Massena
Clear Sky Chart
History

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

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% 11% 4 9% 5% 5% 5% 4 5% 6% 31%	132314
	Night	18% 13% 4 9% 5% 4 4 3 5% 6% 28%	130818
Transparency	Day	53% 5% 12% 20% 9% 1	135766
	Night	57% 5% 11% 17% 8% 1	135453
Seeing	Day	25% 17% 30% 19% 8% 2	16480
	Night	26% 14% 29% 23% 8% 1	25602

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% 14% 6% 5% 4 3 4 5% 16%	4661
	11th to 20th	Day	11% 18% 8% 16% 7% 6% 5% 3 4 5% 17%	4650
	21st to end	Day	10% 18% 6% 13% 10% 8% 5% 3 4 5% 17%	5258
February	1st to 10th	Day	15% 17% 4 13% 7% 5% 4 3 4 5% 22%	1890
	11th to 20th	Day	16% 15% 5% 12% 7% 5% 4 3 5% 5% 24%	1906
	21st to end	Day	19% 17% 5% 10% 6% 5% 3 3 4 5% 22%	1730
March	1st to 10th	Day	19% 13% 5% 9% 6% 4 5% 3 5% 5% 26%	4576
	11th to 20th	Day	12% 12% 4 10% 6% 5% 5% 4 5% 6% 30%	4967
	21st to end	Day	20% 10% 3 9% 5% 4 3 3 4 5% 35%	5995
April	1st to 10th	Day	21% 13% 3 7% 5% 4 3 3 4 5% 32%	2520
	11th to 20th	Day	22% 10% 3 7% 4 4 4 2 4 5% 35%	2494
	21st to end	Day	22% 10% 3 6% 4 4 4 3 5% 6% 33%	2627
May	1st to 10th	Day	25% 10% 4 9% 5% 4 5% 3 4 6% 25%	6486
	11th to 20th	Day	18% 9% 4 9% 6% 5% 5% 4 5% 6% 31%	6458
	21st to end	Day	22% 9% 3 6% 4 4 4 3 6% 7% 32%	7103
June	1st to 10th	Day	21% 7% 3 6% 6% 5% 4 4 6% 7% 30%	2800
	11th to 20th	Day	15% 5% 2 7% 6% 4 4 5% 6% 9% 37%	2800
	21st to end	Day	21% 7% 3 6% 5% 4 5% 3 6% 8% 32%	2800
July	1st to 10th	Day	12% 7% 3 8% 5% 5% 6% 4 7% 8% 35%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 8% 41%	6360
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 10% 45%	6926
August	1st to 10th	Day	15% 8% 3 7% 4 5% 5% 4 6% 8% 35%	4563
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 8% 40%	4028
	21st to end	Day	16% 6% 2 6% 4 4 5% 4 6% 8% 38%	4312
September	1st to 10th	Day	15% 5% 2 6% 4 5% 4 4 5% 7% 44%	2400
	11th to 20th	Day	13% 6% 2 5% 4 3 5% 3 4 7% 48%	2362
	21st to end	Day	18% 6% 2 6% 4 4 5% 4 5% 7% 39%	2195
October	1st to 10th	Day	20% 8% 2 6% 4 4 4 4 5% 7% 36%	2000
	11th to 20th	Day	19% 11% 3 9% 5% 5% 5% 3 5% 5% 30%	2000
	21st to end	Day	26% 11% 3 8% 5% 4 4 3 4 5% 28%	2002
November	1st to 10th	Day	16% 12% 4 8% 6% 6% 5% 3 5% 6% 30%	1851
	11th to 20th	Day	17% 14% 4 8% 5% 5% 4 4 4 6% 29%	1760
	21st to end	Day	21% 16% 4 11% 5% 6% 4 3 5% 5% 19%	1680
December	1st to 10th	Day	20% 21% 8% 11% 6% 5% 4 4 5% 5% 13%	2680
	11th to 20th	Day	19% 17% 5% 12% 5% 4 4 4 5% 5% 21%	3066
	21st to end	Day	22% 16% 4 11% 6% 5% 4 3 5% 4 20%	4048
January	1st to 10th	Night	15% 23% 7% 14% 5% 4 4 2 3 4 18%	8234
	11th to 20th	Night	13% 20% 8% 17% 7% 6% 5% 3 4 4 13%	8235
	21st to end	Night	13% 17% 6% 12% 8% 7% 5% 3 4 5% 19%	8919
February	1st to 10th	Night	15% 17% 6% 14% 7% 5% 4 4 4 5% 20%	2730
	11th to 20th	Night	15% 14% 6% 12% 7% 5% 4 3 5% 5% 26%	2600
	21st to end	Night	16% 17% 4 10% 6% 4 4 3 4 4 27%	2076
March	1st to 10th	Night	21% 14% 4 9% 6% 5% 4 2 3 4 28%	5484
	11th to 20th	Night	16% 15% 3 8% 5% 4 4 3 6% 7% 30%	5196
	21st to end	Night	19% 12% 4 9% 5% 4 4 3 4 4 32%	5178
April	1st to 10th	Night	23% 11% 3 8% 5% 4 4 3 4 5% 30%	2100
	11th to 20th	Night	22% 11% 3 7% 4 4 4 3 4 5% 32%	2075
	21st to end	Night	21% 10% 3 7% 3 4 3 3 5% 5% 36%	2006
May	1st to 10th	Night	25% 10% 3 9% 5% 4 5% 4 6% 6% 22%	3679
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 3 5% 7% 32%	3655
	21st to end	Night	18% 9% 3 8% 6% 4 5% 3 6% 8% 31%	4014
June	1st to 10th	Night	19% 7% 2 7% 6% 5% 5% 5% 7% 8% 29%	1600
	11th to 20th	Night	16% 7% 2 6% 4 5% 4 3 6% 8% 39%	1600
	21st to end	Night	18% 8% 4 6% 5% 5% 4 4 6% 8% 33%	1600
July	1st to 10th	Night	13% 7% 2 7% 5% 4 5% 4 8% 10% 35%	3600
	11th to 20th	Night	15% 6% 2 6% 4 3 4 3 5% 8% 43%	3600
	21st to end	Night	11% 6% 2 7% 4 5% 5% 5% 6% 7% 44%	3926
August	1st to 10th	Night	16% 9% 2 7% 4 4 4 3 5% 8% 38%	2586
	11th to 20th	Night	17% 7% 3 7% 5% 4 4 3 4 7% 39%	2983
	21st to end	Night	15% 6% 3 7% 4 4 5% 4 6% 7% 40%	3586
September	1st to 10th	Night	14% 6% 3 7% 5% 4 5% 4 5% 6% 43%	2000
	11th to 20th	Night	15% 5% 2 4 4 4 3 3 6% 7% 49%	2037
	21st to end	Night	17% 6% 2 6% 3 4 4 5% 4 6% 41%	2202
October	1st to 10th	Night	21% 6% 2 6% 4 4 4 5% 5% 6% 36%	2400
	11th to 20th	Night	19% 10% 3 7% 5% 4 4 4 5% 5% 34%	2400
	21st to end	Night	26% 10% 3 7% 5% 5% 4 3 5% 6% 27%	2836
November	1st to 10th	Night	21% 11% 4 7% 5% 4 4 3 5% 6% 32%	2667
	11th to 20th	Night	18% 12% 4 9% 4 4 5% 3 5% 6% 30%	2856
	21st to end	Night	22% 15% 5% 9% 5% 5% 4 3 4 6% 22%	2940
December	1st to 10th	Night	19% 21% 6% 12% 6% 5% 4 4 4 4 14%	4720
	11th to 20th	Night	24% 16% 4 10% 5% 4 4 3 4 4 21%	5348
	21st to end	Night	26% 17% 5% 11% 4 4 4 4 5% 4 17%	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	72% 5% 10% 11% 2	4662
	11th to 20th	Day	73% 3 9% 8% 7% 1	4680
	21st to end	Day	72% 4 9% 8% 7%	5258
February	1st to 10th	Day	66% 4 9% 17% 4 1	1890
	11th to 20th	Day	64% 4 12% 15% 6%	1915
	21st to end	Day	65% 5% 10% 12% 7% 1	1730
March	1st to 10th	Day	61% 4 10% 14% 8% 3	4579
	11th to 20th	Day	54% 6% 16% 14% 8% 1	4967
	21st to end	Day	53% 4 8% 18% 16% 2	5995
April	1st to 10th	Day	57% 4 7% 20% 10% 2	2520
	11th to 20th	Day	53% 4 8% 19% 15% 2	2494
	21st to end	Day	54% 4 9% 17% 14% 3	2627
May	1st to 10th	Day	61% 6% 9% 16% 7% 1	6497
	11th to 20th	Day	54% 6% 12% 17% 10% 1	6462
	21st to end	Day	50% 6% 12% 21% 10% 1	7103
June	1st to 10th	Day	52% 7% 11% 18% 11% 1	2800
	11th to 20th	Day	43% 7% 12% 26% 10% 2	2800
	21st to end	Day	50% 8% 11% 20% 10% 1	2800
July	1st to 10th	Day	44% 6% 15% 26% 9%	6290
	11th to 20th	Day	38% 7% 15% 28% 13%	6285
	21st to end	Day	34% 7% 14% 37% 8%	6728
August	1st to 10th	Day	46% 7% 16% 22% 9%	4549
	11th to 20th	Day	42% 6% 18% 28% 6%	4067
	21st to end	Day	42% 6% 18% 24% 10%	4312
September	1st to 10th	Day	39% 6% 14% 29% 12%	2400
	11th to 20th	Day	36% 5% 12% 33% 13% 1	2362
	21st to end	Day	43% 7% 14% 25% 10%	2195
October	1st to 10th	Day	45% 5% 13% 28% 9%	3260
	11th to 20th	Day	49% 5% 16% 24% 6% 1	3240
	21st to end	Day	49% 5% 17% 23% 6%	3214
November	1st to 10th	Day	54% 6% 13% 20% 6% 1	1851
	11th to 20th	Day	57% 5% 13% 15% 9% 1	1760
	21st to end	Day	67% 6% 13% 10% 3	1680
December	1st to 10th	Day	74% 5% 12% 8% 1	2680
	11th to 20th	Day	66% 5% 10% 14% 6%	3066
	21st to end	Day	68% 5% 8% 15% 4	4048
January	1st to 10th	Night	72% 4 11% 10% 3	8234
	11th to 20th	Night	75% 4 8% 8% 5%	8280
	21st to end	Night	68% 5% 8% 11% 8%	8919
February	1st to 10th	Night	68% 4 9% 14% 5%	2730
	11th to 20th	Night	62% 4 10% 18% 5%	2602
	21st to end	Night	61% 4 10% 15% 9% 1	2076
March	1st to 10th	Night	60% 5% 7% 17% 10% 1	5494
	11th to 20th	Night	54% 5% 18% 14% 7% 2	5197
	21st to end	Night	56% 4 7% 22% 10% 2	5178
April	1st to 10th	Night	57% 4 8% 19% 11% 1	2100
	11th to 20th	Night	55% 4 9% 19% 13% 1	2075
	21st to end	Night	51% 4 8% 18% 15% 3	2006
May	1st to 10th	Night	61% 6% 10% 15% 7% 1	3685
	11th to 20th	Night	51% 6% 11% 19% 12% 1	3656
	21st to end	Night	50% 6% 11% 19% 12% 1	4015
June	1st to 10th	Night	50% 7% 13% 17% 12% 1	1600
	11th to 20th	Night	43% 6% 13% 21% 16% 1	1600
	21st to end	Night	49% 7% 12% 19% 12%	1600
July	1st to 10th	Night	42% 5% 18% 22% 12% 1	3560
	11th to 20th	Night	39% 6% 15% 28% 12%	3552
	21st to end	Night	38% 6% 14% 29% 12%	3809
August	1st to 10th	Night	45% 6% 15% 25% 9%	2576
	11th to 20th	Night	46% 6% 16% 24% 8% 1	3010
	21st to end	Night	41% 6% 16% 25% 11% 1	3586
September	1st to 10th	Night	41% 7% 11% 28% 13% 1	2000
	11th to 20th	Night	34% 4 16% 33% 12% 1	2037
	21st to end	Night	43% 7% 11% 25% 13% 1	2202
October	1st to 10th	Night	44% 6% 13% 27% 9% 1	3920
	11th to 20th	Night	46% 4 15% 24% 10% 1	3899
	21st to end	Night	50% 6% 18% 19% 7%	4574
November	1st to 10th	Night	53% 5% 14% 19% 8% 1	2667
	11th to 20th	Night	55% 6% 12% 18% 7% 2	2856
	21st to end	Night	64% 6% 13% 13% 5%	2940
December	1st to 10th	Night	75% 5% 11% 8% 1	4720
	11th to 20th	Night	68% 3 8% 14% 7%	5348
	21st to end	Night	69% 4 7% 13% 6%	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	33% 17% 30% 18% 2	220
	11th to 20th	Day	35% 24% 31% 6% 4	220
	21st to end	Day	22% 24% 35% 16% 3	265
February	1st to 10th	Day	38% 21% 30% 9% 2	330
	11th to 20th	Day	31% 25% 34% 9% 1	393
	21st to end	Day	33% 20% 33% 12% 1	446
March	1st to 10th	Day	29% 24% 30% 14% 4	540
	11th to 20th	Day	31% 22% 31% 12% 3 1	540
	21st to end	Day	35% 22% 24% 13% 5% 1	594
April	1st to 10th	Day	36% 20% 25% 15% 2 1	540
	11th to 20th	Day	35% 21% 24% 14% 5% 2	532
	21st to end	Day	32% 19% 30% 10% 7% 1	540
May	1st to 10th	Day	27% 19% 31% 15% 6% 1	543
	11th to 20th	Day	20% 19% 33% 17% 10% 1	567
	21st to end	Day	23% 17% 30% 21% 9% 1	617
June	1st to 10th	Day	25% 17% 29% 21% 6% 2	530
	11th to 20th	Day	16% 16% 33% 25% 8% 2	530
	21st to end	Day	25% 15% 32% 18% 8% 1	530
July	1st to 10th	Day	13% 10% 33% 28% 13% 2	525
	11th to 20th	Day	15% 10% 34% 29% 10% 2	524
	21st to end	Day	15% 7% 37% 28% 10% 2	576
August	1st to 10th	Day	16% 10% 24% 32% 15% 3	526
	11th to 20th	Day	15% 7% 29% 27% 16% 6%	519
	21st to end	Day	15% 13% 30% 24% 12% 6%	583
September	1st to 10th	Day	16% 12% 28% 22% 16% 6%	530
	11th to 20th	Day	13% 10% 23% 25% 19% 10%	530
	21st to end	Day	19% 13% 31% 20% 13% 4	530
October	1st to 10th	Day	25% 12% 27% 19% 12% 5%	530
	11th to 20th	Day	24% 21% 30% 16% 7% 2	530
	21st to end	Day	33% 17% 27% 17% 6%	473
November	1st to 10th	Day	29% 19% 28% 16% 7%	425
	11th to 20th	Day	28% 23% 30% 13% 4 1	300
	21st to end	Day	35% 21% 31% 9% 3	220
December	1st to 10th	Day	31% 20% 25% 18% 5%	220
	11th to 20th	Day	33% 27% 27% 10% 1 1	220
	21st to end	Day	36% 22% 24% 14% 4	242
January	1st to 10th	Night	32% 19% 30% 16% 3	840
	11th to 20th	Night	32% 20% 26% 18% 4	840
	21st to end	Night	23% 18% 33% 22% 4	924
February	1st to 10th	Night	26% 20% 31% 20% 3	840
	11th to 20th	Night	26% 21% 34% 17% 2	823
	21st to end	Night	28% 17% 31% 22% 2	692
March	1st to 10th	Night	28% 19% 30% 19% 4	840
	11th to 20th	Night	31% 18% 30% 17% 3	840
	21st to end	Night	28% 17% 27% 23% 5%	924
April	1st to 10th	Night	31% 15% 29% 22% 3	840
	11th to 20th	Night	30% 16% 29% 19% 6%	831
	21st to end	Night	28% 14% 30% 21% 6%	746
May	1st to 10th	Night	28% 12% 30% 22% 7% 1	425
	11th to 20th	Night	21% 12% 32% 28% 6%	414
	21st to end	Night	17% 9% 39% 25% 9%	455
June	1st to 10th	Night	20% 8% 33% 33% 6% 1	400
	11th to 20th	Night	20% 11% 27% 30% 11% 1	400
	21st to end	Night	20% 9% 30% 30% 11% 1	400
July	1st to 10th	Night	11% 6% 29% 41% 12% 1	390
	11th to 20th	Night	15% 5% 27% 38% 15%	388
	21st to end	Night	14% 6% 31% 38% 10% 1	438
August	1st to 10th	Night	13% 6% 23% 40% 18% 1	398
	11th to 20th	Night	16% 5% 23% 36% 19% 1	650
	21st to end	Night	17% 6% 29% 30% 16% 2	880
September	1st to 10th	Night	15% 9% 29% 31% 15% 1	800
	11th to 20th	Night	17% 7% 22% 29% 22% 4	800
	21st to end	Night	20% 10% 25% 25% 18% 2	800
October	1st to 10th	Night	24% 11% 26% 24% 15% 1	800
	11th to 20th	Night	26% 11% 31% 23% 9%	800
	21st to end	Night	32% 14% 28% 21% 4	880
November	1st to 10th	Night	30% 17% 26% 20% 6%	820
	11th to 20th	Night	27% 19% 28% 19% 7% 1	840
	21st to end	Night	32% 19% 25% 19% 4	840
December	1st to 10th	Night	34% 18% 27% 18% 3	840
	11th to 20th	Night	33% 20% 29% 14% 4 1	840
	21st to end	Night	38% 16% 27% 15% 4	924

Page generated at 2026-05-29 01:53:29. Version ac07

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