Burlington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burlington clear sky chart from 2005-11-06 to 2025-01-22.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	105192
	Night	18% 13% 5% 10% 5% 5% 4 3 5% 5% 27%	104183
Transparency	Day	30% 46% 7% 12% 5%	108678
	Night	35% 45% 6% 9% 5%	108786
Seeing	Day	25% 17% 28% 19% 8% 2	14872
	Night	26% 14% 26% 24% 9% 1	23956

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	14% 16% 7% 14% 8% 6% 5% 4 5% 4 18%	2597
	11th to 20th	Day	15% 15% 7% 15% 9% 5% 5% 4 4 5% 17%	2600
	21st to end	Day	15% 19% 6% 12% 7% 6% 5% 3 4 5% 17%	2780
February	1st to 10th	Day	14% 15% 5% 11% 9% 5% 4 4 5% 5% 21%	1676
	11th to 20th	Day	11% 16% 5% 14% 7% 6% 4 4 5% 5% 23%	1810
	21st to end	Day	15% 15% 5% 10% 7% 5% 5% 4 4 6% 25%	1570
March	1st to 10th	Day	21% 13% 5% 10% 6% 5% 5% 3 4 5% 22%	3116
	11th to 20th	Day	13% 20% 5% 11% 6% 6% 4 3 4 5% 24%	3256
	21st to end	Day	16% 10% 4 11% 4 4 4 3 4 5% 34%	4166
April	1st to 10th	Day	21% 12% 3 8% 5% 4 4 3 4 6% 31%	2280
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 3 4 5% 37%	2254
	21st to end	Day	23% 10% 3 7% 5% 4 4 3 4 6% 32%	2435
May	1st to 10th	Day	22% 9% 3 8% 5% 5% 4 4 5% 6% 28%	4250
	11th to 20th	Day	16% 9% 3 8% 5% 5% 5% 4 6% 9% 31%	4398
	21st to end	Day	12% 6% 2 6% 5% 6% 5% 5% 7% 8% 37%	4837
June	1st to 10th	Day	22% 7% 2 7% 5% 4 5% 5% 7% 8% 29%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 10% 37%	2660
	21st to end	Day	18% 7% 3 7% 5% 5% 5% 6% 6% 7% 30%	2660
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 5% 7% 11% 37%	4440
	11th to 20th	Day	11% 6% 2 7% 4 5% 5% 5% 8% 10% 36%	4440
	21st to end	Day	12% 6% 2 7% 4 4 5% 4 7% 8% 40%	4814
August	1st to 10th	Day	16% 6% 3 8% 5% 4 5% 4 6% 8% 34%	4423
	11th to 20th	Day	14% 7% 3 8% 5% 5% 4 5% 5% 8% 36%	3902
	21st to end	Day	12% 6% 3 6% 4 4 4 4 6% 9% 43%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 46%	2280
	11th to 20th	Day	14% 6% 2 5% 3 4 4 3 5% 6% 49%	2176
	21st to end	Day	14% 7% 2 6% 5% 5% 4 4 5% 8% 39%	2090
October	1st to 10th	Day	21% 9% 3 8% 5% 4 4 4 5% 6% 32%	2004
	11th to 20th	Day	18% 10% 3 7% 5% 5% 4 3 5% 6% 33%	1853
	21st to end	Day	24% 13% 3 8% 4 5% 4 3 4 4 27%	1881
November	1st to 10th	Day	16% 13% 4 8% 5% 5% 4 3 5% 6% 31%	1761
	11th to 20th	Day	18% 14% 3 10% 5% 5% 4 4 6% 5% 27%	1797
	21st to end	Day	19% 16% 5% 9% 5% 4 6% 4 5% 5% 24%	1600
December	1st to 10th	Day	16% 19% 9% 16% 7% 6% 4 4 4 5% 11%	2600
	11th to 20th	Day	19% 14% 5% 10% 4 5% 5% 4 5% 6% 22%	2986
	21st to end	Day	20% 16% 4 11% 6% 5% 6% 4 5% 6% 17%	3960
January	1st to 10th	Night	16% 19% 9% 14% 6% 4 3 3 3 4 18%	4569
	11th to 20th	Night	13% 17% 8% 19% 7% 6% 5% 3 4 4 16%	4580
	21st to end	Night	18% 19% 6% 13% 7% 5% 3 3 4 4 18%	4899
February	1st to 10th	Night	13% 17% 6% 14% 8% 6% 4 4 4 4 20%	2504
	11th to 20th	Night	13% 15% 5% 15% 8% 5% 5% 4 4 5% 22%	2256
	21st to end	Night	15% 16% 5% 11% 6% 5% 4 2 4 4 27%	1884
March	1st to 10th	Night	21% 15% 4 8% 6% 4 3 3 4 5% 27%	3724
	11th to 20th	Night	16% 21% 4 9% 5% 4 4 2 4 4 26%	3685
	21st to end	Night	16% 16% 5% 10% 4 3 3 3 3 3 33%	3466
April	1st to 10th	Night	21% 12% 4 9% 5% 4 4 3 4 5% 29%	1900
	11th to 20th	Night	23% 12% 4 7% 6% 3 3 3 4 4 31%	1875
	21st to end	Night	21% 12% 4 7% 4 4 3 3 4 5% 33%	1743
May	1st to 10th	Night	23% 11% 3 9% 5% 5% 4 3 5% 7% 25%	2720
	11th to 20th	Night	19% 11% 4 9% 5% 5% 4 3 4 5% 32%	2495
	21st to end	Night	14% 7% 2 7% 4 4 5% 4 7% 8% 37%	2738
June	1st to 10th	Night	22% 9% 3 6% 4 4 4 5% 5% 8% 31%	1520
	11th to 20th	Night	16% 6% 2 8% 5% 3 5% 4 6% 8% 37%	1520
	21st to end	Night	19% 7% 3 7% 6% 3 4 4 6% 6% 33%	1520
July	1st to 10th	Night	13% 5% 3 8% 5% 6% 6% 6% 6% 8% 35%	2520
	11th to 20th	Night	14% 5% 2 7% 5% 5% 4 4 6% 8% 39%	2520
	21st to end	Night	12% 7% 3 7% 5% 5% 5% 5% 6% 7% 37%	2739
August	1st to 10th	Night	18% 8% 3 7% 4 4 5% 3 5% 7% 35%	2506
	11th to 20th	Night	15% 8% 3 9% 6% 4 5% 4 5% 7% 36%	2890
	21st to end	Night	13% 6% 3 6% 4 4 4 4 7% 8% 42%	3476
September	1st to 10th	Night	13% 5% 2 7% 5% 4 4 3 6% 7% 44%	1900
	11th to 20th	Night	14% 7% 2 5% 4 3 3 2 5% 6% 48%	2004
	21st to end	Night	16% 6% 2 5% 4 4 5% 4 5% 7% 41%	2090
October	1st to 10th	Night	23% 9% 2 6% 5% 4 5% 3 4 7% 32%	2175
	11th to 20th	Night	22% 9% 3 8% 5% 3 4 3 5% 6% 32%	2327
	21st to end	Night	26% 11% 3 7% 5% 4 5% 3 4 5% 27%	2717
November	1st to 10th	Night	19% 12% 3 7% 5% 4 3 4 6% 5% 31%	2537
	11th to 20th	Night	18% 13% 4 8% 5% 5% 4 3 5% 6% 28%	2600
	21st to end	Night	20% 17% 5% 10% 5% 4 4 3 5% 5% 22%	2800
December	1st to 10th	Night	17% 29% 10% 13% 5% 4 4 2 3 3 10%	4580
	11th to 20th	Night	24% 15% 5% 11% 5% 5% 4 3 4 4 20%	5208
	21st to end	Night	21% 17% 6% 12% 7% 6% 4 3 4 4 16%	6996

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	44% 39% 8% 7% 1	2598
	11th to 20th	Day	45% 39% 8% 6% 2 1	2600
	21st to end	Day	43% 45% 7% 4 2	2780
February	1st to 10th	Day	24% 65% 4 4 2 1	1676
	11th to 20th	Day	24% 64% 3 6% 3	1819
	21st to end	Day	21% 66% 4 5% 4 2	1570
March	1st to 10th	Day	39% 46% 4 6% 4 1	3119
	11th to 20th	Day	41% 42% 6% 5% 6% 1	3256
	21st to end	Day	32% 42% 5% 9% 12% 1	4166
April	1st to 10th	Day	21% 66% 3 7% 3 1	2280
	11th to 20th	Day	19% 66% 2 7% 5% 1	2254
	21st to end	Day	20% 65% 4 6% 5%	2435
May	1st to 10th	Day	36% 45% 5% 12% 2	4264
	11th to 20th	Day	30% 47% 10% 10% 3	4402
	21st to end	Day	24% 44% 9% 17% 6%	4837
June	1st to 10th	Day	18% 66% 3 7% 6%	2660
	11th to 20th	Day	15% 65% 4 9% 5% 1	2660
	21st to end	Day	18% 64% 4 9% 4 1	2660
July	1st to 10th	Day	27% 36% 9% 19% 8%	4370
	11th to 20th	Day	27% 36% 10% 23% 3	4365
	21st to end	Day	28% 37% 7% 22% 6%	4661
August	1st to 10th	Day	32% 38% 10% 14% 5%	4409
	11th to 20th	Day	34% 38% 11% 16% 2	3941
	21st to end	Day	24% 37% 13% 15% 10%	4180
September	1st to 10th	Day	12% 61% 5% 14% 6%	2280
	11th to 20th	Day	14% 60% 6% 13% 6% 1	2176
	21st to end	Day	15% 61% 7% 12% 4 1	2090
October	1st to 10th	Day	27% 36% 7% 23% 6%	3329
	11th to 20th	Day	31% 37% 9% 16% 8%	3056
	21st to end	Day	30% 37% 11% 20% 2	3081
November	1st to 10th	Day	28% 58% 4 7% 2	1761
	11th to 20th	Day	25% 57% 5% 8% 5%	1797
	21st to end	Day	29% 58% 6% 5% 2	1600
December	1st to 10th	Day	55% 36% 5% 3 1	2600
	11th to 20th	Day	47% 32% 5% 12% 3	2986
	21st to end	Day	51% 28% 6% 10% 6%	3960
January	1st to 10th	Night	45% 38% 9% 6% 2	4569
	11th to 20th	Night	46% 40% 7% 4 2	4580
	21st to end	Night	46% 41% 6% 4 2	4899
February	1st to 10th	Night	25% 65% 3 4 2	2504
	11th to 20th	Night	22% 64% 4 6% 4	2258
	21st to end	Night	19% 65% 4 6% 4 1	1884
March	1st to 10th	Night	36% 42% 6% 8% 7% 1	3734
	11th to 20th	Night	38% 41% 6% 7% 7% 1	3686
	21st to end	Night	36% 41% 4 7% 11% 1	3466
April	1st to 10th	Night	21% 65% 3 5% 5%	1900
	11th to 20th	Night	21% 66% 2 6% 5%	1875
	21st to end	Night	21% 65% 3 5% 5% 1	1743
May	1st to 10th	Night	37% 44% 6% 10% 2	2726
	11th to 20th	Night	34% 43% 7% 12% 4	2496
	21st to end	Night	26% 43% 9% 12% 10% 1	2739
June	1st to 10th	Night	19% 66% 3 7% 5% 1	1520
	11th to 20th	Night	15% 66% 5% 7% 5% 1	1520
	21st to end	Night	18% 65% 4 10% 4	1520
July	1st to 10th	Night	31% 36% 9% 15% 8%	2480
	11th to 20th	Night	30% 37% 8% 20% 6%	2472
	21st to end	Night	31% 36% 8% 16% 8%	2651
August	1st to 10th	Night	36% 37% 8% 14% 5%	2496
	11th to 20th	Night	35% 38% 11% 12% 4	2917
	21st to end	Night	26% 37% 10% 16% 10% 1	3476
September	1st to 10th	Night	14% 62% 6% 12% 6% 1	1900
	11th to 20th	Night	14% 61% 6% 13% 6%	2004
	21st to end	Night	13% 61% 6% 12% 7% 1	2090
October	1st to 10th	Night	37% 36% 5% 16% 5%	3630
	11th to 20th	Night	32% 37% 6% 16% 9%	3863
	21st to end	Night	34% 37% 8% 17% 5%	4467
November	1st to 10th	Night	26% 57% 6% 8% 3	2537
	11th to 20th	Night	26% 57% 5% 7% 4	2600
	21st to end	Night	29% 58% 6% 5% 2	2800
December	1st to 10th	Night	56% 36% 4 3	4580
	11th to 20th	Night	50% 33% 5% 7% 6%	5208
	21st to end	Night	53% 28% 4 9% 6%	6996

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	27% 25% 27% 18% 4	200
	11th to 20th	Day	32% 26% 31% 7% 4 1	200
	21st to end	Day	23% 25% 36% 12% 5%	200
February	1st to 10th	Day	33% 33% 25% 8% 2	254
	11th to 20th	Day	27% 28% 34% 9% 2	418
	21st to end	Day	31% 21% 34% 12% 2	382
March	1st to 10th	Day	32% 19% 28% 18% 3	460
	11th to 20th	Day	26% 27% 28% 15% 4 1	460
	21st to end	Day	32% 22% 26% 12% 6% 2	506
April	1st to 10th	Day	35% 18% 25% 15% 6% 1	460
	11th to 20th	Day	31% 25% 20% 15% 7% 2	452
	21st to end	Day	31% 20% 28% 13% 6% 2	460
May	1st to 10th	Day	30% 19% 26% 17% 8% 2	463
	11th to 20th	Day	21% 15% 32% 23% 8% 2	487
	21st to end	Day	19% 18% 33% 21% 8% 1	529
June	1st to 10th	Day	28% 13% 31% 20% 7% 1	490
	11th to 20th	Day	19% 15% 32% 22% 10% 2	490
	21st to end	Day	23% 16% 31% 20% 8% 1	490
July	1st to 10th	Day	17% 10% 29% 30% 12% 3	485
	11th to 20th	Day	14% 9% 34% 28% 12% 2	484
	21st to end	Day	19% 7% 34% 30% 10% 1	532
August	1st to 10th	Day	16% 9% 29% 26% 17% 2	486
	11th to 20th	Day	18% 10% 23% 30% 14% 5%	479
	21st to end	Day	15% 14% 28% 26% 11% 6%	539
September	1st to 10th	Day	17% 14% 29% 22% 12% 5%	490
	11th to 20th	Day	17% 14% 19% 22% 19% 8%	490
	21st to end	Day	15% 14% 30% 22% 14% 5%	490
October	1st to 10th	Day	27% 13% 26% 16% 15% 3	490
	11th to 20th	Day	29% 17% 26% 20% 8% 1	465
	21st to end	Day	38% 16% 25% 17% 4	429
November	1st to 10th	Day	32% 18% 27% 17% 5% 1	395
	11th to 20th	Day	31% 27% 21% 14% 7% 1	397
	21st to end	Day	38% 20% 28% 14% 1	200
December	1st to 10th	Day	28% 25% 29% 17% 3	200
	11th to 20th	Day	32% 27% 30% 10% 2	200
	21st to end	Day	28% 27% 29% 12% 3	220
January	1st to 10th	Night	29% 21% 32% 17% 3	800
	11th to 20th	Night	30% 18% 30% 18% 4	800
	21st to end	Night	22% 18% 31% 24% 4	841
February	1st to 10th	Night	24% 17% 34% 22% 2	760
	11th to 20th	Night	26% 20% 33% 19% 3	743
	21st to end	Night	27% 19% 29% 20% 5%	628
March	1st to 10th	Night	30% 16% 27% 25% 3 1	760
	11th to 20th	Night	28% 21% 25% 20% 5% 1	760
	21st to end	Night	31% 17% 25% 20% 7% 1	836
April	1st to 10th	Night	29% 16% 26% 25% 4	760
	11th to 20th	Night	31% 18% 21% 22% 8%	751
	21st to end	Night	28% 18% 26% 21% 7%	603
May	1st to 10th	Night	30% 12% 25% 24% 8% 1	508
	11th to 20th	Night	24% 9% 32% 26% 8% 1	374
	21st to end	Night	17% 10% 27% 34% 11% 1	411
June	1st to 10th	Night	27% 8% 25% 31% 9% 1	380
	11th to 20th	Night	19% 7% 27% 34% 13% 1	380
	21st to end	Night	22% 5% 26% 36% 10% 1	380
July	1st to 10th	Night	16% 3 23% 42% 16% 1	370
	11th to 20th	Night	11% 4 23% 41% 18% 2	368
	21st to end	Night	17% 5% 20% 42% 15%	416
August	1st to 10th	Night	16% 4 17% 40% 22% 1	378
	11th to 20th	Night	18% 4 21% 32% 22% 3	617
	21st to end	Night	16% 6% 23% 31% 21% 1	836
September	1st to 10th	Night	17% 8% 25% 33% 16% 2	760
	11th to 20th	Night	18% 8% 18% 29% 23% 4	760
	21st to end	Night	20% 9% 27% 25% 18% 2	760
October	1st to 10th	Night	28% 12% 20% 24% 15% 1	760
	11th to 20th	Night	31% 11% 23% 26% 9% 1	760
	21st to end	Night	32% 15% 27% 21% 5%	836
November	1st to 10th	Night	29% 18% 25% 21% 6% 1	780
	11th to 20th	Night	30% 17% 26% 18% 8% 1	800
	21st to end	Night	33% 20% 25% 17% 5% 1	800
December	1st to 10th	Night	34% 20% 28% 14% 4	800
	11th to 20th	Night	29% 22% 28% 17% 4	800
	21st to end	Night	33% 17% 30% 17% 3	880

Page generated at 2025-01-19 03:06:48. Version ac07

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