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 2025-03-12.

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	18% 9% 3 7% 4 4 4 3 5% 7% 36%	108448
	Night	19% 10% 3 7% 5% 4 4 3 5% 6% 33%	110590
Transparency	Day	47% 6% 12% 21% 12% 2	112023
	Night	50% 5% 12% 20% 11% 1	115180
Seeing	Day	22% 9% 27% 27% 13% 2	16623
	Night	25% 11% 28% 26% 10% 1	24801

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	17% 12% 4 9% 5% 5% 4 4 5% 6% 29%	3272
	11th to 20th	Day	14% 12% 4 9% 4 3 4 3 4 5% 37%	3570
	21st to end	Day	13% 10% 3 9% 4 6% 5% 3 6% 6% 35%	4328
February	1st to 10th	Day	17% 13% 3 7% 6% 6% 4 3 7% 9% 26%	1800
	11th to 20th	Day	15% 10% 4 8% 5% 5% 5% 4 6% 7% 31%	1753
	21st to end	Day	13% 10% 3 6% 5% 5% 4 3 6% 8% 36%	1650
March	1st to 10th	Day	24% 10% 3 7% 4 4 4 3 4 6% 31%	3370
	11th to 20th	Day	17% 11% 2 7% 5% 5% 6% 4 7% 8% 28%	3491
	21st to end	Day	28% 10% 2 7% 4 4 4 4 5% 5% 28%	3816
April	1st to 10th	Day	20% 10% 3 6% 6% 4 4 4 5% 6% 33%	2209
	11th to 20th	Day	20% 8% 2 5% 4 4 4 2 5% 7% 39%	2442
	21st to end	Day	21% 7% 2 6% 4 3 3 3 6% 6% 38%	2470
May	1st to 10th	Day	19% 8% 2 8% 4 4 4 4 5% 8% 34%	4106
	11th to 20th	Day	18% 8% 2 7% 4 4 5% 4 5% 7% 37%	4171
	21st to end	Day	16% 8% 2 6% 5% 4 5% 4 7% 8% 34%	4948
June	1st to 10th	Day	22% 9% 2 6% 4 4 4 4 6% 8% 31%	2850
	11th to 20th	Day	20% 8% 2 6% 4 4 3 4 6% 7% 37%	2850
	21st to end	Day	25% 9% 3 7% 4 4 4 4 5% 7% 28%	2850
July	1st to 10th	Day	16% 9% 3 9% 5% 4 5% 4 6% 8% 31%	4760
	11th to 20th	Day	16% 9% 3 7% 4 4 4 3 6% 8% 37%	4581
	21st to end	Day	18% 9% 2 5% 5% 4 4 4 6% 8% 35%	4563
August	1st to 10th	Day	19% 10% 3 7% 4 4 5% 4 5% 7% 31%	4105
	11th to 20th	Day	16% 8% 3 7% 4 5% 4 4 5% 6% 38%	4045
	21st to end	Day	11% 6% 2 4 3 3 4 4 5% 8% 51%	4532
September	1st to 10th	Day	12% 6% 2 4 3 4 3 3 6% 8% 50%	2228
	11th to 20th	Day	16% 5% 2 5% 2 3 3 3 5% 7% 50%	2090
	21st to end	Day	17% 5% 2 6% 3 4 3 3 4 7% 45%	2090
October	1st to 10th	Day	16% 6% 3 6% 5% 3 3 3 5% 7% 42%	1961
	11th to 20th	Day	18% 5% 1 5% 4 4 5% 4 4 8% 42%	1900
	21st to end	Day	21% 7% 2 7% 4 4 3 3 5% 5% 39%	1962
November	1st to 10th	Day	20% 8% 3 6% 4 3 4 3 5% 6% 38%	1761
	11th to 20th	Day	21% 6% 2 6% 3 3 4 3 5% 8% 38%	1605
	21st to end	Day	22% 10% 2 6% 4 4 4 3 5% 5% 35%	1600
December	1st to 10th	Day	23% 9% 2 6% 5% 4 4 4 6% 6% 33%	2610
	11th to 20th	Day	24% 9% 3 6% 5% 4 3 3 4 6% 34%	2633
	21st to end	Day	22% 12% 3 6% 3 4 5% 3 4 6% 33%	3476
January	1st to 10th	Night	14% 13% 4 9% 6% 5% 4 3 5% 6% 31%	6670
	11th to 20th	Night	15% 12% 4 9% 5% 4 4 3 5% 6% 32%	6315
	21st to end	Night	12% 10% 3 7% 5% 5% 5% 4 5% 6% 37%	6613
February	1st to 10th	Night	19% 11% 3 6% 6% 5% 5% 4 6% 6% 28%	2600
	11th to 20th	Night	16% 11% 3 9% 5% 5% 5% 4 6% 6% 30%	2528
	21st to end	Night	16% 11% 3 7% 6% 4 3 3 5% 6% 36%	1980
March	1st to 10th	Night	26% 11% 4 7% 5% 5% 4 3 4 4 28%	3690
	11th to 20th	Night	17% 11% 3 8% 7% 5% 5% 5% 6% 8% 25%	3497
	21st to end	Night	30% 9% 3 6% 4 4 4 3 4 5% 27%	3816
April	1st to 10th	Night	24% 10% 3 6% 5% 3 4 3 5% 6% 32%	1967
	11th to 20th	Night	23% 9% 2 6% 4 4 4 5% 5% 6% 33%	1688
	21st to end	Night	27% 8% 2 6% 4 4 4 3 5% 7% 31%	1710
May	1st to 10th	Night	23% 6% 3 6% 5% 3 3 3 5% 8% 35%	2834
	11th to 20th	Night	19% 7% 3 7% 4 5% 6% 5% 6% 7% 31%	2722
	21st to end	Night	17% 10% 3 8% 5% 5% 4 4 6% 7% 31%	2666
June	1st to 10th	Night	25% 9% 3 7% 4 4 4 4 5% 7% 27%	1330
	11th to 20th	Night	21% 9% 3 7% 4 3 4 3 5% 6% 34%	1330
	21st to end	Night	29% 9% 3 7% 5% 3 3 4 4 6% 27%	1330
July	1st to 10th	Night	18% 12% 4 9% 6% 5% 5% 4 7% 7% 25%	2210
	11th to 20th	Night	18% 9% 3 8% 4 5% 5% 4 7% 8% 29%	2380
	21st to end	Night	17% 11% 3 7% 4 4 4 4 5% 8% 33%	2956
August	1st to 10th	Night	23% 11% 4 8% 4 4 4 3 6% 6% 26%	2825
	11th to 20th	Night	16% 9% 3 8% 4 4 4 4 7% 9% 31%	2782
	21st to end	Night	12% 6% 3 6% 3 4 4 4 5% 7% 48%	3124
September	1st to 10th	Night	15% 7% 2 4 5% 4 4 3 6% 7% 44%	1948
	11th to 20th	Night	17% 7% 2 4 3 3 4 3 4 6% 47%	2090
	21st to end	Night	18% 7% 2 5% 3 3 3 2 5% 7% 44%	2090
October	1st to 10th	Night	18% 6% 2 6% 4 4 4 3 6% 7% 40%	2218
	11th to 20th	Night	17% 7% 2 5% 4 4 4 3 5% 8% 41%	2280
	21st to end	Night	22% 9% 2 7% 4 3 4 3 4 5% 36%	2631
November	1st to 10th	Night	19% 7% 2 6% 4 4 5% 4 5% 6% 39%	2537
	11th to 20th	Night	19% 7% 3 7% 4 4 5% 3 5% 6% 37%	2793
	21st to end	Night	22% 9% 2 6% 4 4 4 4 6% 7% 32%	2800
December	1st to 10th	Night	19% 10% 3 8% 4 4 4 3 5% 7% 33%	4580
	11th to 20th	Night	23% 9% 2 5% 4 4 4 3 5% 6% 34%	5558
	21st to end	Night	23% 11% 3 7% 4 4 4 3 5% 6% 32%	7502

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 15% 20% 4 1	3273
	11th to 20th	Day	52% 3 11% 23% 9% 2	3600
	21st to end	Day	50% 5% 11% 17% 14% 3	4328
February	1st to 10th	Day	56% 4 14% 15% 11% 1	1800
	11th to 20th	Day	51% 4 15% 18% 10% 1	1761
	21st to end	Day	45% 5% 13% 23% 10% 4	1650
March	1st to 10th	Day	56% 4 10% 16% 10% 4	3374
	11th to 20th	Day	49% 10% 12% 16% 11% 2	3491
	21st to end	Day	59% 4 6% 15% 14% 2	3816
April	1st to 10th	Day	52% 4 9% 17% 15% 3	2209
	11th to 20th	Day	44% 5% 11% 23% 15% 2	2442
	21st to end	Day	46% 5% 9% 21% 16% 3	2470
May	1st to 10th	Day	49% 7% 13% 22% 8% 1	4120
	11th to 20th	Day	45% 8% 14% 23% 9% 1	4175
	21st to end	Day	44% 10% 14% 17% 13% 1	4948
June	1st to 10th	Day	51% 7% 12% 19% 10% 1	2850
	11th to 20th	Day	46% 6% 11% 20% 15% 2	2850
	21st to end	Day	54% 7% 11% 16% 10% 2	2850
July	1st to 10th	Day	51% 6% 12% 19% 11% 1	4685
	11th to 20th	Day	46% 7% 14% 23% 10%	4501
	21st to end	Day	47% 7% 13% 23% 10% 1	4417
August	1st to 10th	Day	52% 7% 11% 22% 7%	4092
	11th to 20th	Day	46% 6% 18% 21% 9%	4084
	21st to end	Day	32% 6% 13% 28% 21% 1	4532
September	1st to 10th	Day	33% 6% 14% 28% 18% 2	2228
	11th to 20th	Day	35% 5% 11% 27% 19% 3	2090
	21st to end	Day	40% 5% 9% 30% 16% 1	2090
October	1st to 10th	Day	43% 5% 13% 28% 10%	3260
	11th to 20th	Day	33% 4 10% 37% 15%	3140
	21st to end	Day	36% 5% 17% 23% 17% 2	3212
November	1st to 10th	Day	47% 6% 11% 23% 13% 1	1761
	11th to 20th	Day	44% 4 14% 22% 14% 2	1605
	21st to end	Day	52% 6% 15% 21% 7% 1	1600
December	1st to 10th	Day	53% 5% 15% 20% 6%	2610
	11th to 20th	Day	53% 4 15% 13% 10% 4	2633
	21st to end	Day	54% 5% 13% 15% 10% 2	3476
January	1st to 10th	Night	55% 4 13% 22% 5% 1	6670
	11th to 20th	Night	54% 4 12% 21% 8% 1	6360
	21st to end	Night	47% 5% 12% 19% 14% 4	6613
February	1st to 10th	Night	56% 4 13% 14% 11% 1	2600
	11th to 20th	Night	55% 5% 11% 18% 10% 2	2531
	21st to end	Night	50% 4 11% 20% 13% 2	1980
March	1st to 10th	Night	60% 4 7% 15% 12% 2	3699
	11th to 20th	Night	53% 9% 12% 14% 10% 1	3498
	21st to end	Night	60% 3 6% 17% 12% 2	3816
April	1st to 10th	Night	54% 4 8% 16% 14% 4	1967
	11th to 20th	Night	50% 5% 9% 20% 15% 1	1688
	21st to end	Night	54% 4 9% 16% 15% 2	1710
May	1st to 10th	Night	48% 8% 16% 19% 9% 1	2840
	11th to 20th	Night	49% 10% 15% 18% 7% 1	2723
	21st to end	Night	50% 8% 15% 19% 8% 1	2667
June	1st to 10th	Night	55% 6% 12% 19% 7% 1	1330
	11th to 20th	Night	51% 4 10% 21% 11% 2	1330
	21st to end	Night	59% 5% 9% 17% 7% 3	1330
July	1st to 10th	Night	59% 5% 11% 14% 11%	2175
	11th to 20th	Night	52% 8% 12% 19% 9% 1	2337
	21st to end	Night	49% 7% 11% 19% 13% 1	2862
August	1st to 10th	Night	58% 6% 10% 18% 7%	2813
	11th to 20th	Night	49% 6% 16% 22% 8%	2809
	21st to end	Night	36% 6% 10% 27% 18% 2	3124
September	1st to 10th	Night	39% 6% 10% 27% 17% 1	1948
	11th to 20th	Night	39% 4 11% 25% 20% 1	2090
	21st to end	Night	40% 4 9% 29% 17% 1	2090
October	1st to 10th	Night	43% 5% 12% 26% 12% 1	3699
	11th to 20th	Night	36% 4 11% 28% 20%	3779
	21st to end	Night	44% 4 11% 26% 14% 2	4331
November	1st to 10th	Night	45% 5% 13% 22% 13% 1	2537
	11th to 20th	Night	48% 5% 14% 19% 13% 1	2793
	21st to end	Night	52% 5% 14% 19% 8% 1	2800
December	1st to 10th	Night	52% 3 12% 25% 7%	4580
	11th to 20th	Night	51% 4 12% 18% 12% 2	5559
	21st to end	Night	54% 4 13% 17% 10% 2	7502

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% 33% 19% 6%	200
	11th to 20th	Day	26% 18% 34% 17% 5% 1	200
	21st to end	Day	19% 15% 37% 23% 4 1	380
February	1st to 10th	Day	25% 18% 33% 19% 5% 1	400
	11th to 20th	Day	21% 19% 40% 16% 3 1	396
	21st to end	Day	17% 16% 36% 25% 6%	414
March	1st to 10th	Day	23% 16% 36% 21% 4	500
	11th to 20th	Day	20% 16% 32% 22% 9% 1	464
	21st to end	Day	24% 15% 30% 24% 6% 1	506
April	1st to 10th	Day	28% 13% 29% 22% 6% 2	460
	11th to 20th	Day	23% 10% 34% 24% 9%	452
	21st to end	Day	24% 7% 30% 27% 10% 2	460
May	1st to 10th	Day	26% 6% 31% 26% 11% 1	463
	11th to 20th	Day	20% 4 26% 32% 17% 1	538
	21st to end	Day	25% 4 28% 28% 13% 2	735
June	1st to 10th	Day	25% 4 25% 31% 13% 2	680
	11th to 20th	Day	22% 4 22% 29% 19% 3	680
	21st to end	Day	30% 3 21% 28% 14% 3	680
July	1st to 10th	Day	22% 2 18% 38% 17% 2	670
	11th to 20th	Day	21% 2 17% 34% 22% 4	568
	21st to end	Day	19% 3 18% 39% 20% 2	532
August	1st to 10th	Day	17% 3 17% 36% 24% 3	486
	11th to 20th	Day	22% 2 13% 37% 22% 3	479
	21st to end	Day	17% 4 18% 33% 23% 5%	539
September	1st to 10th	Day	14% 2 20% 41% 20% 2	490
	11th to 20th	Day	20% 5% 21% 26% 22% 5%	490
	21st to end	Day	17% 4 23% 33% 17% 5%	490
October	1st to 10th	Day	19% 10% 19% 29% 20% 3	422
	11th to 20th	Day	19% 7% 27% 29% 14% 3	390
	21st to end	Day	23% 10% 33% 23% 10% 1	429
November	1st to 10th	Day	22% 14% 31% 23% 9% 2	395
	11th to 20th	Day	24% 16% 33% 21% 7% 1	400
	21st to end	Day	25% 18% 34% 20% 3 1	400
December	1st to 10th	Day	29% 13% 34% 18% 5% 1	400
	11th to 20th	Day	30% 20% 30% 14% 5%	215
	21st to end	Day	22% 18% 34% 18% 6% 2	220
January	1st to 10th	Night	26% 18% 31% 20% 3	870
	11th to 20th	Night	27% 17% 33% 18% 5%	800
	21st to end	Night	21% 19% 38% 18% 4	880
February	1st to 10th	Night	27% 19% 34% 17% 4	800
	11th to 20th	Night	24% 22% 33% 17% 3 1	783
	21st to end	Night	22% 17% 34% 23% 4	660
March	1st to 10th	Night	24% 14% 38% 21% 3	800
	11th to 20th	Night	22% 16% 31% 26% 5% 1	767
	21st to end	Night	23% 14% 32% 23% 6% 1	836
April	1st to 10th	Night	29% 12% 31% 22% 5%	703
	11th to 20th	Night	27% 4 34% 27% 7% 1	564
	21st to end	Night	30% 4 29% 26% 10%	570
May	1st to 10th	Night	26% 5% 29% 29% 10% 2	570
	11th to 20th	Night	27% 2 27% 32% 12% 1	562
	21st to end	Night	23% 4 26% 35% 11% 2	572
June	1st to 10th	Night	31% 3 18% 35% 11% 1	380
	11th to 20th	Night	26% 2 18% 36% 17% 1	380
	21st to end	Night	33% 2 12% 38% 14% 1	380
July	1st to 10th	Night	24% 2 17% 41% 17%	370
	11th to 20th	Night	25% 3 13% 37% 21% 1	368
	21st to end	Night	23% 2 14% 41% 18% 2	544
August	1st to 10th	Night	18% 3 15% 43% 20% 1	568
	11th to 20th	Night	22% 3 15% 38% 20% 2	562
	21st to end	Night	18% 3 16% 36% 24% 3	627
September	1st to 10th	Night	19% 2 17% 39% 20% 2	642
	11th to 20th	Night	19% 4 21% 30% 22% 4	760
	21st to end	Night	21% 4 22% 33% 18% 3	760
October	1st to 10th	Night	22% 5% 22% 31% 17% 2	760
	11th to 20th	Night	20% 10% 29% 25% 13% 2	760
	21st to end	Night	28% 13% 29% 22% 7%	836
November	1st to 10th	Night	23% 12% 32% 23% 9% 1	780
	11th to 20th	Night	23% 14% 34% 21% 8% 1	897
	21st to end	Night	28% 18% 29% 18% 6% 1	900
December	1st to 10th	Night	33% 13% 33% 17% 4	900
	11th to 20th	Night	27% 22% 35% 13% 3	900
	21st to end	Night	29% 17% 32% 17% 4	990

Page generated at 2025-03-09 08:08:43. Version ac07

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