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 2024-11-06.

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	20% 16% 5% 11% 6% 5% 4 3 5% 6% 20%	101649
	Night	20% 16% 6% 12% 6% 5% 4 3 4 5% 19%	97561
Transparency	Day	63% 8% 11% 13% 5%	105149
	Night	63% 8% 11% 13% 4	102179
Seeing	Day	27% 16% 30% 20% 6% 1	18186
	Night	27% 16% 32% 20% 5%	24688

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	17% 16% 10% 18% 6% 5% 4 3 4 5% 13%	2216
	11th to 20th	Day	17% 15% 7% 18% 8% 5% 4 3 4 3 16%	2442
	21st to end	Day	15% 17% 8% 18% 7% 5% 6% 3 4 5% 13%	2783
February	1st to 10th	Day	18% 15% 7% 15% 9% 7% 5% 4 4 4 13%	1679
	11th to 20th	Day	20% 17% 7% 15% 8% 5% 4 4 4 5% 11%	1663
	21st to end	Day	14% 16% 8% 15% 10% 7% 4 2 3 4 14%	1555
March	1st to 10th	Day	25% 14% 6% 15% 6% 5% 4 3 3 4 16%	3174
	11th to 20th	Day	19% 19% 10% 15% 6% 5% 4 3 4 4 12%	3480
	21st to end	Day	21% 19% 8% 13% 6% 5% 4 3 4 5% 13%	3817
April	1st to 10th	Day	19% 20% 7% 12% 7% 5% 4 3 4 5% 15%	2286
	11th to 20th	Day	23% 20% 6% 9% 5% 4 3 3 4 4 20%	2441
	21st to end	Day	21% 20% 7% 9% 4 4 4 3 4 5% 20%	2470
May	1st to 10th	Day	23% 26% 7% 8% 4 3 3 2 4 5% 14%	4105
	11th to 20th	Day	23% 19% 6% 12% 5% 4 4 3 4 5% 14%	4429
	21st to end	Day	19% 21% 6% 9% 5% 4 4 3 5% 6% 19%	5173
June	1st to 10th	Day	27% 19% 5% 9% 6% 4 3 3 5% 5% 15%	2850
	11th to 20th	Day	22% 16% 3 7% 5% 5% 4 4 5% 6% 23%	2850
	21st to end	Day	21% 11% 4 9% 6% 5% 4 4 5% 7% 24%	2850
July	1st to 10th	Day	26% 12% 4 9% 4 4 4 3 5% 6% 23%	4750
	11th to 20th	Day	16% 10% 4 10% 6% 5% 6% 5% 6% 6% 26%	4750
	21st to end	Day	15% 9% 3 7% 5% 4 4 4 6% 8% 36%	4846
August	1st to 10th	Day	23% 11% 4 11% 6% 5% 5% 3 5% 6% 23%	4145
	11th to 20th	Day	19% 11% 3 9% 6% 5% 5% 4 6% 7% 27%	4046
	21st to end	Day	21% 10% 3 7% 4 4 5% 3 6% 7% 30%	4532
September	1st to 10th	Day	19% 10% 3 9% 4 4 4 4 5% 7% 31%	2282
	11th to 20th	Day	21% 11% 3 7% 5% 4 3 4 5% 6% 31%	2090
	21st to end	Day	18% 11% 3 8% 5% 4 4 3 6% 7% 32%	2090
October	1st to 10th	Day	22% 13% 3 7% 5% 5% 4 4 5% 7% 25%	1974
	11th to 20th	Day	22% 17% 3 9% 6% 4 4 3 5% 5% 22%	1882
	21st to end	Day	22% 21% 4 9% 6% 5% 4 3 4 4 17%	1881
November	1st to 10th	Day	19% 17% 5% 10% 6% 4 4 3 4 6% 22%	1661
	11th to 20th	Day	18% 18% 6% 9% 6% 5% 5% 4 5% 6% 18%	1520
	21st to end	Day	20% 23% 6% 9% 5% 4 4 2 4 5% 16%	1497
December	1st to 10th	Day	20% 20% 7% 12% 6% 4 4 3 4 6% 15%	1330
	11th to 20th	Day	13% 21% 8% 15% 8% 5% 4 3 4 5% 15%	1668
	21st to end	Day	16% 21% 9% 15% 6% 6% 4 3 5% 4 11%	2442
January	1st to 10th	Night	16% 19% 9% 16% 9% 7% 4 3 4 3 10%	4739
	11th to 20th	Night	16% 13% 6% 21% 7% 5% 5% 3 4 5% 14%	4524
	21st to end	Night	13% 16% 9% 18% 7% 5% 6% 3 4 4 16%	4884
February	1st to 10th	Night	19% 14% 7% 16% 9% 5% 5% 3 5% 4 13%	2499
	11th to 20th	Night	20% 16% 6% 15% 9% 5% 4 3 4 4 13%	2403
	21st to end	Night	14% 16% 9% 16% 6% 7% 4 3 4 4 17%	1896
March	1st to 10th	Night	23% 13% 7% 12% 6% 4 4 3 4 4 19%	3666
	11th to 20th	Night	15% 16% 7% 17% 7% 6% 4 3 5% 5% 14%	3479
	21st to end	Night	26% 19% 8% 12% 4 3 4 3 3 3 15%	3815
April	1st to 10th	Night	22% 20% 7% 8% 5% 4 4 3 3 4 19%	1891
	11th to 20th	Night	23% 18% 5% 9% 6% 4 3 2 4 4 22%	1688
	21st to end	Night	21% 19% 6% 11% 5% 4 4 3 3 3 20%	1710
May	1st to 10th	Night	24% 24% 8% 9% 4 3 3 2 3 4 14%	2845
	11th to 20th	Night	23% 21% 7% 12% 5% 4 3 2 3 5% 15%	2470
	21st to end	Night	22% 18% 6% 10% 5% 4 3 4 5% 5% 18%	2412
June	1st to 10th	Night	24% 20% 4 9% 5% 5% 5% 3 4 4 17%	1330
	11th to 20th	Night	23% 14% 2 8% 7% 4 5% 4 7% 7% 19%	1330
	21st to end	Night	22% 12% 3 8% 6% 4 5% 4 6% 8% 23%	1330
July	1st to 10th	Night	33% 12% 4 8% 4 4 4 3 5% 5% 18%	2220
	11th to 20th	Night	19% 13% 4 10% 5% 7% 6% 5% 7% 7% 17%	2220
	21st to end	Night	17% 8% 3 7% 5% 5% 5% 4 6% 6% 36%	2716
August	1st to 10th	Night	22% 12% 3 8% 4 4 5% 4 7% 6% 24%	2793
	11th to 20th	Night	23% 10% 3 7% 4 3 4 3 5% 7% 28%	2791
	21st to end	Night	27% 9% 3 6% 4 4 4 4 4 6% 28%	3135
September	1st to 10th	Night	19% 10% 3 7% 4 4 5% 4 6% 7% 30%	1896
	11th to 20th	Night	24% 12% 3 8% 4 5% 4 3 5% 7% 27%	2090
	21st to end	Night	19% 14% 3 6% 5% 5% 4 3 5% 6% 30%	2090
October	1st to 10th	Night	21% 13% 4 8% 6% 4 4 2 5% 6% 26%	2205
	11th to 20th	Night	23% 16% 4 8% 6% 5% 4 3 5% 6% 21%	2294
	21st to end	Night	24% 19% 4 8% 4 4 4 3 4 5% 20%	2717
November	1st to 10th	Night	21% 17% 5% 8% 5% 5% 5% 3 4 5% 22%	2537
	11th to 20th	Night	20% 17% 7% 11% 5% 4 4 4 5% 6% 19%	2660
	21st to end	Night	17% 19% 6% 11% 5% 4 5% 4 5% 6% 19%	2680
December	1st to 10th	Night	18% 21% 7% 13% 6% 4 4 3 3 4 17%	2850
	11th to 20th	Night	17% 20% 8% 16% 8% 5% 5% 4 4 4 10%	3531
	21st to end	Night	17% 20% 7% 13% 5% 4 4 3 3 4 17%	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	65% 9% 8% 11% 5% 2	2217
	11th to 20th	Day	66% 9% 9% 11% 5% 1	2442
	21st to end	Day	67% 7% 7% 12% 7%	2783
February	1st to 10th	Day	70% 9% 8% 7% 6% 1	1679
	11th to 20th	Day	69% 9% 9% 9% 4 1	1670
	21st to end	Day	69% 7% 10% 7% 6% 1	1555
March	1st to 10th	Day	69% 6% 8% 11% 5% 1	3179
	11th to 20th	Day	71% 10% 8% 8% 3	3480
	21st to end	Day	73% 7% 8% 9% 2 1	3817
April	1st to 10th	Day	71% 6% 7% 10% 5% 1	2286
	11th to 20th	Day	67% 6% 8% 11% 8% 1	2441
	21st to end	Day	68% 5% 8% 10% 8% 1	2470
May	1st to 10th	Day	69% 9% 8% 9% 4	4120
	11th to 20th	Day	69% 10% 8% 9% 3	4433
	21st to end	Day	62% 10% 9% 14% 5%	5173
June	1st to 10th	Day	73% 5% 7% 11% 3 1	2850
	11th to 20th	Day	61% 8% 12% 13% 5%	2850
	21st to end	Day	60% 10% 10% 15% 5%	2850
July	1st to 10th	Day	61% 7% 12% 14% 5%	4675
	11th to 20th	Day	56% 8% 17% 13% 5%	4668
	21st to end	Day	46% 7% 20% 21% 6%	4692
August	1st to 10th	Day	62% 7% 11% 17% 3	4131
	11th to 20th	Day	56% 8% 13% 18% 4	4085
	21st to end	Day	52% 7% 16% 23% 3	4532
September	1st to 10th	Day	51% 7% 12% 22% 7%	2282
	11th to 20th	Day	53% 6% 12% 18% 10%	2090
	21st to end	Day	51% 7% 16% 20% 6%	2090
October	1st to 10th	Day	64% 7% 10% 14% 4	3280
	11th to 20th	Day	55% 9% 14% 15% 8%	3120
	21st to end	Day	65% 7% 8% 14% 6%	3092
November	1st to 10th	Day	61% 8% 15% 11% 5%	1661
	11th to 20th	Day	66% 7% 9% 13% 4 1	1520
	21st to end	Day	69% 7% 11% 9% 4	1497
December	1st to 10th	Day	70% 7% 8% 11% 3	1330
	11th to 20th	Day	70% 7% 10% 9% 4	1667
	21st to end	Day	72% 8% 9% 10% 2	2442
January	1st to 10th	Night	64% 12% 8% 9% 5% 1	4739
	11th to 20th	Night	64% 10% 11% 11% 3	4524
	21st to end	Night	65% 8% 12% 11% 4	4884
February	1st to 10th	Night	70% 8% 9% 9% 4 1	2499
	11th to 20th	Night	68% 9% 9% 10% 3	2407
	21st to end	Night	65% 7% 9% 12% 5%	1896
March	1st to 10th	Night	63% 8% 10% 14% 4	3674
	11th to 20th	Night	65% 11% 11% 9% 3	3480
	21st to end	Night	72% 6% 8% 11% 3 1	3815
April	1st to 10th	Night	66% 7% 7% 12% 8% 1	1891
	11th to 20th	Night	65% 6% 7% 13% 8% 1	1688
	21st to end	Night	69% 5% 7% 11% 8% 1	1710
May	1st to 10th	Night	71% 7% 8% 10% 4	2850
	11th to 20th	Night	72% 7% 6% 11% 5%	2471
	21st to end	Night	62% 12% 8% 11% 6%	2413
June	1st to 10th	Night	70% 8% 8% 10% 4	1330
	11th to 20th	Night	61% 8% 15% 11% 5%	1330
	21st to end	Night	59% 8% 13% 15% 5%	1330
July	1st to 10th	Night	67% 8% 8% 13% 4	2186
	11th to 20th	Night	62% 11% 15% 9% 3	2178
	21st to end	Night	47% 8% 17% 23% 4	2631
August	1st to 10th	Night	57% 9% 16% 16% 3	2782
	11th to 20th	Night	53% 9% 14% 19% 4	2818
	21st to end	Night	54% 8% 14% 21% 3	3134
September	1st to 10th	Night	50% 9% 14% 19% 7% 1	1896
	11th to 20th	Night	57% 7% 13% 15% 8% 1	2090
	21st to end	Night	55% 6% 13% 19% 7%	2090
October	1st to 10th	Night	64% 6% 13% 14% 3	3686
	11th to 20th	Night	53% 11% 16% 13% 6%	3805
	21st to end	Night	59% 8% 10% 16% 6%	4467
November	1st to 10th	Night	62% 8% 13% 12% 5%	2537
	11th to 20th	Night	65% 8% 11% 12% 3 1	2660
	21st to end	Night	61% 8% 13% 11% 5%	2680
December	1st to 10th	Night	68% 8% 9% 11% 4	2850
	11th to 20th	Night	74% 7% 8% 7% 4	3533
	21st to end	Night	64% 10% 11% 13% 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% 33% 13% 3 1	370
	11th to 20th	Day	26% 22% 35% 12% 3 1	370
	21st to end	Day	26% 22% 34% 15% 2	407
February	1st to 10th	Day	25% 24% 31% 16% 4 1	370
	11th to 20th	Day	29% 27% 33% 9% 3	366
	21st to end	Day	17% 27% 36% 16% 3	307
March	1st to 10th	Day	26% 28% 34% 9% 3	370
	11th to 20th	Day	23% 22% 32% 17% 5% 2	370
	21st to end	Day	27% 24% 31% 13% 5% 1	407
April	1st to 10th	Day	29% 26% 28% 12% 4 1	492
	11th to 20th	Day	31% 20% 26% 15% 7% 1	639
	21st to end	Day	30% 18% 31% 16% 4	650
May	1st to 10th	Day	31% 17% 28% 16% 7% 1	653
	11th to 20th	Day	26% 12% 32% 22% 7% 1	674
	21st to end	Day	26% 14% 33% 21% 5% 1	735
June	1st to 10th	Day	38% 12% 27% 17% 5%	680
	11th to 20th	Day	31% 13% 29% 20% 6% 2	680
	21st to end	Day	26% 8% 30% 26% 8% 2	680
July	1st to 10th	Day	26% 9% 33% 24% 7% 1	670
	11th to 20th	Day	22% 8% 32% 28% 9% 1	668
	21st to end	Day	24% 11% 29% 27% 9% 1	740
August	1st to 10th	Day	23% 8% 31% 28% 9% 1	675
	11th to 20th	Day	22% 11% 24% 32% 10% 1	667
	21st to end	Day	24% 10% 25% 27% 13% 1	748
September	1st to 10th	Day	22% 8% 30% 27% 11% 2	541
	11th to 20th	Day	29% 14% 29% 21% 7% 1	390
	21st to end	Day	25% 13% 32% 22% 8% 1	390
October	1st to 10th	Day	28% 10% 33% 23% 6%	390
	11th to 20th	Day	29% 14% 30% 18% 7% 2	390
	21st to end	Day	31% 23% 25% 16% 3 1	429
November	1st to 10th	Day	27% 23% 27% 18% 5% 1	381
	11th to 20th	Day	31% 21% 26% 15% 7%	370
	21st to end	Day	31% 23% 31% 12% 3 1	370
December	1st to 10th	Day	28% 23% 27% 16% 6%	370
	11th to 20th	Day	27% 32% 27% 12% 2	370
	21st to end	Day	25% 22% 34% 15% 3 1	407
January	1st to 10th	Night	26% 22% 35% 14% 3	850
	11th to 20th	Night	28% 19% 35% 16% 3	850
	21st to end	Night	25% 20% 34% 18% 2	935
February	1st to 10th	Night	25% 25% 33% 16% 2	850
	11th to 20th	Night	28% 22% 35% 12% 3	833
	21st to end	Night	21% 20% 35% 20% 4	633
March	1st to 10th	Night	26% 21% 35% 16% 3	725
	11th to 20th	Night	20% 21% 29% 24% 7%	570
	21st to end	Night	31% 16% 31% 19% 2	627
April	1st to 10th	Night	28% 20% 30% 15% 6% 1	570
	11th to 20th	Night	32% 16% 29% 19% 5%	564
	21st to end	Night	29% 16% 31% 19% 5%	570
May	1st to 10th	Night	31% 12% 27% 24% 6% 1	570
	11th to 20th	Night	29% 10% 31% 21% 8%	562
	21st to end	Night	26% 12% 32% 24% 5% 1	616
June	1st to 10th	Night	34% 9% 30% 21% 6%	570
	11th to 20th	Night	26% 11% 29% 24% 9% 1	570
	21st to end	Night	25% 12% 28% 26% 8% 1	570
July	1st to 10th	Night	24% 7% 35% 28% 5% 1	556
	11th to 20th	Night	25% 6% 34% 28% 7%	552
	21st to end	Night	24% 6% 33% 29% 8%	623
August	1st to 10th	Night	23% 6% 29% 33% 8% 1	568
	11th to 20th	Night	24% 7% 30% 31% 8%	562
	21st to end	Night	26% 7% 30% 30% 8%	627
September	1st to 10th	Night	20% 8% 34% 29% 8% 1	570
	11th to 20th	Night	27% 12% 30% 25% 6%	570
	21st to end	Night	28% 9% 31% 25% 7% 1	570
October	1st to 10th	Night	28% 10% 32% 23% 6%	631
	11th to 20th	Night	30% 14% 30% 19% 6% 1	684
	21st to end	Night	32% 18% 27% 19% 5%	946
November	1st to 10th	Night	27% 20% 31% 17% 5%	859
	11th to 20th	Night	26% 17% 31% 20% 5%	850
	21st to end	Night	26% 22% 33% 15% 4	850
December	1st to 10th	Night	26% 22% 31% 16% 5%	850
	11th to 20th	Night	31% 25% 31% 10% 2	850
	21st to end	Night	24% 20% 33% 18% 4 1	935

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