St.John's
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St.John's clear sky chart from 2005-11-06 to 2024-01-16.

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	19% 13% 5% 9% 7% 4 5% 5% 5% 6% 21%	74644
	Night	20% 13% 5% 9% 7% 4 5% 5% 5% 6% 20%	75149
Transparency	Day	62% 8% 11% 13% 5%	74334
	Night	62% 9% 11% 12% 5%	74994
Seeing	Day	26% 15% 30% 22% 7% 1	16999
	Night	26% 15% 31% 21% 6%	23656

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	19% 15% 9% 11% 8% 5% 6% 5% 5% 6% 12%	1326
	11th to 20th	Day	18% 14% 6% 12% 10% 4 6% 3 4 6% 15%	1425
	21st to end	Day	19% 14% 8% 10% 8% 4 7% 4 5% 7% 14%	1584
February	1st to 10th	Day	18% 12% 6% 10% 9% 6% 7% 6% 5% 5% 15%	1597
	11th to 20th	Day	19% 13% 6% 11% 8% 6% 7% 5% 6% 7% 13%	1573
	21st to end	Day	13% 13% 9% 13% 10% 6% 6% 5% 5% 5% 15%	1462
March	1st to 10th	Day	17% 14% 7% 11% 9% 6% 6% 5% 3 5% 16%	1831
	11th to 20th	Day	17% 13% 7% 10% 8% 5% 6% 4 5% 6% 19%	1980
	21st to end	Day	22% 16% 7% 10% 8% 4 5% 4 3 5% 15%	2178
April	1st to 10th	Day	20% 13% 6% 11% 9% 4 5% 6% 4 5% 17%	2164
	11th to 20th	Day	23% 15% 6% 9% 8% 3 5% 3 4 4 20%	2311
	21st to end	Day	24% 17% 6% 8% 7% 3 3 4 3 5% 20%	2340
May	1st to 10th	Day	21% 16% 7% 10% 8% 3 5% 4 4 5% 18%	2340
	11th to 20th	Day	20% 15% 4 8% 7% 3 5% 4 5% 6% 21%	2489
	21st to end	Day	19% 13% 4 7% 6% 4 5% 4 6% 7% 24%	2918
June	1st to 10th	Day	24% 20% 5% 9% 7% 4 4 3 4 4 15%	2700
	11th to 20th	Day	21% 16% 5% 7% 5% 3 5% 5% 5% 6% 21%	2700
	21st to end	Day	21% 10% 4 9% 7% 4 6% 4 6% 7% 23%	2700
July	1st to 10th	Day	17% 10% 3 7% 7% 3 5% 5% 6% 6% 29%	2700
	11th to 20th	Day	16% 8% 3 7% 8% 5% 6% 5% 7% 8% 26%	2700
	21st to end	Day	19% 10% 4 8% 8% 3 6% 6% 6% 7% 24%	2768
August	1st to 10th	Day	23% 10% 5% 7% 6% 3 6% 5% 5% 7% 23%	2347
	11th to 20th	Day	19% 10% 4 9% 7% 4 5% 6% 5% 8% 25%	2305
	21st to end	Day	19% 9% 3 7% 7% 4 5% 6% 6% 7% 25%	2574
September	1st to 10th	Day	17% 10% 4 8% 6% 4 4 5% 5% 7% 30%	2164
	11th to 20th	Day	22% 10% 3 6% 5% 4 4 5% 5% 7% 30%	1980
	21st to end	Day	18% 9% 3 7% 5% 4 4 4 5% 8% 32%	1980
October	1st to 10th	Day	19% 10% 4 8% 6% 3 5% 5% 7% 6% 26%	1868
	11th to 20th	Day	22% 17% 3 7% 6% 4 5% 4 5% 4 22%	1787
	21st to end	Day	22% 17% 6% 8% 8% 4 4 4 4 5% 17%	1782
November	1st to 10th	Day	19% 14% 5% 9% 7% 3 5% 5% 4 6% 23%	1610
	11th to 20th	Day	18% 14% 7% 10% 6% 3 6% 5% 5% 6% 19%	1520
	21st to end	Day	20% 18% 7% 9% 9% 3 4 4 4 5% 17%	1501
December	1st to 10th	Day	21% 17% 7% 10% 7% 3 5% 4 4 5% 16%	1330
	11th to 20th	Day	14% 18% 8% 12% 9% 5% 6% 4 4 6% 16%	1668
	21st to end	Day	16% 17% 10% 13% 9% 4 5% 4 5% 5% 12%	2442
January	1st to 10th	Night	19% 15% 8% 12% 10% 5% 6% 5% 5% 4 13%	2839
	11th to 20th	Night	19% 15% 6% 10% 8% 4 6% 5% 5% 6% 15%	2644
	21st to end	Night	18% 12% 6% 11% 9% 4 6% 5% 6% 6% 16%	2772
February	1st to 10th	Night	19% 10% 6% 12% 12% 5% 6% 5% 5% 5% 15%	2362
	11th to 20th	Night	20% 12% 5% 10% 9% 5% 8% 6% 5% 5% 15%	2273
	21st to end	Night	13% 13% 9% 11% 11% 6% 6% 5% 4 5% 17%	1790
March	1st to 10th	Night	18% 12% 5% 10% 8% 4 7% 5% 5% 5% 19%	2116
	11th to 20th	Night	14% 12% 5% 10% 8% 5% 6% 6% 6% 7% 21%	1979
	21st to end	Night	24% 16% 7% 11% 8% 5% 4 3 4 3 15%	2178
April	1st to 10th	Night	22% 14% 8% 8% 6% 3 4 4 4 5% 21%	1793
	11th to 20th	Night	24% 15% 4 9% 6% 3 4 4 4 5% 23%	1598
	21st to end	Night	24% 18% 5% 8% 7% 2 4 3 3 5% 21%	1620
May	1st to 10th	Night	24% 17% 6% 9% 6% 3 4 5% 4 6% 17%	1620
	11th to 20th	Night	21% 12% 6% 8% 6% 5% 4 4 5% 8% 23%	1401
	21st to end	Night	25% 11% 4 7% 7% 2 5% 5% 5% 7% 23%	1356
June	1st to 10th	Night	26% 17% 5% 8% 6% 3 5% 5% 5% 5% 16%	1260
	11th to 20th	Night	22% 12% 4 6% 7% 4 5% 6% 6% 7% 19%	1260
	21st to end	Night	21% 11% 5% 7% 6% 3 4 4 4 8% 25%	1260
July	1st to 10th	Night	19% 10% 5% 8% 7% 3 5% 5% 6% 9% 24%	1260
	11th to 20th	Night	17% 10% 4 6% 6% 4 8% 7% 7% 8% 23%	1260
	21st to end	Night	20% 9% 4 7% 8% 3 7% 5% 6% 8% 24%	1546
August	1st to 10th	Night	20% 10% 4 7% 6% 4 6% 4 6% 8% 25%	1590
	11th to 20th	Night	21% 12% 5% 6% 6% 4 4 4 4 7% 27%	1595
	21st to end	Night	21% 10% 4 5% 5% 3 4 5% 6% 8% 30%	1782
September	1st to 10th	Night	18% 10% 3 6% 5% 3 5% 5% 7% 9% 30%	1795
	11th to 20th	Night	23% 11% 3 6% 6% 3 5% 4 5% 7% 28%	1980
	21st to end	Night	19% 12% 3 6% 5% 3 4 4 4 7% 32%	1980
October	1st to 10th	Night	19% 11% 4 8% 7% 4 5% 4 5% 6% 27%	2092
	11th to 20th	Night	22% 14% 4 8% 7% 3 5% 4 5% 6% 21%	2168
	21st to end	Night	23% 17% 4 7% 7% 4 4 5% 4 6% 20%	2574
November	1st to 10th	Night	21% 13% 4 8% 7% 4 5% 5% 5% 6% 23%	2465
	11th to 20th	Night	19% 14% 7% 10% 6% 4 5% 5% 5% 6% 20%	2660
	21st to end	Night	18% 15% 5% 9% 8% 4 5% 5% 5% 6% 20%	2675
December	1st to 10th	Night	18% 18% 6% 10% 6% 4 5% 5% 5% 5% 17%	2850
	11th to 20th	Night	19% 17% 7% 13% 9% 5% 6% 5% 4 4 12%	3531
	21st to end	Night	18% 16% 6% 11% 8% 4 5% 4 5% 5% 18%	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	71% 9% 10% 7% 3	1327
	11th to 20th	Day	68% 8% 12% 7% 4 1	1425
	21st to end	Day	67% 9% 8% 9% 6%	1584
February	1st to 10th	Day	68% 9% 10% 7% 7% 1	1597
	11th to 20th	Day	66% 10% 11% 9% 4 1	1580
	21st to end	Day	69% 7% 12% 6% 5% 1	1462
March	1st to 10th	Day	67% 7% 9% 11% 5% 1	1836
	11th to 20th	Day	63% 7% 12% 12% 6%	1980
	21st to end	Day	70% 7% 9% 9% 4 2	2178
April	1st to 10th	Day	66% 6% 8% 12% 7% 1	2164
	11th to 20th	Day	67% 6% 8% 11% 8% 1	2311
	21st to end	Day	66% 7% 8% 11% 8% 1	2340
May	1st to 10th	Day	66% 7% 9% 12% 6% 1	2340
	11th to 20th	Day	62% 8% 11% 13% 6%	2493
	21st to end	Day	56% 9% 13% 15% 6%	2918
June	1st to 10th	Day	73% 6% 7% 9% 3 1	2700
	11th to 20th	Day	62% 10% 11% 11% 6%	2700
	21st to end	Day	60% 10% 11% 15% 5%	2700
July	1st to 10th	Day	53% 10% 13% 16% 8%	2625
	11th to 20th	Day	54% 10% 15% 15% 5%	2618
	21st to end	Day	57% 12% 13% 14% 4	2613
August	1st to 10th	Day	58% 10% 11% 16% 5%	2333
	11th to 20th	Day	56% 10% 12% 15% 7% 1	2305
	21st to end	Day	54% 9% 16% 18% 4	2574
September	1st to 10th	Day	50% 9% 13% 21% 7%	2164
	11th to 20th	Day	52% 8% 11% 17% 11%	1980
	21st to end	Day	49% 8% 17% 19% 7% 1	1980
October	1st to 10th	Day	55% 7% 14% 16% 8% 1	1868
	11th to 20th	Day	63% 7% 10% 15% 5%	1787
	21st to end	Day	67% 8% 10% 10% 5%	1782
November	1st to 10th	Day	60% 8% 15% 12% 5%	1610
	11th to 20th	Day	62% 9% 11% 12% 5% 1	1520
	21st to end	Day	68% 6% 13% 9% 4	1501
December	1st to 10th	Day	68% 9% 10% 9% 4	1330
	11th to 20th	Day	67% 8% 12% 8% 4	1667
	21st to end	Day	72% 8% 9% 9% 2	2442
January	1st to 10th	Night	69% 10% 10% 7% 4 1	2839
	11th to 20th	Night	67% 11% 9% 8% 5%	2644
	21st to end	Night	63% 11% 10% 11% 5%	2772
February	1st to 10th	Night	68% 8% 10% 9% 5%	2362
	11th to 20th	Night	64% 12% 11% 10% 3	2277
	21st to end	Night	66% 8% 10% 9% 6% 1	1790
March	1st to 10th	Night	62% 9% 12% 10% 7% 1	2124
	11th to 20th	Night	59% 9% 13% 12% 6% 1	1980
	21st to end	Night	71% 6% 8% 9% 5% 1	2178
April	1st to 10th	Night	64% 6% 9% 12% 9% 1	1793
	11th to 20th	Night	62% 6% 10% 13% 8% 1	1598
	21st to end	Night	66% 6% 7% 11% 8% 1	1620
May	1st to 10th	Night	66% 7% 11% 10% 6%	1620
	11th to 20th	Night	59% 8% 9% 16% 6% 1	1402
	21st to end	Night	59% 10% 12% 13% 5%	1357
June	1st to 10th	Night	71% 7% 7% 10% 4	1260
	11th to 20th	Night	61% 10% 12% 11% 5%	1260
	21st to end	Night	57% 9% 12% 16% 5%	1260
July	1st to 10th	Night	55% 11% 12% 16% 6%	1226
	11th to 20th	Night	54% 12% 14% 15% 5%	1218
	21st to end	Night	58% 12% 10% 16% 4	1461
August	1st to 10th	Night	56% 10% 14% 15% 4	1579
	11th to 20th	Night	57% 8% 11% 16% 7%	1595
	21st to end	Night	52% 8% 17% 19% 4	1782
September	1st to 10th	Night	48% 11% 13% 20% 7% 1	1795
	11th to 20th	Night	55% 9% 12% 16% 8% 1	1980
	21st to end	Night	53% 7% 13% 19% 8%	1980
October	1st to 10th	Night	56% 8% 11% 18% 6%	2092
	11th to 20th	Night	61% 8% 13% 12% 5%	2168
	21st to end	Night	65% 7% 11% 10% 6% 1	2574
November	1st to 10th	Night	59% 10% 14% 12% 5%	2465
	11th to 20th	Night	62% 10% 13% 11% 3 1	2660
	21st to end	Night	61% 8% 13% 11% 5% 1	2675
December	1st to 10th	Night	66% 10% 9% 11% 5%	2850
	11th to 20th	Night	70% 9% 11% 6% 4	3533
	21st to end	Night	63% 10% 13% 12% 3	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	28% 22% 31% 15% 2 1	370
	11th to 20th	Day	24% 21% 36% 15% 3 1	355
	21st to end	Day	24% 24% 32% 17% 3	374
February	1st to 10th	Day	24% 26% 32% 16% 2	340
	11th to 20th	Day	27% 25% 35% 11% 1	336
	21st to end	Day	19% 24% 35% 18% 3	280
March	1st to 10th	Day	22% 30% 34% 10% 3	340
	11th to 20th	Day	24% 19% 31% 21% 4 2	340
	21st to end	Day	27% 20% 34% 12% 6% 1	374
April	1st to 10th	Day	27% 24% 27% 16% 5% 1	452
	11th to 20th	Day	28% 17% 31% 17% 7% 1	589
	21st to end	Day	30% 12% 32% 20% 6% 1	600
May	1st to 10th	Day	27% 15% 35% 14% 7% 2	603
	11th to 20th	Day	25% 10% 32% 24% 9% 1	624
	21st to end	Day	24% 12% 30% 27% 6% 1	680
June	1st to 10th	Day	35% 10% 27% 22% 6%	630
	11th to 20th	Day	29% 10% 27% 25% 7% 2	630
	21st to end	Day	25% 6% 24% 32% 10% 2	630
July	1st to 10th	Day	24% 8% 30% 28% 8% 2	620
	11th to 20th	Day	22% 7% 29% 32% 10% 1	618
	21st to end	Day	25% 7% 26% 32% 11% 1	685
August	1st to 10th	Day	26% 6% 28% 28% 10% 2	625
	11th to 20th	Day	23% 6% 22% 36% 13% 1	617
	21st to end	Day	23% 7% 26% 29% 14% 1	693
September	1st to 10th	Day	19% 8% 31% 29% 12% 2	506
	11th to 20th	Day	28% 13% 29% 23% 7% 1	360
	21st to end	Day	22% 11% 32% 27% 7% 1	360
October	1st to 10th	Day	24% 10% 34% 26% 6%	360
	11th to 20th	Day	28% 14% 29% 19% 8% 1	360
	21st to end	Day	29% 19% 29% 18% 5% 1	396
November	1st to 10th	Day	23% 22% 29% 19% 5%	365
	11th to 20th	Day	28% 20% 29% 16% 6%	370
	21st to end	Day	29% 24% 32% 13% 2	370
December	1st to 10th	Day	29% 19% 32% 15% 5%	370
	11th to 20th	Day	27% 29% 29% 12% 2	370
	21st to end	Day	22% 23% 35% 15% 4	407
January	1st to 10th	Night	26% 23% 36% 12% 3	850
	11th to 20th	Night	26% 20% 35% 15% 4	826
	21st to end	Night	25% 21% 35% 18% 2	880
February	1st to 10th	Night	25% 25% 36% 13% 1	800
	11th to 20th	Night	28% 22% 35% 12% 2	783
	21st to end	Night	22% 19% 36% 18% 5% 1	598
March	1st to 10th	Night	25% 22% 34% 17% 3	684
	11th to 20th	Night	19% 19% 31% 25% 7% 1	540
	21st to end	Night	31% 17% 31% 18% 4	594
April	1st to 10th	Night	28% 19% 30% 17% 6% 1	540
	11th to 20th	Night	31% 14% 30% 19% 6%	534
	21st to end	Night	32% 11% 30% 19% 7% 1	540
May	1st to 10th	Night	31% 9% 28% 23% 8% 1	540
	11th to 20th	Night	28% 6% 31% 24% 9% 1	532
	21st to end	Night	26% 10% 28% 29% 6% 1	583
June	1st to 10th	Night	34% 8% 28% 22% 7% 1	540
	11th to 20th	Night	28% 8% 25% 27% 12% 1	540
	21st to end	Night	28% 6% 23% 31% 11% 1	540
July	1st to 10th	Night	24% 6% 29% 33% 7% 2	526
	11th to 20th	Night	22% 5% 30% 34% 9%	522
	21st to end	Night	24% 6% 26% 34% 11%	590
August	1st to 10th	Night	26% 4 22% 36% 10% 1	538
	11th to 20th	Night	26% 5% 24% 32% 12% 1	532
	21st to end	Night	25% 7% 27% 32% 9%	594
September	1st to 10th	Night	20% 7% 30% 35% 7% 2	540
	11th to 20th	Night	25% 11% 32% 25% 7% 1	540
	21st to end	Night	26% 9% 30% 29% 6% 1	540
October	1st to 10th	Night	25% 10% 34% 23% 7% 1	596
	11th to 20th	Night	27% 15% 29% 20% 7% 1	638
	21st to end	Night	30% 19% 28% 18% 5%	891
November	1st to 10th	Night	26% 20% 31% 18% 5%	830
	11th to 20th	Night	26% 17% 31% 20% 5%	850
	21st to end	Night	26% 22% 33% 15% 3	850
December	1st to 10th	Night	27% 22% 30% 16% 4	850
	11th to 20th	Night	30% 26% 31% 11% 2	850
	21st to end	Night	23% 21% 32% 18% 5% 1	935

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