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 2025-02-25.

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%	108653
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 30%	110000
Transparency	Day	52% 3 12% 22% 10% 1	112142
	Night	55% 3 11% 20% 10% 1	114675
Seeing	Day	23% 16% 29% 21% 9% 2	14804
	Night	23% 12% 30% 25% 9% 1	23993

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	16% 20% 6% 15% 5% 4 4 3 3 4 21%	3597
	11th to 20th	Day	13% 16% 8% 14% 6% 5% 5% 3 5% 5% 22%	3570
	21st to end	Day	12% 19% 7% 11% 5% 6% 5% 3 5% 5% 22%	3988
February	1st to 10th	Day	15% 17% 4 12% 6% 4 4 4 5% 5% 25%	1800
	11th to 20th	Day	15% 15% 5% 11% 7% 4 4 4 4 5% 26%	1813
	21st to end	Day	19% 15% 5% 10% 5% 6% 4 3 4 4 25%	1610
March	1st to 10th	Day	21% 12% 4 10% 6% 5% 4 3 4 5% 27%	3116
	11th to 20th	Day	15% 18% 4 11% 5% 4 4 3 4 5% 27%	3374
	21st to end	Day	16% 8% 2 8% 6% 4 4 4 4 6% 39%	4098
April	1st to 10th	Day	23% 13% 3 6% 4 4 3 3 4 5% 33%	2280
	11th to 20th	Day	21% 10% 3 7% 5% 3 3 3 4 6% 35%	2254
	21st to end	Day	23% 10% 3 8% 5% 4 4 3 4 5% 31%	2398
May	1st to 10th	Day	22% 8% 3 8% 5% 4 5% 4 5% 6% 30%	4426
	11th to 20th	Day	20% 8% 3 8% 5% 5% 4 3 5% 7% 32%	4398
	21st to end	Day	17% 6% 2 7% 4 5% 5% 4 6% 8% 37%	4837
June	1st to 10th	Day	24% 8% 2 6% 6% 4 4 4 5% 7% 29%	2660
	11th to 20th	Day	15% 6% 3 6% 4 5% 5% 4 6% 8% 36%	2660
	21st to end	Day	21% 8% 2 7% 4 4 5% 5% 6% 8% 31%	2660
July	1st to 10th	Day	13% 7% 3 7% 6% 5% 5% 4 7% 9% 34%	4440
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 5% 7% 9% 37%	4440
	21st to end	Day	12% 6% 2 5% 4 4 4 4 7% 9% 43%	4814
August	1st to 10th	Day	15% 7% 3 8% 5% 4 5% 4 7% 8% 34%	4423
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 7% 8% 39%	3942
	21st to end	Day	16% 5% 2 7% 4 5% 5% 4 5% 8% 39%	4180
September	1st to 10th	Day	14% 6% 2 6% 4 4 5% 4 6% 7% 43%	2280
	11th to 20th	Day	14% 5% 2 6% 3 3 4 3 5% 7% 48%	2237
	21st to end	Day	18% 7% 2 6% 3 3 4 3 5% 7% 41%	2090
October	1st to 10th	Day	21% 8% 3 6% 4 4 5% 4 6% 6% 36%	1905
	11th to 20th	Day	21% 11% 4 9% 5% 5% 4 3 4 6% 30%	1900
	21st to end	Day	25% 11% 3 6% 4 4 5% 3 5% 6% 28%	1886
November	1st to 10th	Day	17% 9% 4 8% 5% 4 5% 4 5% 6% 33%	1761
	11th to 20th	Day	18% 13% 3 8% 5% 5% 4 4 6% 6% 30%	1670
	21st to end	Day	22% 15% 3 9% 6% 5% 5% 4 5% 6% 21%	1600
December	1st to 10th	Day	21% 21% 6% 9% 5% 5% 4 4 5% 5% 15%	2600
	11th to 20th	Day	19% 17% 5% 11% 5% 4 4 3 4 5% 24%	2986
	21st to end	Day	23% 17% 4 10% 5% 4 4 3 4 4 23%	3960
January	1st to 10th	Night	15% 22% 8% 13% 5% 4 4 3 3 4 19%	6349
	11th to 20th	Night	11% 17% 7% 16% 7% 6% 5% 3 4 4 18%	6315
	21st to end	Night	14% 17% 6% 12% 7% 5% 5% 3 4 5% 22%	6953
February	1st to 10th	Night	15% 14% 5% 11% 8% 6% 5% 4 5% 5% 23%	2600
	11th to 20th	Night	14% 14% 4 11% 7% 5% 5% 4 4 5% 27%	2472
	21st to end	Night	16% 16% 5% 9% 6% 4 4 3 4 5% 29%	1939
March	1st to 10th	Night	21% 11% 4 8% 5% 4 4 3 4 5% 32%	3724
	11th to 20th	Night	19% 17% 4 9% 6% 5% 3 3 3 6% 26%	3582
	21st to end	Night	14% 11% 3 8% 4 4 4 3 4 5% 38%	3533
April	1st to 10th	Night	23% 10% 3 7% 4 5% 3 3 5% 6% 31%	1900
	11th to 20th	Night	22% 9% 3 7% 4 4 4 3 4 5% 34%	1875
	21st to end	Night	22% 9% 3 7% 4 4 3 3 5% 5% 34%	1796
May	1st to 10th	Night	21% 9% 2 7% 5% 4 5% 5% 5% 7% 30%	2516
	11th to 20th	Night	23% 8% 2 5% 4 4 4 3 4 6% 37%	2495
	21st to end	Night	16% 6% 2 7% 4 4 5% 4 6% 8% 38%	2738
June	1st to 10th	Night	19% 7% 2 6% 6% 6% 5% 4 6% 9% 30%	1520
	11th to 20th	Night	18% 6% 3 6% 4 3 4 5% 5% 7% 40%	1520
	21st to end	Night	19% 7% 2 7% 4 5% 5% 4 7% 6% 35%	1520
July	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 4 6% 7% 35%	2520
	11th to 20th	Night	14% 6% 2 7% 4 4 4 4 6% 8% 42%	2520
	21st to end	Night	13% 6% 3 6% 4 4 4 4 6% 7% 43%	2739
August	1st to 10th	Night	15% 7% 3 7% 4 4 4 4 6% 8% 39%	2506
	11th to 20th	Night	15% 7% 2 6% 4 5% 4 4 5% 7% 40%	2850
	21st to end	Night	14% 5% 3 7% 5% 5% 4 3 5% 8% 41%	3476
September	1st to 10th	Night	12% 5% 2 7% 5% 4 5% 4 5% 6% 44%	1900
	11th to 20th	Night	15% 5% 1 6% 4 3 2 3 4 6% 50%	1943
	21st to end	Night	17% 5% 2 6% 4 4 4 3 4 7% 44%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 5% 6% 37%	2271
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 4 4 6% 33%	2280
	21st to end	Night	23% 10% 4 8% 4 4 4 3 4 5% 29%	2712
November	1st to 10th	Night	20% 10% 3 7% 5% 4 3 3 5% 6% 33%	2537
	11th to 20th	Night	18% 11% 3 9% 5% 4 5% 4 5% 5% 31%	2725
	21st to end	Night	21% 14% 4 9% 6% 5% 3 3 4 5% 24%	2800
December	1st to 10th	Night	18% 18% 6% 11% 7% 5% 5% 4 4 5% 17%	4580
	11th to 20th	Night	24% 16% 5% 9% 5% 4 4 3 3 3 25%	5208
	21st to end	Night	27% 17% 4 9% 3 3 3 3 4 5% 22%	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	69% 1 10% 15% 4 1	3598
	11th to 20th	Day	65% 2 9% 15% 9% 1	3600
	21st to end	Day	64% 3 11% 12% 9% 1	3988
February	1st to 10th	Day	63% 2 8% 20% 6% 2	1800
	11th to 20th	Day	61% 3 11% 17% 8% 1	1822
	21st to end	Day	62% 2 10% 14% 10% 1	1610
March	1st to 10th	Day	62% 1 8% 19% 8% 1	3119
	11th to 20th	Day	62% 1 10% 14% 10% 2	3374
	21st to end	Day	50% 1 6% 21% 19% 2	4098
April	1st to 10th	Day	56% 2 6% 20% 13% 3	2280
	11th to 20th	Day	53% 2 5% 21% 17% 2	2254
	21st to end	Day	57% 2 8% 16% 13% 4	2398
May	1st to 10th	Day	57% 2 7% 23% 10% 1	4440
	11th to 20th	Day	53% 2 14% 20% 9% 1	4402
	21st to end	Day	46% 2 11% 26% 14% 1	4837
June	1st to 10th	Day	55% 2 10% 20% 12% 1	2660
	11th to 20th	Day	45% 3 11% 25% 13% 2	2660
	21st to end	Day	51% 4 14% 20% 10% 1	2660
July	1st to 10th	Day	44% 4 13% 27% 11% 1	4370
	11th to 20th	Day	42% 4 15% 31% 8%	4365
	21st to end	Day	37% 6% 14% 34% 10%	4661
August	1st to 10th	Day	47% 4 16% 24% 9%	4409
	11th to 20th	Day	42% 4 17% 30% 7%	3982
	21st to end	Day	42% 4 17% 24% 12% 1	4180
September	1st to 10th	Day	40% 3 14% 30% 13%	2280
	11th to 20th	Day	36% 3 12% 33% 15% 1	2237
	21st to end	Day	43% 3 14% 28% 10%	2090
October	1st to 10th	Day	47% 3 12% 31% 8%	3165
	11th to 20th	Day	47% 2 16% 27% 8%	3140
	21st to end	Day	48% 3 19% 23% 7%	3086
November	1st to 10th	Day	51% 3 13% 23% 9% 1	1761
	11th to 20th	Day	56% 4 10% 18% 12% 1	1670
	21st to end	Day	64% 4 13% 14% 5%	1600
December	1st to 10th	Day	70% 4 12% 12% 2	2600
	11th to 20th	Day	64% 4 9% 16% 7%	2986
	21st to end	Day	66% 2 8% 17% 6%	3960
January	1st to 10th	Night	71% 2 11% 12% 4	6349
	11th to 20th	Night	71% 2 9% 13% 5%	6360
	21st to end	Night	64% 2 9% 12% 11% 1	6953
February	1st to 10th	Night	63% 3 8% 18% 7% 1	2600
	11th to 20th	Night	59% 3 10% 20% 8%	2474
	21st to end	Night	58% 2 8% 18% 13% 1	1939
March	1st to 10th	Night	56% 1 8% 22% 10% 3	3734
	11th to 20th	Night	63% 1 9% 16% 9% 2	3583
	21st to end	Night	51% 1 4 24% 17% 3	3533
April	1st to 10th	Night	56% 2 7% 19% 14% 2	1900
	11th to 20th	Night	53% 3 6% 22% 15% 2	1875
	21st to end	Night	52% 2 7% 19% 15% 4	1796
May	1st to 10th	Night	55% 1 9% 22% 10% 2	2522
	11th to 20th	Night	50% 2 11% 21% 13% 2	2496
	21st to end	Night	45% 2 11% 22% 18% 2	2739
June	1st to 10th	Night	51% 3 11% 22% 12% 1	1520
	11th to 20th	Night	43% 4 11% 23% 18% 2	1520
	21st to end	Night	48% 3 13% 21% 14% 1	1520
July	1st to 10th	Night	47% 4 13% 22% 14% 1	2480
	11th to 20th	Night	40% 4 15% 32% 8%	2472
	21st to end	Night	39% 5% 16% 25% 15%	2651
August	1st to 10th	Night	43% 4 15% 28% 9%	2496
	11th to 20th	Night	44% 4 17% 28% 8%	2876
	21st to end	Night	42% 4 15% 25% 13% 1	3476
September	1st to 10th	Night	41% 3 10% 28% 16% 1	1900
	11th to 20th	Night	36% 2 12% 35% 13% 1	1943
	21st to end	Night	42% 3 11% 30% 13%	2090
October	1st to 10th	Night	43% 4 14% 29% 9%	3791
	11th to 20th	Night	46% 3 13% 29% 9%	3779
	21st to end	Night	49% 3 17% 20% 10%	4462
November	1st to 10th	Night	52% 2 13% 22% 9% 1	2537
	11th to 20th	Night	54% 3 11% 21% 10% 1	2725
	21st to end	Night	62% 2 13% 17% 6%	2800
December	1st to 10th	Night	70% 3 11% 12% 3	4580
	11th to 20th	Night	66% 2 6% 16% 9% 1	5208
	21st to end	Night	67% 2 7% 14% 10%	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	26% 22% 32% 18% 4	200
	11th to 20th	Day	28% 27% 30% 12% 4 1	200
	21st to end	Day	20% 20% 38% 17% 5%	227
February	1st to 10th	Day	31% 29% 29% 9% 2	300
	11th to 20th	Day	26% 28% 36% 10%	360
	21st to end	Day	29% 20% 32% 17% 2	398
March	1st to 10th	Day	26% 19% 32% 19% 4	460
	11th to 20th	Day	25% 25% 31% 16% 2 1	460
	21st to end	Day	31% 22% 23% 16% 8% 1	506
April	1st to 10th	Day	30% 18% 31% 15% 5% 1	460
	11th to 20th	Day	32% 21% 22% 16% 7% 2	452
	21st to end	Day	29% 21% 26% 15% 8% 1	460
May	1st to 10th	Day	24% 16% 33% 18% 6% 2	463
	11th to 20th	Day	19% 17% 31% 21% 10% 2	487
	21st to end	Day	19% 18% 32% 22% 9% 1	529
June	1st to 10th	Day	27% 11% 27% 25% 8% 2	490
	11th to 20th	Day	16% 14% 31% 27% 11% 2	490
	21st to end	Day	25% 11% 31% 19% 11% 3	490
July	1st to 10th	Day	13% 11% 29% 29% 15% 3	485
	11th to 20th	Day	14% 10% 32% 27% 15% 2	484
	21st to end	Day	17% 8% 29% 31% 13% 2	532
August	1st to 10th	Day	15% 8% 26% 31% 16% 3	486
	11th to 20th	Day	15% 8% 22% 33% 16% 7%	479
	21st to end	Day	15% 11% 27% 27% 15% 6%	539
September	1st to 10th	Day	17% 12% 28% 21% 16% 6%	490
	11th to 20th	Day	13% 10% 21% 24% 21% 11%	490
	21st to end	Day	18% 13% 29% 20% 15% 5%	490
October	1st to 10th	Day	23% 16% 25% 21% 12% 3	490
	11th to 20th	Day	25% 20% 28% 18% 8% 1	490
	21st to end	Day	32% 12% 31% 19% 6%	432
November	1st to 10th	Day	29% 18% 26% 19% 7% 1	395
	11th to 20th	Day	25% 21% 32% 17% 6%	270
	21st to end	Day	30% 21% 30% 15% 5% 1	200
December	1st to 10th	Day	30% 18% 33% 16% 4	200
	11th to 20th	Day	31% 25% 32% 12% 1 1	200
	21st to end	Day	31% 23% 29% 15% 2	220
January	1st to 10th	Night	27% 17% 35% 17% 4	800
	11th to 20th	Night	28% 16% 31% 21% 5% 1	800
	21st to end	Night	21% 14% 36% 24% 5%	880
February	1st to 10th	Night	22% 16% 36% 22% 4	800
	11th to 20th	Night	21% 19% 37% 19% 4	783
	21st to end	Night	25% 15% 32% 24% 3	647
March	1st to 10th	Night	23% 15% 34% 23% 4	760
	11th to 20th	Night	26% 16% 33% 21% 3 1	760
	21st to end	Night	24% 14% 29% 26% 7%	836
April	1st to 10th	Night	30% 12% 30% 24% 4	760
	11th to 20th	Night	26% 16% 32% 21% 6%	751
	21st to end	Night	27% 14% 28% 22% 8%	656
May	1st to 10th	Night	26% 8% 30% 26% 8% 2	382
	11th to 20th	Night	22% 11% 30% 27% 9% 1	374
	21st to end	Night	16% 7% 38% 29% 9%	411
June	1st to 10th	Night	20% 7% 29% 35% 9% 1	380
	11th to 20th	Night	19% 6% 28% 32% 13% 1	380
	21st to end	Night	18% 5% 31% 29% 16% 1	380
July	1st to 10th	Night	11% 8% 28% 37% 16% 1	370
	11th to 20th	Night	12% 5% 28% 40% 15%	368
	21st to end	Night	13% 5% 29% 37% 15% 1	416
August	1st to 10th	Night	15% 3 23% 41% 18% 1	378
	11th to 20th	Night	15% 4 21% 35% 23% 2	589
	21st to end	Night	15% 5% 26% 33% 18% 2	836
September	1st to 10th	Night	14% 5% 28% 37% 15% 1	760
	11th to 20th	Night	18% 7% 18% 32% 22% 3	760
	21st to end	Night	18% 8% 27% 27% 18% 2	760
October	1st to 10th	Night	23% 8% 28% 28% 12% 1	760
	11th to 20th	Night	25% 11% 31% 24% 9%	760
	21st to end	Night	27% 13% 31% 24% 5%	836
November	1st to 10th	Night	27% 14% 26% 25% 8%	780
	11th to 20th	Night	23% 18% 32% 18% 9% 1	800
	21st to end	Night	29% 17% 28% 19% 7%	800
December	1st to 10th	Night	29% 15% 31% 20% 5%	800
	11th to 20th	Night	31% 18% 28% 18% 4 1	800
	21st to end	Night	37% 15% 28% 16% 4	880

Page generated at 2025-02-22 06:51:39. Version ac07

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