Weymouth Pines Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Weymouth Pines Observatory clear sky chart from 2005-11-06 to 2024-06-17.

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	16% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	89556
	Night	16% 11% 4 9% 5% 4 5% 4 5% 6% 31%	89187
Transparency	Day	50% 8% 14% 18% 9% 1	89316
	Night	51% 7% 13% 18% 10% 1	89032
Seeing	Day	18% 11% 28% 24% 14% 5%	14466
	Night	19% 10% 29% 29% 11% 1	23740

By Month

Percentage Cloud Cover SE (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% 20% 7% 12% 5% 6% 4 3 4 4 18%	2508
	11th to 20th	Day	13% 21% 9% 18% 7% 5% 4 4 5% 4 10%	2840
	21st to end	Day	25% 21% 9% 11% 6% 4 3 3 3 3 13%	3124
February	1st to 10th	Day	17% 16% 4 12% 9% 5% 5% 4 5% 5% 18%	1710
	11th to 20th	Day	15% 13% 7% 15% 7% 6% 4 3 5% 5% 20%	1670
	21st to end	Day	17% 16% 5% 12% 5% 5% 4 4 5% 5% 22%	1570
March	1st to 10th	Day	20% 14% 6% 10% 5% 4 4 3 4 5% 27%	3340
	11th to 20th	Day	13% 14% 5% 10% 6% 4 4 4 5% 7% 29%	3480
	21st to end	Day	18% 12% 4 9% 5% 5% 4 3 5% 5% 31%	3815
April	1st to 10th	Day	16% 13% 4 8% 5% 5% 4 3 5% 7% 29%	2152
	11th to 20th	Day	19% 10% 3 6% 5% 5% 3 4 5% 8% 32%	2432
	21st to end	Day	20% 9% 4 8% 5% 4 4 3 5% 6% 33%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 4 6% 8% 33%	4082
	11th to 20th	Day	16% 9% 3 7% 4 5% 4 4 7% 9% 32%	4081
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 5% 8% 45%	4792
June	1st to 10th	Day	12% 5% 2 7% 6% 5% 5% 4 7% 8% 38%	2660
	11th to 20th	Day	11% 6% 3 6% 5% 4 5% 5% 6% 9% 40%	2783
	21st to end	Day	11% 7% 2 5% 4 4 5% 4 7% 9% 40%	2700
July	1st to 10th	Day	9% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	2690
	11th to 20th	Day	11% 5% 2 7% 5% 4 6% 4 7% 11% 38%	2395
	21st to end	Day	9% 7% 2 6% 5% 5% 6% 5% 6% 10% 38%	2547
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 6% 4 8% 10% 39%	2327
	11th to 20th	Day	10% 6% 3 8% 5% 6% 5% 5% 7% 10% 35%	2303
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 6% 9% 41%	2548
September	1st to 10th	Day	11% 6% 2 7% 6% 5% 5% 5% 7% 7% 39%	2100
	11th to 20th	Day	11% 6% 2 5% 4 5% 4 4 6% 9% 44%	1980
	21st to end	Day	17% 7% 3 6% 4 5% 5% 4 7% 7% 37%	1980
October	1st to 10th	Day	17% 8% 3 7% 5% 3 5% 4 6% 8% 35%	1845
	11th to 20th	Day	21% 9% 3 9% 5% 5% 5% 4 6% 7% 27%	1800
	21st to end	Day	24% 11% 4 10% 6% 5% 4 3 4 6% 23%	1940
November	1st to 10th	Day	15% 11% 3 8% 6% 4 4 4 6% 8% 32%	1672
	11th to 20th	Day	16% 14% 4 9% 4 4 6% 5% 6% 7% 27%	1573
	21st to end	Day	20% 16% 6% 10% 5% 5% 5% 4 5% 6% 18%	1520
December	1st to 10th	Day	16% 17% 7% 12% 6% 5% 4 4 6% 6% 18%	1520
	11th to 20th	Day	18% 19% 7% 12% 6% 5% 5% 4 5% 5% 14%	1910
	21st to end	Day	27% 21% 6% 12% 5% 3 4 2 4 5% 9%	2697
January	1st to 10th	Night	17% 18% 7% 13% 6% 5% 4 3 4 5% 17%	4417
	11th to 20th	Night	15% 18% 8% 16% 8% 7% 7% 5% 4 4 10%	4120
	21st to end	Night	25% 16% 7% 14% 5% 4 3 3 4 5% 13%	4532
February	1st to 10th	Night	17% 15% 5% 11% 7% 5% 4 4 5% 6% 20%	2470
	11th to 20th	Night	16% 15% 5% 9% 6% 6% 5% 4 5% 7% 23%	2394
	21st to end	Night	17% 13% 5% 10% 7% 6% 5% 4 5% 5% 24%	1884
March	1st to 10th	Night	17% 12% 4 9% 5% 4 4 3 5% 5% 32%	3512
	11th to 20th	Night	11% 9% 4 8% 6% 4 4 3 6% 8% 35%	3480
	21st to end	Night	16% 11% 4 9% 5% 4 4 3 4 4 37%	3817
April	1st to 10th	Night	18% 11% 3 6% 5% 4 4 4 6% 6% 33%	2027
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 6% 8% 35%	1711
	21st to end	Night	15% 9% 2 7% 5% 5% 5% 4 5% 7% 35%	1710
May	1st to 10th	Night	19% 8% 3 6% 4 3 4 3 5% 7% 38%	2813
	11th to 20th	Night	11% 8% 3 8% 5% 5% 6% 5% 6% 8% 36%	2812
	21st to end	Night	11% 5% 2 4 3 3 5% 3 6% 8% 51%	2746
June	1st to 10th	Night	13% 5% 2 5% 3 4 5% 4 6% 9% 43%	1520
	11th to 20th	Night	9% 6% 2 5% 4 3 5% 5% 8% 9% 43%	1315
	21st to end	Night	10% 5% 2 5% 4 4 5% 5% 6% 7% 47%	1260
July	1st to 10th	Night	6% 4 2 5% 4 4 3 3 5% 9% 55%	1266
	11th to 20th	Night	9% 6% 2 4 4 4 4 3 6% 10% 49%	1561
	21st to end	Night	7% 4 2 6% 4 5% 4 5% 7% 9% 47%	1771
August	1st to 10th	Night	7% 5% 3 7% 4 5% 5% 4 7% 8% 47%	1611
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 7% 9% 49%	1598
	21st to end	Night	8% 5% 2 4 4 4 5% 4 5% 9% 49%	1788
September	1st to 10th	Night	8% 7% 3 7% 4 4 4 4 6% 7% 46%	1858
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 5% 7% 51%	1980
	21st to end	Night	16% 6% 2 6% 4 5% 4 3 5% 7% 42%	1980
October	1st to 10th	Night	14% 7% 3 7% 4 5% 4 3 5% 7% 41%	2114
	11th to 20th	Night	20% 9% 3 8% 5% 3 4 3 5% 7% 34%	2160
	21st to end	Night	22% 11% 4 8% 5% 4 5% 4 5% 6% 26%	2412
November	1st to 10th	Night	15% 8% 3 7% 4 4 4 4 6% 7% 39%	2406
	11th to 20th	Night	16% 13% 4 8% 6% 5% 5% 4 6% 8% 27%	2605
	21st to end	Night	21% 14% 4 8% 5% 5% 5% 4 5% 7% 22%	2660
December	1st to 10th	Night	20% 16% 5% 10% 5% 5% 5% 4 5% 7% 18%	2660
	11th to 20th	Night	15% 20% 6% 10% 5% 5% 5% 4 4 6% 21%	3285
	21st to end	Night	26% 21% 6% 11% 5% 4 4 2 4 4 12%	4932

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	68% 8% 11% 10% 3	2509
	11th to 20th	Day	75% 10% 8% 4 2	2840
	21st to end	Day	76% 6% 9% 6% 2	3124
February	1st to 10th	Day	67% 6% 11% 11% 4 1	1710
	11th to 20th	Day	65% 6% 10% 13% 6%	1679
	21st to end	Day	62% 8% 12% 12% 6% 1	1570
March	1st to 10th	Day	59% 6% 11% 19% 4	3340
	11th to 20th	Day	52% 8% 16% 17% 6% 1	3480
	21st to end	Day	52% 7% 12% 17% 10% 1	3815
April	1st to 10th	Day	53% 6% 12% 19% 10% 1	2152
	11th to 20th	Day	49% 7% 13% 18% 12% 1	2432
	21st to end	Day	50% 7% 13% 16% 12% 2	2470
May	1st to 10th	Day	45% 8% 15% 19% 10% 2	4120
	11th to 20th	Day	46% 10% 18% 18% 8% 1	4085
	21st to end	Day	35% 8% 13% 19% 19% 5%	4806
June	1st to 10th	Day	40% 8% 15% 24% 12% 2	2660
	11th to 20th	Day	37% 10% 14% 22% 17% 2	2783
	21st to end	Day	37% 9% 13% 25% 15% 1	2700
July	1st to 10th	Day	33% 8% 13% 25% 18% 3	2616
	11th to 20th	Day	36% 7% 17% 25% 14% 1	2322
	21st to end	Day	36% 10% 16% 22% 14% 2	2405
August	1st to 10th	Day	36% 10% 17% 26% 10% 1	2314
	11th to 20th	Day	41% 9% 17% 22% 10% 1	2303
	21st to end	Day	38% 8% 15% 25% 13% 1	2548
September	1st to 10th	Day	40% 9% 17% 21% 12% 1	2100
	11th to 20th	Day	35% 7% 15% 30% 14%	1980
	21st to end	Day	44% 7% 14% 23% 10% 1	1980
October	1st to 10th	Day	44% 8% 14% 20% 12% 1	1845
	11th to 20th	Day	53% 8% 15% 16% 8% 1	1800
	21st to end	Day	61% 7% 12% 13% 6%	1940
November	1st to 10th	Day	49% 8% 14% 20% 7% 2	1672
	11th to 20th	Day	53% 9% 17% 12% 8% 1	1573
	21st to end	Day	64% 8% 14% 12% 2	1520
December	1st to 10th	Day	65% 8% 13% 11% 3	1520
	11th to 20th	Day	68% 9% 12% 9% 2	1906
	21st to end	Day	78% 7% 10% 4 1	2697
January	1st to 10th	Night	65% 9% 13% 10% 3	4417
	11th to 20th	Night	73% 10% 10% 5% 2	4120
	21st to end	Night	70% 8% 11% 8% 2	4532
February	1st to 10th	Night	62% 9% 11% 13% 5%	2470
	11th to 20th	Night	58% 6% 14% 16% 6%	2396
	21st to end	Night	59% 7% 12% 15% 6%	1884
March	1st to 10th	Night	52% 7% 15% 20% 6%	3512
	11th to 20th	Night	41% 9% 18% 20% 11% 1	3480
	21st to end	Night	47% 7% 12% 20% 13% 2	3817
April	1st to 10th	Night	49% 8% 11% 19% 13% 2	2027
	11th to 20th	Night	46% 6% 11% 19% 16% 2	1711
	21st to end	Night	46% 6% 12% 17% 15% 3	1710
May	1st to 10th	Night	45% 6% 12% 18% 15% 5%	2840
	11th to 20th	Night	43% 9% 15% 21% 9% 2	2813
	21st to end	Night	30% 9% 13% 22% 22% 4	2753
June	1st to 10th	Night	36% 7% 12% 27% 15% 3	1520
	11th to 20th	Night	32% 9% 16% 23% 19% 2	1315
	21st to end	Night	33% 8% 14% 25% 19% 1	1260
July	1st to 10th	Night	28% 6% 10% 30% 22% 5%	1231
	11th to 20th	Night	31% 7% 13% 28% 17% 3	1511
	21st to end	Night	30% 10% 17% 23% 17% 3	1672
August	1st to 10th	Night	31% 9% 15% 30% 14% 1	1600
	11th to 20th	Night	31% 7% 16% 31% 14% 2	1598
	21st to end	Night	30% 8% 14% 29% 17% 2	1788
September	1st to 10th	Night	35% 7% 16% 24% 15% 2	1858
	11th to 20th	Night	31% 5% 15% 31% 17% 1	1980
	21st to end	Night	42% 6% 15% 23% 13% 1	1980
October	1st to 10th	Night	41% 7% 13% 22% 16% 1	2114
	11th to 20th	Night	50% 5% 14% 20% 10% 1	2160
	21st to end	Night	57% 7% 11% 16% 9% 1	2412
November	1st to 10th	Night	41% 7% 15% 24% 12% 1	2406
	11th to 20th	Night	51% 8% 15% 17% 8% 1	2605
	21st to end	Night	59% 8% 17% 13% 3 1	2660
December	1st to 10th	Night	64% 7% 16% 10% 3	2660
	11th to 20th	Night	63% 8% 14% 11% 4	3288
	21st to end	Night	75% 7% 11% 6% 1	4932

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	21% 22% 31% 19% 6% 1	245
	11th to 20th	Day	18% 20% 43% 13% 4 1	270
	21st to end	Day	28% 14% 35% 19% 4	297
February	1st to 10th	Day	25% 20% 37% 14% 4	270
	11th to 20th	Day	25% 22% 37% 15% 1	270
	21st to end	Day	24% 28% 36% 11% 1	225
March	1st to 10th	Day	23% 15% 39% 17% 6% 1	399
	11th to 20th	Day	20% 17% 33% 24% 5% 1	460
	21st to end	Day	28% 14% 31% 20% 6% 1	506
April	1st to 10th	Day	19% 17% 33% 22% 8% 1	460
	11th to 20th	Day	26% 15% 28% 19% 9% 4	452
	21st to end	Day	22% 14% 30% 23% 8% 2	460
May	1st to 10th	Day	22% 12% 27% 25% 10% 3	463
	11th to 20th	Day	17% 9% 26% 25% 17% 6%	487
	21st to end	Day	12% 8% 26% 28% 19% 8%	529
June	1st to 10th	Day	13% 6% 33% 29% 15% 4	490
	11th to 20th	Day	12% 9% 27% 32% 16% 4	651
	21st to end	Day	12% 8% 27% 33% 16% 4	630
July	1st to 10th	Day	9% 6% 20% 30% 26% 10%	621
	11th to 20th	Day	15% 5% 22% 30% 20% 8%	495
	21st to end	Day	10% 4 21% 32% 24% 9%	488
August	1st to 10th	Day	9% 4 18% 28% 26% 15%	446
	11th to 20th	Day	13% 2 17% 27% 26% 15%	439
	21st to end	Day	12% 5% 20% 26% 25% 11%	495
September	1st to 10th	Day	12% 4 23% 29% 20% 12%	450
	11th to 20th	Day	10% 3 22% 24% 28% 14%	450
	21st to end	Day	16% 11% 22% 26% 15% 9%	450
October	1st to 10th	Day	20% 8% 26% 22% 18% 6%	450
	11th to 20th	Day	19% 15% 36% 22% 7% 1	450
	21st to end	Day	26% 14% 35% 19% 5% 1	455
November	1st to 10th	Day	21% 16% 34% 17% 10% 3	270
	11th to 20th	Day	25% 20% 30% 16% 6% 2	205
	21st to end	Day	27% 17% 36% 17% 3	180
December	1st to 10th	Day	24% 19% 33% 17% 6% 1	180
	11th to 20th	Day	26% 23% 30% 16% 5%	180
	21st to end	Day	30% 19% 32% 16% 2 1	198
January	1st to 10th	Night	23% 17% 37% 16% 5% 1	886
	11th to 20th	Night	29% 16% 31% 20% 4	760
	21st to end	Night	22% 11% 36% 25% 6%	836
February	1st to 10th	Night	24% 14% 36% 23% 3	760
	11th to 20th	Night	23% 15% 32% 26% 5%	743
	21st to end	Night	24% 14% 38% 21% 3	628
March	1st to 10th	Night	19% 12% 37% 27% 6%	760
	11th to 20th	Night	18% 14% 36% 24% 7% 1	760
	21st to end	Night	23% 12% 29% 27% 8% 1	836
April	1st to 10th	Night	21% 14% 33% 26% 5%	760
	11th to 20th	Night	22% 11% 33% 25% 9% 1	587
	21st to end	Night	19% 9% 35% 30% 8% 1	570
May	1st to 10th	Night	20% 7% 28% 32% 12% 1	570
	11th to 20th	Night	14% 5% 27% 41% 12% 2	561
	21st to end	Night	11% 4 28% 40% 17% 1	426
June	1st to 10th	Night	14% 4 29% 40% 13% 1	380
	11th to 20th	Night	13% 3 26% 42% 16%	374
	21st to end	Night	9% 4 24% 47% 15% 1	360
July	1st to 10th	Night	6% 2 19% 48% 23% 2	356
	11th to 20th	Night	11% 2 17% 41% 26% 2	522
	21st to end	Night	9% 3 17% 47% 23% 2	591
August	1st to 10th	Night	9% 1 12% 45% 30% 4	537
	11th to 20th	Night	8% 2 14% 38% 33% 5%	534
	21st to end	Night	11% 3 18% 37% 28% 3	600
September	1st to 10th	Night	10% 5% 20% 36% 23% 6%	720
	11th to 20th	Night	11% 5% 16% 36% 28% 4	720
	21st to end	Night	17% 7% 22% 32% 18% 5%	720
October	1st to 10th	Night	17% 6% 26% 31% 18% 2	720
	11th to 20th	Night	24% 11% 27% 27% 10% 1	720
	21st to end	Night	27% 10% 32% 26% 4	792
November	1st to 10th	Night	18% 12% 27% 30% 11% 1	740
	11th to 20th	Night	22% 11% 38% 21% 6% 2	760
	21st to end	Night	27% 13% 30% 24% 6%	760
December	1st to 10th	Night	29% 14% 33% 18% 5%	760
	11th to 20th	Night	23% 17% 38% 18% 3	760
	21st to end	Night	28% 13% 36% 21% 3	871

Page generated at 2024-06-14 13:06:10. Version ac07

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