Metacom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Metacom Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	17% 6% 3 5% 5% 3 4 4 5% 7% 41%	74816
	Night	18% 7% 3 5% 4 3 4 4 5% 6% 40%	74904
Transparency	Day	42% 7% 12% 21% 15% 3	74522
	Night	44% 6% 12% 21% 15% 2	74732
Seeing	Day	23% 19% 33% 18% 6% 2	14010
	Night	22% 16% 33% 22% 6% 1	23037

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% 8% 3 5% 4 2 5% 4 4 6% 44%	1517
	11th to 20th	Day	20% 7% 2 6% 4 2 3 5% 5% 6% 39%	1456
	21st to end	Day	15% 7% 3 5% 4 3 4 4 5% 7% 45%	1584
February	1st to 10th	Day	21% 7% 2 5% 4 3 5% 5% 5% 6% 37%	1724
	11th to 20th	Day	14% 8% 3 5% 5% 3 4 5% 3 7% 42%	1748
	21st to end	Day	20% 9% 2 5% 5% 3 5% 4 5% 5% 37%	1480
March	1st to 10th	Day	17% 7% 3 4 4 2 4 4 6% 7% 41%	1797
	11th to 20th	Day	17% 7% 3 4 4 2 5% 4 6% 7% 40%	1898
	21st to end	Day	19% 8% 3 6% 5% 3 3 4 4 5% 40%	2288
April	1st to 10th	Day	20% 7% 3 4 4 3 3 5% 5% 7% 38%	2160
	11th to 20th	Day	18% 6% 3 5% 4 3 4 4 5% 7% 40%	2138
	21st to end	Day	21% 7% 3 5% 5% 3 4 4 4 6% 37%	2340
May	1st to 10th	Day	25% 8% 4 5% 4 2 4 3 5% 6% 33%	2340
	11th to 20th	Day	19% 6% 2 5% 5% 3 3 4 4 7% 41%	2301
	21st to end	Day	15% 6% 2 4 5% 3 4 4 5% 8% 43%	2722
June	1st to 10th	Day	20% 6% 3 5% 5% 3 5% 5% 7% 9% 34%	2520
	11th to 20th	Day	16% 5% 3 5% 6% 3 5% 5% 6% 8% 37%	2520
	21st to end	Day	15% 6% 2 4 5% 3 5% 6% 6% 9% 39%	2520
July	1st to 10th	Day	12% 5% 3 6% 5% 3 5% 5% 7% 8% 41%	2520
	11th to 20th	Day	14% 6% 3 5% 6% 3 4 5% 7% 10% 38%	2520
	21st to end	Day	12% 5% 3 5% 5% 4 6% 6% 7% 9% 39%	2744
August	1st to 10th	Day	12% 6% 2 5% 5% 4 5% 6% 7% 9% 40%	2327
	11th to 20th	Day	13% 5% 2 5% 6% 4 5% 6% 5% 8% 39%	2261
	21st to end	Day	13% 5% 2 5% 5% 4 5% 6% 5% 7% 43%	2376
September	1st to 10th	Day	15% 5% 3 5% 5% 3 4 5% 5% 6% 45%	2150
	11th to 20th	Day	13% 5% 2 4 3 3 4 3 5% 6% 51%	1980
	21st to end	Day	20% 5% 2 5% 4 2 4 4 4 6% 44%	1980
October	1st to 10th	Day	23% 6% 2 4 4 2 3 3 3 5% 43%	1980
	11th to 20th	Day	16% 5% 2 5% 4 2 3 4 5% 7% 47%	1778
	21st to end	Day	20% 5% 2 4 5% 3 4 4 5% 6% 41%	1782
November	1st to 10th	Day	16% 7% 2 5% 4 2 3 4 4 6% 46%	1671
	11th to 20th	Day	18% 5% 2 4 4 2 3 3 5% 7% 45%	1710
	21st to end	Day	17% 7% 3 4 4 3 4 4 4 6% 44%	1710
December	1st to 10th	Day	21% 7% 2 5% 4 3 4 4 4 6% 39%	1596
	11th to 20th	Day	21% 7% 3 4 4 2 3 2 4 5% 45%	1906
	21st to end	Day	21% 10% 4 7% 4 3 4 4 4 5% 35%	2772
January	1st to 10th	Night	17% 8% 2 5% 4 2 4 3 3 6% 44%	2649
	11th to 20th	Night	21% 10% 3 5% 5% 3 4 4 4 6% 35%	2549
	21st to end	Night	15% 10% 3 5% 5% 3 4 4 5% 5% 43%	2772
February	1st to 10th	Night	18% 9% 4 6% 5% 3 4 4 4 5% 40%	2231
	11th to 20th	Night	19% 8% 4 5% 4 3 4 4 5% 6% 39%	2098
	21st to end	Night	19% 9% 3 6% 4 2 5% 4 4 5% 41%	1776
March	1st to 10th	Night	16% 7% 2 5% 4 3 4 5% 5% 7% 42%	2150
	11th to 20th	Night	16% 8% 3 6% 5% 3 5% 5% 4 6% 38%	2060
	21st to end	Night	18% 9% 3 5% 4 3 3 4 4 5% 40%	2066
April	1st to 10th	Night	19% 8% 3 6% 5% 3 5% 4 4 6% 38%	1800
	11th to 20th	Night	20% 6% 2 6% 4 3 5% 4 6% 6% 39%	1771
	21st to end	Night	23% 6% 3 6% 4 3 4 4 4 5% 39%	1620
May	1st to 10th	Night	25% 8% 4 6% 5% 2 4 4 4 6% 31%	1620
	11th to 20th	Night	20% 6% 3 5% 5% 3 4 5% 5% 7% 36%	1593
	21st to end	Night	19% 7% 3 6% 5% 3 5% 4 6% 7% 35%	1567
June	1st to 10th	Night	19% 7% 3 6% 5% 3 4 4 5% 8% 36%	1440
	11th to 20th	Night	19% 5% 3 6% 5% 3 5% 4 5% 8% 37%	1440
	21st to end	Night	18% 7% 2 4 3 3 4 4 6% 10% 39%	1440
July	1st to 10th	Night	14% 6% 3 5% 6% 3 6% 6% 6% 8% 38%	1440
	11th to 20th	Night	15% 7% 2 5% 5% 3 5% 5% 7% 10% 35%	1440
	21st to end	Night	13% 6% 3 6% 5% 4 5% 5% 6% 9% 38%	1574
August	1st to 10th	Night	10% 7% 3 5% 5% 3 4 7% 7% 9% 41%	1594
	11th to 20th	Night	11% 6% 3 6% 5% 5% 6% 6% 6% 9% 38%	1636
	21st to end	Night	14% 5% 2 4 5% 3 3 4 5% 8% 47%	1980
September	1st to 10th	Night	15% 5% 2 6% 5% 4 4 5% 5% 7% 42%	1809
	11th to 20th	Night	15% 6% 2 5% 4 2 3 4 3 6% 51%	1980
	21st to end	Night	19% 6% 3 5% 4 3 4 4 4 5% 43%	1980
October	1st to 10th	Night	22% 6% 3 5% 4 3 3 3 4 6% 41%	1980
	11th to 20th	Night	16% 6% 1 4 4 2 4 4 5% 8% 46%	2177
	21st to end	Night	21% 8% 3 5% 5% 2 3 4 4 6% 38%	2574
November	1st to 10th	Night	16% 5% 3 5% 4 3 4 3 5% 5% 47%	2407
	11th to 20th	Night	18% 7% 2 4 4 2 3 4 4 6% 45%	2470
	21st to end	Night	16% 5% 3 5% 4 2 4 4 5% 7% 46%	2470
December	1st to 10th	Night	22% 7% 3 5% 4 3 4 4 4 5% 40%	2579
	11th to 20th	Night	19% 7% 2 5% 4 3 4 4 4 6% 42%	3288
	21st to end	Night	21% 12% 4 6% 4 3 3 3 4 5% 36%	4884

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	42% 5% 9% 25% 16% 4	1518
	11th to 20th	Day	46% 8% 13% 19% 11% 3	1456
	21st to end	Day	39% 5% 12% 25% 17% 3	1584
February	1st to 10th	Day	48% 6% 13% 16% 14% 3	1724
	11th to 20th	Day	42% 6% 12% 22% 15% 3	1757
	21st to end	Day	49% 4 10% 19% 15% 3	1480
March	1st to 10th	Day	42% 6% 13% 21% 14% 5%	1800
	11th to 20th	Day	41% 7% 12% 22% 15% 4	1898
	21st to end	Day	47% 5% 9% 16% 17% 6%	2288
April	1st to 10th	Day	45% 6% 11% 19% 16% 3	2160
	11th to 20th	Day	42% 7% 9% 21% 17% 3	2138
	21st to end	Day	47% 6% 10% 17% 15% 4	2340
May	1st to 10th	Day	51% 6% 10% 18% 13% 2	2340
	11th to 20th	Day	43% 7% 12% 18% 18% 3	2305
	21st to end	Day	39% 9% 15% 22% 14% 2	2722
June	1st to 10th	Day	46% 9% 13% 21% 11% 1	2520
	11th to 20th	Day	44% 8% 12% 20% 14% 2	2520
	21st to end	Day	41% 9% 15% 21% 13% 1	2520
July	1st to 10th	Day	40% 9% 12% 23% 14% 3	2450
	11th to 20th	Day	41% 8% 15% 22% 11% 2	2445
	21st to end	Day	38% 10% 15% 20% 13% 3	2591
August	1st to 10th	Day	39% 10% 17% 21% 12% 1	2314
	11th to 20th	Day	40% 10% 13% 22% 13% 1	2261
	21st to end	Day	38% 9% 13% 21% 18% 2	2376
September	1st to 10th	Day	39% 7% 12% 21% 20% 1	2150
	11th to 20th	Day	35% 5% 11% 22% 24% 3	1980
	21st to end	Day	41% 5% 9% 21% 22% 2	1980
October	1st to 10th	Day	45% 6% 9% 21% 16% 3	1980
	11th to 20th	Day	37% 6% 11% 28% 17% 1	1778
	21st to end	Day	43% 6% 13% 19% 16% 4	1782
November	1st to 10th	Day	41% 5% 13% 21% 18% 2	1671
	11th to 20th	Day	40% 5% 11% 21% 20% 3	1710
	21st to end	Day	42% 5% 13% 26% 12% 3	1710
December	1st to 10th	Day	46% 5% 13% 17% 17% 2	1596
	11th to 20th	Day	43% 5% 14% 16% 16% 6%	1906
	21st to end	Day	50% 6% 12% 21% 10% 1	2772
January	1st to 10th	Night	43% 4 11% 23% 17% 3	2649
	11th to 20th	Night	51% 6% 12% 20% 9% 2	2549
	21st to end	Night	44% 5% 11% 20% 18% 3	2772
February	1st to 10th	Night	47% 5% 13% 21% 13% 2	2231
	11th to 20th	Night	47% 5% 10% 19% 15% 4	2100
	21st to end	Night	45% 5% 9% 23% 15% 3	1776
March	1st to 10th	Night	42% 5% 11% 22% 16% 5%	2160
	11th to 20th	Night	45% 6% 10% 17% 17% 4	2061
	21st to end	Night	47% 4 8% 18% 17% 6%	2066
April	1st to 10th	Night	47% 6% 11% 17% 16% 3	1800
	11th to 20th	Night	44% 7% 9% 19% 18% 3	1771
	21st to end	Night	47% 6% 9% 19% 14% 4	1620
May	1st to 10th	Night	53% 7% 11% 15% 11% 3	1620
	11th to 20th	Night	45% 8% 13% 18% 11% 4	1594
	21st to end	Night	47% 9% 16% 16% 11% 1	1568
June	1st to 10th	Night	46% 8% 12% 20% 13% 1	1440
	11th to 20th	Night	46% 6% 12% 22% 13% 1	1440
	21st to end	Night	40% 9% 16% 22% 12% 1	1440
July	1st to 10th	Night	42% 9% 14% 21% 14% 1	1400
	11th to 20th	Night	41% 9% 16% 24% 9% 1	1392
	21st to end	Night	40% 9% 14% 24% 11% 2	1486
August	1st to 10th	Night	37% 10% 15% 24% 12% 2	1583
	11th to 20th	Night	40% 10% 17% 23% 11%	1636
	21st to end	Night	35% 8% 12% 25% 19% 1	1980
September	1st to 10th	Night	41% 7% 11% 22% 16% 2	1809
	11th to 20th	Night	35% 6% 11% 21% 25% 2	1980
	21st to end	Night	43% 6% 8% 20% 20% 3	1980
October	1st to 10th	Night	46% 5% 12% 20% 13% 4	1980
	11th to 20th	Night	37% 7% 14% 28% 14% 1	2177
	21st to end	Night	47% 6% 11% 19% 14% 2	2574
November	1st to 10th	Night	39% 7% 13% 21% 18% 3	2407
	11th to 20th	Night	41% 4 10% 22% 19% 3	2470
	21st to end	Night	38% 5% 13% 27% 13% 3	2470
December	1st to 10th	Night	47% 5% 13% 20% 15% 1	2579
	11th to 20th	Night	43% 6% 14% 18% 17% 2	3288
	21st to end	Night	49% 7% 10% 23% 11% 1	4884

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	28% 28% 26% 16% 2	180
	11th to 20th	Day	26% 31% 33% 7% 2	164
	21st to end	Day	23% 31% 34% 10% 2 1	176
February	1st to 10th	Day	35% 23% 29% 12% 1	374
	11th to 20th	Day	28% 33% 31% 7% 1	416
	21st to end	Day	30% 25% 32% 10% 3	346
March	1st to 10th	Day	30% 21% 33% 14% 2	420
	11th to 20th	Day	29% 27% 30% 10% 4	420
	21st to end	Day	27% 25% 32% 10% 5% 2	462
April	1st to 10th	Day	33% 23% 27% 10% 6% 1	420
	11th to 20th	Day	25% 26% 32% 12% 3 1	412
	21st to end	Day	28% 24% 30% 14% 2 2	420
May	1st to 10th	Day	34% 24% 27% 12% 2 1	423
	11th to 20th	Day	24% 17% 42% 12% 4	447
	21st to end	Day	19% 16% 34% 22% 6% 1	485
June	1st to 10th	Day	20% 16% 36% 20% 7% 1	450
	11th to 20th	Day	17% 18% 40% 19% 4 1	450
	21st to end	Day	18% 15% 36% 24% 6% 1	450
July	1st to 10th	Day	17% 9% 34% 29% 10% 2	445
	11th to 20th	Day	16% 8% 35% 27% 12% 2	444
	21st to end	Day	14% 11% 39% 27% 8% 1	488
August	1st to 10th	Day	13% 11% 35% 30% 10% 2	446
	11th to 20th	Day	15% 11% 32% 27% 12% 3	439
	21st to end	Day	14% 12% 34% 24% 12% 5%	495
September	1st to 10th	Day	20% 11% 29% 24% 12% 4	450
	11th to 20th	Day	17% 13% 30% 24% 9% 6%	450
	21st to end	Day	25% 12% 32% 20% 6% 4	450
October	1st to 10th	Day	29% 13% 26% 19% 8% 5%	450
	11th to 20th	Day	19% 18% 34% 17% 11% 1	403
	21st to end	Day	26% 20% 27% 17% 7% 2	396
November	1st to 10th	Day	22% 15% 34% 17% 9% 2	365
	11th to 20th	Day	27% 23% 31% 14% 5%	370
	21st to end	Day	25% 22% 31% 15% 7% 1	370
December	1st to 10th	Day	22% 30% 33% 10% 4	256
	11th to 20th	Day	32% 27% 33% 6% 2	180
	21st to end	Day	28% 25% 33% 9% 3 2	198
January	1st to 10th	Night	23% 22% 35% 17% 3	760
	11th to 20th	Night	29% 22% 33% 14% 2	729
	21st to end	Night	21% 24% 34% 17% 3	792
February	1st to 10th	Night	25% 20% 36% 18% 1	720
	11th to 20th	Night	27% 24% 35% 13% 1	703
	21st to end	Night	25% 24% 33% 16% 2	592
March	1st to 10th	Night	24% 20% 37% 16% 3	720
	11th to 20th	Night	22% 23% 36% 17% 3	720
	21st to end	Night	25% 20% 33% 17% 4	792
April	1st to 10th	Night	23% 23% 34% 17% 3	720
	11th to 20th	Night	23% 20% 35% 19% 3	707
	21st to end	Night	25% 17% 37% 18% 3	540
May	1st to 10th	Night	30% 13% 34% 19% 4	540
	11th to 20th	Night	22% 17% 39% 20% 2	532
	21st to end	Night	22% 8% 36% 28% 6%	406
June	1st to 10th	Night	19% 9% 31% 33% 9%	360
	11th to 20th	Night	21% 6% 34% 31% 8%	360
	21st to end	Night	19% 6% 33% 36% 6% 1	360
July	1st to 10th	Night	17% 5% 33% 36% 9%	350
	11th to 20th	Night	16% 5% 30% 39% 10% 1	348
	21st to end	Night	14% 5% 31% 41% 9%	394
August	1st to 10th	Night	13% 5% 37% 37% 8%	520
	11th to 20th	Night	13% 6% 29% 40% 12%	572
	21st to end	Night	15% 6% 26% 36% 16% 2	792
September	1st to 10th	Night	18% 5% 33% 33% 11% 1	720
	11th to 20th	Night	17% 8% 29% 28% 16% 2	720
	21st to end	Night	23% 8% 28% 27% 12% 2	720
October	1st to 10th	Night	25% 12% 26% 24% 11% 2	720
	11th to 20th	Night	20% 11% 34% 22% 11% 1	720
	21st to end	Night	26% 16% 32% 19% 7%	792
November	1st to 10th	Night	18% 14% 34% 22% 10% 1	740
	11th to 20th	Night	24% 20% 33% 17% 6%	760
	21st to end	Night	22% 20% 33% 20% 4 1	760
December	1st to 10th	Night	26% 18% 35% 16% 4	760
	11th to 20th	Night	27% 20% 32% 18% 2 1	760
	21st to end	Night	26% 21% 34% 16% 2	836

Page generated at 2024-01-10 01:25:03. Version ac07

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