Bay Roberts
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bay Roberts clear sky chart from 2005-11-06 to 2025-12-18.

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 4 5% 21%	127222
	Night	20% 16% 6% 12% 6% 5% 4 3 4 5% 19%	124056
Transparency	Day	62% 6% 11% 15% 5%	130704
	Night	64% 7% 11% 13% 5%	128688
Seeing	Day	27% 17% 29% 19% 6% 1	19685
	Night	28% 17% 30% 19% 5%	26297

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% 18% 8% 17% 6% 3 3 2 3 4 15%	3176
	11th to 20th	Day	17% 22% 9% 15% 5% 4 4 2 3 3 14%	3545
	21st to end	Day	11% 16% 8% 18% 8% 6% 5% 3 4 5% 17%	3982
February	1st to 10th	Day	19% 16% 7% 12% 8% 7% 5% 3 4 4 14%	1736
	11th to 20th	Day	20% 18% 7% 13% 7% 6% 4 4 4 4 13%	1765
	21st to end	Day	13% 19% 7% 15% 8% 6% 4 4 3 4 16%	1650
March	1st to 10th	Day	23% 16% 6% 14% 7% 6% 4 2 3 3 14%	4514
	11th to 20th	Day	21% 16% 8% 12% 7% 4 4 3 4 5% 17%	4980
	21st to end	Day	22% 23% 9% 11% 6% 4 3 3 3 4 13%	5467
April	1st to 10th	Day	20% 21% 8% 12% 6% 5% 3 2 5% 4 15%	2415
	11th to 20th	Day	24% 19% 5% 8% 5% 4 3 3 4 4 22%	2571
	21st to end	Day	26% 19% 5% 8% 5% 4 3 2 4 5% 19%	2600
May	1st to 10th	Day	22% 25% 6% 9% 4 3 3 2 3 5% 17%	5885
	11th to 20th	Day	21% 18% 5% 10% 5% 4 4 3 4 5% 20%	6376
	21st to end	Day	20% 23% 5% 9% 4 5% 4 3 4 5% 19%	7428
June	1st to 10th	Day	30% 17% 5% 8% 5% 4 3 2 3 4 17%	3000
	11th to 20th	Day	24% 14% 3 7% 5% 4 4 4 4 6% 25%	3000
	21st to end	Day	22% 13% 4 10% 6% 4 4 3 5% 6% 23%	3000
July	1st to 10th	Day	22% 14% 5% 10% 5% 5% 4 3 6% 6% 21%	6800
	11th to 20th	Day	14% 11% 4 10% 7% 6% 5% 4 5% 6% 28%	6759
	21st to end	Day	16% 11% 3 8% 5% 5% 4 4 6% 8% 31%	6927
August	1st to 10th	Day	19% 12% 6% 11% 5% 4 4 3 5% 6% 24%	4320
	11th to 20th	Day	17% 11% 4 9% 6% 5% 5% 4 6% 7% 27%	4176
	21st to end	Day	18% 10% 3 8% 5% 4 4 3 5% 7% 30%	4675
September	1st to 10th	Day	19% 11% 3 7% 5% 4 5% 4 5% 7% 31%	2391
	11th to 20th	Day	22% 9% 4 7% 5% 5% 4 4 5% 7% 29%	2200
	21st to end	Day	18% 9% 3 8% 5% 5% 4 3 5% 7% 33%	2200
October	1st to 10th	Day	20% 13% 3 9% 4 4 4 4 5% 7% 27%	2100
	11th to 20th	Day	22% 16% 4 9% 6% 4 4 4 5% 4 23%	1952
	21st to end	Day	25% 16% 4 8% 6% 5% 5% 3 4 5% 18%	1980
November	1st to 10th	Day	20% 16% 4 10% 6% 4 4 3 5% 5% 22%	1820
	11th to 20th	Day	23% 17% 6% 10% 5% 5% 4 3 4 6% 17%	1680
	21st to end	Day	24% 21% 5% 9% 5% 4 4 3 4 4 16%	1617
December	1st to 10th	Day	17% 14% 5% 11% 6% 5% 5% 4 6% 8% 19%	2360
	11th to 20th	Day	22% 16% 6% 11% 5% 5% 3 3 3 4 21%	2677
	21st to end	Day	21% 20% 8% 14% 6% 4 5% 3 4 4 11%	3498
January	1st to 10th	Night	18% 22% 9% 13% 7% 5% 4 3 4 4 13%	6789
	11th to 20th	Night	16% 19% 9% 18% 7% 5% 4 3 3 4 12%	6358
	21st to end	Night	11% 11% 8% 17% 8% 6% 5% 4 5% 5% 18%	6996
February	1st to 10th	Night	19% 16% 6% 15% 8% 5% 4 3 5% 4 14%	2663
	11th to 20th	Night	21% 15% 5% 12% 9% 5% 5% 3 4 4 15%	2518
	21st to end	Night	14% 17% 7% 13% 6% 6% 5% 3 5% 5% 18%	1980
March	1st to 10th	Night	23% 12% 6% 14% 7% 5% 5% 3 4 5% 16%	5326
	11th to 20th	Night	16% 17% 9% 16% 7% 5% 5% 3 3 5% 14%	4979
	21st to end	Night	25% 19% 8% 12% 6% 4 4 3 4 3 13%	5465
April	1st to 10th	Night	23% 22% 5% 10% 5% 4 3 2 4 4 18%	1980
	11th to 20th	Night	24% 15% 5% 10% 5% 3 4 2 4 4 24%	1778
	21st to end	Night	25% 21% 5% 9% 5% 4 3 2 3 4 19%	1800
May	1st to 10th	Night	25% 20% 8% 11% 5% 3 3 2 3 4 16%	4075
	11th to 20th	Night	26% 17% 5% 11% 4 3 4 3 4 5% 19%	3534
	21st to end	Night	22% 23% 5% 9% 4 4 4 3 4 6% 17%	3468
June	1st to 10th	Night	26% 17% 4 9% 4 5% 5% 4 4 4 19%	1400
	11th to 20th	Night	24% 13% 3 8% 6% 4 4 5% 5% 7% 22%	1400
	21st to end	Night	23% 13% 4 10% 6% 5% 5% 3 5% 5% 22%	1400
July	1st to 10th	Night	29% 12% 5% 12% 5% 4 4 3 4 6% 16%	3179
	11th to 20th	Night	14% 12% 5% 13% 6% 6% 6% 4 6% 6% 22%	3218
	21st to end	Night	13% 10% 4 13% 6% 5% 5% 4 5% 6% 30%	3948
August	1st to 10th	Night	16% 10% 5% 13% 5% 5% 4 4 6% 7% 24%	2825
	11th to 20th	Night	25% 7% 3 8% 4 4 4 4 5% 7% 28%	2881
	21st to end	Night	24% 10% 3 8% 4 3 4 3 6% 7% 28%	3234
September	1st to 10th	Night	19% 11% 4 8% 4 5% 4 4 5% 7% 30%	2005
	11th to 20th	Night	23% 11% 3 9% 4 4 4 4 5% 6% 27%	2200
	21st to end	Night	20% 11% 3 9% 5% 4 4 3 4 7% 32%	2200
October	1st to 10th	Night	20% 12% 4 9% 5% 4 4 4 5% 7% 26%	2300
	11th to 20th	Night	24% 16% 3 7% 5% 5% 4 3 5% 7% 23%	2445
	21st to end	Night	24% 17% 4 9% 4 4 4 3 4 5% 21%	2860
November	1st to 10th	Night	21% 15% 4 9% 6% 5% 4 3 4 6% 22%	2696
	11th to 20th	Night	24% 17% 5% 10% 5% 4 3 3 4 5% 19%	2940
	21st to end	Night	20% 18% 5% 11% 6% 4 5% 4 5% 5% 18%	2999
December	1st to 10th	Night	17% 18% 5% 11% 6% 5% 5% 3 4 5% 21%	5050
	11th to 20th	Night	25% 17% 5% 11% 6% 4 4 3 4 4 16%	5687
	21st to end	Night	21% 19% 7% 13% 6% 4 5% 3 3 4 16%	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	72% 6% 5% 11% 5% 1	3177
	11th to 20th	Day	71% 5% 9% 9% 5% 1	3574
	21st to end	Day	66% 5% 7% 12% 9%	3982
February	1st to 10th	Day	71% 7% 8% 7% 7% 1	1736
	11th to 20th	Day	70% 7% 9% 9% 4 1	1772
	21st to end	Day	69% 6% 9% 8% 7% 1	1650
March	1st to 10th	Day	69% 6% 7% 11% 6% 1	4519
	11th to 20th	Day	67% 5% 10% 10% 5% 2	4980
	21st to end	Day	73% 5% 6% 10% 5% 1	5467
April	1st to 10th	Day	70% 6% 7% 11% 5% 1	2415
	11th to 20th	Day	64% 6% 8% 13% 9% 1	2571
	21st to end	Day	67% 5% 8% 12% 8% 1	2600
May	1st to 10th	Day	69% 6% 8% 11% 6% 1	5897
	11th to 20th	Day	63% 8% 10% 14% 5%	6380
	21st to end	Day	65% 6% 9% 16% 4	7428
June	1st to 10th	Day	70% 5% 7% 12% 5% 1	3000
	11th to 20th	Day	58% 8% 13% 15% 7%	3000
	21st to end	Day	60% 8% 11% 15% 6%	3000
July	1st to 10th	Day	58% 7% 15% 16% 3	6725
	11th to 20th	Day	51% 8% 17% 16% 7%	6677
	21st to end	Day	48% 7% 20% 21% 4	6730
August	1st to 10th	Day	58% 6% 12% 18% 5%	4306
	11th to 20th	Day	50% 8% 16% 23% 3	4215
	21st to end	Day	50% 7% 16% 25% 3	4675
September	1st to 10th	Day	50% 7% 11% 22% 9%	2391
	11th to 20th	Day	52% 6% 13% 18% 10%	2200
	21st to end	Day	49% 7% 15% 20% 8%	2200
October	1st to 10th	Day	61% 7% 11% 15% 5%	3430
	11th to 20th	Day	52% 6% 13% 19% 10%	3165
	21st to end	Day	61% 7% 9% 17% 6%	3191
November	1st to 10th	Day	62% 6% 15% 12% 5%	1820
	11th to 20th	Day	66% 8% 9% 12% 5%	1680
	21st to end	Day	70% 5% 11% 9% 5%	1617
December	1st to 10th	Day	58% 7% 14% 14% 6%	2360
	11th to 20th	Day	63% 6% 12% 11% 7%	2676
	21st to end	Day	74% 5% 8% 10% 3	3498
January	1st to 10th	Night	73% 6% 6% 8% 5% 1	6789
	11th to 20th	Night	72% 8% 10% 7% 3	6404
	21st to end	Night	62% 7% 10% 13% 6% 1	6996
February	1st to 10th	Night	71% 6% 9% 8% 5% 1	2663
	11th to 20th	Night	68% 8% 10% 10% 4	2522
	21st to end	Night	67% 6% 10% 10% 6%	1980
March	1st to 10th	Night	66% 6% 8% 13% 6%	5334
	11th to 20th	Night	71% 6% 9% 9% 5% 1	4980
	21st to end	Night	72% 4 8% 11% 3	5465
April	1st to 10th	Night	67% 6% 8% 12% 7% 1	1980
	11th to 20th	Night	62% 6% 8% 14% 8% 1	1778
	21st to end	Night	67% 6% 8% 12% 7%	1800
May	1st to 10th	Night	71% 5% 8% 13% 3	4080
	11th to 20th	Night	68% 4 8% 13% 6%	3535
	21st to end	Night	67% 6% 10% 12% 4	3469
June	1st to 10th	Night	68% 6% 8% 13% 5%	1400
	11th to 20th	Night	59% 7% 14% 15% 5%	1400
	21st to end	Night	58% 8% 13% 16% 4	1400
July	1st to 10th	Night	64% 7% 13% 12% 3	3146
	11th to 20th	Night	50% 12% 16% 19% 3	3176
	21st to end	Night	46% 8% 18% 24% 3	3831
August	1st to 10th	Night	52% 9% 17% 18% 4	2814
	11th to 20th	Night	49% 6% 18% 23% 3	2908
	21st to end	Night	53% 7% 14% 23% 4	3233
September	1st to 10th	Night	50% 9% 12% 21% 7% 1	2005
	11th to 20th	Night	57% 7% 14% 14% 8%	2200
	21st to end	Night	52% 7% 14% 19% 8%	2200
October	1st to 10th	Night	62% 6% 14% 14% 4	3755
	11th to 20th	Night	51% 6% 16% 18% 9%	3981
	21st to end	Night	58% 6% 13% 17% 6%	4610
November	1st to 10th	Night	62% 7% 13% 12% 5%	2696
	11th to 20th	Night	66% 8% 11% 12% 3 1	2940
	21st to end	Night	65% 7% 13% 11% 4	2999
December	1st to 10th	Night	61% 7% 9% 16% 7%	5050
	11th to 20th	Night	68% 6% 14% 8% 3	5689
	21st to end	Night	70% 6% 9% 11% 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	30% 22% 33% 12% 3 1	400
	11th to 20th	Day	26% 26% 29% 13% 4 1	400
	21st to end	Day	26% 26% 33% 13% 2	440
February	1st to 10th	Day	27% 25% 29% 16% 3 1	400
	11th to 20th	Day	28% 31% 29% 9% 2	396
	21st to end	Day	21% 30% 31% 16% 3	331
March	1st to 10th	Day	28% 29% 30% 9% 3 1	400
	11th to 20th	Day	23% 24% 31% 17% 3 3	400
	21st to end	Day	30% 24% 28% 13% 5% 1	440
April	1st to 10th	Day	32% 22% 29% 13% 4	525
	11th to 20th	Day	31% 20% 27% 15% 6% 1	689
	21st to end	Day	32% 19% 28% 16% 4 1	700
May	1st to 10th	Day	31% 19% 26% 17% 6% 1	703
	11th to 20th	Day	24% 15% 31% 20% 8% 2	724
	21st to end	Day	26% 18% 31% 19% 5% 1	790
June	1st to 10th	Day	38% 11% 25% 17% 7% 1	730
	11th to 20th	Day	30% 11% 29% 22% 8% 1	730
	21st to end	Day	25% 11% 30% 25% 7% 2	730
July	1st to 10th	Day	26% 9% 34% 21% 9% 2	720
	11th to 20th	Day	22% 8% 34% 26% 10% 1	718
	21st to end	Day	22% 11% 31% 25% 9% 1	795
August	1st to 10th	Day	23% 9% 30% 25% 10% 3	725
	11th to 20th	Day	22% 9% 28% 27% 11% 2	717
	21st to end	Day	22% 12% 28% 26% 12% 1	803
September	1st to 10th	Day	21% 11% 27% 29% 11% 2	561
	11th to 20th	Day	26% 14% 30% 22% 7% 1	420
	21st to end	Day	21% 19% 33% 19% 8% 1	420
October	1st to 10th	Day	25% 13% 31% 24% 7%	420
	11th to 20th	Day	30% 16% 29% 15% 9% 1	420
	21st to end	Day	29% 23% 24% 17% 5% 2	462
November	1st to 10th	Day	27% 24% 29% 16% 3	425
	11th to 20th	Day	32% 21% 27% 15% 5%	430
	21st to end	Day	33% 28% 24% 10% 4	430
December	1st to 10th	Day	27% 24% 28% 17% 4	430
	11th to 20th	Day	31% 26% 29% 10% 2	421
	21st to end	Day	28% 20% 31% 15% 5% 1	440
January	1st to 10th	Night	28% 21% 33% 14% 4	900
	11th to 20th	Night	28% 21% 34% 13% 5%	900
	21st to end	Night	25% 24% 33% 16% 2	990
February	1st to 10th	Night	26% 26% 33% 12% 2	900
	11th to 20th	Night	30% 24% 32% 11% 2	876
	21st to end	Night	22% 23% 30% 19% 5%	660
March	1st to 10th	Night	24% 25% 33% 13% 3	785
	11th to 20th	Night	22% 19% 30% 24% 6%	600
	21st to end	Night	33% 19% 28% 17% 3	660
April	1st to 10th	Night	29% 20% 31% 14% 6% 1	600
	11th to 20th	Night	31% 17% 31% 18% 4	594
	21st to end	Night	32% 15% 30% 18% 4 1	600
May	1st to 10th	Night	30% 13% 29% 21% 6% 1	600
	11th to 20th	Night	30% 10% 31% 20% 9% 1	592
	21st to end	Night	29% 13% 32% 21% 5%	649
June	1st to 10th	Night	33% 10% 28% 22% 6%	600
	11th to 20th	Night	30% 9% 28% 25% 7% 1	600
	21st to end	Night	26% 10% 34% 23% 7% 1	600
July	1st to 10th	Night	25% 7% 37% 25% 5% 1	586
	11th to 20th	Night	24% 7% 37% 27% 6%	582
	21st to end	Night	24% 7% 35% 27% 7%	656
August	1st to 10th	Night	26% 5% 30% 31% 8% 1	598
	11th to 20th	Night	25% 6% 28% 33% 7% 1	592
	21st to end	Night	24% 10% 31% 28% 7%	660
September	1st to 10th	Night	22% 10% 31% 30% 8% 1	600
	11th to 20th	Night	29% 11% 29% 26% 5% 1	600
	21st to end	Night	25% 15% 29% 24% 7%	600
October	1st to 10th	Night	25% 14% 32% 23% 6%	655
	11th to 20th	Night	31% 15% 28% 19% 7%	755
	21st to end	Night	31% 19% 25% 20% 5%	1001
November	1st to 10th	Night	30% 22% 29% 16% 3	930
	11th to 20th	Night	31% 19% 27% 17% 5%	950
	21st to end	Night	29% 24% 30% 14% 3	950
December	1st to 10th	Night	27% 24% 28% 16% 5%	950
	11th to 20th	Night	33% 26% 27% 11% 2	936
	21st to end	Night	28% 20% 29% 18% 4 1	990

Page generated at 2025-12-15 02:13:50. Version ac07

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