Machias
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Machias 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	20% 9% 3 6% 4 4 4 3 5% 7% 36%	137621
	Night	20% 9% 3 6% 4 4 4 3 5% 6% 36%	135129
Transparency	Day	49% 6% 12% 20% 11% 2	141155
	Night	49% 6% 12% 20% 12% 2	139685
Seeing	Day	25% 19% 32% 18% 6% 1	18382
	Night	25% 16% 31% 22% 6% 1	26418

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% 11% 3 7% 4 4 4 4 6% 6% 36%	4395
	11th to 20th	Day	19% 11% 3 8% 4 3 4 2 3 4 39%	4650
	21st to end	Day	12% 9% 3 7% 4 4 5% 4 5% 6% 41%	5518
February	1st to 10th	Day	17% 11% 3 7% 4 5% 4 4 5% 7% 33%	1890
	11th to 20th	Day	15% 9% 4 7% 5% 5% 5% 4 4 7% 36%	1876
	21st to end	Day	14% 9% 3 7% 5% 4 4 4 5% 7% 38%	1730
March	1st to 10th	Day	26% 10% 2 7% 4 4 4 3 4 5% 29%	4752
	11th to 20th	Day	22% 11% 3 6% 4 4 4 4 5% 7% 31%	5090
	21st to end	Day	28% 11% 3 6% 4 4 4 3 4 5% 28%	5587
April	1st to 10th	Day	22% 12% 3 7% 4 3 3 3 4 7% 32%	2447
	11th to 20th	Day	23% 9% 2 6% 3 4 4 3 5% 6% 36%	2702
	21st to end	Day	23% 8% 3 6% 4 3 3 2 5% 6% 37%	2730
May	1st to 10th	Day	29% 12% 3 6% 4 4 3 3 4 5% 26%	7639
	11th to 20th	Day	20% 8% 2 6% 4 4 4 3 6% 7% 35%	7643
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 5% 7% 32%	9335
June	1st to 10th	Day	23% 8% 3 7% 4 4 4 3 5% 8% 31%	3150
	11th to 20th	Day	21% 8% 3 6% 4 3 3 3 5% 7% 36%	3150
	21st to end	Day	26% 10% 3 6% 5% 4 4 3 5% 7% 28%	3150
July	1st to 10th	Day	18% 9% 3 7% 5% 5% 5% 4 6% 9% 29%	6970
	11th to 20th	Day	19% 9% 2 6% 4 3 4 3 5% 9% 36%	6492
	21st to end	Day	17% 6% 2 5% 4 4 4 4 6% 8% 40%	6614
August	1st to 10th	Day	21% 8% 3 6% 4 4 5% 4 5% 8% 32%	4235
	11th to 20th	Day	19% 8% 2 6% 4 4 5% 3 6% 8% 34%	4175
	21st to end	Day	11% 5% 2 4 4 4 4 4 6% 8% 48%	4675
September	1st to 10th	Day	13% 5% 2 4 3 4 4 3 6% 7% 48%	2329
	11th to 20th	Day	16% 5% 2 5% 3 3 3 3 4 5% 50%	2200
	21st to end	Day	18% 5% 2 6% 4 4 4 3 5% 6% 44%	2200
October	1st to 10th	Day	17% 7% 2 6% 3 4 4 4 5% 6% 42%	2085
	11th to 20th	Day	19% 5% 2 5% 3 4 5% 4 5% 7% 40%	2000
	21st to end	Day	22% 8% 2 6% 3 4 4 4 5% 5% 38%	2043
November	1st to 10th	Day	20% 7% 2 7% 3 3 5% 4 5% 6% 38%	1851
	11th to 20th	Day	20% 7% 2 5% 3 4 4 3 5% 7% 42%	1731
	21st to end	Day	21% 10% 3 5% 3 3 4 3 4 6% 38%	1680
December	1st to 10th	Day	21% 9% 2 4 3 2 4 3 5% 6% 42%	2666
	11th to 20th	Day	23% 9% 2 5% 4 4 3 3 4 5% 38%	2688
	21st to end	Day	22% 11% 3 5% 3 3 4 2 4 6% 38%	3553
January	1st to 10th	Night	14% 11% 4 8% 4 4 4 3 4 5% 39%	8496
	11th to 20th	Night	19% 12% 3 8% 4 4 4 3 5% 6% 31%	8235
	21st to end	Night	12% 10% 3 6% 4 4 4 3 6% 6% 42%	8660
February	1st to 10th	Night	18% 9% 3 6% 5% 4 4 3 5% 7% 35%	2730
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 3 5% 6% 38%	2626
	21st to end	Night	16% 10% 3 7% 4 3 4 4 4 6% 38%	2076
March	1st to 10th	Night	26% 10% 3 8% 4 4 4 2 4 5% 29%	5307
	11th to 20th	Night	18% 12% 4 7% 4 4 4 4 5% 7% 30%	5089
	21st to end	Night	30% 8% 3 6% 4 4 4 3 4 5% 29%	5587
April	1st to 10th	Night	25% 10% 3 6% 4 3 4 4 5% 5% 32%	2170
	11th to 20th	Night	23% 9% 3 6% 4 3 4 3 6% 6% 32%	1868
	21st to end	Night	25% 9% 3 6% 4 5% 4 3 5% 6% 32%	1890
May	1st to 10th	Night	31% 10% 3 6% 4 3 3 2 3 5% 30%	5259
	11th to 20th	Night	23% 8% 2 6% 4 4 4 4 6% 7% 32%	5202
	21st to end	Night	18% 10% 3 8% 5% 5% 4 3 6% 6% 31%	4913
June	1st to 10th	Night	25% 8% 3 6% 4 4 4 3 6% 7% 29%	1470
	11th to 20th	Night	23% 9% 2 7% 3 4 4 3 5% 7% 35%	1470
	21st to end	Night	29% 10% 3 6% 5% 4 4 2 5% 6% 29%	1470
July	1st to 10th	Night	19% 11% 3 8% 7% 5% 6% 4 7% 6% 24%	3230
	11th to 20th	Night	23% 12% 3 6% 4 4 4 3 5% 6% 30%	3563
	21st to end	Night	16% 9% 3 6% 4 4 4 4 6% 7% 38%	4190
August	1st to 10th	Night	25% 11% 3 6% 5% 4 4 4 5% 7% 27%	2915
	11th to 20th	Night	20% 9% 3 6% 4 5% 4 4 6% 8% 30%	2872
	21st to end	Night	12% 7% 3 6% 4 4 4 4 5% 6% 46%	3223
September	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 5% 6% 45%	2066
	11th to 20th	Night	16% 6% 2 4 3 3 3 3 4 6% 48%	2200
	21st to end	Night	19% 7% 1 6% 3 3 3 2 6% 7% 44%	2200
October	1st to 10th	Night	19% 6% 2 5% 4 3 4 4 5% 7% 42%	2314
	11th to 20th	Night	19% 6% 2 6% 4 3 3 3 4 7% 43%	2400
	21st to end	Night	23% 8% 2 5% 4 3 3 3 5% 6% 38%	2795
November	1st to 10th	Night	20% 6% 2 6% 3 3 5% 3 5% 5% 42%	2667
	11th to 20th	Night	19% 7% 2 6% 4 4 4 3 5% 5% 41%	2888
	21st to end	Night	21% 8% 2 6% 4 4 4 4 6% 6% 36%	2940
December	1st to 10th	Night	19% 9% 3 6% 3 3 3 3 5% 6% 39%	4740
	11th to 20th	Night	24% 8% 2 4 3 3 3 3 3 5% 42%	5741
	21st to end	Night	22% 10% 2 6% 3 3 3 3 4 6% 38%	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	50% 5% 13% 23% 8% 1	4396
	11th to 20th	Day	51% 5% 10% 22% 11% 1	4680
	21st to end	Day	45% 6% 11% 19% 15% 4	5518
February	1st to 10th	Day	52% 6% 13% 17% 10% 2	1890
	11th to 20th	Day	49% 6% 15% 19% 9% 2	1884
	21st to end	Day	45% 7% 13% 20% 11% 4	1730
March	1st to 10th	Day	55% 6% 9% 12% 13% 5%	4756
	11th to 20th	Day	49% 8% 15% 17% 9% 1	5090
	21st to end	Day	57% 4 7% 15% 14% 2	5587
April	1st to 10th	Day	50% 6% 11% 16% 15% 3	2447
	11th to 20th	Day	46% 7% 10% 22% 13% 3	2702
	21st to end	Day	46% 6% 10% 18% 16% 3	2730
May	1st to 10th	Day	58% 7% 13% 16% 6% 1	7651
	11th to 20th	Day	47% 7% 15% 21% 8% 2	7647
	21st to end	Day	48% 8% 12% 18% 13% 1	9336
June	1st to 10th	Day	52% 6% 12% 19% 10% 1	3150
	11th to 20th	Day	49% 6% 11% 18% 14% 2	3150
	21st to end	Day	57% 6% 10% 16% 9% 2	3150
July	1st to 10th	Day	59% 6% 12% 15% 8%	6895
	11th to 20th	Day	57% 7% 11% 17% 8% 1	6415
	21st to end	Day	47% 7% 13% 21% 12% 1	6425
August	1st to 10th	Day	56% 8% 9% 19% 8%	4222
	11th to 20th	Day	51% 7% 16% 17% 9%	4214
	21st to end	Day	35% 7% 11% 26% 20% 1	4675
September	1st to 10th	Day	36% 7% 13% 24% 18% 1	2329
	11th to 20th	Day	37% 6% 10% 26% 19% 3	2200
	21st to end	Day	41% 6% 10% 28% 15% 1	2200
October	1st to 10th	Day	41% 7% 15% 25% 11% 1	3397
	11th to 20th	Day	30% 5% 11% 35% 18%	3240
	21st to end	Day	35% 5% 19% 23% 16% 3	3280
November	1st to 10th	Day	45% 6% 13% 22% 12% 1	1851
	11th to 20th	Day	42% 6% 13% 23% 14% 3	1731
	21st to end	Day	49% 7% 15% 21% 7% 1	1680
December	1st to 10th	Day	44% 5% 16% 22% 12%	2666
	11th to 20th	Day	51% 4 14% 15% 12% 4	2688
	21st to end	Day	48% 8% 12% 19% 11% 3	3553
January	1st to 10th	Night	48% 5% 12% 24% 10% 1	8496
	11th to 20th	Night	55% 6% 11% 18% 9% 1	8280
	21st to end	Night	43% 5% 11% 22% 14% 4	8660
February	1st to 10th	Night	51% 6% 14% 17% 10% 2	2730
	11th to 20th	Night	48% 6% 11% 21% 12% 2	2629
	21st to end	Night	47% 6% 10% 21% 13% 3	2076
March	1st to 10th	Night	57% 5% 8% 12% 13% 5%	5316
	11th to 20th	Night	51% 8% 18% 15% 7% 1	5090
	21st to end	Night	57% 4 6% 17% 14% 1	5587
April	1st to 10th	Night	53% 6% 8% 15% 15% 3	2170
	11th to 20th	Night	51% 5% 10% 19% 13% 1	1868
	21st to end	Night	53% 4 10% 16% 14% 2	1890
May	1st to 10th	Night	58% 5% 12% 15% 9% 1	5265
	11th to 20th	Night	50% 7% 14% 19% 9% 1	5203
	21st to end	Night	50% 7% 12% 20% 10% 1	4914
June	1st to 10th	Night	54% 6% 11% 20% 8% 1	1470
	11th to 20th	Night	52% 6% 9% 20% 11% 2	1470
	21st to end	Night	57% 6% 8% 18% 8% 2	1470
July	1st to 10th	Night	62% 7% 10% 14% 7%	3195
	11th to 20th	Night	59% 7% 10% 15% 9% 1	3517
	21st to end	Night	48% 7% 13% 19% 12% 2	4065
August	1st to 10th	Night	59% 6% 10% 18% 7%	2903
	11th to 20th	Night	53% 7% 14% 19% 7% 1	2899
	21st to end	Night	39% 6% 9% 25% 18% 2	3223
September	1st to 10th	Night	39% 6% 11% 26% 17% 1	2066
	11th to 20th	Night	39% 5% 11% 25% 19% 2	2200
	21st to end	Night	41% 4 10% 27% 17% 1	2200
October	1st to 10th	Night	40% 6% 14% 25% 14% 1	3782
	11th to 20th	Night	33% 5% 12% 27% 22%	3899
	21st to end	Night	40% 5% 10% 28% 14% 2	4508
November	1st to 10th	Night	44% 5% 13% 22% 15% 1	2667
	11th to 20th	Night	46% 6% 12% 21% 14% 2	2888
	21st to end	Night	48% 6% 15% 20% 10% 1	2940
December	1st to 10th	Night	48% 5% 12% 26% 10%	4740
	11th to 20th	Night	47% 5% 14% 19% 13% 2	5742
	21st to end	Night	49% 7% 13% 16% 13% 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	29% 25% 31% 11% 3	220
	11th to 20th	Day	33% 20% 35% 7% 4	220
	21st to end	Day	20% 26% 33% 18% 2	379
February	1st to 10th	Day	25% 26% 30% 15% 3	430
	11th to 20th	Day	24% 31% 31% 11% 2	444
	21st to end	Day	24% 27% 32% 15% 3	446
March	1st to 10th	Day	29% 27% 30% 12% 2	540
	11th to 20th	Day	28% 27% 28% 13% 4	540
	21st to end	Day	32% 25% 27% 11% 3 1	594
April	1st to 10th	Day	34% 25% 31% 7% 2 1	540
	11th to 20th	Day	31% 25% 29% 11% 4 1	532
	21st to end	Day	26% 22% 35% 13% 3 1	540
May	1st to 10th	Day	30% 23% 30% 14% 3	543
	11th to 20th	Day	24% 19% 34% 18% 5% 1	572
	21st to end	Day	26% 19% 31% 17% 7%	845
June	1st to 10th	Day	24% 16% 31% 22% 6%	780
	11th to 20th	Day	25% 15% 31% 21% 8% 1	780
	21st to end	Day	32% 10% 30% 21% 6% 1	780
July	1st to 10th	Day	22% 12% 36% 21% 8% 1	770
	11th to 20th	Day	22% 10% 34% 24% 8% 2	578
	21st to end	Day	17% 13% 37% 25% 7% 1	576
August	1st to 10th	Day	16% 10% 34% 29% 10% 1	526
	11th to 20th	Day	19% 10% 31% 29% 10% 2	519
	21st to end	Day	16% 13% 34% 25% 10% 2	583
September	1st to 10th	Day	15% 12% 36% 28% 8% 1	530
	11th to 20th	Day	20% 15% 29% 23% 10% 4	530
	21st to end	Day	19% 15% 32% 22% 9% 2	530
October	1st to 10th	Day	19% 16% 31% 22% 10% 2	467
	11th to 20th	Day	21% 19% 29% 22% 8% 1	420
	21st to end	Day	25% 17% 35% 18% 5%	462
November	1st to 10th	Day	25% 21% 29% 19% 5% 1	425
	11th to 20th	Day	26% 23% 33% 14% 5%	430
	21st to end	Day	28% 25% 28% 15% 3	430
December	1st to 10th	Day	28% 21% 31% 17% 3	419
	11th to 20th	Day	36% 28% 25% 9% 2	220
	21st to end	Day	33% 25% 25% 14% 2	242
January	1st to 10th	Night	24% 22% 34% 17% 3	889
	11th to 20th	Night	27% 20% 33% 16% 3	840
	21st to end	Night	20% 26% 36% 15% 4	924
February	1st to 10th	Night	25% 23% 34% 15% 3	840
	11th to 20th	Night	24% 27% 32% 16% 2 1	823
	21st to end	Night	24% 19% 37% 17% 3	692
March	1st to 10th	Night	25% 21% 36% 17% 2	840
	11th to 20th	Night	26% 20% 30% 20% 4	840
	21st to end	Night	25% 19% 34% 17% 5% 1	924
April	1st to 10th	Night	30% 20% 33% 14% 3	801
	11th to 20th	Night	29% 14% 35% 20% 2	624
	21st to end	Night	29% 14% 32% 18% 7%	630
May	1st to 10th	Night	28% 12% 31% 24% 5%	630
	11th to 20th	Night	31% 10% 34% 21% 4 1	622
	21st to end	Night	23% 12% 35% 22% 7% 1	604
June	1st to 10th	Night	28% 6% 31% 27% 7% 1	420
	11th to 20th	Night	25% 7% 31% 29% 6% 1	420
	21st to end	Night	32% 5% 23% 35% 6%	420
July	1st to 10th	Night	23% 6% 28% 34% 8%	410
	11th to 20th	Night	25% 4 25% 36% 9% 1	398
	21st to end	Night	24% 7% 28% 31% 10%	548
August	1st to 10th	Night	20% 6% 29% 35% 9%	598
	11th to 20th	Night	23% 5% 26% 34% 10% 1	592
	21st to end	Night	18% 5% 29% 35% 12% 1	660
September	1st to 10th	Night	20% 5% 34% 30% 11% 1	711
	11th to 20th	Night	19% 8% 28% 29% 14% 2	800
	21st to end	Night	21% 10% 31% 26% 11% 2	800
October	1st to 10th	Night	23% 9% 28% 28% 11% 1	800
	11th to 20th	Night	23% 14% 29% 23% 10% 1	800
	21st to end	Night	27% 17% 30% 21% 5%	880
November	1st to 10th	Night	25% 16% 30% 22% 6% 1	820
	11th to 20th	Night	25% 20% 30% 18% 7% 1	923
	21st to end	Night	27% 21% 29% 17% 5% 1	950
December	1st to 10th	Night	32% 17% 32% 16% 3	950
	11th to 20th	Night	30% 25% 29% 13% 3	950
	21st to end	Night	28% 24% 30% 15% 3	1045

Page generated at 2026-07-13 03:14:46. Version ac07

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