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 2024-01-17.

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	17% 10% 4 7% 6% 3 5% 5% 5% 6% 32%	74700
	Night	16% 11% 4 7% 6% 3 4 4 5% 6% 32%	75117
Transparency	Day	51% 5% 12% 21% 10% 1	74400
	Night	52% 5% 12% 20% 10% 1	74952
Seeing	Day	22% 15% 32% 20% 8% 3	14073
	Night	22% 12% 29% 27% 9% 1	23387

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% 20% 9% 9% 6% 4 4 5% 4 5% 21%	1328
	11th to 20th	Day	15% 17% 8% 11% 5% 3 4 4 4 6% 23%	1397
	21st to end	Day	16% 16% 6% 9% 7% 4 5% 5% 4 5% 23%	1738
February	1st to 10th	Day	11% 18% 5% 10% 8% 4 5% 5% 5% 5% 23%	1620
	11th to 20th	Day	13% 16% 6% 8% 8% 3 4 4 4 5% 28%	1573
	21st to end	Day	15% 18% 6% 11% 8% 3 5% 3 4 5% 24%	1399
March	1st to 10th	Day	14% 13% 4 7% 6% 4 5% 4 5% 6% 32%	1912
	11th to 20th	Day	13% 12% 4 9% 6% 4 5% 4 4 5% 35%	1980
	21st to end	Day	16% 12% 4 7% 6% 3 4 3 4 6% 36%	2178
April	1st to 10th	Day	20% 13% 4 7% 5% 3 4 4 5% 7% 29%	2109
	11th to 20th	Day	21% 9% 3 5% 6% 3 5% 4 4 6% 35%	2312
	21st to end	Day	23% 9% 4 6% 4 3 3 3 3 6% 35%	2340
May	1st to 10th	Day	19% 7% 3 6% 6% 3 5% 4 5% 7% 34%	2344
	11th to 20th	Day	18% 7% 3 6% 5% 3 4 5% 6% 6% 37%	2478
	21st to end	Day	15% 6% 2 4 6% 3 5% 5% 5% 7% 42%	2769
June	1st to 10th	Day	17% 7% 3 7% 6% 3 4 5% 7% 7% 34%	2700
	11th to 20th	Day	12% 6% 3 7% 6% 4 5% 5% 6% 8% 39%	2700
	21st to end	Day	17% 7% 3 6% 5% 3 5% 5% 6% 7% 34%	2700
July	1st to 10th	Day	10% 5% 2 6% 5% 3 5% 5% 5% 9% 44%	2700
	11th to 20th	Day	12% 6% 3 5% 6% 4 5% 6% 6% 8% 39%	2700
	21st to end	Day	12% 7% 2 5% 6% 4 5% 6% 7% 8% 38%	2679
August	1st to 10th	Day	14% 6% 3 6% 5% 3 5% 6% 6% 9% 38%	2327
	11th to 20th	Day	15% 6% 2 4 6% 4 5% 5% 6% 8% 40%	2303
	21st to end	Day	15% 6% 3 6% 5% 4 4 6% 7% 8% 37%	2568
September	1st to 10th	Day	14% 6% 3 6% 6% 3 5% 5% 5% 8% 39%	2160
	11th to 20th	Day	15% 5% 2 5% 6% 3 5% 4 5% 8% 42%	1991
	21st to end	Day	21% 7% 3 6% 5% 3 4 4 5% 5% 35%	1980
October	1st to 10th	Day	19% 7% 3 6% 5% 4 5% 4 5% 7% 34%	1807
	11th to 20th	Day	25% 12% 4 7% 6% 4 4 5% 5% 6% 23%	1800
	21st to end	Day	26% 13% 4 7% 5% 3 5% 4 5% 5% 23%	1886
November	1st to 10th	Day	17% 13% 3 8% 6% 3 4 3 6% 7% 30%	1558
	11th to 20th	Day	18% 13% 4 10% 6% 4 5% 4 5% 5% 26%	1520
	21st to end	Day	24% 19% 5% 9% 7% 3 4 4 3 5% 19%	1520
December	1st to 10th	Day	14% 19% 6% 11% 7% 3 3 6% 5% 6% 20%	1520
	11th to 20th	Day	18% 18% 5% 8% 6% 3 4 5% 4 5% 23%	1673
	21st to end	Day	24% 22% 6% 11% 6% 3 4 4 3 4 14%	2431
January	1st to 10th	Night	16% 16% 7% 10% 8% 3 5% 4 5% 5% 22%	2838
	11th to 20th	Night	17% 17% 7% 10% 5% 3 5% 4 4 5% 22%	2698
	21st to end	Night	14% 12% 6% 10% 8% 4 5% 5% 5% 6% 26%	2615
February	1st to 10th	Night	12% 15% 6% 11% 8% 3 5% 6% 5% 6% 24%	2340
	11th to 20th	Night	12% 13% 6% 10% 7% 4 5% 5% 5% 5% 28%	2273
	21st to end	Night	14% 14% 6% 9% 7% 4 4 5% 4 5% 25%	1852
March	1st to 10th	Night	13% 10% 4 8% 7% 3 4 4 5% 7% 35%	2034
	11th to 20th	Night	16% 11% 3 8% 6% 4 4 4 4 6% 34%	1979
	21st to end	Night	16% 9% 3 7% 5% 3 4 4 4 6% 40%	2178
April	1st to 10th	Night	20% 11% 5% 6% 6% 2 4 5% 5% 6% 31%	1866
	11th to 20th	Night	19% 8% 3 5% 6% 2 4 4 4 5% 39%	1597
	21st to end	Night	20% 8% 3 7% 7% 3 4 4 5% 5% 32%	1620
May	1st to 10th	Night	14% 7% 4 6% 6% 4 5% 5% 6% 7% 36%	1616
	11th to 20th	Night	14% 5% 3 5% 5% 3 6% 6% 6% 7% 39%	1415
	21st to end	Night	11% 6% 3 6% 6% 3 4 5% 5% 8% 43%	1504
June	1st to 10th	Night	13% 6% 3 6% 7% 3 5% 6% 6% 7% 39%	1260
	11th to 20th	Night	14% 5% 2 4 4 3 5% 6% 6% 9% 42%	1260
	21st to end	Night	14% 5% 3 6% 4 2 5% 4 6% 9% 42%	1260
July	1st to 10th	Night	7% 4 2 4 5% 3 5% 6% 8% 10% 46%	1260
	11th to 20th	Night	9% 5% 2 5% 5% 3 6% 5% 6% 8% 47%	1260
	21st to end	Night	9% 5% 3 5% 5% 3 5% 6% 6% 8% 46%	1633
August	1st to 10th	Night	10% 6% 4 5% 5% 4 4 5% 5% 8% 45%	1611
	11th to 20th	Night	13% 5% 2 5% 5% 2 3 5% 6% 7% 47%	1598
	21st to end	Night	14% 8% 3 5% 4 3 4 5% 6% 6% 42%	1782
September	1st to 10th	Night	13% 5% 2 4 6% 3 5% 5% 5% 7% 47%	1787
	11th to 20th	Night	13% 5% 2 5% 4 3 4 4 5% 7% 48%	1966
	21st to end	Night	18% 6% 2 5% 5% 3 4 4 4 7% 41%	1980
October	1st to 10th	Night	21% 8% 3 5% 6% 3 4 4 5% 6% 36%	2152
	11th to 20th	Night	25% 10% 4 5% 6% 3 3 3 4 7% 30%	2160
	21st to end	Night	25% 12% 3 8% 6% 3 4 4 4 5% 25%	2466
November	1st to 10th	Night	17% 11% 4 6% 5% 3 4 4 5% 6% 34%	2520
	11th to 20th	Night	18% 12% 5% 8% 7% 4 5% 5% 5% 5% 27%	2660
	21st to end	Night	22% 14% 4 7% 6% 3 5% 6% 5% 6% 22%	2660
December	1st to 10th	Night	18% 17% 5% 10% 6% 4 5% 4 3 5% 22%	2660
	11th to 20th	Night	19% 15% 4 8% 7% 3 4 4 5% 6% 26%	3521
	21st to end	Night	23% 21% 5% 12% 6% 3 3 3 3 4 16%	5236

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	66% 4 10% 15% 4	1329
	11th to 20th	Day	63% 4 9% 15% 7% 2	1397
	21st to end	Day	62% 5% 7% 16% 10% 1	1738
February	1st to 10th	Day	62% 4 11% 15% 6% 1	1620
	11th to 20th	Day	58% 4 10% 15% 11% 1	1582
	21st to end	Day	64% 4 8% 16% 9%	1399
March	1st to 10th	Day	52% 5% 14% 16% 13% 1	1915
	11th to 20th	Day	51% 3 9% 24% 10% 2	1980
	21st to end	Day	51% 3 9% 21% 13% 3	2178
April	1st to 10th	Day	55% 4 13% 17% 10% 2	2109
	11th to 20th	Day	51% 3 8% 25% 12% 1	2312
	21st to end	Day	52% 3 9% 18% 15% 3	2340
May	1st to 10th	Day	48% 5% 10% 21% 13% 3	2344
	11th to 20th	Day	46% 5% 10% 22% 15% 2	2482
	21st to end	Day	40% 6% 14% 24% 13% 3	2769
June	1st to 10th	Day	46% 6% 12% 22% 13% 1	2700
	11th to 20th	Day	43% 5% 10% 24% 17% 1	2700
	21st to end	Day	47% 7% 12% 21% 10% 2	2700
July	1st to 10th	Day	34% 6% 16% 27% 16% 1	2626
	11th to 20th	Day	40% 7% 13% 29% 11% 1	2619
	21st to end	Day	41% 7% 14% 27% 11%	2530
August	1st to 10th	Day	41% 7% 16% 23% 11% 1	2314
	11th to 20th	Day	40% 8% 18% 26% 9% 1	2303
	21st to end	Day	43% 6% 16% 26% 8%	2568
September	1st to 10th	Day	43% 7% 13% 26% 10% 1	2160
	11th to 20th	Day	40% 6% 16% 29% 9%	1991
	21st to end	Day	50% 6% 15% 23% 6%	1980
October	1st to 10th	Day	49% 6% 13% 21% 11% 1	1807
	11th to 20th	Day	60% 6% 11% 15% 7% 1	1800
	21st to end	Day	63% 5% 14% 12% 7%	1886
November	1st to 10th	Day	53% 6% 13% 20% 7%	1558
	11th to 20th	Day	60% 5% 11% 17% 7%	1520
	21st to end	Day	70% 4 10% 11% 5%	1520
December	1st to 10th	Day	64% 6% 10% 15% 4 1	1520
	11th to 20th	Day	63% 4 11% 18% 4 1	1673
	21st to end	Day	74% 4 8% 11% 3	2431
January	1st to 10th	Night	64% 5% 10% 14% 7%	2838
	11th to 20th	Night	65% 4 10% 13% 8% 1	2698
	21st to end	Night	59% 4 9% 18% 10% 1	2615
February	1st to 10th	Night	59% 6% 11% 16% 7% 1	2340
	11th to 20th	Night	58% 5% 12% 18% 7% 1	2275
	21st to end	Night	61% 5% 10% 15% 9% 1	1852
March	1st to 10th	Night	49% 4 12% 19% 14% 2	2044
	11th to 20th	Night	51% 4 11% 18% 13% 2	1980
	21st to end	Night	47% 4 11% 18% 15% 4	2178
April	1st to 10th	Night	54% 4 9% 20% 12% 2	1866
	11th to 20th	Night	49% 3 6% 24% 16% 2	1597
	21st to end	Night	54% 4 9% 16% 16% 2	1620
May	1st to 10th	Night	47% 5% 11% 21% 12% 4	1616
	11th to 20th	Night	41% 7% 9% 24% 17% 2	1416
	21st to end	Night	39% 7% 12% 22% 17% 3	1505
June	1st to 10th	Night	42% 7% 12% 24% 13% 3	1260
	11th to 20th	Night	37% 6% 13% 24% 19% 2	1260
	21st to end	Night	40% 7% 15% 22% 15% 2	1260
July	1st to 10th	Night	28% 7% 15% 29% 18% 3	1225
	11th to 20th	Night	33% 7% 16% 28% 16% 1	1218
	21st to end	Night	36% 6% 18% 26% 13% 1	1542
August	1st to 10th	Night	36% 7% 20% 24% 11% 1	1600
	11th to 20th	Night	35% 6% 18% 29% 11% 2	1598
	21st to end	Night	42% 5% 15% 25% 12% 1	1782
September	1st to 10th	Night	38% 6% 13% 29% 12% 2	1787
	11th to 20th	Night	35% 5% 16% 35% 9%	1966
	21st to end	Night	44% 6% 14% 28% 9%	1980
October	1st to 10th	Night	49% 5% 12% 22% 12%	2152
	11th to 20th	Night	55% 5% 11% 23% 6%	2160
	21st to end	Night	61% 5% 10% 15% 7% 1	2466
November	1st to 10th	Night	50% 6% 14% 23% 8%	2520
	11th to 20th	Night	58% 5% 13% 17% 7% 1	2660
	21st to end	Night	62% 7% 12% 14% 5%	2660
December	1st to 10th	Night	64% 5% 10% 16% 4	2660
	11th to 20th	Night	60% 5% 12% 15% 8% 1	3520
	21st to end	Night	73% 3 9% 10% 4	5236

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% 21% 31% 16% 8% 1	180
	11th to 20th	Day	20% 14% 35% 20% 9% 1	215
	21st to end	Day	26% 14% 33% 17% 9% 2	264
February	1st to 10th	Day	28% 23% 32% 13% 3	240
	11th to 20th	Day	23% 25% 39% 10% 2	240
	21st to end	Day	31% 27% 32% 10% 1	198
March	1st to 10th	Day	22% 21% 35% 17% 4	355
	11th to 20th	Day	22% 20% 35% 16% 6% 1	420
	21st to end	Day	28% 18% 31% 18% 5% 1	462
April	1st to 10th	Day	25% 15% 34% 17% 8% 1	420
	11th to 20th	Day	31% 20% 21% 17% 8% 3	412
	21st to end	Day	30% 16% 29% 15% 8% 2	420
May	1st to 10th	Day	26% 11% 33% 18% 9% 3	423
	11th to 20th	Day	23% 16% 30% 17% 10% 4	447
	21st to end	Day	20% 16% 32% 20% 9% 2	529
June	1st to 10th	Day	18% 17% 38% 21% 5%	630
	11th to 20th	Day	16% 17% 38% 21% 6% 2	630
	21st to end	Day	20% 13% 36% 22% 8% 1	630
July	1st to 10th	Day	10% 14% 37% 28% 10% 2	621
	11th to 20th	Day	14% 13% 34% 26% 10% 4	618
	21st to end	Day	13% 9% 32% 29% 12% 5%	554
August	1st to 10th	Day	20% 6% 25% 27% 16% 5%	446
	11th to 20th	Day	14% 5% 27% 27% 18% 9%	439
	21st to end	Day	18% 11% 29% 24% 11% 8%	495
September	1st to 10th	Day	18% 12% 29% 22% 12% 6%	450
	11th to 20th	Day	15% 8% 30% 30% 12% 5%	450
	21st to end	Day	24% 12% 28% 19% 13% 3	450
October	1st to 10th	Day	21% 16% 27% 22% 11% 2	450
	11th to 20th	Day	28% 18% 31% 18% 5% 1	450
	21st to end	Day	35% 17% 29% 15% 2 1	401
November	1st to 10th	Day	28% 17% 37% 14% 4	216
	11th to 20th	Day	21% 22% 39% 12% 5% 1	180
	21st to end	Day	37% 16% 27% 13% 6% 1	180
December	1st to 10th	Day	24% 15% 33% 21% 6%	180
	11th to 20th	Day	28% 22% 34% 11% 4	180
	21st to end	Day	34% 16% 33% 11% 6%	198
January	1st to 10th	Night	23% 15% 32% 23% 6% 1	950
	11th to 20th	Night	26% 16% 29% 23% 7%	933
	21st to end	Night	21% 10% 31% 28% 9% 1	833
February	1st to 10th	Night	21% 18% 38% 20% 4	720
	11th to 20th	Night	21% 15% 35% 24% 6% 1	703
	21st to end	Night	23% 18% 32% 23% 4	592
March	1st to 10th	Night	18% 17% 36% 24% 5%	720
	11th to 20th	Night	23% 15% 33% 22% 6% 1	720
	21st to end	Night	20% 13% 34% 24% 7% 1	792
April	1st to 10th	Night	26% 15% 29% 25% 4	718
	11th to 20th	Night	23% 13% 28% 26% 9% 1	533
	21st to end	Night	24% 12% 27% 29% 9%	540
May	1st to 10th	Night	18% 9% 29% 34% 10% 1	536
	11th to 20th	Night	16% 10% 31% 32% 10%	354
	21st to end	Night	13% 8% 37% 32% 10%	389
June	1st to 10th	Night	15% 7% 35% 34% 9%	360
	11th to 20th	Night	17% 11% 25% 38% 9%	360
	21st to end	Night	16% 8% 29% 32% 15%	360
July	1st to 10th	Night	8% 6% 30% 46% 9% 1	350
	11th to 20th	Night	11% 5% 26% 41% 16% 1	348
	21st to end	Night	10% 5% 28% 38% 18% 2	522
August	1st to 10th	Night	12% 4 24% 39% 18% 2	537
	11th to 20th	Night	15% 4 22% 32% 24% 3	534
	21st to end	Night	17% 7% 22% 31% 21% 2	594
September	1st to 10th	Night	15% 7% 28% 30% 19% 2	707
	11th to 20th	Night	15% 10% 26% 29% 18% 3	720
	21st to end	Night	21% 8% 25% 28% 17% 3	720
October	1st to 10th	Night	25% 10% 27% 25% 12% 1	720
	11th to 20th	Night	32% 10% 28% 23% 7% 1	720
	21st to end	Night	30% 14% 28% 23% 4 1	792
November	1st to 10th	Night	26% 12% 30% 24% 8% 1	740
	11th to 20th	Night	26% 15% 28% 25% 6%	760
	21st to end	Night	29% 14% 30% 21% 6%	760
December	1st to 10th	Night	28% 15% 31% 21% 5% 1	760
	11th to 20th	Night	27% 15% 31% 20% 5%	945
	21st to end	Night	30% 16% 26% 22% 6%	1045

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