February	1st to 10th	Day	15% 16% 4 12% 6% 4 4 4 5% 5% 25%	1890
	11th to 20th	Day	15% 14% 5% 11% 7% 4 5% 4 5% 5% 26%	1906
	21st to end	Day	19% 15% 5% 10% 5% 6% 4 3 4 5% 24%	1730
March	1st to 10th	Day	19% 13% 5% 12% 5% 5% 4 3 4 5% 25%	4576
	11th to 20th	Day	13% 14% 4 10% 6% 5% 4 3 5% 6% 30%	4938
	21st to end	Day	19% 10% 3 8% 6% 4 3 3 3 5% 35%	6004
April	1st to 10th	Day	22% 13% 3 7% 4 4 3 3 4 5% 32%	2520
	11th to 20th	Day	21% 11% 3 7% 5% 3 3 3 4 5% 34%	2494
	21st to end	Day	23% 10% 3 7% 5% 4 4 4 4 5% 31%	2651
May	1st to 10th	Day	24% 9% 3 8% 5% 5% 5% 4 6% 6% 24%	8237
	11th to 20th	Day	19% 9% 3 8% 5% 4 5% 3 5% 7% 32%	8221
	21st to end	Day	22% 9% 2 6% 4 4 4 4 5% 6% 34%	9060
June	1st to 10th	Day	23% 8% 2 6% 6% 4 4 4 5% 7% 29%	2940
	11th to 20th	Day	15% 6% 3 6% 5% 5% 5% 4 6% 8% 36%	2940
	21st to end	Day	20% 8% 2 6% 5% 4 5% 5% 6% 8% 31%	2940
July	1st to 10th	Day	13% 6% 3 8% 6% 6% 6% 4 7% 9% 33%	6360
	11th to 20th	Day	12% 6% 2 7% 4 5% 5% 4 6% 8% 41%	6360
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 10% 46%	6926
August	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 4 7% 8% 35%	4563
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 7% 8% 39%	4070
	21st to end	Day	16% 5% 2 7% 4 5% 5% 4 5% 8% 39%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 6% 8% 44%	2400
	11th to 20th	Day	13% 5% 2 6% 3 3 4 3 5% 7% 50%	2355
	21st to end	Day	19% 7% 2 5% 3 3 4 3 5% 7% 41%	2200
October	1st to 10th	Day	20% 7% 3 6% 3 3 4 4 5% 6% 38%	2005
	11th to 20th	Day	20% 10% 4 9% 5% 5% 4 3 4 6% 31%	2000
	21st to end	Day	25% 11% 3 7% 4 4 4 3 5% 5% 28%	1985
November	1st to 10th	Day	17% 10% 5% 8% 5% 4 5% 4 5% 6% 32%	1851
	11th to 20th	Day	17% 13% 4 8% 5% 5% 4 4 5% 6% 29%	1753
	21st to end	Day	22% 16% 3 10% 6% 5% 4 4 4 5% 21%	1680
December	1st to 10th	Day	21% 21% 7% 9% 5% 5% 4 4 5% 5% 15%	2680
	11th to 20th	Day	18% 17% 5% 11% 5% 4 4 3 4 5% 24%	3066
	21st to end	Day	23% 17% 4 10% 5% 4 4 3 4 4 23%	4048
January	1st to 10th	Night	14% 20% 8% 14% 6% 4 4 3 4 4 20%	8234
	11th to 20th	Night	12% 18% 7% 18% 7% 6% 5% 3 4 4 16%	8235
	21st to end	Night	12% 15% 5% 11% 8% 7% 5% 3 4 5% 24%	9000
February	1st to 10th	Night	14% 14% 5% 11% 8% 5% 5% 4 5% 5% 23%	2730
	11th to 20th	Night	14% 14% 4 11% 7% 5% 5% 4 4 5% 28%	2599
	21st to end	Night	15% 15% 4 10% 6% 4 4 3 4 5% 29%	2076
March	1st to 10th	Night	21% 13% 4 8% 5% 5% 4 3 4 4 29%	5484
	11th to 20th	Night	15% 13% 4 8% 5% 5% 4 4 5% 8% 29%	5237
	21st to end	Night	18% 11% 3 9% 5% 4 4 3 4 5% 32%	5169
April	1st to 10th	Night	23% 10% 3 7% 4 4 4 3 5% 6% 31%	2100
	11th to 20th	Night	22% 10% 3 7% 4 4 4 3 4 5% 34%	2075
	21st to end	Night	23% 9% 3 7% 4 4 3 3 4 5% 35%	1984
May	1st to 10th	Night	21% 9% 3 8% 6% 6% 6% 5% 6% 7% 23%	4662
	11th to 20th	Night	19% 8% 3 7% 4 5% 4 4 6% 6% 33%	4639
	21st to end	Night	19% 9% 3 7% 5% 4 5% 4 6% 7% 32%	5114
June	1st to 10th	Night	19% 7% 2 6% 5% 6% 5% 4 6% 8% 31%	1680
	11th to 20th	Night	18% 6% 3 6% 4 4 4 4 5% 7% 40%	1680
	21st to end	Night	19% 7% 2 7% 4 5% 5% 4 6% 6% 35%	1680
July	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	3600
	11th to 20th	Night	13% 6% 3 7% 5% 4 4 3 5% 7% 43%	3600
	21st to end	Night	11% 5% 3 6% 4 4 4 4 6% 8% 46%	3926
August	1st to 10th	Night	14% 7% 2 7% 4 4 4 4 6% 8% 39%	2586
	11th to 20th	Night	15% 7% 2 6% 4 5% 4 4 5% 7% 41%	2941
	21st to end	Night	14% 5% 3 7% 5% 5% 4 4 5% 8% 41%	3586
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 4 5% 6% 45%	2000
	11th to 20th	Night	14% 5% 1 6% 4 3 3 3 4 7% 50%	2045
	21st to end	Night	17% 5% 2 6% 4 4 5% 3 4 7% 43%	2200
October	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 5% 6% 39%	2391
	11th to 20th	Night	20% 9% 3 7% 5% 4 5% 4 4 6% 34%	2400
	21st to end	Night	23% 10% 4 8% 4 4 4 3 4 5% 30%	2855
November	1st to 10th	Night	21% 10% 3 8% 5% 4 3 3 5% 6% 33%	2667
	11th to 20th	Night	17% 11% 4 9% 5% 4 5% 4 5% 5% 31%	2861
	21st to end	Night	21% 14% 4 10% 6% 5% 3 3 4 5% 23%	2940
December	1st to 10th	Night	18% 18% 6% 11% 7% 5% 5% 4 4 5% 17%	4720
	11th to 20th	Night	23% 16% 5% 10% 5% 4 4 3 3 3 24%	5348
	21st to end	Night	27% 17% 4 10% 4 3 3 3 4 5% 22%	7150

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	67% 2 11% 16% 4	4662
	11th to 20th	Day	67% 2 8% 13% 9% 1	4680
	21st to end	Day	67% 3 10% 11% 9% 1	5166
February	1st to 10th	Day	62% 2 8% 21% 6% 2	1890
	11th to 20th	Day	60% 3 10% 18% 8% 1	1915
	21st to end	Day	63% 2 9% 14% 10% 1	1730
March	1st to 10th	Day	63% 2 8% 14% 10% 3	4579
	11th to 20th	Day	56% 2 15% 15% 10% 2	4938
	21st to end	Day	55% 1 5% 17% 18% 2	6004
April	1st to 10th	Day	56% 2 7% 20% 13% 3	2520
	11th to 20th	Day	54% 2 5% 21% 16% 2	2494
	21st to end	Day	56% 3 8% 17% 13% 4	2651
May	1st to 10th	Day	60% 4 6% 20% 9% 1	8249
	11th to 20th	Day	53% 3 12% 23% 8% 1	8225
	21st to end	Day	51% 3 10% 25% 11% 1	9061
June	1st to 10th	Day	54% 3 9% 21% 13% 1	2940
	11th to 20th	Day	46% 3 11% 25% 13% 2	2940
	21st to end	Day	50% 4 14% 21% 10% 1	2940
July	1st to 10th	Day	47% 4 13% 27% 9%	6290
	11th to 20th	Day	39% 5% 13% 31% 12%	6285
	21st to end	Day	34% 5% 14% 38% 9%	6728
August	1st to 10th	Day	46% 4 16% 25% 9%	4549
	11th to 20th	Day	42% 4 16% 31% 7%	4110
	21st to end	Day	42% 4 17% 25% 12% 1	4312
September	1st to 10th	Day	39% 3 14% 32% 12%	2400
	11th to 20th	Day	35% 3 12% 34% 16% 1	2355
	21st to end	Day	43% 3 14% 28% 11% 1	2200
October	1st to 10th	Day	45% 3 12% 31% 9%	3265
	11th to 20th	Day	47% 2 15% 27% 8% 1	3240
	21st to end	Day	48% 3 18% 23% 7%	3185
November	1st to 10th	Day	52% 3 12% 23% 9% 1	1851
	11th to 20th	Day	57% 4 11% 17% 11% 1	1753
	21st to end	Day	65% 4 13% 13% 5%	1680
December	1st to 10th	Day	70% 4 12% 12% 2	2680
	11th to 20th	Day	65% 4 9% 16% 7%	3066
	21st to end	Day	66% 2 8% 17% 6%	4048
January	1st to 10th	Night	69% 2 11% 13% 5%	8234
	11th to 20th	Night	73% 2 8% 11% 6%	8280
	21st to end	Night	63% 2 8% 15% 12% 1	9000
February	1st to 10th	Night	62% 3 9% 18% 7% 1	2730
	11th to 20th	Night	59% 3 9% 21% 8%	2601
	21st to end	Night	58% 2 8% 19% 13% 1	2076
March	1st to 10th	Night	60% 2 6% 17% 12% 3	5494
	11th to 20th	Night	55% 3 13% 17% 9% 3	5238
	21st to end	Night	56% 2 4 22% 13% 2	5169
April	1st to 10th	Night	56% 2 7% 19% 14% 2	2100
	11th to 20th	Night	54% 2 6% 21% 15% 1	2075
	21st to end	Night	52% 2 7% 19% 16% 4	1984
May	1st to 10th	Night	59% 3 10% 19% 8% 1	4668
	11th to 20th	Night	51% 3 10% 23% 11% 1	4640
	21st to end	Night	51% 3 10% 20% 15% 1	5115
June	1st to 10th	Night	51% 3 10% 22% 13% 1	1680
	11th to 20th	Night	44% 4 11% 23% 17% 2	1680
	21st to end	Night	48% 4 13% 21% 14% 1	1680
July	1st to 10th	Night	45% 5% 16% 22% 11%	3560
	11th to 20th	Night	40% 4 14% 31% 11%	3552
	21st to end	Night	36% 5% 13% 31% 15%	3809
August	1st to 10th	Night	42% 4 16% 29% 9%	2576
	11th to 20th	Night	43% 4 16% 28% 8%	2967
	21st to end	Night	43% 4 15% 25% 12% 1	3586
September	1st to 10th	Night	41% 2 10% 30% 16% 1	2000
	11th to 20th	Night	36% 2 12% 36% 13% 1	2045
	21st to end	Night	42% 3 11% 29% 14%	2200
October	1st to 10th	Night	42% 4 14% 29% 10% 1	3911
	11th to 20th	Night	45% 3 13% 29% 9%	3899
	21st to end	Night	48% 3 17% 21% 10%	4605
November	1st to 10th	Night	53% 3 12% 22% 9% 1	2667
	11th to 20th	Night	54% 3 11% 21% 10% 1	2861
	21st to end	Night	62% 2 13% 17% 6%	2940
December	1st to 10th	Night	69% 3 11% 13% 3	4720
	11th to 20th	Night	66% 2 6% 16% 9% 1	5348
	21st to end	Night	67% 2 7% 14% 10%	7150

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	25% 21% 33% 17% 4	220
	11th to 20th	Day	30% 25% 30% 10% 3 1	220
	21st to end	Day	20% 20% 37% 17% 5%	250
February	1st to 10th	Day	28% 28% 30% 11% 2	330
	11th to 20th	Day	25% 27% 37% 11%	393
	21st to end	Day	30% 21% 33% 15% 2	446
March	1st to 10th	Day	28% 21% 31% 17% 4	540
	11th to 20th	Day	27% 25% 30% 15% 2 1	540
	21st to end	Day	32% 23% 24% 14% 7% 1	594
April	1st to 10th	Day	34% 18% 29% 14% 4 1	540
	11th to 20th	Day	34% 20% 23% 14% 7% 2	532
	21st to end	Day	30% 21% 26% 14% 7% 1	540
May	1st to 10th	Day	26% 17% 33% 17% 6% 1	543
	11th to 20th	Day	20% 18% 31% 19% 10% 2	567
	21st to end	Day	22% 18% 31% 21% 8% 1	617
June	1st to 10th	Day	26% 11% 28% 25% 8% 2	570
	11th to 20th	Day	17% 15% 31% 26% 9% 2	570
	21st to end	Day	23% 13% 32% 19% 11% 3	570
July	1st to 10th	Day	13% 11% 30% 28% 14% 3	525
	11th to 20th	Day	13% 10% 32% 27% 15% 2	524
	21st to end	Day	16% 10% 30% 30% 13% 2	576
August	1st to 10th	Day	14% 8% 26% 32% 17% 3	526
	11th to 20th	Day	15% 8% 23% 31% 17% 6%	519
	21st to end	Day	15% 10% 28% 26% 15% 6%	583
September	1st to 10th	Day	16% 12% 28% 21% 17% 7%	530
	11th to 20th	Day	12% 9% 22% 24% 22% 11%	530
	21st to end	Day	18% 14% 29% 19% 15% 4	530
October	1st to 10th	Day	22% 15% 25% 22% 13% 3	530
	11th to 20th	Day	24% 21% 29% 18% 8% 1	530
	21st to end	Day	31% 12% 31% 19% 7%	465
November	1st to 10th	Day	31% 17% 26% 18% 7% 1	425
	11th to 20th	Day	25% 21% 31% 17% 5% 1	293
	21st to end	Day	31% 21% 28% 14% 5%	220
December	1st to 10th	Day	30% 18% 33% 16% 3	220
	11th to 20th	Day	30% 25% 34% 10% 1 1	220
	21st to end	Day	31% 22% 31% 14% 2	242
January	1st to 10th	Night	27% 16% 36% 17% 4	840
	11th to 20th	Night	29% 16% 30% 20% 4 1	840
	21st to end	Night	21% 14% 35% 24% 5%	924
February	1st to 10th	Night	21% 16% 36% 23% 4	840
	11th to 20th	Night	21% 19% 38% 18% 4	823
	21st to end	Night	25% 15% 32% 25% 3	692
March	1st to 10th	Night	25% 16% 34% 21% 4	840
	11th to 20th	Night	27% 17% 33% 21% 3	840
	21st to end	Night	25% 15% 29% 24% 6%	924
April	1st to 10th	Night	31% 13% 30% 23% 3	840
	11th to 20th	Night	27% 15% 32% 20% 5%	831
	21st to end	Night	27% 14% 28% 22% 7%	724
May	1st to 10th	Night	26% 10% 30% 26% 7% 2	422
	11th to 20th	Night	23% 10% 31% 26% 9% 1	414
	21st to end	Night	17% 9% 37% 28% 9%	455
June	1st to 10th	Night	20% 7% 29% 35% 9%	420
	11th to 20th	Night	21% 7% 27% 31% 12% 1	420
	21st to end	Night	19% 5% 31% 29% 15% 1	420
July	1st to 10th	Night	11% 7% 27% 38% 16% 1	390
	11th to 20th	Night	12% 5% 28% 40% 14%	388
	21st to end	Night	13% 5% 29% 37% 14% 1	438
August	1st to 10th	Night	14% 3 23% 42% 18% 1	398
	11th to 20th	Night	15% 4 22% 35% 23% 2	620
	21st to end	Night	15% 5% 27% 33% 17% 2	880
September	1st to 10th	Night	14% 5% 28% 37% 16% 1	800
	11th to 20th	Night	18% 6% 18% 33% 22% 3	800
	21st to end	Night	19% 8% 27% 27% 18% 2	800
October	1st to 10th	Night	22% 8% 29% 29% 12% 1	800
	11th to 20th	Night	24% 11% 32% 25% 9%	800
	21st to end	Night	27% 13% 31% 24% 5%	880
November	1st to 10th	Night	28% 14% 26% 25% 7%	820
	11th to 20th	Night	23% 18% 32% 18% 9%	840
	21st to end	Night	28% 17% 29% 19% 7%	840
December	1st to 10th	Night	29% 15% 31% 21% 4	840
	11th to 20th	Night	30% 19% 28% 18% 4 1	840
	21st to end	Night	37% 16% 27% 16% 4	924

Page generated at 2026-06-28 02:10:47. Version ac07

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