Burwash
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burwash clear sky chart from 2005-11-06 to 2026-04-17.

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 8% 5% 4 4 4 5% 6% 33%	131452
	Night	15% 12% 4 9% 5% 4 4 4 5% 6% 31%	130817
Transparency	Day	51% 4 11% 22% 11% 1	134952
	Night	53% 4 11% 20% 10% 1	135392
Seeing	Day	22% 15% 32% 20% 8% 2	17022
	Night	22% 12% 30% 27% 9% 1	26318

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	13% 20% 7% 11% 5% 4 4 3 4 5% 24%	4094
	11th to 20th	Day	10% 19% 8% 19% 6% 5% 5% 4 5% 5% 16%	4398
	21st to end	Day	11% 16% 7% 15% 7% 5% 5% 4 4 5% 21%	5645
February	1st to 10th	Day	11% 18% 5% 11% 6% 5% 5% 4 4 5% 24%	1890
	11th to 20th	Day	12% 18% 6% 10% 7% 4 4 3 4 5% 27%	1843
	21st to end	Day	13% 18% 6% 13% 6% 4 4 3 4 5% 24%	1636
March	1st to 10th	Day	20% 15% 4 8% 4 4 4 3 4 5% 29%	4894
	11th to 20th	Day	14% 14% 4 10% 5% 5% 5% 3 5% 6% 27%	5090
	21st to end	Day	15% 15% 6% 10% 5% 4 4 3 4 4 30%	5586
April	1st to 10th	Day	19% 14% 3 8% 4 4 4 3 5% 6% 30%	2461
	11th to 20th	Day	22% 10% 3 6% 4 4 4 4 4 5% 34%	2650
	21st to end	Day	23% 10% 3 7% 4 3 3 2 4 6% 35%	2600
May	1st to 10th	Day	19% 8% 3 7% 5% 5% 4 3 5% 6% 36%	5906
	11th to 20th	Day	15% 7% 3 6% 4 4 4 4 5% 6% 42%	6318
	21st to end	Day	20% 9% 3 6% 4 3 4 3 4 6% 37%	7077
June	1st to 10th	Day	16% 8% 3 8% 6% 4 5% 5% 7% 7% 34%	3000
	11th to 20th	Day	12% 7% 2 8% 5% 5% 5% 4 6% 8% 40%	3000
	21st to end	Day	18% 8% 3 7% 4 5% 5% 4 6% 7% 33%	3000
July	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 9% 34%	6819
	11th to 20th	Day	11% 5% 2 6% 5% 4 4 4 5% 8% 46%	6820
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 9% 48%	6738
August	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4234
	11th to 20th	Day	18% 6% 2 5% 4 4 4 4 6% 8% 40%	4174
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	4654
September	1st to 10th	Day	14% 7% 3 7% 5% 4 5% 4 5% 8% 38%	2400
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 3 6% 8% 44%	2211
	21st to end	Day	21% 8% 3 6% 5% 4 5% 3 5% 5% 36%	2200
October	1st to 10th	Day	17% 7% 3 7% 4 5% 5% 3 6% 7% 37%	2007
	11th to 20th	Day	24% 12% 3 8% 4 5% 4 3 5% 6% 26%	2000
	21st to end	Day	26% 14% 4 8% 4 4 5% 3 5% 4 24%	2095
November	1st to 10th	Day	18% 13% 3 9% 5% 4 4 3 6% 6% 30%	1726
	11th to 20th	Day	17% 15% 4 10% 6% 5% 4 4 5% 5% 26%	1680
	21st to end	Day	23% 20% 5% 10% 6% 4 4 3 3 4 18%	1680
December	1st to 10th	Day	13% 19% 6% 13% 7% 4 4 4 5% 6% 17%	2680
	11th to 20th	Day	17% 17% 5% 12% 5% 4 4 3 4 5% 24%	2693
	21st to end	Day	24% 21% 6% 12% 4 4 3 3 3 4 15%	3553
January	1st to 10th	Night	11% 15% 7% 13% 6% 5% 5% 4 6% 6% 21%	8831
	11th to 20th	Night	12% 20% 6% 12% 6% 4 5% 4 5% 5% 22%	8499
	21st to end	Night	8% 15% 7% 15% 7% 6% 6% 4 5% 5% 22%	8540
February	1st to 10th	Night	11% 16% 5% 12% 7% 4 5% 5% 5% 6% 25%	2730
	11th to 20th	Night	11% 15% 6% 11% 7% 5% 4 4 5% 6% 26%	2663
	21st to end	Night	13% 16% 5% 10% 7% 6% 4 4 5% 5% 25%	2165
March	1st to 10th	Night	18% 13% 3 8% 5% 4 4 3 5% 6% 33%	5165
	11th to 20th	Night	14% 13% 5% 10% 5% 5% 5% 4 6% 7% 27%	5089
	21st to end	Night	18% 12% 5% 8% 5% 5% 4 3 4 5% 32%	5588
April	1st to 10th	Night	19% 12% 4 7% 5% 4 4 3 5% 6% 30%	2176
	11th to 20th	Night	19% 9% 3 6% 5% 3 3 3 4 5% 38%	1831
	21st to end	Night	20% 8% 3 9% 5% 4 4 4 5% 5% 32%	1800
May	1st to 10th	Night	17% 7% 3 7% 4 4 4 4 5% 6% 39%	4035
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 4 6% 8% 42%	3575
	21st to end	Night	16% 8% 3 8% 5% 4 4 4 5% 7% 37%	3802
June	1st to 10th	Night	13% 8% 2 6% 6% 4 5% 5% 6% 7% 38%	1400
	11th to 20th	Night	14% 6% 2 5% 4 5% 5% 5% 6% 8% 42%	1400
	21st to end	Night	14% 6% 3 7% 3 4 4 3 7% 8% 42%	1400
July	1st to 10th	Night	13% 7% 3 7% 4 4 4 4 6% 8% 40%	3160
	11th to 20th	Night	11% 4 2 6% 4 3 4 3 5% 7% 49%	3160
	21st to end	Night	9% 5% 2 6% 4 3 4 3 5% 8% 50%	4101
August	1st to 10th	Night	10% 7% 3 6% 4 4 5% 4 6% 7% 43%	2915
	11th to 20th	Night	14% 6% 2 6% 3 3 4 3 5% 8% 46%	2875
	21st to end	Night	12% 7% 2 6% 3 4 4 3 6% 7% 47%	3223
September	1st to 10th	Night	13% 6% 1 5% 4 4 4 4 5% 7% 46%	1987
	11th to 20th	Night	12% 5% 2 5% 3 4 4 3 5% 7% 50%	2185
	21st to end	Night	18% 7% 2 6% 4 4 3 3 4 7% 42%	2200
October	1st to 10th	Night	20% 8% 3 6% 4 4 3 3 5% 6% 38%	2392
	11th to 20th	Night	24% 11% 3 6% 5% 3 4 2 5% 6% 31%	2400
	21st to end	Night	24% 12% 3 9% 5% 4 4 3 4 5% 27%	2740
November	1st to 10th	Night	17% 11% 3 7% 5% 4 5% 3 5% 6% 33%	2792
	11th to 20th	Night	17% 14% 4 9% 5% 5% 4 3 5% 5% 27%	2940
	21st to end	Night	22% 16% 4 9% 5% 4 4 4 5% 5% 22%	2940
December	1st to 10th	Night	16% 17% 5% 11% 5% 6% 5% 4 5% 6% 20%	4720
	11th to 20th	Night	15% 16% 4 13% 6% 5% 4 3 4 6% 24%	5731
	21st to end	Night	21% 23% 5% 13% 5% 3 3 2 3 5% 16%	7667

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	63% 3 7% 20% 6% 1	4095
	11th to 20th	Day	70% 4 7% 11% 7% 1	4428
	21st to end	Day	64% 3 6% 15% 11%	5645
February	1st to 10th	Day	62% 4 11% 16% 7% 1	1890
	11th to 20th	Day	60% 4 10% 15% 10% 1	1852
	21st to end	Day	64% 4 7% 17% 8% 1	1636
March	1st to 10th	Day	58% 4 10% 10% 15% 3	4897
	11th to 20th	Day	57% 4 13% 16% 9% 1	5090
	21st to end	Day	57% 3 10% 18% 10% 2	5586
April	1st to 10th	Day	55% 4 12% 18% 10% 2	2461
	11th to 20th	Day	52% 4 7% 24% 13% 1	2650
	21st to end	Day	52% 3 9% 19% 15% 3	2600
May	1st to 10th	Day	47% 5% 7% 23% 13% 4	5915
	11th to 20th	Day	42% 5% 12% 23% 16% 2	6322
	21st to end	Day	48% 4 11% 19% 16% 3	7077
June	1st to 10th	Day	46% 6% 11% 22% 14% 1	3000
	11th to 20th	Day	42% 4 10% 25% 17% 1	3000
	21st to end	Day	48% 6% 12% 21% 11% 1	3000
July	1st to 10th	Day	45% 5% 16% 25% 9%	6746
	11th to 20th	Day	35% 5% 14% 38% 8%	6739
	21st to end	Day	32% 5% 15% 34% 13%	6547
August	1st to 10th	Day	41% 5% 13% 30% 10% 1	4221
	11th to 20th	Day	41% 6% 16% 27% 10%	4213
	21st to end	Day	39% 5% 13% 32% 9% 1	4654
September	1st to 10th	Day	44% 7% 13% 26% 10% 1	2400
	11th to 20th	Day	37% 5% 16% 30% 11% 1	2211
	21st to end	Day	49% 6% 14% 23% 8%	2200
October	1st to 10th	Day	40% 4 11% 31% 13%	3267
	11th to 20th	Day	48% 5% 13% 25% 8%	3240
	21st to end	Day	63% 3 13% 14% 6%	3358
November	1st to 10th	Day	54% 6% 13% 21% 7%	1726
	11th to 20th	Day	60% 5% 11% 17% 7%	1680
	21st to end	Day	70% 4 10% 12% 5%	1680
December	1st to 10th	Day	67% 4 15% 11% 3	2680
	11th to 20th	Day	64% 3 8% 17% 7% 1	2693
	21st to end	Day	73% 3 6% 12% 6%	3553
January	1st to 10th	Night	61% 5% 9% 17% 8%	8831
	11th to 20th	Night	64% 3 11% 12% 9%	8544
	21st to end	Night	64% 4 7% 14% 10% 1	8540
February	1st to 10th	Night	58% 5% 10% 19% 7% 1	2730
	11th to 20th	Night	59% 5% 11% 18% 7% 1	2665
	21st to end	Night	60% 5% 9% 16% 9% 1	2165
March	1st to 10th	Night	52% 4 9% 16% 14% 4	5175
	11th to 20th	Night	55% 4 14% 17% 8% 2	5090
	21st to end	Night	55% 3 7% 18% 13% 3	5588
April	1st to 10th	Night	55% 4 9% 20% 11% 1	2176
	11th to 20th	Night	49% 3 7% 23% 16% 2	1831
	21st to end	Night	54% 4 9% 16% 16% 2	1800
May	1st to 10th	Night	45% 4 8% 23% 15% 4	4042
	11th to 20th	Night	39% 6% 11% 23% 18% 3	3576
	21st to end	Night	46% 5% 8% 24% 13% 4	3803
June	1st to 10th	Night	42% 7% 12% 24% 14% 3	1400
	11th to 20th	Night	37% 6% 12% 25% 18% 2	1400
	21st to end	Night	41% 7% 14% 23% 15% 2	1400
July	1st to 10th	Night	41% 5% 13% 28% 12% 1	3125
	11th to 20th	Night	33% 4 14% 36% 11% 1	3118
	21st to end	Night	33% 4 13% 33% 17%	3978
August	1st to 10th	Night	39% 5% 16% 26% 13% 1	2904
	11th to 20th	Night	37% 4 20% 29% 9% 1	2902
	21st to end	Night	36% 4 14% 32% 12% 1	3223
September	1st to 10th	Night	37% 5% 14% 30% 11% 2	1987
	11th to 20th	Night	33% 5% 16% 35% 11%	2185
	21st to end	Night	43% 6% 13% 27% 11%	2200
October	1st to 10th	Night	39% 4 10% 32% 14%	3912
	11th to 20th	Night	45% 4 12% 32% 7%	3899
	21st to end	Night	53% 5% 18% 16% 6% 1	4414
November	1st to 10th	Night	51% 5% 13% 22% 8%	2792
	11th to 20th	Night	58% 4 13% 17% 7% 1	2940
	21st to end	Night	63% 6% 12% 14% 5%	2940
December	1st to 10th	Night	64% 5% 14% 14% 3	4720
	11th to 20th	Night	62% 4 9% 13% 12% 1	5730
	21st to end	Night	72% 3 7% 12% 6%	7667

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	24% 18% 32% 17% 8%	220
	11th to 20th	Day	23% 13% 36% 19% 7% 1	278
	21st to end	Day	24% 16% 34% 17% 8% 1	363
February	1st to 10th	Day	27% 23% 33% 13% 4	330
	11th to 20th	Day	23% 24% 40% 11% 2	330
	21st to end	Day	30% 24% 35% 10% 1	273
March	1st to 10th	Day	27% 20% 34% 16% 3	465
	11th to 20th	Day	24% 20% 34% 16% 5% 1	540
	21st to end	Day	29% 19% 32% 16% 4 1	594
April	1st to 10th	Day	28% 16% 33% 15% 7% 1	540
	11th to 20th	Day	33% 20% 21% 16% 7% 3	516
	21st to end	Day	31% 16% 29% 14% 7% 2	500
May	1st to 10th	Day	25% 11% 36% 18% 8% 2	503
	11th to 20th	Day	22% 15% 31% 19% 9% 4	527
	21st to end	Day	22% 15% 31% 21% 9% 1	623
June	1st to 10th	Day	18% 18% 38% 21% 5%	730
	11th to 20th	Day	16% 18% 38% 21% 6% 2	730
	21st to end	Day	21% 14% 36% 20% 7% 1	730
July	1st to 10th	Day	11% 14% 37% 26% 10% 2	721
	11th to 20th	Day	13% 13% 36% 26% 9% 3	718
	21st to end	Day	13% 9% 33% 28% 12% 5%	649
August	1st to 10th	Day	18% 7% 26% 28% 15% 5%	526
	11th to 20th	Day	14% 6% 28% 26% 17% 9%	519
	21st to end	Day	17% 11% 29% 24% 11% 8%	583
September	1st to 10th	Day	18% 13% 29% 22% 12% 6%	530
	11th to 20th	Day	13% 8% 27% 30% 14% 8%	530
	21st to end	Day	24% 11% 28% 20% 14% 3	530
October	1st to 10th	Day	20% 17% 27% 23% 11% 2	530
	11th to 20th	Day	27% 17% 33% 17% 5% 1	530
	21st to end	Day	34% 17% 29% 17% 2 1	478
November	1st to 10th	Day	30% 18% 35% 13% 4	264
	11th to 20th	Day	23% 20% 40% 12% 5%	220
	21st to end	Day	36% 17% 29% 12% 5%	220
December	1st to 10th	Day	24% 17% 32% 20% 7%	220
	11th to 20th	Day	30% 20% 34% 12% 4	220
	21st to end	Day	35% 15% 32% 12% 5%	242
January	1st to 10th	Night	22% 14% 34% 24% 6%	1050
	11th to 20th	Night	27% 15% 29% 22% 6%	1050
	21st to end	Night	20% 10% 32% 28% 8% 1	972
February	1st to 10th	Night	20% 17% 36% 22% 4	840
	11th to 20th	Night	21% 15% 36% 23% 5%	823
	21st to end	Night	22% 17% 34% 23% 3	692
March	1st to 10th	Night	19% 17% 37% 22% 5%	840
	11th to 20th	Night	24% 16% 33% 21% 5% 1	840
	21st to end	Night	21% 15% 34% 23% 7% 1	924
April	1st to 10th	Night	26% 16% 30% 24% 4	837
	11th to 20th	Night	23% 13% 29% 24% 8% 1	611
	21st to end	Night	24% 12% 28% 27% 9%	600
May	1st to 10th	Night	17% 9% 30% 33% 10% 1	595
	11th to 20th	Night	15% 9% 32% 34% 10%	394
	21st to end	Night	15% 9% 34% 32% 10%	433
June	1st to 10th	Night	15% 8% 36% 33% 8%	400
	11th to 20th	Night	17% 11% 26% 38% 8%	400
	21st to end	Night	17% 8% 31% 31% 14%	400
July	1st to 10th	Night	9% 6% 29% 46% 8% 1	390
	11th to 20th	Night	11% 4 28% 40% 16% 1	388
	21st to end	Night	9% 5% 28% 38% 18% 2	581
August	1st to 10th	Night	12% 4 24% 41% 18% 2	597
	11th to 20th	Night	15% 5% 23% 32% 23% 3	594
	21st to end	Night	16% 7% 22% 33% 21% 1	660
September	1st to 10th	Night	15% 7% 27% 30% 19% 1	787
	11th to 20th	Night	14% 9% 24% 30% 20% 4	800
	21st to end	Night	21% 7% 25% 28% 17% 3	800
October	1st to 10th	Night	23% 10% 27% 26% 12% 1	800
	11th to 20th	Night	31% 10% 28% 24% 7% 1	800
	21st to end	Night	30% 13% 28% 24% 4 1	880
November	1st to 10th	Night	26% 13% 30% 24% 7%	820
	11th to 20th	Night	25% 14% 29% 25% 6%	840
	21st to end	Night	30% 14% 30% 20% 6%	840
December	1st to 10th	Night	27% 15% 31% 22% 5%	840
	11th to 20th	Night	27% 15% 32% 21% 5%	1045
	21st to end	Night	30% 17% 27% 21% 6%	1155

Page generated at 2026-04-14 02:44:28. Version ac07

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