Eastport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eastport clear sky chart from 2005-11-06 to 2026-07-16.

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	19% 9% 3 7% 4 4 4 3 5% 7% 35%	137741
	Night	20% 10% 3 7% 4 4 4 3 5% 6% 33%	135014
Transparency	Day	48% 5% 12% 21% 12% 2	141274
	Night	51% 5% 11% 20% 11% 1	139571
Seeing	Day	22% 9% 27% 28% 13% 2	18521
	Night	24% 11% 28% 26% 10% 1	26465

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% 12% 4 9% 5% 5% 5% 5% 5% 7% 29%	4247
	11th to 20th	Day	18% 13% 4 9% 4 3 3 3 3 4 35%	4650
	21st to end	Day	11% 10% 3 8% 5% 6% 6% 4 6% 6% 35%	5601
February	1st to 10th	Day	16% 13% 3 7% 6% 6% 4 3 6% 9% 26%	1890
	11th to 20th	Day	15% 10% 3 8% 4 5% 5% 4 6% 7% 33%	1843
	21st to end	Day	13% 10% 3 6% 5% 5% 4 3 6% 8% 37%	1730
March	1st to 10th	Day	24% 10% 3 8% 4 4 4 4 4 5% 30%	4799
	11th to 20th	Day	19% 12% 2 6% 4 4 5% 4 6% 8% 30%	5090
	21st to end	Day	28% 10% 3 7% 4 4 4 4 5% 6% 28%	5587
April	1st to 10th	Day	21% 9% 3 6% 5% 4 4 4 5% 7% 33%	2442
	11th to 20th	Day	20% 9% 2 5% 4 4 4 2 5% 7% 38%	2702
	21st to end	Day	21% 7% 2 6% 4 3 3 3 6% 6% 38%	2730
May	1st to 10th	Day	28% 10% 3 7% 4 4 4 3 4 6% 29%	7639
	11th to 20th	Day	20% 7% 2 6% 4 4 4 4 5% 7% 35%	7799
	21st to end	Day	18% 8% 3 7% 4 4 5% 4 6% 7% 34%	9255
June	1st to 10th	Day	21% 8% 2 6% 5% 4 4 4 6% 8% 32%	3150
	11th to 20th	Day	20% 8% 3 6% 4 3 3 3 6% 7% 37%	3150
	21st to end	Day	25% 8% 3 6% 4 4 4 4 5% 7% 29%	3150
July	1st to 10th	Day	16% 10% 4 9% 5% 4 5% 4 6% 8% 30%	6970
	11th to 20th	Day	15% 10% 3 6% 4 4 4 3 6% 8% 38%	6632
	21st to end	Day	14% 8% 2 5% 4 4 4 4 6% 9% 40%	6563
August	1st to 10th	Day	19% 10% 3 7% 4 4 5% 4 6% 7% 32%	4235
	11th to 20th	Day	16% 8% 3 7% 4 4 4 4 5% 6% 39%	4175
	21st to end	Day	11% 6% 2 4 3 3 4 4 5% 8% 51%	4675
September	1st to 10th	Day	12% 5% 2 4 3 4 3 4 6% 7% 50%	2345
	11th to 20th	Day	15% 5% 2 5% 2 3 3 3 5% 7% 51%	2200
	21st to end	Day	17% 6% 2 6% 3 4 3 3 4 7% 46%	2200
October	1st to 10th	Day	16% 6% 3 5% 5% 3 3 3 5% 7% 44%	2064
	11th to 20th	Day	18% 6% 2 5% 4 4 5% 4 5% 8% 41%	2000
	21st to end	Day	20% 7% 3 7% 4 4 4 4 5% 5% 38%	2065
November	1st to 10th	Day	20% 8% 3 6% 4 3 5% 3 5% 6% 38%	1851
	11th to 20th	Day	20% 6% 2 6% 3 3 4 3 6% 8% 39%	1685
	21st to end	Day	21% 9% 2 7% 4 5% 4 4 5% 5% 34%	1680
December	1st to 10th	Day	23% 9% 2 6% 5% 4 4 3 6% 5% 33%	2690
	11th to 20th	Day	23% 9% 3 7% 5% 4 3 3 4 6% 34%	2704
	21st to end	Day	22% 12% 3 6% 3 4 5% 3 4 6% 33%	3553
January	1st to 10th	Night	15% 13% 4 9% 5% 5% 5% 3 5% 5% 31%	8651
	11th to 20th	Night	19% 13% 4 9% 5% 4 4 3 5% 6% 29%	8235
	21st to end	Night	12% 11% 3 6% 5% 5% 5% 4 5% 6% 39%	8565
February	1st to 10th	Night	18% 10% 3 6% 6% 5% 5% 4 6% 6% 29%	2730
	11th to 20th	Night	16% 11% 3 9% 5% 5% 4 4 5% 5% 32%	2658
	21st to end	Night	16% 11% 3 7% 5% 4 4 3 5% 6% 36%	2076
March	1st to 10th	Night	26% 11% 4 7% 5% 5% 4 3 4 4 28%	5261
	11th to 20th	Night	19% 11% 3 7% 5% 4 5% 4 5% 7% 29%	5089
	21st to end	Night	31% 9% 2 5% 4 4 4 3 4 6% 28%	5587
April	1st to 10th	Night	24% 10% 3 7% 5% 3 4 3 5% 6% 31%	2174
	11th to 20th	Night	23% 9% 3 6% 4 4 4 5% 5% 6% 33%	1868
	21st to end	Night	26% 8% 2 6% 4 4 4 3 5% 7% 31%	1890
May	1st to 10th	Night	31% 8% 3 6% 4 3 3 2 4 5% 30%	5259
	11th to 20th	Night	22% 8% 3 6% 4 4 5% 4 5% 7% 32%	5066
	21st to end	Night	16% 9% 3 8% 6% 5% 4 4 6% 7% 32%	4994
June	1st to 10th	Night	24% 9% 3 7% 4 4 4 4 6% 8% 29%	1470
	11th to 20th	Night	21% 10% 3 7% 4 3 4 3 5% 6% 34%	1470
	21st to end	Night	28% 9% 3 7% 5% 3 3 4 5% 6% 27%	1470
July	1st to 10th	Night	16% 12% 4 10% 6% 6% 6% 5% 6% 7% 23%	3230
	11th to 20th	Night	17% 13% 4 9% 4 5% 5% 3 6% 7% 29%	3430
	21st to end	Night	14% 9% 3 7% 4 4 5% 4 5% 9% 36%	4241
August	1st to 10th	Night	23% 11% 4 8% 4 4 4 3 6% 6% 27%	2915
	11th to 20th	Night	16% 9% 3 8% 4 4 4 4 7% 8% 32%	2872
	21st to end	Night	12% 6% 3 6% 3 4 4 4 5% 7% 47%	3223
September	1st to 10th	Night	15% 7% 2 4 4 4 4 3 6% 7% 44%	2051
	11th to 20th	Night	16% 6% 2 4 3 3 4 3 4 7% 48%	2200
	21st to end	Night	18% 7% 2 5% 3 3 3 3 5% 7% 45%	2200
October	1st to 10th	Night	17% 6% 2 6% 4 3 4 3 5% 7% 42%	2335
	11th to 20th	Night	17% 8% 2 6% 4 4 4 3 5% 8% 40%	2400
	21st to end	Night	22% 9% 2 7% 4 3 4 3 4 6% 36%	2770
November	1st to 10th	Night	20% 7% 2 6% 4 4 5% 4 5% 6% 39%	2667
	11th to 20th	Night	19% 7% 3 7% 4 4 5% 3 5% 6% 37%	2933
	21st to end	Night	21% 9% 2 6% 4 4 4 4 6% 7% 32%	2940
December	1st to 10th	Night	19% 10% 3 8% 4 4 4 3 5% 7% 33%	4720
	11th to 20th	Night	23% 9% 2 5% 4 4 4 3 5% 6% 34%	5707
	21st to end	Night	22% 11% 3 7% 4 4 4 3 5% 6% 33%	7667

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	56% 4 14% 20% 5% 1	4248
	11th to 20th	Day	55% 3 9% 22% 10% 1	4680
	21st to end	Day	50% 5% 12% 18% 13% 2	5601
February	1st to 10th	Day	55% 4 13% 16% 10% 1	1890
	11th to 20th	Day	50% 4 14% 20% 10% 1	1851
	21st to end	Day	45% 5% 13% 23% 11% 4	1730
March	1st to 10th	Day	57% 4 9% 13% 13% 4	4803
	11th to 20th	Day	49% 8% 14% 17% 10% 1	5090
	21st to end	Day	58% 3 6% 17% 15% 2	5587
April	1st to 10th	Day	51% 4 9% 16% 16% 3	2442
	11th to 20th	Day	45% 5% 10% 23% 14% 2	2702
	21st to end	Day	45% 5% 9% 22% 16% 3	2730
May	1st to 10th	Day	57% 5% 10% 19% 8% 1	7651
	11th to 20th	Day	48% 6% 12% 22% 9% 2	7803
	21st to end	Day	48% 7% 12% 18% 14% 1	9256
June	1st to 10th	Day	50% 7% 12% 20% 10% 1	3150
	11th to 20th	Day	46% 6% 11% 21% 15% 2	3150
	21st to end	Day	54% 7% 11% 17% 10% 2	3150
July	1st to 10th	Day	53% 6% 13% 19% 9% 1	6895
	11th to 20th	Day	46% 6% 13% 22% 11% 1	6552
	21st to end	Day	41% 7% 14% 26% 12% 1	6376
August	1st to 10th	Day	51% 7% 11% 22% 8%	4222
	11th to 20th	Day	45% 6% 18% 21% 10%	4214
	21st to end	Day	32% 6% 13% 28% 21% 1	4675
September	1st to 10th	Day	33% 6% 14% 27% 18% 1	2345
	11th to 20th	Day	35% 5% 11% 27% 20% 3	2200
	21st to end	Day	39% 5% 8% 30% 17% 1	2200
October	1st to 10th	Day	42% 5% 13% 28% 11% 1	3363
	11th to 20th	Day	34% 4 10% 37% 15%	3240
	21st to end	Day	37% 5% 17% 23% 16% 2	3315
November	1st to 10th	Day	47% 6% 11% 22% 13% 1	1851
	11th to 20th	Day	44% 4 14% 23% 13% 2	1685
	21st to end	Day	52% 6% 14% 20% 7% 1	1680
December	1st to 10th	Day	52% 5% 15% 21% 6%	2690
	11th to 20th	Day	53% 4 14% 14% 10% 4	2704
	21st to end	Day	54% 5% 12% 16% 10% 2	3553
January	1st to 10th	Night	56% 3 12% 21% 6% 1	8651
	11th to 20th	Night	58% 4 10% 19% 9% 1	8280
	21st to end	Night	46% 4 12% 20% 14% 4	8565
February	1st to 10th	Night	55% 4 13% 16% 11% 1	2730
	11th to 20th	Night	54% 5% 11% 19% 10% 2	2661
	21st to end	Night	50% 4 11% 21% 13% 2	2076
March	1st to 10th	Night	61% 3 6% 12% 14% 4	5270
	11th to 20th	Night	52% 8% 17% 15% 7% 1	5090
	21st to end	Night	58% 3 5% 19% 13% 1	5587
April	1st to 10th	Night	55% 4 8% 16% 14% 3	2174
	11th to 20th	Night	51% 5% 9% 19% 15% 1	1868
	21st to end	Night	53% 4 9% 17% 15% 2	1890
May	1st to 10th	Night	58% 5% 12% 16% 9% 1	5265
	11th to 20th	Night	50% 7% 12% 20% 9% 2	5067
	21st to end	Night	50% 6% 12% 21% 10% 1	4995
June	1st to 10th	Night	53% 6% 12% 20% 8% 1	1470
	11th to 20th	Night	51% 4 10% 21% 11% 2	1470
	21st to end	Night	58% 5% 9% 17% 8% 3	1470
July	1st to 10th	Night	59% 6% 11% 15% 8%	3195
	11th to 20th	Night	55% 6% 11% 19% 9% 1	3387
	21st to end	Night	46% 7% 13% 21% 13% 1	4114
August	1st to 10th	Night	57% 6% 10% 19% 8%	2903
	11th to 20th	Night	48% 6% 16% 22% 8%	2899
	21st to end	Night	36% 6% 10% 27% 18% 2	3223
September	1st to 10th	Night	39% 6% 10% 27% 17% 1	2051
	11th to 20th	Night	38% 4 11% 25% 20% 1	2200
	21st to end	Night	40% 4 9% 29% 17% 1	2200
October	1st to 10th	Night	42% 5% 12% 26% 13% 1	3816
	11th to 20th	Night	36% 4 11% 29% 20%	3899
	21st to end	Night	44% 4 11% 26% 14% 2	4470
November	1st to 10th	Night	45% 5% 13% 22% 14% 1	2667
	11th to 20th	Night	48% 4 13% 20% 13% 1	2933
	21st to end	Night	52% 5% 15% 19% 8% 1	2940
December	1st to 10th	Night	53% 3 12% 24% 8%	4720
	11th to 20th	Night	51% 4 12% 18% 12% 2	5708
	21st to end	Night	54% 4 13% 17% 10% 2	7667

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% 18% 35% 18% 5%	220
	11th to 20th	Day	26% 18% 35% 16% 5% 1	220
	21st to end	Day	19% 16% 37% 24% 4	410
February	1st to 10th	Day	23% 17% 33% 20% 6% 1	430
	11th to 20th	Day	20% 19% 39% 17% 4 1	426
	21st to end	Day	18% 16% 36% 25% 5%	446
March	1st to 10th	Day	23% 16% 37% 21% 4	540
	11th to 20th	Day	22% 16% 32% 22% 8% 1	540
	21st to end	Day	25% 15% 30% 22% 6% 1	594
April	1st to 10th	Day	28% 13% 32% 21% 5% 1	540
	11th to 20th	Day	25% 10% 32% 25% 8%	532
	21st to end	Day	24% 7% 28% 28% 11% 2	540
May	1st to 10th	Day	28% 6% 30% 25% 10% 1	543
	11th to 20th	Day	21% 4 26% 32% 15% 1	624
	21st to end	Day	24% 4 28% 30% 12% 2	845
June	1st to 10th	Day	24% 3 24% 32% 15% 2	780
	11th to 20th	Day	22% 4 23% 29% 18% 3	780
	21st to end	Day	30% 3 19% 30% 15% 3	780
July	1st to 10th	Day	21% 2 18% 38% 18% 2	770
	11th to 20th	Day	21% 2 18% 34% 22% 3	637
	21st to end	Day	18% 3 19% 39% 20% 2	576
August	1st to 10th	Day	16% 3 16% 37% 25% 4	526
	11th to 20th	Day	21% 2 13% 36% 24% 4	519
	21st to end	Day	17% 3 19% 33% 22% 5%	583
September	1st to 10th	Day	14% 2 19% 42% 20% 3	530
	11th to 20th	Day	19% 5% 21% 26% 22% 6%	530
	21st to end	Day	17% 4 23% 34% 18% 5%	530
October	1st to 10th	Day	18% 9% 19% 29% 21% 3	455
	11th to 20th	Day	19% 8% 27% 29% 15% 3	420
	21st to end	Day	23% 10% 33% 23% 10% 1	462
November	1st to 10th	Day	22% 15% 31% 23% 8% 1	425
	11th to 20th	Day	23% 15% 33% 21% 7% 1	430
	21st to end	Day	24% 17% 34% 20% 4	430
December	1st to 10th	Day	29% 13% 34% 19% 5%	430
	11th to 20th	Day	29% 21% 30% 15% 5%	236
	21st to end	Day	21% 18% 35% 18% 6% 2	242
January	1st to 10th	Night	26% 18% 31% 21% 3	917
	11th to 20th	Night	27% 17% 33% 18% 5%	840
	21st to end	Night	21% 20% 38% 17% 4	924
February	1st to 10th	Night	25% 18% 35% 17% 4	840
	11th to 20th	Night	23% 22% 33% 18% 3 1	823
	21st to end	Night	22% 17% 35% 22% 4	692
March	1st to 10th	Night	23% 15% 39% 21% 3	840
	11th to 20th	Night	22% 16% 31% 25% 5%	840
	21st to end	Night	24% 14% 32% 23% 6% 1	924
April	1st to 10th	Night	29% 12% 32% 21% 5%	777
	11th to 20th	Night	28% 5% 33% 27% 7%	624
	21st to end	Night	30% 5% 29% 26% 10%	630
May	1st to 10th	Night	27% 5% 29% 27% 10% 2	630
	11th to 20th	Night	28% 3 26% 31% 11% 1	622
	21st to end	Night	22% 4 27% 34% 11% 2	633
June	1st to 10th	Night	29% 4 18% 37% 12% 1	420
	11th to 20th	Night	25% 3 19% 36% 17% 1	420
	21st to end	Night	31% 2 13% 39% 14% 2	420
July	1st to 10th	Night	23% 2 17% 41% 17%	410
	11th to 20th	Night	24% 3 13% 36% 22% 1	398
	21st to end	Night	23% 2 14% 41% 18% 2	573
August	1st to 10th	Night	18% 3 14% 43% 21% 1	598
	11th to 20th	Night	21% 3 14% 38% 21% 3	592
	21st to end	Night	18% 3 16% 37% 23% 3	660
September	1st to 10th	Night	19% 2 17% 39% 20% 3	676
	11th to 20th	Night	18% 4 21% 30% 23% 4	800
	21st to end	Night	20% 4 22% 34% 17% 3	800
October	1st to 10th	Night	21% 6% 23% 31% 17% 2	800
	11th to 20th	Night	20% 10% 29% 26% 13% 2	800
	21st to end	Night	28% 13% 29% 23% 8%	880
November	1st to 10th	Night	23% 13% 32% 22% 9% 1	820
	11th to 20th	Night	23% 14% 33% 21% 8% 1	947
	21st to end	Night	27% 17% 31% 18% 6% 1	950
December	1st to 10th	Night	33% 13% 32% 18% 4	950
	11th to 20th	Night	26% 23% 35% 13% 3	950
	21st to end	Night	28% 18% 33% 17% 4	1045

Page generated at 2026-07-13 03:14:51. Version ac07

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