Cabot Head
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cabot Head clear sky chart from 2005-11-06 to 2024-11-05.

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	14% 11% 4 9% 5% 4 4 3 5% 6% 34%	101537
	Night	14% 13% 5% 11% 6% 5% 4 3 5% 6% 28%	97568
Transparency	Day	48% 7% 13% 20% 11% 1	105068
	Night	56% 7% 11% 17% 9% 1	102125
Seeing	Day	17% 6% 19% 30% 21% 6%	15244
	Night	21% 9% 25% 27% 15% 3	24437

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% 22% 13% 16% 8% 5% 4 2 2 4 7%	2208
	11th to 20th	Day	12% 21% 10% 26% 11% 6% 4 3 2 2 4	2526
	21st to end	Day	19% 21% 10% 14% 7% 6% 5% 3 4 3 8%	3093
February	1st to 10th	Day	13% 19% 7% 16% 10% 5% 4 3 3 4 16%	1710
	11th to 20th	Day	10% 16% 7% 14% 8% 7% 5% 3 5% 5% 19%	1663
	21st to end	Day	12% 18% 5% 12% 7% 5% 6% 3 4 5% 22%	1532
March	1st to 10th	Day	15% 14% 4 9% 5% 4 4 3 5% 6% 31%	3304
	11th to 20th	Day	10% 14% 7% 12% 7% 5% 4 3 4 5% 27%	3480
	21st to end	Day	14% 12% 5% 9% 5% 5% 5% 4 4 6% 32%	3815
April	1st to 10th	Day	17% 13% 3 9% 5% 4 4 4 5% 5% 32%	2205
	11th to 20th	Day	18% 10% 2 6% 4 4 3 3 5% 5% 40%	2442
	21st to end	Day	19% 10% 3 6% 4 3 4 3 5% 7% 37%	2470
May	1st to 10th	Day	16% 7% 3 6% 5% 3 4 3 5% 7% 42%	4108
	11th to 20th	Day	12% 7% 2 6% 3 4 4 4 5% 8% 44%	4270
	21st to end	Day	14% 5% 2 5% 4 4 4 3 4 7% 48%	4859
June	1st to 10th	Day	13% 6% 2 5% 5% 4 6% 4 6% 7% 41%	2850
	11th to 20th	Day	9% 6% 2 6% 4 4 4 4 6% 8% 45%	2850
	21st to end	Day	13% 6% 2 6% 4 4 4 4 5% 8% 44%	2850
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 3 6% 7% 42%	4760
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 6% 8% 53%	4702
	21st to end	Day	9% 5% 2 4 4 3 4 3 6% 7% 54%	4539
August	1st to 10th	Day	11% 5% 2 6% 3 4 5% 4 7% 9% 45%	4104
	11th to 20th	Day	15% 6% 2 5% 3 4 4 4 6% 9% 43%	4044
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 8% 47%	4532
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 44%	2247
	11th to 20th	Day	12% 4 2 6% 4 4 5% 4 5% 8% 46%	2090
	21st to end	Day	18% 7% 2 8% 4 4 5% 3 6% 7% 36%	2090
October	1st to 10th	Day	17% 10% 3 7% 5% 4 4 3 5% 7% 34%	1933
	11th to 20th	Day	22% 14% 3 9% 5% 5% 4 3 5% 6% 23%	1900
	21st to end	Day	24% 16% 4 10% 4 4 4 4 4 6% 19%	1990
November	1st to 10th	Day	16% 18% 5% 9% 4 5% 5% 4 5% 6% 23%	1661
	11th to 20th	Day	16% 17% 5% 12% 7% 7% 5% 4 6% 5% 18%	1520
	21st to end	Day	20% 22% 6% 12% 6% 6% 6% 3 5% 3 11%	1520
December	1st to 10th	Day	16% 26% 7% 17% 7% 5% 4 3 4 3 8%	1520
	11th to 20th	Day	19% 21% 7% 19% 6% 5% 3 3 4 3 10%	1719
	21st to end	Day	26% 24% 6% 19% 5% 4 3 2 3 3 5%	2431
January	1st to 10th	Night	16% 21% 8% 19% 8% 5% 4 3 4 3 7%	4748
	11th to 20th	Night	13% 17% 8% 22% 12% 7% 5% 3 4 3 6%	4440
	21st to end	Night	16% 18% 9% 18% 9% 6% 5% 3 3 4 10%	4563
February	1st to 10th	Night	11% 19% 6% 15% 9% 5% 4 4 5% 5% 16%	2470
	11th to 20th	Night	12% 16% 6% 13% 7% 6% 5% 4 5% 4 22%	2403
	21st to end	Night	14% 14% 6% 11% 7% 5% 5% 3 6% 5% 24%	1919
March	1st to 10th	Night	12% 11% 4 9% 5% 5% 4 3 4 6% 38%	3535
	11th to 20th	Night	9% 13% 5% 9% 5% 4 5% 3 5% 7% 36%	3479
	21st to end	Night	12% 10% 4 10% 6% 5% 5% 4 6% 6% 32%	3817
April	1st to 10th	Night	20% 11% 3 7% 5% 4 4 3 5% 5% 33%	1990
	11th to 20th	Night	18% 8% 3 6% 3 5% 4 3 5% 7% 37%	1687
	21st to end	Night	20% 9% 3 7% 6% 4 4 4 5% 6% 32%	1710
May	1st to 10th	Night	14% 7% 3 7% 4 4 5% 4 5% 7% 39%	2833
	11th to 20th	Night	11% 6% 3 7% 5% 5% 4 4 5% 9% 40%	2623
	21st to end	Night	12% 7% 3 6% 4 5% 5% 3 5% 7% 44%	2713
June	1st to 10th	Night	12% 8% 3 6% 6% 5% 5% 3 5% 9% 39%	1330
	11th to 20th	Night	9% 6% 2 6% 5% 5% 4 5% 6% 7% 45%	1330
	21st to end	Night	11% 7% 2 6% 5% 5% 6% 4 7% 7% 42%	1330
July	1st to 10th	Night	10% 7% 3 6% 4 4 3 3 5% 8% 48%	2210
	11th to 20th	Night	10% 4 2 6% 4 4 4 3 6% 7% 50%	2264
	21st to end	Night	7% 6% 3 5% 4 3 4 4 5% 7% 52%	3016
August	1st to 10th	Night	10% 7% 2 6% 4 4 4 4 6% 8% 45%	2825
	11th to 20th	Night	13% 6% 3 6% 5% 4 4 4 5% 9% 42%	2785
	21st to end	Night	10% 5% 2 6% 5% 3 5% 4 6% 7% 47%	3124
September	1st to 10th	Night	10% 5% 2 6% 5% 4 4 4 5% 7% 47%	1908
	11th to 20th	Night	12% 5% 1 5% 4 4 4 4 6% 7% 48%	2090
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 7% 38%	2090
October	1st to 10th	Night	18% 9% 3 10% 5% 5% 4 4 5% 6% 34%	2247
	11th to 20th	Night	22% 12% 4 9% 5% 5% 4 3 5% 6% 25%	2280
	21st to end	Night	23% 14% 5% 9% 6% 5% 5% 3 5% 6% 20%	2605
November	1st to 10th	Night	18% 14% 4 10% 6% 4 5% 4 5% 5% 25%	2515
	11th to 20th	Night	15% 18% 5% 12% 7% 4 5% 4 5% 6% 18%	2660
	21st to end	Night	20% 20% 5% 12% 7% 5% 5% 3 5% 5% 13%	2660
December	1st to 10th	Night	18% 23% 8% 15% 6% 5% 5% 3 5% 3 9%	2660
	11th to 20th	Night	16% 23% 8% 16% 7% 6% 4 3 4 4 10%	3473
	21st to end	Night	24% 20% 8% 17% 7% 5% 4 2 3 3 7%	5236

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	85% 6% 6% 2	2209
	11th to 20th	Day	89% 6% 2 2	2526
	21st to end	Day	78% 8% 8% 4 1	3093
February	1st to 10th	Day	71% 6% 9% 11% 1	1710
	11th to 20th	Day	66% 8% 11% 9% 5%	1672
	21st to end	Day	61% 7% 11% 17% 5%	1532
March	1st to 10th	Day	52% 8% 15% 14% 10% 1	3307
	11th to 20th	Day	55% 7% 13% 19% 5% 1	3480
	21st to end	Day	46% 8% 17% 17% 10% 2	3815
April	1st to 10th	Day	51% 6% 12% 19% 11% 1	2205
	11th to 20th	Day	45% 6% 9% 24% 15% 2	2442
	21st to end	Day	46% 5% 13% 20% 13% 3	2470
May	1st to 10th	Day	40% 8% 13% 20% 18% 2	4120
	11th to 20th	Day	36% 10% 14% 25% 13% 1	4274
	21st to end	Day	36% 8% 13% 19% 21% 4	4859
June	1st to 10th	Day	39% 8% 12% 25% 14% 1	2850
	11th to 20th	Day	35% 6% 12% 27% 18% 1	2850
	21st to end	Day	38% 7% 14% 26% 13% 2	2850
July	1st to 10th	Day	39% 8% 16% 23% 13% 1	4686
	11th to 20th	Day	27% 7% 17% 35% 13% 1	4621
	21st to end	Day	28% 7% 12% 31% 20% 1	4395
August	1st to 10th	Day	32% 7% 16% 29% 14% 1	4091
	11th to 20th	Day	36% 8% 18% 27% 11%	4083
	21st to end	Day	31% 7% 16% 34% 11% 1	4531
September	1st to 10th	Day	38% 8% 14% 28% 12% 1	2247
	11th to 20th	Day	34% 7% 17% 29% 12% 1	2090
	21st to end	Day	45% 8% 15% 23% 9%	2090
October	1st to 10th	Day	39% 7% 13% 25% 16%	3206
	11th to 20th	Day	53% 5% 12% 21% 8%	3140
	21st to end	Day	58% 7% 13% 16% 4	3253
November	1st to 10th	Day	61% 7% 13% 14% 5%	1661
	11th to 20th	Day	68% 9% 11% 8% 4	1520
	21st to end	Day	77% 7% 9% 6% 1	1520
December	1st to 10th	Day	83% 6% 6% 3 2	1520
	11th to 20th	Day	81% 8% 6% 5%	1719
	21st to end	Day	86% 7% 5% 2	2431
January	1st to 10th	Night	84% 7% 6% 3	4748
	11th to 20th	Night	85% 7% 4 3 1	4440
	21st to end	Night	78% 9% 7% 5% 1	4563
February	1st to 10th	Night	69% 6% 9% 12% 3	2470
	11th to 20th	Night	65% 7% 10% 13% 5%	2405
	21st to end	Night	59% 9% 11% 13% 7%	1919
March	1st to 10th	Night	46% 7% 16% 18% 11% 1	3545
	11th to 20th	Night	46% 8% 13% 22% 10% 2	3480
	21st to end	Night	48% 8% 13% 19% 10% 2	3817
April	1st to 10th	Night	51% 5% 10% 21% 11% 2	1990
	11th to 20th	Night	46% 6% 7% 22% 17% 2	1687
	21st to end	Night	52% 6% 9% 15% 15% 3	1710
May	1st to 10th	Night	41% 8% 12% 20% 16% 2	2840
	11th to 20th	Night	39% 9% 10% 21% 18% 2	2624
	21st to end	Night	38% 8% 12% 20% 16% 4	2714
June	1st to 10th	Night	42% 8% 9% 21% 18% 3	1330
	11th to 20th	Night	34% 8% 12% 25% 20% 1	1330
	21st to end	Night	39% 7% 14% 24% 13% 2	1330
July	1st to 10th	Night	34% 5% 15% 24% 17% 4	2175
	11th to 20th	Night	31% 7% 10% 37% 14% 1	2222
	21st to end	Night	30% 8% 12% 24% 25% 1	2920
August	1st to 10th	Night	35% 7% 15% 27% 15% 1	2814
	11th to 20th	Night	39% 8% 17% 22% 13% 1	2812
	21st to end	Night	34% 7% 14% 32% 13% 1	3124
September	1st to 10th	Night	35% 8% 13% 28% 14% 1	1908
	11th to 20th	Night	36% 8% 15% 29% 12%	2090
	21st to end	Night	45% 7% 15% 23% 10%	2090
October	1st to 10th	Night	39% 7% 10% 29% 15%	3754
	11th to 20th	Night	52% 6% 14% 20% 8%	3779
	21st to end	Night	56% 8% 15% 16% 5%	4292
November	1st to 10th	Night	60% 8% 10% 17% 4	2515
	11th to 20th	Night	68% 8% 13% 7% 3 1	2660
	21st to end	Night	77% 8% 10% 5% 1	2660
December	1st to 10th	Night	83% 6% 6% 4 1	2660
	11th to 20th	Night	79% 7% 8% 5% 1	3472
	21st to end	Night	85% 5% 7% 2	5236

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	19% 13% 34% 23% 8% 1	180
	11th to 20th	Day	21% 12% 35% 21% 10% 1	268
	21st to end	Day	28% 6% 23% 32% 10% 1	297
February	1st to 10th	Day	23% 10% 33% 27% 7% 1	270
	11th to 20th	Day	15% 10% 36% 33% 5% 1	270
	21st to end	Day	16% 18% 36% 28% 3	225
March	1st to 10th	Day	19% 6% 30% 34% 11% 1	379
	11th to 20th	Day	17% 11% 27% 32% 12% 2	460
	21st to end	Day	23% 6% 25% 33% 11% 2	506
April	1st to 10th	Day	18% 6% 24% 36% 13% 3	460
	11th to 20th	Day	23% 6% 23% 29% 11% 7%	452
	21st to end	Day	24% 5% 21% 32% 17% 2	460
May	1st to 10th	Day	21% 2 15% 36% 22% 3	463
	11th to 20th	Day	17% 2 12% 34% 26% 9%	487
	21st to end	Day	13% 2 10% 35% 31% 10%	538
June	1st to 10th	Day	12% 2 15% 35% 30% 6%	680
	11th to 20th	Day	11% 3 15% 34% 32% 6%	680
	21st to end	Day	16% 3 13% 34% 28% 6%	680
July	1st to 10th	Day	8% 2 9% 39% 34% 8%	671
	11th to 20th	Day	10% 2 14% 31% 34% 8%	668
	21st to end	Day	11% 2 10% 33% 36% 7%	579
August	1st to 10th	Day	15% 3 12% 26% 33% 12%	486
	11th to 20th	Day	14% 1 10% 23% 39% 13%	479
	21st to end	Day	13% 5% 14% 31% 27% 9%	539
September	1st to 10th	Day	15% 4 14% 30% 27% 10%	490
	11th to 20th	Day	12% 4 13% 26% 32% 13%	490
	21st to end	Day	18% 6% 16% 26% 24% 9%	490
October	1st to 10th	Day	22% 7% 22% 25% 17% 7%	490
	11th to 20th	Day	24% 11% 26% 28% 9% 1	490
	21st to end	Day	29% 14% 25% 25% 7% 1	439
November	1st to 10th	Day	23% 10% 28% 28% 10% 1	260
	11th to 20th	Day	22% 15% 32% 23% 7% 1	180
	21st to end	Day	25% 14% 33% 26% 2	180
December	1st to 10th	Day	24% 18% 28% 24% 6%	180
	11th to 20th	Day	27% 17% 33% 17% 6%	180
	21st to end	Day	31% 16% 35% 15% 2 1	198
January	1st to 10th	Night	24% 17% 30% 21% 7% 1	950
	11th to 20th	Night	23% 15% 32% 23% 7% 1	950
	21st to end	Night	21% 8% 32% 28% 10% 1	854
February	1st to 10th	Night	19% 12% 39% 24% 6% 1	760
	11th to 20th	Night	19% 10% 34% 27% 10% 1	743
	21st to end	Night	21% 8% 35% 30% 6% 1	628
March	1st to 10th	Night	16% 7% 34% 32% 9% 1	760
	11th to 20th	Night	16% 8% 35% 29% 10% 2	760
	21st to end	Night	18% 6% 28% 32% 16% 1	836
April	1st to 10th	Night	25% 8% 23% 32% 11% 1	746
	11th to 20th	Night	23% 7% 21% 29% 15% 4	563
	21st to end	Night	24% 6% 22% 29% 16% 3	570
May	1st to 10th	Night	16% 2 18% 38% 23% 3	570
	11th to 20th	Night	16% 3 15% 36% 26% 4	450
	21st to end	Night	16% 2 12% 40% 23% 7%	411
June	1st to 10th	Night	16% 2 14% 41% 21% 6%	380
	11th to 20th	Night	11% 3 16% 39% 27% 4	380
	21st to end	Night	13% 2 12% 38% 30% 4	380
July	1st to 10th	Night	7% 3 10% 44% 30% 6%	370
	11th to 20th	Night	10% 3 12% 35% 32% 8%	396
	21st to end	Night	8% 3 11% 41% 34% 3	624
August	1st to 10th	Night	12% 3 14% 31% 34% 7%	567
	11th to 20th	Night	13% 3 13% 28% 34% 10%	564
	21st to end	Night	16% 3 17% 29% 29% 6%	627
September	1st to 10th	Night	12% 5% 18% 29% 24% 11%	740
	11th to 20th	Night	15% 4 16% 26% 29% 10%	760
	21st to end	Night	21% 6% 17% 25% 23% 8%	760
October	1st to 10th	Night	24% 7% 23% 25% 18% 4	760
	11th to 20th	Night	29% 12% 22% 24% 11% 2	760
	21st to end	Night	34% 11% 26% 22% 6% 1	836
November	1st to 10th	Night	27% 13% 25% 23% 11% 1	760
	11th to 20th	Night	25% 18% 30% 19% 9%	760
	21st to end	Night	31% 14% 28% 21% 6% 1	760
December	1st to 10th	Night	32% 17% 30% 15% 6% 1	760
	11th to 20th	Night	28% 18% 36% 13% 5% 1	897
	21st to end	Night	33% 14% 32% 16% 5%	1045

Page generated at 2024-11-03 02:11:10. Version ac07

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