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 2024-04-10.

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	15% 11% 5% 8% 6% 3 5% 4 5% 6% 32%	82864
	Night	15% 12% 5% 10% 7% 4 5% 4 5% 6% 27%	85931
Transparency	Day	52% 7% 12% 18% 9% 1	82569
	Night	59% 7% 11% 15% 7% 1	85761
Seeing	Day	18% 6% 19% 30% 21% 6%	14366
	Night	21% 9% 25% 27% 15% 3	23810

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% 14% 10% 4 5% 3 2 4 7%	2208
	11th to 20th	Day	12% 21% 10% 22% 15% 5% 4 4 2 2 4	2526
	21st to end	Day	19% 20% 11% 12% 9% 4 5% 4 4 4 8%	3093
February	1st to 10th	Day	13% 18% 8% 14% 11% 4 4 4 3 4 16%	1710
	11th to 20th	Day	10% 15% 9% 13% 9% 5% 6% 5% 5% 5% 19%	1663
	21st to end	Day	13% 17% 6% 11% 8% 4 7% 4 4 5% 22%	1532
March	1st to 10th	Day	16% 13% 4 8% 6% 3 4 4 4 6% 32%	3304
	11th to 20th	Day	10% 14% 8% 11% 8% 3 5% 4 4 5% 28%	3480
	21st to end	Day	14% 11% 5% 8% 6% 4 5% 5% 4 6% 32%	3815
April	1st to 10th	Day	18% 11% 4 8% 6% 3 5% 5% 5% 5% 31%	2194
	11th to 20th	Day	17% 9% 3 6% 4 3 4 4 4 6% 40%	2312
	21st to end	Day	19% 10% 3 5% 4 2 4 4 5% 7% 37%	2340
May	1st to 10th	Day	17% 7% 3 5% 6% 2 4 4 5% 8% 39%	2340
	11th to 20th	Day	15% 7% 3 5% 4 3 3 4 5% 7% 44%	2406
	21st to end	Day	11% 4 2 5% 5% 2 4 4 5% 8% 49%	2733
June	1st to 10th	Day	12% 6% 3 4 5% 4 5% 6% 6% 7% 42%	2700
	11th to 20th	Day	10% 5% 2 5% 5% 4 4 5% 6% 9% 45%	2700
	21st to end	Day	12% 6% 2 5% 5% 3 4 4 5% 8% 45%	2700
July	1st to 10th	Day	8% 4 2 4 4 3 4 4 5% 8% 53%	2700
	11th to 20th	Day	10% 5% 2 4 4 4 5% 4 6% 9% 47%	2670
	21st to end	Day	9% 6% 2 4 5% 2 4 5% 6% 8% 49%	2592
August	1st to 10th	Day	13% 5% 2 4 3 2 4 4 6% 8% 49%	2327
	11th to 20th	Day	10% 4 3 5% 5% 3 4 5% 7% 9% 47%	2303
	21st to end	Day	13% 7% 2 5% 5% 3 4 5% 5% 8% 42%	2574
September	1st to 10th	Day	13% 6% 2 5% 5% 3 4 5% 5% 7% 44%	2129
	11th to 20th	Day	13% 4 2 6% 5% 3 5% 5% 5% 8% 44%	1980
	21st to end	Day	18% 6% 3 7% 5% 3 5% 4 6% 7% 36%	1980
October	1st to 10th	Day	18% 10% 3 6% 6% 3 5% 4 5% 7% 33%	1832
	11th to 20th	Day	23% 14% 4 7% 7% 4 5% 4 5% 6% 22%	1800
	21st to end	Day	25% 16% 5% 9% 5% 3 4 5% 4 5% 19%	1886
November	1st to 10th	Day	17% 17% 5% 8% 6% 4 6% 5% 5% 6% 23%	1625
	11th to 20th	Day	17% 15% 6% 10% 8% 5% 5% 5% 6% 5% 18%	1520
	21st to end	Day	20% 21% 6% 11% 7% 4 7% 5% 5% 3 11%	1520
December	1st to 10th	Day	17% 24% 8% 15% 8% 4 4 4 4 3 8%	1520
	11th to 20th	Day	19% 19% 8% 16% 10% 4 5% 3 3 3 10%	1719
	21st to end	Day	26% 23% 7% 18% 7% 3 3 3 3 3 5%	2431
January	1st to 10th	Night	17% 20% 8% 17% 10% 4 5% 4 4 3 8%	4748
	11th to 20th	Night	14% 16% 8% 18% 16% 5% 5% 5% 4 3 6%	4440
	21st to end	Night	16% 17% 9% 16% 11% 5% 5% 4 3 4 10%	4563
February	1st to 10th	Night	11% 17% 7% 13% 11% 4 5% 5% 5% 5% 17%	2470
	11th to 20th	Night	12% 14% 7% 13% 8% 5% 5% 5% 5% 5% 22%	2403
	21st to end	Night	14% 13% 7% 10% 8% 4 5% 4 5% 5% 25%	1919
March	1st to 10th	Night	12% 11% 4 8% 6% 4 4 4 4 6% 38%	3535
	11th to 20th	Night	9% 12% 5% 8% 5% 4 4 4 5% 7% 36%	3479
	21st to end	Night	12% 9% 5% 9% 7% 4 5% 4 6% 6% 32%	3817
April	1st to 10th	Night	20% 9% 4 6% 6% 3 4 4 5% 6% 32%	1990
	11th to 20th	Night	17% 8% 4 5% 4 4 4 4 5% 7% 39%	1597
	21st to end	Night	20% 9% 3 6% 7% 3 4 4 5% 6% 33%	1620
May	1st to 10th	Night	15% 8% 3 5% 6% 3 6% 5% 5% 8% 37%	1620
	11th to 20th	Night	14% 6% 3 5% 6% 4 4 5% 5% 7% 41%	1487
	21st to end	Night	11% 5% 2 5% 5% 4 5% 5% 5% 8% 46%	1538
June	1st to 10th	Night	12% 7% 2 6% 6% 4 5% 4 5% 8% 40%	1260
	11th to 20th	Night	10% 6% 2 5% 5% 3 5% 6% 6% 8% 45%	1260
	21st to end	Night	10% 7% 3 5% 5% 4 4 6% 7% 7% 43%	1260
July	1st to 10th	Night	7% 4 2 3 4 3 4 4 5% 9% 54%	1260
	11th to 20th	Night	8% 4 2 6% 5% 3 5% 4 7% 9% 47%	1286
	21st to end	Night	7% 5% 2 4 4 2 5% 6% 6% 8% 50%	1726
August	1st to 10th	Night	9% 6% 3 4 3 2 5% 5% 6% 8% 50%	1611
	11th to 20th	Night	9% 4 3 5% 5% 2 4 5% 6% 9% 48%	1598
	21st to end	Night	12% 6% 2 6% 6% 3 4 5% 6% 6% 44%	1782
September	1st to 10th	Night	10% 5% 2 5% 5% 3 4 5% 5% 8% 47%	1807
	11th to 20th	Night	12% 6% 2 4 5% 3 4 5% 6% 7% 46%	1980
	21st to end	Night	17% 8% 3 5% 5% 3 5% 4 5% 7% 38%	1980
October	1st to 10th	Night	19% 9% 3 8% 6% 3 4 5% 5% 6% 33%	2128
	11th to 20th	Night	23% 12% 4 8% 6% 4 5% 4 5% 6% 24%	2160
	21st to end	Night	24% 14% 5% 8% 7% 3 4 4 5% 5% 19%	2467
November	1st to 10th	Night	18% 13% 4 9% 7% 3 5% 5% 4 6% 25%	2451
	11th to 20th	Night	16% 17% 6% 11% 8% 4 5% 5% 5% 6% 19%	2660
	21st to end	Night	21% 18% 6% 11% 8% 4 5% 4 5% 5% 13%	2660
December	1st to 10th	Night	19% 21% 9% 13% 7% 4 5% 4 5% 4 9%	2660
	11th to 20th	Night	16% 21% 9% 15% 9% 4 5% 4 4 4 10%	3473
	21st to end	Night	24% 19% 8% 16% 8% 4 4 3 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	52% 6% 12% 18% 11% 1	2194
	11th to 20th	Day	45% 6% 9% 24% 15% 2	2312
	21st to end	Day	46% 5% 13% 20% 13% 3	2340
May	1st to 10th	Day	42% 5% 11% 23% 14% 4	2340
	11th to 20th	Day	40% 6% 9% 26% 18% 2	2410
	21st to end	Day	33% 7% 17% 24% 16% 3	2733
June	1st to 10th	Day	37% 8% 12% 26% 15% 1	2700
	11th to 20th	Day	35% 6% 12% 27% 18% 1	2700
	21st to end	Day	37% 7% 15% 26% 13% 2	2700
July	1st to 10th	Day	28% 8% 15% 29% 18% 2	2626
	11th to 20th	Day	31% 9% 15% 31% 12% 2	2589
	21st to end	Day	32% 9% 15% 27% 15% 1	2448
August	1st to 10th	Day	31% 7% 18% 28% 14% 1	2314
	11th to 20th	Day	32% 9% 19% 28% 12%	2303
	21st to end	Day	37% 8% 18% 25% 12% 1	2574
September	1st to 10th	Day	38% 8% 14% 27% 12% 1	2129
	11th to 20th	Day	35% 7% 18% 29% 10%	1980
	21st to end	Day	45% 9% 16% 23% 7%	1980
October	1st to 10th	Day	50% 7% 13% 19% 10% 1	1832
	11th to 20th	Day	64% 7% 12% 13% 5%	1800
	21st to end	Day	67% 7% 10% 12% 4	1886
November	1st to 10th	Day	61% 7% 12% 14% 5%	1625
	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	52% 5% 10% 20% 11% 2	1990
	11th to 20th	Night	44% 5% 7% 23% 18% 2	1597
	21st to end	Night	52% 6% 9% 15% 15% 2	1620
May	1st to 10th	Night	44% 7% 12% 20% 14% 3	1620
	11th to 20th	Night	42% 6% 7% 23% 20% 2	1488
	21st to end	Night	35% 7% 15% 22% 16% 4	1539
June	1st to 10th	Night	41% 7% 8% 22% 18% 3	1260
	11th to 20th	Night	34% 8% 12% 25% 20% 1	1260
	21st to end	Night	38% 7% 15% 24% 14% 2	1260
July	1st to 10th	Night	27% 6% 14% 29% 21% 4	1225
	11th to 20th	Night	31% 8% 13% 29% 17% 2	1244
	21st to end	Night	31% 9% 15% 27% 17% 1	1630
August	1st to 10th	Night	31% 8% 19% 26% 14% 2	1600
	11th to 20th	Night	33% 9% 17% 26% 14% 1	1598
	21st to end	Night	39% 7% 15% 25% 12% 2	1782
September	1st to 10th	Night	35% 8% 14% 27% 15% 2	1807
	11th to 20th	Night	38% 8% 15% 29% 10%	1980
	21st to end	Night	46% 7% 15% 24% 8%	1980
October	1st to 10th	Night	54% 7% 9% 20% 10%	2128
	11th to 20th	Night	63% 8% 12% 14% 3	2160
	21st to end	Night	69% 7% 9% 10% 5%	2467
November	1st to 10th	Night	60% 8% 10% 18% 4	2451
	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	19% 6% 23% 36% 12% 3	457
	11th to 20th	Day	22% 6% 22% 30% 12% 8%	412
	21st to end	Day	24% 4 21% 33% 16% 2	420
May	1st to 10th	Day	22% 2 16% 36% 21% 4	423
	11th to 20th	Day	17% 2 12% 35% 25% 9%	447
	21st to end	Day	13% 2 10% 34% 31% 10%	493
June	1st to 10th	Day	12% 2 14% 37% 30% 6%	630
	11th to 20th	Day	11% 3 14% 33% 33% 6%	630
	21st to end	Day	14% 3 12% 35% 30% 6%	630
July	1st to 10th	Day	7% 1 8% 39% 36% 9%	621
	11th to 20th	Day	11% 2 13% 29% 35% 9%	618
	21st to end	Day	11% 2 10% 34% 37% 6%	533
August	1st to 10th	Day	16% 2 9% 26% 34% 13%	446
	11th to 20th	Day	13% 1 9% 23% 41% 14%	439
	21st to end	Day	14% 5% 14% 30% 27% 10%	495
September	1st to 10th	Day	14% 3 14% 30% 27% 11%	450
	11th to 20th	Day	12% 4 14% 28% 31% 10%	450
	21st to end	Day	18% 6% 17% 25% 24% 10%	450
October	1st to 10th	Day	23% 7% 20% 25% 18% 7%	450
	11th to 20th	Day	25% 12% 25% 29% 8% 1	450
	21st to end	Day	30% 13% 24% 24% 7% 1	401
November	1st to 10th	Day	23% 10% 28% 28% 10% 1	248
	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	22% 7% 22% 30% 15% 4	533
	21st to end	Night	25% 6% 21% 30% 16% 3	540
May	1st to 10th	Night	17% 2 18% 37% 23% 4	540
	11th to 20th	Night	17% 3 16% 35% 25% 4	426
	21st to end	Night	15% 2 11% 41% 23% 7%	389
June	1st to 10th	Night	15% 2 14% 43% 20% 6%	360
	11th to 20th	Night	12% 3 15% 39% 28% 4	360
	21st to end	Night	13% 2 11% 38% 31% 4	360
July	1st to 10th	Night	7% 3 9% 44% 30% 7%	350
	11th to 20th	Night	10% 2 12% 34% 33% 9%	374
	21st to end	Night	8% 3 11% 42% 33% 3	591
August	1st to 10th	Night	12% 2 14% 31% 34% 7%	537
	11th to 20th	Night	12% 3 12% 28% 34% 10%	534
	21st to end	Night	17% 3 16% 29% 29% 6%	594
September	1st to 10th	Night	12% 4 18% 30% 24% 11%	701
	11th to 20th	Night	16% 4 17% 27% 27% 9%	720
	21st to end	Night	21% 6% 17% 25% 23% 9%	720
October	1st to 10th	Night	25% 6% 22% 25% 18% 4	720
	11th to 20th	Night	30% 12% 22% 24% 10% 2	720
	21st to end	Night	36% 10% 25% 22% 6% 1	792
November	1st to 10th	Night	27% 13% 25% 23% 11% 1	740
	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 2024-04-07 09:28:12. Version ac07

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