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 2025-11-03.

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% 16% 6% 11% 6% 4 4 3 4 5% 21%	126895
	Night	19% 17% 6% 12% 6% 4 4 3 4 5% 19%	123391
Transparency	Day	63% 7% 11% 14% 5%	130377
	Night	64% 8% 11% 13% 5%	128026
Seeing	Day	27% 17% 30% 19% 6% 1	19577
	Night	27% 16% 31% 20% 5%	26044

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% 21% 11% 14% 5% 4 4 2 3 4 12%	3176
	11th to 20th	Day	16% 20% 9% 18% 7% 5% 3 2 3 3 14%	3477
	21st to end	Day	11% 16% 8% 20% 8% 5% 6% 3 4 5% 15%	3982
February	1st to 10th	Day	18% 15% 7% 15% 9% 6% 5% 4 4 4 13%	1768
	11th to 20th	Day	20% 17% 7% 15% 8% 5% 4 3 4 5% 12%	1753
	21st to end	Day	14% 16% 8% 16% 10% 7% 4 2 3 4 14%	1635
March	1st to 10th	Day	21% 14% 6% 17% 8% 6% 4 3 3 4 14%	4562
	11th to 20th	Day	20% 17% 8% 16% 6% 4 3 3 3 3 16%	4980
	21st to end	Day	18% 20% 9% 13% 6% 5% 4 3 4 4 14%	5467
April	1st to 10th	Day	18% 20% 7% 12% 7% 5% 4 3 4 5% 15%	2407
	11th to 20th	Day	23% 19% 6% 9% 5% 4 3 3 4 4 21%	2571
	21st to end	Day	22% 20% 6% 9% 4 4 4 3 4 5% 19%	2600
May	1st to 10th	Day	21% 26% 6% 9% 4 3 3 2 3 4 18%	5885
	11th to 20th	Day	20% 20% 6% 11% 4 4 4 3 4 5% 19%	6356
	21st to end	Day	18% 23% 6% 8% 4 4 3 3 4 6% 19%	7428
June	1st to 10th	Day	26% 19% 5% 9% 6% 4 3 3 5% 4 16%	3000
	11th to 20th	Day	22% 16% 4 7% 5% 4 4 4 5% 6% 24%	3000
	21st to end	Day	21% 12% 4 9% 5% 5% 4 4 5% 7% 24%	3000
July	1st to 10th	Day	23% 12% 4 9% 5% 4 4 3 5% 7% 23%	6800
	11th to 20th	Day	15% 9% 4 9% 6% 5% 6% 5% 6% 6% 29%	6800
	21st to end	Day	17% 9% 3 7% 5% 4 5% 4 6% 8% 33%	6971
August	1st to 10th	Day	22% 11% 4 10% 6% 5% 4 3 5% 6% 25%	4276
	11th to 20th	Day	19% 10% 3 8% 6% 5% 5% 4 6% 7% 28%	4176
	21st to end	Day	21% 10% 3 7% 4 4 5% 4 6% 7% 30%	4675
September	1st to 10th	Day	19% 10% 3 8% 4 4 4 4 5% 7% 33%	2401
	11th to 20th	Day	21% 11% 3 7% 5% 5% 3 4 5% 6% 30%	2200
	21st to end	Day	18% 11% 3 8% 5% 4 4 3 6% 7% 32%	2200
October	1st to 10th	Day	21% 13% 3 7% 5% 5% 4 4 6% 7% 26%	2078
	11th to 20th	Day	22% 19% 3 8% 6% 4 4 3 5% 4 22%	1981
	21st to end	Day	22% 20% 4 9% 6% 5% 4 4 4 4 17%	1980
November	1st to 10th	Day	19% 19% 5% 10% 5% 4 4 3 4 6% 21%	1719
	11th to 20th	Day	20% 19% 6% 9% 6% 5% 4 4 5% 6% 17%	1600
	21st to end	Day	20% 23% 6% 10% 6% 4 4 2 4 5% 16%	1575
December	1st to 10th	Day	17% 19% 6% 10% 5% 4 5% 3 5% 7% 20%	2290
	11th to 20th	Day	14% 20% 7% 13% 6% 4 3 2 4 4 21%	2628
	21st to end	Day	16% 21% 11% 18% 6% 5% 3 3 4 3 10%	3498
January	1st to 10th	Night	17% 22% 10% 14% 7% 6% 3 3 3 3 10%	6789
	11th to 20th	Night	15% 20% 9% 19% 6% 5% 4 3 3 4 12%	6424
	21st to end	Night	10% 13% 9% 20% 8% 5% 5% 3 4 4 18%	6996
February	1st to 10th	Night	19% 14% 7% 16% 9% 6% 5% 3 5% 4 13%	2630
	11th to 20th	Night	19% 16% 7% 15% 9% 5% 4 3 4 4 13%	2533
	21st to end	Night	13% 16% 9% 16% 7% 7% 4 3 4 4 17%	1992
March	1st to 10th	Night	20% 14% 8% 15% 6% 5% 4 3 4 5% 16%	5278
	11th to 20th	Night	19% 16% 7% 17% 7% 5% 4 3 4 4 14%	4979
	21st to end	Night	23% 20% 9% 14% 4 3 4 3 3 3 14%	5465
April	1st to 10th	Night	22% 20% 7% 9% 5% 4 4 3 3 4 19%	1990
	11th to 20th	Night	23% 18% 5% 9% 5% 4 3 2 4 4 23%	1778
	21st to end	Night	21% 19% 6% 12% 6% 4 4 3 3 3 19%	1800
May	1st to 10th	Night	24% 25% 7% 9% 4 3 3 2 3 4 17%	4075
	11th to 20th	Night	22% 21% 6% 11% 5% 4 3 2 3 4 18%	3540
	21st to end	Night	21% 22% 6% 10% 4 3 3 3 5% 5% 18%	3468
June	1st to 10th	Night	23% 20% 4 10% 5% 5% 5% 4 4 4 18%	1400
	11th to 20th	Night	22% 14% 3 8% 6% 4 5% 4 7% 7% 20%	1400
	21st to end	Night	21% 12% 3 8% 6% 4 5% 4 6% 7% 24%	1400
July	1st to 10th	Night	29% 14% 4 9% 5% 4 5% 3 5% 6% 16%	3179
	11th to 20th	Night	18% 12% 3 8% 5% 6% 6% 5% 7% 8% 23%	3180
	21st to end	Night	16% 10% 3 8% 5% 5% 4 4 6% 6% 34%	3901
August	1st to 10th	Night	22% 12% 3 8% 4 4 5% 4 7% 6% 25%	2882
	11th to 20th	Night	23% 10% 3 7% 4 3 4 3 5% 7% 29%	2881
	21st to end	Night	27% 10% 3 6% 4 4 4 4 4 6% 28%	3234
September	1st to 10th	Night	19% 10% 3 7% 4 4 5% 4 6% 7% 31%	1996
	11th to 20th	Night	23% 12% 3 8% 4 5% 4 3 5% 7% 26%	2200
	21st to end	Night	19% 14% 3 6% 5% 5% 4 3 5% 6% 31%	2200
October	1st to 10th	Night	21% 13% 4 8% 6% 5% 4 2 5% 6% 27%	2321
	11th to 20th	Night	23% 17% 4 8% 5% 5% 3 3 5% 6% 21%	2415
	21st to end	Night	24% 18% 5% 8% 4 4 4 3 4 5% 20%	2860
November	1st to 10th	Night	21% 18% 4 8% 5% 5% 5% 3 4 5% 21%	2622
	11th to 20th	Night	21% 18% 7% 11% 5% 4 4 4 5% 5% 18%	2800
	21st to end	Night	17% 21% 6% 11% 5% 4 5% 3 5% 6% 18%	2822
December	1st to 10th	Night	15% 20% 6% 10% 5% 4 4 3 4 4 25%	4900
	11th to 20th	Night	15% 21% 7% 15% 7% 5% 4 3 4 4 15%	5581
	21st to end	Night	17% 22% 8% 15% 7% 4 4 3 3 3 15%	7480

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% 7% 6% 10% 5% 1	3177
	11th to 20th	Day	71% 8% 7% 10% 4 1	3506
	21st to end	Day	65% 8% 8% 12% 7%	3982
February	1st to 10th	Day	70% 9% 8% 7% 6% 1	1768
	11th to 20th	Day	69% 9% 9% 9% 4 1	1760
	21st to end	Day	70% 7% 9% 7% 6% 1	1635
March	1st to 10th	Day	72% 6% 8% 9% 4 1	4567
	11th to 20th	Day	67% 10% 8% 9% 4 2	4980
	21st to end	Day	73% 7% 7% 9% 4 1	5467
April	1st to 10th	Day	71% 6% 7% 10% 5%	2407
	11th to 20th	Day	66% 5% 8% 11% 8% 1	2571
	21st to end	Day	68% 5% 8% 10% 7% 1	2600
May	1st to 10th	Day	70% 7% 7% 11% 5% 1	5897
	11th to 20th	Day	66% 9% 9% 13% 4	6360
	21st to end	Day	65% 7% 9% 16% 3	7428
June	1st to 10th	Day	72% 5% 7% 11% 4 1	3000
	11th to 20th	Day	60% 8% 12% 14% 6%	3000
	21st to end	Day	59% 10% 10% 16% 5%	3000
July	1st to 10th	Day	60% 7% 14% 16% 3	6725
	11th to 20th	Day	54% 7% 17% 15% 7%	6718
	21st to end	Day	49% 7% 20% 21% 4	6773
August	1st to 10th	Day	61% 6% 11% 17% 4	4262
	11th to 20th	Day	55% 8% 13% 19% 4	4215
	21st to end	Day	52% 7% 16% 22% 3	4675
September	1st to 10th	Day	50% 7% 12% 24% 7%	2401
	11th to 20th	Day	53% 6% 13% 18% 10%	2200
	21st to end	Day	51% 7% 16% 20% 7%	2200
October	1st to 10th	Day	63% 7% 10% 14% 5%	3384
	11th to 20th	Day	55% 9% 14% 15% 7%	3219
	21st to end	Day	64% 7% 9% 14% 5%	3191
November	1st to 10th	Day	62% 8% 14% 11% 5%	1719
	11th to 20th	Day	67% 7% 9% 12% 4 1	1600
	21st to end	Day	70% 7% 11% 9% 4	1575
December	1st to 10th	Day	61% 8% 14% 13% 5%	2290
	11th to 20th	Day	66% 6% 11% 11% 6%	2627
	21st to end	Day	73% 8% 8% 9% 2	3498
January	1st to 10th	Night	68% 11% 6% 8% 5% 1	6789
	11th to 20th	Night	71% 8% 10% 8% 3	6470
	21st to end	Night	61% 8% 12% 14% 5% 1	6996
February	1st to 10th	Night	69% 8% 9% 9% 5% 1	2630
	11th to 20th	Night	68% 9% 9% 10% 3 1	2537
	21st to end	Night	66% 8% 9% 12% 5%	1992
March	1st to 10th	Night	66% 8% 10% 12% 5%	5286
	11th to 20th	Night	68% 9% 10% 8% 4 1	4980
	21st to end	Night	72% 8% 7% 10% 3	5465
April	1st to 10th	Night	67% 7% 7% 11% 7% 1	1990
	11th to 20th	Night	63% 6% 7% 14% 8% 1	1778
	21st to end	Night	70% 5% 7% 11% 7% 1	1800
May	1st to 10th	Night	71% 6% 7% 13% 3	4080
	11th to 20th	Night	69% 7% 7% 12% 6%	3541
	21st to end	Night	66% 9% 8% 12% 4	3469
June	1st to 10th	Night	69% 8% 8% 10% 4	1400
	11th to 20th	Night	61% 8% 15% 12% 5%	1400
	21st to end	Night	58% 8% 12% 17% 5%	1400
July	1st to 10th	Night	67% 8% 10% 11% 3	3146
	11th to 20th	Night	56% 9% 14% 17% 3	3138
	21st to end	Night	50% 7% 16% 23% 3	3786
August	1st to 10th	Night	56% 9% 15% 16% 4 1	2871
	11th to 20th	Night	52% 9% 14% 20% 4	2908
	21st to end	Night	54% 8% 14% 21% 3	3233
September	1st to 10th	Night	50% 9% 14% 20% 7% 1	1996
	11th to 20th	Night	57% 7% 13% 15% 7% 1	2200
	21st to end	Night	53% 6% 14% 19% 8%	2200
October	1st to 10th	Night	63% 6% 13% 14% 4	3802
	11th to 20th	Night	54% 11% 16% 13% 6%	3926
	21st to end	Night	60% 8% 10% 16% 5%	4610
November	1st to 10th	Night	62% 8% 13% 12% 5%	2622
	11th to 20th	Night	66% 8% 11% 12% 3 1	2800
	21st to end	Night	63% 8% 13% 11% 5%	2822
December	1st to 10th	Night	60% 8% 10% 15% 8%	4900
	11th to 20th	Night	69% 7% 12% 9% 3	5583
	21st to end	Night	69% 9% 9% 10% 3	7480

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% 23% 33% 13% 3 1	400
	11th to 20th	Day	27% 22% 35% 12% 4 1	400
	21st to end	Day	27% 23% 33% 15% 2	440
February	1st to 10th	Day	26% 25% 30% 16% 4 1	400
	11th to 20th	Day	30% 28% 32% 8% 3	396
	21st to end	Day	19% 26% 35% 16% 3	331
March	1st to 10th	Day	27% 28% 34% 9% 3	400
	11th to 20th	Day	24% 22% 32% 16% 4 2	400
	21st to end	Day	27% 24% 31% 12% 5% 1	440
April	1st to 10th	Day	30% 27% 27% 12% 4 1	533
	11th to 20th	Day	31% 20% 27% 14% 7% 1	689
	21st to end	Day	31% 18% 30% 16% 5%	700
May	1st to 10th	Day	31% 18% 29% 15% 6% 1	703
	11th to 20th	Day	26% 14% 31% 21% 6% 1	724
	21st to end	Day	26% 15% 33% 20% 6% 1	790
June	1st to 10th	Day	37% 12% 28% 17% 6%	730
	11th to 20th	Day	30% 13% 29% 19% 7% 2	730
	21st to end	Day	26% 9% 30% 25% 8% 2	730
July	1st to 10th	Day	26% 9% 35% 22% 7% 1	720
	11th to 20th	Day	21% 9% 34% 27% 9% 1	718
	21st to end	Day	24% 12% 31% 26% 8% 1	795
August	1st to 10th	Day	22% 9% 32% 27% 9% 1	725
	11th to 20th	Day	22% 11% 24% 32% 10% 1	717
	21st to end	Day	26% 11% 26% 26% 12%	803
September	1st to 10th	Day	22% 8% 30% 27% 11% 2	580
	11th to 20th	Day	29% 15% 29% 20% 7% 1	420
	21st to end	Day	26% 14% 32% 21% 7% 1	420
October	1st to 10th	Day	28% 10% 34% 22% 5%	420
	11th to 20th	Day	29% 16% 30% 16% 7% 1	420
	21st to end	Day	31% 21% 26% 16% 3 2	462
November	1st to 10th	Day	28% 24% 26% 17% 5%	401
	11th to 20th	Day	32% 21% 27% 14% 7%	400
	21st to end	Day	33% 22% 30% 12% 3 1	400
December	1st to 10th	Day	28% 23% 28% 16% 6%	400
	11th to 20th	Day	27% 32% 28% 12% 2	400
	21st to end	Day	26% 21% 33% 15% 4 1	440
January	1st to 10th	Night	26% 22% 34% 14% 4	900
	11th to 20th	Night	27% 18% 34% 16% 4	900
	21st to end	Night	26% 21% 34% 17% 2	990
February	1st to 10th	Night	25% 25% 33% 15% 1	900
	11th to 20th	Night	29% 23% 34% 12% 2	883
	21st to end	Night	22% 20% 34% 20% 5%	665
March	1st to 10th	Night	26% 22% 34% 15% 3	763
	11th to 20th	Night	21% 21% 29% 23% 7%	600
	21st to end	Night	31% 17% 31% 18% 2	660
April	1st to 10th	Night	29% 21% 29% 15% 6% 1	600
	11th to 20th	Night	31% 17% 29% 18% 5%	594
	21st to end	Night	30% 16% 30% 19% 5%	600
May	1st to 10th	Night	31% 12% 27% 23% 6% 1	600
	11th to 20th	Night	28% 12% 31% 21% 8%	592
	21st to end	Night	26% 12% 32% 24% 5% 1	649
June	1st to 10th	Night	34% 10% 30% 20% 6%	600
	11th to 20th	Night	26% 12% 30% 24% 8% 1	600
	21st to end	Night	25% 12% 28% 26% 7% 1	600
July	1st to 10th	Night	25% 7% 35% 27% 5% 1	586
	11th to 20th	Night	24% 6% 34% 29% 6%	582
	21st to end	Night	24% 6% 34% 28% 7%	656
August	1st to 10th	Night	22% 6% 29% 33% 8% 1	598
	11th to 20th	Night	24% 7% 29% 31% 8%	592
	21st to end	Night	26% 8% 30% 29% 7%	660
September	1st to 10th	Night	20% 8% 33% 30% 8% 1	600
	11th to 20th	Night	28% 12% 30% 25% 6%	600
	21st to end	Night	27% 11% 31% 25% 7% 1	600
October	1st to 10th	Night	27% 11% 32% 24% 6%	667
	11th to 20th	Night	31% 14% 30% 18% 6% 1	725
	21st to end	Night	32% 17% 26% 20% 5%	1001
November	1st to 10th	Night	28% 20% 31% 16% 5%	891
	11th to 20th	Night	28% 17% 31% 19% 5%	900
	21st to end	Night	27% 22% 32% 15% 3	900
December	1st to 10th	Night	26% 22% 31% 16% 5%	900
	11th to 20th	Night	31% 25% 31% 10% 3	900
	21st to end	Night	25% 19% 33% 18% 4 1	990

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