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 2024-11-25.

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% 10% 4 8% 5% 5% 5% 4 6% 7% 31%	101846
	Night	15% 11% 4 8% 5% 4 4 4 5% 7% 32%	97523
Transparency	Day	48% 7% 14% 19% 10% 1	105473
	Night	48% 7% 13% 19% 11% 1	102024
Seeing	Day	18% 11% 28% 24% 14% 5%	15096
	Night	19% 10% 29% 29% 12% 1	24287

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 6% 5% 6% 9% 40%	2839
	21st to end	Day	11% 7% 2 6% 4 4 6% 4 7% 9% 39%	2850
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 39%	4736
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 8% 11% 41%	4217
	21st to end	Day	8% 6% 2 6% 5% 6% 6% 5% 6% 9% 41%	4466
August	1st to 10th	Day	15% 5% 2 6% 5% 5% 5% 4 7% 9% 38%	4104
	11th to 20th	Day	10% 7% 3 8% 5% 6% 5% 5% 7% 11% 33%	4044
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 5% 6% 9% 41%	4478
September	1st to 10th	Day	11% 6% 2 7% 6% 5% 5% 5% 7% 7% 40%	2216
	11th to 20th	Day	11% 6% 2 5% 4 5% 4 4 6% 8% 46%	2090
	21st to end	Day	17% 8% 3 6% 4 5% 5% 4 7% 7% 35%	2090
October	1st to 10th	Day	16% 7% 2 7% 5% 4 5% 4 6% 8% 36%	1947
	11th to 20th	Day	20% 9% 3 9% 4 4 5% 4 5% 7% 29%	1900
	21st to end	Day	23% 11% 4 10% 6% 5% 4 4 5% 6% 23%	2047
November	1st to 10th	Day	15% 11% 3 7% 6% 4 4 4 6% 8% 32%	1762
	11th to 20th	Day	16% 14% 4 8% 4 4 6% 5% 6% 7% 26%	1655
	21st to end	Day	20% 17% 6% 10% 6% 5% 5% 4 5% 6% 17%	1552
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 6% 4 4 5% 5% 8% 9% 43%	1336
	21st to end	Night	10% 5% 2 5% 5% 4 5% 5% 6% 7% 46%	1330
July	1st to 10th	Night	7% 5% 2 4 4 4 3 4 5% 11% 50%	2230
	11th to 20th	Night	9% 5% 2 4 4 3 3 3 5% 10% 52%	2742
	21st to end	Night	6% 4 2 6% 4 5% 5% 5% 7% 9% 48%	3087
August	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 6% 8% 45%	2825
	11th to 20th	Night	10% 8% 2 6% 4 3 4 3 6% 7% 48%	2785
	21st to end	Night	8% 5% 2 6% 4 3 5% 4 6% 9% 48%	3144
September	1st to 10th	Night	8% 7% 3 7% 4 4 4 4 6% 7% 47%	1962
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 5% 7% 53%	2090
	21st to end	Night	16% 7% 2 7% 4 5% 4 3 5% 6% 41%	2090
October	1st to 10th	Night	14% 7% 3 6% 4 5% 4 3 5% 7% 43%	2232
	11th to 20th	Night	20% 9% 3 8% 4 3 4 3 4 7% 35%	2280
	21st to end	Night	21% 11% 4 8% 5% 4 5% 4 5% 6% 28%	2546
November	1st to 10th	Night	15% 8% 3 7% 4 4 4 4 6% 6% 38%	2536
	11th to 20th	Night	16% 13% 4 8% 6% 5% 5% 4 6% 7% 26%	2743
	21st to end	Night	21% 14% 4 8% 5% 5% 5% 4 5% 6% 22%	2723
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% 21% 17% 2	2839
	21st to end	Day	38% 9% 13% 25% 15% 1	2850
July	1st to 10th	Day	39% 5% 14% 25% 14% 3	4662
	11th to 20th	Day	35% 5% 14% 32% 13% 1	4144
	21st to end	Day	36% 7% 16% 20% 19% 1	4324
August	1st to 10th	Day	42% 6% 15% 23% 13% 1	4091
	11th to 20th	Day	43% 6% 16% 26% 8% 1	4083
	21st to end	Day	38% 5% 15% 30% 11% 1	4478
September	1st to 10th	Day	39% 8% 16% 22% 13% 1	2216
	11th to 20th	Day	34% 7% 14% 30% 15%	2090
	21st to end	Day	45% 7% 14% 23% 10% 1	2090
October	1st to 10th	Day	37% 6% 15% 25% 17% 1	3233
	11th to 20th	Day	42% 5% 13% 23% 16% 1	3140
	21st to end	Day	50% 5% 16% 22% 6%	3349
November	1st to 10th	Day	49% 7% 14% 21% 8% 1	1762
	11th to 20th	Day	53% 9% 16% 12% 9% 1	1655
	21st to end	Day	65% 7% 14% 11% 2	1552
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	33% 8% 15% 22% 19% 2	1336
	21st to end	Night	34% 7% 14% 25% 19% 1	1330
July	1st to 10th	Night	31% 4 13% 28% 18% 7%	2195
	11th to 20th	Night	30% 4 14% 31% 19% 2	2692
	21st to end	Night	30% 7% 18% 22% 20% 3	2988
August	1st to 10th	Night	37% 5% 14% 25% 17% 1	2814
	11th to 20th	Night	36% 5% 14% 32% 12% 1	2812
	21st to end	Night	33% 5% 12% 32% 17% 1	3144
September	1st to 10th	Night	35% 7% 15% 25% 16% 2	1962
	11th to 20th	Night	30% 5% 14% 31% 18% 1	2090
	21st to end	Night	44% 6% 14% 23% 13% 1	2090
October	1st to 10th	Night	30% 5% 9% 29% 26% 1	3726
	11th to 20th	Night	44% 3 16% 21% 16% 1	3779
	21st to end	Night	44% 5% 16% 25% 11%	4182
November	1st to 10th	Night	42% 7% 14% 24% 12% 1	2536
	11th to 20th	Night	52% 8% 14% 16% 8% 1	2743
	21st to end	Night	59% 7% 16% 13% 3 1	2723
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% 8% 28% 32% 16% 4	669
	21st to end	Day	12% 9% 28% 32% 15% 4	680
July	1st to 10th	Day	10% 6% 21% 29% 25% 9%	671
	11th to 20th	Day	15% 5% 24% 28% 20% 8%	538
	21st to end	Day	10% 4 20% 32% 25% 10%	532
August	1st to 10th	Day	10% 5% 19% 27% 25% 14%	486
	11th to 20th	Day	13% 3 19% 27% 24% 14%	479
	21st to end	Day	11% 5% 21% 27% 25% 10%	539
September	1st to 10th	Day	12% 4 24% 28% 20% 11%	490
	11th to 20th	Day	9% 3 20% 23% 29% 14%	490
	21st to end	Day	17% 11% 23% 27% 14% 8%	490
October	1st to 10th	Day	20% 8% 27% 22% 17% 6%	490
	11th to 20th	Day	18% 14% 35% 22% 8% 2	490
	21st to end	Day	25% 15% 34% 20% 5% 1	496
November	1st to 10th	Day	21% 18% 34% 16% 9% 2	300
	11th to 20th	Day	25% 20% 31% 16% 6% 2	227
	21st to end	Day	28% 16% 35% 16% 4 1	188
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	12% 3 26% 43% 15%	380
	21st to end	Night	9% 5% 24% 46% 15% 1	380
July	1st to 10th	Night	6% 2 20% 48% 23% 2	377
	11th to 20th	Night	11% 3 17% 41% 26% 2	552
	21st to end	Night	8% 2 17% 47% 24% 2	624
August	1st to 10th	Night	9% 2 13% 43% 29% 3	567
	11th to 20th	Night	9% 2 14% 38% 32% 4	564
	21st to end	Night	11% 3 18% 38% 28% 3	634
September	1st to 10th	Night	9% 6% 21% 35% 23% 5%	760
	11th to 20th	Night	10% 5% 15% 37% 30% 4	760
	21st to end	Night	18% 7% 21% 33% 17% 5%	760
October	1st to 10th	Night	17% 6% 27% 31% 18% 2	760
	11th to 20th	Night	23% 11% 26% 27% 11% 1	760
	21st to end	Night	25% 10% 32% 26% 5%	836
November	1st to 10th	Night	19% 13% 28% 29% 11% 1	780
	11th to 20th	Night	23% 12% 37% 21% 6% 2	800
	21st to end	Night	27% 13% 30% 24% 6%	779
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 2024-11-22 08:02:26. Version ac07

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