Bonavista
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bonavista clear sky chart from 2005-11-06 to 2024-01-27.

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	21% 13% 5% 9% 7% 4 5% 4 5% 6% 22%	74721
	Night	23% 15% 6% 10% 7% 3 5% 4 4 6% 19%	75328
Transparency	Day	62% 8% 12% 13% 5%	74409
	Night	66% 6% 11% 11% 5%	75175
Seeing	Day	28% 13% 28% 23% 8% 1	17048
	Night	30% 14% 29% 21% 6% 1	23776

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	21% 16% 9% 11% 10% 3 5% 4 4 4 12%	1326
	11th to 20th	Day	19% 16% 7% 15% 13% 4 5% 3 4 6% 9%	1431
	21st to end	Day	20% 16% 6% 14% 10% 5% 6% 4 4 4 11%	1633
February	1st to 10th	Day	20% 12% 5% 11% 14% 5% 6% 5% 5% 5% 12%	1534
	11th to 20th	Day	20% 15% 6% 12% 10% 6% 5% 4 5% 5% 14%	1573
	21st to end	Day	16% 12% 6% 12% 11% 5% 6% 4 4 6% 18%	1462
March	1st to 10th	Day	17% 12% 6% 11% 9% 4 5% 4 5% 5% 22%	1808
	11th to 20th	Day	19% 14% 6% 8% 7% 5% 5% 3 5% 6% 22%	1980
	21st to end	Day	25% 16% 5% 11% 6% 3 3 3 4 5% 18%	2178
April	1st to 10th	Day	19% 13% 5% 9% 6% 4 5% 4 5% 7% 23%	2193
	11th to 20th	Day	23% 13% 4 7% 5% 3 5% 4 5% 5% 26%	2311
	21st to end	Day	22% 15% 6% 8% 6% 3 4 4 5% 6% 22%	2340
May	1st to 10th	Day	22% 18% 5% 9% 6% 3 4 4 4 5% 21%	2340
	11th to 20th	Day	24% 14% 4 6% 6% 3 5% 4 5% 7% 23%	2588
	21st to end	Day	22% 12% 4 6% 6% 3 5% 4 5% 7% 25%	2918
June	1st to 10th	Day	29% 16% 5% 9% 6% 3 5% 4 4 5% 15%	2700
	11th to 20th	Day	26% 13% 4 7% 5% 3 4 4 4 5% 25%	2700
	21st to end	Day	20% 11% 4 7% 6% 4 5% 6% 6% 8% 24%	2700
July	1st to 10th	Day	21% 10% 3 6% 5% 4 5% 5% 5% 7% 29%	2700
	11th to 20th	Day	17% 9% 3 7% 6% 4 6% 6% 7% 8% 28%	2700
	21st to end	Day	19% 10% 5% 7% 7% 4 5% 6% 6% 8% 24%	2801
August	1st to 10th	Day	23% 11% 3 6% 5% 3 5% 5% 6% 8% 25%	2409
	11th to 20th	Day	20% 10% 3 6% 5% 3 5% 5% 5% 7% 31%	2305
	21st to end	Day	19% 10% 3 7% 6% 3 5% 6% 6% 8% 27%	2574
September	1st to 10th	Day	19% 8% 3 5% 6% 3 5% 5% 6% 8% 32%	2182
	11th to 20th	Day	27% 9% 3 5% 4 3 4 4 5% 6% 30%	1980
	21st to end	Day	19% 10% 3 6% 5% 3 5% 4 6% 7% 34%	1980
October	1st to 10th	Day	21% 12% 4 7% 6% 2 4 4 5% 6% 27%	1877
	11th to 20th	Day	27% 15% 5% 8% 6% 3 4 4 5% 5% 19%	1746
	21st to end	Day	25% 18% 3 8% 5% 4 4 4 5% 6% 18%	1782
November	1st to 10th	Day	22% 16% 4 7% 6% 3 5% 5% 5% 6% 21%	1594
	11th to 20th	Day	21% 16% 7% 9% 7% 3 5% 3 5% 6% 18%	1520
	21st to end	Day	23% 16% 8% 9% 5% 3 4 4 4 4 18%	1416
December	1st to 10th	Day	24% 17% 8% 9% 6% 4 5% 4 5% 5% 13%	1330
	11th to 20th	Day	21% 16% 7% 13% 9% 3 4 4 4 5% 13%	1668
	21st to end	Day	21% 18% 8% 18% 10% 4 5% 4 3 4 7%	2442
January	1st to 10th	Night	22% 15% 8% 15% 10% 4 5% 4 4 4 10%	2839
	11th to 20th	Night	19% 16% 8% 14% 10% 4 5% 4 4 5% 10%	2746
	21st to end	Night	20% 14% 5% 14% 9% 5% 5% 4 3 5% 16%	2867
February	1st to 10th	Night	19% 15% 6% 14% 13% 5% 4 4 4 5% 13%	2425
	11th to 20th	Night	22% 16% 6% 12% 10% 3 4 4 4 5% 14%	2273
	21st to end	Night	16% 15% 6% 12% 8% 5% 6% 4 4 5% 19%	1790
March	1st to 10th	Night	19% 14% 7% 9% 6% 3 5% 5% 5% 7% 20%	2139
	11th to 20th	Night	16% 13% 5% 9% 8% 4 5% 5% 5% 7% 23%	1979
	21st to end	Night	27% 18% 5% 10% 6% 3 4 3 3 4 17%	2178
April	1st to 10th	Night	23% 16% 6% 9% 5% 3 4 3 4 5% 21%	1765
	11th to 20th	Night	24% 14% 6% 8% 5% 2 5% 4 3 7% 23%	1598
	21st to end	Night	25% 18% 7% 6% 4 2 4 3 4 4 23%	1620
May	1st to 10th	Night	25% 17% 7% 7% 5% 2 5% 4 5% 6% 17%	1620
	11th to 20th	Night	26% 11% 5% 6% 6% 3 5% 5% 5% 5% 23%	1300
	21st to end	Night	28% 13% 4 6% 5% 3 5% 5% 5% 7% 21%	1356
June	1st to 10th	Night	31% 16% 5% 8% 5% 2 3 3 5% 6% 16%	1260
	11th to 20th	Night	31% 11% 4 7% 6% 3 3 4 5% 6% 19%	1260
	21st to end	Night	24% 13% 4 6% 5% 3 4 5% 5% 8% 23%	1260
July	1st to 10th	Night	22% 11% 4 7% 5% 3 5% 6% 5% 9% 25%	1260
	11th to 20th	Night	19% 9% 3 7% 5% 4 6% 5% 5% 8% 29%	1260
	21st to end	Night	21% 12% 5% 7% 5% 4 5% 5% 5% 6% 25%	1513
August	1st to 10th	Night	24% 10% 3 7% 5% 3 5% 5% 6% 8% 25%	1529
	11th to 20th	Night	20% 11% 3 7% 6% 4 4 5% 5% 7% 28%	1595
	21st to end	Night	22% 9% 3 6% 4 2 4 6% 6% 8% 29%	1782
September	1st to 10th	Night	21% 8% 3 6% 4 3 4 4 5% 6% 35%	1776
	11th to 20th	Night	24% 10% 3 6% 4 3 5% 4 5% 6% 30%	1980
	21st to end	Night	23% 11% 3 6% 5% 3 5% 4 6% 8% 27%	1980
October	1st to 10th	Night	24% 12% 4 8% 5% 3 5% 5% 5% 6% 25%	2083
	11th to 20th	Night	26% 15% 4 8% 6% 4 5% 4 4 6% 19%	2212
	21st to end	Night	29% 17% 4 7% 6% 3 4 3 4 5% 19%	2574
November	1st to 10th	Night	22% 18% 5% 9% 6% 4 5% 4 4 6% 17%	2484
	11th to 20th	Night	23% 17% 7% 8% 5% 3 5% 3 4 6% 18%	2660
	21st to end	Night	20% 17% 7% 11% 7% 4 5% 4 4 6% 17%	2759
December	1st to 10th	Night	23% 17% 9% 11% 7% 3 5% 4 4 4 14%	2850
	11th to 20th	Night	25% 20% 8% 15% 9% 3 4 3 3 3 6%	3531
	21st to end	Night	20% 17% 8% 17% 9% 4 4 4 4 4 10%	5225

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	75% 6% 10% 6% 3	1327
	11th to 20th	Day	76% 6% 8% 7% 3 1	1431
	21st to end	Day	75% 5% 7% 7% 6%	1633
February	1st to 10th	Day	71% 7% 12% 7% 3	1534
	11th to 20th	Day	71% 6% 10% 10% 3	1580
	21st to end	Day	68% 5% 10% 10% 6% 1	1462
March	1st to 10th	Day	63% 6% 10% 13% 7% 1	1813
	11th to 20th	Day	63% 7% 9% 12% 7% 1	1980
	21st to end	Day	68% 6% 9% 10% 6% 1	2178
April	1st to 10th	Day	61% 8% 9% 13% 8% 1	2193
	11th to 20th	Day	59% 8% 9% 14% 10% 1	2311
	21st to end	Day	64% 7% 10% 11% 8% 1	2340
May	1st to 10th	Day	66% 7% 8% 12% 6% 1	2340
	11th to 20th	Day	61% 9% 11% 13% 6% 1	2592
	21st to end	Day	58% 8% 13% 14% 6%	2918
June	1st to 10th	Day	73% 6% 7% 10% 4	2700
	11th to 20th	Day	62% 7% 12% 13% 5% 1	2700
	21st to end	Day	57% 10% 15% 13% 5%	2700
July	1st to 10th	Day	53% 8% 15% 18% 6%	2625
	11th to 20th	Day	50% 12% 16% 16% 5%	2618
	21st to end	Day	56% 12% 15% 14% 4	2644
August	1st to 10th	Day	55% 11% 14% 16% 4	2395
	11th to 20th	Day	52% 10% 15% 17% 6%	2305
	21st to end	Day	52% 11% 17% 16% 3	2574
September	1st to 10th	Day	49% 8% 13% 23% 8% 1	2182
	11th to 20th	Day	53% 8% 13% 17% 8%	1980
	21st to end	Day	49% 8% 19% 17% 6% 1	1980
October	1st to 10th	Day	57% 7% 12% 16% 8%	1877
	11th to 20th	Day	67% 7% 11% 12% 3	1746
	21st to end	Day	67% 7% 9% 12% 4 1	1782
November	1st to 10th	Day	63% 7% 14% 11% 5%	1594
	11th to 20th	Day	68% 6% 10% 12% 5%	1520
	21st to end	Day	69% 5% 12% 8% 5% 1	1416
December	1st to 10th	Day	71% 6% 9% 10% 3	1330
	11th to 20th	Day	74% 6% 10% 8% 2	1667
	21st to end	Day	80% 7% 7% 4 2	2442
January	1st to 10th	Night	76% 6% 9% 7% 2	2839
	11th to 20th	Night	74% 6% 9% 7% 3	2746
	21st to end	Night	69% 5% 11% 11% 4	2867
February	1st to 10th	Night	72% 4 10% 9% 4 1	2425
	11th to 20th	Night	72% 5% 10% 11% 3	2277
	21st to end	Night	67% 4 9% 13% 6% 1	1790
March	1st to 10th	Night	61% 7% 13% 12% 6% 1	2147
	11th to 20th	Night	60% 6% 11% 14% 8% 1	1980
	21st to end	Night	71% 5% 6% 11% 6% 1	2178
April	1st to 10th	Night	67% 4 7% 14% 7% 1	1765
	11th to 20th	Night	62% 6% 10% 14% 7% 1	1598
	21st to end	Night	66% 5% 7% 13% 8% 1	1620
May	1st to 10th	Night	68% 5% 9% 11% 6%	1620
	11th to 20th	Night	61% 6% 11% 16% 6%	1301
	21st to end	Night	64% 8% 12% 9% 6% 1	1357
June	1st to 10th	Night	70% 7% 9% 10% 4	1260
	11th to 20th	Night	65% 8% 11% 10% 6%	1260
	21st to end	Night	60% 9% 13% 13% 5% 1	1260
July	1st to 10th	Night	56% 9% 15% 15% 5%	1226
	11th to 20th	Night	52% 12% 13% 16% 6%	1218
	21st to end	Night	58% 9% 14% 16% 2	1430
August	1st to 10th	Night	55% 9% 17% 15% 3	1518
	11th to 20th	Night	54% 8% 15% 16% 6%	1595
	21st to end	Night	51% 9% 18% 18% 5%	1782
September	1st to 10th	Night	48% 7% 16% 19% 9% 1	1776
	11th to 20th	Night	54% 7% 13% 16% 8% 1	1980
	21st to end	Night	55% 7% 15% 17% 6%	1980
October	1st to 10th	Night	59% 7% 12% 16% 6% 1	2083
	11th to 20th	Night	67% 6% 11% 12% 4	2212
	21st to end	Night	68% 6% 10% 10% 5% 1	2574
November	1st to 10th	Night	66% 8% 12% 9% 4	2484
	11th to 20th	Night	66% 6% 12% 11% 4	2660
	21st to end	Night	67% 6% 13% 10% 4 1	2759
December	1st to 10th	Night	73% 6% 10% 9% 3	2850
	11th to 20th	Night	83% 5% 6% 4 1	3533
	21st to end	Night	72% 8% 11% 6% 2	5225

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	32% 19% 29% 13% 5% 1	370
	11th to 20th	Day	23% 23% 36% 15% 3	370
	21st to end	Day	25% 21% 34% 17% 3	393
February	1st to 10th	Day	24% 26% 32% 14% 4	340
	11th to 20th	Day	24% 23% 39% 12% 1	336
	21st to end	Day	20% 20% 36% 17% 6%	280
March	1st to 10th	Day	21% 21% 36% 16% 5%	340
	11th to 20th	Day	27% 14% 31% 20% 6% 2	340
	21st to end	Day	30% 16% 31% 16% 6% 1	374
April	1st to 10th	Day	26% 17% 28% 23% 5% 1	463
	11th to 20th	Day	28% 12% 29% 22% 7% 1	589
	21st to end	Day	28% 12% 29% 25% 6% 1	600
May	1st to 10th	Day	30% 14% 28% 19% 7% 2	603
	11th to 20th	Day	29% 8% 27% 23% 11% 2	624
	21st to end	Day	28% 8% 30% 27% 6% 1	680
June	1st to 10th	Day	42% 7% 24% 20% 6% 1	630
	11th to 20th	Day	33% 7% 24% 26% 9% 2	630
	21st to end	Day	22% 7% 24% 31% 12% 4	630
July	1st to 10th	Day	26% 7% 26% 29% 10% 2	620
	11th to 20th	Day	22% 6% 24% 32% 16% 1	618
	21st to end	Day	26% 5% 21% 36% 11%	685
August	1st to 10th	Day	28% 4 23% 31% 13% 1	625
	11th to 20th	Day	24% 7% 22% 31% 15% 1	617
	21st to end	Day	24% 8% 22% 31% 14% 1	693
September	1st to 10th	Day	21% 5% 25% 32% 15% 2	510
	11th to 20th	Day	32% 15% 21% 25% 7%	360
	21st to end	Day	24% 13% 33% 21% 7% 1	360
October	1st to 10th	Day	24% 12% 34% 20% 8% 1	360
	11th to 20th	Day	34% 12% 25% 19% 8% 2	360
	21st to end	Day	30% 20% 27% 16% 7% 1	396
November	1st to 10th	Day	32% 19% 29% 17% 3	365
	11th to 20th	Day	32% 18% 28% 17% 6% 1	370
	21st to end	Day	32% 18% 34% 13% 2	370
December	1st to 10th	Day	31% 15% 32% 16% 5% 1	370
	11th to 20th	Day	31% 27% 28% 10% 4	370
	21st to end	Day	24% 22% 32% 15% 6%	407
January	1st to 10th	Night	29% 22% 29% 15% 5%	850
	11th to 20th	Night	28% 22% 32% 13% 5%	850
	21st to end	Night	27% 19% 37% 14% 2	914
February	1st to 10th	Night	26% 23% 36% 13% 2	800
	11th to 20th	Night	31% 21% 35% 10% 3	783
	21st to end	Night	24% 17% 37% 16% 5% 2	598
March	1st to 10th	Night	25% 19% 35% 16% 5%	707
	11th to 20th	Night	22% 15% 30% 23% 9% 1	540
	21st to end	Night	35% 14% 26% 20% 5%	594
April	1st to 10th	Night	31% 14% 29% 17% 6% 2	540
	11th to 20th	Night	31% 11% 29% 22% 6% 1	534
	21st to end	Night	32% 7% 32% 23% 5% 1	540
May	1st to 10th	Night	34% 6% 27% 25% 6% 2	540
	11th to 20th	Night	31% 5% 27% 27% 9% 1	532
	21st to end	Night	32% 8% 26% 25% 9%	583
June	1st to 10th	Night	38% 7% 26% 23% 6% 1	540
	11th to 20th	Night	37% 4 20% 28% 11% 1	540
	21st to end	Night	31% 5% 24% 27% 11% 2	540
July	1st to 10th	Night	25% 5% 29% 32% 7% 2	526
	11th to 20th	Night	24% 3 28% 34% 10%	522
	21st to end	Night	26% 6% 24% 33% 11% 1	590
August	1st to 10th	Night	28% 5% 22% 33% 10% 1	538
	11th to 20th	Night	24% 5% 25% 33% 12% 1	532
	21st to end	Night	26% 5% 22% 34% 12% 1	594
September	1st to 10th	Night	23% 7% 29% 30% 10% 1	540
	11th to 20th	Night	29% 7% 28% 31% 5%	540
	21st to end	Night	31% 9% 28% 25% 6% 1	540
October	1st to 10th	Night	28% 12% 28% 23% 7% 1	591
	11th to 20th	Night	37% 11% 22% 23% 8%	682
	21st to end	Night	39% 12% 24% 19% 6%	891
November	1st to 10th	Night	32% 17% 30% 17% 4	830
	11th to 20th	Night	32% 16% 28% 18% 5%	850
	21st to end	Night	29% 22% 32% 15% 3	850
December	1st to 10th	Night	30% 18% 32% 17% 4	850
	11th to 20th	Night	34% 25% 27% 11% 3	850
	21st to end	Night	25% 21% 30% 19% 5% 1	935

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